A method for testing thermal resistance of gallium nitride power module

Abstract

The application provides a method for testing thermal resistance of a gallium nitride power module, which utilizes a liquid cooling plate to adjust different temperatures to make the module reach different temperatures, obtains module on-state resistances corresponding to the temperature points, then tests a temperature rising and falling curve of the module by means of a double-interface separation method, and obtains two impedance curves by means of mathematical analysis of an analysis software, so that a separation point of the curves is the thermal resistance value of the module. The method can accurately represent the highest temperature in the module by taking the on-state resistance of the device as an electrical parameter for representing the junction temperature of the module, and realizes accurate measurement of the thermal resistance of the module in combination with a thermal resistance testing system. The overall process is simple and clear, and easy to realize.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power semiconductor, in particular to a testing method of gallium nitride power module. BACKGROUND

[0002] With the development of power electronics technology, the continuous demand for high efficiency and high power density design makes the performance of power semiconductor reach the limit of silicon material. Wide bandgap semiconductor material GaN (gallium nitride) gradually gets application in the market of power devices, such as electric vehicles, energy conversion, motor drive field, etc., compared with Si (silicon) material, due to its own characteristics such as high current density, low loss, high switching speed and high working temperature, etc.

[0003] Although GaN devices develop rapidly, the related research and application are continuously deepened, but the method for testing the thermal resistance of GaN devices is still less. The traditional optical measurement thermal resistance method needs to remove the cap of the packaged device, which cannot guarantee the original shape of the module. Some documents mention that the junction temperature of the device is measured by using the characteristic that the electrical characteristics of the Schottky diode between the gate and the source of the gallium nitride chip change with temperature. However, because the positions of the gate and the source of the chip are not the positions of the highest junction temperature of the chip, the thermal resistance calculated by this method will be inaccurate under high power working mode. Therefore, a new thermal resistance testing method is needed to accurately characterize the thermal resistance of the module. SUMMARY

[0004] In view of the above problems, the present application develops a new thermal resistance testing method of gallium nitride power module, which uses the characteristic that the on-resistance of the module changes with temperature to characterize the internal temperature of the module, and then realizes the accurate measurement of the thermal resistance of the module.

[0005] Specifically, the present application adopts the following technical solutions:

[0006] A method for testing the thermal resistance of a gallium nitride power module, comprising the following steps:

[0007] 1) providing a liquid cooling plate, mounting the gallium nitride power module to be tested on the liquid cooling plate, and appropriately applying pressure to make the heat dissipation surface of the gallium nitride power module fully contact with the liquid cooling plate;

[0008] 2) providing a thermal resistance testing system, connecting the gallium nitride power module to be tested with the thermal resistance testing system, and applying a fixed voltage between the gate and the source to turn on the device;

[0009] 3) applying a detection current to the module, adjusting the temperature of the liquid cooling plate to make the module and the liquid cooling plate in thermal equilibrium, measuring the k curve of the on-resistance of the module changing with temperature, and calculating the k coefficient of the module;

[0010] 4) Set the temperature of the liquid cooling plate to a fixed value, apply a heating current to the module to heat the module, measure the on-resistance of the module during the heating process, then determine the temperature of the module during the heating process through the k coefficient to obtain the first temperature rise curve of the module;

[0011] 5) After the module reaches thermal equilibrium, switch the heating current to the detection current, at this time the module starts to cool until the temperature of the liquid cooling plate reaches thermal equilibrium again, record the on-resistance of the module during the cooling process, and obtain the temperature during the cooling process through the k coefficient to obtain the first temperature drop curve of the module;

[0012] 6) Remove the module from the liquid cooling plate, coat the module with a heat-conducting material on the heat dissipation surface, and apply appropriate pressure to make the module fully contact with the liquid cooling plate, repeat steps 4) to 5) above to obtain the second temperature rise curve and the second temperature drop curve, respectively;

[0013] 7) The thermal resistance analysis software of the thermal resistance test system analyzes the first and second temperature rise curves and the first and second temperature drop curves to obtain the first and second thermal resistance curves, and the separation point of the two curves is the thermal resistance of the module.

[0014] Preferably, the heat transfer medium in the liquid cooling plate is water, oil or other fluid materials capable of transferring heat.

[0015] Preferably, in the above method, the k curve is obtained by adjusting the liquid cooling plate to heat or cool the liquid cooling plate at a certain temperature interval, setting temperature nodes, recording the drain-source voltage of the module at each temperature node, obtaining the relationship between the on-resistance of the module and the temperature, and drawing a curve.

[0016] Preferably, in the above method steps, the temperature interval of the liquid cooling plate adjustment is 10℃, and the adjustment range is 25-85℃, and a period of time is waited at each node to make the module and the liquid cooling plate thermal equilibrium.

[0017] In the above method, the heating current used is much larger than the detection current. More preferably, the heating current is at least 100 times the detection current.

[0018] In the method of the present application, the formula Rds-on=k*T+c is used to calculate the k coefficient and obtain the first and second temperature rise curves and the first and second temperature drop curves, where Rds-on is the on-resistance of the module, k is the slope of the curve, T is the temperature of the module, and c is the constant of the first equation.

[0019] The present application provides a method for testing the thermal resistance of a GaN module, which uses the on-resistance of the device as an electrical parameter to represent the junction temperature of the module, and can accurately represent the highest temperature in the module. Combined with a thermal resistance test system, the method realizes accurate measurement of the thermal resistance of the module. The overall process is simple and clear, and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 for an exemplary test procedure of the method of the present invention;

[0021] Figure 2 schematic diagram of the principle for measuring the k curve of a gallium nitride module;

[0022] Figure 3 schematic diagram of a module k curve measured in an example;

[0023] Figure 4 schematic diagram of a thermal impedance curve in an example. EMBODIMENT

[0024] The present invention addresses the problems in the prior art, according to the development status of existing GaN devices, a GaN device junction temperature measurement method is provided, which uses the characteristic that the on-resistance of the module changes with temperature to represent the temperature inside the module, and then realizes the accurate measurement of the thermal resistance of the module. And this method has fewer operation steps than the previous measurement method, and the measurement result is accurate.

[0025] The method of the present invention measures the thermal resistance by means of a thermal resistance test system, adjusts different temperatures by means of a liquid cooling plate to make the module reach different temperatures, obtains the on-resistance of the module corresponding to each temperature point, then tests the temperature rise and fall curve of the module by means of the double-interface separation method, and obtains two impedance curves by means of the analysis software of the thermal resistance test system. The separation point of the curve is the thermal resistance value of the module.

[0026] In an exemplary embodiment, the GaN device junction temperature measurement method of the present invention includes the following steps:

[0027] Place the module to be tested on the liquid cooling plate;

[0028] Connect the module to be tested and the thermal resistance test equipment together, and measure the k curve of the on-resistance of the module changing with temperature;

[0029] Reconnect the module and the thermal resistance equipment, apply pressure to the module to make the module and the liquid cooling plate fully contact;

[0030] Make the module heat and the liquid cooling plate reach a thermal equilibrium state, and obtain the first temperature rise curve of the module changing with time by the thermal resistance test equipment;

[0031] Make the module not heat and let it and the water cooling plate reach a thermal equilibrium state again, and obtain the first temperature drop curve of the module changing with time by the thermal resistance test equipment;

[0032] Separate the module and the liquid cooling plate, apply thermal conductive silicone grease to the heat dissipation area of the module, and reattach the module and the liquid cooling plate together after the application is completed, and apply pressure to make them fully contact;

[0033] Repeat the above operation to obtain the second temperature rising curve and the second temperature falling curve after the module is coated with the thermal conductive silicone grease;

[0034] According to the first and second temperature rising and falling curves, mathematical analysis and calculation are performed to obtain the thermal resistance curve of the module before and after the module is coated with the thermal conductive silicone grease, and the separation point of the curve is the thermal resistance of the module.

[0035] In the above method, the heat transfer material in the liquid cooling plate can be water, oil or any other commonly used or newly developed heat transfer material. In the following, water will be taken as an exemplary material, that is, a water cooling plate will be taken as an exemplary device for description, but it should be understood that the water cooling plate should not limit the protection scope of the present application, and any other available device can also be used as a heat transfer device. The thermal resistance test device can use any commonly used or newly listed device on the market as long as it can complete the functions required in the method steps described in the present application, for example, the T3ster thermal resistance test system described in the present application for exemplary description, but it should be understood that other models of the same manufacturer or similar models or other models of other manufacturers can also be used in the present application, so the model should not limit the protection scope of the present application. Similarly, the thermal conductive silicone grease described above is only because silicone grease is the most commonly used thermal conductive material in the prior art, and the thermal conductive silicone grease should not limit the protection scope of the present application, for example, in some cases, thermal conductive resin can also be used in the method of the present application.

[0036] In the above method, the test method for measuring the k curve of the temperature change of the module on-resistance is as follows:

[0037] A fixed voltage is applied between the gate and the source of the module to be tested to completely turn on the module;

[0038] The temperature of the water cooling plate is adjusted to gradually increase or decrease, and some temperature nodes are set during the temperature increasing or decreasing process. The water cooling plate is kept at each temperature node for a period of time, so that the module and the water cooling plate reach thermal equilibrium.

[0039] A small detection current is applied between the drain and the source of the module, and the drain-source voltage of the module is measured when the thermal equilibrium is reached, which becomes the k curve of the temperature change of the module on-resistance through mathematical calculation.

[0040] In the above method, the test method for the first temperature rising curve of the temperature change of the module with time is as follows:

[0041] The water cooling plate is set to a fixed temperature, and a large current is applied between the drain and the source of the module to heat the module. The state is maintained until the module and the water cooling plate reach thermal equilibrium, and the thermal resistance test device records the curve of the temperature change of the module with time during the process.

[0042] In the above method, the test method for the first temperature falling curve of the temperature change of the module with time is as follows:

[0043] After reaching thermal equilibrium, switch the heating large current to the detection small current, keep this state until the module and the water-cooled plate reach thermal equilibrium again, and record the curve of the module temperature changing with time during this process using the thermal resistance test equipment.

[0044] In the above method, after the module heat dissipation surface is coated with a thermal conductive silicone grease, the above procedure is repeated to obtain a second temperature rising curve and a second temperature falling curve of the module.

[0045] In the above method, the thermal resistance curves before and after the module is coated with the silicone grease are obtained through mathematical analysis and calculation, and the mathematical analysis process is performed in the calculation and analysis software of the thermal resistance test equipment, for example, when a T3ster thermal resistance tester is used, the mathematical analysis and fitting calculation are performed through the T3ster calculation and analysis software. The calculation and analysis software differentiates and integrates the temperature rising and falling curves of the module to obtain the curves of the thermal resistance impedance changing with time before and after the module is coated with the silicone grease. The coating of the silicone grease changes the heat transfer path between the module and the water-cooled plate, and the thermal resistance impedance separation point is also the separation point of the module thermal resistance before and after the coating of the silicone grease. Specific embodiments

[0046] The application provides a method for testing the thermal resistance of a gallium nitride power module, which adjusts different temperatures of a liquid-cooled plate to make the module reach different temperatures, obtains the module on-state resistance corresponding to each temperature point, then tests the temperature rising and falling curves of the module by means of a double-interface separation method, and obtains two impedance curves by means of analysis software for mathematical analysis, and the curve separation point is the module thermal resistance value. The method takes the on-state resistance of the device as an electrical parameter for representing the module junction temperature, which can accurately represent the highest temperature in the module, and realizes the accurate measurement of the module thermal resistance in combination with a thermal resistance test system. The overall process is simple and clear, and easy to implement.

[0047] The principles and schemes of the application will be described below in combination with specific embodiments, and the technical solutions in the embodiments of the application will be described more clearly and completely in combination with the drawings of the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0048] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "both ends", "one end", "the other end" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0049] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "connection" and the like should be broadly understood, for example, "connection" can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0050] The specific operation of the technical solution can be seen from Figure 1 .

[0051] Step 1: Mount the GaN power module on the water-cooled plate, apply appropriate pressure through screws to make it fully contact with the water-cooled plate, and the water-cooled plate can be filled with water, oil or other materials that can bring or take away heat.

[0052] Step 2: Connect the T3ster thermal resistance test system and the GaN module to be tested, and apply a fixed voltage to the gate and source of the GaN power module to make the device fully open.

[0053] Step 3: Apply a detection current to the drain and source of the module, detect the voltage across the two terminals, and the detection current is a constant small current. The detection current is selected according to the current level of the module. In this embodiment, the detection current of 800mA is selected, and the on-resistance at this time is obtained through the relationship between voltage and current, U=I*R, U is the voltage of the drain and source of the module, I is the selected detection current, and R is the on-resistance to be obtained. It should be understood that the 800mA detection current selected in this embodiment is only an exemplary current size. In general, as long as it can meet the condition that the module does not heat or does not heat a lot and can meet the current which is 50~100 times lower than the heating current or even a larger difference, such as 1A, 600mA, 500mA, 400mA, 300mA, 200mA or even smaller. Similarly, the values of the heating current described below are also only exemplary, and other currents that can make the module heat obviously can also be used.

[0054] Step 4, adjust the temperature of the water-cooled plate, gradually increase or decrease the temperature, specifically from 25℃ to 85℃, interval every 10℃ as a temperature node, stay at each temperature node for a period of time to ensure that the module reaches thermal equilibrium, specifically can be 2 minutes, through the water-cooled plate to transfer heat to the module. In this application, the term "thermal equilibrium" refers to the GaN module and the water-cooled plate in contact, the internal temperature of the module does not change and remains stable, and there is no heat exchange on the heat transfer path of Figure 2 In this application, it should be understood that the above temperature range and interval temperature node are only exemplary and should not limit the protection scope of the present application. The exemplary temperature range and temperature node are only for illustrating the drawing of the k curve, and a larger or smaller range and a more sparse or denser temperature node can also be used as a sampling range for drawing the k curve and calculating the k coefficient of the method of the present application.

[0055] Step 5, after reaching thermal equilibrium at each temperature node, measure the drain-source voltage of the module at this time.

[0056] Step 6, through the measurement of the previous steps, draw the k curve of the GaN module, which is the relationship between the drain-source voltage and the temperature under a constant measured current. The k curve of the module can be seen in Figure 3 The k coefficient of the module is calculated by T3ster calculation software using the formula Rds-on=k*T+c, where Rds-on is the on-resistance of the module, k is the slope of the curve, T is the temperature of the module, the temperature unit can be K, ℃ or ℉, and c is the constant of the first equation. In this embodiment, the k coefficient of the module calculated by the software is 0.072mv / ℃.

[0057] Step 7, set the temperature of the water-cooled plate to a fixed value, specifically 40℃, apply a large current between the drain and source of the module, specifically 80A, so that the module starts to heat up, and at the same time the on-resistance of the module during heating can be obtained through the voltage and current between the drain and source, and then the temperature of the module during heating can be determined through the k coefficient obtained by the above calculation, and the temperature rising curve of the module can be obtained.

[0058] Step 8, after the module reaches thermal equilibrium, switch the heating large current 80A to the detection small current 800mA, at this time the module will gradually cool down until the temperature of the module and the water-cooled plate reaches thermal equilibrium again, and the drain-source voltage is monitored in the process, the temperature in the cooling process is obtained through the k coefficient, and the temperature falling curve of the module can be obtained.

[0059] Step 9, remove the module from the water-cooled plate, apply a heat-conducting silicone grease or other heat-conducting material on the bottom of the module, place it again on the water-cooled plate, apply pressure to make the module and the water-cooled plate fully contact, at this time repeat the above operation, increase the current of the module to make it reach thermal equilibrium to obtain the temperature rise curve, then switch the large current to the detection current to obtain another temperature drop curve of the module.

[0060] Step 10, after obtaining the temperature rise curve and the temperature drop curve of the module before and after applying the silicone grease, use the T3ster thermal resistance analysis software in the computer to perform mathematical differentiation and integration calculation on the two curves, and the impedance curve of the impedance of the two curves changing with time can be obtained. Because the heat transfer path changes before and after the module is coated with heat-conducting silicone grease, the impedance curve will have a separation point, at which the separation point represents the thermal resistance of the module. According to the impedance curve, the thermal resistance of the module is 0.11℃ / W, which is very close to the result of 0.105℃ / W simulated by the software, indicating that the method of using the on-resistance of the module as an electrical parameter to represent the highest temperature in the module and then obtaining the thermal resistance of the module is accurate and reliable. Figure 4

[0061] The present application provides a method for testing the thermal resistance of a GaN module, which uses the on-resistance of the device as an electrical parameter to represent the junction temperature of the module, and can accurately represent the highest temperature in the module. Combined with the T3ster thermal resistance test system, the method realizes accurate measurement of the thermal resistance of the module. The overall process is simple and clear, and easy to implement.

[0062] The embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.​

Claims

1. A method for testing the thermal resistance of a gallium nitride power module, characterized in that, The method comprises the following steps: 1) providing a liquid cooling plate, mounting the gallium nitride power module to be tested on the liquid cooling plate, and appropriately applying pressure to make the heat dissipation surface of the gallium nitride power module fully contact the liquid cooling plate; 2) providing a thermal resistance test system, connecting the gallium nitride power module to be tested with the thermal resistance test system, and applying a fixed voltage between the gate and the source to make the device turn on; 3) applying a detection current to the module, adjusting the temperature of the liquid cooling plate, making the module and the liquid cooling plate reach thermal equilibrium, measuring the k curve of the on-resistance of the module with temperature change, and calculating the k coefficient of the module; 4) setting the temperature of the liquid cooling plate to a fixed value, applying a heating current to the module to heat the module, measuring the on-resistance of the module during the heating process, then determining the temperature of the module during the heating process through the k coefficient, and obtaining the first heating curve of the module; 5) after the module reaches thermal equilibrium, switching the heating current to the detection current, at this time the module starts to cool until the temperature of the module and the liquid cooling plate reaches thermal equilibrium again, recording the on-resistance of the module during the cooling process, and obtaining the first cooling curve of the module through the k coefficient; 6) removing the module from the liquid cooling plate, coating a heat-conducting material on the heat dissipation surface of the module, appropriately applying pressure to make the module fully contact the liquid cooling plate, repeating the above steps 4) to 5), and obtaining the second heating curve and the second cooling curve, respectively; 7) the thermal resistance analysis software of the thermal resistance test system analyzes the first and second heating curves and the first and second cooling curves to obtain the first and second thermal resistance curves, and the separation point of the two curves is the thermal resistance of the module.

2. The method of gallium nitride power module thermal resistance testing of claim 1, wherein, The heat transfer medium in the liquid cooling plate is water, oil or other fluid materials capable of transferring heat.

3. The method of gallium nitride power module thermal resistance testing of claim 1, wherein, The method for obtaining the k curve is: adjusting the liquid cooling plate at a certain temperature interval to heat or cool the liquid cooling plate, setting temperature nodes, recording the voltage between the drain and the source of the module at each temperature node, obtaining the relationship between the on-resistance of the module and the temperature change, and drawing a curve.

4. The method of testing thermal resistance of gallium nitride power modules of claim 3, wherein, The temperature interval of the liquid cooling plate adjustment is 10℃, the adjustment range is 25-85℃, and a period of time is waited at each node to make the module and the liquid cooling plate reach thermal equilibrium.

5. The method of gallium nitride power module thermal resistance testing of claim 1, wherein, The heating current is much larger than the detection current.

6. The method of testing thermal resistance of gallium nitride power modules of claim 5, wherein, The heating current is at least 100 times the detection current.

7. The method of gallium nitride power module thermal resistance testing of claim 1, wherein, The formula Rds-on=k*T+c is used to calculate the k coefficient and obtain the first and second heating curves and the first and second cooling curves, wherein Rds-on is the on-resistance of the module, k is the slope of the curve, T is the temperature of the module, and c is the constant of the first order equation.

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