Capillary (Wicking) Around Components in Conformal Coating

Capillary flow (wicking) occurs when conformal coating is drawn away from target areas and pulled into gaps, component edges, or interfaces. The result is a patchy, uneven finish with thin or bare regions that can compromise protection and reliability.

Collage of conformal coating capillary flow and wicking defects around PCB components.

What is Capillary Flow (wicking) in Conformal Coating?

Definition: Capillary flow is where the coating pulls or runs away from certain areas of a PCB and redistributes to more energetically favourable zones (e.g., around device bodies and gaps), leaving a patchy surface.
Impact: Non-uniform coverage reduces insulation resistance, increases moisture ingress risk, and creates variability in coating thickness that can drive premature failure.

Causes of Capillary / Wicking in Conformal Coating

  • Low coating viscosity encouraging flow into gaps and away from flat surfaces.
  • Excess material applied (over-wet film) that readily re-distributes.
  • Low surface energy substrates or poorly cleaned surfaces.
  • High coating surface tension relative to the substrate finish.

How to Prevent Capillary Effects

  • Increase viscosity: Use a higher-viscosity mix or allow solvent flash-off before second passes.
  • Reduce film build: Apply lighter coats; avoid pooling around components.
  • Improve cleanliness: Clean and rinse to raise surface energy and promote uniform wetting.
  • Select suitable chemistry: Where possible, prefer solvent-based materials over water-based or 100% solids for better wetting control.
  • Pre-heat the assembly: Warm boards prior to coating to improve flow and reduce wicking into gaps.

Conformal Coating Defects and Their Importance

Conformal coating protects printed circuit boards (PCBs) from moisture, corrosion, and electrical leakage. However, defects such as capillary wicking, de-wetting, orange peel, pinholes, bubbles, foam, cracking, delamination, and corrosion/ionic contamination can compromise that protection.

Even small imperfections create pathways for contaminants, lower insulation resistance, and increase the risk of premature failure. These defects may result from incorrect viscosity, poor surface preparation, unsuitable spray settings, or stress during curing.

Understanding and preventing these issues is essential for process control, quality assurance, and long-term reliability.

Training on Conformal Coating Defects & More

SCH provides conformal coating training that goes beyond theory. Our courses teach engineers and operators how to recognise, prevent, and repair defects such as capillary wicking, de-wetting, orange peel, cracking, and delamination. We cover:

  • Failure mechanism recognition.
  • Root cause analysis & troubleshooting.
  • Materials, masking, and application techniques.
  • Process optimisation and inspection 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.

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