Correct way to apply thermal paste - thick or thin ?

[Woelund]

Hi,

as I am new to building PCs (nowadays ... I remember replacing my 286 with a 386 back then ...) I would like to ask some advice on applying thermal paste during assembly of a new system:

1) Is it OK to add "a bit more for safety" even if the past squeezes out underneath the block (for example, if I use a water cooling block) ? (In other words: is it a real problem if paste touches the outside of the CPU, or is this just an aesthetic problem ?)

2) Is there a technical reason to keep the paste as thin as possible ? Or would it be even beneficial to apply a thicker film (of course limited by the pressure the water block puts on the CPU) ?

I do not yet own a water cooling system but I saw in the advertisements that some blocks come with "thermal paste preapplied". Should I trust such setup or should I rather add extra paste before assembly, just to be safe ?

This brings me to my last question:

3) Is it a problem to mix pastes ? Do I HAVE to clean the pre-applied paste before applying my own, if I wanted to do that ? Or can I mix the two without any issue ?

Thanks !

Woelund

[MeanMachine]

Hi Woelund

A commonly asked question on what to use and how to apply TIM. (Oils ain't Oils and TIM ain't TIM)
It does make a difference as to what you use. I use either AS5 or MX4 which have very similar thermal conductive properties. A TIM is good if it is like grease in consistency and not a thick oil. It should be applied as sparingly as possible to fill just the tiniest of Voids. TIM should not squeeze out the sides of the thermal plate as it can cause issues and applying too much will deplete thermal efficiency.
The most common practice is to apply a small pea sized blob to the center of the CPU and tighten down the brackets in a crosswise pattern in incremental steps and only finger tight.
Most pre-applied pastes are OK but I personally clean it off and meticulously clean both surfaces with Isopropyl Alcohol 95%. I'm probably a little pedantic as I will lap the CPU ground surface if its too coarse.
To get it right for first timers its best to have a trial run, apply then check the spread.
The good TIM contains metallic oxides and as dissimilar metals can react, It's best not to mix them.

For those technically inclined, TIM is rated by its thermal conductivity.
Thermal conductivity λ is defined as the ability of material to transmit heat and it is measured in Watts per
square metre of surface area for a temperature gradient of 1 K per unit thickness of 1 m. W/mK
AS5 = 8.9 W/mK
MX4= 8.4 W/mK
Some pastes are only 1.2 W/mk and should be avoided.
Some pastes harden and become an adhesive causing damage when thermal plate is removed.

[Woelund]

Hi MeanMachine,

excellent - that was exactly the answer I was looking for ... thanks for explaining the technical aspects of this. (I also was kind of releaved that I was not the only one having such a beginner's question :-) ) So the TIM needs to be spread only very thinly, only in order to seal all small crevices between the two metal surfaces - that makes sense - before my mental eye I see the microscopic view of two rough metal sufaces touching each other on some points with the TIM filling the tiny gaps and voids in between the two surfaces. More and "thicker" is thus not necessary and makes no sense ... understood !

Thanks for also mentioning that the efficiency is degraded for the TIM if it is thicker than necessary - that I was completely unaware of !

You inadvertently cleared up another question I had, but forgot to put in my post: so 95% isopropyl alcohol is the solvant of choice when it comes to cleaning the surfaces from the TIM. Very good - I will get me some of that. I will also then not try to mix the pastes - what you say makes perfect sense: you really do not know what metals the TIMs contain and you would not want these metals to react with each other ...

Thanks for the excellent and in-depth answer - much apreciated !

Best regards,

Woelund

[Nate152]

Hi guys

Thermal Grizzly Kryonaut is one of the best non conductive TIM's.

12.5 W/mk

http://www.performance-pcs.com/therm...grease-1g.html

[damianme]

You don't really need a lot. Just the same size as a grain of rice would suffice. Now, thermal pastes are made differently in the sense that some of them are really good at heat dissipation while others are not. I agree that you should use the Arctic Silver 4 or 5 as it is inexpensive but it is proven to be effective.

[Iormangund]

Actually if there is too little paste then you can have heat problems. Using too much paste only matters if you are using an electrically conductive paste and it goes over the edge of the cpu cover. You could empty out a whole tub of paste on the cpu and although it would make a hell of a mess, it would work just as well as using a pea sized amount.

Using too little paste is the only situation in which you would get negative performance. There are a few vids and reviews around where people have tested and proven that (I think there was one on Linus' youtube channel a while ago). I have also tried myself using too much paste as an experiment on an old cpu and there was zero temp difference from a pea sized amount.

Personally I use a pea(ish) sized amount and that has always worked great for me, not a fan of the spread method. Point is, as long as it's at least a pea sized amount and spreads evenly across the surface (by block pressure, credit card spreading etc), quantity isn't something to freak out about too much.

[Decoman]

Not too little not too much:

Suggestion: Try apply some amount, then fit the fan with the screws.. then unscrew the fan.. and then take a look at how well the paste had spread out. You can expect the past to look funny after taking off the cooler, though you will get a good idea if there is too much or too little then I think.
Note: If you do this, clean the old paste away, and redo the paste, don't use the old paste already on the cpu.

I will try a small thin "cross" pattern on my next fitting job. I usually just put down a rice grain size of paste for my Intel stuff. Unsure if the cpu heatsink is different in size between intel and AMD.

[Menthol]

Hi guys

Thermal Grizzly Kryonaut is one of the best non conductive TIM's.

12.5 W/mk

http://www.performance-pcs.com/therm...grease-1g.html

This is the best TIM you can purchase at this time. PK-1 or PK-3 are also very good with PK-1 being the easiest to use in MO, all of these are non conductive, a conductive TIM may need extra care in use for obvious reasons

[Chino]

I use the dot/rice/bean method.

[Woelund]

Gentlemen,

thanks a lot for the replies. Much appreciated. I will for sure then go with the Kryonaut - thanks, that is a valuable tip. If it is a non-conductive paste that is even better ... I was worried a bit about the paste touching the "outside" too much and possibly being conductive, but if it is non-conductive then it really comes down to being an aesthetic problem if the paste spreads too far.

Probably generally a non-issue more or less. I see that common sense is the way to go here ... still, these are the things that go through my head as someone who is about to build his first system.

I think I will go with the suggestion to try out how the paste spreads under pressure on glass vs metal. This way I could see the result. Watched a few videos too about this and for example "The 8auer" (well known German Overclocker, if I am not mistaken) showed that just applying the paste in the middle of the CPU may not cover the complete housing, but rather fit a circule on top of it. This way you would get a bit less area covered than the complete (rectangular) housing and may loose some heat sinking capacity. But even he was vague in his assessment what the actual impact of this would be. I guess it comes down to using a bit more paste then.

Thanks for all the answers and good advice ! In summary: Kryonaut, in medium quantities, with a test beforehand to see spreading characteristics, use isopropyl alcohol to clean. That is the way I will go about this.

Thanks all for the great advice !

Woelund