| Summary: | As people enter the era of the IoT (Internet of Things), more and more microelectronic devices and flexible electronic devices have been developed and applied. A novel Bi–In–Sn–Zn quaternary solder system is presented, aiming at improving mechanical properties of low-melting solders for flexible electronics. The study examines the differences in the microstructure of the Sn–Bi–In ternary solders before and after the addition of the Zn element, furthermore, it analyzes the role of the Zn element in the Bi–In–Sn system. The results indicate that the Zn element partially exists in the form of a Zn phase, while the remaining portion dissolves in the eutectic structure of the Sn–Bi–In alloy. Moreover, a significantly higher amount of Zn is found to dissolve in the (In,Bi)Sn4 phase compared to the BiIn phase. The dissolved Zn element enhances the strength of the solder by increasing the lattice distortion in the (In,Bi)Sn4 phase and refining the grains of the Sn–Bi–In alloy. Subsequently, the 53Bi30In17Sn–Zn equilibrium phase diagram was obtained by CALPHAD (Calculation of Phase Diagrams) method based on thermodynamic calculation, providing new idea for the future research and development of solder used in the electronic packaging field.
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