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How to Choose the Best Conformal Coating for Your PCB

Posted by diamondmtblog

Friday, October 29, 2021 4:12

@ 4:12 PM

01-Conformal-Coating-for-PCBs

Printed circuit boards (PCBs) are the foundational building blocks of almost all modern electronic devices. Therefore they can be found almost anywhere, including in smartphones, cars, planes and many other locations. Because these boards are essential to the operation of many electronic devices, especially ones that require high dependability, they must be protected from any and all elements that could alter their functionality through the application of conformal coating.

Within this article, we will walk through how PCBs can be protected with conformal coating, the different types of conformal coating and how to choose the best conformal coating for a PCB.

What Is Conformal Coating for PCBs?

To start things off, we will first look at what conformal coating for a PCB is. A conformal coating is a thin polymeric film applied to a PCB to protect the board and its components from the environment and corrosion. The film completely conforms to the shape of the PCB to protect all of the solder joints, leads of electronic components, exposed traces, and any other areas that are vulnerable to corrosion.

So why do you need conformal coating? Essentially, when you apply a conformal coating to a PCB, you are extending and enhancing its working life. Applying a conformal coating can allow for higher voltage gradients and closer track spacing, which enables designers to meet and exceed standards. On the other hand, having a device failure can lead to serious consequences. Therefore, it is important that your equipment is adequately protected from external elements. These elements can include but are not limited to moisture, salt spray, chemical exposure, and temperature extremes.

Types of Conformal Coating for PCBs and Their Pros and Cons

Now that we have laid the foundation of what conformal coatings are, we will take a look at some of the different types of conformal coating, as well as the pros and cons of each type. Each type has different features, strengths, and weaknesses that should be considered when making your PCB coating selection.

Acrylic (AR)

Acrylic conformal coatings are the most popular type due to their ease of application and removal and their forgiving nature.

Pros

  • Easily applied/removed
  • Easy  rework and repairs
  • No shrinkage during the curing process
  • Affordable

Cons

  • Low chemical and solvent resistance
  • Low abrasion resistance
  • Struggles in harsh environments
  • Not ideal for high-temperature applications

Epoxy Resin (ER)

Epoxy conformal coatings are typically available as a two-part compound that begins curing upon mixing. Single part coatings can be cured thermally or with UV exposure.

Pros

  • Abrasion and moisture resistance
  • Great chemical resistance
  • Good humidity resistance
  • Durability in harsh environments

Cons

  • Hard to remove
  • Shrinks during the curing process
  • Soldering iron required for rework or repair

Silicone Resin (SR)

Silicone resin conformal coatings are single-component compounds that are typically applied to electronics that will be used in extreme temperature ranges.

Pros

  • Good in extreme temperatures
  • Excellent humidity and corrosion resistance
  • Good chemical resistance
  • Adheres to most PCB components/materials

Cons

  • Very difficult to remove
  • Requires strong chemical strippers and harsh abrasion for removal
  • Localized repairs only

Parylene (XY)

Parylene conformal coatings are applied using the chemical vapor deposition process. The process turns the perylene into a gas and, after heating, is put into a vacuum chamber where it polymerizes it into a film that is placed over the electronics.

Pros

  • Best solvent and extreme temperature resistance
  • Transparent and colorless
  • Forms at room temperature and does not require curing time
  • High dialect strength

Cons

  • Hard to remove and must be abraded off
  • Not ideal for long-term outdoor exposure
  • Special equipment needed for application

02-Considerations-for-Selecting-PCB-Conformal-Coating-Material

Considerations for Selecting PCB Conformal Coating Material

What is the best conformal coating for your PCBs? Since there are so many options to choose from when it comes to selecting the right conformal coating for a PCB, there is a lot that needs to be taken into consideration. Below we will walk through the top three areas to consider when choosing your conformal coating.

Product Use

The first and most crucial aspect to take into consideration is the intended use of your product. Matching the type of conformal coating based upon its pros and cons to the use of your product is key in selecting the best PCB conformal coating for your products.

An example would be if you are looking to protect against extreme moisture exposure. Based on the characteristics of all the conformal coatings, a perylene coating may be the best option for you. Perylene coating is known for its moisture protection, and some coatings even provide liquid submersion protection.

Temperature Range

When determining the type of coating for your product, you should have a clear understanding of the minimum and maximum temperatures it will be exposed to. Temperature ranges are an extremely important factor to take into account. If this is not taken into consideration, it can cause a PCB to be damaged. Below we will cover an example where temperature extremes are absolutely crucial to the type of coating selected.

An example of a situation in which temperature extremes are an essential consideration is PCB use for aircraft. Planes can see extreme temperature ranges that can include -65 degrees Celsius (-85 degrees Fahrenheit) when in the air and over 100 degrees Celsius (212 degrees Fahrenheit) when on the runway. Silicone coatings are the only option that can handle extended use at this range.

Environmental Factors

There are numerous environmental factors that conformal-coated PCBs can be exposed to that will help you determine the best conformal coating for your PCBs. For example, suppose a PCB is going to be placed in partially sealed protective housing. In that case, the only environmental factors that would need to be taken into consideration are condensation and humidity. Below we will list some of the other common environmental factors that should be taken into consideration:

  • Extreme humidity
  • Salt-spray environments
  • Corrosive gasses
  • Immersion environments

03-Diamond-MT’s-Conformal-Coating-Services

Diamond-MT’s Conformal Coating Services

If you are in the process of looking for conformal coating services and trying to choose the best conformal coating for your PCBs, then look no further. At Diamond-MT, we offer perylene, acrylic, urethane, silicone, and epoxy conformal coating services to ensure all of your PCBs have the necessary protection. As a company with over 20 years of experience and an industry leader, our team is committed to providing the highest quality services with every order.

For more information on our services, help on selecting the best conformal coating for your PCBs, or to request a quote, contact us today!

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