How Thick should Silicone Conformal Coating be Applied?

Silicone conformal coating is commonly used because of its excellent moisture resistance, short cure time and high temperature capabilities. It is also one of the easiest conformal coatings to work with. In order for the coating to function optimally, it has to be applied at the proper thickness.

Maintaining appropriate thickness is critical for silicone conformal coating because it is applied very thick compared to other conformal coatings. If applied too thin, its protective properties may be compromised. Conversely, if applied too thick, it may create excessive stresses on solder joints and components, particularly glass-bodied components. For this reason, the IPC created J-STD-001 to regulate and standardize coating thicknesses. J-STD-001 specifies silicone coatings should be applied at a thickness of 0.00197 to 0.00827 in.

To achieve the ideal thickness, silicone conformal coating can be applied three ways:

• Spray
• Dip
• Brush

Spray application can be done via hand-spray, aerosol can or by robotics. When applied manually or with aerosol, the material is usually diluted with solvents to get to a predetermined viscosity and is sprayed from all four quadrants at a 45 degree angle.

Dip coating is typically done by an automated machine, although it can be done manually as well. The assemblies are typically hung by an arm and then lowered in a dip tank containing the coating. The immersion rate is determined by the PCB’s population density and the desired coating thickness.

Brush coating is done manually by an operator with a brush. This application method is mainly employed during coating touchup operations or for conformal coating rework.

In conclusion, maintaining the right thickness of silicone conformal coating is crucial to prevent compromising properties or creating excessive stresses. The application methods of spray, dip and brush offer flexibility depending on the specific needs of the components. Whether through hand-spray, automated dip coating, or manual brush application, adhering to the J-STD-001 standards ensures optimal performance and protection for electronic assemblies.