Materials interaction between inherent barrier Pb-free Sn-Zn-Al solder and Cu contact

Abstract

The Pb-free Sn-Zn-Al solder was dip coated on a Cu contact to investigate the interaction between them under aging conditions at 150/spl deg/C for up to 1000 hours. The results of EPMA analysis indicate that Al gathers at the Cu/solder interface and inhibits the interdiffusion between Cu and Sn. This solder itself provides a diffusion barrier for the Cu contact and thus is termed inherent barrier solder. Cu was found to be able to diffuse to solder under long term heat treatment but not Sn. Nevertheless, Cu was not found to form any compound with Sn in this study. The as-dipped solder reacts with Cu to form an Al/sub 4.2/Cu/sub 3.2/Zn/sub 0.7/ compound. The high temperature heat treatment transforms the compound to Cu/sub 5/Zn/sub 8/, Al/sub 4/Cu/sub 9/ in a heating duration up to 400 hours. The final product is Cu/sub 5/Zn/sub 8/ after 600 hours of aging.