Joining Methodology
Metal joining processes utilize reactive components to create direct hermetic seals between ceramic insulators and metallic conductors without the need for prior metallization layers. Vacuum environments typically facilitate active brazing where titanium or vanadium is added to the filler metal to promote wetting of the ceramic surface. This technique eliminates several steps in the assembly of sensor housings or feedthroughs.
Reactive Chemistry
Molten alloy interacts with the oxide or nitride structure of the ceramic to form a thin reaction layer. Because active brazing incorporates reactive elements directly into the braze preform, the interface develops a chemical bond that withstands high mechanical loads. The absence of a separate moly-manganese coating reduces process variability and improves the thermal conductivity of the joint.
Interface Integrity
Surface preparation remains a primary factor in the success of the bond. Proper cleaning of the ceramic substrate ensures that the active elements react uniformly across the entire contact area. Impurities or moisture can lead to brittle phases or voids that weaken the hermetic seal over time.
Joint Performance
Differential expansion between the ceramic and metal parts introduces mechanical tension during cooling from the high liquidus temperature. Manufacturers select filler alloys with specific melting points to control the depth of the reaction zone. Precise control of the cooling rate minimizes the risk of ceramic fracture near the bond line.
