Growth mechanisms of Cu 3Sn on polycrystalline and single crystalline Cu substrates

Abstract

A comprehensive transmission electron microscopy (TEM) study was conducted to investigate the growth mechanisms of Cu 3Sn on polycrystalline and single crystalline Cu substrates in solder joints. On single crystalline Cu the solder reflow process resulted in the growth of columnar Cu 3Sn grains aligned in a thin uniform layer perpendicular to the interface, while a thick Cu 3Sn layer formed from fine equiaxed grains on the polycrystalline substrate. In the subsequent solid state aging, columnar growth of Cu 3Sn continued on the single crystalline Cu before it was replaced by nucleation and growth of new triangular Cu 3Sn grains at the triple junction sites of the Cu/Cu 3Sn interface. On the polycrystalline Cu the solid state aging caused much more rapid growth of the Cu 3Sn layer due to nucleation and the growth of new Cu 3Sn grains at both the Cu/Cu 3Sn and Cu 6Sn 5/Cu 3Sn interfaces. These different growth behaviors of Cu 3Sn were related to the diffusive supply of reactive elements.