Abstract
Cu and Ni thin films are widely used as under-bump-metallization (UBM) and diffusion barriers in the current electronic packaging fields. Recently, because Co and its alloy possess high wettability and great corrosion resistance, they are regarded as a potential alternative as diffusion barriers and UBM materials. In this study, the interfacial reactions in Cu/Pb-free solder/Co couples during the reflow and solid-state aging process were investigated. The results show that the CoSn3 phase was formed at Pb-free and Co interface in all samples, however, the presence of Cu from the opposite substrate was found to significantly suppress the growth of CoSn3 intermetallic compounds. The kinetic mechanism of interfacial reaction was discussed and corresponding activation energy was calculated. The results of growth mechanism of intermetallic compound for both pure Sn and Sn96.5Ag3.5 solder joints were also compared. The morphology of the intermetallic compounds formed at both interfaces will be examined as well.