Chip to System Levels Thermal Needs and Alternative Thermal Technologies for High Brightness LEDS

Abstract

Light emitting diodes (LEDs) historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors has allowed them to penetrate specialty and general illumination applications. The increased electrical currents used to drive the LEDs have resulted in higher heat fluxes than those for average silicon integrated circuits (i.e., ICs). This has created a need to focus more attention on the thermal management engineering of LED power packages. The output of a typical commercial high brightness, 1mm2, LED has exceeded 100lm at drive levels approaching 3W. This corresponds to a heat flux of up to 300W∕cm2. Novel thermal solutions need to address system architectures, packaging, phosphors for light color conversion, and encapsulants and fillers for optical extraction. In this paper, the effect of thermal management on packaging architectures, phosphors, encapsulants, and system design are discussed. Additionally, discussions of microscopic defects due to packaging problems as well as chip active layer defects are presented through experimental and computational findings.