Researchers from the University of Barcelona have developed a bonding technique to build intelligent flexible hybrid circuits using an inkjet printer with silver nanoparticles ink.
The need for a fast yet reliable and cheap process for developing circuits that also helps to reduce the environmental impact of standard fabrication processes was the basis for the development of the bonding technique. Researchers chose nanoparticles of silver for the ink because it is widely available and easy to reproduce into stable ink. While silver itself is not cheap, the amount used in the process was low enough to keep costs of the technique down, researchers say.
The goal of the project was to use the same equipment while improving the performance of standard silicon-based manufacturing by using inkjet printing for the circuitry and bonding of the chips. "We developed several electronics circuits with inkjet printing, and many times we had to insert a surface mounted device (SMD) chip to reach the objectives,” says Javier Arres, a member of the research team at the University of Barcelona. “Our approach was to use the same machine for bonding that was used for the printed circuit.”
How They Did It
In the bonding technique, silver ink droplets were deposited close to the overlapping area between the SMD device pads and the printed bottom conductive paths. The ink then flowed through the interface by capillarity. This worked like a sponge as the small voids absorbed the liquid allowing the fluid to be drawn up from a surface.
Silver nanoparticle (AgNP) ink has a high electrical conductivity after the thermal process at very low temperatures, and researchers were able to form a high electrical conductive interconnection during the process. Researchers were able to create an intelligent flexible hybrid circuit on paper where different SMDs where assembled by AgNP ink.
The development could have implications for future applications. “We believe that our work will improve the existing RF [radio frequency] tags, boost and promote smart packaging, enhance wearable electronics, flexible electronics, paper electronics...our results make us believe that everything is possible,” Arrese says.