Reliability of RFID tag inlay assembled by anisotropic conductive adhesive

ACA bonding is one of the main stream in a mass production for the fast and low cost RFID tag inlay assembly, however, its reliable issue is facing the increasing challenge due to the trend of using low cost materials and fast process. In this work, ACA was prepared by mixing Ag particles into thermoset epoxy resin. The inlays were manufactured by assembling the RFICs in a flip chip mode with this kind of ACA on the aluminum/PET antenna under 180degC, 12 sec. To investigate the variation of the contact resistance and the flex behavior, some RFICs were sputtered with a gold film on their bump face and became a conductor on the aluminum antenna terminals. The ACA assembled inlays were submitted to various electric and mechanical reliability tests. It was found that the resistance of the inlay with dummy die exhibited a periodic variation but totally an ascending trend in a wind test, indicating that the flex or bend action had a large influence on the conductivity of the adhesive joint. Further, pure bend test with die facing down exhibited a less damage on the resistance than that with die facing up, because the former exerts a press while the latter was tearing. Although the resistance shift of the adhesive joint may occur, the high frequency regular inlays of 13.56 MHz remained 10 cm response distance upon hot humidity test and the 50 periods wind test. The results suggested that an improvement is necessary on the aluminum-antenna inlay packaged by ACA.