A welded joint vs a brazed joint
Today Altair has innovated ways to braze Copper, Stainless Steel and other refractory metals to Aluminum while avoiding brittle intermetallic phases, leaving a strong and hermetic bond.
Copper brazed to Aluminum
We have also developed a braze technique for achieving a 360-degree thermal bond on a heating element surrounded by Aluminum. The semiconductor community has been using heating element for decades, but the full circumferential bond allows for higher power densities and also provided better temperature uniformity.
For the best possible appearance, vacuum brazed assemblies are typically final machined after vacuum brazing, offering a nice, aesthetically pleasing appearance where the braze joint is barely noticeable (see our Blog Post(s) on Brazing Aluminum). The vacuum tight assembly shown in the photo below was made from four separate 6061 Aluminum components and has two cooling channels hidden within the walls of the assembly.
Vacuum aluminum brazing typically uses a Silicon-rich aluminum alloy such as 4047, which has a slightly lower melting temperature (~600°C) than the base metals to be brazed. Aluminum can be a difficult metal to braze because it forms an oxide layer at room temperature; therefore components are chemically etched/cleaned and sealed before use. The process of assembly is quick and once the thermal cycle begins, it is not uncommon to introduce a partial pressure of Mg gas to help strip residual oxides allowing for good wetting and bonding of the base material. As the thermal process takes place, the Silicon is both vaporized into the furnace’s vacuum and diffused into the surrounding aluminum components. The resulting braze joint is very close in composition to the base materials and is both strong and hermetic.
At Altair Technologies, the process of vacuum brazing of aluminum is highly controlled and boasts a nearly perfect first-pass yield. one on of our semiconductor ESC Cooling Assemblies we brazed over 2,700 consecutive assemblies with perfect 100% yield.