Parylene is a transparent polymer that offers uniform and pinhole-free conformal coatings for printed circuit boards, medical devices, and microelectronics. Varieties of parylene are made available through a modification of the molecular structure of para-xylylene (Parylene N, C, D, and F-AF4, and F-VT4). Each modification results in a set of material properties that are applicable in different service conditions.

Parylene conformal coatings are highly reliable and are highly sought after in applications such as military sensors to medical implants. Because, parylene coatings are colorless (transparent), thin (micro-scale) and uniformly deposited all over the target surface they are hardly visible to the naked eye. However, there are methods to detect or test the quality of the coatings that are designated by standards (MIL-STD, ASTM). These standards test coatings for the encapsulation properties of Parylene conformal coatings depending on where they will be used.  Leakage current and accelerated lifetime tests under different conditions (salty water, temperature, etc.)

Implications of Parylene Coating Thickness:

Parylene is a transparent polymer offering uniform and pinhole-free conformal coatings. Different varieties of parylene (Parylene N, C, D, AF4, and F) formed by a modification in their molecular structure. Each modification results in a set of material properties that are applicable in different service conditions. The basic type of parylene derivatives is the Parylene N (poly-para-xylylene) monomer.

A natural process, corrosion enacts chemical/electrochemical reactions that degrade and gradually destroy materials or components within a functional environment.  The outcome can be dangerous and costly to repair.  

Parylene (XY) polymers provide robust, dielectric, micron-thin conformal coatings for a considerable range of electronic devices, most prominently printed circuit boards (PCBs).  XY’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

 Used as moisture and dielectric barriers, polymer parylene (p-xylylene/XY) coatings are conformal and pinhole free.  Applied by a unique chemical vapor deposition (CVD) method, parylene penetrates beneath substrate facades, simultaneously attaching above surfaces at the molecular level.  CVD generated films cover crevices, exposed internal regions, points and sharp edges uniformly, without gaps or breaches.  Compared to liquid coating materials – acrylic, epoxy, silicone and urethane -- XY film layers are micron-thin, enhancing their utility for microelectricalmechanical systems (MEMS) and nano technology (NT). 

For conformal coatings, elongation is a measure of material ductility -- a specific coating's ability to undergo significant plastic deformation before rupture.  A coating’s yield elongation is the maximum stress the material will sustain before fracture.  Thus, computed parylene (XY) elongation measurements represent the total quantity of strain the conformal film can withstand before failure.  While elongation is equal to a material’s operating failure strain, it has no exclusive units of measurements.  Typically,

Parylene (XY) conformal coatings are applied to substrate materials through a specialized chemical vapor deposition (CVD) process that completely eliminates the liquid phase of wet coatings.  No initiators or catalysts are involved in CVD polymerization, which synthesizes truly conformal protective film in-process.  This is in stark contrast to wet coating materials such as acrylic, epoxy, silicone and urethane, which are synthesized prior to application via, brush, dip or spray methods.  Wet during application, liquid-coated substrates requiring further drying and curing.

Parylene:  Properties and Processes