Mechanical Properties and Solder Joint Reliability of Low-Melting Sn-Bi-Cu Lead Free Solder Alloy

Abstract

The influence of alloy composition on mechanical properties and solder joint reliabilities of the low-melting Sn-Bi-Cu lead-free solder alloys were investigated. The optimum alloy composition is Sn-40Bi-0. 1Cu (mass%). By containing 40mass%Bi, the low ductility is improved and the fillet-lifting is prevented, which are problems of the lead-free solder with Bi. The addition of copper improves the ductility of Sn-40Bi. Sn-Bi and Sn-Bi-Cu with 30~45mass%Bi show super plasticity. That is, the elongation of Sn-40Bi reaches 121% at 25°C, and that of Sn-40Bi-O. lCu reaches 171% at 25°Cand 516% at 80°C which are 2. 5 times those of the conventional Sn-37Pb solder alloy. The joint strength, thermal fatigue resistance and copper leaching resistance for PWB of the Sn-40Bi-0. 1Cu solder joints are superior to those of Sn-37Pb. © 2002, The Japan Institute of Electronics Packaging. All rights reserved.