Fatigue Failure Mechanism And Life Evaluation Of Converter Power Device

High-power converters are increasingly used in new energy power generation,electric vehicles,high-voltage DC transmission,aerospace and other fields.In these high-reliability applications,the requirements for the reliability of high-power converters are also increasing.However,the reliability of high-power converters is not high.The main reason is that the high-power devices in the high-power converter are very easy to fail.As one of the commonly used components of large converters,IGBT modules are closely related to the reliability of converters.Carrying out IGBT failure analysis is helpful to improve the reliability of the converter.The bonding wire and the solder layer are the weak points in the IGBT module structure.Cracks and voids will appear under the stress impact,and gradually expand to cause module failure.According to the analysis of the failure mechanism of IGBT module,the module life prediction research was carried out in this thesis.The main research contents wre as follows:(1)The fatigue failure mechanism of bonding wire was studied.By establishing an electric-thermal-mechanical multiphysics coupling model of IGBT module bonding wires,the failure mode and mechanism of bond wire shedding and breaking were studied,and It was pointed out that the shear stress caused by the mismatch of the thermal expansion coefficients was the main reason for the failure of the bonding wire.Then the quantitative analyzed of the influence of the evolution of the crack and shedding of the bonding wire on the temperature,stress and equivalent resistance of the IGBT module.Cracks have a greater influence on the bond equivalent resistance.An evaluation method of the bond wire damage degree using the bond wire equivalent resistance was proposed.(2)The void failure mechanism of the solder layer was studied.Through the establishment of a multi-physics coupling simulation model and aging test of the solder layer,the effect of the size,location and distribution of the solder layer cavity on the junction temperature and stress of the module was studied;a solder layer cavity growth model was proposed,and the Cauer thermal network model and parameter update method were used,Accurately calculated the junction temperature of IGBT module under different aging degree of solder layer.The evaluation method of the aging degree of the solder layer using the thermal resistance of the module was given.Using power cycle aging equipment,ultrasonic testing device and junction temperature test platform to verify the research content.(3)The thermal safety and life assessment of photovoltaic power devices considering the aging effect of holes were studied.Taking the photovoltaic converter as the background,using the improved Cauer thermal network model and the nonlinear update method of the Cauer thermal network parameters considering the aging of the solder layer,combined with the actual light intensity and air temperature,an IGBT module junction temperature simulation model considering the aging effect was established to improve The accuracy of the junction temperature calculation.Taking the winter and summer data of a place in the southern hemisphere as an example,the model was used to evaluate the thermal safety of the converter power module under different aging degrees,and then the life of the converter power module was predicted.The results of the prediction methods were compared to verify the validity of the life prediction model proposed in this thesis.