- 學位論文
使用全域-局部有限單元法於電力模組功率循環測試之熱傳分析與可靠度評估
Thermal Analysis and Reliability Assessment of Power Module under Power Cycling Test Using Global- Local Finite Element Method
摘要
絕緣雙柵極電晶體(Insulated Gate Bipolar Transistor, IGBT)功率模組因高切換速度與低導通損失等特性，目前已廣泛應用於電力模組上。而IGBT功率模組於實際操作下將承受往復之電流負載，如此會造成晶片的接面溫度大幅地變化，加上材料間熱膨脹係數(Coefficient of Thermal Expansion, CTE)的不匹配，導致功率模組有熱應力產生，此熱應力乃為焊錫接點(Solder Joint)及鋁導線(Wire Bonding)與晶片之接合面發生損壞的主要因素，並影響其長時間運作下的可靠度。 本研究依據實際樣本建立三維有限單元模型，為了減少計算時間且提升研究效率，使用多點約束(Multi-Point Constraints, MPC)有限單元法進行暫態熱-結構直接耦合模擬分析，藉由模擬方法得到功率模組於功率試驗中之溫度分佈，以及循環之溫度變化下所產生的應力與應變分佈情形。由模擬結果發現，在電流負載為40安培下，晶片最大接面溫度發生於晶片中心處，其值約為112.5 ˚C。本熱傳模擬結果與實際功率循環試驗所量測之溫度分佈符合，說明本研究之多點約束暫態熱-結構直接耦合分析模型具一定之可行性。對於功率模組進行力學行為分析，發現IGBT功率模組在承受往復之溫度變化時，因材料間熱膨脹係數不匹配，導致鋁導線與晶片界面呈現熱應力集中現象，因此導線在晶片界面的結構強度相對較弱。根據文獻所提之壽命預估模型，進行鋁導線之可靠度評估，探討功率循環試驗中熱應力與熱應變對於功率模組可靠度之影響。
並列摘要
An insulated gate bipolar transistor (IGBT) power module has acquired fast switching and low conduction loss characteristics. Because of its electrical characteristic, the IGBT has been widely applied in power supplies, e.g. hybrid electric vehicle, wind power generation, etc. However, the IGBT during rapid transient operation under high power can cause the IGBT chip to lead high junction temperature and high temperature gradients. Furthermore, because of the coefficient of thermal expansion (CTE) mismatch between the various material layers, the bonding wire and the solder are subjected to thermo-mechanical stress which cause solder fatigue and bonding wire failure, and affect the reliability of IGBT under actual operation conditions. A 3-D finite element (FE) model was established base on real test samples. In order to reduce calculation time and increase the research efficiency, multi-point constraints (MPC) method were used to simulate and direct-field coupling thermal-structural FE analysis were conducted to analyze the temperature distribution of IGBT and the mechanical behavior of bonding wire under cyclic power cycling test. The simulation results found that the maximum junction temperature 112.5 ˚C was observed at the middle of IGBT chip under the load current of 40 A. The predicted temperature history and experiment results under the cyclic current load were identical, which indicates the reliability of direct-field coupling thermal-structural FE analysis. Then analyze the mechanical behavior of IGBT, the structural simulation results showed that under a cyclic power environment, the stress concentration within the wire, caused by the CTE mismatch between the wire and the IGBT chip. Therefore, the bonding interface between the bonding wire and chip are the weaker portion of the power module. Finally, according to the life prediction models of literatures, this paper assessed the reliability of bonding wire in order to investigate the effects of thermal stress and strain on reliability during power cycling test.