"Tiny Cooling Fan" Hot Road and temperature calculation is a schematic diagram of the semiconductor device is mounted on the radiator, seen from the figure, the chip is soldered to the housing base. Thermal power chip produced by conduction reached base housing by the chip, and then from the shell in the form of a small amount of heat convection and radiation to spread to the environment, but most of the heat through the base via an insulating spacer directly to the radiators, radiator finally reached the air. Thus, "Tiny Cooling Fan" heat transfer process is very complex, precise calculation is very difficult to conduct. In engineering, such as in the range of permissible error 5 ~ 10 ℃, even if accurate enough. To this end, according to the principle of introducing the concept of similarity therm electric heat of the road. Because "Tiny Cooling Fan" in the heat capacity of the thermal path exists, so transient, the resistance is a function of time, when the steady-state thermal resistance Rth nothing to do with time.