Thermal analysis of high power LEDs on the MCPCB

The management of the reduced junction temperature of LEDs is a critical issue because it will affect many physical parameters such as light output, wave length and LED's lifetime. The model used in this simulation consists of a metal core PCB attached with six chips(GaN on sapphire, Ag paste, cathode/anode, silicone encapsulant, mold frame) for 5W LED module. The MCPCB is composed of an aluminum base plate, a thin layer of dielectric, and a layer of copper. The temperature distribution of the developed LED module was simulated, and the thermal behavior within this 3-D model was investigated by using a commercial computational fluid dynamic code (Fluent 6.3). The results showed that the temperature variation along the vertical direction is more dominant than that in the circumferential direction due to the heat spreading effect of the copper layer. The ratio of heat dissipation through the each thermal path was calculated and compared for various input conditions. Several parameters that increase the junction temperature, such as the thermal conductivity and thickness of the dielectric layer and the encapsulate material, heat transfer coefficient and input power were also examined. Finally, a combination of designs for attenuating the junction temperature was proposed.