Pinholes, Bubbles & Foam Defects in Conformal Coating

Pinholes, bubbles and foam in conformal coating are common defects that can compromise PCB protection. Understanding how these defects form—and how to prevent them—is key to improving reliability and reducing costly rework.

Side-by-side comparison of bubbles, pinholes & foam defects in conformal coating on PCB under UV inspection

What are Pinholes, Bubbles & Foam in conformal coating?

  • Bubbles — trapped pockets of air under the coating film.
  • Pinholes — burst bubbles that break through to the PCB surface.
  • Foam — extensive bubbling across the coated area.

These conformal coating defects reduce insulation resistance and can accelerate corrosion or failure of the PCB.

Causes of Pinholes, Bubbles & Foam Defects in Conformal Coating

  • Skinning of the wet film traps solvent beneath, which later bursts out.
  • Excessive thickness or high viscosity prevents bubbles settling before cure.
  • Air under components is expelled during drying/curing and forms bubbles.
  • Pressure pots absorbing air cause “champagne” bubbles on application.
  • Brush over-working or viscous material introduces bubbles during application.
  • Incorrect spray setup (head/pressure) creates excessive bubbles or foam.

How to Prevent Pinholes, Bubbles and foam

  • Use multiple thin coats with proper flash-off instead of one heavy pass.
  • Control cure temperature to avoid surface skinning.
  • Reduce air entrapment under parts: slower dip entry, dwell time, and lower viscosity.
  • Manage pressure pots: depressurise when idle; don’t leave >50% standing under pressure.
  • Brush technique: flow the coating; avoid working it into the board.
  • Optimise spray parameters: verify head type and atomising/flow pressures.

Conformal Coating Defects and Their Importance

Conformal coating protects printed circuit boards (PCBs) against moisture, dust, corrosion and electrical leakage.
However, defects such as pinholes, bubbles, foam, orange peel, de-wetting, delamination, and cracking
can compromise that protection. Even small imperfections provide pathways for contaminants, lower insulation resistance, and increase the risk of premature failure.

These coating defects arise from issues such as incorrect viscosity or film thickness, trapped air or solvent,
poor surface preparation, unsuitable spray settings, or stress during cure. For example, pinholes, bubbles & foam are typically linked to air entrapment or skinning of the wet film, while orange peel often results from viscosity and flow mismatches. De-wetting points to contamination or low surface energy, and delamination highlights adhesion or curing problems.

Understanding these failure mechanisms is essential for process control, quality assurance, and long-term reliability.By recognising how and why these defects form, manufacturers can optimise application methods, materials, and operator technique to eliminate rework, improve yield, and ensure consistent performance.

This section provides a practical overview of the most frequent conformal coating defects, linking symptoms to likely causes and offering guidance on how to diagnose, prevent, and correct them in production.

Training on Conformal Coating Defects & More

SCH offers conformal coating training that goes beyond theory. Our courses teach you how to recognise and prevent defects such as pinholes, bubbles, foam, orange peel, de-wetting, delamination, and cracking. We also cover process analysis, troubleshooting, materials, and application methods.

Explore Conformal Coating Training →

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 by aerospace, medical, defence, automotive, and electronics industries worldwide.
  • 🛠️ End-to-End Support – Guidance on coating selection, Parylene grades, masking strategies, application methods, inspection, and ProShieldESD integration.
  • 📈 Scalable Solutions – From small prototype batches to full-scale, high-volume production, SCH delivers flexible capacity that grows with your needs.
  • 🌍 Global Reach – Responsive technical support and supply coverage across Europe, North America, and Asia.
  • ✅ Proven Reliability – A strong reputation built on quality, consistency, and customer satisfaction across services, equipment, and materials.

📞 Call: +44 (0)1226 249019
✉ Email: sales@schservices.com
💬 Contact Us ›