Abstract: The effect of Zn on formation of Kirkendall voids on the interface was studied through the reaction between SnxZn solders (x = 0,0.2%,0.5%,0.8%) and the electroplated Cu substrate. During the thermal aging of Sn/Cu joints,a number of Kirkendall voids were formed in the Cu₃Sn layer and on the Cu₃Sn/EPC interface. With the increase of Zn content in solder,the growth of Cu₃Sn layer was greatly suppressed,and the formation of Kirkendall voids was effectively inhibited. The concentration of Zn on the reaction interface also significantly increased. Zn participated in the interface reaction, (Cu,Zn)₆Sn₅,Cu₆(Sn,Zn)₅ and Cu-Zn solid-solution alloy were formed,among which the Cu-Zn solid-solution alloy layer can greatly affect the diffusion of Cu. Zn served as a diffusing element during the interface reaction,which can improve the unbalanced diffusion of Cu and Sn to a great degree,and suppress the formation of voids effectively.