Conformal Coating Process: The Ultimate FAQ Guide

Before you start PCB conformal coating, read this guide.

It will help you understand the basic and advanced techniques of printed circuit board coating process.

Keep reading to learn more.

How is a Conformal Coating applied on a PCB?

There are several approaches in the application of a conformal coating on printed circuit boards.

The common application methods are:

  • By spraying
  • By dipping
  • Utilizing a brush
  • By selective coating

What are the Factors Affecting the Choice of Conformal Coating application?

Choosing a conformal coating is based on factors such as cost, area of application, the environment of use, and processing time.

Conversely, the process of application of the conformal coating is also dependent on several dynamics.

These dynamics will determine the relevance of the coating on your application achieving the best results.

They include:

  • The cost involved in applying the coating.

While some application methods are simple employing regular equipment, others require specialized equipment that is expensive to obtain.

  • The volume of boards to be worked on.

Manual application processes are only suitable for small volumes whereas large volumes will be efficiently covered with automation.

  • The design of the board will also influence the choice of conformal coating application.

Complex designs will better off handled by programmed machines rather than be done by hand.

  • The required thickness of the coating. Some application procedures can only allow the achievement of a limited thickness range.
  • The depth of penetration desired.

When coating PCBs, the choice of application will determine how deep the coating adheres to the board.

Why is the Brush Method Lowly favored in the PCB Conformal Coating Process?

Using a brush is a manual application process that is employed for single boards or limited quantities.

You can apply conformal coatings with a brush when doing reworks or repairs too.

You find this method is not the first choice for many due to the following reasons.

  • The outcome is usually thicker than other application procedures
  • The surface of the coating is uneven with brush streaks that make the finish unattractive.
  • Since it is done by hand, it takes a longer time to complete a single coating process.

Consequently, using the brush method is only considered when other means are unavailable or costly.

Is the Spray Conformal Coating Method Effective for Large PrintedBoard Productions?

Spray conformal coating

 Spray conformal coating

In spraying a coating over a PCB surface, a pressurized canister filled with the coating resin is used.

The coating is forced out through a nozzle releasing a coating spread.

The spray method is easily affordable and results in an even surface formation that is cosmetic.

However, since the action of spraying is done by hand, it would be uneconomical and ineffective for use on large batches.

Furthermore, when using the spray method, you need to cover areas that are not to be coated.

Consequently, coating a single board takes some time.

You also find the resulting coat lacks the penetration depth achieved with other processes.

How is the Dipping Conformal Coating Method carried out?

The dipping method is a coating process that requires the board to be immersed in the coating fluid before being removed.

You find this method perfect for boards requiring coatings on both sides.

For areas not to be coated, a tight mask has to be placed over them to prevent the coating seeping through.

The dipping method is an economical method to use for large batch processing.

It is also a quick method that results in a uniform coating surface.

The penetration offered by the dipping method is also remarkable.

What is the Selective Conformal Coating Method?

The selective coating method employs an automated approach to the spray method.

It utilizes programmed nozzles to deposit the coating on defined areas of the circuit board.

You find this method appropriate for large PCB productions as it is a quick and efficient process.

One aspect that makes this process efficient is the selective application of the coating.

Consequently, the long and intricate procedure of covering areas not to be coated with masks is removed.

Additionally, the surface finish achieved by selective coating is also impressive.

What does the Curing of Conformal Coating mean?

Conformal coats are commonly provided in the solvent form.

To transform them into a solid coat that adheres to the PCB surface, a chemical process known as curing is employed.

To conduct the curing process, heat, ultraviolet radiation, and chemical additives can be used.

Some of the cures used for conformal coatings are:

  • Heat cure
  • Ultraviolet cure
  • Moisture cure

How is a Heat Cure Conducted on PCB Conformal Coatings?

A heat cure involves the use of heat to initiate the curing process.

In this method, the primary concern is to stimulate the evaporation of the solvents containing the coating pigment.

While it can occur gradually on exposure, heat hastens the process.

However, care needs to be taken to maintain the coating’s core aspects which would otherwise be affected.

Carrying out a heat cure can result in enhanced properties such as better resistance to chemical infractions.

Alternatively, you get better resistance to humidity when you let the evaporation process take a natural course.

Nonetheless, some materials have the same results for their property coatings regardless of the speed used of evaporation.

Why is a UV Cure commonly used alongside other Conformal Coating Curing Techniques?

UV cure employs ultraviolet radiation to initiate the curing process for coatings.

Its use is preferred due to its quickness as curing almost happens promptly.

Upon curing, you can proceed to other processes without having to break quickening the overall board fabrication process.

Consequently, you will find this curing process is used in large production runs.

However, due to the PCB’s irregular features, some board sections are obstructed from the UV radiation.

As a result, another curing mechanism is required to initiate the curing of coating in these areas.

Moisture cure is commonly used in the preceding curing process due to its compatibility with the UV cure process.

You can also employ heat cure which will take considerably longer and require elevated temperature values.

Some manufactures provide modified UV cures that eliminate the need for a second cure process.

Can you use Moisture in Dry Area for PCB Conformal Coating?

Conformal Coating on PCB

Conformal coating on PCB

To carry out a moisture cure, the atmospheric moisture content is necessary.

You find that in this process, the higher the humidity the faster the curing process.

However, the low moisture content in the atmosphere can be supplemented by humidifiers.

Humidifiers generate humidity and when used in the curing chambers, can be sufficient to initiate a cure process for the conformal coating.

Chambers can also be left exposed to accumulate moisture that initiates the curing process.

How are the Standards for Conformal Coatings Set?

Several standards are used to monitor the quality of conformal coatings to suit their applications.

These standards can range from industry related to military specifications.

To determine these standards, a variety of tests have to be carried out on the coatings.

These tests typically involve different temperature and humidity values to which the coatings are continuously exposed.

These conditions provide an extreme scenario for the application environments and determine the capability of these coating properties.

Furthermore, the response of the coatings in their protective capacity is established.

What are Some of the Standards provided for Conformal Coatings?

Conformal coating standards are used to ensure that certain qualities are achieved by coatings for use in particular environments.

Standards ensure the use of a certain coating will provide the desired service in an application.

Some of the standards used for conformal coatings are:

· MIL/I/46058C

This standard is a military insulating compound designation for conformal coatings that is currently inactive.

However, for applications involving military equipment, the coatings used still have to conform to this standard which needs independent approval.

· IPC/CC/830B

This standard preceded the MIL/I/46058C and is currently active.

It shares similar specifications to those of the MIL/I/46058C.

· UL94V0

This standard guides the flammability of a conformal coating used on PCBs with FR-4 laminates.

Various sub-standards are used for this standard to illustrate the material’s ability to resist combustion.

UL746E

With this standard, the focus is on the dielectric properties of the conformal coating.

Additionally, it seeks to identify its compatibility with the prevailing standards of safety in the industry.

What are the Directives when using an Aerosol Coating on PCBs?

Aerosol coatings are usually enclosed in a container allowing the deposition of a coating through the nozzle.

With this coating application type, you find simplicity in its use being effective for small volumes of boards.

When using aerosol coating, you need to ensure the following:

  • The area is well aerated with minimal contamination such as a spray cubicle.
  • You have personal protective equipment such as gas masks to prevent inhaling of the fumes.
  • You should not shake the aerosol can to prevent bubble formation that can hamper the evenness of the surface formed.
  • The angle of separation between the circuit board and aerosol should be 45 degrees.
  • The distance between the nozzle and the board surface should be at least ten inches.
  • The application of the coating should be zigzagged with the same period allowed.
  • You should work for the board in ninety-degree rotations with the same application process to ensure uniformity.

How can the Board Layout be Modified to allow a Simple Conformal Coating Process?

The PCB layout has a high influence on the coating process of circuit boards.

For instance, a large board populates cause obstruction during UV cure.

Therefore, the way a board is laid out will help allow the effective application of the coating.

Some of the strategies you can use to improve the board layout to accommodate effective coating application are:

  • You can locate the components and board features that are to remain uncoated along a single boundary.

Their location on a single edge can allow for a faster coating procedure to be used such as dipping.

  • You should also minimize the use of components with discrete qualities.

These components exhibit unusually elevated capillary forces making application of a coating difficult.

Consequently, this limits the board area under cover causing the coating to be insufficient in its protective role.

  • Furthermore, you need to minimize the use of large components which can obstruct the curing process of shadow areas.

Such components also cause splashing and need to be located in areas where the coating is pivotal.

Do you need to Clean the PCB before applying a Conformal Coating?

Yes, you do.

Cleaning the PCB surface is vital to prevent contaminants such as dust and moisture trapped under the coating.

A conformal coating offers the PCB protection from these contaminants external to the board.

However, when the board is not cleaned and the coating is applied, these contaminants will be locked in.

You find these contaminants can cause performance issues such as conveying weak conductivity when moisture is ionized.

Electrical issues can develop as a result of hampering the board’s reliability.

Additionally, you find that contaminates can cause the coating application outcome to be ineffective while initiating corrosion underneath.

Is the Thickness of a Conformal Coating important?

Conformal coating thickness on PCB

Conformal coating thickness

The thickness of a conformal coating has a major influence on the level of protection it offers.

Establishing an appropriate thickness for your application is pivotal since there are negative effects to using smaller or greater thickness.

For instance, when you use a lesser thickness, it will be vulnerable to permeable contaminates.

Conversely, using an excess thickness can create areas with solvent traces due to the failure in total duration.

At the same time, an extra thick coating can result in crevice formation during the curing process.

Such surface fractures can also develop when the board is subjected to different temperature values and minor shocks.

Why is it Important to Apply the PCB Conformal Coating in a Controlled Environment?

Environmental elements such as temperature and humidity affect the quality of the conformal coating.

Consequently, the environmental aspect is one to be seriously considered when applying conformal coating on PCBs.

You find temperature influences the conformal coating’s tendency to resist flow.

When temperatures are elevated, it can cause the coating to soften and trickle if not controlled.

Subsequently, you will have board areas with thinner and more vulnerable coatings.

Conversely, when the temperatures are very low, they will cause the coating to thicken at certain points.

You find difficulty in flowing to contribute to this and hence result in a non-uniform surface.

On the other hand, humidity levels can alter the coating features at two levels: before and during the application process.

The result is usually an imperfectly cured conformal coat or a reduced lifespan.

You note that only increased humidity levels influence the conformal coating.

When the coating application is through an open system such as dipping, it is easily affected by the atmospheric moisture content.

Furthermore, you will find moisture a concern in other hand-operated procedures such as aerosol spraying where it causes blooming.

Areas in which conformal coating is being applied should also be well aerated.

You find this ensures the personal safety of the persons involved in the process and also the quality of the process.

The use of forced air such as electrical fans should be avoided to prevent the airflow from affecting the coating spread.

Additionally, you find it important to have particle-free air in this area to prevent their contamination of the process.

Small and light particles such as hair and dust can land on the coating resulting in an uneven and unappealing surface.

What is the Conformal Coating Cycle Time in PCBs?

The coating cycle time is the period involved to completely apply a coating on the necessary areas of a PCB.

The cycle time can affect the quality of the coating.

Consider the selective coating method which is the most popular for commercial ventures.

Robots are used to conduct the application process on instruction.

PCBs are normally marked for areas to be coated and those to be left uncoated.

To facilitate the coating process a system that deposits the coating as a pattern is established.

This system implements the coating as stripes of about three mils to avoid excess deposition and splattering thereby increasing accuracy.

In this regard, the cycle time can be prolonged when coating needs to be done on areas less than three mils.

In this case, you find the need to implement a provisional maneuver to apply the coating.

Furthermore, the boundary between the areas to be coated and those not to be needs extra care.

At less than 3 mm of each other they ultimately extend the coating cycle time.

In case you have any question about conformal coating process, feel free to contact Venture Electronics Team.

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