Methods for predicting the lifetime of power devices under low pressure

Abstract

This invention provides a method for predicting the lifetime of power devices under low air pressure, comprising the following steps: acquiring environmental parameters of the environment in which the power device under test is located, including at least air pressure and ambient temperature; determining the heat transfer coefficient of the heat sink surface of the power device under test based on the environmental parameters of the environment in which the power device under test is located; determining the equivalent thermal resistance from the heat sink to the air based on the heat transfer coefficient of the heat sink surface of the power device under test; determining the case temperature and junction temperature of the power device based on the equivalent thermal resistance from the heat sink to the air, and determining the inelastic strain rate of the solder layer and the substrate solder layer of the power device based on the case temperature and junction temperature; determining the cycle life of the power device based on the strain value of the solder layer and the substrate solder layer of the power device; effectively ensuring that the predicted lifetime of the power device under low air pressure is basically consistent with the actual lifetime, effectively ensuring the safe and stable operation of the photovoltaic power generation system.

Description

Technical Field

[0001] This invention relates to an analysis method for power devices, and more particularly to a method for predicting the lifetime of power devices under low gas pressure. Background Technology

[0002] In photovoltaic power generation, power devices are the core components of photovoltaic power converters, and their reliability affects the stability of the photovoltaic system. High-altitude areas above 3000m have abundant solar energy resources and are the main gathering places for photovoltaic power generation. However, as the altitude increases, the air pressure decreases, the heat transfer capacity of the air decreases, and the thermal fatigue degradation of power devices accelerates, resulting in a shortened lifespan of power devices under low air pressure conditions, thus affecting the stability of the photovoltaic power generation system.

[0003] In existing technologies, the methods for predicting the lifespan of power devices in photovoltaic systems are generally based on indoor accelerated aging tests. This method does not take into account the impact of low air pressure on the lifespan of power devices. If applied directly, it will lead to the predicted lifespan of power devices being higher than the actual lifespan, resulting in power device failure and affecting the safe and stable operation of the converter subsystem in the entire photovoltaic system.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for predicting the lifespan of power devices under low pressure. Based on the air pressure and temperature information of the low-pressure environment in which the power device is located, the heat transfer coefficient of the heat sink of the power device is determined. Then, the case temperature and junction temperature of the power device are determined by the heat transfer coefficient, and the lifespan of the power device is evaluated. This method can effectively ensure that the predicted lifespan of the power device under low pressure is basically consistent with the actual lifespan, and effectively ensure the safe and stable operation of the photovoltaic power generation system.

[0006] This invention provides a method for predicting the lifetime of power devices under low gas pressure, comprising the following steps:

[0007] Obtain the environmental parameters of the environment in which the power device under test is located. These environmental parameters include at least air pressure and ambient temperature.

[0008] The heat transfer coefficient of the heat sink surface of the power device under test is determined based on the environmental parameters of the environment in which the power device under test is located.

[0009] The equivalent thermal resistance from the heat sink to the air is determined based on the heat transfer coefficient of the heat sink surface of the power device under test.

[0010] The case temperature and junction temperature of the power device are determined based on the equivalent thermal resistance from the heat sink to the air, and the inelastic strain rate of the solder layer of the power device and the substrate solder layer are determined based on the case temperature and junction temperature.

[0011] The cycle life of the power device is determined based on the strain values ​​of the solder layer of the power device and the solder layer of the substrate.

[0012] Furthermore, the cycle life of the power device was determined using the following method:

[0013]

[0014] in: Indicates the cycle life of the substrate solder layer of power devices. C represents the cycle life of the chip bonding layer of a power device. 11 C represents the fatigue ductility coefficient of the substrate solder layer of a power device. 12 The fatigue ductility index of the substrate solder layer of power devices. C represents the inelastic strain rate of the substrate solder layer of a power device. 21 C represents the fatigue ductility coefficient of the chip bonding layer of a power device. 22 The fatigue ductility index of the chip bonding layer of a power device. This represents the inelastic strain rate of the chip bonding layer of a power device.

[0015] Furthermore, the inelastic strain rates of the chip bonding layer and the substrate bonding layer of the power device are determined as follows:

[0016]

[0017] Where: K A The coefficients are set, and Q1 and Q2 represent activation energies. Activation energy refers to the energy threshold required to overcome irreversible deformation (such as dislocation slip and void nucleation) of the internal microstructure (e.g., dislocations, grain boundaries) of the chip bonding layer material of a power device. This represents the stress coefficient of the substrate solder layer of the power device. m represents the equivalent stress of the substrate solder layer of a power device. A1 The strain sensitivity coefficient of the substrate solder layer of the power device is represented by R, which represents the universal gas constant, and T is the strain sensitivity coefficient of the substrate solder layer of the power device. C (P a T represents the case temperature of the power device. J (P a This indicates the junction temperature of the power device. Indicates the strain of the substrate solder layer. This represents the stress coefficient of the chip solder layer of a power device. m represents the equivalent stress of the chip bonding layer of a power device. A2 This represents the strain sensitivity coefficient of the chip bonding layer of a power device.

[0018] Furthermore, the case temperature T of the power device is determined using the following method. C (P a ):

[0019]

[0020] Where: P loss T represents the power device loss. cmax R represents the maximum case temperature of the power device during the power pulse cycle. th,ch C represents the thermal resistance from the power device's casing to its heatsink. th,ch T represents the heat capacity from the power device's casing to its heat sink, and t represents the time it takes for the heat sink to change temperature. h (P a ) represents the temperature of the heat sink of the power device, t p This indicates that the temperature of the power device's heatsink has reached its maximum value, T. hmax The duration, t d This indicates the duration of the high level of the power pulse from a power device within one cycle.

[0021] Furthermore, the junction temperature T of the power device is determined using the following method. J (P a ):

[0022]

[0023] Where: T jmax R represents the maximum junction temperature of the power device during the power pulse cycle. th,jc C represents the thermal resistance from the PN junction of a power device to its casing. th,jc This represents the heat capacity from the PN junction of a power device to its casing.

[0024] Furthermore, the temperature T of the heat sink of the power device is determined by the following method. h (P a ):

[0025]

[0026] Where: T hmax R represents the maximum temperature of the heat sink of a power device during a power pulse cycle. th,ha (P a C represents the equivalent thermal resistance from the heatsink of the power device to the ambient air. th,ha T represents the heat capacity of a power device from its heat sink to ambient air. a This indicates the ambient temperature of the power device.

[0027] Furthermore, the equivalent thermal resistance R from the heatsink to the air of the power device is determined using the following method. th,ha (P a ):

[0028]

[0029] in:

[0030] R th,hai (P a h represents the equivalent thermal resistance from the i-th surface of the heat sink of a power device to the air. hai (P a Let A be the heat transfer coefficient from the i-th surface of the heat sink of the power device to the air. i This represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink of the power device. When i is 2, it represents the lower surface of the heat sink of the power device. When i is 3 to 6, it represents the side surface of the heat sink of the power device.

[0031] Furthermore, the heat transfer coefficient of the heat sink surface of the power device is determined by the following method:

[0032] When i is 1:

[0033]

[0034] When i is 2:

[0035]

[0036] When i is between 3 and 6:

[0037]

[0038] Where: K a (P a ) represents the thermal conductivity of air, L s L represents the characteristic length of the upper and lower surfaces of the heat sink of a power device. h Ra(P) is the vertical height of the side surface of the heat sink of the power device. a ) represents the Prandtl number, Pr(P a () represents the Rayleigh number;

[0039]

[0040] Where: β represents the air volume expansion coefficient, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the gravitational acceleration, R represents the universal gas constant, and c a P represents the specific heat capacity of air, ΔT represents the air temperature deviation, and P represents the specific heat capacity of air. aThis indicates the air pressure value of the environment in which the power device is located.

[0041] The beneficial effects of this invention are as follows: By using this invention, the heat transfer coefficient of the heat sink of the power device is determined based on the air pressure and temperature information of the low-pressure environment in which the power device is located. Then, the case temperature and junction temperature of the power device are determined by the heat transfer coefficient, and the lifespan of the power device is evaluated. This can effectively ensure that the predicted lifespan of the power device in the low-pressure environment is basically consistent with the actual lifespan, and effectively ensure the safe and stable operation of the photovoltaic power generation system. Attached Figure Description

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0043] Figure 1 This is a flowchart of the present invention.

[0044] Figure 2 This is a schematic diagram of the power period and heat sink of the present invention. Detailed Implementation

[0045] The present invention will be further described in detail below:

[0046] This invention provides a method for predicting the lifetime of power devices under low gas pressure, comprising the following steps:

[0047] S1. Obtain the environmental parameters of the environment in which the power device under test is located. These environmental parameters include at least air pressure and ambient temperature.

[0048] S2. Determine the heat transfer coefficient of the heat sink surface of the power device under test based on the environmental parameters of the environment in which the power device under test is located;

[0049] S3. Determine the equivalent thermal resistance from the heat sink to the air based on the heat transfer coefficient of the heat sink surface of the power device under test.

[0050] S4. The case temperature and junction temperature of the power device are determined based on the equivalent thermal resistance from the heat sink to the air, and the inelastic strain rate of the solder layer of the power device and the substrate solder layer are determined from the case temperature and junction temperature.

[0051] S5. The cycle life of the power device is determined based on the strain values ​​of the solder layer of the power device and the solder layer of the substrate. This invention determines the heat transfer coefficient of the power device's heat sink based on the air pressure and temperature information of the low-pressure environment in which the power device is located. Then, the case temperature and junction temperature of the power device are determined using the heat transfer coefficient, thereby evaluating the lifespan of the power device. This effectively ensures that the predicted lifespan of the power device in low-pressure environments is basically consistent with the actual lifespan, effectively ensuring the safe and stable operation of the photovoltaic power generation system.

[0052] In this example, in step S5, the cycle life of the power device is determined by the following method:

[0053]

[0054] in: Indicates the cycle life of the substrate solder layer of power devices. C represents the cycle life of the chip bonding layer of a power device. 11 C represents the fatigue ductility coefficient of the substrate solder layer of a power device. 12 The fatigue ductility index of the substrate solder layer of power devices. C represents the inelastic strain rate of the substrate solder layer of a power device. 21 C represents the fatigue ductility coefficient of the chip bonding layer of a power device. 22 The fatigue ductility index of the chip bonding layer of a power device. This represents the inelastic strain rate of the chip bonding layer of a power device. The power device comprises a semiconductor chip and a substrate. The semiconductor chip is encapsulated on the substrate via a bonding layer. The substrate of the power device also has a bonding layer, primarily composed of copper foil and ceramic electrodes. The cycle life of these two bonding layers is often difficult to determine in low-pressure environments. The method described above can accurately determine the cycle life in low-pressure environments. Once these two cycle lives are determined, they can be used as inputs in COMSOL simulation software to obtain the cycle life for the entire power period. The process by which COMSOL simulation software obtains the cycle life for the entire power period from the cycle life of the substrate bonding layer and the chip bonding layer is existing technology and will not be elaborated upon here.

[0055] In this example, the inelastic strain rates of the chip bonding layer and the substrate bonding layer of the power device are determined as follows:

[0056]

[0057] Where: K A The coefficients are set, and Q1 and Q2 represent activation energies. Activation energy refers to the energy threshold required to overcome irreversible deformation (such as dislocation slip and void nucleation) of the internal microstructure (e.g., dislocations, grain boundaries) of the chip bonding layer material of a power device. This represents the stress coefficient of the substrate solder layer of the power device. m represents the equivalent stress of the substrate solder layer of a power device. A1 The strain sensitivity coefficient of the substrate solder layer of the power device is represented by R, which represents the universal gas constant, and T is the strain sensitivity coefficient of the substrate solder layer of the power device. C (P a T represents the case temperature of the power device. J (P a This indicates the junction temperature of the power device. Indicates the strain of the substrate solder layer. This represents the stress coefficient of the chip solder layer of a power device. m represents the equivalent stress of the chip bonding layer of a power device. A2 The strain sensitivity coefficient of the chip bonding layer of a power device;

[0058] Specifically, the case temperature T of the power device is determined by the following method. C (P a ):

[0059]

[0060] Where: P loss This represents the power device's losses, which can be determined by the device's voltage and current. This is existing technology. (T) cmax R represents the maximum case temperature of the power device during the power pulse cycle. th,ch C represents the thermal resistance from the power device's casing to its heatsink. th,ch T represents the heat capacity from the power device's casing to its heat sink, and t represents the time it takes for the heat sink to change temperature. h (P a ) represents the temperature of the heat sink of the power device, t p This indicates that the temperature of the power device's heatsink has reached its maximum value, T. hmax The duration, t d This indicates the duration of the high level of the power pulse of a power device within one cycle. The power pulse of a power device refers to the power device operating in the form of a pulsed current.

[0061] The junction temperature T of the power device is determined by the following method. J (P a ):

[0062]

[0063] Wherein: T jmax R represents the maximum junction temperature of the power device during the power pulse cycle. th,jc C represents the thermal resistance from the PN junction of a power device to its casing. th,jc This represents the heat capacity from the PN junction of a power device to its casing.

[0064] The temperature T of the heat sink of the power device is determined by the following method. h (P a ):

[0065]

[0066] Wherein: T hmaxR represents the maximum temperature of the heat sink of a power device during a power pulse cycle. th,ha (P a C represents the equivalent thermal resistance from the heatsink of the power device to ambient air. th,ha T represents the heat capacity of a power device from its heat sink to ambient air. a This indicates the ambient temperature of the power device.

[0067] The equivalent thermal resistance R from the heatsink to the air of the power device is determined using the following method. th,ha (P a ):

[0068]

[0069] in:

[0070] R th,hai (P a h represents the equivalent thermal resistance from the i-th surface of the heat sink of a power device to the air. hai (P a Let A be the heat transfer coefficient from the i-th surface of the heat sink of the power device to the air. i This represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink; when i is 2, it represents the lower surface; and when i is 3 to 6, it represents the side surface. (Specific details are omitted as they are not provided in the original text.) Figure 2 As shown, Figure 2 The heat sink for a power device is equivalent to a cuboid, and each heat sink can be equivalent to a corresponding cuboid.

[0071] The heat transfer coefficient of the heat sink surface of a power device is determined by the following method:

[0072] When i is 1:

[0073]

[0074] When i is 2:

[0075]

[0076] When i is between 3 and 6:

[0077]

[0078] Where: K a (P a ) represents the thermal conductivity of air, L s The characteristic lengths of the upper and lower surfaces of the heat sink of a power device are represented by... Figure 2It can be seen that the characteristic lengths of the upper and lower surfaces of the power device are equal; L h Ra(P) is the vertical height of the side surface of the heat sink of the power device. a ) represents the Prandtl number, Pr(P a () represents the Rayleigh number;

[0079]

[0080] Where: β represents the air volume expansion coefficient, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the gravitational acceleration, R represents the universal gas constant, and c a P represents the specific heat capacity of air, ΔT represents the air temperature deviation, and P represents the specific heat capacity of air. a This represents the air pressure value of the environment in which the power device is located, in μ. a This refers to dynamic viscosity.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for predicting the lifetime of power devices under low air pressure, characterized in that: Includes the following steps: Obtain the environmental parameters of the environment in which the power device under test is located. These environmental parameters include at least air pressure and ambient temperature. The heat transfer coefficient of the heat sink surface of the power device under test is determined based on the environmental parameters of the environment in which the power device under test is located. The equivalent thermal resistance from the heat sink to the air is determined based on the heat transfer coefficient of the heat sink surface of the power device under test. The case temperature and junction temperature of the power device are determined based on the equivalent thermal resistance from the heat sink to the air, and the inelastic strain rate of the solder layer of the power device and the substrate solder layer are determined based on the case temperature and junction temperature. The cycle life of the power device is determined based on the strain rate of the solder layer of the power device and the solder layer of the substrate. The cycle life of the power device is determined by the following method: in: Indicates the cycle life of the substrate solder layer of power devices. C represents the cycle life of the chip bonding layer of a power device. 11 C represents the fatigue ductility coefficient of the substrate solder layer of a power device. 12 The fatigue ductility index of the substrate solder layer of power devices. C represents the inelastic strain rate of the substrate solder layer of a power device. 21 C represents the fatigue ductility coefficient of the chip bonding layer of a power device. 22 The fatigue ductility index of the chip bonding layer of a power device. This represents the inelastic strain rate of the chip bonding layer of a power device; The inelastic strain rates of the chip bonding layer and the substrate bonding layer of the power device are determined as follows: Where: K A This represents the set coefficients, and Q1 and Q2 represent the activation energies. This represents the stress coefficient of the substrate solder layer of the power device. m represents the equivalent stress of the substrate solder layer of a power device. A1 The strain sensitivity coefficient of the substrate solder layer of the power device is represented by R, which represents the universal gas constant, and T is the strain sensitivity coefficient of the substrate solder layer of the power device. C (P a T represents the case temperature of the power device. J (P a This indicates the junction temperature of the power device. Indicates the strain of the substrate solder layer. This represents the stress coefficient of the chip solder layer of a power device. m represents the equivalent stress of the chip bonding layer of a power device. A2 The strain sensitivity coefficient of the chip bonding layer of a power device; The case temperature T of the power device is determined by the following method. C (P a ): Where: P loss T represents the power device loss. cmax R represents the maximum case temperature of the power device during the power pulse cycle. th,ch C represents the thermal resistance from the power device's casing to its heatsink. th,ch T represents the heat capacity from the power device's casing to its heat sink, and t represents the time it takes for the heat sink to change temperature. h (P a ) represents the temperature of the heat sink of the power device, t p This indicates that the temperature of the power device's heatsink has reached its maximum value, T. hmax The duration, t d This indicates the period during which the power device withstands the power pulse; The junction temperature T of the power device is determined by the following method. J (P a ): Where: T jmax R represents the maximum junction temperature of the power device during the power pulse cycle. th,jc C represents the thermal resistance from the PN junction of a power device to its casing. th,jc This represents the heat capacity from the PN junction of a power device to its casing. The temperature T of the heat sink of the power device is determined by the following method. h (P a ): Where: T hmax R represents the maximum temperature of the heat sink of a power device during a power pulse cycle. th,ha (P a C represents the equivalent thermal resistance from the heatsink of the power device to the ambient air. th,ha T represents the heat capacity of a power device from its heat sink to ambient air. a This indicates the ambient temperature of the power device.

2. The method for predicting the lifetime of power devices under low pressure according to claim 1, characterized in that: The equivalent thermal resistance R from the heatsink to the air of the power device is determined using the following method. th,ha (P a ): in: R th,hai (P a h represents the equivalent thermal resistance from the i-th surface of the heat sink of a power device to the air. hai (P a Let A be the heat transfer coefficient from the i-th surface of the heat sink of the power device to the air. i This represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink of the power device. When i is 2, it represents the lower surface of the heat sink of the power device. When i is 3 to 6, it represents the side surface of the heat sink of the power device.

3. The method for predicting the lifetime of power devices under low pressure according to claim 2, characterized in that: The heat transfer coefficient of the heat sink surface of a power device is determined by the following method: When i is 1: When i is 2: When i is between 3 and 6: Where: K a (P a ) represents the thermal conductivity of air, L s L represents the characteristic length of the upper and lower surfaces of the heat sink of a power device. h Ra(P) is the vertical height of the side surface of the heat sink of the power device. a ) represents the Prandtl number, Pr(P a () represents the Rayleigh number; Where: β represents the air volume expansion coefficient, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the gravitational acceleration, R represents the universal gas constant, and c a P represents the specific heat capacity of air, ΔT represents the air temperature deviation, and P represents the specific heat capacity of air. a This represents the air pressure value of the environment in which the power device is located, in μ. a This refers to dynamic viscosity.

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