About PCB Conformal Coating: You Need to Know the Final Guide

What is PCB Conformal Coating?

When it comes to the world of PCBs, you may hear of the term PCB conformal coating? But what exactly is PCB conformal coating?

As the name suggests, PCB conformal coating applies a thin film of some protective material to a circuit board.

The coating protects the entire board and its parts.

These parts include the component leads, exposed traces, solder joints, and exposed metal. 

The conformal coating shields the metal parts from fungus, moisture, spray, and other environmental contaminants. 

The use of PCB Conformal Coating

The primary purpose of PCB conformal coating is to shield electronic components from environmental factors and corrosion;

• To serve as an insulating material of a PCB while minimizing the ecological pressure during PCB assembly. It helps in eliminating the need to have complex housings;

• To protect PCBs from heat, moisture, fungus, and airborne contaminants such as dirt and dust.

Advantages of PCB Conformal Coating

There are plenty of benefits that come with PCB conformal coating, as listed below:

Insulation and heat resistance

Light in weight

Protection of PCB components

Reduce environmental hazards to PCB boards and prevent the entry of pollutants.

Less footprint of PCB components

Enhanced product reliability

Extends the life of a printed circuit board

Very easy to apply

Can PCB Conformal Coating be Waterproof and Moisture-proof?

It’s not easy for a PCB conformal coating to be waterproof and moisture-free simultaneously.

A PCB coating’s primary function is to shield the board from dust, temperature extremes, chemicals, and, mostly, moisture.

But, PCB conformal coatings do have their limits. Most layers, regardless of whether they are thick or thin, provide a lot of moisture protection. 

The importance of PCB Conformal Coating

PCB conformal coating is necessary, especially in the printed circuit board industry. Without it, we would still have PCBs.

Unfortunately, such printed circuit boards will encounter a short shelf-life.

There will also be some potential damage when in use. That’s not to forget the complete failure of the equipment that relies on them. 

As mentioned earlier, conformal coating shields printed circuit boards from damaging effects.

Remove them from the scene; we have boards whose shelf life and functionality are less desirable than intended.

With a conformal coating, board protection is assured at all times.

PCB Conformal Coating Type

The conformal coatings that PCB designers use when layering printed circuit boards are divided into two groups: traditional and modern.

This section highlights several types of conformal coating and touches on their advantages and disadvantages, among other things.

• Traditional protective coating

An apt example of a standard traditional protective coating is Polyethylene. PCB designers have used it to coat PCBs for as long as possible.

PCB makers noticed some advantages and disadvantages of traditional protective coatings.

A better explanation is in the table below. 

Advantages	Disadvantages
Very cheap to purchase	Very poor in terms of thermal management
Easily available	Too hard when undertaking rework
Abrasion-resistant	Environmentally hazardous
Good wear	Very heavy on printed circuit boards

Besides traditional protective coating, there are also other types of PCB coating, as highlighted below:

• Polyurethane resin (UR)

This resin type is highly appreciated in the PCB industry due to its excellent chemical and moisture resistance.

Additionally, polyurethane resin is abrasion-resistant, making it very hard to remove.

It is ideal for aerospace applications where exposure to fuel vapor is standard. 

Advantages 

Excellent dielectric properties

Excellent moisture resistance 

Abrasion-resistant

Good resistance to moisture

Disadvantages 

Environmentally unfriendly

Long complete cure time

• Epoxy resin (ER)

These are mainly available in a two-part compound and tend to create some of the hardest PCB coatings.

Unlike others, they are challenging to remove once the curing process is over. Therefore, they are very useful in building and construction applications. 

Advantages 

Excellent humidity resistance

Good dielectric properties

High chemical and abrasion resistance

Disadvantages 

Complex mix ratios

Difficult to remove and rework

• Acrylic resin (AR)

These acrylic polymers are soluble in solvents, providing general protection and good elasticity.

Acrylic resins are widely used in bathtub liners, aquarium windows, and cellphone display screens.  

Advantages 

Affordable 

No shrinkage during curing

Easy to repair and rework

Easy to apply and remove

Disadvantages 

Low abrasion resistant

Not suitable for harsh environments 

• Silicone resin (SR)

These single-component compounds are often ideal for electronics in extreme temperate conditions.

They are also common in the making of coatings and paints. 

Advantages 

Performs well under extreme temperatures

Excellent chemical resistance

Good corrosion and humidity resistance 

Disadvantages 

Very difficult to remove

Localised repairs only

• Parylene (XY)

Chemical vapor deposition is the application process of this type of coating.

When heated, perylene becomes a gas, and after cooling, it polymerizes and subsequently turns into a thin film.

Equipment such as moisture barriers and electrical insulation rely heavily on them. 

Advantages 

Colourless and transparent

No need for curing time

High dielectric strength 

Best solvent at extreme temperatures

Disadvantages 

•  Challenging to get rid of

•  Not suitable for long-term outdoor exposure

Application areas of PCB Conformal Coating

Initially, the conformal coating was very applicable in printed circuit boards intended only for high-tech environments.

However, this is not the case today, with PCB conformal coating application areas continuing to grow exponentially.

At this point, we are going. We will focus on the use or application of PCB conformal coating.

Typical application areas of PCB conformal coating include: 

7.1 Automotive Industry PCB

Looking across the automotive industry, you’ll notice something different.

Electronic systems are finding a lot of use across this domain lately.

Thus, printed circuit board conformal coating does a lot here.

It protects automobiles’ crucial parts, especially in salt fog and gasoline vaporization.

All these and many more ensure the long-term reliability of motors. 

7.2 Consumer Electronics PCB

Printed circuit board conformal coating is also applicable outside the automotive sector.

For instance, it protects circuits meant for home appliances, solving many problems.

With PCB conformal coating in your home appliances, you can rest assured of better functioning. 

7.3 Navigation product PCB

Salty sea water and freshwater may cause damaging effects on the circuits that are in the sailing equipment.

Here, the material is prone to some damage when they come in contact with water.

But all is not lost, thanks to PCB conformal coating procedures.

A conformal coating prevents corrosion speeds.

It reduces corrosion at the exterior of the device and also underwater components. 

7.4 Medical device PCB

The medical field is another area that relies on PCB conformal coating. Conformal coatings seem to play an essential role in this industry.

For instance, it protects electronic medical devices from cases of corrosion.

Chemical agents are used widely in the medical field and tend to harm equipment that this industry relies on daily.

But, with conformal PCB coating now with us, there’s the avoidance of such problems. 

7.5 PCB for military products

Electronic equipment meant for military applications operates under the most demanding conditions.

Military equipment must be in a position to withstand constant and heavy vibrations.

Also, they should be able to work well under extreme temperature conditions. To protect such equipment from damage, PCB must conformal coating.

Thanks to PCB conformal coating, protecting military equipment is now possible.

It’s far easier to protect them from instances of oxidation and corrosion.  

7.6 New high-tech product PCB

High-tech fields like science, technology, engineering, and mathematics often use high-tech equipment.

In a laboratory setting, for instance, you’ll find high-tech equipment. Some include shakers, test chambers, stirrers, and vacuum chambers are common.

All these have essential components that must function without failure.

With PCB conformal coating, there’s the avoidance of any challenges that could occur.

It is because it’s possible to apply PCB conformal coating here too. 

How to Choose the Right PCB Conformal Coating

Selecting the right PCB conformal coating is one of the most tedious and complex processes.

It’s because there are some crucial factors that you may have to analyze before you conclude.

Failure to consider essential aspects is risky.

For instance, you may purchase a coating that won’t suit your needs. Having said this, here are a few essential factors to consider.

These factors are critical when choosing the right PCB conformal coating for your project:

• Consider the PCB board operating temperature, the highest point, and the lowest point

The first parameter you may need to assess concerns the operating temperature range.

This is because it will affect the chemistry you must apply when coating.

For instance, using a silicon-based layer in high temperatures is advisable.

Also, use urethanes and acrylics if dealing with less critical temperature resistance. 

• Degree of chemical resistance

This one also matters a lot. It is easy to remove Acrylic materials for rework.

Unfortunately, they are prone to attacks by solvents.

Polyurethane materials provide more chemical resistance but are not easy to amend. 

• Level of corrosion protection

How far can the conformal coating protect your equipment in terms of corrosion?

In short, you must ensure that you purchase only the best layer, known for being robust in resisting corrosion. 

• Long Shelf Life

Shelf life is the length of time a product remains useful on the shelf under the specified storage, display, and distribution conditions.

You do not want to shop for products that will go bad in a few days.

Unfortunately, some paints can’t guarantee a long shelf life.

Silicone conformal coating is one of the best choices based on its long shelf life. 

• Performance and Engineering Characteristics

Before you select the type of coating you intend to use, ensure it won’t cause stress on the components, especially during thermal extremes. 

PCB Conformal Coating Thickness

The thickness of the conformal coating is one of the essential elements that will determine the longevity of your electronic devices.

A minimum coating thickness is necessary to bring about the required function or role of the conformal coating.

If the conformal coating is too thick, it may adversely affect the level of protection you desire for your boards. So, what’s the importance of coating thickness?

How do you go about measuring PCB conformal coating? Are there any types of coating thicknesses?

Below is a clear explanation touching a lot on PCB conformal coating thickness.

9.1 Importance of protective coating thickness

Paints are coatings acting as protective layers. Paints also shield the surface from damage emanating from the environment.

When carrying out a painting task, it’s essential to ensure that you use a high-performance coating.

The thickness of the layer is critical.

It will impact the performance and functionality of your equipment. 

However, there is a concept that the thicker the protective coating (especially on the PCB), the better the protective effect. But again, this isn’t always the case.

A thick protective layer may cause an uneven texture finish or cracking due to external forces.

But again, protective coating ensures the surface doesn’t suffer damage from the external environment.

However, it is best to remember that low-coating thicknesses, such as those below 25 µm, might be risky.

It might be dangerous because dielectric strength might not have been tested based on standardized methods.

Also, high coating thicknesses above the limit rarely protect the PCB as intended. 

9.2 Coating type and typical thickness

As mentioned above, there are several types of coating, including a handful of special ones.

But the five main basic categories are epoxy resin (ER), urethane resin (ER), acrylic resin (AR), parylene (XY), and silicone resin (SR). 25-250μm (micrometers) is the standard or typical thickness. 

Such thickness can protect the circuitry. It shields circuits against dust, moisture, temperature extremes, and chemicals. 

9.3 How to measure PCB conformal coating

Achieving a coat that’s even with the right desired thickness is a big challenge. When applying a conformal coating on a PCB, getting an even thickness isn’t easy.

A coat that’s too thin is risky. It may expose the electronic assembly to potential environmental risks.

It is an aspect that will defeat the purpose of the coating itself. 

Also, a coat that’s too thick isn’t right. It might leave the electronic components on the PCB non-functional, rendering the entire electronic assembly useless.

Coating thickness needs to meet the specified quality specifications. Measuring conformal coating isn’t a tasking process.

Several methods of measuring PCB conformal coating exist, but two are the most common. 

First, there’s the dry measurement method. PCBs must be completely dry before measuring to avoid damaging the conformal film.

Here, you can use several methods to assess the depth of the coating thickness.

The easiest way involves the use of calipers.

With calipers, you can measure the width of a printed circuit board. 

You do this by noting the actual dimensions before applying the conformal coating. Secondly, there’s what we refer to as Wet Measurement.

This PCB conformal coating measurement type allows designers to ensure quality control of the coating thickness.

Remember that designers do this while the film is still wet.

Here, a wet-film gauge does the work of measuring conformal coating that hasn’t dried yet.

9.4 How to determine the thickness of PCB conformal coating

Determining the depth of PCB conformal coating is not a complicated process.

The average PCB conformal coating thickness should be between 1 to 5 mils.

But that’s not all.

Designers use many ways to determine the depth of the PCB conformal coating. Here are four ways of doing so:

• Wet film thickness gauge

Here, wet film thickness measurement is achievable using a series of teeth and notches.

Each tooth contains a calibrated length.

Designers place the gauge directly into the wet film and then multiply the measurement by the percentage of solids.

It enables them to come up with an approximation of the dry coating thickness. 

• Micrometre

With this method, measurements are taken on a PCB at different locations.

You have to do this before and after coating.

To determine the thickness of the layer, you need to subtract the width of the cured layer from the uncoated measurements.

After that, you divide it by 2. This method determines the thickness of a single side of the board.

This type of measuring the thickness of PCB conformal coating is highly accurate.  

• Eddy’s current probe

Here, test probes are used to measure coating thickness directly.

It is through the creation of an oscillating magnetic field.

This mode of measuring conformal coating is ideal because it produces very accurate thickness measurements.

If the probe is poorly positioned in the test area, the readings will not be accurate. 

• Ultrasonic thickness gauge

This is the measurement of coating thickness using ultrasonic waves. Unlike eddy current probes, metal backplanes are not needed here.

The thickness calculation begins when the sound waves start traveling from the transducer through the coating, bouncing off the boards’ surface and back.

The Curing Mechanism of PCB Conformal Coating

Curing is essential when considering the long-term reliability of the circuit board.

There are several notable cure mechanisms for conformal coatings worth noting.

As explained below, you’ll get a better understanding. Of importance is that each one has its key features. 

•  Drying—Drying involves coating the printed circuit board, making it suitable for operators to handle. It may only take a few minutes or even several days after the application process.

It depends on plenty of factors. 

•  Oxidation—This involves curing conformal coatings by means or through atmospheric oxygen. Usually, the drying process occurs first since many oxidative cure coatings are solvent-based. 

•  Moisture—Here, conformal coatings cure with ambient humidity in the atmosphere and condensation in the cure system. The volume of moisture in the air impacts the cure rate. 

•  Heat—Here, conformal coatings cure in elevated temperatures. Most layers don’t begin healing unless they reach the required temperature. The heat cure method is ideal because it is one of the fastest cure methods compared to room temperature cure. 

•  Chemistry—Also known as Catalytic Cure, these are combinations of two-part material conformal coatings. These combinations start the reaction and the curing process, and it’s impossible to stop the curing process when a combination occurs. 

•  UV light—These are conformal coatings that cure under UV light. Energy and the wavelength significantly influence the surface’s ability and rate of healing. UV cure coatings mostly consist of secondary cure mechanisms. The mechanisms ensure that any coating that fails to cure under UV light eventually cures. 

How to Cover PCB Conformal Coating

PCB designers use conformal coating in a handful of ways to cover the surfaces of their PCBs.

The following are some of the most common printed coating formulas that you can use:

•  Manual spray: This method, as the name suggests, involves manually spraying a conformal coating onto the PCB surface.

You can achieve manual application by aerosol or in a spray booth. Of importance is that the result might not be perfect.

•  Automatic spraying: Automatic spraying is available to buy using specialized automated or robotic equipment. The automatic spray is a bit costly.

But it produces some of the best conformal coating results. Compared to manual spraying, automatic spraying is the best.  

•  Selective coating： Selective coating employs robotic spray nozzles to effectively apply a conformal coating to specific regions of a printed circuit board.

The particular surface is a high-volume method, meaning that it is accurate and fast. It applies a layer to the exact intended places of the board. 

•  Impregnation – This one also goes by the name saturation coating. It is a coating process that designers use to coat the porous substrates of a printed circuit board. It is ideal for PCBs with pores penetrating the entire substrate. 

•  Paint—Paint is a mechanically bonded surface coating that provides a barrier film between the environment and the steel. The paint system involves using several sheets of layers and different paint formulations, depending on the operating environment of your boards. 

Determine the Failure of PCB Coating

As noted above, the coating protects printed circuit boards.

With surface, PCBs are in a position to perform well in the intended operational circumstances. However, there are instances where boards fail despite having undergone coating protection. 

12.1 The two most essential failure mechanisms: corrosion and insulation loss

•  Corrosion: Unprotected boards tend to rust quickly. Corrosion is one of the biggest reasons for poor board functionality and may lead to total board failure.

Copper is a common base material on a printed circuit bay.

Copper is highly susceptible to corrosion when you don’t coat it properly.

To avoid such a case, you only have to undertake proper conformal coating.

•  Insulation loss: Poorly performing coatings risk insulation damage at the surfaces of a printed circuit board.

Water can condense and combine with several iconic impurities, forming conductive pathways between the printed circuit board tracks.

Undoubtedly, condensation tests the insulation resistance of a conformal coating you use. 

12.2 How to prevent the failure of PCB conformal coating

PCB conformal coating can fail for plenty of reasons. PCB failure may render the whole coating process a waste of time.

However, several ways exist to prevent the collapse of printed circuit board conformal coating.

First, you need to ensure that you apply the layer only to the recommended thickness.

Don’t use too little or too much coat on your printed circuit board. 

Secondly, ensure that you apply the coat in several thin coats. This allows the bubbles to dissipate between the layers properly.

Third, you may want to use a low-viscous version of a conformal coating.

Fourth and last, if you are brush coating, blend the surface so it flows smoothly into every other part of the substrate. 

12.3 Reparability of PCB conformal coating

Fortunately, it’s possible to repair PCB conformal coating using a soldering iron.

Something impressive about PCB conformal coating is its reparability function.

With a soldering iron, the surface will melt away, leaving behind clear joints of the sheet.

With other layers, you may realize the material’s char.

But this is a small issue you must discuss with your quality department. 

How to remove PCB Conformal Coating

You must know almost everything to do with a conformal coating. For instance, you know its types, uses, and thickness, to mention but a few.

Now, it’s time to understand something else. It’s time to learn the best removal strategies for removing or replacing the conformal coating on your PCBs. 

13.1 Why remove the protective coating?

When selecting the type of conformal coating material to use, you need to factor most efficient to remove it should you want to do so.

Removing the coating can damage your PCB, especially if it is wrong. 

You may have to undertake PCB conformal removal for many reasons.

For instance, you may want to do so due to the wrong choice of the coating material.

It may also be due to inadequate coating coverage or a PCB design that doesn’t need a coating. There are plenty of reasons.  

13.2 Removal method

There are several PCB conformal removal methods worth mentioning. Some of the most common ones include: 

• The chemical solvent method removes a PCB conformal without affecting the board and its components.

It’s important to note that no particular solvent is ideal for all applications.

The water must be safe to work with and environmentally friendly. 

•  Stripping method： You’ll need many solvents to remove the conformal coating.

This process involves swabbing and brushing the area with water until the coating is removed. Stripping is effective in removing different types of circuit board coatings. 

•  Heating method—You’ll have to use very low-temperature heat to burn and melt the coating gently. You may have to use some low-temperature control tools to ensure you don’t damage the PCB. It’s not suitable for using a soldering iron.

•  Grinding and scraping method： Removing conformal coating requires several rubbing and scraping equipment.

All this depends on the composition of the PCB coating material.

Most people use a dental-style scraper and a hand-held drill when grinding. 

•  Miniature sandblasting machine to remove the conformal coating： Sandblasting involves propelling finely graded abrasive powder into compressed air streams through an abrasive-resistant hose and out tiny nozzles that you automatically or manually place at the workpiece.

This method can be used to remove several coatings, including acrylic, epoxy, urethane, perylene, and silicone. 

How to Choose High-quality PCB Conformal Coating

There seems to be some rapid miniaturization of electronics and circuitry globally.

It is an aspect that has seen matters to do with a conformal coating of PCBs increasing.

As mentioned above, conformal coatings are necessary to protect PCBs from extreme temperatures, moisture, and dust, among other things.

But how do you go about choosing high-quality PCB conformal coating material?

What are some of the things that you need to watch out for the best PCB conformal coating material?

Here’s what you need to look out for when choosing a high-quality conformal coating to guarantee you the best result:

The surface has to feature excellent flexibility

Also features low toxicity levels and a cost

It should be easily reworkable

Feature a vast range of operating temperature range

At high speeds, it should be able to cure without generating by-products

Has to shield the board from low/high temperatures and mechanical impact

It must have a long shelf life

It must be easy to spray and feature low-viscosity

Regulatory Considerations

Safety and environmental concerns are paramount when selecting the type of conformal coating material to use.

Some elements, once they become obsolete, may end up bringing some damaging effects to the environment.

Besides all these, there are several regulatory bodies tasked with the mandate of ensuring that PCB coating materials are environmentally friendly:

•  Occupational Safety and Health Administration (OSHA)—This is a statutory body in the US that ensures worker safety.

Plenty of coatings are flammable, contain high toxicity levels, and emit fumes.

OSHA ensures that all companies producing PCBs put safety measures in place to protect their workers.

OSHA provides that all PCB manufacturers have personal protection equipment for their workers and that the company has enough ventilation. 

•  EPA (the United States Environmental Protection Agency)—Again, in the US, all PCB producers strictly adhere to EPA requirements. For instance, the EPA severely restricts chemicals that affect the ozone layer. Fortunately, most of the restricted chemicals aren’t readily available, so matters concerning ozone depletion appear not to be a big concern. 

•  CARB (California Aviation Review Board) and other regional regulations： For the longest time possible, the CARB, in conjunction with other local authorities, has continuously played more prominent roles to ensure that they enforce environmental restrictions aimed at the protection of the environment.

Some of these restrictions include VOC (volatile organic compounds) or smog-producing chemicals. The latest environmental topic under discussion is the Global Warming Potential (GWP). 

Summary

This article is about the knowledge of PCB protective coating and 15 things you want to know about PCB conformal coating.

Are you looking for the best conformal-coated printed circuit board that can generally work on the market?

If so, you can contact us, and we can discuss any questions about PCB protective coating together. I believe we can solve problems and learn more knowledge from them.

I hope this article is helpful to you, and then we will be pleased!