Parameter Extraction Of Cauer Model Of IGBT Module Based On Dynamic Thermal Boundary And Bonding Line Aging Monitoring Method

Insulated Gate Bipolar Transistor（IGBT）is a combination of Bipolar Junction Transistor（BJT）and Metal Oxide Semiconductor Field Effect Transistor（MOSFET）.Because of its high input impedance,low saturation voltage drop and low driving power,it is widely used in photovoltaic power generation,wind power generation,electric vehicles,electric traction and other fields.Due to the increasing demand for power density in practical applications,IGBT modules need to face a more P_lossoperating environment.Therefore,as the core device of power converter,the reliability of IGBT has been paid more and more attention by researchers.Research shows that about 60%of power device failures are due to increased thermal resistance or additional P_lossinduced junction temperature rise.However,since the IGBT module has a multi-layer structure,obtaining junction temperature is a complex task.The main failure modes of IGBT module caused by junction temperature fluctuation are bond wire failure and solder layer failure.In the IGBT module with aluminum bonding wire process,the module damage caused by bond wire failure accounts for about 70%,so the failure analysis is more focused on bond wire.This paper takes IGBT module as the research object,and based on the traditional Cauer model,through theoretical and experimental analysis,studies the junction temperature estimation method of IGBT module under variable working conditions and during heating up process,and analyses the aging of bond wires caused by junction temperature fluctuation.The specific research is as follows:（1）A method for extracting the parameters of the Cauer model using the dynamic thermal diffusion boundary is proposed.First,a number of grating fiber temperature sensors are reasonably arranged with appropriate gaps on the baseplate.According to the law,a reasonable initial isotherm is selected as the thermal diffusion boundary,and the selected isotherm is tracked in real time.The law of its change with different working conditions is analyzed to obtain the accurate value of the circular heat conduction area under different working conditions.Furthermore,the accurate thermal resistance and heat capacity are calculated online according to the thermal conductivity area under the current working condition.Finally,the Cauer model is modified by using the real-time updated thermal resistance and heat capacity values to obtain more accurate junction temperature（2）The method of heat migration based on temperature distribution coefficient and the position of bond wire falling off is proposed.Firstly,the temperature distribution coefficient k in the healthy state was determined by using the grating fiber temperature sensor to capture the temperature at the bottom,middle position and the edge of the base plate in a fixed position.Then,the FEM was used to analyze the heat source migration caused by different numbers and positions of bond wire falling off,and the law between temperature distribution coefficient k and heat source migration was explored.Finally,an experimental platform was built to verify the law of heat source migration and temperature distribution coefficient k,and the specific bond wire drop position was determined according to the value and change of temperature distribution coefficient k on both sides of the IGBT module.（3）The equivalent equivalent resistance analysis method considering temperature distribution coefficient is proposed.Firstly,the temperature distribution coefficient k is determined by capturing the temperature measurement points at the bottom of the chip,at 45°diffusion angle and at the edge of the baseplate using the grating optical fiber temperature sensor.The value changes with the aging of the solder layer,but is not affected by the P_loss.Then,based on the principle of temperature distribution coefficient k,the formula is deduced and the V_cevalue of IGBT module is iterated inversely according to the temperature measurement point,which is divided into two parts,which change with temperature and aging of bond wire.Finally,according to the IGBT output characteristic in the data manual,the change of Vce caused by aging of bondwire is determined,and the change of equivalent resistance of bondwire is determined by the current working condition electrical parameters.