Hot-Wire Your 3D Printer

When most people think about a complex electronic circuit, their mind first turns to the traditional FR4-based printed circuit boards (PCBs) that they are usually laid out on. This sort of PCB is used in nearly all electronic products, after all. But while these boards have served us very well over the decades, they are not ideal for every situation. This is especially true when the circuit needs to be packed into a tight area. Standard PCBs lay out circuits in two-dimensional sheets, which prevents them from fully taking advantage of the available three-dimensional volume inside the case of an electronic device.

A team led by researchers at the National University of Singapore has just unveiled a new technology that could make it possible to manufacture complex electronic circuits of any shape in the future. Their innovation is called CHARM3D (conductive high-aspect-ratio metal 3D printing), and it allows for the fabrication of three-dimensional, self-healing circuits. This technique can produce free-standing conductive metallic structures via 3D printing, and it does not require any support structures or other fiddling to make it work.

Previously, these sorts of structures would have been printed using a method called direct ink writing, in which viscous conductive inks are used to slowly build up a conductive framework. However, these inks are limited in their conductivity, which makes them unsuitable for many applications. They are also slow to print and require support structures and other manual interventions to produce.

A key factor in overcoming these past issues was in the choice of material. The team used Field’s metal, which is a mixture of indium, bismuth and tin. This combination of metals causes the melting point of the composite material to be lowered to about 143 degrees Fahrenheit, making it far easier (and safer) to work with than other metals. Field’s metal also solidifies rapidly, which makes it possible to create complex free-standing designs without support structures. And unlike the inks used in direct ink writing, this metal is highly conductive.

The other key to the success of CHARM3D is the way that the printer exploits the tension between the molten metal still in the nozzle, and the recently printed portion of the structure. This makes it possible to print uniform microwires as small as the thickness of a human hair. These wires can be printed at a rate of up to 100 millimeters per second to create cubic frameworks, scalable helices, and other complex, free-standing structures.

Using the CHARM3D technique, the researchers demonstrated that they could print the circuit for a wearable, battery-free temperature sensor and an antenna for wireless vital sign monitoring. While they focused on healthcare-related applications, the team believes CHARM3D will be useful in many other scenarios, like in signal sensing and processing, in the future. At present, they are investigating other types of metals that might enhance the technology, and also additional applications areas that may benefit from it.