Effect of Sintering Aid and Glass-frit on the Densification and Resistivity of Silver Paste

The effect of sintering aids and glass-frit on the densification and resistivity of silver paste was investigated in an effort to enhance the sintered density and electrical conductivity of the silver electrode. To prepare Pb-free silver paste for use at low sintering temperatures, two commercial silver powders (0.8 µm and 1.6 µm in size) and 5wt.% lab-synthesized nanoparticles (30-50 nm in size) as a sintering aids were mixed with 3 wt.% or 6 wt.% of glass frit (Bi O -based) using a solvent and three roll mills. Thick films from the silver paste were prepared by means of screen printing on an alumina substrate followed by sintering at 450 C to 550 C for 15 min. Silver thick films from the paste with bimodal particles showed a high packing density, high densification during sintering and low resistivity compared to films created using monomodal particles. Silver nanoparticles as a sintering aid enhanced the densification of commercial silver powder at a low sintering temperature and induced low resistivity in the silver thick film. The glass frit also enhanced the densification of the films through liquid phase sintering; however, the optimum content of glass frit is necessary to ensure that a dense microstructure and low resistivity are obtained, as excessive glass-frit can provoke low conductivity due to the interconnection of the glass phase with the high resistivity between the silver particles.