Effect of In addition on mechanical properties of Sn-9Zn-In/Cu solder

In this study, trace amounts (0.5-2 wt%) of indium (In) are added to the Pb-free Sn-9Zn solder. Expect to improve the mechanical properties and find out the optimum conditions of Sn-9Zn-In solder. Tests are conducted to measure microhardness and shear strength while microstructure and morphology of fracture surface are observed using scanning electron microscope with elemental composition analyzed by energy dispersive spectrometer. Results show that addition of In to Sn-9Zn solder alloy leads to needle-shaped precipitates formed in the substrate. This not only increases micro-hardness, but also enhances shear strength at Sn-9Zn-In/Cu solder joints. Improvements in both micro-hardness and shear strength confirm that adding In to the solder alloy can contribute to better mechanical properties of Sn-9Zn-In/Cu joints with proper control of soldering temperature and time.