Formation of double-layer Cu3Sn in solid-state aging process at the interface of eutectic SnBi solder and (100) single crystal Cu

Transmission electron microscopy (TEM) observations were carried out to investigate the microstructural evolution of SnBi/single crystal (100) Cu interface during reflow and solid-state aging process. It was found that there were two kinds of IMCs, Cu₆Sn₅ and Cu₃Sn, at the interface after reflow. The Cu₃Sn grains grew along [100] direction of Cu with columnar morphology. During aging, new triangle Cu₃Sn grains were found at the triple junction sites of Cu/Cu₃Sn interface. With the prolonging of solid-state aging, two distinct Cu₃Sn layers formed between Cu and Cu₆Sn₅ layer. Bi segregation was detected at the Cu/Cu₃Sn interface after the sample was solid-state aged for 360 hrs at 393 K.