Growth behavior of intermetallic compounds at Sn–Ag/Cu joint interfaces revealed by 3D imaging

Abstract

In this study, the morphologies of intermetallic compounds (IMCs) at the as-soldered and thermal aged Sn–Ag/Cu joint interfaces were observed by SEM and measured using Laser Confocal Microscope, and their three-dimensional (3D) shapes were revealed using 3D imaging technology. The observation reveal that during the soldering process the Cu6Sn5 grains at the joint interface evolve from hemispheroid to a bamboo shoot-shaped body with increasing liquid state reacting time, and their grain size increases sharply. After thermal aging, the Cu6Sn5 grains change into equiaxed grains, while the top of some prominent Cu6Sn5 grains changes little. Due to the higher active energy of the Sn atoms at the grain boundary, the growth rate of IMC grains around the grain boundaries of the solder is higher during the aging process. From the evolution in morphology of the IMC layer, it is demonstrated that the IMC layer grows through grain boundary diffusion of the Cu and Sn atoms during the aging process, and the volume diffusion is very little. The 3D imaging technology is used to reveal the shape and dimension of the IMC grains.