Investigation of wet chemical-treated poly(tetrafluoroethylene) surface and its metallization with SIMS, XPS and atomic force microscopy

Surface modification and metallization of poly(tetrafluoroethylene) (PTFE) surface via a wet chemical treatment was studied. The wet process included a pretreatment using Na/naphthalene/THF solution as an etchant followed by an electroless copper plating. The existence of Na in the substrate top layer down to several micrometers was detected by Secondary Ion Mass Spectrometry (SIMS) and was thought to be the key element which made it possible to deposit electroless copper onto the PTFE surface. The topographies of the pretreated surfaces were examined by SEM and the nanometer-size surface roughnesses were characterized by Atomic Force Microscopy (AFM). Chemical changes on the surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. A comparison of copper adhesion was performed by the scribe-grid test and a good agreement with F/C ratio was obtained. The effects of treatment time and Na/naphthalene ratio on wettability, surface roughness, fluorine removal: copper adhesion as well as the locus of failure are discussed.