Ultra high reliable lead free alloy to meet high reliability requirement

(90iSC)

Henkel Loctite Corporation

AE Adhesive Electronics

South China

Technical Engineer

Forrest Lin

Cell Phone: + 86 13923738177

Email: forrest.lin@henkel.com

August 27, 20142

Agenda

• Background

• Alloy research

• Theory

• Element selection

• Optimization

• Alloy property

• Physical property

• Reliability

• Questions

• Summary

August 27, 20143

Background

• Electronics industry implemented lead free, lead and lead alloy

forbidden

• Traditional lead free material SAC alloy facing challenges at high

reliable field, such as, aerospace, military , medical and automotive

etc..

August 27, 20144

Background continued

• As professional supplier Henkel Loctite fully recognized these issues

• From 2006, partner with customers, material suppliers and academy

together developing the new alloy.

• Definition new alloy CTQ

• Lead free

• Can withstand continuous 150 + Celsius

• Bear ultra high thermal shock (-55 ~ 150 Celsius)

• Reflow peak lower than 230 Celsius

• Meet ROHS

August 27, 20145

Partners

• Initiative • Siemens Berlin (central lab)

• Academy

• University of Bayreuth

• Fraunhofer inst. IZM

• Industrial customers

• Siemens

• Bosch

• Motorola

• Suppliers

• Henkel (Multicore)

• Stannol

• Cookson (Alpha Metals)

• Seho

• Infineon (Munich)

• TI (Munich)

• Epcos (Munich)

• Ruwel

August 27, 20146

Research

August 27, 20147

Theory

.constN plcf (Coffin/Manson)

pl = pl = pl reliability

SnAgCu 90iSCSnPb(Ag)

120°C 150°C80°C

equal cycles to failure N f

Hypothesis: Reducing plastic strain per cycle pl by increasing creep

resistance will increase cycles to failure N f

August 27, 20148

Alloy selection

Improving the creep strenth

Solid solution hardening

Disperse solution hardening

Grain refinement

Element selection

Bi Solid solution hardening, lower the

melting point.

Sb Solid solution hardening, increase

the alloy melting point.

Ni Disperse solution hardening

Elements RejectedIn Cost, slight toxicity

Cs toxic

Te highly toxic, Tm

Ce toxic, Eutectic 220 °C

Ba Compounds toxic, Tm

Fe Tm

August 27, 20149

Optimization

• Compression creep test

• Cylindrical samples

• 6mm diameter

• 9mm height

• Temperature range: - 40C to 175C

• Strain rates: 10-1 to 10-4 s-1

• Creep stress σ (N/mm2 plateau stress) is measured as a function of

strain rate

• Exponent n is slope in log-log plot

August 27, 201410

Optimization

True Stress:

1w

True Strain:

)1ln( w

Different alloy creep property

0

40

80

120

160

0 40 80 120

wahre Dehnung [%]

wa

hre

Sp

an

nu

ng

[N

/mm

²]

SAC SAC+Ni0,2

SAC+Sb5 SAC+Bi8

13105,5 s

T = 25 °C

K: Creep stress

(SAC=SnAg3.8Cu0.7)

Tru

e S

tres

s

True Strain

August 27, 201411

Optimization

• Different alloy creep property

Ambient

]/[ mmN

][ 1s

150C

0,0001

0,001

0,01

0,1

1

10 100 300

SnPb n=9

SAC n=10

6-part n=13

10 100

0,0001

0,001

0,01

0,1

1

5

SnPb n=5

SAC n=7

6-part n=7][ 1s

]/[ mmN

(SAC=SnAg3.8Cu0.7,

6 part = SAC+Bi3Sb1.5Ni0.2)

August 27, 201412

Optimization

80

100

120

140

160

180

180 200 220 240 260 280

Soldering temperature [°C] (Wetting tests)

Maxim

um

op

era

tin

g t

em

pera

ture

[°

C]

(Cre

ep

resis

tan

ce)

SnPb37

SAC

SAC+Ni0,2

SAC+Sb2,5

SAC+Sb3,75

SAC+Sb5

SAC+Bi4

SAC+Bi6

SAC+Bi8

SAC

+Bi+Sb+Ni

SAC+Bi+Sb+Ni

SnPb37

SnAg3,8Cu0,7Bi-addition

Ni-addition

Sb-addition

• Different alloy with different melting point：

August 27, 201413

Optimization

• 90iSC melting point range within 209 – 218℃.

-1.6

-1.2

-0.8

-0.4

0.0

150 175 200 225 250

Temperature [°C]

DS

C-S

ign

al

[mW

/mg

]

SnAg3,8Cu0,7

SnAgCu+Bi+Sb+Ni

Tsol = 217 °C

Tsol = 209 °C

Heating rate: 10 K/min

Potential for lowered reflow

temperature?

+ Thermal load component /PCB

+ Interface properties

90iSC Alloy Composition Solution: SnAg3.8Cu0.7Bi3Sb1.4Ni0.15

Real running DSC

August 27, 201414

August 27, 201415

United States of America Patent

August 27, 201416

Alloy Performance

August 27, 201417

Physical property

• Alloy melting point range from 209 Celsius to 218 Celsius

• Other properties close to SAC 387

August 27, 201418

Metallergy

Structure of Standard lead-

free solder (SnAg3,8Cu0,7)

Sn-Matrix

Ag3Sn

Cu6Sn5

Structure of 6 component solder

(SnAgCu+Bi+Sb+Ni)

Sn-Matrix

(Sb,Bi)

Ag3Sn

(Cu,Ni)6Sn5

August 27, 201419

SEM

Structure of 6-part alloy

(SnAgCu+Bi+Sb+Ni)

Sn-Matrix

(Sb,Bi)

Ag3Sn

(Cu,Ni)6Sn5

Ag3SnBi

Ag3Sn

Bi

1 µm

10 µm

2 µm

20 µm

August 27, 201420

Reliability testing

August 27, 201421

90iSC, SAC387 and SN63 Thermal cycling

40 Chip-components from CR0402 -

CR2512 per Board, no failures on

TO263, QFP and SO16

TBG4

Electronical failure with thermal cycle

August 27, 201422

90iSC，SAC387 and SN63 thermal cycling comparison

Structure after

1000 Cycles

SnPb

SnAgCu

Innolot

(90iSC)

micro structure after 1k cycle

90iSC Solder SEM

August 27, 201423

90iSC Solder SEM

August 27, 201424

90iSC Solder SEM

August 27, 201425

90iSC EDX

August 27, 201426

90iSC IMC by EDX SEM Element Image

August 27, 201427

90iSC IMC EDX

August 27, 201428

Alloy Element EDX Quantification

August 27, 201429

Alloy micro shape and Angular

August 27, 201430

August 27, 201431

90iSC , SAC387 and SN63 Thermal cycling

Shear strength

1206 resistor

TBG1 / TCT –40/+125°C Solder alloy

August 27, 201432

90iSC and SAC387 Shear strength

Example: 0201 Chip resistor

Shows that 90iSC

alloy at –40 +150C

is equivalent to SAC

at –40 to +125C

Reliability

Hypothesis

Sh

ea

r S

tren

gth

90iSC solder

SAC+Bi3Sb1.5Ni0.2

August 27, 201433

Vibration testing

August 27, 201434

90iSC and SAC387 Vibration testing

Failure characteristics in vibration testing with/without thermal cycling (TCT), 0603 resistor

SAC alloy,

0 temperature cycles

90iSC alloy,

0 temperature cycles

SAC alloy,

500 temperature cycles

90iSC alloy,

500 temperature cycles

August 27, 201435

Vibration testing

Table vibrates vertically. Inertia

gives alternating stress in joint

Solder joints in a copper rod

clamped into a stainless steel

holder

Source: N. Barry PhD thesis

(Goodrich, Birmingham Univ.)

August 27, 201436

Vibration testing

Source: N. Barry PhD thesis

(Goodrich, Birmingham Univ.)

Vibration testing 2 FEA

August 27, 201437

August 27, 201438

Vibration test result

90iSC performs

similarly to SnPb

Clearly outperforms

SAC 305 & SnCu (Sn100C)

From Nathan Barry PhD

Thesis “Lead-free solders for

high-reliability applications:

high-cycle fatigue studies"

(Metallurgy and Materials

Dept, University of

Birmingham, October 2008).

Raw data

August 27, 201439

August 27, 201440

August 27, 201441

Drop test

August 27, 201442

Drop test result

August 27, 201443

Drop test result

OSP NiAu Combined

August 27, 201444

X-ray Analysis

Cu OSP / Voiding

QFN SO20

August 27, 201445

X-ray Analysis

Cu OSP / Voiding

CC1206 CR1206

August 27, 201446

Issues

• 90iSC alloy not compatible with Tin-lead surface finish of PCB and

component

• SnPbBi easily form low temperature eutectic (98C)

• 90iSC ONLY suitable for lead free process

• 90iSC slight lower spreading capability, solder wire difficult to

manufacture however Henkel developed well the halogen free – 0

halogen 90iSC C400 solder wire

August 27, 201447

Summary

• Within -40 to 150 Celsius thermal cycling found, 90iSC alloy

obviously better than SAC387

• Found after 500 cycling of vibration, 90iSC obviously better than

SAC387

• Very close performance at drop testing

• 90iSC uncompatible with tin lead surface finish and component metal

Thank you!