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Microstructure evolution and mechanical property of Sn-37Pb and Sn-3.0Ag-0.5Cu BGA solder joints under extreme temperature environment

In this study, the microstructure evolution, mechanical property and fracture behavior of ball grid array (BGA) solder joints under extreme temperature environment (−196 °C to 150 °C) were investigated. Two different kinds of solders, Sn-37Pb and Sn-3.0Ag-0.5Cu (SAC0305) (all wt.%) were employed in this work. A continuous Cu6Sn5 intermetallic compound (IMC) layer was formed at the interfaces between both the Sn-37Pb and SAC0305 solders and the substrate during reflow. After thermal shock, Cu3Sn was formed between Cu6Sn5 layer and Cu pad. The thickness of interfacial IMC layer increased and the morphology of IMC layer transferred from scallop-like to planar-like during extreme temperature thermal shock. With increasing number of extreme temperature thermal shock cycles, the shear forces of Sn-37Pb and SAC0305 solder joints both decreased, and the fracture mode of SAC0305 solder joints transformed from ductile fracture to mixed fracture of ductile fracture and interfacial fracture, while the fracture mode of Sn-37Pb solder joints changed from ductile fracture to a brittle fracture with partial ductile fracture, because of the thickening of IMC layer.