Electrospray deposition of in-situ UV-photoactivated polyimide films

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.