Silicone Conformal Coatings: A Popular, Growing Technology

January 5, 2021 Cadence PCB Solutions

Key Takeaways

  • Silicone conformal coatings function in the same way as other conformal coating types—protecting electronic components and PCBs from damage.

  • Silicone conformal coatings are unique because they are useful for flexible PCBs and high-temperature applications that most other coating types cannot withstand.

  • Silicone conformal coatings typically require a solvent; however, a new type of solventless coating has recently been developed.

Silicone Conformal Coatings: A Popular, Growing Technology

Silicone conformal coating

Silicone conformal coating in progress.

Conformal coatings are thin coatings of various materials used to protect PCBs and their electronic components from damage. Most conformal coatings can protect electronics from a variety of damage types, including physical, mechanical, and chemical damage. 

The interest in silicone conformal coating has grown in recent years, as this type of coating can be used in places where other conformal coatings fail. As PCB technology evolves, conformal coatings evolve with it, and silicone conformal coating represents a great advance towards protecting modern electronics.

What Is Silicone Conformal Coating?

Silicone conformal coatings are made with silicone resin, which can protect PCBs over a wider temperature range than other coatings. This type of coating is resistant to chemicals, moisture, and vibration, but can be difficult to remove or repair. 

Due to its unique properties, silicone conformal coating has grown in popularity over the years. 

Unique Characteristics 

Silicone conformal coatings adhere well to most PCB materials and are included in IPC electronics standards for application of conformal coatings for modern PCBs. They are also compatible with thermal paste, which is a key component of high-temperature PCBs.

Despite their ability to repel water when applied properly, silicone conformal coatings are more likely to absorb moisture during their application process than other coatings. Applying these coatings evenly is particularly important, as any defect can be a place where water might collect. Tiny deposits of water can erode a coating over time. Water can also carry corrosive materials with it, further endangering the lifespan of the coating. 

Since conformal coatings must be made of non-conductive material, erosion of silicone conformal coatings by water can disrupt the electrical flow in PCBs. The rubbery nature of the coating can also cause it to flow and change thickness over time, similar to how glass panes flow and create thinner areas at their tops.

Silicone Conformal Coating Is Flexible 

Flexible PCBs rely on many of the same circuit and component types as rigid PCBs, but their substrate allows them to bend into shapes that aren’t possible with rigid boards. Therefore, flexible PCBs need a conformal coating that bends as well, which is something silicone conformal coating makes possible. Other types of conformal coating cannot bend as silicone coating can, so attempting to cover flexible PCBs with other coatings would result in uneven protection. This uneven protection could cause flexible PCBs to fail.

The Coating Process Is High-Risk and High-Reward

Silicone conformal coating by spraying

Spraying silicone conformal coatings.

Silicone conformal coating can be cost-effective when applied properly. However, if designers ever have to go back and remove the coatings, the process is a difficult one. This makes the silicone conformal coating process high-risk and high-reward, unlike other types of conformal coatings that can facilitate repairs more easily. Mistakes in silicone conformal coating can be costly, and the process that removes the coating requires long chemical treatments that can delay production. Any circuits under the coating are vulnerable to physical or chemical damage during the coating removal process, so removing the coating may force a manufacturer to implement additional repairs. Successful silicone conformal coatings require careful application and careful planning to account for any mistakes.

Industry Usage

As the fastest-growing type of coating in the conformal coating market, silicone conformal coatings are being used in many industries. Since they can withstand extreme temperature stresses, either hot or cold, for long periods of time, they are commonly used on automotive parts.

How Has Silicone Conformal Coating Technology Advanced?

Silicone conformal coatings usually require a solvent to be applied properly. In the last year, however, a new type of silicone conformal coating that doesn’t require a solvent has been developed. The new coating can be cured with UV light or at room temperature over time. Solventless silicone conformal coatings are currently optimized for rigid PCBs since they can compensate for incomplete UV curing by finishing the cure process at room temperature. This would be significantly more difficult to do with a flexible PCB since the unpredictable angles could lead to variations in the curing process.

It is usually vital for conformal coatings, including silicone conformal coatings, to have a completely smooth and clean surface for application, since deformations can promote erosion of the coatings. Some forms of silicone conformal coatings, according to new research, can prevent deformation of the surface beneath them. The particles of silicon in these coatings must be tiny, only a micron wide. This new type of silicone conformal coating has the potential for increased application in the aerospace industry and is already being tested for use in spacecrafts. The silicon conformal coatings that are currently available commercially employ larger silicon pieces, which prevent them from having the same level of protection as this new variant.

A cured PCB with silicone conformal coating

A cured PCB with silicone conformal coating.

Consider including silicone conformal coating in your manufacturing processes to produce reliable and durable electronic components that can withstand high temperatures while remaining flexible. The PCB Design and Analysis overview page at Cadence Design Systems provides a wide variety of information on silicone conformal coating. Learn what’s new in OrCAD or use the OrCAD PCB Designer to keep your PCB design processes both time and cost-efficient. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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