Comparative study of electrically conductive thick films with and without glass

An air-fireable, glass-free, electrically conductive thick-film material (96.6% Ag, 1.38% Cu, 0.28% Al, 0.35% Ti, and 1.39% Sn by weight) and a conventional glass-containing, electrically conductive thick-film materials (96.6% Ag and 3.4% glass frit by weight), both on alumina substrates, were studied by electrical, mechanical, thermal, and microscopic methods. The volume electrical resistivity of the glass-free thick film (2.5×10⁻⁶ Ω·cm, 30-μm thick) is lower than that of the glass-containing thick film (3.9×10⁻⁶ Ω·cm, 19-μm thick), with each film processed at its optimum firing temperature. The optimum firing temperature is 930°C and 850°C for glass-free and glass-containing thick films, respectively, as indicated by the criteria of low resistivity and high scratch resistance. The glass-free thick film has a higher scratch resistance than the glass-containing thick film, both fired at their respective optimum temperatures, suggesting that the former has higher bond strength to the alumina substrate. The formation process of the glass-free and glass-containing thick films is similar. The process involves solid-state diffusion of silver, which results in a silver network and grain boundaries. However, the sintering of silver particulates in the glass-containing thick film is enhanced by the viscous flow of glass.