Research On Measurement Method Of Temperature Distribution Characteristics On The Chip In Power Cycling Test

Power semiconductor devices are the core devices of various power electronic equipment,which realize the high-efficiency operation of electrified systems.With the rapid development of power electronics technology,various power electronics industries have put forward higher requirements for the reliability of power semiconductor devices.The power cycling test can expose the weak points of the device package in advance by simulating the junction temperature swing in the actual application of the device,and it is considered to be the most important test to assess the reliability of the device package.In the power cycling test,the junction temperature is a very important experimental parameter,and the accurate junction temperature measurement is of great significance to ensure the accuracy and fairness of the test results.However,with the continuous development of modern power devices in the direction of high voltage level and high power density,the temperature distribution in the chip is not uniform,showing a significant temperature gradient,which poses a serious challenge to the reliability of power devices and brings a series of problems to reliability research.Compared with a single junction temperature,obtaining chip temperature distribution characteristics can provide more information for reliability analysis of power devices.Therefore,in this paper,the thermal characteristics of the chip will be characterized from the perspective of field analysis,and the experimental measurement method of chip temperature distribution characteristics is carried out in power cycling test,which lays the measurement foundation for the development of new reliability analysis theory and the establishment of physical lifetime model.Firstly,the calibration method of high-voltage and high-power devices is studied,which lays a foundation for the subsequent junction temperature measurement using the thermosensitive electrical parameter method.In terms of calibration data acquisition,the different influencing factors of the nonlinearity of the calibration curve are theoretically analyzed,the mechanism of the nonlinearity of the calibration curve in the high temperature region caused by the resistance of the base region of the high-voltage device is revealed,and a new method for collecting data over the full temperature range and performing polynomial fitting is proposed.In terms of calibration equipment,the solution idea of replacing heat convection with heat conduction and distributed heat source instead of centralized heat source is proposed,and a constant temperature equipment based on electromagnetic heating is designed.Compared with traditional oven and resistance heating plate,the calibration efficiency and accuracy are greatly improved,and the calibration cost and difficulty are reduced.In particular,combined with the package structure characteristics of double-sided heat dissipation devices,a constant temperature equipment with double-sided heating is proposed,and the effectiveness and accuracy of the method are confirmed by finite element simulation analysis and experimental verification.Secondly,the realization methods of different thermo-sensitive electrical parameter methods in the power cycling test and their physical meaning are studied,and a combined electribcal parameter measurement method of the vertical temperature gradient of the IGBT chip is proposed.The realization method of PN junction voltage drop method and threshold voltage method under a small current for junction temperature measurement in different power devices is proposed,including diode,IGBT and MOSFET.Different from the single conduction mode of diode and IGBTS,MOSFET has three conduction modes,and the junction temperature measurement circuit and control method are different in different modes.Based on theoretical analysis and experimental verification,the physical meaning of the junction temperature measured by the VCE(T)method and the Vth(T)method on the veritical temperature distribution is revealed.The former mainly reflects the temperature information at the PN junction on the collector side,which is approximately the temperature information of the collector surface,and the latter mainly reflects the temperature information of the channel region on the emitter side,which is approximately the temperature information of the emitter surface.Further,an electrical measurement method of the veritical temperature gradient of the IGBT chip is proposed by combining the two methods.Thirdly,the calculation method of virtual junction temperature measured by the VCE(T)method in finite element simulation is studied,and the physical meaning of virtual junction temperature on the lateral temperature distribution of the chip is revealed.Taking advantage of the strong symmetry of the temperature distribution on the surface of a single chip,a method for extracting the average temperature of the chip surface that can remove the influence of the bonding wire is proposed.Compared with the traditional integration method,the efficiency and accuracy of the infrared method for extracting the average temperature of the chip surface are improved.A diode parallel model considering the temperature distribution characteristics is established,and a "circuit simulation method" that can simulate the virtual junction temperature in the circuit simulation software is proposed.Further,a"numerical calculation method" that can be better combined with finite element simulation software is proposed,which overcomes the difficulty that the "circuit simulation method" that is difficult to be incompatible with the simulation accuracy and simulation difficulty,and realizes fast calculation of virtual junction temperature under different temperature distribution states.The deviations between the virtual junction temperature and the average chip temperature under different temperature distributions is compared through experimental and simulation.The results show that the junction temperature measured by the VCE(T)method is always higher than the average temperature of the chip surface in any case,and it is found that the deviations are essentially positively correlated with the temperature gradient.The virtual junction temperature under different measurement currents is calculated,which breaks the traditional perception that the virtual junction temperature is a fixed value,and it is determined that it increases with the decrease of the measurement current,and the reason is explained based on the calculation results of the measurement current distribution.Furthermore,the average mechanism of virtual junction temperature is revealed,and an equivalent experiment is designed to fully demonstrate the conclusion.Finally,the measurement method based on VCE(T)method of chip lateral temperature distribution characteristics is studied,including the temperature distribution on a single chip and among multiple chips,and the thermal characteristics of the device are analyzed from this perspective.Taking advantage of the characteristics that virtual junction temperatures measured by different measurement currents is different under the same temperature distribution,a multi-current VCE(T)method for temperature distribution measurement on a single chip is proposed,a reasonable measurement current injection strategy is formulated to ensure the equivalence of the temperature distribution at the time of injection.The temperature distribution can be obtained by alternately injecting different measurement currents to measure the virtual junction temperature,and then constructing a nonlinear equation system for numerical solution.To reduce the dimension of the solution variables,a temperature distribution function is introduced to characterize the temperature distribution of a single chip,which greatly reduces the measurement difficulty and improves the solution accuracy.The temperature distribution measurement of the multi-chip crimp IGBT device is carried out by applying the sequential VCE(T)method.The results show that the junction temperature of the edge chip is higher than that of the center chip,and the junction-to-case thermal resistance of the press-pack IGBTs is predicted to be dependent on the load current.Furthermore,a measurement method for simultaneously measuring the junction-to--case thermal resistance of both sides under double side cooling condition is proposed,which confirms the predicted results.And the thermo-mechanical bi-directional coupling finite element model is built to reveal the impact mechanism that the deformation of device causes the change of internal heat flow distribution.