What is Parylene Coating?
Parylene conformal coating is a thin film coating technology used to improve the capabilities of leading-edge technologies. Applied as vapor, the coating layer perfectly conforms to complex shapes and provides complete and even coverage.
Product designers use parylene to waterproof electronics, add dry lubricity or enhance adhesion to other coatings. Parylene coatings are a popular choice in applications where reliability and performance matter most. Learn how VSi helps customers incorporate parylene technology.
What makes parylene unique:
- Ultra-thin coating, starts at 0.5 microns thick
- Exceptional moisture and chemical protection
- Thermal range from -270ºC through +200ºC
- Drug and hydrophilic coating adhesion tie-layer
- FDA approved for human implantable devices
- Dry lubricity comparable to PTFE
- Truly conformal barrier layer
What is Parylene Coating Used For?
Parylene has many benefits that can be customized to your specific application. We’ve selected the most common benefits below. If you do not see a benefit you are looking for listed below, please contact us to find out more.
Often a first consideration in selecting high value coatings for medical industries, parylene is an FDA approved material that meets USP Class VI and ISO 10993 biocompatibility requirements for use on human implantable devices. Standing the test of time, the use of parylene is well-documented in an increasingly wide range of medical coating applications over the past 40 years.
Parylene provides superior protection from moisture, corrosion, salt spray, solvents, airborne contaminants and many hostile environments. It is chemically inert, ultra-thin, pinhole-free and conforms to components evenly and consistently. Due to parylene’s unique molecular-level deposition, this high level of protection is achieved with 10% of the mass than spray or dip coatings.
Parylene enables the design of smaller, more compact electronics by providing protection from internal and external electrical interference due to its combination of high dielectric strength, low dielectric constant and very low dissipation factor properties. It is often used in implantable medical devices as parylene forms an electrical barrier between the device’s electronics and electrical signals produced in the body.
When applied as a sub-micron layer, parylene provides a lubricious surface that bonds completely to a variety of device substrates. Improving lubricity, without the risk of shedding particles, reduces the resistance force of of pushing catheters, guidewires or stents through restricted anatomy. The molecular deposition process produces a smooth, homogenous coating topography that remains flexible.
Parylene’s inert and biocompatible properties enable it to be an important bonding layer for drug-eluting medical technologies. Parylene acts as a release control agent when it applied between the metal or polymer substrate and pharmaceuticals. Additionally, the vapor deposition process allows complex shapes to be consistently coated with a high level of control.
Parylene’s completely-conformal properties are used to physically reinforce and add strength and rigidity to delicate connections on printed circuit boards (PCBs). Think of this as parylene welding. The combination of parylene’s crevice-penetrating ability along with its consistent coating thickness provide a protective “jacket” that greatly reduces failures caused by solder fatigue from thermal cycling and vibration, without board redesign.
Want to learn the ins and outs of parylene coating?
Check out VSi’s comprehensive eBook “The Complete Guide to Parylene Coatings.”
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What you’ll learn:
- Parylene benefits and applications
- How the vapor deposition process works
- Detailed material properties of parylene
- Compare parylene to other coatings
- Design guidelines
What is parylene coating used for?
Waterproof barriers help make sure critical electronics perform in a wide range of environments. Parylene offers unmatched protection from airborne contaminants, corrosion, chemicals, gases and moisture. It achieves this level of protection with 10% of the mass of spray or dip coatings.
Parylene has a very high dielectric strength compared to other materials. The ability to apply a very thin dielectric layer is helpful for many designs. As a result, parylene is often used to control the electrical path or eliminate arcing when space is limited.
Parylene acts as an adhesion layer when it is applied between a metal or polymer part and a top coating. Parylene’s biostability and chemical inertness make it a unique solution for bonding drug and hydrophilic coatings to drug-eluting devices or catheters.
A very thin layer of parylene applied to a part acts as a lubricating layer. Parylene’s low coefficient of friction is comparable to PTFE (Teflon). Compared to PTFE, PVP and silicone parylene can be a better choice if flaking and particulates are a concern. Dry film lubricity is important in the design of medical devices that interact with a patient vessels. Parylene is also used on common elastomers to reduce tackiness and improve cleanliness.
How is Parylene Deposited?
Parylene’s unique vapor deposition process provides many benefits. Learn the details of the parylene deposition process in the guide below.
Chemical Vapor Deposition
Parylene is deposited through the process of Chemical Vapor Deposition (CVD) which gives it many unique benefits compared to dip and spray coatings. Parylene films are “grown” as vapor deposits molecule by molecule in a room temperature vacuum chamber. Thin film deposition occurs directly on parts, anywhere the vapor reaches. Because the vapor is able to get in all the nooks and crannies, parylene thin film coatings are truly conformal.
The end result is a pinhole free coating without any by-products. Parylene protects the most complex structures at a microscopic level. It can encapsulate complex shapes and evenly cover sharp edges. The thin film is highly uniform, ranging from hundreds of angstroms to a hundred microns.
Unlike parylene coatings, liquid conformal coatings are not truly conformal, and tend to collect and pool in low crevices while pulling away from raised edges and sharp points. Bubbling, cracking, pinholes and orange peel are typical in liquid coatings.
The major benefit of parylene’s gaseous deposition process is its unique ability to penetrate and grow a thin, uniform coating molecule-by-molecule on surfaces that are simply unreachable by liquid coatings.
The Parylene Coating Process
The parylene coating process consists of four steps that make sure the coating properly adheres to the substrate and sections remain uncoated as needed.
Before we begin depositing parylene, we take a few steps to ensure success. When parts arrive, we perform an incoming inspection to make sure parts are in good condition and clean. After incoming inspection, we prepare the parts to be coated.
Most parts go through a parylene adhesion promotion step. This process encourages the parylene layer to adhere when deposited on the part substrate. We offers a variety of solutions to achieve the results you are looking for.
A-174 Liquid Silane Adhesion Promotion
During this process the parts are submerged in a series of liquid baths that rinse and modify the surface energy of the substrate. A-174 works well for a wide variety of surfaces, but it does have some limitations. Some products can’t be submerged in liquid and certain substrates require more suitable chemistries.
Plasma Adhesion Promotion
We can also incorporate plasma treatment to promote adhesion when a more robust adhesion is required or parts can’t be exposed to liquid. Plasma treatment, a weak version of plasma etching, can also be applied to parylene after parts have been coated to promote adhesion to silicone overmolding or epoxyon top of the parylene.
Many products are built with a combination of materials which can introduce adhesion challenges. VSi Parylene’s engineers have successfully solved complex adhesion challenges with custom designed solutions.
Next, any areas that need to remain free of parylene are masked and sealed so that parylene cannot deposit on the masked area. The masking step is a very important step for many applications. VSI Parylene has developed novel techniques that make us the industry leader for precise, small part applications.
After all the above steps are taken, parts are then carefully fixtured into the vacuum deposition chamber.
After the parts are prepared and placed into the chamber, a calculated amount of dimer is loaded into the vaporizer. Dimer, or paracyclophane, is the solid white granular powder that is the source material of parylene, contributing to the raw materials cost of the process.
The system is then sealed and put under vacuum. There is a start-up period we call “chilling and grilling”. The cold trap needs to “chill” to its cold setpoint. The furnace and gauge heaters need to “grill” to their hot operating temperature. The pressure in the system needs to reach the set base pressure. The time needed to reach the vacuum base pressures depends on the amount of outgassing from the chamber load and the size of the chamber.
The thin film deposition process ends when all of the loaded dimer has been vaporized. The coating process is complete but there are a few important steps remaining.
No cure time means that parts can be removed from the chamber immediately. First the coating thickness is measured. The parylene thickness layer is measured on sample coupons placed throughout the deposition chamber. The sample coupons provide a very repeatable and easy way to measure the thickness.It is also possible to measure the coating thickness directly on parts in some applications through spectral reflectance.
After the thickness has been measured, the parts are carefully removed from the coating fixture. If the application requires that some areas do not have coating, the sealed masking will be removed. For some applications parylene can be ablated or removed with other methods.
Finally, parts are inspected to ensure they meet customer specifications. The inspection requirements vary depending on customer’s workmanship standards. It is common to inspect the quality of parts under a microscope. Once the inspection is complete, the parts are prepared for shipping.
Though many factors go into determining the final cost of adding parylene in your production process, there are three main factors to consider: coating thickness, masking complexity and component size
Impacts: Machine Hours
Optimal coating thickness is determined by your specific application and benefits desired. As coating thickness increases, additional time inside the deposition chamber is required increasing total machine hours.
Impacts: Labor Hours
Masking complexity is determined by your product’s design and operating requirements. As complexity increases, operators must take more time to process each individual part increasing total operator hours.
Size of a Component
Impacts: Batch Size
Parylene coating is applied inside a vacuum deposition chamber of fixed, physical size. As individual component size increases, total quantity of product’s coated decrease reducing batch size.
Parylene Type C
Parylene C is the most popular parylene type because it provides a combination of barrier and dielectric properties while also having cost and processing advantages.
Parylene C is produced from the same raw material as parylene N but substitutes a chlorine atom for one of the aromatic hydrogens. This gives parylene C very low permeability for better protection from moisture, chemicals and corrosive gases.
Parylene C deposits much faster than other parylene types which allow a thicker layer to be applied with less machine time.
Parylene C is the best choice for:
- Implantable medical devices.
- Pinhole-free barrier layers to electronics or materials from harsh environments.
- Encapsulating electronics to provide dielectric protection.
- Meeting IPC-CC-830 or MIL-I-46058C standards.
Parylene Type N
Parylene N is the base structure of the parylene group. Parylene N has excellent dielectric properties. It has a very low dissipation factor, high dielectric strength, and a low dielectric constant that does not change with frequency.
Parylene N is more molecularly active than parylene C during the deposition process. An advantage of the higher activity is increased crevice penetration, which allows parylene N to get farther into tubes and small openings. A disadvantage of the higher activity is slower deposition rates which increase the machine time and cost for thicker layers.
Parylene N is the best choice for:
- Dry lubricity.
- High frequency/RF applications because of its low dissipation factor at high frequencies.
- Applications that require high penetration.
Parylene Type F
Parylene F fills a niche because it is capable of higher operating temperatures and is more resistant to UV than parylene C or parylene N. Parylene F also has very good dielectric properties and good crevice penetration.
The chemical structure of Parylene F has four fluorine atoms on the aromatic carbons. Parylene F has a slower deposition time and the raw material is more expensive.
VSI Parylene offers parylene F for applications that require the increased temperature and UV resistance parylene F offers.
Parylene F is the best choice for:
- Applications with higher temperature requirements.
- Applications that require UV resistance.