Frequently Asked Questions (FAQs)
Our FAQs hub brings together the most common questions on conformal coating, Parylene, cleaning, masking, equipment, materials, and services. Expand a category to explore concise answers, then follow the suggested link targets to dive deeper.
FAQ Categories
- Fundamentals – Basics of conformal coating, standards and uses.
- Cleaning & Reliability – PCB cleaning, no-clean controls and testing.
- Processes & Methods – Application, curing, inspection and automation.
- Parylene Coating – CVD process, grades, thicknesses and limitations.
- Masking & De-Masking – Boots, tapes, gels and efficiency improvements.
- Defects & Quality – Common issues, causes, prevention and testing.
- Materials & Chemistry – Chemistries, adhesion promoters and nano coatings.
- Removal & Rework – Stripping methods and rework guidance.
- Equipment & Support – Systems, consumables, training and service.
Fundamentals
What is conformal coating?
A thin polymer film (10–100 µm) applied to PCBs to protect against moisture, dust, and electrical leakage.
Why is conformal coating used on PCBs?
It improves reliability, prevents corrosion, and extends product life in harsh conditions.
What industries use conformal coating?
Conformal coatings are widely used across many industries, including aerospace, automotive, defence, energy, medical, and industrial electronics, where they play a vital role in ensuring long-term reliability.
What’s the difference between conformal coating and potting?
Coating is thin, lightweight and reworkable; potting is a thick resin mass for extreme protection.
What international standards apply to coatings?
Commonly IPC-A-610, IPC-CC-830, IEC 60664, MIL specs and customer-specific requirements.
What is pollution degree classification?
A rating (PD1–PD4) of environmental contamination that affects insulation design and coating needs.
How thick should a conformal coating be?
Liquid conformal coatings are typically applied at 25–75 µm, while Parylene is 5–25 µm. IPC-CC-830 and IPC-A-610 specify acceptable thickness ranges and require measurement on coated test coupons for verification.
Do coatings affect circuit performance?
They raise surface insulation resistance and reduce leakage; added capacitance is negligible at normal thicknesses.
Cleaning & Reliability
Should I clean my PCB before conformal coating?
Yes. Flux and ionic residues can cause poor adhesion, dewetting, and long-term failures.
Can I coat a PCB that is “no-clean”?
Possibly, but many specs still mandate additional cleaning; “no-clean” residues may still impair adhesion.
What happens if I don’t clean before coating?
It is possible to apply conformal coating over no-clean assemblies, but the process demands much tighter controls. Flux residues must be minimal and consistent, and you’ll need strict validation of cleanliness, adhesion, and long-term reliability to avoid defects.
How clean should a PCB be before coating?
Align to IPC cleanliness expectations (e.g., ionic contamination limits) verified by ROSE or ion chromatography.
What cleaning methods are used pre-coating?
Aqueous spray-in-air, vapour degreasing, ultrasonic, plasma—selected by contaminant type and assembly design.
How do you test PCB cleanliness?
ROSE testing, ion chromatography and SIR testing confirm ionic and reliability performance.
Can SCH provide cleaning as a standalone service?
Yes—pre-coating cleaning and ionic testing offered standalone or integrated with coating services.
Does cleaning add cost to the coating process?
It adds process time/cost but typically lowers rework and field failure risk—reducing total cost of ownership.
Processes & Methods
What are the main application methods?
Spraying, dipping, brushing, robotic selective coating, and vapour deposition (Parylene).
How do spraying and dipping compare?
Spraying suits complex geometries; dipping gives fast, uniform coverage for high volume.
What is vapour deposition?
A vacuum CVD process for Parylene that coats all exposed surfaces with pinhole-free films.
How do coatings cure?
By solvent evaporation, heat, UV, or moisture-activated cross-linking depending on chemistry.
Why is cleaning vital before coating?
Surface residues lower surface energy and trigger defects like dewetting or poor adhesion.
How do you measure coating viscosity?
Zahn/Ford cups or inline sensors to maintain consistent application parameters.
What inspection methods are used?
UV inspection & magnification for validation and root cause analysis.
Can conformal coating be automated?
Yes—selective robots improve consistency, reduce labour and control deposits precisely.
What are common process challenges?
Bubbles, bridging, shadowing and uneven thickness; solved by setup, viscosity and masking optimisation.
Parylene Coating
What is Parylene?
A vacuum-deposited polymer offering uniform, pinhole-free 3D coverage with excellent barrier and dielectric properties.
How is Parylene applied?
By chemical vapour deposition (CVD) under vacuum, polymerising directly on surfaces.
What thicknesses are typical for Parylene?
Commonly 5–25 µm for electronics; medical/aerospace may require tighter windows.
How does Parylene compare to liquid coatings?
Superior 3D coverage and barrier; higher cost and specialised equipment vs liquids.
What grades of Parylene exist?
N, C, F (and HT variants) balancing dielectric properties, moisture barrier and temperature performance.
Can Parylene be repaired or reworked?
Yes—laser/plasma/micro-abrasion enable precise local removal for access or repair.
Is Parylene biocompatible?
Certain grades meet medical biocompatibility requirements and are widely used on devices/sensors.
What are the limitations of Parylene?
Higher cost, longer cycle times and more complex masking compared with liquid coatings.
What drives Parylene cost?
Dimer consumption, masking effort, load density and vacuum cycle time dominate cost.
Masking & De-Masking
Why is masking important?
It protects keep-out zones (connectors, test points) ensuring functional interfaces remain coating-free.
What masking materials are used?
Silicone boots, tapes, dots, gels, liquid masks and custom shapes depending on geometry and process.
Can masking boots be reused?
Often yes; inspect for wear, swelling or residue to maintain seal integrity and repeatability.
Masking for Parylene vs liquid coatings?
Parylene needs airtight vapour seals; liquids rely on surface barriers and careful tape selection.
Common masking challenges?
Leakage under tape, adhesive residue, inconsistent coverage—solved via fixtures, boots and process control.
How do you speed up de-masking?
Use pre-formed boots/shapes, optimise takt time, and train operators on efficient removal techniques.
Defects & Quality
What are common conformal coating defects?
Bubbles, dewetting, orange peel, bridging, cracking and delamination are frequently encountered.
What causes dewetting?
Low surface energy or contamination; improve cleaning, surface prep and consider adhesion promoters.
What is orange peel?
A textured finish from viscosity/spray setup/dry-time imbalance; tune solvents, flow and atomisation.
What causes bubbles?
Entrapped solvents/moisture or poor application technique; adjust flash times and application parameters.
What is delamination?
Loss of adhesion due to contamination or stress; address surface prep and primer compatibility.
How do you measure coating thickness?
Coupons/flat areas per IPC guidance, optical methods, or calibrated gauges depending on chemistry/spec.
What adhesion tests are used?
Cross-hatch tape, pull-off and surface energy checks to validate bond strength and wetting.
How do you inspect coatings?
UV inspection with IB100 booths, magnification/AOI and occasional destructive cross-sections.
Materials & Chemistry
What coating chemistries are available?
Acrylics, polyurethanes, silicones, epoxies, UV-curables and Parylenes—selected by environment and rework needs.
How do I choose the right chemistry?
Match hazards (temp, chemicals, condensate) and serviceability; test on coupons when in doubt.
What are adhesion promoters?
Primers (e.g., silanes) that raise surface energy and bonding—vital for Parylene and low-energy substrates.
What are nano coatings?
Ultra-thin hydrophobic/oleophobic layers for splash resistance/easy clean; not a full replacement for conformal protection.
Are coatings RoHS/REACH compliant?
Most modern chemistries are; always verify supplier declarations and MSDS for your region.
Do coatings outgas?
Some do—select low-outgassing materials for aerospace/space and verify with appropriate testing.
Removal & Rework
Can conformal coating be removed?
Yes—chemical stripping, laser, plasma or micro-abrasion depending on chemistry and tolerance.
What removal methods exist?
Chemical strippers, abrasion/micro-blasting, plasma and laser ablation—each suits different coatings.
Can you solder through conformal coating?
Not reliably—locally remove the coating before soldering to ensure a clean metallurgical bond. Use either a wet stripping process in WS100 wet stripping system or an ESD micro blast system like ProBlast 3.
How do you strip Parylene?
Plasma, laser, micro-abrasion or targeted chemistries, chosen by area size and precision needed.
When should you rework vs recoat?
Localised defects → rework; widespread issues → strip and recoat for consistent performance.
What equipment removes coatings?
WS100 stripping systems, micro-abrasion blasters and laser workstations are typical platforms.
Does removal damage the board?
With correct methods and controls, no; incorrect removal risks pad lift or solder-mask damage.
Equipment & Support
What coating equipment is available?
Dip tanks, spray booths, selective robots, Parylene systems and drying/curing cabinets.
Do you provide turnkey solutions?
Yes—integrating equipment, process setup, masking, consumables and operator training.
Do you supply conformal coating consumables?
Yes – We supply masking boots/tapes/dots, adhesion promoters, Parylene dimers and more.
Do you provide operator training?
Yes—from fundamentals to advanced troubleshooting, onsite or online.
What support do you offer for equipment?
Installation, validation, spares and ongoing technical consultancy to maintain yield and quality.
