A new technology allows manufacturers to apply conductive metal circuits to plastic substrates using a cost-effective and sustainable process.

Flexible circuits are found in more and more products where space and weight considerations are important, such as cars, cameras and inkjet printers. However, prices for raw materials such as copper and palladium have risen 150 percent in the past three years.

During the recent K 2010 plastic show in Dusseldorf, Germany, the Fraunhofer Institute for Surface Engineering and Thin Films (IST) displayed new technology that allows manufacturers to apply conductive metal circuits to plastic substrates in a more cost-effective and sustainable process.

Plasma Printing and Packaging Technology (P3T) involves considerably fewer steps than existing processes and it conserves raw materials. Unlike previous methods, the process does not start with a polymer film metalized over its entire surface, from which excess metal is then removed to create the circuits.

To produce flexible circuit boards, manufacturers traditionally apply circuits made of copper to the film that serves as a substrate. In the case of biosensors, palladium is used. They use plasma at atmospheric pressure and galvanization, instead of vacuum-pressure, and laser-based methods.

“During production of circuits for an RFID antenna, you often have to etch away between 50 percent and 80 percent of the copper used,” says Dr. Michael Thomas, director of the IST research group. “This results in considerable amounts of copper scrap that either has to be disposed or reprocessed, using relatively elaborate methods.”

The IST approach is different. Thomas and his colleagues use an additive process to apply the structures they want directly to the substrate sheeting.

The first two process steps are plasma printing at atmospheric pressure and metallization using well-known galvanization methods. “Plasma printing uses the kind of deeply engraved roller familiar from the area of conventional rotogravure printing,” explains Thomas. During the printing process, microplasms are electrically generated in the engraved recesses of the roller. They chemically alter the surface of the plastic substrate where the circuits are to be applied later in the process.

“The process gas from which the plasma is created is usually a mixture of nitrogenous gases,” says Thomas. “The chemical changes we need begin to form on the surface of the film; these changes ensure that the plastic can be wetted with water in these precise areas and will be ‘metallizable’ using suitable plating baths. This means considerable savings of energy and material.”

Thomas and his colleagues are currently attempting to improve the individual processes involved in the manufacture of flexible circuit boards and biosensors. They are closely scrutinizing all of the P3T production steps-from plasma printing to assembly-and coordinating all of the processes with one another in a production line.