Numerical Analysis on Temperature Field in a LED Module

Abstract:

The working temperature has great effect on the reliability of LED modules. In this paper, numerical analysis is carried out on predicting the temperature field in a LED module based on simplified two-dimensional model. It is found that the highest temperature manifests in the LED chip and more than 99% of the heat generated by the LED chip are transferred out through the copper heat sink. Parametric study shows significant temperature increment from 327K to 384K in the LED lighting chip by decreasing 10 times of the thermal conductivity values of conductive layer from 24.5W/(m.K) to 2.45W/(m.K). It is concluded that the key factor in heat transfer process inside the LED module is the thermal resistance of the thermal conductive layer lying between LED chip and copper heat sink.

• Periodical: Advanced Materials Research (Volume 221)
• Pages: 604-609
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.221.604
• Online since: March 2011
• Authors: Dong Xing Du, Ying Ge Li, Xiao Bing Luo
• Keywords: LED Module, Numerical Analysis, Temperature Distribution

References

[20] Other boundaries, including the surfaces of PC lens and the plastic foundation, are given the convective heat transfer conditions, with natural convection coefficient of 4W/(m2. K) and the environmental temperature of 295K (22℃). Heat source of the studied system is the LED lighting chip with equivalent volume heat generate rate of W/m3. Computations are carried out to study the working temperature field inside the LED module with finite difference method. Numerical results are extracted based on the observation that the calculated total surface heat transfer flux lies within 1% of the designated heat generation values. Table 1. Thermal conductivity values for the materials in a LED module PC lens Silicon encapsulent LED chip Thermal conductive glue (TCG) Copper Plastic 0. 16 1. 8 150 24. 5 398 0. 24 Results and Discussions Temperature field in the LED module. The color-filled working temperature contours in the LED module are illustrated in Fig. 3. It can be easily observed that the highest temperature manifests in the region of heat generating LED lighting chip, and the biggest temperature difference is 13K recorded between LED lighting chip and heat sink bottom. Besides, heat flux analysis shows the heat transferred from the copper heat sink is 1. 04W, while the heat dissipated from other surfaces though natural convection is only 0. 1W, indicating more than 99% generated heat is dissipated through the copper heat sink. The temperature distribution along the central axis is plotted in Fig. 4, with x=0m and x=0. 0054m corresponding to the peak of the PC plastic lens and the bottom of copper heat sink respectively. It is clearly seen that the maximum temperature of 326. 7℃ manifests in the LED lighting chip and there exists a sharp temperature gradient through the layer of thermal conductive glue. Due to the fact that more than 99% of the generated heats are transferred through the route of LED chip, thermal conductive glue and copper heat sink, it can be concluded the main thermal resistance is presented by the thermal glue layer. Fig. 3 Temperature field in the Fig. 4 Temperature distribution along the central LED module axis of the LED module Effect of thermal conductivity of the conductive glue on the temperature field. To show the effect of thermal conductivity of conductive glue on the heat conduction process in the LED module, we carried out parametric analysis by designating the thermal conductivity of 2. 45W/(m. K) for the thermal conductive glue, which is 10 time lower than our benchmark case. The working temperature field obtained at lower conductivity value of 2. 45W/(m. K) is shown by cloudy-contours in Fig. 5. Significantly higher temperature increment is observed between the heat sink bottom and the LED light chip. As indicated in Fig. 6 where the temperature values on the central axis are plotted, the peak temperature in LED lighting chip is above 384K and this temperature could invoke serious problems for LEDs' working reliability. Under the lower thermal conductive value of 2. 45W/(m. K), the temperature difference through the thermal glue layer is above more than 100K, indicating the decisive role of the thermal glue conductivity on the thermal resistance network of the whole LED system. Fig. 5 Temperature field in the Fig. 6 Temperature distribution along the central LED module at lower λTCG values axis of the LED module at lower λTCG values Conclusions Numerical analysis is carried out in this paper to study the heat transfer characteristics in a LED module. A simplified two dimensional model in cylindrical coordinates is employed and the temperature field in the LED lighting system is numerically obtained. It can be concluded that, 1. More than 99% of the generated heat by LED lighting chip are dissipated from the copper heat sink and the natural convection heat loss from other surfaces of the LED module can be reasonably neglected; 2. The thermal conductive glue plays the decisive role in thermal resistance network of the whole LED module. Decreasing the thermal conductivity values by 10 time from 24. 5W/(m. K) to 2. 45 W/(m. K) leads to significant increment of the LED chip temperature from 327K to 384K, which could seriously deteriorate the reliability of the LED module. The investigation on thermal management of LED packaging is far from complete. It is expected our work could make some contributions in this challenging and promising field. Acknowledgment The work is sponsored by National Science Foundation of China (No. 50876038). Reference.

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