Thermal and chemical stability of a spin-coated epoxy adhesive for the fabrication of a polymer optical waveguide

Spin coating is a common method for depositing very thin polymeric film across a planar surface in a short period of time. Thinning occurs due to the combined effects of centrifugal spin-off and evaporation. The evaporation of any reactive component during spinning plays an important role on the stability of spin-coated polymeric film. An investigation was carried out to study the effects of spinning on the thermal and chemical stability of the epoxy adhesive. The thermal stability of both spin-coated and without spin-coated epoxy adhesive was measured by thermogravimetric analysis (TGA) at heating rate of 10°C/min in an inert environment. A lower thermal stability was observed for the spin-coated epoxy adhesive. At the center of the substrate it is more stable than the other locations. Thermal stability greatly deviates at the border side of the spin-coated substrate. Higher chemical stability was also observed at the center than the other locations of the spin-coated layer when immersed in the metal (nickel) etchant chemical solution. The lower thermal and chemical stability is mainly due to changes in the material properties during the spinning process. From this study it is proposed to use the reactive components that are less volatile, having higher intermolecular forces, and allow a greater part of the thinning behavior to occur without significant changes in the fluid properties during the spinning process. Lower spin speed also suggested to reduce the mechanical degradation of the polymeric adhesive for the fabrication of a polymer optical waveguide.