Growth structures of electroless copper films for printed wiring boards

Abstract

Though a mature process, electroless copper deposition occupies an important economic and technological position in the electronics industry today. Virtually all multilayer circuit boards require the process for through hole connections enabling the miniaturization of the board to keep apace with the total electronics trend to higher densities and smaller components. This trend places more stringent requirements on adhesion of the copper and reliability of the film. The process itself consists of two deposition stages, a surface catalyzation with a palladium colloid followed by deposition of copper. The surface presents a composite substrate of greatly different materials on which adhesion is required: copper, silicate glass, and polymeric resins of diverse compositions. To facilitate study of surface structures, we have used highly oriented pyrolitic graphite as a substrate. Scanning tunneling microscopy (STM) has shown the incipient stages of the palladium catalyst and electroless copper. The results of STM investigations have revealed the nucleation, the microisland formation and the surface growth morphology. The surface composition at each step is identified by scanning tunneling spectroscopy. The surface structures and the defect formation on printed circuit board materials are also investigated by AFM.