Of course, no one forbids exploiting the disassembled Skylake with the heat dissipator removed, but this entails several serious problems at once, and the danger of damaging the fragile semiconductor crystal by the cooler's bottom is only the smaller of them. In addition, you will have to refrain from the regular fastening of the cooler, remove the metal clip from the processor socket and, in addition, cut the top of the corners of the LGA1151 connector, which have a higher height than the Skylake crystal. But that's not all. Problems will also arise due to the thickness and sliminess of the processor board, which must be pressed in the processor socket not only in the center, but also along the contour, otherwise it deforms and does not provide connections to the LGA1151 contacts located along the perimeter of the connector. Using Skylake collects all these problems in one fell swoop, while experiments show that the metal cover between the processor chip and the cooler increases the temperature of the CPU cores by only a couple of degrees. In other words, the real practical sense is that after replacing the thermal interface does not collect the processor back, not too much.
So first of all we decided to see how the test Core i7-6700K will show up in overclocking, if the standard thermal interface material located under the cover is replaced with an average Arctic MX-2 thermal paste with heat conductivity of 5.6 W / (m · K).
The fact that the Arctic MX-2 has a noticeably better thermal conductivity than the thermal paste that it places under the Intel processor cover does not raise any doubts. In particular, when the Arctic MX-2 was laid under the processor cover, when the processor was overclocked to 4.6 GHz, the processor remained 6 degrees colder under maximum load. Moreover, the MX-2 allowed to move the overclocking limit to 100 MHz: with this thermal paste our CPU instance worked stably at 4.7 GHz frequency, which was not accessible before scalping. And the maximum temperature of our Core i7-6700K at this frequency did not exceed 92 degrees, although its supply voltage was increased to 1.48 V.
The result is not bad, but you can not stop here. In most cases, the ultimate goal of scalping is to replace the standard thermal interface material with liquid metal, which is closest to the legendary solder used in the Sandy Bridge generation processors in terms of its thermal conductivity. Only such a thermal interface, the thermal conductivity of which is an order of magnitude better than the thermal conductivity of any thermal grease, can provide a truly effective transfer of all the heat generated by the Skylake crystal to a metal heat dissipator. And in this case, overclocking can, finally, not rest against the overheating of the processor cores, but will be determined by the frequency potential of the chip itself.
In the following table and on the graph, you can see how our Core i7-6700K accelerates if a Coollaboratory Liquid Pro thermal interface with a thermal conductivity of about 82 W / (m · K) is laid between the processor chip and the heat dissipating cover. It is important to emphasize that between the surface of the processor cover and the cooler, we continue to lay the Arctic MX-2 layer. The fact is that the structure Coollaboratory Liquid Pro includes gallium, which is aggressive towards most metals, accelerating their oxidation and forming compounds with them – gallids. Therefore, the use of this thermal interface at the contact point of the two metal surfaces leads to their rapid corrosion. And since the contact area between the processor cover and the base of the cooler is about seven times larger than the contact area between the lid and the crystal, the use of a highly efficient thermal interface in this case does not give the same pronounced effect.
The use of liquid metal has changed the situation at the root. With this thermal interface, the Core i7-6700K really stopped suffering from overclocking from any overheating. Replacing the standard thermal paste on the Coollaboratory Liquid Pro under the processor cover while the CPU is operating at a frequency of 4.6 GHz allowed the temperature to drop by as much as 20 degrees. This is a very impressive achievement, which also opened the way to the conquest of higher frequencies. In particular, our Core i7-6700K could accelerate another 200 MHz – up to 4.8 GHz, the frequency that is more typical for Sandy Bridge than for modern chips. To do this, however, it was necessary to increase the voltage V Core to 1.56 V, otherwise the system did not pass the stability test, but even in this case the maximum temperature did not exceed 81 degrees, that is, it was very far from its upper limit.
By the way, such a low heating of the processor when overclocking to 4.8 GHz leaves room for further increase in frequency. However, we did not go for it because of the need to raise the CPU voltage too much. According to the specification, the maximum permissible voltage for long-running operation of desktop Skylake is 1.52 V, and Intel strongly does not advise to climb much higher than this value.
Thus, we came to the situation to which we aspired. Thanks to the scalping and replacement of the regular Intel thermal paste under the processor lid with liquid metal, the increased heat generation and the overheating of the processor chip ceased to play the role of limiting the overclocking factors. The frequency potential of Skylake was revealed completely, and we were able to make sure that in fact the Core i7-6700K can operate at frequencies up to 4.8 GHz. And for the cooling of the processor in this case, no special methods are required – with the removal of heat, the air coolers can also cope.
It should be emphasized that we obtained such an optimistic result for the first serial processor with a sufficiently high VID level. And if the process of scalping is preceded by the selection of more successful specimens on this parameter, then most likely the overclocking results will be even more impressive.
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