Engineering Resource

What Kovar is and why it is specified

Kovar is an iron-nickel-cobalt alloy with a coefficient of thermal expansion of roughly 5.1 ppm/K, closely matched to borosilicate glass and several ceramics. That match is the whole point: a Kovar pin sealed into a glass insulator expands at the same rate, so the joint stays hermetic through temperature cycles.

It is specified for glass-to-metal seals, hermetic packages, microwave and optical housings and sensor bodies, wherever a metal-to-glass or metal-to-ceramic joint has to survive thermal cycling without leaking.

Why Kovar is difficult to machine

• Gummy: Kovar tears and forms a built-up edge instead of cutting cleanly.
• Work hardens: rubbing hardens the surface and dulls tooling quickly.
• Poor heat conduction: heat stays at the cutting edge, so thermal control matters.
• Burr-prone on exits: edges need controlled deburring, not aggressive mechanical methods.

Process controls that work

Sharp, positive-geometry tooling and a constant feed that always cuts under the hardened skin; light finishing passes; attention to heat at the edge; and stress-aware sequencing so a thin flange or sealing face does not move after machining. Where the geometry calls for it, a stress-relief step before finishing protects the sealing surfaces.

Where it is used

Optical and laser packages, microwave components, vacuum feedthroughs, sensor bodies and any metal-to-glass assembly that has to stay leak-tight over its service life.

Verification and documentation

Critical dimensions are verified on a Zeiss CMM and material grade is confirmed by spectrometer, with EN 10204 3.1 certificates available. For components carrying an RF or vacuum performance requirement, that paperwork is not optional.