Slashdot Mirror
Coating a Motherboard In Thermal Resin?
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?
yeah, it's called conformal coating
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,
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.
Wouldn't that conduct the heat from the CPU over to the other components?
The technical term you're looking for is Potting.
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'
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
If you use immersion, why do you need fans?
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.
I'm a big tall mofo.
I'd imagine you'd want to sort out your future memory or disk capacity needs before dipping.
Yeah? Well I think you're overrated too.
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.
Anything like this?
http://www.engadget.com/2007/11/13/ipod-gets-exploded-trapped-in-resin/
Terrorists can attack freedom, but only Congress can destroy it.
Potting is used to keep the components from moving (usually in high-G environments. Sometimes you use it to keep close conductors from shorting (like solder-cup connector), but again the risk there is mostly movement of the conductors, not the environment. Potting materials usually do not have good thermal dissipation properties, and aren't really the best thing for environmental protection (humidity, liquid immersion etc) either. Conformal coating is what you want for the latter.
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
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.
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?
You can't see ANYTHING from a car, You've got to get out of the goddamned contraption and walk...Edward Abbey
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.
...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.
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.
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.
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.
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.
Bavarian Purity Law of Rice Krispie Squares: Rice Krispies, Marshmallows, Butter, Vanilla.
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.
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
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.
I am always doing that which I can not do, in order that I may learn how to do it. - Pablo Picasso
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.
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.).
use a non-conductive liquid for cooling, such as oil. This has been done before, and even a cursory google 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.
https://www.eff.org/https-everywhere
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. 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.
The land shall stone them with the bread of his son.
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.
There are such resins, but:
1. They are really expensive; $100 is about 2" sq, half an inch thick.
2. It has to be cast around the electronic assembly in a vacuum; this is harder than it sounds.
3. To cure properly, and without voids, it has to be poured into a custom mold at around 150C. In a vacuum. :)
I have seen electronics cast like you are talking about, but I doubt a mobo would take the process and live. The casting temperature is too hot, and kills most electronics.
If it worked, you could dunk the whole thing to cool it. Liquid Nitrogen would even work, as long as the thermal shock was controlled. Cool or heat it too fast, and the stuff breaks.
The standard procedure for the assemblies I saw,was to make 10, and hope a few work afterward.
Truth isn't Truth - Guliani
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.
There's no failure quite as dissatisfying as a complete and total solution to the wrong problem.
I think this is a product that should do what you're looking for. I haven't had a chance to use it yet, but the info at the link leads me to believe it could fit the bill. Masterbond-Potting & Encapsulation Materials http://masterbond.com/produse/produse_pe.html
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/ http://smoothon.com/ and http://tapplastics.com/
Yeah, but not of resins.
I'm obviously not a materials scientist, but this one says it's a two-part epoxy with a 5 minute pot time and a Shore D hardness of 80, which I looked up to be equivalent to nylon. That's a resin, no?
Though at .84 W/M K it's not nearly as efficient as the one you found. Neat.
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
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 that the real winner was the team which had came up with one of those conventional erector-set type designs.
The point which led me to this idea was that I'd noticed in the scoring formula there was no limit on the amount of glue we were allowed to use. I'd considered making a solid log of glue with a single strut buried inside it, but the drying times wouldn't have allowed me to finish the project before testing day. I think one of my purposes in going through the school system was to spend as much energy as possible challenging the silliness of conventional thinking, though at the time I was giggling too much to take notice.
-FL
http://www.octools.com/index.cgi?caller=articles/submersion/submersion.html
Just disrupt the deflector shield with a tachyon burst.
"--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.
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.
Who is this that even the wind and the waves obey Him? Surely this computer must submit also!
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?".
Free PC version of ChipWits at http://www.breueronline.de/klaus/chipwits/
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.
Ah, yes. 3M Fluorinert. That stuff seems to pop up here in discussion every once in a while. I don't believe they actually manufacture it anymore -- what you can buy is basically "New Old Stock" -- and it's staggeringly expensive. (For the home hobbyist, anyway; if you're actually maintaining a Fluorinert-cooled system in production, it's probably nothing.)
The common alternative you can play with at home is mineral oil, although it's not nearly as good. What makes Fluorinert useful is its relatively low boiling point. It's liquid at room temperature and on most idle parts, but on a hot component, it will boil. It's the boiling, not just the submersion in liquid, that draws the heat away so effectively. Most home liquid-submersion experiments miss this entirely.
Personally I've always wondered about coolant solutions that use the solid/liquid state change rather than the liquid/gas one; maybe a slurry of solid, low-melt-point crystals suspended in a liquid carrier. I've worked with some plasticizers that have basically room-temperature freezing points, but I've never seen that particular property taken much advantage of. (Most of them actually become more dense as they freeze, rather than less dense like water, so you could put your hot parts at the bottom of a tank filled with slurry, and when the coolant melted the liquid would rise to the top and more frozen coolant would fill in over the part. It would be similar to Fluorinert boiling, but without the gas production.)
"Ladies and gentlemen, my killbot features Lotus Notes and a machine gun. It is the finest available."