Non-Conductive Films (NCFs) with Multi-Functional Epoxies and Silica Fillers for Reliable NCFs Flip Chip On Organic Boards (FCOB)

Non-conductive 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 multi-functional epoxy and the addition of silica fillers on thermo-mechanical 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 multi-functional epoxies, and silica fillers of various contents (0 wt%, 10 wt%, and 20 wt%) were used. The curing behavior and thermo-mechanical properties of NCFs were measured for the NCF materials characterization. According to the results, NCFs using multi-functional epoxy had higher glass transition temperature (T_g), lower coefficient of thermal expansion (CTE), and higher storage modulus (E´) in high temperature region than NCFs using difunctional epoxy. And, as the silica filler content increased, the CTE and storage modulus of cured NCFs deceased and increased respectively. Thermal cycling test (-40 degC ~ 150 degC, 1000 cycles) was performed to investigate effects of thermo-mechanical properties of cured NCFs on thermal cycling reliability of NCFs FCOB assemblies. After 1000 cycles, scanning acoustic microscopy (SAM) and scanning electron microscopy (SEM) were used to detect delaminations and voids in test assemblies. According to the results, NCFs FCOB assemblies using NCFs with multi-functional 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 electro-plated Au bump application and the stud Au bump application respectively. Consequently, thermo-mechanical properties of NCFs- , especially T_g, should be improved and the amount of added silica fillers should be optimized for high thermal cycling reliability of NCFs FCOB assemblies.