How do I brush coat my conformal coating?

The correct technique for applying conformal coating by brush is to flow the coating on.

The material should not be brushed on like you are decorating with paint. The coating should be loaded on to the brush and flowed onto the printed circuit board.

What conformal coatings can be applied by brush?

All conformal coatings can be applied by brush and most lend themselves well to the technique. The key points to be aware of are the material pot life and the conformal coating viscosity.

• Material pot life. The pot life of the material may be finite so the conformal coating could cure during use. This may make the material useless to apply after a certain amount of time.
• Conformal coating viscosity. The way the conformal coating flows is critical when applied by brush coating. Therefore, the viscosity of the coating material is highly influential on the flow so control of the viscosity is critical to allow good coverage.

What Factors Control the Quality of Conformal Coating Finish with Brushing?

Although brushing is often considered the simplest conformal coating application method, achieving a consistent, defect-free finish requires careful control of several interacting variables. Unlike automated processes, brushing relies heavily on human input, making process understanding and training especially important.

The key factors that influence coating quality when brushing include:

• Operator skill and technique – Brush loading, stroke direction, pressure control, overlap, and rework handling all directly affect film thickness, edge definition, and defect formation. Inconsistent technique is a common cause of bubbles, streaking, and uneven coverage.
• Brush quality and selection – Bristle material, stiffness, tip shape, and cleanliness determine how evenly the coating is deposited. Poor-quality or worn brushes can introduce fibres, air entrapment, and surface texture defects.
• Viscosity of the conformal coating – Coatings that are too viscous may leave heavy brush marks or uneven films, while overly thinned coatings can lead to runs, pooling, or insufficient coverage. Viscosity must be matched to both the coating chemistry and the brushing technique.
• Coating environment – Temperature, humidity, airflow, and cleanliness influence solvent evaporation, levelling, and cure behaviour. Uncontrolled environments can increase the risk of bubbles, contamination, and poor surface finish.
• Board size, layout, and complexity – Dense assemblies, fine-pitch components, connectors, and vertical features increase the likelihood of shadowing, wicking, and thickness variation when brushing. Design choices can significantly impact how practical brushing is as an application method.
• Conformal coating material type – Acrylics, silicones, polyurethanes, epoxies, and UV-curable coatings all behave differently under manual application. Dry time, reworkability, solvent content, and levelling characteristics must be understood to avoid defects.

The Role of Training in Brushed Conformal Coating

Because brushing is highly operator-dependent, training is one of the most effective ways to improve quality, repeatability, and yield. Structured training helps operators understand not just how to apply a coating, but why defects occur and how to prevent them.

SCH provides conformal coating training covering:

• Correct brush selection and handling techniques
• Coating preparation, thinning, and viscosity control
• Defect recognition (bubbles, streaking, dewetting, pinholes)
• Environmental control and best-practice setup
• Inspection criteria aligned with IPC standards
• Rework and repair considerations for brushed coatings

Training can be delivered as part of a wider process review or focused specifically on manual application methods, helping manufacturers reduce rework, improve consistency, and build operator confidence.

To learn more, explore our conformal coating training programmes or review our wider guidance in the Conformal Coating Processes Hub, which covers brushing, spraying, dipping, selective robotic coating, and Parylene deposition.

Need to know more about using a conformal coating in your application process?

Contact us now and we can discuss how we can help you. Give us a call at (+44) 1226 249019 or email your inquiries at sales@schservices.com