1. From Visual Acceptance to Engineering Verification
In vacuum coating applications, determining whether a coating layer is qualified should never rely solely on visual inspection.
A coating suitable for mass production must be evaluated using measurable, repeatable, and traceable engineering criteria.
Whether optical, decorative, or functional coatings, qualification typically involves five key evaluation dimensions.
2. Visual Appearance and Surface Integrity
2.1 Surface Uniformity and Defect Inspection
A qualified coating layer should exhibit:
Uniform color and gloss
No visible particles, pinholes, streaks, or shadowing
No peeling, flaking, or localized discoloration
Common inspection methods include:
Visual inspection under standardized lighting
Surface microscopy (optical microscopy / SEM)
3. Film Thickness and Uniformity Control
3.1 Thickness Accuracy
Film thickness must meet design specifications and tolerances. Common measurement techniques include:
Quartz crystal monitoring (QCM)
Profilometry
Ellipsometry
3.2 Thickness Uniformity
For large-area or batch coating, thickness uniformity directly affects performance consistency.
Uniformity is typically evaluated using maximum deviation or standard deviation (σ).
4. Adhesion and Interfacial Bonding Strength
4.1 Adhesion Test Methods
Common adhesion evaluation methods include:
Cross-cut test
Tape peel test
Scratch test
Insufficient adhesion may lead to:
Local delamination
Failure under thermal cycling or mechanical stress
5. Functional Performance Verification
5.1 Optical Performance (for Optical Coatings)
Including:
Visible light reflectance / transmittance
Refractive index and spectral stability
Color difference (ΔE)
5.2 Electrical and Functional Properties (for Functional Coatings)
Including:
Sheet resistance or surface resistivity
Conductive or insulating performance
Shielding or corrosion resistance
6. Environmental Reliability and Durability Testing
Qualified coatings must withstand application-specific reliability tests, such as:
High-temperature and high-humidity testing (85°C / 85% RH)
Thermal cycling
UV aging
Abrasion and wear testing
After testing, coatings should show:
No significant color change
No performance degradation
No structural failure
7. Mass Production Consistency and Process Stability
A truly “qualified” coating is not only acceptable in a single run, but also demonstrates:
Batch-to-batch consistency
Process repeatability
Full process traceability
This is typically achieved through:
Closed-loop process control
Automated recipe management
Process monitoring and SPC analysis
8. Conclusion
Determining whether a coating layer is qualified is essentially a comprehensive evaluation of film structure, performance, and process stability.
Only by establishing standardized and data-driven quality criteria can vacuum coating processes achieve scalable, stable, and highly reliable manufacturing.
–This article was published by vacuum coating equipment manufacturer Zhenhua Vacuum
Post time: Dec-23-2025