Elastic properties of coarse grained lead-free solder alloys

Because of health and environmental concerns about lead, lead-free solder alloys in most consumer electronics have been required in the European Union since 2006. Many of these alloys are prone to mechanical failure over time, leading to less reliable circuitry. The source of these failures is not well known and many have conjectured that the coarse grained alloys become more brittle over time when exposed to elevated temperatures (~100 °C). Our group, in collaboration with Cisco Systems, has recently studied the effects of aging on the mechanical properties of Sn-Ag-Cu (SAC) solder alloys using using both resonant ultrasound spectroscopy (RUS) and conventional pulse-echo methods. With grain sizes on the order of 100's of microns, the heterogeneity of these alloys present a particular problem for RUS and interpretation of pulse-echo data. Resonance data exhibiting the effect of the heterogeneity will be presented and discussed. Elastic moduli derived from pulse-echo methods as a function of temperature an...