Surface characterisation of plasma treated flexible substrates for waveguide-on-flex application

This paper reports the physical and chemical effects of argon, nitrogen and oxygen plasma treatments on the surface properties of flexible circuit materials. Both KaptonHN™ and Vecstar™ films selected as optical flexible substrates under plasma irradiation were studied by atomic force microscope (AFM), contact angles, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The etch rate enhancement of the polymeric materials is more pronounced in oxygen plasma than in argon or nitrogen plasma. The increases of surface functional groups (–COOH, –CNOH) of plasma-modified polymer films are correlated with the increased presence of polar component in surface free energy. While the plasma treatment on KaptonHN™ substrates have been widely discussed in literature, the detailed characterisation of both pristine and different plasma surface modified Vecstar™ films is reported and compared for the first time.