Quaternary low melting point Sn-Bi-in-xGa solder with improved mechanical performance for advanced electronic packaging

Managing thermal stress is important for ensuring the yield of chip integration and packaging. The development of appropriate low melting point solders has become the key to mitigating thermal stress during the assembling, which aligns well with the demands of next-generation interconnection technologies. In this study, we developed a quaternary low melting point solder based on Sn-Bi-In-xGa (x = 0, 0.1, 0.3, 0.5, 1.0, 1.5, wt%). The addition of Ga not only lowers the solder's melting point but also enhances its wettability. We also studied how the increase of Ga in the solder alloy influences the microstructure and shear test failure mechanism during aging. Upon subjecting solder joints to a 10-min reflow process at 100 °C with Cu substrates, two distinct types of intermetallic compound (IMC) were observed: Cu₆(Sn, In)₅ when Ga content was ≤0.1 wt% and γ₃-Cu₉Ga₄ when Ga content was ≥0.3 wt%. The stable property of γ₃-Cu₉Ga₄ IMC ensures the mechanical stability of the joints during aging. Therefore, the addition of an appropriate amount of Ga (0.3 wt%) can improve the mechanical performance of solder joints during aging. These findings offer valuable insights for the development of high-performance low-melting-point solders in microelectronics, shedding light on the mechanisms underlying the influence of Ga content on solder microstructures and mechanical reliability during thermal aging.