Nanoindentation study on the creep resistance of SnBi solder alloy with reactive nano-metallic fillers

SnBi alloy is an attractive soldering material for temperature-sensitive electronic devices. With its excellent yield strength and fracture resistance, SnBi alloy has become one of the promising candidates to replace Pb-based solders. However, due to the low melting temperatures of this alloy, the prominent time-dependent deformation at service temperatures hinders its wide applications. In this study, low concentration (no more than 4 wt%) of reactive nano-metallic fillers, i.e., Cu and Ni, have been added into the Sn-58Bi alloy aiming to enhance its creep resistance. The elastic, plastic and creep properties are characterized by nanoindentation constant strain rate (CSR) technique. The addition of the fillers has refined the microstructure of the solder matrix leading to moderate strengthening and hardening. The creep resistance of the Sn-58Bi alloy has been improved with the filler addition. Two regions of stress-dependent creep rates were found in the alloys with and without fillers. An optimum filler concentration for creep resistance enhancement is identified at which there is a balance between the effects of particle pinning and microstructure refinement.