Effect of indium on microstructure, mechanical properties, phase stability and atomic diffusion of Sn-0.7Cu solder: Experiments and first-principles calculations

Sn-0.7Cu–In ternary alloy solders have received much attention because of their excellent weld stability and wettability. However, how to inhibit or slow down the formation of defects at the welding interface has always been the focus of research. The effects of In on melting point and microstructure of Sn-0.7Cu solders and phase stability and growth rate of intermetallic compounds (IMCs) in the solders were investigated by means of experiments and first-principles calculations. The Rietveld refinement results showed that the lattice constants of β-Sn and η′-Cu6Sn5 (Cu6Sn5) phases increase after In addition. Moreover, In can decrease the melting point, but increase the melting range of Sn-0.7Cu solders. After adding In, the ultimate tensile strength (UTS) increases, while the elongation decreases. From the first-principles calculation results, the stability of Cu6Sn5 increases after In doping, and In doping results in the formation of new chemical bonds between In atom and the neighboring Cu and Sn atoms. Ultimately, the diffusion activation energy and atomic migration barrier of the Cu atom increase after In doping, which in turn decreases the growth rate of Cu6Sn5.