There are basically four joint constructions:-

COMPRESSION SEAL
After brazing, this joint is in compression at room temperature. During brazing the braze material fills the micro-voids between the metal member and ceramic. On cooling, contraction of the metal member places the ceramic in compression producing an extremely strong hermetic joint which will normally withstand repeated thermocycling.

BUTT SEAL
Normally only employed where the application requirements and the physical loadings are lower than those where a compression seal would be specified. This joint construction offers the advantage of improved track length over a compression seal within a more compact assembly. Butt seals are not recommended for applications where there are large temperature gradients.

EDGE SEAL
Properly constructed and manufactured this method will provide a more "flexible" joint than a butt seal with minimal risks of braze voids for similar applications.

INTERNAL SEAL
This joint construction has design/application advantages over those mentioned above, e.g. multi-pin plug/socket arrangements, but has the major disadvantage of being structurally very much weaker. It is also more difficult to manufacture and will not withstand repeated thermocycling as successfully as a compression seal since the ceramic-to-metal joint is effectively in tension as a result of the contraction of the metal member away from the metallized alumina during cooling to room temperature. On any custom built assembly the customer is strongly advised to consult our technical staff before proceeding too far at the design stage.