Effect of Microwave Plasma Surface Treatment for Improved Adhesion Strength of Direct Copper Plating on Polyterafluoroethylene (PTFE)

摘要

The purpose of this study is to investigate the effect of plasma surface modification to improve adhesion strength betweenpolytetrafluoroethylene (PTFE) and electroless copper plating. PTFE is widely used in many industries because of itsunique electrical, thermal, and mechanical characteristics. However, because of its low surface energy, it is difficult toacquire enough adhesion strength between PTFE and other substances without surface modification. Plasma is well knownas one of the surface modification techniques that improve adhesion strength.In this study, high-electron density microwave plasma with nitrogen and hydrogen gas was applied. Nitrogen and hydrogenmicrowave plasma can modify the surface of PTFE with surface defluoration and the nitrogen functional group. Surfacemodification techniques with the nitrogen functional group are frequently applied to surface activation for medical devices.In this experiment, so as to understand the effect of nitrogen functional groups for the plating on PTFE, microwave plasmatreatment was conducted under various conditions in terms of treatment pressure. In all conditions, before nitrogen andhydrogen microwave plasma treatment, pre-plasma treatment was conducted with argon gas in order to activate the surface ofthe PTFE. In this experiment, surface energy of the PTFE after plasma treatment was calculated from the contact angle ofwater and diiodomethane. The results of surface energy measurement showed that nitrogen and hydrogen microwaveplasma treatment was preferable for activating the surface of PTFE. In addition, x-ray photoelectron spectroscopy (XPS)and atomic force microscope (AFM) measurements were conducted after the microwave plasma treatment to characterize themodified PTFE surfaces both physically and chemically. The result of XPS measurement showed the nitrogen functionalgroup was generated on the surface of PTFE after plasma treatment. The intensity of the nitrogen functional group was afunction of treatment pressure.AFM measurements showed that there was no marked physical difference between before and after short time plasmatreatment. After those measurements, electroless copper plating was conducted on the surface of modified PTFE. Afterthe plating, adhesion strength was observed in order to understand correlation between adhesion strength and the results ofchemical and physical measurements. The results showed that the PTFE surface modified by microwave plasma underspecific treatment conditions of nitrogen and hydrogen gas could improve the adhesion strength between the PTFE andelectroless copper plating.