aws sm hdbk 2nd ed 1977 soldering manual

AWS S M * I N D E X ** R 078q2b5 000b l lL7 8 R

Soldering Manual

COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

AWS S M * I N D E X ** I 078L1265 00061118 T I

SOLDERING MANUAL Second Edition, Revised

Prepared by AWS Committee on Brazing and Soldering

Under the Direction of AWS Technical Activities Committee

Approved by AWS Board of Directors, April 1,1977

AMERICAN WELDING SOCIETY, INC. .2501 N.W. 7th Street, Miami, Florida 33125


AWS S M m I N D E X ** 07842b5 0006439 3

Library of Congress Number: 77-90783 International Standard Book Number: 0-87171-151-6

American Welding Society, 2501 N.W. 7th Street, Miami, FL 33125

@ 1978 by American Welding Society. All rights reserved.

Note: By publication of this manual, the American Welding Society does not insure anyone utilizing the manual against liability arising from the use of such manual. A publication of a manual by the American Welding Society does not carry with it any right to make, use, or sell any patented items. Each prospective user should make an independent investigation.

Printed in the United States of America


AWS S M U I N D E X ** I 07842b5 000b420 B E

CONTENTS

Personnel vii Introduction ix

1. Principles of Soldering 1 2. Solders 3 3. Fluxes I3 4. Joint Design 21 5. Precleaning and Surface Preparation 35 6. Equipment, Processes, and Procedures 41 7. FluxRemoval 49 8. Inspection and Testing 51 9. Copper and Copper Alloys 63 10. Steel 69 11. Coated Steels 71 12. Stainless Steels 75 13. Nickel and High-Nickel Alloys 79 14. Lead and Lead Alloys 83 15. Aluminum and Aluminum Alloys 91 16. Magnesium and Magnesium Alloys 97 17. Tin and Tin Alloys 101 18, CastIrons 105 19, Precious Metal Coatings and Films 107 20. Printed Circuits 109 21. Safety and Health Protection 113 22. The Soldering of Pipe and îbbe 117 23. Physical and Mechanical Properties of Solder and Solder Joints 125

Index 145

V


AWS S M * I N D E X ** m 0784265 0006112L T m

PERSONNEL R.L. Peaslee, Chairman

*G.M. Slaughter, Chairman M.M. Schwartz, Vice Chairman

*D.J. Spillane, 1st Vice Chairman *R.E. Ballentine, 2nd Vice Chairman

T.J. Olivem, Secretary W.G. Bader

R.E. Beal C.R. Behringer

J.R. Bonnar J.P. Brodenck G.D. Cremer

A.S. Cross, Jr. D.C. Dilley F.C. Disque R.M. Evans

E. B. Gempler R.G. Gilliland

K. Gustafson A.N. Kugler

A.H. Lenk J.B. Long

R.O. McIntosh J.A. Mehaffey

M.T. Merlo E.J. Minarcik

W.J. Reichenecker M.N. Ruoff

J.F. Smith G.K. Sosnin H.A. Sosnin

H.W. Spaletta J.R. Terril1

D. Wireman *Commencing June, 1974

Wail Colmonoy Corp. Oak Ridge National Lab, Rohr Corporation General Electric Co. Westinghouse Electric Corp. American Welding Society Bell Telephone Laboratories IIT Research institute Western Gold & Platinum Co. Handy and Harman Eutectic and Castolin Institute International Harvester Co. Engelhard Minerals & Chemicals Consultant Alpha Metals Incorporated Battelle Memorial Institute United Aircraft Products Pelton Steel Westinghouse-Hanford Consultant Reynolds Metals Co. Tin Research Institute National Electronics Stanley Flagg and Co. Chemetron Corporation NL Industries Westinghouse Electric Corp. General Electric Co. Lead Industries Association The ELEE. Company Consultant Aerojet Nuclear Co. Aluminum Company of America Aerobraze Corporation


AWS S M * I N D E X ** I 0784265 ûûOb1122 L I

viiiPersonnel

Advisory Members

N.C. Cole Combustion Engineering

T. Hikido Pyromet Industries

M. Prager Consultant

O.S. Gschwind United Aircraft of Canada, Ltd.

W.S. Lyman Copper Development Association

H.S. Sayre U.S. Naval Ship Engineering Center

Subcommittee on Soldering

W.G. Bader, Chairman T.J. Olivera, Secretary

R.E. Beal P.J. Bud

C. DiMartini F,C. Disque

K. Lazar J.B. Long

M.T. Merlo E.J. Minarcik

M. Prager W.J. Reichenecker

J.F. Smith W.R. Studnick

, J. J. Stokes H.A. Sosnin J. Sylvester

Bell Telephone Laboratories American Welding Society IIT Research Institute Electrovert Incorporated American Smelting & Refining Company Alpha Metals Incorporated Refinery for Electronics Tin Research Institute Chemetron Corporation NL Industries Consultant Westinghouse Electric Corp. Lead Industries Association Western Electric Aluminum Company of America Consultant Hexacon Electric Co.

Past Subcommittee members who assisted in the preparation of this Manual

T. Agne Lead Industries Association R.M. Healy Kester Solder

J.A. Kennedy Hexacon Electric J,F. Lockwood DowChemical .


AWS S M * I N D E X ** W 0784265 0006423 3 W

INTRODUCTION

Soldering is one of the oldest and most widely practiced methods of joining metals. The art and science of soldering have continuously advanced since the Soldering Manual was first published in 1959. Considerable impetus was provided by the revolutionary changes in the electronics industry where solders were required to join hundreds of components on printed circuits. At the present time, soldering is utilized on microcircuits to provide joints as small as 150 microns. Joint reliabib ity is required for applications ranging from automotive radiators to the most sophisticated

who are familiar with the fundamentals of soldering may proceed directly to chapters on specific metals or applications to obtain information for which they have an immediate need.

While every attempt has been made to provide the most recent and reliable information on soldering, the Committee realizes that all the needs of the specialist will not be filled. However, it is hoped that the manual will provide the necessary information to direct his efforts towards a more complete solution of his problems.

Since the trend in American industry is to computers in environments that range from convert to the use of metric units, all U.S. cus- households to outerspace. As a result of these tomary measurements were converted to metric. diverse applications, much new technical infor- The metric units used are those of the Système mation has been generated on solders, their in- . Internationale d'Unités (SI), which is the interna- teraction with base metals, and the properties of soldered joints. This second edition of the Solder- ing Manual incorporates these many advances and new data along with the fundamentals of the soldering process.

The American Welding Society defines soldering as "a group of welding processes which produces coalescence of materials by heating them

tionally accepted metric system. Where tolerances are not essential, metric measurements were rounded off to the nearest O or 5; for example, 150" C (-3000 F)-note that the symbol

i s used to indicate approximation. Where commercial products (which are still available mostly in U.S. customary units) are described, the metric unit is rounded off to the nearest Oor 5 ,

I s = * * -

to a suitable temperature and by using a filler and the word nominal precedes it. For example, a metal having a liquidus not exceeding 450" C nominal i .5 kg (3 Ib) solder bar. Throughout the (8400 F) and below the solidus of the base mate- text, U.S. customary units are included paren- rials. The filler metal is distributed between the thetically. closely fitted surfaces by capillary attraction." Comments, inquiries, and suggestions for fu- The liquidus temperatureof4$0° Cdifferentiates ture revisions of this manual are welcome. Ad- solders from brazing filler metals. dress them to Secretary, AWS Committee on

The data in this manual have been arranged in Brazing and Soldering. American Welding Soci- what the Committee! believes ta be the proper ety, 2501 N.W. 7th Street, Miami, Florida order for the reader who wishes to study each 33125. aspect of the soldering pr.ocess. However, those

I

ix


AWS S M * I N D E X ** I 0784265 000b424 5

INDEX

abrasion: cleaning. 37; solders. 95 abrasion tools: for aluminum alloys. 95: for magnesium

ac6clerated aging. f i x . . 5.î acid cleaning. 35.37 acids: for clcaning. 35-32; inorganic. 14. fable. 15 activaicd rosin fluxes, 16 ape-hardenable alloys, 79 alloying. 2 , 125 alloys. melting and solidification process of. 3 aluminum and aluminum alloys, 5 . IO. 13. 91.96.

aluminum coated sieels. 7 I American Society for Tcsiing Matcnals. See ASTS1 Kmencan Standard 2 49. I . I 13. I I4 amines. i n iniermcdiate fluxcs. 15 ammonium chloride. 14, 17 aniimony, 5. 7. 8. 123. rable, 6, 7, I2Y ASTM. 5 . I I . 130

base meial: alloying of. 125: corrosion oí by flux rc- siducs. 49; selection of. 92; scleciion oí. i n joini design. 21.34

alloys. 98

f i g . . 93

bell and spigot joints, 87 bisniurh: soldenng oí. IO; properties of I O U meliing

blowpipe for tin soldering. 101 brass: soldcrs. 63: surface prcparaiion oí. 64 bridging, 33,j ix . , 5 9 Brinell hardness, 60, 127 bronzes: flux Tor soldering. 19: solders for, 63 butt joinis. 21, 22,fig., 2 2 , 138, fable. 1-39 cable sheath joints. 8 8 4 ~ s . . 84-86 cadmium coaied steel. 72 cadmium-silver solder, 9, fable. 10 cadmium-zinc solders. IO , fable. 10 calorizcd tips. 42 can manuíaciuring industry. soldering for. 4. 73

alloys of, 133, iablr, 134 Sre also fusible alloys

capillary flow: in joini design. 23-?6,ji~., 26: in i in-

capillary iesis, I , 5 I carbon tetrachloride, as a health hazard. I 15 cast coppcr and'copper allo), rable. 67 casi irons, 105. 106 caustic cleaners for aluminum alloys. 95 chemical hazards. I15 chloride5 in fluxes. 15 chromium plaied steels. 7 2 circuii board joinis./ips., 32, 33 clcaning. 2 . 35.39: with acid, 3 5 ; b y abrasive

techniques. 35; by chemical means. 35, 73; by deprcasing. 35: by mechanical means. 37, 120: of pipe and lube. 120: of precious metal, 108; of printed circuiis, I I ? ; of stainless steels. 75-76

clcarances: for joinis in steel. 70: for coafcd sicel joints. 71

coaied copper bast alloys. 65 coaied sieels. 7 I cald solder joint. fable. 57,jig.. 58 commercial forms of solder. fahle. 12 conlaminants: ionic./ig.. 61: surface. 13 contamination checks. 61 -62 conveyors. 48 cooling method. 2 copper and copper alloys. I , 63-68. iablcs. 66.68,

coppcr tips. in soldering irons, 43 copper tube. sizes and weights of, fables, 1/11 corrosion, 9 I corrosive fluxes, 2, 14-15, 64,ïü creep sirenph, 127. 128. robles. 129, 131, 132 creep iesi, 60 cup joint in lead pipe, 88

antimony.lcad solders, 8

jig. 65

dcfects in soldered joints, table. 57. /¡R.. 58 design of soldered joinis. See joint design


AWS S M * I N D E X ** W 07842b5 000b425 7 I

146llnde.r

destructive testing. 51.62; fatigue test, 60; impact test, 61; peel test. 59; shear test.rable. 60: stress rupture . test, 60; tension test. 59

dewctting,fig.. 59 dip soldering. 4. 43 direct spread test, 5 I disturbed soldered joint,fig. 58 dry flux and solder for casi irons, 105 dry f lux for steels. 70 dust, metal, t 15 dye penetrant inspection. 58

edge dip lest. 52 effects of impurities on solders. 4 -5 electrical conductivity of solder, 127. rableJ. lt7, 134 electrical connections, 27-33. fables andfigs., 30.33 electrical heating, precautions for. I13 electrical resistance method for testing soldered joints,

electrically heated soldering irons, 4 1-42. See' also

electrochemical surface cleaning for cast irons, 105 electrodeposited coatings. 73 electroplating. 39. 95 enibriitlement of nickel and high nickel by Icad solders,

environmental tests, 61 equipment. 4 1-43 etching, 37 ' euiectic compositions. 3 excess solder in joints, fable. 57, fi^.. 58 expansion, thermal. See thermal expansion

59

soldering irons

79

w

facc fed joints, 48 failure, cyclic, 49 fast cooling. 2 fatigue: in lead and lead alloys. 33: tests for, 60 Federal Specifications. 16: address for obtaining. I I :

flame heated soldering irons. 41 flow point. 3 fluidity of molten solder, I fluorides i n fluxes. 15 flux action. l3 ,&. , I4 fluxes. 13-20; activated rosin. 16: for air conditioning

and refrigerating equipment, 17; for aluminum and aluminum alloys, 94; for aluminum coated steels. 71; ammonium chloride and zinc chloride mixtures, 123; for auto bodies. 17: for auto radiators, 17: for cadmium coated steels. 72; for cast irons, 105.06; chemical. 94; corrosive. 2, 14-15. 17-19, iablc, 18; for coated sieels. 71; for copper and copper alloys, 63; intermediate constituents of, IS. 19, roble, 15: inorganic salts and acids in. 14-15,

limiti,ng impurities in tin-lead solderr. 4. 5

ioblc. IS: for lead and lead alloys, 87; for mag. nesium, 98; for nickel and high-nickel alloys, 80; for nickel plated steels, i 2 : nonconosivc 16, 20; paste, 16: forpipeandtube, 121. 123:forplumbing and heating applications. 117; for precious metals. 108; for printed circuits. I 1 I ; reaction. 17, 94; selection of, 18. 19. rablc. 18: self-neutralizing. 2; for stainless steels. 76: for steels. 70; surface con. taminants of, 13; for terneplate. 72: testing of, 20; theories of. 13; for t in , 101; for tinplate. 72: types of. 14-17; zinc chlonde. 14. IS. 17- 19.49: for zinc coaled steels, 74

fluxless soldering: magnesium and magnesium alloys. 97-99; of aluminum alloys. 95

flux removal. 2 .47.49, 50 flux residues, 14: corrosive, 49-50; on aluminum al-

loys. 91; paste. 50 focused infrared soldering. 46 fracture initiation strength of joints, 138. roble. / 4 0 fusible alloys. IO. table. IO. See bismuth

galvanized iron. See zinc coated steels gas-handling equipment. 114 globule solderability tesi.fig., 52 gold. 107. table, Iûü

hardness: of4ead joints. 83; tests for. 60. 127 hwards: from chemicals. 115: from fumes. 114: health

and safet!, I t3 -15 ; from heat. I13 heat conductivity: of aluminum.*coated steels, 7 I ; oí

cast iron. 105-06: of magnesiuni allo)s. 98 heating methods. 2: for cast iron. 105-06: for copper

and copper alloys. 64: for lead and lead alloys. 87; for magnesium, 98: for nickel and high-nickel solders, 79; for pipe and tuhing, 12 l , 122: for stainless steels, 76; for steels. 69; for terneplate, 72; for tin. 101-02

I

hot gas soldering. 46 high-nickel alloys. composition of, roble, 80

'hoses for gas fuel, i 14 hydrochloric acid, IS. 17: for acid cleaning. 36 hydrofluoric acid, IS; lor acid cleaning. 36

impact strength, fables, 126, 129 impurities. 5 indium solders. I I . rubles, II, /Ox induction heating. 4. 44, 114 inorganic salts and acids. 14, roble, 15 inspection and testing of soldered join&, 5 1-62 insufficient solder in joint, fable. 57 intergranular penetration. 92 intermediate fluxes. 15.16, roble, 15 intermetalli.c compounds, 8. 140 ionic contaminants.fig.. 61 Izad impact test, ruble, 129


AWS S M * I N D E X ** W 0784265 OOCIb42b 9 W I

jigging, 2, 2 4 . j i ~ . , 25, fable. 31 joint clcarancc, 23. 24, 26,JiR.. 26. 133; for coated

sicels. 71: for pipe and iubc, 117; for steel, 70; tor tin-antimony-lead solden. 8; for tin-lead solders, 4

joini design, 21.33.figs.. 22-26 ,32 ,33 , fables. 28-32; for aluminum alloys. 94.95: for lead and lead al. toys, 87; for magnesium, 98: for nickcl and nickcl alloys. 80: for precious mcials. 108: for stainlcss sicel, 77; for s1ccI. 70; for icrncptaic, 72; for iin. 102-03

joini fit-up. 2 joini properties,.? I, 129.43, fahlrs. 129-35, Ij4-42,

joinis, dclects in. /ahIr, 57; in pipes and iubcs. I24 jigs.. 136-38. 140-43

land spacing, 27 lap joints, 21, 22. 27 lap shear icst, 59 Icad and Icad alloys, 83-89; fatiguc of. 83; fluxes of.

87; hardness of. 83; heating mcihods, 87; mcchani- cal clcaning of, 83; mechanicjd propcnics of, 83; ' pori soldering treatment of, 88; soldcring of. 8X: soldcrs for, 83; suríace prcparaiion of. 8 3 : icchnique for wiping,/igs., RJ-86; thermal cxpan. sion oi,/igs., 28.29; types of joints of. 87, 88; wetting ability of, I

lcad.bismuth solders. 91 Icad pipc and plumbing joints, 87, 88 Icad pull icst,fig., 60 lead.silver soldcn, 9 , iahlts, 9, II lead-iin antimony, I2X.?Y lead-tin soldcrs, 3.5, fi^., 5. /ablr , 6 .7 . liquidus iempcraturcs, I , 3-12, 132.35, fahles, 6.7,

In.), joints, 22.24,/lx.. 23: for Icad and lead alloys. 87 low iempcraiure (room iemperaiurc) propenics of sol.

dcr, 125, iahlr, 126 (cryogcnic) 12X. iublr, 129 low icnipcraiurc soldering. 133, fahle. 134

magncsium and magnesium alloys, 97.99. rahlc, 98 nicltinp characicrisiics. 3. I I ./i~.. 5 , fablcc. &7. 9-11 ,

mctal coaiings on sicels, iahlr, 74 motor-generator cquipnicni for induciion heating. 45 movement in soldered joint.fig.. 58

nickel and cobalt plated steels. 72 nickcl and high nickcl alloys, 79-8 I , rahlr, 80: acids

nitric acida,36 nondcsiructive icsiing of soldercd joints, 57-59. I24

organ pipes of soldercd t in . / iR. . 10.7 organic acids in intermediate fluxes. I5 organic hydrohalidcs uscd in iniermcdiaic fluxes, 15 cirnanicntal trim of solúcrcd stainless steel. 77

9-12, 132-35, f i x . . 5

132.35

for cleaning, 37

ttidexl1.17

orthophosphoric acid. 15; Cor acid cleaning. 36 oven soldering, 4, 46 oxidc fiims: on aluminum alloys. 91; on magnesium

alloys. 97: removal oí. 13

palladium, 107 paste fluxcs. 16 pasic solder, 16 peel test, 59,jig.. 60, 138. 140. fahle, 141 pcrceniagc of solder f i l l . 23./ig., 26 pcrsonal cleanliness. I I S pcwicr soldering, IOI.O3,j58., IO? pipe and lubes. 117-24, fahles. 118-20, j ig.# 124 pipe joints in Icad and lead alloys. 87 pipe of t in . 101.03 plaicd magnesium. 99 plumbers soil. 83 polishcd stainless stccl soldering. 76 post soldcnnp treatmcnt: for cast irons. 106: for copper

and copper alloys. 65: for lead alloys. 88: for mag. nesium alloys, 9X-99: for nickcl and high-nickel alloys, 80; for pipe and iubcs. 123: for prccious mcials. iahlc. 108: for stainless stccls, 77; for t in and i in alloys. 103

'

potassium chloride in flux, I S precious mctalq. 107-0X.jg.. IiKI, rahlr. /OH precoaiing. 2, 37; for indium solden. IO; of nickel and

high.nickcl alloys. 79-80: of steel. h9 preformcd l cads , / i~ . , 33 preheating in wave soldcripp. 47 pressure ratings for coppcf tubing. 136, ruhlr, 139 prcssurc icstinp. 58 ruhic. 139 prciinning. YS-96 printed circuits, 32-31. fahle. 32, j i ~ s . . 32, 3 3 , 61.

procedures for soldering. I , 2 processsoldenng: torch. 43: dip, 43: induciion hcaiing, 4: rcsistancc hcating. 45: oven, 46; ultrasonic. 46; ftxruscd infrared. 46; hot gas, 47

properties of soldcrcd joints. 2 1 , 129-43 propcnies of solders a i clcvared ienipcraturcs. I28

io9-i2.jiR.. 110

radiaiors. 4. 2 5 radiography. 59. 124. / i~. , 124 reaction fluxes for aluminum and aluminum alloys. 94 reactions bcrween solder and coppcr, 140,fi~s,. 142,

removal of surface films by ultrasonic vibration, 46,

rcpair of printed circuiis, I12 rcsidues, 14, 49.50. See also f lux removal; flux

rcsisiance hcating. 45: of tubular parts./ig.. 122; flux

143

95.97

residues

selection, 32


I 4 8 Diidex

hodium, 107 msin base flux. 2, 9. 16, 20, 102 rosin joint. rable, 57.fig. , 58 rotary dip tesi, 53,fig.. 53

safely and health proieciion. 113-15, 136. rahle. 139 sanitary cans, 73 sealing solder, 88 self-jigging suppon, 24. 25. 3 l , f i ~ s . , 25. 31 shear strength. 125, 130. rable. 130 shear tesis, óO.fi8.. 60 silver. 7, 107, 108. roble. 108 sockct joini lor tubes, 23.fix.. 23 sodium chloride in fluxes. 15, 17 solder coatings on aluminum alloys, 95 solder cups. 117 solder joini deíecis. 57-59. roble, 57 . j ig . . 58. 5Y solder pois. 113, I14 solderability, 52-55; of aluminum alloys, rable. !73: oí

cadmium plated steels. 72; of copper alloys. roble 68; of high-nickel alloys. rohle, HO

solderability tests. I , 5?.55./i~s.. 52.56 soldered cable joti ts, 88 soldsred joints: corrosion or. 91; designs of. II -33; of

eicciricai circuiis. robles. 313.32: inspeciion and iesting oí, 51-62: oí lead and lead alloys. 87. 88. of printed circuits. 109-12; of siainless sieel ai high ieniperaiure~~'76; propcnies of. 129.44; visual

soldering: applicaiions of. 2; oí aluminum allovs, 91 596; of cadmium coaied'sieels, 71, 72; oí coated steelb. 71 -74; of copper and copper alloys, 63.68; ai elevaied temperatures. 13 I ; equipment For. 41.43; of leid and lead alloys. 83.89; of lead cable sleeve>, 88; ai low tempcraiures, 133: oímagnesiuni alloys. 97.99: of nickel and nickel a l l r y . 79.8 I ; oí nickel plaicd steels, 72; oí pewicr. IOI-03.jix.. 102; oí pipe and tubcs. 117.23; oí plaicd niagnesiuni, 99; of precious metals, 102-OK: principlcs of, I ; of printed circuiis. 109.12; proccsses of. 43.48; of stainless steels. 75.77; of steels. 69-70: sieps in . 2; oí terneplaie, 72; of t i n . 10143; oí tubular joints. I l ? , 121

soldering irons. 4 Id3, f i~s . 4 2 , 4 4 ; for lead joints. 87; for soldering sieel. 69; grounding of, I14

soldering tcmperaiure, 133

Cexaminaiion oí. 57

'solders. 3-12; abrasion, 95; for aluminum alloys. 91-96; for brdss pipe and tubing. 123; cadmiuni: silver, 9 , fable, 10: cadmium-zinc. 10, rable, 10, 91.92; for cast iron. 105; for coated steels, 71-74; commercial forms of. rohle, 12: for copper and copper alloys. 63. 123; fusible alloy. 10.rablc. /O; indium, I I . rohle. I / : for lead and lead alloys. 83; Icad.bisrnuth. 91, 93: lead-silver, 9 , rnblr, I l ; Tor magnesium and magnesium alloys. 97.98. rahlr.

98; for nickel alloys, 79; for nickel and cobalt p l a id steels. 72; for precious mcials, 107-08, fa - ble, 108; preplacement of. fig., 24: for printed circuits, I 1 I ; propenìes of. 125-44; forse&..lp. 88; for slainless steels, 75; for siecl. 69; for t in. 101; tin, table, II: tin-antimony, 8 , roble. 7 ; t i n . antimony.lead, 8: tin-cadmium. 98; (in-lead. 4, roble, 6, 91, 93. 97, 98: tin-silver. 8 , rahle, 7 ; lin-zinc, 8, rable. 9. 91, 93, 97, 98; tin-tinc- cadmium, 97. 98; Tor zinc. 5; zinc-aluminum, I O , rable, IO; for zinc coated steels, 73

solid state conveners for induction heating, 4 5 solidus iemperaiure, I . 3. 4 , 98 solvent depreasing, 35 . spray gun soldering, 43 stainless steels, 75.77 stannous chloride in ñuxes. 15 sicaric acid as a f lux , 83

sires) during elevated iemperaiures, 13 I . roble, 131. 140.jí8.. t41

s u m rupiure iests. 60 substrate composition. 133 sulphuric acid lor cleaning. 36 surface contaminants, 13 suríacc films. See oxides ' surlace preparation, 35-39; of aluminum and aluminum

alloys. 61. 95; oí cast irons, 105: 01 copper and copper alloys, 3 6 , h ; of lead and leadalíoys, 83: of magnesium 98; of nickel alloys. 37.79; oí precious meials. 108: of printed circuits. I I I ; of siainlcss steels, 37, 75: of steel. 69; of tin. 101

ruble, 128

Sicels. 69-70

surface tension of solder. 127; test. 55-56,Jig.. 56

lank-io-tube plaie joini. 26.fig., 26 iCnsilC strength. 8. 125. iable. 126: lest. 60 lemeplaie. 69, 72, rahle. 74 tesiinp oí soldered joinis. S 1-62 thermal conductivity: of copper. 63: oí magnesiuni. 98;

Of siainless steel. 76: oí solders. iahlr. 127 thermal expansion. 125. 1 2 7 ; of aluminum and

aluminym alloys. 91; oí rneials and alloys. /ahles. 28. 29: oí soldcn and babe metals. I I ; oí siainless steels, 26

thickness of joint propenies. 129 time, soldering. i30 tin and tin alloys, 101.03; i n tin.aniimony solders. 8 .

rable,7; i n iin-antimony-lead solders. 8; in i in-

cadmium solders. 97, 98; in tiplead-alloy system. j~., 5:in tin-lead solders. robles. 6-7.89,97,98; in t in4lver solders. 8, roble. 7 ; i n tin-zinc solders, 8-9. roble. 10. 97, 98; in tin-zinc-cadmium solders. 97.98

tin coated steels, 73 tia pipe. 102-03


AWS S M * I N D E X * * W 0784265 O006428 2 I

Index/ I49

tinning, 1 warpage, 2 torch soldering. 4, 43; of pewter, f i g . , 102: of tin

torsional suength. 138, rabie, 144: tests, 59 TRI-Moorc lest, 53 Tube connections: socket joint,Jig., 26; knk-to-tube

water soluble flux residue, 59

wave shapes, 48 . wave soldering, 47-48.Jig., 65 wetting characteristics, 1, 2 ; of aluminum alloys,

93-94; oí solders for magnesium, 97; testing of, 1 , 53,/igs., 54. 55: oí tinzlead solders. 4

alloys, 101 wave fluxing, 47

plaie&., 23

width oí reaction layer. 140,Jig., 143 wiped joints, 87 , f ig s . , 84-86 wiping solder, 83

ultrasonic soldering. 46; of aluminum alloys. 95-96: of magnesium alloys, 97

wire connections, 27. 30-32,Jg.. 32 wTapping test. 51

zinc.’¡. 5 , ! O , rabies. 10, I I ; cadmium-tinc solden. IO.tab’!c, 10. 91. 92, tin-zinc solders. 8. IO.tob/e, I I . 91. 92; zinc-aluminum solder. IO. rabie, IO

vacuum rube oscillator for induction heating. 45 venr¡laiion. I 13, I I5 venting oí closed-end joint. 23,Jig.. 23 viscosity, mb/e. 128 visual examinaiion. 57 visual method for grading solder deíccts. fable, 57, zinc chloride. 2, 14, 17, 18. 19

zinc coated sheets, 73 Jig.. 58

I


CHAPTER 1

PRINCIPLES OF SOLDERING

GENERAL PROCEDURES

Soldering is a group of welding processes which produces coalescence of materials by heating them to a suitable temperature and by using a filler metal having a liquidus not exceeding 450” C (840” F) and below the solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the joint by capillary attraction.

WETTING, ALLOYING, AND CAPILLARITY

When a molten. solder leaves a continuous, permanent film on the base metal surfacesit is said to wet that surface. Wetting is frequently incorrectly referred to as tinning, which actually means precoating the base metal with solder, whether or not the solder contains tin. Without wetting there can be no soldering action. In order for wetting to occur, theremust be a stronger attraction between certain atoms of the solder and the base metal than among the atoms of the solder itself. Inter- metallic reactions usually take place at the infer- face between the base metal and the solder. This wetting action is partly chemical in nature.

Wetting is greatly facilitated by the ability of a solder to alloy with the base metal. For example, pure lead does not readily wet (or adhere to) either copper or steel, whereas a tin-lead solder readily wets both. Lead does not alloy with copper or iron but tin does. Some other metals, such as zinc, increase the wetting properties of lead.

Wetting is often associated with the ease of intermetallic compound formation. Although heat is applied to facilitate wetting, prolonged heating must be avoided when some solders are applied to certain metais. Excessive intermetallic reactions, due to prolonged heating, may cause brittleness or a reduction in joint strength.

The fluidity of molfen solder is an important property which influences the spreading of the solder over the met. surfaces. The flowability, or spread, of a solder may be determined by a variety of methods. The simplest method is to melt a given volume of solder by uniform heating on a standard metal plate with a specific flux. The area covered by the solder is a measure of the solder’s flow properties on that metal.

The flow of solder into narrow spaces by capillary attraction is important, and a number of tests for determining this property have been devised, for example, measuring the rise of molten solder between standard twisted wires or between plates with a small, measured gap. Such tests are useful for qualification work. The introduction of automated, high rate sol-

dering operations has added a new dimension to solder testing. In addition to wetting, flow, and capillary, it has become necessary to measure the rate at which wetting occurs. Several fully automated instruments, “Solderability Testers,” have been developed to provide these data. The instruments quantitatively record the reaction force between the base metal specimen and the molten solder, as a function of time. The recorded data provide a quantitative evaluation of a solder

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2ISOLDERING MANUAL

system. showing both static and dynamic charac- teSStics. The instruments are used in soldering product and process development and for quality control functions.

BASIC STEPS IN SOLDERING Joint Fit-Up

Clearances between the parts being joined should be such that the solder can be drawn into the space between them by capillarity, but not so large that the solder cannot fill the gap. A clearance of 0.15mm (=O.O05 in.) is suitable for most work except when precoated metals are used, in which case a clearance of 0.025 mm (=O.O01 in.) or less is advisable (see Chapter 4 for further details).

hecleaning A clean, oxide-free surface is imperative to ensure uniform quality and a sound soldered joint. If all grease, oil, dirt, And oxides have been carefully removed from the base metal before soldering, there is a much better chance of obtaining a sound joint because only then can uniform capillary attraction be obfained. Chapter 5 contains a detailed discussion of cleaning methods.

Application of Nux The flux that is applied to the surfaces to be soldered should have the following characteristics:

1. It should be fluid and effective in removing oxides and other nonmetallic materials that might be present at soldering temperatures.

2. It should be a banier to reoxidation of the metal surface that has been previously cleaned.

3. It should permit displacement by thesolder. 4. It should promote wetting of the surface by

The various types of soldering fluxes used are the solder.

discussed in Chapter 3.

Application o€ Heat After the flux is applied, the next step in a soldering operation generally is the application of heat. A number of different heating methods are used; they are described in detail in Chapter 6.

Applying the Solder Soldering takes place in two steps: wetting the metal surfaces and then filling the gap between them with solder. The two steps can be carried out separately or together, depending upon the conditions dictated by the application. In general, each sfep is better done separately because the conditions can be more easily controlled. It is frequently desirable to precoat the base metal, especially if it is difficult to solder, with solder or solderable metals.

Cooling the Joint After the surfaces of the joint have been wetted and the space between them filled with solder, the next step is to cool the joint to room temperature.

Properjigging, assembly, or controlled cooling may be employed to prevent excessive deformation of the joint or failure of the joint during solidification of the solder. The solder should be cooled and solidified as rapidly as possible, commensurate with the requirements of the assembly and the solder used, as slow cooling may cause excessive alloying resulting in embrittlement. Fast cooling from too high a temperature may cause warpage and may also cause small fractures in the solder.

Cooling may normally be achieved either by conducting the heat away to the main mass of the assembly or by accelerating it with a water spray or air blast. The cooling method should be varied to suit each individual job.

Flux Residue ïkeatment

After the soldered joint is completed, there is a flux residue which may or may not be removed, depending upon its degree of corrosiveness. Noncorrosive fluxes, which generally have a rosin base, do not require removal of the residue unless appearance is a prime factor or the joint area is to be painted or otherwise coated. On the other hand, corrosive fluxes, such as those having a zinc chloride or other corrosive base, leave a fused residue which, if not removed, would most likely cause corrosion. The self-neutralizing fluxes vary from slightly to highly corrosive and should be treated accordingly as to the removal of the residue(for more detailed information referto Chapter 7).


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CHAPTER 2

GENERAL

A better understanding of the nature of solders, and how to select one for a specific application, can be obtained by examining the melting characteristics of metais and alloys. Pure metals trans- form from the solid to liquid state at one temperature. The melting of alloys is more complicated because they may melt over a temperature range. Any alloy system can best be studied by examining the phase diagram which shows the melting characteristics in relation to chemical composition.

The Tin-Lead Diagram The tin-lead phase diagram is shown in Fig. 2.1. The terms used are defined as follows:

The solidus temperature is the highest temper- aNre at which a metal or solder is completely solid (curve ACEDB of Fig. 2. i).

The liquidus temperature is the lowest temperature at which a metal or solder is completely liquid (AEB of Fig. 2.1).

Melting point and flow point are terms which have been in common use, but they have not always been applied with the same meaning. For this reason the terms solidus temperature and liquidus temperature, which can be more clearly defined, will be used.

Eutectic compositions are those specific solder compositions that melt at one temperature and

3

not over a range. In this respect eutectic solders behave like pure metals. In any binary system having a eutectic, the eutectic is that composition where two descending liquidus curves meet. Thus the eutectic composition (point E in Fig. 2. I ) has a lower liquidus temperature than its neighboring compositions.

Asshownin Fig.2.1,100%lead hasamelting point of 327' C (621' F) (point A), whereas 100(.70 tin has a melting point of232' C(450' F) (point B).

It will be observed that the tin-lead solders containing from 19.5% tin (point C) to 97.5% tin (point D) have the same solidus temperature- 183" C (361" Figure 2.1 shows that the eutectic composition is approximately 63% tin and 37% lead (point E). When this composition melts, it becomes completely liquid at 183" C (361" F). Any composition other than the eutectic composition will not become completely liquid until a higher temperature is reached. For example: 50% tin-50% lead solder has a solidus temperature of 183" C (361" F) and liquidus temperature of 216" C (421' F). This combination of tin and lead will begin to melt at 183' C (361' F) and will become completely liquid at 216" C(421" F).

At temperatures between the solidus and liquidus lines, the solder is partially melted. The region between the solidus (ACEDB) and liquidus (AEB) lines is called the melting range.

o COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

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4/SOLDERING MANUAL

TYPES OF SOLDERS

Tin-Lead Solders

The tin-lead alloys are the most widely used solders and are used for joining most metals.

Joint clearances of O. 1 to O. 15 mm (0.003 to 0.005 in.) are optimum, but variations are allowable in specific instances. Capillary attraction, as a force to fill gaps with solder, does not function with clearances grezter than 0.25 mm (0.010 in.). All cleaning and soldering processesmay be used with the tin-lead solders. Fluxes of all types are used with these solders. The selection is dependent on the type of metais to be joined. The treatment of the flux residues is dictated by the flux used. These solders have good corrosion resistance to most of the common media. Some characteristics of the tin-lead solders are shown in Table 2.1.

The 2A and 5A solders have relatively high solidus temperatures with a short melfing range? The wetting and flow characteristics are poorer than those of the higher tin content solders, which necessitatesextra care in surface preparation. The high leadcontaining solders, used for some a u t e motiveradiators, havebetter strength properties at 150" C (=300" F) than tin-lead solders containing more tin. The high soldering temperature limits the use of organic base fluxes such as rosin or those of the intermediate type (see Chapter 3). The 5A solder is particularly adaptable to torch, dip, induction, or oven soldering. The low tin sol-

, ders are used for sealing precoated containers, coating and joining metals, and for moderately elevated temperature uses.

The 10B, 15B, and 20B solders have lower liquidus and solidus temperatures but wider melting ranges than the 5A solder. The wetting and flow characteristics are also better. Joint clearances are the sameas already described. Extreme care must be taken to avoid movement of the solder joint during solidification to prevent hot tearing. Fluxes of all types and all heating methods are applicable. These solders are used for fabricating automobile radiators and coating and joining of metals where service temperatures are low enough to permit their use.

'The solder classification system used in this document conforms to that given in ASTM B32.

The 25A and 30A solders have lower liquidus temperatures than all previously mentioned alloys but have the same solidus temperature as the 20B solder. Therefore, the melting range is narrower. Ali standard cleaning, fluxing, and soldering techniques can be used with these solders. Machine and torch soldering are widely used. Many automobile radiators and cans are made with solders of this type.

The 35A, N A , 45A, and 50A solders have liquidus temperafures low enough to be easily worked. The solidus temperature is the same as that for 20B to 30A solders. The melting ranges, therefore, are relatively narrow. Solders of this group have the best combination of wetting properties, strength, and economy and, as such, are widely used. These tin-lead solders are the general purpose solders and are used for wiping and sweating solders. Soldering automobile radiator cores, electrical connections, roofing seams, and heating units are but a few of the typical applications for these solders. The 40% tin-60% lead solder has become a very popular general purpose solder and is used extensively in sheet metal work. It is used as arosin cored wire for radio and television applications.

The 60A and 63A solders are generally referred to as fine solders and are used wherever temperature requirements are critical. These solders are most commonly used for wave and dip soldering of electronic assemblies. Ali methods of cleaning, fluxing, and heating may be used with these solders.

The 70A solder is a special purpose solder used where high tin content is necessary Ail soldering techniques are applicable.

Effects of Impurities on the Performance of Tin-Lead Solders

Impurities in tin-lead solders can result not only from carelessness in the refining and alloying operations but can also be added inadvertently during normal usage. Impurity pickup, however, can readily occur during many soldering operations. Because refining of metais requires specialized equipment and close metallurgical control, purification of solders by the user is not generally recommended.


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SolderslS

400

350

300

250

200

v 150

100

50

O

Lead 10 20 30 40 50 60 70 80 90 Tin Tin percent

Fig. 2.1 - Phase diagram for the tin-lead alloy system

Zinc and Aluminum. The soldering properties of tin-lead solders are acutely affected by small traces of aluminum or zinc. More than 0.005% of either metal may cause lack of adhe- sion, grittiness, or susceptibility to failure during solidification. Both ASTM and federal specifications limit the maximum amount of either of these metals to 0.005%.

Iron. The presence of iron-tin compounds makes tin-lead solders hard and gritty, although harmful effects are not ordinarily detectable below 0.1%. ASTM and federal specifications limit iron content to 0.02%.

Copper. There is considerable discrepancy between British and American standards on copper limits in tin-lead solders. The British Standard Specification has a value of 0.5% maximum compared to a limit of 0.088 for both ASTM and federal specifications. Copper amounts above 0.3% may adversely affect the appearance of soldered joints.

Antimony. Antimony can play a dual role in tin-lead solders. Depending on the purpose for

which the solder is to be used, it can be considered as either an impurity or as a substitute for some of the tin in the solder. Federal Specifica- tion QQ-S-571 requires antimony content of 0.2 to 0.5% maximum for compositions Sn 70, Sn 63, Sn 62, Sn 60, Sn 50, Sn 40, Sn 30, and Sn 20. However, grades Sn 35, Sn 30, and Sn 20 require antimony contents up to approximately 6% of the tin content. ASTM B32, Class A, specifies a maximum of 0.12% antimony €or solders containing more than 35% tin, and Class B requires 0.2 to 0.508 antimony content. Class C covers solders containing 20 to 40% tin and specifies that the antimony content is not to exceed 6% of the tin content.

Arsenic. Contaminatjon well in excess (2 to 4 times) of the specified 0.02-0.03% arsenic may cause dewetting on brass or copper. Spots may occur on bar solder, but soldered joints will not be

Excessive Contamination in Dip Soldering. Excessive contamination in dip soidering is usually indicated when, after operating for some

frosty.


6ISOLDERING MANUAL

l l l l N l l l l l l l l l l l l l l l l l 1 1


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I I I I I

I l I I I

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Solders17

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8/SOLDERING MANUAL

time at a reasonable solder pot temperature, it becomes necessary to increase the pot temperature substantially to overcome what appears to be sluggishness in the solder. Excessive contamination is also characterized by a rough and gritty solder bond. The increase of the pot temperature to overcome sluggishness is only a temporary expedient since the increased temperature will further accelerate contamination.

ASTM and federal solder specifications which specify maximum allowable concentrations of impurities for different grades of solders are intended only as a basis for purchasing solder. Their use as a guide for determining when solder is contaminated could result in discarding solder that is still very satisfactory for the purpose intended. Thus, although the federal specifications require that the iron content be less than 0.02%, bad effects, such as grittiness, are usually not detectable below O. 1%.

Some iron and copper can be removed from the contaminated solder by taking advantage of the lower solubility of copper-tin and iron-tin compounds at the liquidus temperatures. For best results the temperature of the solder should be lowered to just above the liquidus temperature of the uncontaminated solder, at which point the copper-tin and iron-tin compounds will crystal- lize. These crystals (dross) can be removed with a perforated ladle.

Tindntimony-Lead Solders

Antimony may be present as an impurity in solder, or deliberately added. The solders for which 0.2 to 0.5% antimony is the specified range are generally classed as B solders, Le., 20B, 30B, 40B, etc. Federal Specification QQ-S-571 requires the presence of antimony to prevent the possible phase change from beta tin to alpha tin (called the tin pest), with the accompanying change in volume and drastic loss of solder strength. These solders may normally be used, except in very special cases, for the same applications as the A solders. Antimony may be added to a tin-leadsolderasasubstitute forsome of the tin. The addition of antimony up to 6% of the tin content increases the mechanical properties of the solder with but slight impairment of the soldering characteristics,

Joint clearances for the tin-antimony-lead solders should be from O. l to O. 15 mm (=0.003 to 0.005in.), whereas0.25 mm(O.0 loin.) isapracti- cai maximum to obtain capillary flow. All standard methods of cleaning, fluxing, and heating may be used with these solders. Their use is not recommended on aluminum, zinc, or zinc coated metals, such as galvanized iron. Solders containing antimony, when used on zinc or zinc alloys, form an intermetallic compound of zinc and antimony which causes the solder joint to become brittle.

The 20C to 4ûC solders have melting properties closely approximating those of equivalent A solders containing 5% more tin (see Table 2.1). The tensilesîrength, creep strength, and hardness ofthesolderedjointsarehigherthanthoseobtained with nonantimonial solders, but solder flow and capillarity are somewhat lower. The use of these solders i s limited to soldering non-zinc- containing metais or coatings.

Tin-Antimony Solder

The tin-antimony sold& shown in Table 2.2 has excellent soldering and strength characteristics. It is useful for application where moderately elevated temperature is a factor. It has a higher electrical conductivity than the tin-lead solders and is also recommended in applications such as in food handling vessels where lead contamination must be avoided. This solder may be easily applied with rosin fluxes.

Tin-Silver Solders

The characteristic of the tin-silver solder, listed in Table 2.3, is similar to those of the tin-antimony solder. The tin-silver solders are usually used for fine instrument work and some specialty tube joining because the cost is pro- hibitive for general purpose soldering. They are easy to apply with rosin flux.

Tin-Zinc Solders

A large number of tin-zinc solders, some of which are listed in Table 2.4, have come into use for the joining of aluminum. Galvanic corrosion of soldered joints in aluminum is minimized ifthe metals in the joint are close to each other in the electrochemical series. Thus, alloys containing


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70 to 80% tin, balance zinc, have been highly recommended. These alloys have liquidus tem; peratures between 260" and 310" C (500" and 5900 F). In recent years the tendency has been to add 1 to 2% aluminum or to raise the zinc content to as high as 40%. These solders are more corrosion resistant but they have higher liquidus temperatures and are therefore a little more difficult to apply (see Chapter 15 on aluminum).

Lead-Silver Solders

Lead-silver solders listed in Table 2.5 have solidus temperatures high enough to make them useful where strength at moderately elevated temperatures is required. Although pure lead melts at 327" C (621" F), a comparatively high temperature for solder, it is not used because lead normally does not wet steel, cast iron, or copper and its alloys. The addition of silver to lead re- suits in alloys which will more readily wet steel and copper. Flow characteristics, however, are very poor. The lead-silver solders are susceptible to humid atmospheric corrosion in storage and may become unusable as solders. The addition of I% tin to a lead-silver solder increases its wetting and flow characteristics and, in addition, reduces its susceptibility to humid atmospheric corrosion.

%bible 2.4 -Tin-zinc solders

Composition Temperature (weight %I Solidus Liquidus

Sn 2 n "C O F O C "F

91 9 199 .390 199 390 80 20 199 390 270 518 70 30 199 390 311 592 60 40 199 390 341 645 30 70 199 390 376 708

Solders19

The addition of tin to a lead-silver solder containing more than 1.75% silver causes the segregation of tin-silver intermetallic crystals. Therefore, silver content is generally limited to 1.5% when tin is to be added.

The tensile, creep, and shear strengths of these solders at temperatures up to 175" C ( ~ 3 5 0 ' F) are good. Their fatigue properties are considerably better thanthose of the solders that do not contain silver. The lead-silver solders require higher soldering temperatures and special fluxing techniques. The use of a zinc chloride base flux to produce a good joint on uncoated metals is recommended. Rosin fluxes are readily decomposed at the higher soldering temperatures and can be used only when the soldering time is relatively short (see Chapter 3).

Cadmium-Silver Solder

The 95% cadmium-5% silver solder has melting characteristics shown in Table 2.6. The primary use of this solder is in applications where service temperatures will be higher than permissible with lower melting solders. At room temperature butt joints in copper can be made to produce tensile strengths of 170MPa (25 o00 psi). At 220" C (=425"F) a tensiiestrength of 18 MPa (2600 psi) can be obtained.

Joining of aluminum to itself or dissimilar metals is possible with cadmium-silver solder. However, as is generally true in joining aluminum with dissimilar metals, electrolytic corrosion must be considered. Improper use of this solder may lead to health hazards (see Chap- ter 21 for safety precautions).

%able 2.5 -Lead-silver solders

ASTM Fed. Composition (weight '75) Temperature Alloy Spec. Solidus Liquidus Grade QQ-S-571 Pb Ag Sn "C "F "C "F

2.5 S Ag 2.5 97.5 2.5 - 304 579 304 579 5.5 s Ag 5.5 94.5 5.5 - 304 579 365 689 1.5 s Ag 1.5 97.5 1.5 1.0 309 588 309 588


IO/SOLDERING MANUAL

Cadmium-Zinc Solders 3. Step soldering operations where a low soldering temperature is necessary in order to avoid destroying a nearby joint that has been made with a higher melting temperature solder.

4. On temperature sensing devices where the failure of a soldered joint is required at a relatively low temperature, which is known as the yield temperature.

The cadmium-zinc solders, listed in Table 2.7, are useful for soldering aluminum. These solders develop joints with intermediate strength and corrosion resistance when used with the proper flux. The40% cad~um-6O%zincsolderhasfoundcon- siderable use in the spot soldering of aluminum lamp bases. Improper use of these solders may lead to health h a i d s (see Chapter 21 for safety precautions).

Zinc-Aluminum Solder 'Iàble 2.6-Cadmium-silver solder

Composition Temperature The zinc base solder, shown in Table 2.8, is weight %.) Solidus Liquidus specifically for use on aluminum and develops CL Ag "C "F "C "F joints with high strength and good corrosion resistance. The solidus temperature of the sdder is 95 5 338 640 393 740 high, which limits its use to applications where soldering temperatures in excess of 370" C ( =70O0 F) can be tolerated. This solder is extensively used in ultrasonic soldering of aluminum heat exchanger return bends.

Table 2.7- Cadmium-zinc solders -

Fusible Alloys Bismuth-containing solders, the so-called fusible alloys, are useful for soldering operations where a soldering temperature below 183" C (361" F) (lower than that available with the tin-lead solders) is required. The melting characteristics and compositions of a representative group of fusible alloys are shown in Table 2.9.

Fusible alloys have applications in cases such as the following:

1. Soldering heat treated surfaces where higher soldering temperatures would result in a soften- ing of the part.

2. Soldering joints where adjacent material is very temperature sensitive and would deteriorate if a higher soldering temperature were necessary.

Composition Temperature (weight %.) Solidus Liquidus

Cd Zn O C "F "C O F

82.5 17.5 265 509 265 509 40 60 265 509 335 635 10 90 265 509 399 750

Table 2.8-Zinc-aluminum solder

Composition Temperature . (weight %) Solidus Liquidus Zn AI "C OF "C "F

95 5 382 720 382 720

Table 2.9 -Typical fusible alloys

Yield

Sn Bi Pb Cd Others "C "F "C "F "C O F

Composition (weight %) Solidus Liquidus temperature

13.3 50.5 26.7 10 - 70 158 70 158 70 158 15.5 52.5 32.0 - - 90 203 90 203 90 203 14.5 48.0 28.5 - antimony9.0 103 217 227 440 116 241 - 55.5 44.5 - - 124 255 124 255 124 255 43 57.0 - - - 138 281 138 281 138 281


AUS S M * C H * 2

Many of these solders, particularly those containing a high percentage of bismuth, are very difficult to use successfully in high speed soldering operations. Particular attention must be paid to clean metal surfaces and the use of strong fluxes to obtain satisfactory joints on uncoated metal surfaces such as copper or steel. On uncoated surfaces it is very unlikely that satisfactory soldering can be obtained with a noncorrosive type flux. If a plated surface, such as tin, silver, or cadmium, canbeprovidedforsoldering, then there is the possibility of using a noncorrosive. flux. Joints produced with these solders exhibit v e y low creep strengths, particularly above room temperature (see Chapter 4 for recommended joint designs).

Indium Solders Indium solders possess certain properties which make them valuable for some special applications. Their usefulness for any particular application should be checked with the supplier. The melting characteristics and compositions of a representative group of indium solders are shown in Table 2.10.

The standard 97.59 lead-2.5% silver solder does not wet most metais well. Adding 1 to 2% indium to this solder improves its wetting properties. Thus, a higher melting solder can be used without precoating the parts to be soldered. The lead-silver-indium solders are especially applicable where alkaline corrosion is a problem.

Solders1 1 1

Solders containing tin, lead, and indium having more than 25% indium also show very gocd resistance to corrosion by alkaline solutions. However, they start melting at a much lower temperature and have a wider pasty range than thelead-silver-indiumsolder. A 50% indium-50% tin solder adheres to glass readily and may be used for glass-to-metal and glass-to-glass soldering. The low vapor pressure of this alloy makes it useful for seals in vacuum systems.

Indium solders generally do not require special techniques during use. The low melting indium solders containing bismuth do require the use of acid fluxes or precoating. All of the heating methods, fluxes and techniques which are used with the common tin-lead solders are applicable with indium solders.

COMMERCIAL FORMS OF SOLDERS

Typical commercial forms of solder aregivenin Table 2.11.

The tables in this chapter pertaining to solder specification are excerpts. Copies of the latest complete specification should be secured from the following organizations: ASTM American Society for Testing and

Materials, 1916 Race Street, Philadel- phia, Pa. 19103

QQ Federal Specifications, Naval Publica- tion and Forms Center, 5801 Tabor Avenue, Philadelphia, Pa. 19120

Table 2.10-lndium solders

Composition (weight c/r 1 Temperature Solidus Liqu idus

Tin Indium Bismuth Lead Cadmium OC "F "C O F

8.3 19.1 44.7 22.6 5.3 47 117 47 117 12 il 49 18 - 58 136 58 136 12.8 4.0 48.0 25.6 9.6 61 142 65 149 50 50 - - - 117 243 127 260 48 52 - - - 117 243 117 243

/- ci COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

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1 LISOLDERING MANUAL

Table 2.11-Commercial forms of solders

Solders are commercially available in various sizes and shapes which can be grouped into about a dozen classifications. These major groups are listed below. This listing is by no means complete, inasmuch as any desired size, weight, or shape is available on special order.

P ìg Available in nominal 22.5 and 45 kg (50 and 100 Ib.) pigs.

Segment ordrop

Triangular bar or wire cut into any desired number of pieces or

iiigots weighing nominal 1.5,2.5, and 4.5 Wire, Solid Diameters of nominal 0.25 to 6.5 kg (3,5 and i0 Ib.). mm (0.010 to 0.250 in.) on spools.

Bars Available in numerous cross sec- Wire, Solder cored with rosin, organic, tions, weights and lengths. or inorganic fluxes. Diameters of

Ptiste Available as a mixture of pow- nominal 0.25 to 6.5 mm (0.010 to dered solder and suitable flux in 0.250 in.). paste. Preforins Unlimited range of sizes and Available in various thicknesses shapes to meet special require-

Clrkes or Rectangular or circular in shape, lengths.

Flia Cored

Foil, Sheet or Rild~ori and widths. ments.


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CHAPTER 3

FLUXES

DEFINITION

A soldering flux _.. a liquid, solid, or gaseous material which, when heated, is capable of pro- moting or accelerating the wetting of metals by solder. The purpose of a soldering flux is to remove and exclude oxides and other impurities from the joint being soldered. Anything that in- terferes with the attainment of uniform contact between the surface of the base metal and the molten solder wilt prevent the formation of a sound joint. An efficient flux removes films and oxides from the.meta1 and solder and prevents reoxidation of the surfaces when heated. It is designed to lower the surface tension of the molten solder so that the solder will flow readily and adhere to the metal. The flux should be readily displaced from the metal by the molten solder.

THE NATURE OF SURFACE CONTAMINANTS

Surfaces to be soldered are often covered with films of oil, grease, paint, heavy oxides or atmospheric grime which must be removed. Cleaning methods are outlined in Chapter 5.

Chemical reactions occur on clean metal surfaces at room temperature and deposit fresh surface films. Although nitrides, sulfides, and car- bides are formed in some instances, the prevalent reaction is oxidation. The rate of oxide formation, its structure, tenacity and resistance to re-

13

mova1 with a flux varies with each base metal. Aluminum, magnesium, stainless and high alloy steels, aluminum and silicon bronzes, when exposed to air, form hard adherent oxide films. Highly active and corrosive fluxes must be used to remove and prevent the reformation of the tenacious films during soldering. Copper and silver, on the other hand, when exposed to air, form less tenacious films, and at a slower rate, so that mild fluxes remove them easily and prevent them from reforming.

THEORIES OF FLUX ACTION

Many theories have been proposed to explain flux action, and some of these theories have been useful in the development of new fluxes. The most widely held view is that the flux removes the oxide film from the base metal and solder by reacting with and loosening the film and floating it off into the main body of the flux, Because of the refractory nature of many oxide films, it has been suggested that the flux wets, coagulates, and suspends the oxide which has been loosened by a penetrating and reducing action. The molten flux then forms a protective blanket over the bare metal, which prevents the film from reforming. Molten solder displaces the flux and reacts with the base metal to form an intermolecular bond. The solder layer builds up in thickness and when the heat is removed, it solidifies (see Fig. 3.1).


14/SOLDERING MANUAL

c- Direction of movement of soldering iron

A. Flux ove; oxidized metal B. Boiling flux removes oxide C. Base metal in contact with molten flux D. Molten solder displaces molten flux E. Solder alloys with base metal F. Solder solidifies

Fig. 3.1 - Mechanism of flux action

TYPES OF FLUX

Fluxes are frequently classified on the basis of their residues. They are divided into threemain groups: corrosive, intermediate, and noncorrosive fluxes. The mildest flux that will perform satisfactorily in a specific application should always be selected.

Corrosive Fluxes The corrosive fluxes, consisting of inorganic acids and salts, are used to best advantage where conditions require rapid and highly activated fluxing. They can be applied as solutions, pastes, or as dry salts and function equally well with all heating methods, since they do not char or bum.

Corrosive fluxes can be formulated to be stable over various temperature ranges. They are more versatile in this respect than the less corrosive fluxes. Corrosive fluxes are almost always required when the higher melting temperature solders are used.

Corrosive fluxes can be formulated to penetrate the most tenacious of the oxide films. Com- mercial fluxes are available for specific appiica- tions in the form of dilute and concentrated solu-

tions, as pastes, or as fillers for acid core solder wire.

The corrosive fluxes have one distinct disadvantage: The residue remains chemically active after soldering. The residue, if not removed, may cause severe corrosion at the joint. Adjoining areas may also be attacked by residues from the spray or flux vapors. For this reason corrosive fluxes ate not used to solder closed containers such as thermostats or bellows nor to solder assembled electrical equipment. Removal of flux residues is covered in Chapter 7.

The inorganic salts and acids listed in Table 3.1 all have a fluxing action on metals when heated. If a water solution is used, the water rapidly evaporates on heating, and the molten salt reacts with the base metal to produce a protective environmenf which insulates the metal from contact with the air.

Corrosive Flw Ingredients Zinc Chloride. The main ingredient in most corrosive fluxes is zinc chloride. It can be prepared by adding an excess of zinc to concentrated hydrochloric acid or can be purchased as fused zinc chioride, which is more convenient to use. Zinc chloride has a melfing temperature well above the solidus temperature of most commercial tin-lead solders, which means that if it is used alone, unmelted salt particles may be entrapped in the joint. These inclusions will corrode and weaken the joint. It is good practice, therefore, to mix other inorganic chlorides with zinc chloride to lower the melting temperature of the flux.

Ammonium Chloride. A water solution of ammonium chloride may be used as a flux. When the water evaporates, the ammonium chloride sublimes as a white fume. It is less effective than zinc chloride because the protective action of a molten sait is not present and the base metal may reoxidize before it reaches soldering temperature. A combination of one part ammonium chloride to thee parts zinc chloride forms a eutectic flux mixture which melts at 175" C (~350" F). This mixture takes advantage of the excelient oxide reducing properties of the ammonium chloride and the excellent protective action of the zinc chloride to form a flux which is considerably more effective than either con-

-stituent when used alone. A one to nine ratio of


AWS S M * C H * 3 ** 0784Zb5 000b3b4 2 E

Fluxes1 15

I s b l e 3.1-Inorganic salts and acids

(a) Zinc chloride (b) Ammonium chloride (c) Stannous chloride (d) Sodium or potassium chloride (e) Lithium chloride (f) Aluminum chloride

the salts (1 part ammonium chloride to 9 parts zinc chloride) is commonly used without fear of flux inclusionsin the soldered joint.

Stannous Chloride. Stannous chloride is formed by dissolving metallic tin in hydrochloric acid. It is commercially available in the anhy- drous and hydrated forms. Stannous chloride is a highly effective flux when used alone in powder, paste or molten form. It is also effective when mixed with zinc-and ammonium chlorides.

Sodium or Potassium Chloride. Sodium chloride is not effective as a flux when used alone, but is effective in diluting zinc chloride and lowers its melting point. A low melting flux can be obtained by mixing nine parts of zinc chloride with two parts of sodium chloride. A ternary eutectic mixture, melting at 203" C (397" F) is obtained by mixing 75 parts zinc chioride, 11 parts sodium chloride, and 14 parts potassium chloride.

Other Chlorides and Fluorides. Lithium and aluminum chlorides and fluorides are seldom used alone, but they are used effectively as fluxes when mixed with other compounds.

Hydrochloric Acid. Hydrochloric acid has limited use when used alone as a flux. When hydrochloric acid is applied to galvanized iron, the zinc coating is dissolved toformzincchloride, which acts as the flux, Hydrochloric acid is used to activate the zinc chloride type fluxes. Mixtures of inorganic salts and hydrochloric acid are the basis of stainless steel fluxes.

Hydrofluoric Acid: Hydrofluoric acid is extremely corrosive. It is added to zinc chloride base fluxes for the purpose of dissolving silicon inclusions on the surface ofcast iron (see Chapter 21 for safety in handling).

Orthophosphoric Acid. Orthophosphoric acid is an effective flux for steel, copper, and brass. It leaves a glassy residue which serves as a protective coating. A diluted solution is espe-

~~

(g) Sodium or potassium fluoride (h) Boron trifluoride (i) Hydrochloric acid Cj) Hydrofluoric acid fi) Orthophosphoric acid (1) Fluoboric acid

cially effective on high tensile manganese bronze.

Intermediate Fluxes The intermediate fluxes, as a class, are weaker fluxes than the inorganic salt types. They consist mainly of mild organic acids and bases and Cer- tain of their derivatives such as the hydrohalides (see Table 3.2). These fluxes are active at soldering temperatures, but theperiod of activity is short because of their susceptibility to thermal decomposition. Their tendency to volatilize, char, or bum when heated limits their use with torch or flame heating. They are useful, however, in quick spot soldering operations and, when properly used, their rekidue is relatively inert and easily removed with water.

Table 3.2-Typical intermediate flux constituents

Organic acids (a) Lactic acid (b) Citric acid (c) Oleic acid (d) Stearic acid (e) Glutamic acid (f) Benzoic acid (g) Oxalic acid (h) Phthalic acid (i) Abietic acid

(a) Glutamic acid hydrochloride (b) Aniline hydrochloride or phosphate (c) Hydrazine hydrobromide or hydrochloride (d) Cetyl trimethyl ammonium bromide (e) Ethyl dimethyl cetyl ammonium bromide (f) Cetyl pyridinium bromide

(a) Urea (b) Diethylene di- or triamine (c) Glycerol

Organic hydrohalides

Amines and others


I6/SOLDERING MANUAL

Intermediate fluxes are particularly useful in applications where small quantities of flux can be applied and where sufficient heat can be applied to fully decompose or volatilize the corrosive constituents. Caution is necessary where unde- composed flux may spread to insulating sleeving or in soldering closed systems where corrosive fumes may be deposited on critical parts of the assembly. When stranded wire is soldered, caution is necessary to avoid entrapment of the corrosive constituents.

Noncorrosive Fluxes

Noncorrosive fluxes all have rosin as a common ingredient. Rosin has unique physical and chemi- cai properties which make it ideal as a flux. It melts at 127" C (260" F) and remains active in the molten stafe up to 315" C ( =600" F). The active constituent of rosin (abietic acid) is inert in the solid state, active whed molten,. and returns to an inactive state when cooled. Thus it is widely used in the electrical and electronics industries because the flux residue is noncorrosive and nonconductive.

Three types of rosin fluxes are in common use - nonactivated, mildly activated, and activated rosin.

Nonactivated Rosin. Nonactivated rosin consists of rosin plasticized with an inert plasticizer for core solder or dissolved in an inert solvent as a liquid flux. No additives for the purpose of increasing flux activity are used. This is the mildest of the rosin fluxes, and only extremely clean and solderable metals can be soldered reliably with nonactivated rosin. Federal Specifications MIL-F-14256 and QQ-S-571 designafe this type asR. '

Mildly Activated,Rosin. Because of the slow fluxing action of nonactivated rosin, mildly activated rosin is also used. It contains additives which improve the fluxing action of the rosin but leave residues which are noncorrosive and non- conducting. Mildly activated rosin is used in high reliability electronic assemblies, and removal of the flux residue is optional. Mildly activated rosin can be plasticized for core solder or dissolved in an organic solvent to provide a liquid flux. Federal Specifications MIL-F- 14256 and QQ-$571 designate this type as RMA.

Activated Rosin. The activated rosin fluxes are the most active of all and depend on the

addition of small amounts of complex organic compounds for their increased activ.ity. Hydro- halides of amines such as hydrazine hydrohalide, glutamic acid hydrochloride, cetyl pyridinium bromide, aniline hydrochloride and organic acids such as benzoic and succinic have been disclosed in patent literature as additives for activated rosin fluxes to be used in liquid form or as a core material. Additive amounts varying from 0.2 to 5% have been suggested. Fluxes of this type are designated RA.

The use of activated rosin as a noncorrosive flux is based on the theory that the activator is decomposed by heat and that the residue is not electrically conductive or corrosive. High production-line speeds have demanded more highly active fluxes, but the question of harmful flux residues is still a mafter of debate in critical applications where corrosion resistance is the foremost consideration. Paste Fluxes It is sometimes convenient to have the flux in paste form. Paste fluxes can be more easily localized at the joint and have the advantage of not draining off the surface or spreading to other parts of the work where the flux would be harmful. The paste-forming ingredients may be water, petroleum jeiiy, tallow, or lanolin, with glycerine or other moisture-retaining substances. If the pastes contain inorganic salts, such as zinc or ammonium chloride, they are classed as corrosive fluxes.

'

Solder and Flux Pastes

A true paste solder is a stable blend of finely divided metallic solder with inorganic or organic chemicals acting as the flux in a neutral vehicle or carrier. These paste solders are not merely mechanical mixtures of flux and metal. The blending agents prevent a drying action and set- tling of heavy metallic particles. The size and shape of the particle of the metal ingredient have a definite bearing on the stability of the pastes.

Paste solders are well suited for preplacement in oven, radiant heat, resistance and induction heating applications. Automatic preplacement methods have been developed for the paste solders and include dipping, brushing or rolling, point feeding, and line feeding. Corrosive and noncorrosive paste solders are available com-

-- __ . COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

Fluxes I I 7

mercially. The solder composition may vary from 2 5 8 to 60% tin, balance lead.

Reaction Fluxes Reaction fluxes are a special group of corrosive fluxes developed for soldering aluminum. Their action depends on the decomposition of the flux to form a metallic film on the aluminum (see Chapter 15).

SELECTING THE FLUX

The following factors influence the choice of flux:

1. The assembly being soldered 2. Accessibility of the p a t for cleaning after

3. Solderability of the base metals 4. Rate of soldering required 5. Heating method. It is good practice to use the mildest flux that

will do the job. (see Table 3.3). The soldering of complicated electrical equipment requires the choice of a noncorrosive flux, since corrosive residues cannot be tolerated and postcleaning is virtually impossible. Corrosive fluxes can be used when the parts can be thoroughly washed after soldering as, for example, in the assembly of radiators.

Where a small degree of corrosion can be tolerated and removal of the flux residue is impractical, the intermediate fluxes, properly used, are sufficiently active and fast for soldering the more difficult-to-solder metals. The more corrosive fluxes are often demanded, however, because of increased speed in soldering.

Although the base metal is a big factor in flux selection, the converse is also sometimes the case. Thus, in the electrical industry, dífficult-to- solder metals are precoated with metals such as silver, tin, cadmium and copper to permit the use of rosin fluxes.

Methods of heating may govern the choice of flux and, conversely, the flux may determine the choice of heating method. The inorganic salt type fluxes can be eifectively used with any heating method, since they do not char or decompose readily. The intermediate fluxes and rosin base

soldering

fluxes, however, are sensitive to the heating method. Since they are of essentially organic origin, they will decompose and become ineffec- tive when overheated. Torch or flame heating methods, unless carefully controlled, are not generally recommended for intermediate and rosin base fluxes.

TYPICAL FLUX COMPOSITIONS

Proprietary flux formulations are available from solder and flux manufacturers for evexy soldering application. The following flux compositions will show some of the formulations which are used. More detailed information is available from most manufacturers.

Corrosive General Purpose Fluxes These fluxes are effective on low-carbon steel,

copper, brass, and bronze. Applications are in the production of auto radiators, air conditioning and refrigerating equipment, body soldering, and sheet metal assembly.

1. Zinc chloride 1130g &oz. Ammonium chloride í i o g 402. Water to make 4L l g a l

2. Zinc chloride 1020g 3602. Sodium chloride 280g 1Ooz Ammonium chloride 15g 1/2oz. Hydrochloric acid 3 0 g l o z Water to make 4L l g a l

Sodium chloride 170g 60z. 3. Zinc chloride 6oog 21 oz.

(Dryjlux for molten solder cover in dip soldering)

4. Zinc chlonde 7íOg 2502

Petroleum jelly 184Og 6502 Ammonium chloride 1OOg 3-1/2 OZ.

Water 180 g 6-íLZ OZ.

Corrosive Special Purpose Flwes These fluxes can be used for soldering stainless steel, alloy steel, nickel alloys, silicon and aiunhum bronzes, zinc coated sheet, cast iron and aluminum.


AWS S M * C H * 3 **

lS/SOLDERING MANUAL

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i, 'Zinc chloride 2410 g 85 oz. Diethanol diamine í í û g 4oz. Ammonium Chloride 18Og 6-1/2 oz Diethanol triamine 285g 1Ooz Stannous Chloride 260g 9 o z (For soldering aluminum)

Water to make 4 L 1 gal 9. Potassium chloride 1280g 45oz. Wetting agent (optiona1)-O. 1% by weight Sodium chloride 850g 30.0~.

(For stainless steel and galvanized iron) Lithium chloride 4258 15oz.

Ammonium chloride 140 g 5 OZ. pyrophosphate 8 5 g 302 Hydrochloric acid 85g 3oz (For soldering aluminum) Water to make 4 L lga l

Wetting agent (optional)- O. 1% by weight 10. Triethanolamine 710g 2 5 o z (For stainless steel) Fluoboric acid 8 5 g 302

3. Zinc chloride 4558 1 6 0 ~ . (Chloride-free organic flux for soldering Ammonium chloride 455 g 16 oz aluminium. Fluxing range 175" to 275" C[ =350" Glycerin 455 g 16 oz to 525" F). The viscous liquid can be dissolved Water 0 . 5 ~ 1 pint with water or alcohol fo any desired concentra-

4. Orthophosphoric 11. Stannous chloride 1250g 44oz.

Water 4558 16oz. Sodium fluoride 30g loz. (Reaction type flux for soldering aluminum. Fluxing range 280" to 380' C [ 440" to 720" FI or higher. It may be used as a dry powder mixture or it may be suspended in alcohol.)

Hydrochloric acid 6 o g 202

Potassium fluoride 200g 70z. 2. Zinc chloride 136Og 4 8 0 ~ . Sodium

Cadmium fluoborate 5 5 g 20z.

(For Monel) tion.)

acid (859) 96Og 34oz. Ammonium chloride 14og 5oz.

(Forhigh tensile manganese, 6ronZG copper, brass)

9l0 32 oz 4 oz.

5. Zinc chloride Ammonium chloride Sodium chloride 225 g 8OZ. 12. Zinc chloride 125og 4402. Hydrochloric acid 2258. 8oz. Ammonium chloride 14og 5oz. Water to make 4 L l g a l Sodium fluoride 3 0 g l o z

(Reaction flux for soldering aluminum. It may be used as a dry powder or mixed with water or

(For cast iron)

130 40 oz 6, Zinc chloride Ammonium chloride f l o g 4 0 2 alcohol.) Hydrofluoric acid 35g 1-1/40z Intermediate Fluxes Water to make 4 L i. 1 gal These fluxes contain organic compounds which

decompose at soldering temperatures. When 7. Stannous chloride 2350 g 83 OZ. properly used, the mildly corrosive elements in

the flux volatilize, leaving a residue relatively chloride* 200 g 7 OZ. inert and easily removed with water. They are

effective on all materials which are solderable hydrobromide* 2858 100~. with mild fluxes. Typical compositions are as

(Paste Jux for soldering aluminum)

(For cast iron)

Zinc dihydrazinium

Hydrazine

Water 2858 1 0 0 ~ follows:

1. Glutamic acid 8. Cadmium fluoboride 14og 5oz. hydrochloride 540g 19oz.

Zinc fluoboride 14og 5oz. Urea 310g l l o z . Fluoboric acid 170g 6oz. Water 4 1 1 gal Diethanol amine 570 g 20 oz. Wetting agent- 0.2% by weight


20/SOLDERING MANUAL

2. Hydrazine monohydrobromide* 280 g 10 oz.

Water 2550g 90oz. Nonionic wetting

agent 1 .5g 1/200z.

3. Lactic acid (85%) 260g 902.

Wetting agent 3 g 1/10 oz. Water 1190g 4202.

(For beryllium copper)

Noncorrosive Fluxes

The rosin base fluxes - nonactivated, mildly ac- tivatedand activated-belong in thisclass. For all electronic and critical soldering applications, water white rosin dissolved in an organic solvent (item 1 below) is the safest known flux. Ac- tivators added to the rosin increase the activity, but the flux residue from these fluxes should pass tests for noncorrosivity and nonconductance when used on electronic applications. These fluxes are effective on clean copper, brass, bronze, tinplate, terneplate, electrodeposited tin and in alloy coatings, cadmium, nickel, and silver.

i. Water white rosin: 10-25% by weight Alcohol, turpentine or petroleum: balance

Glutamic acid hydrochloride: 2% by weight Alcohol: balance

2. Water white rosin: 40% by weight

3. Water white rosin: 40% by weight Cetyl pyridinium bromide: 4% by weight Alcohol: balance

4. Water white rosin: 40% by weight Stearine: 4% by weight Alcohol: balance

5. Water white rosin: 40% by weight Hydrazine hydrobromide 2% by weight Alcohol: balance

*Stock solution to bewed in concentration of 2-1576 in alcoho€. Hydrazine salts and compounds are highly toxic, and fluxes containing these should be used with caution.

TESTING OF FLUXES

Laboratory tests on fluxes are of questionable value as a final indication of the effectiveness of the flux. However, the following tests are used to classify fluxes according to their efficiency and corrosivity.

F l w Efficiency

The test varies fromone laboratory to another, but the details may be generalized. A circular strand of solder of known weight is placed in the center of a one-inch square piece of clean copper sheet and a few drops ol the flux applied. The copper sheet is placed on a thermostatically controlled hot plate at 260" C ( 5 0 " F) for 60 seconds and then carefully removed. The spread of the solder is measured with a planimeter. The apparatus can be improved by eliminating air currents which may affect the spread or by raising or lowering the sheet onto the hot plate mechanically fo avoid disturbing the solder. A control test with a standard flux is made along with each test as a com- parison of flux efficiency. Although this test procedure is fairly standard, it must be appropriately modified for use with base metals other than copper.

Flux Corrosivity

One method for measuring potential corrosivity of the flux is the measurement of the resistivity of a water extract. The water extract test is a means by which the chemica€ character of flux residues is determined. As the test is outlined in theFederal Specification QQ-S-57 1, much care is required to obtain correct and reproducible results. The specification requires that the specific resistivity of a water extract of the flux be at least 100 O00 a m for R and RMA and 45 o00 a m for RA types. Details ofthe test procedure appear in Federal Specification QQ-S-571. Other corrosion tests for rosin base fluxes are given in MILF- 14256, QQ-S-57 1, and ASTM B284.


CHAPTER 4

JOINT DESIGN

INTRODUCTION

In general, solders have lower strength properties than thematerials to which they arejoined. Struc- turally loaded joints must therefore be carefully evaluated so that they will be capable of sustain- ing the applied stresses for an adequate lifetime. Long-term joint properties are more important than short-time tensile or shear tests in the determination of an appropriate joint cross-sectional area once the design has been selected. Bulk solder alloy properties must not be utilized in design, since they are not reflected in actual joint strengths.

Electrical conductivity of soldered connections is also an important factor. Solderresistivity values vary widely and must be considered in selecting a suitable joint design or connection. The soldered joint should relate to the maximum expected capacity of the electrical circuit and be designed to prevent localized heating or resistance changes that would influence overall circuit performance.

BASE METAL

The base metal's properties will have.a strong influence on joint selection. The designer must have a thorough knowledge of the part or assembly and its intended functions in order to arrive at the best joint design, material, and solder for the job. The initial design criteria will eliminate

many materiais and solders from consideration. However, it is very likely that several solder-base metal combinations will remain after the engineering assessments. The next most important criterion to consider is cost effectiveness, including relative processing and material costs.

Physical and mechanical properties of the soldered joint are discussed in Chapter 23. As already explained, however, the range of pos- sibilities in configuration variations is such that some test work is mandatory on a proposed joint design and soldering procedure if a specific performance requirement is to be met. When joint designs are compared, the soldering operations must be performed under carefully controlled and similar conditions so that the joint itself is under test and not the method of joining.

Relative thermal expansion of lhe solder and the base metal are important in processing as well as in service. In processing, joint overstressing can lead to solder joint fracture on solidification. In service, differential thermal expansion or residual stresses from processing can accelerate joint failure by creep or corrosion mechanisms. As service stresses increase, attention should be given to the joint by (1) placing the joint in a relatively low stress area, (2) supporting the joint mechanically, say, by a lock-seam, and (3) re- sorting to a higher strength solder with suitable strength or creep resistance.

Lap joints are the most widely used and are usually preferable. Butt joints can be made but have limited value. Many variations in joint de-

21


22/SOLDERING MANUAL

sign are feasible, a good number of which are presented in Figs. 4.1 and 4.2. Dimensions of the lap joint may be varied so that the joint can adequately sustain service loading or produce failure in the base metal to which it is attached. Most reported test data on joint strengths are not useful to the designer, since in solder joints the ability to withstand load to failure in a short-time room-temperature test generally does not bear much relationship to what that joint can sustain in service. Often the data are meaningless for the designer because sufficient details of the actual test performed are lacking. The shear strength of a solder joint can apparently be doubled or halved depending on the speed of test in tension. Therefore, engineering design must proceed on the basis of test comparisons, using book

T

Angle T

Flanged T

AWS S M * C H * 4 ** m 0784265 0 0 0 6 3 7 3 T m

i

Flanged edge

values as an initiai guide to solder and base metal selection. Joint design with a simple lap joint is more complex than relating a unit cross-section stress or shear value to a developed configuration. Rarely can a solder joint be designed to take a pure shear load. The length and quality of the exposed joint edge is just as important as joint area in strength determination under shear load. Perhaps the most definite work on shear loading of soldered joints was performed by Maupin and Swanger, who fully characterized the load- carrying capabilities of copper tube with sleeve- type joints or fittings. Their results can be effectively interpreted, since overall dimensions are known in addition to the loads applied. Typical copper tube and fitting sizes are found in Chap- ter 22.

’

Corner Single strap butt

Corner Flanged butt

Flanged corner Line contact

Double lap

Flush lap

Flat lock seam Flanged bottom Flanged bottom

Fig. 4.la - Joint designs frequently used in soldering. Solder joints terminology has not been standardized


AWS S M * C H * 4 ** 07842b5 000b372 L i

Solder is placed here before heating

Single iine of I contact

Fig. 4.lb - Typical socket joint design. Note flange which holds solder preform and the single line of contact between inner member and inner wall. The molten solder flows easily beneath the contact line to form a fillet on the other (lower) side

Joint Design123

Joint clearance in a lap joint is critical for optimum performance. Too small clearances frequently lead to flux entrapment, inadequate solder flow, and numerous voids in the joint. Con- versely, if joint clearances are too large, capillary flow of the solder filler metal is impaired; or if the joint is heated too vigorously, the solder runs out or leaves only a bridge at the edge or opening. Correct joint clearance in lap joints is approximately O. 10-0.15 mm (0.004-0.006 in.), which achieves a balance between competing processes of flux and solder flow, capillary action, and solder retention. A good design criterion for lapped solder joints is to consider 70% filled joint to be adequate provided the voids are small and discretely dispersed. A practical range for copper tube joint filling is 70-90%; this can readily be checked in most situations by X-ray techniques (see Fig. 4.3).

Jb Vent I

Flattened side

Fig. 4.lc - Venting of closed-end joints can be done by drilling a hole, as at lefi , or by crimping or flattening one member, as at right

Fig. 4.ld-Several lock seam designs used in soldering sheet. Sequence of formation is shown by the sketches


24/SOLDERING MANUAL

Fig. 4.le - Joint showing (left) solder preplacement before soldering and (right) after soldering

Radiators and heat exchangers are among the require close fit-up, but it uses large quantities of commonest applications of soldering. Tubes are solder. Quantity production of small parts or joined by a lock seam and then joined to tank small joints can best be handled with wire or strip headers by a lap joint; the remaining joint be- preforms. Joints are designed for solder reten- tween the header plate and tank is a trough joint, tion, for example, widening a gap or indenting a shown in Fig, 4.4. These joints arerequired to be part for precise joint configuration. Parts are

'structurally capable of operating at elevated made for automatic sorting and placement. temperature and pressure under cyclic condi- Capillary action of liquid solder is necessary tions. Test work has demonstrated that lap joint for good joint formation in lapped or locked strength data are not applicable to the trough seams in tube sleeves and in some wire type system, but a peel test provides a quantitative connections. The maximum capillary rise measure of the comparative merits of solder achievable is directly related to joint gap (see Fig. fillers for header tank use. Joint design in the 4.5) and is given by the equation radiator is controlled by the need for rapid assembly, and solder selection is necessarily pro- gressive because.the joints have to be made in

. 2 u c o s 0 h =

sequence. Success depends on the total concept where h = capillary height, in which joint design has an imporfant place but .cannot be separately considered.

Process selection, details of which can be found in Chapter 6, can dictate the appropriate joint design or, coniersely, a particular joint design may be limited to a particular process or heating method. For example, in sheet metal J&nt tolerances are critical to proper capillary work the lock seam has the obvious advantage of action and to the displacement of flux from the being self-jigging, and parts can be roughly han- joint by the molten solder. These two require- died and still be joined satisfactorily. The ideal ments are conflicting and result in the known use ofthe lap joint is in tubing where a sleeve fit is optimum lap joint gap of O. 1 to O. 15 mm (==0.003 easy to assemble for subsequent joining. Both to 0.005 in.). A smaller gap may produce flux can be hand-soldered or automatically handled inclusions; a larger gap reduces capillary flow with liquid solder or solid wire feed material and may also produce voids. application. The trough system is particularly Joint design must be adequate for liquid solder useful for rapid automatic production; it does not flow. Several factors affect joint design and must

u = surface tension, dynes 0 = contact angle, d = capillary gap, p = solder density, g = gravity.


AWS S M * C H * 4 ** W 0784265 0006374 5

Mechanically Hydraulically Spot welded expanded expanded Pressed

!

Lock seamed Clipped

Joint Design125

Staked Crimped

Screwed or riveted

! I

I

Countersunk and spun A B

Swaged

A Formed B Pressed C Peened Slitting and earing

Pin flange to tube

Gravity Staked / Welded \ Pinned

.Solder

Spun or Knurled and Expanded swaged pressed fit Crimped

Fig. 4.2 -Twenty-one methods that can be used to make solder joints self-jigging


AWS S M * C H * 9 ** I 0789265 000b375 7 I

8 200- .O 150- o 100- o

C .- -4-

50-

26ISOLDERING MANUAL-

-

A- - n -n

300 - -

250 - -

200 - E E

- 150 -

S - 100 -

- 50 -

-

25 50 75 100

% Solder fill in joints

Fig. 4.3 - Histogram ofjoint areas filled with soft solder. From collection of 812 fitting joints considered to have been giving satisfactory service prior to their removal from service due to building demolition

I Fig. 4.4 - Section of tank-to-tube plate joint

o ’ I I I I I , I I I I I , I I I O 0.05 0.1 0.15 0.2 0.25 0.3 0.35

d mm

Fig. 4.5 - Maximum head height versus capillary gap dimension between parallel plates for 50% tin-50% lead solder with flux present


be considered if a sound joint is to be produced: 1. A reservou of molten solder 2. A feed path to the capillary 3. A suitable capillary entrance and exit 4. Controlled gap to provide capillary driving

force 5. A balanced mass for even heating and con-

trolled liquid solder flow 6. A joint suitable for the proposed method of

heating 7. Enough joint freedom to prevent flux en-

trapment. A conscious effort is necessary in joint detail-

ing to provide highly reliable optimum joints. A widely used practical joint is the interlock or

locked seam. From a joint design and ease-of- soldering standpoint, the joint is also one of the most difficult. Usually the heating system has at least three thicknesses to penetrate, and the inner part of the joint may not be hot enough to provide the free solder flow. Sometimes interlocked joints are provided with perforations to assist in observing solder flow.

Soldered joints are widely used in the elec-* tronics industry (see Tables 4.1 and 4.2). Joint design for electrical applications has the dual function of providing satisfactory electrical con- tinuity in addition to permanently affixing components and leads for reliable service. Electrical joints for wires and more recently joints in the printed circuit and integrated circuit industries have increasingly been required to be capable of withstanding a variety of service conditions.

The three basic types of joint for the wire-to- tab connection are shown in Fig. 4.6. The lap joint is useful for many electrical applications, The through-lead with or without plated through-holes is widely used but. generally not suitable for vibrating or high acceleration service because of soldered joint creep problems. A wrapped or clinched j d n t i s prefcrable. Several variations are possible here from the wire-to-wire wrap joint to aclinched wire onto aprintedcircuit board (see Table 4.3). Some advantages can be gained by the use of larger pad areas and longer leads to increase solder mass. Thinner boards help in reducing thermal expansion, and a thick plated

Joint Design/21

through-hole with solder fill will provide a larger crack propagation path as demonstrated in Fig. 4.7. Component placement is instrumental in re- straining movement. Some electrical designs allow a strain-relieved lead but, conversely, an offset component can lead to mechanical or thermal fatigue of the joint if not carefully designed as in Fig. 4.8. See Fig. 4.9 for some helpful tips on component mountings. Swaged terminals should not be soldered to both sides of the joint. A lead wire should be used if a second joint is necessary.

Wire-to-hole ratio and land spacing are two other important factors. Again, selection of both is bound to lead to compromise. A satisfactory minimum radial clearance in a hole for a wire is 0.1 mm (=0.003 in.). Adequatesolderingin the hole is more important in the plated through-hole where this area is probably included in the electrical design. Component densities tend to increase, reducing space between conductors and allowing less room for adequate land spacing. Land shape shouId be related to the conductor shape and size to allow the best fillet formation at the joint area. Some configurations are presented in Table 4.4. Safety factors in joint design are subjective; there are no clear rules because of the numerous variables and compromises that have been made during the designing process. The final tesf must be a verification trial for manufacturing and a test and inspection program for service. Review and modification of new designs must be included in the cost and time accounting and should not necessarily be regarded as a “mis- take.” Much remains to be learned, and many pitfalls can be avoided by proper attention.

High density electronic packaging requires close attention to joint design to suit the process. Lead bend angle has profound effects on reported mechanical strengths. Lead mass can affect optimum time-temperature profiles in joint production. A fiat length or lead pad of 1.5 mm (-0.050 in.) is needed for conductor attachment, and path widths should preferably be 0.15 mm (-0.005 in.) minimum each side of the lead. Overlapping the conductor produces lower quality joints. Two joints are illustrated in Fig. 4.10.


AWS S M * C H * 4 mx 07842b5 0006377 O W

28/SOLDERING MANUAL

Table 4.1-Linear thermal expansions of metals and alloys

Temperature Coefficient of expansion (in./in.P F X

"C "F

ALUMINUM ALLOYS 1100 ............................ o to 100 32 to 212 3003 ............................ o to 100 32 to 212

32 to 212

3004 ............................ o to 100 32 to 212 5052 ............................ o to 100 32 to 212 6062. , .......................... o to 100

23.6 13.1 23.2 12.9 23.9 13.3 23.8 13.2 22.2 12.4 .

COPPER AND COPPER ALLOYS Electrolytic (ETP)

32 to 212 17.6 9.8 Deoxidized (DLP) ........... o to 100 Oxygen-fiee (OF)

Commercial bronze. 90 Cu-lo Zn ..... Red brass. 85 Cu-15 Zn ............. Low brass. 80 Cu-20 Zn Cartridge brass. 70 Cu-30 Zn ......... Muntz metal. 60 Cu-40 Zn ........... Leaded brass; low. medium and high ... Naval brass ...................... Phosphor bronze,.8 (Grade C) ........ Cupro.qicke1. 70 Cu-30 Ni .......... Cupro.nicke1. 90 Cu- 10 Ni ..........

............

Nickel silver. 65 Cu- 15 Ni ........... Aluminum bronze. 92 Cu-8 Al ....... IRONS AND STEELS Ingotiron ........................ Wroughtiron ..................... Gray cast iron .................... "Ni-Hard:' low-or high-carbon ....... Carbon steel, SAE 1020 ............. Cast alloy steel .................... Iron-silicon alloy .................. "Durichlor" ......................

o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100

o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100

32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32to212 32 to 212 32 to 212

32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212

18.4 10.2 18.7 10.4 19.1 10.6 20.0 11.1 20.9 11.6 20.3 11.3 21.2 11.8 18.2 10.1 16.2 9.0 16.7 9.3 16.2 9.0 16.2 9.0

11.7 12.1 10.8

8.6 11.7 12.1 6.5 6.5

6.5 6.7 6.0 4.8 6.5 6.7 3.6 3.6

STAINLESS STEELS 301.302.304.309. 310 ............. 321. 347 ......................... 316. 317 ......................... 410, 4 30 ......................... 414.420 ......................... 431 ............................. 446. .............................

20 to 100 20 to 100 20 to 100 20 to 100 20 to 100 20 to 100 20 to 100

68 to 212 68 to 212 68 to 212 68 to 212 68 to 212 68 to 212 68 to 212

14.4 14.9 15.8 9.2 9.9

11.7 10.3

8.0 8.3 8.8 5.1 5.5 6.5 5.7


AWS S M * C H * 4 ** W 07842b5 0006378 2 W

Joint Design129

Table 4.1 -Linear thermal expansions of metals and alloys continued -

Temperature Coefficient of expansion (in./in./” F X

“C “F

NICKEL AND NICKEL ALLOYS Nickel (pure) . . . , . . . . . . . . . . . . . . . . . Nickel (wrought or cast) . . . . . . . . . . . . Low-carbon nickel , . . . , . . . . . . . . . . . . Monel (wrought) . . . , . . . . . . . . . . . . . . Monel (cast), , . . . . . . . . . . . . . . . . . . . . Inconel (wrought or cast). . . . . . . . . . . . “Hastelloy” Alloy A . . . . . . . . . . . . . . . “Hastelloy” Alloy B . . . . . . . . . . . . . . . “Hastelloy” Alloy C . . . . . . . . . . . . . . . “Hastelloy” Alloy D , . . . . , . . . . . . . . .

o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100 o to 100

32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212 32 to 212

13.3 7.4 13.0 7.2 13.0 7.2 14.0 7.8

. 12.2 6.8 11.5 6.4 11.0 6.1 10.0 5.6 11.3 6.3

. 11.0 6.1

TIN,LEAD.AND LEAD ALLOYS Corroding lead. , . , . . . . . . . . . . . . . . . . 17 to 100 63 to 212 29.3 16.3 Hard lead (4 Sb) . . . . . . . . . . . . . . . . . . . 20 to loo 68 to 212 24.6 15.4 8% antimonial lead (8 Sb) . . . . . . . . . . . 20 to 100 26.6 14.8 20-80 Solder (20 Sn) . . . . . . . . . . . 15 to 110 59 to 230 26.5 14.7 Lead base babbitt (80 Pb,15 Sb,5 Sn). . . 20 to 100 68 to 212 23.9 13.3

19.6 10.9 Lead base babbitt (75 Pb, 15 Sb, 10 Sn). . o to 100 32 to 212 23.0 12.8 Pure tin . . . . . . . . . . . . . . . . . . . . . . . . .

68 to 212

20 to 100 68 to 212

MISCELLANEOUS PURE METALS Tungsten . . . . . . . . . . . . . . . . . . . . . . . . Molybdenum . . . , . . . . . . . . . . . . . . . . . Silver . . . , . . , . , . , . . . . . . . . . . . . . . . . Gold ....................... ..... Platinum , . . . . . . , . . . . . . . . . . . . . . . . Palladium., . . . . . . . , . . . . . . . . . . . . . . Tantalum . . , . . . . . . . . . . . . . . . . . . . . . Zinc . . . . , . . . . . . . . . . . . . . . . , . . . . . . Titanium . . . . . . . . . , . . . . . . . . . . . . . . Magnesium . . . . . , . . . . . . . . .. . . . , . . Chromium ....................... Cadmium . , . . . . . . . , . . . . . . . . . . . . . .

near 20 near 68 4.3 2.4 25 to 100 4.9 2.7

19.6 10.9 o to IO0 14.2 7.9 20 68 8.8 4.9 20 68

11.9 6.6 20 68 near 68 6.5 3.6

68 to 482 29.8 22.1 20 to 250 8.5 4.7 20 68

20 to 100 68 to 212 25.9 14.4 6.1 3.4 20 68

Room Temperature 29.9 16.6

77 to 212 32 to 212

near 20


Fixtures

ya

Yes

Yes

Current

Small

Small

Small

1

2

3

Round to

round

Square to

square

Rectangle to

rectangle

AWS S M * C H * 4 ** m 07842b5 000b377 4 m

30/SOLDERING MANUAL Table 4.2-Data for electrical-connections design'

Group I-No mechanical security prior to soldering . .

Butt c'onnectipns

Diagram

nections

Round* to

round Large Yes

Round to flat

DCI )ptional Large

Fat to fiat

Iptional Large

-Wire to

post Medium No

No

Dptionai

Wire to

CUP Large

I

Wire to

hole Medium

'H.H. Manko, How to Design the Soldered Electrical Connection, Prod. Eng., June 12, 1961, p. 57.


AWS S M * C H * 4 ** 0784265 0006380 O

Joint Design13 I Table 4.3-Data for electrical-connections design -

Group II-Partial mechanical security prior to solderhg Hook

connections Iq 5 P e Diagram I Controlling I Conditions I Fixtures for mu I a

I I l I

Round

round 1 to

P C l Pc2 Aci S A C * N O

Hook 3 180" Round

2 to

MJ-J ñat ?ci\,.

I I I I I

Group III-Full mechanical security prior to soldering* *

Current

Large

Medium

Wrap I inections I

5 P e I Diagram

I Round

to round

I I

Round to

post

Controlling ïormula

Lj = %Dei 2

_ _ _ ~ ~ ~

Conditions

PCI a Pcz Dc1 DC2

N > 1

Pcr 3 P C 2

Ac, Ac2 N = 1

P C l 3 Pc2 DCI Dc2

N 3 1

Fixtures Current + No Large

No Medium

No Large

Dci - Diameter of smaller conductor Aci - Area of smaller conductor S -Solder W -Width

T -Thickness N - Number of Turns 6 - Resistivity Ratio ps

PCI Lj - Length of joint p - Resistivity (Microhm- cm)

*Use only when large conductor diameter is 3 to 4 times larger than small diameter; otherwise use round-to- Rat lap-joint formula.

should be specified. **In cases where loosen¡ng or breaking of the joint would result in a hazardous condition, mechanical security


AWS S M * C H * 4 ** I 07842b5 0006381 2 H

32/SOLDERING MANUAL

@ Round

pl Rect.

Delta [p:::.

Table 4.4 - Configurations of printed- circuit lands i

I Remarks I Solder fillet contour will be I Preferred

direction for cornnonent lead

Good design.

contact area Toward Even, and Enlarged long end almost round

I The Any universal

I I round pattern I I Not

. widely used I Uneven I Toward tip

Not Toward a corner or long end Uneven widely used

Used if

I Toward base I Uneven space very I limited

A

f l

B U

C

. Fig. 4.6 - Methods of making wire-to-tag joints

Epoxy fiberglass A

/ Sdder Stronger \ Lead joint Longer ,

Lead Plated hole

Thickboard

Fig. 4.7 -How to improvejoint strength, For single-sided boards, A, larger pads and longer leads increase solder mass; a thinner double- sided board, B, is better because it provides a longer path for crack propagation


AUS SM*CH*rLr **

Organic protective coating (encapsulant)

Cracked joint

Fig. 4.8 - Restraint of the expanding lead by protective-coating bridging, mechanical fas- tening, adhesive bonding, or a hard spacer will all reduce the thermal fatigue life

= 1.5 mm (0.05 in.)

= H A 22.2-28.9 = % A 15.5-22.2

Joint Design133

r I Thin coating avoids bridging

Fig. 4.9-For small parts (resistors and diodes) on uncoated boards, use single-sided boards, A; on coated boards, use plated through-holes, B . For moderate-size parts (TO-5 cans) on uncoated boards, provide clearance, C; when coated, D, use a very thin coating to avoid bridging. For heavy, side-mounted parts with moderate size leads, E, use plated through-holes; with heavy leads, F, weld, braze, or solder on a flexible lead

A = 1.5 mm (0.05 in.)

length strength, N B = 44 A 17.8-24.5 B = % A 11.1-17.8 B = ?4 A 4.5-11.1

Fig. 4.10 - 60" and 80" preformed leads


- - AWS SM*CH*4 * * I 07842b5 000b383 b M

34/SOLDERING MANUAL

REFERENCES

1. Alcoa, 1972, Soldering Alcoa aluminum. Pittsburgh.

2. Coombs, C.F., Jr. 1961. Printed circuits handbook. New York: McGraw-Hill.

3. Jayne, T.D. and Martin, L. 1970. Improving control of soft soldering in copper piping joints. In ASME Paper 70-PVP-21.

4. Lampe, B.T. 1973. Reflow soldering of integ-

rated circuit flatpacks. Welding journal, 52, 1:

5. Manko, H.H. 1964. Solders and soldering New York: McGraw-Hill.

6. Mohler, J.B. 1971. Solder joints vs. time and temperanire. Machine design, April 15.

7. Rubin, W., and Allen, B.M. 1965. Soldering in the electronic industry. British welding jortrnal, 12, 12.

23-30.

8. TRI Publication 369, 1965.


- / \

AWS S M * C H * S ** O784265 0 0 0 6 3 8 4 8 a

CHAPTER 5

PRECLEANING AND SURFACE PREPARATION

Proper surface preparation is essential to successful soldering. The more frequent precleaning methods are degreasing, acid cleaning, mechanical abrasion, and etching.

DEGREASING

Organic films such as oils and greases are frequently encountered on the surface of metais to be soldered. Such oils and greases must be removed because they prevent wetting acfion by the flux and solder. Degreasing may be accomplished by immersion of the parts in a liquid or suspension of the parts in vapors of a suitable solvent.

The halogenated hydrocarbons are the most widely used solvents because of their range of solvency power and lack of flash point. Constant boiling (azeotropic) blends of several solvents are sometimes employed to remove both nonionic and ionic soils.

Impingement of the solvent upon the surface significantly improves the efficiency of the cleaning process. Considerable mechanical remova1 of the soil csn be obtained by agitation, ultrasonics, bmshing, or in any manner impinging the solvent upon the surface to be cleaned.

With liquid cleaning, there is always some soil in solution in the cleaning solvent. It is impractical to remove all the liquid cIeaner from the

surface. Any cleaner remaining after cleaning will evaporate from the surface cleaned. Being nonvolatile, the soil that was in solution will remain on the object cleaned. To prevent this condition and obtain a higher levei of cleanliness, vapor degreasing is used. The parts to be cleaned are suspended in vapors of a boiling cleaning solvent. Because the parts are colder than the vapors, the vapors condense to a liquid, dissolve the soil, and drip off the parts. When the parts have reached vapor temperature, condensation ceases and dry parts may be removed from the vapor degreaser. If a large enough quantity of cleaner of sufficient solvency strength condenses on the parts, the result is clean, dry parts.

The effectiveness of the degreasing can be easily determined by dipping the part in a liquid; if the liquid uniformly adheres to the surface, the part is clean.

ACID CLEANING

The purpose of pickling or acid cleaning is to remove rust, scale, and oxides or sulfides from the metal to provide a chemically clean surface for soldering. The inorganic acids- hydrochloric, sulfuric, orthphosphoric, nitric, and hydrofluoric-singly and mixed, all fulfill this function, although hydrochloric and sulfuric acid are the most widely used.

35

1.


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36/SOLDERING MANUAL

Hvdrochloric Acid tent rises to 8%, the pickling solution should

Thecommercial form of hydrochloric acid has be Sulfuric acid is a suitabre medium for pickling a specific gravity of 1.14 and contains approxi-

mately 25% by weight hydrogen chloride, F~~ steel and copper alloys. For the latter, it is eus- tomary to add either 1%- by weight of sodium pickling iron and steel in cold solutions, the dichromate or 2% by volume of nitric acid. commercial acid is diluted in the range of 1 part

commercial acid to 2 parts water (10% HCI), to 3 Orthophosphoric Acid

A dilute solution of orthophosphoric acid parts of acid to 1 part water (21%HCI).

(specific gravity 1.87 for 100% acid) is used Hydrochloric acid is an effective pickling soh- tion at ordinary shop temperatures, and in most occasionally for pickling such metais as stainless cases no provision is made for heating it. The steel and manganese bronze. Solutions of 10% to acid increases its temperature due to the heat of 40% by volume are used. reaction or by introducing heated work. The recommended acid temperature, however, is be- Hydrofluoric Acid tween 30" and 38" C ( ~ 8 5 " and 100" F) but never Hydrofluoric acid is extremely corrosive, and Over 'O" (= 12'" m. bright3 an- contact with the skin should be carefully avoided. nealed stock can be pickled in three minutes at A mixture of 5% hydrofluoric acid and 5% sul- 300 ' (=85" Or ten at ''" ' furic acid by volume is sometimes used on cast (65" FI. Lightly scaledwork may require 15to30 iron, high silicon alloys, and aluminum (see minutes, whereas heavily scaled work may re- Chapter 21 for safety in handling). quire 45 minutes or more. During use, the acid content will fall and the solution, if not re- Nitric Acid plenished with fresh acid, will become iess effec- acid (70% "o3) is sel- tive. When the iron content reaches 12%, the dom without dilution or mixing with other pickling solution should be replaced. An in- acids. A simple and effective pickling solution hibitor is sometimes added to prevent pitting of for copper contains 15% to 20% by volume of the metal after the scale is removed. A solution of commercial concentrated acid in water. The 10% HCI is used in some instances to prepare solution is used cold, and h e time required is aluminum surfaces for soldering. normally from 2 to 5 minutes.

Mixture of Acids Sulfuric Acid Some mixtures of acids give a bright, etched

Sulfuric acid is commercially available in var- finish on metals that do not respond to single ious concentratiofis. The 96-98% acid has a acids. Some typical acid mixtbres are listed specificgravityof 1.84,whereasthe77%acidhasa here:* specific gravity of 1.70. Sulfuric acid pickling

Copper Aììoys solutions vary from 5 to 10% by volume of the commercial acid (77%) added to the water. Sul- Brass furic acid does not work efficiently unless it is Sulfuric Acid 8L** 2gal.

4 L 1 gal. heated to temperatures above 70" C (= 160" F). and best results are obtained at 82" C (180" F). Bright, annealed or relatively clean work nor- Hydrochloric acid 0.015 L 1/2 fl OZ

mally requires only 30 seconds to 2 minutes im- Njckel&lver mersion, whereas heavily scaled work normally re- sulfuric acid 8 L 2 gai. quires no longer than 15 minutes. A black smut Sodium dichomate 0.25 kg 1/2 Ib which forms may be rinsed off with water. In- Water 20 L 5 gal. hibitors, added to sulfuric acid, will help prevent pitting. The acidity of the solution is maintained with periodic additions of fresh acid. When the free acid content falls below l% or the iron con-

Concen&ated

Nitric Acid Water 1 L 1 qt.

+See Chapter 21 for safe of these materia,s. * * ~ ~ b i ~ conversions X e approximate for easy mea-

surement.

_--- o COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

Precieaning and Surface Preparation 137

As mentioned above, a repair of an abraded surface to remove embedded particles may be necessary. A surface may appear clean and in- deed be platable (will accept electrodeposited metals), yet not be solderable. Copper surfaces that are solder plated, such as printed circuit boards, sometimes exhibit this defect. Repair of the surface after plating is difficult and costly. The plating must be stripped and the surface

Nickel Alloys Inconel

1 gal.

2 gal.

Nitric acid 4L Hydroflouric acid 0.5 L Water 8 L

1 pt.

Btainiess Steel 1.Sulfuric acid 4L 1 gal.

gal, gal. etched.

2Nitric acid 4L 1 gal.

Hydrochloric acid 4L Water 32 L

Hydrofluoric acid Water After pickling, if droplets of watershow on the

metal surfaces, there may still be traces of grease or other contaminants on the surface which should be removed before proceeding. The articles should be thoroughly washed in hot water after pickling and dried as quickly as possible.

The coating of the base metal surfaces with a more solderable metal or alloy prior to the soldering operation is sometimes desirable. Coatings of tin, copper, silver, cadmium, iron, nickel, and alloys of tin-lead, tin-zinc, and tin-copper are used for this purpose. The advantages of precoat-

MECHANICAL PREPARATION

ing are twofo1d:Soldering is more rapid and uniform, and strong acidic fluxes are avoided at the assembly. The precoating of metals which have - tenacious oxide films, such as aluminum, aluminum bronzes, highly alloyed steels, and cast iron, is almost mandatory. Precoating of steel, brass, and copper, although not absolutely essen-

Various abrasive techniques are frequently employed to clean metallic surfaces before Sol-

dering. They are effective and economical methods but have one definite limitation: particles of the abrasive may become embedded in the surface being cleaned (see Fig. 5.1); These abrasive materials - sand, grit, ceramic, steel wool, etc. -are generally not solderable. Although the surface may appear to be clean, if sufficient abrasive particles to significantly reduce the anchor- age area have been embedded in the surface, the result is reduced solderability (see Fig. 5.2). A simple solderability test should be performed following abrasive cleking. An etch treatment following abrasive cleaning may be required to remove sufficient surface material to eliminate the embedded abrasive.

%TC H I WB

The removal of a small amount of material from the surface to be soldered is a common cleaning and repair technique. A nonplated copper surface particularly lends itself to this technique. Copper etchants such as ferric chloride, copper chloride, and ammonium persulfate are used.

tial, is of great value in some applications.

Fig. 9.1 - Intermetallic compound crystals with inclusions at surface which have formed during soldering of copper cleaned with fine abrasive


38/SOLDERING MANUAL

Meta1 surfaces may be precoated by a number of different methods. Solder or tin may be applied with a soldering iron, an abrasive wheel, by an ultrasonic soldering iron, immersion in molten metal, electrodeposition, or by chemical displacement.

Hot dipping may be accomplished by dipping the parts, one at a time, in molten tin or soider of any composition. Small parts are placed in a wire basket, cleaned, dipped in the molten metal, and rotated in a centrifuge to remove excess metal. Hot dipped coatings can be applied to carbon

steel, alloy steel, cast iron, copper and certain copper alloys and, to a lesser extent, brass and aluminum.

Precoating by electrodeposition may be done in stationary tanks, conveyorized plating units, or in barrels. This method is applicable to all steels, copper alloys, nickel alloys, zinc base die castings, and aluminum. The coating metals are not limited to tin and solder; in addition, copper, cadmium, silver, precious metais, nickel, iron, and alloy platings such as tin-copper, tin-zinc, tin-cadmium, and tin-nickel are commonly used.

Fig. 5.2-Effect of conditions of pumice cleaning solderability. Lef-handpair-with water lubrica- tion; right-hand pair-dry abrading; top row-light pressure; bottom row-heavy pressure. Speci- mens immersed in 60% tin-40% lead solder at 250" C for 5 seconds with activated rosin flux


AWS S M * C H * S ** m 07842b5 0006388 5 . -. . - . . . .

Methods for the electroplating of these metals or alloys are given in the Metal Finishing Guidebook(Ref. I). .

Certain combinations of electrodeposited metals, where one metal is plated over another, are becoming more popular as an aid to soldering. A coating of 0.005 mm (0.0002 in.) of copper plus 0.01 mm (0.0004 in.) oftin is particularly useful for brass. The solderability of aluminum is assisted by a coating of 0.0015 mm (==O.ooOO5 in.) of nickel, followed by 0.01 mm (=O.O003 in.) of tin or by a combination of zincate (zinc), copper, and tin. An iron plating followed by tin plating is extremely useful over a cast iron surface.

Bader & Baker (Ref. 2) have shown that a solder coating is preferable to a tin coating to preserve solderability under adverse storage conditions for extended periods of time. A minimum of 1.5 p m ( ~ 5 0 pin,) of solder is required. Such a coating is effective in preserving solderability under severe industrial exposure for one year.

Immersion coatings or chemical displacement coatings of tin, silver, and nickel may be applied to most of the common base metals. These coatings are usually very thin and generally have poor shelf life.

Precleaning and Sugace Preparation/39

The shelf life of a precoating is defined as the length of time the coating can withstand storage conditions without impairment of solderability, Hot tinned and flow-brightened electrotin coatings have excellent shelf life; electrotinned coatings of inadequate thickness have limited shelf life. Coating thicknesses of 0.005mm (0.0002 in.) to 0.015 mm (=0.0005 in.) of tin are generally recommended to assure maximum solderability after prolonged storage.

ACKNOWLEDGEMENT

Figures 5.1 and 5.2 are courtesy of Tin Research Institute, Inc.

REFERENCES

1. Metal jnisking guidebook directory. West- wood N.J.: Finishing Publications.

2. Bader, W.G. and Baker, R.G. 1973. Solder- ability of electrodeposited solder and tin coatings after extended storage. Plating, March.

,


CHAPTER 6

EQUIPMENT, PROCESSES, AND PROCEDURES

EQUIPMENT

Soldering Irons

The soldering iron (see Fig. 6.1) should provide constant heat to parts being soldered, ensuring that the partsare joined using minimal contact time, thereby safeguarding that components in close proximity and areas adjacent to the soldering connection are not adversely affected by heat absorption.

Flame Heated Irons. Flame.heated soldering irons are chosen where electric power is not readily available (sheet metal work, fQr example).

Eìectricaììy Heated Irons. Electrically heated irons are more convenient than gas heated irons for use in manual, high speed, repetitive operations where weight and ease of manipula- tion are of primary ìmportance. The wide assort- ment of electric soldering irons available and the lack of definitive performance specifications make it necessary to exercise care in selection. Available diagnostic equipment will provide tip temperature measurements under dynamic conditions whi1.e the soldering is taking place. Such measurements will insure that the soldering iron chosen will perform within the required thermal working zone.

Industrial soldering irons are available with both plug and screw tips.

Soldering irons can be broadly divided into six

1, Instrument irons 2. Medium duty industrial irons 3. Heavy duty industrial irons 4. Temperature controlled irons 5 . Transformer type pencil irons 6. Soldering guns I. Instrument irons are designed for intermit-

tent and continuous light soldering tasks or electrical repair work. They are available in a wide selection in both copper and iron plated tips to allow for matching the tip to any soldering operation.

2. Medium duty indusrriai irons are designed for continuous production operations and ate built to withstand use in high-speed production situations. These irons are also available with a wide tip selection and v?rious handle and case sizes and configurafions.

3. Heavy duty industrial irons are designed for continuous use on fast production soldering operations. These irons are avai!able in a number of sizes and wattages to insure good heat stability under heavy soldering loads.

4 . Temperature controlled irons are now available with sensors in the tip which react to small tip temperature changes, actuating solid state circuitry controlling the power to the element.

groups:

41


42/SOLDERING MANUAL

Fig. 6.1-Traditional soldering iron

Therefore, the iron will be adjusted automatically to match the. heat sinking requirements of the work being soldered. These irons provide very tight femperature control for any soldering task.

5 . Transformer íype pencil irons are intended for light soldering repair work and production operations. The pencil iron is available with a number of different tip sizes. These irons are designed for low voltage (less than 12 volts AC), with a rheostat, or voltage taps, or both, on the transformer to regulate heat output.

6. Soldering guns areused for light, intermit- fent soldering of electrical connections and are' not intended for continuous operation. The operator does not have control of the heat output of a soldering gun, which could result in overheating connections, components, and adjacent areas if the gun is nof used carefully.

Metemids The properties required for soldering iron tips

are: 1. High thermal conductivity to insure that

heat transfer is rapid and efficient. 2. Ease of tinning to insure a liquid metallic

path through which the heat ofthe tip surfacemay be readily transmitted to the work.

3. Low oxidation to insure good heat transfer from tip to work and to prevent the tip from freezing in the soldering iron.

4. Resistance to corrosion from soidering fluxes if acid core, acid paste, and water soluble fluxes are used.

5. Resistance to erosion by the molten solder. Four basic types of tips can be used: 1. Copper 2. Iron plated with coated shank 3. Iron plated with stainless steel shank 4. Calorized

1. Copper Tips. Copper has high thermal conductivity and excellent tinning properties. How- ever, copper tips have the disadvantage of high oxidation and rapid tip erosion. The tip erosion is caused by the dissolution of copper in tin at soldering temperatures and removal of tip mate- fiai. This creates the need for frequent tip shaping and oxidation removal to maintain original tip shape and retain the proper heat transfer from the heating element to the working surface of the tip. The fast oxidation rate of copper also causes the tip to freeze in the soidering iron core, making it difficult to remove the tip without damaging the heating element.

2. Ironplated Tip with CoatedShank. This tip is made of copper with iron electrodeposited uniformly over the entire tip. Iron is used because it dissolves in tin very slowly, thereby ensuring extended tip life-in most cases 20 to 50 times that of copper. The front of the tip is selectively tinned, and the shank is protected from oxidizing by platings of nickel and chromium. The thickness of the iron plating can be between 0.2 mm (0.008 in.)and 0.6mm (0.022 in.). The greater thickness extends the life of the tip but will reduce heat conductivity.

3. Iron Plated Tip with Stainless Steel Shank. Like the iron plated tips described above, this design resists corrosion and offers all the benefits of long tip life. Additionally, it does not allow the shank to freeze in the iron.

4 . Calorized Tip. A calorized coating is created by diffusing aluminum into a copper tip to prevent oxidation at high temperatures and prevent soldering iron shanks from freezing. Calorizing is used primarily on screw tips in irons with internal cartridge type elements. Because calorized coatings resist wetting, the working area of the tip is iron plated and factory tinned.

Design. Although great emphasis has always been placed on the selection of the proper soldering iron, one must also recognize the importance


Equipment, Process, and Proceduresl43

governed by the size, mass, and configuration of the assembly to be soldered.

The flame from a torch will heat large masses of material rapidly but is likely to cause burning or carbonization of the flux. This is less likely to occur when flux core solders with chloride fluxes are used. One way to prevent carbonization or decomposition is to preheat the assembly (without causing excessive oxidation) before applying the solder and flux.

The elevated temperature of the flame from a torch can cause damage to heat sensitive components or fo areas adjacent to the soldered connection.

of using a tip that is designed properly. The following factors influence good tip design:

i. Length. Length should always be minimal. This positions the contact area as close to the heating element as possible, #insuring g o d temperature stability.

2. Tipsize. Selection ofthelargest tip size will ensure the greatest thermal reserve.

3.Contact Area. The contact area should match the soldering connection to insure the greatest possible heat transfer rate.

4.Shupe. The shape of the tip is chosen to provide the greatest contact area.

General Guide to Iron and Tip Sizes Table 6.1 is a general guide for the selection of

soldering irons and tips. The performance of electrically heated industrial irons cannot be measured solely by the power rating. The materials used and the design of the iron will affect the heat reserve and temperature recovey of the tip.

Use of Soldering Irons The correct angle to apply the soldering iron

tip to the work is of importance in delivering the maximum heat. The flat side of the tip should be applied to ensure the maximum contact x e a with the soldering connection. Flux cored solder should not be melted on the soldering iron and carried to the connection .because that destroys the effectiveness of the flux and results in defec- tive connections. The cored solder should be touched fo the soldering tip to initiate good heat transfer, and the solder should be melted on the work parts to complete the solder joint. The tip can be wiped clean on a wet sponge. The working surface should be kept tinned. Soldering iron holders must be selected carefully. Poorly designed holders may heat sink an iron, causing. temperature losses of up to 110°C (200" F.),

PROCESSES

Torch Soldering

Torch soldering is commonly used for automotive body work, plumbing and structural joints, and in locations where electricity is not readily available. Torch selection and gas mixture are

Dip Soldering

Dip soldering is useful and cost-effective because an entire unit, comprising any number of joints, can be soldered merely by dipping the prefluxed part in a bath of molten solder. It is necessary to use jigs or fixtures to contain the unit and keep the proper clearance at the joint until the solder solidifies.

A preliminary treatment of the unit such as degreasing, cleaning, and fluxing is also required before dip soldering. Care should be taken when immersing the parts in the pot (see Chapter 21 for safety precautions). The molten bath of solder supplies both the heat and solder necessary to complete the joint. The solder pot should be large enough so that at a given rate of production the units being dipped will not appreciably lower the temperature of the solder bath. Pots of adequate size allow the use of lower operating temperatures while stili supplying sufficient heat for soldering.

Spray Gun Soldering Two types of guns are used to spray solder. The

first uses propane with oxygen or natural gas with air to heat and spray a continuously fed solid solder wire of approximately 3 mm( 118 in.) diameter. With ordinary procedures about 90% of the solder wire is melted by the flame of the gun, and contact with the work piece is made by the solder in a semiliquid form. The workpiece then supplies the balance of the heat required to melt and flow the solder. The solder is then wiped automafically or by hand. Adjustments can be


AWS SM*CH*6 ** 0784265 0006392 7

44ISOLDERING MANUAL

made within the spray gun to deposit completely liquified solder or a series of fine drops.

The second type of spray gun lias a small, electrically heated cone into which solid solder wire approximately 6 mm (1/4 in.) in diameter is fed. Through an orifice in the small end of the cone, the molten solder is directed into a compressed a u stream which transmits the solder a distance of from 25 to 75 mm (= 1 to 3 in.).

Induction Heating

Induction heating generally is applicable for soldering operations having the following requirements:

1. Large-scale production 2. Localized application of heat 3. Minimum oxidation of surface adjacent to

the joint

Table 6.1-General guide for iron and tip size

Electrically-heated Soidering irons

Choice of Power tip diam.

shank' (watts) rating iron group3

Critical soldering: flexible circuits, heat sensitive components, and low temperature solders

Printed wiring boards 0.5 mm (0.020 in.) thick, thin films, wires 30 gage or smaller, lugs designed for this size wire Printed wiring boards, O. 8 mm (0.030 in.) wire 24 gage, miniature turrets and relay hooks, small chassis and printed wiring board cup type connectors Printed wiring boards 1.5 mm (0.060 in.) wires 20 gage, medium turrets, tube sockets, bifurcated terminals, medium chassis connectors Production work on medium turrets, tube sockets, terminal strips, wires 16-18 gage, limited ground or buss wire work High speed production work or radio or T V assembly where twenty or more connections are made in a minute or less High speed production work or radio or TV assembly where extra heavy lugs or several wires on same lug or several ground connections are soldered Hermetic sealing of relay, transformer, or condensor cans, light gage sheet metal Heavy sheet mefal or large transformer cans Intermittent soldering, repair shop, hobby

mm up to 6.4

3 -2-4.8

3.2-4.8

4.8-6.4

6.4-7.9

6.4-9.5

9.5-15.9

15.9-22.2

25.4-44.5 4.8-6.4

in, 114

1/8-31 16

1/8-3116

3116- 114

114-5116

114-318

318-518

518-718

1-1-314 3116-114

Temper- ature

control2 10-20

20-30

40-50

50-70

80- 175

150-200

200-300

300-800 30-50

4

1 5

1 5

1 5

2 5

3

3

3

3 1

kit, home use wire tip 100-325 6 The tip diameters vary with the manufacturer of electrically-heated irons and sizes used depend upon theworking space avai1able:Metricconversions are exact because these products areavailable only in U.S. customaj units. Soldering iron selected must be self-regulating to maintain proper temperature and avoid heat damage to components. Refer to selection of soldering irons, page 41.


4. Good appearance and consistently high joint quality

5. Simple joint design which lends itself to mechanization.

If induction heating is to be used, the following facts must be considered:

1. Components must have consistently clean surfaces.

2. Clearances on parts must be maintained ac- curately

3. Solders having rapid spreading and good capillary flow properties are generally required. 4. Preplaced solder often affords the best

means of supplying the correct amount of solder and flux to the joint.

5. induction heating equipment represents a large capital investment.

6. Design of the induction coil is critical for efficient heating and operation of the equipment.

The only requirement for a material to be induction heated is that it be an electrical conductor. The rate of heating of the material is depén- dent upon the induced current flow; distribution of heat obtained with induction heating is a function of the induced current frequency. The higher frequencies concentrate the heat at the surface.

There are available today four main types of equipment which are used for induction heating: the vacuum tube oscillator, the resonant spark gap, the motor generator unit, and the solid state converter.

The vaciium tube oscillator is available in frequencies from 200 kHz to more than 8 MHz. The most popular units for general use have a frequency of approximately 500 kiiz. These units are available with power outputs from 1 fo more than 100 kW, but ihe units most often used for soldering are below 25 kW. The availability of low power units has made the vacuum tube oscillator the most suitable for soldering operations.

The resonant spark gap unit produces frequencies from 100 kHz to 300 kHz with power output up to 20 kW. The variations in output may create problems in maintaining the spark gap.

Motor-generator equipment is capable of producing frequencies up to 15 Wz. The power available from this type of unit is very substantial, often more than 1000 kW.

Equipment. Processes, and Procedures 145

Solid state converfers have output power ratings in the range of 100 kW to 300 kW at frequencies of 1 kHz to 3 ki-iz. These units convert three phase line frequency fo single phase high fre- que nc y.

To achieve maximum heating efficiency, the work coil should be kept close to the part. Both corrosive and noncorrosive fluxes can be used in the induction soidering operations. In either case solvent should be used sparingly to reduce the amount of volatile material being driven off during the heating cycle, as incomplete evolution of ,

gases sometimes results in porosity in the joint. When induction soldering dissimilar metals,

particularly joints composed of both magnetic an$ nonmagnetic components, attention must be given to the design of the heating coil in order to bring both parts to approximately the same temperature. Fixtures to be used in the vicinity of the induction coil are generally made of nonconduct- ing materials in order to prevent them from being heated by the magnetic field.

Resistance Heating

In resistance heating, the work to be soldered is connected either between a ground and a movable electrode or between two movable electrodes to complete an electrical circuit. The heat is applied to the joint both by the electrical resistance of the metal being soldered and by conduc- tance from the electrode, which is usually carbon.

Resistance soldering equjpment consists of a heavy-duty variable transformer which converts the normal line voltage to a lower voltage with correspondingly increased amperage. A wide variety of accessories can be attached to the irans- former.

In one method of resistance soldering, the work is attached to a ground lead by either an alligator clip or Gclamp. The single movable electrode used in conjunction with the ground attachment is carbon mounted in a nonconduct- ing handle. A variation may be achieved by fix- ing the electrode in position and bringing the grounded work to be soldered into contact with the eleftrode while simultaneously applying the solder.


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46/SOLDERING MANUAL

Another method uses a two-circuit soldering tool consisting of two carbon electrodes mounted in a nonconductive handle, eliminating the necessity of a ground lead.

The electrodes may be held with pliers so that pressure and heat are applied simultaneously.

Production assemblies can be made with multiple electrodes, rolling electrodes, or special electrodes depending on which are most suitable for the job at hand.

Resistance soldering electrode tips generally cannot be tinned, and the solder must be fed directly into the joint. The flux and solder must therefore be in the proper position. Electrodes and holders are usually light in weight and are shaped to do a particular job.

A resistance element bridging the electrodes of a parallel gap welding head provides a method of pulsing the element, which serves as the soldering tip, to soldering temperatures and back to ambient in 4-6 seconds. The process offers excellent control over soldering time, temperature, and pressure, depending upon the sophistication of the control equipment, and is well suited for automating reflow soldering applications. The resistance element, usually made of a high nickel alloy, can be designed to make several solder connections simultaneously.

Oven Soldering Ovens have long been used successfully for

high production soldering. Although conveyorized setups normally result in higher pro- ductivity than batch type operations, both are commonly used; in either case large production NnS are needed to justify the cost of the furnaces and required tooling.

Several factors to be evaluated when consìder- ing this process are

1. The entire assembly must be designed to withstand the temperatures required for soldering.

2. Fixtures are required to hold the parts of the assembly together while heating and cooling. The parts being soldered must not be able to move relative to one another - especially during the cool down cycle - or fractured, weak joints could result.

3. The areas of the assembly to be soldered must be prefluxed, and preforms of solder, solder

cream, or something similar must be put in place before the assembly is placed in the furnace. 4. The heating rate is critical. An excessively

fast heating rate can cause distortion and also hinder the proper cleaning action of the flux. Too slow a rate would defeat the purpose of this process- high production.

5. Good controls are needed on the heat source to maintain the proper temperature inside the furnace and guarantee solder connections of consistent high quality.

6. The parts must be at soldering temperatures for a period of time long enough to allow the solder to form a good joint.

7. The use of an inert atmosphere inside the oven does not eliminate the need for a flux but will prevent further oxidation of the parts.

Ultrasonic Soldering

This soldering method has limited use but vibrating units are available for dip soldering pots. A transducer produces high frequency vibrations which break up tenacious oxide films on base metais such as aluminum, thereby exposing the base metal to the wetting action of the liquid solder. Ultrasonic units are useful in soldering the return bends to the sockets of aluminum air con- ditioner coils. Ultrasonic soldering is also used to apply solderable coatings on difficult-to-solder metais.

Focused Infrared Soldering Optical soidering systems are available which

are based on focusing infrared light (radiant energy) on the joint by means of a lens. Lamps ranging from 45 to 1500 watts can be used for different application requirements. The devices can be programmed through a silicon-controlled power supply with an internai timer.

Hot Gas Soldering

The principie is to use a fine jet of inert gas, heated to above the liquidus of the solder. The gas acts as a heat transfer medium and as a blanket to reduce access of air around the joint.

WAVE SOLDERING

A liquid wave is generated by circulating molten solder by a pump in an appropriafely designed soldering machine. The prime functions of the


wave are to serve as a heat source and heat transfer medium and to supply solder to the joint area. A properly functioning solder \wave, as a con- sequence of its geometry, thermodynamics, and fluid mechanic characteristics, will contribute to the wetting of the metal surfaces, promote through-hole penetration, and ensure formation of reliable solder joints and fillets.

A wave soldering production line includes fluxing, preheating, and soldering stations and a means of conveyance of the assembly. In-line cleaning and drying can also be included in the operation.

Methods of F l u Application

The method used for wave fluxing is the application of flux using the liquid wave principie to form a wave of flux which touches the workpiece while the assembly passes through it. By this method the flux Coats the areas to be. soidered.

Foam Fluxing. The flux foam is generated from liquid flux by means of a porous medium immersed in the flux. Low pressure air is forced through the pores of the diffuser and generates fine bubbles of foam. These are guided to the surface by a nozzle to form a foam heaö or wave through which the assembly is passed.

Blush Fluxing. A rotating brush partly immersed in flux is used as a means to transfer flux to the workpiece.

Spray Fluxing. Flux is applied to the workpiece by means of jets or spray nozzles. One method of spray fluxing employs a drum with fine stainless screen partially immersed in flux and rotated in it. The flux wets the screen, and air jets inside the dnim blow off the flux as minute droplets in the direction of the assembly. The amount of flux transferred in unit time is controlled by the rotational speed of the drum and the air pressure.

Preheating

The essential function of preheating is the evaporation of the flux solvent. Proper preheat will also promote wetting and reduce thermal shock.

A preheat temperature of 75" to 80" C (= 170" to 180" F) is usually employed for evaporation of the solvent in rosin base fluxes. For water-soluble

Equipment, Processes, and Procedures147

fluxes, a preheat temperature somewhere above the boiling point of water may be necessary. Fluxes with other solvents may require extended preheat times. Printed wiring boards, when heavily loaded with connector parts, may require higher preheat temperatures.

Drying and preheating of printed circuit assemblies to required temperatures must be performed rapidly in view of the short time the assembly spends in the preheating zone. The dwell time of a moving printed circuit assembly over a O. 5 m ( =2 ft) preheating zone is 2 minutes at a speed of 0.3 mlmin. (1 ftlmin.) and only 7.5 s at 5m/min. (= 16 ftlmin.).

Radiant heating has proven to be the most efficient method for preheating printed circuit assemblies at practical conveyor speeds. Heat is commonly provided by a radiation panel (hot plate) or sheathed (rod, flat) type heater element. Other sources include tubular quartzlamps, fused quartz heaters, infrared lamps and panel heaters.

A combination prefieating process is sometimes employed. The first stage is low intensity radiant heat in combination with warm forced air flow. The latter serves as a supplementary heat transfer medium and as a ventilation means, continuously eliminating the solvent vapors. The second stage consists of a high intensity panel preheater to elevate the printed circuit board to the appropriate temperature. The heat output of both stages can be adjusted for different conveyor speeds. The total output of these combination preheaters varies from 7 to 14 kilowatts.

Soldering Station The essential feature of the soldering machine

is the generation of a wave of molten solder. Modern systems are capable of pumping wave widths (or lengths) from 50 to 600 mm (2 to 24 in.), and wave heights to 20 mm (3/4 in.). They have relatively large solder capacities to maintain soldering temperature and provide satisfactory flow patterns. An automatic solder feed mechanism is used on high production units to maintain a constant solder level without affecting fhe thermal balance of the pot.

Some machines utilize an oil intermix feature to reduce the incidence of solder bridges and icicles in printed circuit assemblies. A layer of oil floating on the solder surface is continuously fed

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: I


481SOLDERING MANUAL

to the input end of the solder pump. The ratio of oil to solder is controllable. The oil is sucked in by the pump, intermixed with the solder, and the mixture then driven to the wave surface. There is, however, the possibility of oil inclusions and entrapments in the solder joints. Recirculation of the oil results in its degradation, requiring changes to maintain the basic properties for which it was introduced and to limit sludge and carbon deposits around the pump. The oil must be replaced approximately every 4 to 8 hours of operation.

Wave Shapes

A solder wave is characterized by its width, a dimension perpendicular to the direction of travel (also called length); height from nozzle edge to apex or top; geometrical contact length between workpiece and wave, referred to also as the width of the contact band or the width of the area of contact. The contact length and speed of travel will determine the dwell time: the time during which a printed circuit board or other workpiece is in contact with the solder. Width and size of the wave are limited by the capacity of the pump and usually do not offer a contact length greater than 75 mm (=3 in.).

Solder waves with a parabolic shape offer a relatively narrow contact length between printed circuit board and solder without excessive de- pression of the workpiece in the wave, thereby limiting conveyance speeds to 0.5 to 1 d m i n (=2 to 4 fdmin).

Wide waves offer a relatively flat, elongated contact ârea in the direction of travel, permitting conveyance speeds of 2 to 2.5 d m i n (=6 to 8 ft/min) or higher.

A recent development combines a controlled wide wave with an inclined conveyor. With the use of supporting plates, an inclined planar wave has been developed that can be controlled to generally parallel the angle of incline of the conveyor. As a result, conveyor speeds up to 5.5 mlmin are possible.

Cascade soldering machines employ an inclined plane with ridges perpendicular to the direction of solder flow. Solder flows down the incline and produces multiple small waves. This system permits high conveyor speeds.

Conveyance Conveyors move parts through the soldering

station and are frequently designed to be integrated with component assembly, fluxing, and preheating and cleaning operations to form one continuous production line. Conveyors are designed to provide a smooth, vibration-free movement of the printed circuit assembly at fixed or adjustable slopes ranging from horizontal to 8 degrees and speeds to 6 m/mh (20 fdmin).

Thereare basically two types of conveyor. One is a chain conveyor which requires the use of board holding carriers to secure the workpiece or pallets. The other is an adjustable width finger type conveyance for use when a large variety of different size printed wiring boards are to be wavesoldered. The fingers are usually made of titanium to resist flux, high temperatures, and prevent solder adherence. Multitrack systems are a variation of the finger type, which permit soldering printed circuit assemblies of two different sizes simultaneously.

Flux Removal Adequate cleaning is particularly important in

printed circuit applications. The techniques for flux removal can be divided into two basic approaches: batch type cleaning, in which the operation is separated in time and space from soldering, and in-line cleaning, where the cleaning positions fóllow immediately after the soldering position, forming one continuous system.

Batch cleaning includes the use of dishwasher type cleaners, ultrasonic dip tanks, and vapor degreasers. These methods are generally used for small parts and low volume processing systems as part of a hybrid process. In-line cleaning, particularly where a production volume exists, has become the generally accepted method. Cleaning stations utilize liquid waves, immersion tanks, forced sprays, rotating brushes, ultrasonic tanks, vapor immersion, and combinations of the above with the appropriate solvent for the flux to be removed. Drying stations following cleaning employ air knives, infrared, and air blasts.

The lastest development for high production cleaning is the use of biodegradable water detergent solutions in combination with multiple stage in-line spray cleaning systems.


AWS S M * C H * 7 ** I 07842b5 0006337 b f---------7.

CHAPTER 7

FLUX REMOVAL

After the joint is soldered, flux residues that are liable to corrode the base metal or otherwise prove harmful to the effectiveness of the joint must be removed or made noncorrosive. It is especially important to remove flux residues if joints will be subjected to humid environments.

Corrosive flux residues contain inorganic salts and acids and should be removed completely. Intermediate, or self-neutralizing, fluxes may be composed of very mild organic acids such as stearic, oleic, and ordinary tallow; or of the corrosive combinations of urea and various organic hydiochlorides. Those composed of the mild organic acids can receive the same treatment the noncorrosive fluxesreceive. On the other hand, if the composition includes some of the more active acids, the flux residue should be removed completely. Where no indication of the composition- of these intermediate or self-neutralizing fluxes is given, the safest procedure is to treat them as if they are corrosive.

The noncorrosive flux residues, generally having a rosin base, need not be removed unless appearance is the prime factor or the joinf area is to be painted or otherwise coated.

The activated rosin fluxes have a rosin base into which haue been incorporated small amounts of complex, usually self-neutralizing, organic compounds. These can generally be ireated in the same manner as the noncorrosive fluxes.

CORROSIVE FLUX RESIDUES

Where flux residue removal prokedures are not practical and the nature of the soldered assembly is such that the flux corrosion would either interfere with its operation or substantially shorten its life, corrosive fluxes must not be used. Corrosive fluxes can be used in precoating operations where flux residue removal can be accomplished before the parts are assembled.

Zinc chloride fluxes leave a fused residue which, if not removed, will absorb water from the atmosphere to the extent that droplets of a highly corrosive water-zinc chloride mixture will form around the soldered joint. Removal is best accomplished by first thoroughly washing the part in hot water containing 2% concentrated hydrochloric acid.

This acidified water removes the white crust of zinc oxychloride (which is insoluble in ordinary water) but retards removal of the residue beneath. As a further precaution, the work should then be washed in hot water containing some crystals of washing soda (sodium carbonate) followed by aclear waterrinse. Occasionally some mechanical scrubbing may be required to further insure the removal of all traces of flux residue.

Acidified rinse water, if used on copper articles, such as a radiator core, may build up in

49


AWS S M * C H * 7 ** 0784265 00063ïä 8 W

SO/SOLDERING MANUAL

copper salt content and cause unsightly darken- ing of the soldered joints. When this occurs, the acidified rinse may be regenerated with a small amount of potassium ferrocyanide which precipi- tates the copper salts from solution.

The residues from reaction fluxes, which are described in the chapter on aluminum (Chapter 15), usually respond to a rinse in warm water. If difficulty is experienced, the joint on aluminum may be scrubbed with a brush and then immersed in 2% sulfuric acid followed by immersion in 1% nitric acid. A final warm water rinse removes ali acidic compounds.

The residue from intermediate or self- neutralizing organic fluxes is usually quite soiu- ble in hot water. Doubie rinsing in warm water is always advisable.

OILY OR GREASY FLUX PASTE RESIDUES

Residues of oily or greasy flux pastes are generally removed with an organic solvent. Soldering pastes are usually emulsions of petroleum jelly and a water solution of zinc-ammonium chloride. Because of the corrosive nature of the acids contained in the flux, residues must be removed where good electrical properties are required and no corrosion can be tolerated.

NONCORROSIVE FLUX RESIDUES

Nonactivated rosin residues are soluble in al- cohols, petroleum spirits, turpentine, trichlorethylene, cyclohexanol, and most common organic solvents.

Mildly activated rosin and activated rosin residues require different treatment for the complete removal of the residues. The above- mentioned solvents will remove the rosin but in most cases will leave behind the additives. The additives are generally polar in nature and cannot be entirely removed by nonpolar organic solvents. For complete removal a second treatment with water is necessary to remove the additives. Certain proprietary solvents which contain polar and nonpolar solvents are available which will give complete cleaning in one operation.

Rosin flux residues may be removed by mechanically scrubbing the assembly with the appropriate cleaner or by complete immersion or vapor degreasing, provided the assembly will not be damaged by these methods.

The extent of removal of ionic residues following a cleaning procedure can be measured by several means. Measurement of insulation resistance of printed wiring assemblies is one method in use. Qualitative measurement of the presence of halide ions using silver nitrate test solutions or silver chromate tesf paper may also be used. Other methods based on measuring theresistivify or conductivity of reused water are in use. In- struments developed for removing residue contaminants and measuring the amounts are available. See Fig. 8.14 of Chapter 8 for example.


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CHAPTER 8

INSPECTION AND TESTING

Requirements for inspection and testing of soldered joints are entirely dependent upon the application. Soldering operations are so diverse that many detailed test programs have been developed. Numerous industrial and military standards apply to electronic and electrical component and connection manufacture. Plumbing fittings are covered by careful dimensionalcontrol.

Inspection and testing for soldering commences with analysis of materials, of geometric accuracy, of uniformity of fluxes, and assessment of surface conditions. In-process monitoring of joining parameters is next for consistent quality in any good inspection program. Finally, after the joint is soldered, a wide variety of test procedures, including mechanical and environmental, may be required for verification of joint performance.

Precoating of base metals is used extensively for production of more solderable surfaces to facilitafe longer storage or increase subsequent environmental resistance. Required thicknesses and types of coating used are covered in Chapter 5 . Inspection techniques depend upon the base and coating materials. Thickn'ess measurements are made by magnetic gages on ferrous base metals or by electrochemical test devices. Ad- herence of coatings may be determined by wrap- ping the test specimen around a specific mandrel diameter and examining it microscopically for cracking and flaking of the plated or coated surfaces. Visual inspection, by itself, i s not

sufficient to determine the adherence of the coating since it is possible to plate over dirty or contaminated surfaces. Other ways to determine the adherence of coatings include heating the part to a predetermined temperature and examining it for evidence of blisters, Another heat test uses an adhesive tape.

Solderability is probably the most difficult factor to define. Perfect surface condition and cleanliness are impractical, so soldering is always performed on an imperfect surface. Normal precautions in cleaning and preparation are essential, and yet the criteria of solderability remain somewhat subjective. A number of tests for solderability have been developed. Some of these tests ultimately rely on experienced visual examinations; more recent tests provide quantitative data.

The earliest tests probably were the direct spread tests and the capillary tests. In the spread test specially prepared solder samples are placed on specific-sized specimens of the material to be tested, and both are placed in an oven for a prescribed length of time at temperature. After removal, areas of spread for the standard amount of solder and final height of specimen plus solder are used to evaluate solderability on a comparative basis. Capillary tests have long been used to evaluate the flow characteristics of bulk solder. Two general methods are used. One method utilizes a twisted wire, at one-inch pitch, which is dipped into a liquid bath of solder for a prescribed

51


52ISOLDERING MANUAL

time, say 15 seconds. Results are measured by examination of the height of rise achieved. A second method is to use a specially drilled block of metal with two or more hole diameters; again, comparative heights of rise of molten solder are measured after a prescribed exposure period.

À method specifically designed for component leads and wires is the solder globule test, as shown in Fig. 8.1 (IEC Publication 68-2“Test T Solderability”). The technique is to measure the wetting time of a wire immersed in a molten globule of solder. Volume of solder is dictated by wire diameter under test. The test is a good dis- criminator, as shown by Fig. 8.2, in determining solderability variations.

The solderability test standard (ANSI-EIA RS-178) is widely used in U.S. industry and was adopted in MILSTD-202 as Method 208. Pro- vided to test wire up to 1.2 mm (-0.045 in.) diameter, the test uses the device shown in Fig. 8.3. Evaluation is made on the basis of the uniformity of the resulting solder coating.

Larger surfaces, such as printed circuit boards, may be examined using three essentially very similar tests wherein the material to be tested is lowered into a molfen solder bath under controlled conditions, removed, and then the specimens are. examined for uniformity of the solder film achieved. These tests are the edge dip test, the rotary dip test, and the meniscus test.

The edgedip test (ANSI-EIA RS 319, IPC 8Ól) is intended to provide a mutually agreeable quality determination of the stock or surface coating to be soldered and to ensure that no in-process procedure results in deterioration of the materials to be joined. An Sn 60 or Sn 63 solder is designated, together with a specified flux type. Test samples must be at least nominal 15 mm (il2 in.) ’

wide. After fluxing, the sample is immersed in molten solder edgewise, with an insertion rate of 25 mm/s (1 in./s), a dwell time o f $ s, and then slow withdrawal. A uniformly adherenf coating is required to cover a minimum of 95% of the specimen area.

A B

Fig. 8.1-Globule solderability test for round component terminations. A, commencement of globule solderability test for round component terminations. Timing is commenced when the wire bisects the molten globule. B,end of globule test showing solder completely encasing wire, when time is stopped, The time in seconds to achieve this is an indication of solderability of the wire


ao 1 As received

Inspection and Testing153

Test temperature 235" C Activated flux

Soldering time, seconds

Fig. 8.2-The effect of accelerated aging for 16 hours at 155" Con the distribution of soldering times of a single batch of resistor terminations tested by the globule method. An activated rosin flux was used in the tests. Note the significant proportion of wires having times above 3 seconds indicating a probable serious loss of solderability under normal storage conditions

The rotary dip test is used in Europe. The apparatusis shown in Fig. 8.4. The test technique requires subjecting a number of specimens to progressively longer times in contact with molten solder and, by visual examination, defermining the time for complete wetting to be attained. Typical results are presented in Fig. 8.5. In addition, the test may be prolonged to induce dewetting action. Although the test is qualitative-in relying on visual exahination, it does produce more information than the direct edge-dip test as

Fig. 1.3-Suggested dipping device for solderability test

specified. However, the edge-dip test can be made to perform similarly.

Fig. $.$-Rotary dip solderability test for printed circuit specimens and tags, designated the TRI-Moore test. A ptfe (Teflon-like plastic) paddle immediately precedes the specimen to clear the solder bath surface of oxide and flux residues. Solderability of plated through-holes may also be determined


AWS SM*CH*â ** H 07â4265 00061102 6

M/SOLDERING MANUAL

æ Resin acquei -

Roller - Sn

O. 5 - -

Au

O. 5 - Immersion -

m 0% si 0% P o. 8

Roller

- - -

m 0% si

7.5

osbp

-

B

Sn

5. O

- -

m 9

Au - 5. O -

ElectroDlaied

13.

a Sn, Ni - 5. O -

= Sn;Ni + Au .5Sni - ).2Ai

Fig. 8.5-Minimum wetting time as determined by rotary dip test of several coatings tested both fresh and after different types of aging.Thickness: 5pm( ==0.0002 in.). Short black columns represent good solderability, and shaded regions indicate very variable wetting time; points on top of columns indicate no significant wetting after 10 s.


Inspection and Tesring155

Spring arm

Fig. 1.6-A surface tension balance device, using solder bath which can be automatically raised and lowered by the test mechanism. No mechanical coupling exists between specimen and measuring system

A recently developed technique monitors the kinetics of wetting action by measuring surface tension forces between specimens and molten solder during the critical initial wetting stages. The apparatus used is shown in Fig. 8.6. The solder bath is moved upward towards the specimen carefully mounted above and connected to a sensitive transducer. As the molten bath covers the specimen, an upward thrust equivalent to.the displaced material is produced which lessens as wetting of the specimen commences, proceeding under good wetting conditions until a downward force is produced by the meniscus acting on the specimen. Illustrated in Fig. 8.7 are the three possible conditions: good wetting, slow wetting, and no wetting. The test method can be appliedto a wide range of samples including printed circuit laminates, component leads, and other solder surfaces that may be suspended on the tension balance. A timer allows selection of a specificdwell period, temperature is carefully controlled, and the results are presented on an X-Y recorder.

So far no single solderability test has proved capable of providing an overall assessment of this important factor. The number of tests developed is partly attributable to the complexity of the subject, to the considerable efforts made to un- derstand the wetting process, and to the need to describe certain specific acticns by a viable test procedure. Clearly, the user now has a better choice of suitable tests for his particular production situation, and the development engineer has a continuing challenge to produce more quantitative test criteria for solderability assessment.

IN-PROCESS MONITORING

Descriptions of soldering requirements for various materiais and products in other sections of this book illustrate the progression of soldering technology. Success in manufacture arises from knowledgeable control. In manual operations, the necessary process control may be a simple


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56/SOLDERING MANUAL

Rise due to withdrawn meniscus

I I

I I I Fluctuating force o I I I duetodewetting I

I I I I I I l 2 - I I I

s

I I I I

u)

I I

% I I I I . A Y

I I I I I 1 1 I

I I

I I I I l I I I I l I I I I i !

J// I I I I I

I

I I I

I I i I I I Wetting I I time I I I

Wetting I I time - 1 I

-B -7 I I Withdrawal -+i I I I I I

immersion

I l

I & - A T ...

' O - I immersion I Withdrawal -+i I I

Fig. 8.7-Typical recorder trace obtained from surface tension balance during a solderability test. CurveA represents a material of high solderability, whereasB has a much slower rate of wetting. With material C , the forces only just reach zero and wetting is never achieved. Note fluctuating withdrawal force when dewetting occurs due to breakdown of the meniscus

check on the heating rate of solder torches and the pH value of the flux. To ensure an adequate product in large quantity production, a complete process control system with digital and analog modules may be reqyired using sensing from thermocouples, tachometers, photocells, etc., and converting the information to direct on-line control of vaIves, actuators, power controls and motors, etc.

The first ,steps in providing monitoring systems should be seriously considered. Continuous temperature measurement of solder alloys for critical operations really is essential for quality

confrol. On-stream pH sensors now are available to provide a constant check on fluxes, with immediate response if pH values fall outside a prescribed limit. Photocells can perform a number of information-gathering tasks which assist in ensuring adequate process control. Monitor- ing the number of parts, the rate of travel, and the positioning of components on a line can readily reduce possible defects and provide direct evidence of process changes. The ease with which a soldered joint is made should not reduce the effort needed to make consistently good soldered joints. Monitoring the


process can be simple or complex. The importance of the exercise is to assign values to the critical factors controlling production. Cost- effectiveness must be considered. However, when probrems do occur, information monitoring can be the tool to quickly return the quality to its original level. Coupled with other inspection and testing techniques, the monitoring program is a vital link between materials and the final product.

FINAL INSPECTION PROCEDURES

Nondestructive Visual examination is probably the most

widely used method of nondestructive soldered joint examination. Primarily the experienced in- spector will work from workmanship samples and design drawings to facilitate overall judg- ment of joint quality. Visibility of the joint from

Inspection and Testing157

both sides obviously is advantageous for the in- spector to properly execute his task. Factors considered in examination are geometry and general design conformance, wetting, quality and quantity of solder and, finally, cleanliness of the product for its intended service.

Table 8.1 and Fig. 8.8 summarize some potential soldering defects. Additionally, Fig. 8.9 shows an example of nonwetting and dewetting on the same component. Bridging between component terminations is illustrated in Fig. 8.10, where leads were too close for the soldering conditions. Finally, Fig. 8.11 shows an example of vapor entrapment producing a large void in the fillet.

Wetting defects arise from incomplete cover- age of a surface to be soldered. Nonwetting is identified by the original surface finish. The problem can arise from insufficient heating of the joint, poor fluxing activity, or contaminated surfaces.

AWS S H * C H * & ** M 078L12b5 000b405 L

Table 8.1-Solder joint defects

Classification Amearance of ¡oint

Bare-no solder Cold solder

(Fig. 8.86) Disturbed solder

(Fig, 8.8d) Excess solder

(Fig. 8.8e)

Solder ground Insufficient solder

(Fig. 8.8f) '

Rosin joints (Fig. 8 . 8 ~ )

Solder short - Sharp point in high voltage circuit Dewetted joint

Connection not soldered Sharp demarcation at solder interface with poor flow . caused by lack of heating Connection displays a chalky or crystallized appearance caused by movement of the joint during solidification In general, the solder should be one-third the thickness of the wire attached to the terminal with the outline of the wire still visible. Joints with solder exceeding this amount fall into this classification Connections grounded by solder drips or overhangs Insecure union of the wire to the terminal

A portion of the terminal and the wire are separated by a thin coat of rosin flux caused by insufficient heat or poor solderability The solder forms an undesirable electrical path Solder points may cause potential arcing or corona effects

Large angle between solder and base metal. Globules or residue on base metal


58ISOLDERING MANUAL

A B

E F

Fig. 8.1-Properly and improperly made sbldered joints. A, properly made joint; B , cold solder; C, rosin joint; D, disturbed joint; E, excess solder; F, insufficient solder

Deivetting and nonwetting look alike to the untrained eye. Dewetted parts are characterized by a residual solder colored film with discrete globules or beads where the solder originally flowed, then refracted. Contaminated surfaces, dissolved surface coatings, or overheating prior to soldering can produce this defect. For repair purposes, recleaning of nonwetted or dewetted surfaces is essential for good joint production. In large area lap jointsit is not unusual to have up fo a 20% void area usually comprising a collection of small voids.

Joints that have moved excessively during solidification have a frosty appearance. Pressure testing of soldered joints is applied to

tube and piping systems, radiators, cans, and other vessels fabricated by soldering. Service duty of the component dictates the type of pressure test applied. For example, in high-pressure water or sprinkler systems, astatic pressure test at aload value that is a specific percentage in excess of service duty loads is applicable. Automotive radiators are pressure tested in the same manner and then, in addition, subjected to a dynamic pressure cycling program that reflects their use in service. Pressure tests on soldered joints are usually by purchaser agreement because of the varied products subject to the test.

Dye penetrant and fluorescent dye examinations are sometimes appropriate for the detection


Fig. 8.9-Example of faulty joint showing &wetting of solder on land and nonwetting on component termination

Fig. 8.10-Bridge of solder between component terminations due to incorrect spacing or incorrect soldering conditions

Fig. 8.11-Cavity within solder fillet in joint probably due to entrapment of flux vapors. This may not be considered as cause for rejection for certain applications

Inspection and Testing/59

of surface defects. Radiography is applicable to uniform, relatively large area joints such as pipes and tubes or lapped joints in sheet or plate. Views through fwo walls are more difficult to assess since, as previously stated, up to 20% void area is considered to be good quality.

Electrical measurements are made on individual joints but generally are more applicable to the examination of systems. Usually soldered joints are designed with up to 300% electrically excess material, which is satisfactory provided no joint cracks are present. Electrical systems analysis is more definitive in locating the difficult joint through simulated job performance. on soldered circuitry, for example. Here, repetitive testing soon clarifies whether defects are arising in specific design areas or are caused by a general materiais problem. For high volume production, manual observation techniques cannot compete with such sophisticated inspection systems.

Mechanical Testing

Mechanical tests serve two functions: first, to evaluate alternative designs, soldering parameters, and materials; and secondly, to verify the quality of joints made in production. The three main classifications -tension, shear, and peel - are illustrated in Fig. 8.12. Most solder joint data in the literature are obtained on lap-shear sam- pies. Testing procedures should be in accordance with ASTM Standards. In butt tensile joints the diameter-to-width ratio of the soldered area directly influences the actual measured strength values. Joint strength first increases and then decreases as diameter-to-width ratio is increased. Lap-shear tests can give a wide range of apparent strengths depending upon the width, depth, and cross section of the specimen. Preferably, tests should be performed on joints at least a nominal 15 mm (1/2 in.) wide with all dimensions clearly stated. Peel tests are applicable in certain instances; here results are quoted in terms of load per linear inch of joint, and two values are utilized - load to initiate fracture and load to propagate the fracture. In all three cases it is imperative, if data are to be meaningful, to state the strain rate at which tests were made.

Mechanical testing of solderjoints made with a formed flat-pack lead and the basis board depend for strength on the fillet formed at the heel or bend. Together with the pull angle, these are the


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7.0

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5.0 h

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2.0

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60/SOLDERING MANUAL

- - - - - - -

Tension

Shear

Peel

Fig. 8.12-Main classifications of joint testing of solders

chief determining factors in a lead pull test (see Fig. 8.13).

Results of solder joint mechanical tests should be handled statistically. Reference should be made to ASTM Standards for appropriate methods. inherently, a range of strength values

45/30

07842b5 O006408 7 W

will be obtained in ostensibly the same joint. Recognition of this fact is important to the successful application of the soldered joint in service. Quoting an average joint strength will not suffice if 10% of the product is useless because the natural spread in joint strength is wider than the safety factor ascribed to an average value. Frequency distributions of joint strength tend toward less deviation during long term stress- rupture or creep strength determinations.

Engineering test data for soldered joints are derived from creep, stress-rupture, and fatigue tests. Creep tests are performed by stressing the joint at a specific load to determine the rate of strain obtained. Stress-rupture tests are usually performed under constant stress at the solder joint and record the time to joint failure at a given load. Fatigue tests may be required at high stress with relatively low cycle failure or at low stresses under highly cyclic or vibrational conditions. Lead-tin solders are subject to a frequency de- pendency on the number of cycles to failure; therefore, testing rate must always be stated when data are reported. Hardness tests are sometimes used for quality control purposes.

45/45

1 13!30 1 6145 45/30 60160

90/90 I 4160 60190

I I Plating thickness = 1 .O8 mils Plating thickness = 1.66 mils

(Numbers indicate lead bend/pull test angle) Fig. 8.D-Effects of lead bend angle and pull test angle on pull strength (test data were reported in U.S. customary units)

I-

CI COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

Inspection and Testing16 I

Conductivitv I cells

/ I ICIVI\ I I ístainiess steel\ I / Spinbars I I -c- Flow

t 1 I % Srn - 1 Plastic tank

Recorder

I I 1 I

Fig. 8.14.- Setup for quantative measurement of ionic contaminants on printed wiring boards and components

Environmental Tests A number of tests have been developed to

evaluate systems which include soldered joints. These include salt spray corrosion, temperature cycling to induce stresses, humidity tests for residue corrosion, moisture resistance in circuit packages, life tests under simulated service conditions, high impact shock resistance for rough handling, vibration effects on transportation equipment, and acceleration effects such as aircraft operations. A comprehensive catalogue of fest methods is compiled i n .MILSTD-202 for electronic and electrical parts, which in principle can be readily applied to other areas of solder joint usage. The main objective is to provide in the laboratory a reasonable means of closely simulating actual service conditions existing in the field and, by so doing, provide a uniform basis of acceptance of systems. Environmental testing of newly designed systems or for full assessment of new alloys is' strongly recommended.

Contamination Checks The soldering operation almost always in-

volves the use of a fluxing material designed to be aggressive to the surface material at least sufficiently to allow the solders to flow freely at temperature. These fluxes range from strong acid chlorides and fluorides to very weak organic acids and salts or completely acid radical-free materials such as rosins. Normally, soldering fluxes are washed away from the surfaces adjacent to the solder joint area. If not, these fluxes can leave residues that become corrosive to the solder and the connecting materials. Tests used on electrical products for flux activity are the copper mirror test, which specifies that a flux must nor penetrate a mirrored copper coating 800 A thick on a surface after 24 hours at 50% relative humidity; a chloride and bromide radical check; a pH test according to ASTM E70; and a solder spread test, which indirectly gives a measure of corrosivity since better spread is generally obtained with the more corrosive fluxes. A setup for quantitative measurement of ionic contaminants

Conductivity mon it or


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62/SOLDERING MANUAL

on printed circuit boards after soldering is shown in Fig. 8.14.

Automotive engineering limits the chloride content in the rinse water after postcleaning or flushing radiators, since high- temperature fluxes usually contain inorganic chlorides. Other industries rely on the natural flushing (in piping or plumbing systems, for example) to clear from the joint area any residues that may cause corrosion.

As soldering technology develops and joints are subjected to increased structural requirements or stringent corrosion codes, inspection and fest-

ing become all the more important. In addition, the inspection programs must be carefully molded to accommodate new products and technology and be responsive to change.

ACKNOWLEDGEMENT Figures 8.1, 8.4, and 8.8 are courtesy of Tin Research institute, Inc.

REFERENCES Bud, P.J. 1973. Procedures for production line

solderability testing. Evaluation engineering, Jul y/August .


CHAPTER 9

COPPER AND COPPER ALLOYS

Copper and copper alloys are among the most frequently soldered engineering materials. Sol- dered copper is used in such diverse applications as plumbing, aerospace hardware, automotive radiators, and printed circuits. Solders are usually filler metals of tin alloyed with lead, antimony, or silver. The general families of wrought and cast copper metais are described in Tables 9.1 and 9.2 with pertinent information on conductivity and composition.

The solderability of copper alloys, as described in Table 9.3, ranges from excellent to poor. In order of their decreasing solderabilities, copper alloys may be roughly classified as follows: copper, copper-tin, copper-zinc, copper- nickel, copper-chromium, copper-beryllium, copper-silicon, and aluminum bronzes.

There are no serious problems in soldering most of the copper base metais. However, those alloys with beryllium, silicon, and aluminum require special fluxes.

The high thermal conductivity of copper and some of its alloys requires that a high rate of heat input be used if localized heating is necessary.

SOLDERS*

Limitations on the use of any particular solder are generally imposed by production methods and final performance requirements. Factors to be

*See Chapter 2

considered include maximum allowable soldering temperature, cost of the solder, joint strength, and other physical properties.

The most widely used solders are alloys of tin and lead. Tin, the active component, readily reacts with and diffuses into copper, and an intermetallic phase Cu6Sn5 is created during soldering operations. This intermetallic is formed at the interface while the solder is still liquid; however, aging of the soldered joint promotes the growth of Cu6Sn5 and formation of Cu3Sn. Elevated temperature accelerates the aging. The effect of time and temperature on the intermetallic is discussed on p. 140.

FLUXES**

The noncorrosive fluxes are excellent for the coppers and may be used with some success on copper alloys containing tin and zinc, depending on initiai cleanliness. The flux should be applied to clean surfaces and only enough should be used to lightly coat the areas to be joined.

The intermediate fluxes are used on copper, copper-tin, copper-zinc, copper-beryllium, and copper-chromium alloys. Some of the more active fluxes may be adequate for the copper- nickels and the silicon bronzes, but a generaliza- tion in this respect could be misleading.

**See Chapter 3

63


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The corrosive fluxes can be used on all the copper base mefals, but they are really needed only on those that develop refractory oxides such as the silicon and aluminum brònzes. The aluminum bronzes are especially difficult to solder and require special fluxes or copper plating. Chloride fluxes are useful for soldering the silicon bronzes and copper-nickels.

Oxide films may reform quickly on copper and copper alloys after they have been cleaned. Therefore, the flux should be applied as soon as possible after cleaning.

The fluxes best suited to the use of 50% tin- 50% lead and 95% tin-5% antimony solders on copper plumbing tube systems are mildly corrosive liquid or petrolatum pastes containing chlorides of zinc and ammonium. Many liquid fluxes for plumbing applications are self- cleaning, but. there is a risk of corrosion in their use. Thereis no doubt that a strong corrosive flux can remove some oxides and dirty films. How- ever, when highly corrosive fluxes are used as an alternative to proper cleaning, there is always an uncertainty as to whether uniform cleaning has been achieved and whether corrosive action con- tinues after soldering. It is always best to use a clean surface and the minimum amount of least active flux.

SURFACE PREPARATION

Solvent or alkaline degreasing procedures are suitable for cleaning copper base mefals; mechanical methods, wire brushing, sanding, etc. may be used to remove oxides. Chemical removal of oxides requires proper choice of a pickling solution followed by thorough rinsing. Typical procedures used for chemical cleaning are as follows*:

Aluminum Bromes

needed:

' mixture.

Successive immersions in two solutions is

1. Cold 2% hydrofluoric and 3% sulfuric acid

2. A solution of 5 volume percent sulfuric acid

Repeat until clean. at 25" to 5O"C(=8O0 to 120°F).

*See safety precautions in Chapters 5 and 21.

Chromium-Copper and Copper-Nickel

Immerse in hot 5 volume percent sulfuric acid.

Copper-Silicon Alloys

Immerse in hot 5 volume percent sulfuric acid, then in a mixture of cold 2 volume percent hydrofluoric and 5 volume percent sulfuric acid.

Brass and Nickel-Silver Aiioys

acid.

Copper

immerse in cold 5 to 15 volume percent sulfuric acid.

Mechanical cleaning is used on the arsenicil and antimonial brasses rather than pickling to avoid the development of surface contamination (slimes). These contaminants may interfere with soldering and produce brittle joints. After heat treatment, copper-beryllium exhibits an oxide coating which requires pickling in a one-to-one aqueous solution of sulfuric acid at a temperature of 65' to 75" C(=150° to 170" F). The original oxide is changed to a reddish oxide which may be removed in a solution of 8 liter (=2 gal) sulfuric acid, 4 liter (i gal) nitric acid, 1 liter (-1 qt) of water and 14 g (=1/2 oz.) of hydrochloric acid. Following this treatment, it is possible to solder the beryllium-copper with a plain or activated rosin flux. Mechanical cleaning is also recommended as an alternative cleaning procedure for beryllium-coppers.

Immerse in cold 5 volume percent sulfuric

HEATING METHODS

With few exceptions, rapid heating and cooling is desirable. The reasons for this are as follows:

1. Flux tends to degrade when hot and could lose its effectiveness before soldering is completed.

2. The base metal surfaces may oxidize and become difficult to solder.

3. Prolonged contact with molten solder could cause unacceptable changes in the base metal through intermetallic compound formation, erosion, and solution.

(such as electrical properties of electronic devices) may occur.

4. Degradation of desirable characteristics.


All the heating methods described in Chapter 6 can be used on copper and copper alloys. The types of soldering equipment most commonly used are soldering iron, solder pots (including baths, waves, jets, cascades), torch, oven, induction, hot oil bath, electrical resistance, and elec- fromagnetic radiation (infrared). An example of a rapidly soldered component is the wave soldered pin in a circuit board shown in Fig. 9.1. Process parameters of approximately 270" C (-515" F) wave temperature and about i-i/4 seconds immersion time are typicai.

In the dip soldering of copper and brass, contamination of the solder bath with copper and zinc is always a problem, and the degree to which this is controlled has a direct bearing upon the quality of the joint being soldered. The lowest bath temperature which will bring the parts to soldering temperature rapidly will minimize contamination. The bath should have sufficient heat capacity to bring the parts to temperature rapidly, with the solder temperature no more than 65°C (-1500 Rabove its liquidus for printed circuit boards and as much as 175°C(=350" F)for heat exchangers such as automotive radiators. Solder baths are commonly held to less than 0.3 weight percent copper for wave soldering of electronic components.

Copper and Copper Alloys/65

COATED COPPER BASE ALL0998

The mosf commonly employed coatings are tin, lead, tin-lead, nickel, chromium; and silver. The soldering of copper base metais coated with any of these mefals is done considering only the characteristics of the coating, except that the thermal conductivity of the base metal will govern. Except for chromium plate, none of the coatings offers any serious problem. For chromium plated copper, the chromium should be removed before soldering.

POST SOLDERING TREATMENT

Whenever there is any possibility that flux residues may adversely affect the service life or performance of the soldered joints, the appropriate treafment described in Chapter 7 should be applied.

Manufacturers of soldering fluxes can provide guidance as to the aggressiveness of their flux products and can usually provide appropriate chemicals for removal of flux residues.

ACKNOWLEDGEMENT

Figure 9.1 is courtesy of Tin Research institute, lnc.

Fig. 9.1-Wave-soldered printed circuit board

._ ~

.-


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66/SOLDERING MANUAL

Table 9.1-Wrought coppers and copper alloys

Number series Descnotion Comwsition ranees

Representative electrical

conductivities, % IACS

i01 to 107 Oxygen-free 99.95% Cu or better 109 to 142 Tough-pitch and deoxidized Contain oxygen or deoxidizers 145 to 147 Free-machining Small additions of S, Te, etc. 150 to 194 High copper alloys

205 to 240 Red brasses Up to 20% Zn 250 to 298 Yellow brasses From 25 to 50% Zn 310 to 385 Leaded brasses 405 to 485 Tin brasses 502 to 529 Copper-tin alloys From 1 to 11% Sn

532 to 546 Leaded phosphor bronzes 606 to 642 Aluminum bronzes 647 to 661 Silicon bronzes 665 to 697 Alloy brasses 701 to 720 Copper nickels 732 io 798 Nickel silvers . From about 43 to73% Cu, from7 to 23% Ni,

Neighborhood of 1 or 2% additions of Cd, Be, Cr, Co, Fe, Ni, Zn, andor Sn

From 10 to 45% Zn and up to 4.5% Pb To 5.5% Sn, to 48% Zn

(phosphor bronzes) i to 4% Pb, about 5% Sn, some with additions of Zn From2.6 to 13% Al, to 5% Fe, some with additions of Si or Ni From 1 to 3.5% Si, some with Mn, Si, or Sn Zinc-containing alloys with additions of Ni, Sn, Mn, AI, and Si From 2 to 40% Ni, additions of Fe, Be, Mn, or Cr

some with Pb or Mn, balance Zn

NOTE F o r q w S i c compositions and properties see Standards Handbook No. 2, Copper Developmenf Association, N.Y.

=- 100 80 to 100 >90 20 to 85

35 to 60 25 to 35 25 to 45 25 to 30 10-50

10-20 10-20 7-12

20-25 4- 10 5-10


-_- . . - . .. -. -

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Copper and Copper Alloys/61

Table 9.2 -Cast coppers and copper alloys

Representative electrical

Number conductivities, series Description Composition ranges % IACS

801 to 8 11 Coppers Minimum of 9.70% Cu and remainder Ag 92-100

833 to 838 Red brasses 115-40 842 to 848 Semi-red brasses 15-20 852 to 858 Yellow brasses 18-28

813 to 828 High copper alloys Additions of up to about 2.5% Be, Co, Si, Ni, andlor Cr 83 to 93% Cu, to 12% Zn with lesser amounts of Sn, Pb

20-80

76 to 80% Cu, 8 to 15% Zn with lesser amounts of Sn, Pb

55 to 67% Cu, additions of Fe, Ni, Mn, Ai, balance Zn 57 to 72% Cu, balance primzuily Zn, 1 to 2% Sn, Pb, Ni, or Al

861 to 868 High-strength 7-22 yellow brasses

872 to 879 Silicon brasses and silicon bronzes 65 to 90% Cu, about 3 to 5% Si, some with large amounts of Zn 6-15

7-15 12

3-13 4- 11 4-5

902 to 945 Tin bronzes 3 to 19% Sn, some with large amounts of Pb, less Zn, Ni

7 to 11% Al, at least 71% Cu, balance Ni, Fe, Mn, andor Si 947,948 Nickel-tin bronzes About 5% Sn and 5% Ni, to 2.5% Zn, Alloy 948 has 1% Pb 952 to 958 Aluminum bronzes %2 to 966 Copper nickels 973 to 978 Nickel silvers

10 to 31% Ni, about 1% additions of Fe, Cb, Si, Mn andor Si 55 to 65% Cu, Pb and.Sn additions, 12 to 25% Ni, balance Zn

NOTE: For specific compositions and properties see Standards Handbook No. 7, Copper Development Association, N.Y.


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Table 9.3-Solderability of copper and copper alloys

Type Solderability and remarks' Coppers (Includes tough-pitch, oxygen-free, properly cleaned. phosphorized, arsenical, silver-bearing, leaded, tellurium, and selenium copper.) Copper-tin alloys

Copper-zinc alloys

Excellent. Rosin or other noncorrosive flux is used when

Good. Easily soldered with activated rosin and intermediate fluxes. Good, Easily soldered with activated rosin and - - intermediate flux. Good, Easily soldered with intermediate and Copper-nickel alloys .. corrosive fluxes.

Copper-chromium and Good. Require intermediate and corrosive fluxes copper-beryllium and precleaning. Copper-silicon alloys Fair. Silicon produces refractory oxides that require use of

corrosive fluxes. Should be properly cleaned. Copper-aluminum alloys Difficult. High aluminum alloys are soldered with help of

very corrosive fluxes. Precoating may be necessary. High-tensile manganese bronze Not recommended. Should be plated toensure consistent

soiderabili ty.

9efinitions of descriptive terms for fluxes are given in Chapter 3.


CHAPTER 10

STEEL

INTRODUCTION

Steel can readily be soldered if the proper procedures and techniques are employed and if special attention is given to surface preparation and the selection of fluxes. Precoating with more solderable metals is often required.

SOLDERS

There are few limitations on the types of solders that may be used on steel. Tin-lead solders containing 20 to 50% tin are widely employed for joining steel, with the 40% tin-60Q lead solder predominating.

The choice of a solder is governed somewhat by the intended end use of the assembly. The soldering process and speed ofthe operation also affect the selection. For example, all other factors being equal, it is often more economical to use a more expensive lower melting temperature solder, since the higher melting temperature low-tin solders require higher soldering temperature and usually a longer processing time.

A tin-lead solder’s ability to wet steel increases with tin content. For leak-proofjoints, therefore, it may be more advantageous to use a 40% tin- 60% lead solder than a 5% tin-9$% lead composition. It may often be desirable to try various solders until an optimum combination of properties and soldering conditions is reached.

69

SURFACE PREPARATION

The precleaning and surface preparation techniques recommended in Chapter 5 should be carefully followed. Owing to corrosion or oxidation, steel readily forms films and scales which must be completely removed before soldering. Because of this strong tendency to corrode, surface Protektion is required up to the time that the solder flows over the surface. The protection may be afforded by painting, hot-dip coating, or electroplating.

Steel coated with other metals is generally used for applications involving soldering. A comparatively small amount of steel is soldered without precoating. Terneplate, which is one of the commercially coated sheet steels, has a film of a tin-lead alloy applied on its surface. Terne- plate can readily be soldered with the mildest noncorrosive fluxes. Tinplate, or tin coated steel, has a film ofTure tin applied on the surface by hot-dip or electrolytic methods. Tinplate is also very easy to solder at high speeds with noncorrosive fluxes. The coated steels are treated in more detail in Chapter 11.

HEATING METHODS

All soldering processes and techniques are used to solder steel. For small jobs soldering irons are usually adequate. Torches may be required, how-


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70/SOLDERING MANUAL

ever, for the manual soldering of larger pieces which dissipate heat more rapidly. Induction and resistance soldering are particularly adaptable to steel, and oven soldering may be the most suitable for certain applications (for further details on processes and procedures see Chapter 6).

FLUXES

After preliminary cleaning, fluxing is necessary. The stronger corrosive fluxes are necessary, since the residual oxide of iron is not easily dissolved by mild or noncorrosive fluxes. The zinc- ammonium chloride liquid fluxes, either alone or dispersed in petrolatum pastes, are suitable. For certain types of work, mixtures of powdered solder and dry or paste flux may be found useful, These mixtures are used to precoat dents and irregularities in automobile bodies prior to filling them with solder.

JOINT TYPES

The conventional types of joints covered in Chapter 4 are all used for steel. The strongest joints are obtained when O. 10 to O. 15 mm (0.004 to 0.006 in.) clearances are used. Joints with greater clearances are less dependable, while joints with clearances of less than 0.1 mm (==0.003 in.) may be weak due to poor joint penetration and flux inclusions. Refer to Chap- ter 23 €or mechanical properties of joints.


The corrosive nature of the flux residues requires a rigid cleaning schedule after soldering. Wash- ing with dilute hydrochloric acid (1% HCl), followed by a clear water rinse, removes the zinc oxychloride. After drying, the final assembly may be painted or electroplated.


CHAPTER 11

COATED STEELS

Mill-finished low and medium carbon steels find use in many manufactured products. Soldering is a useful method for joining mili-finished low and medium carbon steels. Solderable metallic coatings on steel normally applied at the mills include tin (tinplate), tin-lead (terneplate), zinc (galvanized steel), and aluminum (aluminum coated steel). In addition, many fabricated steel parts are coated with metals to improve solderability, or to protect the steel by providing sacrificial or anodic coatings that corrode in preference to steel.

Protective metal coatings used on steel and the method by which these coatings are applied are given in Table 11.1. In addition, this table lists some of the uses for the different coated steels.

The surfaces of ail coated steels must be clean and free of soils, dirt, passivation films, and rust before soldering. Specific cleaning schedules are required for each metal coating. Joint design rec- ommendations for coated sheet steels should be followed for maximum joint strengths. Joint clearances of 0.025 to 0.150 mm ( a O . 0 0 1 to 0.005 in.) are usually satisfactory for coated steels. Lap joints or interlocking joints are used where practicable to provide optimum joint strength. Choice of solder composition largely depends on the coating or the intended application of the finished assembly.

ALUMINUM COATED STEEL

Chemical or mechanical cleaning methods should be used to remove or modify the oxide film on aluminum coated steel before soldering. A dip in 5% trisodium phosphate solution, followed by water rinsing and drying, will assist in the preparation of the aluminum coating for soidering.

Heating of the aluminum coatings must be rapid, and electric or ultrasonic soldering irons with sufficient heating capacity to raise the work to soldering temperature should be used.

Some aluminum coated steels may be soldered without fluxes by heating the metal surface sufficiently to melt a small amount of solder touched to the hot surface to form a molten pool. The aluminum under the solder pool is then abraded using the stick of solder, the tip of the soldering iron, or by use of specially designed brushes which assist in displacing the oxide films.

Specially formulated fluxes are commercially available €or soldering aluminum coated steel sheets. These fluxes should be applied sparingly with a fine brush, and soldering should be performed quickly to avoid excessive oxidation of surfaces, oxidation of the solderedjoint, and also to prevent alloying of the aluminurncoating with

71


7ZhOLDERING MANUAL

the base steel to an undesirable extent. Suitable solders for making joints in aluminum coated steel are listed in the chapter on aluminum. Usu- ally these soIders are supplied in the form of sticks, but flux cored aluminum solders and pastes are available.

CADMIUM COATED STEEL

Cadmium is most frequently plated on steel parts fhat have been formed or machined prior to plating operations. Electrodeposits are usually 0.0015 to 0.010 mm (-0.00005 to 0.0003 in.) thick, and it is extremely important that the steel base underlying the coating be clean before plating to avoid the risk of wrinkling or blistering of the coating when soldered joints are made. Clean, fresh cadmium coatings offer good solderability with rosin base fluxes and tin-rich solders. However, solderability decreases rapidly with time, and stronger fluxes may be required toremove thickened or adherent films which may interfere with the soldering process. Torch soldering is not recommended for soldering cadmium coatings because of the evolution of volatile and toxic cadmium compounds during heating. Soldering irons are used most effectively in soldering cadmium coated steel.

CHROMIUM PLATED STEEL

Soldering is not recommended for joining chromium plated steel.

NICKEL AND COBALT PLATED STEEL

Nickel plated steel is produced by flashing the steel with copper to a thickness of 0.0015 mm (=0.00005 in.) or less and then plating nickel to a thickness of 0.0015 mm to 0.010 mm (O.ooOo5 to 0.0003 in.).The higher tin solders (Sn 50, Sn 60, Sn 63) are generally used for making the joint, and activated rosin fluxes can be used success-

adequately cleaned. Often thickened or passi- vated nickel oxide films can be removed before fluxing and soldering by a dip in a 10% solution of hydrochloric acid. Electroless nickel and cobalt coatings on steel can be difficult to solder because a high percentage of phosphides is often present in the coating. A maximum of 5 to 7% phosphorous in the electroless nickel coatings is preferred for solderability. Corrosive fluxes are required to solder these coatings.

COPPER COATED STEEL

Copper coated steel usually offers no soldering difficulties if the surface is clean and free of heavy oxide films. The type of flux used depends on the condition of the coating and the application. A full range of tin-lead, antimony and silver-containing solders may be used. As in the case of soldering pure copper and its alloys, the joints should be made quickly to avoid excessive buildup of intermetallic copper-tin compounds when tin base solders are used.

TERNEPLATE [LEAD -TINCOATINGS) AND LEAD COATED STEEL

Terneplate is low carbon steel with an alloy coating of 10 to 25% tin, balance lead. The lead-tin coatings assist in the soldering of the steel. Terne and lead coatings do not require further preparation other than the removal of oil, grease or atmospheric grime. Long term storage may cause surface discoloration, and a light abrasion may sometimes be necessary before soldering to insure the highest solderability possible.

Although gas heated soldering irons or heavy duty electric heated irons are used to an advantage in joining terneplate or lead coated steel, any of the heating methods outlined in Chapter 6 can be used. The selection of the best method is based on the application and design of the product. Rosin fluxes are satisfactory in most instances for soldering terneplate or lead coated steel. Corro- sive fluxes are used where joint design and assembly allow for removal of any residues remain-

fully if the surface of the plating has been ingonthejoinisurfaces.

1.


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TIN COATED STEEL

Tin coatings, used in the manufacture of tinplate, are commercially available in thicknesses of O.OOO1 to approximately0.0025mm (0.000004in. to approximately O.oooO9 in.). Over 809 of the material is used in the manufacture of food and beverage containers. In addition, many steel parts are coated with tin to improve solderability during assembly, or provide corrosion resistance to the steel base. Tin thickness in these applications may be from 0.0025 to 0.025 mm (0.OOOi to 0.001 in.).

Except for the removal of the surface contaminants, such as forming oils or atmospheric grime, the tinplate usually needs no special preparation for soldering. Rosin base fluxes are satisfactory for soldering to tinplate and tin coated steels.

Soldering irons, induction and dip soldering units, as well as controlled torch soldering are used in joining tinplate and tin coated steel parts. Tin-lead solders are used as filler metais with solders containing 40, 50, and 60% tin, balance lead, being most useful because of ease of application, low melting temperatures, and excellent wetting and spreading properties.

In the manufacture of sanitary cans, tinplate is cut into body blanks which are notched and formed into cylinders. After the bodies are made, the interlocking side seams are formed and fluxed. The can body then travels along a soldering horn over the top of a rotating roller which delivers solder from the melting pot to join and seal the can side seams.

Some can si& seams are soldered by passing the bodies, which.have been notched and have their interlocking seams already formed, through a high frequency electromagnetic field to preheat the seam area to approximately 315" C (=615OF) in about 0.3 seconds. The hot seam is then sealed with a thread of molten solder which is injected under pressure through a fine orifice into the can side seam. A post heating station, in line with the soldering horn, has another high frequency heating coil which maintains seam temperatures sufficiently to allow the molten solder to uniformly fill all voids. Normally, 2% tin-98% lead solders are used in making side seams in cans, but some

Coated Steel173

special purpose cans use pure tin as well as solders containing small amounts of antimony or silver.

TIN ALLOY COATINGS ON STEEL

Electrodeposited coatings of tin-cadmium, tin- copper, and tin-zinc on steel should have a thickness of 0.0065 mm (=0.00025 in.) minimum to provide solderability and extended shelf life. These alloy coatings are soldered, with activated rosin fluxes and tin-lead solders with tin contents of 40,50, or 60%. Sometimes corros¡ve fluxes are used when speed of operafion is required and flux residues can be removed from the assembly. Tin-nickel coatings on steel usually have a thin (0.0025 mm [O.OOOl in.]) undercoat of copper. Tin-nickel coatings 0.01 mm (0.0003 in.) thick are usually soldered after fluxing with corrosive fluxes.

,

ZINC COATED STEEL

Zinc coated steel is available in a variety of coating specifications. Hot dipped sheet may be temper rolled, wiped, oiled, chemically treated (either for painting or corrosion resistance) or heated to produce an alloy coating (galvannealed sheet). The sheet may be brightly spangled or unspangled. Electrogalvanized sheet is also commercially available. Galvanized sheets are sold on the basis of coating weights nominal 0.04 to 0.08 kg/m2 (1.25 to 2.75 oz/ft2) and in steel gages between 8 and 30.

It has been shown that electrogalvanized steel offers better solderability than hot dipped zinc coatings. Minimally spangled hot dipped coatings interfere slightly with solder wetting, but are solderable with acid or organic type fluxes. In general, chromating treatments, used to prevent humid storage staining, interfere with solder flow. The effect of chromate treatments on solderability is complex. However, some of these treatments may improve the soldering of heated surfaces or have negligible effects.


74/SOLDERING MANUAL Table 11.1-Metal coatings on steel

Coating process I

Aluminum - X X X X - Signs, automotive parts, storage bins Cadmium x - - - - - Radio TV chassis, electronic hardware Chromium x - - - - - Decorative parts, hardware Cobalt x - - - - X Substitute coating for nickel Copper X - X X - - Housewares,conductors,electronicparts Lead x x x - - - Chemical apparatus, coffins Nickel X - X X - X Appliances, electrical goods, hardware Tin X X X X X - Containers, electricalparts, foodhandling,

Tin-cadmium X - - - X - Electricparts,hardware Tin-copper x - x x - - Electronic parts Tin-lead (teme) X X X X - - Gasoline tanks, caskets, flashing, gutters,

Tin-nickel x - - - - - Electrical parts, power plugs, connectors,

Tin-zinc x x x - x - Electrical parts, chassis Zinc X X - X X - Gutters, downspouts, furnacepipe,

ductwork, storage bins

equipment

roofing

hardware

Phosphated galvanized surfaces are difficult to solder. The phosphate films must be removed prior to soldering unless strong mineral acid fluxes or corrosive acid fluxes containing sodium bifluoride are used. Galvannealed surfaces are extremely difficult to solder, but some success can be achieved if fluxes similar to those used in soldering stainless steel are used. However, vig- orous gas evolution occurs when these fluxes are used, and this creates enough back pressure to

prevent penetration of solder into narrow joint clearances. Aged galvanized sheet is soldered more easily than freshly produced sheet.

REFERENCES

Helwig, L.E., and Carter, P.R. 63, 1969. Solder flow on galvanized surfaces. Metal finishing, February.

i.

i> COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

CHAPTER 12

STAINLESS, STEELS

INTRODUCTION

Ali stainless steel alloys contain chromium and many contain nickel. Other elements, such as manganese, molybdenum, columbium,.titanium, aluminum, and copper, may also be present to provide certain metallurgical characteristics. In the standard grades, chromium ranges from something in excess of 11% to values approach- ing 30%. Nickel content vanes within the range of O-22%. There are four basic types of stainless steel: austenitic, ferritic, martensitic, and pre- cipitation hardening. There are also freemachin- ing and stainless clad products.

The corrosion resistance of stainless steels is attributable to the formation of a thin, impervi- ous, surface layer of chromic oxide which spontaneously forms on stainless steels in the presence of oiygen. This surface layer also hin- ders the wettingeand flow of solder on stainless steel. Hence, the successful soldering of stainless steel requires the use of a corrosive flux.

SOLDERS

Commercially available solders can be used to join stainless steels. In general, thehigher the tin content of the solder, the better the wetting and flow on stainless steel. It is generally recommended that tin contents be at least 50% in order to provide good bond strength.

Since stainless steels are used in a wide variety of applications and may be subjected to environments of various degrees of corrosiveness, the solder must be chosen for compatibility with both the environment and the stainless steel. Tin and high-tin alloys provide a good color match with stainless steel and do not darken as noticeably in service as do high lead content solders. Because of their relatively low melting point and rapid loss of strength as temperatures increase, solders must be carefully selected and joints properly designed to minimize mechanical loading of the solder if moderately elevated temperatures are expected in service. Solders are quite weak at even moderately elevated temperatures and are subject to creep if directly loaded.

If articles of stainless steel are fabricated for food or beverage processing, solders containing cadmium or lead should not be used.

SURFACE PREPARATION

Standard shop practices suffice for preparhg stainless steels. Appropriate procedures include vapor, solvent, or caustic degreasing; acid pickling; grit or shot blasting; wire brushing or abrading with stainless steel wool or emery cloth. The method chosen should be appropriate to the type of foreign material to be removed. Shot or wire brushes, if used, should be stainless steel to

’

75


76/SOLDERING MANUAL

avoid rust spots. If surfaces are highly polished, it is best to roughen them slightly before cleaning and soldering by using an emery cloth, file, or other suitable means.

Soldering should, if possible, be done immediately after cleaning. if soldering cannot be done promptly, the parts should be precoated with solder or tin immediately after cleaning. An acid flux should be used, and the assembly should be thoroughly washed to remove flux residues.

Many joint designs have recessed and hidden surfaces that makes post 8oldering cleaning to remove flux residues difficult. Furthermore, these recessed or blind areas represent problems in soldering because it is not possible to visually verify that solder has flowed into these areas to completethe joint. Therefore, it is offen desirable to precoat with solder or tin the specific areas involved in the joint before assembling the pieces for final soldering. Precoating is done by the use of acid fluxes which can be more readily removed before the individual pieces are assembled, or suitable electroplating coatings usually may be applied. Final soldering of the joint can then be accomplished with a rosin type flux, the residues of which are innocuous and cause no serious corrosion problem even if not completely removed.

HEATING METHODS

Stainless steel assemblies can be heated by ali the techniques commonly used in production. Be- cause stainless steels have low thermal conductivity, the rate of travel along the joint should be slow enough to permit all parts of the joint to reach a temperature which will permit the solder to flow into ali areas to be joined. Attempts to increase the rate of travel by using higher temperatures are not recommended inasmuch as there is danger of destroying the flux and generating excessive oxidation of the solder and base metal. In general, soldering temperatures on the order of approximately 30" to 85" C ( 4 0 " to 150" F) over the melting point of the solder are desired.

Ausfenitic stainless steels have high coefficients of thermal expansion, which may cause buckling and warpage. Jigs and fixtures may be required to obtain and maintain proper alignment and fit-up. On long seams, it is helpful to tack the

joint at intervals before soldering. If warpage becomes a serious problem, it is often helpful to complete a joint by soldering short lengths of the seam at a time and alternating positions along the joint so that the heat is spread more uniformly over the joint length.

FLUXES

Fluxes suitable for soldering stainless steel are corrosive and care must be exercised in their use to prevent damage to eyes, skin, and clothing. Orthophosphoric acid and hydrochloric acid fluxes are satisfactory as are aqueous solutions of zinc chloride along with other compounds. if molybdenum, titanium, columbium, or aluminum are present, the flux should contain some hydrofluoric acid. There are also commercial fluxes which do a satisfactory job. Rosin fluxes are not satisfactory for soldering stainless steel but can be used if the parts are first precoated with solder using an acid flux. All residues of the acid flux should be removed by neutralizing and washing prior to final assembly with the rosin flux. Flux cored solders containing 'acid" cores are also useful, but it may be necessary to supplement the flux core by the addition of extra flux externally applied.

Residues of fluxes, except rosin, used on stainless steel are hygroscopic, and in the presence of moisture are corrosive to stainless steels. Simi- larly, fumes generated during soldering can condense on colder parts of the assembly, leaving a flux residue that is corrosive in the presence of moisture. Therefore, it is imperative that these residues be thoroughly removed after soldering, preferably immediately after.

Stainless steels are passive under almost all conditions of service in which they are normalty used; however, if passivity is destroyed locally and prevented from being restored, local corrosion (pitting) may cause rapid penetration at the point of initiation. This is because a local electrolytic cell is formed between the large cathodic (passive) area and the small anodic (active) area. Oxygen acts as a depolarizer and pitting occurs. Solutions containing chlorides are especially troublesome in that they promote the formation of such cells. Other halide salts and some sulfates


Stainless Steels177

softer than the base metal to avoid scratching. Water spots or other minor surface discoIorations can be removed by scrubbing with a powdered cleanser or buffing with metal polish.

may also be a source of attack. Cracks, crevices, and gasketed areas are also troublesome in that they may lead to stagnant conditions and localized attack. Elimination of stagnant pockets, cracks, crevices, and thorough removal of acid soldering flux residues will minimize pos- sibilities for corrosion. TYPICAL APPLICATIONS


The only post soldering treatment required is the removal of the.flux residue if a corrosive flux has been used. Rosin flux residues are noncorrosive and need not be removed except for appearance. Detailed instructions for removing various flux residues are given in Chapter 7. If desired, excess solder can be removed from the joint area with a stainless steel scraping tool. The tool should be

Soldered stainless steel articles are found in a wide variety of applications. These include roofs, roof drains, flashing, gutters, ornamental trim, and other architectural items. Seams in buckets, pails, and other types of containers are often solder sealed. Since stainless steels are chosen for corrosion resisfance and heat resistance, it is imperative that soldered joints be employed oniy in those applications where the presence of a soidered joint would not detract from the serviceability of the part.


CHAPTER 13

NICKEL AND

ALLOYS HIGH-NICKEL

INTRODUCTION

Solder can be employed to join nickel and high- nickel alloys either to themselves or to any other solderable metal. Table 13.1 gives the chemical composition and solderability of some high- nickel alloys. In designing a solder joint in any high-nickel alloy, however, it is advisable to take into consideration some of the special characteristics of the base metal.

Many times, the high-nickel alloys are used for a given application because of their resistance to corrosive attack. When corrosion is a factor, the corrosion resistance of the solder must also be considered. In some cases it is necessary to locate the joint so that the solder will not be exposed to thecorrosive environmenf. The higher tin content solders, such a s 9 5 9 tin-59 antimony, may result in a better color match if appearance is important. However, the solder may oxidize in a different manner than the base metal and the joint may become noticeable after exposure.

PROBLEMS IN SOLDERING NICKEL ALLOYS

If soldering is to be done 6n any of the age- hardenable materiais, the soldering should be done after aging. The temperature involved in soldering will not soften such metais as Dur-

anickel, K Monel, and Inconel X which have been fully age-hardened.

The high-nickel alloys are subject to embd- tlement at high temperatures when in the presence of lead and many other low melting metaIs. This embrittlement will not occur at normal soldering temperatures; however, overheating should be avoided. If welding, brazing, or other heating is to be done on an assembly, it is imperative that these operations be done before soldering.

SOLDERS

Any of the common types of solders may beused to join the high-nickel alloys. It is usually desirable, however, to choose a relatively high tin solder such as the 60% tin-40% lead or 50% tin-50% lead composition.

SURFACE PREPARATION

Nickel and nickel alloys heated in the presence of sulfur become embrittled. These alloys should be clean and free from sulfur bearing materials such as grease, paint, crayon, and lubricants before heating.If the surfaces of the high-nickel alloys to be soldered are adequately precleaned as outlined in Chapter 5, it will be possible to produce a sound joint.

79


80ISOLDERING MANUAL

Table 1 3 , l P h e m i c a l composition and solderability of high-nickel alloys ~~~ ~

Alloy Composition (%) Solderability Ni Cu Cr Fe Ti Al

Monel 67 30 - - - - Good - - - - - Good

0.40 - Good Nickel 99 Permanickel 98 Duranickel 94 - - - 0.50 4.5 Good “K” Monel 66 29 - - - 2.75 Good Inconel 77 - 15 7 - - Fair Incoloy 34 - 21 45 - - Fair Nimonic “75” 75 - 20 1.75 0.25 0.35 Fair Inconel “X” 73 - 15 7 2.50 0.75 Fair Ni-Span-C 42 - 5.25 49 2.00 0.50 Fair

- - -

Joints with long laps, and joints which will be inaccessible for cleaning after soldering, should be precoated prior to assembly. Precoating is generally accomplished using the same alloy to be employed for soldering. The parts may be dipped in the molten solder or the surfaces may be heated, fluxed, and the solder flowed on. Ex- cess solder may be removed by wiping or brushing the joint. High-nickel.alloys may also be precoated by tin plating or hot tin dipping.

EQUIPMENT, PROCESSES, AND PROCEDURES

The equipment, processes, and procedures listed in Chapter 6 may be used for soldering nickel and the high-nickel alloys. Some minor differences in procedure may be required because of the lower thermal conductivity of these alloys.

FLUXES

Generally, rosin fluxes are not active enough to be used on the high-nickel alloys. A chloride flux is desirable for soldering nickel or the nickel- copper alloys, such as Monel. Fluxes containing hydrochloric acid are required for the chromium-containing alloys, such as Inconel,

Many of the proprietary fluxes used for soldering stainless steel are satisfactory for use on In-

conel as well as other nickel base alloys (see Chapter 3 for a more thorough discussion of fluxes).

JOINT TYPES

The low strength of soldered joints is apparent when compared to base metals, such as the high-nickel alloys which have relatively high strength. Therefore, the precautions outlined in Chapter 4 concerning joint design are of the ut- most importance when dealing with nickel base alloys, The strength of the joint should never depend on the solder alone. Lock seaming, rivet- ing, spot welding, bolting, or other means should be employed to carry the structural load, whereas the solder is employed only to seal the joint.

POST TREATMENT

Because corrosive fluxes are required for soldering the high-nickel alloys, it is necessary to thoroughly remove lhe residue after soldering. This subject is dealt with in Chapter 7.

TYPICAL APPLICATIONS

Illustrations of solder fabrications of nickel alloys are the transistors shown in Figs. 13.1 and 13.2.


Nickel and High-Nickel Alloys/û i -

Fig. 13.2-Several transistors soldered on printed wiring board

Fig. 13.1-Tránsistor having nickel alloy leads


CHAPTER 14

LEAD AND LEAD ALLOYS

INTRODUCTION

Lead and lead alloys are easily soldered when proper care is taken not to melt the relatively low melting temperature base metal. Lead pipe and sheet are widely used in the pumbing, architectural, and chemical construction fields. Power and telephone transmission lines use lead as a cable sheathing material. Soldered joints in lead, however, are generally confined to the plumbing field, some architectural uses, and joining lead sheathed cables. The use of soldered lead joints in the chemical construction field, or where highly corrosive chemicals are confined or trans- ported, is not generally recommended. Joints should be welded for such applications.

PROBLEMS IN SOLDERING LEAD

Pure lead melts at 327" C (621" F) and certain of the antimonial-lead alloys start to melt at 232" C (450" F). Solders for joining these metals should @ chosen so that they can be worked without melting the base metal. Careful preparation of the areas to be soldered and close tolerances on the joints will alleviate most of the problems connected with soldering lead. However, its relatively low tensile strength (1 1 to 28 MPa), with elongations from 25 to 60% and Brinell hardness of 4.5 to 10.0, should be carefully considered in designing a joint in lead and lead alloys.

SOLDERS

Wiping is a technique unique to lead soldering and requires special solders to yield a smooth, gas tight joint (see Fig. 14.1). Wiping solder for lead contains between 30 and 40% tin, up to 2% antimony, and the balance lead. These solders are solid up to approximately 182" C (360" F) and completely liquid at approximately 238" C (460" F) providing a pasty or working range of approximately56" C (100" F). Solder containing 34.5% tin, 1.25% antimony, 0.11% arsenic, balance lead, is widely used in cable joining. A 50% tin-50% lead solder is widely used for joining lead sheet.

SURFACE PREPARATION

The areas that are to be joined should be thoroughly cleaned by wire brushing or shaving. Tallow or stearic acid flux should then be applied promptly to prevent reoxidation of the cleaned areas, A very thin flat film is advisable, so that it will not spread out beyond the area of the joint upon application of heat.

Excessive use of the cleaning tools should be avoided. Their overuse may cause fatigue failures due to chatter and thinning of the lead near the critical section of the joint. Gummed paper strips and plumber's soil are often useful to limit the flow of solder beyond the area of the joint and to help form and build a bead at the joint.

83


84/SOLDERING MANUAL

Fig. 1 4 . 1 ~ -Wiping solder is poured on the joint

. o COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

Lead and Lead Alloys/85

Pig. 14.18 -Wiping begins

i

0 COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

- - , , -

0784265 (3006277 2

861SOLDERING MANUAL

Fig. 1 4 . 1 ~ -Wiping near completion


HEATING METHODS

The low melting point of lead and its alloys limits the choice of heating methods. Soldering irons are usually used for soldering sheet lead joints. When joints are wiped, the heat for soldering is supplied by the molten solder poured over the parts until the base metal is wetted, and the bulk of the solder is in a pasty, workable condition.

FLUXES

The soldering of lead and its alloys can be accomplished without the use of the corrosive fluxes. Tallow and rosin fluxes are generally used.

JOINT TYPES

Lap Joints Lap joints are more satisfactory than butt joints

and should be made with a minimum lap of 10 mm (3/8 in.) for sheet lead up to and including 3 mm ( l / S in.) thick (3.5 kg [81b.]). The contacting areas ofthe two sheets that form the lap should be cleaned and fluxed with tallow. The cleaned and fluxed area of the bottom sheet should extend 3 mm (1/8 in.) beyond the leading edge of the lap. The edge and upper side of the top sheet, to a distance of approximately 10 mm (3/8 in.). should also be cleaned and fluxed. The sheets are then fitted together and dressed down with a wooden or rubber mallet to fit snugly. They are then tacked at intervals with solder.

The application ofadditional flux is often advisable. Flux may be applied by using rosin cored or Stearine cored wire solder. When bar solder is used, Stearine or powdered rosin may be applied to the joint.

Soldering is usually done with an iron and 50% tin-50% lead solder.

Lock Joints Lock joints provide considerably more

strength and are preferred whenever the joints are to be in tension. They are made in much the same manner as lap joints, using locks of 15 mm (= 1/2 in.) or more. The solder should flow in between


the two lower surfaces in contact in the lock (see Chapter 4 for illustrations of joints).

Butt Joints Butt joints are the least desirable type for join-

ing lead sheets. Their use should ,@ confined to those situations where it is impractical to use other joint designs.

The abutting edges of the lead sheets are beveled with a shave hook so that they make an angle of 45 deg or more with the vertical. The edges to be joined are placed firmly together and tacked at intervals of 100 to 150 mm (=4 to 6 in.). Gum- med paper strips pasted paralIel to the seam and 6 to 10 mm (i /4 to 3/8 in.) away aid in building up the solder and reflowing it in the finishing operation. Additional flux, as described in the lap joint section, is advisable.

Solder is fed into the joint and melted by the soldering iron as it is drawn along the seam. Sufficient solder should be applied to build up a slightly convex surface.

Pipe Joints Preparation of the joint is as important to suc-

cessful results as the actual soldering. The joint is made in a bell and spigot manner with the flared end made in the pipe into which the water or liquid will flow. The inlet or spigot end is beveled to fit snugly into the flared end.

The area.encompassing the entire wiped joint is lightly shaved clean as is the contacting area within the joint. A thin coat of tallow is then applied. The area beyond the joint on both sides is then coated with plumber's soil or paper to prevent the solder adhering at these points. The joint is assembled, the flare end is dressed down tightly (swaged with a wooden tool), and the entire assembly is braced so that it will not move during the subsequent soldering operation.

In horizontal pipe, the joint is then wiped by slowly pouring solder at the proper temperature (approximately 315" C [ =600" FI) on top of the joint while the operator manually directs and holds the solder. For this purpose he uses a tallow coated cloth and wipes or forms the joint while the solder is in its pasty stage. When completed, the joint should be chilled.

In vertical pipe, joints are prepared and wiped in much the same manner except that the solder is


88/SOLDERING MANUAL

applied around the pipe at the top of the joint and additional thin coating of flux is applied. Gum- the cloth held directly under the ladle at the bot- med paper or plumber's soil is applied to prevent tom of the joint. The ladling or splashing on of the adherence of solder at points beyond the joints. solder is continued around the joint. The joints are then wiped in a manner similar to

Branch joints in lead pipe are made by cuttinga that used for lead pipe. small oval shaped hole in the main line and draw- As a precaution against porosity of wiped ing up sdficient lead to form a collar or hub into joints .in cable sheathing, the use of a sealing which the beveled branch line is fitted sungly. solder melting at approximately 95" C (=200" F) Preparation and wiping are essentially the same is recommended. The sealing solder, in the form as previously described. of a thin stick, is applied aver the entire joint as

Cup joints are similar to bell and spigot joints soon as possible after the wiped solder has sol- except that the flared end is not dressed down, idified. The residual heat melts the sealing solder and a soldering iron is used rather than wiping. which is then smoothed out over the joint with the These joints can only be made in the vertical wiping cloth. One sealing solder contains 52.5% position although they can be used in any posi- bismuth, 32% íead, and 15.5% tin. tion. Preparation of the joint includes beveling of the inlet or spigot end, flaring the bell, cleaning and fluxing with tallow only those areas that are to become a part of the joint. Plumber's soil or paper should be applied beyond these points. The pipes are then fitted together and spot soldered. With a sharp pointed iron, solder is then flowed The soldering of lead alloys, with the possible

rest of the cup is filled with solder using a blunted leads can be performed in the same manner as iron. described for lead itself. Ornamental castings of

two per cent or higher antimonial lead alloy are Cable Joints also frequently soldered. These alloys have a

Joints in lead sheathed cable, because of the solidus temperature under 315" C ( 4 û O " F) and, increased bulk of the spliced conductors, are of as a result, the temperature factor is more critical. greater diameter than the cable itself and require Therefore, in soldering, it i s necessary to use the use of a lead sleeve encompassing the joint extreme care to avoid melting the base metal. area.

A lead sleeve of the proper diameter is first selected to contain the spliced cgnductors and SOLDERING LEAD TO OTHER have sufficient length to overhang the lead shea- METALS thing several inches on both sides of the joint. The inside of both ends of the sleeve are then scraped clean back approximately 25 mm (1 in,) All metals that can be precoated can be joined to and are immediately fluxed with tailow or stearic lead pipe or sheet by means of the wiping cloth, acid. The outside of the slewing, back approxi- torch or soldering iron. The precoating should be mately 50 to 75 mm (=2 to 3 in.) depending on confined to those areas of the other metal that are the diameter, is also scraped clean and fluxed and to become an integral part of the joint. The lead the sleeve placed around either end of the cable. should be prepared just as described for joining Splicing of the conductors is then completed. lead to lead.

The areas on the cable sheathing that are to become part of each joint are scraped clean and fluxed. The sleeve is then ceniraiiy located over POST SOLDERING TREATMENT the joint and both ends are dressed or drawn down with a wooden tool until they fit snugly against Ordinady, no post soldering treatment is re- thecleaned and fluxed areas of thesheathing. An quired.

SOLDERING OF LEAD ALLOYS

around until the joint is filled about haIf way. The exception of two per cent or higher antb"lial


. . -


soldering iron, are also used to join lead pipe to copper fittings for connecting the lead piping to piping made from other metals. Lead sheathed

Soldered lead pipe is used to convey water un- cables for telephone, telegraph, and electrical derground from the water main to theconsumer's power transmission also use solder extensively. property line and also serves a multitude of pur- Sheet lead for waterproofing, such as shower poses in the plumbing, drainage, and venting sys- pans and safe pans, also utilize soldering for tem. Joints, made either by wiping or with a makingjoints.


t b


AWSSH*CH*xLS ** H 078YZb5JOOb301 O _=_= -____ ~

CHAPTER 15

ALUMINUM AND ALUMINUM ALLOYS

INTRODUCTION

The soldering of aluminum differs from the soldering of copper, brass, steel, and most other common metals in several ways. Perhaps the most important difference is that aluminum forms a more tenacious and refractory oxide, which in most cases necessitates the use of active fluxes that are specifically designed for aluminum. Noncorrosive fluxes cannot be used. A second difference is that special techniques are required to produce flow into certain types of joints. A third important difference is that the corrosion resistance of soldered aluminrim joints is much more depqdent upon the composition of the solder than it is for similar joints in copper, brass, or steel.

Because of these differences, the soldering of aluminum is not as well understood, and it has not been as extensively used as soldering of other metais.

PROBLEMS IN SOLDERING ALUMINUM

The difference between the melting point of the aluminum alloys and the liquidus temperature of some solders can be as low as approximately 26OoC(470"F). This is substantially less than the 780" C (1400" i?) differential for soldered copper.

This in turn means that greater care must be taken in heating, especially in heating complicated assemblies. Since the coefficient of linear thermal expansion is greater for aluminum than for most other common materials, greater distortion can be expected in aluminum assemblies than in comparable assemblies of copper and steel. The coefficient of expansion of some aluminum alloys is found in Table 4. l

The oxide film that forms on aluminum and aluminum alloys is tenacious and chemically resistant; corrosive fluxes or special soldering techniques must be used to remove this oxide. Because most of the fluxes used on aluminum contain fluoride, the usual precautions should be taken (see Chapter 21 for safety in handling). To minimize corrosion, scnipulous flux residue removal is also mandatory for most applications.

The use of solders containing a high percentage of zinc is usually recommended. The tin-lead solders are not recommended because the resulting joints have poor corrosion resistance. Lead-bismuth solders provide greatly improved corrosion resistance over the tin-lead solders.

The corrosion resistance of soldered aluminum joints may depend upon the choice of solder, degree of flux residue removal, and the environment to which the joint is exposed. Soldered joints made with tin-lead or other tin-bearing, low melting temperature solders must be protected by a suitable protective coating in any but

91


92/SOLDERING MANUAL

dry indoor environment. Unprotected assemblies joined with zinc base solders, on the other hand; exhibit long service life even in marine exposure. In most cases corrosion is accelerated by the presence of electrolytes. It is important, therefore, that the residues of sait type fluxes be completely removed after soldering.

SELECTION OF ALUMINUM ALLOYS FOR SOLDERING

While aluminum and all the aluminum alloys can be soldered, alloying elements influence the solderability, as shown in Table 15. l . The commonly soldered aluminum alloys are 1060, 1100, 1145, 3003,5005,6061,7072, and 8112.

Aluminum alloys containing 0.5% or more magnesium suffer intergranular penetration by molten tin solders. Zinc will also penetrate the aluminum-magnesium alloys intergranularly, but the extent of penetration is usually not significant until the magnesium content of the base metal exceeds 0.79 . The intergranular penetration by molten solder of aluminum-magnesium alloys is aggravated if the part is prestressed by cold working, but this can be significantly reduced if the assembly is stress relieved by heating the part to 370" C (700" F) before soldering. If the solder being used is 958 zinc-5% aluminum, which has a melting temperature of 382" C (720" F), the part will be stress relieved before the molten solder will actually contact the surface of the aluminum. Therefore, a stress relief treatment will not be required in this case. The addition of 4% or more aluminum to a solder also tends to reduce the extent of intergranular penetration or general dissolution of all aluminurn alloys.

The addition of up to 1% magnesium to aluminum does not significantlyreduce the effectiveness of the flux in preparing the surface of the aluminum alloy for soldering. However, in general, the surface of alloys containing greafer than 1% magnesium cannot be satisfactorily soldered using chemical fluxes, and alloys containing greater than 1.59 magnesium are difficult to solder using reaction fluxes.

The addition of silicon to aluminum (4XXX series) also reduces the effectiveness of fluxes. Alloys containing 5 9 or more silicon are gener-

ally soldered using ultrasonic or mechanical abrasion techniques for oxide removal.

Aluminum-magnesium-silicon alloys (6061- 6063 series) are less susceptible to intergranular penetration than the binary aluminum- magnesium alloys and more solderable than the binary aluminum-silicon alloys.

The aluminum alloys that have copper (ZXXX series) andzinc (7XXX series) as the major alloying elements are generally complex, high strength, heat-treatable alloys containing appreciable quantities of other elements. During heat treatment films that hinder soldering form on these alloys, and chemical surface pretreatment is usually necessary to remove such films before soldering. Since most of these alloys are subject to intergranular penetration by solder, they are not generally soldered.

Aluminum castings are generally alloys containing substantial quantities of copper, silicon, magnesium, or zinc. As a group, they have poor solderability by virtue of their composition. In addition, castings are likely to exhibit surface conditions that are detrimental to soldering.

SOLDERS

Solders for aluminum can be grouped conveniently into low temperature, intermediate temperature,and high temperature solders. Low temperature solders for aluminum, which melt below approximately 260" C (500" F), are composed primarily of low melting temperature metais such as tin, lead, cadmium: and bismuth. They may also contain higher melting temperature metais such as zinc, aluminum, copper, nickel, and silver. intermediate temperature solders, which melt between 260" C (500" F) and 370" C (=700" F), contain appreciable amounts of both lower melting and higher melting temperature metals. High temperature solders, which melt between 380" C (=720° F) and 425" C ( 4 0 0 " F), have zinc as the major constituent, along with small amounts of high melting temperature metals,such as aluminum,copper, nickel, and silver. The properties of a number of typical solders for aluminum are discussed in Chapter 2. *See Chapter 21 on Safety


- - - - .

A W J S M * C H * I S ** 07&42h5 OOOb303 4 __I

Low temperature solders for aluminum are generally tin-zinc alloys in which tin is present in the larger amount. Lead-bismuth solders are also used to solder aluminum at low temperatures. One low temperature solder is the tin-zinc eutectic containing 91% tin and 9% zinc. Another solder contains 78.5%. lead, 18.5% bismuth and 3% silver. These alloys melt at about 205" C (=4ûO" F), wet aluminum readily, flow easily, and have high resistance to corrosion. Tin-lead solders, in general, forma highly anodic interface between the aluminum and solder and have poor corrosion resistance. Although the tin-lead solders are not recommended for aluminum, the addition of even afew percent zinc or cadmium to such solders improves both their soldering characteristics and their resistance to corrosion. The lead-bismuth solders exhibit the best corrosion resistance of the low temperature solders. in

Aluminum and Aluminum Alloys/93

general, assemblies made with low temperature solders have poorer corrosion resistance than assemblies made with high temperature solders and should not be used in corrosive environments unless some protective coating is applied to the solder joints.

Intermediate temperature solders are usually either tin-zinc or cadmium-zinc alloys containing from 30 to W%zinc. They may also contain other metais, such as lead, bismuth, silver, nickel, copper, and aluminum. Among the more common of these solders are the 70% tin-30% zinc, 70% zinc-30% tin, and 60% zinc-40% cadmium solders. Because of their higher zinc content, these intermediate temperature solders generally wet aluminum more readily, form larger fillets, and give stronger and more corrosion resistant joints than the low temperature solders.

.

Table 15.1 -Solderability of aluminum alloys

Typical Recommended alloy Solderability flux

1 xxx 1060 Good Chemical or reaction (Commercial 1100 Good Chemical

purity or or reaction higher)

2 x x x 2014 Fair' Reaction (Al-CU)

3xxx 3003 Good Chemical (AI-Mn) or reaction

4 x x x 4043 POOP None

5xxx3 5005 Good Chemical or reaction

(Al-Si)

(Ai-Mg or 5050,s 154 Fair' Reaction AI-Mg-Mn) 5456,5083 Poor' Reaction

6XXX 606 1 Good' Reaction (Al-Mg-Si)

7 x x x 3 7072 Good Reaction (Al-Zn) 7075 Poor Reaction

8XXX3 81 12 Good Reaction (Al-other)

Susceptible fo intergranular penetration by solder.

Solderability greatly affected by composiJion. * Solderable only with abrasion or ultrasonic techniques.


94/SOLDERING MANUAL

The high temperature solders contain 90 to 100% zinc, along with small amounts of such metals as silver, aluminum, copper, and nickel. These additions are made to lower the soldering temperature, to obtain a wider melting range, and to improve wetting of the aluminum. The high temperature solders are the strongest solders for aluminum. They also produce joints which have corrosion resistance properties markedly superior to those of low and intermediate temper- .ature solders. To assure the best possible corrosion resistance, the high temperature solders should be as free from lead, tin, cadmium, bismuth, and other low melting metals as is practicable. High purity zinc (99.99% at least) should be used in the preparation of these solders.

All solders for aluminum can be prepared in either cast or wrought forms. The wrought forms of low and intermediate temperature solders should not contain aluminum because it embnt- tles them and makes them difficult to extrude without cracking.

FLUXES

Fluxes for soldering aluminum may be divided into two general classes: the chemical and the reaction fluxes. Both types are corrosive.

The chemical fluxes are composed of a boron trifluoride-organic addition compound such as boron trifluoride-monoethanolamine, a flux vehicle such as methyl alcohol, a heavy metal fluoborate such as cadmium fluoborate, and a plasticizer such as stearic acid. They may or may not contain other modifiers such as zinc flouride, zinc chloride, and ammonia compounds. The chemical flux compositions originally proposed did not contain chlorides, but some subsequent commercial formulations have incorporated metallic chlorides to act as accelerators.

Chemical fluxes are most often used where the soldering temperatye (actual temperature measured at the joint) is less than 275" C ( 4 2 5 " F). However, in some applications the maximum temperature can be raised successfully to 325°C ( ~ 6 2 0 " F). At temperatures in excess of 275°C (-525" F), the chemical fluxes tend to decompose, and at temperatures in excess of 325°C (=620" F), the rate of decomposition is so rapid

that it is usually impractical to use this type of flux. For this reason the chemical fluxes are generally used with the low melting temperature solders. For best results, the magnesium content of the aluminum alloy being soldered should not exceed 1%, and the silicon content should not exceed 5%. In general, it is recommended that the flux residue be removed, especially if the assembly is used in electrical equipment.

The reaction fluxes usually contain zinc chloride, tin chloride, or both, in combination with other halides. The metal halides are the primary fluxing agents. Other chemical compounds, such as ammonium chloride and metal fluorides, are added to impro've fluidity, reduce the melting point, improve the wetting characteristics, and provide a flux cover that prevents reoxidation of the cleaned surface.

These fluxes penetrate the oxide film, allowing the flux to contact the underlying aluminum. At the reaction temperature of 315-382" C (600-720" F), the metal chloride is reduced by aluminum to form the metal (tin or zinc) and gaseous aluminum chloride. The rapid formation of aluminum chloride breaks up the oxide film, and the freshly deposited film of zinc or tin facilitates wetting by the solder. No significant fluxing occurs below the reaction temperature of the flux, and solder will not flow below this temperature even though it may be above its liquidus temperature. Fluxes containing tin chloride generally react at approximately 315-340" C (=600-640" F) and are used primarily with tin-zinc solders of similar melting characteristics. The zinc chloride base fluxes, which react at approximately 340- 380°C (2640-720" F), are used with pure zinc and other zinc base, high melting temperature solders. Fluxes containing tin chloride should not be used with the high melting temperature solders, since the presence of tin in the solderedjoint can seriously reduce i.ts corrosion resistance.

JOINT DESIGN

The joint design used in a soldered assembly determinesto someextent the strength, corrosion resistance, and ease of fabrication of the assembly. The designs used for soldered aluminum assemblies are basically similar to those used


Aluminum and Aluminum AlIoysI95

Some solders in rod form, called abrasion solders, have melting characteristics that enable them to perform as both the solder and the abrasion tool. The aluminum surfaces are heated by a torch or other method until they will melt the end of the solder stick. The stick breaks the oxide and allows the solder to flow beneath i t and loosen it. The oxide can then be brushed aside with the solder stick exposing the surface wet with solder. Additional solder may now be applied to surfaces wet in the manner described to form a strong, stable joint. The process cannot be applied to close-fitting joints where capillary flow is necessary. Ultrasonic soldering is another method of obtaining a solder coated aluminum surface.

with other metals. The most commonly used designs are lap, lock seam, and T type joints. Joint clearances will vary with the soldering method, base metal composition, solder composition, joint design, and flux composition. However, as a guide, clearances of from 0.15 to 0.40 mm (-0.005 to 0.015 in.) are maintained when a chemical flux is used and from 0.05 to 0.25 mm ( ~ 0 . 0 0 2 to 0.010 in.) when a reaction flux is used (for further information on joint design, see Chapter 4).

SURFACE PREPARATION

A prerequisite for soldering aluminum is careful surface preparation. Surface preparation treatments designed to remove lubricant, dirt, and oxide from the surface of aluminum prior to soldering are described in Chapter 5. The use of strong caustic cleaners should be avoided because they attack aluminum rapidly.

When fluxes formulated specifically for soldering aluminum are used, no further surface preparation is necessary. There are a number of surface preparation techniques, however, that are often used to facilitate soldering with ordinary fluxes. Other techniques make possible fluxless soldering of aluminum. These surface preparation methods can be divided conveniently into three groups: electroplating, solder coating, and cladding.

Electroplating aluminum with a metal, such as copper or nickel, produces a surface that can be soldered in the same manner as copper or nickel. The deposition of copper is generally preceded by a zincate or stannate treatment in which aluminum oxide is removed from the surface and zinc or tin is deposited by galvanic displacement.

Solder coatings can be applied to aluminum by mechanically abrading the surfaces in the presence of molten solder. The solder wets and bonds with the aluminum as the oxide is removed. Among the best abrasion tools are fiber glass brushes, fine-strand stainless steel brushes, and stainless steel wool. Ordinary carbon steel brushes should be avoided because strands that are lost from the brush into the solder will accelerate corrosion.

FLUXLESC SOLDERING

There are a number of methods by which aluminum can be fluxlessly soldered to itself, to copper, or to steel. These methods are primarily used on tubular components. The methods may be broken down into either coated or bare types.

In the coated methods, the parts may be prepared by electroplating, abrasion, or in an ultrasonic solder pot. The components are designed to include an interference (0.25 to 0.65 mm [ =0.010 to 0.025 in.] on the diameter) prior to coating. After coating the parts are preheated to solder melting temperature and pressed or twisted slightly together. The joint may be either a straight or tapered design, but tapered is preferred when only one component is coated.

Ultrasonically coating the components is better suited for production applications than is abrasion soldering with a solder stick. In this method the degreased parts are heated, crazing the oxide and permitting the agitation of the solder pot to remove the oxide and deposit a coating of solder on the metal surface. One or both components may be coated; however, if only one member is coated, then the greater interference 0.65 mm (=0.025 in.) is suggested.

For multiple joints such as air conditioning condenser or evaporator coils, two ultrasonic processes can be employed, one requiring pretinning of the return bends, the other not requiring


AWS SM*CH*LS * * 0784265 __- O006306 T __ -- -~-- -~~ ~

96/SCLDERING MANUAL

pretinning. In the first case, a tapered joint is HEATING METHODS suggested to facilitate alignment and insertion of the return bends. The return bends only are me heating methods described in Chapter 6 are coated, inserted into the coil, heated, then pressed applicable to aluminum assemblies. At solder- with a pressing platen into the joint at the proper ing temperature, aluminum is much closer to its temperature. The units being free of any flux melting point than other commonly soldered contaminant residuais are then ready for testing. met&. Greater c m must be taken, therefore, In the second case, the immersion approach, nib- to provide uniform, well controlled heating. bed return bends are forced into the coil bells, the Long, unsupported spans should be avoided to unit is preheated in the inverted position, and prevent excessive sag, torch or iron so&.hg, immersed in the Ultrasonic solderpot. The retuni the heat source should be applied away fro'm the bends are nibbed to permit passage of heated air joint area to avoid overheating the flux. Because out of the joint area so solder can fill the joint. d u h u m is soluble in most solders, especially The unit is then withdrawn and ready for testing. those that c o n t h large quantities of zinc and

The bare fluxless soidering methods also tin, excessive dloyhg may occur unless heat- Utilize UltraSOniC soldering equipment. h Single- ing is discontinued as soon % the h% been joint applications,the one member is belled with soldered. approximately 1.5 mm (~0.060 in.) diameter clearance and a solder ring placed at the joint. TYPICAL APPLICATIONS The joint area i s then heated to solder melting temperafure and subjected to uitrasonics via a ~ ~ b e - f i ~ consmction, light bulb bases, and tel- small hand gun. The bottom ofthe joint must be lular products are some of the assemblies that relatively tight fitting lest the solder flow through have been soldered. In addition, motor and trans- the joint and restrict the tube passageway. For former windings can be added to the list of appli- dissimilar joints the steel Or copper n ~ m b e r cations. Heat exchanger coils for air conditioners should be Precòated as Previously described represent a large application of the aluminum under coated methods. soldering process. The soldering of copper tubing

The solder used for fluxless soldering is gener- to aluminum ceiling panels is another large-scale ally 95 zinc-5 aluminum. This solder has excel- application. lent strength and corrosion resistance. Replenish- With improvements in the design and man- ing the pot is frequently done with commercially ufacture of ultrasonic soldering pots, it is now pure zinc since some aluminum will be dissolved possible to perform soldering operations with the from the component parts during the coating or high temperature (95% zinc-5% aluminum) sol- soldering operation. ders at 425"C(80O0 F). This method is particu-

lady applicable to the soldering of return bends to heat exchanger coils.


CHAPTER 16

MAGNESIUM AND MAGNESIUM ALLOYS

1NTRODUCTION

Magnesium tends to form a highly refractory oxide film when heated in air. This oxide film must be removed or disrupted to allow the solder to bond to the magnesium. Because no satisfactory flux has as yet been developed to remove this oxide film, bare magnesium surfaces are soldered by the friction (mechanical abrasion) or ultrasonic methods (see Chapter 6 for a discussion of ultrasonic soldering). All magnesium alloys can be soldered in this manner, but such soldering is usually confined to the filling or repair of surface imperfections in magnesium printing plates and in noncritical areas of magnesium sheets and castings. Soldering is not recommended if the soldered area is required to withstand significant stress because the soldered joint is of low strength and low ductility.

The difficulties associated with soldering bare magnesium surfaces are overcome by application of a coating of an easily solderable metal such as copper, tin, zinc, or silver.

SOLDERING TECHNIQUES

Since only the friction or ultrasonic soldering methds can be used on bare magnesium, careful precleaning of the surface, followed by precoating with a solder composition having good wet-

ting characteristics toward magnesium is a prime necessity. Precoating by the friction method is accomplished by rubbing the surface with the solder stick, soldering iron, or some other tool to abrade and break up the oxide film under the molten solder. Pure tin and tin-zinc solders containing 70 to 90% tin possess the best wetting characteristics on magnesium. Once the surface is precoated, any other solder composition can be used to complete the job.

SOLDER COMPOSITION

Solders based on tin, zinc, and cadmium: as listed in Table 16.1, are most generally used on magnesium. Solders that contain lead, suchas the standard 50% tin-50% lead solder, can be used but they cause severe galvanic attack in the presence of moisture. The tin-zinc solders generally have lower melting points and better wetting Characteristics than the tin-zinc-cadmium solders but form less ductile joints. The high-cadmium solders, especially the 60% cadmium-30% zinc- 10% tin solder, form the strongest and most ductile joints.

The most widely used soldering practice for bare magnesium consists of precoating the joint

*See Chapter 21 on Safety

91

i> COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

98/SOLDERING MANUAL

Table 16.1-Solders for magnesium

Temperafure Composition (5%) Solidus Liquidus

"C "F "C O F

Use

60Cd-30Zn-lOSn 157 90Cd- 1OZn 265 72Sn-28Cd 177 91Sn-9Zn 199 60Sn-4ûZn 199 70Sn-30Zn 199 50Sn-50Pb I83 80Sn-20Zn 199 4ûSn-33Cd-27Zn -

315 509 350 390 390 390 361 390 -

288 550 299 570 243 470 199 390 341 645 311 592 211 421 270 518 - -

Low temperature-below 150" C High temperature-above 150" C Low temperature-below 150" C High temperature-above 150" C High temperature-above 150" C Precoating solder Filler solder on precoated surface Precoating solder Filler solder

area with 70% fin-309 zinc solder and following with the ó09 cadmium-30% zinc-10% tin solder to maximize strength. In the repair of photoen- graving plates, the standard 5 0 5 tin-50% lead solder instead of the cadmium base solder is applied over the precoated surface even though susceptibility to corrosion is greater. For this application, however, the workability of the solder outweighs this consideration, especially since the normal use and storage of engraved plates is tinder low or cpntrolled humidity conditions nof conducive to corrosion.

SURFACE PREPARATION

the tip contacting the underside of the area to be soldered. A gas flame or torch can also be used to gently heat the surface from the top to bottom. An electric hot plate used either with or without a soldering iron is ais0 a very effective heating method, and heat is more easily maintained.*

FLUXES

Flux is not used in soldering bare magnesium surfaces because no suitable flux has as yet been developed. None of the fluxes described in Chap- ter 3 is applicable.

Surfaces to be soldered should be mechanically cleaned to a bright metallic lustre immediately before soidering. This may be accomplished by The joints used in the fluxless soldering of bare mechanically abrading with a stiff wire bmsh, magnesium are limited to the fillet and defect stainless steel wool, file, aluminum oxide abra- filling types due to the absence of capillary flow. sive cloth, or with a routing tool. Lap joints are used only to a limited extent. Joints

on plated magnesium can be the same as normally used if the plated metal were the base

TYPES

HEATING METHODS metal.

Conventional heating methods can be used satis- POST SOLDERING TREATMENT factorily on magnesium. However, because of its high heat conductivify, irons of adequate heat No special post soldering treatments are required output - a 350 watt iron for thicknesses up to for magnesium. However, unprotected soldered nominal 1.5 mm (O.O@ in.) and a 550 watt iron joints should be avoided on bare magnesium be- for heavier thicknesses - are required. The heat- cause the marked difference in solution pofential ing may be accomplished with the hot tip directly in contact with the surface to be soldered or with *See Chapter 21 on Safety, Hazards from Fumes


Magnesium and Magnesium AlloysI99

between the magnesium and the solder can lead use on magnesium electronic parts because it to severe galvanic attack in the presence of an provides excellent protective value and ease in electrolyte. Therefore, it is common practice to. soldering. Soldering of eIectroplated magnesium apply a suitable protective coating to soldered is then carricd out the same as if the entire part magnesium assemblies to prolong their life and weremade of the electroplated metal. serviceability.


Soldering is used primarily for the repair of magnesium printing plates and for filling surface defects in noncritical areas of wrought and cast magnesium products. Significant amounts of magnesium are also electroplated with copper or tin for easier soldering and hermetically sealing electronic equipment cans and covers.

SOLDERING PLATED MAGNESIUM

Electroplated coatings of copper, tin, or silver applied to magnesium offer an excellent soldering base. Fused tincoatings obtained by immersing thin tin electrodeposits (O. 1-0.15 mm [ =O.Oo3-0.005 in.]) in a hot oil bath also offer an excellent solder base. This coating is in common


AWS S M * C H * 1 7 ** 0784265 0006310 L ;-,

CHAPTER 17

TIN AND TIN ALLOYS

Tin is a metal with low strength properties and is usually alloyed with other metals to provide materiais of adequate structurai strength. Wrought tin materials which are soldered include sheet for lining tanks, foil, and pipe for convey- ing pharmaceuticals, beer, and carbonated bever- ages. Tin alloys used in making modern pewter, condensers, and some organ pipes are also soldered.

PROBLEMS IN SOLDERING TIN

When tin or tin alloys are soldered, careful control of the heating method is necessary to avoid melting areas which are not at the joint. Only solders having a liquidus temperature below 232OC(450"F), the melting point of tin, are recommended.

SOLDERS

The 63% tin-37% lead eutectic solder or the 60% tin-40% lead solder have been used satisfactorily on tin and pewter. These solders melt at about 50" C (90" F) below the melting point of tin, and the color match with tin is good. Fusible alloys (see Chapter 2) with liquidus temperatures below

183" C (362OF) are also used as solders in joining tin and tin alloys, although other considerations may limit their use.

SURFACE PREPARATION

Tin and tin alloys seldom need any surface preparation other than degreasing treatments. How- ever, light abrasion of the surfaces to be joined is sometimes helpful in providing fresh surfaces for soldering.

HEATING METHODS

Since tinand tin alloys have a low melting point, the heat source used during the joining process should be weil controlled. A torch with a small pointed flame will provide a localized source of heat which should be applied only a short time. In adjusting gas heated torches, the tip and gas mixture should be adjusted so that the flame does not deposit unburned carbon (soot) on the surfaces to be soIdered, since this will prevent the flow of solder to the joint interface.

A mouth-held blowpipe is often helpful for directing the gas flame to joint surfaces. Electric soldering irons are used as heat sources for sol-

101


IOZ/SOLDERING MANUAL

Fig. 17.1-Torch soldering pewter beer mug handle

denng tin, but care must be exercised to avoid fluxes may also be used. Usually no flux is re- overheating or melting the metal adjacent to the quired when the 509 tin-509 indium fusible joint surfaces, alloy is used on clean tin surfaces.

FLUXES JOINT TYPES

Tin and tin alloys have a thin nafural oxide film which may be removed with plain rosin or rosin base fluxes. Stearine or mildly activated rosin

The lap joìnf with a minimum lap of 10 mm (3/8 in.) is the preferred type of joint for soldering sheet tin withthicknesses up to and including


Tin and Tin Alloys/ 103

ders of the same composition as the pewterware being joined are used, but there is considerable risk of melting the base metal if proper heating is not maintained. Often a dam of molding clay or solder resist is necessary to prevent the spread of the solder to other parts of the assembly.

Organ pipes are made by soldering suitably shaped pieces of cast tin alloy sheet (see Fig. 17.2). The flat rectangular pieces are formed to a tubular shape on a wooden mandrel and a V-shaped seam is made to form the joint interface. Solder is run continuously into the seamat a uniform rate of about 25 mm/s (1 i d s ) . The heat source, usually a soldering iron, should be just hot enough to melt the solder filler metal. Solidification of the solder should occur within approximately6 mm(114 in*) from thesoldering iron tiP. R e j o i n t usually requires two soldering passes: The first pass places the solder and the second pass smooths and completes the seam.

3 mm (1/8 in.). An interlocking type of joint affords greater strength and is used in lighter gage sheet. Butt joints are used to join abutting edges of beveled sheet or wherethereare broad surfaces (Le., attachmentof precast handles, feet, hinges, etc. on pewterwares).

Tin pipes are joined using bell and spigot joints. Steel and brass pipes, lined with tin, are best joined using pipe fittings, which are soldered with 50% t in -509 lead solder around fhe periphery of their flanges to provide leak-tight joints.

$OLDEG(INQ TREATMENTS

Rosin base flux residues may be removed with suitable solvents. Additional details are found in Chapter 7.

ACKNOWLEDGEMENT TYPICAL APPLICATIONS Figures 1% 1 and 1%2 arecourtesy of Tin Research Institute,ínc. --

Sheet tin, when used to line podable or high punty water storage tanks, is formed into interlocking joints or butt joints with beveled edges. The joints are filled with pure tin, paying special care to apply the heat source sparingly. A brushing motion is often helpful in the distribution of the heat when a gas fired torch is used.

In the manufacture of capacitors which have frequencies over 2000 Hz, two strips of tin foil are wound with a paper or mica dielectric en- closed within the pack. The use of tin foil makes possible the soldering of connections to terminais and the soldering together of the foil packs. Tin foil and noncorrosive rosin base fluxes are used because the use of corrosive fluxes might cause the impairment of the insulating properties of the impregnated paper dielectric and because tin foil can be easily soldered with the eutectic tin-lead solder,

Attachments such as feet, hinges, or ornamen- tals are joined to cast or spun pewterwares by use of noncorrosive rosin base fluxes and 60% fin- 40% lead solder (see Fig. 17. i). Sometimes sol-

Fig, 1'7.2-Soldering together a mitered joint in an organ pipe made of specially shaped cast tin sheet


CHAPTER 18

CAST IRONS

INTRODUCTION

In general, cast irons are difficult to solder but with proper surface treament gray, malleable, and nodular cast iron may besoldered. White cast iron is rarely soldered. Normal soldering temperatures do not cause any structural changes or transformations.

PROBLEMS IN SOLDERING CAST IRONS

Graphitic carbon present in cast iron cannot be wetted by molten solder and may cause inadequate bonds. The problem is most pro- nounced with gray cast iron.

SURFACE PREPARATION

methods. One proprietary electrochemical surface cleaning method produces a surface essentially free of carbon, silicon, sand, and oxides. The process employs a catalyzed molten salt bath operating at 455" to 510" C(=850" to 950" F). Direct current is passed through the bath using the work as one electrode and the steel tank as the other. The direction of current flow is occasionally reversed to producereducing, oxidizing, and again, reducing conditions. A water rinse completes the surface preparation.

Other methods of cleaning include searing with an oxidizing flame, grit blasting, and chemical cleaning (see Chapter 5).

Small areas of cast iron may be coated with solder using steel wool dipped into a dry mixture of powdered solder and flux. Preheating the casting and rubbing with the solder-flux impregnated steel wool usually is sufficient to clean the surface by abrasion and allow the solder to wet the surface.

Surfaces to be soldered should be free of oil, dirt, and other extraneous matter. The as-cast surface is difficult to solder without proper preparation. i t HEATING METHODS is usually desirable to machine or file the surface of a casting to secure proper fitting and remove Cast iron can be soldered by any of the standard sand inclusions that interfere with wetting. techniques. Care should be exercised in heating

When the wetting of cast iron becomes a prob- so that localized overheating will not cause the lem, it is necessary to resort to special cleaning casting to crack.

I05


IM/SOLDERlNG MANUAL

FLUXES TYPICAL APPLICATIONS

Corrosive fluxes similar to those used for solder- The majority of the soldering done on cast iron is ing steel are used. in repairing of broken or worn castings. Surface

cracks and depressions caused by inclusions or other metal-mold reactions can be filled with

POST SOLDERING TREATMENT solder if the defects are superficial and the application is not critical.

Due to the poor heat conductivity of cast iron, it is necessary to cool the soldered joint uniformly to prevent tearing of the solder.


CHAPTER 19

PRECIOUS METAL COATINGS AND

PROBLEMS IN SOLDERING PRECIOUS METALS SOLDERS

Two problems are encountered when soldering to precious metal coatings. The fist is that some precious metais dissolve rapidly in molten tin-

Solders that are used for solderíng to precious metalcoatings with their applications are given in Table 19.1,

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108/SOLDERING MANUAL

Ifible b.1-Solders for precious metal coatings

Nominal solder composition (%)

Sn Pb Ag In Zn Bi Coatingsused

Temperature OC

6 2 3 6 2 - - - Silver coatings 53 29 - 17 0.5 - Goldcoatings 60 40 - - - - Platinum,

palladium, rhodium coatings only.

- 95 - 5 Goldcoatings - -

heating after the application of the paste to a surface. Normal cleanliness of the coating surface should be maintained.

HEATING METHOD

Heat for soldering is obtained by all of the methods of Chapter 6. Fig. 19.l-Dissolu!ion rates at various temper-

atures for a number of metais in úû%tin-40% - lead solder


FLUXES

Rosin type fluxes are used for these applications where cleanliness and freedom from corrosive and conductive residues is a necessity.

JOINT TYPES

Removal of rosin flux residues is accomplished by washing with solvents such as alcohol, chlori- nated hydrocarbons, etc.

REFERENCES

1. Bader, W.G. 1969. Dissolution of Au, Ag, Pd, Pt, Cu and Ni in a molten tin-lead soldei.

cember. pp. 551-s to 557-s.

The joints used are usually simp1e lap and butt Welding jourml research supplement, De- joints.

2. Braun, J. D., trans. 1964. A.S.M. quarterly 57,568.

SURFACE PREPARATION 3. Thwaites, C. J. 1973. Some aspects of soldering gold surfaces. Electroplating & metal

Precious metal coatings are applied by plating, finishing, AudSept. evaporation, or by the use of special pastes in 4. Tin Research Institute. Soft soldering gold which the volatile binder may be removed by coated surj¿aces. Publication TRI-431.


AWS S M * C H * 2 0 ** 078426C 0006327 i a

CHAPTER 20

PRINTED CIRCUITS

INTRODUCTION

Printed circuitry is comprised of printed wiring boards on which separately fabricated components are attached. Component side and solder side of three typical printed circuit assemblies are shown in Fig. 20.1. Printed wiring provides a conductive pattern, usually of copper 0.036 mm (0.0014 in.) or greater in thickness on one or both sides of an insulating substrate. The conductive pattern can be formed by chemical etching, electroplating, or electroless deposition.

TYPES OF PRINTED WIRING

There are two types of printed wiring boards: rigid and flexible. Rigid boards are manufactured from the following materials:

1. Paper impregnated with phenolic resin 2. Paper impregnafed with epoxy resin 3. Fiber glass with epoxy resin 4. Epoxy coated steel. Flexible boards are manufactured from the fol-

lowing materials: 1. Ethylene glycol and terephthalic acid 2. Polyimide. The three forms of rigid boards are single side,

double side, and multilayer. Simple products such as radios, switch controls, and power supplies use a single-sided circuit pattern; the

electrical path is on one side and the components are mounted on the other side. More complex circuits, such as computers, utilize double-sided circuit patterns. Additional plating or assembly steps are required to allow the connection of the circuits through the insulating substrate. These steps may consist of plating the holes (plated through-holes), using eyelets, staking of pins, or inserting bus wire at the time the board is assembled with components. The extremely complex circuits, such as those used for memory applications, employ multiple layer boards. These boards utilize the methods of circuit connection as described above, but are manufactured with both single- and double-sided boards laminated together into a single board. Assembling of the printed circuit follows a common procedure. The components are mounted on one side and the leads are passed through the insulating material to the circuit pattern on the other side of the board where they are soldered by a hand-held soldering iron or an automatic soldering machine.

Flexible circuits have their circuit patterns on or imbedded in the film. The components are carefully positioned so that flexibility is not affected and the leads pass through the film where they are soldered to the exposed areas, or pads, of thecircuit patterns. Flexible circuits are designed to meet special requirements such as trimline telephones and connector cables.

I09


i IOISOLDERING MANUAL

Component side Soldered side

Fig. 20.1-Three typical printed circuit assemblies

PROBLEMS IN SOLDERING PRINTED WIRING BOARDS

The most common problems and their corresponding causes in soldering printed wiring boards are as follows:

1. Icicling i s an exfessive amount of solder that forms a conical shapeat freezing and ends in a sharp point. Causes of icicling are poor soldera-

bility, empty component holes, slow speed of the conveyor, low solder temperature, and low sol- deringairon tip temperature.

2. Webbing is solder that adheres to the insu- lated surfaces between the metalliclands. Causes of webbing are noncompatible protective coating, poor curing of the laminate material, high nonmetallics, and contaminants in the solder bath.


3. Pinholes and blowholes are holes in the pad or land solder formed from gases or oils entrapped as the solder freezes, Causes are organic contamination, moisture, and plating residues.

4. Oil entrapment occurs when the soldering oil used in automatic soldering machines is locked in the solder fillet as the solder freezes. Causes are slow conveyor speeds that extend soldering time and low solder temperature.

5. Bridging is a short circuit which occurs when two or more land or pad areas are connected by excessive solder. Poor design, poor alignment of components, excessive dross, high nonmetallics, and contaminants in the solder may cause bridging.

.

SOLDERS

Solders used in printed circuit soldering are chosen for their melting and wetting characteristics. Due to the speed, intricacy of pattern design, and nature of the material used in printed circuits, high tin solders are used. The eutectic 63% tin- 37% lead or near eutectic 60% tin-40% lead solders are most commonly used in military and industrial applications. Soldering iron soldering requires a high-tin alloy of 50-639 tin with a medium diameter (1.0-0.8 mm, 0.040-0.032 in.). The flux percentage is usually 2.5%-3.5% by weight.

FLUXES

The principal fluxes used in printed wiring boards are rosin, activated rosin, and organic. Rosin fluxes which consist of water white rosin and a solvent are extremely mild and are seldom used in automatic soldering. Rosins modified with a chemical additive to make them mildly active or fully active rosins are most often used in automatic and soldering iron soldering. Additional information on these fluxes may be found in Chap- ter 3. Activated rosin fluxes are most commonly used and are considered the safest due to the nature of rosin. This characteristic permits soldering of open components such as trimmers,

’ Printed Circuits1 I i 1

tuners, and variableresistors; it permits soldering when complete cleaning after soldering is not practical and when long-lifereliability is desired. Organic fluxes are used when the printed circuit assembly is designed with sealed componenfs and stand-Offs and the total assembly can be thoroughly washed in water. Fluxes may be applied by wave, spray, or foam. Refer to Chapter 6.

JOINT DESIGN

Joint and circuit design are critical factors. Com- ponent placement and hole size shbuldbe as close in tolerance as mechanically and electrically possible. The pattern should be designed to run in the same direction that it travels over the solder wave machine. Refer fo Chapter 4.

SURFACE PREPARATION

Solderability is the most important factor to maintain in the assembly and soldering of printed circuitry. Items of importance are the land areas and pads, the component leads, and the operators’ tools, hands, and work habits. If a solder resist is used, care must be taken to insure its complete drying and setting.

Careful attention to printed wiring boards and component leads prior to and during assembly will result in a higher percentage of acceptable soldered connections and a much lower rejection rate. The circuit patterns should be chemically cleaned. Mechanical and abrasive cleaners may leave unwanted foreign particles or residues which cannot be removed and will affect solderability. It is imperative to maintain an oxide-free surface by protecting the freshly cleaned copper. Rosin base organic coatings are used for short periods of storage. To ensure the solderability for extended periods, hot solder coating or fused electroplate provides the best surface. Due to the properties of laminate materials, they must be kept dry. If the moisture is not removed from the laminate, gas evolution may occur, causing blowholes and pinholes during soldering.


I IZ/SOLDERING MANUAL

METHODS OF SOLDERING PRINTED WIRING BOARDS

Hand-held soldering irons and soldering machines are both used in the soldering of printed wiring boards. The hand-held soldering iron yields the best results if a small quantity of printed circuits is being manufactured and if iabor costs are low.

REPAIR, REWORK, AND TOUCH-UP

There is little that can be done to repair printed circuit boards. Minor circuit design correction can be made with copper wire. Land or pad areas that have lifted from the laminate cannot be properly repaired. For more details on printed circuit board repairs, refer to IPC Manual 'IOA.

POST SOLDER CLEANING

The degree of cleanliness required of a printed wiring board must be determined by the end use of the board. Once this is determined, the method and cleaner can be established. In general, rosin and activated rosin fluxes, if they must be removed, are cleaned by a chemical solvent system. Proprietary solvents throughouf the industry have varying degrees of solvent strength. Testing of the materials to be cleaned is of prime importance to provide solvent component compatibility and the proper degree of cíeanliness of the printed circuit assembly. Organic and inorganic flux residues must beremoved. The usual method of cleaning is to use a neutralizer, then a detergent wash, followed by a water rinse, ending in either an alcohol dip or a circulating hot air dryer.


CHAPTER 21

SAFETY AND HEALTH PROTECTION

INTRODUCTION Soldering is a safe operation when proper practices and procedures are followed. It is essential that soldering operators be informed of potential hazards and instructed in how to guard against them. It is recommended that each operation be studied carefully, preferably by a competent safety or industrial health engineer, and necessary precautions taken for the particular job. Where applicable, reference should be made to the requirements given in the Occupational Safety and Health Standards (OSHA), part 1910.

The possible sources of injury are heat, fumes, chemicals, and electrical hazards. Efficient venti- lafion of the soldering area, protection of the operators from bums, and training in the handling.of materials, fluxes,and chemicals will be instrumental in making the soldering operation safe. One hazard which cannot be covered by any text, that of personal carelessness, can be com- batted only by constant care and vigilance.

HAZARDS FROM HEAT AND HEAT SOURCES Since soldering requires heat, the usual precan- tions should be taken for the handling of hot objects to prevent the occurrence of burns to personnel. American National Sfandard (ANSI) 249.1, Safety in Welding and Cutting, published by the American Welding Society, discusses in detail elements of safety which are common to

I13

welding, brazing, and soldering. Proper clothing and face protection should be provided.

Dip or immersion solder pots may contain solder in amounts varying from a few ounces to several tons. At the operating temperature, water introduced below the surface of the solder becomes superheated steam, and its very explosive expansion will cause the molten solder to be expelled in all directions. This molten solder will not only cause burns to operators but may ignite combustible material. Solder pots, if not properly maintained, can develop leaks or cracks which permit the molten solder to flow onto the floor. Solder pots should be covered during each initiai heating operation.

Parts on which fluxes dissolved in water have been used should be immersed in a solder pot cautiously to provide an opportunity for the excess water to evaporate above the surface of the solder. If the parts p e large, it may be more desirable to dry the excess water out of the flux before introducing the parts into the pot. The configuration of parts should be such that water willnot be trapped in pocketswhere steam can be formed. When fluxes dissolved in alcohol, acetone, or toluol are used, care should be taken to avoid ignition.

A new pot should be thoroughly dried before molten solder is introduced. When new solder is added to a heated pot, it should be placed on the edge of the pot and allowed to preheat sufficiently to drive off any moisture which may be

I

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I 14/SOLDERING MANUAL

present. Solder which has been stored out of doors in winter will have considerable condensation present when brought into the workroom. After the solder is dried, it should be slipped into the pot slowly to avoid splashing. when electrical immersion heaters are used, they should be of the proper voltage rating, and the pot should be thoroughly grounded. Thermostatic control should be employed on solder pots to avoid overheating.

In buildings equipped with automatic water sprinklers, solder pots should be suitably hooded so that the water will not be sprayed onto the pot in case a sprinkler opens.

Electrically heated soldering irons should have their exposed metal parts grounded. They should be placed in a fireproof holder and never allowed to lie on a floor, chair, or table where they can come in contact with combustible material or be touched accidentally by any person. They should not be left unattended without being discon- nected. Excess solder should be wiped off the tip rather than flipped off the molten solder can cause bums or may even cause a fire.

GASES AND GAS-HANDLING EQUIPMENT

The handling and use of gases and gas equipment is covered thoroughly in ANSI 249.1 and requirements are specified by OSHA.

Equipment should always be kept in good operating condition. Hose clamps should be used, and the hose should never be allowed to become excessively worn. Worn hose should either be replaced entirely or the worn portion should be cut off and the connections replaced in the sound portion of the hose. The hose should be kept away from the flame ahd out of contact with heated metal and away from sources of physical damage. The use of pliers or pipe wrenches on torch parts or on regulators should be discour- aged.

A torch should never be used to solder on a tank or container which has contained flammable material until the tank has been emptied and then thoroughly cleaned using the cleaning procedure recommended by the American Welding Society in AWS A6.0, Safe Practices for Welding and

Cutting Containers That Have Held Combusti- bles. AI1 tanks and similar containers should be vented. Entering tanks or confined spaces requires extreme precautions.

ELECTRICAL HEATING

When using resistance heating with carbon blocks for soldering, the voltage should not exceed 24 volts. It should be obtained from the secondary of a dual-winding transformer with the secondary isolated electrically from the primary winding.

When soldering in resistance heated furnaces, care should be taken that neither the operator nor the parts can come in contact with the current- carrying elements.

In induction soldering, one should not contact the coil or the conductors or come close enough to them to draw an arc.

All electrical heating wiring should be in accordance with the National Electrical Code and local requirements.

HAZARDS FROM FUMES

Fumes often arise from the foreign materials on the surface of the parts to be soldered. Examples are lubricants or drawing compounds which have not been completely removed prior to soldering. During soldering of these parts, these residues evolve clouds of smoke which may be irritating, annoying, or toxic.

Ali soldering fluxes give off fumes or smoke while soldering heat is applied. Some fluxes, such as the rosin, petrolatum, and reaction type fluxes, give off considerable smoke depending on the soldering temperature and the duration of heating. The American Conference of Gov- emmental Industrial Hygienists has established a threshhold limit value for pyrolysis products of rosin core solder of 0.1 mg/m3 aliphatic al- dehydes, measured as formaldehyde. This value has not been incorporated by OSHA.

Other fluxes give off fumes that are h’armful if breathed in any but small quantities. Prolonged inhalation’of halides and some of the newer organic fluxes should be avoided. The aniline type fluxes and some of the amines also evolve fumes


which are harmful and can cause dermatitis. Fluorine in a flux may create still another undesirable health condition.

Cadmium, lead, zinc, and other metals as well as their oxides are toxic when present in the atmosphere as fumes or dusts. Since they may be present in the base metal as coatings or as constituents of solders, the solderer should take care to minimize the evolution of fumes by avoiding overheating the solder or base metal. Threshold limit values have been promulgated by OSHA for cadmium, lead, zinc oxide, zinc chloride, and other toxic fumes, gases, and dusts.

In ali soldering operations, the potential hazards from smoke and fumes should be evaluated. Adequate ventilation is an absolufe necessity to avoid fume and smoke hazards.

HAZARDS FROM CHEMICALS

Acids, alkalis, and other chemicals are used daily in all soldering operations, and precautions

Safety and Health Precautions/ I i 5

should be taken in their handling and use to avoid getting them on the skin and eyes. These chemi- cais, which are commonly used both in fluxes and cleaners, can produce bums, irritation, and dermatitis if allowed to come in contact with eyes and skin. Prompt washing of the exposed parts will reduce the effects of the acids and alkalis.

Several chemicals deserve special attention. Zinc chloride may produce severe bums and dermatitis if allowed toremain on the skin for any length of time. Carbon tetrachloride had long been used as a cleaner and degreaser, but it has been found to be one of the most dangerous materials in common use. The safest rule is not to use this material. Parts which have been degreased with other organic solvents should be completely dry before soldering, as their decomposition products may be toxic.

Solders, fluxes, and cleaners contain materials which should not be ingested. Operators should be cautioned to wash their hands thoroughly before eafing after handling solders or fluxes.


CHAPTER 22

THE SOLDERING OF PIPE AND TUBE

INTRODUCTION

Soldered tubular joints are widely used for plumbing, heating and cooling applications in both domestic and commercial service, and in industrial applications for services such as compressed air, hot and cold water, and some processes.

The most common use of soldered joints is in copper tube for plumbing, heating, and cooling services. Aluminum, steel, and stainless steel tubular members are also joined by soldering. Very few other materials are joined commercially by soldering. The basic rules of cutting, sizing, fluxing, heating, and cooling are the same for ali the soldered joints, the only variation in the process being a choice of flux and solder.

CUTTING AND SIZING Pipe or tubing must be cut square to seat evenly on the shoulder at the bottom of the fitting socket, and all uneven or burred surfaces formed by the cutting operation should be removed. Hack saws or abrasive cut-off discs are suitable for cutting lengths of pipe and tubing. Smaller size tubing, such as copper water service tubing, can be cut with a roller cutter. Duringany cutting operation, the tube ends should not be severely clamped to cause distortion in the wail diameter. Care should

be exercised to insure that the ends for joining are true and round. Both fittings and tubing are sized to provide joint clearances for capillary flow of the solder and joint strength.

Tables 22.1 and 22.2 show thestandard dimen-, sions of copper tube and copper and cast bronze socket type fittings. Table 22.3 provides the di- mensionsfor stainless steel pipe. The dimensions given in these tables generally allow approximately O. 10 mm (0.04 in.) clearance between the outside wall of the tubing and the inner wall of the solder cup. The overall difference in diameter between the male end (tube end) and the female end (solder cup) is approximately 0.23 mm (0.009 in.). Usually a clearance of 0.10 mm (0.004 in.) will assure a sound metallurgical joint. Joint clearances of less than 0.1 mm (=;.0.003 in.) may produce flux inclusions or poor solder penetration, and clearances larger than 0.15 mm (-0.005 in.) may reduce capillary flow and produce voids.

After cutting, the tube should be reamed to remove burrs or uneven cut edges which will interfere with the flow of the solder or the alignment of the mating parts. A half-round file can be employed to remove surface burrs and irregularities. Care should be exercised to prevent distortion or excessive flaring of the tube ends or increasing the joint clearance by over- reaming of the fitting sockets.

117

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5 i i f

t COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

AWS S M * C H * 2 2 ** m 078q265 0006335 b M

I 18/SOLDERING MANUAL

Table 22.1-Sizes and weights of copper water tube Outside diameter Inside diameter

Types Nominal size K-L-M-DWV Type K Type L Type M Type DWV mm in. mm in. mm in. mm in. mm in. mm in.

6.4 114 9.5 0.375 7.75 0.305 8.00 0.315 8.00 0.325 - - 9.5 318 12.7 0.500 10.21 0.402 10.92 0.430 11.43 0.450 - -

12.7 II2 15.9 0.625 13.39 0.527 13.84 0,545 14.45 0.569 - - 15.9 SI8 19.1 0.750 16.56 0.6S2 16.92 0.665 17.53 0.690 - -

19.1 .314 22.2 0.875 18.92 0.745 19.94 0.?85 20.60 0.811 - - 25.4 I 28.58 1.125 25.27 0.995 26.0.1 1.025 26.80 1.055 - - 31.8 I I(4 34.93 1.375 31.62 1.245 32.13 1.265 32.79 1.291 32.89 1.295 38.2 I I I2 41.28 1.625 37.62 1.481 38.23 1.505 38.79 1.527 39.14 1.541 93.8 2 53.98 2.125 49.76 1.959 50.42 1.985 51.03 2.09 51.84 2.041

63.5 2 il2 M.68 2.625 61.85 2.435 62.61 2.465 63.37 2.495 - - 76.2 3 79.38 3.125 73.84 2.90? 74.80 2.945 75.72 2981 77.09 3.035 88.9 3 112 92.08 3.625 85.98 3.385 87.00 3.425 87.86 3.459 - -

101.6 4 IM.78 4.121, 97.97 3.857 99.19 3.905 99.94 3.935 101.83 4.009 127 5 130.18 5.125 12205 4.805 123.83 4.875 124.64 4.907 126.52 4.981

I52 6 155.58 6.125 145.82 5.741 148.46 5.845 149.38 5.881 151.36 5.959

203 8 206.38 8.125 192.61 7.583 196.22 7.725 191.74 7.785 200.84 7.907 254 IO 257.18 10.125 240.00 9.449 244.48 9.625 246.41 9.701 - - 305 I2 307.98 12.125 287.40 11.315 293.75 11.565 295.07 11.617 - - -*Slightvanat¡% from these weights must be expected in practice.

Table 22.2-Dimensional data, solder joint fitting ends

Tolerances-solder joint fittings Female end

. (Fitting connection) (solder cup) Male end

Nominal size O D max O D min I D max I D min mm in. mm in. mm in. mm in. mm in. 6.4 I 14 9.55 0.376 9.50 0.374 9.65 0.390 9.60 0.378 9.5 318 12.73 0.501 1267 0.499 12.83 0.935 1278 0.503

12.7 I 12 15.90 0.626 15.85 0.624 16.00 0.630 15.95 0.628 15.9 SI8 19.08 0.751 20.19 0.749 19.18 0.755 19.13 0.753 i9.J 314 2225 0.876 22.20 0.874 2235 0.880 22.30 0.878

25.4 I 28.61 1.1265 28.54 1.1235 28.71 0.1305 28.66 1.1285 31.8 I 114 34.% 1.3765 34.89 1.3735 35.06 1.3805 35.01 1.3785 38.2 I 112 41.33 1.627 41.22 1.623 41.44 1.6315 41.38 1.629 50.8 2 54.03 2.127 53.92 2.123 54.14 2.1315 54.08 2.129 63.5 2 112 66.73 2627 66.62 2.623 66.84 2.6315 66.78 2.629

76.2 3 79.43 3.127 79.32 3.123 19.54 3.1315 79.48 3.129 88.9 3 112 92.13 3.627 92.02 3.263 92.25 3.632 92.18 3.629

101.6 4 IW.8 4.127 104.7 4.123 130.4 5.132 1W.9 4.129 127 5 IM.2 5.127 130.1 5.123 13 .4 5.132 130.3 5.129 152 6 155.6 6.127 155.5 6.123 155.8 6.132 155.7 6.129

203 8 206.4 8.W7 M6.3 8.123 206.6 8.132 206.5 8.129 254 IO 257.2 lO.l27 257.0 10.119 251.4 10.132 257.3 10.129 305 12 308.0 I2127 Un.8 12119 308.2 12132 308.1 12129

'For general plumbing use. **For copper drainage use.


The Soldering of Pipe and Tubel 1 19

Wall thickness Weight'

VpeK ' W L Spey VpeDWV VpeK VpeL VpeM 5 6 D W V mm in. mm. in. mm in. mm in. kglm Ib/ft kglm IbKt kglm Iblft k g h Iblft 0.89 0.035 0.76 0.030 0.064 0.025 - - 0.216 0.145 0.187 0.126 0.158 0.106 - - 1-24 0.049 0.89 0.035 0.064 0.025 - - 0.400 0,269 0.295 0.198 0.216 0.145 - - 1.24 0.49 1.02 0.040 0.71 0.028 - - 0.512 0.344 0.424 0.285 0.304 0.204 - - 1.24 0.49 1.07 0.042 0.76 0.030 - - 0.622 0.418 0.539 0.362 0.391 0.263 - - 1.65 O.Oó5 1.14 0.045 0.81 0.032 - - 0.954 0.641 0.677 0.455 0.488 0.328 - - 1.65 0.065 1.27 0.050 0.89 0.035 - - 1.25 0.839 0.975 0.665 0.692 0.465 - - 1.6) 0.065 1.40 0.055 1.07 0.042 1.02 0.W 1.55 1.04 1.32 0.884 1.01 0.682 O. 0.650 1.83 0.072 1.52 0.060 1.24 0.049 1.07 0.042 2.02 1.36 1.70 1.14 1.40 0.940 I . 0.809 2.11 0.083 1-78 0.070 1.47 0.01 1.07 0.42 3.07 2.06 260 1.75 2.17 1.46 1. 1.07

241 0.095 2.03 0.080 1.65 0.065 - - 4.36 2.93 3.70 2.48 3.02 2.03 - - 2.77 0.109 2.29 0.090 1.83 0.072 1.14 0.045 5.95 4.00 4.% 3.33 3.W 2.68 2. 1.69 3.05 0.120 2.54 0.100 2.11 0.083 - - 7.62 5.12 6.38 4.29 5.33 3.58 - - 3.40 0.134 2.79 0.110 2.41 0.095 1.47 0.058 9.69 6.51 8.01 5.38 6.93 4.66 4. 2.87 4.06 0.160 3.18 0.125 277 0.109 1.83 0.072 14.4 9.67 11.3 7.61 9.91 6.66 6. 4.43

4.88 0.192 3.56 0.140 3.10 0.122 2.11 0.083 20.7 13.9 15.2 10.2 13.3 8.92 9. 6.10

6.88 0.271 5.08 0.200 4.32 0.170 277 0.109 38.3 25.9 28.7 19.3 24.6 16.5 IS. 10.6 8.59 0.338 6.35 0.250 5.38 a212 - - 60.0 40.3 44.8 30.1 38.1 25.6 - - 10.29 0.405 7.11 0.280 6.45 0.254 - - 86.0 57.8 60.1 40.4 54.6 36.7 - -

Solder joint fittings; Solderjoint fittings*' cast bronze, wrought copper Fitting end length Solder cup depth Fitting Solder cup Wrought Cast Wrought Cast

end length length drainage drainage drainage drainage mm in. mm in. mm in. mm in. mm in. mm in.

7.9 5/16 - 9.5 31s 9.5 3ls - 11.1 7/16 127 IL? - 14.3 9/16

17.5 11/16 15.9 51% - 20.6 13/16 19.1 3H - 24.6 31/32 23.0 29/32 - 26.2 1 1/32 24.6 31/32 17.5 11/16 11.2 0.44 15.9 9.7 0.38

0.44 0.50

29.4 I 5/32 27.8 I 3/32 19.1 35.7 I 13/32 34.1 I 11/32 20.6 38.9 I 17/32 37.3 I 15/32 - - - 50.0 1 31/32 48.4 ll9/32 - - - - - - - - 564 2 7/32 54.8 2 5/32 31.8 1 IH 26.9 1.06 30.2 I 8/16 25.4 1.00 69.1 23/32 67.5 2 21/32 - - 3x3 1.31 - - 31.8 1.25 80.2 3 5/32 78.6 3 5/32 - - 41.1 1.62 - - 38.2 1.50

102.4 4 1/32 100.8 3 31/32 - - 53.8 2. I2 - - 50.8 2.00

117.5 4 51s 114.3 4 ID - - - - - -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

11.2 127 0.50 17.5 11/16 127 13/16 0.56 19.1 314 - 14.2 - - - -

43.7 I 23/32 421 I 2 l ß 2 25.4 1 20.6 0.81 23.8 15116 19.1 O 75

- - - - - - - - 104.8 4 I Æ 101.6 4 - -


12O/SOLDERING MANUAL

Table 22.3-Stainless steel pipe

Schedule 40

Nominal Wall pipe size OD ID thickness

in. mm in. mm in. mm in. mm 3.2 10.29 0.405 7.80 0.307 1.24 0.049

10.41 0.410 1.65 0.065 1.65 0.065

6.4 114 13.72 0.540 9.5 17.15 0.675 13.84 0.545 12.7 318 112 21.34 0.840 17.12 0.675 2.11 0.083 19.1 314 26.67 1.050 22.45 0.884 2.11 0.083

O. 109 25.4 1 33.40 1.315 27.86 1.097 2.77 31.8 1 114 42.16 1.660 36.63 1.442 2.77 O. 109 38.2 1 112 48.26 1.900 42.72 1.682 2.77 O. 109 50.8 2 60.33 2.375 54.79 2.157 2.77 O. 109 63.5 2 112 73.03 2.875 66.93 2.635 3.05 o. 120 76.2 3 88.90 3.500 82.80 3.260 3.05 o. 120 88.9 3 1/2 101.6 4.000 95.50 3.760 3.05 o. 120 101 4 114.3 4.500 108.2 4.260 3.05 o. 120 127 5 141.3 5.563 134.5 5.295 3.40 O. 134 152 6 168.3 6,625 161.5 6.357 3.40 O. 134 203 8 219.1 8.625 211.6 8.239 3.76 O. 148

Schedule 5

Nominal Wall pipe size OD ID thickness

mm in. mm in. mm in. mm in. 12.7 1 12 .21.34 0.840 18.03 0.710 1.65 0.065 19.1 314 26.67 1.050 23.37 0.920 I .65 0.065 25.4 1 33.40 1.315 30.10 1.185 1.65 0.065 31.8 1 114 42.16 1.660 38.86 1.530 1.65 0.065 38.2 1 1/2 48.26 1.900 44.96 1.770 1.65 0.065 50.8 2 60.33 2.375 57.02 2.245 1.65 0.065 63.5 . 2 112 73.03 2.875 68.81 2.709 2.11 0.083 76.2 3 88.90 3.500 84.68 3.334 2.11 0.083 88.9 3 112 101.6 4.000 97.38 3.834 2.11 0.083 101.6 4 114.3 4.500 110.1 4.334 2.11 0.083

CLEANING

The ends of tubing or pipe as well as the internal surfaces of fittings must be thoroughly cleaned to provide surfaces which allow for wetting (allay- ing) and distribution of the solder at the joint interfaces. All traces of dirt, grease, lacquers, or oxides on the base metals must be removed. Degreasing with organic solvents will often remove various oils, but solvents will not ordinarily be effective in removing oxides or organic coatings which are applied to provide oxidation resistant surfaces. Cleaning should be performed

so that only the surface contaminants are removed without excessive loss of the base metals. This is best accomplished by lightly abrading the tube ends and solder cups with small wire brushes, steel wool, or fine grades (00) of abrasive papers or cloth. Embedding of abrasive particles in the joint surfaces should be avoided, and any material resulting from the mechanical cleaning operation must be removed.

Although mechanical cleaning of steel or cop- p x pipe and tubing is usually adequate, mineral acids and alkaline cleaners are occasionally used to prepare surfaces for soldering (see Chapter 5).

,


The Soldering of Pipe and Tubel 121

FLUXING OPERATIONS feathered To adjust an acetylene flame to its

~l~~~~ are required for soldering of tubing or neutral state, light a flame which has an excess of

dissolve or remove very thin oxide films already increase the oxygen flow Slowly until the cone present on precleaned surfaces, fluxes should not just starts to feather* be used as a primary cleaner of joint surfaces. A The flame should be directed SO that it wraps small bmsh or clean cloth will assist in coating itself around small diameter pipe or fittings. Mul- the joint interfaces with flux, and flux should be tiple tip torches or even additional heating applied as soon as possible after cleaning. torches may be required to solder large diameter

Only surfaces which are to be wetted by sol- (over 100 - [4 in.]) Pipe. The Pipe Or tube ders should be coated with flux, and an applica- should be heated before the fittings, and after a tion of flux to the inside surfaces of pipe should short heating period, the flame is directed alter- be avoided, Often flux inclusions in the finished nately to the pipe and then to the fitting. This joint can be minimized by preplacing a ring of will bring the fittings and pipe UP to equal heat. solder at the seat of the pipe joint. Upon heating Holding the flame at one location on the fitting or and distribution of the solder in the joint, the pipe will cause localized overheating, excessive metal will flow outward, displacing the flux. drying of the flux, distortion of the pipe, and

possible cracking of the fitting, and should be avoided.

The inner cone tip of the flame should not ASSEMBLY impinge directly on the shoulder of the tube and

fitting or into the socket of the fitting. The sharp Before any joining operation, the assembly Point Of the inner cone of the flame should just should be carefully aligned and adequately sup- touch the surfaces and the flame h ~ l d be ported, Misalignment will affecf the joint by kept in motion so that heat is distributed evenly to changing the clearance between the tube and the as large an area as Possible. fittings. Vertical pipe runs should be plumb to The correct temperature for making solder prevent any inconsistencies in joint spacing. pipe joints can be tested by touching the solder to Supports and fixtures should allow for expansion the heated junction between the Pipe and fitting and contraction of the assembly during the join- and observing the flow of the solder. The flux ing operation. should be very fluid on both fitting and pipe.

When the solder begins to melt, it is fed into the capillary space with a gentle pressure. At the same time, the torch is moved around the fitting with the solder being fed to the joint just behind the bath of the flame. Heat should not be applied

Most of the pipe and tubing assemblies are made directly to the solder. If the torch flames are with gas torches fueled with acetylene, propane, directed to the heel or 6ottom of the socket of the nafural gas, and other gases in the presence of fitting, the solder will distribute itself throughout oxygen (see Chapter 21 and AWS A6.2, Lens the joint. Shade Selector). Usually the size of the pipe or Opinions differ as to whether or not a fillet is tubing being joined will control the selection of necessary or desirable on pipe joints. Often a full, t.orch tips and the amount of heat to be delivered annular fillef indicates good solder penetration to the joint. A low velocity bulbous flame of and distribution in the joint. However, generous sufficient size to permit rapid and even heating is fillets at the bottom of the assembly may be ordinarily used. The flame should be neutral or caused by accumulation of the solder, which has only slightly reducing. A neutral flame has a solidified after flowing over relatively cold smooth, even inner cone which is as large as can metal. Heating the bottom of the fitting will be obtained without making the end of the cone largely eliminate this condition.

pipe. Since the main purpose of fluxing is to acetylene, then reduce the flow of the gas, Or

APPLYING HEAT AND SOLDERS


IZZ/SOLDERING MANUAL

Induction, furnace, radiant, and resistance heating can also be used to solder pipe and tubing assemblies. Resistance heating of tubular parts is accomplished by the use of electrical tongs (see Fig. 22. I ) . Tongs are usually employed for joining pipe or tubing of 50 mm (==2 in.) diameter or smaller. The tongs are applied to the joint area, and the current is turned on and maintained until solder wire touched to the pipe begins to flow. The current is then shut off, and the solder is

moved around the periphery of the joint to ensure even distribution.

In induction, furnace, and radiant heating, the solder is usually preplaced in the fluxed joint. Alternatively, solder pastes may be used wherein the joint surfaces are painted with mixtures of flux and powdered alloys before joining. When mixtures of this type are used, additional solder may be added to assure a filled soldered joint.

Mg. 22.1-A solderer using a resistance heater simply holds solder wire to the lip of the joint with the heat tongs on the solder cup. Solder will not begin flowing until the solder joint is at the required temperature


SOLDERS AND FLUXES FOR JOINING PIPE AND TUBING

Solders are used to join pipe and tubing because they possess reasonably high strength and ductility and are economical in their use. The strength of soldered capillary joints depends on the strength of the solder in shear. Although the eutectic 63% tin-379 lead composition provides the maximum shear strength of the binary tin- lead filler metals, the filler metal does not have a melting range and therefore does not allow for easy mainipulation in forming plumbed joints. Most solderers prefer to use solder compositions which have a somewhat lower tin content to provide a greater melting range, ease of application, and distribution of the solder in the joinf during soldering.

Low and medium carbon steel pipe and tubing are usually joined with solders containing 40 to 60% tin, balance lead. Acidified zinc-ammonium chloride base fluxes are most satisfactory. If the pipe is galvanized, the zinc coating must be removed from joint surfaces by mechanical abrasion or chemically stripping the coating before heat is applied.

Copper and brass pipe and tubing are most frequently joined by soldering with tin-lead solders containing 20 to 60% tin. The 50% tin-50% lead solder is commonly employed to provide strong joints under ambient temperatures and normal operating pressures. Under conditions of moderately elevated temperature or higher pressures, the 95% tin-% antimony solder is sometimes used. Tin-silver solders have comparable properties but should be qualified by tests as alternates.

When 95% tin-59 antimony solders are used, it must be remembered that they have a narrower pasty range and a higher liquidus temperature than tin-lead solders and therefore require different techniques and more control to assure properly filled joints.

The tin-antimony solders are often useful in refrigeration applications where soldered copper tubing is subjected to very low temperatures.

Normally, proprietq liquid or paste fluxes containing zinc and ammonium chlorides or organic base fluxes are used to solder copper pipe and tubing. These fluxes have higher heat stabil-

The Soldering of Pipe and Tuber123

ity than rosin base fluxes and are preferred when heat is applied by a fuel gas-air soldering torch.

In soldering nickel or stainless steel, tin-rich solders such as 60% tin-40% lead or 50% tin- 509 lead are usually desirable. Corrosive flux mixtures of zinc chloride, ammonium chloride, and hydrochloric acid are required to remove oxide films when soldering these metals.

Aluminum and aluminum alloy pipe and tubing require tin-zinc or cadmium-zinc solders. Tin-lead solders are not recommended for aluminum because of the poor corrosion resistance of joints soldered with these solders. Soi- ders containing 409 tin-óû% zinc wet aluminum well and provide a useful melting range.

Aluminum alloys containing 0.5% or more of magnesium are susceptible to intergranular corrosion by molten tin base solders. However, solders containing a minimum of 4% aruminurn will reduce intergranular penetration and dissolution. A solder containing 959 zinc-5% aluminum has been found useful in joining aluminurn alloys containing magnesium.

Aluminum and its alloys have a tenaceous oxide film which must be displaced by highly reactive fluxes during the soldering operation. Fluxes incorporating zinc and often stannous (tin) chloride react at approximately 280" to 340" C ( ~ 5 4 0 " to 640" F) and are used primarily with tin-zinc solders. If temperatures above this are used in joining, the tin-containing flux should not be used. Zinc-chloride base fluxes are preferred in this instance. Adequate post cleaning is required after soldering with these fluxes to prevent joint corrosion.

Often it is not practical to clean flux residues from soldered aluminum tubing assemblies and the nonchloride, organic fluxes are recommended. These fluxes are considered to be a nonhygroscopic, and their residues produce little or no corrosion if left in place.

-

POST CLEANING OPERATIONS

After the solders have solidified, the remaining flux and residues can be removed from wrought fittings by wiping with a wet cloth or by wet brushing. Often a cloth is dipped into water containing a small amount of sodium bicarbonate to


124ROLDERING MANUAL

assist in neutralizing any flux residues on the finished joints. Cast fittings should be allowed to cool naturally before applying swabbing to the joints.

INSPECTION

Though soldered joints are very rarely examined or inspected by NDTmethods other than visual, it is possible to conduct both radiogfaphic and ultrasonic inspections. Ultrasonic inspection is fairly quick and easy but usually does not give a permanent record. Radiography is more time- consuming, but it does give a permanent record and may be a better inspection tool. Such inspection techniques are expensive and are not recommended except in critical areas or for spot checking.

Figures 22.2,22.3, and 22.4 show radiographs of solder joints with various amounts of voids.

Pig. 22.2 - Radiograph of nominal 32 mm (1% in.) copper tube and coupling. The bright white spots are drops of excess solder on the bottom. The darker gray areas in the gray solderioints are

Fig. 22.3 - Radiograph of T-joint in nominal 25 X 13 mm (1 X % in.) copper tube. The bright white spots are drops of excess solder. The darker gray areas are voids. There is a difference in density and contrast between the voids on the top and those on the bottom

Fig. 22.4 - Radiograph of L-shaped joint in nominal 20 X 13 mm (%I X ?4 in.) copper tube. The bright white spots are excess soldet On the 20 mm (% in.) side there is also considerable excess solder on the inside. On the 15 mm í% in.) side there is a maior. serious void voids. There is a fairly larie ioid on-the right . I .


CHAPTER 23

PHYSICAL AND MECHANICAL PROPERTIES OF SOLDER AND SOLDERED JOINTS

INTRODUCTION

Although the mechanical properties of solder can be determined by standard tests, solder joints are generally designed to take advanfage of the properties of the base metal rather than relying upon the strength of the solder alone. Due to this de- pendency upon the joinf design, experience best dictates what can or should be soldered with the expectation of reasonable service life.

However, design problems occasionally arise which warrant reference to test data for successful resolution. The following information may be helpful in such cases.

ROOM TEMPERATURE PROPERTIES OF BULK TIN-LEAD SOLDER

Fairly extensive data are available on the bulk properties of tin-lead solders despite the fact that these solders are seldom, if ever, used in the bulk form. While these bulk data may not be identical to those developed for soldered joints, they frequently can be used to afford some reasonable basis for design.

Typically, the room temperature properties of tin-lead solders vary gradually over common solder compositions, maximizing or minimizing at or near the eutectic composition of 63% Sn-37% Pb. The properties of bulk solders can vary considerably depending upon such things as

the casting conditions, thermo-mechanical his- tory of the solder, or even the timeof storage prior to testing. In view of this, whenever a conflict in data exists, the more conservative value is reported. Some mechanical properties of particular interest are shown in Table 23. 1.

The tensile strength of solders, as measured by tensile testing at strain rates of 0.5 m d m d m i n , increases with increasing tin content, reaching a maximum of about 54 O00 kPa (7800 psi) at the eutectic composition. Although easy to determine and quite reproducible, the significance of tensile strength data for any design application is moot, since it is only a measure of the maximum uniaxially applied load a specimen can withstand at rapid rates of straining. And, of course, due to alloying with the base metal, the tensile strength of a solderedjoint would likely be superior to the tensile strength of the bulk solder.

As with tensile strength, the shear strength of solders increases with increasing tin content. It might be noted that: (1 ) the shear strength of bulk solder is less than the tensile strength for all compositions of solder tested, particularly at the lower tin confents, and (2) the shear strength increases nearly linearly with tin content up to about 60% tin.

The elongation of solders (the ratio of increase of length of a gage section of the specimen to its original length) would be expected to vary in- versely with tensile strength. It should be noted that the elongation of solders is quite siructure-

125

ci COPYRIGHT American Welding Society, Inc.Licensed by Information Handling ServicesCOPYRIGHT American Welding Society, Inc.Licensed by Information Handling Services

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i26/SOLDERING MANUAL

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Physical and Mechanical Properties of Solder and Soldered Joints(l27

sensitive so that very largevariations can occur in elongation measurements for a given solder. Nevertheless, even with conservative data, it can be seen that solders are quite ductile over the composition range of interest.

The ratio of the tensile stress to strain in the elastic region is defined as the modulus of elastic- ity, or Young's Modulus. Consequently, the modulus is a measure of the stiffness of a material-that is, ,the greater the modulus the stiffer the material or smaller the elastic strain resulting from the application of a given stress. While the modulus increases in a nonlinear manner with increasing tin content, it should be recognized that the values of Young's Modulus for solders are, like all soft metals, highly dependent upon the rate of loading.

The Brinell hardness of bulk solders increases with idcreasin2 tin content. It is interesting, as in the case with many metals, that the Brinell hardness of solders appears to correlate directly to the tensile strength of the solders: Tensile strength equals 400 to 450 times the Brinell hardness number.

The impact strength of solders, as measured by the Izod impact test, is relatively low, increasing with increasing tin content up to about 40% tin. However, the fact that the ductile solders do not fracture in conventional Izod impact tests brings into question the relevancy of such impact data for design.

Solders will plastically deform, or creep, under sustained loads constituting only a small fraction of their tensile strength. This critical influence of duration of the load on the stress-strain relationship severely restricts the use 6f tensile data for design. Consequently, in most applications the creep resistance is the most important design parameter. Unfortunately, creep data do not exist for the entire range of interest for solders. How- ever, the available data do indicate that solders have generally low creep strength. Specifically, the stress to produce creep rates of 0.0001 mm/rnm/day at room temperature for several commonly used solders containing 30-50% tin is only of the order of 830 kPa (120 psi). It should be noted that this creep rate is quite rapid, equivalent to an extension of about 3.5% per year.

Other physical properties of bulk solder which would likely be of interest to designers are the density, electrical and thermal conductivities, and linear expansion. For tin-lead solders, as showi in Table 23.2, these properties vary in a predicta- ble and linear manner with tin content.

Measurements have also been made of the surface tension and viscosity of several solders, as shown in Table 23.3. These properties of the molten solder vary only slightly at the test temperature over the range of compositions investi- gated.

Table 23.2-Physical properties of tin-lead solders

Electrical Coefficient3 of Tin conductivity' Thermal conductivity3 linear thermal

w/o g/cm3 of copper IACS (btu/ft*/in./" F/s) per "C X ("FX content Density' percent W/m*K expansion

O 11.34 5 10.80

10 10.50 20 10.04 30 9.66 40 9.28 50 8.90 60 8.52 63 8.34 70 8.17

references

7.9 8.1 8.2 8.7 9.3

10.1 10.9 11.5 11.8 12.5

34.8 0.067 35.2 0.068 35.8 0.069 37.4 0.072 40.5 0.078 43.6 0.084 47.8 0.090 49.8 0.096 50.9 0.098

29.3 28.4 27.9 26.6 25.6 24.7 23.6 21.6 21.4 20.7

16.3 15.8 15.5 14.7 14.2 13.7 13.1 12.0 11.8 11.5


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Table 23.3-Physical properties of molten tin-lead solders

Tin Surface content Temperature tension4 Viscosity4

wlo "c "F dynes poise

O 391 735 439 0.0244 20 282 540 467 0.0272 30 282 540 470 0.0245 40 282 540 474 0.0229 50 282 540 476 0.0219 63 282 540 490 0.0197

4see references

PROPERTIES OF SOLDER AT ELEVATED TEMPERATURES

The low solidus temperature of most tin-lead solders limits their use for structural joining of materials for elevated temperature service. For example, at 150" C ( =300" F) the tensile strength of bulk tin-lead solders is approximately 14 O 0 0 kPa (2000 psi) regardless of tin content. As expected, the elongation of these solders at elevated temperature is substantial (see Table 23.4).

Table 23.4-Tensile properties of bulk tin-lead solders at 150°C [ =300" F)

Tin

wlo kPa psi elongation5 content Tensile strength5 Percent

O. 5

10 20 30 40 50 60

5500 10 o00 13 O00 13 O 0 0 13 O00 13 000 13 O00 12 O00

800 1500 1900 1900 1900 1900 1900 1800

65 35 70

120 140 140 145 150

%ee references

Most important, however, is the fact that the creep strength of tin-lead solders is quite markedly reduced at elevated temperatures. Available data indicate that at 80°C (== 180°F) tensile stresses of only 205-415 kPa (30-60 psi) would be sufficient to produce minimum creep rates of

O.OOO1 mmlmmlday in 5 9 tin-lead solder would containing 30-60% tin. Lower tin-bearing solders, say of the order of 5% tin, with higher solidus temperatures have somewhat superior creep properties at elevated temperatures. By in- terpolation, the estimated stress a t 80°C (==iSO"F) required to produce a creep rate of O.OOO1 mmlmmlday in ASTM Grade A solders be approximately 690 kPa (100 psi).

PROPERTIES OF SOLDER AT LOW TEMPERATURES

Measured properties of solders at cryogenic temperatures are found, as shown in Table 23.5, to be directly proportional to the tin content. That is, the tensile strength and shear strength of the solders increase with increasing tin content and decreasing test temperature. Ductility, as measured by elongation, decreases with increasing tin content and decreasing temperature. Because of embrittlement of joints at temperatures below 13" C (55" F) (Le., tin pest), concern is often expressed about the stability of solders in service at low temperatures.

However, the retarding effect of lead may ameliorate any problems with tin pest in solder joints used in low temperature service. Since it has been reported that antimony reduces the tendency of the solder to form tin pest, the ASTM Grade B solders, which contain 0.20-0.509 Sb, are often selected for cryogenic use.

TIN-LEAD SOLDERS CONTAINING ANTIMONY

It has been long recognized that one part antimony couId be used as a substitute for two parts of the tin in tin-lead solders without seriously affecting the soldering characteristics of the solders. This substitution is customarily limited so that the total amounf of antimony added does not exceed 6 4 of the tin content of the solder. These ASTM Grade C solders have certain mechanical properties, such as shear and tensile strength, superior to their tin-lead equivalents, as shown in Table 23.6.


Physical and Mechanical Properties of Solder and Soldered Joints/ 129

làb le 23.5-Mechanical properties of bulk tin-lead solders at cryogenic temperatures

Tin Tensile Shear

w/o temperature kPa psi kPa psi elongation6 content Test strength6 strength6 Percent

10 - 73eC --100"F 41 O00 5900 31 O00 4500 34 20 - 73°C --100°F 48 O00 7000 37 O00 5300 32 40 - 73°C --100"F 48 o00 6900 40 O00 5800 43 60 - 73°C --100"F 59 O00 8500 54 O00 7900 48

10 -196OC --320°F 59 O00 8600 43 O00 6300 27 20 -196°C z-320°F 85 o00 12 400 58 O00 8400 30 40 -196°C z-320°F 87 O00 12 600 77 O00 11 200 30 60 -196°C z-320°F 130 O 0 0 18 800 110 000 15 900 10

%ee references

Table 23.6-Mechanical properties of tin-lead-antimony solders

Anti- Tin mony Tensile? Shear?

content. content strength strength wlo wlo kPa psi kPa psi

30 1.0 4 6 0 0 0 6600 3 0 0 0 0 4400 40 2.5 49 O00 7100 37 O00 5300 50 3.0 52 000 7500 42 O00 6100 60 3.6 61 O00 8800 42 O00 6100

Impact? strength (IZO4

J fplbs

Stress to produce2 %' creep rate of

Elong- 0.001 mm/mm/day ation kPa psi

15.3 11.3 14.1 10.4 15.0 11.1 16.0 11.5

21 2000 295 34 2900 420 29 3300 480 18 3300 480

'see references

The addition of antimony to solders causes an improvement in creep resisfance. That is, at room temperature these solders can sustain a higher load for a given creep rate than equivalent tin- lead solders. As with the tin-lead solders, the creep resistance of solders containing antimony is markedly reduced at elevated temperatures. For example, the loads needed to produce minimum creep. rates of 0.0001 c / c per day in antimonial solders at 80" (1 (-180" F) are about 20% of those needed at room temperature, Le., 480-830 kPa (70-120 psi).

operation the tin contained in the molten solder reacts with the base metal. This reaction can result in solution strengthening and/or the formation and growth of intermetallic compounds, such as Cu,Sns or FeSn,, in the joint area with copper or iron base metals.

Unfortunately, it is difficult to obtain rigorous data for the soldered joint because the properties of the joint can be markedly influenced by a number of soldering parameters other than the composition of the solder used. Acareful study of some of the factors which have an effect on the properties of the soldered lap joints reveal the following:

1. Thickness ofthe Joint. The strength of the solder joint is a function'of the spacing between

PROPERTIES OF THE SOLDERED JOINT

the soldered inferfaces. On steel, copper, and brass the optimum joint strength was obtained when the surfaces were separated by 0.1- O. 15 mm (~0.003-0 .005 in.). Thicker joints

The properties of the soldered joint can be Sig- nificantly different from those of the bulk soiders. The reason for this is that in the soldering


I30/SOLDERING MANUAL

usually have joint strengths which approach those of the bulk solder, while joints thinner than 0.1 mm (=0.003 in.) may be weak from poor solder penetration and flux inclusions. 2. Solder Temperature. The optimum solder-

ing temperature must be high enough to allow the flux to flow adequately and clean the area to be soldered and not so high as to cause the solder to flow out of the joint area or to build up a thick intermetallic layer. Good results are obtained at soldering temperatures approximately 55" C (100°F) above the liquidus of the solder. The base metal at the point of soldering must be above the solder's melting point.

3. Soldering Time. Within normal soldering cycles, the time of contact with molten solder has little or no influence on joint strength. However, prolonged heating may result in rapid deterioration of the tearing strength of the soldered joint due to a buildup of a brittle intermetallic layer. 4. Quantity of Solder in Joint. Excess solder

does not add to the strength of the joint provided that the joint space is full and that there is sufficient solder to round out sharp corners.

These properties of soldered joints are only meaningful and can be compared meaningfully only if the joints are made in a controlled and reproducible manner. The test data on joints pre-

sented here were developed with full cognizance and control of these parameters.

rn general, the two mechanical properties of the soldered joint of greatest interesf are the shear and creep strengths.

SHEARSTRENGTHOFSOLDERED JOINTS

The shear strength of soldered joints was determined by pulling lap joints at a strain rate of 0.5 m d m d m i n . The results of these tests for ASTM Grade A and Grade C solders are shown in Table 23.7. As can be seen, the shear strengths of joints made in either copper, brass, or steel were maximized with solders containing approximately 50% tin, under the soldering conditions used. When shear strength data are applied to design, it is important to remember that, in practice, the forces acting to pull apart lap joints are generally not pure shear but rather a combination of shear, tensile, and peel stresses. In some instances, the application of a load fo a solder joint, particularly a joint in thin stock, can cause a concentration of stress at the edge of the joint. This in turn causes a slow tearing action or peeling at this point, which can result inlow values of joint strength.

Table 23.7- Shear strength of soldered lap joints

Tin Joint between? Joint between7 Joint between7 content mild sfeel members copper members brass members

wlo kPa psi kPa psi kPa psi

ASTM grade A tin-lead solders

ASTM grade C tin-lead- antimony solders

10 20 30 40 50 60

19 O00 2700 28 000 4000 32 000 4700 34 O 0 0 5000 34 O 0 0 5000 33 000 4800

~ ~

14 O00 2100 21 O00 3000 28 O00 4000 34 O00 5000 39000 5600 39 O00 5700

~~

12 o00 19 O00 23 o00 28 O 0 0 31 O00 30 O00

1800 2800 3300 4000 4500 4300

10 20 30 40 50 60

12 O00 1800 21 O00 3100 28 O00 4000 32 O00 4600 34 o00 4900 31 O00 4500

14 O00 2100 21 O00 3100 29 000 4200 34000 5000 39 o00 5700 42 O00 6100

12 o00 19 O00 23 O00 28 O00 28 O00 28 O00

1800 2800 3300 4000 4000 4000

'see references -


Physical and Mechanical Properties of Solder and Soldered Joints1 13 1

CREEP STRENGTH OF SOLDERED JOINTS

The ability of a soldered joint to safely withstand a sustained load without failure is probably the single most important mechanical property for design. For example, the specific measure of this characteristic is the determination of the maximum allowable stress which will not cause failure of lap joints in a service life of ten years. Data pertinent to this are presented in Table 23.8. As can be seen, the maximum allowable stress tin-lead soldered joints can sustain over their service life decreases with increasing tin content. A similar relationship exists between joint strength and tin content at elevated temperatures, although the limiting loads at the higher temperatures are quite reduced from room temperature loads. The data in Table 23.8 were developed for lap joints in copper.

FATIGUE STRENGTH OF SOLDERED JOINTS

Although soldered joints are often exposed to vibratory loads, such as in automobile radiators, which could result in fatigue failure, explicit data on the fatigue strength of soldered joints are not available. One reason for this is that soldered lap joints produced with thin gauge material cannot sustain compressive loading along their length;

therefore, it is not possible to conduct fatigue fests on such joints under conditions of alternating tension and compression.

SOLDERS FOR USE AT ELEVATED TEMPERATURES

High-Tin Alloys Joints formed with tin-lead and also

antimonial-tin-lead solders containing upwards of approximately 15% tin have a low solidus temperature of 183" C (361" F). This low solidus temperature generally precludes consideration of these solders for joints which will be subjected to stresses at or above 150" C (==300" F).

There are, however, high tin-containing solders which can be applied at low temperatures but have appreciably higher solidus temperatures than the common lead-tin solders. One such group of solders is the tin-antimony solders. AS shown in Table 23.9, although the iiquidus temperatures of these solders are about the same order as typical lead-tin solders, their solidus temperatures are higher.

Consequently, these tin-antimony solders maintain some strength up to relatively high temperatures of 200" C (400" F). It should be noted that at this temperature lead-tin solders containing above 15% tin would be completely or partially melted and would therefore have no load-caqing capacity.

Table 23.8-Maximum sustained stress at various temperatures which will not cause failure of soldered lap joints in 10 years (in air)

Tin content 20" CB 68" F 100" Ce 212" F 149" C8 300" F

wlo kPa psi kPa psi kPa psi

5 3400 500 10 3200 470 20 2500 360 30 2100 300 40 1800 260 50 1700 250 60 1700 250

1700 250 1400 200 830 120 620 90 520 75 520 75 520 75

1000 150 690 100 340 50 210 30 210 30 210 30 210 30

*see references

I 'i


1321SOLDERING MANUAL

Table 23.9-Properties of tin-antimony solder

Composition Liquidusg Solidusg Tin Antimony wlo wlo "C "F "C "F

100 97 3 95 5 93 7

232 450 239 462 242 468 244 471

232 450 235 455 237 458 239 462

* 10 see references

The tin-silver eutectic solder (96.5% Sn-3.5% Ag), having a melting point of 221" C (430" F), might be considered for use in elevated temperature service although the cost of this söider is generally high.

Joints to be soldered with tin-antimony or tin- silver solders for high temperature service should be free of lead. Any lead in the joint can dissolve in these solders and possibly produce low melting ternary eutectic phases in the soldering process At elevated temperatures these eutectic phases melt, resulting in hot shortness and joint failure.

Lead-Tin-Silver Solder

The most widely used solders for high temperature application are ternary lead-tin- silver solders in the composition range of O-5% Sn, O- 1.5% Ag. The tin content of these solders is

low enough to maintain a relatively high solidus temperature while yielding reasonable solderability and corrosion resistance. The silver is added for improved creep resistance.

The effects of using low tin and silver can be appreciated by examining the data in Table 23.10 in which copper lap joints, soldered with these solders, were evaluated over a wide temperature range by a stepped loading test. That is to say, the lap joint was stressed to some low level for 24 hours and the load incremented daily until failure occurred. Although the stepped loading characteristics are not directly relatable to the creep resistance ofthe soldered joint, they do afford an excellent semiquantitative measure of this most important property. The superiority of the lead- tin-silver solders to eutectic tin-lead solders, under test conditions, is clearly evident.

Table 23.lû-Stepped loading creep tests on nominal 15 mm x 3 mm (1/2 in. X 1/8 in.) overlap joints on copper

Composition Breaking stress

20°C10 68°F 1000C1o 212qF 1500C10 30. Pb Sn Ag Liquidus Solidus WlO WlO WlO "C "F "C "F kpa psi kPa psi kPa psi

98 2 319 608 304 580 4100 600 <2000 C300 95 5 312 594 270 518 3100 540 e2000 c 3 0 0 97.5 1 1.5 313 595 301 573 11 o00 1640 6100 900 4800 700 96.5 2 1.5 306 583 301 573 10 O00 1500 6000 880 4800 700 93.5 5 1.5 304 579 301 573 8500 2150 5500 800 3800 560

70 30 256 491 183 361 6100 900 2600 375 6 0 4 0 238 466 183 361 5800 850 2000 300 5 0 5 0 216 421 183 361 6000 875 2000 300

'O see references


AUS S M * C H * 2 3 ** ____ - 07&42bS 0006350 2 m - - ~___-

Physical and Mechanical Properties of Solder and Soldered Joints1 133

Tensile strength at various temperatures1°

25°C 80°F 66°C 150O.F 149°C 300qF 204°C W , F kPa psi kPa psi kPa psi kPa psi

13 O00 1900 28 O 0 0 1400 20 O00 3000 11 O00 1600 38 O00 5600 38 500 4200 13 500 2000 10 O00 1500 48 O00 7000 34 O00 5000 13 500 2000

LOW TEMPERATURE SOLDERING

There are many fusible solders, generally based upon eutectics of bismuth, which can be used when low temperature soldering is required.

Table 23.11 presents some data concerning the properties of these commonly used solders. It is important to note that while these low melting solders have relatively high tensile strengths and hardnesses, they are not very creep resistant. i n fact, sustained tensile loads of approximately 70 kPa (10 psi) are often sufficient to produce creep rates in the solders in excess of 1% per year. This creep sensitivity is intensified by structural characteristics of the solder. Rapidly solidified fine grain will, as a rule, exhibit less creep resistance than a coarse grain solder.

The poor creep strength of these solders must be recognized in any application in which the solders will be exposed to continuous loads.

PROPERTIES OF SOLDERED COP PER JO1 NTS

Goc i design practice generally requires that the soldered copper joint will be stressed primarily in shear, and then the area will be adequate to assure that the stress will be below levels which can cause tensile, creep, or fatigue failure.

The mechanical properties of a soldered copper joint are different from those of the bulk solder itself and depend on a number of process

variables in addition to solder composition. Of importance are joint clearance, base metal composition, cleaning procedures, flux, soldering temperature, soldering time, and cooling rate.

Designs for sfrucfural applications usually have soldered members loaded in shear. Shear strength (under rapid application of load) and creep strength in shear are the important mechanical properties. For specialized applica- fions such as auto radiators, peel strength and fracture initiation strength are thought to be important. In a few cases tensile strength is of interest. There are no known techniques for relating one mechanical property to another.

Shear Strength

Shear strength is determined using single- or double-lap specimens or sleeve type cylindrical specimens and testing at cross-head rates of the order of 25 or 2.5 mm/min (1.0 or 0.1 in./min). The duration of loading is then very short, either seconds or minutes. The shear strengths of copper joints soldered with lead-tin solders are shown in Fig. 23.1. The maximum strengthis obtained with solders roughly of the eutectic composition(63% tin, 37% lead). Ifthejoints areaged at room temperahire or moderately elevated temperature for several weeks prior to test, measured short-timeshear strengthmay decreaseupto 30%. Reported strengths are sometimes at variance due to differences in procedures for soldering and testing. The properties reported here for soldered copper may not apply on other materials.



Table 23.1111 -Some properties of low melting solder of bismuth

A B

Solder composition (%): Bi 45 49 - -

Pb 23 18 Sn 8 12 Other 5 Cd 21 In

19 In

Liquidus O C, OF Solidus C, O F Pastymnge OC, O F

Specific gravity 20" C, 68" F

Density kg/m3

Tensile strength MPa

lbs /in.3

psi

47,117 47,117

O

8.9

8850 0.32

37 5400

58, 136 58, 136

O

8.6

8600 0.31

43 6u)O

Brinell hardness 12 14

Electrical conductivity as % of copper (1.72 microhmslcm)

Thermal conductivity, solid (cal/cm2/cm/" C/s) (copper is 0.94)

4.5%* 3%*

- 0.05*

Specific heat, liquid (cal/gl"C) 0.035* 0.032*

Lafent heat of fusion J/kg (btullb 1

Coefficient of linear thermal expansion, mm/mm/" C mean

14 OOO* 6'

Volume change liquid-solid - 1.4% -1.5%

see references 11

* Approximate value

Note: A segment of the safety device industry sometimes defies a yield temperature as the temperature under which the solder will rupture under a standard load.

Volume change (linear growth on solidification)

0.05%. 0.05%



C -

50 27 13 10 Cd

70,158 70, 158

O

9.4

9400 O. 339

41 6Ooo

9

4%*

0.045*

D

55 45

-

124,255 124,255

O

10.3

10 300 0.371

44 6400

10

3%*

0.04*

E

58 42

138,281 138, 281

O

8.7

8700 0.315

55 8000

22

4.5%*

o.os*

L F -

42 38 11 9 Cd

70, 158 88, 190 18, 32

9.4

9450 0.341

38 5500

9

4%*

o.os*

G -

48 28 15 9 Sb

103, 217 227,440 124,223

9.5

9500 O. 343

90 13 OOO'

19

3%*

O . W * 0.03" 0.045* 0.040* 0.045*

32 MO* 16 OOO* 46 500* 23 OOO* 14* 72 20* 10*

o.ooo022 - O~ooo015 O.ooOo24

- - -

- 1.7% -1.5% +0.77% -2% - 1.58

O. 6% 0.3% O.OS%* 0.38 0.5%


c I

- 6000 -

- .- u> LI

2ooor 40000

m 30 O00 5

O I I I I I O 20 40 60 80 1 O0

Percent tin

G ?! 0 C

c

20000 ; o 5 1 - 10 O00

Fig. 23.1-Shear strengths of copper joints soldered with tin-lead solders (Ref. 12)

Shear strength decreases with increasing temperatures, as shown in Fig. 23.2. Many solders, especially those high in lead content, remain ductile at cryogenicfemperatures (to at least - 195" C [ =-320" FI), and strength increases significantly with decreasing temperature below room temperature (Ref. 13).

Creep Strength

The creep strength in shear of a soldered copper joint is considerably less than its short-time shear strength. Creep strength is defined as the maximum stress that will not cause failure under continuous application of the load. Failure can occur at stresses less than 10% of the short-time strength. The creep strengths of a number of solders, including 95% tin-5% antimony and 50% lead-50% tin solders, the two solders most often used in plumbing installations, are presented in Fig. 23.3. Although these two solders have similar short-time shear strengths, there are considerable differences between their creep strengths, the 95% tin-5% antimony solder being considerably stronger. Tin base solders with from 3.5 to 5% silver offer creep strengths comparable to

those of the 95% tin-5% antimony solders (Ref. 15).

Pressure ratings for soldered copper tubing with either wrought copper or cast bronze pressure fittings are based upon creep strengths shown in Fig. 23.3. Safety factors are included to make allowance for defects in workmanship and stress concentrations. Rated working pressure for joints in soldered copper tube systems are given in Table 23.12.

The bursting strength of a soldered connection is determined by increasing the pressure in the tubing until failure occurs. Normally, the duration of the fest is short, and stresses close to the shear strength of the joint would be required to rupture the solder bond. However, the tube itself normally bursts before the joint fails. The area of the fittings is large enough so that the tube splits before the solder fails. In contrast, pressure ratings based onthe creep strength of the solder joint are much lower. Table 23.13 compares thecalcu- lated bursting pressures of soldered copper joints with their pressure ratings. The calculated burst strengths are more than twenty times higher than the ratings. This provides a large margin of safety against failures due to pressure surges and other sudden or short-time applications of stresses.



Temperature, "C 200 150 O 50 1 O0

I I I I I

._ 6000- v> P

95% tin-5% antimony

VI

2000 -

50 O00

40 o00 2

m

m al .c

2 0 o00

10 O00

I I I I O 1 O0 200 300 o -

Temperature, " F

FiB. 23.2 -Shcar strengths at elevated temperatures for copper joints soldered with 50% tin-507¿ lead a id OS'%-S'% antiinony alloys (Ref.12)

Temperature, "c 150 200 250 O 50 1 O0

I I I 1 I I I I

1200 t i I

Curve I Solder

1 i 95% tin-5% antimony -(*WO ~

2 95% lead-5% tin

3 50% tin-50% lead

Temperature, o F Fig. 23.3-Creep strengths at elevated temperatures for copper joints soldered with several alloys

. (Ref.14)



Tensile Strength

Typical tensile strengths for butt joints soldered with fivedifferent lead-tin solders oncopper are presented in Table 23.14. Tensile strengths are much higher than shear strengths and also increase with increasing tin content up to the eutectic composition. Butt joints are not normally recommended for soldered systems because applied stresses and strains will tend to concentrate in the very narrow layer of solder. Also, any defects in the soldei layer will act as sharp crack starters when the joint is stressed in tension,

the fluxused. Also, it has been shown that soldering in an inert atmosphere can improve the peel test propedies obtained with some fluxes.

Fracture Initiation Strength

At the start of the peel test, the applied load rises to an abrupt maximum and then rapidly drops to a relatively constant peel strength. The high initial load is necessary to initiate a crack which then propagates at lower loads. Typical values of the fracture initiation strength of soldered copper are given in Fig. 23.5. Fracture initiation strengths may be several times higher than the corresponding peel strengths.

Peel Strength Torsional Strength In some applications stresses tend to tear open

the solder bond rather than shear it. For these cases the peel strength of the soldered copper joint is of interest. To measure peel strength, two thin strips are soldered together at one end to form a sort of wishbone specimen. The bond is then broken by peeling the strips apart, and the load required to propagate a crack is recorded.

Peel strength, like all mechanical properties, is dependent upon the soldering parameters. Exam- pies of the influence of flux and soldering temperature are shown in Fig. 23.4. The optimum temperature for soldering appears dependent on

When a soldered joint is twisted, torsional shear stresses are developed in the solder. The strength of such a joint will be somewhat different from that found in lap shear because stresses are not constant across the cross-section. Plastic deformation may occur, lehding to a stress pattern which is difficult to analyze. Torsional strengths of butt-joined copper bars have been determined for a number of solders. The reported values in Table 23.15 do not take into account the stress gradient, so the values appear to be higher than the shear strengths measured in lap shear for the same solders.

Soldering temperature, OC 300 350 400 450 500 550 600 650 700 750

25 I I I I I I I I I I i 1

20 1 1 5 0

97.5% Pb-1 %Sn-l.5% Ag Fluxes F,, F2, F,, F,

I I I I I I I I 1 500 600 700 800 900 1000 1100 1200 1300 1400

Soldering temperature,”F

Fig. 23.4-Peel strength of copper joints soldered with four fluxes over a range of temperatures (Ref. 17)


AWS .~~

6.4mm (ah in.) to 31.8mm (1% in.) to 63.5mm (2% in.) io 2 5 . 4 1 ~ 1 (I in.) incl. 50.8mm (2 in.) incl. 102mm (4 in.) incl.

"C "F MPa psi MPa psi MPa psi 38 100 1.4 200 1.2 175 0.9 150 66 I50 1.0 150 0.9 125 0.6 100 50% tin-

50%1ead 93 200 0.7 100 0.6 90 0.5 75 "Idera 121 250 0.6 85 0.5 75 0.3 50

38 100 3.4 500 2.8 400 2.1 300 "% 66 150 2.8 400 2.4 350 1.9 275

93 200 2.1 300 1.7 250 1.4 200 5% antimony 121 250 1.4 200 1.2 175 1.0 150 solder a

127mm (5 in.) to 203mm (8 in.) incl.

MPa psi 0.9 130 0.6 90

. 0.5 70 0.3 50 1.9 270 1.7 250 1.2 180 0.9 135

Table 23.13-Burst pressures!* and pressure ratings for soldered copper tube CalcuIated burst * *

pressure for Pressure Tube size, soldered joint, rating at 38" C (100" F)

Solder - MPa psi MPa psi 99 14 400 1.4 200

106 15400 1.4 200 I 50% lead-50% tin 109 15 900 1.4 200

106 15400 3.4 500 i 95% tin-5% antimony 109 15900 3.4 500

mm in. 12.7 1/2 50% Iead-50% tin 19. i Y4 50% lead-50% tin 25.4

2 50% Iead-50% tin 80 11 600 1.2 50.8 12.7 1/2 95% tin-5% antimony 99 14400 3.4 19. I 3/4 95% tin-5% antimony 25.4 50.8 2 95% tin-5% antimony 80 l i 600 2.8

*'lSrpical shear strength of 31 Mpa (4,500 psi) assumed for both solders

175 500

400

**Tube will fail at lower pressures.

Table 23.14-Tensile strength of soldered copper butt joints Solder Tensile, strengthfi

Lead, wt. % MPa psi Tin, wt. % 20 80 78 11 300 30 70 -95 13,800

60 i 16 i6 800 50 125 18 200

40 50 63 37 135 19 600

%ee references



Soldering temperature, "C

300 350 400 450 500 550 600 650 700 I 1 I I I 1 I 1 1

97.5% Pb-1% Sn-l.5% Ag - Fluxes F,, F2, Fa, F, KI Y

500 +--

400 $, 300 :$

o> c

C O

.- K .-

200 g c O !!!

100 u.

O 600 700 800 900 1000 1100 1200 1300

Soldering temperaturePf

Fig. 23.5-Fracture initiation strength for copper joints soldered with four fluxes over a range of temperatures (Ref.17)

Factors Infïuencing Strength ing tin content and temperature of the solder bath. Reactions take place at the interface between . These data show that soldering time should be

the liquid and solid during soldering. These reac- minimized and that time is most critical when the tions account for the apparent wetting of the solid soider has a high tin content. by the liquid and influenie the strength of the The volume of liquid solder in contact with the final joint. During the soldering of copper with solid is also important. The larger the volume, tin alloys, immetal l ic compounds a 6 S n 5 and the more rapid the reaction. Fig. 23.9 shows that Cu,Sn form at the solid-liquid interface. They the width of the reaction layer increases as the may €TOW to appreciable thicknesses, and as volume of the solder between the mating surfaces thicknesses increases, strength decreases. For increases. soldered copper and brass, Fig. 23.6 shows the Joint spacing has long been recognized as im- reduction in peel strength as the thickness of the portant to the strength of soldered fittings. Most reaction layer increases. investigators report thaf a clearance of the order

Intermetallic layers will grow during storage of O. 1 to o. 15 ( 4 . 0 0 3 to 0.006 in.) provides or service at room or elevated temperatures, and maximum shear strength for copper soldered this can reduce the mechanical properties. For with tin-lead solders. The influeme ofjoint spac- example, the total intermetallic compound thick- ing on shear strength may be seen in Fig. 23.10. ness on 60% tin-40% lead solder coated copper The foregoing discussion indicafes the impor- has been observed to follow the relations shown tance of treating each solder problem individu- in Fig. 23.7. The presence of stress during ele- ally By understanding the effects of design, vated temperature exposure may alter the growth equipment, and process parameters, the proper- rate of the compounds. ties of soldered copper may be optimized without

Fig. 23.8 shows that the rate of reaction be- making major changes in manufacturing mate- tween solder and copper increases with increas- rials and equipment.


AWS S M * C H * 2 3 ** 9 0784Zb5 0006358 7 Wp

Physical and Mechanical Properties of Solder and Soldered Joinfsl14 1

0.005 0.010 0.015 0.020 0.025 0.030 0.035mm 35 I I I l I I

225 37% ~ ~ 6 3 % sn Solder

30 t O 510" F

O 510" F Copper 102: A 680" F

25 m

150. j

F 125 2

Copper 102 Y VI t

c

<u a"

15 1 O0

o Reaction layer thickness, 0.001 in.

Fig. 23.6-Influence of reaction layer thicknesses on the peel strength of copper no. 102 and copper alloy no. 260 (Ref.19)

25

20

15

10

5

m e (days) Fig. 23.7-Compound thickness when 60% tin-40% lead solder coatings on annealed copper are stored for various times and temperatures (Ref. 201



37 70 85 95

1

1

1

b

Lead (100) Solder Composition, % (100)

Fig. 23.8-Effect of temperature and tin content on the reaction rates of lead-tin solders with copper and brass (Ref. 21) (Test data reported in U.S. customary units)


Physical and Mechanical Properties of Solder and Soldered Joints1 143 mm

0.50 1.01 1.52 2.03 2.54 0.025 1 .o I I I I 1 I I I

850 F

5 c v)

2000

Volume per unit area, inches

Fig. 23.9-Influence of volume of solder on the reaction of copper alloy no. 260 with 70% lead- 30% tin (Ref.21)

- 2 0 0 0 0 6

- - 10 O00

Fig. 23.10-Effect of joint spacing on the shear strength of copper soldered with 56% tin-44% lead alloy and zinc chloride flux (Ref.22)


IU/SOLDERING MANUAL

Table 23.15-Torsional shear strength of soldered copper *

Sn Pb Sb Ag MPa psi 100 - - - 47 6880 50 50 - - 52 7580 63 37 - - 55 8000 40 60 - - 57 8280 95 - 5 - 76 I I 080

- - 5 73 10 610 - 98 - 2 30 4420

Solder, % by wt. Torsional shear strength,

. 95

*Copper rods 20 mm (% in.) in diameter were butted together and joined with solder in a clearance of 0.13 mm (0.005 in.) (Ref. 5)

REFERENCES

1. Greenfield, L.T., and Forrester, P.G. The properties of tin alloys. Tin Research Insti- tute, Publication 155.

2. Baker, W.A. 1939. Creep properties of soft solder and soft soldered joints. J . insfiture of metals: 65.

3. American Society for Metais. 1961. Metals handbook. Ist ed.

4. Latin, A. 1946. Capillary flow in the soldering process and some measurements of the penetration coefficients of soft solders. J . Institute of Metals: 72.

5. Lead Industries Association. 1952. Lead in modern industry.

6. Christian, J.L., and Wilson, J.F. Tensile and shear properties of several solders ar cryogenic temperatures. Society of Auto- motive Engineers, Publication 595E.

7. Nightingale, S. J.,, and Hudson, O. F. 1942. Tin solders: a modern study of the properties of tin solders and soldered joints. British Non-Ferrous Metals Research Association.

8. American Smelting and Refining Co. 1961. SoldeF-its natiire, properties and uses.

9. Hansen, M. 1958, Constitution of binary alloys, New York: McGraw-Hill.

10. McKeown, J. 1948. Properties of soft solders and soldered joints. British Non- Ferrous Metals Research Association, Monograph 5.

11. American Smelting and Refining Co. 1962. ASARCOLo fusible alloys.

12. Maupin, A.R., and Swanger, W.H. 1940. Strength of soft-solderedjoints in copper tubing. NBS Report BMS 58, September.

13. Christian, J . L. 1963. Design criteria for solders in cryogenic environment. Elec- trotechnology 7 1, 6: 109- I i 2.

14. Maupin, A.R., and Swanger, W.H. 1942. Strength of sleeve joints in copper tubing made with various lead-base solders. NBS Report BMS 83, May 5.

15. Zurn, H., and Nesse, T. 1966. Contribution to the long-time test behavior of soldered joints made with tin solders at room temperature. Schweissen and Schneiden 18:2- 10, January.

16. Miller, V.R., Schwaneke, A. E., and Jan- sen, J. W. 1967. Test for tin-lead solders and solder joints. U . S . Department of Interior,

- Bureau of Mines Report of Investigations 6963.

17. Beal, R.E. 1969. How soldering process variables affect joint strengrh. CDA Report 80419, August.

18. Rhines, F.N., and Anderson, W.A. 1941. Substitute solders. Metals and alloys, November: 704-7 1 1.

19. Howes, M;A.H., and Saperstein, Z.P. 1968. Mechanical properties of soldered

joints in copper alloys. CDA Report 80118, June.

20. Unsworth, D. A., and MacKay, C. A. 1972. A preliminary report on growth of compound layers on various metal bases plated with tin and tin alloys. CDA-ASM Conference on Copper, October 16-19, 1972, Cleveland, Ohio.

21. Howes, M. A. H., and Saperstein, Z. P. 1967. The reaction of tin-lead solders with copper alloys. CDA Report 80417, Sep- tember.

22. Nightingale, S . J . , and Hudson, O.F. 1942. Tin solders. British Non-Ferrous Metals Re- search Association.

i


aws sm hdbk 2nd ed 1977 soldering manual

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