Development of hybrid process for double-side flexible printed circuit boards using roll-to-roll gravure printing, via-hole printing, and electroless plating

A hybrid process including roll-to-roll (R2R) gravure printing, via-hole printing, and electroless plating was investigated for the creation of a double-side flexible printed circuit board (FPCB). A R2R gravure process with an Ag seed layer that includes front- and back-side printing with a polyimide film at the center was investigated. The gravure-printed Ag pattern was laser drilled for high accuracy. A via hole was filled with a low-viscosity Ag ink using the drop-casting method. In addition, an electroless Cu plating process was performed to increase the conductivity of the printed circuit. The interconnection performance was confirmed from the resistance values obtained using a feed-through test and microscopic images. To evaluate the reliability of the FPCB, a cyclic bending motion test was performed; stable electrical performance was observed even after 400,000 cycles. The results obtained in this study suggest that the proposed hybrid process for double-side FPCBs is viable for a mass production system.