Influence Of Field-limited Ring Structure On Device Insulation Performance In Press-pack IGBT

Press pack IGBT has gradually replaced bonded power module in the field of flexible DC power transmission that is constantly being promoted because of its advantages such as large current capacity,easy series connection,and short circuit failure mode.In such high voltage and power applications,the insulation measures in the IGBT device package is worthy of attention.Bonded power module is generally filled with silicon gel as an insulating medium,but some press pack IGBT packages are only filled with air which has low insulation strength,making the insulation problem within the package severe.The research object of this thesis has a low pass rate in the high temperature reverse bias experiment.To solve the problem,this thesis improves the packaging simulation model of westcode press pack IGBT sub module on the basis of predecessors,and introduces the semiconductor physical model of the terminal area in the silicon chip.Based on finite element simulation software,this thesis combines semiconductor physics with traditional electrostatic field,starting with the main voltage resistant structure: field limit ring,using Silvaco TCAD software to analyze the influence of the field limiting ring structure on the chip’s withstand voltage capability and the electric field on the interface between polyimide passivation layer and air.Then,the surface potential of the silicon chip calculated by TCAD is input into COMSOL electrostatic field as the first kind of boundary condition for further calculation.Finally,the electric field distribution in the press pack IGBT package is obtained,which provides some guidance for the insulation design of the device package.The research content of this thesis is the electric field simulation analysis of the chip terminal area structure and the sub module packaging structure of the press pack IGBT.Through Silvaco TCAD semiconductor simulation software,this thesis analyzes the mechanism of field limiting ring to enhance the withstand voltage capability and the influence of several variables of field limiting ring such as number,width,spacing and junction depth on the chip breakdown voltage.Based on this,a two-D model of the terminal area with 3300 V withstand voltage level is preliminarily established.In order to optimize the peak value of electric field intensity at the interface between polyimide layer and air on the chip surface,the parameters of field limiting ring were adjustedbased on the original model,and a better surface electric field distribution and high breakdown voltage are obtained.Then this thesis proves that it is reasonable to input TCAD calculation results into COMSOL.In this thesis,the COMSOL software is used to build the model of the press pack IGBT sub-module.The chip surface potential distribution obtained in TCAD is used as the first type of boundary condition to input COMSOL,and the electric field distribution inside the package is obtained at 3300 V and 4500 V voltage levels.this thesis points out four areas where the electric field is concentrated,namely the surface of the chip terminal area,the longitudinal and horizontal gap between the chip and the PEEK frame,and the gap between the silver sheet and the PEEK frame.And the above electric field concentration areas are optimized and analyzed.