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Introduction to Electronics Assembly 1

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Introduction

Components

Interconnections

Electronics Assembly

Industry Overview

Electrostatic Discharge

Assembly Processes

Incoming Inspection

Through-Hole Assembly

Automatic Insertion

Manual Insertion

Wave Soldering

Hand Soldering

Surface Mount Assembly

Solder Paste Application

Component Placement

Reflow Soldering

Adhesive Application

Cleaning

Electrical Test

Rework and Repair

Conformal Coating

Final System Assembly

GLOSSARY

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Introduction to Electronics Assembly 2 Introduction to Electronics Assembly 3

Introduction

Look around. Electronic prod-ucts are everywhere. They’re inour homes, offices, schools,hospitals, airports, banks andstores. And year after year thereare innovations - products getbetter and better, they’re easierto use and their value increasesas they do more for the same orlower cost.

Personal computers are a per-fect example. Ten years agothey were priced high and ranslow. Now they’re a lot fasterand cheaper.

If you were to take the cover offan electronic product you’d seecomponents and interconnec-tions.

An inside view of a typicalelectronic device.

An ATM machine is an electronic device we all use.

A laptop and cell phone atwork in the field.

IntroductiontoElectronics Assembly

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Interconnections

The interconnections are thepathways where electricityflows between components.These pathways are almostalways printed circuit boards, orprinted wiring boards. These aresometimes referred to as PCBsor PWBs. The printed boards arebasically a pattern of electronicconductors that are formed onan insulating base material, orlaminate.

Electronics Assembly

Electronics assembly is theprocess of attaching componentleads or terminations to thelands, or conductors, on the cir-cuit board, and then solderingthem to make both mechanicaland electrical connections.These circuit board assembliesare at the heart of our electron-ic products - allowing the prod-ucts to be both complex andcompact.

Industry Overview

Electronics assembly is per-formed by Original EquipmentManufacturers (OEMs), and bymembers of the ElectronicsManufacturing Services Industry,also known as EMS providers.

OEMs are companies thatdesign and manufacture theirown electronic products.Usually these companies do allor some of the electronics

A printed circuit board with no components.

A typical Electronics Assembly Facility.

A circuit board assembly isinserted into a metal chassis.

Components

Components are devices thatalter the flow of electricity. Themajority of electronic compo-nents are semiconductors -meaning they have propertiesof both conductors and insula-tors. A conductor is ametal/material that carries elec-trical signals. An insulator is anymaterial that has a high resist-ance to the flow of electricalcurrent.

Resistors and capacitors arecalled passive components.That means the basic functionof these components does notchange when they receive a sig-nal. Resistors slow down, orresist the flow of current to pro-vide the proper amount.Capacitors store an electricalcharge for a period of time, thendischarge it over a longer orshorter period of time -depending on the requirementsof the circuit.

Transistors, diodes and integrat-ed circuits, or ICs, are calledactive components. That meansthe basic function of these com-ponents will change when theyreceive a signal. ICs can storeinformation, perform calcula-tions and move the informationaround. A microprocessor chipthat contains millions of transis -tors and diodes is an exampleof a very sophisticated IC.

Training References:IPC-CD-18 Component ID Training (CD)

IPC-DRM-18 Component ID Desk Reference Manual

Components prior to assembly onto circuit board.

An IC in a Dual-In-LinePackage.

A capacitor and resistor of theThrough-hole variety.

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tronics industry as a wholeemploys more people than theaerospace, steel and automo-tive industries combined.

Electrostatic Discharge

One of the critical issues in elec-tronics assembly is control ofelectrostatic discharge, or ESD.ESD occurs when static electric-ity from your body or a chargedsource comes in contact withand is discharged into an elec-tronic component. This electric-ity can degrade or destroy theoperation of many types ofcomponents. There are a widevariety of materials and tech-niques to eliminate the build upand discharge of static electricity.

Training References:IPC-VT-19 ESD Control (Video)

IPC-CD-19 ESD Control (CD-ROM)

Technical References:IPC-A-610 Acceptability of Electronic Assemblies

Assembly Processes

There are two primary cate-gories of electronic compo-nents; through-hole and surfacemount. Through-hole compo-nents have leads that are insert-ed through the holes in the cir-cuit board. Surface mount com-ponents have leads or termina-tions that attach directly ontothe lands on the surface of theboard. A third category of com-ponents are those actuallyembedded in or on the surface

An ESD sensitive component getting “ZAPPED” by an operatornot wearing his grounding strap.

A component placementworkstation.

This board has through-hole componentson the left, and smaller surface mount

components on the right.

assembly work themselves. Fora variety of reasons, there aretimes when OEMs send out allor some of their design andassembly to EMS providers.EMS providers are differentiatedfrom OEMs in that they don’tproduce their own products.They provide assembly andsometimes design services.

Before the assembly processcan begin the components andcircuit boards must be pro-cured. Then these circuit boardsand components go throughspecific manufacturing process-es to create the solderedassemblies. After processing,the assemblies are tested. Theassembler, whether OEM orEMS provider, usually performsany rework and repair that’sneeded. Occasionally, an EMSprovider also performs the finalsystem assembly, as well as sys-tem and reliability testing.

Sometimes the OEM will haveassembly operations that notonly perform circuit boardassembly, test and systemassembly for their own prod-ucts, but also accept assemblywork from other OEMs. Thatmakes the company both anOEM and an EMS provider.

In recent years there has beensignificant growth in the EMSindustry. The industry plays adynamic role in today’s informa-tion and entertainment-orient-ed world. It also provides manyjobs and enjoys exciting careeropportunities. In fact, the elec-

Assembly design is a complex process.

A training session for EMSProviders.

Component insertion is sometimes done by hand.

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required. Incoming inspection isa method of verifying that orderrequirements have been met.This includes the correct num-ber and type of products, thecondition of the products uponreceipt and the function ofthose products.

Many companies use a systemof certified suppliers to mini -mize incoming inspection —sometimes called dock to stock.In this system, the suppliertakes responsibility for the qual -ity of the materials being pur-chased by the customer by thor-oughly inspecting and testingthe circuit boards and compo-nents before they are shipped.This means that when thematerials arrive on the loadingdock at the customer’s facilities,they can be left in the packag-ing; the associated paperworkchecked for part number andrevision level; and sent to thestockroom. There is no incom-ing inspection or testing neededfor verification of the customer.

When more detailed incominginspection is required, there area number of characteristics thatmay be checked by inspection.For example, a sample of circuitboards may be checked forproper dimensions, hole pat-terns and sizes, solder maskand solderability, and marking.A shipment of electronic com-ponents could be checked forcount, condition, marking andsolderability.

Checking board dimensionsduring incoming inspection.

Training References:IPC- VT-57 Stockroom Materials - Storage and Distribution (Video)

IPC- CD-63 Bare Board Acceptability (CD)

Technical References:IPC/EIA J-STD-002 Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires

ANSI/J-STD-003 Solderability Tests for Printed Boards

IPC-6011 Generic Performance Specification for Printed Boards

IPC-6012 Qualification and Performance Specification for Rigid Printed Boards

IPC-A-600 Acceptability of Printed BoardsIPC- DRM-18 Component Identification Desk Reference Manual

Verifying components duringincoming inspection.

of a printed wiring board. Aprinted wiring board (PWB)with embedded components iscalled a printed circuit board(PCB).

This reference manual will dis -cuss many of the through-holeand surface mount processesinvolved in electronics assem-bly. (Embedded components inPCBs are not discussed in thisdocument because they arepart of the board fabricationprocess.) The overall assemblyprocesses includes incominginspection and preparation ofcircuit boards and components;automatic component insertionand placement; manual inser-tion of components; wave andreflow soldering; hand solder-ing; assembly cleaning; electri -cal test; rework and repair; con-formal coating and final systemassembly.

Training References:IPC-VT-32 Introduction to Electronics Assembly (Video)

IPC-VT-53 Electronics Assembly Industry Overview (Video)

IPC-VT-24 Handling in Electronics Assembly (Video)

Technical References:IPC-T-50 Terms and Definitions for Interconnecting and Packaging Electronic Circuits

IPC-EIA J-STD-001 Requirements For Soldered Electrical And Electronic Assemblies

Incoming Inspection

Electronic components and cir-cuit boards need to function as

Board inspection after the solder paste printing operation.

Certified supplier checking componentsprior to shipment to assembler.

Incoming inspection of boards at theassembler.

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DIP inserters have universal cir-cuit board fixtures that positionthe board to exact locationsunderneath the insertion head.The tubes containing DIP com-ponents are loaded in specificfeeder locations. The compo-nents are picked up from theproper feeder, and are posi -tioned in the insertion head.The machine is programmed sothe fixture moves the boardunder the insertion head andthe leads are inserted into thecorresponding holes in the cir-cuit board.

Axial and radial inserters oper-ate a little differently than theDIP inserters. Axial and radialcomponents are supplied ontape and reel. A sequencer isused to cut and retape the com-ponents in a specific order, orsequence, for automatic inser-tion. Sometimes the sequenceris part of the axial or radialinserter. Sometimes thesequencer is a separatemachine. Once the compo-nents are sequenced, they aremoved by metal feeders to theinsertion head. A driver withforming fingers pre-forms theleads, and places them into theholes on the circuit board. Onetype of process uses toolingunderneath the board to cut theleads and bend them slightly.The bend, or clinch, allows thecomponent to be mechanicallyretained during subsequentoperations.

Operator checking newly tapedcomponents on a sequencer.

Axial inserter for through-holecomponents.

Sequencer close up view.

Through-Hole Assembly

Through-hole assembly basical -ly consists of component inser-tion and soldering.

Through-hole components,such as ICs, often come in dual-in-line packages, or DIPs. Theyusually arrive from the supplierin anti-static plastic tubes.

Small axial-lead components,such as resistors, capacitors anddiodes, are usually packaged ontape and reel for automaticsequencing and insertion.Some through-hole compo-nents such as transistors arepackaged in bags or boxes andmay require lead forming andmanual insertion.

Training References:IPC-VT-27 Introduction to Through-Hole Assembly (Video)

Technical References:IPC-CM-770 Component Mounting Guidelines for Printed Boards

IPC-DRM-40 Through-Hole Solder Joint Evaluation Desk Reference Manual

Automatic Insertion

Automatic insertion machinesmake it possible to insert manycomponents into the holes of acircuit board in a very shorttime. There are three types ofautomatic insertion machines -DIP inserters, axial inserters andradial inserters.

DIP components in static -proof tubes.

A DIP componentinsertion machine.

Axial components come packaged on tape and reels.

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Fluxing is the process of apply-ing flux to the assembly. Flux ismade up of a combination ofchemicals. The purpose of theflux is to remove oxides andother contaminants from thesurfaces of the metal parts to besoldered. Oxides begin to formon the component leads andthrough-hole lands wheneverthese metals come in contactwith air. If these oxides, or con-taminants, are not removed thesolder won’t form a reliablebond between the leads andthrough-hole lands. The twomost common methods of fluxapplication are foam and spray.

The next part of the wave sol -dering process is preheating.During preheating, the entireassembly is slowly heated to atemperature that will activatethe flux. This allows the flux toreact with and condition themetals for the soldering opera-tion. Preheating also reducesthermal shock when the assem-bly contacts molten solder inthe next part. Thermal shockcan cause damage to the PWBand components.

After preheating, molten solderis delivered to the underside ofthe assembly in the form of awave. As the bottom of theassembly passes over the crestof the wave, the solder is forcedup through the holes in a wick-ing or capillary action. Wavesoldering completes the electri -cal and mechanical connectionsof the components to the circuitboard, and allows thousands ofsolder connections to be madein a very short time.

Preheating activates the fluxprior to soldering.

Training References:IPC-VT-47 Wave Soldering (Video)

Technical References:IPC-EIA J-STD-001 Requirements For Soldered Electrical And Electronic Assemblies

IPC-EIA J-STD-004 Requirements For Soldering Fluxes

IPC-EIA J-STD-006 Requirements For Electronic Grade Solder Alloys For Fluxed And Non-Fluxed Solid Solders For Electronic Soldering Applications

The assembly passes over awave of molten solder.

Manual Insertion

There are two situations thatrequire manual insertion ofcomponents. First, some com-ponents, because of their sizeand shape, simply do not fit inthe automatic insertionmachines. The second situationoccurs when there are very fewthrough-hole componentsrequired for an assembly. Itbecomes more cost effective toinsert them by hand.

The leads of many of these com-ponents need to be first pre-formed to the proper position formanual insertion. After preform-ing, the components are insert-ed into the correct holes on theboard, and the leads maytrimmed and clinched.

Training References:IPC-VT-44 Component Preparation and Manual Insertion (Video)


IPC-A-610 Acceptability of Electronic Assemblies

Wave Soldering

After all through-hole compo-nents have been inserted intothe circuit board, the assemblyis ready for the wave solderingoperation. Wave soldering con-sists of three basic steps - flux-ing, preheating and soldering.Each of these parts of a wavesoldering machine are intercon-nected by a conveyor system.

Manual insertion is used forsome components.

A foam fluxer applies the flux.

Some leads must be bent, or pre-formed, in order to fit in the assembly.

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Training References:IPC-VT-33 Introduction to Surface Mount Assembly (Video)

IPC-VT-71-75 Surface Mount Evaluation Series

Technical References:IPC-TP-1115 Selection and Implementation Strategy for a Low-Residue, No-Clean Process

IPC-DRM-SMT Surface Mount Solder Joint Evaluation Desk Refernce Manual

Solder Paste Application

Solder paste is a mixture of fluxand tiny balls of solder in pasteform. The application of solderpaste is commonly done usinga stencil printing process.Solder paste is pressed throughopenings in a stencil screenonto the corresponding circuitboard lands with a squeegeemade of hard rubber or stain-less steel. The stencil openingsare called apertures. They aredesigned to make sure the rightamount of solder paste isdeposited onto each land. Theapertures must be in perfectalignment with the surfacemount lands.

Training References:IPC-VT-34 Solder Paste Printing IPC-VT-35 Solder Paste Printing Defect Analysis and Prevention (Videos)

Technical References:IPC-7525 Stencil Design Guidelines

IPC/EIA J-STD-005 Requirements for Soldering Pastes

Inspecting a surface mount assemblyafter component placement.

Solder paste printing on a different machine.

The solder paste printingprocess.

Hand Soldering

An assembly may also containodd-form and temperature sen-sitive components such as bat-teries, switches, connectors, orunsealed parts that will have tobe manually inserted and handsoldered after the wave solder-ing operation.

Soldering iron selection, tip sizeand desired heat range shouldbe considered for the work athand. An important factor inhand soldering is solder wireselection.

Training References:IPC-VT-42/43 Hand Soldering IPC-VT-49 The Seven Sins of Hand Soldering

IPC-VT-36 Hand Soldering With Low Residue Fluxes (Videos)

Technical References:IPC-7711 Rework of Electronic Assemblies

IPC/EIA J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies

IPC-A-610 Acceptability Of Electronic Assemblies

Surface Mount Assembly

Surface mount technology isnewer than through-hole tech-nology. Rather than beinginserted through holes in thecircuit board, surface mountcomponent leads sit on landson the surface of the board.Surface mount assembly con-sists of three basic processes -solder paste application, com-ponent placement and reflowsoldering.

Operator at hand solderingworkstation.

Chip component soldered to asurface mount land.

Hand soldering up close.

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Other features of placementmachines are a conveyor sys-tem to transfer circuit boardsinto and out of the machine; atable that keeps the board sta-tionary using vacuum or clamp-ing; pins or fixtures used to sup-port the board on the table; avision system used to verify cor-rect board and component ori -entation; and a computer pro-gram which contains thedescription of the board to beassembled. The program alsospecifies the componentsrequired, their location on theboard in X/Y coordinates, theirorientation and the order inwhich they will be placed.

Sometimes, as with through-hole components, surfacemount components are mount-ed by hand to a board in orderto realize cost benefits whenthe quantity of boards beingassembled is low.

Training References:IPC-VT-39 Surface Mount Component Placement (Video)



Reflow Soldering

After component placement,the surface mount assembliesare ready for reflow soldering.The two most common heatingmethods to reflow the solderare forced convection andinfrared.

A high speed chip shooter at work.

Convection ovens are used toreflow solder paste.

Another type of placement machine.

Component Placement

Once solder paste is properlyapplied to the lands, the circuitboard is typically moved to oneor more automatic placementmachines for component place-ment.

Surface mount components areusually supplied in three differ-ent ways - on tape and reel, intubes or in matrix trays.

Surface mount chip compo-nents, such as resistors andcapacitors, are usually suppliedon perforated tape woundaround a reel. The reel is loadedonto a feeder. The feeder isthen connected to a placementmachine. The high speed place-ment machines for these typesof components are called chipshooters. Chip shooters haverotating turrets with many noz-zles. The turret rotates aroundto the feeder, picks up the com-ponent, orients it correctly andplaces it onto the solder pastecoated lands at 60,000 or morecomponents per hour.

Medium sized surface mountcomponents are usually sup-plied in tubes or on tape andreel. The larger components aregenerally in matrix trays. Slowerpick and place machines haveheads that may be fitted withnozzles of different sizes. Thenozzles pick up the componentfrom the trays, tubes or reels,and accurately place them intothe solder paste on the lands ofthe circuit board.

Inspecting components in a tray.

The pick and place machine.

An operator loading a reelof components on tape

onto the feeder.

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Adhesive Application

There is an additional surfacemount operation that may beused for certain types of assem-blies. In many of today’s dou-ble sided circuit board designs,surface mount chip compo-nents are attached to the sec-ondary, or bottom side of theboard, and a combination oflarge surface mount compo-nents and some through-holecomponents are attached to theprimary, or top side. This com-bination of surface mount andthrough-hole components onthe same circuit board is calleda mixed technology assembly.

The purpose of adhesive appli -cation is to keep the surfacemount components that areplaced on the secondary side ofthe board from falling off beforethey’re securely soldered duringwave soldering.

In this case, the assembly oper-ation would begin with the sur-face mount process from theprimary side of the board. Aftersolder paste printing, the largersurface mount components areplaced in their proper locationson the board. This is followedby reflow soldering.

Next, the board is flipped overand adhesive is applied so thatthe chip components can beplaced and glued onto the sec-ondary side of the circuit board.Adhesive may be applied usingan adhesive dispenser or stencil

Chip components on the secondaryside of the circuit board.

Adhesive dispensing process priorto component placement.

Larger surface mount and somethrough-hole components on theprimary side of the circuit board.

In convection systems, air ornitrogen is heated and blownonto the circuit board to melt orreflow the solder. Infrared usesheat panels that radiate theheat to reflow the solder. Mostmodern reflow solderingmachines use a combination ofthese two heating systems.

The first area inside a reflow sol -dering machine is a preheatzone. Preheating allows the cir-cuit board to be exposed to acontrolled temperature rise. Ifall the required heat wereapplied immediately, the circuitboard and some of the compo-nents might be damaged fromheating up too quickly. The pre-heat operation also causes theflux in the solder paste to acti-vate. As in wave soldering, thisactivation allows the oxides tobe removed from the metal sur-faces. If the assembly is in thepreheat area too long, the fluxmay “burn out” and oxidationwill recur before solder reflow.When this happens proper wet-ting may not occur.

The assembly proceeds by con-veyor to the next heating zoneswhere higher temperaturescause reflow and solder wettingto take place. The final step is acool down zone which may ormay not be augmented by cool-ing fans. Reflow soldering com-pletes the surface mountassembly process.

Training References:IPC-VT-15/16 Reflow Soldering(Video)

Infrared ovens are also usedto reflow solder paste.

The end result, a surface mountedlead soldered onto a land.

A board moves through a pre-heat zone before solder reflow.

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Cleaning

Some companies use no-cleansoldering operations that do notrequire any cleaning process tofollow assembly and soldering.Others require a cleaning oper-ation that removes undesirablecontaminants including any fluxresidues that may be left overfrom the soldering operation.Depending on the type of fluxused, cleaning may be accom-plished using water or a moreactive cleaning agent. If certaintypes of flux residues are notremoved, corrosion and ulti-mately assembly operatingproblems can occur.

Training References:IPC-VT-47 Wave Soldering (Video)

IPC-VT-36 Hand Soldering With Low Residue Fluxes (Video)

Technical References:IPC-TP-1115 Selection and Implementation Strategy for a Low-Resdiue,No-Clean Process

IPC-SC-60 Post Solder Solvent Cleaning Handbook

IPC-SA-61 Post-Solder Semiaqueous Cleaning Handbook

IPC-AC-62 Post-Solder Aqueous Cleaning Handbook

IPC-CH-65 Guidelines for Cleaning of Printed Boards and Assemblies

IPC-9201 Surface Insulation Resistance Handbook

Hand soldering with a low-residue flux.

A No Clean flux label.

The cleaning operation.

printer. The glue dots areapplied between the chip com-ponent lands, rather than onthe lands themselves. If theadhesive were placed on thelands, the components would-n’t be able to be reliably sol-dered to the lands. In otherwords, the adhesive wouldblock the solder.

After adhesive application, thecomponents are positionedusing automated placementequipment. The adhesive isthen cured. Curing allows theglue to achieve its full strength.

Next, the required through-holecomponents are inserted fromthe primary side of the board.The fully assembled circuitboard is then passed through awave solder machine. The sol-der wicks up the holes to solderthe through-hole leads. The sur-face mount chip componentsglued to the bottom side of theboard are also soldered at thistime. This completes the mixedtechnology assembly process.

Training References:IPC-VT-51 Adhesive Application for Surface Mount (Video)

Technical References:IPC-CA-821 General Requirements for Thermally Conductive Adhesives

Applying adhesive using thestencil printing method.

An assembly surfs the solder waveto complete the process.

Placing chip components ontop of adhesive temporarily

holds them in place.

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test electronics are designed tocreate an operational environ-ment for the assembly that’ssimilar to the finished product.For example, a modem assem-bly might be tested to dial upand establish a connection.

Functional test can be per-formed on both the circuitboard assembly and on the fin-ished product. ICT is only doneon the assembly.

When an assembly fails ICT orfunctional test, the error mes-sage is examined and the prob-lem can usually be identified.Sometimes troubleshooting isused to determine which com-ponent or components are fail -ing. Once the problem is identi-fied, the assembly can bereworked and/or repaired.

Training References:IPC-VT-17 Electrical Test in Electronics Assembly (Video)


IPC-7721 Repair and Modification of Printed Boards and Electronic Assemblies

Rework and Repair

Rework involves removing andreplacing defective componentsor correcting defective solderconnections. Repair is donewhen the circuit board lami -nate, conductors or lands aredamaged during the assemblyor rework operations. Reworkand repair methodology may

An assembly passes in-circuit test.

Reworking a bad solder joint.

Troubleshooting a problem.

Electrical Test

Testing usually follows in theassembly process to guaranteethat assemblies work. There aretwo basic categories of testingthat will be described here.These are in-circuit test, or ICT,and functional test.

ICT checks the assembly forunwanted open and short cir-cuits by testing components formanufacturing defects. ICT isperformed on automatic testequipment that uses a bed-of-nails fixture consisting of aseries of spring loaded probesto connect the tester to specificsolder connections and testpoints.

Functional test checks the oper-ation of the entire circuit boardassembly by applying powerand input signals, then checkingthat the output signals are cor-rect. The difference betweenfunctional test and ICT is thatfunctional test doesn’t check aspecific component. It is actual-ly testing a group of compo-nents by testing the differentfunctions, or electronic opera-tions designed into the assem-bly.

One method of functionallytesting the assembly is accom-plished on automatic testequipment. There is usually aspecial connector fixture to gainaccess to the circuitry on theassembly.

The assembly can also be testedon a technician’s bench. Special

Close up view of bed-of-nailstest probes.

A functional bench test workstation.

Using an automated functional test machine.

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Special kits may be required toaccomplish some repairs.

The assembly is re-tested fol -lowing the rework and/or repairoperation.


IPC-7721 Repair and Modification of Printed Boards & Electronic Assemblies

IPC-EIA J-STD-001 Requirements For Soldered Electrical & Electronic Assemblies


Conformal Coating

Some finished assemblies aredestined for operational envi-ronments that are very harshwhen compared to the environ-ment a normal householdassembly will encounter. Theremay be temperature extremes,humidity, corrosive atmosphere,and salt water. These environ-ments may be encountered inapplications such as automotive“under the hood”, aerospace,medical and military. When thisoccurs, there is a need for a pro-tective barrier between theassembly and the environment.These protective barriers arecalled conformal coatings.Conformal coatings have alsobecome necessary on fine-pitchhigh-density circuitry to retardfailures caused by electromigra-tion.

There are a variety of conformalcoatings and each one has spe-

Repair in progress.

Spraying conformal coating.

A conformally-coated assembly.

also be used to incorporatedesign changes for assemblies.

Rework on through-hole andmany surface mount compo-nents may be done using handtools. For through-hole compo-nents, the tools are often just asoldering iron with the propertip installed and a vacuumextractor.

The smaller and more denselypacked surface mount compo-nents have made rework andrepair more difficult. To dealwith this challenge, specializedhand tools have been devel -oped to make surface mountrework more manageable.These hand tools are especiallyeffective in low volume reworkapplications.

Today, there are componentpackage styles that make it vir-tually impossible to performrework operations with handtools. A couple of examplesinclude ultra fine pitch leadedparts and Ball Grid Arrays, orBGAs. The rework requirementsfor these types of componentshave resulted in the develop-ment of “rework stations.”Rework stations are self-con-tained systems that providecontrolled removal and replace-ment of these types of surfacemount components. They arealso effective for high volumerework applications.

Repair involves using specialtools and procedures to correctdamaged lands, conductors andcircuit board laminate material.

A rework hand tool removes the component.

Training References:IPC- VT-97A/B Land and Conductor Repair for Electronic Assemblies

IPC- VT-97C Plated-Through Hole RepairIPC- VT-41 Through-Hole ReworkIPC- VT-91 Intro to Surface Mount ReworkIPC- VT-92 Rework of Surface Mount Chip Components

IPC- VT-93 Gull Wing ReworkIPC- VT-94 Rework of J-Lead ComponentsIPC- VT-95 Surface Mount Rework Stations

IPC- VT-96 Ball Grid Array Rework(All Videos)

Aligning component leads to circuit board lands on a rework station.

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A simple version of a stress testis to turn a product on and offmany times, and to verify it stilloperates properly. A more com-prehensive reliability test is toplace the assemblies in a ther-mal chamber for a period oftime. During this time, tempera-tures are repeatedly raised andlowered at a controlled rate.We call this type of stress testing“environmental stress screen-ing” or ESS.

After the assemblies areremoved from the oven, theyare given a functional test.Passing the test indicates theassembly should work reliablyfor many years under normaloperating conditions. The prod-ucts are then shipped to cus-tomers and distributors.

Training References:IPC-VT-46 Mechanical Assembly (Video)

IPC-VT-17 Electrical Test in Electronics Assembly (Video)

The electronics assembly indus-try has grown rapidly during thepast decade. New technologieshave allowed products tobecome more functional, fasterand more compact, as well asless expensive. Innovation andquality keep electronics assem-bly successful in an increasinglycompetitive world market.

An operator loads assembliesin a thermal chamber for a

burn-in reliability test.

Rapid growth of the EMS industry.

One last functional test is doneto verify assembly reliability.

cific characteristics. Once theproper coating is selected forthe intended use, it can beapplied by brush, spray, dip,curtain coat, or vacuum deposi -tion. It is important to makesure that all other process stepshave been completed prior toconformal coating. Once theconformal coating has beenapplied, it will prevent normalin-circuit test using a bed ofnails tester, and will make itmuch more difficult to modifythe assembly in any way.

Final System Assembly

Assemblies that pass ICT andfunctional test can be installedin the final system. This phaseof the overall assembly processis called final system assembly,or box build. During box build,all of the hardware required forthe finished product is installedinto the equipment chassis. Thisincludes racks, wire harnesses,power supplies, heat sinks, fans,front panel switches and dis-plays, connectors - and the elec-tronic assemblies.

The assembled product is givena final functional, or system testto make sure it is operatingproperly. Companies often usereliability, or stress testing toweed out components that mayfail after the first few hours ofoperation. This type of testing issometimes part of a burn-inprocess and usually guaranteesa higher level of reliability forthe product.

Technical References:IPC-EIA J-STD-001 Requirements For Soldered Electrical & Electronic Assemblies

IPC-A-610 Acceptability Of Electronic AssembliesIPC-CC-830 Qualification and Performance of Electrical Insulating Compound for Printed Board AssembliesIPC-TR-476A Electro-Chemical Migration: Electrically Induced Failures in Printed Wiring Assemblies

Performing final test on a computerized telephone system.

Connecting a ribbon cableduring a box build.

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FORCED CONVECTION: Reflow soldering using forced hot air or inert gas(nitrogen) as the primary source of heat.

FUNCTIONAL TEST: A test that analyzes the unit under test as a completefunctional entity by applying inputs and sensing outputs.

HARDWARE: The components that go into the final system during box build.Includes circuit board assemblies, card racks, power supplies, wire harness-es, heat sinks. fans, switches, connectors - and the materials used to mountthem.

IN-CIRCUIT TEST: The application of test signals directly to a device’s inputterminals and sensing the results directly from the device’s output terminals.

INFRARED REFLOW: Reflow soldering using infrared heating as the primarysource of energy.

INSULATOR: A material with a high resistance to the flow of electrical cur-rent.

INTEGRATED CIRCUIT: A combination of inseparable associated circuit ele-ments that are formed in place and interconnected on or within a single basematerial to perform a microcircuit function.

LAMINATE: The base material of a circuit board upon which a conductivepattern is formed.

LANDS: The portion of conductive pattern on a circuit board designed for theconnection and/or attachment of components.

LEAD: A length of insulated or uninsulated metallic conductor that is usedfor electrical interconnections.

LOW RESIDUE FLUX: Flux that uses different kinds of chemicals than in tradition-al fluxes. This type of flux becomes inert in the reflow process and can be left onan assembly after soldering without causing deterioration.

MICROPROCESSOR CHIP: A sophisticated integrated circuit that performsalmost all of the high speed functions in a computer.

MIXED TECHNOLOGY ASSEMBLY:An assembly that has both surface mountand through-hole components.

NO-CLEAN: A soldering process that uses low residue fluxes so the assem-bly will not need to be cleaned after soldering.

ACTIVE COMPONENT: An electronic component whose basic function is tomodify an applied signal . (This includes diodes, transistors and integrated cir-cuits that are used for the rectification, amplification, switching, etc., of ana-log or digital circuits in either monolithic or hybrid form.)

APERTURES: The openings in a stencil or screen that correspond to the landpatterns of a circuit board. Solder paste or adhesive is pushed through theseopenings with a squeegee during printing.

AXIAL COMPONENTS: Through-hole components such as resistors and capaci-tors that have lead wire extending from the component along its longitudinal axis.

BED-OF-NAILS FIXTURE: A test fixture consisting of a frame and a holdercontaining a field of spring-loaded pins that make electrical contact with aplanar test object.

BOX BUILD: Final assembly of a system. Includes attaching all the neededhardware, along with the circuit board assemblies into a box or chassis.

CHIP COMPONENTS: Very small surface mount resistors and capacitors.

CHIP SHOOTER: A high-speed placement machine that mounts surfacemount chip components to a circuit board assembly.

CONDUCTOR: A metal, such as copper, or metallic based material, such asconductive ink or tape that carries or conducts electrical signals.

DIP (Dual In-Line Package): A basically rectangular component package thathas a row of leads extending from each of the longer sides of its body thatare formed at right angles to a plane that is parallel to the base of its body.

EMSI (Electronics Manufacturing Services Industry): Companies that per-form electronics assembly for Original Equipment Manufacturers.

ESD (Electrostatic Discharge):Occurs when static electricity from a body orobject comes in contact with and is discharged into an electronic component.

FLUX: A chemically and physically active compound that, when heated, pro-motes the wetting of a base metal surface by molten solder by removingminor surface oxidation and other surface films and by protecting the sur-faces from reoxidation during a soldering operation.

GLOSSARY

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REWORK: The act of reprocessing non-complying articles, through the use oforiginal or alternate equivalent processing, in a manner that assures compli -ance of the article with applicable drawings or specifications.

SECONDARY SIDE: The side on an assembly that is opposite the primary side(it is usually the same as the “solder-source side” on through-hole mountingtechnology).

SEQUENCER: A machine that cuts and retapes axial or radial components ina specific order for automatic insertion.

SOLDER: An alloy that melts at lower temperatures than any of the basemetals and is used to join or seal metals with higher melting points.

SOLDERABILITY: The ability of a metal to be wetted by molten solder.

SOLDER PASTE: Finely divided particles of solder, with additives to promotewetting and to control viscosity, tackiness, slumping, drying rate, etc., that aresuspended in a cream flux.

STENCIL PRINTING: The act of pressing solder paste through openings in aa stencil or screen onto corresponding lands on a circuit board. The pressingis done with a squeegee.

STRESS TESTING: Exposing an assembly to controlled extreme operatingconditions to ensure reliability before shipping the product.

SURFACE MOUNT: A technology that uses components having leads or ter-minations that attach directly onto lands on the surface of the PWB.

THROUGH-HOLE: A technology that uses components having leads that areinserted through holes in the PWB.

WAVE SOLDERING: A process wherein an assembled printed board isbrought in contact with the surface of a continuously flowing and circulatingfountain of solder.

WETTING: The formation of a relatively uniform, smooth, unbroken andadherent film of solder to a basis metal.

WICKING: The capillary movement of solder between metal surfaces, suchas strands of a wire.

OPEN CIRCUIT: A fault that occurs when two electrically connected pointsbecome separated.

OEM (Original Equipment Manufacturer): A company that designs andmanufactures its own electronic products.

OXIDES: The contamination that forms on component leads and circuit boardlands whenever these metals come in contact with the oxygen in the air.

PASSIVE COMPONENT: A discrete electronic device whose basic functiondoes not change while it processes an applied signal. (Includes componentssuch as resistors and capacitors.)

PATHWAY: A single conductive path in a conductor pattern.

PREFORMING LEADS: Bending the leads of a component to fit into theholes in a circuit board.

PREHEATING: The raising of the temperature of a material(s) above theambient temperature in order to reduce the thermal shock and to influencethe dwell time during subsequent elevated temperature processing.

PRIMARY SIDE: The side of an assembly that usually contains the mostcomplex or the most number of components.

PCB (Printed Circuit Board): A printed wiring board that provides point-to-point connections in a predetermined arrangement on a common base andthat has embedded components.

PWB (Printed Wiring Board): A printed board that provides point-to-pointconnections in a predetermined arrangement on a common base and doesnot have any embedded components.

RADIAL COMPONENTS: Components that have two or more leads extend-ing from the same face of the component, as opposed to axial componentswhich have them coming out opposite sides.

REFLOW SOLDERING: The joining of surfaces that have been tinned and/orhave solder between them, placing them together, heating them until the sol-der flows, and allowing the surface and the solder to cool in the joined position.

REPAIR: The act of restoring the functional capability of a defective article ina manner that precludes compliance of the article with original drawings orspecifications.

RESISTANCE: The restriction of the flow of electricity.

Technical References: IPC-T-50 Terms and Definitions for Interconnecting and Packaging Electronic Circuits

IPC-DRM-18 Component Identification Desk Reference Manual

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