Neither the surface of the IHS of the processor nor that of the base of the heatsink are completely flat, so for a good heat transfer to take place it is necessary to use thermal grease, a special compound that does not is not a conductor of electricity but has very good properties for conducting temperature and which helps the heatsink to efficiently remove the heat produced by the processor.Without the thermal compound in between there would be a lot of empty spaces and the heat transfer could not take place efficiently, that’s clear to us, but what if you put too little thermal paste ? What if you put too much? We will see him.
How much thermal grease should you put on your CPU?
To be able to assess whether you are using too much or not enough thermal grease, you need to know the correct amount of thermal grease to apply. The ideal is to apply a very thin layer, the thinnest possible (since the ridges and valleys which are in the IHS and the radiator are not really too large) but which is completely homogeneous and which covers the entire surface. surface of the IHS, which is where we apply it.
An example of the correct amount of thermal paste we should apply is in heat sinks (especially liquid cooling AIOs) that have it pre-applied; Here you can see both the shape and thickness of the layer that would be ideal to apply.
A “trick” to knowing if you’ve put in too much thermal grease is that when you place and press the heat sink into place, above the IHS processor, you’ll see that the thermal grease is spilling out from the sides, a clear indication that you have exceeded the quantity. In the following example image, you can see that not only was the thermal paste applied unevenly, but also seeped from both sides when putting the heat sink in place.
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 it is “bald” and that it is not evenly distributed, you will have it. a clear clue. Also, when you install the heat sink and then remove it, you will be able to see if the “footprint” it leaves is correct or if it is irregular, as in the following example.
What is the effect of putting too much or too little on the temperature?
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 not enough thermal grease, because as you will suppose, thermal performance can vary wildly.
Too much thermal paste
In most heat sinks, there is maximum pressure from these that can be exerted on the processor IHS, usually because the screw threads have a stopper so that they do not damage the processor by over-tightening. This means that the very small distance between the IHS and the base of the radiator is always the same and therefore it is impossible to have, for example, a 1mm thick layer between the two components. This means that no matter how much thermal grease you put in, if you install the heat sink correctly, there will be no negative effect on the CPU temperature (yes, it would be advisable to clean all the thermal grease that has been forced out) fine.
Assuming we could have a considerable layer of thermal grease between the IHS CPU 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
- Processor area in square meters.
- Thickness of the thermal paste layer, in meters.
The formula would be as follows:
Rpaste = (thickness / surface) x (1 / thermal conductivity)
Let’s take an example to see 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 a thickness of 1 millimeter of thermal paste, with which obviously we will have put too much. In this 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 millimeter thickness, 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 grease on the CPU is that it is “bald” and therefore the contact of the IHS with the heat sink 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 you will essentially have temperature spikes which in many cases can be so dangerous that systems processor temperature protection trips and you turn off the PC.
Conclusion: better than to miss
As we said before, the ideal is to apply a very thin layer of even thermal grease on top of the IHS of the processor and that’s it, although there are many followers of the technique. “grain of rice” (you can see the example of this in the image above, it consists of putting a grain of thermal paste in the center and leaving when you place the processor, the pressure distributes it over any the surface).
What is clear is that if you put thermal paste in, the greatest effect you will have will be that it oozes from the sides and you will be forced to clean it (or that if it takes too long before removing the heatsink again, you realize that this paste has solidified and the heatsink is stuck to the processor), but it usually does not have any adverse effects in terms of operating temperature. However, if you are unable to put thermal paste in, you may see adverse temperature effects, so it is better to go too far than to fall short in this case.