Solvent Attack & Substrate Damage Defects in Conformal Coating

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Solvent attack and substrate damage occur when a conformal coating (or its thinner/cleaner) softens, swells, crazes, stains, lifts, or chemically degrades materials on the assembly. The most common victims are plastics, labels, printed inks, and occasionally solder mask systems that are not fully cured or are solvent-sensitive.

This page explains what solvent attack looks like in production, how to confirm the mechanism quickly, and how to prevent recurrence without compromising coverage or protection.

For a complete index of defect types and links to each technical article, use the Conformal Coating Defects Hub.

Article Quicklinks

Topic	More
What it is: solvent attack & substrate damage	🔗
How it shows up: symptoms & “tell-tale” patterns	🔗
Root causes: materials, process, contamination, cure state	🔗
Prevention: compatibility checks & control window	🔗
Troubleshooting: confirm the mechanism fast	🔗
Repair & rework: when to touch-up vs strip	🔗

What is Solvent Attack / Substrate Damage?

In conformal coating, solvent attack means the coating (or its solvent system) interacts with materials on the assembly in a way that causes visible or functional damage.

• Plastics: swelling, softening, whitening, crazing (micro-cracks), deformation, stress cracking.
• Labels: edge lift, adhesive smear, bubbling, wrinkling, delamination, print smudge.
• Inks & markings: bleed, fade, smear, staining into the coating film.
• Solder mask (less common, but real): softening, staining, reduced adhesion, surface “drag” or imprinting, poor intercoat behaviour.

This is not just cosmetic. Substrate damage can create adhesion failures, contamination sources, and reliability risks that show up later as cracking, delamination, corrosion, or leakage.

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How Solvent Attack Presents (Common Symptoms)

Plastics & connector materials

• Whitening / stress whitening around corners, clips, or moulded features.
• Crazing (fine crack network) especially on clear plastics or under mechanical stress.
• Softening or deformation where solvent dwell is highest.

Labels & print

• Label edge lift after coating or cure; adhesive “ooze” at edges.
• Print smear / bleed into the coating film or onto masks/fixtures.
• Wrinkling if solvent penetrates the label laminate or adhesive layer.

Board finish / film behaviour (secondary clues)

• Local haze or “milky” patches over attacked areas as solvent redistributes or traps volatiles.
• Intercoat issues (wrinkling, rippling) where solvents re-activate a partially cured layer.
• Adhesion loss at boundaries where attacked contaminants migrate into the film.

Pattern clue: solvent attack is often localised to specific materials (labels, connector bodies, potting edges) rather than occurring uniformly across the PCB.

Sanity check (look-alikes):
If the main symptom is milky haze without obvious substrate deformation, route to Haze / Whitening / Blushing. If the coating retracts and leaves bare patches, route to De-wetting. If the defect is a re-coating texture (ripples/ridges), route to Wrinkling (Re-coating Defects).

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Root Causes of Solvent Attack

Material compatibility (the big one)

• Solvent-sensitive plastics (varies by polymer, grade, fillers, mould stress, and age).
• Label laminates / adhesives not rated for solvent exposure or bake cycles.
• Inks and markings that re-dissolve or migrate when exposed to solvent vapour or wet film contact.

Process & technique

• Excessive solvent dwell from slow flash-off, over-wet passes, or heavy local build.
• Thinners / reducers added outside the validated window (changes solvency and attack risk).
• Cleaning solvents (pre-clean or rework) that are harsher than the coating’s own solvent system.
• Masking interactions: tape/boot residues can dissolve and migrate, creating local “hot spots” of solvency and contamination.

Cure state & substrate condition

• Partially cured solder mask / inks that are more easily attacked and more likely to release extractables.
• High mould stress in plastics (stress cracking/crazing is more likely).
• Heat history: some materials become more sensitive after multiple bakes or rework exposure.

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How to Prevent Solvent Attack

1) Build a compatibility gate (fastest long-term win)

• Identify at-risk materials: connector bodies, housings, labels, inks, elastomers, potting edges.
• Run a simple exposure test on representative samples (wet contact + vapour exposure + bake profile).
• Lock approved label/ink specs for coated assemblies (don’t treat them as “cosmetics”).

2) Control the solvency window (process discipline)

• Keep viscosity within a validated range (uncontrolled thinning changes attack behaviour).
• Use multiple light coats with defined flash-off rather than one heavy pass.
• Manage flash-off: avoid solvent pooling around plastics/labels; ensure predictable booth airflow.

3) Reduce secondary sources of attack

• Cleaning and rework solvents: standardise approved chemistries and dwell times.
• Masking materials: avoid residues; select products compatible with your coating solvent system.
• Handling & staging: prevent solvent vapour accumulation around staged assemblies.

If solvent attack is recurring at boundaries, also review your masking discipline and post-mask inspection in the Masking Hub.

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Troubleshooting & Diagnosis

1) Confirm it’s substrate change (not just coating appearance)

• Localisation: does the defect map to a specific plastic/label/ink area?
• Touch/feel (where safe/allowed): softening, tack transfer, imprinting, deformation.
• Magnification: crazing networks, edge-lift initiation, print migration into the film.

2) Check the three “solvent exposure” drivers

• Solvent strength: was thinner/reducer used; did the formulation change; is the batch correct?
• Solvent dwell: heavy local build, poor airflow, slow flash-off, pooling at features.
• Material sensitivity: new label supplier, new connector resin, or different ink system.

3) Rule out look-alikes

• Haze/whitening driven by moisture/rapid evaporation: Haze / Whitening / Blushing
• Recoating texture from cure mismatch: Wrinkling (Recoating Defects)
• De-wetting from contamination/surface energy: De-wetting

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Repair: What to Do When Solvent Attack is Found

• First decision: is the underlying material compromised (cracked plastic, lifted label, smeared ID marking)? If yes, treat as a material nonconformance first, not just a coating rework.
• Local cosmetic smear (non-critical marking, no adhesion risk): controlled clean + local touch-up may be acceptable if permitted by the product spec.
• Adhesion-risk areas (labels/ink within coated zones, connector bodies): stripping and recoating may still fail unless the underlying compatibility issue is fixed.
• Repeated events: stop and implement a compatibility gate (approved labels/inks/materials) before continuing production.

For removal workflows and best-fit methods, see the Removal & Rework Hub.

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Looking for Other Defect Types?

This page covers solvent attack and substrate damage. For the complete index of defect types and links to each technical article:

Explore the Defects Hub ↗

Training on Conformal Coating Defects

SCH offers conformal coating training that goes beyond theory—recognising and preventing solvent attack, recoat defects, haze/blushing, de-wetting, delamination, cracking, and contamination-driven failures. We cover process control, troubleshooting, materials compatibility, and production discipline.

Explore Conformal Coating Training ↗

Industry Standards We Work To

SCH Services aligns coating services, training, equipment supply and materials to 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: electronics.org/ipc-standards ↗

Why Choose SCH Services?

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• 🛠️ End-to-End Support – Selection, masking, inspection and troubleshooting.
• ✅ Process Discipline – Recipes, control windows and repeatability.
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Note: This article provides general technical guidance only. Final design, validation, and compliance decisions must be verified by the product manufacturer and validated against the applicable standards.