Researchers at the Centre for Additive Manufacturing (CfAM), which is based at the University of Nottingham, have developed a new method to rapidly 3D print fully functional electronic circuits. The process can produce electrically-conductive metallic inks and insulating polymeric inks in a single inkjet printing process complete with LED UV curing.
As a result it can be used to produce fully functional components such as 3D antennae and fully printed sensors from multiple materials including metals and plastics. Other products could include, for example, a wristband which includes a pressure sensor and wireless communication circuitry could be 3D printed and customised for the wearer in a single process.
Professor Chris Tuck, Professor of Materials Engineering and lead investigator of the study, explained: “Being able to 3D print conductive and dielectric materials (electrical insulators) in a single structure with the high precision that inkjet printing offers, will enable the fabrication of fully customised electronic components. 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.”
The key to this approach is the UV curing. The team found that silver nanoparticles in conductive inks are capable of absorbing UV light efficiently. The absorbed UV energy is converted into heat, which evaporates the solvents of the conductive ink and fuses the silver nanoparticles. This process affects only the conductive ink and thus, does not damage any adjacent printed polymers.
The researchers used the same compact, low cost LED-based UV light to convert polymeric inks into solids in the same printing process to form multi-material 3D structures. A video showing how the concept works is available here
It’s worth pointing out that the Israeli company Nano Dimensions has also developed a 3D printer that can produce printed circuit boards. This too jets both a silver-based conductive ink and a dielectric. Nano Dimension has a number of prototypes in the field on beta test and an actual product, the DragonFly 2020 Pro.
The main difference between the two approaches is the curing method, with Nano Dimensions using infrared heaters to evaporate the ink solvents and sinter the nanoparticles after each pass of printing. This heat can damage the polymer material, particularly if used to cure a large number of layers of the conductive ink.
The Nottingham team have instead used UV curing, based on an LED light source. Dr Ehab Saleh, research fellow at the Centre for Additive Manufacturing, explains: “Our recent publication uses UV light to photo-thermally evaporate the solvent of the conductive ink and sinter the metal nanoparticles taking advantage of the fact that nanoparticles absorb such wavelength efficiently, and convert the UV energy into localised heat specific to the conductive ink. Hence in our approach we were able to stack multiple layers of conductive and polymeric inks and were able to build a true 3D structures that contain both materials.” Using LED UV curing essentially avoids heating the substrates, meaning that it is very flexible in the range of materials that the conductive inks can be used alongside of.
So far the project has led to several collaborations to develop medical devices, radio frequency shielding surfaces and novel structures for harvesting solar energy. But this does seem to be a significant breakthrough in additive manufacturing technology, one that will allow electronic elements to be printed directly alongside other materials to create more functional parts.
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