With companies like Nano Dimension, Voxel8, and BotFactory recently jolting the industry with their electronics 3D printers, the ability to manufacture functional electronic products right on the print bed seems imminent. In order to make wearable electronics and other circuit board-driven products, the process of placing conductive wiring in a complex 3D architecture does not come easily or cheap. But, that potential just became a bit more actualized thanks to a new unique 3D printing process developed by researchers from the prestigious Harvard University. The process, which is essentially a hybrid between inkjetting and laser-based 3D printing techniques, is capable of producing free-standing and highly conductive metallic wires.
The dual-step process begins as if it were a standard inkjet 3D printer, as silver nanoparticle inks are dispersed through a glass nozzle. Almost instantaneously, that ink is rapidly annealed by an infrared laser beam, which increase the density of the nanoparticles, and thus, transforms the material into a shiny silver wire. The Harvard researchers demonstrated a complex array of silver wires that approached insane resolutions, from sub-micron up to 20µm.
With this new hybrid technique, the researchers were able to produce conductive wires with curved features, which was accomplished with a rotary stage that allowed the wire to be patterned in a direction parallel to the laser-nozzle axis. The process was also able to print with sharp features too, which was done by positioning the annealing laser as close to the printing nozzle as possible without conducting to the silver ink that lines the nozzle. After figuring out how to mend these competing factors with computer simulations, the end result was 3D printed conductive wire with exceptional mechanical properties.
Even after the Harvard team proved the new technique a success, they continued to tool around with different parameters to optimize the annealing process. Using intensive computer simulations, the researchers found the the conductive silver wire’s resistance could be varied in three different magnitudes, which are wholly dependent on the conditions of the laser. This essentially allowed the Harvard researchers to create patterns of silver wiring with both low and high resistance.
They also proved able to print these conductive wires onto polymer substrates like PET (polyethylene terephthalate). To test this, the team 3D printed sub-micrometer silver wires on PET films, which proved to exhibit exceptional optical transparency. So, what exactly will this new 3D printing process technically be used for? What are the devices and products that will be enhanced by this hybrid technology?
Well, the research team also showcased the efficiency of their approach by 3D printing helical spring wires, which exhibited great elasticity when tested with stretching and compression. They also managed to print out spiral arrays that are similar to spiral antennas used in numerous electronic applications, such as wideband communications and frequency spectrum monitoring. Finally, they found some more playful uses for their new innovative approach, creating different wire butterfly shapes.
Their research, which is entitled “Laser-assisted direct ink writing of planar and 3D metal architectures”, was recently published in the Proceedings of the National Academy of Sciences journal. Ultimately, their findings showcased the potential of on-demand patterning of high-resolution and functional conductive metal wiring with complex structures. The approach could just be the next major breakthrough in customized electronics, aiming to enhance our ability to manufacture flexible wearables and other consumer electronics. In all likelihood, the technique will probably be licensed by the electronics 3D printing company Voxel8, seeing as their co-founder, Jennifer A. Lewis, was a co-author on the study (along with Mark Skylar-Scott and Suman Gunasekaran).
