Initial propagation stage of direct copper plating on non-conducting substrates

The initial propagation stage of direct copper plating on non-conducting resin substrates was studied by a high resolution transmission electron microscope, an electron diffraction and a scanning electron microscope analysis to confirm the mechanism. In this process, ABS resin substrate was catalyzed by Pd/Sn mixed catalyst and accelerated in a solution containing copper ions before the direct plating. Cubic Cu₂O crystals approximately 20-50 nm in size were formed along the migration front of direct copper plating to provide stepping stones for copper propagation, while few such crystals were found on a residual uncovered catalyst area. At the thicker copper plated area, Cu₂O crystals were embedded in a flat copper deposit which was composed of small crystals 10-20 nm in size. The Cu₂O crystals should be activation sites for copper deposition by the formation of additive free metallic copper according to disproportionation reaction and so that promote the propagation speed. This effect can be explained by 'a modified stepwise propagation mechanism' in which Cu₂O crystals act a critical roll for the copper propagation as stepping stones in addition to dispersed Cu particle seeds and Pd catalyst cluster seeds.