Silver content effect on rheological and electrical properties of silver pastes

The novelty of this work is laboratory formulation of environmentally friendly, water-based silver inks adapted for screen printing. The challenge was also to elaborate inks that can withstand temperatures as high as 900 A degrees C. Indeed, when printed on ceramic substrate, they were sintered at these high temperatures. These inks can replace conductive silver pastes present in the market, today, and containing irritant solvents such as terpineol and other aromatic solvents. Besides, screen printing is considered as an additive technique, thus allowing reducing wastes. Furthermore, only with 72.5% silver, considered as low content compared to commercial inks (a parts per thousand yen75%), prepared inks presented good electrical resistivity, 23 na"broken vertical bar m, close to that of bulk silver resistivity, 16 na"broken vertical bar m. Formulation of silver inks with spherical particles, 2-3 mu m mean diameter, was performed. The aim of the study was to determine silver content effect on pastes rheological behaviour, lines properties (width, thickness and roughness) and electrical properties. Therefore, rheological behaviour of inks was studied; in particular, Casson and Bingham models were applied in order to determine the yield stress. Viscosity evolution as a function of shear rate was also determined. Besides, the thixotropic behaviour of inks was highlighted. Inks were then screen printed on alumina sintered substrates and cured at different temperatures during 15 min. Topography measurements were performed. Line resistivity as small as 35 na"broken vertical bar m was measured on cured lines. These inks, printed on ceramic tapes, can be used to print microwave transmission lines, for which resistivities lower than 1 ma"broken vertical bar m are requested.