Thermal Fatigue Life Prediction Of IGBT Based On Structure Function

Insulated Gate Bipolar Transistor(IGBT)IGBTs usually operate under high voltage and high current conditions.It will be subject to heat and power shocks,causing thermal fatigue.Its storage environment,high and low temperature changes cause thermal expansion and contraction of the device structure and also lead to fatigue problems.This thermal fatigue problem can lead to the degradation of thermal and electrical parameters,and even the device failure.the entire equipment and system reliability is seriously affected.For the thermal parameters,thermal resistance is the important indexes to identify the thermal characteristics of the device.Structure function curve based on the thermal resistance measurement of the device can reflect the entire distribution of device internal thermal resistance and heat capacity.The mainstream equipment for testing and analyzing the thermal resistance of the device is Phase11 from the United States and T3Ster from Hungary.Temperature cycling test is a necessary way of assessing the thermal reliability of the device.Therefore,this paper studies the thermal resistance structural function and thermal fatigue reliability.The research project of this paper is IGBT.Based on the structure function algorithm,this paper analyzes the thermal characteristics and lifetime of object by software development,finite element analysis and temperature cycling thermal fatigue test.The main contents are as follows:1.Research and implementation of structure function algorithm,and verify the results.The structure function algorithm mainly includes the extraction of time constant spectrum and the conversion of network model.Use Bayesian iterative algorithm to achieve constant spectral extraction,pass points and remove the algorithm to achieve the network model conversion.This paper uses self-designed high-precision data types to optimize the network model conversion,achieves unlimited precision network conversion.The effective bits are greater than the double data type.Complete the design of structural function analysis software by C#language,including interface design,database module,algorithm analysis,graphics rendering and so on.The results are verified by the equivalent circuit method,the simulation model and the actual sampling result method.2.Finite element heat and thermal simulation.Using ANSYS finite element analysis software,the three-dimensional thermal model of IGBT is established,and the transient simulation is carried out by controlling the simulation step and time.The simulation results are taken as the input of the structural function analysis software to analyze the thermal resistance of each structure layer in the simulation model.By adjusting the structure layer size,parameters and the existence of void and other settings,combined the structural function curve under the different states,this paper analyzes IGBT thermal characteristics.Secondly,the IGBT three-dimensional thermal model is established to carry out temperature cycle simulation of different temperature ranges.The results show that the edge interface of the solder layer between the chip and the copper substrate is the most stress,and the fatigue is most severe.According to the simulation results,the number of failure cycles in different temperature ranges is estimated,and the parameters of the life model are fitted to predict the life of the device under actual storage conditions.3.Use the high and low temperature cycle test chamber to complete the-40~oC-125~oC temperature cycle test.Combined with Tektronix370,Keithley4200semiconductor parameter tester and thermal resistance tester,the measured device parameters are measured.The microstructures were examined by ultrasonic scanning microscopy and X-Ray as the auxiliary method.The results of temperature test were observed and analyzed.Using the structural function curve,the thermal resistance change before and after the test is analyzed.Based on the experimental data,the number of failure cycles of the device is fitted and the fatigue life of the device is estimated.