Interfacial Reactions in Sn-57Bi-1Ag Solder Joints with Cu and Au Metallization

Abstract

This paper investigated interfacial reactions in two Sn-57Bi-1Ag (mass%) solder joints, bonded to Cu and Au metallization. As the melting point of Sn-57Bi-1Ag is 138℃, bonding was conducted at 170℃ and the bonding time was varied from 1 min to 60 min. The melting properties and microstructure of each solder joint were investigated. Results indicated that the melting point of the Sn-57Bi-1Ag solder joint bonded to Cu was approximately 140℃ even after heating at 170℃ for 60 min, and that the lamellar structure of Sn and Bi phases was similar to the structure at an initial state. Conversely, the melting start point of the Sn-57Bi-1Ag solder joint bonded to Au metallization was approximately 230℃ after heating at 170℃ for 60 min and the differential scanning calorimeter peak at 138℃ disappeared. The microstructure of the solder joint did not show the lamellar structure of Sn and Bi phases, but rather consisted of an Au-Sn intermetallic compound, Bi phase, and Ag₃Sn phase. The occurrence of voids in the solder joint was possibly suppressed by optimum loading.