Effects of Cu and in on the Microstructure Evolution and Mechanical Properties of Sn-20Bi/Cu Solder Joints

The effects of Cu and In additives on the tensile strength, interfacial reaction, and shear strength of the Sn-20Bi solder system are investigated. The Sn-20Bi-xCu-yIn (x = 0.3, 0.5 wt.%, y = 1, 2, 3 wt.%) alloy is prepared by muffle furnace melting, and the microstructure and tensile strength of the alloy are studied. The solid solution strengthening of In is the main reason for the increase in tensile strength. To evaluate the interfacial properties of the alloy, the shear strength and shear fracture morphology are analyzed. Mechanism and shear fracture mode analysis to predict intermetallic thickness change by SEM–EDS characterization. The shear strength increased with the In and Cu contents. The Sn-20Bi-0.5Cu-2In/Cu joint has the best fracture properties.