Kovar
Kovar is a trademark of the US company CRS Holdings inc. and denotes alloys that have a low coefficient of thermal expansion , typically around 5 ppm / K, which is less than the coefficient of typical metals.
A typical composition is 54% iron , 29% nickel and 17% cobalt (data in percent by mass).
Some technical ceramics (e.g. aluminum oxide Al 2 O 3 , aluminum nitride AlN) and semiconductor materials have coefficients of thermal expansion of the same order of magnitude. In the field of microelectronics and microsystem technology , Kovar is therefore used as a housing material or as a submount . Submounts lie between the actual carrier material and material with usually a significantly higher coefficient of expansion ( sandwich principle ). The Kovar submount thus serves as a compensating element, which absorbs or reduces the thermomechanical stresses caused by the different thermal expansion coefficients of the other materials.
In the same way, Kovar materials are used for metal-glass feedthroughs in electronic components, material transitions in vacuum chambers and the like. For example, there are special borosilicate glasses that have the same size as Kovar, so they can be fused directly with the alloy and the alloy can be used, for example, to supply power to X-ray tubes .
The similar invar denotes alloys with a coefficient of thermal expansion close to 0.
Individual evidence
- ↑ United States Patent and Trademark Office: Trademark Assignment Abstract . 1993. Retrieved June 18, 2014.
- ↑ Material sheet at Parmaco (pdf; 23 kB)