Questions regarding thermal paste...

Haswellx86 · February 5, 2022

1) Why is thermal paste required?

2) You don't cover the whole processor IHS with thermal paste, just a little dot in the center, why? But then you cover the whole GPU die with the thermal paste.

3) Doesn't the processor IHS result in a penalty in heat transfer? Just like in graphics cards, we can integrate the cooler with the processor to completely remove the IHS and give direct cooling.

4) Why don't we just use liquid metal more often than thermal paste? It is way cooler.

OhioYJ · February 5, 2022

24 minutes ago, RTXboy123 said:

1) Why is thermal paste required?

To fill in the tiny inconsistencies / gaps in the surfaces of the heatsink / CPU IHS. These surfaces aren't perfectly flat, so you need something to fill in these spaces to allow for better thermal conductivity.

24 minutes ago, RTXboy123 said:

2) You don't cover the whole processor IHS with thermal paste, just a little dot in the center, why? But then you cover the whole GPU die with the thermal paste.

I do cover the hole IHS. I spread the paste? CPUs generally have more mounting pressure and will spread the paste even if you don't. Also with a GPU it's critical to get the paste coverage everywhere as just part of a GPU can die. Not all of a CPU "needs" covered, although if it is better if it is covered.

24 minutes ago, RTXboy123 said:

3) Doesn't the processor IHS result in a penalty in heat transfer? Just like in graphics cards, we can integrate the cooler with the processor to completely remove the IHS and give direct cooling.

Yes as it's another layer between things. Hence why delidding is a thing. There are also heatsinks meant for "naked" CPUs. However it's also much easier to damage a CPU without a IHS.

24 minutes ago, RTXboy123 said:

4) Why don't we just use liquid metal more often than thermal paste? It is way cooler.

The amount of work and maintenance it creates. The cleanup involved. Liquid metal isn't exactly straight forward to apply to get the best results. Incompatibility with some coolers? Have you used liquid metal before? Here is one of my delidded CPUs, notice the scarring / marking of the CPU die, that's after only a week:

Needfuldoer · February 5, 2022

1. It fills in all the microscopic cracks and gaps in between the heatspreader and the bottom of the heatsink. It's not as good as direct metal-on-metal contact, but it's not cost effective to manufacture these parts with the exacting precision that would require. Thermal compound conducts heat far more effectively than the air that would otherwise fill those gaps.

2. The dot in the middle squishes out to the edges as the cooler gets tightened down against the CPU's integrated heat spreader.

3. Yes it does, but bare dies have their own disadvantages. Back in the Pentium III and Athlon XP days, processors didn't have integrated heat spreaders. If you got the heatsink on crooked, you could crack the silicon and kill the processor die. To loop back to #2, you have to make sure an exposed die is completely covered with paste so you're effectively cooling the entire thing. If you don't, there's a chance an area of the die that doesn't have a temperature sensor near it can overheat and fail. Graphics cards come with heatsinks already attached, and generally if you're swapping aftermarket cooling onto a GPU you're expected to know what you're doing. GPUs are also limited in height, so the manufacturers try to cram as much cooling as they possibly can given the amount of space they have to work with.

4. Liquid metal is electrically conductive and messy. Regular gray thermal paste is very easy for assembly robots to just glob onto factory heatsinks. That means easier installation for the end user, and fewer potential RMAs and warranty claims for OEMs.