Apart from special illumination, high power light emitting diodes (LEDs) will soon be used in general illumination because of its distinctive advantages including high efficiency, good reliability, long life, variable colors and low power consumption. An expectation about high power LED is that it will be a dominant lighting technology by 2025 [
1]. Theoretically, higher operating current delivers more light output from LED. Unfortunately, the light output power of the LED decreases as the increasing of LED temperature [
2]. It has been reported that the thermal problem is a main factor which is related to most of the main parameters of LEDs. Driving current and forward voltage are interdependent, and they influence the light output and the efficiency of LEDs. Optical power degradation occurred due to junction temperature (
TJ) increasing, therefore, proper thermal management is a key issue in power LED based lighting applications [3]. When two solid surfaces are joined, asperities of each surface limit their actual contact to a very small fraction, perhaps it is just 1%–2% of the apparent area for lightly loaded interfaces. The flow of heat across such interfaces involves not only the conductions of solid-to-solid in the area of actual contact (
Ac), but also the conduction through the fluid occupying the noncontact area (
Anc) of the interface. This constriction of heat flow is manifested as thermal contact resistance (
Rc) at the interface [
4].