Conformal Coating: What It Is and How to Choose the Right One

Conformal coatings protect PCBs by forming thin, flexible polymer films that guard against moisture, chemicals, salt, and vibration. Modern options include acrylics, silicones, polyurethanes, parylene, and UV/waterborne systems. Select a coating based on operating environment, electrical requirements, board layout, reworkability, and production process; follow qualification standards and supplier test data.

What is conformal coating?

Conformal coating is a thin polymer film applied to printed circuit boards (PCBs) and electronic assemblies to protect them from moisture, chemicals, dust, salt, and vibration. The coating follows the contours of the board and components to form a lightweight, flexible barrier that reduces corrosion, leakage currents, and failure rates.

Common types of coatings

Manufacturers offer several chemistries with different trade-offs:

• Acrylics: Fast-drying, easy to apply and rework; good general protection for consumer and commercial products.

• Silicones: Flexible over wide temperature ranges and resistant to moisture; useful for harsh environments.

• Polyurethanes: Tough, chemical-resistant films for industrial and automotive use.

• Epoxies and solvent-borne systems: Provide durable protection but can be brittle; used where mechanical robustness is required.

• Parylene (vapor-deposited): Creates a pinhole-free, conformal film with excellent dielectric and moisture resistance.

• UV-curable and waterborne coatings: Growing in use to reduce volatile organic compounds (VOCs) and speed processing.

Benefits and typical applications

Coatings increase reliability, prevent current leakage on closely spaced traces, and enable miniaturization by allowing tighter designs. They also improve cosmetic appearance and can hide circuitry when pigment is added.

Typical applications now include consumer and IoT devices, automotive electronics, aerospace and defense systems, marine equipment, medical devices, and industrial controls.

How to choose the right coating

Match the coating to these factors:

• Operating environment: Consider temperature swings, humidity, salt spray, chemicals, and vibration.

• Electrical requirements: Dielectric strength, volume resistivity, and breakdown voltage must suit the board's spacing and voltages.

• Board layout and components: Plan for uncoated areas - connectors, sockets, adjustable controls, and test points - by locating them for minimal masking or using removable mask products.

• Reworkability: Some chemistries are solderable-through; others require mechanical removal, solvents, or specialty processes like plasma or laser ablation.

• Process compatibility: Spray, dip, selective robotic application, and conformal coating lines each suit different production volumes.

Practical tips

• Keep component leads trimmed so the coating forms a continuous film.

• Use peelable mask where components must remain exposed.

• For high-power or thermal-critical circuits, consider how any coating will affect heat transfer and plan heatsinking accordingly.

• Choose low-VOC or UV/waterborne systems where regulatory or facility VOC limits apply.

Standards and qualification

Follow industry standards and test methods when qualifying a coating for production. Look for supplier data on adhesion, thermal cycling, humidity, salt spray, and dielectric tests, and confirm compliance with applicable military or industry specs.

Conformal coating is a practical, widely used reliability strategy. The right selection and process controls extend product life and reduce warranty costs.

1. Confirm current typical cured film thickness range for common conformal coatings and update numeric values if needed.
2. Verify the current IPC and relevant military/industry specification numbers and names for conformal coating qualification (e.g., IPC-CC-830 revision status and any commonly referenced MIL specs).