Abstract: Based on the home-made in-situ observation device, the microstructure and the growth kinetic of Sn-3.0Ag-0.5Cu solder/Cu joint were investigated under 110℃ thermal exposure condition. The intermetallic compounds(IMCs) presented at interface was thickened with increasing exposure time. At the same time, the growth of IMCs have three-dimensional characteristics. The Cu₆Sn₅ varied evidently in the longitudinal direction with a gradual decrease of height, while it was changeed slowly in in the transverse direction with the aging time. The SEM shows that the microstructure of IMCs varied from the scallop-shape to a layered structure with stratified phenomenon.