A Study on Nano-Sized Silica Contents and Size Effect in Non-conductive Films (NCFs) for Ultra Fine-Pitch Cu-Pillar/Sn-Ag Micro-Bump Interconnection

Ultra fine-pitch interconnection technologies using non-conductive films (NCFs) have been actively developed in electronic packaging industry. However, NCFs that are based on polymer material has different material properties compared with silicon resulting in critical reliability issues. Particularly, reliability degradation from NCFs delamination and interconnection crack can take place due to coefficient of thermal expansion (CTE) mismatch between NCFs and silicon. In order to reduce such problem, nano-sized silica filler is introduced in NCFs for reducing its CTE. Contents and diameter of silica filler in NCFs can affect curing behavior and thermo-mechanical properties. In this study, the effect of silica filler contents and size on NCFs material properties and interconnection performance have been investigated for 40 μm pitch chip-on-board (COB) interconnection. NCFs was formulated with 7~300 nm size of silica powder as fillers, and filler contents on NCFs was introduced up to 20 wt%. Then, viscosity, curing property and CTE were compared for investigation of the effect of silica filler contents and size on the NCFs material properties. In addition, bonding process conditions were also optimized at each filler contents and size condition in terms of solder wetting area on pad, gap size, IMCs(Inter-metallic Compounds) growth, and electrical resistance. And high temperature storage test (HTST) and thermal cycle (T/C) test were performed to compare Cu pillar/SnAg on Cu pad interconnection with various filler contents and size of NCFs Finally, reliability result COB using NCFs with optimized filler condition was compared with that of conventional underfill assembled COB.