Interfacial reaction in Cu/Sn/Cu fine pitch interconnect during soldering

The interfacial reaction in Cu/Sn/Cu fine pitch interconnects during soldering at 250 °C was investigated in the present work. The morphological evolution and growth kinetics of the interfacial intermetallic compounds (IMCs) were studied. Cu₆Sn₅ scallops formed at the Sn/Cu interface and ripened with increasing reaction time. The dependence of average grain number on reaction time t followed t^-0.70 relationship. During the solid-liquid interfacial reaction, different growth behavior of interfacial Cu₆Sn₅ scallops presented between the direction vertical to the interface and that parallel to the interface. According to the ratio of R/H, the growth of interfacial Cu₆Sn₅ could be divided into three stages, i.e., the initial stage, the ripening stage and the thickening stage. The growth of Cu₆Sn₅ scallops was controlled by grain boundary diffusion, while that of Cu₃Sn was controlled by volume diffusion.