A three-dimensional thermal model of LED illuminating device is established by using the finite element method. The natural convective boundaries are applied on the lateral surfaces, and an equivalent convective boundary on the bottom surface is utilized to represent the real effects of heat sinks or fins on LEDs. In this paper, the dielectric layer of LED die bonding is discussed and the influences of external and internal thermal resistances are analyzed. When we enhance the external convective effect, the external thermal resistance is reduced obviously. The thermal conductivity of material and the thickness of dielectric layer are important factors on the internal thermal resistance. We may propose these results to design and develop the global principle for the heat-dissipating package of LED device to increase the performance of LED.
This study will discuss the heat dissipation effect of light emitting diode (LED) device applied a commercial miniature heat pipe (MHP). For lowering the thermal resistance of LED, the MHP can reduce the working temperature and raise the allowable input power of LED chip obviously. By comparing with a copper rod, the LED temperature was decreased about 19% at 1.59W input power and the LED power was increased about 43% under 118°C chip temperature. On the other hand, the thermal resistance of LED also can be reduced by using a thinner slug. Moreover, the results showed that the thermal spreading effect was significant. The MHP could be used to avoid the hot spot of LED packaging due to its excellent heat spreading property. Simultaneously, a LED thermal simulation was carried out to verify the optimum value of slug thickness.