How to apply thermal paste?

rubilips

macrumors newbie
Original poster
Mar 12, 2017
2
0
I'm upgrading a Mac Pro 4,1 from 4 core to 6 core. It seems straightforward enough EXCEPT for how to apply the thermal paste to the CPU. Some say a pea sized blob in the middle, others say a diagonal line, and others say apply a thin coat to the entire surface. Any suggestions as to the optimum method?

Thanks
 

mpta

macrumors member
Jan 17, 2013
41
8

Go with method nr 2 but use very very thin layer, use flat plastic (like credit card) to apply it.
Other methods are maybe ok when u can screw the radiators with a lot of force to the plate behind the mainboard without risk of breaking the mainboard.
FOr mac pro u use 4 screws and u should not screw it very very strong :) so I suggest method nr 2.
 

kjmff5

macrumors regular
Mar 27, 2011
185
23
I typically use a pea size blob in the middle and apply the heat sink directly on it, letting it spread out as you attach it on. You don't want too much thermal paste or it inhibits the transfer of heat, and you don't want to apply too little because then it won't conduct the heat. 'you want just the right amount' lol. I am with you, the more research you do, the more answers you find. you can always do a CPU stress test and see if it is staying cool. hope this helps and doesn't confuse you more!
 

Ph.D.

macrumors 6502a
Jul 8, 2014
548
465
I'm upgrading a Mac Pro 4,1 from 4 core to 6 core. It seems straightforward enough EXCEPT for how to apply the thermal paste to the CPU. Some say a pea sized blob in the middle, others say a diagonal line, and others say apply a thin coat to the entire surface. Any suggestions as to the optimum method?

Thanks
Thermal paste is designed to fill in any gaps between the two metal surfaces (CPU and heatsink). You want the most direct coupling as possible, using the least paste that will fill any gaps, since the heat conduction of the paste is very likely less than the metal it is in contact with.

There are plenty of wrong ways to do it and several ways that are fine. The "pea size blob" approach should be fine, but I personally don't favor it because it does little to insure that a completely even coat is the end result, and one may wind up with excess spilled out the sides. Assuming that the surfaces are both very flat, I prefer to spread a thin coat myself, e.g. using a card or piece of paper under your finger. If not flat, then I might go with the blob approach after all (but a little bigger blob), since spreading it yourself may miss some larger gaps.

Edit: I agree that No. 2 has too much paste slathered on. Thinner than that.
 
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h9826790

macrumors G5
Apr 3, 2014
14,278
6,870
Hong Kong
AFAIK, most of those method generate more or less the same result, the temperature difference usually just 1-2 degree C, well within normal error. So, I will say it doesn't really matter. In fact, if you use AS5, their website has recommendation to use which method for a particular CPU model. Or if you go for the Mac Pro's technician manual, there is also a recommended method. Interestingly, none of your 6 pictures including those recommendations from AS5 or Apple.

I personally go for the Apple method (like a stop sign, but turn 90 degree), and put the heatsink on. After that I will remove the heatsink straight away to check if the paste is enough to cover the whole surface. If not, apply a little more on the dry area, then install the heatsink (if obviously too much, remove some paste). I know some people may say that's the worst I can do, because I make lots of bubbles inside the paste etc. But from my real world experience, it works very well. What I found is that the paste amount is the most important factor, but not the application method. May be AS5 is not that sensitive to application method. As long as I use this method to ensure the thermal paste just able to cover the entire surface, I always have good result (that's including my cMP, graphic card, PS4...)
 

pastrychef

macrumors 601
Sep 15, 2006
4,520
1,027
New York City, NY
How you apply it doesn't matter too much. What matters is the end result. Ideally, a very thin coating to fill in gaps is best.

There are exceptions though... The "liquid metal" stuff needs to be applied with little brushes or swabs and the entire surface area should be covered, again, with a very thin layer. It's also a good idea to apply a tiny bit on the heatsink side.
 

dotnet

macrumors 65816
Apr 10, 2015
1,187
854
Sydney, Australia
If you're not experienced with applying thermal paste I'd recommend to steer clear of the metal based pastes. Use something like AS Ceramique instead.
 

Theophany

macrumors 6502a
Nov 16, 2008
633
186
NW London.
If you're not experienced with applying thermal paste I'd recommend to steer clear of the metal based pastes. Use something like AS Ceramique instead.
AS5 is non-conductive.

I've always used the blob method. That way the paste fills in the gaps where necessary under the pressure of the heatsink. Applying a thin layer to the entire IHS seems wasteful and unnecessary, especially considering majority of heat will be generated at the centre of the IHS.

But as has already been said, the difference in style is a couple of degrees at most - unless you really over or under do it. I've done custom water cooling loops a few times on PCs and the pea sized blob never caused any issues.
 
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