Effects of alloy composition and intermetallic compounds on the solder properies of Sn alloys on Cu substrate

Abstract

Influence of solder alloy composition on the wettabiliy and the shear stress of the solder joint was investigated. Also, the effect of the growth of the intermetallic compounds on the shear stress of Sn-Bi and Sn-Pb solder joints was investigated. Sn-Bi and Sn-Pb alloys were electroplated on a Cu plate from methane sulfonate bath and then reflowed at 250℃. The wetting angle of Sn-Bi solder was increased with increasing Sn content in the solder due to increase in the surface energy. Two Cu plates electrodeposited with Sn-Bi and Sn-Pb were clamped each other and soldered at 220℃ to produce solder joints. The solder joints were pulled to failure at strain rate from 3.3×10 exp (-4) to 3.3×10 exp (-2) / s to measure the shear strength of the solder joints. At low strain rate, the shear strength of the Sn-Bi solder joint decreased with increasing Sri content in the solder, but at high strain rate, the shear strength increased due to the brittleness of Bi. The shear strength of the 80Sn-2OPb solder joint was higher than that of the 60Sn-4OPb solder joint at all strain rate. The shear strength of the 42Sn-58Bi solder joint was higher than that of the 8OSn-2OPb at low strain rate, but lower at high strain rate. The shear strength was increased with increasing aging time until 24 hours because the rough surface of the intermetallic compounds acted as wedge at the intermetallic compound/solder interface. After 24 hours, the increase in thickness of the brittle intermetallic compound layer decreased the shear strength of the 42Sn-58Bi solder joint.