Multi-sensor feedback control for the flash sintering of printed nano-silver ink

Abstract The fabrication of conductive patterns using the flash sintering of nano-silver ink has advantages such as high production efficiency and low process temperature. However, the stability of flash-sintered conductive patterns is questionable owing to the vulnerable surface morphology. To improve stability, this study proposes an online sintering state monitoring method using feedback control based on multi-sensor data. The flash-sintered conductive patterns exhibit different surface morphologies at different sintering states. To determine the degree of sintering, an imaging system is implemented to analyze the near-infrared light reflections from the conductive patterns. Meanwhile, a non-contact thermometer is used to measure the temperature difference between the conductive patterns and the substrate. Since the thermal conductivity of the conductive pattern changes during flash sintering, the temperature difference can represent the degree of sintering. By combining the near infrared image and temperature data, the sintering state can be accurately evaluated, and the sintering parameters can be optimized to achieve closed-loop flash sintering. As an example, this method was successfully applied to fabricate microstrip antenna arrays whose return loss and antenna gain are consistent with performances of conventional screen-printed microstrip antenna.