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#1
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Why so very small amount of thermal compound?
I have read posts that suggest minimal thermal compound. The Arctic Silver
instructions also suggest a very small amount. http://www.arcticsilver.com/arctic_s...structions.htm I understand this advice if the concern is that too much compound may contaminate the pins and cause electrical problems. But, I don't understand it if the concern is heat transfer. I realize that the objective is to only fill the microscopic gaps between the two surfaces. After the heat sink is mounted, the force pushing the two surfaces together is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? Am I missing something? Thanks, Navid |
#2
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I understand this advice if the concern is that too much compound may
contaminate the pins and cause electrical problems. But, I don't understand it if the concern is heat transfer. The thermal conductivity of any fluid or suspension, however well-designed, will never be as good as the thermal conductivity of a metal. This is due to the way in which heat flows - heat is a consequence of the random motion of atoms and is transmitted more efficiently if the atoms are bonded in a regular (dense) structure, with lots of (relatively) weak bonds to transmit the random vibrations along. Hence, you want to apply as little as possible, only filling the valleys between the surfaces (removing air which does not conduct heat well), but not adding any more layers (of less thermal conductivity than the heatsink) than is absolutely necessary between the chip and the sink. The ultimate 'thermal compound' would be liquid metal that gets poured between the chip and sink and forms a perfect seal upon cooling. However, this would destroy your chip... I realize that the objective is to only fill the microscopic gaps between the two surfaces. This is because the thermal conductivity of your Arctic Silver (or even generic thermal grease) is greater than that of air, so you remove all air pockets. After the heat sink is mounted, the force pushing the two surfaces together is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? There will always be a small amount of thermal compound between the peaks, however little, as it will be nigh-on impossible to remove all of it purely by pressure. However, the separation between the peaks will be much less than that between valleys, as the force is indeed rather large. |
#3
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After the heat sink is mounted, the force pushing the two surfaces together
is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? Well, the same theory could be applied to water under a car's tires, and yet cars DO hydroplane. You are right the force is great, but some small amount will remain. |
#4
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Navid wrote:
I have read posts that suggest minimal thermal compound. The Arctic Silver instructions also suggest a very small amount. http://www.arcticsilver.com/arctic_s...structions.htm I understand this advice if the concern is that too much compound may contaminate the pins and cause electrical problems. But, I don't understand it if the concern is heat transfer. I realize that the objective is to only fill the microscopic gaps between the two surfaces. After the heat sink is mounted, the force pushing the two surfaces together is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? Am I missing something? The force isn't as high as you think and the thermal compound doesn't flow as easily as you think. Thanks, Navid |
#5
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"David Besack" wrote in message ... After the heat sink is mounted, the force pushing the two surfaces together is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? Well, the same theory could be applied to water under a car's tires, and yet cars DO hydroplane. You are right the force is great, but some small amount will remain. OK. So, the pressure is not enough to get rid of all the compound between the peaks, and a small layer remains. Thanks for correcting me. |
#6
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"Navid" wrote in message . com... I have read posts that suggest minimal thermal compound. The Arctic Silver instructions also suggest a very small amount. http://www.arcticsilver.com/arctic_s...structions.htm I understand this advice if the concern is that too much compound may contaminate the pins and cause electrical problems. But, I don't understand it if the concern is heat transfer. I realize that the objective is to only fill the microscopic gaps between the two surfaces. After the heat sink is mounted, the force pushing the two surfaces together is so high that any extra compound will be squeezed out of the sides. The compound is a fluid after all. There will be no compound between the peaks (only in the valleys). Is that not true? Am I missing something? A layer will always remain, impeding heat transfer. That said, you can glop on as much compound as you like, and the pressure of the heatsink will push out enough to always give you half-decent temperatures. Unless you're a mad overclocker who wants every single megahertz and every single 0.1 degree, you shouldn't worry about it. I certainly don't, and I overclock, AND I've never had heat issues. |
#7
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On Thu, 17 Jun 2004 01:17:45 -0400, "Mercury"
wrote: "Navid" wrote in message .com... I have read posts that suggest minimal thermal compound. The Arctic Silver instructions also suggest a very small amount. http://www.arcticsilver.com/arctic_s...structions.htm A layer will always remain, impeding heat transfer. That said, you can glop on as much compound as you like, and the pressure of the heatsink will push out enough to always give you half-decent temperatures. Unless you're a mad overclocker who wants every single megahertz and every single 0.1 degree, you shouldn't worry about it. I certainly don't, and I overclock, AND I've never had heat issues. A wonderful approach. The moron's guide to unending stupidity. ...of course, those with IQ's over 40 understand it's easier to just use less. but... the morons will always be with us. Let's have a hand for the moron. And let me say it's always been such a pleasure working with people like you. |
#8
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A layer will always remain, impeding heat transfer.
True, but it won't impede heat transfer as much as air will - that's why you apply the stuff in the first place. Adding too much could cause the stuff to glop out and bridge 2 pins. Some thermal compounds are conductive, so you have just b0rked your system by doing that. AS is slightly capacitive, so it could do nasty things to system stability if it were to flow across 2 pins, and others are electrically neutral (like their Ceramique compound) so you could smear your whole board in it and suffer no ill effects. Plus your syringe of AS will last longer if you use the tiny amounts prescribed. |
#9
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Lech Staniewicz wrote:
A layer will always remain, impeding heat transfer. True, but it won't impede heat transfer as much as air will Not necessarily true. With the proper amount there is contact with only the voids filled but with too much there is a layer of the thermal compound between the two surfaces, separating them. Where, before, with 'dry, you had contact with some air, too much has thermal compound between all of it and that layer can be worse than the smaller amount of air in the dry mating. See he http://power.ece.uiuc.edu/Balog/imag...lectronics.pdf The principles are the same for processor heatsinks. - that's why you apply the stuff in the first place. Adding too much could cause the stuff to glop out and bridge 2 pins. Some thermal compounds are conductive, so you have just b0rked your system by doing that. AS is slightly capacitive, so it could do nasty things to system stability if it were to flow across 2 pins, and others are electrically neutral (like their Ceramique compound) so you could smear your whole board in it and suffer no ill effects. Plus your syringe of AS will last longer if you use the tiny amounts prescribed. |
#10
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wrote in message
... Let's have a hand for the moron. Maybe instead of calling me a moron you could explain what it is I said that you consider wrong. Obviously glopping on heatsink compound is wasteful and runs the risk of causing electrical problems. My point was that one shouldn't worry about getting the impossibly-ultra-thin layer that is mentined in the AS3 instructions. And it's not "easier to use less". I tried the "half-grain of rice", and I don't have the patience or dexterity to work with it. I put on enough to get a nice even layer using a credit card. Like buttering toast. If you don't like it, do it your own way, and don't me a moron. |
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