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

Spray application is one of the most widely used methods for applying conformal coating to printed circuit boards (PCBs). It is ideal for prototypes, low-to-medium volume manufacturing and rework. This guide walks you through cleaning, masking, spraying, curing and inspecting a PCB using manual or aerosol-based conformal coating techniques while preventing common defects such as bubbles, dewetting and orange peel.

nfographic showing how to spray coat a PCB with conformal coating – clean, mask, spray and cure steps

1) Tools & Materials You’ll Need

  • Conformal coating: Aerosol or material blended to the right viscosity for a spray-gun  (acrylic, polyurethane, silicone, etc.)
  • Spray equipment: Aerosol can or HVLP spray gun
  • Masking materials: Tapes, dots, liquid latex, reusable boots or shields
  • PPE: Gloves, safety glasses, fume extraction or spray booth
  • Inspection tools: UV light, white light, wet film gauge, PosiTector (dry thickness gauge)

2) Step 1 – Clean & Prepare the PCB

Conformal coating adheres best to a clean, dry PCB. Remove flux residues, dust, oils and ionic contamination using IPA wiping, DI water wash and bake, ultrasonic cleaning or engineered cleaning solutions. Ensure moisture is completely removed—particularly from connectors and under components—and avoid touching cleaned surfaces with bare hands.

3) Step 2 – Mask Components That Must Not Be Coated

Mask any areas where conformal coating is not allowed: connectors, switches, gold fingers, test pads or keep-out zones.

  • Barrier masking: Tapes, dots or liquid mask—ideal for flat areas and pads
  • Shield masking: Reusable boots or caps for connectors—fast and consistent
  • Liquid mask: Useful for odd geometries, but must fully cure before spraying

Learn about masking strategies and how to mask for barrier protection in the Masking Hub.

4) Step 3 – Set Up Your Spray Environment

  • Temperature: 18–25 °C
  • Humidity: < 60% RH
  • Airflow: Use a spray booth or extraction system with good lighting
  • Aerosol prep: Shake for 1–2 minutes
  • Spray gun prep: Mix coating to correct viscosity and set pressure to 15–25 psi
  • PCB position: Flat or tilted at 45° for good visibility and drainage

5) Step 4 – Spray the Conformal Coating

Technique: Hold the spray 15–25 cm from the PCB and use smooth, steady passes with approximately 50% overlap. Spray horizontally, then rotate the board 90° and repeat to ensure side coverage and an even film. Keep moving during the spray—pausing causes runs and pooling.

Target film thickness: Around 30–75 µm wet, resulting in 10–50 µm dry depending on the coating system and specification.

Avoid: Spraying too close (runs, bubbles), too thick (solvent entrapment, cracking), or too far (dry spray, orange peel).

PCB spray coated with conformal coating showing an even protective film on components

6) Step 5 – Flash-Off and Cure

  • Flash-off: Allow a min of 2–5 minutes between coats and follow manufacturers instructions
  • Multiple coats: Apply thin layers rather than one heavy coat
  • Curing: Air-dry or force-cure at 60–80 °C (follow coating datasheet)
  • UV-curable coatings: Use correct UV lamp exposure if applicable

7) Inspection & Quality Control

  • Visual inspection: Check for full coverage, no bubbles, pinholes, skips or bridging
  • UV check: Use UV light if the coating fluoresces to reveal thin areas or misses
  • Thickness verification: Wet film gauge or dry film measurement (PosiTector)
  • Standards: Verify compliance with IPC-A-610 and IPC-CC-830 criteria

8) Common Defects and How to Prevent Them

Defect Cause Prevention
Bubbles / Foam Over-aggressive shaking, high humidity, too close Mix gently, control RH, maintain correct distance
Orange Peel Cold coating, high viscosity, dry spray Warm material, correct pressure and distance
Dewetting / Fish Eyes Surface contamination (oil, flux, silicone) Thorough cleaning and no handling after clean
Runs / Sags Spraying too heavily or pausing Apply thin coats and maintain steady movement
Mask Bleed Poor tape adhesion or incorrect masking material Use proper masking, seal edges, consider reusable boots

9) Training & Industry Standards

If you want to develop skilled operators or achieve repeatable, audit-ready conformal coating processes, formal training is essential. SCH provides hands-on training in spray coating, masking, inspection and IPC-A-610 / IPC-CC-830 acceptability standards, delivered on-site or at our training centre.

For official guidance on conformal coating inspection criteria and acceptance limits, you can also refer to the IPC standards:

To discuss training or certification pathway for your team, contact us here.

10) Useful Links & Next Steps

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Conformal Coating, Parylene & ProShieldESD Solutions, alongside equipment, materials, and training, all backed by decades of hands-on expertise.

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