The effect of Ag on the growth of intermetallics at the interface of Sn5Zn/Cu interconnects

The reliability of electronic packages is primarily affected by the growth of the intermetallic compound (IMC) between the solder and the copper interconnection. It is therefore necessary to study the effect of element addition on the growth of the IMC interface with respect to an improvement in the package reliability. In this study, the influence of Ag on the growth of intermetallic compounds in the Sn5Zn solder/copper interconnection interface was investigated. The results revealed that in comparison with Sn5Zn/Cu, the interfacial IMC thickness decreased initially and then increased in accordance with an increase in the doping amount of alloying elements in the solder. Further, it was observed that the doping of the alloying element (Ag) can significantly reduce the IMC growth rate at the interface. Compared with the Cu₅Zn₈ unit cell formation energy (-0.632eV), one dopant atom and two dopant atoms of Ag can reduce the formation energy of a Cu₅Zn₈-based unit cell to the minimum values of -0.636 eV and –0.640 eV, respectively; consequently, the stability is increased. The maximum diffusion activation energies of Cu atoms and Zn atoms in a Cu₅Zn₈-based unit cell are 3.419 eV and 1.692 eV, which increase to 3.512 eV and 1.971 eV, respectively, after doping with Ag.