Multifunctional circuits printed in a single process

Printing electronic components allows for the rapid manufacture of flexible, low-cost devices. These printed devices typically use just one material, meaning that the printed components can only perform limited functions.

Multifunctional additive manufacturing, however, involves printing multiple materials from a single 3D printer to create more complex components with a range of functions. Printing electronic devices containing different materials (metallic inks to form conductors and polymeric inks to form insulators) requires a range of heat sources such as ovens or hot plates to solidify each material. This renders the process highly inefficient, particularly when hundreds of layers are required to form a component.

“The main limitation of current methods is the way that the conductive ink is converted from liquid to a solid counterpart,” Dr Ehab Saleh, of the Centre for Additive Manufacturing, told E&T.

“Usually this is achieved by heat using conventional heat sources at temperatures around or above 150°C […] such temperatures are usually destructive to polymers, hence it limits the number of layers that can be printed containing both [conductors and insulators] to form only 2D or 2.5D structures.”

Dr Saleh and his colleagues at the centre have developed a new approach to printing multifunctional circuits, which combines standard 2D printed electronics with 3D printing and allows multifunctional circuits to be printed more efficiently.

The researchers found that silver nanoparticles in conductive inks are capable of efficiently absorbing UV light. When this light is absorbed, it heats the ink, causing the solvents in the ink to evaporate, and the nanoparticles to fuse. Due to the heat being localised, this method does not damage printed polymers nearby, but the same light source can be used to photo-cure polymeric ink.

“Hence a single apparatus – an LED-based UV light – was used to solidify conductive and insulator inks in one structure with minimal effect of one material over the other,” said Dr Saleh.

Through this approach the researchers demonstrated that it is possible to print the conductive and insulating components in a single, streamlined process, with each layer setting in less than 60 seconds.

This could allow for the manufacture of fully functional electronic components, such as 3D antennas and sensors. In a single process, the researchers say, it would be possible to print a wristband with pressure sensors and wireless communication circuitry. Already, the project has led to collaborations to develop medical equipment, structures for harvesting solar energy and other devices.

“Being able to 3D-print conductive and dielectric materials [insulators] in a single structure with the high precision that inkjet printing offers will enable the fabrication of fully customised electronic components,” said Professor Chris Tuck, professor of materials engineering at the University of Nottingham.

“You don’t have to select standard values for capacitors when you design a circuit, you just set the value and the printer will produce the component for you.”