Rheological behaviors of silver conductive pastes with ethyl cellulose

Abstract

Purpose The interaction between the silver powder and organic vehicle largely determines the rheological behavior of silver conductive paste. This study aims to prepare silver conductive paste with an organic vehicle system consisting of ethyl cellulose (EC) and terpineol/butyl carbitol acetate solvent mixtures. The study also aims to measure the rheological behaviors of the silver conductive pastes with different solvent mixtures, EC molecular weights and silver content, to investigate the interaction among the polymer, solvent and silver powder and determine the main factors affecting the thixotropic index and maximum silver content. Design/methodology/approach The rheological behaviors of silver conductive pastes with different solvent mixtures, EC molecular weights and silver content were investigated using viscometer. Findings The shear thinning became significant with increasing EC molecular weight. The EC solvation with higher molecular weight in solvent is better than that of EC with lower molecular weight. This leads to a stronger interaction between the silver powder and EC with higher molecular weight and consequently good silver particle dispersion. The relative viscosity of silver conductive paste at 10 s−1 increases significantly with increasing silver content, but the relative viscosity at 100 s−1 is much less sensitive to the silver content. The viscosities at low and high shear rate can be increased by increasing the silver content and EC molecular weight, respectively. Originality/value The interaction among the polymer, solvent and silver powder was investigated for the silver paste with high solid content. The main factors affecting the viscosities at high and low shear rates, thixotropic index and maximum silver content were determined.