Wire harnesses account for a significant weight of the vehicle. The integration of advanced driver assistance systems into automotive platforms has seen the emergence of a number of safety features, including lane departure warning, driver alertness monitoring, cross-traffic alert, guidance, navigation, and control. Touch surfaces in the automotive platform are presently used for little more than aesthetic appeal. However, the integration of human-machine interfaces on the touch surfaces requires additively printed in-mold electronics. The processes for the printing of sensors, in addition to the integration of surface mount electronics for signal processing, are not yet known for additively printed conformal electronics.
The proliferation of advanced driver assistance systems (ADAS) has contributed to the rise in cabling on the automotive platform to connect numerous sensors and surfaces to control units [Trommneau19, Reiff11]. Modern cars have thousands of wires that can total several kilometers in length [Ernst14], and the wire harnesses in some models can weigh as much as 36 kg [A2Maci18]. This increase in weight has become problematic for automakers, particularly given stricter CO2 emission standards [Yamano11]. There is now a strong interest in developing lighter and cheaper wire harnesses to reduce the carbon footprint of cars [Ruis17]. However, conventional wire harnesses possess design limitations that necessitate the use of connectors and receptacles to integrate them into the automobile's body and link them to the control units. 3D printed in-mold electronics (IME) is a cutting-edge technology that is gaining traction in the electronics industry owing to its ability to minimize wire harnesses and carbon footprint.
In this paper, a number of additive print processes have been studied for their process-performance interactions in thermos-formed in-mold electronics. Specifically, printed circuits with surface mounted components have been explored with direct write printing and gravure offset printing. There are several substrates which are compatible with the thermoforming process required for the creation of in-mold-electronics such as polyethylene terephthalate glycol (PETG), polycarbonate (PC), high impact polystyrene (HIPS). Applications examined include signal processing and electrodermal sensors for the measurement of the galvanic skin response. Electrodermal sensors measure the surface conductance of the skin to determine the state of the autonomous nervous system. These wearables could acquire biosignals with high accuracy, which makes them beneficial in scenarios like assessing a driver's emotional and medical condition during various driving scenarios. Components have been attached using electrically conductive adhesives, low temperature solders and ultra-low temperature solders. Signal process performance has been demonstrated through the fabrication and characterization of AC-DC converters. Performance parity has been assessed through comparison of the thermoformed circuits with conventional rigid circuits with identical design. Impact of variables including print speed, print pressure, nozzle temperatures, platen temperatures, sintering temperature, sintering time, reflow profile or curing profile on the realized circuit performance has been assessed. For the electrodermal sensors, the in-mold sensor response has been compared with that of the medical grade sensor to demonstrate the sensor accuracy, repeatability, sensitivity, and long-term stability.
