Adhesive Improvement of Metallic Films onto PTFE Surface-modified by using Ar Plasma － Effect of Cu Seed-layer Formation by a Sputtering Method－

Polytetrafluoroethylene (PTFE) has excellent characteristics. By utilizing these characteristics, PTFE is applied in various fields. In recent years, PTFE has attracted attention for the application to a flexible printed circuit board, however, PTFE exhibits the poor adhesion against other materials. To improve adhesion, the chemical surface modification and removal of a low molecular weight fragile layer are required to improve adhesion. In addition, to prevent a transmission loss due to high frequency signals, the surface smoothness has to be maintained. In this study, the surface modification was performed by Ar plasma treatment and Ti or Cu thin films were coated onto the surface-modified PTFE by a sputtering method. These processes were performed consistently in a high vacuum under 5.0×10-4 Pa. The Ti or Cu thin film adhesion on the treated PTFE was investigated by a scratch test with a continuous load of 0–0.98 N. The optimum adhesion of a Cu film was obtained by 180 s in an Ar plasma treatment time at 200 W in an input power. The obtained Cu films on treated PTFE satisfied the condition of a high-frequency printed circuit board about surface roughness or electrical conductivity and also it was anticipated these Cu thin films prepared by sputtering play the role of a seed layer for the wet plating film formation. © 2021 The Institute of Electrical Engineers of Japan.