Effect of minor Ag and Cu additions on melting characteristics, wettability and microstructures of Sn58Bi solder

Abstract

Low temperature soldering can reduce the thermal damage which is caused by thermal expansion mismatch among various materials in an electronic package. Eutectic Sn58Bi solder is a promising low temperature lead-free solder due to its lower melting temperature. The effects of Ag and Cu additions on melting characteristics, wettability and microstructures of Sn58Bi lead-free solder were investigated. Only Sn phase and Bi phase like net-type distribute uniformly in the Sn58Bi matrix. Sn58Bi0.1Ag, Sn58Bi0.1Cu and Sn58Bi0.05Ag0.05Cu solder show the Ag3Sn particles in the Sn matrix around net-like Bi phase. With the addition of Cu, Cu6Sn5 intermetallic compound was observed. Addition of Ag and Cu decreased the melting temperature of Sn58Bi lead-free solder from 142.5°C to 140.5°C which was possible mainly due to the existence of Ag3Sn and Cu6Sn5 intermetallic compounds. Moreover, the wettability of Sn58Bi1.0Cu solder was best of all, and the N2 atmosphere can enhance the wettability obviously, which can provide the reference support of the research of SnBi solders.