A Soft Spot for Vias - Hackster.io

Soft and flexible electronics technologies present us with innumerable opportunities for innovation. They, for example, enable the development of wearable devices that can be integrated into clothing, accessories, or even functional skin patches. Soft electronics can also be used to create implantable medical devices, such as pacemakers, cardioverter-defibrillators, and neural implants. And the list of possibilities goes on and on, from flexible displays to soft robots and prosthetic limbs.

Great strides have been made in this area in recent years, with new methods of producing flexible printed circuit boards (PCBs) and novel conductive inks having been introduced. But when reading up on these advances as more of an interested observer than someone actually working in the field, it can be easy to forget that every component needs to be soft to create a truly soft and flexible device.

The problem is that many components, like integrated circuits, are still rigid and there seems to be no practical soft replacement on the horizon. At Virginia Tech, a small team of engineers decided to tackle one particular element of a modern circuit design that is incompatible with flexibility — the via. Vias may not be the most exciting part of a PCB, but we could not build complex circuits without them. They handle the important job of routing signals from traces on one layer of the board to another layer.

But today’s vias are rigid. And not only that, but a hole must be drilled into a PCB to install it. That is fine for a rigid PCB, but it may compromise the integrity of a flexible PCB — not to mention any issues that may crop up with maintaining a good electrical connection as the board flexes.

Instead of using traditional rigid materials, the team’s new vias rely on liquid metal microdroplets that self-assemble into a stair-like structure within a soft material, allowing current to pass between circuit layers. The fabrication process involves using the natural imperfections that occur during ultraviolet light exposure — typically a manufacturing obstacle — to guide the droplets into a specified, three-dimensional conductive path. When the liquid metal droplets settle in this controlled pattern, they form connections across multiple layers in the soft circuit, which is then solidified to maintain stability.

This innovative approach not only simplifies the creation of soft, multilayered electronics but also maintains the flexibility, durability, and stretchability needed for next-generation applications, such as wearable devices and soft robotics. By eliminating the need for drilled holes and relying on parallel stratification of liquid metal droplets, these soft vias allow for fast, repeatable, and scalable manufacturing of flexible electronics that can perform similarly to rigid systems.