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Any user who has ever assembled a PC knows that between the CPU and the heat sink it is necessary to put thermal paste to promote heat transfer. There are many techniques when applying it, but what happens if you put too much or too little thermal paste ? In this article, we are going to tell you how not reaching or going over the thermal paste affects the temperature of the processor.
Neither the surface of the IHS of the processor nor that of the base of the heatsink are completely flat, so in order for a good heat transfer to take place it is necessary to use thermal paste, a special compound that is not conductive to electricity but has very good properties. to conduct temperature and that helps the heatsink to efficiently evacuate the heat produced by the processor. Without the thermal compound in between, there would be many empty gaps and the heat transfer could not occur efficiently, that is clear to us, but what happens if you put too little thermal paste? What if you put too much in it? Let’s see it.
How much thermal paste should you put on your CPU?
To be able to assess whether you are using too much thermal paste or too little, you need to know the correct amount of thermal paste to apply. The ideal is to apply a very thin layer, as thin as possible (since the ridges and valleys that are in the IHS and the heatsink are not really too big) but that is totally homogeneous and that covers the entire surface of the IHS, which is where we apply it.
An example of the correct amount of thermal paste that we should apply is in the heatsinks (especially liquid cooling AIOs) that have it pre-applied; Here you can see both the shape and the thickness of the layer that would be ideal to apply.
A “trick” to know if you have put too much thermal paste is that when you place and press the heatsink in place, on top of the processor IHS, you will see that the thermal paste overflows from the sides, a clear indication that you have exceeded the amount. In the following example image you can see that not only has the thermal paste been applied in a non-homogeneous way, but it has also seeped from both sides when putting the heatsink.
Knowing if you have put too little thermal paste on the CPU is more complicated to know, but if when you put the initial layer you see that they are “bald” and that it is not evenly distributed, you will have a clear clue of it. Also, when you install the heatsink and then remove it, you will be able to see if the “footprint” that it leaves is correct or if it is irregular, as in the following example.
What effect does putting too much or too little on the temperature have?
Once the above is explained, we are going to see what effect it will have on the operating temperature of the processor to put too much or too little thermal paste, since as you will suppose the thermal performance can vary enormously.
Too much thermal paste
In most heatsinks there is a maximum pressure of these that can be done on the IHS of the processor, generally because the threads of the screws have a stop in order not to damage the processor by tightening too much. This means that the very small distance between the IHS and the base of the heatsink is always the same, and therefore it is impossible to have, for example, a 1 mm thick layer between both components. This means that no matter how much thermal paste you put in, if you install the heatsink correctly, there will be no negative effect on the CPU temperature (yes, it would be advisable to clean all the thermal paste that has been expelled out by pressure) well. .
Assuming that we could have a considerable layer of thermal paste between the CPU IHS and the base of the heatsink, things would change. To determine this effect we need to know 3 values in total:
- The thermal conductivity of the paste, expressed in W / mK
- CPU area in square meters.
- Thermal paste layer thickness, in meters.
The formula would be the following:
Rpaste = (thickness / area) x (1 / thermal conductivity)
Let’s take an example to see it better. Suppose a thermal paste with a conductivity of 12.5 W / mK with an Intel 1151 socket processor (its dimensions are 29.5 x 29.2 mm, and therefore its area is 0.0008614 m²) and we put it a thickness of 1 millimeter of thermal paste, with which obviously we will have put too much. In that case we would have a value of Rpaste = (0.001 / 0.0008614) x (1 / 12.5) = 2.66. If we now repeat the calculation with 0.1 millimeters thick, then the value it gives us is 1.45, so the heat transfer will be much better.
Very little thermal paste
What can happen if you put too little thermal paste in the CPU is that they are “bald” and that therefore the contact of the IHS with the heatsink is not perfect, causing areas much hotter than others. The effect on temperature will vary depending on the processor and the location, size and shape of your die, but essentially you will have temperature spikes that in many cases can be so dangerous that the processor’s temperature protection systems trip and you turn off the PC.
Conclusion: better than missing
As we have said before, the ideal is to apply a very thin layer of homogeneous thermal paste on top of the IHS of the processor and that’s it, although there are many supporters of the “grain of rice” technique (you can see the example of this in the image above, it consists in putting a grain of thermal paste in the center and letting when we place the processor, the pressure spreads it over the entire surface).
What is clear is that if you put on thermal paste the greatest effect you will have will be that it seeps from the sides and you will be forced to clean it (or that if it takes too long until you remove the heatsink again, you will realize that this paste has solidified and the heatsink stuck to the processor), but it does not generally have harmful effects in terms of operating temperature. However, if you fall short when it comes to putting thermal paste, you can find detrimental effects on the temperature, so it is better to go too far than to fall short in this case.