Slashdot Mirror

← Back to Stories (view on slashdot.org)

Coating a Motherboard In Thermal Resin?

Posted by timothy on from the oh-did-you-want-to-use-it-afterwards-too? dept.

Bat Country writes "I've had an idea in the back of my head for some time (and I'm surely not the only one) that it would be a worthwhile project to coat a motherboard in thermally conductive electrically insulating resin — complete with all of its various components — for the purpose of immersion, shock resistance, whatever. I'm curious to find out if anyone's undertaken a similar project or if it's known to be a shockingly bad idea (due to shrinkage during the curing process) already. Thoughts?" If you've done anything similar (even an experiment that failed), how did you go about it?

17 of 272 comments (clear)

  1. Conformal Coating by DeathOverlord3 · · Score: 5, Informative

    yeah, it's called conformal coating

    1. Re:Conformal Coating by Anonymous Coward · · Score: 5, Informative

      Conformal coat is generally a thin film applied over the board and components. I get the idea he is talking about something more like 'potting'.

    2. Re:Conformal Coating by Animats · · Score: 5, Informative

      Right, it's conformal coating. People do that all the time. I've used Fine-L-Kote on boards.

      Boards with connectors or jumpers have problems. If the CPU and RAM are soldered to the board (as they often are in industrial, consumer, mobile, and automotive devices), just mask off the connectors, jumpers, switches, battery contacts, etc. with masking tape and start spraying. Fine-L-Kote is transparent, but glows in UV, so you can use a UV lamp to check if you missed anything. There are much heavier coatings, ones that really encapsulate the board, and those are widely used for automotive, boat, and aircraft applications.

      PC-type motherboards aren't a good choice for this, because of all those connectors. Those are a weak point for corrosion anyway, so protecting the soldered-in components may not be all that useful. But if, say, you're putting something like a single-board PC on your boat, it's quite reasonable.

    3. Re:Conformal Coating by Raistlin77 · · Score: 5, Insightful

      Except that conformal coating would not be the greatest idea for use with immersion cooling. You would have to coat everything together, including memory modules, pci cards, power connectors, etc..., making them permanently attached and impossible to replace if/when necessary. Since it seems Bat Country's intention for this is so that a non-conductive coolant is not required for immersion, leading me to believe water or some other electrically conductive coolant is to be used, you add the risk that the coolant may enter through small holes and cracks that may develop at the places where the components are connected, immediately bringing everything to a halt.

      For immersion, the only sensible means is to use a non-conductive coolant and not worry about having to protect your hardware from the coolant it will be immersed in. It might be more expensive than just cooling with water, but it will likely be cheaper than having to replace ALL of your hardware that you just fried.

    4. Re:Conformal Coating by effigiate · · Score: 5, Informative
      We conformal coat our circuit boards at my current job and I can assure you that it is not what he's looking for.

      Conformal coating is typically a thin layer of silicone/urethane/acrylic used to keep moisture from getting at the parts on the board. It can not sustain immersion in liquid.

      He's looking for epoxy potting, which we also do occassionly. The trouble with epoxy potting is getting the heat out of the board. You need to leave the thermally conductive parts outside of the potting so that you can remove the heat. The epoxy itself isn't thermally conductive enough to get processor heat out, even on a processor with passive cooling.

      You can do this yourself if you have enough time and epoxy, though I'm not sure how much success you'll have. A failed attempt probably means a board that is no longer useable.

      The very best ones get cured in a vacuum so that all of the air bubbles are pulled out. There are many other types you can use that don't require a vacuum.

    5. Re:Conformal Coating by DeusExMach · · Score: 5, Interesting

      Same industry, and yeah, you're right. Also: with conformal coating you CAN NOT get that stuff on the contacts if you want the components to work correctly. And if you're not sealing up your connection points, you're still going to get a short if you use a non-electrically neutral fluid (like water) to cool your system. You CAN use CC if that really floats your boat, but considering the cost way outweighs the benefit on personal electronics equipment, I don't know why you'd want to...

    6. Re:Conformal Coating by Cor-cor · · Score: 5, Informative

      The trouble with epoxy potting is getting the heat out of the board. You need to leave the thermally conductive parts outside of the potting so that you can remove the heat. The epoxy itself isn't thermally conductive enough to get processor heat out, even on a processor with passive cooling.

      Coming from a materials engineering background, this was my first thought about the question. A material which is very thermally conducting while also electrically insulating sounds like a pretty tall order to me. The reason is that one of the primary methods of heat transfer is through transferring excited electrons.

      The two others are phonon transmission through the lattice and radiation. A lot of things which block electrons also block phonon movement (basically heat transfer through vibration) and I'm guessing radiant heat is not going to be sufficient. The one material I do know of which has high thermal conductivity and low electrical conductivity is diamond. It's kind of an oddball, though. I'd be interested to know if there are other, more common materials that would suit this application.

      Then there's also the CTE mismatch issue mentioned later in the thread. Whether you design the specs for the high-heat state while it's in use or the cool state when it's off, the other state is going to put a lot of thermal strain on your circuit board components. I'd imagine you could solve some of these problems, but I doubt you're going to be able to take care of them all.

  2. Not sure by linxdev · · Score: 5, Insightful

    The issue I see is with immersion. Sure you can coat the MB but what about the USB, VGA, etc connectors? Can you guarantee water will not leak in. Water has a way of getting inside any way it possibly can. Coating may be beneficial when you do not intend to put in case. Maybe to protect the MB as a bench system.

    1. Re:Not sure by Lurker2288 · · Score: 5, Funny

      ...or just go buy mineral oil and spare yourself some strange looks at the vet's office.

    2. Re:Not sure by Anonymous Coward · · Score: 5, Funny

      You: Hello Doctor! 5 gallons of your finest horse laxative please!

      Vet: Oh, got a sick horse then? Are you it needs a laxative?

      You: No, it's for me, eh I mean, it's for my computer!

      Vet: Ah, the computer! I see. Say no more. *wink wink*

    3. Re:Not sure by Anti_Climax · · Score: 5, Informative

      It is important to keep in mind that light mineral oil like that, while not as bad as other choices, will leech plasticizers out of insulators. The power supply wiring on my machine very quickly became stiff and brittle and it dissolved the soft rubber that was holding the fan assembly to the processor's heat sink. Not sure if it will have any long term effect on the plugs of the electrolytic caps on the board but I wouldn't be surprised.

      If you can afford to split the difference between mineral oil and florinert (perfluorocarbon), you might consider a low viscosity silicon oil. That should bu much nicer to natural rubber compounds and plastic insulators.

      --
      Even people that believe in pre-destiny look both ways before crossing the street.
  3. SUN used to do it. by UseTheSource · · Score: 5, Interesting

    When they offered the SUN Crypto Accelerator cards for offloading SSL computations, almost the entire PCI card was coated in resin to prevent tampering. I don't think they're still available for purchase from SUN but I'm sure we've still got a few in storage at work somewhere.

    --
    "Ein Volk, ein Reich, ein Führer." -Adolf Hitler
    "We are one Nation, we are one People." -The One 'leader'
    1. Re:SUN used to do it. by noidentity · · Score: 5, Interesting

      Someone guy unpotted a Votrax module and refurbished the damaged components so that it still worked afterwards and he could reverse-engineer it. It's interesting and has lots of pictures of before and after. The thing starts out as a a big block of epoxy and ends up a normal-looking circuit board.

  4. Look into Fluorinert by grimsnaggle · · Score: 5, Informative
    http://en.wikipedia.org/wiki/Fluorinert

    It is electrically insulating and is commonly used for cooling electronics (think Cray supercomputers).

    Part of the problem with conformal coat is that it makes it hard to service the electronics after it is cured. It also may or may not be uniformly distributed and thus may not pass muster in a tank of conductive liquid.

    There are conductive epoxies like Stycast, but they're not particularly good conductors. The only reason to do immersion cooling is for good thermal contact to all components. A thick epoxy layer between your components and your liquid will quickly destroy that advantage.

    Also, if you have connectors to the circuit board (like PCI connectors), then you cannot fill the pins. Last time I checked, most PCI connectors are just slots and have no bottom fill. Water will certainly get in under the coating through the slot.

  5. You should see the IBM version by sirwired · · Score: 5, Interesting

    The IBM crypto processors had the module containing the key wrapped in wires (which, if broken, or changed in length, would erase the key) and internal to the module were thermal and x-ray sensors to prevent sniffing the contents of the module that way.

    SirWired

  6. Potting blocks air cooling, of course by Animats · · Score: 5, Informative

    Electronics has to be designed for potting, at least if it dissipates any significant power. You have to provide a heat path (usually a metal heat sink) out of the potted block. This is done routinely for DC-DC brick power supplies. But it's not going to work on a PC motherboard.

  7. cockroaches by doug · · Score: 5, Interesting

    Years ago I worked at a company which had had problems with some telecom equipment in the field and no one could ever find any smoking gun. Random problems pointed to several different places on one particular board. One technician must have been working late, because apparently the CO filled with cockroaches once the sun went down. One of the theories was that bugs crawling across the board caused random short circuits. The customer was getting pissed, so management opted for a shotgun approach. Half a dozen shot-in-the-dark fixes were made, including adding an insulating coating. No one knows which one (or combination) of the fixes did the trick, but the random outages went away. That was engineering at its finest.