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Reliability Analysis of RFID Tags in Changing Humid Environment

Radio frequency identification (RFID) tags with anisotropic conductive adhesive (ACA) joints are used in various applications where the environmental conditions may impair their reliability. Therefore, it is essential to investigate the effects of different environmental stresses on reliability and to analyze failure mechanisms. The purpose of this paper was to study the effects of changing humidity conditions on the performance of a passive ultrahigh frequency RFID tag with ACA joints. The tags were tested in a humidity cycling test where the humidity varied from 85%RH to 10%RH and temperature from 85 °C to 25 °C. Tags with four different sets of bonding parameters were tested. Significant differences in reliability between tags with different bonding parameters were observed. Different failure times, failure modes, and failure mechanisms were observed. Full-wave electromagnetic antenna simulations were used to support the analysis on the failure mechanisms manifesting themselves through changes in the common tag performance parameters. Changes in impedance matching between the chip and the antenna were found to be the most likely failure mechanism. The impedance matching may have changed due to cracks formed in the antenna during testing or due to chemical and mechanical changes in the ACA joints. It was observed that several failure factors might act simultaneously.