Growth orientation of Cu–Sn IMC in Cu/Sn–3.5Ag/Cu–xZn microbumps and Zn-doped solder joints

Abstract

In this study, the evolution of grain structures in Cu/Sn–3.5Ag/Cu–xZn (x=0 or 15wt%) microbumps and SAC305/Cu–xZn solder joints was investigated. Due to the small size of microbumps, impingement of interface IMCs easily occur. In a Cu/Sn–3.5Ag/Cu (wt%) microbump, the grain orientation of combined intermetallic compounds (IMCs) tends to be homogenous and closely-grouped, allowing cracks to more easily propagate. In order to examine the grain evolution of Cu–Sn IMCs, EBSD analysis was applied to microbumps and conventional-sized solder joints. Replacing the Cu substrate with Cu–Zn causes the grain orientation of Cu–Sn IMCs to become more random and dispersed, which may hinder crack propagation. It is thus expected that the reliability of Zn-doped microbumps and solder joints is superior to that of Cu substrate joints.