Enhancement of electrical stability of anisotropic conductive film (ACF) interconnections with viscosity-controlled and high Tg ACFs in fine-pitch chip-on-glass applications

This paper describes how anisotropic conductive film (ACF) properties including viscosity affect the electrical stability of ACF interconnections for fine pitch chip-on-glass (COG) applications. In this study, new ACFs for COG applications were designed by combining a high viscosity ACF layer and a low viscosity NCF layer to prevent the electrical shortage between bumps. As expected, the viscosity-controlled ACF showed better electrical insulation stability than a conventional ACF in fine pitch COG assemblies. According to the results of thermo-mechanical analysis (TMA) and dynamic-mechanical analysis (DMA), the viscosity-controlled ACF showed the improved thermo-mechanical properties such as lower coefficient of thermal expansion (CTE), higher storage modulus (E′) at higher temperature region, and higher glass transition temperature (Tg) than the conventional ACF. Furthermore, hot air reliability test and pressure cooker test (PCT) results showed that the viscosity-controlled ACF with higher Tg had better hot air test and PCT reliabilities than the conventional ACF.