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

Abstract

The degree of cure of anisotropic conductive films (ACFs) was theoretically predicted and experimentally measured to investigate the effect of the degree of cure of ACFs on the electrical and mechanical stability of ACF joints and the reliability of chip-on-flex (COF) assemblies. The cure reaction of ACFs, observed by an isothermal differential scanning calorimetry (DSC) analysis, followed an autocatalytic cure mechanism, and the degree of cure of ACFs as a function of time and temperature was mathematically derived from an autocatalytic cure kinetics model. To simulate the ACF temperature field accurately during the COF bonding process, the thermal properties of the ACF such as the thermal diffusivity (alpha), specific heat capacity (C(p)), and thermal conductivity (lambda) were characterized experimentally. The degrees of cure of ACFs as functions of the bonding time during the COF bonding process were theoretically predicted by the incorporation of autocatalytic kinetics modeling and ACF temperature simulation. The predicted degrees of cure of ACFs were well matched with the experimental data measured by attenuated total reflectance/Fourier-transform infrared (ATR/FT-IR) analysis. The contact resistances of the ACF joints and the peel adhesion strengths of the COF assemblies were evaluated for electrical and mechanical interconnection stability. According to these results, the ACF contact resistances decreased and the ACF peel adhesion strengths increased as the degree of cure of ACFs increased. In addition, to investigate the effect of the degree of cure of ACFs on the reliability of COF assemblies, an 85 degrees C/85% relative humidity (85 degrees C/85% RH) test was performed. These results showed that the reliability of COF assemblies also strongly depends on the degree of cure of the ACFs.