Materials screening and characterization for functional printed automotive interiors parts

Flexible printed electronics (PE) has attracted strong interest during the last two decades and is one of the successful trends in material science, representing the future of PEs. This research work evaluates the use of screen-printing technology and materials for producing functional circuits for automotive interior parts, which can be subsequently processed through in-mold electronics (IME). Since the selection of the materials to build the printed system is of utmost importance, this study evaluates combinations of commercial polycarbonate substrates (LEXAN 8A13E, DE 1-4 060007 and LM 905 2-4 160009) and silver-based inks (ME603, ME604 and CP 6680), all suitable for IME. Different electrically conductive tracks varying in width and spacing (0.5, 0.3 and 0.2 mm) and two capacitive sensors were printed. Tensile tests and surface energy characterizations of the different polycarbonate substrates were carried out, then morphological, electrical, and thermoforming studies were performed on the printed substrates. Morphological characterization showed successful printing for wider lines (0.5 and 0.3 mm), but problems with screen clogging occurred for smaller line widths (0.2 mm). The electrical conductivity of printed tracks was in accordance to the printed layer thickness and ink solids percentage. The proof-of-concept of the electrical functionality was successful, when integrating the sensors into the PCB with SMD LEDs. Thermoforming showed limited functionality, with the best overall performance observed for specific combinations of substrate and ink. In essence, the results indicate that although all the selected substrates and silver-based inks have great compatibility among themselves and can be considered as materials for the production of functional automotive interior parts, there is no ideal pairing of inks and substrates. Therefore, this study emphasizes the importance of defining product specifications for a more suitable material selection.