Abstract
Serious Joule heating is expected to bring new reliability challenges in advanced packaging technology and thermomigration of solder joints is regarded as one of critical reliability issues. Recently, Co has been proposed as a candidate for under-bump metallization (UBM) because of its high wettability, great corrosion resistance and lower growth rate of intermetallic compound (IMC) during reflow process as compared to Cu and Ni. In this study, thermomigration behavior of Co/SnAg/Co and Cu/SnAg/Co sandwich structure is investigated. For Co/SnAg/Co structure, faster growth of CoSn3 IMC at the hot end than the cold end is observed and Sn is found to dominate the interfacial growth under a temperature gradient. In contrast to Co/SnAg/Co structure, Cu6Sn5 and Cu3Sn IMCs in Cu/SnAg/Co structure grow faster at the cold end than that at the hot end and Cu is the dominant diffusion species during thermomigration. In addition, no Co signal is detected near Cu substrate under a temperature gradient in Cu/SnAg/Co structure, demonstrating that Co possesses better thermomigration resistance than Cu and Sn.
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