Ceramic — Ceramic joining using glass frit for high temperature application

High temperature electronics for the exploration and monitoring of down-hole activities in geothermal wells and other oil and gas industry applications must operate reliably at a minimum temperature of 300°C for as long as 500 hours continuously. This study investigates if ceramic to ceramic bonding, using glass frit as the intermediate layer, is able to tolerate a high temperature environment of 300°C for 500 hours. Since glasses have the potential to join to ceramic due to chemical compatibility between the two materials, the use of glass frit for ceramic to ceramic bonding is considered a simple and yet robust method that is often used for hermetic sealing of microelectronic packages. The materials used in this study were alumina substrate and bismuth-based glass frit paste 4115DS-1Ha from Asahi Glass Company (AGC). The study includes an initial characterisation of the glass frit and evaluation of the shear strength of the bonding. The average hot shear strength (shear test performed at 250°C) for samples after thermal aging at 300°C for 500 hours was found to be 28.72 MPa. This value is approximately 3.6 times above the minimally required shear strength of 7.9 MPa according to the MIL-STD-883G specification. Further aging till 1000 hours showed only a 30% drop in shear strength to 19.72 MPa. Based on this study, the use of glass frit as a joining layer for ceramic to ceramic bonding for use in a high temperature environment was concluded to be qualified, at least from the perspective of shear strength retention.