Microstructures Transformation in Sn-Base Solders under the Isothermal and Thermal-Shearing Cycling Condition

The diffusion of the atoms and growth behavior of intermetallic compounds (IMCs) at Sn-3.5Ag-0.5Cu/Cu interfaces under the isothermal aging and thermal-shearing cycling condition were investigated. The results show that there is a Cu₆Sn₅ IMC layer formed at Sn-Ag-Cu/Cu interface, and the morphology of the Cu₆Sn₅ changes from scallop-type microstructure to planar-type one with the thermal-shearing cycling increasing, while there are two kinds of IMC, Cu₆Sn₅ and Cu₃ Sn, formed at the Sn-Ag-Cu/Cu interfaces after isothermal aging 100 hours. The IMCs growth follows parabola growth kinetics, implying that the IMC growth is controlled by Cu atoms´ diffusion. In Sn-Ag-Cu solder, Ag₃Sn, forming uniform particles after reflowing, congregates gradually to grow up to chunk-like