Conformal Coating Viscosity Control

Why viscosity matters in process control

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Effective conformal coating viscosity control is essential for consistent coverage, defect prevention, and long-term PCB reliability. If viscosity is too low, coatings can run or thin out; too high, and you risk bubbles, voids, poor flow and texture defects. Managing viscosity is a cornerstone of stable, repeatable coating processes.

Viscosity must be treated as a controlled parameterβ€”defined by a target window, measured consistently, recorded for traceability, and linked to thickness/inspection results for closed-loop control.

Conformal coating viscosity control – Zahn cup measurement with stopwatch for process consistency
Zahn cup + stopwatch measurement is common for production control of solvent-borne conformal coatings.

Why Viscosity Matters in Conformal Coating

Viscosity influences how a coating wets, flows, levels and builds thickness. It also changes how the coating atomises (spray), drains (dip), and behaves at edges and component bodies.

  • Too low: runs, pooling, thin coverage on edges/high points, wicking under parts, longer tack/contamination risk.
  • Too high: poor levelling, texture/orange peel, air entrapment, bridging, voids, inconsistent thickness and edge definition.
  • Drifting viscosity: β€œrandom” defects that correlate to solvent loss, temperature changes, open tank time, or poor make-up control.

Viscosity must be controlled alongside temperature, solids content, humidity/airflow and cure profileβ€”because these variables interact.

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Measuring Conformal Coating Viscosity

Production-friendly measurement is usually a flow cup (e.g., Zahn/Ford) plus a stopwatch. Consistency depends on doing the test the same way every time.

  • Use the correct cup type/size for the coating and target range.
  • Control temperature (or record it every timeβ€”viscosity is temperature-sensitive).
  • Use a consistent sampling method (same depth, same container, same stir/settle time).
  • Define the end-point clearly (first break / continuous stream end) and train operators.

Tip: If you need higher accuracy (e.g., 2K systems, critical specs), add periodic cross-checks using a rotational viscometer and/or solids checksβ€”then correlate back to the cup readings used on the line.

Why measurement matters

  • Ensures consistent coating flow and application
  • Supports repeatable film thickness and quality
  • Reduces risk of bubbles, runs, or orange peel
  • Forms part of IPC-aligned process control

Go to the control plan β†’

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Best Practices for Viscosity Control

Good control means more than taking a readingβ€”it ties specification limits, trained operators, and verification plans together. Build viscosity into work instructions and link checks to thickness verification for a closed-loop process.

  • Define viscosity windows per coating + application method (spray/dip/selective/brush).
  • Set a measurement cadence (start of shift, every X hours, after top-ups, after long idle, after filter changes).
  • Standardise make-up rules (approved thinner only; max % addition; add in steps; mix time; re-test before release).
  • Record for traceability (operator, batch/lot, time, temp, cup/time result, any additions) and trend via SPC.
  • Correlate to thickness using coupons/witness boards and inspection outcomes (UV coverage + dry film thickness).

Minimum record set (recommended)

  • Date/time, coating ID, batch/lot, cup type, seconds, temperature
  • Tank/container ID, filter status, any thinner/top-up amount
  • Related process settings (spray pressures / dip withdrawal speed) if changed
  • Linked thickness/inspection result (pass/fail + notes)

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Troubleshooting: When Viscosity Is (Probably) the Root Cause

  • Runs / pooling / thick edges: viscosity too low, over-wet passes, excess thinner, high temperature, poor drain orientation.
  • Orange peel / rough texture: viscosity too high, excessive solvent flash (airflow/distance), poor levelling window. (Related: Orange Peel)
  • Bubbles / pinholes: viscosity too high or aerated material, aggressive mixing, solvent imbalance, trapped volatiles. (Related: Pinholes, Bubbles & Foam)
  • Inconsistent thickness shift-to-shift: temperature not controlled, sampling method inconsistent, top-ups not standardised, evaporation in open tanks.
  • Masking leakage suddenly increases: viscosity drift (often lower) + wet passes + capillary routes; confirm viscosity and re-check demask/touch-up rules.

If viscosity is stable but defects persist, broaden the investigation to cleanliness, surface energy/contamination, airflow/booth conditions, and cure profile.

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Downloads, Support, Training & Equipment

SCH helps teams implement robust viscosity managementβ€”from operator training and process audits to supply of flow cups and accessories. Our specialists optimise coating parameters so you reduce rework, improve yield, and meet customer/industry standards.

  • Training on viscosity measurement, material handling and make-up control
  • Process setup and optimisation consultancy
  • Supply of measurement tools and consumables

Contact SCH to discuss viscosity control β†’

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Why Choose SCH Services?

Partnering with SCH Services means more than just outsourcing β€” you gain a complete, integrated platform for
Conformal Coating, Parylene & ProShieldESD Solutions, alongside equipment, materials, and training, all backed by decades of hands-on expertise.

  • ✈️ 25+ Years of Expertise – Specialists in coating technologies trusted by aerospace, medical, defence, automotive, and electronics industries worldwide.
  • πŸ› οΈ End-to-End Support – Guidance on coating selection, Parylene grades, masking strategies, application methods, inspection, and ProShieldESD integration.
  • πŸ“ˆ Scalable Solutions – From small prototype batches to full-scale, high-volume production.
  • 🌍 Global Reach – Responsive technical support and supply coverage across Europe, North America, and Asia.
  • βœ… Proven Reliability – A strong reputation built on quality, consistency, and customer satisfaction across services, equipment, and materials.

πŸ“ž Call: +44 (0)1226 249019
βœ‰ Email: sales@schservices.com
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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.