Electrospray deposition ofin‐situ UV‐photoactivatedpolyimide films

Abstract

In electrospray deposition, a precursor solution, composed of a solute material in a volatile carrier solvent, is atomized into a spray of charged microdroplets under the influence of a strong electric field. As the droplets are in‐flight, the carrier solvent evaporates, leaving behind the solute material that can be delivered to a target surface to create a film. In this work, we employ electrospray deposition to create films of UV‐photosensitive polyimide. Films were deposited using in‐situ UV exposure, where the in‐flight droplets and deposited material were exposed to UV during deposition. The characteristics of these films were compared to films exposed to UV only after deposition (referred to as post‐UV exposure). The microstructure of the deposited films was notably different for the two exposure modes, in which the in‐situ UV exposed films have a wavy/dimpled surface, compared to the flat and smooth surface of the post‐UV exposed films. However, thermogravimetric analysis and Fourier transform infrared spectroscopy showed that the UV activation of the in‐situ UV and post‐UV exposed films was nearly identical. Breakdown testing was conducted to evaluate the dielectric strength of the films. Overall, the in‐situ UV and post‐UV exposed films exhibited similar breakdown strengths of approx. 430–450 V/μm. The use of in‐situ UV exposure cuts in half the processing time for producing thin polyimide films.