Improving Adhesion of Polytetrafluoroethylene to Aluminum, Copper, and an Adhesive by Ar + Irradiation with and without
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IPFFE surface, and the third is a change of the interface between the metal and PTFE. The wettability of the PTFE surface was also determined by dropping water droplets on the modified surfaces. The contact angle between water droplets and the irradiated surface of PTrFE samples decreased with ion dose up to I x 1015 ions/cm-. increased at higher dose, and finally increased to the extent that no wetting was possible at I x 1017 ions/cm 2. The PTFE samples irradiated with Ar+ without O0gas environment had lower contact angle than those with 02, even though the samples with 02 developed hydrophilic groups on the irradiated surface. This result on wettability is not consistent with our earlier results on PMMA and PC and is due to the unusually high level of surface roughness of PTFE caused by Ar+ bombardment. I. INTRODUCTION Ion irradiation of polymers has attracted increasing number of researchers in recent years because it could be used to tailor chemical, physical, mechanical, and electrical properties of polymers. Such property tailoring or enhancements have been observed by Pae et al. on crystallinityl 11, Puglisi et al. on wettability [2], Forest et al. on crystallinity [31, Rao et al. on wear resistance 141, Basheer et al. on conductivity 151, Calcagno et al. on density 161, and Koh et al., Chang et al., and Baglin et al. on adhesion 17-9]. Various mechanisms for the enhancement of the polymer properties have been attributed to chain scission, cross linking [10), carbonization 1111, chemical reactions [8-101, and surface roughness 18,91 depending on the experimental conditions. Solubility of polymers has been varied with changes in molecular weight which were caused by scission of main chain. Crystallinity has been increased by chain scission and loose335 Mat. Res. Soc. Symp. Proc. Vol. 396 © 1996 Materials Research Society
ning entangled chains. Wettability has been improved by changing the surface chemistry and increasing surface roughness. PTFE is widely used because of its low frictional coefficient, high stability against heat, high resistance to chemical reagents, and/or high electric resistance. However, its poor adhesion property with other materials limited its application in microelectronics devices, coatings, etc. Many attempts have been made to improve its adhesion property by using rf plasma 1121, glow discharge 1131, electron beam [ 141, and ion irradiation 18,9]. Nevertheless, no significant adhesion enhancement has been achieved with plasma, glow discharge, and electron beam methods. Ar÷ and O+ irradiation improved Cu/PTFE adhesion. Rather, the treatment caused damage to the surface. Recently, we reported that ion irradiation with 1 keV energy under a reactive gas environment improved significantly the wettability of PMMA and PC 115] to water and adhesion of the polymers to Al and Cu films. In this paper, we present the results of a study of Ar' irradiation on PTFE which led to dramatic improvement of adhesion of PTFE to Al and Cu films and an adhesive (Crystal Bond) and also to worsening of w
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