Method for obtaining temperature profile of hot air reflow soldering

Abstract

The application relates to the technical field of computer-aided design, and provides a temperature curve acquisition method for hot air reflow soldering. In the temperature curve acquisition method, a python script is used to create a preprocessing TCL script of hypermesh software, a finite element model of an overall circuit board assembled with components is generated, a 2D grid is generated from a grid of the overall circuit board in an INP file of the finite element model of the overall circuit board assembled with components, a geometric outer surface of the overall circuit board model is generated through the 2D grid, a 3D geometric entity of the overall circuit board model is generated from the geometric outer surface of the overall circuit board model, a Boolean operation is performed on a geometric model of an area where the overall circuit board model is located in a cavity model of a hot air reflow furnace by using the geometric entity of the overall circuit board model, then a tetrahedral mesh is divided in the area which has been subjected to the Boolean operation in the cavity model of the hot air reflow furnace, a grid model of the cavity of the hot air reflow furnace with the finite element model of the overall circuit board assembled with components being built-in is obtained, and finally a temperature curve is obtained. The operation process is simple and fast.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of computer-aided design, in particular to a temperature curve acquisition method of hot air reflow soldering. BACKGROUND

[0002] Hot air reflow soldering is a soldering method that uses a convection jet nozzle or a hot air blower to force air circulation to heat the workpiece. This kind of equipment began to rise in the 1990s. Because of this heating method, the temperature of printed circuit board (PCB) and components is close to the temperature of the gas in the given heating temperature zone, completely overcoming the local temperature difference and shielding effect of infrared reflow soldering, so it is widely used at present. Soldering defects are caused by unreasonable setting of reflow soldering process parameters, and the existing reflow soldering process parameter design is to set the process parameters of the reflow furnace through the physical printed board assembly, and then collect the temperature curve through the furnace temperature tester and other tools, and gradually approach the ideal (or acceptable) target curve by using the trial-and-error method, so as to realize the setting of the reflow furnace process parameters.

[0003] And by establishing a virtual model of the hot air reflow furnace through the finite element simulation method, and optimizing the model through some correction method, the physical hot air reflow furnace can be converted into a virtual hot air reflow furnace in the computer, so as to realize virtual simulation under the aid of computer, and then establish a finite element model for different states of the printed board assembly, and import the designed virtual model of the hot air reflow furnace, so as to realize low-cost and efficient parameter setting of the hot air reflow furnace.

[0004] In order to use the computer to simulate the process of circuit board soldering, it is necessary to import the finite element model of the whole circuit board assembled with components into the grid model of the inner cavity of the hot air reflow furnace. At present, this import process needs to be operated through the software interface, which is low in efficiency and complicated in process. SUMMARY

[0005] In view of the problems of low operation efficiency and complicated process of importing the finite element model of the circuit board into the grid model of the inner cavity of the hot air reflow furnace in the prior art, the present application provides a temperature curve acquisition method of hot air reflow soldering.

[0006] The temperature curve acquisition method of hot air reflow soldering comprises:

[0007] S21: creating an inner cavity model of the hot air reflow furnace;

[0008] S22: selecting an INP file of the inner cavity model of the hot air reflow furnace as a whole;

[0009] S23: the python script reads the position information of the inner cavity model of the hot air reflow furnace in the INP file of the inner cavity model of the hot air reflow furnace as a whole;

[0010] S24: create a pre-processing TCL script of the hypermesh software with a python script, calculate the midpoint (X1, Y1, Z1) through the maximum and minimum values of the X coordinate, Y coordinate and Z coordinate of the inner cavity model of the hot air backflow furnace; create six points P7 (X1, Y1, Z1), P8 (X1+1, Y1, Z1), P9 (X1, Y1+1, Z1), P10 (X2, Y2, Z2), P11 (X2+1, Y2, Z2), P12 (X2, Y2+1, Z2), wherein the plane (P10, P11, P12) is the initial welding position of the hot air backflow furnace;

[0011] Move the finite element model of the whole circuit board assembled with components from the plane (P7, P8, P9) to the plane (P10, P11, P12);

[0012] S25: generate a 2D grid for the grid of the whole circuit board in the finite element model INP file of the whole circuit board assembled with components, generate a geometric outer surface of the whole circuit board model through the 2D grid, then generate a 3D geometric entity of the whole circuit board model from the geometric outer surface of the whole circuit board model, perform a Boolean operation on the geometric model of the area where the whole circuit board model is located in the inner cavity model of the hot air backflow furnace using the geometric entity of the whole circuit board model, then perform tetrahedral meshing on the area in the inner cavity model of the hot air backflow furnace that has been subjected to the Boolean operation, obtain the grid model of the inner cavity of the hot air backflow furnace with the finite element model of the whole circuit board assembled with components, and output the grid model file calculated in the Fluent software;

[0013] S26: the python script reads the information of each component and its material, and obtains the process parameters of the hot air reflow soldering;

[0014] S27: generate the UDF and TUI pre-processing scripts of the Fluent software through the python script, perform solving in the Fluent software, and obtain the temperature curve.

[0015] In an embodiment, the information of each component and its material is read by searching for keywords in S26.

[0016] In an embodiment, in S26:

[0017] After reading the information of each component and its material, save the name, density, thermal conductivity and specific heat capacity of the component;

[0018] The obtained process parameters of the hot air reflow soldering include the air speed and temperature of each temperature zone in the inner cavity model of the hot air backflow furnace, and the moving speed of the whole circuit board in the inner cavity model of the hot air backflow furnace.

[0019] In an embodiment, the speed of the overall circuit board movement is defined in the UDF file and loaded to the boundary conditions, and the material information of the components is contained in the TUI file and loaded to the material properties of the corresponding circuit board and components.

[0020] In an embodiment, the method for obtaining the INP file of the finite element model of the overall circuit board assembled with components in S24 comprises:

[0021] S11: Establish a database of finite element grid model INP files of various components;

[0022] S12: Select the finite element grid model INP file of the circuit board and establish a coordinate system;

[0023] S13: Use the python script to read the setting information of the components, identify and save the height of the components, the corresponding local coordinate system and the material in the finite element grid model INP file of the components;

[0024] S14: Use the python script to create the pre-processing TCL script of the hypermesh software, rotate and move the local coordinate system of each component according to the design position;

[0025] S15: Rename the material and local coordinate system of different components according to the order of reading the components, realize the automatic assembly of the components, and output the finite element model INP file of the overall circuit board assembled with components.

[0026] In an embodiment, the database of finite element grid model INP files of components contains material information and position information of components;

[0027] The position information of the components takes the center of the bottom of the component as the coordinate origin.

[0028] In an embodiment, the coordinate system established in S12 takes the lower left corner of the plane where the top of the circuit board is located as the coordinate origin, and takes the length and width directions of the circuit board as X and Y axes respectively.

[0029] In an embodiment, the absolute value of the difference between the maximum and minimum values of the Z coordinate in S13 is taken as the height of the component.

[0030] In an embodiment,

[0031] S14 rotates and moves the local coordinate system of each component according to the design position, which comprises:

[0032] Use the "rotate" function to select the origin of the component and rotate it around the Z axis by α degrees;

[0033] Using the "position" function, create P1(0, 0, 0), P2(1, 0, 0), P3(0, 1, 0), P4(X, Y, Z), P5(X+1, Y, Z), P6(X, Y+1, Z) six points, move the components from the plane (P1, P2, P3) to the plane (P4, P5, P6).

[0034] The temperature curve acquisition method of the hot air reflow soldering provided by the application uses a python script to create a pre-processing TCL script of the hypermesh software, generates a 2D grid of the grid of the overall circuit board in the finite element model INP file of the overall circuit board assembled with components using the "findfaces" function, generates a geometric outer surface of the overall circuit board model through the 2D grid, generates a 3D geometric entity of the overall circuit board model from the geometric outer surface of the overall circuit board model, performs a Boolean operation on the geometric model of the position of the overall circuit board model in the inner cavity model of the hot air reflow furnace using the geometric entity of the overall circuit board model, then performs tetrahedral meshing on the region in the inner cavity model of the hot air reflow furnace that has been subjected to the Boolean operation, obtains a grid model of the inner cavity of the hot air reflow furnace in which the overall circuit board assembled with components is built-in, outputs the grid model file calculated in the Fluent software, and finally obtains the temperature curve, which is simple and fast in operation process.

[0035] In order to further clarify the aspects and advantages of the embodiments disclosed in the application, it will become apparent from the following description part or be understood through the practice of the embodiments disclosed in the application. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings are used to provide further understanding of the application and constitute a part of the specification, and together with the following detailed embodiment, serve to explain the application, but do not constitute a limitation on the application.

[0037] Figure 1 The logic flow chart of the temperature curve acquisition method of the hot air reflow soldering provided for the embodiment 1 of the application;

[0038] Figure 2 The temperature curve diagram of two positions obtained by the temperature curve acquisition method of the hot air reflow soldering provided for the embodiment 1 of the application;

[0039] Figure 3 The schematic diagram of the coordinate system established in S12 in the embodiment for obtaining the INP file of the finite element model of the overall circuit board assembled with components provided in the embodiment 1 of the application. DETAILED DESCRIPTION

[0040] The principles and characteristics of the present application are described below in conjunction with the accompanying drawings, which are only used to explain the present application and are not intended to limit the scope of the present application.

[0041] Embodiment 1

[0042] This embodiment provides a temperature curve acquisition method for hot air reflow soldering, referring to Figure 1 , comprising:

[0043] S21: creating an inner cavity model of the hot air reflow furnace;

[0044] S22: the inner cavity model of the hot air reflow furnace can contain multiple temperature zones, and in this embodiment, the inner cavity model of the hot air reflow furnace can contain 10 temperature zones, and the INP file of the inner cavity model of the hot air reflow furnace as a whole is selected;

[0045] S23: the python script reads the position information of the inner cavity model of the hot air reflow furnace in the INP file of the inner cavity model of the hot air reflow furnace as a whole;

[0046] S24: creating a pre-processing TCL script of the hypermesh software by using the python script, calculating the midpoint (X1, Y1, Z1) through the maximum and minimum values of the X coordinate, Y coordinate and Z coordinate of the inner cavity model of the hot air reflow furnace; using the "position" function, creating six points P7 (X1, Y1, Z1), P8 (X1+1, Y1, Z1), P9 (X1, Y1+1, Z1), P10 (X2, Y2, Z2), P11 (X2+1, Y2, Z2), P12 (X2, Y2+1, Z2), wherein the plane (P10, P11, P12) is the initial welding position of the hot air reflow furnace;

[0047] moving the finite element model of the whole circuit board assembled with components from the plane (P7, P8, P9) to the plane (P10, P11, P12);

[0048] S25: using the "find faces" function in the TCL script to generate a 2D grid for the grid of the whole circuit board in the finite element model INP file of the whole circuit board assembled with components, generating a geometric outer surface of the whole circuit board model through the 2D grid, and then generating a 3D geometric entity of the whole circuit board model from the geometric outer surface of the whole circuit board model, performing a Boolean operation on the geometric model of the area where the whole circuit board model is located in the inner cavity model of the hot air reflow furnace, and then performing tetrahedral meshing on the area in the inner cavity model of the hot air reflow furnace that has been subjected to the Boolean operation, obtaining a grid model of the inner cavity of the hot air reflow furnace for the finite element model of the whole circuit board assembled with components, and outputting the MSH format grid model file calculated in the Fluent software;

[0049] In this step, a grid model of the inner cavity of the hot air reflow oven of the finite element model of the overall circuit board with components built-in is obtained without overlapping grids.

[0050] S26: The python script reads each component and its material information to obtain the process parameters of the hot air reflow soldering.

[0051] S27: The python script generates the UDF and the TUI pre-processing script of the Fluent software, and solves in the Fluent software to obtain a temperature curve, as shown in the following figure. Figure 2 The hot air reflow soldering process parameters are adjusted according to the temperature curve. In the UDF file, the speed of the overall circuit board movement is defined and loaded into the boundary condition, and in the TUI file, the material information of the components is included and loaded into the material properties of the corresponding circuit board and components in the MSH file.

[0052] In this embodiment, the keyword is searched to read each component and its material information in S26.

[0053] In S26 of this embodiment, after reading each component and its material information, the name, density, thermal conductivity, and specific heat capacity of the component are saved.

[0054] The obtained process parameters of the hot air reflow soldering include the air speed and temperature of each temperature zone in the 10 temperature zones in the inner cavity model of the hot air reflow oven, and the speed of the overall circuit board moving in the inner cavity model of the hot air reflow oven, a total of 21 parameters.

[0055] The hot air reflow soldering process analysis method provided in this embodiment can improve the welding quality by simulating the temperature and speed in the process to obtain a temperature curve of the process, and adjusting the hot air reflow soldering process parameters according to the temperature curve.

[0056] Compared with clicking operations through a software interface, the python script is used to create the pre-processing TCL script of the hypermesh software in this embodiment, and the operation process is simple and fast.

[0057] The simulation model of the inner environment of the hot air reflow oven can use the method described in the patent document with publication number CN116151067A.

[0058] This embodiment also provides an implementation of obtaining the INP file of the finite element model of the overall circuit board with components built-in, which includes:

[0059] S11: A database of finite element grid models INP files of multiple components is established.

[0060] Some operations are performed by using the script provided internally by the hypermesh software, including:

[0061] S12: Select the finite element mesh model INP file of the circuit board used to establish the coordinate system;

[0062] S13: Use the python script to read the setting information of the component, identify and save the height of the component, the corresponding local coordinate system and the material in the finite element mesh model INP file of the component;

[0063] S14: Use the python script to create the pre-processing TCL script of the hypermesh software, use the "rotate" function, select the origin of the component, rotate alpha degrees around the Z axis, use the "position" function, create six points P1(0, 0, 0), P2(1, 0, 0), P3(0, 1, 0), P4(X, Y, Z), P5(X+1, Y, Z), P6(X, Y+1, Z), and move the component from the plane (P1, P2, P3) to the plane (P4, P5, P6); according to the design position, rotate and move the local coordinate system of each component accordingly; realize the placement of the model of each component on the circuit board model according to the design position;

[0064] S15: According to the order of reading the component, the materials and local coordinate systems of different components are renamed respectively to realize the automatic assembly of the components, and the finite element model INP file of the whole circuit board assembled with the components is output.

[0065] The above embodiment is based on the hypermesh software for circuit board assembly, and the information of the INP format file is read by using Python, and then the internal script of the hypermesh software is written, so that the circuit board assembly process is fast, convenient and can process the assembly of multiple components.

[0066] In this embodiment, the database of the finite element mesh model INP file of the component includes material information and position information of the component;

[0067] The position information of the component is taken as the bottom center of the component as the coordinate origin.

[0068] In this embodiment, the coordinate system established in S12 takes the lower left corner of the plane where the top of the circuit board is as the coordinate origin, and takes the length and width directions of the circuit board as X and Y axes, respectively, as shown in Figure 3 .

[0069] In this coordinate system, the X coordinate, Y coordinate and rotation angle alpha around the Z axis of the origin of each component are set.

[0070] The heights of different components in the database are not uniform, and the height information of each component cannot be ensured to be known when assembling the circuit board. Therefore, the height of the component in the finite element mesh model INP file of the component is identified in S13 of the embodiment. Specifically, all node information of the component in the INP file is read through a script, and the absolute value of the difference between the maximum and minimum values of the Z coordinate is taken as the height of the component, thereby providing a more accurate circuit board model for subsequent process analysis.

[0071] In S14 of the embodiment, the local coordinate system of each component is rotated and moved according to the design position, including:

[0072] Using the "rotate" function, the origin of the component is selected, and the component is rotated by α degrees around the Z axis.

[0073] Using the "position" function, six points P1(0, 0, 0), P2(1, 0, 0), P3(0, 1, 0), P4(X, Y, Z), P5(X+1, Y, Z), and P6(X, Y+1, Z) are created, and the component is moved from the plane (P1, P2, P3) to the plane (P4, P5, P6).

[0074] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "circumferential", 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 technical solution and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the technical solution.

[0075] In the technical solution, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, can be fixed connection, or can be detachable connection, or can be integrated; can be mechanical connection, or can be electrical connection; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the technical solution can be understood according to the specific circumstances.

[0076] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present technical solution. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0077] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for obtaining a temperature profile for hot air reflow soldering, characterized in that Comprise: S21: create the inner cavity model of the hot air reflow oven; S22: select the INP file of the inner cavity model of the hot air reflow oven as a whole; S23: the python script reads the position information of the inner cavity model of the hot air reflow oven in the INP file of the inner cavity model of the hot air reflow oven as a whole; S24: create a pre-processing TCL script for hypermesh software with a python script, calculate the midpoint (X1, Y1, Z1) through the maximum and minimum values of the X coordinate, Y coordinate and Z coordinate of the inner cavity model of the hot air reflow oven; create P7 (X1, Y1, Z1), P8 (X1+1, Y1, Z1), P9 (X1, Y1+1, Z1), P10 (X2, Y2, Z2), P11 (X2+1, Y2, Z2), P12 (X2, Y2+1, Z2) six points, wherein the plane (P10, P11, P12) is the initial welding position of the hot air reflow oven; Move the finite element model of the whole circuit board assembled with components from the plane (P7, P8, P9) to the plane (P10, P11, P12); S25: generate 2D grid for the grid of the whole circuit board in the finite element model INP file of the whole circuit board assembled with components, generate the geometric outer surface of the whole circuit board model through the 2D grid, and then generate the 3D geometric entity of the whole circuit board model, and then perform Boolean operation on the geometric model of the area where the whole circuit board model is located in the inner cavity model of the hot air reflow oven, and then perform tetrahedral mesh division on the area in the inner cavity model of the hot air reflow oven which has been subjected to Boolean operation, to obtain the grid model of the inner cavity of the hot air reflow oven with the whole circuit board assembled with components, and output the grid model file for calculation in the Fluent software; S26: the python script reads the material information of each component and obtains the process parameters of the hot air reflow soldering; S27: generate UDF and TUI pre-processing scripts for Fluent software through python script, solve in Fluent software, and obtain temperature curve.

2. The temperature profile acquisition method of claim 1, wherein, In S26, the keyword is searched to read the material information of each component.

3. The temperature profile acquisition method of claim 1, wherein, In S26: After reading the material information of each component, save the name, density, thermal conductivity and specific heat capacity of the component; The obtained process parameters of the hot air reflow soldering include the air speed and temperature of each temperature zone in the inner cavity model of the hot air reflow oven, and the moving speed of the whole circuit board in the inner cavity model of the hot air reflow oven.

4. The temperature profile acquisition method of claim 1, wherein The speed of the whole circuit board is defined in the UDF file and loaded into the boundary condition, and the material information of the component is included in the TUI file and loaded into the material properties of the corresponding circuit board and component.

5. The temperature profile acquisition method of claim 1, wherein The method for obtaining the INP file of the finite element model of the whole circuit board assembled with components in S24 comprises: S11: establish a database of finite element grid models INP files of various components; S12: select the finite element grid model INP file of the circuit board, and establish a coordinate system; S13: reading the setting information of the component by using the python script, identifying and saving the height of the component, the corresponding local coordinate system and the material in the finite element grid model INP file of the component; S14: creating the pre-processing TCL script of the hypermesh software by using the python script, rotating and moving the local coordinate system of each component according to the design position; S15: renaming the material and local coordinate system of different components according to the reading sequence of the components, realizing the automatic assembly of the components, and outputting the finite element model INP file of the whole circuit board assembled with the components.

6. The temperature profile acquisition method of claim 5, wherein, The database of the finite element grid model INP file of the component contains the material information and position information of the component; The position information of the component takes the bottom center of the component as the coordinate origin.

7. The temperature profile acquisition method of claim 5, wherein, The coordinate system established in S12 takes the lower left corner of the plane where the top of the circuit board is located as the coordinate origin, and takes the length and width directions of the circuit board as the X and Y axes respectively.

8. The temperature profile acquisition method of claim 7, wherein, In S13, the absolute value of the difference between the maximum and minimum values of the Z coordinate is taken as the height of the component.

9. The temperature curve acquisition method according to claim 5, characterized in that, In S14, rotating and moving the local coordinate system of each component according to the design position includes: Using the "rotate" function, selecting the origin of the component, and rotating around the Z axis by α degrees; Using the "position" function, creating six points P1(0, 0, 0), P2(1, 0, 0), P3(0, 1, 0), P4(X, Y, Z), P5(X+1, Y, Z), P6(X, Y+1, Z), and moving the component from the plane (P1, P2, P3) to the plane (P4, P5, P6).

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