Press Pack IGBT Failure Analysis

Power electronic devices have been widely used in the field of DC transmission,grid connection of new energy sources and charging of electric vehicles.At present,the Press Pack IGBT has been used in HVDC,but its failure process and mechanism still need to be studied.Although IGBT press-pack reliability is a hot topic,the researches on its failure mechanisms and are very limited published data and information.In this research work firstly the state of the art of press-pack IGBT possible failure mechanisms will be introduced and discussed in order to give a strong background for the researchers about it and to give a better understanding of the physics of failure of press pack IGBT.Then three cases of simulating press-pack IGBT using COMSOL Multiphysics commercial software are presented with time changing to analyze a possible failure cases to help in optimizing and improving the design.The first case is 2D model simulating a real failure scenario,that when a high electrical and thermo mechanical stresses are applied to IGBT sub-module until it fails.This case uses electric field distribution,temperature distribution and mechanical displacement to show the places which are subjected to the stresses more than the other places;which shows the weak points in the design and lead to complete failure.Also it shows the mechanical deformation and the level of the stress clearly.Afterwards,the second case takes a tiny(?m scale)cubic cross sectional area from silicon and polyimide layers and assumes availability of spherical shaped air gap(or any kind of gases)is located between these layers at the polyimide layer.Then high stresses are applied to this tiny spheroid using simplified 2D model and the results are analyzed to see the effects of finding an air gaps or gas spots at the polyimide layer as a result of improper manufacturing.Finally,the third case studies the effect of partial contact loss between different layers and it is effects on the press pack IGBT failure.Also this case compares briefly between the different locations which have partial contact.Through the above research,this paper reveals the mechanism and development process of common failures in IGBT,and analyzes the influence of different factors.