Design and Development of Biometric Sensor Wearable Band Using Flexible Electronics

Flexible electronics have a myriad of potential applications in fields such as healthcare, soldier situational awareness, soldier rehabilitation, sports performance, and textile manufacturing among other areas. The primary benefits that flexible electronics provide to both the producers and consumers are their light weight, low power consumption, efficiency, low cost of production, flexibility, and scalability. In comparison to rigid electronics, these systems would be subjected to a greater amount of mechanical and thermal stress in real-time due to their ability to be flexed, rolled, folded, and stretched. Environmental conditions such as bending, mechanical shock, water immersion, sweat, UV radiation, and temperature exposure could degrade the performance of these embedded electronic systems. At this time, there is a lack of suitable test standards and reliability data about flexible electronics manufacturing, assembly, and real-time use. In this paper, a fully flexible medical electronics system was built in full dimension to study the assembly and operation-related failure mechanisms of flexible and wearable electronics. The fabricated flexible electronics system measures pulse and muscle activity, and then transmits this data to a paired mobile device. The pulse rate was measured using an LED and a photo diode, while an electromyography (EMG) sensor was used to measure muscle activity. After collecting the data, the microcontroller sends it to a Bluetooth module, which can in turn transmit this information to a paired mobile device. Through experimentation with the fabricated flexible electronics device, unexpected degradation and quality issues were observed. In flexible PCBs, the space between the IC lead could not be isolated by the solder mask because of its large feature size and as a result, increases the risk of shortage between IC leads when subjected to mechanical stress. In addition, during the assembly process, high reflow temperature was found to subject a huge thermal stress on the connections between the solder pad and copper trace. Proper support of the solder pad should be designed to compensate the thermal stress during the reflow process, and prevent the copper joint on top of the board from being damaged. A set of guidelines for flexible medical electronics and an implementable reliability test standard can, therefore, be established for medical device manufacturers based on these reliability assessments.