Conformal Coating in PCB Manufacturing: The Ultimate Guide

Many manufacturers are getting pushed more and more to adhere to high IP ratings. Some consider the IP67 or higher ratings to be mandatory for new devices, especially portable ones.

One way to give additional water resistance, even with a lower IP rating, is through utilizing a conformal coating on printed circuit boards or PCBs. This article is will become your essential guide to conformal coating for your printed circuit board.

Keep reading to learn about conformal coating types and uses in PCB manufacturing, as well as their advantages and disadvantages.

Benefits of PCB Conformal Coating

There are many reasons why conformal coatings are preferred, compared to a naked or uncoated PCB. Six main benefits stand out. 

• The spacing of PCB conductors can get reduced due to increased insulation properties
• Sophisticated, complex enclosures are reduced or eliminated by using conformal coatings
• Conformal coatings provide lightweight options for enhancing the PCB
• Corrosive and chemical attacks on the PCB get almost entirely eliminated
• Environmental protection against performance degradation
• PCB assembly environmental stresses are mitigated and reduced

Conformal coatings acting as a barrier to moisture and humidity and increasing insulation properties may be the biggest benefits of all. It prevents current leakage, crosstalk, and electromagnetic interference. It also prevents electrochemical migration that may occur with some plating elements.

All things considered, conformal coatings enhance the PCB’s function and protect it from elements and corrosion.

What Are the Types of Conformal Coating Available?

Conformal coatings are a type of protective film that can get applied to circuit boards. It acts as a barrier between the board and the environment, including contaminants. There are five main types of conformal coating used on PCBs.

• Urethane resin (UR)
• Epoxy resin (ER)
• Acrylic resin (AR)
• Silicone resin (SR)
• Parylene (XY)

Urethane and Polyeurethane

Urethane or polyurethane conformal coating is an organic liquid with beneficial dielectric material properties. It has resistance to solvents, moisture, and abrasion.

One of the biggest issues with urethanes is the long cure times and unaesthetic look of soldered components coated with it. It’s difficult to remove if over-coated and may peel off in sheets.

Epoxy Resin

Epoxy resin is an organic thermoset product with good dielectric properties and a high glass transition temperature. It’s most effective at 150°C and boasts good abrasion resistance.

For all the good of epoxy resins, it too is difficult to remove and could shrink during the curing process. Because it’s so durable one of the only means of reworking or repairing epoxy resin conformal coatings is to use a soldering iron to melt it off.

Acrylic Resin

Acrylic is another organic liquid that is easily reworked, has a simpler drying process than most other coatings, and has good moisture resistance. Its ease of use properties includes good characteristics for viscosity adjustment.

It doesn’t have very good abrasion resistance, or chemical and solvent resistance. Due to these issues, Acrylic isn’t suited for harsh environments or high-temperature applications.

Silicone Resin

Silicone resin is an inorganic liquid that remains steady at a large range of temperatures. It also has a high glass transition temperature (Tg) like epoxy resins. It’s solvent resistant and has good dielectric strength. It fluoresces in UV light, making it easy to inspect and repair.

Again, disadvantages prevent silicone resin from getting used in every application. It requires the use of strong chemical strippers, abrasion, or both for removal. Only localized repairs can get made — the whole PCB can’t be reworked.

Parylene (Polyparaxylylene)

Parylene or polyparaxylylene is applied only through vapour phase deposition. A complicated process, that yields incredible uniformity and coverage. They show excellent dielectric voltages even lower than one-micrometre thickness.

There’s no perfect conformal coating that we’ve found, yet. While Parylene is close, it’s very difficult to remove. Only abrasion can remove it, as it has bonded to the substrate. Also, the use of special equipment in vapour deposition does make it more expensive.

Additionally, it isn’t good in long-term outdoor exposure situations.

How Is a Conformal Coating Applied?

Conformal coatings get applied to PCBs by several possible means. Some methods are more suitable for application or production size than others.

• Brush application
• Spray application
• Dipping
• Vapour deposition

Vapour deposition is one of the more expensive and difficult processes to apply a conformal coating. That said, it gives an excellent, even coating that is very effective in protecting against moisture and other contamination.

Dipping is the traditional PCB conformal coating application process. It consists of literally dipping the PCB into a tank of coating liquid of acrylic or urethane.

Dipping is a high-speed process, usually done inline and in batches. The speed of immersion, dwell time and withdrawal speed all play roles in the success of the coating.

Spray application covers aerosols, batch spraying and even selective spraying. Selective spraying is similar to having a stencil over your canvas and spraying paint over it. Although, when it comes to applying conformal coatings it’s far more advanced and technical than that.

Batch spraying is usually performed in a spray booth with a spray gun. There’s a low cost of setup and multiple coatings can get applied.

Aerosol spraying is also done by way of a spray gun, although it is a solvent-based coating method. This too is a very cost-effective, high-speed process.

Brushing is time-consuming and takes a lot of skill for the operator to brush the PCB correctly. Many factors make this method less appealing. For low-volume work, or reapplication it’s suitable, and perhaps even preferred.

ConRo Electronics: Providing Your Conformal Coating Needs

ConRo Electronics prides itself on more than our role as a leading industry supplier for conformal coating. Major brands like Humiseal, Metcal, and Henkel Loctite trust us with distributing and selling their products every day.

We don’t only sell products to our customers. For more than 20 years we’ve continued to provide essential value-added services. Services such as sourcing and procurement on a global scale, managed inventory, kitting & repacking, and consignment stocking.

With ConRo Electronics you have a partner in the industry you can trust, with the highest level of customer service on hand for your benefit.

Contact us today to see how a partnership with ConRo Electronics can benefit you now and into the future.