ABSTRACT
Metallization of insulators is an effective way to render insulators conductive without incurring the weight and cost of the bulk metal. It is also occasionally used to impart metallic sheen and lustre to an otherwise unappealing look o f the plastics. Depending on applications, the metal layer can vary in thickness from 0.5 pm to 40 pm. Metallization can be carried out by physical means such as vapour deposition, direct application o f a conductive ink to the surface, or by chemical methods which
i Present address: Institute of Microelectronics, Singapore
sensitize the surface for chemical deposition of metal in subsequent steps M . The cost associated with the physical methods of deposition is relatively high and as such the methods are limited to applications that do not call for heavy build-up of thickness. In contrast, the chemical methods are more adaptable to engineering applications that require sufficiently thick deposits o f metal only in selected areas o f the surface, e.g. metallization of circuit patterns on a printed-circuit board (PCB). Such process involves many steps which invariably begin with the photolithographic generation of selected areas for metal deposition on the insulating surface, use of palladium-tin colloidal systems to sensitize the selected areas, and the activation of the palladium-tin colloids by an activating agent (e.g. a mild acid) to form an adherent layer of palladium metal that catalyses the ensuing process of electroless metal (e.g. copper) deposition . The processing cost depends on the metallization area, and could be prohibitive if the metal coverage on the surface is extensive. In this paper, we present an alternative process which can achieve the same end results while using a much simplified procedure and relatively inexpensive starting materials. The process is particularly attractive to prototyping and the low cost production of flexible circuits.
