Electronics fail in harsh environments without proper protection. Moisture, temperature extremes, chemicals, and vibration destroy unprotected circuit boards in industrial, outdoor, and mobile applications.

Conformal coating and potting provide the environmental protection your electronics need to survive demanding conditions. However, these protection methods require design consideration from the start. You can't simply apply coating to any board and expect good results.

Understanding when to use coating versus potting, and designing boards that can be effectively protected, ensures your electronics survive their intended environment.

Common Environmental Threats

Moisture and Humidity: Water causes corrosion, creates unwanted electrical paths, and enables metal migration between conductors. Electronics in outdoor installations, marine environments, or high-humidity facilities face constant moisture exposure.

Temperature Extremes: Temperature cycling creates mechanical stress through thermal expansion mismatches, causes condensation when warm air meets cold surfaces, and degrades materials over time. Automotive electronics routinely face -40°C to +125°C with thousands of thermal cycles.

Chemical Exposure: Industrial environments expose boards to hydraulic fluids, cleaning solvents, acids, and salt spray. Agricultural equipment faces fertilisers and pesticides. Marine applications face saltwater.

Vibration and Contamination: Mobile equipment subjects electronics to continuous vibration that fatigues solder joints. Airborne dust creates shorts between traces and reduces cooling efficiency.

Conformal Coating: Protection for Most Applications

Conformal coating applies a thin protective layer (25-250microns) over assembled PCBs. It's the most common protection method for moderately harsh environments.

Coating Types

Acrylic (AR) Good moisture resistance, easy to apply and rework, relatively inexpensive. Limited chemical resistance. Best for general industrial electronics and outdoor enclosures.

Silicone (SR) Excellent moisture resistance, wide temperature range (-60°C to +200°C), remains flexible. Difficult to rework. Best for automotive and outdoor installations.

Urethane (UR) Excellent moisture and chemical resistance, good mechanical protection. More difficult to remove than acrylic. Best for industrial controls and chemically aggressive environments.

Parylene (XY) Ultra-thin (5-50 microns), highly uniform, superior protection. Requires specialised equipment, extremely difficult to rework. Best for medical devices and aerospace applications.

When to use Conformal Coating

Coating suits applications requiring protection from moisture, dust, and moderate chemicals whilst maintaining inspection access and rework capability. It's typically sufficient for:

• Industrial controls in protected facilities
• Outdoor electronics in weatherproof enclosures
• Automotive electronics in protected locations
• Consumer products with occasional moisture exposure

Design Considerations for Coating

Components That Can't Be Coated

• Connectors (unless designed for coating)
• Switches and adjustable components
• Battery holders and sockets
• Display modules and LEDs
• Heatsinks and thermal interfaces
• Test points requiring probe access

Specify coating-tolerant components or plan masking for sensitive areas.

Keep-Out Zones Create clear keep-out areas around components that must not be coated. Document these on assembly drawings with specific dimensions.

Test Points Coating covers test points, making them inaccessible. Either design test points in keep-out areas, use pogo pins that penetrate coating, or complete all testing before coating.

Thermal Impact Coating adds thermal resistance. Components dissipating significant heat may see temperature increases of 5-15°C. Factor this into thermal design.

Potting: Maximum Protection

Potting completely embeds assemblies in solid polymer, providing maximum environmental protection. The trade-off is no rework capability and no inspection access after potting.

Potting Materials

Polyurethane Most common. Good mechanical protection and moisture resistance. Available in various hardness levels from soft/flexible to rigid. Flexible versions accommodate thermal expansion better.

Epoxy Excellent mechanical strength and chemical resistance. Rigid material can stress components during thermal cycling. Essentially impossible to rework.

Silicone Excellent temperature range (-60°C to+200°C) and flexibility. Lower mechanical protection but excellent long-term reliability in thermally demanding applications.

When to use Potting

Potting is necessary for:

• Sustained immersion in water or chemicals
• Extreme vibration or mechanical shock
• IP67 or IP68 rating requirements
• High-voltage assemblies requiring arc suppression

Outdoor energy equipment, subsea instrumentation, and military electronics typically require potting rather than coating.

Design Considerations for Potting

Component Stress: Potting creates mechanical stress on components during cure and thermal cycling. Stress-sensitive components include large ceramic capacitors, crystal oscillators, MEMS sensors, and plastic-package ICs with long leads.

Use flexible potting compounds or avoid stress-sensitive components where possible.

Thermal Management: Potting compounds conduct heat poorly. Components generating significant heat require heatsinks outside the potting boundary, thermally conductive compounds, or derating to operate within temperature limits.

Avoiding Voids: Air voids reduce protection. Design to avoid deep cavities that trap air, provide vent paths for air escape, and consider vacuum potting for critical applications.

Connector Sealing: Use connectors designed for potting applications with proper back shells or cable glands providing environmental seals.

IP Ratings Explained

IP (Ingress Protection) ratings quantify environmental protection using two digits: IP XY.

First Digit (Solid Particles):

• 5: Dust protected
• 6: Dust tight

Second Digit (Liquids):

• 4: Splashing water
• 5: Water jets
• 6: Powerful jets
• 7: Temporary immersion (1m, 30 min)
• 8: Continuous immersion

Achieving IP Ratings:

• IP54: Conformal coating plus reasonable enclosure sealing
• IP65: Good coating plus well-sealed enclosures with gaskets
• IP67: Potting or very thick coating plus hermetic seals
• IP68: Complete potting with appropriate connectors

Design Process Integration

Environmental protection must be considered from the concept stage.

During Circuit Design

Select coating-compatible components. Avoid stress-sensitive components for potted applications. Position heat-generating components considering thermal impact of protection. Design test strategies that work with protected boards.

During PCB Layout

Create documented keep-out zones. Position connectors considering protection boundaries. Route critical traces away from shadowing areas under tall components. Maintain clearances from board edges.

During Prototyping

Build prototypes with representative protection to validate component compatibility, assembly feasibility, thermal performance, and IP rating achievement. Discovering protection problems during prototyping is far easier than during production.

Documentation

Clearly specify on assembly drawings which coating or potting material to use, keep-out zones with dimensions, coating thickness requirements, and any special application instructions.

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ABL's Conformal Coating and Potting Services

We provide both conformal coating and potting services as part of our PCB assembly and contract manufacturing capabilities.

Our team works with designers during development to ensure boards are designed for effective protection. We provide design review feedback on component selection, layout considerations, and protection method selection.

We apply all our coatings using our in-house dedicated spray systems for consistent coverage. For potting applications, we work with polyurethane, epoxy, and silicone compounds in various hardness levels.

Our process includes proper material handling, cure control, quality inspection, and post-protection testing to verify functionality. We maintain documentation of coating thickness, coverage, and any deviations for traceability.

Whether you're designing industrial controls, outdoor equipment, or electronics for mobile applications, we can advise on the appropriate protection method and ensure it's applied correctly.

Common Mistakes to Avoid

Choosing Protection Method Too Late: Deciding on coating or potting after the board is designed often creates problems. Components might not be compatible, test points might be inaccessible, and thermal issues might emerge.

Inadequate Keep-Out Documentation: Vague instructions like "do not coat connectors" lead to inconsistent results. Specify exact keep-out zones with dimensions.

Ignoring Thermal Impact: Coating and potting add thermal resistance. Boards that ran cool unprotected might overheat after protection is applied.

Over-Specifying Protection: Not every board needs potting. Conformal coating is sufficient for most applications and maintains rework capability. Use potting only when genuinely required.

Testing After Protection: Once coated or potted, boards are difficult or impossible to rework. Complete as much testing as practical before applying protection.

Getting Started

If you're designing electronics for harsh environments, contact us to discuss protection requirements. We can review your design for protection compatibility, recommend appropriate coating or potting materials, advise on design modifications to improve protection effectiveness, and explain application processes and quality control.

Early engagement produces better outcomes. Design decisions made during development affect protection effectiveness throughout your product's life.

Request a quote or call us on 01462 894 312 to discuss environmental protection for your electronics. Whether you're at the design stage, prototyping, or ready for production, we'll provide practical guidance on protecting your electronics in harsh environments.