In situ study on dissolution and growth mechanism of interfacial Cu6Sn5 in wetting reaction

Synchrotron radiation real-time imaging technology was used for in situ study of dissolution and growth behavior of interfacial Cu6Sn5 intermetallic compound (IMC) in Sn/Cu solder interconnect during reflow soldering. The pre-formed Cu6Sn5 grains dissolved into the liquid solder with decreasing aspect ratio in the heating stage, maintained a thin layer of scallop-type in the dwelling stage, and re-precipitated on the existing Cu6Sn5 grains at a faster growth rate with increasing aspect ratio in the cooling stage. The Cu concentration gradient at the interface is responsible for the aspect ratio variation (corresponding to dissolution and re-precipitation of interfacial Cu6Sn5 grains), which is also supported by the simulation of atomic diffusion in the solder based on Fick׳s second law. The growth behavior was well explained by a proposed model based on the Cu concentration gradient.