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

Abstract

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 Sn-rich 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 low-temperature welding.