Direct Electroplating of Cu on Insulators with WO₃ Film as Conductive Layer

Plating technologies are widely employed by various industries to coat ceramics and plastics with metals. If direct electroplating onto insulating substrates becomes feasible, it would eliminate the need for precious metal catalysts typically employed in electroless plating, thereby simplifying the overall processing steps. When applying constant reductive current to a WO3-coated fluorine-doped tin oxide in an electroplating bath with CuSO4, the WO3 film exhibited no color changes or shifts in its X-ray diffraction peaks, while Cu electroplating occurred on the oxide. This suggests that WO3 behaves as a conductor at potentials that are more negative than its flat band potential. Furthermore, we demonstrated the feasibility of direct electroplating WO3-coated insulating substrates using a quartz glass substrate. As a result, a Cu plating film was deposited around the electrical contacts prepared for the initial conductive path. Additionally, the area plated with Cu covered the surface of the WO3 film and gradually expanded. Although the initial electrical resistance of WO3 is high, WO3 is expected to function as a conductive layer for electroplating insulating substrates when combined with a plating reaction in which the reaction product itself is conductive. These findings provide valuable insights into the design and development of conductive layer materials for direct electroplating of insulating substrates.