Metal deposition on liquid crystal polymers for molded interconnect devices using physical vapor deposition

Abstract

We report on a new metallization process on thermoplastic materials for molded interconnect devices (MIDs) to obtain smooth and adherent metal layers. The process includes deposition of a thin chromium interlayer and a subsequent copper layer by physical vapor deposition (PVD) on commercial liquid crystalline polymers (LCPs) followed by electroless plating of nickel and immersion gold to the desired thickness. Adhesion strength of the metal layer to LCP could be further improved by plasma treatment of the LCP substrate before plating. The properties of the multilayer metal system were compared to an electrolessly plated only sample. By combining PVD and electroless plating we obtained smooth metal layers with good adhesion to LCP. No decrease in adhesion strength of the metallization (Cu/Cr layer) was observed after electroless plating. We conclude that combination of PVD and electroless plating is well suited for fabrication of finest pitch metal layers on MIDs.