- 學位論文
以ALE法應用於LED打線接合製程之模擬分析研究
Research on Analysis of LED Wire Bonding Process Using Arbitrary Lagrangian-Eulerian Method
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摘要
發光二極體是一種發光的半導體元件，在日常生活中已被廣泛的運用在不同的照明設備上，其中打線接合為發光二極體之重要製程，用以導通內部之電訊。熱超音波打線接合是最常被使用在發光二極體上的接合方式，其過程為一複雜之物理行為，大致可以分為衝擊階段、超音波震動階段和拉伸階段。在接合過程中常見的破壞模式有墊片剝落、破裂、脫層等，這些破壞都會影響發光二極體電訊的傳遞。因此如何有效預估打線接合時之應力，對其結構破壞之改善是一重要的課題。 打線過程中，衝擊階段以夾具擠壓自由球體，而球體相對夾具為相當軟的材料，球體在受擠壓拉扯後造成結構大變形，並與晶片結構區之墊片產生接觸。以有限元素模擬時，大變形行為容易造成網格嚴重扭曲變形，使得計算之精確性與收斂性出現問題，嚴重時甚至會造成數值分析計算發生終止的情形，為了防止這樣的問題發生，許多研究裡會採取減少夾具之下移量，或是在自由球體部分網格進行加密之動作以確保模擬分析之品質。然而，下移量不足可能造成模擬結果失真，加密的結果會使計算時間拉長，但其網格嚴重變形之情形依舊無法解決。 本研究將以商用有限元素軟體ANSYS®/LS-DYNA建立外顯式處理法之有限元素模型，使用二階精度之ALE座標描述法及不同的網格平滑演算法進行網格重新劃分，用以解決大變形行為時網格扭曲之問題。在研究最終，藉由使用ALE及平衡網格平滑演算法，建立出有效的外顯式處理法之有限元素模型，並在衝擊結束時，其模擬結果之幾何外型與實際製程結果外型相符，且應力集中位置與實際樣品破壞位置相同。總而言之，此模擬方法有效的解決以有限元素法模擬打線過程時，夾具下壓不足及網格嚴重變形之問題。
並列摘要
Light emitting diode (LED), which has widely applied in different illuminations, is a kind of luminous semiconductor devices. Wire bonding is one of the main processes used for connecting the signal of chip. Thermosonic bonding is often applied in the LED wire bonding process, and it’s a multi-physic process including impact stage, ultrasonic vibration stage, and lift off stage. The failures of LED such as pad peeling, cracking, and delamination might influence the power connecting of chip. In a word, predicting and analyzing the failure of LED chip during wire bonding process is an important issue. In the impact stage of wire bonding process, the material property of free air ball (FAB) is much softer than capillary, which compresses the FAB to land on pad. Thus, a large deformation phenomenon comes out on FAB during wire bonding process. Due to the large deformation problem, it’s easy to have element distortion issue on FAB while executing simulation work of wire bonding process. To avoid the divergent problem of finite element (FE) analysis, many researches reduce the compression distance of capillary on their contact simulation or increase mesh density. However, reducing distance would lack fidelity, and increasing mesh density would take more time in calculation. The element distortion issue still cannot be solved. This research will construct FE models to discuss the element distortion issue using commercial software ANSYS®/LS-DYNA with explicit method and utilize 2nd level accuracy arbitrary Lagrangian-Eulerian algorithm, and ALE method with different mesh smoothing algorithms to solve the element distortion problem. In the end of research, utilizing ALE method with equilibrium mesh smoothing algorithm demonstrates better element quality with excellent geometry prediction in impact stage of bonding process. In summary, this simulation method not only conquers the element distortion problem and lack of capillary displacement problem, but proposed an effective methodology for simulating wire bonding process. It is believed the stress/strain history and contact force will give better accuracy than other mesh smoothing algorithms or non-ALE methods.
參考文獻
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