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

近年来，同轴电缆和印制电路板对低介电常数、低介质损耗因子的材料提出了更高的要求。氟碳聚合物具有优异的高频性能。然而，由于它们的表面能很低，很难在其表面形成高度粘合的金属图案。对氟碳聚合物进行金属化前的表面改性是必不可少的一步。我们提出了一种氟碳聚合物的表面改性技术，通过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镀铜膜/氟碳聚合物的附着力。研究了中压或常压等离子体对聚偏氟乙烯(tetrafluoroetylene-perfluoroalkylvinylethercopolymer)表面化学镀铜层结合强度的影响。常压氦等离子体处理的粘接强度是中压氦等离子体处理的两倍。经90°剥离试验后，FTIR分析表明，化学镀铜膜表面有一个很强的CF2键红外谱峰，因此中压He等离子体辐照容易在PFA的块体中形成一层损伤层。

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.