Pattern Formation of Cu Layer by Photocatalytic Reaction of ZnO Thin Film

A new, fully additive‐based, electroless plating process for the formation of fine Cu patterns without using a conventional photoresist has been developed which utilizes a photocatalytic reaction on thin films prepared on ceramic substrates for printed circuit boards. The layer serves both as an adhesive layer and as a photosensitive layer. The Cu patterns could be easily fabricated in an electroless Cu plating bath after Pd nuclei, which act as catalytic sites for the electroless plating, were patterned via an area‐selective photocatalytic reaction. This was achieved by adsorbing Pd(II) onto the surface and selectively exposing the surface with UV light through a photomask. The unexposed regions can be freed of Pd(II) using ethylenediamine, which can form a stable complex with Pd(II). Cu patterns 17 μm wide, with adhesion strengths suitable for practical use, have been achieved on alumina substrates with this electroless plating method.