Conformal Coating Thickness Measurement: Wet, Dry & Optical Methods

Accurate conformal coating thickness measurement underpins reliability, cost control, and compliance. This guide explains when to use wet film gauges, dry film gauges (after cure), and optical film thickness measurement for Parylene and ultra-thin coatings—plus setup, verification, and common pitfalls.

Conformal coating thickness measurement with a dry film gauge – SCH Services UK

Why Thickness Control Matters

  • Reliability: Meeting the specified micron window reduces early-life failures.
  • Compliance: Supports acceptance criteria aligned with IPC-A-610.
  • Cost: Prevents over-application (waste) and under-application (scrap/rework).
  • Process stability: Enables SPC monitoring and faster first-time yield.

Measurement Methods

Wet Film Measurement for Conformal Coating Processes (In-Process)

Use a wet film gauge at the point of application to set passes, speed, and viscosity so the final dry thickness lands on target consistently.

  • Immediate feedback during spray/dip setup
  • Best for liquids (acrylic, urethane, silicone, epoxy)
  • Pair with cure factors to estimate final dry film

View Wet Film Thickness Gauges →

Dry Film Gauges in Conformal Coating Thickness Control (After Cure)

After curing, use a dry film gauge (e.g., PosiTector 6000) on suitable substrates and coupon panels to verify coating windows for QA release.

  • Rapid QA checks and data logging for traceability
  • Use representative flat areas or dedicated coupons
  • Ideal for routine verification during inspection

See PosiTector 6000 Dry Film Gauges →

Optical Film Systems for Conformal Coating Thickness Measurement (Parylene & Ultra-Thin)

For Parylene and very thin transparent films, use optical film thickness measurement—a fast, non-destructive method suited to coupons or flat, representative areas. Principles are aligned with metrology best practice from bodies such as NIST.

  • Non-destructive; ideal for Parylene C/N and thin liquids
  • Supports process development and SPC
  • Use on smooth, flat surfaces or dedicated coupons

Explore Optical Thickness Measurement →

Wet film thickness gauge used during conformal coating application – SCH Services UK
Optical film thickness system for Parylene and ultra-thin coatings – SCH Services UK

Which Method Should I Use?

  • Setting up the process: Wet film gauge
  • Routine QA after cure (liquids): Dry film gauge
  • Parylene or ultra-thin films: Optical thickness

Many teams use a combination: wet film for setup, dry film for QA, and optical for thin films and Parylene.

Set-Up, Verification & SPC

  • Coupons: Use representative test panels for repeatable readings.
  • Sampling: Define AQL and measurement points in your WI.
  • Records: Log results for traceability and trend analysis (SPC).
  • Correlation: Calibrate wet-to-dry factors during process development.

Common Pitfalls (and How to Avoid Them)

  • Measuring on rough/uneven areas: prefer flat coupons or planar board areas.
  • Assuming wet=dry: validate conversion factors for each coating/process.
  • Ignoring cure effects: under/over-cure skews thickness and properties.
  • Parylene with contact gauges: use optical; contact methods are unsuitable.

Download the Original Technical Bulletin

Prefer the original PDF version of this article? Download it here:

📄 Download Technical Bulletin: Conformal Coating Thickness Measurement (PDF)

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Whether you need thickness measurement equipment, operator training, or outsourced inspection services, SCH can help. We supply wet film gauges, PosiTector dry film gauges, and optical systems alongside our coating services.

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