光學同調斷層掃描用於發光二極體封裝材料其熱膨脹係數測量之研究

Abstract

在本論文研究中，我們提出一個具有前瞻性的策略:利用光學同調斷層掃描技術來決定發光二極體封裝膠的熱膨脹係數。由於發光二極體的封裝膠與封裝材料的膨脹係數不匹配，在高電流注入情況下，晶片裡封裝膠嚴重的熱膨脹勢必會造成發光二極體元件的失效。因此一項能迅速且精確地評估發光二極體晶片封裝膠的熱膨脹係數技術是需要的。光學同調斷層掃描具有非侵入性、高速以及高解析的特性，以至於可以直接、未破壞性地透過光學同調斷層掃描系統重建二維和三維影像來評估發光二極體晶片封裝膠橫截面影像的高度變化。另一方面，通過順向電壓法與紅外線熱影像法可以得知注射電流與發光二極體溫度之間的重要關係。經過分析與比較，利用順向電壓法與紅外線熱影像法得到發光二極體晶片封裝膠（聚苯乙烯）之熱膨脹係數分別是16.5×10-5 /℃與51.64×10-5 /℃。這說明了利用順向電壓法得到發光二極體的溫度更接近晶片封裝膠的外在環境溫度，因此與之前文獻結果相比，我們提出的方法更能準確地評估晶片封裝膠的熱膨脹係數數值。最重要的是，我們相信我們提出的方法不僅可以提高發光二極體晶片封裝膠的熱膨脹係數數值的準確性，還能提供比傳統檢測器—熱機械分析儀具非破壞性且更有效率的檢測方法。In this study, we proposed a promising strategy by using the optical coherence tomography (OCT) technology to determine the coefficient of thermal expansion (CTE) for an encapsulant light-emitting diodes (LED) chip. Under a high current injection condition, a serious thermal expansion within the encapsulant LED chip, due mainly to the large CTE mismatch between epoxy glue and epitaxial materials, will inevitably cause a device failure. Therefore, an effective and accurate estimation of CTE for an encapsulant LED chip is required. The OCT has non-invasive, high-speed and high-resolution properties, so that a direct and undestroyed evaluation for the height variation of cross-sectional images of the encapsulant LED chip is feasible through the reconstructed two- and three-dimensional images of OCT system. On the other hand, the important correlation between the LED temperatures with injected currents is obtained through both forward-voltage dropping and infrared thermography methods. As a result, the CTE values of epoxy glue (polystyrene) are 16.5×10−5/℃ and 51.64×10−5/℃ for the OCT system associated with forward-voltage dropping and infrared thermography methods, respectively. It suggest the LED temperature derived by the forward-voltage dropping method is more closed to the atmosphere temperature of epoxy glue of LED chip, so that can provide a much accurate estimation of CTE value as compared to previously published results. Most importantly, we believe our proposed method can not only improve the accuracy to estimate the CTE value of encapsulant LED chips, but provide a non-destructive and efficient way over the traditional inspection method by the thermal mechanical analyzer.