The effect of conductive layer thickness on the function of screen printing fabric-based microstrip line

Electrical properties of screen printing layers determine the high frequency application such as flexible sensors and antennas. As one of the most important factors to affect the electrical properties, printing thickness and uniformity are usually ignored as it is hard to control during the screen printing process. In this paper, in order to study the relationship of printing thickness and electrical properties, both direct current (DC) and radio frequency (RF), a group of transmission lines were fabricated with different thickness by reprinting. The surface morphology and cross-section of printing films were observed by microscope and the conductive mechanism of multiple printing layers was clarified. The thickness varies from less than 20 μm to highest 80 μm, and the uniformity of thickness gets better at first and then worse when increased reprinting from one to fifteen times. As a result, the smallest resistance is 0.07 Ω/□ or 0.02 Ω/cm when the thickness is 38 μm after 10 times reprinting, while the transmitting loss is lowest and equal to bulk copper when the thickness is 25 μm after 5 times reprinting. Furthermore, it established the equivalent resistance model to explained conductive mechanism of conductive ink. Generally, it is the foundation of printing wearable electronics especially in high frequency applications.