FIGURE 1. 3D printed signal conditioning circuit.
The use of existing electronics CAD design software for layout and routing of 3D printed electronic devices is possible when the 3D shape can be represented initially as a flat
2D surface and then ‘‘deformed’’ to a final intended 3D shape;
such cases include a volume that can be represented as an
‘‘unfolded’’ outer surface (e.g. six sides of a cube) or a curved surface that has been ‘‘wrapped’’ about an axis of revolution (curved side of a cylinder). Mechanical CAD software can later ‘‘deform’’ 2D circuits generated from electrical CAD software with curved and folded edges. However, limiting routing to 2D planes foregoes the capability of realizing inter- connects between layers - relegating the circuits to simple networks without the use of cross-over points. Utilizing more than one surface as well as connections between multiple surfaces (similar to vias in PCBs) are necessary to pro-vide complex circuit networks regardless of the underlying deformation geometry. Fig. 2(a) shows the application of the above-described methodology for a battery charge protection circuit that can be implemented on a 2D surface without cross-over points and thus only required a single surface of interconnect. The circuit was first placed and routed in electrical CAD software and subsequently imported into mechanical CAD software to be ‘‘deformed’’ around a cylinder, which in this example contains a lithium polymer battery. Fig. 2(b) illustrates the final representation from both sides. Cavities are formed to place components and UV curable material is used as adhesive to hold the devices in place. Each interconnect trace was designed into the surface with a trench to allow for depositing ink without the concern of the conductive inks spreading and resulting in electrical shorts prior to thermal curing. With the trenches, the SL process dictates the routing density based on the laser resolution rather than the resolution of the micro-dispensing system or the viscosity of the inks. In this example, line pitches (e.g. center to center minimum distances) were 560 microns.FIGURE 2. A) Battery charging circuit to be deformed and B) both sides of the final mechanical representation.
Fig. 3 illustrates a more complex design with a microcon- troller and accelerometer in surface mount packaging technol-