Electrospray Deposition of Photosensitive Polyimide with In-Situ UV Exposure*

Electrospray deposition uses strong electric fields to atomize a liquid suspension into a spray of charged micro-droplets, and solute material dispensed within the suspension will be contained in the droplets. While the droplets are in-flight, the volatile solvent evaporates, leaving behind solute material that is delivered to a target to grow a film. In this work, we use electrospray deposition to grow thin films of UV-photosensitive polyimide (PSPI). In-situ UV exposure was used to activate the UV-photosensitive components in the precursor, while simultaneously depositing the material on the surface to create a film. The characteristics of the in-situ UV films were compared to films with post-deposition UV exposure (post-UV). The microstructure of the in-situ UV films was different to that of post-UV exposure. In-situ UV exposure caused a wavy/dimpled surface (compared to a very flat surface for post-UV), resulting from the change in viscosity of the droplets under in-situ UV exposure. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) both showed that the UV activation of the in-situ UV was nearly identical to that of post-UV. Lastly, breakdown testing was conducted to evaluate the dielectric strength of the deposited films. Both the in-situ UV and post UV films exhibited similar performance, with high breakdown strengths of approx. 430 – 450 V/µm.