Best condensation protection options for servicable hobby projects? - Page 1
Forum section: electronics / general

author: evb149
author_rank: Regular Contributor
timestamp: April 10, 2022, 03:51:23 am
content: I'm interested in what the comparison is for condensation protection options forhobby domain (as in making from 1-100 units, not volume commercial production) projects?I'm aware there are tons of different available industrially suitable coatings, encapsulants, potting compounds, epoxies, waxes, polymers, etc. which I can easily find from 3M or MG or dupont or whoever but I'm also considering factors like:* Green & low environmental impact over whole life cycle (toxicity, biodegradability, micro plastic minimization, waste, ...)* Shelf life of supplies and materials needed (being hobby projects I'd want the supplies to last years after reclosure and occasional use ideally since use will be intermittent, prefer to work on stuff that's respiratory safe in preparation low VOC, etc.)* Lowish cost supplies / materials sufficient for a couple square meters of mixed PCBAs or so and ability to handle down to 2cm x 2cm level PCBAs up to larger 100x100mm or so assemblies for reasonable cost / waste / effort / time.* Being personal projects I'd prefer easy repairability so if there are coatings then things that are easily removed without lots of solvents / pollution and don't hugely interfere with future soldering after removal, also easy way to expose / mask connectors, terminal blocks, ethernet jacks, LEDs, etc. Don't really want to have to 3D print or otherwise make molds for where the stuff goes / not for every PCBA so something that admits easy manual or whatever masking / keep out would be nice.* Probably most applications won't use AC mains voltages but maybe POE or USB so should be fairly compatible with DC voltages at least up to 56VDC without any present conductivity causing problems. Also logic level MCU signals etc.IP6x enclosures are a possible part of the solution but since there will be one or more cables coming in and out there will be glands and such so I'm not confident of a hermetic seal being easy / permanent.Operating conditions: Cool, wet, humid with seasonal temperature swings from -10C at worst to +70C maybe on PCBA hot spots. 90%-100% RH levels in the area common as temperatures fluctuate from 25F-30F-50F range over a few hours day / night and cool unheated apparatus may be frequently cooler than air temperatures etc.

author: Styno
author_rank: Regular Contributor
timestamp: April 10, 2022, 08:28:33 pm
content: For the pcb conformal coating I use multiple layers of lacquer (Plastik from Contakt Chemie). The small can lasts for ages on a shelf but contains solvents so you need to take care of ventilation or just use it outside. For repair jobs you can solder through the coating. Before coating I mask off contacts with some tape (e.g. kapton).Inside hand soldered connectors (the cable side) inject some warmed-up vaseline to keep moisture away.And inside standard enclosures I use glands and/or chassis mount connectors and apply again some vaseline around the hole on the inside. Adding some silica gel packets increases the lifetime of the product.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 11, 2022, 01:46:07 pm
content: PLASTIK 70 requires multiple coatings, you'll run out of a 200ml spray can fairly fast when doing singles, the propellant at least.It is solder-through, so repair is not problem. You can also remove it with acetone. Not terribly dangerous substances so far.When repairing ventilation with a fume extraction box is recommended, but it was already with lead-free solders anyway.You can buy small nailpolish like bottles with acrylic coating when recoating repair work.The PLASTIK 70 Super has an UV tracer to inspect the coating quality. It is fairly tricky to getright.I found this document very helpful.http://www.conformalcoatinghelp.com/wp-content/uploads/2016/02/Solving-conformal-coating-problems-in-the-application-process.pdfI recommend cleaning off flux residue in ultrasonic bath with flux cleaner solvent before coating. Thisstuffworks great. Of course you have to rinse and dry the boards in an oven for a while afterwards.It won't prevent condensation, and that is still a risk. You can only prevent that with heating.

author: evb149
author_rank: Regular Contributor
timestamp: April 12, 2022, 02:30:02 am
content: Thank you very much, that is helpful information.One thing I don't entirely understand your implications of is the comment:"It won't prevent condensation, and that is still a risk. You can only prevent that with heating."Yes, that is true, if there is a sufficient temperature difference and humidity dew / condensation will form on a cooler surface.Sufficiently protective conformal coatings might provide enough direct contact moisture protection that the small amount that condenses inside a rainproof enclosure can either evaporate or run off and go out of the enclosure drain without harm to the PCBAs.So what I'm wondering is if you're meaning that this thin type of non-crosslinked (IIRC) acrylic coating is still too moisture permeable that it shouldn't be used as condensation protection against non-salty moisture such as could condense inside a weather shielding enclosure that does have an air vent / drain but is unheated?Yes I could use a thicker coat of a more impervious silicone, epoxy, urethane or whatever coating and it could be at that point totally humidity / condensation / water proof but I was hoping to solve the dew issue without heating and without using such an impervious coating that it also was going to much more significantly impair repair and be more difficult to apply etc. etc.So for 0-48VDC SELV circuits is this kind of acrylic coating not good enough for non-marine outdoor environments in unheated non hermetically sealed drained / vented enclosures from the standpoint of a non-commercial personal project that should be OK for a few years but doesn't have to be of industrial quality weather proofing if this dew is the only considered problem (ignoring possible fungus, mold, insect, ... issues also)?I suppose I can add heating but then I'd have to increase my power budget (I was assuming this could all run from say POE or similar few watts sources) and/or insulation coverage a fair amount.

author: Styno
author_rank: Regular Contributor
timestamp: April 12, 2022, 01:17:57 pm
content: Well, if you're using breathing enclosures instead of hermetically sealed ones I would ask if coating is necessary anyway, especially if you mount the board vertically?I have hundreds of non-hermetically sealed SELV devices in the field (24VC AC), mounted externally on a small cabinet without conformal coating that are working fine for many years in temperatures between -20C to +60C. As an anecdote I once serviced (firmware update) one where the cabinet also housed an ant colony so ants were everywhere. While the enclosure was open, an ant wandered in an touched the power section of the board and got fried with nice sparks and smoke while everything continued to work fine.The only problem I have with these uncoated devices is very close to the sea where salt spray sometimes gets in (but I was not aware that they were going to be used there, otherwise those would have been coated or even sealed/potted).

author: Jeroen3
author_rank: Super Contributor
timestamp: April 12, 2022, 02:08:02 pm
content: As far as I'm aware the acrylic coating only protects against humidity. As long as no droplets form on the surface of the board.More protective coatings do exist, polyurethane pour, dip or complete encapsulation. But you will lose on price, reparability, long shelf life, safe chemicals...Also component selection is tricky, not all connectors can do it, the wicking effect may make them unusable.Electrolube sells pouches of various hardness potting compounds, basically all urethanes two component and have typically 6 months to a year of shelf life.For salt mist, I would definetely recommend full encapsulation or a good enclosure. Near the sea nothing lasts long.If you board is inefficient enough self heating may be already enough to prevent condensation.

author: cdevidal
author_rank: Regular Contributor
timestamp: April 12, 2022, 05:59:30 pm
content: To add to what Styno said, I had read someplace that hermetically-sealed boxes never stay that way for long. With heat differential either hotter inside the enclosure or outside, it is inevitable that some air will leak past the seal. As moisture in the air creeps in, it gathers on the components. I was planning to mount my Raspberry Pi Zero vertically and include both screened weep holes in the bottom, and a louvered vent in the top. And yes, conformal coating as well.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 12, 2022, 06:12:06 pm
content: Note that most/all plastics are permeable to moisture, to varying degrees. If it's permeable at all, then after a long enough time, the humidity inside will equilibriate with the outside. You can seal an enclosure, but it won't quite be hermetic unless it's wholly inorganic: made of metal and glass/ceramic.This is important to food packaging as well, especially for oxygen that rapidly degrades product quality (especially fats and flavors). So we might gain some perspective looking at their solutions, as well.For electronics, we're almost entirely concerned about liquid water: water is an ionic solvent, causing electrolytic corrosion and metal migration under applied voltage. Pure water isn't actually very conductive, but that's still enough to be a problem over time; and it's such an aggressive solvent (in this respect) that it's almost impossible to prepare water so pure, for very long. Ambient moisture and oxygen aren't important, as we use metals that either don't corrode (gold), or have a protective oxide layer (even copper does, actually, as well as tin and iron, but most importantly for the much more reactive metals like zinc, aluminum, titanium, etc.).And it's not even so much the presence of water at all, as most of these materials are similarly resistant to immersion (in and of itself); it's mainly just the electrolysis, forming a conductive path between connections, that really screws things over.(Waterwith saltshowever, can corrode metals by itself. Salts like chloride especially, can attack the metal atomically (forming a soluble complex), while the conductive electrolyte allows action due to the small batteries formed by slight differences in the material's structure. Notably this is how steel rusts, the porous deposit also serving as a sponge for salt and moisture. Dry, clean steel can last centuries, but moisture is bad, and saltwater is devastating.)So, the fact that humidity varies over the year, means it could be okay with nothing more than a box, if the average outside humidity is low enough, and the expected lowest temperature is above the dewpoint at that average humidity level. This might work in a desert, for example. (Note that, a dewpoint below freezing won't necessarily do it; if warmed slowly, it can sublimate away, but otherwise can melt, and then you get liquid water, albeit only briefly.) I would guess that a typical ABS/PC enclosure, IP6x sealed with usual rubber o-rings and whatnot, would change at this kind of a rate, so, although this is a fairly limited use case, it could do already.In more temperate climates, dewpoint absolutely will be crossed from time to time, and so we need either a solution to prevent moisture ingress, or prevent water access.The former is afforded by better and better seals, or means of removing moisture. Seals can be improved by making them wider/thicker, adding metal layers to reduce the cross-section of permeable plastics, and increase the path length (slowing permeation even further). A metallized foil pouch does this well: it's a sandwich of foil and resin, the foil serving to block gasses, while the seal is a thin, wide layer of plastic: it's still permeable, but not over time scales we might worry about (years, decades?). This works even with astonishingly thin foils -- hence the metallized film used in food packaging.And, moisture can be removed by absorbing or condensing it; this might only last so long, but if your enclosure is adequately low-permeability, and the product lifetime just needs a few more years (or decades, as the case might be?), or service intervals -- this can work out just fine, say with the silica gel packet. (Silica gel can be recycled by heating it, so this works as a maintenance thing too.) Alternately, a condenser would have to have a pump and some kind of exhaust, but this might indeed be feasible say for a very large installation (an environmental control facility might be an example; it might not be hermetically sealed, but nonetheless has similar requirements!).Water access, can be prevented by simply filling the space first. If we clean down to bare plastic/metal surfaces, then gum them up with resin, we can still have use permeable materials (plastics/resins), but with nowhere for water to condense inside them, there's no problem. Obviously, conformal coating acts as something of a splash guard -- which might help sometimes, too! -- but it's actually this mechanism that's giving the real protection.(There's another part to it, which might not be obvious, but also doesn't come up very often, fortunately. If the material is low-energy enough that voids can form inside it, then those voids can grow and condense water. Or, the voids are already there (bubbles in the material), and they grow due to whatever mechanism makes gas diffusion into them favorable. Have you ever seen a sticker, poster, decal, etc. that's bubbling up? Likely such a mechanism is taking place!)So, for effective conformal coating, ideally: any exposed surfaces get coated, including the underside of components; any surfaces that can't be coated (say it's too viscous to flow under components), should be entirely insulated so that water can condense there and it doesn't matter (avoid untented vias under components?); and anything that could attract water and form trapped bubbles, needs to be gone. So, the board needs to be clean of salts, including the small amount of salts that may be present in some solder fluxes.And, not everything can be potted or coated, so inevitably you'll have to deal with, say, the pins underneath connectors (can't coat them because of contact surfaces), or vias underneath components, etc. Well, vias can be tented, so that helps. Connectors, the pins are usually bigger, so can survive for longer (decades+), or you can also consider other mitigation strategies (like say, cutting board slots between pins, allowing either injection/seepage of resin under the connector body, or at least increasing the creepage path length between pins).So yeah, all that said -- the usual strategy is conformal coating, to occupy the conductive surface, also mostly insulating it from contaminants, surface condensation, spray, etc. If a more thorough job is required, potting can be done: filling not just the component surfaces but the enclosure (in part or whole). Which has advantages for vibration and heat dissipation as well (well, heat dissipation to a point; you may need to consider design changes before potting, say because heatsinks can't convect when potted).And this alone (coating/potting) works for a lot of equipment that's not expected to be exposed to water (drip, immersion, spray..). Outdoors equipment that's merely splash-proof can handle this quite well.For conditions with more pervasive moisture -- misting, salt spray, high pressure jetting, or outright immersion -- a combination with an IP65+ enclosure is certainly a good idea. Even moreso for full potting, especially for immersion where the filling also communicates hydrostatic pressure, so, something can be good for quite deep dives without needing a hard shell enclosure.There's also liquid filling, usually oil; but this I think is when potting isn't used for whatever reason (perhaps to keep convection heat flow), and although it fills a space, it doesn't have any strength or energy with respect to droplets of water, so you could still end up with water rolling around inside, causing mysterious failures. On top of the mess, I think these are usually hermetically sealed, or closer to it, anyway, and really only used when the other advantages take priority (like super high voltages, oil is good insulation).But again, that said -- oil filled spaces, still prevent water from forming tracks/streams between points. The above example of petroleum jelly is kind of a mix of these: it's semisolid, so, easy to apply and stays in place; squidges out of the way of contacts (but, beware if the application sees a lot of vibration -- it might work its way into vibrated contacts, giving less reliable contact that otherwise, perhaps?); and fills space, preventing water from filling in and bridging between contacts.I would just caution that, plain old  petroleum jelly is low-melting; it will drain out even on just merely warm days. You really want something stabilized as a gel or grease. You probably don't want a (regular, lubricating) grease, exactly, either (might be more hygroscopic (water absorbing) or conductive than you'd expect?); but, there's likely something intended for filling connectors in this way -- if you need to be absolutely sure, while handling the widest of temperature swings.Tim

author: nctnico
author_rank: Super Contributor
timestamp: April 12, 2022, 10:30:04 pm
content: The biggest mistake to make is to think you can make an enclosure moisture tight. You can't. Always leave a hole open at the lowest point so the water that will (not can) condensate inside the casing can get out. Secondly use a conformal coating on the board. Plastik 70 sounds like a good solution to me; coincidentally I ordered a can of that stuff for an outdoor project recently.The dissipation of the circuits will heat the boards so condensation on the boards themselves likely isn't an issue.

author: Jeroen3
author_rank: Super Contributor
timestamp: April 13, 2022, 05:55:12 am
content: You can't make a enclosure completely closed because of air pressure, if you try you have to use pressure compensation elements.https://www.bopla.de/nl/behuizingstechniek/product/intertego/drukcompensatie-elementen/dae-m12-metall.htmlAn outdoor camera I took apart used rubber gaskets to get sealed for droplets, included a 10g silica gel pouch inside and an heating element to prevent lens fogging.

author: Styno
author_rank: Regular Contributor
timestamp: April 13, 2022, 07:04:46 am
content: Quote from: cdevidal on April 12, 2022, 05:59:30 pmPlus, your Rpi zero will produce enough heat to keep moisture from condensing, unlike low power battery devices.Quote from: Jeroen3 on April 13, 2022, 05:55:12 amThose pressure compensating elements with Goretex work well to keep water out but not moisture and when you are in an environment with permanent high humidity (e.g. below ground) you still end up with water inside.Theseare quite economical for plastic enclosures.Solutions are never universal and the best (mix of) solution has to be chosen based on the target environment.