Conformal Coating Selection

Posted by Scott Curtis on Tuesday, March 28, 2017

Selecting the winning team to advance in the NCAA Men’s Basketball Tournament can be agonizing. There are a number of factors when trying to predict your bracket winner such as seeding, head-to-head match-ups, win-loss records, and strength of schedule. The process is difficult and there are many so-called “experts” attempting to offer meaningful analysis and insight to help you win your bracket pool.

March Madness is one of the most overwhelming and unpredictable sporting events of the year. Games are especially great when they come down to the wire and are decided by buzzer-beater clutch shots or plays that can leave you breathless with exhilaration. Of course, having the team you were rooting for win the game certainly helps.

Fortunately, selecting the right conformal coating to properly protect your printed circuit board (PCB) isn’t nearly as difficult as choosing the winning team from a 68-team field in a sudden death tournament. At Para-Coat Technologies, we offer five types of conformal coating materials and below we will cover each coating as well as their advantages and disadvantages.
What is Conformal Coating?
Conformal coating is a thin film polymeric material that covers and conforms to printed circuit boards and electronic assemblies. Its primary purpose is to protect electronics from environmental elements, chemical attack, and corrosion. The coating acts as protective barrier or shield for a PCB.

Types of Conformal Coating
The five main types of conformal coating are: Acrylic (AR), Polyurethane (UR), Silicone (SR), Epoxy (ER), and Parylene (XY). When selecting a coating, the most critical consideration should be the application and required functionality of your electronics within that application.

1. Acrylic (AR)
Acrylic conformal coatings are the most popular due to their ease of application, removal and forgiving nature. Acrylic coatings dry rapidly, reaching optimum physical properties in minutes, are fungus resistant and provide long pot life. Additionally, it exhibits high corrosion and abrasion resistance and moderate dielectric constant. However, this coating can easily chip, flake or scrape off, and you will only receive the benefit of selective chemical resistance.

2. Polyurethane (UR)
Polyurethane conformal coatings are available as either single or two-component formulations. Both formulations provide excellent humidity resistance and far greater chemical resistance than acrylic coatings. Single component polyurethanes, while easy to apply, enjoy long pot life, but sometimes require very lengthy cure cycles to achieve full or optimum cure. Also, this coating offers medium bond strength and has a tendency to flake or peel off in large pieces. It is necessary to use a stripping agent in order to remove all of the coating for repairs.

3. Silicone (SR)
Silicone conformal coatings are a transparent, soft, flexible coating which offers excellent moisture and corrosion resistance, good dielectric properties, and has exceptional light transmission capabilities for solar applications. Silicone coatings are very durable, able to hold up in extreme temperatures ranging from -67°F to 392°F. It provides good chemical resistance and salt spray resistance. It functions well in high temperate applications and is resistant to UV light and dirt pick-up. This coating can be “solder-through” for easy repair. However, silicone is not solvent soluble and require chemical strippers for removal or repairs.

4. Epoxy (ER)
Epoxy conformal coatings are usually available as two-part compound that start curing upon mixing, but single part coatings that can be cured thermally or with UV exposure are also available. Epoxy resins can be applied by brush, spray, or dip-coating. It exhibits good abrasive and chemical resistance, as well as reasonable humidity resistance. However, the epoxy coating is virtually impossible to remove and rework requires burning through with a soldering iron.

5. Parylene (XY)
Parylene is a vapor-deposited conformal coating, so it surrounds the target and perfectly follows its contours, achieving total encapsulation. Parylene films are commonly used as transparent, flexible coatings in electronic devices and biomedical applications, exhibiting barrier properties against corrosion, low dielectric constant, and moisture resistance. Parylene conforms to virtually any shape, provides pinhole-free coverage, and offers a high level of chemical and abrasion resistance. However, Parylene requires expensive specialized equipment to process and can be costlier than the other conformal coating options. Additionally, it is not easy to repair, but its perks often make it the best choice.

When choosing a conformal coating for your printed circuit board or electronic assembly, keep the application and the functionality requirements in mind. Although it’s important to protect the board, protecting it with the most suitable material is crucial. Consider the environmental conditions, along with the rework and repair needs when selecting a coating type.

Unlike “expert” March Madness analysis, Para-Coat Technologies’ experienced staff will make your conformal coating selection process easy and stress-free. Just as a clutch performance leads a team to an outstanding victory, all of our coatings are held to highest standards to ensure optimum performance and enhanced reliability.

Need help selecting the right conformal coating for your project? Contact us today!

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