Study Of IGBT Junction Temperature Model Considering Heat Flow Distribution And Fatigue Aging

Insulated Gate Bipolar Transistors(IGBTs)have become a core component of power conversion systems with the advantages of high power density,high efficiency,flexibility and ease of integration.However,IGBT modules are also one of the most fragile components in power converters and thermal stress is the main reason for IGBT modules to fail.Therefore,this paper mainly investigates the factors that lead to abnormal junction temperature of IGBT modules,and discusses the influence of chip solder layer aging,thermal grease aging and bond wire aging on the junction temperature.The related junction temperature model is established,and the accuracy of the model is verified by simulation and experiment.Firstly,this paper takes the IGBT module as the research object,establishes a finite element model,and analyses the junction temperature change pattern of the IGBT module when the chip solder layer has voids.It is found that when the void fraction increases from0% to 40%,the chip layer temperature difference increases from 9.591℃ to 109.86℃.Based on the heat flow law in the presence of solder layer voids,a thermal network model considering the solder layer voids was established.It is proved by finite element simulations and experiments that the proposed model not only has higher accuracy in junction temperature calculation compared with the traditional Cauer model,but also can accurately monitor the horizontal temperature difference of the chip layer.Secondly,there is a thermal coupling effect when the IGBT module works with multiple chips.In normal use,thermal grease is generally applied between the copper baseplate of the IGBT module and the heat sink to ensure heat dissipation efficiency.But as the thermal grease dries and pumps out,it affects the accuracy of the junction temperature calculation of the thermal coupling model.By studying the real heat transfer pattern of the IGBT module when the thermal grease ages,the heat transfer angle and heat transfer area of each layer of the material are corrected.A thermal coupling network model considering the ageing of the thermal grease is established,which can accurately correct the self and coupled thermal impedance.Experimental tests and finite element simulation results show that the error of the model in calculating the junction temperature is within 0.8℃ when the thermal grease is missing,which verifies the accuracy of the model.Finally,the aging of the bonding wires of the IGBT module is investigated.Based on the on-state voltage drop of the IGBT module,the effect of package resistance is eliminated by algebraic operation,and the temperature-sensitive parameter chip on-state resistance difference value which is not affected by bonding wires aging is proposed.Under high current loading,the temperature sensitivity of chip on-state resistance difference value and on-state voltage drop are 0.29%/°C and 0.12%/°C respectively,which showed a significant improvement in the temperature sensitivity of chip on-state resistance difference.It is demonstrated that the chip on-state resistance difference value has better junction temperature prediction capability than the on-state voltage drop and is not affected by the bond wires aging.