Microstructure and properties of Sn-Zn-Ga-xPr lead-free solder

Effects of rare earth element Pr additions on the microstructure and properties of Sn-Zn-Ga solder were studied in this paper.The wettability of solder was significantly improved by 0.08% Pr addition.However,the wettability of solder would deteriorate when the Pr addition exceeds 0.12% due to the oxidization of Pr element at the liquid surface.Moreover,the mechanical property of solder joint was improved by Pr addition and the maximum shear strength was obtained when 0.08% Pr was added.The Zn-rich phase in the solder matrix was refined by Pr but the thickness of interface layer showed no obvious difference when Pr was less than 0.08%.When excessive Pr was added,the interface layer thickness of the joint increased significantly,so that the optimal content of Pr in the Sn9Zn0.5Ga solder is about 0.08%.