Effect of Bi on Properties of Sn-9Zn Alloy for Interconnections

With the rapid development of electronics devices, solder joints are critical for electronic packaging. Meanwhile, traditional Sn-37Pb solder has been replaced by lead-free alternatives, Sn-9Zn alloy gains attention due to its melting point being close to that of Sn-37Pb and its good mechanical properties. However, their oxidation resistance and ductility are relatively poor. Research has shown that the addition of Bi can improve the wettability of the alloy and lower melting temperature. This study investigates the effects of minor Bi additions on the microstructure, mechanical properties, and thermal aging behavior of Sn-9Zn alloys. The results demonstrate that adding Bi effectively lowers the melting temperature of Sn-9Zn and enhances its tensile strength. Microstructural analysis indicates that Bi additions significantly affect the growth and precipitation behavior of the Zn phase, leading to notable changes in the microstructure. The alloy maintains good stability after thermal aging treatment. Overall, the findings suggest that Sn-9Zn-Bi alloys show potential as low-temperature solder materials.