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The Electrical Insulating Benefits of Parylene
By Dave Pribish, General Manager, Para-Coat Technologies W
hen looking for a protective coating in the medical, aerospace, automotive, military, and commercial markets, parylene has
been a trusted choice for more than 50 years. Pary- lene’s unique blend of mechanical, thermal, barri- er, and chemical attributes make it one of the most well-rounded conformal coating materials. Specifi- cally, parylene’s electrical properties have broad- ened its reach to projects that may not have been identified in the past.
Common Forms of Parylene The three most commonly used types of
parylene are denoted N, C and D. Parylene N provides particularly high dielectric strength and a dielectric constant that is independent of frequency. Because of its high molecular activity during deposition, parylene N has the highest penetrating power and is able to coat relatively deep recesses and blind holes. Its low dissipation factor and dielectric con- stant suit high-frequency substrates where the coating is in an electromagnetic field. Parylene C has a chlorine atom added to
the parylene N benzene ring, which gives it an excellent combination of electrical and physical properties, including a low perme- ability to moisture and corrosive gases. Pary- lene C deposition is substantially faster than parylene N, and therefore, its crevice pene- trating ability is reduced, when compared with the more active parylene N molecule.
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Parylene D has two chlorine atoms added to
the benzene ring. This form has a higher degree of thermal stability than parylene N or C, but has the lowest crevice penetration of the three.
Application Parylene is applied using specialized vacuum
deposition equipment to achieve an extremely uni-
form, pinhole-free film of coating beginning at roughly 0.2 mil (5 µm). The material’s unique properties and applica-
tion process include precise conformance to sub- strate topography and the ability to penetrate and coat complex surfaces. The lack of pinholes helps Parylene prevent
electrical arcing and tin whisker formation. Pary- lene’s barrier properties also protect against conductive contamination material that can lead to electrical shorts. Parylene does not conduct electricity,
which is very important for a thin film that coats and separates conductive areas on elec- tronics and other devices. The insulating properties of parylene in-
crease with thickness. Both parylene types have excellent dielectric strength, but pary- lene C is superior to N at thicknesses of 0.2 mil (5 µm) or fewer. At the 0.2 mil (5 µm) thickness range,
parylene N begins to exhibit greater dielectric strength, withstanding voltage up to 7,000 V/mil (276 V/µm) at 1 mil (25.4 µm) thickness. Parylene’s electricity-blocking properties can be dialed in by adjusting the thickness of the coating, while still offering the other protec-
tive properties of the material. Contact: Para-Coat Technologies, Inc.,
Parylene N coatings provide
high dielectric strength and a constant independent of frequency.
Adjustable SMT Machining Services Ful l Process Carrier
17 Johns Street, Johnstown, PA 15901 % 814-254-4376 E-mail:
dpribish@pctcc.com Web:
www.pctcc.com r
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September, 2020
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1 Gwinnup Road • Blairstown, NJ 07825 Phone: 908.362.5588 • Fax: 908.362.5115
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