Composition design, microstructure and mechanical properties of bismuth-doped In–Sn-based low-temperature solder alloy

In-48Sn eutectic solder is an ideal candidate for flexible electronics equipment packaging because of its low melting point (118 °C) and low electrical resistivity (0.14 × 10^–6 Ω·m), but its low tensile strength and solder joint shear strength give some cause for concern. In this paper, the microstructure, thermal physical and mechanical properties of Bismuth-doped In–Sn-based low temperature solder alloy were simulated by using JMatPro software, and the optimized alloy composition was In-45.6Sn-5Bi. The experimental results show that ‘In–Sn–Bi ternary eutectic reaction in In-45.6Sn–5Bi alloy leads to the formation of a certain amount of BiIn intermetallic compounds (IMCs) which significantly refines the grains of β and γ phases, thus improving the mechanical properties of the alloy. Through the synergistic effect of second phase strengthening and fine grain strengthening, the tensile strength of the alloy is improved to 23.1 MPa, Vickers hardness is improved to 6.2 HV_0.2, and the shear strength of solder joint is improved to 5.8 MPa. Compared with the traditional experimental “trial and error” material development model, this paper provides a more efficient, low-cost and high-precision low-temperature solder development method, which provides a theoretical and experimental basis for developing high-strength low-temperature solder.