The Effect of Fillers in Nonconductive Adhesive on the Reliability of Chip-on-Glass Bonding with Sn/Cu Bumps

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 degrees C to 125 degrees 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 m Omega to 39.3 m Omega. 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.