A feedthrough fails in a way a blank flange cannot: it has to hold vacuum and pass a conductor through the same wall. That makes the ceramic-to-metal joint and the flange seat a single leak path, and it has to be tested as one assembly rather than as two parts.
What a feedthrough has to do at once
It has to transfer power, signal or motion across a vacuum boundary without leaking, without outgassing beyond the system budget, and without electrically or thermally shorting to the chamber. Those requirements conflict: the ceramic that gives electrical isolation is brittle and has a different expansion coefficient from the flange, so the joint has to be designed so the ceramic is in compression rather than tension.
Common configurations
Power feedthroughs for heaters and electrodes; thermocouple and instrumentation feedthroughs for temperature and pressure measurement inside the chamber; multipin connectors for signal bundles; and coaxial and shielded types where RF or low-level signals require it. Motion feedthroughs — rotary and linear — are a separate family and are usually bought as complete assemblies rather than built from a flange body.
What we machine and what we test
We machine the flange body, the ceramic seat and the conductor bore in one setup so the assembly is concentric, then leak test the finished feedthrough as an assembly by helium mass spectrometer. Testing the flange and the ceramic separately and assuming the combination is tight is how a feedthrough passes goods-in and fails on the chamber.
Choosing a flange size
The flange has to be large enough to carry the conductor count and the ceramic diameter, not just the conductor. Packing more pins into a flange than the ceramic can carry is the usual cause of a feedthrough that leaks at the seal rather than at the pin.
What we control in-house
- 304 / 316L stainless steel and 6061 / 5083 aluminium fabrication
- Clean-environment TIG welding with full penetration and no micro-porosity
- Helium mass-spectrometer leak testing to 1 × 10⁻⁹ mbar·l/s
- In-house electropolishing and passivation — not subcontracted
- Chamber bake-out to 150–400 °C for UHV outgassing control
- Precision-machined ISO-KF, ISO-K and CF (ConFlat) flanges
- Zeiss CMM verification to ±0.02 mm across large work envelopes
- 12 m gantry CNC machining — 12 m × 4 m × 2 m envelope
- SEMI-referenced documentation and inspection protocols
Frequently asked questions
What is a vacuum feedthrough?
A vacuum feedthrough is a sealed component that carries a conductor, a thermocouple, an optical fibre or a mechanical motion through the wall of a vacuum chamber without breaking the vacuum.
What is the most common failure mode?
Leakage at the ceramic-to-metal seal, usually caused by a design that puts the ceramic in tension or by machining the seal seat out of concentricity with the flange bore. Testing the finished assembly by helium mass spectrometer catches it before it reaches the chamber.
Should I choose a CF or KF feedthrough?
CF if the feedthrough will be baked or the chamber must reach UHV, because the seal is metallic. KF is acceptable for HV service and where the feedthrough will be changed frequently, but the O-ring limits the bake-out temperature.
Can you machine a custom feedthrough flange?
Yes. We machine flange bodies to standard CF and KF dimensions and to customer drawings, including non-standard conductor counts and bore patterns.
Do you supply the ceramic and the pins as well?
We machine the flange body and the sealing features, and build and test the complete assembly to the customer specification. Whether the ceramic subassembly is bought in or specified by the customer depends on the configuration.
Related capabilities
Need this made to spec?
Send the drawing or the specification and we will come back with a DDP price, lead time and inspection plan.