Vacco Industries,, South El Monte, Calif., (vacco-etch.com) says adding diffusion bonding to its existing photochemical etching and laser-cutting processes lets the company make complex, homogeneous, hermetically-sealed components that contain tiny flow channels and holes. Diffusion bonding is a solid-state process that joins metal to metal directly. Examples include microchips, parts for dental devices, filters to micron ratings, and channeling systems for heat-sinking applications.

The process works like this: The company first photo etches holes and channels in sheets of the same kind of metal -- titanium, stainless steel, or nickel -- and stacks them on top of each other. “Layering flat, blank sheets on top of ones with holes or channels creates the tiny tubes or through-channels,“ says Rick Hoppe, engineering manager. “Some applications might require six to twelve layers while others, such as the filters, take 200 layers, each about 0.001-in. thick.“ Layers can be mixed in size, with one layer 0.002 and the next 0.005-in. thick.

The next step places the stacks into a ceramic or molybdenum fixture, which goes into a vacuum furnace. A hydraulic ram places a load on the fixture, with surface finish, flatness, layer thickness, and hermetic-seal requirements dictating the pressure.

The company then heats the parts to a temperature that anneals, but does not melt, the material. This is usually between 800 and 1,000°C. The combination of heat, pressure, and vacuum reorganizes the grains of the metal and makes them grow larger. In areas with metal-to-metal contact, this results in grain growth across the boundary. Completed components are pressurized with helium to check for leaks.

“We can make more than one part at a time in what$s called a fret. This comprises several layers of twelve or sixteen different parts. And we can place several stacks in the same fixture, or put multiple fixtures in the press at the same time,“ says Hoppe. The company assembles and processes parts that must remain ultra-clean in a cleanroom.