FFKM O-Ring Chemical Resistance — Acids, Bases, Solvents, And Plasma

Why Does FFKM Chemical Resistance Matter?

 

FFKM chemical resistance matters because the elastomer must survive the specific chemistry of the process tool (acid, base, solvent, plasma) without swelling, hardening, cracking, or losing sealing force, and FFKM is the only elastomer that provides the broadest resistance across all four chemistry categories. Standard elastomers (FKM, EPDM, silicone) fail in one or more categories.

 

The four chemistry categories and FFKM resistance:

Chemistry category FFKM resistance Standard elastomer resistance

Concentrated acids Excellent Limited (HNO₃, HF fail most)

Bases Excellent Good (EPDM)

Solvents Excellent Limited (acetone, NMP fail FKM)

Plasma Compound-dependent Poor (most elastomers fail)

For semiconductor tools that combine multiple chemistries (wet + dry process), FFKM is the only elastomer that provides reliable service across the full process flow.

 

 

How Is FFKM Chemical Resistance Tested?

 

FFKM chemical resistance is tested per ASTM D471 (immersion in the test fluid at the target temperature for 70 hours, followed by measurement of volume, hardness, and tensile changes), with the acceptance criterion typically < 10 % volume change, < 5 hardness points change, and < 50 % tensile change. Vendor data sheets report ASTM D471 results for standard chemicals.

Test Standard Method

Immersion ASTM D471 70 h at target temperature

Volume change ASTM D471 % swell

Hardness change ASTM D471 Shore A delta

Tensile change ASTM D471 % change

Visual ASTM D471 Cracking, blistering

For non-standard chemistries, prototype testing in the actual process fluid is recommended. ASTM D471 is a screening test; actual service may differ.

 

 

What Is the Acid Resistance?

FFKM is resistant to most concentrated acids including HCl, H₂SO₄, HNO₃, acetic acid, and HF (with limitations), with typical volume change < 5 % at room temperature and < 15 % at +100 °C. HF resistance is compound-dependent and requires careful compound selection.

Acid Concentration FFKM volume change (70 h, RT) Notes

HCl 37 % < 2 % Excellent

H₂SO₄ 98 % < 5 % Excellent

HNO₃ 70 % < 5 % Excellent

HF 49 % < 10 % (compound-dep.) Compound-dependent

Acetic acid Glacial < 3 % Excellent

Aqua regia HCl / HNO₃ < 10 % Excellent

For HF service, special FFKM compounds (e.g., Kalrez 6375) are required. Standard FKM and EPDM fail rapidly in HF.

 

 

What Is the Base Resistance?

 

FFKM is resistant to most concentrated bases including NaOH, KOH, NH₄OH, and amines, with typical volume change < 3 % at room temperature and < 10 % at +100 °C. Base resistance of FFKM is excellent across the standard semiconductor wet chemistries.

Base Concentration FFKM volume change (70 h, RT) Notes

NaOH 50 % < 2 % Excellent

KOH 45 % < 2 % Excellent

NH₄OH 28 % < 3 % Excellent

TMAH (tetramethylammonium hydroxide) 25 % < 5 % Standard developer chemistry

Amines Various < 5 % Compound-dependent

For semiconductor wet-process (developer, stripper), FFKM provides excellent base resistance where FKM and EPDM may swell or degrade.

 

 

What Is the Solvent Resistance?

 

FFKM is resistant to most organic solvents including acetone, IPA, toluene, NMP, DMF, and methylene chloride, with typical volume change < 5 % at room temperature. Solvent resistance is a key advantage over FKM, which fails in many solvents.

Solvent FFKM volume change (70 h, RT) FKM volume change

Acetone < 3 % 30–50 % (fail)

IPA < 2 % < 5 %

Toluene < 3 % 10–20 %

NMP (N-methyl-2-pyrrolidone) < 5 % 30–50 % (fail)

DMF (dimethylformamide) < 5 % 30–50 % (fail)

Methylene chloride < 5 % 30–50 % (fail)

Acetonitrile < 3 % 10–20 %

Methanol < 2 % < 5 %

For photoresist strip and solvent cleaning, FFKM is the standard because FKM and EPDM fail rapidly.

 

 

What Is the Plasma Resistance?

 

FFKM plasma resistance is compound-dependent and chemistry-dependent, with most FFKM compounds losing 5–200 nm/min of surface under aggressive plasma and forming a passivation layer that protects the bulk elastomer. The plasma resistance determines seal lifetime in dry-process equipment.

Plasma chemistry FFKM erosion rate (typ.) Compound selection

O₂ plasma 20–100 nm/min Compound-dependent

CF₄ plasma 10–50 nm/min Compound-dependent

SF₆ plasma 30–80 nm/min Compound-dependent

Cl₂ / HBr plasma 20–60 nm/min Compound-dependent

Ar sputter 50–200 nm/min All compounds erode

H₂ plasma < 5 nm/min Excellent resistance

N₂ plasma < 10 nm/min Good resistance

For O₂ plasma (ash / strip), FFKM compounds with high filler content (e.g., Kalrez 4079) provide the longest lifetime. For halogen plasma (etch), Kalrez 6375 is preferred.

 

 

What Is the Temperature Resistance?

 

FFKM  temperature resistance depends on the compound, with standard compounds rated +200 °C continuous (Kalrez 4079, 6375, 9100, 1050LF) and high-temperature compounds rated +300 to +325 °C continuous (Kalrez 9500, Chemraz 555). Excursion temperatures can be +50 to +100 °C above the continuous rating for short durations.

Compound Continuous temperature Excursion Notes

Kalrez 4079 +200 °C +250 °C Standard semiconductor

Kalrez 6375 +200 °C +250 °C Broad chemical

Kalrez 9100 +200 °C +250 °C Low compression set

Kalrez 9500 +325 °C +350 °C High-temperature

Kalrez 1050LF +200 °C +250 °C Low friction

Chemraz 555 +325 °C +350 °C High-temperature

For ALD, PVD, and high-temperature process chambers, Kalrez 9500 or Chemraz 555 are required. For standard etch / CVD / load lock, Kalrez 4079 or 6375 are standard.

 

 

What Are the Standard FFKM Compounds and Their Chemical Profile?

 

The standard FFKM compounds and their chemical profiles are matched to the process chemistry and temperature, with the most common semiconductor compounds being Kalrez 4079, 6375, 9100, 9500, and 1050LF. Each compound has a specific chemical and mechanical profile.

Compound Acid Base Solvent Plasma Temperature

Kalrez 4079 Excellent Excellent Excellent Excellent (CF₄, O₂) +200 °C

Kalrez 6375 Excellent (incl. HF) Excellent Excellent Excellent (halogen) +200 °C

Kalrez 9100 Excellent Excellent Excellent Excellent +200 °C

Kalrez 9500 Excellent Excellent Excellent Excellent +325 °C

Kalrez 1050LF Excellent Excellent Excellent Excellent +200 °C

For most semiconductor applications, Kalrez 4079 or 6375 is the standard. For halogen etch, 6375 is preferred. For high-temperature, 9500 is required.

 

 

How Does FFKM Compare to PTFE?

 

PTFE (polytetrafluoroethylene) provides similar chemical resistance to FFKM but is not an elastomer (it is a rigid thermoplastic), so it cannot provide the elastic recovery required for static and dynamic sealing. FFKM is used where elastomeric sealing is required; PTFE is used where rigid gaskets or machined shapes are acceptable.

Property FFKM PTFE

Form Elastomer Rigid thermoplastic

Hardness 70–90 Shore A 55–60 Shore D

Elastic recovery Yes No

Compression set 15–30 % n/a (plastic deformation)

Chemical resistance Excellent Excellent

Temperature +200 to +325 °C +260 °C

Vacuum Excellent Excellent

For O-ring and dynamic seal applications, FFKM is required. For rigid gasket and machined seal applications, PTFE is used.

 

 

How Is FFKM Selected for Multi-Chemistry Service?

 

For multi-chemistry service (e.g., wet + dry process in the same tool), FFKM is the standard because it provides resistance across acids, bases, solvents, and plasma; standard elastomers fail in at least one chemistry category. The selection process for multi-chemistry:

 

List all chemistries the seal will contact.

List all temperatures (continuous + excursion).

List all mechanical requirements (static vs. dynamic).

Select the FFKM compound with the broadest chemical compatibility.

Verify with prototype testing in the actual chemistry mix.

 

Hitron's Kalrez O-Ring family covers the standard FFKM compounds for multi-chemistry service.

 

 

What Are the Limitations of FFKM?

 

FFKM has four main limitations: cost (highest among elastomers), low-temperature flexibility (typ. −10 °C, brittle at lower temperatures), limited dynamic seal capability (high friction), and specific compound requirements for plasma resistance. Each limitation is addressable.

Limitation Mitigation

High cost Use FFKM only where required; FKM elsewhere

Low-temperature brittleness Use EPDM or silicone for cold service

High friction (dynamic) Use Kalrez 1050LF (low friction)

Plasma erosion Compound selection, low-duty plasma

For dynamic seal applications with frequent motion, FFKM is limited to < 1 m/s surface speed. For higher speeds, PTFE or metal seals are preferred.

 

 

Frequently Asked Questions

 

Q: What is FFKM chemical resistance?

A: FFKM is resistant to most concentrated acids (HCl, H₂SO₄, HNO₃, HF with compound selection), bases (NaOH, KOH, NH₄OH), solvents (acetone, IPA, toluene, NMP), and semiconductor plasmas (O₂, CF₄, SF₆, Cl₂, HBr) at elevated temperatures.

 

Q: Can FFKM withstand HF?

A: Yes, with proper compound selection (e.g., Kalrez 6375). Standard FFKM compounds may swell in HF; HF-resistant compounds are required.

 

Q: Can FFKM be used in acetone?

A: Yes. FFKM is resistant to acetone where FKM and EPDM fail.

 

Q: What is the temperature range of FFKM?

A: Standard compounds rated +200 °C continuous; high-temperature compounds (Kalrez 9500, Chemraz 555) rated +325 °C continuous.

 

Q: Can FFKM be used at low temperature?

A: FFKM has a glass transition around −10 °C and becomes brittle below that. For sub-zero service, EPDM or silicone are preferred.

 

Q: How does FFKM compare to PTFE?

A: FFKM is an elastomer with elastic recovery; PTFE is a rigid thermoplastic. FFKM is used for O-ring and dynamic seal; PTFE for rigid gasket.

 

Q: What is the best FFKM compound for halogen plasma?

A: Kalrez 6375 is the standard for halogen plasma service because of its broad chemical compatibility and halogen resistance.

 

Q: Does Hitron offer multi-chemistry FFKM compounds?

A: Yes. Hitron's Kalrez O-Ring family includes standard and multi-chemistry FFKM compounds for semiconductor wet + dry process service.

 

Q: Can FFKM seals be reused after chemical exposure?

A: FFKM seals are typically single-use, replaced at preventive maintenance. Reused seals may not provide reliable sealing due to compression set.

 

 

Conclusion

 

FFKM provides the broadest chemical resistance of any elastomer family, withstanding concentrated acids, bases, solvents, and semiconductor plasmas at elevated temperatures. Compound selection (Kalrez 4079, 6375, 9100, 9500, 1050LF) is driven by the specific chemistry, temperature, and mechanical requirements. For multi-chemistry service (wet + dry process), FFKM is the standard. Hitron's Kalrez O-Ring family covers the standard FFKM compounds for semiconductor wet and dry process service, with the Slit Valve Door family providing FFKM-sealed wafer transfer interfaces and the Product page listing the full chamber component range. For product range, certifications, and engineering support, consult the About Us and Contact Us pages.