Tailoring the surface morphology of polyimide for improved adhesion

Semiflexible polyimide structures are not amenable to good adhesion because of their a) spontaneous orientation of the polymer chains parallel to the film substrate during curing, b) formation of an ordered skin, and c) smooth surface topography. We briefly discuss these structural features with regard to metal-on-polyimide (metal/Pl) adhesion. A method is proposed to improve adhesion by tailoring the surface and bulk morphology of the Pl to circumvent these properties. In this method, different precursors of the same polyimide (PMDA-ODA) are blended. Phase separation induces spontaneous roughening of the Pl surface. This novel technique reduces the extent of chain orientation, gives rise to topographical and morphological surface heterogeneities, and produces a discontinuous ordered skin. A variety of topographical features with nanoscale dimensions are produced that range from 'mounds' to 'dimples.' The process does not alter the overall chemical composition of the Pl, occurs spontaneously, and is extendable to other polyimides or polymer systems. Threefold and ninefold enhancements of adhesion over that of a conventionally cured PMDA-ODA film are obtainable for electroless and vapor-deposited Cu on Pl, respectively.