Self-Aligned Capillarity-Assisted Printing of High Aspect Ratio Flexible Metal Conductors: Optimizing Ink Flow, Plating, and Mechanical Adhesion

High-resolution, low-resistance, flexible metal interconnects that are many centimeters long were additively manufactured on plastic substrates using a roll-to-roll compatible print and plate process. Connected networks of ink-receiving reservoirs and capillary microchannels were first roll-to-roll molded on plastic films. Silver ink was jetted into the easily-targeted ink-receiving reservoirs, and the connected microchannels were fed and coated with ink by capillary flow and drying. Subsequent electroless plating of copper into the silver-coated channels created solid, high aspect ratio conductive traces. Processing windows for uniform silver deposition were identified as a function of ambient humidity, ink flow time, and channel geometry. Plating conditions were also optimized to alleviate copper stress development and debonding and to allow conductor flexibility. Overall, the optimized print-and-plate process is promising for additively manufacturing micron-scale, high aspect ratio (>1), low-resistance (linear resistance similar to 1 Omega/cm) conductors embedded in plastic, addressing a long-standing fabrication challenge for flexible printed electronics.