Copper is one of the most commonly brazed metals here at Altair Technologies. It is a vacuum compatible material with excellent electrical and thermal conductivity properties. Copper is used in many high-vacuum and high-temperature applications as well as in virtually all ion beam and electron beam devices such as accelerators, x-ray tubes and traveling wave tubes. While we do perform vacuum brazing of Copper, we primarily use Hydrogen brazing because it is arguably the best process for bonding metals and ceramics regardless of the application.
Hydrogen (H2) gas acts as a fluxing agent, reducing native oxides and removing hydrocarbon contamination producing an ultra clean raw metal surface. Many oxides, like Copper Oxide, are easily reduced by H2. Copper is usually brazed in wet Hydrogen, however, depending on the other materials being brazed, like stainless steel where the removal of oxides is necessary, dry Hydrogen can be used.
“Hydrogen Brazing” requires special vacuum grade OFE Copper 101. We’ve learned over the years that not all OFE is equal and more importantly not all suppliers of OFE Copper are reputable. Here at Altair Technologies, we source direct all of our Copper and virtually any material to be used in a high vacuum application. When non-OFE Copper is used, oxide inclusions form water-vapor in a hydrogen furnace. This phenomenon results in “blisters,” “bulges,” or rough surfaces, where the copper part(s) expand permanently and the braze alloy/filler disappears into opened grain boundaries. In this scenario, vacuum leaks are inevitable.