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Glass-to-metal seals provide a way to hermetically pass
an electrical conductor from one environment to another.
The glass, as well as providing the seal, acts as an insulator
between the pins and the housing. These conductor feedthrus
can be used for many applications such as: vacuum components,
sensor or transducer housings, feedthrus for harsh environments,
battery headers, and medical implantable devices.
Matched vs. Compression Seals
Glass-to-metal hermetic seals
available in industry today are typically one of two types:
Matched Seals
To create a matched hermetic seal, housing and
glass materials are selected to have similar coefficient
of thermal expansion. The strength of a matched seal comes
primarily from a chemical bond between the glass and an
oxide formed on the metal parts. Matched seals are most
often made with Kovar housings and pins, and borosilicate
glass.
Compression Seals
A compression hermetic seal is made with the housing
material thermal expansion rate much higher than that of
the glass. Upon solidification of the seal during the manufacturing
process, the housing will contract around the glass, applying
a desirable compression stress on the glass bead. The strength
of the glass-to-metal seal is reinforced mechanically as
well as chemically, creating a stronger, more reliable part.
Compression seals are often made using steel or stainless
steel housings, nickel iron pins, and barium alkali glass.
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