Grafted-to Polymeric Layers Enabling Highly Adhesive Copper Films Deposited by Electroless Plating on Ultra-Smooth Three-Dimensional-Printed Surfaces

A process has been developed to produce highly adhesive metallic layers onto polymeric surfaces. It is specifically aimed at ultra-smooth polymeric substrates produced by stereolithography (SLA) with applications in the field of radiofrequency components. By combining the wet deposition of an azide-based primer and high molecular weight polyacrylic acid (PAA), a dense polyelectrolyte layer can be grafted to various plastic surfaces. Conformal metallization is achieved by electroless plating. Adhesion of the metal layer to the plastic substrate is promoted by specific affinity and chelating binding of the grafted layer to the catalyst, its robust anchoring to the plastic substrate by covalent bonds via nitrene insertion, and deep interpenetration with the metal layer. This process is highly versatile since it is effective on various polymeric substrates, environmentally friendly and chromium-free, and adaptable to three-dimensional (3D) geometries. It has been shown to provide high adhesion onto surfaces with nanometric roughness without using surface roughening techniques. This method has been extended to produce micrometric metallic patterns by selective electroless metallization. Patterns of grafted-to PAA were printed by aerosol jet printing, and the electroless copper bath was adapted to achieve selectivity of the electroless copper on the chosen patterns. The printing and plating process also aims to be compatible with the surfaces of 3D-printed plastics and composites.