Finite element method-based thermal analysis method for high-heat-consumption-rate SiC MOSFET (Metal Oxide Semiconductor Field Effect Transistor) power device

Abstract

The invention discloses a finite element method-based thermal analysis method for a high-heat-consumption-rate SiC MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) power device, which comprises the following steps: step 1, loading material information, step 2, carrying out three-dimensional modeling, namely carrying out modeling according to the three-dimensional size and the arrangement position of each part to obtain a three-dimensional model; step 3, model correction: carrying out arc processing and simplification processing on edges and corners of the three-dimensional model; dividing a computational grid based on the simplified model; step 4, setting: setting material attributes of each part of the simplified model; setting boundary conditions of the simplified model; and 5, obtaining a steady-state temperature, selecting a solid heat transfer physical field model, and solving the steady-state temperature of the high-heat-consumption SiC MOSFET power device to be analyzed by using a finite element numerical method of a heat conduction equation. According to the method, the working steady-state temperature of the SiC MOSFET power device with the high heat consumption rate can be calculated more efficiently, and the calculation speed can be increased under the condition that the engineering error requirement is met by using the simplified SiC MOSFET model.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a thermal analysis method for a high heat consumption rate SiC MOSFET power device based on a finite element method. Background Art

[0002] In modern power electronic systems, SiC MOSFET is becoming the first choice for power devices. Compared with traditional Si-based devices, SiC MOSFET has excellent properties such as low switching loss, high switching frequency and high operating temperature. Therefore, SiC MOSFET has been widely used in emerging and traditional fields such as electric vehicles, 5G base stations and power systems. However, as power devices are developing in the direction of high power and small size, they will inevitably face increasingly serious thermodynamic problems. The operating temperature has a huge impact on the performance and reliability of electronic devices. Existing studies have shown that the large thermal stress caused by high temperature is one of the main reasons for the failure of power semiconductor devices. Therefore, the research on thermal analysis simulation technology of power devices is of great significance.

[0003] The purpose of thermal analysis is to obtain the thermal characteristics of power semiconductors such as SiC MOSFET during operation, and to serve as a reference for optimizing the design of the heat dissipation system and reliability assessment. When conducting thermal analysis of SiC MOSFET, numerical simulation methods such as finite element analysis (FEA) can be used to establish a three-dimensional thermal model of MOSFET, and comprehensively consider factors such as its internal structure, material properties, and working conditions to calculate parameters such as its temperature distribution, thermal resistance, and thermal conduction.

[0004] The solution method for thermal analysis using the finite element method is to establish a grid to model the entity with finite discretization, establish energy conservation and heat conduction, heat convection and other equations for each grid unit, and solve the equilibrium equation of the entire entity in parallel to obtain the temperature value of each grid as the simulation result. The finite element thermal analysis method has high reliability and short calculation time. Based on the finite element simulation, the device structure design can be optimized, the heat dissipation system can be improved, and the working efficiency and reliability of the device can be improved.

[0005] Current research usually focuses on the optimization of single SiC MOSFET packaging technology, or the research objects are mostly low heat rate devices with sufficient heat dissipation space. However, as SiC MOSFET is continuously integrated into various fields, the challenges of high power and poor heat dissipation conditions become more and more urgent to overcome. Therefore, a thermal analysis method for high heat rate power devices based on finite element method is urgently needed. Summary of the invention

[0006] To meet the above needs, the present invention aims to provide a thermal analysis method for high heat consumption power devices based on the finite element method, construct a simplified SiC MOSFET model to fit the actual heat source, and optimize the thin layer structure when establishing the overall model, so that when performing finite element simulation, the final steady-state result can be obtained more quickly while ensuring accuracy.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A thermal analysis method for a high heat rate SiC MOSFET power device based on a finite element method comprises the following steps:

[0009] Step 1, loading material information, wherein the material includes materials contained in various components of the high heat rate SiC MOSFET power device to be analyzed;

[0010] Step 2: 3D modeling, modeling is performed according to the 3D size and arrangement position of each component to obtain a 3D model;

[0011] Step 3: Model modification: rounding and simplifying the edges and corners of the three-dimensional model. When there is a segmented structure, the segmented structure is merged as a whole or in part to obtain a simplified model; and the calculation grid is divided based on the simplified model.

[0012] Step 4: Setting: setting the material properties of each part of the simplified model; setting the boundary conditions of the simplified model;

[0013] Step 5: Obtain the steady-state temperature, select the solid heat transfer physical field model, and use the finite element numerical method of the heat conduction equation to obtain the steady-state temperature of the high heat consumption rate SiC MOSFET power device to be analyzed.

[0014] Preferably, step 2 comprises the following steps:

[0015] Step 2.1, ignore the internal structure of each component in the 3D modeling, simplify the theoretical thermal resistance of the model, and calculate it according to the 45° heat conduction model;

[0016] Step 2.2: When performing 3D modeling, ignore the part whose thickness is much smaller than other components, convert it into a surface boundary condition, and set the corresponding physical properties.

[0017] Preferably, the simplified model is constructed as follows:

[0018] Two rectangular blocks made of SiC and Cu are set up, the scales of the two rectangular blocks are equal to the actual products, and a square in the middle of the interface is selected as the heat source; pins are added to the model, and the number and material of the pins are equal to the number and material of the pins of the high heat consumption rate SiC MOSFET power device analyzed.

[0019] Further preferably, the side length of the square is 4 mm.

[0020] Preferably, the theoretical thermal resistance calculation method of the simplified model is as follows:

[0021]

[0022] Where: L i is the thickness of the i-th layer of material; a i , b i are the length and width of the lower surface of the i-th layer of material respectively; K i is the thermal conductivity of the i-th layer material, then the theoretical thermal resistance from junction to case of the SiC MOSFET power chip is R jc for:

[0023] R jc =Σ i R thi .

[0024] Furthermore, the theoretical thermal resistance calculation method of the simplified model also includes:

[0025] Compare and select R from SiC MOSFET data sheets jc The theoretical R of the above model jc , ensuring that the error is within a reasonable range.

[0026] Preferably, the error is within a reasonable range, that is, the error is less than 20%.

[0027] Preferably, step 4 comprises the following steps:

[0028] Step 4.1: Set the thermal convection coefficient of the contact surface exposed to air;

[0029] Step 4.2: Simplify the model into a thin layer with surface boundary conditions, set the corresponding material properties, and set the thermal convection coefficient of the thin layer;

[0030] Step 4.3: Simplify the heat sink model and replace it with an equivalent method of increasing the heat convection coefficient of the area where the heat sink is located.

[0031] Further preferably, it is characterized in that

[0032] In step 4.1, set the heat convection coefficient of the contact surface exposed to air to 5-20 (W / m2 K);

[0033] In step 4.2, the thermal convection coefficient of the thin layer is set to 0;

[0034] Preferably, the heat conduction equation is as follows:

[0035]

[0036] Where ρ is the density, C p is the specific heat capacity, u is the velocity vector, is the temperature gradient, is the divergence of the heat flux vector q, k is the thermal conductivity, Q and Q ted They are internal and external heat sources respectively.

[0037] The beneficial effects of the present invention are as follows:

[0038] The present invention can more efficiently calculate the operating steady-state temperature of a SiC MOSFET power device with a high heat consumption rate, and the simplified SiC MOSFET model used can improve the calculation speed while meeting the engineering error requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention discloses a flow chart of a thermal analysis method for a high heat consumption rate SiC MOSFET power device based on the finite element method. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0041] Example 1

[0042] This embodiment discloses a thermal analysis method for a high heat consumption rate SiC MOSFET power device based on a finite element method, such as Figure 1 As shown, the specific steps include:

[0043] Step 1: Set up the material: According to the predetermined working temperature, the physical parameters of the material should be within a reasonable range.

[0044] Step 2: Establish a 3D model of the power device. According to the design of the device, determine the 3D size and layout of each component, and model it in the finite element software. Specifically:

[0045] Step 2.1: Build three-dimensional models of each component of the power device in turn. The main dimensions of each three-dimensional model must be equal to the actual product.

[0046] Step 2.2: For high heat consumption rate SiC MOSFET power devices, SiC MOSFET is the main heat source and has a complex internal structure. Its 3D model needs to be simplified and its internal structure ignored. Set up two cuboids made of SiC and Cu respectively. The scale of the two cuboids is temporarily set to be equal to the actual product, and a square with a side length of 4mm in the middle of the interface is selected as the heat source; the model needs to add copper pins, the number and material are equal to the selected product.

[0047] Step 2.3: The theoretical thermal resistance of the simplified model can be calculated based on the 45° thermal conduction model, and the error between it and the given nominal value of the selected device should be within the engineering allowable range. If the theoretical thermal resistance of the currently tentative simplified model meets the engineering error condition, it does not need to be modified. If it does not meet the engineering error condition, the dimensions of the two rectangular blocks of SiC and Cu need to be corrected. When correcting, the order of thickness first and then length and width should be followed. The correction value of length and width should not be too large. The calculation method of the theoretical thermal resistance is as follows:

[0048]

[0049] Among them, L i is the thickness of the i-th layer of material; a i , b i are the length and width of the lower surface of the i-th layer of material respectively; K i is the thermal conductivity of the i-th layer material, then the theoretical thermal resistance from junction to case of the SiC MOSFET power chip is R jc for:

[0050] R jc =Σ i R thi

[0051] Compare and select R from SiC MOSFET data sheets jc The theoretical R of the above model jc , ensuring that the error is within a reasonable range.

[0052] Step 2.4: In the 3D model, ignore the parts whose thickness is much smaller than other components, convert them into surface boundary conditions, and set the corresponding physical properties.

[0053] Step 3: Modify the model, round the edges and corners of the 3D model, and partially merge the complex segmented structure into a whole; divide the calculation grid based on the simplified model, and the grid division should ensure a reasonable density and size change rate, as follows:

[0054] Step 3.1: After the 3D model is established, the sharp structures and small-sized bent structures of the model need to be rounded to reduce the appearance of edges and corners, which is convenient for the division of the mesh here and the final solution. For example, when the pins of the SiCMOSFET model are in contact with the PCB board, they are usually bent and then welded, resulting in the pins being repeatedly bent during modeling. If the rounding process is not performed, the mesh density here will be large, the mesh change rate will be too fast, resulting in poor mesh quality and inability to solve problems.

[0055] Step 3.2: Divide the simplified model into computational grids. The quality of the grid is related to the speed and results of the calculation. The specific considerations include unit shape, grid density, and grid type. The details are as follows:

[0056] Mesh type: Select the correct type of mesh according to the model. In the thermal analysis method for high heat rate SiC MOSFET power devices based on the finite element method proposed this time, although some surface boundary conditions are simplified separately, the mesh setting for these surface boundary conditions is not performed separately, but it is regarded as part of the 3D mesh.

[0057] Unit shape: The divided grid units should avoid irregular shapes. This embodiment adopts regular 3D grids such as regular hexahedrons to reduce shape errors and improve calculation accuracy. The aspect ratio of the grid unit should be close to 1 to avoid precision loss caused by too large aspect ratio. For some complex structures, such as SiC MOSFET pins, the unit shape is not mandatory.

[0058] Mesh density: The mesh density should be adjusted appropriately according to the characteristics of different areas of the model. In this embodiment, in areas with large changes in heat flux gradient, such as heat flux concentration areas near heat sources or boundary layers, the mesh density should be increased to obtain a more detailed temperature distribution cloud map; in areas with gentle changes, a mesh with a larger change rate can be used to reduce the resources occupied during calculation and improve the calculation speed.

[0059] Mesh refinement: This embodiment selects an adaptive mesh refinement method, which determines the area that needs to be refined through error estimation.

[0060] The grid division of this embodiment needs to comprehensively consider the accuracy of the results, the convergence of the calculation results and the computing resources to achieve the best effect.

[0061] Step 4: Set the material properties of each part of the modified model; set the boundary conditions of the model, which must meet the actual physical conditions; equate the thin layer structure to the surface boundary conditions, and set the corresponding attribute parameters; equate the radiator model to the additional convection coefficient of the radiator contact surface, and determine the range of the convection coefficient according to the selected radiator type, as follows:

[0062] Step 4.1: Set the heat convection coefficient of the model surface exposed to air to 5-20 (W / m 2 K), select the appropriate coefficient within this range according to the corresponding environmental conditions;

[0063] Step 4.2: Simplify the model into a thin layer with surface boundary conditions. For example, the welding layer also needs to set the corresponding material properties, but since it is a contact surface, its heat convection coefficient needs to be set to 0;

[0064] Step 4.3: Simplify the heat sink model and replace it with an equivalent method of increasing the heat convection coefficient of the area where the heat sink is located. This embodiment provides two equivalent heat convection coefficient values ​​for heat dissipation models. The equivalent heat convection coefficient of the forced air cooling method is 100 (W / m 2 K), the equivalent thermal convection coefficient of the external heat sink combined with air cooling is 550 (W / m 2 K).

[0065] Step 5: Select the solid heat transfer physical field model in the finite element software. The three main modes of heat transfer are heat conduction, heat radiation and heat convection. The heat transfer mode between solid and gas with temperature difference is mainly in the form of heat convection, which is manifested as heat exchange from solid to ambient air. The corresponding parameter settings have been given in the above interface. The main heat transfer mode between each solid grid unit is still heat conduction, and heat convection and heat radiation can be ignored. Therefore, the steady-state temperature of the power device can be obtained using only the finite element numerical method of the steady-state heat conduction equation, as follows:

[0066] The heat conduction equation for obtaining the steady-state temperature of the model is:

[0067]

[0068] Where ρ is the density, C p is the specific heat capacity, u is the velocity vector, is the temperature gradient, is the divergence of the heat flux vector q, k is the thermal conductivity, Q and Q ted They are internal and external heat sources respectively.

[0069] Finally, by establishing energy conservation and heat conduction, heat convection and other equations for each grid unit, and solving the equilibrium equation of the entire entity in parallel, the temperature value of each grid is obtained as the simulation result.

[0070] Example 2

[0071] In order to better understand and implement the present invention, based on Example 1, this example discloses a thermal analysis example of a SiC MOSFET power device with a high heat consumption rate, as follows:

[0072] First, determine the information of the components used in the power device, including materials and main dimensions, as shown in Table 1:

[0073] Table 1: Model information

[0074]

[0075] Table 1 shows the materials and main dimensions of the main components. For the welding layer, due to its small thickness, it is set as a surface boundary condition and set to a small value. More specific settings can be made through the surface condition interface.

[0076] The physical parameters of the material are loaded into the finite element simulation software, and then a three-dimensional model is established through the modeling system built into the software. For the SiC MOSFET model, it is established in the form of a simplified model, that is, it is divided into two rectangular blocks of SiC and Cu, and the heat source is set as a square with a side length of 4mm at the interface.

[0077] The model is then circularized and meshed. The mesh used is a regular hexagonal mesh, and a regular quadrilateral mesh is used at the bent pins. The mesh change rate is 1.10.

[0078] The equivalent heat convection coefficients for different radiator models are shown in Table 2:

[0079] Table 2: Equivalent heat convection coefficients of different heat sink models

[0080]

[0081] In the finite element software interface, the steady-state equations of solid heat transfer and heat conduction are selected according to Example 1, and the errors between the final simulation results and the test results are within an acceptable range.

[0082] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A thermal analysis method for high heat consumption rate SiC MOSFET power device based on finite element method, characterized in that: The following steps are involved: Step 1, loading material information, wherein the material includes materials contained in various components of the high heat rate SiC MOSFET power device to be analyzed; Step 2: 3D modeling, modeling is performed according to the 3D size and arrangement position of each component to obtain a 3D model; Step 3: Model modification: rounding and simplifying the edges and corners of the three-dimensional model. When there is a segmented structure, the segmented structure is merged as a whole or in part to obtain a simplified model; and the calculation grid is divided based on the simplified model. Step 4: Setting: setting the material properties of each part of the simplified model; setting the boundary conditions of the simplified model; Step 5: Obtain the steady-state temperature, select the solid heat transfer physical field model, and use the finite element numerical method of the heat conduction equation to obtain the steady-state temperature of the high heat consumption rate SiC MOSFET power device to be analyzed.

2. The high heat rate SiC MOSFET power device thermal analysis method based on the finite element method according to claim 1 is characterized in that: Step 2 includes the following steps: Step 2.1, ignore the internal structure of each component in the 3D modeling, simplify the theoretical thermal resistance of the model, and calculate it according to the 45° heat conduction model; Step 2.2: When performing 3D modeling, ignore the part whose thickness is much smaller than other components, convert it into a surface boundary condition, and set the corresponding physical properties.

3. The high heat rate SiC MOSFET power device thermal analysis method based on the finite element method according to claim 2 is characterized in that: The construction method of the simplified model is as follows: Two rectangular blocks made of SiC and Cu are set up, the scales of the two rectangular blocks are equal to the actual products, and a square in the middle of the interface is selected as the heat source; pins are added to the model, and the number and material of the pins are equal to the number and material of the pins of the high heat consumption rate SiC MOSFET power device analyzed.

4. The high heat rate SiC MOSFET power device thermal analysis method based on the finite element method according to claim 3 is characterized in that: The side length of the square is 4 mm.

5. The method for thermal analysis of a high heat rate SiC MOSFET power device based on the finite element method according to any one of claims 1 to 4, characterized in that: The theoretical thermal resistance calculation method of the simplified model is as follows: Where: L i is the thickness of the i-th layer of material; a i , b i are the length and width of the lower surface of the i-th layer of material respectively; K i is the thermal conductivity of the i-th layer material, then the theoretical thermal resistance from junction to case of the SiC MOSFET power chip is R jc for: R jc =S i R thi 。 6. The high heat rate SiC MOSFET power device thermal analysis method based on the finite element method according to claim 5 is characterized in that: The theoretical thermal resistance calculation method of the simplified model also includes: Compare and select R from SiC MOSFET data sheets jc The theoretical R of the above model jc , ensuring that the error is within a reasonable range.

7. The high heat rate SiC MOSFET power device thermal analysis method based on the finite element method according to claim 6 is characterized in that: The error being within a reasonable range means that the error is less than 20%.

8. The high heat rate SiC MOSFET power device thermal analysis method based on finite element method according to claim 1, characterized in that: Step 4 includes the following steps: Step 4.1: Set the thermal convection coefficient of the contact surface exposed to air; Step 4.2: Simplify the model into a thin layer with surface boundary conditions, set the corresponding material properties, and set the thermal convection coefficient of the thin layer; Step 4.3: Simplify the heat sink model and replace it with an equivalent method of increasing the heat convection coefficient of the area where the heat sink is located.

9. The high heat rate SiC MOSFET power device thermal analysis method based on finite element method according to claim 8, characterized in that: In step 4.1, set the heat convection coefficient of the contact surface exposed to air to 5-20 (W / m 2 K); In step 4.2, the thermal convection coefficient of the thin layer is set to 0.

10. The high heat rate SiC MOSFET power device thermal analysis method based on finite element method according to claim 1, characterized in that: The heat conduction equation is as follows: Where ρ is the density, C p is the specific heat capacity, u is the velocity vector, ▽T is the temperature gradient, ▽q is the divergence of the heat flux density vector q, k is the thermal conductivity, Q and Q ted They are internal and external heat sources respectively.

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