發光二極體封裝之熱分析及最佳化

Thermal Analysis and Optimization of Light-Emitting Diodes Packaging

黃益良(Yi-Liang Huang)

指導教授 ： 葉孟考

國立清華大學/工學院/動力機械工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00017

摘要

發光二極體(Light-Emitting Diodes, LEDs)是以半導體材料製作成具p-n接面之結構，將電能轉換成光能的元件。隨著磊晶技術的提升，發光效率已接近取代傳統照明元件的水準，然而成本及散熱問題是其進ㄧ步普及的關鍵。封裝結構可以保護晶片和其他內部材料、提供有效的導光路徑、多樣化的造型設計，同時為熱量傳遞的重要途徑，而良好的熱管理，能夠確保元件具有穩定的光、電、機械性質與可靠度。
本文以商業軟體ANSYS模擬5 mm燈泡型 LED及3W三晶片白光LED之穩態溫度場與熱應力分佈；前者與文獻上的結果比對，確認數值模型的準確性，接著以最佳化設計理論中的反應曲面法(Response Surface Methodology, RSM)，透過實驗設計法和最小平方迴歸分析，建立元件熱阻與所選擇設計變數之近似數學模型，討論可以有效增加結構散熱能力的參數，結果顯示採用熱傳導係數較高的材料製作導線架、加寬導線架至一臨界值，以及較高的封膠，可以有效地降低其熱阻。
白光LED則以紅外線熱像儀量測表面溫度、與二極體接面溫度之理論值比較，以光學軟體TracePro模擬照度分佈，並根據多目標值函數最佳化的理論，討論能同時增進熱傳與光學特性的封裝結構，由分析結果可知增加金屬散熱片及矽樹脂之高度、減少介電層之厚度，可增進其散熱能力，而提高矽樹脂的厚度、增加透鏡的厚度及半徑使其接近半球狀，可提升亮度。

關鍵字

發光二極體 ； 熱阻 ； 照度 ； 最佳化 ； 反應曲面法

並列摘要

Light-emitting diodes (LEDs) convert electrical current into light based on electroluminescence phenomenon and p-n junction. With the rapid improvement in epitaxial growth, luminous efficacy of LEDs already exceeded that of traditional incandescent bulbs. However, cost-effective and heat dissipation issues are still the main problems needed to overcome. Thus excellent thermal management plays an important role in package designs.
In this study, the steady-state temperature distribution and the corresponding thermal stresses of packaged lamp type and high power RGB LEDs were investigated numerically via three-dimensional finite element analysis. For LED lamps, the results were compared with available literature. Then the simulation-based design optimization method, the response surface methodology (RSM), was used to achieve the optimum design. It can be found that the junction-to-ambient thermal resistance was reduced by increasing thermal conductivity of lead frame material, by increasing the height of encapsulation, and by widening the cathode no more than a critical value.
For high power RGB LED, the surface temperature distribution was measured by a noncontact infrared thermography system to verify the numerical results. The junction temperature was compared with the theoretical value. Moreover, optical simulation was performed to investigate the illumination of RGB LED. Thereafter multiobjective optimization was adopted to improve the thermal and optical performances. Thermal resistance can be reduced by thinning the dielectric layer, and increasing the thickness of heat sink and silicone. Illumination can be enhanced by using spherical lens and by increasing the height of silicone.

並列關鍵字

light-emitting diodes ； thermal resistance ； illumination ； optimization ； response surface methodology

參考文獻

2.S. Chhajed, Y. Xi, Y. L. Li, Th. Gessmann and E. F. Schubert, “Influence of junction temperature on chromaticity and color-rendering properities of trichromatic white-light sources based on light-emitting diodes,” Journal of Applied Physics, Vol. 97, pp. 054506-1~8, 2005.

3.E. F. Schubert and J. K. Kim, “Solid-State Light Sources Getting Smart,” Science, Vol. 308, pp. 1274-1278, 2005.

4.N. Narendran, Y. Gu, J. P. Freyssinier, H. Yu and L. Deng, “Solid-state lighting: Failure analysis of white LEDs,” Journal of Crystal Growth, Vol. 268, pp. 449-456, 2004.

6.E. F. Schubert, Light-Emitting Diodes, Cambridge University Press, Cambridge, 2003.

7.S. Nakamura, T. Mukai and M. Senoh, “Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes,” Applied Physics Letters, Vol. 64, pp. 1687-1689, 1994.