Thermoformable Conductive Compositions for Printed Electronics

The development of three-dimensional printed electronics has garnered significant interest due to the ease of integration of electronic circuitry on 3D surfaces. However, it is still very challenging to achieve the desired conformability, stretchability, and adhesion of conductive pastes used for printing on thermoformable substrates. In this study, we propose the use of novel thermoformable ink composed of copper flakes coated with silver, which enables us to prevent the oxidation of copper, instead of the commonly used silver inks. Various polymer/solvent/flake systems were investigated, resulting in thermoformable conductive printing compositions that can be sintered under air. The best inks were screen printed on PC substrates and were thermoformed using molds with different degrees of strain. The effects of the various components on the thermoforming ability and the electrical properties and morphology of the resulting 3D structures were studied. The best inks resulted in a low sheet resistivity, 100 mΩ/□/mil and 500 mΩ/□/mil before and after thermoforming at 20%, respectively. The feasibility of using the best ink was demonstrated for the fabrication of a thermoformable 3D RFID antenna on PC substrates.