Why use thermal paste? Where is it used?

As the heart of a computer, the heat generated by the CPU is quite amazing. 
Generally, the CPU guides the heat into the radiator through the thermal paste to achieve the purpose of heat dissipation. When the CPU heat is too high, the system will have blue screen, crash, restart, etc. Therefore, the heat conduction of the CPU becomes particularly important. Then, when installing a cooling fan, it is best to apply thermal paste between the heat sink and the CPU. The role of the thermal paste is not only to quickly and evenly transfer the heat produced by the CPU to the heat sink. In many cases, the thermal paste can also be used. Increase the thermal contact between the uneven lower surface of the heat sink and the CPU, and the thermal paste has a certain viscosity. When the metal shrapnel that fixes the heat sink is slightly aging and loosened, it can prevent the heat sink from contacting the CPU to a certain extent. The surface is separated to maintain the efficiency of the cooling fan.