Parylene Coating Blog by Diamond-MT

Nano Coating vs Parylene

Posted by Sean Horn on Fri, Feb 24, 2017 @ 08:00 AM

Although its basic component is remarkably small – with 25,400,000 nanometers included in just one inch(!!) -- nanotechnology encompasses a growing, interdisciplinary field with an unlimited future.  Nanowires and nanotubes are used in transistors for printed circuit boards (PCBs) and associated electronic assemblies.  Bio-nanobatteries, capacitators, LCDs, and microprocessors represent just a few nano-applications, which include uses for aerospace, agricultural, automotive, consumer, industrial, medical, military and oceanic products. 

Nano coatings can also be applied to a wide variety of substrates, like ceramics, glass, metals, polymers, and even other nano coatings.  They impart corrosion resistance andPercenta-Nano-coating.jpg hydrophobic/oleophobic properties that enhance the PCB’s conductive/insulative properties.

Uses of Nano Coatings

Conformal coatings provide PCBs, and a vast spectrum of components/devices, with sufficient protection from moisture and contaminants to assure their functionality under stressful operating conditions.  In comparison to liquid coatings and parylene, nano coatings represent a viable alternative for safeguarding these devices. 

Like other electronic assemblies, nano components require protection during operation and storage.  Because of their microscopic size, nano coatings are, at first glance, the optimal protective covering choice for nano devices.  That is particularly the case in comparison to liquid conformal coatings – acrylic, epoxy, silicone, and urethane.  The film thickness required for wet coatings to provide effective protection is too great for nano devices, essentially defeating the advantages of their exceptionally minute proportions by interfering with their function.  

In Comparison to Parylene

To be effective, coating thicknesses/coverage for both nano and parylene coatings need to demonstrate the following properties:   

  • Complete film homogeneity/substrate adhesion.
  • Coverage of specified PCB/assembly areas only.
  • Absence of surface blisters, fractures or other conditions that might affect coatings’ sealing competence or assembly operation.
  • Freedom from bubbles, cracks, foreign material, peeling, voids, or wrinkles that expose PCB/assembly components or conductors, or violate specified electrical clearances.

Unlike liquid coatings, parylene has been shown effective for most MEMS/nano applications, even though its conformal films are considerably thicker than those generated by nano technology.  Nano coatings dry to a thickness of 100 – 5,000 nanometers (0 – 0.0002 inches).  In contrast, parylene coatings typically measure 0.000394 - 0.00197 inches.  Statistically, the parylene measurements are significantly larger; parylene’s smallest coating thickness (0.000394 in.) is nearly twice as substantial as the largest nano coating (0.0002[00] in.).  However, the thicknesses of both coatings are miniscule; parylene’s remain sufficiently small for effective MEMS/nano conformal coating. 

Also, parylene’s utility is more apparent for larger-scale PCBs and related products.  Depending on the particular application – its function and size – parylene easily matches nano’s uses for a wide range aerospace, automotive, consumer, defense and medical purposes.  And while certain nano coatings can generate no-mask solutions that deliver the benefits of conformal protection against water/moisture, they often lack the impact-resistance and corrosion defense of parylene.  This can be a primary production consideration.  Nano’s superior capacity for coating rework is largely negated by its comparative lack of resilience and strength under the same range of operating circumstances common to parylene coatings.   

Other production considerations involve application.  Nano coatings can be applied through wet dip or atomized-spray methodologies.  Wet applications are cost-effective, since they can be employed:

  • without investment in costly capital equipment for vacuum-based or plasma manufacturing, while
  • eliminating production-quantity restrictions caused by both batch processing inherent to vacuum/plasma procedures, and
  • the need for masking operations.

Unlike liquid coatings, nano post-application curing is generally limited to air drying, when it needs to be enacted at all. 

While nano coatings can now be readily applied by conventional liquid methods, their application via chemical vapor deposition (CVD) and single-step plasma deposition techniques is very like parylene.  Parylene CVD applies gaseous parylene deep into substrate surfaces in a specialized deposition chamber.  The process is expensive, and production batches small compared to liquid methods, but the resultant films offer significant advantages:

  • biocompatibility/bio-Stability (sterilization possible),
  • complete surface conformability,
  • low dielectric constant,
  • optical clarity,
  • pinhole/stress-free application,
  • reliable dielectric/moisture barriers,
  • ruggedization potential,
  • superior electrical insulation, and
  • zero outgassing of volatile chemicals.

CVD-applied nano coatings offer a similar range of advantages.

Nano plasma deposition uses no solvents and requires no curing.  It utilizes a single-step process to apply a thin, uniform nano film, often negating masking requirements for connectors and contacts, lowering production cost/time. 

Liquid application of nano coatings are faster and more economical than use of plasma or CVD methods.  In such cases, nano coatings are also produced more cheaply and quickly than parylene.

Conclusion

Nano coating can be applied over parylene and other coatings to obtain additional performance and protection.  However, doing so is neither always beneficial nor recommended.  The typical value-proposition with nano coating relies on its cost effectiveness, ease of application and scalability replacing a parylene coating, developments that do not always occur; in those situations, doubling down (applying nano coating on-top parylene) is more effective if extra coverage is required.  It should also be remembered that unless nano coatings are CVD or plasma applied, their spray or other liquid applications may not combine favorably to CVD-applied parylene, potentially causing adhesion issues.    

To learn more about parylene coating and how it compares to other coatings, download our whitepaper:

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Tags: parylene, parylene properties, conformal coating, parylene disadvantages, nano coating