Patterned Adhesion of Electrolessly Deposited Copper on Poly(tetrafluoroethylene)

Abstract

Electroless deposition of Cu on Na naphthalenide‐etched poly(tetrafluoroethylene) (PTFE) leads to adherent Cu film growth through a three‐step solution process involving (i) sensitization by adsorption of SnII, (ii) reduction of PdII by adsorbed SnII to produce Pd0 nucleation sites, and (iii) reduction of CuII by formaldehyde for Cu film growth. Cu film thickness is determined by exposure time in the CuII solution. Adhesion is determined partly by the initial SnII sensitization step: Sn from an aqueous solution is adsorbed onto and absorbed into the rough, porous, etched surface to produce a mechanically interlocked “Sn‐base” for the subsequent steps. Patterned deposition of adherent Cu is achieved via area‐selective irradiation of the surface to produce cross‐linking and, subsequently, area selective etching. This results in major differences in adhesion strength of the resultant Cu film between the irradiated and nonirradiated areas: the Cu film on nonirradiated areas is not affected by a “Scotch‐tape” peel test while on irradiated areas XPS spectra show that the Cu film, the Sn sensitizer layer, the Pd nucleation sites, and a major fraction of the etched layer are all easily and cleanly removed. After selective peeling of the Cu film and the active layer, continuation of Cu deposition in the solution results in Cu deposition only on the remaining Cu film. Because the Sn/Pd sensitization/nucleation steps are general, the present results apply to all metals that can be electrolessly deposited.