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PCB Coating Types and Selection Guide

Applying PCB resin coating

Using a suitable material to coat your PCB makes it more dependable. This overview of PCB coating types will examine your options, explaining the qualities of each choice. It also has a selection guide to help you decide wisely, especially if you need help choosing between protection level and board reparability.

What is PCB Coating?

PCB coating is the thin polymer film (about 12-200 microns) applied to populated boards. It offers electrical insulation and safeguards the board from external elements—or the adverse conditions of its usage environment. The harsh elements include (but are not limited to) the following:

  • Chemicals
  • Abrasive materials
  • Temperature changes
  • Moisture or high humidity levels
  • Airborne contaminants like fungi, dust, and dirt

PCB protective film is also called “conformal coating.” That’s because it takes on the board’s profile, shielding component leads, solder joints, and electrical tracks from corrosion and other damage.

You can use various methods to apply the film: brushing, spraying, dipping, or chemical vapor deposition (CVD). The application process may also involve automated industrial equipment for high-volume boards or manual methods for minor coats.

PCB protective coating for automotive application
PCB protective coating for automotive application
Resource: https://www.assemblymag.com

Benefits of Conformal Coating

Conformal coating ensures your PCB meets the needs of its application, making it an essential part of the board’s production. It also makes circuit boards satisfy specific industry standards. In a nutshell, the film offers these benefits.

  • Dependability – your board remains shielded from environmental hazards, increasing reliability
  • Performance Benefit – it allows your PCB to operate at higher voltage gradients and improves its performance
  • Space Savings – the dielectric properties of the PCB conformal film help reduce the space between tracks, making smaller designs possible.
  • Extended Lifespan – the suitable material increases the life of your PCB by preventing corrosion and other forms of damage
  • Cost Reduction – the protective nature of these films can save you the cost of bulky and expensive enclosures
An example of PCB conformal coating
An example of PCB conformal coating
Resource: https://epsnews.com

PCB coating Types

Different PCB coating types offer varying protection levels. Besides cost differences, some are simpler to apply or remove than others. They include silicone, acrylic, epoxy, urethane, and parylene. Below is a description of their properties.

1. Silicone Resin Coat

Silicone exhibits various positive characteristics, making it one of the most favorable PCB conformal coating types. It has a moderately high resistance to abrasion and moisture and can excellently withstand temperature variations.

Rubbery and highly elastic, it resists vibrations, making it ideal for most outdoor applications. Its soft nature also makes it suitable for sensitive circuit board components.

On the downside, the film offers low resistance to chemicals and oils. It’s also challenging to remove, requiring aggressive agitation and the use of specific solvents. It’s comparatively expensive, too.

2. Acrylic Resin Coat

Acrylic is the simplest of all PCB coating types, inexpensive, and straightforward to apply. It’s equally easy to strip when reworking or repairing your board. You only need a solvent.

But these attributes make it less effective as a protective film, with lower resistance to chemicals, salt spray, and other environmental conditions like moisture and abrasion.

On the other hand, it has good physical and electrical properties and cures in no time. These qualities make it the best choice for low-budget boards for use in mild environments or applications with limited exposure to adverse conditions.

3. Epoxy Resin Coat

Epoxy hardens into an abrasion-resistant film, making it one of the most used PCB coating types. It also responds well to various hazards, including chemicals, moisture, and other environmental elements.

With these qualities, epoxy requires effort to remove when reworking your PCB. It also takes time to cure and doesn’t suit high production runs.

Additionally, PCB epoxy coating is prone to cracking in extreme vibration environments. Its use is, therefore, mainly confined to applications with special requirements.

4. Urethane Resin Coat

Urethane offers good performance in protecting against various forms of damage. It not only resists abrasion but can also withstand moisture and chemicals.

These properties make it a preferred material for most application conditions. On the downside, it takes a long time to harden and may not suit high-volume boards.

Urethane films are also one of the hardest to remove, requiring long soaks and a combination of particular solvents, among other steps.

5. Parylene Coat

Parylene is a type of thin film applied using a unique technique called chemical vapor deposition. Of all PCB coating types, it offers unmatched resistance and can withstand extreme temperature changes, higher humidity levels, corrosive materials, etc.

However, that also makes the film challenging to apply or strip. It requires specialized equipment for the vapor deposition process, which increases application ease and costs.

Applying waterproof PCB coating
Applying waterproof PCB coating
Resource: https://forum.qorvo.com

Conformal Coating Comparison Chart

We have already looked at the qualities of PCB coating materials and how they affect the protection of your assembled PCB in different environments. Here is a quick comparison of those qualities.

Silicone

Acrylic

Epoxy

Urethane

Parylene

Ease of Application

Difficult

Easiest

Fairly Difficult

Easy

Most Difficult

Dielectric Strength

Fair

Good

Excellent

Excellent

Excellent

Adhesive Properties

Excellent

Good

Excellent

Good

Excellent

Chemical Resistance

Good

Good

Excellent

Excellent

Excellent

Temperature Resistance

Excellent

Fair

Good

Good

Excellent

Water Resistance

Fair

Poor

Good

Good

Excellent

Abrasion Resistance

Fair

Good

Excellent

Excellent

Good

Cure/Drying Time

Long

Short

short

Fairly Long

Short

Removal Difficulty

Difficult

Easiest

Most Difficult

Low

Most Difficult

As you can see, different coats behave differently. That can make selecting a suitable material difficult. In the next section, we look at the factors to consider when choosing a material for your board.

Conformal coating inspection
Conformal coating inspection
Resource: https://www.eenewseurope.com

How to Select PCB Coating Material

Various factors come into play when selecting the type of PCB protective coating. That’s because environmental conditions vary, and the most suitable material will depend on the required protection level. Consider the following factors when making your choice:

Application Conditions

Identify your board’s most significant threats. Outdoor PCBs require more protection than those meant for indoor environments. Specific threats also vary, so choose your conformal coating accordingly.

For example, a PCB for the automotive industry might need a film that can withstand heat, dust, and vibrations, making silicone a good choice. For a mild environment, an acrylic film would do.

Board Reparability

How easy is the material to apply or strip? Acrylic is the simplest to coat with or remove. However, it offers minimal resistance and may not be suitable for harsh operating conditions. In such cases, epoxy and parylene would be worthy alternatives.

You want the material to be straightforward to use while allowing board reparability. You also want it to remain suitable for the board’s conditions. Therefore, weigh every requirement to ensure the best for your specific use.

Coating Certifications

Various certifications define PCB protection films, indicating material properties, such as viscosity and toxicity, and their suitability to coat your board. The most used are IPC and UL.

Have your coating satisfy these certifications. Doing so ensures your PCB meets the required standards and has a qualified film to protect it against its specific application hazards.

Conclusion

Different PCB coating types provide varying protection levels. Always select the ideal material for this film based on your board’s application environment. You want the film to be easy to remove for rework and repair. But most importantly, you want to offer the required protection level.

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