Chemical Seal: Chemical Compatibility

Elastomers can swell and/or degrade in chemical seal environments through reactions with the polymer backbone and cross-link system, or by reactions with the filler system. In the semiconductor industry, this degradation can be seen in increased contamination and reduced seal life.

Polymer Backbone and Cross-link:

• Polar Attack
• Nucleophilic Attack-main mechanism for cross-linking. However, when it occurs in chemical media, it may lead to excessive cross-linking and embrittlement.
• Dehydrofluorination-attack resulting in the formation of unsaturated bonds on the fluorocarbon backbone. It can be caused by the attack of primary and secondary aliphatic amines.

Filler System:

• Oxidation—degradation of carbon black fillers
• Chemical Attack—i.e., HF acid attack of silica fillers

Special Considerations:

• Contamination
• Particle Generation
• Elemental Extractables
• Residual Gas Contamination

Special Chemical Environments:

• Plasma Resistance
• Vacuum—volatile condensable material
  (VCM) 125°C 10^-6 Torr JPL

Test Methods:

• ISO 1817 (Liquids)
• ASTM D471, D1460, D3137 (Liquids)

Volume Swell

The most common measure of chemical compatibility for a chemical seal is volume swell. The following formula is used in reporting volume swell measurements. This takes into account dimensional changes in all three dimensions, and is more relevant than specific dimensional change readings for a chemical seal.