Loading rate and size effect on the fracture behavior of BGA structure Cu/Sn-3.0Ag-0.5Cu/Cu interconnects

The miniaturization of solder interconnects may lead to the excessive growth of brittle intermetallic compounds (IMCs) at the interface of solder joints, and this has brought serious reliability concern to flip chip (FC) and ball grid array (BGA) packages, in particular for the drop impact reliability of the solder joints in portable electronic products. In this study, the lap-shear behavior and critical factors affecting the drop impact performance of single BGA structure Cu/Sn-3.0Ag-0.5Cu/Cu joints with different standoff heights (or volumes) were characterized. The experimental results show that the shear strength change of joints with standoff height exhibits a parabolic trend regardless of the shear loading rate, and the thermal aging can deteriorate the joints' strength significantly. The failure position of the joints changes from the middle of the solder matrix to near the interface with increasing standoff height regardless of the shear loading rate and isothermal aging treatment. It seems that the drop resistance of small joints is only slightly influenced by the isothermal aging and loading rate. In addition, the probability of brittle fracture of the joints with 0.50 mm standoff height increases with increasing the loading rate and undergoing isothermal treatment. The geometry of the joints (standoff height) plays a dominant role in influencing the joints' properties. While the interactive effect of the evolution of microstructure and standoff height results in the different brittle fracture modes of the joints after undergoing isothermal aging at 125°C.