A study of degradation of ACF joints in chip-on-glass assenblies

The epoxy-based anisotropic conductive adhesive films (ACF) joints have been widely used in a number of interconnect applications, including direct chip attachment, i.e. chip on glass, chip on ceramics, etc. However, the ACF joints have the potential of being exposed to relative high humidity environment and susceptible to moisture sorption, especially in the elevated temperature. In this study, the hygrothermal environment (85C/85%RH) test was used as an accelerator for the degradation of ACF joints in chip-on-glass (COG) assemblies, which were designed in the form of the single-lap joints. The effects of aging on the adhesion strengths were measured by shear mode tests at the accelerated aging time of 125, 250, 375 and 550 hours, respectively. In order to further interpret the hygrothermal-induced damage from the view of mechanics, the analytical model is established through introducing one factor of the interfacial fracture energy damage. It can be concluded that the long-term hygrothermal aging can irrevocably damage the epoxy system, physically (plasticization, as well as the formation of cracks and crazes) and/or chemically (hydrolysis). Furthermore, the absorbed moisture can attack the adhesive/inorganic substrates interfaces and the hydrolysis occurs in the interfacial region