Online monitoring method for junction temperature and thermal impedance of power device in power cycle heating process

Abstract

The invention provides an online monitoring method for junction temperature and thermal impedance of a power device in a power cycle heating process, which comprises the following steps of: in the power cycle process, setting a relationship between conduction voltage drop and junction temperature of a tested device on line; on the basis of the relationship between the conduction voltage drop and the junction temperature, calculating the junction temperature of the tested device in the heating process on line by using the conduction voltage drop; on the basis of the junction temperature, calculating the transient thermal impedance of the tested device on line; in the power cycle process, a criterion is set to automatically judge and reset the relationship between the conduction voltage drop and the junction temperature, so as to ensure the accuracy of the junction temperature and the transient thermal impedance. The method overcomes the influence of device aging on the measurement accuracy of the junction temperature and the thermal impedance, can be completed only by using original hardware equipment for power circulation, and has the advantages of convenience and high efficiency in implementation.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to an online monitoring method for junction temperature and thermal impedance of a power device during a power cycle heating process. Background Art

[0002] Power cycling is a key experimental method for studying the aging failure laws of power semiconductor devices. In power cycling experiments, the fluctuation of junction temperature is the main cause of device aging. Therefore, it is necessary to monitor the junction temperature and thermal resistance of the device under test online to evaluate the aging degree of the device solder layer under given thermal stress conditions. Among them, the junction temperature in the cooling process is usually measured using the on-state voltage drop under a small current. This method is very mature and widely used. However, the junction temperature in the heating process is usually difficult to measure. In addition, in the power cycling experiment, the cooling curve can only be used to calculate the thermal resistance at the moment of heating current removal and cannot obtain complete transient thermal impedance information, but the heating curve can be directly used to calculate the transient thermal impedance of the device under test. Therefore, measuring the junction temperature during the power cycle heating process is of great significance to the device reliability assessment.

[0003] Using the on-state voltage drop under high current to monitor the junction temperature during the heating process in the power cycle is less invasive and does not require additional measurement equipment. It is an ideal method for online monitoring of junction temperature. However, as the number of cycles increases, the on-state voltage drop under high current will increase due to device aging, and its relationship with the junction temperature will also change, which will cause errors in the junction temperature measurement and monitoring failure. Summary of the invention

[0004] In view of the defects in the prior art, an object of the present invention is to provide an online monitoring method for junction temperature and thermal impedance of a power device during a power cycle heating process.

[0005] According to one aspect of the present invention, there is provided a method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process, comprising:

[0006] During the power cycle, the relationship between the on-state voltage drop and the junction temperature of the device under test is adjusted online;

[0007] Based on the relationship between the on-state voltage drop and the junction temperature, the junction temperature of the device under test during the temperature rise process is calculated online using the on-state voltage drop;

[0008] Based on the junction temperature, online calculating the transient thermal impedance of the device under test;

[0009] During the power cycle, the set criterion automatically determines and re-adjusts the relationship between the on-state voltage drop and the junction temperature to ensure the accuracy of the junction temperature and the transient thermal impedance.

[0010] Preferably, during the power cycle process, online setting of the relationship between the on-state voltage drop and the junction temperature of the device under test includes:

[0011] A heating current is passed through the device under test for a specified period of time, causing its junction temperature to rise due to self-heating.

[0012] Cutting off the heating current flowing into the device under test, and injecting a constant small current, and measuring the junction temperature of the device under test at the moment before the heating current is cut off by using the on-state voltage drop under the small current;

[0013] Changing the duration of the heating current to create different junction temperature conditions, and measuring the on-state voltage drop under high current at different junction temperatures;

[0014] Based on the on-state voltage drops at different junction temperatures, a linear function is used to fit the relationship between the on-state voltage drop and the junction temperature.

[0015] Preferably, the heating current is a constant direct current, the magnitude of which is consistent with the heating current used in the power cycle; the duration of passing the heating current is shorter than the heating duration used in the power cycle experiment to avoid overheating of the device.

[0016] Preferably, the changing of the duration of passing the heating current to create different junction temperature conditions and measuring the conduction voltage drop under high current at different junction temperatures includes:

[0017] After using the on-state voltage drop under the small current to measure the junction temperature of the device under test immediately before the heating current is cut off, continue to pass the constant small current through the device under test to measure the junction temperature. After the junction temperature of the device under test drops to close to the case temperature, pass the heating current for another specified period of time to measure the on-state voltage drop at another junction temperature.

[0018] Preferably, the online calculation of the transient thermal impedance of the device under test based on the junction temperature includes:

[0019] Get shell temperature or heat sink temperature;

[0020] The transient thermal impedance is calculated by dividing the junction-case temperature difference or the junction-heat sink temperature difference during the heating process by the product of the on-state voltage drop and the heating current.

[0021]

[0022] Among them, Z th is the transient thermal impedance of the junction-to-case or junction-to-heat sink of the device under test at time t, T j (t) is the junction temperature at time t, T r (t) is the shell temperature or heat sink temperature at time t, V ce (t) is the on-state voltage drop at time t, I c is the heating current.

[0023] Preferably, the transient thermal impedance can be calculated during the temperature rise process of each power cycle.

[0024] Preferably, the device under test includes a power semiconductor device or a power diode; wherein the power semiconductor device is produced using one or more technologies based on module, crimping, and discrete packaging; and the power diode is a semiconductor chip based on silicon, silicon carbide, or gallium nitride.

[0025] Preferably, during the power cycle, setting a criterion to automatically determine and re-adjust the relationship between the on-state voltage drop and the junction temperature to ensure the accuracy of the junction temperature and the transient thermal impedance includes:

[0026] After the temperature rise process of each power cycle ends, a criterion is set to determine whether to readjust the relationship between the conduction voltage drop and the junction temperature;

[0027] If resetting is required, it is performed after the cooling process of the cycle is completed. Each resetting is equivalent to adding several additional heating-cooling cycles during the power cycle.

[0028] Preferably, the criterion includes: automatic resetting after a set number of power cycles.

[0029] Preferably, the criterion includes: setting a threshold value for resetting according to the junction temperature difference calculated in the heating and cooling stages, specifically:

[0030] At the last moment of the power cycle heating stage, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature;

[0031] At the beginning of the power cycle cooling stage, the maximum junction temperature of the device under test is calculated using the on-state voltage drop under low current;

[0032] The junction temperature difference threshold is set. When the junction temperature difference calculated by the two methods exceeds the set threshold, the relationship between the on-state voltage drop and the junction temperature is re-adjusted. The judgment formula is:

[0033] |T j_lc -T j_hc |>T err

[0034] Among them, T j_lc The maximum junction temperature of the device under test is calculated using the on-state voltage drop at a low current at the beginning of the power cycle cooling stage, T j_hc At the last moment of the power cycle heating stage, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature, T err is the set junction temperature difference threshold.

[0035] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0036] The on-line monitoring method for junction temperature and thermal impedance of a power device during a power cycle heating process of an embodiment of the present invention can overcome the influence of device aging on the measurement accuracy of junction temperature and thermal impedance by online setting and correcting the relationship between the on-state voltage drop and junction temperature of the device under test.

[0037] The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process of an embodiment of the present invention utilizes a large current source to cause the device to generate self-heating, and utilizes a small current source to measure the junction temperature; it can be completed using the original hardware equipment of the power cycle experiment, and has the advantages of convenient and efficient implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0039] Figure 1 It is a flow chart of a method for online monitoring of junction temperature and thermal impedance of a power device during a power cycle heating process according to an embodiment of the present invention;

[0040] Figure 2 It is a principle diagram of a setting circuit in a preferred embodiment of the present invention;

[0041] Figure 3 A waveform diagram of heating current, conduction voltage drop and junction temperature during the setting process in a preferred embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of a method for online calculation of junction temperature during a power cycle heating process in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

[0044] In various embodiments of the present invention, two professional terms are involved: large current and small current. Large current is the working current that can cause a device to produce a significant temperature rise, and is usually tens or hundreds of amperes for devices of different capacities; small current is the measurement current that will not cause a device to produce a significant temperature rise, and is usually tens or hundreds of milliamperes for devices of different capacities. The difference between large current and small current is particularly obvious in power cycling experiments, because in order to quickly heat up the device during power cycling, the current used is usually high, usually close to or even exceeding the rated current of the device. The small current is usually only one thousandth of the rated current of the device. In the power cycling experiment, the current passed through the device during the heating stage is a large current, and the current passed through the device during the cooling stage is a small current.

[0045] In one embodiment of the present invention, a method for online monitoring of junction temperature and thermal impedance of a power device during a power cycle heating process is provided. Figure 1 , the main process is:

[0046] Step 1: During the power cycle, the relationship between the on-state voltage drop and the junction temperature of the device under test is adjusted online;

[0047] Step 2, based on the relationship between the on-state voltage drop and the junction temperature set in step 1, the junction temperature of the device under test during the heating process is calculated online using the on-state voltage drop;

[0048] Step 3, based on the junction temperature of the temperature rise process determined in step 2, online calculating the transient thermal impedance of the device under test;

[0049] Step 4: During the power cycle, a criterion is set to automatically determine and re-adjust the relationship between the on-state voltage drop and the junction temperature to ensure the accuracy of the junction temperature and the transient thermal impedance.

[0050] The method for online monitoring junction temperature and thermal impedance of a power device during a rate cycling temperature increase process of the above-mentioned embodiment can overcome the influence of device aging on the measurement accuracy of junction temperature and thermal impedance.

[0051] In a preferred embodiment of the present invention, step 1 is implemented. At the beginning of the power cycle, the relationship between the on-state voltage drop and the junction temperature of the device under test needs to be adjusted. The specific process is as follows:

[0052] A heating current is passed through the device under test for a specified period of time, causing its junction temperature to rise due to self-heating.

[0053] Cutting off the heating current flowing into the device under test, and injecting a constant small current, and measuring the junction temperature of the device under test at the moment before the heating current is cut off by using the on-state voltage drop under the small current;

[0054] Changing the duration of the heating current to create different junction temperature conditions, and measuring the on-state voltage drop under high current at different junction temperatures;

[0055] Based on the on-state voltage drops at different junction temperatures, a linear function is used to fit the relationship between the on-state voltage drop and the junction temperature.

[0056] It should be noted that the heating current is a constant DC current, and its magnitude is consistent with the heating current used in the power cycle. The duration of the heating current is shorter than the heating duration used in the power cycle experiment to avoid overheating of the device.

[0057] When measuring the on-state voltage drop at different junction temperatures, it is important to note that: after using the on-state voltage drop under a small current to measure the junction temperature of the device under test at the moment before the heating current is cut off, continue to pass the constant small current through the device under test to measure the junction temperature; after the junction temperature of the device under test drops to close to the case temperature, pass the heating current for another specified period of time to measure the on-state voltage drop at another junction temperature.

[0058] The core of determining the relationship between the on-state voltage drop and the junction temperature is to measure the on-state voltage drop value at different junction temperatures. The present invention creates different junction temperature conditions by changing the heating time. By ensuring that the junction temperature drops to close to the shell temperature before heating, the starting state of heating can be kept consistent, thereby ensuring that the junction temperature of the device can be different at different heating times. If the next round of heating is performed before the junction temperature drops to close to the shell temperature, the starting state of heating will become uncertain, which will not ensure that the junction temperature of the device can remain different at different heating times. In addition, by ensuring that the junction temperature drops to close to the shell temperature before heating, and controlling the heating time to be shorter than the heating time used in the power cycle experiment, overheating of the device can be effectively avoided. If the device is heated before it is completely cooled down, even if the heating time is shorter than the heating time used in the power cycle experiment, it may still cause the device to overheat.

[0059] In a preferred embodiment of the present invention, a circuit schematic diagram for adjusting the relationship between the on-state voltage drop and the junction temperature is provided as follows: Figure 2 As shown, a large current source is used to make the device generate self-heating, and a small current source is used to measure the junction temperature. The power cycling experiment can be completed using the existing hardware equipment.

[0060] In a specific embodiment, the key current, voltage and temperature change waveforms during the setting process are as follows: Figure 3 As shown, the figure includes the process of obtaining two sets of measurement data with different heating times, and the acquisition of each set of data includes a heating and cooling process.

[0061] The heating process is as follows Figure 3 t on1 With t on2 As shown, a constant large current I is passed through the device c , self-heating is generated so that the junction temperature T j Increase, the conduction voltage drop V ce When the heating time reaches the preset time, the constant high current is cut off, and the on-state voltage drop V under the high current before the cut-off is recorded. ce value.

[0062] The cooling process Figure 3 t off1 With t off2As shown in the figure, after the large current is cut off, the junction temperature of the device gradually decreases to the initial value T0. During the cooling process, a constant small current is injected into the device, and the conduction voltage drop V under the small current is measured. ce And calculate the junction temperature. Since the time required for large current removal is very short, it can usually be considered that the junction temperature calculated by the conduction voltage drop under small current immediately after removal is approximately equal to the junction temperature at the time of removal. Of course, in some other embodiments of the present invention, the junction temperature at the time of removal can also be inferred based on compensation algorithms such as the square root t method.

[0063] according to Figure 3 The process described above performs heating-cooling cycles with different heating durations on the device under test multiple times. After measuring the on-state voltage drop under high current at different junction temperatures, a linear function can be used to fit the relationship between the on-state voltage drop and junction temperature of the device under test under high current. Based on this relationship, the on-state voltage drop is measured during the power cycle heating process, and the junction temperature during the heating process can be calculated online.

[0064] In a preferred embodiment of the present invention, step 3 is implemented to calculate the transient thermal impedance based on the temperature difference between the junction and the shell or the heat sink, and the product of the on-state voltage drop and the current. Specifically, the formula for calculating the transient thermal impedance is:

[0065]

[0066] Among them, Z th is the transient thermal impedance of the junction-to-case or junction-to-heat sink of the device under test at time t, T j (t) is the junction temperature at time t, T r (t) is the shell temperature or heat sink temperature at time t, V ce (t) is the on-state voltage drop at time t, I c The shell temperature and the heat sink temperature are usually measured using temperature sensors, such as thermocouples and thermistors.

[0067] In a preferred embodiment of the present invention, step 4 is implemented to set a criterion during the power cycle process, and determine whether it is necessary to re-adjust the relationship between the on-state voltage drop and the junction temperature according to the number of cycles or the difference in the highest junction temperature calculated during the heating and cooling process. If re-adjustment is required, it is performed after the cooling process of the cycle is completed, and each re-adjustment can be equivalent to adding several additional heating and cooling cycles during the power cycle process.

[0068] Furthermore, in a preferred embodiment, the judgment criterion is: setting a threshold value according to the junction temperature difference calculated in the heating and cooling stages for resetting, etc. Specifically:

[0069] At the end of the power cycle heating phase, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature, and at the beginning of the power cycle cooling phase, the maximum junction temperature of the device under test is calculated using the on-state voltage drop under a small current. A junction temperature difference threshold is set. When the junction temperature difference calculated by the two methods exceeds the threshold, the relationship between the on-state voltage drop and the junction temperature is reset. The judgment formula is:

[0070] |T j_lc -T j_hc |>T err

[0071] Among them, T j_lc The maximum junction temperature of the device under test is calculated using the on-state voltage drop at a low current at the beginning of the power cycle cooling stage, T j_hc At the last moment of the power cycle heating stage, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature, T err is the set junction temperature difference threshold.

[0072] In a specific embodiment, Figure 4 The figure is a schematic diagram of the method for online calculation of junction temperature during the heating process of a power cycle. By adjusting the relationship between the on-state voltage drop and the junction temperature, the junction temperature during the heating process can be calculated by measuring the on-state voltage drop during the heating process. At the same time, the junction temperature during the cooling process can be calculated by measuring the on-state voltage drop during the cooling process (the junction temperature during the cooling process is calculated by injecting a small current and using the on-state voltage drop under a small current). The maximum junction temperature calculated during the heating process in the figure is 149.4℃, and the maximum junction temperature calculated during the cooling process is 152.0℃. The absolute value of the difference between the two is 2.6℃. By comparing this value with the pre-set threshold, it can be determined whether the relationship between the on-state voltage drop and the junction temperature needs to be re-adjusted. By online adjustment and correction of the on-state voltage drop and junction temperature relationship of the device under test, the influence of device aging on the accuracy of junction temperature and thermal impedance measurement can be overcome, and the on-state voltage drop under a large current can be used to accurately monitor the junction temperature during the heating process during the power cycle.

[0073] Of course, in other embodiments, the criterion may also be other methods, such as setting a cycle number threshold, and automatically resetting when the cycle number exceeds the threshold.

[0074] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A method for online monitoring of junction temperature and thermal impedance of power devices during power cycle heating process. It is characterized in that include: During the power cycle, the relationship between the on-state voltage drop and the junction temperature of the device under test is adjusted online; Based on the relationship between the on-state voltage drop and the junction temperature, the junction temperature of the device under test during the temperature rise process is calculated online using the on-state voltage drop; Based on the junction temperature, online calculating the transient thermal impedance of the device under test; During the power cycle, the set criterion automatically determines and re-adjusts the relationship between the on-state voltage drop and the junction temperature to ensure the accuracy of the junction temperature and the transient thermal impedance.

2. According to the method for online monitoring of junction temperature and thermal impedance of power devices during power cycle heating process of claim 1, It is characterized in that During the power cycle process, online setting of the relationship between the on-state voltage drop and the junction temperature of the device under test includes: A heating current is passed through the device under test for a specified period of time, causing its junction temperature to rise due to self-heating. Cutting off the heating current flowing into the device under test, and injecting a constant small current, and measuring the junction temperature of the device under test at the moment before the heating current is cut off by using the on-state voltage drop under the small current; Changing the duration of the heating current to create different junction temperature conditions, and measuring the on-state voltage drop under high current at different junction temperatures; Based on the on-state voltage drops at different junction temperatures, a linear function is used to fit the relationship between the on-state voltage drop and the junction temperature.

3. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 2, It is characterized in that The heating current is a constant direct current, and its magnitude is consistent with the heating current used in the power cycle; The duration of passing the heating current is shorter than the heating duration used in the power cycling experiment to avoid overheating of the device.

4. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 3, It is characterized in that The changing of the duration of the heating current to create different junction temperature conditions and measuring the conduction voltage drop under large current at different junction temperatures include: After using the on-state voltage drop under the small current to measure the junction temperature of the device under test immediately before the heating current is cut off, continue to pass the constant small current through the device under test to measure the junction temperature. After the junction temperature of the device under test drops to close to the case temperature, pass the heating current for another specified period of time to measure the on-state voltage drop at another junction temperature.

5. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 1, It is characterized in that The online calculation of the transient thermal impedance of the device under test based on the junction temperature includes: Get the shell temperature or radiator temperature; The transient thermal impedance is calculated by dividing the junction-case temperature difference or the junction-heat sink temperature difference during the heating process by the product of the on-state voltage drop and the heating current. Among them, Z th is the transient thermal impedance of the junction-to-case or junction-to-heat sink of the device under test at time t, T j (t) is the junction temperature at time t, T r (t) is the shell temperature or heat sink temperature at time t, V ce (t) is the on-state voltage drop at time t, I c is the heating current.

6. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 5, It is characterized in that The transient thermal impedance can be calculated during the temperature rise process of each power cycle.

7. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 1, It is characterized in that The device under test is a power semiconductor device, including a controllable power semiconductor device and a power diode. The packaging of the power semiconductor device adopts one or more of module-based, crimping-based, and discrete packaging technologies; the material of the power semiconductor device adopts one or more of silicon-based, silicon carbide-based, and gallium nitride-based.

8. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 1, It is characterized in that During the power cycle, setting a criterion to automatically determine and re-adjust the relationship between the on-state voltage drop and the junction temperature to ensure the accuracy of the junction temperature and the transient thermal impedance includes: After the temperature rise process of each power cycle ends, a criterion is set to determine whether to readjust the relationship between the conduction voltage drop and the junction temperature; If resetting is required, it is performed after the cooling process of the cycle is completed. Each resetting is equivalent to adding several additional heating-cooling cycles during the power cycle.

9. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 8, It is characterized in that The criteria include: automatic resetting after a set number of power cycles.

10. The method for online monitoring junction temperature and thermal impedance of a power device during a power cycle heating process according to claim 8, It is characterized in that The criterion includes: resetting the threshold value according to the junction temperature difference calculated in the heating and cooling stages, specifically: At the last moment of the power cycle heating stage, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature; At the beginning of the power cycle cooling stage, the maximum junction temperature of the device under test is calculated using the on-state voltage drop under low current; The junction temperature difference threshold is set. When the junction temperature difference calculated by the two methods exceeds the set threshold, the relationship between the on-state voltage drop and the junction temperature is reset. The judgment formula is: |T j_lc -T j_hc |>T err Among them, T j_lc The maximum junction temperature of the device under test is calculated using the on-state voltage drop at a low current at the beginning of the power cycle cooling stage, T j_hc At the last moment of the power cycle heating stage, the maximum junction temperature of the device under test is calculated using the relationship between the on-state voltage drop and the junction temperature, T err is the set junction temperature difference threshold.

Images