Thermal Spreading Resistance Characteristics of a High Power Light Emitting Diode Module

Abstract

In this study, effects of the dimensions and the thermal conductivity of the substrate on the heat transfer characteristics of a LED module are investigated. The total thermal resistance corresponding to a LED module operating at different power levels is measured using a thermal resistance testing system (T3Ster®). In addition, a novel graphite composite material with anisotropic thermal conductivities is used as the substrate of the LED module to investigate the effects of directionally dependent thermal conductivities on the thermal spreading resistance. Furthermore, a finite element method numerical simulation is carried out to analyze the heat transfer phenomena in the LED module. It is found that, for the current experimental conditions, the importance of the thermal spreading resistance effect increases with decreasing substrate thickness and/or increasing input power of the LED module, which corresponds to an increase in the total thermal resistance and correspondingly a higher chip temperature. Experimental and numerical results show that the thermal spreading resistance and thus the chip temperature can be reduced by increasing the substrate thickness or by utilizing materials with high lateral thermal conductivities for the substrate. In consequence, for LED modules with the same substrate thickness, using graphite composite to replace aluminum as the substrate material reduces the spreading resistance by nearly fourteen percent in the current study.