Effects of palladium and solder aging on mechanical and fatigue properties of tin-lead eutectic solder

The effects of (a) 0.5 wt.% of Pd addition, and (b) aging on mechanical and fatigue properties of eutectic solder (63Sn37Pb) were investigated. The creep rate of eutectic solder at room temperature is not affected by Pd addition. However, at 80 °C, solder containing Pd creeps slower than Sn-Pb eutectic. Strain rate dramatically affects yield and tensile stress of eutectic solder with Pd as it does for the binary solder. Isothermal fatigue life of solder at 25 °C is essentially not changed by Pd addition. The microstructure of Pd-containing solder consisted of polyhedral grains of (Pb), (Sn), and a dispersion of PdSn4 intermetallic. Significant microstructural changes and interphase interface phenomena take place during creep deformation at 25 and 80 °C. Ambient aging for seven years leads to solder softening and to moderate increase in isothermal fatigue life.