Condition Monitoring System: A Flexible Hybrid Electronics Approach for Sealed Container Applications

Abstract

A comparative study is presented between two advanced flexible hybrid electronics (FHE) systems designed for monitoring temperature within storage containers across various industries, including food, pharmaceuticals, agriculture, automotive, and defense. The first system, a copper-flex system (CFS), employs an 88.9 µm polyimide substrate with 35 µm thick copper traces, coated with a 12.5 µm polyimide solder mask. The second system, a printed-flex system (PFS), utilizes a 127 µm polyimide substrate with high-temperature resistance and tensile strength. Conductive silver ink was screen-printed on the PFS substrate, and electronic components including a temperature sensor were attached. Functional and reliability tests were performed to check the accuracy and durability of the temperature sensor. Further, environmental and mechanical characterizations including moisture and insulation resistance, corrosion, elongation, bending, and terminal bond strength tests were performed based on ASTM and IPC-TM650 standards. Moisture and insulation resistance test on the PFS test coupons without a coating layer indicated stable resistance of approximately 18 MΩ, while permanent color change indicated oxidation of copper on uncoated CFS test coupons. After 72 hours of corrosion test, both the CFS and PFS “meander line” test coupons covered with polyimide showed negligible change in weight and resistance, approximately 0.35%. A Young’s modulus of 7.17 GPa and 2.6 GPa was calculated from the elongation test for the CFS and PFS, respectively. Bending tests on PFS revealed negligible average resistance change (0.1%) during 180° bending cycles, while no impact was recorded on the CFS. During the terminal bond strength test, soldered wires detached from the CFS test coupons at an average force of 43 N, while it was 3.8 N on the PFS test coupons. Both systems with polyimide coating layer demonstrate robustness and reliability for diverse applications in various industries.