Microstructure, elastic modulus and shear strength of alumina (Al2O3) nanoparticles-doped tin–silver–copper (Sn–Ag–Cu) solders on copper (Cu) and gold/nickel (Au/Ni)-plated Cu substrates

Abstract

This paper investigates the influence of Al2O3 nanoparticles on the morphology of interfacial intermetallic compound (IMC) layer and material properties of Sn–3.0Ag–0.5Cu (wt%) solders on Cu and Au/Ni-plated Cu substrates. In the solder/Cu substrate systems, an island-shaped Cu6Sn5 IMC layer was found to be adhered at the interface in the initial reaction stage. However, a very thin Cu3Sn IMC layer was also observed between the Cu6Sn5 IMC layer and Cu substrate after long time reaction in all solder joints. On the other hand, a ternary scallop-shaped (Cu, Ni)–Sn IMC layer was found in both plain Sn–Ag–Cu solder joints and solder joints containing Al2O3 nanoparticles on Au/Ni-plated Cu substrates. These IMC layer thicknesses were increased with the reaction time. In the solder ball region, Ag3Sn, Cu6Sn5 IMCs were found to be uniformly distributed in the β-Sn matrix in both types of solder joints. However, after adding Al2O3 nanoparticles these IMCs appeared with fine microstructure. Furthermore, the elastic moduli and shear strength of composite solders containing Al2O3 nanoparticles exhibited consistently higher value than that of plain Sn–Ag–Cu solder joints by a second phase dispersion strengthening mechanism. The fracture surface of plain Sn–Ag–Cu solder joints appeared a brittle fracture mode with a smooth surface, while Sn–Ag–Cu solder joints containing Al2O3 nanoparticles showed semi-ductile failure characteristics with rough dimpled surfaces.