Steady-state junction-to-case thermal resistance measuring method based on equal-case-temperature control

Abstract

The invention discloses a steady-state junction-to-case thermal resistance measuring method based on equal-case-temperature control, and the method comprises the steps: installing a to-be-measured module on a radiator, and arranging a temperature sensor which is used for detecting the surface temperature of a housing of the to-be-measured module, so as to judge whether the case temperature reaches a set value or not and keeps stable; driving the to-be-tested module to heat and adjusting the radiator to radiate heat to enable the to-be-tested module to reach a thermal steady state; recording junction temperature and heating power data points of the to-be-tested module in a plurality of thermal steady states; the slope of the junction temperature-heating power curve obtained through linear fitting is the junction-to-case thermal resistance of the module to be tested. The thermoelectric cooler is innovatively adopted as a heat dissipation system in the testing process, the characteristics of quick response, good temperature uniformity and high control precision of the thermoelectric cooler are fully utilized, high uniformity of the surface temperature of the module shell is achieved, the stability of the cooling system is improved, and therefore the repeatability and robustness of junction-to-case thermal resistance testing are remarkably enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of junction case thermal resistance testing, and particularly relates to a steady-state junction case thermal resistance measurement method based on equal case temperature control, which is suitable for thermal performance evaluation of power devices and power modules. BACKGROUND

[0002] In recent years, wide bandgap semiconductor materials represented by silicon carbide (SiC) and gallium nitride (GaN) have been widely used in high-performance electronic systems such as power converters, radio frequency and microwave devices, semiconductor lasers, and new energy vehicles. Wide bandgap semiconductor devices have characteristics such as high switching frequency, high breakdown voltage, and low on-resistance, but their performance depends on proper packaging design. In packaging design, parasitic parameters and junction case thermal resistance are two key indicators. Among them, junction case thermal resistance reflects the ability of the device to conduct heat from the junction to the package shell, and is an important parameter for measuring its heat dissipation performance. Accurate measurement of junction case thermal resistance has important guiding value for the thermal design of device packaging.

[0003] According to the technical standard manual JESD51-1, junction case thermal resistance is defined as: "Junction case thermal resistance is the thermal resistance from the device operating area to the package shell surface closest to the chip mounting surface, and the shell surface needs to be well heat dissipated to minimize the temperature gradient on its surface." However, in practical applications, power devices or power modules are often cooled by air or water coolers. Due to the limited heat dissipation efficiency and the uneven flow of cooling fluid, there is often a significant temperature gradient on the surface of the package shell, making it difficult to achieve ideal uniform shell temperature distribution.

[0004] The traditional direct measurement method of junction case thermal resistance usually takes the highest temperature on the surface of the package shell as the shell temperature, and then calculates the junction case thermal resistance based on the junction temperature. In actual operation, this method requires placing a thermocouple directly below the chip to measure the maximum value of the shell temperature, but the maximum shell temperature does not necessarily coincide with the geometric center of the chip, and for multi-chip or modules where the chip position cannot be determined, it is difficult to accurately find the temperature measurement point. This leads to the direct measurement method being susceptible to measurement errors and the lack of repeatability of the measurement results.

[0005] Specifically, the direct measurement method has the following problems: (1) Measurement point position error: the temperature distribution on the surface of the package shell is uneven, and the thermocouple can only measure the temperature at the contact point, which may deviate from the highest temperature point of the shell.

[0006] (2) Cold plate interference temperature measurement: the temperature measurement point of the thermocouple is usually not fully insulated from the cold plate, and may be affected by cooling from the cold plate or metal wires, resulting in a lower measured shell temperature.

[0007] (3) Clamping pressure introduction error: In the test process, a large clamping pressure needs to be applied to ensure that the module and the heat sink are fully attached, which may mask the delamination problem between the interfaces and affect the accuracy of the thermal resistance measurement.

[0008] (4) Thermocouple mounting hole interference: The thermocouple is installed by drilling a hole in the cold plate, which may introduce significant influence when the module size is small.

[0009] In order to solve the error problem of direct measurement method in junction thermal resistance test, JEDEC proposed a junction thermal resistance measurement method suitable for power devices or modules with single heat dissipation path in technical standard manual JESD51-14, namely transient dual interface method (TDIM). This method obtains two thermal resistance curves by respectively performing transient thermal response test on the device to be tested under the conditions of no thermal grease and coated thermal grease, and extracts the junction thermal resistance value by analyzing the separation point of the two curves. Since this method no longer relies on the direct measurement of case temperature, it avoids the errors and disturbances caused by the case temperature measurement position, uneven case temperature distribution, etc., and can theoretically improve the consistency and repeatability of the measurement. However, the transient dual interface method still has the following shortcomings in practical engineering application: (1) Steady-state difference requirement of thermal resistance curve: The thermal resistance curves obtained by two tests need to have a large enough difference in the steady-state stage, otherwise the separation point is difficult to identify or even cannot be extracted.

[0010] (2) Cooling system stability requirement: The cooling system working condition needs to be constant during the test, and the temperature fluctuation or uneven flow of the cooling liquid will cause the thermal resistance curve to drift, affecting the measurement accuracy.

[0011] (3) Determination standard of separation point: The identification of separation point depends on the mathematical criterion or algorithm set by human, and different criteria may get different results.

[0012] (4) Due to the different heat flow distribution under transient and steady-state conditions, the measured value may not be the same as the steady-state thermal resistance value.

[0013] (5) The temperature nonlinearity (thermal conductivity and heat capacity change with temperature) of some packaging materials may cause the transient thermal resistance curve to separate early.

[0014] (6) Complex test and post-processing: This method needs to test two thermal interface states repeatedly, and the operation steps are complicated; it needs to perform logarithmic transformation, differentiation, fitting and other mathematical processing on the transient thermal resistance curve, which increases the algorithm complexity.

[0015] In addition, some scholars also proposed a method of laminated thermal interface material, which measures the thermal resistance from junction to thermal interface material under the premise of unchanged other test conditions by sequentially stacking thermal interface materials with different thicknesses between the device or module to be tested and the heat sink, draws the curve of the thermal resistance changing with the thickness of the thermal interface material, and fits the curve. The thermal resistance corresponding to the zero thickness of the thermal interface material in the fitted curve is the junction case thermal resistance. This method also avoids the measurement of case temperature and the errors related to the measurement of case temperature. However, the calculation of the thermal resistance from junction to thermal interface material in this method still needs to measure the temperature of the surface of the thermal interface material by using a thermocouple, so the error related to the measurement of the thermocouple is not eliminated. In addition, the thermal interface material needs to be stacked continuously during the test, and the operation process is complicated. At the same time, this method is also sensitive to the stability of the cooling system, and small fluctuations in the cooling conditions will also introduce measurement errors.

[0016] In summary, the existing junction case thermal resistance test methods mainly include direct measurement method, transient double interface method and laminated thermal interface material method. These methods have different degrees of shortcomings, such as large measurement error, complicated test process, high cost of test equipment and time, and it is difficult to meet the requirements of low error, low cost and simple operation of the junction case thermal resistance test at the same time. In addition, the current mainstream air cooling and water cooling systems cannot achieve the uniform temperature distribution required in the definition of junction case thermal resistance, and the stability of the cooling system is poor, which further aggravates the generation of measurement error. SUMMARY

[0017] In view of the shortcomings of the prior art, the present application proposes a steady-state junction case thermal resistance measurement method based on equal case temperature control. This method adjusts the working parameters of the heat sink under different module heat power to maintain the case temperature of the module to be tested constant, and obtains the steady-state junction case thermal resistance by extracting the slope of the junction temperature-power curve, avoiding the error caused by direct measurement of case temperature in traditional methods. At the same time, the present application innovatively uses a thermoelectric cooler as the cooling system during the test, fully utilizes its fast response, good temperature uniformity and high control accuracy, realizes high uniformity of the surface temperature of the module shell, and improves the stability of the cooling system, thereby significantly enhancing the repeatability and robustness of the junction case thermal resistance test.

[0018] To achieve the above object, the technical scheme adopted by the present application is: A steady-state junction case thermal resistance measurement method based on equal case temperature control, comprising the steps of: Step 1, installing the module to be tested on the heat sink, setting a temperature sensor for detecting the surface temperature of the shell of the module to be tested to determine whether the case temperature reaches the set value and remains stable; Step 2, driving the module to be tested to generate heat and adjusting the heat sink to dissipate heat, so that the case temperature of the module to be tested is stabilized at the set value, which is considered to reach thermal steady state; recording the junction temperature of the module to be tested and the heat generation power of the module to be tested under thermal steady state; Step 3, change the heat generation power of the module to be tested, repeat step 2 to obtain multiple data points of the junction temperature of the module to be tested under thermal steady state and the corresponding heat generation power at different heat generation powers; Step 4, linear fitting is performed on the junction temperature and heat generation power data of the module to be tested under multiple thermal steady states, and the slope of the obtained junction temperature-heat generation power curve is the junction shell thermal resistance of the module to be tested.

[0019] The present application converts the traditional junction shell thermal resistance measurement method relying on shell temperature measurement into an equivalent method of keeping the shell temperature of the module to be tested constant at different heat generation powers, fitting the junction temperature-heat generation power curve, and extracting the slope of the curve as the steady-state junction shell thermal resistance, which avoids the error introduced by direct shell temperature measurement and improves the accuracy and repeatability of the measurement. At the same time, the present application has good robustness to the type of thermal interface material and the position of the thermocouple, especially in the low power range; it has good universality and adaptability, and can be applied to power devices or modules with different packaging structures and is compatible with multiple cooling methods.

[0020] Step 1 also includes temperature calibration of the junction temperature measurement method of the module to be tested to obtain the corresponding relationship between the junction temperature and the measurement value. The junction temperature measurement method includes any one of temperature-sensitive parameter method, infrared temperature measurement method, optical temperature measurement method or other measurement methods capable of characterizing junction temperature.

[0021] Preferably, the heat sink is a thermoelectric cooler (TEC), which is the most suitable cooling scheme for implementing the measurement method of the present application due to its fast response speed, simple control, low cost, and good cold end temperature uniformity. The thermoelectric cooler adjusts the cold end temperature by adjusting the input current or voltage to achieve constant control of the shell temperature of the module to be tested. The use of TEC can significantly improve the uniformity of the surface temperature of the shell of the module to be tested, forming a robust region for the placement of temperature sensors within a certain power range, in which the junction shell thermal resistance measured by temperature sensors at different positions is basically consistent, thereby having the advantages of high repeatability, simplified operation, wide applicability, and high measurement efficiency.

[0022] Selecting a thermoelectric cooler (TEC) as a heat sink has the following advantages: (1) High measurement repeatability: even if the thermocouple position is changed in multiple tests, the measured junction shell thermal resistance remains consistent, significantly improving the reliability of the experimental results.

[0023] (2) Simplify experimental operation: accurate control of the thermocouple position or replacement of the thermal interface material is not required to obtain accurate junction shell thermal resistance values, thereby reducing the difficulty of operation and dependence on the experience of the operator.

[0024] (3) Wide applicability: achieving thermocouple position robustness in the low power range makes the method suitable for power module measurement of different packaging structures and cooling conditions.

[0025] (4) High measurement efficiency: The measurement of the junction-to-ambient thermal resistance can be completed quickly without the need for repeated adjustment of the thermocouple or complex data correction, thereby shortening the experimental period.

[0026] The cold end of the heat sink is in full thermal contact with the module to be measured and covers the main heat generating area of the module to be measured to approach the isothermal surface in the definition of the junction-to-ambient thermal resistance as much as possible.

[0027] The hot end of the heat sink is provided with a water-cooled heat sink for maintaining the temperature of the hot end stable and enhancing the cooling capacity of the heat sink for the module to be measured.

[0028] Preferably, during the test, the remaining surface of the module to be measured can be wrapped with thermal insulation cotton or other thermal insulation materials, so that the main heat dissipation path is concentrated on the heat sink, and air cooling and other additional cooling can be ignored, thereby ensuring the accuracy and stability of the measurement result of the junction-to-ambient thermal resistance.

[0029] To further improve the uniformity of the shell temperature, a high thermal conductivity diffusion layer such as a vapor chamber, a graphene heat sink, a thermal conductive sheet, silicone grease, silica gel, a silver sintering layer, or a solder layer can be arranged between the cold end of the heat sink and the module to be measured, so as to improve the thermal contact and enhance the lateral distribution of heat, expand the robust region of the thermocouple position, and further ensure the reliability of the measurement of the junction-to-ambient thermal resistance.

[0030] Preferably, the temperature sensor is a thermocouple, which is arranged as close as possible to the center of the heat generating area of the module to be measured, and the number is 1-5. The judgment condition for the system to reach thermal steady state is that the temperature change of the thermocouple is less than ±0.1K within a predetermined time interval. When the system reaches thermal steady state, only one thermocouple is selected as the criterion for maintaining the shell temperature constant, and the slope of the junction temperature-power curve is extracted according to the criterion, so as to obtain the junction-to-ambient thermal resistance of the module to be measured. The multiple thermocouples arranged are used for: (1) When the thermocouple placement position or the shell temperature distribution is uneven, the minimum value of the multiple junction-to-ambient thermal resistances obtained by selecting multiple thermocouples as constant temperature control criteria is selected as the steady-state junction-to-ambient thermal resistance of the module. (2) To judge whether the selected thermoelectric cooler has sufficient cooling capacity to form a robust region, in which the junction-to-ambient thermal resistances obtained by selecting different thermocouples as constant temperature control criteria are basically consistent, so as to ensure that only one thermocouple is needed for subsequent measurement, and the selection of the thermoelectric cooler can be assisted.

[0031] (3) It should be noted that unless the module to be measured works in the heat generating power range forming the robust position of the thermocouple, the junction-to-ambient thermal resistance measured by a single thermocouple only represents the local junction-to-ambient thermal resistance value of the thermocouple position, rather than the module junction-to-ambient thermal resistance required by the definition.

[0032] In the present application, the method for determining whether the temperature of the module housing to be measured remains constant is not limited to thermocouple temperature measurement, but can also be achieved by methods such as infrared thermal imaging, structural deformation, or temperature-sensitive electrical parameter methods that can indicate constant housing temperature.

[0033] Specifically, for the infrared thermal imaging method, an infrared thermal imager is used to continuously monitor the module housing to be measured, and the module surface temperature distribution map is obtained; when the module surface temperature distribution is consistent under different heating powers and the fluctuation is less than ±0.1 K, it is considered that the shell temperature remains constant.

[0034] For the structural deformation method, displacement sensors or strain gauges can be installed at key positions of the module housing to monitor the deformation amount of the module due to thermal expansion; as the module heats up, the system reaches thermal steady state, and when the deformation amount of each monitoring point on the shell surface is stable and the fluctuation is less than ±0.1%, it is considered that the shell temperature is constant.

[0035] For the temperature-sensitive electrical parameter method, a thin film resistor can be prepared at the position of the module housing where the temperature needs to be monitored, and the shell temperature is monitored by monitoring the change of the resistance value with temperature; when the resistance value of the thin film resistor is stable under different heating powers, and the change amplitude is less than ±0.1%, it is considered that the shell temperature remains constant.

[0036] Preferably, the junction temperature and corresponding heating power data of more than 2 groups of modules to be measured in step 3 are tested, and more preferably, the data of more than 5 groups are tested.

[0037] A high thermal conductivity diffusion layer is provided between the heat sink and the module to be measured to improve thermal contact and improve the uniformity of the module housing temperature. The high thermal conductivity diffusion layer includes one or more of a vapor chamber, a graphene heat sink, a heat-conducting sheet, silicone grease, silicone gel, a silver sintering layer, a solder layer, etc.

[0038] Preferably, in step 4, the working point of the heat sink is selected under thermal steady state, which has sufficient margin of refrigeration capacity relative to the heat load of the heat sink, preferably the data when the heat load is less than 50% of the maximum refrigeration capacity of the heat sink, more preferably less than 30%. Under this condition, a larger area of temperature uniform region can be formed on the surface of the heat sink, i.e. the robustness region of the junction-to-housing thermal resistance value to the arrangement position of the temperature sensor.

[0039] When the temperature sensor is a thermocouple, the power range can be determined by pre-experiment: in the pre-experiment, a plurality of thermocouples are arranged at different positions of the to-be-tested module respectively, and are used as shell temperature constant criteria to measure the junction shell thermal resistance respectively; according to the consistency of the junction shell thermal resistance obtained by each thermocouple, the heating power range capable of forming a robust region is determined. In the robust region, the junction shell thermal resistances obtained by different thermocouple positions are basically consistent, so that reliable measurement can be completed by only one thermocouple in formal measurement, and reference basis is provided for selection of the thermoelectric cooler and power matching of the module.

[0040] Compared with the prior art, the present application has the following beneficial effects: (1) The steady-state junction shell thermal resistance measurement method of the equal shell temperature control has the advantages of simple operation, low cost, high equipment stability, good measurement consistency and reliable measurement results. The test process of the method is simple and intuitive, and no thermal interface material needs to be replaced during the test process, and no complex data processing operation is required. Since the thermoelectric cooler has the characteristics of fast response speed, the time required for the entire measurement process is short, and the test efficiency is high.

[0041] (2) The thermoelectric cooler in the present application has no mechanical moving parts, high stability and high temperature control accuracy. Through repeated testing, the measured junction shell thermal resistance values have good repeatability and consistency. The present application is based on steady-state heat balance condition for testing, and the slope of the junction temperature-power curve extracted is the junction shell thermal resistance under steady-state condition, which is more in line with the actual needs in power device thermal design and reliability evaluation.

[0042] (3) The method can obtain measurement results in the low power region of the thermoelectric cooler, and accurate junction shell thermal resistance values can be obtained without high power excitation, thereby avoiding thermal runaway and device damage that may be caused under high power condition, and having strong adaptability and robustness to actual application environment. The method can be applied to all application scenarios involving thermocouple temperature measurement, and is not limited by the type of heat sink or module. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 FIG. 1 is a schematic diagram of a test device when a thermocouple is used as a shell temperature constant criterion and a thermoelectric cooler is used as a heat sink in the embodiment.

[0044] Figure 2 FIG. 2 is a test principle of the steady-state junction shell thermal resistance measurement method based on equal shell temperature control.

[0045] Figure 3 FIG. 3 is a junction temperature-power curve obtained by using a gallium nitride module as a to-be-tested module and using a gate-to-gate resistance thereof as a temperature-sensitive parameter for junction temperature measurement in Example 1.

[0046] Figure 4 FIG. 4 is a junction temperature-power curve obtained by using a gallium nitride module as a to-be-tested module and using a gate-to-gate resistance thereof as a temperature-sensitive parameter for junction temperature measurement in Example 2. Figure 3Magnified view of the low-to-moderate power region. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application. Those skilled in the art can make modifications or equivalent replacements on the basis of understanding the technical scheme of the present application without departing from the spirit and scope of the present application, which should be covered within the protection scope of the present application.

[0048] The raw materials or devices used in the following specific embodiments can be purchased from the conventional electronic components and experimental consumables platform, including the module to be tested, thermoelectric cooler, thermal interface material, thermocouple, etc. The specifications and models of the materials used should meet the performance requirements of the experiment and can be obtained through the conventional market channels.

[0049] The module to be tested is a gallium nitride high electron mobility transistor single-chip module, the chip model is GS-065-150-1, connected with a copper-clad ceramic plate through nano-silver sintering, and the module is externally provided with a PEEK material protective shell, and heat insulation cotton is covered above the chip for heat insulation treatment, so that the heat of the chip is dissipated as much as possible through the lower thermoelectric cooler.

[0050] The shell temperature characterization adopts a T-shaped thermocouple connected to a thermocouple thermometer to read the temperature measurement data. In this embodiment, four thermocouples are arranged at the corresponding positions directly below the module chip, located between the module and the thermal interface material, and good thermal contact is ensured through a pressing device. The module and the thermoelectric cooler are connected through the thermal interface material, and different thermal conductivity thermal grease (in this invention, a plurality of thermal interface materials are used to verify the robustness of the method to different thermal interface materials, including Limin TF8, Shin-Etsu 7921, Youdu New Material UD7960, Laird thermal grease series, etc.) are used for experimental verification.

[0051] The thermoelectric cooler is of TEC1-19908 type, the cold end of which is closely attached to the module through the thermal interface material, and the hot end is attached to the water-cooled radiator through the thermal interface material to maintain the stability of the cold end temperature. In the embodiment, the input power of the thermoelectric cooler is changed to keep the shell temperature constant at 15℃ under different heat generating powers.

[0052] Example 1 Step 1, install the module to be tested on the thermoelectric cooler through thermal grease Limin TF8, and set thermocouples between the module to be tested and the thermal interface material to determine whether the shell temperature reaches the set value and is stable; the side of the thermoelectric cooler away from the module to be tested is provided with a water-cooled radiator, and the structure after assembly is as shown in Figure 1 .

[0053] Step 2, drive the module to be tested to generate heat, and constantly adjust the input power of the thermoelectric cooler to maintain the shell temperature of the module to be tested at a set value, and the temperature change of the thermocouple is less than ±0.1K for more than 2min, which is considered to reach thermal steady state; record the junction temperature T of the module to be tested under thermal steady state j1 and the corresponding heating power P1, which is considered as working condition 1 (P1, T j1 ); Step 3, change the heating power of the module to be tested, repeat step 2, obtain the junction temperature of the module to be tested and the corresponding heating power when the system reaches thermal steady state under different heating powers, and obtain the data of working condition 2 (P2, T j2 ), …, working condition n (P n , T jn ); Step 4, linearly fit the junction temperature and the corresponding heating power when the system reaches thermal steady state under different heating powers, and the slope of the obtained junction temperature-heating power curve is the junction-to-shell thermal resistance R jc of the module to be tested. The reasoning process is shown in Figure 2 , wherein Tj is the junction temperature of the module to be tested, Tc is the shell temperature of the module to be tested, Rjc is the junction-to-shell thermal resistance of the module to be tested, and Pn is the heating power of the module to be tested.

[0054] The method of the present application converts the measurement of the junction-to-shell thermal resistance into the extraction of the slope of the junction temperature-power curve, thereby avoiding the dependence on the direct measurement of the shell temperature and effectively eliminating the uncertainty and error related to the measurement of the shell temperature. In the present application, the role of the thermocouple is limited to indicating whether the shell temperature remains constant, and does not participate in the calculation process of the junction-to-shell thermal resistance, thereby effectively avoiding the error caused by the measurement of the shell temperature.

[0055] In the test process, different thermal interface materials are used, and under the condition of the same thermal interface material, the thermocouples are arranged at different positions of the module shell to serve as the shell temperature constant criterion, respectively, to obtain the corresponding junction temperature-power curve, as shown in Figure 3 . The thermal interface material 1 is Limin TF8, and the thermal interface material 2 is Youdu Xincai UD7960.

[0056] The test results show that in the low power region, since the cooling capacity of the thermoelectric cooler is much larger than the heating power of the module, the surface temperature distribution of the module shell is uniform, and the slopes of the junction temperature-power curves obtained by the thermocouples at different positions as the shell temperature constant criterion are basically consistent, and the enlarged view of the low power region is shown in Figure 4 .

[0057] It should be noted that in order to expand the robustness of the method of the present application to the placement position of the thermocouple, the thermocouple should be placed as close as possible to the center of the chip heat generating area, and good thermal contact should be ensured between the thermocouple, the module and the thermoelectric cooler. If the above conditions cannot be met, the slope consistency phenomenon of the low power region will be difficult to observe, at this time the junction temperature-power curves obtained by different thermocouple positions will no longer have consistent slopes or obvious inflection points, but only show constant slopes. At this time, the junction case thermal resistance value corresponding to each curve can only reflect the local junction case thermal resistance of the temperature measurement position, and cannot represent the steady-state junction case thermal resistance of the whole module.

[0058] The range of the low power region is closely related to the module type, the geometric characteristics of the heat generating area, the placement position of the thermocouple, and the thermal contact condition between the module and the thermoelectric cooler. At present, it cannot be accurately derived by theoretical formula, but can only be determined by pre-experiment. In the pre-experiment, by arranging multiple thermocouples at different temperature measurement positions and measuring the junction case thermal resistance as a constant criterion for shell temperature, the consistency of the junction case thermal resistance obtained from each thermocouple is used to determine the range of the heat generating power that can form a robust region.

Claims

1. A steady-state superconducting thermal resistance measurement method based on isochoric temperature control, characterized by, The method comprises the steps of: Step 1: install the module to be tested on a heat sink, and set a temperature sensor for detecting the surface temperature of the shell of the module to be tested to determine whether the shell temperature reaches a set value and remains stable; Step 2: drive the module to be tested to generate heat and adjust the heat sink to dissipate heat, so that the shell temperature of the module to be tested is stabilized at the set value, and the thermal steady state is reached; record the junction temperature of the module to be tested and the heat generation power of the module to be tested under the thermal steady state; Step 3: change the heat generation power of the module to be tested, repeat step 2, and obtain multiple data points of the junction temperature of the module to be tested under the thermal steady state and the corresponding heat generation power at different heat generation powers; Step 4: linearly fit the junction temperature and heat generation power data of the module to be tested under multiple thermal steady states, and the slope of the obtained junction temperature-heat generation power curve is the junction-to-shell thermal resistance of the module to be tested.

2. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, Before step 1, the method further comprises: temperature calibration of the junction temperature measurement method of the module to be tested to obtain the corresponding relationship between the junction temperature and the measured value.

3. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, The heat sink is a thermoelectric cooler. And / or, the cold end of the heat sink covers the main heat generation area of the module to be tested.

4. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, The hot end of the heat sink is provided with a water-cooled heat sink.

5. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, The temperature sensor is a thermocouple.

6. The steady state thermal resistance measurement method based on isochoric temperature control of claim 5, wherein, The number of thermocouples is 1-5. And / or, within 2-10 minutes, the temperature change of the thermocouples is less than ±0.1K, which is considered to reach the thermal steady state.

7. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, In step 2, the method for judging the thermal steady state is selected from any one of thermocouple temperature measurement, infrared thermal imaging, structural deformation, or temperature-sensitive electrical parameter method.

8. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, In step 3, at least two groups of data points of the junction temperature and the corresponding heat generation power of the module to be tested are tested.

9. The steady state thermal resistance measurement method based on isochoric temperature control of claim 1, wherein, A high-thermal-conductivity diffusion layer is arranged between the heat sink and the module to be tested.

10. The steady state thermal resistance measurement method based on isochoric temperature control of claim 9, wherein, The high-thermal-conductivity diffusion layer includes one or more of a uniform temperature plate, a graphene heat dissipation sheet, a heat conduction sheet, silicone grease, silica gel, a silver sintering layer, and a solder layer.

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