Effect of rheological properties on the pattern formation in screen printing process

Abstract

Abstract Effect of rheological properties on the pattern formation in screen printing process

Kim Jung Wook School of Chemical and biological engineering The Graduate School Seoul National University

Screen printing process is used in various areas in the production process of printed circuits, thick film integrated circuits, resistors, capacitors, light-sensitive components and thermal components. TiO2 paste is used to make titanium dioxide anode which is used in dye sensitized solar cells (DSSC). The effect of paste composition on the pattern formation of TiO2 electrode was investigated for efficient control and optimization of the main fabrication step of the DSSC. In particular, the effect of binder was focused, and the relationship between the printed patterns and the rheological properties was investigated. The printed patterns were observed using a 3-D confocal laser scanning microscopy. Rheological behavior of the paste was different depending on the binder concentration. Below critical binder concentration (< 2 wt%), there was a strong shear thinning behavior, which causes patterns to be spread. On the other hand, above critical binder concentration (≥ 2 wt%), though there was a slight shear thickening at high shear rate, the viscosity at low shear was much lower and we could obtain clear patterns. Transition of modulus is found near critical binder concentration. Below critical binder concentration (< 2 wt%), storage modulus is higher than loss modulus, on the other hand, above critical binder concentration (≥ 2 wt%), storage modulus is lower than loss modulus which is similar to the tendency of the patterns. To conclude, by measuring the rheological properties, the relationship between the component of the paste and the printed pattern could be found, which may result in a better design of the paste with enhanced processability.