III. 3D PRINTED ELECTRONICS PROTOTYPING
Though typical methodologies like clay models, one-off samples handmade by skilled craftsmen, and more recently AM technologies have largely addressed the need for proto- types, these types of parts have been exclusively made to test appearance and fit of the completed part. When the device included sophisticated electronics, these methodologies could not address the need for prototyping a fully functional part. When required, the traditional procedure to prototype elec- tronics was to implement bread board prototypes and to accept the inherent delays that come with the normal process of electronics manufacturing, possibly weeks or even months. A newly developed 3D printing process of fabricating struc- tural electronics provides an appealing alternative. This novel manufacturing, a hybrid of AM complemented with compo- nent placement robotics and embedding of conductors – can create prototypes that can perform practically the same func- tion within the same form as the final product – although pos- sibly not fulfilling some of the other end-use characteristics such as reliability, surface finish, color, or texture. However, in products outside of the consumer markets, such as in the aerospace or biomedical industries, reliability may stand as the only significant barrier between the prototype becom- ing an end-use final product or not. Improvements in the area of reliability are inevitable with substantial research in materials and AM processing already in progress. Until these end-use requirements can be fulfilled, the proposed hybrid AM process can fabricate prototypes that will enable at least a comprehensive evaluation of the final design, not only for form and appearance, but also for electronics functionality - simultaneously.
A. 3D PRINTED ELECTRONICS CHALLENGES
Although this new manufacturing technology allows for more complete evaluations with high fidelity prototypes, substan- tial challenges remain. The area of electronics design (e.g. schematic capture, simulation, and physical implementation of printed circuit boards – PCBs) includes mature, com- mercially available software packages that allow for com- ponent placement and routing of wires to create electrical interconnects on a PCB. These programs however, operate under the assumption of the workspace being a predefined, two-dimensional surface for the circuit based on traditional PCB manufacturing. As a result, the component placementand routing for 3D printed designs has been done manually in 3D space using mechanical engineering CAD softwarelike SolidWorks without the inherent features for electronics functionality. This lack of software support has relegated
3D printing of electronic devices to relatively simple circuits as routing and placement has been done by hand; however, the circuit designs that have been completed have achieved greater utilization of the available volume given the fabrica- tion freedom offered by the manufacturing technology – with complex geometries easily fabricated in 3D. As an example, Fig. 1 shows a circuit design that utilizes all available surfaces of a pre-defined volume to accomplish layout of components. The routing has likewise utilized all available surfaces as well as the internal volume of the device. The original device was a signal conditioning circuit – the schematic of which was provided by engineers at NASA’s Johnson Space Center as a benchmark circuit in order to demonstrate the volumetric efficiencies of 3D printed electronics. The circuit volume was reduced to a volume of 0.5’’ by 0.5’’ by 0.125’’ as shown with a component and trace density of 27% significantly reduced from the original design.