Reliability Analysis of UHF RFID Tags Under a Combination of Environmental Stresses

Accelerated environmental tests can be used to study the effects of environmental stresses on reliability. The environmental tests are commonly run in parallel. One test is performed for one set of test samples, and new sets of test samples are used for other possible tests. However, the subsequent use of different tests for the same set of test samples may describe the operational environment of the samples more accurately and give more reliable results in a short testing time. In addition, the different stresses may accelerate the effects of other stresses, and such behavior can only be perceived if combinations of environmental tests are used. Passive ultrahigh-frequency radio-frequency identification (RFID) tags were tested with different combinations of environmental tests. Some of the tags were subjected first to a bending test, to a constant humidity test, or to a temperature cycling test and then subjected to a humidity cycling test. As a reference, some of the tags were tested only in the humidity cycling test. Changes in the performance parameters of the RFID tags were examined during testing. Clear changes in the reliability of RFID tags with different test combinations were observed. The exposure to constant humidity test before the humidity cycling test significantly impaired the reliability of tags in the humidity cycling test. On the other hand, bending testing before the humidity cycling test had no noticeable effect. The temperature cycling test only slightly impaired the reliability of the tags in the humidity cycling test. In the failure analysis, no clear failure mechanisms were found. It is possible that several failure mechanisms affected the tags simultaneously during the humidity testing. This study demonstrated the importance of studying combinations of different environmental tests one after another on the same test samples. Although exposure to certain environmental stresses may not immediately cause a device to fail, it may impair the re- iability when the device is later exposed to another environmental stress. Combinatory stress may be critical for the actual product, and therefore, their discovery during environmental testing is crucial.