Conformal coating is a thin protective layer applied to PCBs to shield them from environmental
contaminants, electrical leakage, and mechanical stress. This coating enhances PCB durability by
preventing corrosion and ensuring stable performance in harsh conditions such as high humidity,
extreme temperatures, and chemical exposure. PCB protective coatings are available in different types,
including acrylics, silicones, epoxies, and parylene, each offering unique properties suited to specific
applications.
Conformal coating is often a tricky process with some risk of failure. Some remedies and precautions
that Suntronic takes to reduce the failure rate of conformal coating to less than 1%.
Common Conformal Coating Failures and Their Causes
1. Inconsistent Coating Thickness
Uneven application of the coating is one of the most common issues, leading to either insufficient
protection or excessive material buildup. Common causes include improper spray techniques, incorrect
dip-coating parameters, or operator errors. An inconsistent coating can create weak spots, making the
PCB vulnerable to environmental stress and contaminants.
2. Delamination and Peeling
Delamination occurs when the conformal coating fails to adhere properly to the PCB surface. This can be
caused by contamination, inadequate surface preparation, or improper curing. When peeling occurs, the
PCB becomes exposed to environmental hazards, diminishing its effectiveness. In extreme cases,
delamination can lead to circuit malfunctions due to moisture ingress.
3. Bubbles and Voids
Air entrapment during the PCB conformal coating process results in bubbles and voids, compromising
the protective layer. Incorrect viscosity, improper curing conditions, and rapid solvent evaporation are
contributing factors. Bubbles create gaps in the protection, allowing moisture and contaminants to reach
the PCB surface.
4. Cracking and Shrinkage
Temperature fluctuations, high stress, and improper curing can cause cracking in the coating. These
cracks enable moisture and contaminants to penetrate, reducing the effectiveness of the protective
layer. Cracking is commonly seen in coatings applied too thickly or cured too quickly.
5. Chemical Incompatibility
Using an unsuitable type of circuit board protective coating can cause chemical reactions that lead to
adhesion failure, discoloration, or poor electrical insulation. Certain coatings may react with PCB
materials or components, causing degradation over time. It’s vital to select a coating that is compatible
with both the PCB materials and the operational environment.
6. Poor Coverage in Complex Areas
PCBs with intricate designs and high component density often face difficulties in achieving complete
coverage. Gaps in the PCB protection coating can lead to local exposure, causing corrosion and
performance degradation. Manual or automated touch-ups may be required to ensure full coverage.
Best Practices to Avoid Conformal Coating Failures
1. Proper Surface Preparation
Thorough cleaning of the PCB is essential before applying the protective coating. Residues, oils, or flux
contaminants should be removed using appropriate cleaning agents to ensure proper adhesion. Plasma
treatment or ultrasonic cleaning can further improve surface cleanliness and enhance coating
performance.
2. Selecting the Right Coating Material
Different PCBs require different types of coatings such as acrylics, silicones, epoxies, and parylenes.
Choosing the appropriate material for the operating environment can prevent failures in the PCB coating
process. For instance, silicone coatings are ideal for high-temperature applications, while parylene
coatings offer superior moisture resistance.
3. Optimizing Application Methods
The application method—whether spraying, dipping, or brushing—should be selected based on the PCB
design and production needs. Automated spraying systems ensure consistency, while manual methods
require skilled operators to achieve uniform coverage. Selective coating techniques can be used to avoid
coating-sensitive components while ensuring full protection.
4. Controlling Environmental Conditions
Maintaining stable humidity and temperature levels during the PCB conformal coating process is
essential. Extreme conditions can lead to defects like bubbling, peeling, or improper curing. Proper
ventilation and controlled environments ensure consistent and reliable coatings.
5. Implementing Correct Curing Procedures
Curing is a critical step in the PCB coating process and must be performed under controlled conditions.
UV, heat, or moisture curing should follow manufacturer recommendations to avoid incomplete
polymerization, which can lead to poor adhesion or soft coatings.
6. Conducting Quality Inspections
Regular quality control checks using UV inspection, cross-section analysis, and adhesion testing can help
detect defects early in the circuit board protective coating process. These checks ensure that coatings
meet performance standards before final assembly. Advanced techniques like automated optical
inspection (AOI) can further enhance defect detection.
7. Training and Process Standardization
Ensuring operators are trained in best practices and process standardization helps minimize human error
during the PCB protective coating application. Documenting processes and conducting regular audits can
ensure consistency in large-scale production.
Considerations for Selecting PCB Conformal Coating Material
Choosing the right PCB protective coating is crucial for ensuring long-term reliability. Here are key factors
to consider:
- Environmental Conditions: Select a coating that can withstand the operating environment,
including moisture, temperature variations, and exposure to chemicals. - Electrical Properties: Ensure the coating provides adequate insulation and does not interfere
with the PCB’s electrical performance. - Application Method: Different coatings are suitable for brushing, spraying, dipping, or vapor
deposition. Consider the most efficient method for your manufacturing process. - Rework and Repair Needs: Some coatings are easier to remove or modify than others. Acrylic
coatings, for example, are easier to rework compared to epoxy coatings. - Curing Requirements: The curing process varies by material—UV curing, heat curing, and
moisture curing all have different timeframes and processing needs.
Conclusion
A properly applied conformal coating enhances PCB durability and reliability by preventing failures such
as inconsistent coating, delamination, and chemical incompatibility. By following best practices—proper
surface preparation, material selection, and process control—manufacturers can ensure long-lasting
protection for PCB assemblies. Suntronic provides expert PCB conformal coating solutions tailored to
industry needs, ensuring high-performance protection and reliability. Partner with Suntronic to
safeguard your PCB assemblies with precision and expertise.