I'm looking to protect a piece of electronics that will be put in the Freezer and Outdoors. I've looked into Conformal Coating to protect the pcbs from Condensation. Is this a good solution?
Your first line of defense will be conformal coating. There are various options here. Easiest to apply for DIY electronics would be in spray form (such as Electrolube HPA200H spray)
However, if you have an RF component and/or RF circuity in your PCB, you should be careful with conformal coating. As the frequency goes up and impedance requirements gets tighter, conformal coating becomes harder and harder to use, because it alters the RF circuit behavior. Also, obviously, you should not be coating certain sensors (pressure sensors, humidity sensors, etc).
Your next line of defense is your enclosure. Ideally, all your connectors should be IP67 or IP68 rated, and you should place your PCBs in an enclosure which is itself IP67/IP68 rated. This is usually achieved by using a gasket and designing the enclosure with a proper gasket opening.
If your device is going to be exposed to sunlight, you should make sure that any active IC in your system will not exceed its operating temperature. Metal enclosures exposed to sunlight will heat up considerably. You may want to think about a cooling solution, based on your power dissipation (enclosure with fins, etc).
And if it's a sealed container OP may want to consider a bag of silica gel desiccant. Depending on what else is in the box (or what the box is made of) they might want a vapour phase inhibitor.
Conformal coating is good for protecting against crud on the circuit board in general, so yeah, it'll help against condensation. To be super sure, put the board into an IP68 enclosure with a couple of sachets of 'Do Not Eat', and use IP68 rated cable glands for all cables going into and out of the enclosure to make sure no additional moisture gets in.
Believe it or not, I've had reasonable luck with JB Weld. Just make sure anything that might get warm has a little bit of heat sink poking up through the stuff.
Edit: Looks like you're aiming for an actual product release. There's no substitute for potting your circuit inside its enclosure. I'd look for a silicone based solution as you're aiming for large temperature swings.
If it is only a humidity sensor, then the potting compound outgassing shouldn't poison it. VOC sensors are much more sensitive. I would call the manufacturer of the sensors and ask technical support what they recommend to use.
EDIT: Silicone based compounds can poison many of your sensors! Use epoxy based potting compounds. Again, I would call the manufacturer of the sensor for guidance.
Block out ambient sensors and your antenna w/ foam to keep out the potting compound. You can also use a gore-vent on the ambient sensors to prolong lifespan. I would also suggest spending some time choosing your battery chemistry. It sounds like you will be freezing and thawing which can reduce the lifespan of lithium cells.
A humidity sensor, coated with conformal coating, will simply not function properly.
If you need conformal coating on your PCB, most sensor manufacturers will recommend you to cover the top of the sensor with some material (for example, Kapton tape), apply conformal coating to the PCB, and then remove the tape.
Everything in the freezer with aromatics will add to the flavors of other things that are not completely sealed. Last thing you want is a frozen pizza to taste like silicone glue.
I've had good results with simple plastic cases, as long as a few rules are followed:
- The case must have a gasket on its cover
- Any openings must be on the bottom of the case (including antennae!)
- Cable glands or waterproof connectors must be used on all openings
- All cables must have a little slack, so they hang below the case and come straight up
- Put a couple of dissecant bags inside the box
I've been using this for various DIY outdoor projects for years, like putting mikrotik routerboards, raspberry pis, arduinos, etc. outdoors.
Water will accumulate in all openings not on the bottom of the case, and air pressure changes will cause the box to "suck" this water in, no matter how tightly sealed that cable gland is. That's why the openings should all be at the bottom.
Conformal coating isn't necessarily guaranteed to be rugged against abrasion and handling, so you may still need an enclosure. Also, as others have mentioned, not all components can survive the process. But it has the advantage of being something that a PCB house already knows how to do.
Along the lines of "do things that don't scale," household products such as Household Goop (aka Shoe Goo), silicone sealant, etc., work pretty well.
If you have one or two components that can't be coated, you can leave them off the board and solder them by hand after coating.
However, if you have an RF component and/or RF circuity in your PCB, you should be careful with conformal coating. As the frequency goes up and impedance requirements gets tighter, conformal coating becomes harder and harder to use, because it alters the RF circuit behavior. Also, obviously, you should not be coating certain sensors (pressure sensors, humidity sensors, etc).
Your next line of defense is your enclosure. Ideally, all your connectors should be IP67 or IP68 rated, and you should place your PCBs in an enclosure which is itself IP67/IP68 rated. This is usually achieved by using a gasket and designing the enclosure with a proper gasket opening.
If your device is going to be exposed to sunlight, you should make sure that any active IC in your system will not exceed its operating temperature. Metal enclosures exposed to sunlight will heat up considerably. You may want to think about a cooling solution, based on your power dissipation (enclosure with fins, etc).