Applying thermal paste

Hello Experts,

I've heard different things about applying thermal paste and wanted to know what you think.  Some people say to use the pea/line method and some say to evenly apply a thin layer to entire CPU surface before installing the heat sink.

Not sure which one to go with; it seems that the full coating method will increase the total area of heat transfer and get better results, but wanted to hear your opinions on this.
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epichero22Asked:
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JustInCaseCommented:
Few years back I read that X shape give best results. I am writing X on CPU with thermal grease. :) That was some other article, not this one. But conclusion was the same.
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jmcgOwnerCommented:
The reason people advocate one or the other depends on whether they think it will leave air pockets, which could be a problem. When I last did it, I followed the instructions on the package and used the spreader they supplied. There's no advantage to having a thick layer, so apply just enough to make a thin layer without any gunk squeezing out when you pin down the heat sink. That's harder to control using the pea or line method.
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tailoreddigitalCommented:
FYI,  I've built many systems.   I use to do a nice even layer.   I saw people using a thin line and have tried that myself.    I haven't seen a difference in the temps.
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akbCommented:
Less is best. If you apply too much paste the thermal transfer won't be as efficient. If your paste came with an applicator then use that, otherwise use a plastic credit card to spread it thinly and evenly across the processor surface.
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nobusCommented:
since the main goal of the heatpaste is to fill the tiny gaps on the heat sink, and cpu, you neep only half of the pea really, and even less
would the metal touch each other without gaps - no paste were needed
as for how to apply it, the small pea should spread out over the whole surface when the pressure on the fan is applied, but to ensure it comes eveywhere, most people "help" it by spreading it themself
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Dave BaldwinFixer of ProblemsCommented:
@nobus is correct.  Extra paste will make it worse, not better.  The 'best' for heat transfer is optically flat metal to metal contact.  Thermal paste is used to fill the gaps because we don't have the time or equipment to do that.
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rindiCommented:
Just use a tiny drop of paste. When you connect the heatsink properly, the pressure used to attach it will automatically force that drop to spread evenly across the surface.
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Gary CaseRetiredCommented:
The answer is "it depends" :-)

Different types of thermal compound have different viscosities => and the best method of applying them is dependent on that factor.

With the popular Artic Silver, for example, a small "pea" is best, as it spreads very well with the pressure of the heatsink and as it absorbs heat from the CPU it becomes even more uniformly distributed.    With viscous pastes, using the small spreader they usually come with to uniformly cover the CPU's thermal area is better.

The most important factor is to not use too much -- that will actually make it less effective.   As for the specific application method -- simply follow the instructions that come with the specific compound that you buy.
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epichero22Author Commented:
I saw videos on the pea method where they used transparent plexiglass to show how it would spread on the CPU.  Basically, the pea would form into a circle and while covering most of the CPU surface, it wouldn't cover all of it.

I don't know how this is beneficial.  Why, since the heatsink is fitted to the full area of the CPU surface, would leaving some area of the surface without thermal paste work better than full coverage?

Anyways, another question I had is how long does the thermal paste take to settle in?  I'm noticing fluctuations in the CPU temperature; I left HWMonitor running yesterday and it varied from 25°C to 47°C.  Right now it appears to idle between 29 - 31.  Mind you, this is an HP stock heatsink with the fan plugged into the system_fan connector which keeps it running at a constant 1726 RPM.
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nobusCommented:
when it varied the temp -it was probably doing some task ; updating, or disk refresh, or some background tasks

anyhow -with such low temps i see no problem
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rindiCommented:
Actually ideally you don't need any thermal paste, but that requires the surface of both the CPU and the Heatsink to be absolutely plane without any dents in it. The thermal paste is only there to fill any such uneven features. It also requires the heatsink to be very tightly attached to the CPU, so it makes perfect contact with all of the surface. If it doesn't fit correctly, then you get effect you describe. But in such a situation spreading the thermal paste evenly won't do much good, as the distance between the CPU and the heatsink at the outer parts is too large. As much metal should touch as much metal as possible. Thermal paste can only correct very small gaps.
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epichero22Author Commented:
as the distance between the CPU and the heatsink at the outer parts is too large. As much metal should touch as much metal as possible.

It sounds like a contradiction there.  One one hand, not applying thermal paste to the outer edges will result in too many of these tiny pits and therefore metal wont touch other metal as well as if you spread the paste.  Since the size of the CPU heat spreader matches the size of the contact surface for the heat sink, I would imagine that maximizing this area of contact would allow the heatsink to draw more thermal energy from the heat spreader.

Unless, I'm misunderstanding.  There doesn't seem to be a consensus on this.
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rindiCommented:
If the CPU and Heatsink aren't 100% plane, thermal transfer paste won't help in aiding cooling those areas. It only helps in the very tiny cracks and dents, but those must be extremely small and aren't visible to the eye. Anything that is larger (like the bent surface you get on many CPU's or heatsinks) is too large. So spreading the paste to those "large" gaps won't help at all.
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Gary CaseRetiredCommented:
"... It sounds like a contradiction there.  One one hand, not applying thermal paste to the outer edges will result in too many of these tiny pits and therefore metal wont touch other metal as well as if you spread the paste.  Since the size of the CPU heat spreader matches the size of the contact surface for the heat sink, I would imagine that maximizing this area of contact would allow the heatsink to draw more thermal energy from the heat spreader.  " ==>  

This would be true IF the heat generated from the processor was uniformly distributed over the heat spreader.

But this is NOT the case.   The actual topology of the chip varies for various CPUs.   I've attached a picture that shows a Core i7-4770 with the heat spreader removed ... you can see that the actual CPU area is less than 1/4th of the area under the heat spreader.    By far the most important area that needs to have "perfect" contact is the area over the CPU cores.    In fact, some overclockers actually remove the chip's heat spreader and apply thermal compound to the CPU core area; then re-seat the heat spreader and have reduced the CPU temps by 15-20 degrees C by doing this   Clearly this is a VERY delicate operation that voids your CPU's warranty.

The reality is that if you use a high-quality thermal compound and apply it per the manufacturer's instructions you'll be just fine.     Note that over time ... as the thermal compound is heated/cooled over several cycles ... the compound will tend to migrate to those areas where it's needed (i.e. the microscopic "pits") and its performance will improve.

I7-4770 without heat spreader
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