The modifying microstructure and properties of SnAgCuBiSb-xIn solder alloys: The role of In element

Sn3·0Ag0·5Cu (SAC305) is widely used for its good wettability and mechanical properties, but its high soldering temperature and coarsening of second-phase particles affect reliability. The Sn-1.0Ag-0.7Cu (SAC107) alloy, owing to finer microstructure, better creep and thermal fatigue resistance, and lower cost, is an ideal replacement. Nevertheless, some of their mechanical properties are generally lower than the SAC alloys with a higher Ag content. This study investigates the effects of different In content (0, 1, 4, 7, and 10 wt%) on the microstructure and mechanical properties of the low-silver Sn1·0Ag0·7Cu3·0Bi1·5 S b multicomponent solder alloy. The addition of In significantly decreases the melting point and liquidus temperature, and alters the melting range and undercooling of the alloy. X-ray diffraction results revealed a shift of the overall β-Sn diffraction peaks toward lower angles with increasing In content, indicating that more In element is dissolved into Sn lattice. Moreover, The precipitation of new phases, namely γ-InSn 4 , occurred at 10 wt% In content. Concurrently, In addition also effectively refined the β-Sn grains and increased the proportion of high-angle grain boundaries. The addition of In increases the ultimate tensile strength while decreasing the elongation under the regulation of secondary phases, and shifts the corresponding fracture mechanism from a ductile to a mixed ductile-brittle mode. This study provides a theoretical basis and practical guidance for developing novel multi-alloys for low-temperature applications by modifying Sn1·0Ag0·7Cu3·0Bi1·5 Sb-xIn (x = 0, 1, 4, 7, and 10 wt%) solders microstructure and properties via the control of In content.