Size effect on the interfacial reactions and microstructural evolution of Cu/Sn3.0Ag0.5Cu-ball/Sn3.0Ag0.5Cu-paste/Cu joints in flip-chip on BGA packaging

摘要

Size effect of solder balls on the interfacial reaction and microstructural evolution of BGA structure Cu/Sn3.0Ag0.5Cu-ball/Sn3.0Ag0.5Cu-paste/Cu joints during isothermal aging at 125 °C was systematically investigated. Results show that a large amount of bulk Cu6Sn5 phase distributes in the solder matrix of joints with large solder ball size, resulting from larger outflux Cu atoms from the interface to the molten solder and the low solubility of Cu in the solder matrix. The solder ball size has a significant influence on the interfacial Cu6Sn5 layer thickness at the Sn3.0Ag0.5Cu-ball/Cu interface, which increases with decreasing solder ball size, while showing less effect on that at the Sn3.0Ag0.5Cu-paste/Cu interface. The grain size of Ag3Sn phase in joints decreases with decreasing solder ball size. During isothermal aging, the growth of interfacial IMC layers at both Sn3.0Ag0.5Cu-ball/Cu and Sn3.0Ag0.5Cu-paste/Cu interfaces of joints is mainly controlled by bulk diffusion.