Vacuum Levels and Lubricant Requirements
| Vacuum Level | Pressure Range (mbar) | Suitable Lubricant | Typical Application |
| Rough vacuum | 1000 to 1 | PAO or ester synthetic | General vacuum pumps, roughing systems |
| Medium vacuum | 1 to 10⁻³ | Silicone or low-outgassing ester | Coating chambers, vacuum furnaces |
| High vacuum (HV) | 10⁻³ to 10⁻⁷ | PFPE/PTFE or silicone | PVD sputtering, SEM, wafer handling |
| Ultra-high vacuum (UHV) | < 10⁻⁷ | PFPE/PTFE or dry solid film | MBE, surface science, space simulation |
Outgassing: The Critical Metric
Outgassing is measured by ASTM E595 — the standard test for Total Mass Loss (TML) and Collected Volatile Condensable Materials (CVCM) under vacuum. For space and high-vacuum applications, the acceptance criteria are typically: TML < 1.0% and CVCM < 0.1%. PFPE-based lubricants consistently achieve TML < 0.1% and CVCM < 0.01%, making them suitable for the most demanding UHV and space applications where even trace contamination is unacceptable.
KLÜBER Vacuum Lubricants
- Barrierta L 55/2 — PFPE/PTFE grease rated to 260°C with TML < 0.1%, CVCM < 0.01%. The industry standard for semiconductor wafer handling robots, vacuum valve stems, and UHV bearing applications.
- Barrierta L 25 DL — Lower-viscosity PFPE grease for low-torque vacuum mechanisms and small precision bearings.
- Barrierta EL 102 — PFPE-based lubricating fluid for vacuum pump bearings, chains, and sliding surfaces where a grease is too stiff.
- UNISILKON L 250 L — Silicone-based grease for medium-to-high vacuum applications up to 200°C. Cost-effective alternative to PFPE where ultra-low outgassing is not required.
- UNISILKON TK 44 N 2 — Silicone grease with PTFE for enhanced load-carrying capacity in medium vacuum.
⚠ Warning
Never use silicone-based lubricants in semiconductor cleanrooms where wafers are exposed. Silicone outgassing, even at extremely low levels, can contaminate wafer surfaces and cause die bonding or wire bonding failures. For semiconductor front-end processes, use PFPE-based Barrierta L exclusively. Silicone lubricants may be acceptable in back-end packaging and test areas where wafers are already diced and packaged.
Frequently Asked Questions
Q: Why can't I use standard bearing grease in vacuum?
Standard bearing greases contain volatile base oil fractions, corrosion inhibitors, and oxidation-stabilizing additives that outgas under vacuum. The outgassed materials condense on cooler surfaces — optics, sensors, and wafers — causing contamination. Additionally, the thickener can lose its oil-retention capacity as the base oil evaporates, leaving dry, hardened thickener that provides no lubrication. PFPE greases avoid this because the PFPE base oil has extremely low vapor pressure and evaporates at a negligible rate even at 10⁻⁹ mbar.
Q: How much lubricant should I apply in vacuum?
Apply significantly less than in atmospheric applications. In vacuum, there is no convective cooling, so excess grease cannot dissipate heat and can cause local overheating. Fill bearings to only 10-20% of free space (vs 30-50% for atmospheric applications). The grease should provide a thin film — just enough to separate surfaces — without excess that could migrate or outgas.
Q: Does PFPE lubricant degrade in the presence of Lewis acids?
Yes — this is a known limitation of PFPE lubricants. Certain Lewis acids (AlCl₃, FeCl₃, BF₃) can catalyze PFPE depolymerization at elevated temperatures, generating corrosive byproducts. This is primarily a concern in semiconductor etch chambers using chlorine or fluorine chemistry. If Lewis acid exposure is anticipated, consult KLÜBER for application-specific recommendations, such as using a barrier coating on exposed metal surfaces or selecting an alternative lubricant chemistry.