Abstract
The effect of a nonconductive adhesive (NCA) on the reliability of chip-on-glass (COG) bonding was studied. Double layer bumps consisting of dome-shaped Sn on Cu columns were formed by electroplating and a reflow process, and were used for this study. COG bonding was performed between the reflowed Sn/Cu bumps on the oxidized Si wafer and an indium tin oxide/Au/Cu/Ti/glass substrate using a thermo-compression bonder. Three types of NCAs were applied during COG bonding: NCA-A with no fillers, NCA-B with fluoropolymer fillers, and NCA-C with silica fillers. Thermal cycling from −25°C to 125°C for 2000 cycles was performed to evaluate the effect of NCA type on the reliability of COG joints. The initial contact resistance values of the COG joints ranged from 32.2 mΩ to 39.3 mΩ. The contact resistance increased during the thermal cycling and the trend of contact resistance increment was different among three NCA types. The failure rate was the highest in NCA-C, followed by NCA-B and NCA-A in descending order. After the thermal cycling, the cross-sections of COG joints were observed with scanning electron microscopy to analyze the failure mechanism. The failures occurred primarily due to trapped fillers and NCAs at the interface between Sn/Cu bumps and the ITO substrate.
