The electronic industry now has some official guidelines on what makes up the best alternative to leaded solder. The industry group, IPC, the Association Connecting Electronics Industries, has released the report, “Final Report – Round Robin Testing and Analysis of Lead Free Solder Pastes with Alloys of Tin, Silver, and Copper.” The report was developed by the lead-free testing program conducted by IPC’s Solder Products Value Council (SPVC).
The SPVC set out to answer two key questions. What alloys will most likely be used as a tin lead solder replacement? And what tests can accurately determine the differences (if any) in the properties of the most likely candidates? The SPVC determined that the majority of potential standard replacement alloys are composed of tin, silver, and copper (commonly called SAC) alloys and analyzed the three most commonly used lead-free versions:
* 96.5/3.0/0.5 of tin/silver/copper
* 95.5/3.8/0.7 of tin/silver/copper
* 95.5/4.0/0.5 of tin/silver/copper
The test methods used in the research included DSC melt analysis, wetting balance, area of spread, visual inspection of solder joints, x-ray analysis of solder joint voids, temperature cycle testing, thermal shock testing, and metallurgical analysis.
The data contained in the 50-page final report support SPVC’s recommendation of 96.5/3.0/0.5 of tin/silver/copper as the alloy of choice for lead-free applications. The final report also includes summary findings on the effect of voiding on solder joint reliability. The test compared alternatives to lead tin solder, so there is no data indicating whether the tin/silver/copper alloys performed better or worse than traditional leaded solder.
The IPC’s SPVC is an industry council that includes 17 member companies, including Indium, AIM, EFD, Kester Solder, Amtech, Thai Solder and other companies that typically compete with each other in the solder market. “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 Solder and chair of the SPVC.
The final report is available on CD for $99 for IPC members and $199 for non members at the IPC site (ipc.org). The report comes with 18 appendices on a separate CD. The appendices include nearly 60 megabytes of data covering alloy characterization, down select data, an assembly processing parameter summary, test vehicle description, assembly process data, void data, metallographic analysis of 500 cycles up to and including 6,000 cycles, and results of thermal shock and temperature cycling.