| The IGBT modules are semiconductor devices which achieve power transporting and energy converting. They are widely used in the hybrid electric vehicle, renewable energies, smart grids and transportation fields. The structure of an IGBT module consists of several layers which connected by solder alloy. Internal stress occurs in solder layer due to the thermal expansion mismatch between different layers when IGBT module under temperature variation. The thermal tress will lead to catastrophic burnout or secondary breakdown in IGBT module, ultimately resulting in the failure of whole module. Therefore, exploring failure mechanism and damage evaluation of solder layer in IGBT module have great significance in improving the reliability of the IGBT modules.Currently, many scholars have studied the failure process of the solder layer by surface detection or external electrical parameter analysis, while lacking of failure analysis from physical mechanism. Furthermore, on-line monitoring and life evaluation methods of IGBT modules are inaccurate while the effects of cumulative damage of the solder layer are neglected in research. Based on the above background, the failure mechanism and damage evaluation of the solder layer in an actual IGBT modules SKM50GB12T4 is carried out this paper, which combined with theoretical research, simulation analysis and aging experiment. The cumulative damage effect of the solder layer is considered in the paper, research results can be effectively applied to the reliability evaluation and on-line monitoring of the IGBT module.The main research contents of this paper are shown as follows:(1) In view of existing electro-thermal or thermal-structural models of IGBT module are difficult to analyze electrical, thermal and mechanical properties of IGBT module simultaneously, multi-physics coupling model considering visco-plastic effect of solder layer is established in this paper to analyze failure mechanism of IGBT module. Firstly, the equivalent Foster electro-thermal network model of IGBT module is established in MATLAB/Simulink. This model is used to calculate the power loss of the IGBT under rated current. Secondly, based on the software ANSYS 14.5, the full-scale finite element model of the IGBT module is established to achieve thermal-structure analysis. Finally, the failure process of die-attach solder layer under power cycling is presented in details based on Anand model of solder materials.(2) The input parameters of model are usually related to stress or strain values in present fatigue life model of the solder layer, so life estimation need the time consuming finite element analysis. On that point, a fatigue assessment model of the solder layer was proposed, which takes the junction temperature as the input parameters. Firstly, failure parameters are selected based on fatigue life model of solder layer. Then, the influence of swing of junction temperature, minimum junction temperature and cycle time of power cycling on life of solder layer is researched. Finally, the function between the junction temperature of the power cycling and the fatigue parameters of the solder layer is obtained based on simulation data.(3) The initiation and propagation of crack is one of the important failure modes in the solder layer, however, it is usually ignored when analyze the reliability of IGBT module. Aiming at this problem, a method for evaluating thermal fatigue of solder layer considering crack damage was proposed. Firstly, a cracked IGBT module is established in ANSYS to analyze the characteristics of temperature and stress field in solder layer. Secondly, the correlation between crack length and the thermal resistance of IGBT module is investigated. Then, A fatigue assessment model considering the damage influence is proposed by comparing the failure mechanism of the cracked module to the new module. Finally, the simulation results are verified qualitatively through the aging experiment. |
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