Contamination under conformal coatings
Conformal coatings protect PCBs but can trap ionic contaminants under the coating if cleaning is incomplete. Trapped ions can migrate within microscopic defects or absorb moisture, creating growth and corrosion beneath the coating that is hard to detect.
Qualification of coating processes requires pre-coating cleanliness standards, compatibility testing, and post-coating inspection. When properly applied to clean assemblies, conformal coatings dramatically reduce contamination-driven failures.
Risks associated with conformal coatings
Risks include:
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hidden corrosion and dendrites that develop under the coating
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reduced adhesion and coating delamination due to residues
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false confidence when ROSE shows low surface values but IC reveals problematic species
To mitigate risk, clean to validated ROSE or IC thresholds, perform cross-section analysis, and run SIR tests on coated coupons. ZESTRON offers coating compatibility testing and application guidelines.
Testing and inspection strategies
Recommended strategies:
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ROSE and ion chromatography before coating to ensure low ion load
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SIR testing of coated coupons to detect leakage under coating
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microsectioning and microscopy to inspect coating integrity
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accelerated environmental exposure to simulate field conditions
These steps ensure coatings protect rather than hide latent contamination problems.