Frequently Asked Questions
What is Parylene?
Parylene is a common generic name for Poly-para-xylylenes. This material basically forms a plastic film when applied in a vacuum as a gas to target surfaces. The two most common types of parylene are referred to as: Parylene N and Parylene C
Parylene is applied at room temperature with specialized vacuum deposition equipment that permits control of the coating rate and thickness. The deposition process takes place at the molecular level as the chemical, in a dimer form, is first converted into a gas under vacuum and heat; then pyrolized to cleave the dimer; and finally deposited as a clear polymer film.
The material is applied at rates of 200 microns per hour. Coating thicknesses from 0.1 to 76 microns can be applied in a single operation. Typical coating thickness for circuit boards is 5 to 20 microns. For silicone and rubber components, much parylene coatings are applied in the 1 micron range.
When are Parylene Coatings used?
Parylene is used whenever a thin coating is desired that:
- Is pinhole free;
- Can encapsulate a substrate completely to protect it from environmental attack; or
- Is electrically insulating.
Parylene will conform to any surface that will not outgas in a vacuum environment, regardless of the complexity of the geometry. Parylene is applied in a gaseous state, so there is no chance for bridging, spotting or pooling as can happen with a liquid conformal coating. Parylene coatings also conform to MIL-I-46058 Type XY, IPC-CC-830B and USP Class VI, and ISO 10993 approved for use as a medical biocompatible and implantable material.
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Parylene Types
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Parylene Coating Service offers the two most widely used and commercially available Parylene variants, Parylene N and Parylene C. Each has its own unique electrical and physical properties.
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Parylene N
Type N or Natural, has the highest dielectric strength of the two commercial versions, and a dielectric constant value independent of frequency. It is able to penetrate crevices more effectively than type C because of the higher level of molecular activity that occurs during deposition. Parylene N is commonly used in high frequency applications because of its low dissipation and dielectric constant values. |
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Parylene C
Type C parylene differs chemically from Type N, having a chlorine atom on the benzene ring that results in a useful combination of electrical and physical properties including particularly low moisture and gas permeability. Parylene C deposits on substrates at a faster rate than Parylene N, and has a lower throw capability and an associated reduction in crevice penetration activity. |
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Other types of Parylene Coatings are available if it is necessary that they operate continuously in air temperatures greater than 125°C. However, the deposition rates for these higher temperature capability variants are significantly slower than those for Parylene N or C and the cost of application will increase proportionally. For the majority of commercial applications, utilizing Parylene N or C (depending on the detailed end use requirements) is the logical choice.
What are the common advantages of Parylene over other coatings?
- Hydrophobic, chemically resistant coating with good barrier for inorganic and organic media; strong acids, caustic solutions, gases and water vapor;
- Outstanding electrical isolation with high tension strain and low dielectric constant;
- A biostable, biocompatible coating with a long track record of FDA approval as a medical coating;
- Micropore and pin hole free coating at thickness levels of 0.2 µm and greater;
- Thin and transparent coating with high gap freedom of movement, which makes it suitable for use on complex arranged substrates and edges;
- Coating occurs at ambient temperature in a vacuum environment;
- Resistant to many solvents and corrosive agents;
- Completely homogeneous surface;
- Thermally stable from -200 °C to +125°C;
- Low coefficient of friction;
- Very low permeability to gases;
- High electrical impedance;
- Resistant to fungus and bacteria;
- Can be sterilized with ETO, Gamma Radiation or in an Autoclave;
Contact the PCS engineering department for assistance with the appropriate Parylene coating material selection for your application, as well as determination of the film thickness and substrate preparation requirements.
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