溫度負載形式對功率模組之可靠度影響評估

Reliability assessment of the temperature profiles effect on the power module

黃湘珺(Hsiang-Chun Huang)

指導教授 ： 江國寧

國立清華大學/工學院/動力機械工程學系/碩士(2013年)

摘要

隨著半導體製程的改善，功率元件(Power Device)擁有低轉換損耗及低傳導損耗的特性，因上述特性使絕緣柵雙極性電晶體(Insulated gate bipolar transistor, IGBT)被廣泛應用於功率模組(Power Module)中。當功率模組承受循環溫度負載時，材料的熱膨脹係數不匹配造成熱應力產生，導致材料介面間疲勞。根據不同的操作需求，模組將承受不同的溫度曲線條件。不同的持溫時間和升降溫速率導致不同的應力釋放，最終影響功率模組之可靠度。
　　本研究依據實際樣本建立二維有限元素模型。此模型透過承受-40到125°C的熱循環以探討持溫時間及升降溫速率對於焊料合金潛變行為之影響。結果顯示由於應力釋放，持溫時間會造成潛變應變的累積，尤其是持溫於高溫段會導致更顯著的應力釋放。比較持溫段與升降溫的過程，在一次熱循環中，升降溫過程累積的潛變應變比持溫階段明顯。關於升降溫速率的探討，升降溫速率越慢會使越多的潛變應變累積，而造成可靠度下降。
　　本研究提出潛變應變為物理量之壽命預估模型，即類Darveaux經驗式。藉由三維有限元素模型計算得到之潛變應變搭配實驗結果建立此壽命預估模型。最後，由定義之臨界裂紋長度得到錫銀焊料合金之總壽命值。結果顯示當熱循環的週期越長，功率模組所受之損傷會越嚴重。

關鍵字

功率模組 ； 潛變 ； 升降溫速率 ； 持溫時間 ； Darveaux 壽命預估模型 ； 裂紋長度 ； 溫度循環

並列摘要

Power devices have possessed low switching and conduction loss characteristics with the improvement in semiconductor device manufacturing. Insulated gate bipolar transistors have been widely used in power module because of such characteristics. When the power module is subjected to the cyclic temperature load, the thermal stress resulting from the mismatch between the coefficients of thermal expansion (CTE) of materials causes the interface of the materials to fatigue. According to the different operating requirements, the module is under different temperature profiles. Different dwell times and ramp rates produce different stress relaxation, which eventually affect the reliability of the power module.
　　A two-dimensional finite-element model was established based on real sample. The models were subjected to thermal cycling between -40 and 125 °C to discuss the effect of the dwell time and the ramp rate on the creep behavior of the solder. The results indicated that the dwell time brings accumulative creep strain due to stress relaxation; furthermore, dwell time at the high temperature segment leads to more evident stress relaxation. Compared dwell phase with ramp section, ramp section brings more significant accumulative creep strain than dwell phase in one thermal cycle. About the discussion of ramp rate, decreasing the ramp rate causes more creep strain, and deteriorates the reliability.
　　A creep strain-based life prediction model, i.e. Darveaux-like equation, was proposed in this study. The creep strain was calculated by a three-dimensional finite element model, together with the experimental results, to establish the life prediction model. Finally, the critical crack length was determined to obtain the total life of Sn96.5Ag3.5 solder. The result indicated the longer the period of thermal cycling is, the more damage the power module accumulates.

並列關鍵字

power module ； creep ； ramp rate ； dwell time ； Darveaux life prediction model ； crack length ； thermal cycling

參考文獻

[1] M. Ciappa, “Selected failure mechanisms of modern power modules,” Microelectronics Reliability, Vol. 42, Issue 4-5, pp. 653-667, 2002.

[2] Y. Hua, L. Minghui, and C. Basaran, “Failure modes and FEM analysis of power electronic packaging,” Finite Elements in Analysis and Design, Vol. 38, Issue 7, pp. 601-612, 2002.

[3] J. M. Thebaud, E. Woirgard, C. Zardini, S. Azzopardi, O. Briat, and J. M. Vinassa, “Strategy for designing accelerated aging tests to evaluate IGBT power modules lifetime in real operation mode,” IEEE Transactions on Components and Packaging Technologies, Vol. 26, Issue 2, pp. 429-438, 2003.

[4] M. Bouarroudj, Z. Khatir, S. Lefebvre, and L. Dupont, “Thermo-mechanical investigation on the effects of the solder meniscus design in solder joint lifetime for power electronic device,” International Conference on Thermal, Mechanical and Multi-Physics Simulation Experiments in Microelectronics and Micro-System, pp. 409-415, London, UK, Apr. 16-18, 2007.

[5] M. Bouarroudj, Z. Khatir, S. Lefebvre, L. Dupont, J. P. Ousten, and F. Badel, “Comparison of stress distributions and failure modes during thermal cycling and power cycling on high power IGBT modules,” European Conference on Power Electronics and Applications, pp. 1-10, Aalborg, Denmark, Sep. 2-5, 2007.