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, Cu
6
Sn
5
and Cu
3
Sn, at the interface after reflow. The Cu
3
Sn grains grew along [100] direction of Cu with columnar morphology. During aging, new triangle Cu
3
Sn grains were found at the triple junction sites of Cu/Cu
3
Sn interface. With the prolonging of solid-state aging, two distinct Cu
3
Sn layers formed between Cu and Cu
6
Sn
5
layer. Bi segregation was detected at the Cu/Cu
3
Sn interface after the sample was solid-state aged for 360 hrs at 393K.