Failure Mechanism of Sn-Ag-Cu Flip-chip Solder Joints with Different Cu Weight Contents Under Comparatively Low Current Stressing

摘要

This work presents electromigration reliability and patterns of Sn-3Ag-0.5Cu and Sn-3Ag-1.5Cu/Sn-3Ag-0.5Cu composite flip-chip solder joints with Ti/Ni(V)/Cu under bump metallurgy (UBM), bonded on Au/Ni/Cu substrate pads. The solder joints were subjected to an average current density of 5 kA/cm2 under an ambient temperature of 150掳C. Under the situation when electron charges flow from the UBM towards the substrate, Sn diffuses from the Cu-Ni-Sn intermetallic compound (IMC) developed around the UBM towards the UBM, and eventually causes the Ni(V) layer to deform. Electromigration reliability of Sn-3Ag-1.5Cu/Sn-3Ag-0.5Cu composite flip-chip solder joints was found to be better than that of Sn-3Ag-0.5Cu solder joints. A failure mechanism is proposed according to the Cu weight contents of these two solder joints.