Electromigration behavior of the Ni/SnZn/Cu solder interconnect

Electromigration in the Ni/SnZn/Cu solder interconnect was studied with an average current density of 4.1times10⁴A/cm² for 168.5h at 150degC. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni₅Zn₂₁ and Cu₅Zn₈ were formed at the Ni/SnZn and Cu/SnZn interfaces. The results are similar to those without passage of an electric current. However, upon reversing the current direction where electron flow was from the Cu side to the Ni side, thicker Cu₆Sn₅ phase replaced Ni₅Zn₂₁ phase at the Ni/SnZn interface, whereas at the Cu/SnZn interface, thicker beta-CuZn phase replaced Cu₅Zn₈ phase. Meanwhile, Cu-Sn phases also appeared at the Cu/SnZn interface. A kinetic model, based on the Zn and Cu mass transport in the sample, was presented to explain the growth of the intermetallic compound at the anode and cathode.