Effect of TiO2 nanoparticle addition and cooling rate on microstructure and mechanical properties of novel Sn1.5Sb0.7Cu solders

The effects of TiO2 nanoparticles and cooling rate on the microstructure and mechanical properties of Sn1.5Sb0.7Cu alloy were investigated. A higher cooling rate and TiO2 nanoparticles refined the primary β-Sn dendrites, Cu6Sn5 and SbSn phase. Especially, the microstructure of the Sn1.5Sb0.7Cu composite solders under the rapid-cooled condition exhibited fine dot-like Cu6Sn5 in the eutectic regions. The improvement in strength was mostly attributed to (1) refinement of the β-Sn grain size; (2) the Orowan strengthening effect; (3) CTE mismatch between reinforcement second phase particles (Cu6Sn5 and TiO2) and the matrix; and (4) the load-bearing effect. However, the total elongation of the composite solders was observed to decrease because of micro-voids both at and along the Cu6Sn5 grain boundary regions. The fracture surfaces of all Sn1.5Sb0.7Cu composite solder were confirmed to exhibit the ductile fracture mode.