Almost every HermiCore feedthrough is offered "with CF or KF flanges" — but the two families serve very different vacuum regimes. Understanding the difference prevents embarrassing leaks at first pump-down.
CF (ConFlat) Flanges
ConFlat flanges seal a knife-edge against a soft copper gasket, which flows into the knife edges when the flange bolts are torqued. The result is a metal-to-metal seal that is:
- UHV rated: routinely used below 1×10⁻¹⁰ mbar.
- Bakeable: survives repeated 150–400 °C bakeouts, essential for reaching extreme vacuum.
- Leak-tight and repeatable: gaskets are replaced each time, so seal integrity is consistent.
CF sizes are named by the outside tube diameter: CF16, CF35, CF63, CF100, CF160, CF200. Because the gasket deforms plastically, CF flanges need careful bolt torque in a star pattern and are not suited to frequent disassembly.
KF (ISO-KF) Flanges
ISO-KF is a quick-connect system: an elastomer O-ring or aluminium centering ring is clamped between two flanges by a wing nut and claw. KF is:
- Fast: assemble in seconds without tools — ideal for frequently opened systems and R&D setups.
- High-vacuum suitable: typically to about 1×10⁻⁷ to 1×10⁻⁸ mbar with Viton O-rings; not a true UHV metal seal.
- Limited bakeout: O-ring temperature limits (Viton ~200 °C) restrict bakeout schedules.
Common KF sizes: KF10, KF16, KF25, KF40, KF50.
Decision Guide
| Consideration | CF (ConFlat) | KF (ISO-KF) |
|---|---|---|
| Pressure regime | UHV to XHV | High vacuum |
| Bakeout | Up to 400 °C | ~200 °C (O-ring) |
| Assembly speed | Bolts, torque pattern | Seconds, tool-free |
| Reusability | New gasket each time | O-ring reusable |
| Typical use | Chambers, beamlines, UHV process tools | Pumping lines, R&D rigs, HV systems |
Mixing and Matching
It is common to see CF chambers with KF pump lines, or CF feedthroughs mounted on KF adapters. Just remember: an adapter never improves the seal class of the weaker side. If your process demands 10⁻⁹ mbar, every joint — including the feedthrough — should be metal-sealed CF.
Most HermiCore feedthroughs are available in both CF and KF versions across multiple sizes. Tell us your port, and we will match the flange, pin configuration and electrical rating. Explore power feedthroughs or ask our engineers.
