Effect of Thermal Cycling on Interfacial Microstructure and Mechanical Properties of Sn-0.3Ag-0.7Cu-(α-Al₂O₃) Nanoparticles/Cu Low-Ag Solder Joints

Abstract

The evolution of interfacial microstructures and mechanical properties of joints soldered with Sn-0.3Ag-0.7Cu (SAC0307) and SAC0307-0.12Al₂O₃ nanoparticles (NPs) subjected to thermal cycling were investigated. The joint soldered with SAC0307-0.12Al₂O₃ displayed an enhanced thermal cycling shear force with a ductile fracture mode when compared with the original alloy whose fracture mode showed a mixed feature of ductile and brittle. The enhanced thermal cycling shear force was attributed to a pinning effect by Al₂O₃ NPs on interfacial IMC grain growth. Even after 1200 thermal cycles, SAC0307-0.12Al₂O₃ solder was still structurally characterized by a much more refined microstructure than the non-reinforced solder alloy. Theoretical analysis on the growth of interfacial IMC layer showed that with the addition of Al₂O₃ NPs, the average growth coefficients of total interfacial IMCs (D_T) and Cu₃Sn IMCs ($D_{{{\rm{Cu}}_{3} }}$) were decreased from 9.2 × 10⁻¹¹ cm²/h to 5.6 × 10⁻¹¹ cm²/h, and from 6.9 × 10⁻¹¹ cm²/h to 4.1 × 10⁻¹¹ cm²/h, respectively. Hence, a much thinner IMC layer was produced at the SAC0307-0.12Al₂O₃/Cu interface, thus contributing to an enhanced shear resistance.