SUMMARY

LEDs are being developed as the next generation lighting source due to their high efficiency and long life time, with a potential to save $15 billion per year in energy cost by 2020. State of the art LEDs are capable of emitting light at ~115 lm/W and have lifetime over 50,000 hours. It has already surpassed the efficiency of incandescent light sources, and is even comparable to that of fluorescent lamps. Since the luminous flux of a single LED is considerably lower than other light sources, to be competitive the total light output must be increased with higher forward currents and packages of multiple LEDs. However, both of these solutions would increase the operating temperature, which can degrade the performance of the LED—as the operating temperature goes up, the light intensity decreases and the lifetime is reduced. Critical to the temperature rise in high powered LED sources is the very large heat flux at the die level (100 – 500 W/cm2) which must be addressed in order to lower the operating temperature in the die. It is possible to address the spreading requirements of high powered LED die through the use of power electronic substrates for efficient heat dissipation, especially when the die are directly mounted to the power substrate in a chip-on-board (COB) architecture. In this work, we present an analysis of the integration of power substrates in the packaging of high powered LED (>1W/die) through finite element analysis (FEA) and analytical analysis. In our work LED-chip implementing COB architectures were designed and studied. Substrates for these packaging include insulated-metal-substrates (IMS) and direct-bonded-copper (DBC). After studying thermal characteristic of LED packages by FEA, a thermal resistance network was analyzed to estimate LED junction temperature by simple calculation. With this analysis some design considerations can be made in order to maximize the light output while also maximizing the reliability.