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Exploring the Next-Generation High-Reliability Lead-free Solder Alloy
The novel Alloy 10 solder alloy presented here exhibits exemplary thermomechanical and mechanical reliability in extreme operating conditions, ideal for the future needs of high-reliability electronics, such as in the automotive industry.
Technical Paper
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Authored By:
Pritha Choudhury, Ph.D., Morgana Ribas, Ph.D., Prathap Augustine, Siuli Sarkar, Ph.D., Paul Salerno, Anna Lifton
MacDermid Alpha Electronics Solutions
Bangalore, India
Lijia Xie, Sean Yenyu Lai, David Neal Halbrook, Ganesh Subbarayan, Ph.D., John Blendell, Ph.D.
Purdue University
West Lafayette IN, USA
Summary
The ever-increasing demand for high-temperature reliability and extended fatigue life requirements in more demanding electronic applications, has motivated further investigation on high-reliability lead-free solder alloys. The novel Alloy 10 solder alloy presented here exhibits exemplary thermomechanical and mechanical reliability in extreme operating conditions, ideal for the future needs of high-reliability electronics, such as in the automotive industry.
Recent results showing excellent performance of Alloy 10 when compared to another leading high-reliability alloy, have also raised questions on which features are responsible for such performance. In this work, we present the latest results of a collaborative in-depth study to understand the mechanisms behind the Alloy 10 solder alloy’s improved performance. Solder joint samples are studied for the detailed composition and distribution of phases after reflow and aging treatment under varying aging times. The effect of aging time and temperature on the evolution of the microstructure of the solder joints is then studied. A redistribution of elements and phases are observed after aging; microconstituents are observed to be uniformly distributed after prolonged aging, while intermetallic compounds grow and become distinctly visible upon aging. This discussion is then further expanded by discussing the mechanical behaviour of Alloy 10 as measured by a custom designed micro-precision mechanical tester, which was used to perform isothermal creep, monotonic and fatigue testing of solder test specimens under shear at room temperature.
Conclusions
Increase in complex electronic assemblies exposed to harsh environmental conditions has motivated the need for advancement of solder alloy technology. Migration of automotive industry to electric vehicles and autonomous driving that require extended service life in harsh operating conditions is the driving force for the adoption of high reliability solder alloys. The new high reliability Alloy 10 developed at MacDermid Alpha has been studied in detail to understand the mechanism behind its improved performance.
Key conclusions are:
- Very low undercooling of ~11oC is observed in Alloy 10 compared to a high undercooling of ~45oC in the standard High Rel Alloy has resulted in finer grain size in Alloy 10. The dissolution of Bi and precipitation of SnSb particles helps maintain the high strength of Alloy 10 for a longer time after aging.
- Higher elongation of Alloy 10 during high temperature tensile test indicates a better performance when subjected to thermal cycling in extreme temperature conditions.
- Alloy 10 is also observed to have much higher characteristic life than the High Rel Alloy during thermal cycling.
Work is ongoing on further mechanical and thermomechanical properties evaluation of the Alloy 10 solder joints and the failure analysis to understand the underlying mechanisms.
Initially Published in the SMTA Proceedings
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