Corrosion & Ionic Contamination in Conformal Coating

Corrosion and ionic contamination are serious failure mechanisms in conformal coating. Contaminants left on PCB surfaces can react with moisture and bias, leading to electrochemical migration, dendrite growth, and metal degradation. Preventing corrosion is critical to ensure long-term circuit reliability.

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Conformal coating corrosion and ionic contamination defects on PCB under inspection

What is Corrosion in Conformal Coating?

  • Definition: Chemical/electrochemical reaction between metals and their environment that degrades the metal (e.g., ECA/ECM, dendrites).
  • Main issue: Ionic residues + moisture + electrical bias create leakage paths, dendritic growth, and metal loss under the coating, reducing insulation resistance and functional life.

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Causes of Corrosion & Ionic Contamination

  • Board fabrication residues — ionic salts, etchants, solder mask residues.
  • Contaminated components — flux salts, handling residues, process oils.
  • Assembly residues — incomplete flux activation/removal; rework flux left behind.
  • Inadequate cleaning/rinsing — poor bath control, exhausted chemistry, low rinse quality.
  • Operator handling — fingerprints/salts transferring through inadequate glove discipline.
  • Moisture ingress — insufficient dry-out before coating or porous film/edge breaks.
  • Material incompatibility — cleaner ↔ flux ↔ coating interactions leaving films.

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How to Prevent Conformal Coating Corrosion

  • Validated cleaning — proven wash/rinse/dry cycles to remove ionic residues; monitor conductivity/TOC where appropriate.
  • Incoming inspection — verify solderability/cleanliness of bare boards and components.
  • Dry-out control — pre-bake to remove moisture from boards and components before coating.
  • Low-residue processes — qualified no-clean fluxes/pastes; tight rework discipline.
  • Material compatibility — ensure cleaner/flux/coating systems are compatible.
  • Edge coverage & thickness — adequate film build and meniscus control at leads/pads.
  • Operator discipline — gloves, ESD-safe handling, silicone segregation, FOD control.

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Troubleshooting & Diagnosis

  • Ionic testing — ROSE/ion chromatography to quantify residues; track against SPC limits.
  • Bias/humidity testing — ECM/ECA test coupons to screen susceptibility to dendrites.
  • Residue mapping — UV tracer/white light to find fillets and edge breaks; XPS/FTIR if needed.
  • Bath audits — cleaner concentration, temperature, rinse DI quality, filter condition, bath life.
  • Dry-out verification — weight-loss or temperature/time profiles to confirm moisture removal.
  • Coating review — confirm viscosity/solids, film build, and edge coverage at critical features.

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Where Corrosion & Ionic Contamination Sit Among Other Defects

Corrosion/ionic contamination are cleanliness/moisture/bias-driven. By contrast, de-wetting is surface energy, orange peel is flow/level, pinholes/bubbles/foam are from entrapped air/skinning, and cracking/delamination link to stress/adhesion. Tackling the right mechanism prevents rework and field failures.

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Training on Conformal Coating Defects & More

SCH offers conformal coating training that goes beyond theory—recognising and preventing corrosion/ionic contamination, cracking, delamination, de-wetting, orange peel, pinholes, bubbles, foam, and wicking. We cover process analysis, troubleshooting, materials, and application methods.

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Industry Standards We Work To

SCH Services follows international standards across all our coating services, training, equipment supply and materials. Our processes are aligned to the relevant IPC standards, including:

  • IPC-A-610 – Acceptability of Electronic Assemblies
  • IPC-CC-830 – Qualification & Performance of Conformal Coatings
  • IPC-HDBK-830 – Conformal Coating Handbook (guidance and best practice)

For further details on IPC standards, visit:
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Why Choose SCH Services?

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Note: This article provides general technical guidance only. Final design, safety, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.