Exploring the Next-generation High-Reliability Lead-free Solder Alloy

Abstract

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. Thermal cycling has also been performed on BGA solder joints in extreme temperature conditions and results have been discussed.