Metallization on polymer by catalyzation in supercritical CO2 and electroless plating in dense CO2 emulsion

In this study we propose a novel technique for electroless plating on polymer substrates using a dense CO2 beyond the critical point. Ni–P thin films were fabricated by a novel, hybrid technique consisting of two processes: catalyzation in supercritical CO2 with Pd bis-acetylacetonate and electroless plating in emulsion with dense carbon dioxide. These catalyzation processes were discussed by atomic force microscopic images and the roughness of the surface. Catalyzation in supercritical CO2 enabled the nucleation of a large number of Pd nuclei on a polyimide substrate without chemical pretreatment, and the deposition of a uniform Ni–P metal film. Conventional catalyzation without chemical pretreatment led to the deposition of only a few nuclei in sparse, island-like formations. The deposition behavior of Pd nuclei in supercritical CO2 was different from that in conventional catalyzation. When a polyimide was catalyzed in supercritical CO2 and plated by conventional electroless plating in electrolyte solution, the plated film was pocked with small, peeled sections formed via the hydrogen bubbles of the sub-reaction and nodules formed via crystal growth of Ni–P. In contrast, the electroless plating in emulsion with dense CO2 produced a uniformly plated film without peeling or nodules. The improved uniformity was attained by the solubility and diffusivity of the dense CO2 beyond the critical point in the emulsion.