Effect of Ag addition on the intermetallic compound and joint strength between Sn-Zn-Bi lead free solder and copper substrate

Abstract

This study investigated the effect of Ag addition on the formation of intermetallic compounds and joint strength of the Sn-Zn-Bi based alloys under liquid state aging. The intermetallic compounds were formed by reacting Sn-8Zn-3Bi and (Sn-8Zn-3Bi)-IAg lead free solders on copper substrate. Scanning electron microscope (SEM) was used to see the morphology of the phases and energy dispersive x ray (EDX) was used to estimate the elemental compositions of the phases. It was found that for Sn-8Zn-3Bi solder reacting with Cu substrate, the Cu5Zn8 intermetallic was formed. On the other hand, when 1 % Ag was added into the solder, the CU3Sn and CU6SnS IMC were formed. The morphology of the CusZng intermetallic was flat whereas for CU3Sn and CU6SnS were rather scallop. The addition of Ag into the Sn-Zn-Bi solder increases the shear strength of the solder joint. It is believed the scallop morphology of Cu Sn contribute to strengthening the (Sn-8Zn-3Bi)-IAg/Cu joints.