Accidentally discovered in 1947, by chemist Michael Szwarc, the polymer parylene originally bore his name, and was known for a brief period known as Szwarcite. Working to thermally decompose the solvent p-xylene at temperatures exceeding 1000 °C, Szwarc identified the monomer para-xylylene di-iodide as the only product resulting when para-xylylene was reacted with iodine.
Parylene has developed into one of the world’s most reliable conformal coatings, with uses for aerospace/defense, automotive, consumer, electrical/ electronic, medical, MEMS/nano-tech and numerous other products; it is especially well-regarded for use with printed circuit boards (PCBs) of all kinds. Among parylene’s numerous material uses as a coating for substrates composed of ceramic, ferrite, metal, paper, plastic, resin, and rubber; it provides surface protection from corrosion and outside elements. As a friction-reducing coating, parylene is especially adapted for use with specialized MEMS/nano-tech devices.
However, this seemingly simple word, describing a substance with multiple uses, is regularly misspelled.
All too often he words paralene and paralyne are mistakenly used for parylene.
The term paralene is incorrectly used when applied to conformal coating. Paralene is a component of the substance di-paralene, effective in vitro against many of the fungi causing systemic mycosis; although similarly spelled, it is a pharmaceutical component unaffiliated with parylene or any conformal coating functions.
The word paralyne is used incorrectly even more frequently when discussing conformal coatings. It has been repeatedly confused with parylene and its chemical vapor deposition (CVD) lamination processes, for coatings for items as diverse as automotive components, medical implants and paper. This is simply a case of bad research and substance misidentification, although the frequency of using paralyne incorrectly as the appropriate name for parylene is alarming; it appears abundantly, if erroneously, throughout biomedical literature, a condition Diamond MT and other reputable conformal coating firms take pains to rectify.
It is the substance parylene that is always used for CVD-generated conformal coating, despite any misspellings occurring in the literature. The other products simply could not provide suitable conformal coating performance of any kind.
Basic Uses of Parylene
After Szwarc’s 1947 discovery of parylene, reaction-yield remained low, generally under 5%, for nearly two decades. In 1965, William F. Gorham at Union Carbide developed a more efficient method that used thermal decomposition to deposit at temperatures exceeding 550 °C, considerably lower than processes initiated by Szwarc (1000 °C); green chemistry advantages, minimizing use and generation of hazardous substances, improved in vacuum below 1 Torr. The resulting conformal films were pinhole-free and chemically resistant, requiring no solvents, factors that expanded parylene’s product-uses.
A conformal coating’s primary purpose is to effectively cover and safeguard PCBs, other electronic assemblies and their critical components. They provide a protective shield against such external threats to performance as inclement weather, incursion of chemical solutions, or excessive vibration and impact. Parylene’s dielectric properties limit levels of signal interference that impede device function. Exceptionally light-weight, their micro-thin coatings add virtually nothing to a PCB’s overall mass, making them ideal for medical implants and MEM/nano-technology.
Parylene’s unique CVD-application process allows it to be used as a conformal film that uniformly covers and protects any component configuration. The first vapor deposited polymer ever discovered, parylene CVD offers 100% yield for unparalleled, if expensive, manufacturing efficiency. Biostable and hydrophobic, parylene provides a micro barrier impermeable above thicknesses of 1.4 nanometers; its film-uniformity adheres successfully to a device’s sharp edges, crevices, points, flat and exposed internal surfaces, usable within spaces as narrow as 10µ, and can coat interior elements through openings of just 1mm. In addition, parylene coating performs dependably under pressures, stresses and in environments that would be detrimental to liquid conformal coatings, such as acrylic, epoxy, silicone and urethane.
Depending on the specific use, parylene conformal coatings can be effective in the range of 0.1 - 76 microns' thickness, far finer than competing coating materials. Parylene also exhibits the following beneficial properties:
- excellent substrate adhesion/hydrophobic barrier protection,
- exceptional electrical insulation,
- high-level resistance to attack from fungi and solvents,
- low ionic conduction at coating-substrate interface,
- enhanced circuit/component efficiency through strengthened solder joints/circuit links/wire bonds,
- minimized loading in high frequency applications through low dielectric constancy,
- high tension strain,
- pinhole-free, micro-thin coverage, and
- a completely homogeneous surface, with thermal stability between -200° C to +125° C.
These properties assure the deposited films reliably resist the incursion of acids, bodily fluids, caustic solutions, dust, temperature extremes, water vapor, and numerous other contaminants or failure mechanisms. In addition to consumer and industrial products, conformal coatings have a wide range of aerospace, automotive, military, and medically biocompatible/implantable device uses.
But remember, the substance in question is PARYLENE; paralene and paralyne may sound the same, but are only misspellings of the real thing.
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