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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
The technical term you're looking for is Potting.
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.
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
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.
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.
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 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.
Even people that believe in pre-destiny look both ways before crossing the street.
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.
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.
FC-77 is intended for computer use, not FC-73 (my friend's father works at 3M)
"Politicians and diapers must be changed often, and for the same reason."
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.
didn't someone put up an article awhile ago here on Fluorinert?
I work for the Department of Redundancy Department.
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 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.
Even people that believe in pre-destiny look both ways before crossing the street.
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) we lost about a pint a month of HFE7100 under heavy load.
-nB
whois gawk date unzip strip find touch finger mount join nice man top fsck grep eject more yes exit umount sleep dump
Looks like I should read my MSDS more often...
FC-77:
ATMOSPHERIC FATE:
Perfluoro compounds (PFCs) are photochemically stable and expected to persist in the atmosphere for more than 1000 years. PFCs
have high global warming potentials (GWP), exceeding 5000 (100-yr-ITH). The Ozone Depletion Potential (ODP) is Zero.
HFE-7100:
ATMOSPHERIC FATE: Zero Ozone Depletion Potential (ODP). Atmospheric Lifetime: approximately 4.1 yrs. Global Warming
Potential (GWP): 280 (100 year ITH, IPCC1995 method). Global Warming Potential (GWP): 320 (100 yr ITH, IPCC2001 method).
Atmospheric degradation products are expected to include: for methyl nonafluoroisobutyl ether: predominantly isoperfluorobutyric
acid, CO2, HF, and perhaps also CF3COOH; for methyl nonafluorobutyl ether: n-perfluorobutyric acid, CO2, and HF.
The HFE was developed to address the environmental persistence of FC by photo-decomposition. The byproducts, however, still look to be a BadThing(tm)
-nB
whois gawk date unzip strip find touch finger mount join nice man top fsck grep eject more yes exit umount sleep dump