Why use silicone (SR) conformal coatings to protect electronic circuit board assemblies?

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Silicone (inorganic) conformal coatings can be very different in nature to the organic chemistry coatings like the acrylics and polyurethane materials.

For example, they tend to have a much wider temperature range of operation compared to the other conformal coatings.

Typically, this temperature range can be -55°C to +200°C (-67°F to +392°F) which compares much better to acrylic and urethanes at -55°C to +125°C.

Also, like the organic conformal coatings, they do generally have good moisture protection and good chemical resistance to polar solvents so this can be very effective for protecting printed circuit board assemblies.


Silicone conformal coatings in production

Some silicone coatings are solvent based, to provide the right viscosity for application. Others are solvent-free, non-volatile chemistries that offer the VOC free alternatives required for some industries.

However, it should be understood that SR conformal coatings could require different conformal coating equipment or options.

For example, they are generally higher in viscosity compared to acrylics and polyurethane materials. This can make it more difficult in application.

Also, the general process control of silicone coatings can be more problematic than other types.

This tends to be due to the stability of the coating material in the process. Good housekeeping can minimise these effects.

Curing of silicones occurs through several different mechanisms, depending on the conformal coating. The cure mechanisms include RTV (Room Temperature Vulcanisation), heat, UV, moisture / condensation and catalysed cure.


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