Abstract: The reliability of Sn-Cu-Ni (-Ce) joints on quad flat pack lead in the course of long time thermal cycling was studied, and the effect of thermal cycling on intermetallic compound (IMC) formation and growth behavior was investigated simultaneously. The results indicate that with the increase of thermal cycling times, the pull forces of the joints decrease gradually, while the reliability of soldered joint is improved with 0.05% Ce addition. At the same time, the thickness of the IMC layer increases in the course of long time thermal cycling, and a thin Cu₃Sn layer appears after 2 000 thermal cycling times, which poses a grave problem for the reliability of joints. The small addition of Ce is found to refine the microstructure, depress growth of the IMC in the cycling and decrease the influence of the cycling on reliability.