Characterization of Fast Cure Anisotropic Conductive and Non-Conductive Adhesives

Abstract

Anisotropic conductive adhesives (ACA) and non-conductive adhesives (NCA) are used in adhesive flip chip technology. An optimized cure process for these ACA and NCA materials is critical to develop the ultimate mechanical and electrical properties of the adhesive flip chip joints. Typically, these adhesives are formulated to achieve complete cure in less than 60 seconds at a cure temperature between 180degC and 250degC. This fast cure characteristic poses great difficulties for conventional cure characterization techniques. In this study, advanced cure monitoring techniques including modulated differential scanning calorimetry (MDSC), dielectric analysis (DEA) and fibre Bragg grating (FBG) were explored. Cure shrinkage was also measured using both FBG and thermomechanical analysis (TMA). Findings showed that MDSC is an improved method for analysis of partial-cured sample compared to conventional DSC. It was also demonstrated that cure characterization for these fast-cure materials is feasible using both DEA and FBG. It is worth noting that both DEA and FBG have potential for in-situ cure monitoring since the sensors can be embedded into the material during actual assembly process. For cure shrinkage measurement, feasibility of FBG was demonstrated in addition to using TMA which has been reported in prior work. Cure shrinkage results obtained using both techniques were found to be in good agreement. In summary, this paper has demonstrated the feasibility of several methodologies for cure behaviour characterization of fast-cure ACA and NCA materials. The key findings from this work represent a significant step towards cure process optimization for the development of reliable adhesive flip chip interconnects.