Chip On Board packaging of light emitting diodes and thermal characterizations

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Abstract
High Brightness Light-Emitting Diodes (HB-LEDs) are key devices for the solid state lighting applications. Nowadays, thermal management in LEDs packaging is one of the bottlenecks preventing a wide use of HB-LEDs in lighting systems. Thermal conduction has to be addressed at all levels of packaging but the issue at the chip or device level is the most critical to keep the junction temperature as low as possible. Chip On Board (COB) technology is a way of integrating chips directly onto the board which is very promising since it enables achieving a better miniaturization and a design flexibility. In addition, in the case of LEDs packaging, a better and efficient thermal management is expected since the total thermal resistance can be greatly reduced. In this paper, we present a detailed study of the thermal resistances in COB package technologies. The thermal resistance is derived from thermo-electrical and optical measurements allowing determination of the junction temperature and dissipated power. The measured thermal resistance in COB technology is compared to a classical surface mounting of packaged LEDs exhibiting a peculiar behavior for the former. These measurements are supported by a computed thermal analysis using the ANSYSTM software to discuss the results.