Moisture Evolution from Sealing Glasses: Dry CERDIP Packages

In this investigation the moisture evolution properties of vitreous sealing glasses were evaluated to assess process approaches for producing hermetic CERDIP packages with greatly reduced levels of encapsulated moisture. Four types of commercially-glazed glasses of the KC-series, as supplied on CERDIP lids, were heated in vacuum at 430°C for 3h. During this period the identity, quantity, and evolution rate of gaseous components were measured. In parallel experiments the moisture contents of CERDIP packages sealed with KC-1 and KC-1M glasses were measured for unbaged parts and for parts preseal baked at 150°C for 2h. The outgassing studies show that the quantity and rate of moisture evolution from KC-1 and KC-1M sealing glasses depend in part on the way the glass was initially glazed on the alumina lid: the quantity of water outgassed from glass glazed in the "standard manner" is greater than the amount evolved-from the glass glazed using the "super dry" process. However, the quantity of water outgassed during the first 10 min of heating at 430°C from all 4 sample types, KC-1 (standard), KC-1 (super-dry), KC-1M (standard) and KC-1M (super dry) was sufficiently high to indicate that if sealing occurred during this initial 10 min period the moisture content inside the sealed cavity could exceed 5000 ppmv. Hence a preseal bake of vitreous-glazed package piece parts can contribute substantially to producing dry cavities. The most important factor in determining duration of a preseal bake is rate of-moisture evolution from the glass.