Performance Stability and Reliability of Gravure Offset Printed Thermoformed IME Circuits Subjected to Sustained High Temperature Storage

In-mold electronics (IME) poses an opportunity for the incorporation of electronic circuits into automotive interior structural plastic. Utilizing IMEs has a number of advantages, including minimizing weight and bulk while upholding ergonomic design. There are several substrates that 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). Polycarbonate can sustain relatively higher temperatures owing to its higher heat deflection temperature and Vicat softening temperature, making it a good candidate for automotive applications requiring a high operating temperature capability of 125°C. However, ensuring the long-term performance stability and reliability of polycarbonate-based additive in-mold-electronics circuits under the high operating temperature conditions experienced in automotive environments remains a critical challenge, and its investigation is the objective of the current study. In this study, additively printed traces with specifically thermoformable silver conductible ink have been printed using the gravure offset printing technique on a PC substrate and then have been subjected to vacuum thermoforming wherein the substrates are heated above their Vicat softening temperatures and vacuum formed on an aluminum mold. The printed traces have then been subjected to exposure to the higher operating temperature of 85°C for extended time periods of up to 1000 hours. The resistance evolution of the printed traces has been monitored after every 50 hours of high-temperature testing. Furthermore, printed circuits with RLC components attached have also been subjected to the same kind of testing, and the frequency response characterization of the non-resistive components has also been conducted.