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

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 (Tg), lower coefficient of thermal expansion (CTE), and higher storage modulus (E´) in high temperature region than NCFs using di-functional epoxy. And, as the silica filler content increased, the CTE and storage modulus of cured NCFs deceased and increased, respectively. Thermal cycling test (-40degC ~ 150degC, 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% silica added NCFs showed better thermal cycling reliability than 0 and 20 wt% silica added NCFs. The one of possible reasons for this result is that the captured silica fillers between a chip bump and a substrate - electrode could disturb electrical bump-to-electrode contact during thermal cycling.