Waterproofing Drone Electronics – Conformal Coating Tutorial

You can prolong the life of electronics in an FPV drone with waterproofing, the most common method is Conformal coating. It helps prevent components from moisture and chemical damage when flying in extreme conditions.

Conformal coating is basically a thin film which conforms to the contours of a PCB and protects the components and solder joints on it.

You don’t actually have to fly in the rain or snow to Conformal coat your drone electronics. Conformal coating is a good practice to protect the quad from humidity and wet grass/leaves that can cause electrical short on exposed solder joints. It will even increase the chance of survival if you crash your quadcopter in the water.

The Types of Waterproofing

There are two popular solutions to waterproofing drone electronics: silicone and acrylic.

The main advantage with Acrylic is that it’s easily removable. You can burn through the coating simply with your solder iron.

However, for quadcopters or RC models in general, silicone is better as it can withstand higher temperature than acrylic. Many components in a quadcopter can get very hot, for example, the video transmitters, might melt through acrylic coating.

Buying Silicone Conformal Coating

I use MG Chemical Silicone Modified Conformal Coating, you can get it from:

• Amazon: https://amzn.to/3nkSWyb

These exist in two versions: the older version, and the newer “modified version”. They are basically the same stuff, but the “modified version” fluoresce under UV light (ultra-violet, aka black light). It makes it very handy to verify the full coverage of the coating, strongly recommended!

The board on the left is NOT Conformal coated, on the right is coated – you can tell by the glow under UV light

Its available on Amazon around US$20 for a 55ml bottle, which should last years for an ordinary pilot. It has a nail polish type brush attached to the cap for easy application.

Avoid the spray version because it will get everywhere you don’t want it to be. For example, your USB connector and bootloader button, and they might stop working. And it’s difficult to apply it evenly like you can with a brush.

Don’t forget to grab a cheap UV light torch too, these are cheap:

• Amazon: https://amzn.to/3vbOR2b

Finally, I also recommend getting some isopropyl alcohol (rubbing alcohol). It’s for cleaning your electronics before coating, and it’s useful for removing the coat as well.

• Amazon: https://amzn.to/3gBL6yW

Preparation

It’s best to apply Conformal coating on an existing quad, because getting the stuff on solder pads will make soldering much harder. If you want to do this on a new quad, you should first finish building the quad and fly it to make sure all components are working properly. You don’t want to mess with soldering again after applying.

If you are doing this on an existing quad, then you will want to remove all the tapes and heatshrinks that are covering any PCB. Make sure to clean the electronics to remove any dirt before applying Conformal coating. I use an old toothbrush and isopropyl alcohol for that.

Applying Silicone Conformal Coating on PCB

Warning: Do not sniff the stuff as it is carcinogen! It’s important to have good ventilation when applying it.

Brush it on like nail polish. If you are unfamiliar with the procedure, ask your wife/sister/mother :-p

Brush it on the whole board. There are components you want to avoid:

• flight controller: boot button, USB Port, Barometer
• FPV camera: image sensor
• VTX: channel button
• RX: bind button

It takes about half an hour to dry, though I personally would leave it to dry overnight just in case. Normally, one layer is enough, but if you don’t think you have applied enough or missed a few spots, feel free to repeat for another coat for better result.

At the end you should have a nice, even, shiny layer of plastic coating. Even better, use a blacklight (UV torch) to see if you missed anywhere.

How to Remove Silicone Coating?

Say if I covered the solder pads by mistake and I want to remove it, you can use Isopropyl alcohol. The conformal coating can also be burnt away with a hot soldering iron.

Some FC and ESC come with Conformal coating, such as this Kakute F7 AIO. But as you can see, it clearly was the spray stuff, the coat is uneven, and missed quite a few spots.

Just take a cotton bud, dip it in alcohol, and rub it on the PCB where you want the coating to be removed.

It should only take a few rubs to remove a thin layer of coating.

If you want to remove every bit of coating on a PCB, you will have to dip the whole board in alcohol and clean with a toothbrush. The coating will dissolve, and finally let it dry completely.

Pro Tips

To avoid damaging the connectors, you can try plugging in all the connectors before applying coating. This will ensure it doesn’t ruin the contact inside the header/connector.

As mentioned, Silicone coating can be burnt away by soldering iron. Therefore whenever you re-soldered something, you should apply Conformal coating again to the area.

You can try filling the small gaps, e.g. between capacitors and resistors, by blowing the coating with compressed air (not too close or you can make a mess).

Cap Getting Stuck

It’s important to clean the rim of the bottle with paper towel before putting the cap back on after use. Silicone coating works just like glue and the top can get stuck if you close it with some of the stuff left on the rim.

Here are some ideas what to do when you can’t get the top off:

• Slightly heat up the cap with a hair-dryer or heat gun (don’t melt the plastic though!)
• Smack the edge of the top with a butter knife or against the bench, all around the edge to break the hardened coating

What Happens If You Crashed Into Water?

• Take it out the water and remove battery ASAP
• Rinse it with distilled water to remove any mineral, brush with alcohol even better
• Leave it to dry completely, don’t use rice it’s not practical. Better to use a fan, leave it for at least a day