Heat Dissipation Model of a High-Power LED Headlamp for the Automobile

隨著 LED 封裝製程能力進步與成本逐漸降低，並擁有高效率、壽命長， 輕薄短小、造型設計容易等諸多優勢，近幾年被廣泛的應用在汽車照明光源的使用，並開始往替代舊式鹵素燈與氙氣頭燈來設計發展，成為未來市場上各家製造商積極研究之目標。但由於 LED 本身的發光效率及壽命，將會隨著晶片溫度的升高而遞減，以及 LED 的封裝結構並不耐熱，當 LED 晶片的接面溫度過高時，將會對晶片本身與封裝的材料帶來永久性的傷害。因此如何設計出有效的散熱方式，以提升 LED 發光效率及壽命，將是高功率 LED 上應用的重要關鍵。 本研究利用計算流體分析軟體，針對市售高功率 LED 頭燈之原始模型進行分析與散熱設計。透過加入溝槽式熱管與風扇，以及改變 LED 封裝基板與電路板材質參數，觀察 LED 晶片接面溫度的變化，探討散熱模組之散熱效益。結果顯示，在原始參考模型外觀尺寸不變下，在強制對流下透過加入熱管與提高 LED 散熱基板及 PCB 之熱傳係數，可有效使 LED 晶片接面溫度降低，使高功率 LED 頭燈在安全溫度範圍內，保持元件可靠度。With the improvement of LED packaging process capability and cost, and the advantages of high efficiency, long life, light and short, easy to design, etc., it has been widely used in automotive lighting sources in recent years, and has begun to replace the old halogen. The design and development of lamps and xenon headlamps has become the goal of active research by various manufacturers in the market in the future. However, due to the luminous efficiency and lifetime of the LED itself, it will decrease as the temperature of the wafer increases, and the package structure of the LED is not heat-resistant. When the junction temperature of the LED chip is too high, the wafer itself and the package tape will be come to permanent damage.Therefore, how to design an effective heat dissipation method to improve the LED luminous efficiency and life will be an important key to the application of high power LEDs. This study used computational fluid analysis software to analyze and heat-dissipate the original model of commercially available high-power LED headlamps. By adding the grooved heat pipe and the fan, and changing the material parameters of the LED package substrate and the circuit board, the change of the junction temperature of the LED chip is observed, and the heat dissipation efficiency of the heat dissipation module is discussed. The results show that under the forced convection, the heat transfer coefficient of the LED heat sink substrate and the PCB can be effectively reduced under the forced convection, so that the junction temperature of the LED chip can be effectively lowered, and the high-power LED headlight is safe. Maintain component reliability over temperature.目錄 摘 要 i Abstract ii 目錄 iii 表目錄 vi 圖目錄 vii 第一章 緒論 1 1.1 前言 1 1.2 車用高功率 LED 發展趨勢 4 1.3 高功率 LED 車燈散熱問題 7 1.3.1 散熱器介紹與應用 9 1.4 文獻回顧 12 1.5 研究動機與目的 16 1.6 論文架構 17 第二章 理論分析與散熱模組設計 18 2.1 熱傳遞原理 18 2.1.1 熱傳導(Thermal Conduction) 18 2.1.2 熱對流(Thermal Convection) 20 2.1.3 熱阻定義(Thermal Resistance) 20 2.2 LED 熱阻結構 21 2.2.1 LED 封裝熱阻 22 2.2.2 接觸熱阻(Thermal Contact Resistance) 23 2.3 LED 熱管理論與介紹 24 2.3.1 熱管介紹與工作原理 24 2.3.2 熱管特性限制 26 2.3.3 熱管等效熱阻 28 2.4 流體型態的判定 29 2.5 高功率 LED 封裝散熱基板介紹 31 第三章 參考實驗結果與數值分析方法 36 3.1 高功率 LED 車燈模型與散熱設計 36 3.2 高功率 LED 車燈熱阻介紹 39 3.3 數值模擬分析 40 3.3.1 ANSYS 軟體簡介 40 3.3.2 統御方程式 41 3.3.3 數值計算理論 43 第四章 幾何模型建立與模擬驗證 46 4.1 前處理介紹 46 4.1.1 數值模型建立 46 4.1.2 網格建立 49 4.2 參數設定 50 4.2.1 材料設定 50 4.2.2 邊界條件設定 51 4.2.3 發熱源瓦數與網格設定 52 第五章 數值模擬結果與討論 53 5.1 主動式散熱條件下 PCB 板材料選擇 53 5.2 加入熱管的散熱效益 55 5.3 散熱基板熱傳導係數的改變 67 第六章 結論與未來展望 71 6.1 結論 71 6.2 未來展望 72 參考文獻 7