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Nonconductive films (NCFs) have become one of the promising interconnection adhesives for flip-chip assembly. Because NCFs have many advantages such as low cost, easy handling, and fine-pitch application. However, effects of the material properties of NCFs on the reliability of NCFs flip-chip assemblies have not been fully understood. In this paper, effects of multifunctional epoxy and the addition of silica fillers on thermomechanical properties of cured NCFs and thermal cycling reliability of NCFs flip-chip-on-organic board (FCOB) assemblies were investigated. For the NCF materials, two kinds of thermosetting polymers, di-functional and multifunctional epoxies, and silica fillers of various contents (0 wt%, 10 wt%, and 20 wt%) were used. The curing behavior and thermomechanical properties of NCFs were measured for the NCF materials characterization. According to the results, NCFs using multifunctional epoxy had higher glass transition temperature (Tg), lower coefficient of thermal expansion (CTE), and higher storage modulus (E') in high-temperature regions than NCFs using di-functional epoxy. As the silica filler content increased, the CTE and the storage modulus of cured NCFs decreased and increased, respectively. Thermal cycling test (-40degC - 150degC, 1000 cycles) was performed to investigate effects of thermomechanical properties of cured NCFs on thermal cycling reliability of NCF FCOB assemblies. According to the results, NCF FCOB assemblies using NCFs with multifunctional epoxy had better thermal cycling reliability than those using NCFs with di-functional epoxy, and 10 wt% and 20 wt% silica added NCFs showed the best thermal cycling reliability in the electroplated Au bump application and the stud Au bump application, respectively. Consequently, thermal cycling reliability of NCFs FCOB assemblies could be enhanced with the increased Tg and the improved thermomechanical properties of NCFs by using multifunctional epoxy and the addi- - tion of silica fillers.