The ability to print flexible RFID tags on curved surfaces is an area of great interest to manufacturers. However, flexible antennas have proven to be a challenge.
 
As part of the Met@Link project, begun in October 2015, imec, Quad Industries and Agfa recently developed a demonstrator of a plastic 12-bit RFID tag and read-out system featuring screenprinted circuitry.
 
Quad Industries is a specialist in utilizing screenprinting to produce a variety of touch and switch solutions, smart labels, NFC antennas, batteries and sensors on a variety of substrates, and printed the antenna.
 
“Quad Industries optimizes the screenprinting methodology to obtain highest conductivity with flexible thin layers, and integrates this into a complete integrated solution,” Wim Willaert of Quad Industries noted.
 
Guido Desie, R&D manager at Agfa, said that Agfa supplied its Orgacon nanoparticle-based silver inks for this project. “Agfa-Gevaert develops the nano-particle based inks that provide a much higher conductivity than the comparative flake based inks,” Desie added.
 
Imec manufactured the plastic metal-oxide RFID tag, which uses 438 thin film transistors. Kris Myny, principal member of the technical staff at imec, noted that one of the major challenges is showing that screenprinting is a viable process.
 
“The project Met@linkwas started on October 2015 with five major challenges, of which the first one (IoT example using nano-silver ink and screenprinting methodology) was shown in a real demonstrator,” said Myny.
 
While the demonstrator was designed for badge security, smart packages, wearables and interactive games are potential applications. Myny added that niche packaging applications such as critical medical packages and high-end cosmetic/beverage packages are potential early possibilities.
 
The partners agreed that antenna design was critical to the project.
 
“First of all, the antenna design had to be adapted to the specs of the new inks used and the flexible chip,” Myny pointed out. “Then electrical interference with other circuit characteristics had to be minimized. Lastly, the screenprinting had to be optimized and prepared for later integration into other fabrication requirements.”
 
Willaert said that screenprinting has been shown to be effective for producing the antennas.
 
“It is an additive process that is not wasting metals on these areas where it is not needed,” he added. “It can be done on very large areas on a wide variety of substrates. With these characteristics, it opens the way to integrate the electronic-feature printing into the same printing methodology that is used to put the graphics information onto the packaging applications.”
 
While screenprinting was the first manufacturing process tested, it is not the only production method of interest for this project.
 
“For the future there are still other activities planned to test feasibility of flexo printing (Segers & Balcaen) and inkjet printing (Agfa-Gevaert), develop copper-based conductive inks (AVL Metal Powders, University of Hasselt, University of Ghent, Flamac), and assure HSE issues (VITO),” Myny said.
 
In particular, Myny pointed to inkjet as potentially a good option for printing on flexible materials.
 
“The current tag is printed using large-area printing techniques on flexible substrates, which makes it accessible to the large market of IoT where flexibility and low cost are very important,” Myny said. “In the long run, printing could be done using digital inkjet printing that even opens the path to printing completely individual tags.”