Improvement of bonding properties of PTFE by low pressure plasma treatment

Bonding of rapidly expanded PTFE remains poor unless a special pretreatment of PTFE substrate is performed. The dielectric material PTFE is used in the Printed Circuit Board (PCB) field. Because of the low dielectric constant, it has especially good electrical insulation. In the past mainly chemical primers were used. A replacement for this type of pretreatment, plasma pretreatment, offers advantages from an environmental viewpoint. From the present investigation, where the plasma parameters were systematically varied, it can be concluded that a very short exposure is required. We used the RF plasma to increase the hydrophilic of the PTFE. We found that the surface microstructure was branched. Interestingly, the hydrogen plasma was better than oxygen plasma for stability of surface chain. The peel (bond) strength after plasma pretreatment became even higher than after a primer pretreatment. ESEC analyses of the fracture areas were performed. It was found that a long exposure to the plasma weakened the boundary layer. Especially, the beneficial effect of the plasma pretreatment before bonding lasted in a laboratory environment much longer than after a primer pretreatment.