Optimization and reliability evaluation of COG bonding process

In order to assemble a driver IC onto a LCD glass panel, Chip on glass (COG) bonding technology using Anisotropic conductive film (ACF) has been widely implemented. The key process parameters in the technology are the temperature, pressure and time during the thermo-compression bonding. These factors mainly affect the quality of the assembled ACF joint being represented by the contact resistance and adhesion strength. This study purposes to obtain the optimal process conditions for high reliability of the ACF joint. In order to determine the optimal condition, the experiments based on the response surface methodology were designed. Based on the experiments and statistical analysis, the empirical model of second-order polynomials approximating the relationships between the process conditions and the response variables of contact resistance and adhesion strength were obtained. The optimal process condition to lead lower contact resistance and higher adhesion strength of the ACF joint was also calculated from the relationships. The optimization was verified through the bonding experiments conducted under the derived optimal process condition. In addition, the reliability of the ACF joints according to the variation of the process conditions was evaluated in high temperature and humidity environment (85°C/85%RH). Consequently, it was shown that the reliability of ACF joints assembled under the optimal process conditions was superior to others after the 85°C/85%RH tests.