Roll-to-roll gravure printing of thick-film silver electrode micropatterns for flexible printed circuit board

Abstract

This paper presents a novel method for printing thick silver electrodes with high fidelity using a rotogravure technique and high-viscosity silver ink. The widths and thicknesses of the printed electrodes were investigated with respect to the printing angle and printing speed. In addition, the use of a low-surface-energy polyethylene terephthalate substrate was found to decrease the ink transfer for printing angles of up to 60°, possibly because of the small adhesive force at the interface between the ink and substrate. We therefore employed substrates with higher surface energies, namely polyimide and treated polyimide, to enhance the ink transfer. A lower printing speed of 0.5 m/min and high viscosity of 15 Pa·s are required to obtain better functionality with a lower resistivity. However, using the proposed method, the fidelities of the printed patterns were achieved even with a high printing speed of 10.5 m/min using the high viscosity of 15 Pa·s, necessitating a subsequent sintering process. Therefore, the printed pattern was sintered in an oven at 350°C for 10 min. Patterned silver electrodes 1 m in length, 121 ± 2.2 μm in line width, 6.5 ± 2.2 μm in average thickness, and with a resultant resistivity of 9 µΩ·cm were achieved. The findings of this study confirm the potential of rotogravure printing for fabricating thick electrodes with high fidelity for flexible printed circuit boards with large areas.