Reliability study of flexible inkjet- and thermal-printed RFID antennas in high humidity conditions

The growth of the Internet of Things has created a need for cost-effective and light-weight electronics on flexible substrates. Great potential lies in versatile applications of passive UHF RFID components but their robustness toward various environmental stresses must be ensured. This paper presents a comparison of thermal- and inkjet-printed passive UHF RFID tag antennas on a novel polyester-based substrate (Flexcon THERMLfilm) in high humidity conditions. The tag ICs are coated with two different protective glue materials and the tag performance is evaluated through wireless measurements before and after high humidity testing. According to the results, the coating materials or moisture do not prevent the inkjet-printed tags from working in a tolerable way. The absorbed moisture temporarily shifts the peak read range of the thermal-printed tags to a much lower frequency but the most important reliability challenge is to find a coating material that is compatible with the thermal-printed antennas.