Kovar

Kovar is a nickel–iron–cobalt alloy known for its low coefficient of thermal expansion, which makes it suitable for creating hermetic glass-to-metal seals in electronic devices. The typical composition is about 54% nickel, 29% cobalt, with the remainder iron, plus small amounts of other elements to tailor properties.

Developed in the mid-20th century for electronic packaging, Kovar has been used for metal cans, lids, and feedthroughs that must endure thermal cycling without cracking glass seals.

A key property is its coefficient of thermal expansion, which is close to common glasses such as borosilicate, reducing seal stress during temperature changes. Its CTE is roughly 5 to 6 x 10^-6 per degree Celsius over moderate ranges, though exact values vary with heat treatment and composition.

Kovar is typically supplied in wrought forms such as sheet, tube, and rod, and can be formed, machined, and heat treated with standard techniques. Sealing to glass is achieved by glass-frit bonding or brazing, often in vacuum or inert atmospheres.

Applications include hermetic packages for semiconductor devices, laser diodes, photomultiplier tubes, and MEMS sensors, as well as components of vacuum tubes and high-reliability connections where glass or ceramic seals are required.