Improved polyimide/metal adhesion by chemical modification approaches

To increase their adhesion to silver, polyimide (PI) surfaces were modified by sulfonation reactions by means of different experimental procedures. Th e results of these modification reactions were analyzed in terms of the var iation of the surface chemical composition examined by X-ray photoelectron spectroscopy. Longtime reactions were also followed by monitoring the incre ase in weight of the PI films. Changes in the total surface free energy wer e evaluated by contact angle measurements with the sessil drop method. The influence of the modification reactions on silver/PI adhesion was estimated by means of a 180 degrees peeling test according to ASTM standards. Finall y, the effect of chemical modification on film roughness was investigated b y means of atomic force microscopy. The results obtained showed that a net improvement, that is, over the maximum rate according to the reference ASTM test, was attained via both the gaseous SO3 and concentrated H2SO4 procedu res, with the latter procedure more effective in the presence of silver sul fate as a catalyst. However, the former was judged more convenient because of the low amount of reagents used and the simplicity of cleaning operation s. Interestingly, optimum adhesion levels were attained after only very low contact times with all sulfonating agents, that is, after about 30 s. Thes e results were compared with the effects on PI/silver adhesion of tradition al etching procedures with KOH aqueous solutions at different temperatures. In this case, good adhesion was observed only after longer reaction times, that is, on the order of 1-2 min in the case of IM KOH and 1 h in the case of 0.1M KOH. (C) 2001 John Wiley & Sons, Inc.