Improved Glass-to-Metal Sealing Through Furnace Atmosphere Composition Control

The ability is demonstrated to produce consistently an intergranular oxide layer between 2 µm and 10 µm depth on Kovar alloy using a humidified hydrogen nitrogen furnace atmosphere. Oxidizing the Kovar to a 2-10-µm intergranular depth promotes strong chemical/mechanical bonding between the metal and the borosilicate glass typically used in the production of matched glass-to-metal seals. Furnace dew point, hydrogen concentration, residence time, and decarburization pretreatment were studied to determine their effect on oxide formation. A reproducibility study was performed to demonstrate the high consistency and repeatability of the system in an actual production environment. Bubble formation in the glass after sealing is discussed and is shown to be a result of overoxidation. All three steps of matched sealing (decarburiziug, oxidizing, and sealing) are studied with emphasis on control of the oxidizing step.