Abstract
LED (Lighting Emitting Diode) has various advantages, such as small size, less power consumption, long lifespan and variegated colors, which can extensively be used as LCD (Liquid Crystal Display) backlight source, indicator lamp, automobile instrument, tail light and traffic light, etc.. LED can probably replace traditional light as its power and efficiency increase. In such situation, however, the heat dissipation of LED package becomes more important and needs to be thoroughly studied. This study presents a methodology for investigating the thermal dissipation of the LED package. The IR (infrared) thermography measurement is first performed to investigate the thermal disposition on the surface of the package. The results are verified by the thermal couple measurement and the emissivity coefficients on the surface of the LED package can be thus calibrated. The technique for establishing the TSP (temperature sensitive parameter) curve of the LED is demonstrated and the chip junction temperature Tj can be indirectly measured thereafter. A rigorous three-dimensional finite element model for the heat transfer analysis of the LED package is also constructed by ANSYS® program with proper emissivity coefficients and appropriate heat convection / radiation boundary conditions. Good correlations of the simulated and experimental results are found by comparing the chip junction temperature and temperature distribution on the surface of the LED package. Finally, this study also investigates the influence of various parameters on the thermal performance of the LED package by the finite element model developed, including the input power, thermal conductivity of epoxy lens / lead frame and sizes of lead frame. The results show that appropriate choice of the parameters in LED package studied will decrease the chip junction temperature and increase the application lifespan effectively.