| Press-pack insulated gate bipolar transistor(PP-IGBT)device has the advantages of double-sided heat dissipation,easy large-scale multi-chip parallel connection,easy series connection,and short-circuit failure mode.It is the core component urgently needed for the development of high-voltage and large-capacity flexible DC transmission equipment.The reliability of the PP-IGBT directly affects the safe and stable operation of power equipment and transmission systems.High power PP-IGBT device are usually composed of dozens of IGBT submodules and FRD submodules in parallel.The multicomponent stacking and multi-chip parallel packaging structure inside the device is difficult to achieve the balanced distribution of heat and force of each chip.The uneven thermal-mechanical distribution can lead to mechanical damage or thermal breakdown of some chips in the device,eventually causing the entire device to fail.Therefore,accurate measurement and optimization of thermal-mechanical distribution of PP-IGBT device is the basis for device condition monitoring and reliability optimization.However,the compact parallel packaging of high-power PP-IGBT devices lead to serious electricalthermal-mechanical multi-field coupling between multiple chips and the stacking structure of components makes the surface of the chip electrodes tightly covered.The intrusive measurement and stress optimization methods of conventional wire-bonding IGBT device are difficult to apply to the multi-chip parallel packaging structure of PPIGBT device.It is difficult to support the recognition of the multi-physics coupling mechanism and stress balance control of the PP-IGBT device,and it is urgent to carry out the research on the non-invasive measurement and stress optimization method of the thermal-mechanical distribution of the PP-IGBT device.Aiming at the problems of thermal-mechanical distribution measurement and stress optimization of PP-IGBT device,based on the multi-chip parallel packaging structure of domestic PP-IGBT device,with measurement-modeling-optimization as the main line,the non-invasive measurement method of internal contact pressure and junction temperature distribution of PP-IGBT device,multi-physics model reconstruction and stress influence analysis,and optimization method thermal stress distribution of device are carried out.The main contents of the paper include:(1)Aiming at the problem that the measurement of the internal contact pressure distribution of PP-IGBT device often needs to destroy or change the device package structure,resulting in insufficient measurement accuracy,a method for measuring the contact pressure distribution of PP-IGBT device based on the ultrasonic reflection coefficient method is proposed.Firstly,based on the multi-chip parallel packaging and fixture structure of the PP-IGBT device,an integrated testing scheme of the ultrasonic probe for device contact pressure measurement is proposed and the influence of the elastic probe integrated testing scheme on the internal contact pressure distribution of the device is analyzed.Secondly,a calibration method of ultrasonic reflection coefficient for contact pressure measurement of the device is proposed,and the relationship between the ultrasonic reflection coefficient and the contact pressure is obtained.Finally,an ultrasonic measurement system for contact pressure distribution of PP-IGBT device is established,and the effectiveness of the proposed ultrasonic measurement method is verified by using the quantification method of stress-sensitive films.(2)Aiming at the problem that the multi-component stack structure of the PP-IGBT device makes it difficult to implement the contact temperature measurement method,and the temperature-sensitive electrical parameter method is limited by the lack of multi-chip electrical parameter measurement methods.It is difficult to directly measure the junction temperature distribution of the device.A method for measuring the junction temperature distribution of devices based on temperature-sensitive force parameters is proposed.Firstly,by analyzing the internal thermo-mechanical coupling mechanism of the PP-IGBT device,the coupling relationship between the dynamic contact force and the junction temperature change inside the device is deduced and calibrated.Secondly,considering the influence of the device surface temperature change on the ultrasonic measurement,a coupled interface wave feedback method is used to obtain the fluctuation of the contact force inside the device under the working conditions.Finally,the effectiveness of the proposed junction temperature distribution measurement method is verified by the infrared measurement experiment of the junction temperature distribution of the PP-IGBT device.(3)Aiming at the problem of inaccurate calculation due to the dependence of the electrical contact characteristics on empirical models and three-dimensional modeling only considers ideal tolerance conditions in the existing multiphysics coupling modeling of PP-IGBT device,a multiphysics model reconstruction method of the PP-IGBT device that takes into account electrical contact characteristics is proposed.Firstly,an electrical contact resistance mathematical model is established that considers the material resistivity,contact pressure,roughness and microhardness parameters.The electrical contact resistance model parameters are selected by analyzing the surface characteristics of the material and the validity of the contact resistance model is indirectly verified through the device on-resistance measurement experiment.Secondly,considering the influence of the height tolerance of the device sub-module on the contact pressure distribution,a threedimensional model reconstruction method of the PP-IGBT device based on the estimation of the height tolerance of the sub-module is proposed and the multi-physics model of the device is accurately established.Finally,the internal stress distribution law and its influencing factors of the multi-chip device were obtained by the multi-physics coupling finite element simulation.(4)Aiming at the problem of uneven temperature distribution inside the device due to the inconsistency of the internal contact parameters of the PP-IGBT device,an optimization method for the temperature distribution of the PP-IGBT device based on liquid metal material is proposed.Firstly,considering the fluidity of liquid metal materials at high temperature,it is proposed to use thermal spraying technology to control the thickness of the liquid metal coating.Secondly,a package integration scheme of liquid metal materials based on the step-by-step pressurization method is proposed.The optimization effect of the package integration scheme on the internal temperature distribution of the device is analyzed by finite element simulation.Finally,through the steady-state thermal resistance measurement experiment and reliability test experiment of the PP-IGBT device,the effectiveness of the internal temperature optimization method of the device is verified.The research results of this paper can lay a foundation for the performance evaluation of the multi-chip parallel packaging of PP-IGBT device,and provide support for the optimization of the packaging design of PP-IGBT device. |
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