Five important facts about silicone conformal coatings

  1. Silicone (SR) conformal coatings are inorganic materials. They are polymers in which atoms of silicon and oxygen alternate in a chain. They differ to the organic polymers like the acrylics and urethanes.
  2. The silicone coatings normally have a very wide temperature range of operation compared to the other conformal coatings. Typical range can be -55°C to +200°C (-67°F to +392°F). Like the organic coatings (acrylics and urethanes) they have good moisture protection. They also have good chemical resistance to polar solvents.
  3. SR coatings are generally applied at 2-3 times the thickness dry film compared to organic coatings. This is reflected in the IPC standards on the recommended conformal coating thickness. This increase in material use can lead to increased costs but also better water repellency properties.
  4. Curing of silicones occurs through several different mechanisms, depending on the conformal coating, including RTV (Room Temperature Vulcanisation), Heat, UV, Moisture / Condensation and Catalysed Cure.
  5. In production they can be difficult materials to use due to the cure mechanism being difficult to control. Good housekeeping can minimise these effects. SR coatings can also require different coating equipment or options compared to the organic coatings. This should be considered as part of the holistic approach to conformal coating selection.

The different conformal coating material properties

Conformal coatings can be considered in many different ways.

This includes the different families of materials, their individual properties and the chemistries of these coatings.

The different ways we can examine conformal coatings include:

  • Classification
  • Physical Properties
  • Electrical Properties
  • Chemistry

There is a vast range of options and considerations available.

Click conformal coating material properties to gain a deeper knowledge of conformal coatings.

Need to find out more?

Click silicone conformal coatings for further information or contact us directly and we can help you.

If you are new to Nexus and our work on conformal coatings then a good place to go is our Start Here page or our free conformal coating eBook.

Ask The Expert: Phil Kinner, PVA, Conformal Coating Robotic Solutions on Key Conformal Coating Inspection Challenges

“Many users are looking to automate their inspection process, in order to increase their quality level.  Systems are available that can integrate a camera and lighting, directly into a selective coating robot, or can be used in a standalone fashion separate machine.”

“There are numerous  challenges involved in automating the inspection process, not least of which is the variation in brightness of fluorescence of the conformal coating materials, both batch-to-batch variations and between different conformal coating materials.  Silicone materials in particular can have very low levels of fluorescence.”

“Other issues relate to the 3D nature of the substrate, light scattering leading to distortion of the images, background fluorescence of metallic solder joints/component leads and tall components or component bodies restricting the field of view, rendering it nearly impossible to inspect beneath or around through hole capacitors and connectors.”

Visit the Nexus Associate Experts Section and read what other experts have to say about conformal coating inspection.

Bitesize Nexus Help: The Biggest Cause of Conformal Coating De-wetting Defects

The biggest single cause of de-wetting (a lack of adhesion) of conformal coating on a printed circuit board is silicone contamination accidently introduced in the production line. The silicones can come from many areas including RTVs on the bench and lubricants for machines.

Contact Nexus Consultants for more help on silicone conformal coating de-wetting