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Second Generation Pb-Free Alloys
Second Generation Pb-Free Alloys
Paper covers shortcomings of current alloys, namely SAC305, and presents data for various new alloys which show promise as replacement materials.
Materials Tech

Authored By:
Randy Schueller, Ph.D., Nathan Blattau, Ph.D., Joelle Arnold, and Craig Hillman, Ph.D.
DfR Solutions, College Park, MD, USA
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Summary
This paper will discuss the shortcomings of current LF alloys (namely SAC305) and present recent data for various new alloys which show promise as replacement materials. These newer alloys offer important reliability improvements but do have some issue that need resolution before mass implementation. Shock and vibration data will be provided, as well as thermal cycle data. The primary focus will be on SnCuNi and SAC105X alloys and how they can be used effectively in the Pb-free electronics industry going forward.
Conclusions
The transition from SnPb to Pb-free has been fast and furious for an industry where it can take a decade or more to gather the necessary reliability data. SAC305 was introduced as the Pb-free alloy for surface mount applications and many would argue has been rather successful considering the tight timescale. Deficiencies have since been identified and a transition has begun to newer alloys. For handheld products the first change was to SAC105 for improved shock resistance. It was then recognized that the loss in thermal cycle resistance was not acceptable for other applications.

The next push will be to achieve improvements in shock and thermal cycle behavior. Sn-Cu-Ni, SAC105C, SAC105M, and SACX show promise but all require higher process temperatures. It is likely that one or more of these alloys will become popular for BGA balls and surface mount applications in the future. It is also possible, but less likely, that a lower melting temperature alloy such as SnAgBi could be brought back to the table after the threat of Pb contamination has subsided. In any case, we should be prepared for a period of transition that will be a challenge for both BGA component suppliers and electronic manufacturers.
Initially Published in the SMTA Proceedings
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