The Influence of Standoff Height and Pad Size on the Shear Fracture Behavior of BGA Structured Cu/Sn3.0Ag0.5Cu/Cu Interconnects

The influence of the standoff height, pad size and isothermal aging on the microstructure and shear fracture behavior of Cu/Sn-3.0Ag-0.5Cu/Cu BGA structured interconnects were investigated using the lap-shear test. The experimental results show that the thickness of intermetallic compounds (IMC) layer at the solder/Cu interface increases with decreasing standoff height of the joints. The size of Kirkendall voids and the porosity increase inversely with the standoff height upon isothermal aging treatment. Shear strength of the joints depends strongly on both the solder volume and pad size. Moreover, the isothermal aging treatment doesn't change the shear strength trend of the joints with a pad diameter of 0.48 mm, while varying the shear strength trend of the joints with a pad diameter of 0.32 mm. The typical fracture location of the joints changes from the position near interface gradually to the middle of the solder matrix with decreasing the standoff height of the joints, while being independent of aging time and pad size. In addition, it has been shown that Kirkendall voids play an important role in influencing the fracture mode of the solder joints with the standoff height larger than 0.15 mm.