Research On The Temperature Distribution And Coupling Characteristics Within Press Pack IGBT Device

With the advantages of easy series connection,failure short circuit,and high power density,press pack IGBT(Insulated Gate Bipolar Transistor)has become the key device in high voltage direct current(HVDC).Multiple chips are parallel connected within PP IGBTs(press pack IGBTs)to obtain a higher current rating and the external clamping force is applied on the device to ensure electrical and thermal contact.Compared with traditional IGBT modules,the coupling relationship within PP IGBTs is more complex because of the introduction of the external clamping force.Hence,unbalance pressure,temperature,and current occurs within PP IGBTs and lead to the reduction of the safe operation area and reliability problem.The compact and closed structure of PP IGBTs makes it very difficult to measure the pressure,temperature,or current distribution.The complex coupling relationships also lead to confusion about the coupling characteristics,which becomes one of the bottlenecks limiting the increase of power level and reliability.This paper mainly focuses on the measurement problem and also the coupling characteristics,and conducts an in-depth investigation of four aspects:junction temperature distribution measurement method of parallel chips,thermal network model of parallel chips and thermal resistance parameter extraction method,temperature field-stress field coupling characteristics,and pressure and control method of pressure distribution and temperature distribution.The work in this paper breakthrough the problems that the junction temperature distribution cannot be measured and coupling characteristics are not well understood,which provided the reference for the localization and design of press pack IGBT.Firstly,a series of methods for characterizing the junction temperature distribution and coupling characteristics of parallel chips are proposed.The sequential Vce(T)method is proposed for the junction temperature distribution within PP IGBTs.The junction temperature distribution is firstly measured and the influence of load current,turn-on time,and clamping force on the temperature distribution is revealed for rigid PP IGBTs and complaint PP IGBTs.The extraction method of the thermal step response for parallel chips is proposed and the coupling characteristics are investigated by the experimental method.The experimental evidence for the coupling effect of the temperature field-stress field is also observed.Besides,the asymmetric characteristics of the rise temperature curve and fall temperature curves of parallel FRD chips are observed,and the differences in the heat dissipation paths between the heating and cooling phases are characterized.The proposed method provides an experimental means for the evaluation of devices and the cognition of coupling characteristics in the process of localized independent development.Next,the thermal network model considering the spreading effect and the thermal coupling effect is proposed.The analytical extraction method of electrode thermal resistance is proposed comprehensively.From the perspective of the bounded space Green’s function method,the separation of variables method is applied and analytic formula for the thermal resistance parameters of square and circular electrodes is derived.From the perspective of the unbounded space Green’s function method,the determination method of the image source is proposed for the separable variable problem,and the scope of application of the image method is extended.Another set of analytical formulas for the thermal resistance parameters of square and circular electrodes is also derived through the image method.The accuracy of the analytical formula is verified by numerical examples and experimental measurements.The influence of chip position and spacing,convection heat transfer coefficient,electrode width,and electrode thickness on the self and mutual thermal resistance parameters is investigated,which provides a reference for the package design.Then,the temperature field-stress field coupling model is established for rigid PP IGBTs.The pressure and temperature distribution within the device are revealed,and the calculation results are verified by the junction temperature distribution measurement.The coupling characteristics between the temperature field and stress field are revealed deeply.The separation method for the influence of the electrode lateral and vertical temperature difference is proposed,and the electrode lateral temperature difference is found to be the key factor that leads to the temperature field-stress field coupling.The thermal-mechanical coupling circuit model is also established to reveal the influence of electrode lateral temperature difference on the force deviation and junction temperature deviation within PP IGBTs,which lay the foundation to improve the pressure and temperature distribution.Finally,the method to improve the pressure distribution for the clamping phase and the pressure and temperature distribution for the heating phase is proposed separately.For the clamping phase,the finite element model is established considering the plastic deformation,and the influence of plastic deformation on the pressure distribution is revealed.Then,the prestressed method is proposed to utilize plastic deformation as much as possible.For the heating phase,the uneven pressure and temperature distribution is found could be suppressed approximately only through the pure thermal design.The modification of the electrode diameter and the grouped layout could both decrease the lateral temperature difference and improve the uniformity of the pressure and temperature distribution.This paper fills the gap in the measurement of temperature distribution of parallel chips within PP IGBTs.The proposed measurement,calculation and regulation means provide support for the package design.