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Coating a Motherboard In Thermal Resin? 272

Posted by timothy
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?
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Coating a Motherboard In Thermal Resin?

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  • Conformal Coating (Score:5, Informative)

    by DeathOverlord3 (645635) on Wednesday September 03, 2008 @04:59PM (#24865049)
    yeah, it's called conformal coating
    • Re:Conformal Coating (Score:5, Informative)

      by Anonymous Coward on Wednesday September 03, 2008 @05:16PM (#24865267)

      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'.

    • Re:Conformal Coating (Score:5, Informative)

      by Ethanol-fueled (1125189) * on Wednesday September 03, 2008 @05:17PM (#24865273) Homepage Journal
      Conformal coating [wikipedia.org] is protection against a lot of things, and submersion is not one of them.

      Those of us who work in the electronics industry know that doing CC in-house is a bitch and inspecting an outsourced job is an even bigger bitch, especially when you're dealing with military parts.
      • Re:Conformal Coating (Score:5, Interesting)

        by DeusExMach (1319255) on Wednesday September 03, 2008 @05:33PM (#24865499)
        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...
      • by whoever57 (658626)

        Conformal coating is protection against a lot of things,

        I think most conformal coatings are not good at heat transfer, which might make coating a PC motherboard problematic.

    • Re:Conformal Coating (Score:5, Informative)

      by Animats (122034) on Wednesday September 03, 2008 @05:22PM (#24865353) Homepage

      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.

    • by Raistlin77 (754120) on Wednesday September 03, 2008 @05:23PM (#24865365)
      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.
    • Re:Conformal Coating (Score:5, Informative)

      by effigiate (1057610) on Wednesday September 03, 2008 @05:27PM (#24865419)
      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.

      • Re:Conformal Coating (Score:5, Informative)

        by Zadaz (950521) on Wednesday September 03, 2008 @05:58PM (#24865827)

        I wonder where he could readily get a vacuum chamber big enough to pull the air out. Getting the air bubbles out is going to be pretty vital to not baking the mobo, especially the cavities under components.

        The most readily available vacuum pumps are smaller than a full motherboard + components, used either for basic science, paint or latex molding. Maybe call up Tap Plastics [tapplastics.com] or your local university and see if they have a big one you can borrow. Because you're going to need a real one. A vacuum cleaner on a Tupperware box or a concrete vibrator isn't going to get what you need.

        But my main worry is about thermal expansion. When motherboards get hot they don't expand evenly. Locking everything in resin, not mater how thermally stable, will put a lot more physical stress on the components. And you won't be able to do a damn thing about it except chuck it in the bin and start over again. Though this would probably be lessened with a smaller form factor and lower energy components.

        • by veganboyjosh (896761) on Wednesday September 03, 2008 @06:55PM (#24866451)
          "a concrete vibrator isn't going to get what you need."

          best slashdot quote ever.
        • Re:Conformal Coating (Score:4, Informative)

          by Limecron (206141) on Wednesday September 03, 2008 @09:09PM (#24867911)

          The amount of vacuum needed for most of these kinds of epoxies is pretty minimal (usually a few inches of water).

          Not that this is the recommended method, but we were able to successfully cure epoxy of this nature in a make-shift vacuum chamber. (A plywood box sealed with silicone and a shop-vac.) We even put a clear acrylic window on the front. Of course a real vacuum pump could probably implode our setup, but it was good enough for the epoxy and significantly cheaper than the alternatives.

        • Re: (Score:3, Informative)

          by Verdatum (1257828)
          There are alternatives to vacuum degassing for removing airbubbles/pinhole flaws. What is often done is to use pressure instead of vacuum, in a device called a "pressure pot". instead of trying to pull a vacuum on an object the size of a desktop, it is MUCH cheaper to put it in a pressurized chamber. This has the effect of bringing the air bubbles into solution so when the resin has cured the airbubbles are shrunk to a nonexistent size. Usually in molding and casting, you just vacuum degas the mixed res
      • Re:Conformal Coating (Score:5, Informative)

        by Cor-cor (1330671) on Wednesday September 03, 2008 @07:26PM (#24866823)

        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.

        • Re:Conformal Coating (Score:5, Informative)

          by Artraze (600366) on Thursday September 04, 2008 @02:32AM (#24870327)
          I'm surprised someone with a materials engineering background hasn't heard of it, but Beryllium Oxide [wikipedia.org] would be the other big thermal conductor/electrical insulator. It's a little more popular than diamond since you can actually sinter it into large objects. However, like most beryllium based things it is rather pricey.

          I think the OP's best bet is to coat the mobo with a CVD diamond film and hope that the liquid cooling keeps the temperature down low enough the film doesn't crack.
          • Re: (Score:3, Informative)

            by Mashiki (184564)

            Chances are they have, and avoid it for a good reason. The problem is even small traces of it can cause Berylliosis [wikipedia.org] which is really a bad thing to get and can end up with a slow painful death in the end.

  • Cray blood (Score:5, Insightful)

    by Ritz_Just_Ritz (883997) on Wednesday September 03, 2008 @05:02PM (#24865083)

    Probably a lot easier to source yourself a few liters of Cray blood (or some similar non-conductive coolant) to submerge the board in instead.

    Cheers,

    • Re: (Score:3, Interesting)

      by COMON$ (806135) *
      Ya I had a friend do this with a web server, for kicks of course, the sucker ran fantastic. Was some kind of nonconductive fluid he got on the cheap. Only trick was he had to separate the CD-ROM and hard drive but other than that it ran for a long time, fans and all.
    • You're probably thinking of fluorent, which is an inert (doesn't conduct electricity) liquid used for a variety of tasks. That'd be a good idea except:
      1) That stuff is usually really expensive, which wouldn't be so bad except...
      2) The stuff evaporates really fast, and
      3) If you get any dirt/etc in it then you will need to filter it or completely replace it.
      • Re:Cray blood (Score:4, Insightful)

        by gardyloo (512791) on Wednesday September 03, 2008 @05:22PM (#24865337)

        2) The stuff evaporates really fast

        Some does, some doesn't. I've worked with the HFE-7500 stuff, which DOES evaporate really fast (much, much faster than water) -- as a result, you can also smell it a little bit, which can be annoying after a while. It also has a pretty low viscosity, which means that it tends to leak through any seals.
              On the other hand, the FC-73 stuff (which I've also worked with, though not as much) doesn't evaporate NEARLY so fast as water, and is more viscous, so it doesn't leak very quickly. It also doesn't attack silicone seals nearly so much as the HFE. For home hobby stuff, I'd recommend FC-73 over HFE.

        • Re:Cray blood (Score:4, Informative)

          by Prune (557140) on Wednesday September 03, 2008 @05:37PM (#24865537)
          FC-77 is intended for computer use, not FC-73 (my friend's father works at 3M)
          • Re:Cray blood (Score:4, Informative)

            by networkBoy (774728) on Wednesday September 03, 2008 @08:04PM (#24867299) Homepage Journal

            FC77 and 73 also are longterm environmental hazards and attack the ozone layer. Which is why the HFE family was invented. Like most things of this ilk, the older stuff is better for the task (R12 Vs 134a anyone?)

            I use FC77 and HFE7100 as thermal transfer fluids for ultra-cold applications (-60C and lower) in semiconductor testing. Wicked cool stuff.

            IF you do manage to buy/acquire enough HFE7x00 remember it eats plasticizers for lunch (gloves are almost useless, better just to be careful).
            As such I strongly recommend glass enclosures with as few seams as possible (bend two horseshoes of glass fit them together very tightly then seal with a torch). Obviously a hole for the MB to slide in would be helpful. A tight fitting lid will help to reduce evaporation.

            In our professionally built system, a Temptronic Atlas series chiller and thermochuck (http://www.temptronic.com/Products/ThermoChuck_Overview.htm [temptronic.com]) we lost about a pint a month of HFE7100 under heavy load.
            -nB

    • and if you're cheap, people will actually pay you to take PCBs [wikipedia.org] off their hands.
    • Re:Cray blood (Score:4, Informative)

      by v1 (525388) on Wednesday September 03, 2008 @06:44PM (#24866333) Homepage Journal

      didn't someone put up an article awhile ago here on Fluorinert [wikipedia.org]?

  • Not sure (Score:5, Insightful)

    by linxdev (1020223) on Wednesday September 03, 2008 @05:02PM (#24865089)
    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.
    • Re:Not sure (Score:5, Informative)

      by MozeeToby (1163751) on Wednesday September 03, 2008 @05:07PM (#24865143)

      That's why you don't use water, you use something non-conductive. Mineral oil is a relatively cheap and widely available option (just go to your vet and ask for a few gallons of horse laxative) if you don't want to spend the money on commercial grade cooling fluid.

      • Re:Not sure (Score:5, Funny)

        by Lurker2288 (995635) on Wednesday September 03, 2008 @05:11PM (#24865205)
        ...or just go buy mineral oil and spare yourself some strange looks at the vet's office.
        • Re:Not sure (Score:5, Funny)

          by Anonymous Coward on Wednesday September 03, 2008 @05:19PM (#24865305)

          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*

          • Re:Not sure (Score:5, Funny)

            by Linker3000 (626634) on Wednesday September 03, 2008 @06:05PM (#24865905) Journal

            Vet related too (I do the IT for a group of clinics) but not that relevant:

            Customer: "Are gherkin (pickle) slices bad for dogs?"

            Receptionist: "I'm not sure - I'll ask the vet...well, the vet says in small quantities they should not be harmful...has your dog swallowed one?"

            Customer: "Oh, no, we just wondered whether we should remove it when we buy our dog a burger at the drive-thru"

      • by FauxReal (653820)
        I've seen mineral oil used. In the summer of 94' I went to The Icon Byte Bar and Grill in the SOMA area of SF and they TVs and a computer submerged in mineral oil with the covers taken off sitting in fish tanks. It looked cool and they seemed to work just fine.

        P.S. It was also the first internet cafe I went to, they had a "blazing fast" 14.4 SLIP line and I thought this silly black on grey World Wide Web was a waste of time compared to Gopher.
      • Re:Not sure (Score:5, Informative)

        by Anti_Climax (447121) on Wednesday September 03, 2008 @05:34PM (#24865503)

        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.

        • Re:Not sure (Score:5, Informative)

          by Anti_Climax (447121) on Wednesday September 03, 2008 @07:10PM (#24866623)

          I thought about this a little more and I think I should put this into perspective a little bit.

          The first machine I submerged was done in a plastic tub and covered with 5 gallons of Tractor Oil (no, really) that I bought at the wal-mart for $20. It smelled, it was fairly viscous and it definitely leeched plasticizers and crawled up the interior of cables. I ended up with a small puddle of oil under my optical mouse. Wireless worked okay through it though. I tried submerging hard drives after covering the breather holes - I figured if I was keeping them in a fairly narrow temp range they shouldn't need to equalize. Unfortunately none were sealed sufficiently and all eventually died, though one did make it a month before it flooded.

          The next machine was a recreation of the Puget Systems [pugetsystems.com] submerged machine. I went with light mineral oil from the local feed and tack store but was seriously considering silicon oil in it's place. Light mineral oil was going for about $17 a gallon, was less viscous than the first oil I used, didn't stink and hasn't effected the components as quickly. I can't find it now but I recall silicon oil being somewhere around $100 a gallon. If I had the money to spare I would have gone that route. Looking online the best price I can find for appropriate Fluorinert is around $1,000 a gallon.

          So for 5 gallons of submerged cooling you're looking at $20-$5,000. When you consider the effect it'll have on components, it's probably worth it to use the $500 fill of silicon oil over the $100 fill of mineral oil.

    • Re:Not sure (Score:4, Informative)

      by Anti_Climax (447121) on Wednesday September 03, 2008 @05:29PM (#24865439)

      From my experience with submersion cooling in mineral oil, if your connectors are submerged they will wick oil up the interior through capillary action. If you build a system similar to that made by Puget Systems [pugetsystems.com] it probably won't be a problem, provided you leave some head space at the top of the case. When I built a system similar to theirs I made a short socket extension for the power cord so it didn't have to go under the fluid. everything else was able to stay above the surface of the oil.

      If you submerge your video cards and intend to use the fans as impellers, make sure they can start turning against the resistance of the fluid. All my fans worked when submerged except the video cards.

  • A Bad Thing (tm) (Score:5, Insightful)

    by oni (41625) on Wednesday September 03, 2008 @05:03PM (#24865103) Homepage

    Wouldn't that conduct the heat from the CPU over to the other components?

  • Technical Term (Score:5, Informative)

    by aero6dof (415422) <aero6dof@yahoo.com> on Wednesday September 03, 2008 @05:04PM (#24865113) Homepage

    The technical term you're looking for is Potting [wikipedia.org].

  • SUN used to do it. (Score:5, Interesting)

    by UseTheSource (66510) on Wednesday September 03, 2008 @05:05PM (#24865121) Homepage Journal

    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.

    • by Asmor (775910) on Wednesday September 03, 2008 @05:21PM (#24865329) Homepage

      I saw a documentary on card cheating devices, and one of the early card-counting computers was dipped in something to prevent people from backwards engineering it. It included a failsafe, as well, a thin filament wire designed to be pulled off if the stuff protecting the computer was scraped away, and without that wire in place it would malfunction.

    • by sirwired (27582) on Wednesday September 03, 2008 @05:23PM (#24865355)

      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

    • by noidentity (188756) on Wednesday September 03, 2008 @05:24PM (#24865373)
      Someone guy unpotted a Votrax module and refurbished the damaged components [nyud.net] 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.
    • Re: (Score:2, Interesting)

      by Puzzleer (309198)

      I used to work for a company that makes cards like this (high security tamper resistant encryption cards).

      While it is true that you can encase a card in resin (as a previous poster mentioned, it's called potting), you have to take into consideration the thermal profile of the components on the board. You can't just do it to any old card, and in our case it actually affected which embedded processor we went with.

  • by Anonymous Coward on Wednesday September 03, 2008 @05:07PM (#24865151)

    Tomshardware had a computer in a fishtank full of mineral oil a bit ago. Works well but what a mess.

    http://www.pugetsystems.com/submerged.php

  • by bigtallmofo (695287) * on Wednesday September 03, 2008 @05:13PM (#24865225)
    This sounds almost exactly like something I did back in nineteen dickety two. We had to say "dickety" because the Kaiser had stolen our word for "twenty." I chased that rascal to get it back, but gave up after dickety-six miles.
  • Do a google search on it, or check out the funky aquarium at:

    http://www.pugetsystems.com/submerged.php

  • by lottameez (816335) on Wednesday September 03, 2008 @05:18PM (#24865293)
    I'd imagine you'd want to sort out your future memory or disk capacity needs before dipping.
  • Look into Fluorinert (Score:5, Informative)

    by grimsnaggle (1320777) on Wednesday September 03, 2008 @05:19PM (#24865313)
    http://en.wikipedia.org/wiki/Fluorinert [wikipedia.org]

    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.

  • iPod in resin (Score:3, Interesting)

    by RomulusNR (29439) on Wednesday September 03, 2008 @05:22PM (#24865343) Homepage
  • by Anonymous Coward on Wednesday September 03, 2008 @05:27PM (#24865409)

    My degree is Materials engineering, and I remember an undergrad design course where one of the groups was working with Rockwell Collins on this exact project.

    They already commonly coat their boards in stuff for the very reasons you've listed. All kinds of circuit boards for radios, radar, anything electronic inside a jet fighter. The project was to find less-toxic alternatives that could match performance and cost.

  • by vtcodger (957785) on Wednesday September 03, 2008 @05:27PM (#24865413)

    People have been running PC electronics submerged in mineral oil for decades.

    Advantages:
    1. Not too hard to do
    2. If push comes to shove, you can can probably burn the PC in your fireplace or other suitable container to keep warm. Or just because you are pissed at it.

    Problems:

    1. It's messy.
    2. The oil tends to creep up any wires to the outside world (capillary action?) and eventually show up at the other end.
    3. I'm not sure if non-gas tight connectors are used in modern PCs, but if they are, they may be a problem.
    4. It's messy.

    Did I mention that it is messy?

  • Power supplies for the C-64 were 'potted' as were many power supplies of the day. Can't see why it would not work.

    Gregor

    • Re:Old news (Score:4, Informative)

      by Lisandro (799651) on Wednesday September 03, 2008 @05:41PM (#24865579)

      Power supplies for the C-64 were 'potted' as were many power supplies of the day.

      The original C64 psu was renowed for its poor reilability, which was caused for the poor heat dissipation due to that very epoxy potting. They used big TO-3 transistors which got quite warm during normal operation.

  • by Lisandro (799651) on Wednesday September 03, 2008 @05:32PM (#24865483)

    ...and it's a well known process - i've seen devices from the '80s with epoxy encased parts. Keep in mind though potting does practially nothing for heat dissipation. Even if you managed to get your hands on some thermally conductive resin, in PCs the principal way of heat dissipation is forced convection (coolers, that is), which allows to use very small dissipators for the given power. I don't think you could find a substance that allows good thermal transfer without a large surface area - meaning, a lot of resin.

    If you're planning to pot and then submerge in Fluorinert or a similar compound, the resin coating, no matter how good transfering heat, will only raise the working temperature of the parts.

  • cockroaches (Score:5, Interesting)

    by doug (926) on Wednesday September 03, 2008 @05:32PM (#24865485)

    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.

    • Re: (Score:3, Informative)

      by flyingfsck (986395)
      A bag of moth balls in the equipment would have been cheaper to guard against roach piss.
  • http://www.tomshardware.com/reviews/strip-fans,1203.html [tomshardware.com]

    This is pretty much your guide to getting it done.

  • http://www.plastidip.com/ [plastidip.com]

    I've used this for years to coat electronics for exposure to the elements. Boards up to 6x6".

    It can be cut away and removed if necessary and then reapplied.

    Not sure about the heat tranfer characteristics, tho.

    Your mileage may vary, etc.

  • Like most thermal compounds it may conduct heat better than most non-metals but unless it's a brand new material everything on the market currently is going to be a far worse conducter of heat than air. Encasing thermal components in a material with worse performance than air is going to make them get much hotter.

  • by Mike Rice (626857) on Wednesday September 03, 2008 @05:54PM (#24865739)

    In my former life I worked as an industrial electronics technician. My job was, in a nutshell, to modernize a manufacturing plant from its 1950s style, analog (pneumatic) technology, to digital electronic distributed control systems.

    The environments these devices need to work in are quite harsh, with extreme temperatures and often corrosive atmospheres. The pneumatic control systems were quite robust in those environments... electronic devices need a lot of beefing up to survive these conditions.

    One aspect of this was to treat all circuit boards with a conformal resin coating. The trick is to make sure the thermal coefficient of expansion of the resin, matches the expansion of the circuit board material. I am not a chemist, but I do know such coatings are available.

    Another consideration which has been mentioned is how to treat connectors. The usual method is to apply a rubber like sealing compound after a connector is fitted and tested.

    For less extreme environments, a much less expensive, but quite effective alternative, is to apply a cheap acrylic coating, using readily available sprays such as Krylon 1301. The procedure is...

    Assemble the device (uncoated) and test thoroughly.
    Disassemble the device.
    Apply tape and / or petroleum jelly to connectors and contacts, to prevent damage from the spray.
    Apply the spray to each component.
    Assemble and re-test.

    Hope this lights a bulb for you.

    • by Lisandro (799651)

      For less extreme environments, a much less expensive, but quite effective alternative, is to apply a cheap acrylic coating, using readily available sprays such as Krylon 1301.

      I've done this several times to protect printed circuit boards from moisture with great results. I don't know if i'd expect much more from it though.

  • by gwait (179005) on Wednesday September 03, 2008 @05:57PM (#24865809)

    The characteristic impedance of the surface traces will change.

    The surface traces were designed with the assumption that there is air above the traces.

    Loading up a bunch of gunk will change the impedance, and could screw up your signal integrity. PCI Express or Gig Ethernet could fail for example.

    Google stripline vs microstrip and signal integrity of high speed differential traces.

    I'd be curious how the conformal coating people manage this too, I'd assume the copper trace widths would have to be designed knowing the board was going to be conformal coated.

  • by mapsjanhere (1130359) on Wednesday September 03, 2008 @06:00PM (#24865843)
    a diamond coating. The only material that fulfills your demand for high thermal conductivity and good electrical insulation at the same time. The only problem is that the one good method to apply a diamond coating is chemical vapor deposition, and that is mostly line of sight. So you'll have a real tough time coating around those 1000 pins under your cpu.
  • Potting boards is common in military applications. But it makes 'em harder than heck to repair.

    If it's just a coating, you can sometimes scrape it off enough to put in a new component, and then pot over it. The potting residue makes it difficult to solder and trying to remove it puts the traces and pads at risk. Nasty, but can be done.

    But if it's completely potted, like a brick in which you can dimly see components, when it fails you just throw it away. No point in trying to fix it.

    In your case,

  • Yes it works (Score:5, Interesting)

    by John Sokol (109591) on Wednesday September 03, 2008 @06:23PM (#24866079) Homepage Journal

    When I was doing a start up called Nisvara 2002 (now dead) we were building Silent computers and server rooms that didn't require air conditioning. Something like 50% power savings!

    I was able to Pot or coat, power supply's, hard drive and motherboards in various materials.

    The key is thermal conductivity. Yes some one here mention diamond, but that is expensive in unrealistic although diamond dust power was available from GE at a much lower cost then I expected. Carbon Fiber and other carbons are great except they are electrically conductive so they are ruled out (except diamond that is).

    What worked great was epoxy with silicon carbide which is dirt cheap and sold as sand basting powder. Also boron nitride works great too, but this is a messy white powder and expensive.

    Also a thin layer of silicon carbide or boron nitride epoxy could be applied then a layer of cheaper carbon black or chopped carbon fiber mixed epoxy could be use for making a thicker layer if needed. Non-metallic heat sinks work great using these materials.

    We were able to take a Antec 450 Watt Power supply and run it at full load with no fans or heat sink fins as just one big white sold block of epoxy with boron nitride.

  • by itomato (91092) on Wednesday September 03, 2008 @06:33PM (#24866201)

    I typically remove the plastic casing from all my little dongley peripherals and coat them with a clear, two-part, quick-setting epoxy. I've been at it for years now, and the only problems I have had have been cosmetic.

    The trickiest part of the process is masking the pins, sockets, and other areas where you do *not* want to apply a clear, two-part, quick-setting epoxy.
    I'm sure Vaseline or some similar masking agent can be applied and removed cleanly, given the right environment.

    I usually do it on my kitchen table with a plastic knife. YMMV.

  • by Plasmic (26063) on Wednesday September 03, 2008 @06:56PM (#24866465)

    It's a few hundred dollars, at most, to test this theory. Go try it. I promise the results will be more useful and interesting than anything you'll get back from Slashdot (e.g. theories on mineral oil suspension, stories on potting mainframes in the 70s, etc.).

  • What you do is.. (Score:3, Informative)

    by StikyPad (445176) on Wednesday September 03, 2008 @07:35PM (#24866949) Homepage

    use a non-conductive liquid for cooling, such as oil. This has been done before, and even a cursory google [google.com] turns up lots of interesting results.

    Coating is a waste of time, and it's very difficult to get a good coating over empty expansion slots, USB slots, etc., let alone those with cards in them.

  • Not just immersion (Score:3, Insightful)

    by Bat Country (829565) on Wednesday September 03, 2008 @07:45PM (#24867079) Homepage

    I see a lot of comments about the immersion side of things, for which I know it would probably be a lot cheaper to just pick up some nonconductive coolant.

    How about other reasons for doing it - specifically shock resistance and hardening against slippage caused by vibration?

    Additional value could be found in potting the board in marine/cave/jungle environments where the hardware might be exposed to caustic and humid air.

    Also, presumably resin coating might get around problems with hungry insects [slashdot.org]. I'd imagine a really well designed medium-tight case suspending the components in a nonconductive coolant might work, but it seems like it would be a more bulky solution.

    However, I'd be interested to hear of better solutions than coating the whole shebang in toxic goop.

  • Been done (Score:3, Informative)

    by tietokone-olmi (26595) on Wednesday September 03, 2008 @08:27PM (#24867503)

    Immersion in mineral oil. Need to remove all fans and other spinny things, and you won't be upgrading anything afterward. But it does work, and permits totally quiet computing.

    Long as you don't mind the, you know, tank.

  • by Chris Snook (872473) on Wednesday September 03, 2008 @08:42PM (#24867677)

    The contest was to build the most weight-efficient bridge, using only balsa wood sticks and wood glue. Efficiency was judged by (failure load)/(bridge mass). The highest load, by far, was born by a bridge that had been totally coated with wood glue. Unfortunately for them, this coating raised the bridge mass by nearly 50%, so their bridge was still less efficient than my team's, which used a more conventional truss design, with a coating of glue around the joints. Nearly every bridge in the class failed first at a joint, so reinforcing the beams themselves was a waste.

    The point is that applying the same reinforcement everywhere tends to be a serious waste of resources that would be better applied to the most critical areas. This is why my shiny new motherboard has a few components embedded in epoxy, surrounded by metal heatsink-like rings. Unlike other motherboards I've used, this one has no large components sticking up from the PCB, so I'm guessing that they singled out those bulky components, shrunk them down, and then added the epoxy and rings to allow them to operate safely at a smaller size.

    • Hm. I remember doing that exercise as well. --I think the scoring formula needed to be adjusted, because my solid bundle of sticks soaked in glue creating basically a polymer enhanced log could take all the weight the testing apparatus was able to provide, plus that of the teacher and two students standing in a rope looped over my 'bridge'. It never broke, thus my ham-fisted design won the contest despite the ridiculous number of pieces used to make it.

      It was also generally agreed that I was an ass and t

      • Re: (Score:3, Interesting)

        by Chris Snook (872473)

        I think someone pulled the same stunt on our professor in the past, which is why we were given 6 36" sticks to build a 20" x 2" span. That enforced a somewhat more conventional approach. It's rather difficult to drive a car across a rope.

        • Re: (Score:3, Interesting)

          by Fantastic Lad (198284)

          I think someone pulled the same stunt on our professor in the past, which is why we were given 6 36" sticks to build a 20" x 2" span. That enforced a somewhat more conventional approach. It's rather difficult to drive a car across a rope.

          Suspension bridges are essentially made of rope. --It would take a lot of work, (and probably earn one of those dreaded high marks I routinely tried to avoid), but my immediate thought given the scenario you describe would be to game the system by building a suspension bri

          • Re: (Score:3, Interesting)

            by Chris Snook (872473)

            In our case, it was considered an engineering problem, so there were certain inviolable constraints, but as long as we satisfied those we were free to do whatever we pleased. I'm sure plenty of composite construction techniques could have improved our results, but given the time constraints and the fact that any wood used in testing came out of the total available for construction (quite reasonable real-world engineering constraints) we were forced to innovate conservatively. We hadn't been taught anythin

  • Resin overview (Score:3, Insightful)

    by Verdatum (1257828) on Wednesday September 03, 2008 @09:54PM (#24868289)
    Molding & Casting (through replica propwork and creature prosthetic effecs) is a hobby of mine, so here's what I know about resins. Maybe it will help

    Epoxy resin is good at holding up to high temperatures. It comes in a variety of cure times and is available in small quantities at hardware stores and large quantities at marine supply stores. The fumes are smelly and unsafe, but they at least dissapate soon after curing.

    Polyester resin (aka fiberglass resin) is cheaper than epoxy. It is generally weaker. It's fumes are quite nasty and hang around for days, so it's really an outside thing. It's probably no good for this task as uncured resin ravenously dissolves polystyrene (I don't know if PCs ahve polystyrene, but I wouldn't risk it).

    Polyurethane resins come in the widest variety of formulations. It varies from hard as rock to a very flexible rubber, and any mixture inbetween. It is very low odor, but the fumes are still nothing to mess around with. Some formulations use metal fillers like aluminum (reduces shrinkage/thermal warping), so look out for that. It will certainly shrink a bit, so thicker coatings should be done with more flexible varieties. Shrinkage can be reduced by adding loose chopped fiberglass, though this does raise thickness.

    Silicone rubber, particularly Platinum cure silicone has low to zero shrinkage. It's also by far the least toxic. It's also the most expensive by volume. again wide range of cure times, thickness/thixotropy can be adjusted by adding fumed silica (just don't breath the stuff). It is thermally resistive, so you will want to keep coatings thin, and suppliment it with submersion. Still, if I was tinkering around with such hardhacks, I suspect I'd go this route. Silicone is a great electrical resistor and has fantastic waterproofing abilities

    for thin coats of any of these materials, you'll want to brush or spray the liquid to minimize airbubbles. All types resins have sprayable formulations, either by using specialty spray devices sold by the resin manufacturer, or by thinning the resin with the appropriate solvent. The more solvent you add, the more shrinkage is an issue, which is supplanted by applying thin coats in good ventilation.

    I've done business with all the major online (US) retailers. I've had excellent experiences with all of them; be sure to take advantage of personal customer support. For more information check out http://polytek.com/ [polytek.com] http://smoothon.com/ [smoothon.com] and http://tapplastics.com/ [tapplastics.com]
  • by webweave (94683) on Thursday September 04, 2008 @01:35AM (#24870031)

    "--for the purpose of immersion, shock resistance, whatever."

    Eurotech Finland http://www.eurotech.fi has some nice candy, look in http://www.linuxdevices.com for other manufacturers.

  • SACDIN / SACCS (Score:3, Interesting)

    by skogs (628589) on Thursday September 04, 2008 @01:57AM (#24870159) Journal
    I once had the pleasure of 'removing for proper disposal' a great deal of circuit boards used in the SACDIN systems. (http://www.fas.org/nuke/guide/usa/c3i/saccs.htm)
    I remember they were glossy, and for fun we tossed them around, hit them, generally tried to break them...but could not. They were nuclear radiation and EMP hardened, and when I struck them with my Air Force ring, containing a stone that is supposed to be extremely hard to scratch, the ring scratched instantly and deeply. I've scraped it along a great deal of metal and stone objects, never adding any new scratches.
    Finding the right stuff such as the SACDIN boards were coated with can be very fun indeed.
  • Try before you Post? (Score:3, Interesting)

    by KlausBreuer (105581) on Thursday September 04, 2008 @02:48AM (#24870421) Homepage

    Ummm... why don't you simply try it out? Motherboards are pretty cheap these days; try doing this, and write of your experiences. Much more interesting than simply asking "Should I do this?".

  • Pressure housing (Score:3, Insightful)

    by jonniesmokes (323978) on Thursday September 04, 2008 @06:01AM (#24871287)

    Its not clear what the poster is trying to do. Conformal coating or potting may not be a good option. Is he trying to protect the board from dust, an occasional spraydown, or condensing humidity? Maybe CC or potting would work. THough the heat issues would be pretty bad as mentioned 100 times above.

    I would recommend a pressure housing with o-rings and proper feedthrus or liquid proof connectors. For high pressure and heat dissapation, filling the pressure housing with Flourinert would be a nice solution, just put a small pressure compensating bladder on the pressure housing so little air bubbles aren't a problem.

    If one is pressed for time, a really good ziplock bag filled with Flourinert, and a potted feedthrough for the wires would also work in a pinch.

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