Grain morphology of intermetallic compounds at solder joints

The grain morphology of the intermetallic compound (IMC) that forms at the interface between liquid solders and solid-metal substrates was observed at solder joints. Cu,Sn5 grains on Cu substrates were rough or rounded, and Ni3Sn4 grains on Ni substrates were faceted. Through the energy-based calculations, the relationship between the IMC grain morphology and Jackson's parameter alpha was explained. The Jackson's parameter of the IMC grain with a rough surface is smaller than 2 while it is larger than 2 for faceted grains.