Parylene Coating Blog by Diamond-MT

Benefits of Conformal Coating

Posted by Sean Horn on Fri, Jan 08, 2016 @ 08:07 AM

Electronics manufacturers need devices that withstand heat, cold, rain, snow, vibration, fungus, oxidation, and corrosion through decades of operation.

  • Automotive and aircraft companies need circuit boards that perform for years inside cars, trucks, school buses, construction equipment, commercial aircraft, and even fighter jets.
  • Defense manufacturers need systems that can operate in tanks, rocket boosters, and satellites—just to name a few.
  • Medical device manufacturers need coatings that allow their devices to operate for years inside the body.
  • Cell phone and tablet manufacturers need circuitry that can withstand everyday vibration, moisture, and drops.
  • Makers of wearable fitness trackers need circuits that won’t fail in the rain, sun, snow, or during intense exercise sessions.

The problem is: Normal circuit boards will not survive in these harsh environments.

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Conformal Coatings Protect Circuit Boards and Electronic Devices from Their Environments

Conformal coatings create a protective, non-conductive dielectric layer that's added to a circuit board or electronic device.

There are five primary coating types, each with dozens of variations, meaning there literally hundreds of conformal coatings for you to choose from.

Costs for different coatings vary wildly depending on the material type and application methods.

Parylene dimer, for example, is one popular type of coating material. The material itself can cost anywhere from $100 to $10,000+ per pound, depending on the type and quality.

To choose the right conformal coating, engineers must answer these questions:

  • What conformal coatings will protect my device?
  • Which coatings are cost effective for my situation?
  • Is it better to outsource conformal coating, or should we handle the task in-house?

The challenge is: Few manufacturing companies fully understand which coating is right for their specific application.

3 Steps to Help You Choose the Right Conformal Coating for Your Device

Here are the three steps you can take to choose the right conformal coating for your device.

  1. Define Clear Performance Requirements

It’s critical that you clearly define the performance requirements for your device. What temperature range will it face? Will it have to withstand moisture? What about vibration?

  1. Learn the Five Types of Conformal Coatings

There are five main types of conformal coatings, each with it’s own advantages and shortcomings. We’ll describe these in detail later in this article.

  1. Find a Company That Provides All Five Coatings

Companies that specialize in one type of coating sometimes have an “every problem looks like a nail to a hammer” approach. It’s better to work with a provider that provides all five coatings.

They won’t force you into their prefered coating. Instead, they’ll work with you to find a coating that’s cost effective and meets your performance requirements. They’ll also be able to support you whether you want to outsource the work or keep everything in-house.

The 5 Types of Conformal Coatings and Their Benefits

There are five types of conformal coating. Parylene is applied using a unique vapor phase polymerization process. The rest are applied by either brushing, spraying, or dipping the device into the coating and letting it dry.

Each style of coating has it's own benefits.

  1. Acrylic Resin (Type AR)

Acrylic conformal coatings are fungus resistant and can be easily applied. They dry to the touch at room temperature in minutes and have desirable electrical and physical properties.

Acrylic coatings are typically applied at 0.002 to 0.005 inches thick. Most variations cure in as little as 30 minutes, making them a great choice when you need a short turnaround time.

The most popular acrylic coatings are not good choices for high temperature environments. They can usually only withstand temperatures of up to 125° Celsius.

  1. Epoxy Resin (Type ER)

Epoxy conformal coatings are "two-component" compounds. They deliver a rugged coating with good resistance to damage from humidity, high abrasion, and chemicals.

Epoxy coatings are known for their extreme hardness, making them a good choice when you need toughness and durability.

Their extreme hardness means rework and repair is difficult. Epoxy also tends to experience shrinkage during the polymerization stage, and extreme temperatures tend to reduce the stress resistance properties of epoxy coatings.

  1. Polyurethane Resin (Type UR)

Polyurethane (also called “Urethane”) conformal coatings deliver excellent humidity and chemical resistance. They also provide excellent dielectric properties for long periods of time.

Polyurethane coating is often the optimal choice for devices that will be exposed to chemical solvents. Its dielectric properties also promote miniaturization because it insulates signal traces from circuits that are close together.

Polyurethane retains high dielectric properties over time. It is also often used to mitigate tin whisker growth.

Polyurethane’s resistance to solvents means it can be difficult to remove or rework. It also doesn’t do well in high-vibration or high-heat environments.

  1. Silicone (Type SR)

Silicone conformal coatings perform well in high-temperature environments, even up to 200° Celsius. That makes them a very popular choice for automotive applications.

Silicone has a resistance to humidity and corrosion. It can also be applied in thicker layers than other coatings, which helps in damping any vibration.

Silicone is less resistant to abrasion and solvents than other coatings. It also requires more care to apply correctly.

  1. Parylene (Type XY)

Parylene is often considered the “gold standard” of conformal coatings.

The unique application process for Parylene means it delivers the most uniform coating. Parylene can be applied to virtually any surface and objects of any shape, including glass, metal, paper, resin, plastics, ceramics, ferrite, and silicon.

Parylene is also completely inert, making it an excellent choice for implants and biomedical devices.

Rework is difficult with Parylene due to its unique application process. Operators must also ensure the object to be coated is completely clean and that any areas not to be coated are meticulously masked.

 

Conclusion

Conformal coating is a necessity for anyone who’s building a product with electronics that have to perform well in harsh environments.

If you'd like to know more about how conformal coatings work, download our free guide:

Basics of Conformal Coatings  Whitepaper

Tags: acrylic conformal coating, parylene, conformal coating, silicone conformal coating, urethane conformal coating