Abstract: The morphology and thickness of the intermetallic compounds (IMCs)layer become one of the dominant factors which determine the reliability of the soldered joints in integrate circuit. The effects of Zn and Ni on the reaction of Sn-3.5Ag Cu interface were investigated by adding 1.0% Zn or Ni addition into the eutectic Sn-3.5Ag solder.It is found that, for Sn-3.5Ag Cu interface, the initial product was Cu₆Sn₅ IMC, and Cu₃Sn IMC layer was formed at the following 150℃ thermal aging period.Although Zn addition had little effect on the thickness of reaction lagers, the Cu₃Sn IMC in the reaction layer was found to be depressed, at the some time, non-continuous Cu₅Zn₈ IMC layer was formed, moreover, the thickening rate of the IMC layer decreased.Whereas, the original product was (Cu, Ni)₆Sn₅ as Ni was added, in addition, the initial thickness of the IMC layer was much thicker.However, there was no other product at the aging stage.