Effects of Bi content on melting characteristics, microstructure, and shear strength of Sn-based solders

This study investigates the effects of Bi content (0, 10, 20, 30, 45, 58 wt%) on the wettability, melting characteristics, microstructure, interfacial reactions, and shear strength of Sn-based solders with Cu substrates. The study primarily focused on the evolution of microstructural products and solder properties during the transition from pure Sn solder to Sn–Bi eutectic solder, aiming to establish a foundation for further in-depth research and modification strengthening of Sn–Bi series solders. Compared to pure Sn solder, Sn–58Bi solder exhibited a 67.6 % reduction in wetting angle, achieving 9.28°. The peak temperature was 37.4 % lower at 142.9 °C. The thickness of the intermetallic compound (IMC) layer exhibited an initial increase followed by a decrease as the Bi content rose. A minimum IMC thickness of 5.95 μm was achieved with the Sn–58Bi solder. Furthermore, shear testing revealed that the Sn–58Bi solder joints achieved the peak shear strength of 41.42 MPa, which marked a 72.73 % enhancement over the pure Sn joints.