Fabrication of smart card using UV curable anisotropic conductive adhesive (ACA.) part I: optimization of the curing conditions

Abstract

High demand for green electronics products has driven the use of conductive adhesive as a substitute for using conventional solders. Recently developed UV curable anisotropic conductive adhesive (ACA) is suggested for use in temperature sensitive electronic packages. The aim of this study is to optimize the bonding conditions for fabrication of smart cards using UV curable ACA. A simple designed copper coil plated on a PET was used as the micro strip antenna of the smart card. The entire fabrication process is divided into three parts, high power UV curing, chip-on-flex (COF) bonding and post curing. By varying the UV curing and post-curing parameters, a number of contactless smart cards were made. Chemical analysis using FTIR (Fourier transform infrared spectroscopy) was carried out to determine the curing degree of the UV curable ACA under different curing conditions. In order to quantify the performance of the smart card, the read range between the card reader and the sample was measured. In addition, a shear test was performed; the shear force that is required to break the ACA joint and its failure mode was recorded and discussed. ACA joints of smart cards under different curing conditions were also cross-sectioned and examined using SEM (scanning electron microscope). By comparing the results in curing degree, shear strength of the ACA joint and the reading distance of the smart card samples, a set of parameters which gave better performance of the COF bonding were determined.