Development of very thin coaxial cable using fluorine resin covered with high adhesion electroless copper plating

近年来，同轴电缆和印刷电路板都需要在GHz频段具有低介电常数和低介电损耗因子的材料。氟碳聚合物具有优异的高频性能。然而，由于其表面能较低，很难在其表面形成高度粘附的金属图案。氟碳聚合物金属化前的表面改性是必不可少的一步。我们提出了一种利用常压等离子体处理和液相自组装相结合的方法来提高化学铜（Cu）膜/氟碳聚合物的附着力的表面改性技术。研究了中压或常压等离子体改性四氟乙烯-全氟烷基乙烯醚共聚物（PFA）表面化学镀铜层的粘附强度。常压等离子体处理的黏附强度是中压等离子体处理的2倍。在90°剥离试验后，通过FTIR分析在化学镀铜膜表面观察到CF2键的强红外峰，认为中压He等离子体辐照在PFA中容易形成损伤层。

Recently, a material with a low dielectric constant and low dielectric loss factor in the GHz band is required for coaxial cable and printed circuit boards. Fluorocarbon polymers have excellent high-frequency properties. However, owing to their low surface energy, it is difficult to form highly adhesive metal patterns on their surface. The surface modification of fluorocarbon polymers before metallization is an essential step. We have proposed a surface modification technique for fluorocarbon polymers that enhances the adhesion of electroless copper (Cu) film/fluorocarbon polymers by a combination of atmospheric-pressure plasma treatment with liquid-phase self-assembly. We investigated the adhesion strength of an electroless Cu-plated layer on a tetrafluoroetylene-perfluoroalkylvinylethercopolymer (PFA) surface modified by medium-pressure or atmospheric-pressure plasma. The atmospheric-pressure He plasma treatment resulted in twice the adhesion strength of that obtained by the medium-pressure He plasma treatment. It is considered that a damaged layer is easily formed in the bulk of PFA by medium-pressure He plasma irradiation because a strong IR peak assigned to the CF2 bond was observed from the surface of the electroless Cu film by FTIR analysis after a 90° peel test.