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標題: 高功率發光二極體之熱管理與界面反應
Thermal management and interfacial reactions of high-power light-emitting diodes
作者: 陳佳汝
Chen, Chia-Ju
關鍵字: high-power light-emitting diodes
出版社: 化學工程學系所
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摘要: 近年來高功率發光二極體之產品應用趨增,高功率發光二極體需要比過去更大的電流趨動,但由於目前元件的輸入功率僅有40~50%轉換成光,其餘皆轉換成熱,所以勢必需要更有效率地將元件所產生的熱排放至環境,才能維持其熱穩定性。而目前高功率發光二極體於一階封裝製程中,普遍延續以往使用熱傳導係數不高的銀膠、環氧樹脂與錫膏作為固晶材料,其熱傳導係數皆不足以將元件發光時所產生的熱適時排出。 為降低高功率發光二極體之表面溫度,本實驗採用商用錫膏Sn-3wt.%Ag-0.5wt.%Cu(SAC305)加入具有高熱傳導能力之人工鑽石(~2000W/mK),製成有別以往之高熱傳導固晶物質,再將高功率發光二極體進行網印封裝於散熱基板上。由紅外線熱影像分析儀與熱暫態分析儀的數據結果顯示,此種複合型式的固晶材料能降低元件之表面平均溫度與總熱阻值,結果證實藉由添加高熱傳導物質於固晶層中能提升整體固晶層的熱傳導能力,以使元件能適度降溫,且有效率地將元件發光時所產生的熱傳至散熱基板,並維持其熱穩定性與壽命。 由於高功率發光二極體已成為未來的光源趨勢,為瞭解銲點之可靠度分析,本論文研究高功率發光二極體之固晶層的界面反應,觀察不同迴焊時間與熱處理下的介金屬化合物生成種類及其銲點內部微結構演化,本實驗使用商用錫膏將元件網印封裝於散熱基板上方,經迴焊後,元件之背部金屬處理層中的Au層迅速消耗殆盡,並在晶片背部金屬端的界面處形成(Au,Cu,Pt)Sn4,散熱基板端的界面處則形成(Cu,Au,Pt)6Sn5,隨著熱處理時間拉長,(Au,Cu,Pt)Sn4漸漸從界面處剝離,造成錫膏與背部金屬處理層的Cr層直接接觸,因兩者濕潤性不佳,繼而降低晶片與銲料間之機械性質,為避免失去濕潤性的現象發生,可藉由改變晶片背部金屬層結構以延緩(Au,Cu,Pt)Sn4之剝離現象。 為了瞭解元件在發光時所產生的熱對於介金屬化合物的影響,將封裝完成之高功率發光二極體進行固/固界面反應實驗,其晶片端的介金屬化合物(Au,Cu,Pt)Sn4並不會發生在液固反應中的剝離現象,由於當熱處理的溫度為150oC時,其(Au,Cu,Pt)Sn4並不太微溶出Au原子於熔融的銲料當中,所以介金屬化合物的相才無太大的改變。藉由改變散熱基板上方之金屬處理層為Ni層來探討對於銲點的影響,發現隨著熱處理的時間拉長,晶片端的(Au,Ni,Pt)Sn4遷移到(Ni,Cu)3Sn4上方的情形越明顯。
In recent years, due to the rising ideology of energy saving and environmental friendly policies, the high-power light-emitting diodes (HP-LED) characterized with high efficiency and energy saving that has been a potential candidate for next generation light sources. However, HP-LED requires high current drives than before and then generates much heat. Only 40~50﹪of the input power converts to light and the rest converts to heat. The heat generated by the chip must be dissipated to the environment effectively in order to maintain the thermal stability of the LED devices. But nowadays the using of die attach materials currently used in the first level package are usually epoxy、sliver paste and solder paste, their thermal conductivity is not sufficient to dissipate the heat to the environment. We proposed a new composite die attach material for LED packaging. This composite die attach material is prepared by adding proper amounts of diamond particles into commercial Sn-3wt.%Ag-0.5wt.%Cu (SAC305) solder paste. Since diamond is a highly heat conductive material with an excellent heat conductivity of 2000 W/mk, its incorporation into the SAC305 solder paste (~ 20 W/mk) can promote greatly the heat conductive capacity of the die attach materials and thereby dissipates heat more effectively. From the results of infrared image and thermal resistance analysis confirm that the composite solder is useful in promoting the heat conductivity of die attach layer and dissipating heat more effectively. Interfacial reactions in the LED solder joints were also investigated. The thin Au wetting layer in the chip backside metallization was rapidly consumed in the initial stage of reflow, forming an AuSn4 phase at the interface. Subsequently, the AuSn4 phase detached from the interface, leading to dewetting of the SAC305 solder with the LED chip. In order to avoid dewetting, either a new backside metallization of LED chips should be developed for SAC305 solder. After solid-state aging for 1 day to 20 days at 150oC, the AuSn4 phase at the chip side do not detach from the interface, because 150oC is lower than the melting point, the AuSn4 phase doesn’t dissolve into the molten solder, so the results are not consistent with the liquid-state reaction. It’s not useful to restrain the detachment by electroplating Ni layer on the metallization of heat sink, when rising the reflow time, the (Au,Ni)Sn4 phase migrate to the (Ni,Cu)3Sn4 layer severely, the presence of a layer of brittle (Au,Ni)Sn4 at the interface severely weakens the solder joints.
其他識別: U0005-2707201012005900
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