Three key points you should know about polyurethane conformal coatings when using them for protecting electronic circuit boards


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A polyurethane (urethane for short and designated UR by IPC) conformal coating is part of the organic family of coating materials that also includes the acrylic and epoxy coatings.

Here are three key facts to consider when examining polyurethane conformal coatings:

  1. Most conformal coatings provide good humidity and moisture protection although some are slightly better in performance than others. UR type coatings are just as good on average as acrylic materials.
  2. A polyurethane coating has traditionally been used to protect electronic circuit boards against chemical attack due to their excellent chemical resistance. This protection allows electronic circuit boards to survive in highly aggressive environments and atmospheres such as the aerospace, military and industrial sectors. However, it does make repair a little more difficult as chemical resistance to a coating means more difficult to remove.
  3. Times are changing and whereas acrylic conformal coatings used to dominate 70-80% of the market, there is a shift in emphasis towards alternative materials due to higher specifications for protecting electronics. Many new conformal coatings (UV cure, two part thin film coatings) now comprise of urethane resin bases and are becoming more popular in high volume sectors such as automotive electronics. This is because the urethane resin lends itself to this type of technology more easily than the acrylic based resins.

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What is a hydrophobic acrylic conformal coating?


Nano-coating fluoropolymers Collage 640_SCH UK

There are several reasons for using a conformal coating or Parylene to protect a printed circuit board (PCB).

They include:

  • High insulation protection
  • High moisture and humidity protection
  • Chemical and temperature resistance
  • Ruggedisation
  • Improve dielectric properties
  • Barrier protection against particulates

However, one property that most liquid conformal coatings do not possess that is extremely useful to have is being water repellent or hydrophobic.

A coating that is hydrophobic repels water from the surface by changing the surface energy of the coating.

This makes it energetically unfavourable for the water to wet the surface. Hence, the water “balls up” and rolls off the surface.

This occurs in the fluorinated nano-coatings that are hydrophobic and is an extremely useful property when protecting a circuit board where water may be present.

However, typical conformal coatings are not hydrophobic.

Materials like acrylics and polyurethane coatings are excellent against moisture but not so good as water repellent materials. They do not have a low surface energy.

Conformal coatings like acrylics and urethanes do not have water repellent properties (left). A hydrophobic conformal coating repels the water and does not allow it to wet the surface (right).
Conformal coatings like acrylics and urethanes do not have water repellent properties (left). A hydrophobic conformal coating repels the water and does not allow it to wet the surface (right).

A hydrophobic acrylic conformal coating – the best of both coatings

Now, there exists a hybrid acrylic coating that has both the properties of an acrylic conformal coating at the same thickness plus the benefits of a hydrophobic nano-coating.

These benefits include:

  • Hydrophobic (water repellent) surface
  • High Insulation protection
  • High moisture and humidity protection
  • Ruggedisation
  • Improved dielectric properties
  • Barrier protection against particulates

This new range of conformal coatings can now offer the best properties of both without any cost penalty.

The water wets the surface (left) on a normal acrylic conformal coating. A hydrophobic acrylic conformal coating, with a low surface energy, makes water de-wet from the surface (right) and still has all the benefits of the acrylic conformal coating.
The water wets the surface (left) on a normal acrylic conformal coating. A hydrophobic acrylic conformal coating, with a low surface energy, makes water de-wet from the surface (right) and still has all the benefits of the acrylic conformal coating.

Find out how we can help you with your acrylic hydrophobic coatings now.

Contact us to discuss your needs and let us explain how our hydrophobic coatings could work for you.

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