發光二極體之擴散熱阻效應分析

Abstract

本研究以實驗與理論分析的方式探討擴散熱阻對LED效率之影響。藉由暫態熱阻量測設備與積分球針對LED在不同金屬基板下分析其熱阻和光輸出的變化。實驗結果顯示在光校正前擴散熱阻會隨著輸入電功率的增加而增加，在光校正後的熱阻不會受到輸入電功率的影響而改變。另藉由紅外線熱像儀確認暫態熱阻量測設備所計算的熱阻曲線圖之基板底部溫度與計算結果相符。LED的光電轉換效率隨著輸入的電功率和接面溫度的增加而減少，效率從55%下降到35%、相關色溫隨著輸入的電功率增加而增加，並隨著接面溫度的增加而導致偏移，約有500K的偏移量。本研究並以實驗與解析解進行比對，結果顯示實驗結果高於解析解，以雙層不鏽鋼金屬為例，約高出28%，其原因可由X光照片發現其介面焊接不完全，導致不同金屬層間產生較高接觸熱阻。

The present study investigates the thermal spreading resistance effects of LEDs by experiments. The thermal transient tester and integrating sphere are used to measure the thermal and optical characteristics of LEDs mounting on different kinds of metal substrates. The result shows that the thermal resistance of LEDs increase as electric power increase before optical correction, but after the optical correction is conducted by integrating sphere, the thermal resistance of LEDs does not affect by electric power. Besides, the meaning of the cooling side temperature in the structure function is confirmed by infrared camera. On the other hand, the results also show that the lighting performance has something to with the thermal management. The wall plug efficiency of LEDs decrease when increasing the electric power or junction temperature. The radiant power will increase as electric power increasing. The correlated color temperature will increase as electric power increasing and decrease as junction temperature increasing. Due to the thermal spreading resistance effect, the thermal resistance of compound different dual plates will be different if two materials are changed up side down. Finally, by taking the X ray pictures, we find void in the solder region which will increase the thermal resistance of LED package.