Dual-reductant synthesis of nickel nanoparticles for use in screen-printing conductive paste

This study presents a systematic study in which sodium borohydride and hydrazine were used successively as reducing agents for the synthesis of nickel nanoparticles in an aqueous medium. The size of nickel nanoparticles could be controlled ranging from 11 to 48 nm by adjusting the concentration of hydrazine and the reaction temperature. A product yield of synthesized nanoparticles could achieve as high as 86.5%. As alternatives to silver pastes in some applications, nickel pastes have attracted growing interest because of the lower cost. By the use of nickel nanoparticles as fillers of the conductive pastes, low temperature sintering can be achieved. To avoid film cracking and to improve conductivity, bimodal screen-printing pastes containing different weight ratios of nickel microparticles and nanoparticles were prepared. A micro-to-nanoparticle weight ratio of 2 was found to be the optimal ratio for the nickel paste formulation, resulting in a volume resistivity of 122 μΩ∙cm for a printed film after sintering at a targeted temperature of 600 °C.