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Simple versatile processes combining plasma treatments, micro-contact printing (µCP) or ink-jet printing (IJP), and electroless deposition (ELD) have been developed to produce micrometer and sub-micrometer scale metal (Ni, Ag) patterns at the surface of polymer substrates. Plasma treatments were mainly used to graft the substrate surfaces with either nitrogen-containing functionalities on which a palladium-based catalyst can be subsequently chemisorbed (case of Ni deposition through a tin-free process in solution) or oxygen-containing functionalities on which a tin-based sensitization agent can be subsequently chemisorbed (case of Ag deposition through a redox reaction). µCP of the catalyst or of self-assembled monolayers (SAMs) as well as ink printing were used to obtain locally active or non-active areas at the polymer surfaces. The metal micro-patterns were characterized using optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Surface chemical characterization wa...

The tin-free electroless metallization process developed in our laboratory consists in attaching the Pd(+ 2)-based catalyst on surfaces which were previously grafted with nitrogen-bearing groups. The so-functionalized surfaces lead to the formation of true covalent bonds between palladium and nitrogen-based species. In this work, the different steps of the process are studied, namely: (i) the grafting of nitrogen-bearing groups on an insulating surface by various processes already used in our laboratory, (ii) the seeding of the surface with Pd(+ 2) species, (iii) the reduction of Pd(+ 2) to Pd(0) by different routes (this step is needed due to the use of industrial plating baths which contain strong stabilizers that prevent or delay plating), (iv) the Ni metallization using low- and high-phosphorus plating baths. Phosphorus which originates from the plating bath reducer is partly incorporated in the Ni films and creates some stresses. Adhesion of the resulting films is evaluated by the Scotch® tape test. The main parameters responsible for adhesion and governing the characteristics of the Ni film/substrate interface are: the nature of the substrate, the Pd(+ 2) reduction route and the phosphorus content of the Ni plating bath. All these parameters influence the amount of stresses generated both at the metal/substrate interface and within the film.

Different polymer substrates were copper-plated by electroless deposition without using the Pd-based conventional catalyst to initiate the redox reaction. The principle of the process is based on the deposition of a copper(II) organic precursor film on the polymer surface to be metallized and on the reduction of the Cu(+ 2) ions. This reduction is obtained by different chemical, thermal, photonic or plasma techniques and its results were studied by XPS analysis. A polymer surface densely and homogeneously seeded with Cu(0) species allows to initiate the autocatalytic deposition of copper films. Their thickness was measured by X-ray fluorescence spectrometry and their adhesion evaluated by the Scotch® tape test.

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.

Metallized polymer or polymer-based materials are used in a large range of electronics applications including the fabrication of ohmic contacts, chip-level interconnects, printed circuit boards and shielded materials.1–7 For such technological applications, electroless deposition is the most widely used method in practice today.8 Basically, electroless plating is an autocatalytic redox process occurring in aqueous solution between ions of the metal to be deposited (generally Ni or Cu) and a strong reducer. Typical procedures involve a variety of multi-step sequences for the preparation of the surfaces to be coated. Conventionally, substrates are cleaned with solvents to remove surface contaminants, chemically etched to obtain a micro-roughened oxidized surface, and then seeded with a catalyst such as palladium. Chronologically, the seeding process was first accomplished by using a two-step procedure involving substrate treatment successively in dilute SnC12 (sensitization step) and PdC12 (activation step) acidic solutions. Further, a one-step procedure using a colloidal suspension containing both Sn and Pd species (a SnC12/PdC12 acidic solution) has been developed and is presently in common use in industrial environments. In this last case, the Pd/Sn colloidal particles adsorbed on the polymer surface must be exposed (acceleration step) to a solubilizer (a HCl or NaOH solution) to remove the excess of Sn+2 species surrounding the catalytic Pd-based core of the colloidal particles. As can easily be inferred from the details of such multi-step procedures, it is today highly desirable to develop alternative approaches for making the insulating surfaces catalytically active. These approaches should require no chemical surface etching, reduce the number of process steps, and provide a highly selective, well-defined interaction between the catalytic species and the surface to be coated.9