Following the relevant question I was wondering if adding a pea-sized (or half-pea since there's already some) would hurt ? As far as I'm aware, and have heard from various sources, Thermal paste is one of the few things in this line of work, where "The more the merrier" applies in full force, so long as no paste touches anything but the top of the CPU. CPU is i5-7600

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    Here's a thought: How do you want to apply a thicker layer of thermal paste, if the distance between heatsink and mainboard is pretty much fixed under pressure thanks to the locking mechanism? – Ian Apr 12 '17 at 11:02
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    And certainly, not like this: gfycat.com/GraciousActiveCoral – Dai Apr 13 '17 at 0:51
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    @Dai I told ya guys, the more the merrier: img-9gag-fun.9cache.com/photo/abpBb2L_700b.jpg – Иво Недев Apr 13 '17 at 15:50
  • note: Puget Systems posted an excellent article on thermal paste application techniques. tl;dr: best coverage was from an X shape, diagonally from corner to corner atop the chip. – matt lohkamp Apr 13 '17 at 23:48
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    @mattlohkamp LTT also did thermal-paste application testing, and consistent with Puget's results, it doesn't really matter. Unfortunately, none of them are really scientific, as they only have one trial per condition, so random variations could easily swamp out the 0.25 ℃ difference in measurements. Also note that Puget isn't reporting ambient temperatures, so if they drifted more than a degree or two, all their results are pointless. – Nick T Apr 14 '17 at 22:33

No, adding more would be bad. What you want to do is to clean off all existing paste (use isopropyl alcohol if you can) and apply a bit of fresh paste.

If you're talking about the layer that comes with a new cooler, you can usually use it directly - you don't need to use your own at all. Replacing paste is only really worthwhile for old paste.

Also, the correct saying here is "less is more"1 :)

With thermal transfer from the integrated head spreader (IHS, the metal on top of the CPU die) to the heatsink, it vaguely goes:

  • metal-to-metal contact: best
  • metal-paste-metal contact: alright
  • metal-air-metal contact: very poor

So your best-case scenario is if you can maximise direct metal contact between the IHS and the heatsink. That means they should be as clean and smooth as possible, and a fair amount of pressure pushing them together.

Now, if direct metal contact is best, why do we have paste? Because it's very difficult to get solid metal smooth enough for perfect contact, so you inevitably end up with lots of tiny air bubbles, resulting in poor transfer. Adding paste fills up these little gaps, but adding too much paste1 will either form a thick layer and prevent direct contact, or will end up getting squished out the side.

Even worse is trying to apply fresh paste on top of existing old/dried paste - that way you have the poor performance of dried paste (which can no longer spread effectively once disturbed) plus an additional layer. It's much better to just clean off the existing gunk first.

1 You'd want enough paste. There's a bit of leeway here, but you also don't want to go squeezing a whole tube in - once you have enough, adding more won't help. Keep in mind that what looks like a tiny bit will actually spread out quite far once pressure is applied - you're squeezing a 3mm-high blob into less than a tenth that height. Optimally, you'd have somewhere maybe a little bit over enough.

For those interested, there's further discussion of specific application techniques and their relative effectiveness here: https://www.pugetsystems.com/labs/articles/Thermal-Paste-Application-Techniques-170/

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    Also, if the thermal compound comes out of the sides, you can end up with a short on the CPU (depends on the CPU and if the thermal compound is conductive). Or, the best case scenario, next time you need to do some maintenance, the CPU is glued to the heatsink. This happens a lot and is a real pain to clean up properly. You may risk destroying the CPU or dropping it while "unglueing" the CPU. (I've done the last one, and bent 5 pins on a CPU.) Also, it is a real pain to clean layers of thermal compound, or nearly impossible to remove the older layer. – Ismael Miguel Apr 12 '17 at 10:21
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    In fact the advice used to be to apply a small amount and scrape it level with something like an old credit card, removing much of that small amount at the same time as making the layer even. The thermal conductivity of thermal paste is really low, just much better than the air it replaces. – Chris H Apr 12 '17 at 10:41
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    Also beware that some coolers have thermal compound pre-applied. – Pieter De Bie Apr 12 '17 at 10:44
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    @Tyzoid You seem to be missing the context here, specifically the intention to add more paste on top of existing paste. I stayed away from recommending a specific amount and linked to a very good article for a reason - the intention of this answer was to explain why paste is used and why more paste does not automatically translate to better cooling. If you really want my opinion on how much to apply, I favour the X pattern, which is a fair bit more than absolutely necessary. Doesn't really matter much. – Bob Apr 13 '17 at 3:02
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    I'd note puget systems builds systems commercially and thermal paste is meant to fill gaps, not act as a thermal interface on its own. A lot of builders literally just squeegee a thin coat atop their processors. Quite a lot of thermal paste is conductive, especially on the high end. Adding enough to squeeze out excess is not recommended by many makers of paste. I'd rather trust Puget than Linus personally. – Aibobot Apr 13 '17 at 3:25

Absolutely not. Thermal paste should be just enough to fill any gaps. A thicker than required layer of thermal paste reduces the efficiency of the paste. It is also not a good idea to mix different thermal pastes unless you know they are chemically compatible. Additives in one paste may break down additives in the other, producing compounds that may degrade the paste.

  • Do you have an example of such chemically active additives? All thermal pastes I have seen use some sort of oil/grease as a base and non-conductive powder as filling (the cheapest kinds sometimes use metal powder). I've never seen any warnings about chemical compatibility issues on thermal paste. – Dmitry Grigoryev Apr 12 '17 at 15:53
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    @DmitryGrigoryev Many manufacturers warn about this and caution users to thoroughly clean off old thermal compound before adding new. The only incompatibility I've specifically heard of is thermal compounds containing halogens being incompatible with thermal compounds containing micronized carbon. – David Schwartz Apr 12 '17 at 17:37

There's a reason heatsinks aren't made from enormous formed blobs of thermal compound. The BEST thermal paste is about 8W/m^2*K. Even steel is about 6 times better at conducting heat, at 50W/m^2*K. Aluminum is 205. They're not even close -- use the least amount of paste you can to fill the air gaps (air being 0.024W/m^2*K). You can actually skip thermal compound entirely if you lap the heatsink and CPU to a mirror polish -- high end overclockers do this occasionally.

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    Logically, those overclockers should also mount their heatsinks in clean room conditions, because a few dust particles will prevent good contact even if the surfaces are perfectly polished. – Dmitry Grigoryev Apr 12 '17 at 15:59
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    @DmitryGrigoryev, it's not a clean room, but taking steps to minimize any chance of dust is part of a typical overclocker's heatsink-mounting procedure. – Mark Apr 12 '17 at 23:10
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    @Mark Does the quality of the thermal junction last for long? It'd seem like thermal expansion cycling (the CPU expanding/contracting as it warms/cools due to load/idling) plus vibrations (such as from system fans, especially fans/liquid-circulation on the CPU cooler) would eventually introduce particulates, moisture, or some other type of imperfection. Not that that's a problem for extreme overclockers who're going for short-term extreme performance numbers rather than long-term performance, but just curious how stable that solution might be. – Nat Apr 13 '17 at 5:14
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    @Mark What steps are these? When you have 10 dust particles per cubic cm, you'll get some on your cooler no matter how hard you blow. – Dmitry Grigoryev Apr 13 '17 at 7:06
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    @Mark It's funny how the discussion went from skip thermal compound entirely to applying the thermal compound. – Dmitry Grigoryev Apr 13 '17 at 11:08

You should apply enough paste so that when you put the cooler on, a small amount of paste appears on the sides. Putting less paste means you're still having air gaps which were not completely filled. Putting more means you're wasting paste, and if you apply too much it may spill on the board and you'll have to clean that.

Of course, you should completely remove the old paste before you apply the new one. The old paste has probably dried up compared to a fresh one, and probably accumulated some dirt and dust. This will prevent it from flowing well under pressure, and you will end up with more air cavities as a result.

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