Compression sealing

Compression (mismatched) seals are created when the CTE, coefficient of thermal expansion and contraction, of the header body or housing greatly exceeds that of the glass or electrodes. During the firing process, the metal materials, usually stainless steel, expand at a great rate than glass. During cooling, the metal contracts into the already solidifying glass to form an extremeley robust compression bond. This type of seal is frequently specified for extreme high pressure applications. The working pressure can be as high as 14,000 PSI range. Materials used by Complete Hermetics can include:

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Matched sealing

When the CTE (Coefficient of thermal expansion) of the body or housing material matches are very relatively close, usually within 10% of each other. This results in a product in which the stress in the glass is relatively small. See note. This is extremely important in glass hermetic connectors such as the micro-d because of the rectangular shape of the shell. Matched seals can withstand high thermal and mechanical shock and are easier to manufacture compression hermetic seals. The hermetic seal is made by forming a bond through wetting and chemical reactions between the glass and metal. Kovar is the most commonly used material for matched seals.

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