How much easier the transition to lead free could be if manufacturers didn’t have to research which solder to choose. Now, thanks to the IPC Solder Products Value Council’s (SPVC) lead-free testing program, that research has been done. During the past three years, the SPVC has invested the equivalent of one million dollars in volunteer time, equipment and supplies to come up with the answer. “The final report of the round robin testing and analysis of the lead free alloys is an excellent example of how companies, although fierce competitors in the marketplace, can come together and work for the benefit of the industry”, says Roger Savage, president of Kester and chair of the SPVC. This report answers two key questions for this current change of paradigm in the board-assembly industry: What alloys will most likely be used as tin-lead solder replacement? What tests can accurately determine the differences (if any) in the properties of the most likely candidates? The council determined the majority of potential standard-replacement alloys are composed of tin, silver and copper (commonly called SAC, SnAgCu) alloys and analyzed the three most commonly used lead free alloys: 96.5Sn3.0Ag/0.5Cu 95.5Sn3.8Ag0. 7Cu; and 95.5Sn4.0Ag0.5Cu. Test methods used in the research included melt analysis; wetting balance; area of spread; visual inspection of solder joints; X-ray analysis of voids; temperature-cycle tests; thermal shock testing and metallurgical analysis. The data contained in the final report supports the council’s recommendation of 96.5Sn3.0Ag0. 5Cu (labeled SAC305) as their alloy of choice for lead-free applications. The paper also includes summary findings on the effect of voiding on solder-joint reliability. Although the project was not designed as a head-to-head comparison of lead-free versus tin-lead solders which is also not the question any longer anyway, the report does highlight lf solder-joint performance.
EPP EUROPE 420
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