Is Parylene a Conformal Coating?

If you have been told that Parylene is not a conformal coating because it is not applied in liquid form, that is a misconception. Parylene has consistently established itself as the ultimate conformal coating for a variety of reasons, including:

• Absence of catalysts/initiators during polymerization
• Exceptional material purity, without ionic contamination
• Completely pinhole-free, chemically-inert barrier coating
• Dielectric properties (reliable dielectric strength and high-frequency capacities)
• High bulk/surface resistance
• Complies with USP Class VI Plastics requirements, MIL-I-46058C and IPC-CC-830B
• Film penetration of areas as minute as 0.01mm
• High stress-free tensile strength
• Low permeability to moisture and gases
• Dependable solvent and thermal endurance (-200ºC to +200ºC)

Parylene’s relative superiority is largely based on its unique application method.

Parylene Chemical Vapor Deposition

Liquid coatings, including acrylic, epoxy, silicone and urethane, are the main alternatives to Parylene. While each offers dependable conformal film protection for specific applications, none match Parylene’s surface uniformity, versatility and long-term durability. Liquid coatings use brush, immersion (dip) or spray methods to apply wet coatings to substrate surfaces. Even expert application can result in pooling of the wet film on or along the component’s contours, as well as bridging, dripping or uneven surface areas that ultimately interfere with the coating’s performance and durability.

In contrast, Parylene’s specialized chemical vapor deposition (CVD) converts raw, powdered Parylene dimer into a gaseous monomer, bypassing the need for an intermediate liquid stage. The process is implemented in a vacuum chamber. The Parylene dimer is placed in the vaporizer and heated to temperatures between 100ºC and 150ºC. At this stage, the solid-state Parylene undergoes a molecular transformation into vapor. Subsequently, the process temperature needs to steadily rise to 680ºC, causing the gaseous molecules to break down into monomers.

Drawn by vacuum onto the substrate surface one molecule at a time within the coating chamber, the vaporized Parylene penetrates deeply into the substrate at approximately 25°C. This process allows the Parylene to reach areas that are often inaccessible or inadequately covered by liquid materials. During the final deposition phase in the cold trap, temperatures are lowered to -90ºC to -120ºC to eliminate any residual Parylene materials from the substrate.

In comparison, liquid coatings adhere only to the surface of covered substances. Restricted to the substrate’s surface, they lack Parylene’s ability to deeply penetrate the substrate and enhance film adhesion and performance overall.

Parylene’s deposition process results in a truly conformal, structurally continuous, pinhole-free coating that envelops and protects component topographies characterized by:

• Crevices
• Exposed internal surfaces
• Sharp edges
• Other surface irregularities to a degree far exceeding liquids

Eliminating coating voids that are common with wet material application enhances Parylene’s functionality for various printed circuit boards (PCBs) and related components. This quality is valuable for industries such as medical devices, commercial electronics, automotive systems and military/aeronautics services (DoD and NASA).

Micro-electromechanical Systems (MEMS)/Nanotechnology

Compared to liquid coatings, Parylene’s ultra-thin film thickness is unrivaled. Using CVD processes, it uniformly coats surfaces that are hard to reach with wet technologies, even penetrating spaces as narrow as 0.01 mm. This results in a seamless layer that is devoid of pinholes and impermeable to anything larger than 1.4 nanometers (nm). Such high-level MEMS/nano protection cannot be achieved with liquid materials.

Biocompatibility

Parylene’s MEMS/nano capabilities, paired with its outstanding USP Class VI biocompatibility, make it an ideal choice as a coating for various medical device applications, particularly implants. Its thin coating layers facilitate placement into intricate internal spaces within the body. Additionally, Parylene’s superior dry-film lubricity not only aids in implant positioning but also enhances its utility as a vehicle for drug delivery. Critical medical devices like cardiac-assist devices (CADs), catheters, electrosurgical tools, needles and stents greatly benefit from the application of Parylene conformal coatings.

Conclusion

In conclusion, Parylene’s unique chemical vapor deposition process sets it apart as the ultimate conformal coating solution. Its unparalleled ability to provide pinhole-free, deeply penetrating protection makes it ideal for various industries, including medical devices and electronics. With its exceptional biocompatibility and durability, Parylene stands as a reliable choice for applications requiring precision, reliability, and long-term performance.