Thermo-mechanical evolution of ternary Bi–Sn–In solder micropowders and nanoparticles reflowed on a flexible PET substrate

Abstract

Ternary Bi–Sn–In micropowders and nanoparticles were prepared as a composite solder material via a gas atomization process and a chemical reduction method, respectively. The nanoparticles, with a 71.1°C melting temperature, entered among the intervals of the higher melting temperature (79.4°C) micropowders, and then reflowed at 110°C on a flexible polyethylene terephthalate (PET) substrate. This considerably increased the thermal diffusivity of the nanoparticles to refine the surface morphology of the solder bumps. Their adhesion strength also increased from an average shear force of 0.33–0.43N by viscosity improvement, afforded to the reinforcement of 5.0wt.% added nanoparticles. However, the adhesion strength (0.25N average shear force) of the composite solder bumps deteriorated at 15.0wt.% added nanoparticles and resulted in a high electrical resistivity (72.53±8.54μΩcm) due to the formation of their surface-oxidized phases.