are you ready for lead-free electronics?

884 IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES, VOL. 28, NO. 4, DECEMBER 2005

Open Forum_______________________________________________________________________________

Are You Ready for Lead-Free Electronics?

Valérie Eveloy, Sanka Ganesan, Member, IEEE,Yuki Fukuda, Member, IEEE, Ji Wu, Member, IEEE, and

Michael G. Pecht, Fellow, IEEE

Abstract—An expedient transition to lead-free electronics has becomenecessary for most electronics industry sectors, considering the Europeandirectives1 other possible legislative requirements, and market forces [1],[2]. In fact, the consequences of not meeting the European July 2006 dead-line for transition to lead-free electronics may translate into global marketlosses.

Considering that lead-based electronics have been in use for over 40years, the adoption of lead-free technology represents a dramatic change.The industry is being asked to adopt different electronic soldering mate-rials [3], component termination metallurgies, and printed circuit boardfinishes. This challenge is accompanied by the need to requalify compo-nent-board assembly and rework processes, as well as implement test,inspection, and documentation procedures. In addition, lead-free tech-nology is associated with increased materials, design, and manufacturingcosts.2 The use of lead-free materials and processes has also promptednew reliability concerns [1], as a result of different alloy metallurgies andhigher assembly process temperatures relative to tin–lead soldering.

This paper provides guidance to efficiently implement the lead-free tran-sition process that accounts for the company’s market share, associatedexemptions, technological feasibility, product reliability requirements, andcost. Lead-free compliance, part and supplier selection, manufacturing,and education and training are addressed. The guidance is presented inthe form of answers to key questions.

Index Terms—Lead-free, RoHS, tin–lead soldering.

I. WHAT IS THE VALUE FOR US TO PROVIDE A LEAD-FREE

PRODUCT TO OUR CUSTOMER(S)?

An analysis of consumer reactions shows that to date, the mainbenefit of migrating to lead-free electronics has been increasedmarket share through product differentiation, in terms of productenvironmental friendliness [2]. Manufacturers wish to be consideredenvironmentally conscious, and have been voluntarily migratingto lead-free technology prior to the implementation of legislation.

Manuscript received September 1, 2005; revised September 23, 2005. Thiswork was recommended for publication by Associate Editor Michael G. Pechtupon evaluation of the reviewers’ comments.

The authors are with the Department of Mechanical Engineering, CALCEElectronic Products and Systems Center, University of Maryland, College Park,MD 20742 USA (e-mail: [email protected]).

Digital Object Identifier 10.1109/TCAPT.2005.859353

1The Waste of Electrical and Electronic Equipment (WEEE) directive [4] re-quires manufacturers to reduce the disposal waste of electrical and electronicproducts by reuse, recycling, and other forms of recovery. The Restriction ofthe Use of Certain Hazardous Substances in Electrical and Electronic Equip-ment (RoHS) legislation [5] restricts the use of lead, as well as cadmium, mer-cury, hexavalent chromium, and two halide-containing flame retardants, namelypolybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE),in eight of the ten product categories identified in the WEEE directive. Unlikefor WEEE, whereby EU member states are free to set more severe national leg-islation satisfying the WEEE directive requirements, RoHS is a single marketdirective. Both the WEEE and RoHS directives will become effective on July1, 2006.

2The cost of implementing the RoHS directive in the EU has been estimatedto be US$ 20Bn [6]. Intel Corporation’s efforts to remove lead from its chipshave been estimated to cost the company over US$ 100 million so far [7].

However, once the European Waste of Electrical and Electronic Equip-ment (WEEE) and the Restriction of the Use of Certain HazardousSubstances in Electrical and Electronic Equipment (RoHS) legislationbecomes effective (July 1, 2006), migrating to lead-free electronicswill become a requirement for manufacturers who wish to maintaintheir market in that region.

As an increasing number of electronic suppliers transit to lead-freetechnology, the availability of lead-based items will decrease. Consid-ering that most of the electronics supply chain is migrating to lead-freetechnology, equipment manufacturers who are not prepared for thistransition will be left behind technologically.

The difficulty for manufacturers to manage their design, manufac-turing process, inventory, and logistics to a different set of regulationsfor each region and customer, is prompting them to extend lead-freeproduct compliance to regions outside the EU. This strategy has beenadopted by, for example, Hewlett Packard, who is extending lead-freecompliance on a world-wide basis for nonexempted applications [8].

Major original equipment manufacturers (OEMs) who have suc-cessfully introduced lead-free products include Fujitsu, Hitachi,Matsushita, NEC, Philips, Sony, and Toshiba in the consumer sector[9], which was the first industry to implement lead-free electronics;Dell, HP, IBM (Levono), NEC, and Toshiba in the computer/serverindustry; and Ericsson, Infineon, and Motorola in the telecommunica-tion sector.

II. HOW DO WE CERTIFY LEAD-FREE COMPLIANCE

WITH THE REGULATORY AUTHORITIES?

An overview of current legislation pertaining to lead-free electronicsis available in [2]. As the RoHS directive [5] will be the first legislationto become effective that restricts the use of lead in electronic products,the guidelines provided in this section focus on compliance to this di-rective regarding the usage of lead. However, manufacturers who planto commercialize products in the EU after July 1, 2006, or in regionsaffected by other environmental regulations, will also need to ensurecompliance with any other environmental legislative or regulatory con-straints that may apply to their products.3

The concentration of lead in electrical and electronic products com-mercialized in Europe after July 1, 2006 should be less than 0.1% byweight in homogeneous materials4 [10]. The product categories andapplications of lead currently exempted from the legislation are listedin the RoHS directive. The rationale behind the RoHS exemptions andtheir potential impact on the electronics industry are discussed in [2].

3Other environmental regulations applicable to electronic products are con-cerned with product take-back, reuse, and recycling. These regulations includeThe European Waste from Electrical and Electronic Equipment (WEEE) legis-lation [4], the Japanese Household Electric Appliances Recycling Law [15], andother laws enacted by China and certain states in the United States. China’s Min-istry of Information Industry’s (MII) draft regulation, “Management Methodsfor the Prevention and Control of Pollution from Electronics Information Prod-ucts,” bans the use of lead, cadmium, mercury, hexavalent chromium, PBB, andPBDE in electronic information products. This regulation is scheduled to takeeffect on July 1, 2006. Japan has had voluntary green initiatives in place formany years, and South Korea’s electronic companies have adopted a voluntaryprogram to comply with RoHS [16].

4A homogeneous material is defined as a material that cannot be mechanicallydisjointed into different materials. The terms ’homogeneous’ and “mechanicallydisjointed” can be explained as “of uniform composition throughout” and “sep-arated by mechanical actions such as unscrewing, cutting, crushing, grinding,and abrasive processes,” respectively [10].

1521-3331/$20.00 © 2005 IEEE

IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES, VOL. 28, NO. 4, DECEMBER 2005 885

As of this writing, exemptions include: medical devices and monitoringand control instruments; oil and gas electronics if they are equipmentfor control and monitoring [11]; batteries used in electrical and elec-tronic equipment, but these will be collected with the equipment onceit becomes waste, on the basis of the WEEE directive; and applicationsof lead listed in the annex of the RoHS directive [5]. As avionics andautomotive electronics have not been specifically mentioned among thecategories of electronics covered by the WEEE and RoHS legislations[5], [12], they can be considered to be outside their scope. However, au-tomotive electronics are covered by the scope of the end-of-life vehicle(ELV) legislation [13], effective since November 2003, which estab-lishes a framework to ensure that vehicles are designed and manufac-tured in a way that optimizes opportunities for reuse, recycling, andrecovery. There are also bans for certain substances, but lead used insolders for automotive electronics is specifically exempt [14].

In December 2004 and March 2005, the Technical Adaptation Com-mittee (TAC) of the RoHS directive voted in favor of a draft Commis-sion decision to add new exemptions, and modify existing ones. Theadditional applications of lead proposed were: lead in solders to com-plete a viable electrical connection between semiconductor die and car-rier with integrated circuit (IC) flip chip packages (i.e., flip chip solderjoint interconnections), lead used in compliant pin connector systems,lead as a coating material for the thermal conduction module c-ring,lead in solders consisting of more than two elements for the connec-tion between the pins and the package of microprocessors with a leadcontent of more than 80% and less than 85% by weight, and lead inoptical and filter glass [17], [18]. The legitimacy of the proposed ex-emptions has been questioned by the European Parliament [19]. Twonew proposals, namely the flame retardant deca brominated diphenylether (BDE) in polymeric applications, and lead in lead–bronze bearingshells and bushes, did not obtain a sufficient number of affirmativevotes by the TAC in April 2005, and have been submitted to the Councilfor review [20]. Other exemptions have been requested by various in-dustry stakeholders [21], which will be reviewed by an independenttechnical expert.

In the following sections, guidelines are provided to help establish acompany’s strategy to comply with the lead-free RoHS regulation, andverify product compliance to this regulation.5

A. Company’s Compliance Strategy

The company’s strategy (i.e., legal policies) to comply with theRoHS regulation [5] should be established and documented in theform of a position statement that can be distributed to customersand suppliers. An example of a corporate RoHS compliance positionstatement is given in [8].

A company’s position regarding the RoHS directive should de-fine what product(s) are to become compliant, the date which theseproduct(s) are commercialized, and regions in which they are in-troduced if compliance is extended to regions outside the EU. Themanufacturer should identify whether any of its products and theirapplications are exempt from the RoHS legislation. If necessary,clarification should be obtained from the regulatory body on howexemptions may apply to the company’s specific products and applica-tions. If the company is planning to use any of the RoHS exemptions,these should be specified in the company’s position statement.

5Legislative requirements pertaining to lead-free electronics should be regu-larly monitored for revisions. New and revised standards applicable to lead-freeassembly process, qualification test, and inspection should also be identified(Section XII). A map of which products (and their quantity) are being sold intowhich regions should be established. The regulatory body, regulation/standardand its effective date, that the products must comply with, as well as corre-sponding regulatory requirements (e.g., banned materials, associated thresholdlimits including the level at which it should be measured, recycling require-ments, and reporting methods) should be identified.

Exemptions are likely to remain an option if a lead-free alterna-tive is not technically feasible from a process, reliability or cost view-point. For example, the use of high melting temperature (greater than300 �C) lead-based solder, such as Pb-3Sn, in flip chip ball grid array(FCBGA) applications prevents re-melting of the bumps during lead-free reflow soldering. Alternative bumping metallurgies such as elec-troless nickel/gold and gold, or epoxy bumps, have poor self-alignmentproperties and higher cost. Other examples of almost unavoidable ex-emptions include lead in piezoelectric crystal devices (e.g., oscillators,filters) for microwave telecommunication applications, and lead in dieattach solders for power applications.

Regardless of exemptions, certain manufacturers in exempted indus-tries (e.g., medical electronics, avionics, military electronics) that pur-chase commercial-off-the-shelf (COTS) electronic parts, which are thesubject of the legislation, may be driven to use lead-free technologies,due to part availability and cost considerations [2]. The desire of com-ponent manufacturers and other elements of the supply chain is to op-erate a single line of products, rather than dual lead-free and lead-basedproduction [22], [23]. Furthermore, the exemptions will be subjected toperiodic review by the EU legislative bodies, with the intent to progres-sively eliminate them [23].

B. Certification of Compliance

Once the legislation becomes effective, equipment manufacturerswill be responsible for compliance with the RoHS directive. Althoughno approach has been specified in the EU directives to report compli-ance with the legislation, at this time it is recommended that OEMsadopt the self-certification approach, for which the majority of the EUmember states have indicated their preference [24]. Lead-free compli-ance self-certification should be supported by “compliance” documen-tation from the suppliers, certifying that the procured materials, partsand subassemblies not exempted by the legislation meet the require-ments of the RoHS directive, in terms of the maximum concentrationof lead. Guidance to verify the compliance of procured items is pro-vided in Section II-B1.

A market surveillance may be conducted by national enforcementauthorities to verify producers’ compliance with EU regulations. Uponrequest of the enforcement authority, producers will be required todemonstrate compliance by providing satisfactory evidence. Inspec-tions will be conducted, involving product chemical composition anal-ysis (see Section II-B2). CALCE has found that surveillance will alsobe conducted by competitors.

At this time, the WEEE legislation itself only states that penalties ap-plicable to breaches of the national provisions of the directives shouldbe “effective, proportionate and dissuasive” [4], but EU member stateswill determine the actual penalties.

1) Verification of Compliance for Procured Materials, Parts, andSubassemblies: To ensure that the final product is lead-free, assuranceshould be obtained from all related material, part and subassembliessuppliers that their products do not contain lead with a concentrationabove the RoHS restricted level (0.1% by weight). Manufacturers willbe required to maintain a record of their suppliers’ compliance doc-umentation, that can be shown to the enforcement authorities in thecourse of an inspection.

No format or time frame for producing such compliance documen-tation has been specified. At this time, it is recommended that OEMsissue a formal letter to suppliers and assemblers, requesting self-certi-fication on the basis of chemical composition analysis of the suppliedmaterial and/or parts.6 Examples of lead-free/RoHS compliance state-ments from electronic part manufacturers include [25]–[30].

6A transmitting material safety data sheet is not sufficient for compliance,because elements with content levels below 1% by weight are not shown.


The self-certification request issued to the supplier should be sup-plied along with the company’s RoHS position statement, and a list ofrequirements and restrictions for the procured material, part, or sub-assemblies, including the threshold concentration value of lead. Thelead-free certification request may be included as part of a material dec-laration questionnaire (also referred to as green procurement survey orsupply chain questionnaire) that manufacturers may already issue totheir suppliers [31]. An example of environmental requirements set byan equipment manufacturer for its procured materials, parts and sub-assemblies is provided in [32]. Suppliers may use different units fordefining the concentration of hazardous substances (e.g., part per mil-lion, percentage by weight, percentage by mass). Caution should betaken when examining lead content data, because the lead concentra-tion threshold set by the RoHS legislation is expressed by weight. Veri-fication documentation obtained from suppliers and assemblers shouldbe re-obtained or re-signed whenever there is a change in materials usedin supplied parts or end products, process, or regulatory requirements.

For all procured lead-free items, a lead-free compliance recordshould be included in the material management system or databasethat the company may already employ to convey material chemicaldata for lead-based products. This will permit the lead-free complianceof the procured items to be verifiable throughout the enterprise (e.g.,design, production and logistic departments) and supply chain.

If no appropriate compliance documentation is available from thesupplier, equipment manufacturers should consider an alternative sup-plier with lead-free capability, or conduct a chemical analysis of theprocured part. Chemical analysis methods and providers of lead-freecompliance assessment services are listed in Sections II-B2 and III, re-spectively.

2) Chemical Analysis: Conducting a chemical analysis of the pro-cured materials, parts and subassemblies may be necessary to ensurecompliance with legislative requirements. Lead can be found in manyelectronic packaging materials, namely: solders, component terminalfinishes (i.e., lead finish for leaded packages or solder ball for area arraypackages and flip chip interconnections), separable connector termina-tions, printed circuit board (PCB) pad surface finishes, solder-based dieattach materials, as an alloying element in aluminum-based die-castingmaterials, polyvinyl chloride (PVC), PVC wiring, balance weights forlarge Titan motors, paints, plastic additives, tinned cables, resin stabi-lizers and additives, optical materials, and ferroelectrics.

Two documents have been published on assessing the lead contentof electronic products. EIA/ECCB-952 [33] describes the required el-ements of a plan to assess the lead content of a product, in terms ofhigh-level requirements and areas of concern that must be addressedby the process. Test procedures7 to assess the lead content of polymericand metallic materials, and electronic parts and assemblies, are definedin [34].

Considering the level of expertise required for compositional anal-ysis of electronic assemblies (e.g., in terms of potential limitationsof the experimental method, instrument calibration), manufacturersshould consider subcontracting such analysis to specialized providers(see Section III).

Databases such as offered by i2 [35] and Underwriters Laboratories(UL) [36], which contain information of the chemical content of certainelectronic materials and components, may help identify noncompliant

7Analysis procedures include the use of energy dispersive X-ray fluorescence(EDXRF) or wavelength dispersive X-ray fluorescence (WDXRF) for mate-rial/part qualitative and quantitative screening. The use of inductively coupledplasma-atomic emission spectroscopy (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS), or atomic absorption spectroscopy (AAS) maybe used to confirm the lead content [34]. These experimental methods are dis-cussed in [37], along with energy dispersive X-ray analysis, spark emission anddc arc emission spectroscopy, glow discharge optical emission microscopy, andpolarography.

electronic parts, lead-free alternatives and their suppliers. i2’s databaseprovides material composition data at the component level, includingRoHS-restricted substances. UL’s database covers plastic materials andis expected to expand to include information on restricted substances.However, parts and materials change, and it is critical that guaranteesfor accuracy and compliance be obtained.

III. WHICH COMPANIES CAN TEST ELECTRONIC MATERIALS, PARTS

AND SUBASSEMBLIES FOR LEAD-FREE COMPLIANCE?

Material, part, subassembly, and product compliance analysis canbe subcontracted to third parties such as material analysis companieswith lead-free compliance assessment capabilities. The cost of chem-ical analysis services typically varies from U.S. 500 dollars for stan-dard elemental composition analysis by energy dispersive X-ray spec-troscopy (EDS) or XRF spectroscopy, up to a few thousand U.S. dol-lars for highly sensitive analysis techniques such as mass spectrometry.Although no particular provider of chemical analysis services is advo-cated, examples include [38]–[42].

IV. IS THERE ANYTHING UNIQUE THAT WE NEED TO DO WHEN

SELECTING LEAD-FREE COMPONENTS?

All materials and parts (e.g., components) in final product, whichmay contain RoHS restricted substances in the Bill of Materials (BoM),should be identified. The BoM may represent a single product or as-sembly, or a family of products. As outlined in Section II-B2, identifi-cation of the impacted components may require material analysis. Suchcomponents should be documented in a database.

Non-RoHS-compliant components should be replaced with RoHScompliant alternatives that are selected based on availability, manufac-turability, reliability, and cost considerations. Manufacturability con-siderations include compatibility between lead-free materials used ascomponent terminations, PCB pad finishes and solders; material andpart compatibility with the lead-free manufacturing processes (reflow,wave, rework), and component terminal and PCB pad solderability. Po-tential reliability concerns specific to lead-free materials and processesinclude component moisture and thermal sensitivity, excessive inter-metallic growth, tin whiskering, electrochemical migration, solder jointmanufacturing defects (e.g., poor wetting, fillet lifting, voiding, coldjoint), and material/process incompatibilities in assemblies combininglead-free and lead-based metallurgies.

When outsourcing manufacturing, the component selection processshould be coordinated with the assembly house to ensure compatibilityof the procured parts with the manufacturing processes. Examples ofEMS providers with lead-free capability include [43]–[46].

Specific considerations for lead-free component selection includeterminal finish, moisture and thermal sensitivity, material and processcompatibility, and part tracing.

A. Component Terminal Finish

At present, pure tin (matte finish) is the most widely adoptedfinish material for leadframe components, followed by nickel–pal-ladium–gold leadframe preplating [1]. Other lead-free leadframefinishes include tin–bismuth, tin–copper, and tin–silver.

For array components, tin–silver–copper solder ball metallurgy hasbeen widely adopted.

For connectors, tin–copper (Sn97.3–Cu0.7) and tin–silver–copper(e.g., Sn-Ag3 � 4-Cu0:5 � 0:7) finishes can be employed as replace-ments of tin–lead solder contact finishes. These lead-free alloys exhibitbetter hardness and resistance to fretting corrosion than tin–lead [47],[48]. For cost-driven applications, pure matte tin may be used.


With high tin content finishes, tin whiskers can grow spontaneouslyon the plating surface, and could cause electrical short circuits acrosspart terminals, such as connectors. The whisker tolerance level of thespecific product and application considered should be identified. Forlong-duration or high-reliability applications (e.g., medical, avionics,space, and defense applications), the risk tolerance may be sufficientlylow as to warrant consideration of mitigation strategies [1]. StandardJESD22A-121 [49] specifies test methods to assess the propensity forwhisker’s growth on tin and tin alloy surface finishes. Fang et al. [50],[51], developed a probabilistic method-based algorithm to assess therisk of bridging component terminations with tin whiskers. Mitiga-tions approaches include the use of thick tin coating (with thicknessgreater than 8 �m) or nickel under-plating (with thickness greater than1.27�m) over copper base metal, and avoiding the use of pure bright tinplating without a mitigation strategy [52]. The effectiveness of variousmitigation strategies is discussed in [1] and [53]. Currently, there is nogeneric method to retard whisker growth, that is successful for all basemetal/plating configurations and storage conditions. For example, an-nealing at 150 �C for 1 h has been shown to reduce maximum whiskerlength and growth rate on matte tin-plated copper stored at room tem-perature for up to two years. On the other hand, annealing was not ef-fective in reducing the propensity of whisker growth neither on mattetin plated brass, or on matte tin plated copper exposed to 50 �C/50%RHtemperature/humidity condition for eight months [54], [55]. Examplesof nonstandard vendor tin whisker qualification tests are given in [56]and [57].

Nickel–palladium or nickel–palladium–gold leadframe componentfinishes are not prone to whisker growth [52]. However, there are po-tential disadvantages associated with the use of these finishes [1], in-cluding cost, solderability, and susceptibility to creep corrosion [58],[59].

An example of procurement guidelines set by an equipment man-ufacturer for lead-free components is given in [60]. In this example,the equipment manufacturer specifies its preferred termination finishes,and a number of requirements for tin-based finishes, including platingprocess control, plating characteristics known or suspected to influencewhisker growth, and tin whisker qualification tests.

B. Component Moisture and Thermal Sensitivity

Components may be more prone to mechanical damage (e.g., de-lamination, cracking, popcorning) when exposed to lead-free reflowsoldering temperature profiles compared with standard tin–lead reflow.This is essentially due to higher peak reflow temperatures.

The moisture sensitivity of organic IC packages is characterized interms of component floor life when stored in a PCB assembly envi-ronment, outside moisture-proof packaging. For lead-free assembly,package moisture sensitivity, as defined per IPC/JEDEC J-STD-020C[61] classification, should not exceed moisture sensitivity level (MSL)3. The IPC/JEDEC MSL rating of a plastic component has been foundto decrease by up to one or two ratings for every 10 �C increase in peakreflow temperature [1]. For example, an MSL one-rated component ata tin–lead assembly temperature of 220 �C would become MSL 2 orMSL 3 at a lead-free assembly temperature of 240 �C. Qualificationtests performed by component suppliers should include moisture sen-sitivity level tests. Equipment manufacturers also need to ensure thatthe time out of moisture-proof packaging is appropriately monitoredthroughout the supply chain, by component manufacturers, distribu-tors and contract manufacturers. Baking moisture sensitive components(125 �C, 24 h) before lead-free reflow soldering may be a good precau-tion.

Component temperature rating requirements for lead-free assemblyand rework depend upon package volume and thickness, and arespecified in standards IPC/JEDEC J-STD-020C [61] and JEITA

ED-4701-301A [62]. Large, thin organic packages [e.g., BGAs, thinquad flat packs (TQFPs), chip support packages (CSPs)] are generallymore prone to hygrothermal stress-induced failures. Small volume, thinsurface mount device (SMD) packages (i.e., with small thermal mass)reach higher body temperatures during reflow soldering to boards thathave been profiled for larger packages. Therefore, it should be verifiedthat components with small thermal mass are rated at the appropriatetemperature specified by the standard. Component vendors who followJEDEC J-STD-020 should use the latest version of the standard,JEDEC J-STD-020C, in which temperature rating requirements havebeen revised compared with J-STD-020B. Equipment manufacturersshould track which version of JEDEC J-STD-020 their componentsuppliers have used to qualify the parts. Other standards relating tothe handling and assembly of moisture and/or thermally sensitivecomponents include IPC/JEDEC J-STD-033C [63], which specifieshandling, packing, and shipping requirements for moisture/reflowsensitive surface mount devices, and Mil-Std 202G Method 210F [64].

For passive components such as chip capacitors and resistors, itshould be verified that the component temperature rating is sufficientfor lead-free soldering. In addition, the allowable PCB flexure speci-fied by the component supplier may need to be considered, as passiveceramic components may be more susceptible to mechanical damage(e.g., cracking) due to higher soldering temperature than for tin–leadsoldering, and possibly due to different solder joint metallurgies. Largechip components (1210 in size and above) tend to be more exposed toflexure-induced damage than smaller components.

Optoelectronic components, such as light-emitting diodes (LEDs),are very temperature-sensitive and could suffer optical property degra-dation or mechanical damage when exposed to lead-free reflow sol-dering profiles. Temperature-sensitive devices may require a separateassembly process that is performed after standard reflow of other com-ponents. Thermally sensitive devices may be assembled using eitherpress-fit, hot bar soldering, laser soldering, hand soldering, and/or aconductive adhesive attachment method. Wave soldering may be suit-able for devices having intrusive leads. Assembly should be performedbased on the component manufacturer assembly guidelines.

The majority of connector housings are made of plastic materials,and can be prone to hygrothermal stress-induced defects, similar toIC plastic packages. It should be verified with the manufacturer thatthe connector is rated to a sufficiently high temperature for lead-freeassembly.

C. Material and Process Compatibilities

Due to part availability and cost considerations, equipment man-ufacturers may be constrained or tempted to combine lead-free andlead-containing materials and parts in PCB assemblies. The use oflead-free and lead-based material combinations could potentially af-fect solder joint reliability, and examples of such situations are givenbelow, both for forward and backward assembly incompatibility.

Forward compatibility refers to a component with lead-based ter-minations soldered using lead-free solder and a lead-free temperatureprofile. Forward incompatibility issues can arise due to unavailabilityof a lead-free component in the transition period.

Backward compatibility refers to a component with lead-free termi-nations soldered with tin–lead solder and a tin–lead temperature pro-file. Exempted products may be exposed to backward incompatibilityissues when lead-based components become unavailable.

1) Forward Incompatibility: Lead in lead-based componenttermination (leadframe finish or solder ball) can interact with bis-muth-containing lead-free solder (e.g., Sn–Bi, Sn–Ag–Bi, Sn–Zn–Bi,Sn–Ag–Cu–Bi) during assembly, to form a low-melting point phase(Sn–51Bi–32Pb, melting point of 96 �C) which can cause cracking insolder joints [65].


Lead-containing component termination with lead-free Sn–Ag–Cuor Sn–Ag solder can result in poor solder joint mechanical reliability,due to the formation of a Sn–Pb–Ag eutectic (62Sn–36Pb–2Ag,melting point of 179 �C) during the cooling phase of the assemblyprocess. This phase tends to migrate toward the joint/board interfaceand is the last one to solidify. Consequently, shrinkage stresses inducedon the joint during solidification may lead to fillet lifting (cracking) inwave soldered through hole joints [1].

2) Backward Incompatibility: BGA packages with Sn–Ag–Cusolder balls assembled to a PCB using a conventional tin–lead sol-dering temperature profile may form “cold joints”. A hybrid solderingprocess, which uses higher reflow temperatures compared with stan-dard tin–lead reflow, may be required to melt the balls.

Tin–lead hot air solder leveling (HASL) PCB pad finish cancause solder joint fillet lifting in through-hole lead-free nickel–palla-dium–gold coated components soldered with lead-free Sn–Ag solder[1]. This is due to the formation of 62Sn–36Pb–2Ag eutectic duringthe cooling phase of the assembly process.

Tin–lead HASL PCB pad finish with lead-free Sn–Ag–Cu solder canresult in weak joints with voiding. This has been attributed to depletionof tin from the pad coating, which results in the formation of a weaklead-rich phase [66].

D. Solderability and Reliability

Conformance to standardized solderability criteria, such asIPC/EIA-J-STD-002B [67], should be ensured. However, the wet-tability of most lead-free solders is not as good as that of eutectictin–lead solder, and quality control is critical. The shelf life of thelead-free component finish, which impacts solderability, must becarefully observed.

The relative amounts of plastic and creep damage differ for tin–leadand lead-free solder [68]. This results in two known trends with re-gard to the thermomechanical reliability of lead-free solder joint inter-connections in temperature cycling conditions. Lead-free solder jointthermomechanical fatigue durability is equivalent or better relative totin–lead eutectic joints (considering the same package and board) atsmall levels of mechanical loading (i.e., small thermal expansion mis-match between the component and board, which generally applies toplastic packages). Conversely, lead-free solder joint thermomechanicalfatigue durability is lower relative to tin–lead eutectic joints (consid-ering the same package and board) at high levels of mechanical loading(i.e., high thermal expansion mismatch between the component andboard, and stiff solder joints, which generally applies to ceramic lead-less chip carriers) [69].

V. IS THERE ANYTHING UNIQUE THAT WE NEED TO DO WHEN

DESIGNING OR SELECTING LEAD-FREE CIRCUIT

BOARDS OR CIRCUIT ASSEMBLIES?

Considerations for lead-free board design include PCB pad finishand laminate material selection.

A. PCB Pad Finish

The primary lead-free alternatives to tin–lead HASL are immersionsilver, immersion tin, electroless nickel/immersion gold (ENIG), andorganic solderability preservative (OSP). All these finishes providePCB pads with improved planarity and fine pitch assembly capabilitycompared with tin–lead HASL. OSP is the least expensive finish,followed by immersion tin, immersion silver, and ENIG. Reportedconcerns associated with each finish are summarized below.

Immersion tin used in PCBs subjected to multiple reflow tempera-ture profiles can be prone to Sn–Cu intermetallic formation, resulting ina degradation of pad solderability. On the other hand, immersion silver

can survive multiple reflows due to the lower growth rate of Sn–Ag in-termetallics compared with Sn–Cu intermetallics. However, silver mi-gration may pose a reliability risk for certain applications.

Due to the thinness of OSP and immersion silver finishes (approx-imately 50 and 250 nm for OSP and immersion silver, respectively),these coatings may be prone to mechanical damage (e.g., surfacescratches) during board handling operations, that could expose theunderlying metal and impact pad solderability. Therefore, if OSPor immersion silver finishes are used, care must be taken to avoidsurface defects. In addition, OSP finishes may require more vigorousprobing using bed of nails test fixtures during in-circuit testing (ICT),to establish electrical contact through the nonconductive OSP coating.This can potentially damage the PCB [70].

ENIG is considered a multifunctional (i.e., applicable to soldering,aluminum wire bonding, press fit connections, and contact surface),corrosion resistant surface finish, but can be prone to “black pad” de-fects [71]. Black pad is characterized by the separation of the solderjoint from the surface of the electroless nickel underplate. This is com-monly attributed to excessive phosphorous contamination of the elec-troless nickel.

The shelf life of all finishes impacts solderability, and should there-fore be obtained from the supplier. The shelf life of OSP is the lowestof the finishes.

B. PCB Laminate Material

PCB laminate material selection generally follows the same criteriaas for lead-based products, but there are some exceptions. It should beensured that the laminate can withstand multiple reflows and rework atthe appropriate lead-free processing temperature without thermome-chanical damage. Although FR-4 laminates with glass transition tem-peratures of approximately 140 �C may be suitable, applications ex-posed to high temperature environments (e.g., under-the-hood, oil wellapplications) may require materials with higher glass transition temper-ature, such as high-glass transition temperature FR-4 (e.g., 170 �C).

Potential concerns associated with assembly at lead-free solderingtemperature profiles include increased board warpage, which couldcause planarity problems with large components [72], increasedthrough-plane thermal expansion, which could affect plated-throughhole (PTH) reliability, or possibly delamination of the metalliza-tion [73], [74]. According to [75], one-third of the U.S. industry hasswitched to higher glass transition temperature materials (e.g., 170 �C)for a greater margin in rework.

The laminate material should not contain polybrominated biphenyls(PBB) and polybrominated diphenyl ethers (PBDE). These halide-con-taining flame retardants are prohibited by the RoHS legislation. Fur-thermore, the laminate moisture absorption properties should be veri-fied with the supplier, as well as any specific storage conditions/dura-tion or prebaking that may be required before assembly.

C. PCB Layout

In general PCB design rules for lead-free soldering are the sameas those for tin–lead soldering. However, because of the lower wet-tability of lead-free solder, and the smaller amount of superheat (dura-tion of exposure to temperatures greater than the liquidus) during re-flow, there will be differences in optimized layout between lead-freeand lead-based designs. The following guidelines in PCB layout forlead-free soldered products may be considered.

It is a good practice to design the PCB to achieve even spread of highand low thermal mass components (to minimize temperature gradientsand peak temperature).

PCB design may also need to accommodate hand soldering of cer-tain thermally sensitive components (due to higher reflow temperatureassociated with lead-free soldering).


In some designs, insufficient component spacing can result insecondary reflow of adjacent leadframe components during lead-freerework operations of BGA/CSP components, particularly in high-den-sity component-board assemblies. Typically, the minimum componentspacing between BGA/CSP and leadframe components should be150 mils [1].

The wetting of lead-free solder on PCB pads is not as good as thatfor tin lead solder. In certain applications, unwetted pad surfaces maypose a reliability risk due to corrosion of such surfaces in presence ofatmospheric contaminants. For such applications, pad width may haveto be reduced to minimize the amount of pad surface area without soldercoverage.

The product designer should consult with the PCB manufacturer andassembler to minimize manufacturing concerns.

VI. IS THERE ANYTHING UNIQUE THAT WE NEED TO DO

WHEN SELECTING LEAD-FREE SOLDER ALLOYS?

The International Tin Research Institute (ITRI), InternationalNational Electronics Manufacturing Initiative (iNEMI), EuropeanConsortium BRITE-EURAM, and Japan Electronics and InformationTechnology Industries Association (JEITA) recommend Sn–Ag–Cueutectics as the most promising lead-free solder metallurgies,8, en-dorsing Sn–4.0Ag–0.5Cu, which is the most widely-characterizedalloy [1], as well as Sn–3.0Ag–0.5Cu (JEITA’s recommendation),Sn–3.9Ag–0.6Cu (iNEMI’s recommendation), and Sn–3.8Ag–0.7Cu(BRITE-EURAM’s and Soldertec’s recommendations) [75].

Both for reflow and wave soldering, Sn–3Ag–0.5Cu (liquidus tem-perature, 217–220 �C) currently appears to be the leading candidateadopted by the industry, due to cost considerations. 99.3Sn–0.7Cu (liq-uidus temperature, 227 �C) is a low cost alternative for wave soldering,recommended by iNEMI [76].

Equipment manufacturers should verify the licensing agreements ofthe lead-free solder supplier, and verify that the solder supplier is awareof any potential patent issues in the country of manufacture as well ascountry of sale or customer resale. Typically, royalty cost account for2% to 8% of the solder paste cost. If the procured lead-free solder isnot properly licensed, the alloy composition should be obtained, andan explanation of why the solder supplier believes no license is neces-sary should be sought. In addition, the equipment manufacturer shouldverify whether their company has a worldwide intellectual property(IP) noninfringement warranty and indemnity in place with the soldersupplier or assembly house, as appropriate. Such warranty should beapplication-specific, and may help the equipment manufacturer to re-cover damages in the event of patent infringement issues. However,an indemnity is not an alternative to due diligence. First, an indem-nity would not protect the equipment manufacturer from being sued.Second, the equipment manufacturer would never be fully compen-sated for the damage caused to customer relationships by missed ship-ments. Furthermore, small subcontractors or solder suppliers may nothave the financial strength to honor the indemnity.

Lead-free solder paste should be stored in a container with appro-priate labeling and identification to distinguish it from tin–lead solderpaste. The solder paste should be stored in the refrigerator between35 �F and 45 �F and should be used on a first-in/first-out (FIFO) in-ventory control basis. The shelf life of tin–silver–copper solder pastesat the recommended storage temperature (35 to 45 �F) may be reducedfrom the typical six months expected for tin–lead solder paste, to threeto four months. The materials used in fluxes developed for use with

8An overview of lead-free soldering alloys and their characteristics (includingconstitutive properties, durability, and cost), suppliers and users is provided in[1] with corresponding solder joint characteristics (including metallurgical reac-tions, mechanical properties, electromigration, and current carrying capability).

tin–lead solder paste may attack the higher tin-containing lead-freesolder powder (> 95% tin by weight) more than standard tin–leadsolder powder (63% tin by weight), hence reduce the shelf life of thelead-free paste. Solder paste manufacturers are in the process of devel-oping flux chemistry formulations to improve the shelf life of lead-freepastes. The solder paste should be maintained at room temperature for4 h before opening the container [1].

VII. IS THERE ANYTHING UNIQUE THAT WE NEED

TO DO WHEN SELECTING FLUXES?

The industry is migrating to no-clean flux systems for both cost andenvironmental reasons. Because tin–silver–copper pastes have lowerwettability than tin–lead ones on copper, no-clean flux systems usingslightly more aggressive wetting agents than conventional commercialfluxes (employed with lead-based solders) may be required. Such fluxestend to leave a higher amount of residues on the board after reflow,compared with conventional fluxes. This may cause reduced surfaceinsulation resistance and increase the risk of electrochemical migration.In addition, the flux residues are harder than those formed with tin–leadsoldering due to higher reflow temperatures, which can cause probingdifficulties due to increased electrical contact resistance.

Although water-soluble flux systems eliminate potential surface in-sulation resistance and electrochemical migration issues, little progresshas been made to develop such formulations due to lack of industrydemand. On the other hand, solder paste manufacturers are activelyworking on the development of improved no-clean solder pastes.

Japanese end-users have successfully implemented lead-free wavesoldering with Sn0.7Cu, Sn3.5Ag, and Sn–Ag–Cu alloys using rosin-based no-clean fluxes. In North America and Europe, the preference isto use volatile organic compound (VOC) no-clean fluxes.

VIII. HOW SHOULD WE PERFORM LEAD-FREE

COMPONENT-BOARD ASSEMBLY?

The following guidelines for surface mount and through-hole as-sembly are adapted from [1].

A. Reflow Soldering

Surface-mount assembly consists of three steps: screen printing, pickand place, and reflow. Only qualified lead-free materials should beavailable on the production floor. In addition, it should be ensured thatthe materials selected for assembly are free of other impurities that mayimpact on manufacturability and/or reliability.

Stencil Printing: Studies conducted by many companies haveshown that the same type of stencil printer can be used for lead-freesolder paste as for tin–lead solder. The stencil design guidelines areidentical to those for tin–lead systems. As noted in Section V-C,there is currently no change in PCB pad design guidelines forsoldering lead-free components. The print volume (transfer rate)of lead-free paste has been found comparable to that of lead-tinpaste [1]. The same printing settings can be applied to lead-freesolder pastes as for tin–lead. Settings include printing speed,squeegee pressure, on or off contact, separation speed, separationdistance, and cleaning frequency. For the screen-printing process,high squeegee pressure and low printing speed have been foundto yield better printing results for tin–silver–copper paste [1]. Thestencil release rate has a minimal effect on the printability oflead-free solder pastes. Typical settings tested for lead-free pastesare: squeegee blade pressure (16- inch blade length) = 18 kg,printing speed = 10-20 mm=s, snap off rate = 1 mm=s [1].

Pick and Place: No change is required to pick-and-place machinesto accommodate lead-free components.


Reflow Oven Equipment: Most eight-to ten-zone convection reflowovens are capable of lead-free soldering. Ten-zone ovens enable a moreprecise control of spatial temperature variations across large boards.Currently-available ten-zone convection ovens have a 325 �C to 350 �Ctemperature rating. Typical oven settings would normally not exceed300 �C in the reflow zones, and are capable of heating the boards andcomponents to the temperature range (240 �C to 250 �C) required forlead-free soldering of most products. If necessary, higher temperaturecan be achieved by lowering the conveyor speed. The use of a nitrogenatmosphere may contribute to improve the wetting of the lead-freeparts, and to reduce the amount of no-clean flux residue deposits onprobe surfaces for in-circuit testing [1]. However, nitrogen can increasetombstoning (solder joint lifting) [76].

Reflow Temperature Profile: Typical reflow profile parameters forlead-free tin–silver–copper paste (melting point = 217 �C) are ramprate = 1-2 �C=s or less than 3 �C=s; soak time and temperature range= 100 s at 170–217 �C reflow peak temperature = minimum solderjoint peak temperature (235 �C to 245 �C); reflow time above 217 �Cfor tin- silver- copper = 45-75 s or less than 90 s; cooling rate higherthan 2 �C=s if possible, or lower than 6 �C=s. An example of lead-freereflow process qualification is given in [77].

B. Wave Soldering

As the wave soldering process window for Sn–3Ag–0.5Cu solder isnarrower than for tin–lead wave solder, more precise process controlis required. Using the correct process parameters, lead-free wave sol-dering can be achieved successfully.

Atmosphere: The use of a nitrogen atmosphere typically enablessoldering temperature to be reduced by 10 �C, improves the processwindow, and yields a more reliable joint, but at a higher cost comparedwith air.

Equipment: Wave soldering machines used for lead-free assemblymay require longer contact time to achieve the desired wetting, dueto the lower wettability of lead-free solders relative to tin–lead ones.Once the equipment is modified or upgraded for lead-free processing,a tin–lead process can no more be employed. The wave soldering ma-chine must have an adequate preheating capacity to maintain thermalshock to the assembly when it enters the solder wave to within 100 �C.

The solder pot needs to be drained, cleaned, and refilled with lead-free solders. The surface coatings on the pot pump assembly and nozzlecan be a major issue when handling multiple tin-based chemistries.When normally filled with wet solder, the pot is protected from reac-tion with the atmosphere. With too frequent drainage of wet solder andre-filling with new solder, the solder pot is highly stressed from high tolow temperature and vice versa. Improper cleaning or incorrect cleanerscan cause further damage to the anti-rust and anti-corrosion materiallayer on the surface. Furthermore, high tin-containing solder alloys re-quire the pot coating to be nonreactive, as stainless steel componentsin the wave solder pots are attacked (corroded) by lead-free alloys overtime. Similarly, the compatibility of the lead-free solder paste with thepump impellor and solder bath nozzles should be verified.

Wave soldering machines for which the pot show signs of poor per-formance and aging when used for tin–lead assembly should not beconsidered for lead-free production. New solder pots, pump assem-blies, and lead-free compatible flow ducts should be used where ap-propriate. If required, the wave soldering machine supplier should becontacted for a lead-free upgrade of the equipment.

For existing wave soldering machines that are still relatively new,it is advisable to modify the pump assembly, nozzle, and flow ductof each chip wave and Lambda wave by applying a coating to protectthe equipment from erosion. Typical lead-free upgrade package com-ponents include: first wave (chip wave), pump assembly, nozzle (withcoated layer), flow duct, and secondary wave (Lambda main wave).

Certain wave machines with stainless steel pots cannot be upgradedfor lead-free wave soldering due to the need for solder pot replacement.The jacking stand for the stainless steel pot may not support the newcast iron pot and needs to be changed. Recently, wave solder equip-ment manufacturers have been offering lead-free compatible parts asstandard options.

Process Parameters: For lead-free wave soldering with Sn0.7Cu,the peak temperature registered on the bottom of the board is 255 �C,whereas the peak temperature recorded on the top side is 198.8 �C. Thedwell time in the main contour wave (Lambda) is 3.5 s and the total timeabove the liquidus temperature (227 �C, 217–220 �C) is 9.7 s.

Solderability, Wettability: As most lead-free solders have a highermelting temperature than eutectic tin–lead solder (e.g., 217 to 227 �Cversus 183 �C), oxidation of high-tin solders can become a greaterissue. A higher rate of dross (a metallic oxide) formation can be ob-served on the surface of molten lead-free solder in the presence of air,compared with tin–lead solder. Although the rate of dross formationvaries depending upon the lead-free solder used, this results in degra-dation of solder performance. Conventional no-clean fluxes may dissi-pate or become inactive before reaching the peak solder temperature.Solderability studies of lead-free alloy and component finish in bothair and nitrogen have concluded that lead-free solder has lower solder-ability than tin–lead solder, especially when weaker no-clean VOC-freefluxes are used. In addition, the necessary removal of dross, which ad-heres to the solder pot surfaces as it cools, causes product interruptionand additional labor cost. Studies have also shown that solderabilityis considerably improved when processing takes place in an inert (ni-trogen) atmosphere.

The required process temperatures for good wetting can be reducedwith the use of nitrogen, thereby reducing the potential damage to tem-perature-sensitive components. Nitrogen atmosphere may be neces-sary, especially with complex boards with varying finishes and thermalrequirements. The oxygen levels in nitrogen atmosphere should gener-ally be kept below 350 SCFH when using no-clean VOC-free fluxes,to minimize soldering defects and maximize wetting.

For thick PCBs (such as 14-layer boards), the hole fill capability isnot as good using lead-free solders as for tin–lead solders. Solutionssuch as press-fit connectors or selective soldering technology are beinginvestigated for such situations.

Lead Contamination: May cause fillet lifting at high temperature.Therefore, tin–lead HASL boards should not be used with lead-freewave solder. Lead-free coated components should be used whereverpossible. In addition, the cooling rate/profile needs to be well con-trolled. Lead contamination resulting from the processing of lead-basedparts using lead-free wave soldering equipment can be regarded as “in-tentionally added” substances.

IX. HOW SHOULD WE PERFORM LEAD-FREE REPAIR AND REWORK?

Rework is conducted for defective components using either handsoldering irons for leadframe and chip termination components, orBGA/CSP rework equipment for BGA/CSP components. Challengesin reworking lead-free soldering assemblies include: spacing betweenBGA/CSP and leadframe components to avoid secondary reflow ofleadframe components during BGA/CSP rework, selection of lead-freerework materials which should be able to cater to both surface-mountand wave-assembly operations, rework process temperature profileto minimize the risk of internal delamination or popcorning in mois-ture-sensitive plastic components.

Rework on lead-free assemblies can be performed with existing re-work equipment, both for hand soldering rework and BGA/CSP re-work. However, modifications to existing equipment may be required,


as detailed below for the temperature setting of hand soldering equip-ment. It should be ensured that tools for rework and repair are identifiedas lead-free. In addition, the rework station should be separately located(although most of the rework equipment for tin–lead can still be usedfor the lead-free solders).

Lead-free rework is conducted at higher temperatures (typically,30 �C higher) than for tin–lead solder. As previously noted, the typicalminimum keep-out spacing for BGA/CSP components from leadframecomponents is 150 mils (3.81 mm). This distance is necessary to avoidlocalized secondary reflow of adjacent components during reworkoperations.

Flux and solder selection are critical. For BGA/CSP rework, thesolder paste should be the same as that used for assembly. The rec-ommended lead-free wire for hand soldering rework is Sn3.5Ag, dueto its long history of use. Sn3Ag0.5Cu and Sn0.7Cu are the preferredlead-free wave solder alloys.

The hand soldering equipment temperature settings may need tobe raised by one or two settings to accommodate the higher meltingtemperature of the lead-free solder wire (221 �C for Sn3.5Ag, versus183 �C for tin–lead). Alternatively, the same settings may be used asfor tin–lead, but the hand soldering equipment tip should be left on thereworked part (solder pad and component lead) for a longer time thanfor tin–lead solder before applying the solder wire to ensure reflow.Whether this may cause the solder tip to wear out more quickly needsto be verified.

Further information on the rework of lead-free assemblies is pro-vided in [1].

X. HOW SHOULD WE PERFORM LEAD-FREE

INSPECTION

AND TESTING?

The purpose of inspection is to detect manufacturing nonconformi-ties, both by visual assessment of the appearance of solder joints (e.g.,bridging, insufficient solder, misalignment, opens, nonwetting) usingoptical microscopes, and by automated inspection using X-ray imagingand in-circuit testing. Currently, the same inspection equipment is em-ployed for lead-free and tin–lead joints. However, retraining of the in-spectors and operators may be required due to differences in inspectioncriteria between lead-free and tin–lead joints.

Acceptance Guidelines for Lead-Free Solder Joints at Optical In-spection: The criteria for inspecting visual defects are typically setby industry standards such as IPC-A-610D [78], which has been re-vised to incorporate visual inspection criteria for lead-free solder joints.This revision is due to differences in solder joint visual appearance be-tween lead-tin and lead-free joints (due to the differences in the so-lidification behavior), which are characterized by dullness, reducedsurface smoothness, lower wettability, and potentially more crateringcompared with tin–lead joints. Although dull or shiny joints are accept-able, reduced wetting is not.

At this time, preexisting cracks can be induced by thermal and/ormechanical fatigue of the solder joints from reliability testing. Thismethod can be used in conjunction with electrical continuity measure-ments to determine open or partially open solder joints and their distri-bution for a specific component.

Acceptance Guidelines for Lead-Free Solder Joints at Automated In-spection: Current automated optical inspection criteria, which havebeen optimized for lead-based assemblies, are not suitable for lead-freeassemblies due to differences in solder joint visual appearance. How-ever, using a proper reference standard, the inspection system can beprogrammed to categorize good, marginal, or poor quality lead-free ortin–lead joints. This is possible as most of the combinations of solder

alloys and surface finishes have an impact on the appearance of solderjoints that can be characterized. Therefore, automated optical inspec-tion (AOI) settings require to be adjusted depending on the solder alloy-surface finish combination being inspected.

Regarding automated X-ray inspection, the coefficient of X-ray ab-sorption of lead-free alloys is reduced relative to that of tin–lead alloys,which can alter X-ray images. Calibration coupons can be employed toprogram the X-ray system for lead-free joint inspection.

Acceptance Guidelines for in Circuit Test of Lead-Free Assem-blies: There are no differences in functional testing between lead-freeand tin–lead soldered boards.

XI. HOW DO WE TRACE LEAD-FREE MATERIALS, PARTS

AND SUBASSEMBLIES?

The transition to lead-free manufacturing requires that lead-free ma-terials, parts, subassemblies and final products can be distinguishedfrom the corresponding lead-based ones. This is important for produc-tion, as well as rework and repair of field returns and recycling.

Lead-free products can be identified by their part number or serialnumber, lead-free marking, the effective date of designation change,product change notifications (PCNs), traceable documentation sys-tems, and staff training.

It is recommended that all lead-free materials, components andboards should have new (unique) supplier part numbers (PNs) as-signed to distinguish them from tin–lead ones [79], [80]. Suffix orprefix additions to existing P/N structures are acceptable. However, asurvey conducted by Avnet and Technology Forecasters in November2004 estimates that only 52% of component suppliers are planningto issue new part numbers for lead-free parts, and that 42% plan notto change part numbers, and instead to identify lead-free componentsusing designation printed on component packaging (37%), date ofmanufacture (31%), or marking on the components (27%) [81].

Standards for marking lead-free parts and assemblies include JEDECJESD-97 [82], JEITA ETR-7021 [83], and IPC-1066 [84]. These stan-dards recognize that the lead-free materials contained in the part needto be identified by the end-user, and in the case of both JESD-97 andIPC-1066, that the part process compatibility (maximum process tem-perature) should also be assessed. Equipment manufacturers shouldfamiliarize themselves with these marking methods, and should iden-tify the effective date of change in part designation. However, manyelectronic manufacturers use nonstandard marking methods, and con-sequently the same part may be designated using different markingschemes in different countries.

Manufacturers should monitor PCNs issued by their part supplierswhen transitioning to lead-free electronics. As per JESD46-B [85], allchanges on existing parts should be documented by a PCN issued bythe part manufacturer to notify their customers of product transition tolead-free. An example of PCN issued by a component manufactureris available in [86]. A monitoring scheme of supplier PCNs and sup-plier alerts of the replacement of lead-based parts by lead-free onesshould be established. The PCN-alert database service, and Govern-ment-Industry Data Exchange Program (GIDEP) are examples of alertdatabases. Any changes related to lead-free components should be con-sidered major changes. Sample devices and qualification data should beavailable to customers at the time the PCN is issued or the new productis introduced.

Many component suppliers do not plan to totally discontinue lead-containing products, as they anticipate a continuing demand for leadedproducts from exempted sectors. Component suppliers who plan todiscontinue noncompliant parts typically intend to give customers asix-week to 24-month time frame to return noncompliant products aftera PCN or end of life announcement is issued [81].


It is recommended that manufacturers conduct the shipment and useof tin–lead coated leadframes and chip termination components to de-pletion, followed by the introduction of lead-free coated components.

XII. WHAT ARE THE STANDARDS APPLICABLE TO LEAD-FREE

ASSEMBLY PROCESSES, QUALIFICATION, AND INSPECTION?

The release of new and revised standards applicable to lead-freeassembly process, qualification and inspection should be monitored.These operations may have an impact on part selection, and system de-sign, testing, and manufacturing for equipment manufacturers.

IPC has standards [49], [61], [63], [67], [77], [87]–[91] to addresslead free assembly. Standards [67], [87]–[91] relate to solderability re-quirements and testing of electronic parts and boards, and requirementsfor soldering materials. IPC-A-610D [78] has been revised to incorpo-rate visual inspection criteria for lead-free solder joints.

J-STD-020C [61], JEITA ED-4701-301A [62], J-STD-033C [63],and Mil-Std 202G Method 210F [64] relate to component moistureand thermal sensitivity classification, and the handling, packing, andassembly of moisture sensitive components.

JESD22A-121 [49] specifies procedures for measuring whiskergrowth on tin-based finishes.

Other standards applicable to lead-free assembly process, qualifi-cation and inspection, include [92]–[94]. PCB qualification standards[95]–[98] address lead-free PCB finishes. Common lead-free platingsand coatings are also covered in PCB design [99]–[102] and multichipmodule design [103] standards.

XIII. WHAT EDUCATION, TRAINING AND INFORMATION RESOURCES

ARE AVAILABLE TO HELP IN THE SUCCESSFUL IMPLEMENTATION OF

LEAD-FREE PRODUCT DEVELOPMENT?

Providers of education, training, and information resources onlead-free electronics include research organizations [38], [104]–[106],consulting companies [38], [107]–[109], contract manufacturers [110],vendors of electronic manufacturing products [111], [112], and com-ponent/equipment manufacturers such as [113]. Such providers covertopics ranging from lead-free legislation, implementation, materialand part selection, design, manufacturing, to lead-free reliability.

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Valérie Eveloy received the M.Sc. degree in phys-ical engineering from the National Institute of Ap-plied Science (INSA), Rennes, France, and the Ph.D.degree in mechanical engineering from Dublin CityUniversity, Dublin, Ireland.

She has been involved in the thermal management,packaging and reliability of electronic equipmentfor ten years, and is an Assistant Research Scientistat the CALCE Electronic Products and SystemsCenter, University of Maryland, College Park. Shewas previously with the Nokia Research Center,

Finland, and Electronics Thermal Management Ltd., Ireland. She has authoredor co-authored over 45 conference and refereed journal publications. Apartfrom lead-free electronics, her current research interests focus on electrostaticdischarge failures in integrated circuits, extending the limits of air-coolingfor electronics equipment, computational fluid dynamics, and biomedicalmonitoring.

Dr. Eveloy is a member of several international conference program com-mittees focused on electronics reliability and thermal phenomena in electronicsystems.

Sanka Ganesan (M’00) received the B.E. degreein metallurgical engineering from the University ofMadras, India, the M.E. degree (with distinction)from the Indian Institute of Science, Bangalore,India, and the Ph.D. degree in materials science andengineering from the University of Arizona, Tucson.

He is currently an Associate Research Scientist atthe CALCE Electronic Products and Systems Center,University of Maryland, College Park. His research isin lead-free electronics, advanced materials and inter-faces, low temperature electronics, and sensors and

MEMS. Prior to joining the CALCE EPSC, he worked for 12 years at Motorola,Inc. and was an active contributor in the development and implementation of ad-vanced packaging materials and interconnect technologies. He is the coauthorof Lead-free Electronics (2004). He holds three U.S. patents and three interna-tional applications.

Yuki Fukuda (S’04–M’05) received the B.S. degree in mathematics from ChibaUniversity, Chiba, Japan, in 1999, the M.S. degree in mathematics and computerscience from Ochanomizu University, Tokyo, Japan, in 2001, and the M.S. de-gree in mechanical engineering from the University of Maryland, College Park,in 2005 where she is currently pursuing the Ph.D. degree.

She is a Graduate Research Assistant with the CALCE Electronic Productsand Systems Center, University of Maryland.

Ms. Fukuda is a member of ASME, JIEP, and SMTA.

Ji Wu (S’01–M’03) received the B.S. degree in en-gineering from Tsinghua University, Beijing, China,the M.S. degree in chemistry from the ChineseAcademy of Sciences, Shanghai, and the M.S. andPh.D. degrees in mechanical engineering from theUniversity of Maryland, College Park.

She is a Research Associate with the CALCEElectronic Product and Systems Center, Universityof Maryland. Her research expertise includes reli-ability assessment of lead-free solders electronics,electronic connectors and IC sockets, accelerated

testing, failure analysis, and reliability capability evaluation.

Michael G. Pecht (F’92) received the B.S. degree inacoustics, the M.S. degree in electrical engineering,and the M.S. and Ph.D. degrees in engineeringmechanics, all from the University of Wisconsin,Madison.

He is the Director of the CALCE Electronic Prod-ucts and Systems Center, University of Maryland,College Park, and a Full Professor with a three-wayjoint appointment in mechanical engineering, engi-neering research, and systems research. He is on onthe Advisory Board of the Journal of Electronics

Manufacturing and is currently the Chief Editor for Microelectronics Relia-bility. He has written 18 books on electronic products development, use andsupply chain management. He has also edited a series of books on the Asianelectronics industry including The Chinese Electronics Industry (2004). Heserves on the Board of Advisors for various companies and consults for the U.S.government, providing expertise in strategic planning in the area of electronicsproducts development and marketing. He has consulted for over 50 majorinternational electronics companies, providing expertise in strategic planning,design, test, IP, and risk assessment of electronic products and systems.

Dr. Pecht received the 3M Research Award, the IEEE UndergraduateTeaching Award, and the IMAPS William D. Ashman Memorial AchievementAward for his contributions. He is an ASME Fellow. He served as ChiefEditor of the IEEE TRANSACTIONS ON RELIABILITY for eight years and on theAdvisory Board of IEEE Spectrum. He is an Associate Editor for the IEEETRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGIES.

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