Flow characterization and thermo-mechanical response for anisotropic conductive films

The paper reports investigations of the chip on glass (COG) bonding process using anisotropic conductive films (ACF). Experimental methods and theoretical analyses, by both analytical and numerical means, are applied. Assumptions with regard to the thermo-mechanical and rheological properties of the polymer materials involved in the bonding process are briefly characterized in terms of temperature dependence. The transient development of the temperature field during the bonding process is studied by finite element analysis for dependence on the upper and lower chuck temperatures. Analytical techniques from fluid mechanics are used to predict the flow of the conductive particles during bonding, which are treated as dimensionless points embedded in a viscous matrix. This analytical description allows estimation of the number of conducting particles on a chip bump after bonding. Furthermore, numerical calculations are applied to characterize the influence of viscosity gradients on the particle flow. Finally, nonlinear finite element simulations are used to investigate the stress development and stress relaxation process within the ACF joints