Thermal grease that is just right – good spread and good conductivity.įor example, the thermal conductivity of a high-grade thermal paste is 8.5 W/mK, and the heat conductivity of copper is 385 W/mK, or for aluminum 205 W/mK. That means that the heat conductivity will be done by the thermal paste, not by metal on metal contact of the IHS and heatsink. If the thermal compound is too thick, it will not even out between the CPU and heatsink. We can look at thermal pastes as liquids, so if the compound is sparse it is inevitable to have lower thermal conductivity. Solid materials, metals (like copper, of which water blocks are mainly made) have much higher thermal conductivity than liquids or gases. Thermal grease that is too dense and dry – bad spread on the IHS. A good thermal paste evens out uniformly when the water block or heatsink is fastened by its retention kit. Too little or too much thermal paste is not good. On the other hand, we can see examples where the thermal compound is too thick, so we say it has high viscosity. You can see that some compounds are too soft, and therefore, we can say they have a low viscosity. Thermal grease that is too soft and sparse – low thermal conductivity. We will show you some examples of good and bad thermal pastes. The density can often be determined empirically, simply by applying the thermal compound, mounting the water block, removing the water block and observing the spread pattern of the thermal compound. One more attribute that is sometimes stated by some manufacturers is the viscosity. Some manufacturers use the term specific gravity, some just label it as density and both are expressed in g/cm³ which stands for grams per cubic centimeter. Next stop is the “specific gravity” which in layman’s terms is the density. ![]() The higher the number, the better the thermal conductivity of the compound is. First and probably the most important is the conductivity, which in cases of thermal paste labeling is often expressed in W/mK which stands for Watt per meter by Kelvin. The role of the thermal compound is simple, to fill the tiny gaps between the cooler and the IHS and to promote thermal conductivity (or just to make some additional heat conductivity possible if the two surfaces are convex or concave).įor that role to be fulfilled, the thermal paste has to meet some requirements. The proper terms for these two situations is that the surface is either convex or concave. It happens from sample to sample that the IHS or the cold plate are not geometrically flat. Micro imperfections of the heat spreader and heatsink surface are often not the only problem. If you would join these two surfaces together without any thermal paste, you would have poor thermal conductivity and the CPU would overheat. So, you probably get the picture by now: the surface of the CPU is not smooth enough and the base of the cooling body is not smooth enough either. Some manufacturers deliberately leave machine grooves on the base of their coolers to get a more even spread of the thermal paste. The situation with the coolers and cold plates of water blocks is almost the same, or in some cases, even worse. CPU manufacturers don’t bother much around the IHS and as you can see, it’s not the smoothest surface if we take a closer look. The CPU chip itself is substantially smaller than the IHS, that is made out of copper and is nickel plated. It is the metal piece that covers the CPU. The IHS is short for „Integrated Heat Spreader“. Here is an example of an AMD CPU and its IHS. Both these surfaces appear smooth to the human eye, but if you magnify it, you could see that it is actually quite bumpy and uneven. Imagine the surface of the water block, or any other cooling system and the surface of the CPU on a microscopic level. But we want to go deeper into this topic. First, we need to discuss why we use thermal paste at all. In one of our previous articles, we showed you how to correctly apply the thermal paste. ![]() Customer Support Knowledge database, support tickets.Events EK’s virtual events in one place.Gaming PCs High-end, cost-effective, plug and play PCs for high performance.All-In-One Affordable, easy to install, maintenance-free liquid cooler with class-leading performance.Kits High-performance custom loop liquid cooling kit.Custom Loop Premium segment liquid cooling products for DIY PC enthusiasts.
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