Effects of electromigration on interfacial reactions in the Ni/Sn-Zn/Cu solder interconnect

Electromigration in the Ni/Sn-Zn/Cu solder interconnect was studied with an average current density of 3.51 × 10 ⁴ A/cm ² for 168.5 h at 150°C. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni ₅Zn ₂₁ and Cu ₅Zn ₈ were formed at the Ni/Sn-Zn and Cu/Sn-Zn interfaces. However, upon reversing the current direction, where electron flow was from the Cu side to the Ni side, a thicker Cu ₆Sn ₅ phase replaced the Ni ₅Zn ₂₁ phase at the Ni/Sn-Zn interface, whereas at the Cu/Sn-Zn interface, a thicker β-CuZn phase replaced the Cu ₅Zn ₈ phase.