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

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 (DT) and Cu3Sn IMCs (DCu3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ D_{{{\rm{Cu}}_{3} }} $$\end{document}) 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.