Flexible Hybrid Electronics Based Condition Monitoring System for Sealed Containers

An advanced flexible hybrid electronics (FHE) based system has been designed to track the internal temperature and humidity levels of storage containers used for several applications in various industries including food, pharmaceuticals, agriculture, automotive, and defense. The printed circuit board (PCB) of copper-flexible system (CFS) prototype was created by depositing 35
$\mu\mathrm{m}$
thick copper traces on a flexible polyimide substrate with a thickness of 88.9
$\mu\mathrm{m}$
. The substrate was then coated with a 12.5
$\mu\mathrm{m}$
polyimide yellow coverlay solder mask. The overall thickness of the CFS was measured to be 1.95 mm at the microSD card port. To assess the system's flexibility, durability, and ability to withstand environmental factors, a series of environmental and mechanical tests were conducted based on ASTM and IPC-TM650 standards, which included corrosion test and terminal bond strength test, respectively. After being 72 hours under corrosion test, both coated and uncoated meander line test coupons showed negligible average weight and resistance changes, with measured values of approximately 0.35% and 0%, respectively. The weight change for the comb pattern test coupons after 144 hours was almost 0.25% for the coated samples and 0.33 % for the uncoated samples. During the terminal bond strength test, the soldered wire became detached from the terminal pad at an average force of 43 N. Furthermore, calibration graphs and corresponding equations were incorporated into the programming code of a microcontroller unit (MCU) to enhance the accuracy of the CFS temperature sensor's readings for various humidity ranges.