Size and constraint effects on interfacial fracture behavior of microscale solder interconnects

Abstract

The fracture behavior of solder joints has long been an important issue in the reliability evaluation of electronic components and packages. In this study, experimental and finite element methods were used to characterize the interfacial fracture behavior of “Cu-wire/solder/Cu-wire” sandwich-structured microscale Sn–3.0Ag–0.5Cu solder joints with different diameters (100–575μm) and thicknesses (35–325μm) under quasi-static micro-tension loading, with systematic comparison to Sn–37Pb solder joints. Dynamic stress intensity factors for the microcracks in Cu, Sn–3.0Ag–0.5Cu, and Sn–37Pb under pulse tensile loading and high speed propagation were calculated. The numerical simulation results showed that the interface stress intensity factors KII and KI for the crack set at the solder/IMC interface increased with increasing the thickness of the joints from 35μm to ∼125μm, and thereafter decreased and then became stable. With increasing the diameter of the joints, basically KI increases while KII decreases. Under the quasi-static micro-tension loading, the crack driving forces in Sn–3.0Ag–0.5Cu solder joints are lower than that in Sn–37Pb joints, and this means that fracture is less likely to occur in Sn–3.0Ag–0.5Cu solder joints than in Sn-joints. The rapid expansion of a high hydrostatic pressure region may enhance the mechanical performance of interconnects when the diameter-to-thickness ratios of the joints are very large. As the diameter of the solder joints increases, the evolution of the energy release distribution results in a change of the fracture position and mechanism in the interconnects. Compared to Sn–37Pb solder, the Sn–3.0Ag–0.5Cu lead-free solder shows a lower resistance to rapid crack propagation under constant tensile loading.