Parylene Vapor Deposited Conformal Coating

Parylene conformal coatings are applied at surrounding temperatures with specialized vacuum deposition equipment. Parylene polymer deposition takes place at the molecular level, where films essentially ‘grow’ a molecule at a time on the surface being coated (See Figure 1).
A solid, granular raw material, called dimer, is heated under vacuum and vaporized into a dimeric gas. The gas is then pyrolyzed to cleave the dimer to its monomeric form which is a molecule of low molecular weight capable of reacting with identical or different molecules of low molecular weight to form a polymer. In the ambient temperature deposition chamber, the monomer gas deposits on all surfaces as a thin, transparent polymer film.
Because Parylene conformal coating is applied as a gas, the coating penetrates any crevices and tight areas on multi-layer components, providing complete and uniform encapsulation (See Figure 2). Optimal thickness of the polymer coatings is determined based on the application and the coating properties desired. While Parylene coatings can range in thickness from hundreds of angstroms to several mils, a typical thickness is in the microns range.
Substrate Material: Optimal adhesion of Parylene conformal coating to a wide variety of substrates which are materials which provide the surface on which something is deposited or inscribed, for example the silicon wafer used to manufacture integrated circuits.
Substrate Preparation: One of the defining characteristics of Parylene conformal coating is its ability to coat all surfaces, including deep into multi-layers and crevices. All surfaces in the deposition chamber are coated with Parylene, unless technicians carefully protect, or mask, any areas that are not to be coated.

The parylene polymers are deposited from the vapor phase by a process which in some respects resembles vacuum metalizing. Unlike vacuum metalization, however, which is conducted at pressures of 10-5 torr or below, the parylenes are formed at around 0.1 torr. Under these conditions the mean free path of the gas molecules in the deposition chamber is in the order of 0.1 cm. Therefore, unlike vacuum metalizing, the deposition is not line-of-sight and all sides of an object to be encapsulated are uniformly impinged by the gaseous monomer. This is responsible for the truly conformal nature of the coating. The process consists of three distinct steps as shown in Figure 1.
Figure 1
Since parylene is non-liquid, it does not pool, bridge, or exhibit meniscus properties during application. No catalysts or solvents are involved, and no foreign substances are introduced that could contaminate coated specimens.
In contrast to parylene, the thickness of liquid coatings is related to viscosity, working temperature/humidity, and application process (spray or dip), and can only be controlled to a tolerance of approximately +/- 50% of final thickness.
Parylene thickness is a function of the amount of vaporized dimer and chamber dwell time and can be controlled accurately to within +/- 5% of targeted thickness for most typical applications.
Figure 2
coating comparison graphic
Parylene Engineering provides Parylene Conformal Coating Services and consultation for several industries including, industrial applications, aerospace, avionics, commercial, medical, and the defense electronics industries.
Parylene Engineering was established in 1995 as a parylene service provider serving the aerospace industry. Since then, the company has grown to serve the Aerospace, Space, Medical, and commercial industry. The parylene coating process involves several Mil specs including MIL-I-46058C, Typically, the parylene monomer is deposited on substrates as a gaseous molecule that polymerizes in a vacuum environment. The end result is a pin-hole'-free parylene film. The film itself possesses various mechanical, thermal, and dialectical properties.
A Poly-para-Xylylene coating film formed by the chemical vapor deposition (CVD) process. The coating film is completely pinhole free and the film thickness can be uniformly controlled in the micron range to conform to any irregular shape, whether it has a sharp edge or a complicated internal surface without any thermal stress.
Parylene is a conformal protective polymer coating material utilized to uniformly protect any component configuration on such diverse substrates as metal, glass, paper, resin, plastic, ceramic, ferrite and silicon. Because of its unique properties, Parylene conforms to virtually any shape, including sharp edges, crevices, points; or flat and exposed internal surfaces.
Parylene provides exceptional protection for the most extreme environmental conditions. This polymer is called out as "Type XY" coating in the MIL specs such as MIL-I-46058C, and IPC-CC-830. Parylene is unique as it is deposited through a vacuum deposition system, as gaseous molecules capable of providing a pin-hole free film at 3 microns thickness. This method of application yields a true conformal film complexion that contours all surfaces, exposed or hidden. Further, the thickness of the Parylene film could be very tightly controlled due to this unique method of deposition.
The Parylene film is chemically inert, no acid or alkaline material will attack it in any significant manner. The FDA has approved the Parylene film for human implantable devices. The Parylene film possesses superior dielectric properties, approaching 8000 volts for 1 mil thickness.
Usages for the Parylene coating includes, implantable devices, fish tags, circuit boards (SMT, Thru-hole, or mixed technology) sonar applications, ultrasonic applications, surgical devices, and elastomers. The Parylene coating process involves changing the molecular structure of the Parylene dimer into a monomer, then depositing monomers at room temperature onto the substrate to form the polymeric chain of the Parylene film.
Parylene coatings are completely conformal, of uniform thickness and pinhole free. This is achieved by a unique vapor deposition polymerization process. The advantage of this process is that the coating forms from a gaseous monomer without an intermediate liquid stage.  As a result, component configurations with sharp edges, points, flat surfaces, crevices or exposed internal surfaces are coated uniformly without voids.
Parylene has no curing cycle, unlike other conformal coating materials. Once deposited, it is ready to go to work.
Parylene has chemical resistance similar to Teflon. It resists attack and is insoluble in all organic solvents up to iS00C and is resistant to permeation by most solvents with the exception of aromatic hydrocarbons. Since Parylene coating is a high molecular weight, linear, crystalline polymer having an all carbon backbone without any oxygen, nitrogen, or sulfur atom links in the backbone it is hydrophobic. This carbon backbone, coupled with its substantial crystallinity, makes Parylene quite stable and highly resistant to chemical attack.