Direct write fabrication of high-density parallel silver interconnects

This study investigates the suitability of direct write (DW) technology for the fabrication of high-resolution wear sensors. We demonstrate the production of high-density parallel interconnect traces and provide recommendations for processing conditions to minimize line width and line spacing based on DW ink rheology. To create parallel silver lines with 50 μm center-to-center spacing and 15 μm line width on alumina substrates, we used an nScrypt DW system and sintered the lines at 625 °C in air. The sintered lines exhibited an electrical resistivity of 5.29 × 10−8 Ω m (about three times bulk silver resistivity reported in the literature) with a standard deviation of 3.68 × 10-9 Ω m (ca. 7% variation). To determine the conditions needed to consistently create fine conductive lines, we simulated the volumetric flow rate and analyzed the effects on line geometry of several printing parameters including valve opening, dispensing gap, and substrate translation speed. Our results indicate decreasing the valve opening, decreasing the dispensing gap, and/or increasing the translation speed of the substrate reduces the resultant printing flow rate and cross-sectional area of DW lines. For a fixed valve opening and dispensing gap, we also observed broken lines due to overstretching of the inks at exceedingly high substrate translation speeds.