PCBs that fail in humid weather usually need a conformal coating: a thin protective film that keeps moisture, dust and corrosive vapours off the board. For general protection where you may need to rework later, Micron 3100 Protektor Conformal Coating is a single-component acrylic coating that its page says conforms to IPC-CC-830B and MIL-I-46058C, is rated -70°C to 120°C, and can be removed with Protektor thinner. Other Protektor coatings fit UV inspection, heat and vibration, or UV-cure lines.
Why it happens
- Uncoated boards exposed to humidity and condensation. Moisture on the board surface lets current leak between tracks and starts corrosion.
- Contamination that attracts moisture. Flux residue and dust hold water on the board.
- Salt or caustic vapours. Coastal sites, chemical plants and some process areas speed up corrosion.
You will see intermittent faults in the humid season, green or white corrosion on tracks and pads, fungus on boards, and leakage or arcing on high-voltage sections.
How to fix it
Clean the board first, then pick the coating by your situation:
- General protection, rework possible later: Micron 3100 Protektor Conformal Coating. Acrylic, IPC-CC-830B / MIL-I-46058C, rated -70°C to 120°C, and its page says the cured film can be removed with Protektor Conformal Coating Thinner.
- Coverage must be inspected under UV light: Micron 3110 Protektor Conformal Coating UV, which glows under UV light so coated areas can be verified.
- High temperature, vibration, thermal cycling or outdoor use: Micron 3708 SIL-26 Silicone Conformal Coating, which its page says is flexible and accommodates thermal expansion and vibration without cracking.
- High-speed production line with UV lamp curing: Micron 3608 Protektor PolyCoat UV, which cures when exposed to a medium-pressure mercury vapour UV lamp.
- Only exposed solder joints, connectors or sensors need sealing, by brush or dip: Micron 3307 Protektor Acrylic Sealant.
Clean boards before coating so the film bonds and nothing is sealed underneath. Micron 3400 Protektor PCB Cleaner is listed for preparing a clean surface for coating.
The 3100 page gives a dry-to-touch time of about 30 minutes but no step-by-step directions. Follow the instructions on the can and the TDS, and mask connectors, test points and anything that must stay uncoated.
What to avoid
- Acrylic 3100 and 3110 are rated -70°C to 120°C. Do not use them for hotter service.
- The 3100 aerosol propellant is flammable (stated). Coat unpowered boards only, ventilate the area, and keep away from ignition sources.
- Clean the board first. Coating over flux or dust traps it under the film.
- 3608 needs a UV lamp line with UV safety shields, PPE and ventilation, as its page states.
When to ask an expert
Ask Micron's technical team if:
- you need defence, medical or automotive qualification beyond what the product pages state;
- boards run above 120°C, since 3708's temperature rating is not given as a number;
- coated boards still fail, which may point to contamination under the coating or a design issue.
FAQ
Which conformal coating should I start with?
For general protection with the option to rework, 3100 acrylic is the usual starting point. Choose 3110 if QC needs UV inspection, 3708 for heat and vibration, and 3608 for UV-cure production lines.
Can I remove the coating later to repair the board?
The 3100 and 3110 pages say the cured film can be removed with Protektor Conformal Coating Thinner (3308).
Do I need to clean the board before coating?
Yes. Flux, oil and dust under the coating cause poor adhesion and can trap moisture. 3400 PCB Cleaner is listed for preparing boards for coating.
Can I spray conformal coating on a powered board?
No. The 3100 propellant is flammable. Coat unpowered boards in a ventilated area, away from ignition sources.
See the product: Micron 3100 Protektor Conformal Coating. Related: 3110 UV, 3708 SIL-26, 3608 PolyCoat UV, 3307 Acrylic Sealant. More electronics fixes: electronics hub.