Note well that some of the heatsink & fan units for modern high-speed processors can have some form of sticky heat transfer material on the underside of the heatsink - usually in the form of a small square - that fits over the processor's central core where the main processing chip is housed. This will help the heat to conduct away from the core to the heatsink so that the fan can dissipate the heat into the case. Since it is sticky, a thin protective plastic cover will have to be removed prior to fitting the cooler to the CPU. Failure to do so can cause the processor to overheat rapidly enough to destroy itself.
If the heatsink and fan unit came with a strip of film covering thermal compound, you should not remove the heatsink and fan from the processor after it has been installed and expect the compound to function properly again, because it can only be used once.
If the cooling unit doesn't provide any heat transfer material, you can use thermal paste - or a thermal pad can be used.
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