A Review of the Opportunities and Processes for Printed Electronics (Part 3): Materials, Process Developments

Estimated reading time: 10 minutes

Laser equipment suppliers have developed a method that is an outlier in the realm of printing flexible films. In simple terms, the method is the reverse of printing. A thin film of metal on a flexible base is ablated by a laser beam that prints the reverse (negative) of the circuit pattern leaving a thin metal circuit pattern. One company, LPKF Laser & Electronics AG, had demonstrations on 35mm film, which is a good deal narrower than the current wide web focus area, but it might fill a niche for special products or particular needs.

Beyond simple conductors, resistors and light-emitting diodes, there are still more important emerging technologies for printable semiconducting materials. Printed semiconductors may be the most important and distinguishing features of a printed electronic circuit. A joint venture by two European firms PolyIC GmbH & Co. KG and Thin Film Electronics ASA has produced fully functional, thin film, rewritable polymer memory products using a high-volume, roll-to-roll printing process. The developers claim that the process is high-yielding and suitable for low-end consumer products that require memory, such as toys and games.

Another company, Terepac Inc., which is tackling printed semiconductors from a different approach, has developed a transfer printing process for semiconductor devices using a simple principle of photopolymer release. The method takes advantage of the fact that certain polymers used as adhesives decompose thermally to gases over a narrow temperature range with little or no residue. Additionally, they discovered that the temperature can be drastically reduced by the action of a photogenerated catalyst. The material has been labeled a digital release adhesive (DRA) because it first has the adhesive properties of a typical thermoplastic polymer and then no adhesive properties at all after gasification, since only air is left. In production, the minuscule semiconductor components (as small as 100μm) are first transferred en masse to the printing plate in a laminator called the prepress. The plate has been coated by DRA and may be rigid, or could be produced on a flexible web. In the printing step the components attached to the carrier with the DRA are irradiated through the plate in only those regions where the components should be released, allowing great precision.

Another developer in California  has shown breakthroughs in nanomaterials and printing technology. Kovio Inc. has also developed semiconducting, silicon-based inks that allow for the integration of printed silicon electronics and thin-film technology. The company suggests that the technology will enable the fabrication of stable, high-performance, low-power integrated circuits that can operate at frequencies in the MHz range and potentially above. An advantage of printed silicon technology over organic electronics alternatives is that printed silicon purports to offer significantly higher performance, lower power consumption and environmental stability. The economic viability of the process compared to processes using organic materials is not known at this time, but the solution should prove compelling for some applications, such as RFID tags.

In Part 4, Happy Holden talks about the market applications for printed electronics.

You can read the Part 1 of this article series here, and Part 2 here.

Editor's Note: This paper has been published in the proceedings of SMTA International.

• < Previous Page