Why Use Parylene?
Technology is evolving. Devices are getting smaller and more complex. We want technology to help us live longer lives. We want electronics to go everywhere and we demand longer product life cycles. Engineers need to reinvent what’s possible using the best tools and technology. We see parylene as a tool that should be in every engineer’s toolbox to help advance technologies and to take products to the next level.
There are examples of parylene benefiting almost every industry. Sometimes it is used to enhance products and other times it is the sole fabrication option. Parylene is the most widely used vapor phase conformal coating. It is successfully used in applications ranging from implantable medical devices to satellites in outer space. Parylene protects electronic parts in order to allow products to be used in harsh environments with better reliability. A thin layer of parylene can be used to modify a surface and add dry lubricity. And parylene can act as a thin film dielectric layer in advanced micro devices.
As a material, parylene is a high-performance polymer coating with many superior properties. However, the unique benefits of parylene coatings are a result of the process by which they are deposited.
Molecular Deposition Advantages
Parylene coatings are applied as a vapor, molecule by molecule under vacuum. The deposition takes place at room temperature and the film grows evenly on all surfaces. This lets parylene get into tiny openings and crevices and to perfectly encapsulate parts. The molecular level of protection is unique from other coating types. The process is an environmentally-friendly, self-contained process that produces a highly cross-linked and pinhole-free coating that doesn’t use solvents and has no unwanted side reactions.
Parylene coating equipment applies a thin film to nearly every surface that can be put into a vacuum chamber. Coating services work with metals, plastics, ceramics, fabrics and more. Thickness can be less than 0.5 microns and up to several mills.
Vapor deposition is a powerful technology for surface engineering and thin film coatings. As parts get smaller and more complex, molecular deposition shines. Parylene is the coating of choice when quality and capability matter, even for layers that can be formed by other means.
Drawbacks of Spray and Dip Coatings
Typical conformal coatings are applied with a spray or dip process. For many technologies, the spray or dip application process can reduce product quality and limit the product design.
Common spray and dip conformal coating materials include acrylics, urethanes, silicones, polyimides, and epoxies. All of these coatings start as a liquid and are applied with a spray or dip process and then go through a curing process.
Conformal coatings serve several purposes:
- Protect devices from environmental electrical current, mechanical forces, chemicals, gas and/or moisture.
- Prevent current leakage, arcing and short circuits caused by humidity and contamination.
- Prevent corrosion and oxidation.
- Improve fatigue life of solder joints and wire bonds.
For many advanced technology applications, spray and dip coatings have limitations that either prevent them from being used or they restrict the engineer’s ability to make a better product.
Some of the common problems with dip and spray coatings include:
- The liquid is applied with force and the mass of the liquid can damage fragile components.
- Compared to a gas, a liquid is thick, inconsistent and contains micro-bubbles. The liquid cannot penetrate closely spaced components.
- In order for a liquid to be applied, solvents fillers and other chemicals are added. Some of these additives remain in the coating and reduce the purity. The chemicals continue to off-gas after the coating process.
- Liquid coatings have to be cured. The change in state takes time and introduces forces that can damage fragile parts. Curing also introduces harmful solvents into the environment.
The parylene vapor deposition process avoids all of the problems listed above. The unique benefits of parylene allow coating companies to provide enabling solutions at a reasonable cost.
Key Parylene Benefits Summary:
- Thin-film coating layer, typically 0.5 to 50 microns.
- Bio-compatible and implantable.
- Truly conformal and pinhole free.
- Deposits with uniform thickness on all surfaces.
- Dry film lubricity.
- Very high dielectric strength.
- Excellent barrier properties.
- Sterilizable with many common sterilization methods.
Molecular Deposition Benefits
Truly Conformal and Uniform Thickness
No Thermal Stress, No Cure Force
Chemically Pure and Homogeneous
Particle encapsulation and immobilization
Typical parylene coating thickness ranges from 0.5 microns to 50 microns. Thickness can be controlled in the micron range, regardless of geometry. This allows for high performance protection without taking up critical device space.
With thickness in the microns and density similar to air (~ 1.2 g/cm3), the additional weight added to your device is negligible
The molecular deposition process allows parylene to build up uniformly on all surfaces. It will evenly coat sharp edges, points, crevices, exposed internal surfaces and any complex shape. Because there is no liquid phase, there is no pooling or bridging between close features that is seen with liquid coatings.
Parylene is considered a green technology because there are no by-products or chemicals used that are harmful to our environment. The molecular deposition process doesn’t require any solvents for curing or any other harmful additives.
With liquid and spray coatings, small “pinholes” are created when microbubbles degas during drying. The pinholes create weak points that allow electrical current to leak and compromise the barrier layer.
The parylene deposition process ensures a complete pinhole-free coating because there are no microbubbles and no curing.
Tests have been performed to show completely pinhole-free coatings at thicknesses greater than 0.2μ.
This results in an extremely reliable coating, electrical insulator, cleaner electrical signals and a known barrier layer that will perform consistently over time.
Using spray and dip coatings on fragile devices typically introduces thermal stresses by heating up parts during coating and cooling them down during a cure phase. This temperature change can cause different materials to expand and contract at different rates. This causes cracks to form and bonding surfaces to come loose. In some cases, the coating process is leading to the failure of the device immediately or over time.
Parylene is deposited at room temperature so the coating is applied “stress-free”. Parts stay at room temperature throughout the entire process to help ensure the long term reliability of coated parts.
The room temperature, non-contact, deposition process enables parylene to add a layer of structure to fragile features. This can be the main use for the coating as a MEMS structural layer, or an added benefit when coating for other reasons.
The encapsulating support helps ruggedize devices to help them survive vibrations and other mechanical shocks. Parylene can strengthen delicate wire bonds by a factor of 10.
Parylene is ready for use immediately after it is deposited. There is no waiting. No cracking or settling during the cure process and no outgassing.
The parylene deposition process converts parylene from a pure dimer, to a gas, and finally to a solid.
Liquid-based coatings usually require reagents to promote the chemical reaction. However, after polymerization occurs, the catalysts need to be removed through a secondary process. It is common that some of the species remain behind. These residuals reduce the purity of the polymer film and can have effects on the coating properties.
Parylene is pure and does not require any reagents for a chemical reaction. The final product is a pure and homogeneous parylene film. There are no issues with leaching or outgassing. This results in a reliable coating that is free from any ionic contamination or possible leaching.
Fine particles of conductive dust can be hard to remove from parts because of their strong electro-static attraction. These particles can cause electrical shorts if they bridge wire bonds or conductive paths. A thin coating (2-5 microns) of parylene can be applied to immobilize particles and prevent electrical failures.
This benefit has been required by NASA in some applications to help ensure their system are reliable in space.
Parylene vapor that is under vacuum in the deposition chamber has high molecular activity. It is able to completely penetrate spaces as narrow 0.01mm. It has the ability to penetrate beneath and around closely spaced components.
For a tube, Parylene C will evenly coat a distance into the tube that is 5 times the diameter of the tube and 40 times the diameter for parylene N.
Parylene Property Advantages
In addition to the benefits from the deposition process, parylene is a high-performance polymer with special properties. The molecular arrangement for parylene is linear and crystalline. This creates benefits in strength, chemical resistance, electrical insulation, and stability.
No other material can be applied in such a thin layer and provide benefits equal to parylene.
Parylene Property Benefits
Biostable, Biocompatible and Implantable
Moisture, Chemical and Gas Barrier
Dry Film Lubricity
Hydrophobic (without modification)
Parylene has a long history of uses as a coating for medical devices. Parylene has been a key enabler for some of the most advanced, frequently used medical devices on the market.
Parylene is FDA approved for many applications and has a USP XXII, Class VI biocompatibility rating.
Parylene can endure common sterilization methods including ETO, hydrogen peroxide plasma, gamma radiation and steam.
Note that there can be limits for some medical device designs. Contact us to discuss your specific application.
Parylene is chemically insoluble, biologically inert, highly resistant to corrosion and has low permeability to gases and water vapor.
It offers impressive barrier protection from oxygen, moisture, chemicals, almost every solvent, salt spray, strong acids, caustic chemistries, harsh environments and bodily fluids.
All of this protection is achieved with a thin film coating to keep your product lightweight and compact.
The electrical properties of parylene C and parylene N are excellent. The dielectric strength and bulk/surface resistivities are high. The dielectic constants and dissipation factors are very low - better than most epoxies, silicones and urethanes.
These electrical properties allow parylene to work notably well for high-frequency applications.
Many applications use a thin film of parylene to act as an insulation layer between conductive parts and metal substrates.
See our properties page for a detailed list of parylene's electrical properties.
A nano-thin layer of parylene can be applied to surfaces to act as a dry lubricant. Parylene N has an especially low coefficient of friction to improve slipperiness similar to Teflon (PTFE).
It is also important to note that the static and dynamic coefficients of friction are the same. This means that it doesn’t take an initial start-up force to overcome the resistance from friction.
When parylene is deposited it has a hydrophobic surface. This means that liquids tend to bead up on the surface.
This can be the desired effect for many applications but sometimes a more hydrophilic surface is needed. For example, if glue or epoxy needs to be applied on top of the parylene surface, a more hydrophilic, or wettable, surface would help. VSI Parylene is able to modify the surface energy in many cases. Contact us to discuss your specific application.
Parylene is transparent and colorless. This allows parylene to be used for coating optical elements.
Parylene Standards and Certifications
Parylene coatings conform to MIL-I-46058C, IPC-CC-830B (listed as type XY)
FDA approved -- USP XXII, Class VI and ISO 10993 Standards.
No outgassing - NASA approved
Parylene’s benefits are numerous and many derive from parylene’s properties. For complete information of the electrical, mechanical, thermal, and optical properties of parylene, as well as information on gas permeability and a comparison of parylene to PTFE and other polymer-based coatings, please see our Parylene Properties page. New to parylene? Get an introduction here.