Parylene

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General structure of parylene. Where R 1 , R 2 , R 3 , R 4 and X are hydrogen: poly- p- xylylene

As Parylene a group are inert , hydrophobic , optically transparent , polymeric coating materials designated with a wide range of industrial applications. In addition to the hydrocarbon poly- p- xylylene (often referred to as parylene N ), halogenated polymers are also used.

The coating is applied in a vacuum by resublimation from the gas phase as a pore-free and transparent polymer film on the substrate . Practically every substrate material such as B. Metal , glass , paper , paint , plastic , ceramic , ferrite and siliconecoatable with parylenes. Due to the gaseous deposition, areas and structures can also be reached and coated that cannot be coated with liquid-based methods, such as B. sharp edges and points or narrow and deep crevices. Coating thicknesses of 0.1 to 50  µm can be applied in one operation.

properties

Parylene
Structural formula Parylene basic structure
Substituents X R 1 R 2 R 3 R 4
Parylene N H H H H H
Parylene C. H Cl H H H
Parylene D H Cl H Cl H
Parylene HT F. H H H H

Parylenes are hydrophobic , chemically resistant plastics with good barrier properties against inorganic and organic media, strong acids , alkalis , gases and water vapor. As a thin and transparent coating with high gap clearance, they are suitable for substrates with a complex design. Since parylene has no liquid phase, no edge alignment is formed. Parylenes have good dielectric properties with high dielectric strength and low dielectric constant . As a biostable and biocompatible coating, parylene have an FDA master file. From a layer thickness of 0.6 µm they are free of micropores and pinholes. The coating takes place without thermal stress on the substrates at room temperature in a vacuum . This process offers a very high level of corrosion protection and a uniform layer formation, which - depending on the parylene type - is temperature-stable up to 350 ° C (Parylene HT), mechanically stable and produces low mechanical stress, conditionally (Shore R80-R120; depending on the type ) is abrasion-resistant and does not cause outgassing. This surface can be activated by low pressure plasma or other adhesion promoters.

Manufacturing

Parylenes are produced by chemical vapor deposition . The starting material is p- xylene (1) (or halogenated derivatives ). This is evaporated and passed through a high temperature zone. A reactive [2,2] -paracyclophane (2) is formed, which breaks down to 1,4-quinonedimethane (3). The quinone dimethane polymerizes immediately on surfaces to form chain-like poly- p- xylylene (4).

Representation of poly-p-xylylene

Typical applications

Typical uses for parylene are:

  • conformal coating of electronic components for harsh environmental conditions (meets "MIL-I-46058C, Type XY" (this standard was set to "do not use for new designs" on November 30, 1998))
  • Electronics for the military (extension of shelf life, protection against environmental influences and operational contamination, e.g. salt water, oil, fuel)
  • Electronics for space travel (extension of shelf life)
  • dielectric coating (e.g. cores / coils)
  • hydrophobic coating (protection from moisture)
  • Barrier layers (e.g. for filters, membranes, valves)
  • Corrosion protection for metallic surfaces
  • Reinforcement of microstructures
  • Abrasion protection
  • Protection of plastic, rubber, etc. from harmful environmental influences
  • Reduction of friction (e.g. with guide wires for catheters)
  • biocompatible coating of medical implants (e.g. transponders for animal registration, biomedical tubes, heart implants)

Individual evidence

  1. ^ Arnold Willmes, Pocket Book Chemical Substances , Harri Deutsch, Frankfurt (M.), 2007.

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