Innovative Infrared System Dries and Sinters Printed Electronics Almost 2000 Times Faster than Previously

• Heraeus develops custom-built IR module
• Successful tests carried out at TU Chemnitz with inkjet silver nano particle inks using the roll-to-roll printing process.

The continuous printing of electronics for displays or solar cells, depends on a rapid drying of the surface and good conductivity of the silver inks. A newly developed infrared module from Heraeus Noblelight achieves this in significantly less than one second (0.32 secs) and is consequently almost 2000 times faster than conventional drying techniques. Heraeus developed and installed the made-to-measure module in a roll-to-roll printing system. In tests, the infrared radiation proved far superior to drying and sintering using conventional hot plates or hot air ovens. These trials were carried out in the Department of Digital Printing and Graphics Technology of Chemnitz Technical University and the Fraunhofer Institute for Electronic Nanosystems.
Heraeus will be presenting this exciting innovation, together with other UV, Infrared, and Flashlamp systems for the printed electronics sector at the Lopec exhibition in Munich in April 2016.

Metallic nano particles for printed electronics are often deposited onto flexible and polymeric materials using Inkjet printing and are then dried and sintered. On a laboratory scale, this is mostly achieved using hot plates or hot air. However, for mass production, the Roll-to-Roll (R2R) technique must be used. And this means that drying and sintering must be significantly faster. New techniques have been investigated, such as microwaves, lasers, Intense Pulse Light (IPL) and infrared radiation. The optimum technique must be able to dry and sinter quickly and efficiently, while at the same time causing no damage to the polymer substrate, which is often temperature sensitive.

Heraeus has developed a purpose-built infrared module for an R2R printing system. This has been used to carry out tests on the infrared drying and sintering of inkjet printed silver coatings on polyethylene naphtalate. (PEN). It could be shown that the post treatment of the freshly printed deposit led to a conductivity of up to 15% of pure silver. Compared with drying and sintering with conventional hot plates or hot air, infrared radiation achieved twice the conductivity in only 0.32 seconds. In contrast, using a hot plate, drying and sintering took about ten minutes.

Using electron microscope imaging, the microstructure of the sintered silver particles was then analyzed in relation to the IR parameters (filament temperature of the emitter, duration and power of the radiation and distance of the emitter and reflector from the substrate.) After optimizing these parameters, the silver was then dried at 50 kW/m2 and sintered at 150 kW/m2. Using the same short wave emitter each time, merely requiring control adjustment. The printed electronics on the continuous foil can therefore be dried and sintered in one stage, at high belt speeds of up to 1 m/sec and an irradiation time of less than 0.32 seconds.

This research and development work was recently published in the Journal Materials Chemistry C: E. Sowade, H. Kang, K.Y. Mitra, O.J. Weiß, J. Weber, R.R. Baumann, Roll-to-roll infrared (IR) drying and sintering of an inkjet-printed silver nanoparticle ink within 1 second, J. Mater. Chem. C. 3 (2015) 11815–11826. doi:10.1039/C5TC02291F.

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