Flexible Copper Metal Circuits via Desktop Laser Printed Masks

Abstract

A novel process is demonstrated that produces patterns of electrically conductive copper on a flexible polyimide film substrate using standard desktop laser printed toner and near room temperature aqueous chemistry. The laser toner acts as a mask to selectively block the ion exchange self‐metallization (IESM) reduction reaction that forms nanoscale silver or palladium coatings at the polyimide surface. The silver or palladium IESM coating is then used as a catalyst for electroless deposition of copper. Under appropriate conditions, the copper is deposited selectively on top of the catalyst layer. The resulting copper layer has a measured sheet resistance as low as 0.3 Ohms/sq. Electrical isolation is measured between copper traces spaced as close as 300 microns, and high conductivity is measured along traces with widths as low as 200 microns. The minimum pattern size appears to be limited primarily by the resolution of the laser toner pattern, as the IESM metal layer is observed to follow the contours of individual toner particles. The process avoids the use of high temperature, vacuum, and organic solvents and is thus suitable for very low cost prototyping or distributed manufacturing of simple electronic devices.