TEM Observations of the Growth of Intermetallic Compounds at the SnBi/Cu Interface

Abstract

The microstructure of the eutectic SnBi/Cu interface was investigated by transmission electron microscopy to study the growth mechanisms of the intermetallic compounds (IMCs). Although the growth kinetics of the total IMC layer were similar, the individual Cu₃Sn layer grew faster on polycrystalline Cu than on single-crystal substrates. It was found that, on polycrystalline Cu, newly formed Cu₃Sn grains with a smaller grain size nucleated and grew at both the Cu/Cu₃Sn and Cu₃Sn/Cu₆Sn₅ interfaces during reflow and solid-state aging. The consumption of Cu₆Sn₅ to form Cu₃Sn was faster at the Cu₃Sn/Cu₆Sn₅ interface. While on single-crystal Cu new Cu₃Sn grains nucleated only at the Cu/Cu₃Sn interface, the directional growth of the initial columnar Cu₃Sn controlled the advance of the Cu₃Sn/Cu₆Sn₅ interface.