Investigation of Fine Pitch Chip on Glass with Au-Sn Thermocompression Bonding

Au-Sn thermocompression interconnect technique using nonconductive film (NCF) is proposed to solve the insulation problem between bumps of fine-pitch IC. This paper describes NCF for ultra-fine pitch Chip-On-Glass (COG) application. NCF is a novel material developed for fine-pitch packaging. The effects of bonding temperature and bonding pressure on the microstructure of an NCF-bonded COG package were investigated in this study through optomicroscope and SEM. The contact area between chip bump and substrate pad, thickness of eutectic layer and content percentage of Sn in eutectic layer were observed in present work. High bonding temperature and bonding pressure are beneficial to form larger contact area. Thickness of eutectic layer increases along with bonding pressure decrease and bonding temperature increase, and content percentage of Sn increases accordingly. Reliability test of AHT for Au-Sn thermocompression samples was conducted and some cracks at the root of bump were detected, but no functional failures were detected.