Theoretical prediction and experimental measurement of the degree-of-cure of anisotropic conductive film (ACF) for chip-on-flex (COF) applications

The degree-of-cure of an anisotropic conductive film (ACF) was theoretically predicted and experimentally measured to investigate the effect of the degree-of-cure of the ACF on the electrical and mechanical stability of ACF joints and the reliability of COF assemblies. The cure reaction of the ACF observed by isothermal DSC analysis followed an autocatalytic cure mechanism, and the degree-of-cure of the ACF as functions of time and temperature was mathematically derived from an autocatalytic cure kinetics model. To accurately simulate the ACF temperature field during COF bonding process, the thermal properties of the ACF such as thermal diffusivity (alpha), specific heat capacity (C_p), and thermal conductivity (lambda) were experimentally characterized. The degree-of-cures of the ACF as a function of bonding times during COF bonding process were theoretically predicted by the incorporation of the autocatalytic kinetics modeling and the ACF temperature simulation. The predicted degree-of-cures of the ACF were well matched with the experimental data measured by an ATR/FT-IR analysis. The contact resistances of ACF joints and the peel adhesion strengths of COF assemblies were measured to evaluate the electrical and mechanical interconnection stability. According to the results, the contact resistances decreased and the peel adhesion strength increased as the degree-of-cure increased. In addition, to investigate the effect of the degree-of-cure of the ACF on the reliability of COF assemblies, the 85degC and 85% relative humidity (85degC/85% RH) test was performed. The results showed that the reliability of COF assemblies also strongly depends on the degree-of-cure of the ACF.