Interfacial Reactions of Sn-3.0Ag-0.5Cu Solder with Sputter Cu-Ti Alloy Film UBM

Herein, the influence of Ti additive on the formation of intermetallic compounds (IMC) in a SAC/Cu-Ti soldered joint and corresponding mechanical properties are systematically investigated. The Ti-to-Cu ratio under bump metallization (UBM) is adjusted by tuning the target current during magnetron sputtering. Interestingly, the needle-like IMC, which is different from the traditional scallop-like IMC, is formed in the SAC/Cu-Ti soldered joint after reflow. The growth of Cu₃Sn and Kirkendall voids is significantly inhibited after thermal aging in the SAC/Cu-Ti soldered joint. Overall, the segregation of Ti at grain boundaries forms a titanium-rich layer. Also, the Ti-rich layer acts as a diffusion barrier layer and hinders the diffusion of Cu into IMC. The shear strength test results show that SAC/Cu-Ti has much stronger strength than SAC/Cu both before and after thermal aging. These results confirm that Cu-Ti UBM is beneficial to the improvement of welding reliability.