Effects of Zn addition on mechanical properties of eutectic Sn–58Bi solder during liquid-state aging

Interfacial reaction, tensile strength and creep resistance of Sn–58Bi–xZn (x=0, 0.7, mass fraction, %) solder samples during liquid-state aging were investigated. The coarsening of Bi and the growth of Cu–Sn intermetallic compounds (IMCs) in Sn–58Bi–0.7Zn solder sample were both effectively suppressed. With the addition of 0.7% Zn, ultimate tensile strengths (UTSs) of the Sn–58Bi solder slabs were respectively increased by 6.05% and 5.50% after reflow soldering and liquid-state aging, and those of the Cu/Sn–58Bi/Cu solder joints were also increased by 21.51% and 29.27%, respectively. The increase in strengthening effect of Cu/Sn–58Bi–xZn/Cu solder joints could be attributed to the fracture surface which was changed from the Cu/IMC interface to the IMC/solder interface due to the finer Bi grain. Nanoindentation results revealed that the creep behavior of Sn–58Bi–0.7Zn solder was significantly improved compared with that of the eutectic Sn–58Bi solder after reflow soldering and liquid-state aging.