We offer a range of conformal coating services to improve performance of printed circuit boards.
In today’s guide, I will answer all questions you have been asking about the conformal coating process.
So, if you have any questions about PCB conformal coating, read this guide.
What are the Types of Conformal Coating for PCB?
You find the prevalent use of five common conformal coatings on PCBs.
These coating types have distinctive properties that allow their use in different conditions.
They include:
Conformal coating PCB
- Acrylic Resins: These coatings are widely employed due to their flexibility and easy application and removal.
- Parylene Resin: You find this resin is based on paraxylene and typically applied under vacuum conditions.
- Polyurethane Resins: These resin types can also be found as two-part compositions. They have a relatively longer curing time and impressive resistance to chemical infringement.
- Silicone Resins: The resistant properties of silicone coatings are remarkable, with a transparency level suited for solar functions.
The use of solvents cannot remove these coatings as they are insoluble on them.
- Epoxy Resins: These coatings portray remarkable resistance to physical, moisture, and chemical intrusion.
They can be applied through all available techniques but are challenging to remove.
Which Machine do you need for Conformal Coating Services?
Conformal coating machine
The conformal coating machine and equipment depend on the application technique.
For instance, the equipment used for brush applications will differ from the spray method.
- For brush application, you will need a brush to aid in the coating application. The brush can be furnished with a cloth or soft bristles.
- Spray method of coating application can be employed via a spray gun or aerosol can. Both approaches are manual.
- To carry out a dip coating, you require a bath container to hold the coating material.
- The selective coating technique is an automated process that involves programmed robots.
Are there Standards Requirements for Conformal Coating?
Yes, there are.
Quality standards for conformal coatings guide various aspects of the coating process.
Typically, you find these standards determine:
- The resistance capabilities of the coatings to elements such as moisture, abrasion, and chemicals.
- The flammability of the coating.
- The environmental impact of using the coating material.
- The composition of the coating, especially those based on volatile organic compounds.
Why is Conformal Coating Important in PCB Fabrication?
You find the use of conformal coatings on printed circuit boards is essential for the following reasons:
- Conformal coatings provide insulation to the circuit board by their non-conductive nature.
Furthermore, their use sanctions closer trace spacing on PCBs.
- When you coat a PCB, you do not have to construct a particular casing for protecting the PCB.
- Using a conformal coating will protect your PCB from various elements such as moisture, thermal cycles, abrasion, and chemical infraction.
- Conformal coatings do not significantly impact the overall weight of the printed circuit board.
- You provide the circuit board with mechanical support against vibrations and shocks.
- The reliability of boards is improved by the use of conformal coatings allowing extended use.
What are the Features on Conformal Coating Services used in LED Lighting Circuits?
When using conformal coatings on LED lightings, consideration must be made for the lighting’s quality aspects.
Such aspects include the light color and brightness.
To prevent interference of these quality aspects, coatings used are typically transparent to allow the light to remain as intended.
Furthermore, the coating has to prevent interference from external ultraviolet radiation and environmental elements such as humidity.
Acrylic resins make such coatings transparent, allowing the LED lighting to retain its light quality aspects.
You can employ either solvent-based or water-based conformal coatings.
The achievement of reduced interference to the light quality from an LED array involves using coatings with a minimal thickness.
You find that when a coating is applied over an LED light source, it tempers the color.
How are Conformal Coating Services useful in LED Circuit Applications?
You will note that huge steps have been made in the LED technology market regarding their designs.
Changes have been bolstered by the new environmental awareness requiring such lighting systems to be more safe and reliable.
An essential use of LED lighting is the outdoors, where it is pursued in various applications, including traffic and signal lighting.
LED PCB with conformal coating
The use of outdoor LED lighting has been propelled by LED systems’ ruggedness to withstand the harsh external environment.
The ability to tolerate the challenging environment has also been contributed by the use of conformal coatings.
Such lighting systems encompass an agglomeration of electrical circuits which require such coatings for protection.
In LED lighting systems, conformal coatings protect the LED circuits from environmental elements such as temperature and moisture.
The coatings also offer resistance to ultraviolet radiation, chemical infringement, and physical abrasion.
Consequently, the circuits are safeguarded from the adverse effects of corrosion and the leakage of signals.
Does PCB design affect Conformal Coating Services?
The board design is insignificant in determining the coating material used on PCBs.
However, you find board design heavily influences the choice of application method of the coating.
Intricate board designs with sensitive components will require a more accurate coating method, such as selective coating.
Additionally, the board arrangement will determine whether the coating application will be easy or difficult.
Arranging areas not to be coated along a single board edge makes coating application simple with a reduced masking complexity.
Furthermore, having extensive board features scattered across the board makes the application process challenging.
PCB with and without conformal coating
Are Electrical Properties Important in Conformal Coating Services?
Typically, most conformal coatings are made from polymerized resins, making them non-conductive.
These coatings serve a protection role, including protecting the circuit board from unwanted connections resulting in shorts.
However, you find limited charge transfer as a limitation of water-based coatings.
Nevertheless, an essential electrical property observed for coatings is their surface insulation resistance.
You find this parameter peaks to the coating’s ability to resist electrical charge transfer.
To determine a coating’s SIR, a measurement is taken before being subjected to test conditions such as elevated temperatures.
The test value is compared with the untested value to determine how much the coating’s surface insulation resistance is affected.
Furthermore, the coating’s dielectric properties are equally significant with a high measure desired, especially for high-frequency applications.
Good dielectric properties maintain signal quality by reducing interference.
How do you Determine Coating Technique during Conformal Coating Services?
There are several approaches to applying conformal coatings over printed circuit boards.
Each application method has given pros and cons, which you can use to guide your choice.
The essence of coating is to achieve a dependable board protection level from external elements such as moisture and dust.
Otherwise, some of the factors that will guide the choice of application method include:
- The cost to be incurred in using a particular method.
You find the price is a factor determined by the number of boards and the nature of work done.
For instance, using a simple brush application is sufficient for repair work instead of automated selective coating.
- Alternatively, when faced with a large board volume, an automated coating approach is more cost-effective.
You find using automated means rather than a manual approach like hand-spraying is much faster with high repeatability.
- The availability of equipment for use in the coating process can also influence the choice of application method.
Coating application typically entails the use of equipment such as cloth-brush, spray gun, or aerosol can.
Having the necessary equipment can prove a cheaper option than having to acquire new equipment.
- Another factor is the design of the board. Boards with high component density and areas designated ‘no coat’ are not favorable for dip coating.
Also, board designs with sensitive features are better off handled by an automatic application process.
- Coating processes take a different durations to cure and adhere to the board features. When time is essential, a coating process will be selected based on the average coating cycle time.
This is the time it takes to completely apply a coating on the required area on a single PCB.
Does Miniaturization Affect Conformal Coating Services?
Miniaturization is a technological trend that seeks to make devices such as electrical products smaller and lighter.
You find various approaches used to achieve this, such as eliminating specific procedures or combining processes.
Since conformal coatings are especially crucial for PCBs, dispensing with them is not yet an option.
You find conformal coatings have been modified to offer similar protection standards for miniaturized devices but at smaller thicknesses.
Additionally, since board features are much closer in these devices, the coating’s dielectric properties and surface insulation resistance have been enhanced.
Do you use Solvent Free Coatings during Conformal Coating Services?
Solvent-based coatings have been the standard in the coating industry for a long time.
Nonetheless, currently, solvent-free options have been developed as a response to environmental concerns.
You find the use of solvent-free coatings to have the following advantages:
- The materials used to make solvent-free coatings have low toxicity compared to those used in solvent-based coatings.
Consequently, they pose a lesser threat to the environment with their emissions.
Contrarily, you find solvent-based coatings constitute a significant source of emission of volatile organic compounds.
These substances are harmful to the environment contributing to the damage of the ozone.
- Furthermore, solvent-free coatings produce less pungent fumes, which can cause health problems to operators when inhaled.
- Solvent-free conformal coatings do not catch fire and subsequently pose a lesser danger to the property as a fire risk.
As a result, the insurance required for storage houses of the coatings is much lower.
- You can achieve larger thicknesses using solvent-free coatings with similar standards of performance to solvent-based coatings.
With solvent-free coatings, you can develop two-part coatings with good adhesion.
In short, you should be cautious when using conformal coating spray technique.
Conformal coating spray technique
What Application Modes for Coating are used in Conformal Coating Services?
A coating application is an exercise carried out manually or automatically with the aid of various equipment.
Upon applying a coating, it must proceed through a curing process to develop a dry layer coverage.
Most importantly, the coatings contain a dye that fluoresces, which helps carry out an inspection.
The following options are typically considered for a conformal coating application.
· Brush Coating
Brush coating is similar to painting as the coating is applied via strokes of a loaded brush.
The application’s manual nature makes it only suitable for a few boards use, such as repairs and reworks.
However, you find the aesthetical aspect of brush coating to be mediocre with significant dependency on the operator’s skill.
· Spray Application
Spray coating is another mode of application that is manually executed and applicable for more than a few boards.
Equipment used to aid the spray coating process includes aerosol cans and spray guns.
Spray coating can also be carried out in a unique cubicle where process controls have been placed.
While the coating outcome is still subject to the operator’s skill, the aesthetic result is more appealing than brush coating.
However, this application falters when it comes to penetration with hard to reach areas such as between extensive features.
However, the surface coverage, especially for edged board features and vertical installations, is remarkable.
· Dip Coating
Another unique coating process is dipping the circuit board into a bath of the coating material.
The repeatability of this process is very high and, as such applicable for large PCB numbers.
However, its use is heavily dependent on the board design due to its high penetration.
No coat parts have to be well separated and tightly masked as a result.
· Selective Coating
The selective coating is an automated coating process that is executed by programmable machines.
The board design is fed to computers where the areas to be coated are highlighted and programed.
Robotic machines use this program data to apply coatings only on the determined areas, selectively.
You find the selective coating process has a large capital investment with two modes of application, via spray or needle.
However, this method offers the best in return in terms of speed, accuracy, and repeatability.
The coating’s thickness can be adjusted by altering the coating material’s viscosity and the spray head and needle outlets.
How do you Conduct Curing during Conformal Coating Services?
Curing is a procedure used to hasten the drying rate of the wet conformal coatings process.
Otherwise, solvent-based resins will set and dry naturally by exposure to air.
Some common curing approaches used in conformal coating services are heat curing, moisture curing, and UV curing.
Heat curing is carried out through ovens by the aid of a conveyor system.
Circuit boards are transferred though the ovens allowing interaction for the determined curing period.
When curing water-based coatings, lesser temperature conditions are to be used to prevent coating damage via stress. Therefore, they have longer curing times.
Curing using ultraviolet radiation exposure is commonly applied where the PCB count is large.
UV light sources such as microwave lamps are employed in this process that is simple, fast, and environmentally safe.
Additionally, you achieve higher resistance to thermal cycling when using UV curing.
Moisture curing is employed by exposing the coated boards to moisture presence.
The atmospheric moisture content is sufficient; otherwise, humidifiers are used for dry conditions.
Moisture curing is used for polyurethanes and silicone-based coatings.
While the immediate process is fast, taking a couple of minutes, the setting process can take days.
Why is Inspection Important during Conformal Coating Service?
The inspection of the conformal coating is meant to check for aspects such as coverage and thickness.
These features illustrate the quality of the work and determine whether the expected standards have been met.
Fluorescing dies are typically added to conformal coatings to aid in the inspection process.
The conformal coating inspection can be carried out manually by a specialist employing a UV light source to expose the die.
The specialist examines the board to determine the appropriateness of coverage and quality of work.
Normally, the specialist notes deviations and inconsistencies and separates such boards for rework.
Automatic optical inspection of conformal coatings is also possible to allow for large batch inspections.
Here, high-performance cameras and scanners are employed to capture the coating details, comparing them to the design standard.
Non-compliant boards are identified and separated for correction procedures.
Remember, all these possible conformal coating problems that can compromise performance of the PCB.
How do you Measure Coating Thickness during Conformal Coating Services?
The thickness of the conformal coating is an important measure that illustrates the quality of a coating.
A uniform thickness across different board areas suggests an even and consistent application.
You find that the thickness of a coating influences the level of protection from external elements.
For instance, a very thin coating will barely protect the circuit board features from corrosion agents, such as moisture.
Alternately, a very thick coating will pose problems such as solvent trapping due to inadequate curing.
Additionally, such a coating will succumb to thermal-induced stress resulting in cracks due to thermal cycling.
The thickness of coatings can be determined by several means, some of which are mentioned below:
· By Use of a Wet Film Thickness Gauge
You find these wet film gauges can encompass wet film combs or wet film wheels.
As the name suggests, the thickness is taken for a wet coating material before it dries.
The wet film combs encompass several teeth-like extensions with specific measurements relative to the baseline.
Also, the level the wet coating reaches when placed on the coating determines its thickness.
· Using a Micrometer
A micrometer screw-gauge is used to determine the board thickness in several areas before the coating process.
After that, the same areas are measured for thickness after the coating procedure and the difference established.
The difference corresponds to the thickness of the coating. For double layer coatings, this amount is divided by two.
You find using a micrometer is only convenient for tough coatings due to the pressure applied in securing the micrometer.
The coating consistency can be established by determining the standard deviation of the different board areas’ measurements.
· Using Eddy Current Probes
Another approach to the measurement of coating thickness involves the creation of an electromagnetic field with oscillations.
These oscillations are measured by a test probe for the Eddy currents developed.
Using this method is highly accurate and popular since it does not physically alter the coating structure.
However, you find this method limited as it requires a metallic base to generate the electromagnetic field.
Furthermore, the metallic base should be exposed to allow contact with the test probe for results accuracy.
· Using Ultrasonic Thickness Gauge
Ultrasonic waves are employed in this measurement procedure.
A transducer is placed on the coating surface with water as a conductive medium in between.
You then transmit sonic waves from the transducer that penetrates the coating onto the PCB surface where it bounces back.
The time it takes for this to happen will determine the thickness of the coating.
An ultrasonic thickness gauge is preferred over the eddy current probe since it doesn’t need a metallic base.
Furthermore, this test procedure poses little threat of damage to the coating.
What are the Testing Methods for Coating Removal during Conformal Coating Services?
Removing conformal coatings from circuit boards is necessary for various reasons, such as rework and repair.
Different removal methods depend on various features, such as the coating material used and the thickness.
You can also determine which coating removal method to use by carrying out the following tests.
· Ease of Stripping
The ease of stripping off a coating is dependent on the strength of adhesion.
Meager adhesion forces are required to support removal by stripping.
You can cut through a conformal coating using a knife-edge and attempt to peel off the coating as a test maneuver.
· Solubility
Solvents can be used to remove soluble coatings.
However, some solvents can be destructive to the board features necessitating a solubility test.
Such a test is carried out on a board area with no sensitive features to determine its reaction.
· Hardness
A hardness test is carried out to determine the coating’s toughness and, consequently, the appropriate method of removal.
A very tough coating will require a brass removal approaches such as abrasion.
Soft coatings can be removed by simple efforts such as peeling and brushing.
· Thickness
The thickness of a coating influences the removal process.
Very thin coatings can be removed via brushing or peeling.
Conversely, thick coatings can require the use of an abrasive method such as microblasting.
You can visually determine the thickness of a coating and categories it as thick or thin.
· Transparency
While most coatings are transparent, some are opaque.
Such coatings are challenging to remove since you cannot see underneath.
Therefore, a more precise approach is used to prevent the inadvertent damage of delicate underlying features.
· Thermal Testing
Some coatings can be removed by inducing regulated heat and an edged device.
You can test for a coating’s removal with this procedure by attempting a non-critical area using low heat.
You can progressively increase the temperature and monitor the coating material flow.
A thin flow that streaks and sticks are unsuited for temperature-induced removal.
Which Standards do you use during Conformal Coating Services?
Standards guide the coating process, ensuring quality and safe products are channeled to the market.
For a conformal coating to adhere to a certain standard, it must successfully meet its test requirements.
Two common standards for conformal coatings are the IPC-C-830B and the UL746E.
· IPC-C-830B
The IPC-C-830B standard was derived from a military-specific standard that sought to determine a coating’s quality on various grounds.
The determination is evaluated by a series of tests that touches on:
- The outcome and appearance,
- The coating’s resistance capabilities,
- The elasticity property of the coating, and
- The performance stability
Some of the elements whose resistance is tested include; thermal stress, insulation, moisture, flames, ultraviolet radiation, and molds.
· UL746E
The UL746E standard was created by the Underwriters Laboratory, which is a body that issues safety certifications.
The UL746E determines the safety concerns of coated electronics concerning electrical failure and flammability.
The coatings are subjected to various electrical tests that attempt to unearth the stability of their isolative qualities.
To test the coatings’ flammability, they are set on fire under test conditions, and the duration of combustion is determined.
· IPC-TP-574
The IPC-TP-574 standard is used to test the coating’s ability to be cured by using ultraviolet radiation.
Furthermore, it establishes a coating’s capacity to resist moisture under accelerated conditions.
· BS-5917
The standard is particular to the type of Conformal Coating Material to be used during PCB fabrication.
· SSPC-GUIDE 10
This standard is specific to coatings’ composition.
It describes the requirements for solvent-based coatings regarding the use of volatile organic compounds.
What Determines the Cost of Conformal Coating Service?
The cost of conformal coating services is dependent on a variety of factors and features.
You find the following to significantly influence the cost of conformal coating services.
· Type of Coating Material
You have a variety of options when selecting coating material.
You can use solvent-based coating materials or solvent-free materials.
Furthermore, you can go with acrylic, urethane, silicone, epoxy, or parylene material for the solvent-based coatings.
These options come at different costs.
· Technique of Coating Application
The method of applying your coating choice will also influence the overall cost of your conformal coating service.
The different approaches to coating applications require different equipment and thus attach different costs.
There are four common application methods, brush, spraying, dipping, and automated selective coating.
· Number of Circuit Boards
There is a relationship between the cost of conformal coating services and the number of circuit boards.
The cost of coating per board reduces when the board number increases.
Furthermore, some application techniques, such as dip coating, are much cheaper when used for large board volumes.
· Coverage and Thickness of the Coating
Circuit boards requiring a large area to be coated will employ more coating material and thus increasing the cost per board.
Furthermore, applying thicker coatings increase the coating material used, positively impacting cost.
How long does it take to Finish Conformal Coating Service?
There are several factors that determine the duration of a conformal coating service.
You find the application process and curing procedure as the two main factors that define the duration of the process.
Typically, applying coatings manually is much slower than an automated application.
For instance, the selective coating is faster than a brush application.
Additionally, the choice of curing procedure will affect the time taken to complete a conformal coating service.
Different curing procedures have different curing times.
You find a moisture curing process can take up to forty-eight hours to completely set.
The drying process of a coating begins immediately, taking a few minutes for the surface to feel dry when touched.
Nonetheless, the coating can be let to naturally dry without any accelerated measures such as moisture or temperature curing.
You find that the process takes much longer this way, taking several days that can run into weeks.
Venture Electronics offers a range of conformal coating services.
Depending on your unique specific needs, we can adopt a PCB conformal coating process that meets the specific requirements of your applications.
Contact us today for all your conformal coating process needs.
