Conformal coatings are usually applied as very thin coatings, providing the maximum amount of protection possible while still using the thinnest amount of material. The thinness of the coatings minimize heat entrapment, unnecessary additional weight, and a variety of other concerns. Common thickness with most conformal coatings is anywhere between 1 to 5 mils (25 to 127 microns) with some coatings applied at an even thinner level. Anything greater than this thickness is usually an encapsulate or a potting compound, which typically provides more mass and thickness to protect the boards.

Certifications are an important way to distinguish general purpose varnishes and shellacs from engineered coatings designed specifically for PCB protection. Although there are dozens of user and industry specifications, the two major certifications are IPC-CC-830B and UL746E. When selecting a coating, look for the availability of 3rd party test documentation, rather than coatings with the claim that “they meet the requirements”.  Both standards use the UL94 standard to judge flammability, with a V-0 rating signifying the lowest flammability potential.

Once the type of coating is selected, the next question is how to apply the conformal coating. This decision should be based on the following variables:

Once a coating has passed the UL746E standard, it can be registered with UL and assigned a registration number. Products certified and registered to UL746E standards can include the UL symbol (which looks like a backward “UR”). To maintain the registration, a coating must be retested annually.

The following categories are based on the basic resin of each coating. The chemical composition of each conformal coating determines its major attributes and functions. Choosing the proper conformal coating for your application is determined by the operational requirements of your electronics.

The rest of this article is concerned mainly with what we call “traditional” conformal coatings, but we’ll first cover other coating types to provide a complete picture of the options available.

If all you are doing is replacing a component or working on an isolated area, it is common to simply burn through the coating with a soldering iron. In cases when this is aesthetically unacceptable, contamination is a concern, or components are densely spaced, coating removers are available in pen packaging.

On occasion, it is necessary to remove a conformal coating from the circuit board to replace damaged components or perform other reworking procedures. The methods and materials used to remove coatings are determined by both the coating resins and the size of the area, which can impact the time required for removal.

Underwriters Laboratories (UL) is considered a credible and reliable safety certification body worldwide, and UL certification is commonly required for consumer goods. UL746E tests for the electrical safety and flammable safety of  coated electronics. For electrical safety, there is a battery of tests similar to IPC-CC-830B, but with a cycling current load to constantly measure the failure of the isolative properties of the coating. The flammability test uses the UL94 standard like IPC-CC-830B, which involves attempting to light the cured coating with an open flame and observing the sustainability of the flame.

This standard originated with the military standard MIL-I-46058C, which became obsolete in 1998. The civilian version IPC-CC-830B is nearly identical, so it is generally understood that if a board passes the IPC spec it will also pass the MIL spec., and vice versa. IPC-CC-830B is a battery of tests, some are pass-fail and others provide data that can be referenced and compared to:

With the increased popularity of miniaturized electronics and circuitry, conformal coating use has skyrocketed to solidify its relevance in a wealth of modern PCB-related applications . Choosing the ideal type of coating and application methods for your electronics is crucial. However, processing the vast amount of information online can often present a daunting task.

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What did you think of this guide? Maybe there is something we missed. Let us know by leaving a comment with your feedback. Techspray has experts available that will guide you all the way through the selection and qualification process.

What is Conformal CoatingConformal coating is a special polymeric film forming product that protects circuit boards, components, and other electronic devices from adverse environmental conditions. These coatings ‘conform’ to inherent irregularities in both the structure and environment of the PCB. They provide increased dielectric resistance, operational integrity, and protection from corrosive atmospheres, humidity, heat, fungus, and airborne contamination such as dirt and dust.

While the curing mechanism is not a primary criterion when selecting a coating, it has a direct impact on the type of application method that will be feasible, and the throughput that can be expected. Some mechanisms are relatively infallible, while others are very complex and leave room for application errors when used in an uncontrolled process.

Safety and environmental considerations should always play a part in chemical selection and process design, but different regulatory bodies make this an even more challenging feat, as requirements must be interpreted and matched with product specifications.

This concludes our guide on conformal coating. We hope that it answered your questions and provided proper guidance in selecting the best products and methods for your needs. Like any challenge, selecting the best coating and coating process can be broken apart, analyzed, and solved.

Types of Conformal CoatingApplication MethodsThickness MeasurementCuring MethodsRemoval Methods CertificationsRegulatory Considerations

What we call “traditional” conformal coatings are 1-part systems that have a resin base and can be diluted with either solvent or (in rare cases) water. Traditional coatings are semi-permeable, which is why they are not fully hermetic nor do they seal the coated electronics. They provide resistance to environmental exposure, which increases PCB durability while keeping application and repair processes in practice. However, they are NOT fully water-proof.

Coatings can, and often are, tested to standards that only represent a portion of the whole standard. In the case of UL94, this is helpful when flammability is the main concern. Some specialty coatings may not be tested to the entire IPC-CC-830B or UL746E standards because they may fail parts of the test. These failures may be due to the nature of the product and the coating’s necessary applications, and are not always a reflection of the quality of the product. For example, some coatings intended to coat LEDs leave out the UV indicator to prevent color shift, but this automatically would cause disqualification under IPC-CC-830B. In other words, it is impossible by definition to pass IPC-CC-830B and have optical clarity in the UV part of the spectrum.

There are several options for coating technologies, and the best option for your particular application should depend primarily on your level of necessary protection. The application method and the ease of rework are also important factors, but should generally be considered secondary to the necessary protective performance.

EPA (United States Environmental Protection Agency) – In the US, the EPA requirements must be followed at the national and regional level. The EPA, following the Montreal Protocol treaty, enforced restrictions on ozone-depleting chemicals. Since most of the restricted chemicals are unavailable and have not been used in conformal coating formulation for years, ozone depletion isn’t the current concern. If there are regional agencies (see next paragraph) that have stricter requirements than the EPA, those generally will need to be followed.

CARB (California Air Review Board) and other regional regulations – Local agencies continue to play  a larger-and-larger role in environmental restrictions. CARB was one of the early regulatory bodies, laying down VOC (volatile organic compounds – smog-producing chemicals) restrictions by product category. Other regional agencies followed their lead. Global warming potential (GWP) is the latest environmental topic of discussion.

OSHA (Occupational Safety and Health Administration) - In the US, the OSHA has overriding authority over worker safety concerns. Many coatings are very flammable, and many emit fumes that have a high level of toxicity. Close attention needs to be paid to ventilation (explosion-proof when dealing with flammable fumes) and the appropriate PPE (personal protection equipment) to keep operator exposure down below the appropriate safety threshold. Flammability may be difficult to avoid without exploring more specific water-based coating materials. Newer coatings have been introduced that do not include HAPs (hazardous air pollutants – a government classification of particularly toxic chemicals) like toluene, xylene or methyl ethyl ketone (MEK). The Global Harmonized System (GHS – with those red diamond symbols) needs to be followed for labeling, which is generally taken care of by the manufacturer. Make sure safety data sheets (SDS) are readily available to operators, as they should be for any hazardous chemical in a facility.

In this article, you’ll be given all the information that you need to identify the ideal conformal coating for your application’s requirements. If you are searching for something specific, feel free to use the index for a more selective approach. Otherwise, this article is helpful both for beginners who seek to understand conformal coating methodology and use, and for seasoned applicators and businesses who wish to confirm their knowledge-base and procedural legitimacy. You can also check out our selection of conformal coatings here.