Parylene's deposition process is unique among conformal coatings. Unlike others that start as a liquid, get deposited and dry, it starts as a solid. Parylene coating equipment turns it into a vapor, where it then deposits onto the substrate. This unique four-step method poses some challenges but also brings real advantages.
Applied mechanical processes stimulate the binding force between surface molecules required for parylene adhesion to substrates, which is essential to both good parylene performance and assembly/component functionality.
Parylene is considered by many to be the ultimate conformal coating for protection of devices, components and surfaces in electronics, instrumentation, aerospace, medical and engineering industries. Parylene is unique in being created directly on the surface at room temperature.
Whenever implantable devices come into contact with the human body, long term protection against body fluids, enzymes, proteins, and lipids is vital. Bio-medical surfaces typically require coating to protect from moisture, chemicals, and other potentially harmful substances.
Parylene (XY) conformal coatings are known and recommended because of their many beneficial performance characteristics. They provide uniform, pinhole-free protective films with excellent barrier/dielectric/insulative properties, able to conform to virtually any substrate configuration.
Liquid Teflon’s corrosion resistant qualities are well documented; repelling nearly everything, the bond that exists between its carbon and fluorine atoms is so strong, the substance is nearly bullet resistant.
Because of parylene's strength, for example, many of the methods used to remove or repair other conformal coatings won't work. You can't simply submerge parylene in a solvent like you might with an acrylic-coated component, for instance. Parylene isn't completely impervious to removal tactics, though. Focused heat, mechanical, and microabrasion methods can all be effective means of parylene removal.
Whether the application is a medical device, a printed circuit board (PCB), or a light-emitting diode (LED), a parylene conformal coating is typically applied to protect the product. Sometimes, however, the product actually has to be protected from the parylene conformal coating—or at least parts of it do.
Parylene is often applied to substrates or materials where there is no room for any voids in the protective coating. These materials are likely to be placed in harmful chemicals, a moisture packed environment, or even the human body. These are often mission critical devices which can not allow any environmental factors to alter their performance. Whenever these devices need this stringent level of protection from the elements, parylene is the only logical choice.
In addition to cracking, a range of associated issues may interfere with successful coating of parylene films. Because it is applied via CVD, parylene generates a structurally continuous film covering a PCB or similar assembly. In CVD, the interaction of vapor-phase chemical reactants formulate a non-volatile solid film on a substrate, useful for a variety of applications like corrosion resistance, erosion defense, and high temperature protection.
Applied through chemical vapor deposition (CVD), parylene penetrates deep within substrate surfaces, generating a level of assembly security surpassing that offered by liquid coatings such as acrylic, epoxy, silicone and urethane. Yet, although XY is applied in a vacuum, it’s capacity to provide these extraordinary qualities does not exist in one.
NASA-STD 8739.1 is the Workmanship Standard for Polymeric Application on Electronic Assemblies, which describes NASA’s technical requirements, procedures, and documenting requirements for staking, conformal coating, bonding, and encapsulation of printed wiring boards and electronic assemblies.