Before electroless plating, polymer surfaces must be sensitized and/or activated by using either the conventional twostep or one-step process. The latter stage is a compulsory one to make such surfaces catalytic, e.g., for Ni-P deposition. These processes are performed here using 02, NH3, or N, plasma pretreatments. Reaction mechanisms are proposed for each of the processes and for each type of surface considered (oxygenated or both oxygenated and nitrogenated by the plasma treatment). Direct palladium chemisorption onto nitrogenated groups is highlighted. This allows one to simplify the process making the surface catalytic via elimination of the use of SnCl, and to extend the method to any polymer. An additional interest of the plasma treatments, besides their high efficiency in grafting chemical functions, is to perform this grafting at will on selected areas which results in selective metallization.
InfrocluctionPalladiumchemisorption is a determinant step in metallization by the electroless process. This step allows us to establish strong chemical bonds between the substrate and metallic film. Historically it was first carried out by a twostep process consisting of substrate treatment by the wet way successively in SnCl, then PdCl, dilute solutions. '-'4 It was given up between 1975 and1980 in favor of a onestep process using a mixed SnC1,/PdC1, solution."""The bibliographical study realized in this field shows that the mixed SnCl,,PdCl, solutions are of a great complexity and that their aging plays a significant role in the metallization efficiency. For some authors, 17-18 these solutions are constituted of various Sn-Pd chloride complexes, but for the majority 16,1945 the complexes formed at the very beginning of the solution mixture are rapidly transformed into colloidal particles whose core consists according to Cohen and West'6 of a metallic alloy (Sn/Pd) surrounded by an Sn(II) layer stabilizer. This Sn(II) layer makes the colloid inactive toward metallization initiation so that a supplementary step, called an acceleration step, which consists of dissolving this layer is necessary. In addition, air aging of the mixed solutions, studied among others by Cohen and West 16 and Meek, 19 results in an Sn(II) oxidation followed by a particle agglomeration and precipitation making the solution unusable.Similar problems were encountered at the time of palladium chemisorption by the two-step process. Many authors 34,9,16,1214 have indicated that the SnC1, solutions used for the substrate sensitization consist of Sn(II) chloride and/or hydroxy chloride complex ions. Cohen at at. " and d'Amico et al.4 have shown that complex phenomena occur in these solutions. Their oxidation in air results in the formation of colloidal particles whose size increases with aging leading to the progressive diminution of sensitizer activity then to its canceling out. Further, most authors mention the photosensitivity of SnCl, solutions and some of them" the influence of the order of addition of the reactants on colloidal particle si...
