Copper deposition on textiles via an automated dispensing process for flexible microstrip antennas

A three-axis automatic robot was coupled with a precision liquid dispenser to deposit copper on fabrics to be used as the conductive layer for assembly of textile-based flexible microstrip patch antennas. Two reactive solutions, copper sulfate and sodium borohydride, were sequentially dispensed on fabrics and a conductive copper was produced in situ and in real time, through a simple redox mechanism. Driving pressure, the number of dispensing cycles, concentration and composition (i.e. the addition of a complexing agent sodium citrate to the copper sulfate solution) of the reactive solutions were studied to optimize the dispensing process in favor of rapid copper deposition. The electrical performance of the resulting copper deposit and its adhesion to the textile substrates were characterized. A copper coating of about 0.2 ohm/□ sheet resistance could be prepared in less than 1 hour under a 45 kPa driving pressure, at a 200 mm·s−1 moving speed, and within 60 dispensing cycles.