Shear fracture behavior of Sn3.0Ag0.5Cu solder joints on Cu pads with different solder volumes

To meet the urgent demands of future electronic packages, the solder joints have to become increasingly miniaturized. Compared to the large solder joints, mechanics behavior for the samll solder joints is very different, resulting in a series of reliability issues. Therefore, it is very important to understand the mechanics behavior of the small solder joints. In this paper, the shear test of the as-reflowed and aged Sn-3.0Ag-0.5Cu solder joints on Cu pads with the diameters of 200 mum to 600 mum were conducted, and fracture behavior was observed using SEM. The results show that shear strength of the solder joint increases with the decreasing of the solder joints volumes. For the large volume solder joints, the fracture occurs close to the interface, and the solder joint shows strong brittleness. Whereas, for the small solder joints, the fracture occurs within the bulk solder, and the solder joint shows ductile property. The Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) at the interface region have a prominent effect on the shear property and the propagation of the fracture.