Crevice Penetration of Parylene

Parylene provides a robust, dielectric, micron-thin conformal coating for a considerable range of electronic devices, most prominently printed circuit boards (PCBs). Parylene’s unique chemical vapor deposition (CVD) application method synthesizes in-process, depositing gaseous Parylene deep into a substrate’s surface. CVD occurs on a molecule-by-molecule basis, conforming to all underlying contours, regardless of shape or position, to the nanometer, if necessary. Pre-synthesized liquid coatings lack many of Parylene’s performance properties, having far less ability to successfully and conformally penetrate crevices in the substrate.

Additional CVD advantages include:

• Room temperature processing, allowing stress-free coating of even the most delicate components
• Gaseous molecules flow everywhere inside the coating chamber, coating under parts, inside small crevices and semi-sealed areas
• Sub-surface penetration seals crevices and irregular, tightly-confined areas, while forming an additional layer of conformal protection
• Micro-thin films coat exceptionally confined topographies, without forming bridges, dripping or running like liquid coating materials

Although there are two basic kinds of Parylene dimer — C and N — other formulations exist – including D, ParyFree^® and Parylene HT^®. Each displays specified performance metrics, characterized by different electrical and physical properties.

Parylene C is used more frequently than any other XY variety. It offers better performance across most metrics, generating exceptional protection from corrosive gases, due to low chemical, moisture, and vapor permeability.

Parylene N is the base structure of the Parylene group, offering a higher dielectric strength than other types. In addition, it penetrates crevices and other cracks or gaps in substrate surfaces more capably than the others. Type N does this because enhanced molecular activity occurs during CVD, in comparison to the remaining XY varieties, allowing more efficient coating of relatively deep recesses, blind holes, tubes and small openings.

Parylene HT has the highest penetrating ability, as well as the lowest coefficient of friction and dielectric constant. It has the highest temperature rating of all the Parylenes and also withstands ultraviolet light.

CVD processes convert powdered Parylene dimer into a vapor; the resultant coating substance responds with reliable conformability to surface geometries, including, crevices, hidden areas, points, sharp edges  and exposed internal surfaces.

Only Parylene offers this level of adaptability to highly complex coating problems, generating precise conformance to substrate topography without bridging or pooling. Applied in micron-thin layers, Parylene’s pinhole-free coverage penetrates and coats complex surfaces to a degree impossible with liquid conformal film materials.

Ultimately, CVD is responsible for Parylene’s exceptional crevice penetration. Since the film is formed as a vapor from a molecular state, and deposits on a molecule-by-molecule basis, it readily adapts to the precise configurations of substrate topography, accommodating and filling crevices and fissures in the surface. In any case, the gap is filled with a durable, micron-thin Parylene conformal film, regardless of surface complexity.