Failure Modeling And Analysis Of SiC MOSFET Module Based On Multi Physical Field Coupling

As the core component of high-power system converter devices,such as rail traction,mine hoisting,wind power generation,aerospace and so on,the safe and reliable operation of power module is not only related to the orderly progress of national production and life,but also an important support to promote the green development of society.During the working process,the module is impacted by temperature and stress repeatedly.Due to the cumulative effect of fatigue aging,the material damage in each layer of the device is gradually aggravated,and the performance index is deteriorating,which seriously threatens the stable and reliable operation of the system.Chip solder layer fatigue failure is one of the most common failure modes of power module.Effective solder layer failure identification method is particularly important to ensure the reliable operation of the system.Therefore,understanding the failure mechanism of chip solder layer,mastering the evolution process of module fatigue aging,finding an accurate and appropriate health assessment strategy and guiding the maintenance plan can greatly reduce the system failure rate and prolong the actual service life of the equipment,which is a generally accepted method to enhance the system reliability in the academic and industrial circles.This thesis focuses on the research of solder layer failure of SiC MOSFET module,analyzes its failure mechanism by using the multi physical field coupling theory,establishes a three-dimensional model of multi physical field,simulates the change rule of module electro thermal characteristic parameters under different failure forms,and puts forward a method of chip solder layer failure identification based on the change rate of on resistance.Firstly,the electrical characteristics of SiC MOSFET are analyzed,the similarities and differences between SiC MOSFET and Si IGBT are pointed out,and the switching transient process and loss calculation method of SiC MOSFET are introduced theoretically.Then the thermodynamic characteristics of the module are analyzed.According to the heat transfer mechanism,the heat transfer path inside the module and the heat exchange mode between the module and the outside are explained.According to the theory of material mechanics,the equilibrium equation of stress and strain of each layer of material is given.The failure mechanism of power devices is explored based on the thermodynamic properties of multilayer packaging materials.Based on COMSOL multiphysics simulation software,the electrical thermal mechanical coupling model of SiC MOSFET module is built.The response characteristics of SiC chip to temperature and current and the mechanical viscoplasticity of solder layer material are fully considered.The measured curves of on resistance versus current and junction temperature are imported into the three-dimensional finite element model to improve the accuracy of model parameters.Then the three-phase two-level inverter circuit model of the module is built to simulate the loss and junction temperature of the device in the actual operation.The effectiveness of the three-dimensional finite element model is further verified by calculating the on resistance under different working conditions.Finally,the multi field coupling model is set with boundary conditions and given periodic load,and the fatigue damage mechanism of chip solder layer under power cycle is mainly studied.It is pointed out that the fatigue failure of solder layer is the result of long-term cyclic action of periodic temperature and thermal stress.The change of characteristic parameters of SiC MOSFET module in the failure modes of solder layer cavity,fatigue stratification and bonding line falling off are studied.The relationship between the conduction resistance and the thermal resistance of the shell is analyzed quantitatively in different failure modes.Finally,SiC Based on the change rate of the conduction resistance is proposed The method of solder layer failure evaluation of MOSFET chip has high engineering application value.Combined with theoretical analysis,simulation and experimental measurement,the effectiveness of this method is demonstrated,and a new idea for online monitoring of module health status is provided.