Adhesive Enabling Technology for Direct Metal Deposition on Molding Resin

Abstract

Plating on molding resin is a relatively new field with many possible applications. One possible application is magnetic or electrical EMI shielding of active components. This is currently done mostly by metallic shells or “caps”. However, this technique also increases spatial requirements and reduces flexibility with respect to component layout on the PCB. An alternative and more space saving approach is plated EMI shielding. While sputtering a metallic seed layer in preparation of plating is feasible – this process step is not very cost effective or suitable for mass production. In this respect, classical electroless metallization would be much more desirable but has been so far limited by insufficient adhesion. In this paper we will present a new approach, where components encased by molding resin are directly coated with an electroless copper or nickel layer using an adhesion promoter. By this method spatial requirements are minimized. Also, this process fits into the existing infrastructure within the PCB industry. Due to the extremely high filler content (70-90% wt.) and the wide size distribution (from tens of nm to tens of μm) of fillers, classical Desmear followed by electroless seeding can get a maximum adhesion of only 2-3N/cm. In contrast, with chemical bonding adhesion promoters as presented in this paper, we are able to get up to 5N/cm of peel strength. The plated layer stands up well to reflow shock (260C) and HAST without delamination or significant loss of adhesion – key requirements for this application. These adhesion promoters are applicable to various kinds of molding resins. Extending this technology to embedded components can be another far reaching application.