Short answer: Use FFKM where a seal sees fluorine or oxygen plasma, temperatures above the roughly 204 °C limit of FKM, or chemicals that FKM does not tolerate, such as amines and ammonia. Choose the FFKM grade by process step, not just by family. Then specify the AS568 dash number, because -014, -114 and -214 are three different rings. This post summarises our full tutorial, [Selecting FFKM AS568 O-rings for semiconductor tools](/buying-guides/ffkm-as568-o-rings-semiconductor-tools), which includes a to-scale cross-section drawing and an FAQ.
MST is a distributor. The compounds are made by their manufacturers, for example DuPont (Kalrez). Values come from the Parker O-Ring Handbook ORD 5700 and the DuPont Kalrez semiconductor plasma selector guide.
Step 1: Compare the three families
Chart by MST Engineering from Parker ORD 5700 and the DuPont Kalrez selector guides.
Representative product photo (MORISEAL 5130UP). Colour and finish vary by compound.
| Property | FFKM | FKM | EPDM |
|---|---|---|---|
| Upper service temperature | 275–327 °C depending on grade | Up to 204 °C | Up to 150 °C (204 °C in water or steam) |
| Plasma (F, O radicals) | Best; dedicated plasma grades | Erodes faster | Not a plasma-chamber material |
| Chemicals | Broadest resistance | Not amines, ammonia, alkalis, superheated steam | Hot water, steam, many acids and alkalis; not mineral oils |
| Typical tool location | Chamber lids, gas inlets, slit valves | Milder static seals, pumps, foreline | Wet benches, DI-water lines |
Step 2: Pick an FFKM grade by process
Chart by MST Engineering from the manufacturers' data sheets.
Chart by MST Engineering from the DuPont Kalrez semiconductor selector guides.
| Kalrez grade | Shore A | Max. service temperature | Suggested processes (DuPont) |
|---|---|---|---|
| 9100 | 70 | 300 °C | HDPCVD, conductor etch |
| 9300 | 77 | 300 °C | Conductor and dielectric etch, ash/strip |
| 9500 | 76 | 310 °C | HDPCVD, SACVD/FCVD, PECVD curing |
| 9600 | 70 | 315 °C | PECVD/PEALD, SACVD/FCVD |
| 8002 | 69 | 275 °C | Ash/strip |
| 8705 | 77 | 327 °C | PECVD curing (quartz window seal) |
DuPont states that these are typical values, not specifications. Validate the grade in your own chamber.
Step 3: Check temperature, outgassing and hardness
1. Compare the grade's rating with the actual seal temperature, not the chamber set point.
2. Ask for TML and CVCM measured to ASTM E595, so outgassing data is compared like for like.
3. Hardness is measured to ASTM D2240. About 70 Shore A seals at low force on smooth flanges. About 75–80 Shore A resists extrusion and suits slit-valve service.
Step 4: Specify the AS568 size
| Series | Cross section | Example FFKM sizes on MST Store (nominal ID) |
|---|---|---|
| -0xx | 1.78 mm | [AS568-022](/store/as568-o-rings/AS568-022-FFKM-RFQ) 25.12 mm |
| -1xx | 2.62 mm | [AS568-120](/store/as568-o-rings/AS568-120-FFKM-RFQ) 25.07 mm |
| -2xx | 3.53 mm | [AS568-214](/store/as568-o-rings/AS568-214-FFKM-RFQ) 24.99 mm |
| -3xx | 5.33 mm | [AS568-330](/store/as568-o-rings/AS568-330-FFKM-RFQ) 53.34 mm |
All three "25 mm" rings above have different cross sections and will not fit the same groove. See also [AS568 dash numbers for FFKM O-rings](/community/c/o-rings-seals).
RFQ checklist
Graphic by MST Engineering.
1. Dash number, or groove dimensions and seal type.
2. Tool, seal location, process gases and chemistries.
3. Maximum seal temperature and thermal cycling.
4. Current compound and the failure mode you see.
5. Outgassing, purity and cleanroom-packaging needs, plus quantity.
Original OEM documents (links only)
1. DuPont, Kalrez perfluoroelastomer parts. https://www.dupont.com/brands/kalrez.html
2. Greene Tweed, Chemraz G-series semiconductor data sheet. https://www.gtweed.com/wp-content/uploads/chemraz-G-series-sc-ds.pdf
3. SAE AS568 aerospace size standard for O-rings. https://www.sae.org/standards/content/as568/
4. Parker Hannifin, Parker O-Ring Handbook ORD 5700. https://www.parker.com/content/dam/Parker-com/Literature/O-Ring-Division-Literature/ORD-5700.pdf
5. ASTM E595 outgassing test method. https://www.astm.org/e0595-15.html
Ask an engineer
Send the dash number, process step and seal temperature through [Ask an engineer](/rfq?entry_source=ask_engineer&search_term=FFKM+AS568+O-ring&quantity=1&community_path=%2Fbuying-guides%2Fffkm-as568-o-rings-semiconductor-tools). MST helps shortlist FFKM grades to validate and quotes the sizes you need. Or post a [find-part request](/community/new?kind=part_request&mpn=AS568-214-FFKM-RFQ). For parts outside this list, use a [sourcing RFQ](/services/sourcing-rfq?sourcing_mode=supplier_match).
Catalog parts in this guide