Design and properties of Sn-Bi-In low-temperature solders

Sn-Bi-In low-temperature solder was fabricated by adding In element to tin-bismuth series solder. In this paper, to study the solders with melting temperature around 110°C for replacing the toxic 26Sn-54Bi-20Cd alloy, the microstructures, thermal properties, wettabilities and microhardness of solders were studied respectively. The results show that the microstructure of Sn-Bi-In solders is composed of BiIn2 matrix, InSn4 and Bi phases, and transformed to Snrich matrix, Bi and InBi phases with the In content reduction. In addition, the melting temperatures of solders with 12wt% In content are around 101.5–103.1°C. Wettability is affected by compositions and the increase of Sn content to 50wt% can promote the spreading of solders. Microhardness can be increased by Bi addition and In reduction. Based on these properties study, 50Sn-38Bi-12In solder is comparable to 26Sn-54Bi-20Cd solder, and could be used in the special lowtemperature welding.