# How to Waterproof ESC and Flight Controller with Conformal Coating
Land in wet grass, crash in morning dew, or fly through light rain — and your electronics are at risk. Conformal coating is a thin, transparent protective layer that seals your PCBs against moisture, corrosion, and conductive debris. Applied correctly, it lets you fly in conditions that would otherwise destroy your electronics. Here’s the complete guide.
## What Is Conformal Coating?
Conformal coating is a thin polymeric film (typically 25-75 microns thick) that conforms to the contours of a printed circuit board, protecting it from:
| Protection Against | How It Works |
|——————-|—————|
| Water and moisture | Creates a hydrophobic barrier — water beads and rolls off |
| Corrosion | Prevents oxidation of solder joints and copper traces |
| Conductive debris | Carbon fiber dust, metal shavings, and sand can’t bridge pads |
| Short circuits from wet grass | Dew-soaked grass blades bridging ESC pads = instant fire |
| Salt spray (coastal flying) | Salt accelerates corrosion dramatically — coating is essential |
**What conformal coating does NOT protect against**:
– Full submersion in water (you need full potting or a waterproof enclosure)
– Physical impact damage
– Heat — coating slightly reduces heat dissipation (minimal for our application)
## Choosing the Right Coating
| Type | Drying Time | UV Tracer | Durability | Best For |
|——|————|———–|————|———-|
| Silicone-based (MG 422B) | 10-20 min | Yes (glows under UV) | Excellent, flexible | Best overall for FPV |
| Acrylic-based (MG 419C) | 5-10 min | Yes | Good, harder | Faster drying, cheaper |
| Urethane-based | 30-60 min | Optional | Best, chemical resistant | Extreme environments |
| Nail polish (clear) | 5 min | No | Poor, cracks with flex | Emergency/temporary only |
**Recommendation**: MG Chemicals 422B Silicone Conformal Coating. The UV tracer lets you verify coverage with a UV flashlight, and the silicone formula remains flexible — acrylic coatings can crack when the PCB flexes during a crash.
## What to Coat
| Component | Coat? | Notes |
|———–|——-|——-|
| ESC (4-in-1 or individual) | Yes — full board, both sides | Highest priority — most exposed to wet grass |
| Flight controller | Yes — both sides | Avoid barometer hole if present |
| Receiver | Yes | Extra important — RX failure = failsafe |
| VTX | Yes, except heatsink | Mask heatsink — coating insulates heat |
| Camera boards | Yes, carefully | Avoid lens and image sensor |
| Motor windings | Optional | Already enamel-coated; coating adds unnecessary weight |
| Connectors (USB, JST) | No — mask them | Coating in connectors prevents contact |
| Barometer sensor | No — mask it | Coating blocks the tiny air hole |
| Buttons (boot, bind) | Yes, then work the button | Silicone coating doesn’t prevent button function |
## Step-by-Step Application
### Materials Needed
– Conformal coating (MG 422B recommended)
– UV flashlight (to verify coverage with UV tracer)
– Kapton tape or painter’s tape (for masking)
– Isopropyl alcohol (99%) and cotton swabs (for cleanup)
– Toothpicks (for applying to small areas)
– Disposable gloves
– Well-ventilated workspace (or outside)
### Step 1: Clean the Board
Oil, flux residue, and dirt prevent coating adhesion.
1. Scrub both sides of the board with a soft-bristle toothbrush and 99% isopropyl alcohol.
2. Pay special attention around solder pads — flux residue is invisible but prevents adhesion.
3. Let dry completely (2-3 minutes). The board must be bone-dry before coating.
4. Do NOT use compressed air — it can force moisture under components.
### Step 2: Mask What You Don’t Want Coated
Use Kapton tape (high-temperature polyimide) or blue painter’s tape:
1. **USB port**: Plug in a sacrificial USB cable or stuff the port with tape.
2. **Barometer**: Cover the small silver can with tape. If you coat the barometer hole, altitude readings become erratic or frozen.
3. **Connectors**: Cover JST-SH, JST-GH, and other plug connectors. Coating inside a connector prevents electrical contact.
4. **Boot button**: Can be coated — silicone formula won’t prevent actuation.
5. **Heatsink on VTX**: Cover with tape. Coating is a thermal insulator.
### Step 3: Apply the Coating
The brush-in-cap applicator is precise enough for all FPV boards.
1. Shake the bottle vigorously for 30 seconds.
2. Open and dab excess off the brush on the bottle rim.
3. Apply in thin, even strokes. The coating should look wet but not pooled.
4. **Priority areas**: Solder pads, component leads, vias (small holes), and IC pins.
5. Apply to both sides of the board. Let the first side dry 10 minutes before flipping.
6. Use a toothpick dipped in coating for precision application around tiny SMD components.
7. Avoid heavy application on high-power components (MOSFETs, voltage regulators) — one thin coat, not multiple.
### Step 4: Verify Coverage
After drying 20-30 minutes:
1. Shine a UV flashlight (365nm wavelength) on the board.
2. The coating fluoresces bright blue-white under UV light.
3. Look for dark spots — these are uncoated areas. Touch up with a toothpick.
4. Check component leads and IC pins carefully — these are the most vulnerable points.
### Step 5: Cure and Test
1. Let the board cure for 24 hours at room temperature for full chemical resistance (light handling is fine after 30 minutes).
2. Before reinstalling, power the board on the bench with a smoke stopper.
3. Verify all functions: receiver bind, VTX output, motor spin in Betaflight.
4. The coating is invisible and shouldn’t affect any electrical function.
## Common Mistakes
| Mistake | Consequence | Prevention |
|———|————|————|
| Coating USB connector | No Configurator connection | Plug in cable or mask before coating |
| Coating barometer hole | Erratic altitude in OSD | Mask barometer entirely |
| Heavy coat on MOSFETs | Overheating during punchouts | One thin pass only on power components |
| Coating before cleaning | Coating peels off, taking protection with it | Always clean with IPA first |
| Touching wet coating | Fingerprint-shaped weak spot | Let dry 30 minutes before handling |
| Using acrylic on flexible boards | Cracks form at bend points | Use silicone formula for FPV |
## Advanced: Full Submersion Protection
For flying over water where full submersion is a real risk, conformal coating alone is not enough. Add:
1. **Dielectric grease in connectors**: Pack JST and balance lead connectors with dielectric grease — it displaces water but allows electrical contact.
2. **Corrosion-X on exposed metal**: Spray Corrosion-X HD on motor bearings and screws after every 5-10 wet flights.
3. **Waterproof the battery**: Wrap the LiPo balance lead connector in self-amalgamating tape. The balance leads are the most vulnerable point.
4. **Self-powered buzzer with conformal coating**: A VIFLY Finder with conformal coating on its own PCB survives ejection into water.
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