Bonding metal to ceramic

Claim 1

A method of bonding a travelling wave tube slow wave helix to a plurality of ceramic support rods wherein a first metallic barrier layer is deposited by sputtering upon the slow wave helix, a layer of active metal in elemental form is deposited by sputtering upon the first barrier layer, and a second metallic barrier layer is deposited by sputtering upon the active metal layer; wherein the composition, extent and manner of deposition of the layers is such as to protect the active metal layer from general oxidation; wherein the composition of the barrier layers is such that on their own, or together with material of the active layer, they combine to form a braze that contains at least one of the elements gold, silver, copper, nickel; wherein the composition of the second barrier layer is selected from the group comprising an alloy, a composite layer whose components constitute the precursor of an alloy, and a layer that forms an alloy with the active metal; wherein the support rods are assembled in position around the slow wave helix and the resulting assembly is heated in vacuum or in an inert atmosphere to a temperature sufficient to cause at least some of the active metal to migrate through into the ceramic and metallize it; and wherein further heat is applied to cause the metal of the barrier layers to combine and form a braze joining the helix to the now metallized support rods.

Claim 2

A method of bonding a travelling wave tube slow wave helix to a plurality of ceramic support rods wherein a first metallic barrier layer is deposited by sputtering upon the slow wave helix, a layer of active metal in elemental form is deposited by sputtering upon the first barrier layer, and a second metallic barrier layer is deposited by sputtering upon the active metal layer; wherein the composition, extent and manner of deposition of the layers is such as to protect the active metal layer from general oxidation; wherein the composition of the barrier layers is such that on their own, or together with material of the active layer, they combine to form a braze that contains at least one of the elements gold, silver, copper, nickel; wherein the composition of the second barrier layer is selected from the group comprising an alloy, a composite layer whose components constitute the precursor of an alloy, and a layer that forms an alloy with the active metal; wherein the support rods are assembled in position around the slow wave helix and the resulting assembly is heated in vacuum or in an inert atmosphere to a temperature sufficient to cause at least some of the active metal to migrate through into the ceramic and metallize it; and wherein further heat is applied to cause the metal of the barrier layers to combine and form a braze joining the helix to the now metallized support rods.