The Parylene Deposition Process
Parylene derives many of its benefits through its unique vapor deposition process. Learn the details of parylene deposition 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.
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 can not 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 . Parylene dimer contributes to the process’s raw materials costs. 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.
Parylene is the name for a group of vapor-deposited poly(p-xylylene) polymers. Within the parylene group are different types of organic coatings with a polycrystalline or linear structure. Here is a brief description of the various parylene types.
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 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 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.
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.
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.