LAUSR

Abstract In this work, a novel environmentally friendly method for the microstructuring of metal thin films, which is an essential fabrication step within the production of microchips, is presented. Through employing digital lithography by inkjet printing of inks based on the natural biomaterial shellac, solely comparably safe chemicals (e.g. shellac, ethanol and isopropanol) are employed while hazardous developer solutions needed for conventional masking methods using photoresists are avoided. Within the newly developed process, shellac inks are printed on reusable transfer layers, which highly increase the masking resolution in contrast to directly printing on metal thin films to linewidths of approximately 60 μm and renders the process virtually independent on the surface properties of the material to be structured. The printed shellac mask patterns are thermally transferred onto the metal thin films and stripped after wet etching using ethanol or isopropanol. Using the method presented, rigid and flexible circuits made of copper or aluminum were successfully fabricated and tested. Inkjet printing of different shellac inks was evaluated through contact angle and viscosity measurements and morphology assessments of inkjet printed line patterns, indicating that a shellac/isopropanol ink with a concentration of 0.05 g/mL showed the optimum printing performance. Sorption experiments in common aluminum and copper wet etchants revealed that for low to medium etchant concentrations shellac shows a decrease in swelling for increasing etchant concentrations.