Digital electronics are made possible by the transistor, the integrated circuit, and the printed circuit board. They have revolutionized our lives in ways that we cannot even recognize. But they have one characteristic that is a major obstacle as we advance to wearable devices for Health Tech and other applications; they are hard and inflexible. Some researchers have found ways to print semiconductor components using flexible inks and other materials, but it’s difficult to recreate some of the tiny sensors and power microchips that are build on “old fashioned” silicon wafers.
Engineers at Harvard University have decided that if you can’t beat them, join them. They have created a hybrid 3D printing system that can incorporate both flexible substrates and conductive inks, as well as precision-placed discrete semiconductor components. And they accomplish this using a single machine. They use polyurethane as the primary material, which can be used to print a flexible substrate layer. They add silver flakes to the plastic to create a conductive ink. This can be used to print connective circuits, and even create some sensors that take advantage of the ink’s changes in properties when bent or stretched. The system also uses the plastic as a pad to hold discrete semiconductor components, such as microchip controllers or LEDs. One clever wrinkle is that they use the same ink jet to pick and place these components. Instead of using pressure to eject ink, they use a slight vacuum to grab and hold the component to the ink jet, which can then carry and place it in a precise location. The system can then use conductive ink to connect the rigid components to the rest of the circuitry.
The team has created devices that can stretch up to 30% and still function properly without damage. They have printed a device that measures the amount of bend in a subject’s elbow, and another that provides data that maps the pressure on the bottom of a subject’s foot when standing. This new hybrid printing process could make a wide range of new devices feasible, taking advantage of the low-cost and tiny size of many rigid components while incorporating them in a rugged and flexible device.
