Engineering Resource
Kovar exists to seal to glass. Almost everything about machining it follows from that single purpose.
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 for geometry and position, the TRIMOS V5 height gauge for heights and steps, and the AI-Vision system for fine features, 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.