You have to understand something basic before moving forward and it is nothing more than how the IHS of the CPU works. These are the metal plates that carry the Intel and AMD silkscreen printing, where their function is twofold: to protect the die or dies and above all to transmit the heat of these to the heatsink. Therefore, said heatsink will be in contact with this piece of nickel-plated copper and therefore, it is the first obstacle to deal with.
IHS deformation and how to overcome it to improve contact
Although we think of an IHS as a straight and perfect piece of metal, the reality is totally the opposite. Since the CPUs are currently welded between their dies and said IHS, this plate deforms towards the center by just a few microns, so in terms of height a processor will always have greater distance in its corners than in the center of it.
This means that companies have to take it into account when designing the heatsinks, and here comes the whole problem. The two ways of making contact between the heatsink and the IHS are those already mentioned direct touch and cold plate, so we will explain them very briefly.
Direct touch is based on allowing the heat pipes of the heatsink to touch directly with the IHS, on the other hand, cold plate is a piece of copper that is normally perfectly flat and that in its upper part touches the heat pipes by means of soldering, transmitting the heat of the CPU.
Which of the two types of heatsink is better for CPU?
Heat pipes have the advantage of not having intermediaries, since their direct contact causes heat to be transmitted directly to the tube and this begins to change the state of the internal liquid to gas to begin cooling. But this faces two problems:
- Imperfections and holes in the total surface.
- Impossibility of making a perfect curvature in the total surface.
It is also necessary to specify what we mean by total surface, and it is only the set of the total dissipation area of each model. If more or thicker heat pipes are used, there will be more total surface area and it will be more difficult to make it perfect.
The theory tells us that if the IHS is not perfectly flat, the heatpipes or cold plate have to take a non-flat shape to fit. Normally the IHS are coming out concave, so the two contact methods must be convex to alleviate the error.
This is really difficult to achieve if what you have to cut are 2, 3, 4 or 6 heat pipes plus the surface that welds them, so a straight cut with polishing is usually chosen. But in the case of cold plate, as it is a solid piece on which the heat pipes are then welded on top, this form is easier to do with CNC for example, since there is no risk of splitting solder or breaking one of the tubes.
In addition, a cold plate can achieve a more “pure” surface with fewer imperfections because it is a piece and not a cluster of them, so it usually tends to obtain better overall performance. That is why all high-end or extreme heatsinks use this system, while direct touch is more for the mid-range or entry, where it is also cheaper to manufacture.