In August 2026, VAT Group reaffirmed strong 2026 demand for semiconductor vacuum hardware as AI-driven fab investment accelerated — and Google Trends shows the search signal following the capex: “vacuum feedthrough” and “vacuum bellows” appear consistently in U.S. engineering queries month after month, even in a niche category where most terms are too small to register. When engineers search feedthroughs, they are not browsing; they are terminating a line, a signal or a motion — and the first decision is the flange standard. KF, CF or ISO? And the second is: does the feedthrough need to move?
A vacuum feedthrough carries power, signals, fluids or mechanical motion through the chamber wall while preserving the vacuum envelope. Get the flange standard wrong and you are re-machining a chamber; get the motion seal wrong and you leak on every stroke. Both are avoidable.
The Three Flange Families
KF (KF10 to KF50): quick, small, elastomer-sealed
KF flanges (also called NW or ISO-KF) use a centering ring with an elastomer O-ring clamped by a claw. They are fast to assemble, inexpensive and perfectly adequate for rough and medium vacuum. Limit: the elastomer O-ring outgasses and limits bake-out, so KF is a poor choice below ~1×10-7 mbar. For feedthroughs in load locks, pump lines and utility ports, KF is often the right economic call.
CF (ConFlat): metal-sealed UHV standard
CF flanges (DN16 to DN250+) use a knife-edge that bites into a soft-metal gasket — typically OFHC copper — forming a metal seal rated to 10-11 mbar and full 200–450°C bake-out. CF is the default for UHV chambers, electron optics, metrology and research systems. The costs: precise machining, careful gasket handling, and higher torque discipline. The entire leak-integrity philosophy behind metal seals is covered in our UHV and semiconductor bellows guide.
ISO (ISO-K / ISO-F): large industrial vacuum
ISO flanges serve large-diameter lines — ISO-K with clamps, ISO-F with bolted holes — for pumping stacks, big chambers and process equipment from DN63 to DN500+. They are robust and economical at scale, with elastomer or metal seals depending on the class.
The Second Question: Static or Moving?
A static feedthrough passes a conductor, coolant line or optical fiber through a fixed seal. The demanding class is motion feedthroughs, where the shaft, rod or stage must translate or rotate through the wall. That motion is sealed by a bellows:
Linear and rotary bellows feedthroughs
The shaft rides inside a welded bellows that flexes with the stroke or rotation. Because the seal is a solid metal wall rather than a sliding face, bellows feedthroughs deliver zero sliding wear, zero particle generation and leak rates below 1×10-9 mbar·L/s — the properties that make them standard in wafer handling, stage motion and valve actuation. The design parameters (stroke, bore, spring rate, cycle life) follow the logic of our bellows design guide.
Where bellows feedthroughs appear
Wafer-handling robots, valve stem drives, manipulators, sample stages and metrology tool columns all move through the wall on bellows. If the component moves and the chamber holds vacuum, a bellows feedthrough is very likely the answer.
Matching Feedthrough to Application
- Rough/medium vacuum, small ports, utility → KF with elastomer seal; bellows-sealed KF motion feedthroughs for the moving ports.
- UHV, bakeable, process-grade → CF with copper gaskets; all-metal bellows for motion; vacuum feedthroughs built with welded metal envelopes.
- Large chambers, pump stacks → ISO-K or ISO-F with the appropriate seal class.
Material grades matter as much as geometry — see our 316L vs AM350 vs Inconel 718 comparison for the alloy trade-offs, and our leak testing guide for the acceptance criteria to put on your PO.
Alpha Technology for Feedthrough OEMs and Fabs
Alpha Technology supplies custom edge welded bellows and vacuum feedthroughs — KF, CF and ISO flange options, linear and rotary bellows-sealed motion, semiconductor-grade cleanliness and 100% helium leak testing with serialized documentation. Contact our engineering team with your flange, bore, stroke and vacuum requirements.
FAQ
What is the difference between KF, CF and ISO flanges?
KF (small, quick-clamp, elastomer-sealed, ~10-7 mbar limit), CF (metal-gasket UHV standard to 10-11 mbar and 450°C bake-out), and ISO (large industrial vacuum flanges for big lines and chambers).
When do I need a bellows feedthrough?
Whenever the feedthrough must move — linear, rotary or XY stage motion across the wall — a bellows seals the motion with no sliding wear and no particles.
Can a bellows feedthrough hold UHV?
Yes; welded bellows motion feedthroughs hold leak rates below 1×10-9 mbar·L/s and survive bake-out, making them standard in UHV systems.
Why do semiconductor fabs specify CF and bellows feedthroughs?
Process chambers need metal-sealed, bakeable, particle-free envelopes — exactly what CF flanges and welded bellows provide, as VAT’s 2026 demand outlook confirms.
Choosing feedthroughs for a new chamber? Contact Alpha Technology with your flange and motion specifications.