The Development and Commercialization of Lead-Free Soldering
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The Development and Commercialization of Lead-Free Soldering Katsuaki Suganuma Overview Early in the 1990s in the United States, a series of legislative measures were proposed for banning the use of lead for many applications in industries involving electronic solders. Although electronic solders were ultimately exempted, this argument ignited worldwide concern, and research began on the development of lead-free solders.
The U.S. project, organized by the National Center for Manufacturing Sciences (NCMS), was carried out from 1992 to 1996.1 Major electronics companies and auto manufacturers participated with several national institutes in this project. They first made surveys on toxicology, resources, and availability and selected seven initial sol-
ders for testing. After a series of evaluations, three Sn alloys remained as the candidates: Sn-3.5%Ag, Sn-3.5%Ag-4.8%Bi, and Sn-58%Bi (all compositions cited in this article are in wt%). The features of those solders are summarized in Table I. The conclusion of this project, however, was that no drop-in replacement for Sn-Pb eutectic solder yet exists, and that further work on developing appropriate solders is required. In 1994, the Japan Institute of Electronics Packaging (JIEP) formed a lead-free solder research committee involving companies and several universities in Japan and began an academic project on developing lead-free solders. They first focused on the high-Bi alloys such as Sn-22%Bi-2%Ag and Sn-7.5%Bi-2%Ag-0.5%Cu (“Alloy-H”) that can replace Sn-Pb eutectic solder without modification of the processing conditions, particularly temperature. They stated in their conclusions, however, that high-Bi alloys are very brittle and cause lift-off (“fillet-lifting”), resulting in poor reliability.2 In January 1998, the Japan Electronics Industry Development Association (JEIDA, now known as Japan Electronics and Information Technology Industries Association, JEITA) and JIEP produced a “roadmap” for lead-free soldering to promote its use
Table I: Features of Sn Alloy Solders Recommended by the National Center for Manufacturing Sciences Project on Lead-Free Solders.
Alloy a
Liquidus and Solidus Temperatures
Industry Sectors
Evidence for Recommendation
Sn-58%Bi
139C (eutectic)
Consumer electronics Telecommunications
Simple, two-component eutectic alloy; low eutectic temperature restricts maximum-use temperature. Surface mount technology: better fatigue life than eutectic tin-lead for both thermal-cycling ranges; less fatigue damage than eutectic tin-lead seen in surface mount cross sections. Through-hole technology: mixed results, with fatigue life for CPGA-84b better than for eutectic tin-lead; fatigue life for CDIP-20 c worse than for eutectic tin-lead.
Sn-3.5%Ag-4.8%Bi
205–210C
Consumer electronics Telecommunications Aerospace Automotive
Surface mount technology: longer fatigue life than eutectic tin-lead between 0C and 100C; no failures in 1206 resistors up to 6673 cycles; fatigue life equivalent to eutectic tin-lead between 55C and 125C; less fa
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