Effects of Sc-CO2 catalyzation in metallization on polymer by electroless plating

This study was conducted to examine how catalyzation in supercritical CO2 with Pd-bis(acetylacetonate) influences electroless plating on polymer substrates. Catalyzation in supercritical CO2 enabled the nucleation of abundant Pd nuclei on a polyimide substrate without chemical pretreatment, ultimately leading to 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 area of the substrate occupied by the catalyst particles in Sc-CO2 catalyzation was estimated by visual point counting. At catalyzation times in Sc-CO2 from 1 to 3 min, the area occupied by the catalyst ranged from 1 to 3%, while that by the catalyst rapidly increased to 7% from 3 min to 5 min. The low density and poor uniformity of the catalysts on the polyimide substrate in the electroless plating procedure reduced the coverage of the Ni–P film. A catalyzation time of more than 20 min was essential to induce a conventional catalyzation reaction adequate for complete Ni–P coverage, whereas catalyst nuclei induced by Sc-CO2 catalyzation of only 5 min were well deposited on all parts of the substrate. Moreover, Ni–P coverage ratio was drastically increased from 21 to 91% in catalyst reaction time from 1 to 3 min, and reached full coverage over 5 min. Thus the period from 1 min to 3 min is thought to be the induction period in Sc-CO2 for polyimide metallization. The size of the catalyst and the area of the polymer substrate occupied by the catalyst are the chief factors required for a completely continuous coverage of Ni–P film on polymer substrate. The thorough dispersion of the Pd-complex throughout all of the surface-treated polyimide and the complete coverage by the Ni–P film within the short catalyzation time allotted may have been attributable to the diffusivity of the Sc-CO2 and the good affinity between the Sc-CO2 and polyimide substrate.