Functionalization of polymer surfaces using excimer VUV systems and silentdischarges. Application to electroless metallization

New approaches for electroless plating of nonconductive polymers or polymer -based materials are described. In this work, polyimide substrates were sur face-functionalized (i) in nitrogenated (ammonia at reduced pressure) and o xygenated (air at atmospheric pressure) atmospheres under assistance of vac uum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric- barrier discharge (DBD) device. After functionalization, the substrates wer e "activated" by dipping in a dilute acidic PdCl2 solution or by spin-coati ng of a thin metal-organic film (from a solution of palladium acetate (PdAc ) in chloroform). The catalytic activity of the so-deposited palladium spec ies toward the electroless deposition of nickel was studied before and afte r a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite ) within the electroless, bath. This work confirms the specific interest of grafting nitrogenated functiona lities onto polymer surfaces for attaching covalently the palladium-based c atalyst (in particular in the case of the PdCl2 route), forming thus strong Pd-N-C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxy genated functionalities are surface-grafted, the conventional two-step proc edure using SnCl2 and PdCl2 solutions can be proposed due to the strong che mical affinity of tin toward oxygen. The Ni deposits obtained under these d ifferent conditions pass the standard Scotch(R)-tape test and, therefore, e xhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure cau ses an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the P dAc route. In addition, this work demonstrates that extensive research stil l has to be performed to understand and improve the Ni/polymer adhesion whe n the PdAc route associated with a VUV irradiation is considered.