Tackiness, Soft Cure & Under-Cure Defects in Conformal Coating

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Conformal coating under-cure, tackiness and soft cure describe conformal coating films that do not reach their intended cure state. The coating may feel sticky, rubbery, easily marked, or remain solvent-rich. Beyond handling issues, under-cure can reduce insulation resistance, increase contamination pickup, and create secondary defects such as bubbling, pinholes, delamination and cracking.

This page explains how under-cure presents, how to diagnose the mechanism, and how to prevent recurrence by controlling thickness, flash-off and cure conditions.

For the full defect index, use the Conformal Coating Defects Hub.

Article Quicklinks

Topic	More
Definitions: tacky vs soft cure vs under-cure	🔗
How it happens: cure-state mechanisms	🔗
Root causes: process, material, equipment	🔗
Prevention: control window & verification	🔗
Troubleshooting: isolate the culprit fast	🔗
Repair & rework: touch-up vs strip & recoat	🔗

What Does Tackiness / Soft Cure / Under-Cure Mean?

• Tacky coating — surface remains sticky or “grabby”, attracts dust, or marks easily after the defined cure time.
• Soft cure — film is non-sticky but rubbery/soft, dents with a fingernail, or can be peeled/smeared under light force.
• Under-cure — coating has not reached the intended crosslink / solvent removal state (often evidenced by low hardness, poor chemical resistance, or poor electrical performance).

Why it matters: under-cured films can trap solvent/moisture, pick up contamination, and reduce long-term reliability.
They can also trigger bubbles/pinholes, delamination, and cracking when the film later hardens unevenly.

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How Under-Cure Happens (Mechanisms)

• Insufficient solvent removal — thick films, poor airflow, or inadequate flash-off leave solvent trapped in the film.
• Inadequate cure energy — temperature, time, UV dose, or humidity conditions do not meet the coating’s cure requirement.
• Oxygen inhibition / surface inhibition — some chemistries can remain tacky at the surface if the cure mechanism is inhibited.
• Mix ratio / catalyst errors — 2K systems can remain soft if mixing, induction, or pot-life control is wrong.
• Contamination interference — residues (cleaners, flux, silicone transfer) can inhibit cure locally or reduce crosslink density.

Pattern clue: widespread tackiness often points to cure condition / thickness / flash-off. Local tackiness in patches
often points to contamination or localised over-build.

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Root Causes of Tackiness / Soft Cure

Process & Technique

• Over-thickness — thick films slow solvent escape and can prevent full cure through the depth.
• Insufficient flash-off — coating goes to cure with too much retained solvent.
• Poor airflow / stacking — restricted ventilation during flash or cure traps solvent vapour and slows drying.
• Incorrect cure profile — time/temperature ramp not matched to chemistry (or cure started too early).

Material & Condition

• Solvent imbalance — dilution errors, wrong thinner, or evaporative loss changing solids/flow and cure behaviour.
• Out-of-life / moisture uptake — aged material or moisture-sensitive systems can behave unpredictably.
• Wrong chemistry for the process — cure mechanism not suited to your available cure conditions.

Equipment / Control Failures

• Oven / UV system under-performance — real board temperature or UV dose lower than displayed.
• Temperature mapping not representative — sensors measure air, not the assembly mass or shadowed regions.
• Recipe drift — untracked changes to cure time, loading density, airflow, or lamp condition.

Sanity check (look-alikes):
If the coating is pulling back into islands leaving bare zones, route to de-wetting. If you see widespread voids or blisters, route to pinholes/bubbles/foam.

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How to Prevent Under-Cure

Lock the control window

• Define thickness targets and avoid “single heavy coat” behaviour in production.
• Standardise flash-off (time, airflow, spacing, orientation) before cure.
• Standardise cure conditions (time/temperature/UV dose/humidity as required) and audit them routinely.

Verify what you think you’re doing

• Measure real board temperature (or dose) — not just oven setpoints.
• Use witness coupons for hardness/cure checks aligned to your product requirements.
• Keep mixing/traceability discipline for 2K systems (ratio, induction, pot life, and disposal rules).

If you’re building inspection routines and acceptance rules around cure state, see the Inspection & Quality Hub.

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Troubleshooting & Diagnosis

1) Confirm scope and pattern

• Is it global or local? Whole-batch tackiness suggests cure/flash/thickness. Local patches suggest contamination or over-build.
• Where is it worst? Under components, dense zones, or low airflow areas often indicate solvent retention.

2) Check the “big four” first

• Thickness: confirm no over-build at low points/edges (risk of pooled solvent and delayed cure).
• Flash-off: confirm time, airflow and spacing are actually being followed.
• Cure energy: verify real board temperature/UV dose and loading density.
• Material condition: verify lot, shelf life, correct thinner, and (if applicable) 2K ratio/pot life.

3) Decide if it’s safe to rework or must be stripped

• Electrical risk: if insulation resistance / leakage performance is in doubt, treat as a process escape until proven otherwise.
• Surface contamination pickup: tacky films collect dust/fibres which can create secondary defects and rework complexity.

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Repair: When to Touch-Up vs Strip & Recoat

• Do not “seal in” under-cure: applying more coating over a soft/solvent-rich film often worsens cure-state and adhesion.
• Localized issue: if you can isolate the area, confirm cure state and contamination exposure before attempting controlled repair.
• Widespread tackiness: stripping and recoat is often the only robust route (especially if dust/fibres have embedded).

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

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Looking for Other Defect Types?

This page covers tackiness, soft cure and under-cure. For the full index of defect types and links to each technical article:

Explore the Defects Hub ↗

Training on Conformal Coating Cure Control

SCH offers conformal coating training that covers cure-state control in production: thickness/flash-off discipline, cure profiling, verification strategy, and structured troubleshooting when coatings remain tacky or soft.

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?

You gain a complete, integrated platform for Conformal Coating, Parylene & ProShieldESD—plus equipment, materials and training—backed by decades of hands-on process support.

• 🛠️ End-to-End Support – Selection, masking, inspection and troubleshooting.
• ✅ Process Discipline – Recipes, control windows and repeatability.
• 🌍 Global Reach – Support across Europe, North America and Asia.

📞 Call: +44 (0)1226 249019   | ✉ Email: sales@schservices.com |   💬 Contact Us ›

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.