conductivity of thermal paste

wildrabbitt · 2017-05-09, 11:10

Hi,

does anyone know if CPU paste is conductive? I'm wondering if it should really
be used on a CPU in a submersively cooled machine since the transformer oil makes the paste seep out between the heatsink and the chip.

LaurV · 2017-05-09, 13:17

depends on paste. The silicone based (like the milk-white one) is not conductive. The silver base it is. Those all which need "curing" may also be conductive (they contain small tin balls/coloidal stuff which gets "welded" to your cooler and/or cpu after the first heat, making the thermal transfer much better, but the balls are conductive). You can see the electrical and thermal conductivity in the datasheet if you know the name.

pinhodecarlos · 2017-05-09, 15:21

My advise is to read Incropera.

wildrabbitt · 2017-05-10, 10:05

Thanks.

Does running it with no paste sound like a bad idea or might it work ?

VictordeHolland · 2017-05-10, 11:09

Quote:

Originally Posted by wildrabbitt

Thanks.

Does running it with no paste sound like a bad idea or might it work ?

Bad idea! Cooler and CPUs are never 100% smooth, you risk ruining your CPU by doing that.

LaurV · 2017-05-10, 13:07

@Victor, he is talking about submerged stuff.

@OP: Does the oil bay works by convection, or do you have some pumps moving the oil from here to there? You may be able to run it without paste, and even without a heatsink, if you have a pump that blows oil on it, but you have to try first, reduce the clock, don't give anyhing to do to the cpu, see how the temperature raise, etc... however you are on your own, don't jump at our throats if you fry your cpu, hehe...

You can take the heatsink off, clean everything well, put a drop of oil (the same you use in the bay) and put the heatsink back. This may not work in air, but it will work the same as the paste, in the bay. If your paste make coffee-like oil around the CPU, take it off and use oil. Do not put the cooler "on dry", it may trap microscopic air bubbles that will not get out when you submerge it, and they will impede the heat transfer. Whatever you do, run your system for 30 seconds, up to two minutes, then stop it for 10 minutes, repeat few times (5, etc). The heat-cold shocks will get out all the air from between the sink and CPU (the air balls expand and move when hot, then contract and suck the oil in when cold, etc., until they are completely out.

2017-05-09, 11:10	#1
wildrabbitt Jul 2014 2×3²×5² Posts	conductivity of thermal paste Hi, does anyone know if CPU paste is conductive? I'm wondering if it should really be used on a CPU in a submersively cooled machine since the transformer oil makes the paste seep out between the heatsink and the chip.

2017-05-09, 13:17	#2
LaurV Romulan Interpreter "name field" Jun 2011 Thailand 2²·7·367 Posts	depends on paste. The silicone based (like the milk-white one) is not conductive. The silver base it is. Those all which need "curing" may also be conductive (they contain small tin balls/coloidal stuff which gets "welded" to your cooler and/or cpu after the first heat, making the thermal transfer much better, but the balls are conductive). You can see the electrical and thermal conductivity in the datasheet if you know the name. Last fiddled with by LaurV on 2017-05-09 at 13:43

2017-05-10, 13:07	#6
LaurV Romulan Interpreter "name field" Jun 2011 Thailand 2²·7·367 Posts	@Victor, he is talking about submerged stuff. @OP: Does the oil bay works by convection, or do you have some pumps moving the oil from here to there? You may be able to run it without paste, and even without a heatsink, if you have a pump that blows oil on it, but you have to try first, reduce the clock, don't give anyhing to do to the cpu, see how the temperature raise, etc... however you are on your own, don't jump at our throats if you fry your cpu, hehe... You can take the heatsink off, clean everything well, put a drop of oil (the same you use in the bay) and put the heatsink back. This may not work in air, but it will work the same as the paste, in the bay. If your paste make coffee-like oil around the CPU, take it off and use oil. Do not put the cooler "on dry", it may trap microscopic air bubbles that will not get out when you submerge it, and they will impede the heat transfer. Whatever you do, run your system for 30 seconds, up to two minutes, then stop it for 10 minutes, repeat few times (5, etc). The heat-cold shocks will get out all the air from between the sink and CPU (the air balls expand and move when hot, then contract and suck the oil in when cold, etc., until they are completely out. Last fiddled with by LaurV on 2017-05-10 at 13:18

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2017-05-09, 15:21	#3
pinhodecarlos "Carlos Pinho" Oct 2011 Milton Keynes, UK 1408₁₆ Posts	My advise is to read Incropera.

2017-05-10, 10:05	#4
wildrabbitt Jul 2014 702₈ Posts	Thanks. Does running it with no paste sound like a bad idea or might it work ?