Highly reliable, fine pitch chip on glass (COG) joints fabricated using Sn/Cu bumps and non-conductive adhesives

Abstract

We have developed a reliable and ultra-fine pitch chip on glass (COG) bonding technique using Sn/Cu bumps and non-conductive adhesive (NCA). Sn/Cu bumps were formed by electroplating and reflowed, forming dome shaped Sn bumps on Cu columns. COG bonding was performed between the reflowed Sn/Cu bumps on the oxidized Si wafer and ITO/Au/Cu/Ti/glass substrate using a thermo-compression bonder. Three different NCAs were applied during bonding. Bonding temperature was 150 °C for NCA-A and NCA-B, and 110 °C for NCA-C. The electrical properties of COG joints were evaluated by measuring the contact resistance of each joint through the four-point probe method. All joints were successfully bonded and the electrical measurement showed that the average contact resistance of each joint was approximately 30 mΩ, regardless of NCA types. The COG joints were subjected to a series of reliability tests: high temperature storage test (85 °C, 160 h); thermal cycling test (−40 °C/+85 °C, 20 cycle); and a temperature and humidity test (50 °C/90%, 160 h) were sequentially performed to evaluate the reliability of the COG joints. The contact resistance measurement showed that there were no failed bumps in all specimens and all joints passed the criterion after reliability test.