A study of NiFe alloy as under bump metallurgy (UBM) for Pb-free interconnect has been performed. Intermetallic growth rate of NiFe and SnAg solder is about 10x slower than that of Ni and SnAg solder. The thin and uniform intermetallic compound FeSn2 showed excellent thermal and electromigration stability. By slowing down or stopping the UBM dissolution, NiFe effectively eliminated the early EM fails that are common with Ni UBM. NiFe is an interesting candidate for the chip and substrate surface metallurgy of Pb-free interconnects for high power applications.

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