Selective adsorption of catalyst and copper plating for additive fabrication of conductive patterns and through-holes

A novel patterning-adsorption-plating process to additively fabricate conductive patterns and through-holes of double-sided flexible printed circuit is developed. Firstly, through-holes were drilled in substrate. Then ion-adsorption ink was dip-coated to form the adsorption film on the surfaces of substrate and through-holes. Mask was printed to expose the patterns and the through-holes. Afterwards, silver ion was selectively adsorbed to the exposed parts. Finally, after dissolving the mask, the patterns and the through-holes were metalized by electroless plating of copper. The ion-adsorption ink is composed of polysiloxane and solvent. The polysiloxane was prepared by hydrolyzing 3-aminopropyltriethoxy silane with 3-mercaptopropyltriethoxy silane together, thus the formed ion-adsorption film contains abundant amino and mercapto groups. Amino groups can adsorb silver ion by complexation. Mercapto groups increase the hydrophobicity of the adsorption film, improving the stability in alkaline solution. Special solvent used in the ink leads to the coarse adsorption film, so the mechanical anchor between the deposited copper and adsorption film is improved, resulting in a better adhesion. After 60   min plating, the copper patterns with 1.87   μm in thickness and 9.1   mΩ in square resistance was prepared, the adhesion can reach 5B. The prepared double-sided FPC shows high conductivity and adhesion, proving that PAP process possesses high potential in industrial production.