Screen Printing - August/September 2016 - 36

The ability to pause printing to insert traditional electronic components and then print additional layers of metal and plastic over them opens up further potential applications of 3D printing. Creating More Versatile Test Fixtures FIGURE 2. As electronic components shrink, designs with smaller antennas can suffer from performance problems including reduced bandwidth and frequency. Moving from traditional planar antennas to hemispherical constructions that could only be done with 3D printers could be one solution to the problem. Image courtesy of Voxel8 ideally at room temperature, because they are usually being co-printed with plastic materials that cannot withstand the elevated temperatures typical of standard electronics processing. Silver-based inks are preferred for their high conductivity and ease of dispensing. In the high-value, lowvolume applications associated with 3D printing, cost of materials is not a critical factor. In the long term, if 3D printing extends to higher volume, costsensitive applications, it may be desirable to switch to more economical copper inks. But, at present, the challenges associated with oxidation of copper make it not worth considering. 3D-printed electronics can use standard plastic materials, but other choices may be preferable for optimum performance. Voxel8, a spin-out company from Professor Jennifer Lewis' research group at Harvard, is developing a process to use epoxy because its thermal and mechanical properties are closer to materials that are used in printed circuit boards (PCBs). "We are actively working on new materials all the time," says Karl Willis, VP of product development. "The 3D-printing industry has found a home with high-value applications," which often demand customized materials. 36 screenprinting Real-World Applications of 3D-Printed Electronics Several companies are making commercial products that either combine 3D plastic parts with conductive printed traces or merely print conductive lines onto curved surfaces. The first approach, which is the most exciting and the most likely to change the way electronics are manufactured, merges the capabilities of FDM or SLA with inkjet printers. These 3D printers can co-print filament-based plastics and conductive silver inks to create a single, fully 3D part with either exposed or embedded conductive traces. Voxel8 is rapidly developing this technology. It began shipping its 3D printer in May as a developer's kit consisting of the printer, required software, and printing materials. The plastic filament is PLA, a thermoplastic resin chosen because it's a familiar material that is easy to use. The silver ink is a proprietary formulation that is highly conductive and dries quickly at room temperature. Voxel8 showcased sample products at the Consumer Electronics Show in January, including a printed watch with embedded microcontroller and LEDs and a small quadcopter drone with an embedded PCB. Companies that design hardware need to build custom test fixtures to determine whether it is working as designed. Since test fixtures are a highly customized, low-volume product, they are a perfect application for 3D printers. For example, RightHand Robotics makes robotic arms with fingers that can grasp objects. The tactile sensors on the fingers need to be tested, and Voxel8 designed and built a fixture with an embedded microcontroller and an LED that lights up when the sensors are functioning properly. (See Figure 1.) Similar fixtures could be designed to test a wide variety of electromechanical parts. Printed Antennas Printing antennas is nothing new, but as electronics shrink, shrinking antennas along with the rest of the components causes problems with performance, such as reduced bandwidth and efficiency, and consequently reduced frequency range. One possible way around this problem is to deviate from the traditional planar antenna with a design consisting of lines that meander to fill a hemispherical shape. (See Figure 2.) 3D printers enable printing such an antenna configuration directly. In contrast, traditional methods would involve printing the patterns onto a Kapton sheet, which would then be glued to the structure, resulting in a much weaker construction. Voxel8 has partnered with The MITRE Corporation to produce small, high-performance conformal antennas for a US government project. These antennas would be extremely difficult, if not impossible, to fabricate using conventional methods. As of press time, the companies were preparing to release a prototype.

Table of Contents for the Digital Edition of Screen Printing - August/September 2016