Sealing of alumina using a CO2 laser and a rapidly crystallizing glass

Alumina and sapphire are frequently used as housing materials, because they withstand high mechanical stress and can be used in extreme environment. The required high temperatures in conventional joining procedures are often not suitable for the encapsulation of temperature sensitive components. By contrast, using a laser joining technique, it is possible to restrict the heat-input only into the joining zone for a short period of time. For that purpose, rapidly crystallizing sealing glasses are required which thermal expansion coefficient (CTE) are adjusted to the materials to be joined. For this process, a powdered glass based on the system CaO/Al2O3/SiO2 was investigated predominantly with respect to its sintering and crystallization behavior. The glass can be sintered and subsequently crystallized using a laser process with a tailored temperature-time schedule with a maximum temperature of 990 °C kept for 1 min or less. The CTE of crystallized glass was 8.8 × 10−6 K−1 and hence close to that of alumina.