Study of Voids in the Flexible RFID Tag Inlays Packaged by Anisotropic Conductive Adhesive

RFID is recognized one of the most potential information technologies. The RFID tag is a small tag containing an integrated circuit chip and an antenna. Voids can very often be detected in the non-metalized area of the RFID tags, they generated with unpredictable size and located randomly in the tag. The formation of the voids is the combined action of material properties and bonding parameters. In this work, the formation of the material related voids in the tags was investigated by thermogravimetric analysis. All specimens showed continuous loss of mass to varying degrees during the heating process. The air and moisture entrapped in the polymer matrix in the fabrication process and the process of use are the mainly reason. The loss mass of the etched antenna substrate primarily came from the lamination adhesive has not cured completely. With the simultaneous reaction of thermal stresses and internal vapor/volatile gas pressure drives both pre-existing and newly nucleated voids to grow. In addition, the voids growth under the high temperature (85°C) and high humidity (85%RH) conditions was investigated. The characteristic size of voids increases gradually with the increasing aging time because of the combined effects of the residual stress and the different coefficients of thermal expansion and moisture expansion.