Effect of electromigration on interfacial reaction of Cu/Sn3.0Ag0.5Cu/Ni solder joint at high temperature

The Cu/Sn3.0Ag0.5Cu/Ni (Cu/SAC305/Ni) solder joints were designed to investigate the Cu, Ni atoms diffusion behavior and the interfacial reaction during electromigration (EM) at 180 °C under a current density of 1.0×10⁴ A/cm². For comparison, the Cu/Sn3.0Ag0.5Cu/Ni solder joints were aged at 180 °C for the same durations. In as-soldered state, the (Cu_0.55Ni_0.45)₆Sn₅ and (Cu_0.92Ni_0.08)₆Sn₅ IMCs formed at the SAC305/Ni and SAC305/Cu interfaces, respectively. The interfacial IMC thickness increased with increasing aging time. During EM, the current direction played an important role on Cu consumption. When electrons flowed from PCB side to chip side, the Cu pad dissolved into the solder and microcrack formed at the solder/Cu interface. The dissolved Cu atoms were driven toward the anode side and precipitated as large Cu₆Sn₅ IMCs in the solder matrix along the flowing direction of electrons. While when electrons flowed from chip side to PCB side, no Cu pad consumption was observed and a thick layer-type Cu₆Sn₅ IMC formed at the SAC305/Cu interface; the thickness of the interfacial IMCs increased with increasing EM time and increased to 15.90 μm after EM for 100 h. As to Ni UBM, no significant consumption of Ni was observed even electrons flowed from chip side to PCB side. Ni UBM was more resistant than Cu UBM during EM. After EM for 143 h, the solder joint failed due to the melting of the SAC305 solder bump.