How to Brush Coat a PCB with Conformal Coating | Step-by-Step Guide

Learning how to brush coat a PCB with conformal coating is essential for low and medium volume builds, prototypes and rework where full automation is not justified. With the correct brush technique, viscosity control and masking, manual conformal coating can deliver reliable PCB protection without heavy film build, runs or contamination into keep-out areas.

This guide explains the complete process step-by-step – from preparation and masking through to application, curing and inspection.

All of the tools listed below are the same professional-grade materials we use daily in our SCH coating services. They are available to purchase directly from us, and we can advise on the best combination for your chemistry, build type and production volume.

• Conformal coatings (brush-grade) – Use each of the materials according to their specification and datasheet recommendations.
• Soft, anti-static brushes – flat and angled tips for precision work. These are the identical brushes used by our operators for controlled brush application around fine-pitch components.
• Clean decanting pots / jars – small solvent-resistant glass or metal pots for working quantities. These prevent contamination and reduce solvent loss.
• Masking materials – tapes, dots, custom shapes and reusable connector boots/caps for fast, repeatable masking. We supply the same masking kits used in our production lines.
• PCB holders & fixtures – Use stable, adjustable supports to position boards at the correct angle during brush coating. While we don’t supply fixtures, SCH can coat your existing fixtures with ProShieldESD to provide a durable, ESD-safe surface for handling and grounding during coating operations.
• PPE & safety – gloves, goggles and local extraction or a brush-coating booth for operator safety and process stability.
• Inspection & QC tools – white/UV lamps, wet-film gauges and dry-thickness gauges (e.g. Positector). See thickness measurement tools

Need supplies or advice? Contact us for pricing, availability or guidance on selecting the right tools for your process:📞 +44 (0)1226 249019    ✉️ sales@schservices.com

Coating only adheres to clean, dry surfaces. Before you brush coat a PCB with conformal coating, remove flux residues, dust, oils and ionic contamination by IPA wipe, DI wash and bake, ultrasonic cleaning, or engineered cleaning agents according to your process.

• Ensure moisture is fully removed from under components and inside connectors.
• Handle cleaned boards with gloves – avoid fingerprints and skin oils.
• Confirm cleanliness against your ionic contamination and visual inspection criteria before starting.

Mask all features that must not be coated: connectors, sockets, switches, test points, gold fingers and other keep-outs. Good masking may be critical when using a brush close to components where repair / removal is difficult if coating leaks in.

• Barrier masking: Use tapes/dots or liquid mask. Press edges down firmly to avoid seepage under the tape.
• Shield masking: Use reusable boots/caps for repeat jobs – faster, more consistent, and easier to remove.
• Design tips: Keep labels, test pads and high-voltage clearance areas outside the coated region where possible.

Learn more in the Masking Hub: masking strategies and barrier masking systems.

• Viscosity: Controlling the viscosity of the conformal coating is very important. Check the coating viscosity against your validated process window. Brush-grade conformal coatings are usually used at a higher viscosity suitable for hand application.
• Mixing: Stir gently or roll the container to redisperse solids – avoid shaking that introduces bubbles.
• Decanting: Pour a small working quantity into a clean pot; keep the main container closed to minimise solvent loss and contamination.
• Work area: Use an ESD-safe work surface, adequate extraction and a comfortable board angle (often 30–60°) to reduce runs.
• Lighting: White light plus 365 nm UV (for UV-traced coatings) helps you instantly identify coverage, shadowing and missed areas. We also supply professional UV inspection booths—the same units used in our SCH coating services—for consistent, glare-free inspection environments.

Related reading: Viscosity in Process Control.

The way you load the brush has a huge impact on PCB brush coating technique and film uniformity.

• Light loading: Dip only the first third of the bristles into the conformal coating – avoid fully saturating the brush.
• Remove excess: Gently wipe the brush on the rim of the pot to remove drips and achieve a consistent charge.
• Keep bristles aligned: Use flat or chisel-tip brushes to lay down an even film, not stiff brushes that scratch the surface.
• Change brushes regularly: Replace brushes that have hardened tips or loose bristles.

Tip: Use dedicated brushes for each chemistry; do not mix silicone, acrylic and urethane conformal coatings on the same tools.

Technique: Apply the conformal coating in thin, overlapping strokes, working methodically across the board.

• Start with critical areas (fine pitch, high-voltage regions, edges) before general fill.
• Brush in one direction, then cross-hatch at 90° if needed to build an even film without dragging coating away.
• Avoid scrubbing – let the coating flow and level rather than pushing it around.
• Do not overwork an area once it has started to flash off; this can cause orange peel and brush marks.
• Use UV light periodically to check for missed corners, shadowed areas and coverage under components.

See also: Application Processes Overview.

Brush coating gives good local control – use it to manage edges and sensitive areas.

• Board edges: Lightly pull conformal coating over the edge to achieve wrap-around without excessive edge build.
• Around connectors: Brush coating away from masked connectors and housings to avoid capillary draw.
• Pin fields and fine pitch: Use smaller brushes and thin coats; multiple passes are safer than one heavy application.
• Touch-up and rework: Brush coating is ideal for local repairs after inspection or test.

• Flash-off: Allow the coating to level and solvents to evaporate per datasheet before applying additional coats.
• Multiple coats: Build up thickness using several thin layers rather than one heavy film, especially with solvent-based systems.
• Target thickness: Typical dry film for many conformal coating chemistries is 25–75 µm, but always follow your product specification.
• Cure: Air dry or force-cure at the recommended temperature/time. Avoid moving the board until the film is tack-free.

• Visual inspection: Under white light, confirm wrap-around coverage, no obvious voids or fibre inclusions from brushes.
• UV inspection: For UV-traced conformal coatings, use 365 nm UV to check coverage under components, on edges and in shadowed regions.
• Thickness: Use wet film gauges for initial validation and dry film gauges (e.g. Positector, optical methods) for production checks.
• Standards: Verify against IPC-A-610 acceptance criteria, plus your internal work instructions.

Explore our Defects Hub for examples of common coating issues and acceptable limits.

Defect	Cause	Prevention
Heavy Brush Marks / Orange Peel	Overworking the film; viscosity too high; stiff or contaminated brushes	Thin the conformal coating within spec; use softer brushes; apply lighter, smoother strokes and avoid re-brushing partly dried films
Runs / Sags	Excess film build; too much coating on brush; board angle too steep	Reduce brush loading; apply thinner coats; control board orientation and allow sufficient flash-off
Missed Areas / Shadowing	Poor access around tall components; inadequate inspection under UV	Use smaller/angled brushes for tight areas; inspect under UV after each coat
Dewetting / Fish Eyes	Surface contamination (oil/flux/silicone); low surface energy	Improve cleaning; avoid silicone-based products; use adhesion promoters where appropriate
Cracking	Excess thickness; rapid solvent loss; thermal mismatch during cure	Apply thinner layers; follow datasheet cure profile; stay within specified thickness range

If you need repeatable, audit-ready brush coating processes, formal training helps operators control viscosity, brush technique, masking and inspection for complex assemblies. SCH delivers hands-on training in brush coating, masking, inspection and IPC-A-610 / IPC-CC-830 acceptability.

For official acceptance criteria and guidance, refer to the IPC standards:

• IPC-A-610 – Acceptability of Electronic Assemblies
• IPC-CC-830 – Qualification & Performance of Conformal Coatings

To discuss training or a validation plan for your team, contact us here.

• Process control:  Viscosity in Process Control
• Thickness measurement: Wet, Dry & Optical Methods
• Masking fundamentals: Masking strategies • Barrier masking
• Defect library: Defects Hub
• Removal & Rework: Rework Hub

Why Choose SCH Services?

Partnering with SCH Services means more than just outsourcing — you gain a complete, integrated platform for Conformal Coating, Parylene & ProShieldESD Solutions, alongside equipment, materials, and training, all backed by decades of hands on expertise.

• ✈️ 25+ Years of Expertise – Specialists in coating technologies trusted worldwide.
• 🛠️ End-to-End Support – Coating selection, masking, inspection and process validation.
• 📈 Scalable Solutions – From prototypes to high-volume production.
• 🌍 Global Reach – Responsive support across Europe, North America and Asia.
• ✅ Proven Reliability – Built on quality, consistency and customer satisfaction.

📞 Call: +44 (0)1226 249019
✉ Email: sales@schservices.com
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Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.