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Reliability and long-life

Benefits of Parylene conformal coating
Reliability and long-life

Conformal coatings are commonly used to protect assemblies and devices. Several materials perform adequately, especially in applications that require minimal protection. These more common coatings are typically applied in liquid form by way of spraying, dispensing, brushing or dipping, and there is a wide range of equipment designed to handle these commonly viscous coatings. In addition to each material having its own method of application, each has its own curing requirements and a minimal coating thickness needed to perform the job.

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As modern devices are shrinking in size and increasing in complexity, they simply cannot take on the added dimension or weight that is inherent to many conformal coatings. In addition, leading-edge electronic assemblies are extremely small and contain many tiny inlets, vias and crevices, which simply cannot be reliably protected using traditional coating formulations.
What is Parylene?
Several properties help differentiate Parylene from other conformal coatings on the market. First, Parylene is not applied in the same manner as other coatings – it basically “grows” onto the surface it is protecting. The coatings are applied in a vacuum chamber via a vapor deposition polymerization (VDP) process. The process begins when the raw material dimer (granular powder-like substance) is loaded into the system and vaporized at approximately 150°C. The dimer vapor is then pyrolized at a temperature of 680°C into a monomeric gas. Finally, the monomeric vapor enters the ambient temperature deposition chamber where it spontaneously polymerizes on the substrate. The deposition is not line-of–sight so all sides of parts are uniformly impinged by the gaseous monomer, which results in a truly conformal, pinhole-free coating. Parylene polymerizes as a uniform, thin-film coating that conforms to all surfaces, edges and crevices of a substrate, including the interiors of multi-layer electronic packages.
Parylene adds virtually no dimension or weight to the surface it is protecting. Due to the coating being applied via vapor deposition, the coating penetrates into even the smallest of micron-size crevices, providing unmatched protection of the product, device or circuit. Additionally, because it is applied as a gas, it can be applied in an ultra-thin manner (coating thickness is typically measured in microns) and is lightweight.
Components to be coated are only required to have a reasonable vacuum tolerance. There are no solvents, catalysts or plasticizers involved in the coating process and, since Parylene deposition occurs at ambient temperatures, there are no associated cure stresses. These characteristics further differentiate Parylene as other materials may require catalysts, elevated temperatures or cure cycles.
There are several variants of Parylene commercially available today, but all coatings are part of the same unique polymer series and carry a similar list of basic benefits. Parylenes create a high dielectric, moisture and chemical barrier, offer UV and thermal stability, and provide a low coefficient of friction. Of benefit to medical device applications are Parylene’s inherent biocompatibility and biostability, and their ability to be sterilized.
  • Parylene N is a primary dielectric, exhibiting a very low dissipation factor, high dielectric strength, and a low dielectric constant invariant with frequency.
  • Parylene C has a useful combination of electrical and physical properties, plus a very low permeability to moisture and corrosive gases.
  • Parylene D has properties similar to Parylene C with the added ability to withstand moderately higher temperatures.
  • Parylene HT is particularly useful in more extreme high temperature applications (short-term exposures up to 450°C) and those in which UV stability is required. Parylene HT also has the lowest coefficient of friction and dielectric constant, and the highest crevice penetrating ability of the four variants.
  • Markets and Applications
  • For over 40 years, Parylene conformal coatings have provided protection to an array of devices and substrates, which are used in a host of applications and industries.
General Electronics: Parylene is used as a protective coating for a wide range of electronic applications, including circuit boards, sensors, MEMS, LEDs, testing pins, etc. From devices such as e-readers or mobile phones to water meters, household appliances, large outdoor video displays, street lighting and oil and gas applications, the coating provides reliable protection to ensure the long-life of electronics within consumer and industrial applications.
Automotive: As electronic content continues to grow in the automotive industry, even as the industry continues to advance into electric and hybrid vehicle technologies, the coatings are well suited to protect circuit boards, sensors, MEMS, gaskets and seals from exposure to chemicals, solvents and moisture. It also provides excellent UV and thermal stability.
Defense: Electronics components used in ground equipment, aircraft radar systems or unmanned aerial vehicles, among many other applications, must survive the harsh environments in which they operate. Qualified to MIL-I-46058C and IPC-CC-830 specifications, Parylene coatings offer reliable protection to these and many more defense applications.
Medical: Along with the moisture barrier and electrical properties required by electronic applications, the medical device market also requires biocompatibility and biostability and many end applications must survive sterilization. The coating meets all of these requirements. Parylenes N,C and Parylene HT comply with biological testing requirements for ISO-10993 and are USP Class VI certified, making them an ideal coating to protect components and devices, including electrosurgical tools, stents, pacemakers, cochlear and ocular implants, neurostimulation devices, catheters and endoscopic port seals, to name only a few. Parylene is also ideal for pharmaceutical applications such as prefilled syringes, needles and pharmaceutical containers. Aside from the barrier protection afforded by Parylene, the coatings possess excellent dry-film lubricity characteristics with coefficients of friction nearing those of PTFEs.
Conclusion
Parylene coatings can be applied to nearly any surface material, including metals, resins, elastomers, plastics, ceramics and glass- even many of the newest metals and polymer surfaces. Coating thicknesses range from a few hundred angstroms to several mils and is specific to each application. Whether engineers are looking to solve a problem on an existing application or are in the process of designing the next generation or a completely new device, These conformal coatings offer a host of beneficial properties to ensure reliability and long-life.
Current Issue
Titelbild EPP EUROPE Electronics Production and Test 11
Issue
11.2023
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