Reliability of UHF RFID tags in humid environments

Radio frequency identification (RFID) is an emerging technology in the field of identification and security. With RFID tags it is possible to identify objects individually and reliably using radio waves. However, due to numerous applications, RFID tags are exposed to various environmental conditions which may impair their reliability. Long-term reliability is generally studied using accelerated environmental tests. In earlier studies a combination of high humidity and high temperature has been found to be very harmful to RFID tags. Consequently, in this study failure times and mechanisms between three accelerated humidity tests were compared to find a test which is most suitable for RFID tags. A passive ultra high frequency (UHF) RFID tag with a polyethylene terephthalate (PET) substrate was tested using two constant humidity tests and a humidity cycling test. According to this study, the selection of test conditions for reliability studies in humid environments should be carefully considered. PET substrate is susceptible to hydrolysis when a combination of high humidity and high temperature is present. Consequently, a standard 85°C/85% test is very harsh for RFID tags with PET substrate. On the other hand if a cycling test is used instead of a constant test to acclerate the test, the failure mechanism may alter. Therefore it is important to investigate the effects of changing humidity, but a constant humidity test cannot be directly replaced by the faster humidity cycling test due to the different stresses caused by the tests.