Failure Evaluation of Polyimide Films via Dielectric Behavior under Long-Term Thermal Cycling

Polyimide (PI) films are essential in spacecraft electronics due to their exceptional thermal stability, electrical insulation, and mechanical properties. However, their long-term reliability under extreme thermal cycling conditions remains poorly understood, posing potential risks to aerospace electronic systems. In this study, we investigate the dielectric behavior of PI films subjected to 1000 thermal cycles between −60 and 100 °C, revealing significant dielectric instability despite preserved mechanical properties, highlighting their heightened sensitivity to alternating temperatures. Through dielectric spectroscopy, thermally stimulated depolarization current (TSDC) analysis, and theoretical modeling, we identify a multiscale failure mechanism encompassing space charge accumulation, free volume variations, molecular polarity shifts, and structural evolution. These trends were consistent across different PI architectures, confirming the broader applicability of our findings. Meanwhile, we established a correlation between the dielectric behavior of the PI films and the number of thermal cycles, providing a valuable reference for evaluating electrical failure mechanisms and predicting service life in aerospace applications. These findings offer critical insights into PI durability under extreme conditions and contribute to the development of high-reliability materials for future space exploration.