Key characteristics and uses of Kovar:
Thermal Expansion Matching:
Kovar's most critical property is its coefficient of thermal expansion (CTE) which is very similar to borosilicate glass, allowing for strong, reliable, and hermetic seals between metal and glass or ceramic components. This is crucial for devices where temperature fluctuations are expected.
Applications:
It is widely used in the electronics industry for components requiring glass-to-metal seals, including:
Power tubes, x-ray tubes, and microwave tubes.
Transistors, diodes, and hybrid electronic circuit packages.
Lids and closures for various electronic devices.
Manufacturing and Processing:
Kovar is produced with extensive quality controls to ensure uniform physical and mechanical properties, facilitating operations like deep drawing, stamping, and machining. It can be provided in various forms like wire, rod, bar, strip, and sheet. Recommended treatments for optimal sealing include thermal degassing and decarburizing in a moist hydrogen atmosphere, followed by controlled oxidizing heat treatment to create a tightly adhering surface oxide film.
Corrosion Resistance:
While Kovar exhibits moderate corrosion resistance, specific conditions like temperature, concentration, and pH can affect its performance, and corrosion testing is recommended for critical applications.
Magnetic Properties:
Kovar is ferromagnetic and exhibits a strong magnetic response, unlike Invar which is magnetically soft.
