Ni direct electroless metallization of polymers by a new palladium-free process

Ni films were electrolessly deposited on the surface of different polymer substrates without having to use the conventional palladium catalyst to initiate the redox reaction leading to metallization. With this in view, the surface to be coated was seeded with Ni(+2) species from an organo-nickel precursor. After reduction of the Ni(+2) ions to the Ni(0) oxidation state, it was possible to use the remarkable autocatalytic property of nickel to deposit a metallic film on the polymer by merely immersing in a Ni plating bath. The reduction of Ni(+2) species, less easy than that of Pd(+2) species commonly used in the authors' laboratory in the case of the tin-free process, was performed in the present work either using a chemical path or by plasma treatment in a non-oxidizing atmosphere (H2 or Ar), then checked by XPS. This method was experimented on various polymer substrates using two different industrial Ni plating baths. Adhesion of Ni films evaluated by the Scotch® tape test mainly depends on the phosphorus content of the plating bath used, i.e. on the amount of stresses generated in the film which depends on the quantity of phosphorus present, the latter originating from the plating bath reducer. Both the nature of the polymer surface treatment and especially the route used to perform the Ni(+2) reduction play an important part in the interfacial stresses generated and therefore on film adhesion.