Temperature curve acquisition method for hot air reflow soldering

Abstract

The invention relates to the technical field of computer aided design, and provides a method for acquiring a temperature curve of hot air reflow soldering, which comprises the following steps of: creating a pretreatment TCL script of hypermesh software by using a python script, and establishing a finite element model of an integral circuit board assembled with components into a temperature curve; the method comprises the following steps of: generating a 2D (two-dimensional) grid from a grid of the whole circuit board in a finite element model INP file of the whole circuit board assembled with components, generating a geometric outer surface of a whole circuit board model through the 2D grid, and generating a 3D (three-dimensional) geometric entity of the whole circuit board model according to the geometric outer surface of the whole circuit board model; boolean operation is carried out on a geometric model of an area of the whole circuit board model in an inner cavity model of the hot air reflow oven by using a geometric entity of the whole circuit board model, and then tetrahedral mesh division is carried out on the area subjected to Boolean operation in the inner cavity model of the hot air reflow oven; the mesh model of the hot air reflow oven inner cavity of the finite element model of the integral circuit board with the built-in components is obtained, a temperature curve is finally obtained, and the operation process is simple and rapid.

Description

Technical Field

[0001] The present invention relates to the technical field of computer-aided design, and in particular to a method for obtaining a temperature curve of hot air reflow soldering. Background Art

[0002] Hot air reflow soldering is a soldering method that uses a convection jet nozzle or a heat-resistant fan to force air circulation to achieve heating of the soldered parts. This type of equipment began to emerge in the 1990s. Since the temperature of the printed circuit board (PCB) and components using this heating method is close to the gas temperature in a given heating temperature zone, it completely overcomes the local temperature difference and shielding effect of infrared reflow soldering, so it is currently widely used. Soldering defects are caused by unreasonable settings of reflow soldering process parameters. The existing reflow soldering process parameter design is to design a physical printed circuit board assembly to repeatedly pass through a reflow oven that needs to set process parameters, and then collect the temperature curve through tools such as an oven temperature tester, and use the "trial and error method" to gradually approach the ideal (or acceptable) target curve, thereby achieving the reflow oven process parameter setting.

[0003] By establishing a virtual model of the hot air reflow oven through the finite element simulation method and then optimizing the model through certain correction methods, the physical hot air reflow oven can be converted into a virtual hot air reflow oven in the computer, thereby realizing virtual simulation with the aid of a computer. Finite element models are then established for printed circuit board components in different states and imported into the designed virtual model of the hot air reflow oven, thereby realizing low-cost and efficient hot air reflow oven parameter settings.

[0004] In order to use a computer to simulate the process of circuit board welding, it is necessary to first import the finite element model of the entire circuit board equipped with components into the mesh model of the hot air reflow furnace cavity. Currently, this import process requires clicks through the software interface, which is inefficient and cumbersome. Summary of the invention

[0005] In view of the problem that the operation of importing the finite element model of a circuit board into the grid model of the inner cavity of a hot air reflow oven in the prior art is inefficient and the process is complicated, the present application provides a method for obtaining a temperature curve of hot air reflow soldering.

[0006] The method for obtaining a temperature curve of hot air reflow soldering comprises:

[0007] S21: Create an inner cavity model of a hot air reflow oven;

[0008] S22: Selecting the I NP file of the whole inner cavity model of the hot air reflow furnace;

[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 entire inner cavity model of the hot air reflow furnace;

[0010] S24: Use Python script to create a pre-processing TCL script for HyperMesh software, and calculate the midpoint (X1, Y1, Z1) through the maximum and minimum values ​​of the X coordinates, Y coordinates, and Z coordinates of the inner cavity model of the hot air reflow 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), and P12 (X2, Y2+1, Z2), among which the plane (P10, P11, P12) is the initial welding position of the hot air reflow furnace;

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

[0012] S25: Generate a 2D grid from the grid of the overall circuit board in the finite element model INP file of the overall circuit board equipped with components, generate a geometric outer surface of the overall circuit board model through the 2D grid, and then generate its 3D geometric entity from the geometric outer surface of the overall circuit board model, use the geometric entity of the overall circuit board model to perform Boolean operation on the geometric model of the area where it is located in the inner cavity model of the hot air reflow furnace, and then perform tetrahedral grid division on the area in the inner cavity model of the hot air reflow furnace where the Boolean operation is performed, obtain a grid model of the inner cavity of the hot air reflow furnace with the built-in finite element model of the overall circuit board equipped with components, and output the grid model file calculated in the Fluent software;

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

[0014] S27: Generate UDF and TUI pre-processing scripts of Fluent software through Python script, solve in Fluent software, and obtain temperature curve.

[0015] In one implementation, each component and its material information is read by searching for keywords in S26.

[0016] In one embodiment, in S26:

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

[0018] The obtained process parameters of hot air reflow soldering include the wind speed and temperature of each temperature zone in the inner cavity model of the hot air reflow oven, and the speed at which the entire circuit board moves in the inner cavity model of the hot air reflow oven.

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

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

[0021] S11: Establish a database of finite element mesh model I NP files of various components;

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

[0023] S13: using a python script to read the setting information of the components, and identifying and saving the height, corresponding local coordinate system and material of the components in the finite element mesh model I NP file of the components;

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

[0025] S15: renaming the materials and local coordinate systems of different components respectively according to the order of reading the components, realizing automatic assembly of the components, and outputting a finite element model I NP file of the whole circuit board assembled with the components.

[0026] In one embodiment, the database of the finite element mesh model I NP file of the component includes material information and position information of the component;

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

[0028] In one implementation, 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.

[0029] In one implementation, in S13 , the absolute value of the difference between the maximum value and the minimum value of the Z coordinate is used as the height of the component.

[0030] In one embodiment,

[0031] In S14, the local coordinate system of each component is rotated and moved according to the design position, including:

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

[0033] Use the "position" function to create 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), and move the components from plane (P1, P2, P3) to plane (P4, P5, P6).

[0034] In the method for obtaining the temperature curve of hot air reflow soldering provided in the present application, a pre-processing TCL script of the hypermesh software is created by using a python script, and a finite element model of an integral circuit board equipped with components is generated by using the "findfaces" function to generate a 2D grid from the mesh of the integral circuit board in the INP file of the finite element model of the integral circuit board equipped with components, and the geometric outer surface of the integral circuit board model is generated by the 2D grid, and then the 3D geometric entity of the integral circuit board model is generated from the geometric outer surface of the integral circuit board model, and the geometric entity of the integral circuit board model is used to perform Boolean operations on the geometric model of its position in the inner cavity model of the hot air reflow furnace, and then the area in the inner cavity model of the hot air reflow furnace where the Boolean operation is performed is tetrahedral mesh division to obtain a mesh model of the inner cavity of the hot air reflow furnace with the finite element model of the integral circuit board equipped with components, and the mesh model file calculated in the Fluent software is output, and finally the temperature curve is obtained, and the operation process is simple and fast.

[0035] For further elaboration, various aspects and advantages of the embodiments disclosed in the present application will become apparent in the following description or can be understood through the practice of the embodiments disclosed in the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the invention but do not constitute a limitation to the invention.

[0037] Figure 1 A logic flow chart of a method for obtaining a temperature curve of hot air reflow soldering provided in Example 1 of the present application;

[0038] Figure 2 The temperature curve diagrams of two positions obtained by the temperature curve acquisition method of hot air reflow soldering provided in Example 1 of the present application;

[0039] Figure 3 This is a schematic diagram of the coordinate system established in S12 in the implementation of obtaining an INP file of a finite element model of an entire circuit board equipped with components provided in Example 1 of the present application. DETAILED DESCRIPTION

[0040] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for obtaining a temperature curve of hot air reflow soldering. Figure 1 ,Include:

[0043] S21: Create an inner cavity model of a hot air reflow oven;

[0044] S22: The inner cavity model of the hot air reflow furnace may contain multiple temperature zones. In this embodiment, the inner cavity model of the hot air reflow furnace may contain 10 temperature zones. Select the I NP file of the entire inner cavity model of the hot air reflow furnace;

[0045] S23: a python script reads the position information of the inner cavity model of the hot air reflow furnace in the I NP file of the entire inner cavity model of the hot air reflow furnace;

[0046] S24: Use Python script to create a pre-processing TCL script for HyperMesh software, and 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 furnace; Use the "position" function to 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), and P12 (X2, Y2+1, Z2), among which the plane (P10, P11, P12) is the initial welding position of the hot air reflow furnace;

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

[0048] S25: using the "find faces" function in the TCL script, generating a 2D mesh from the mesh of the overall circuit board in the finite element model INP file of the overall circuit board equipped with components, generating the geometric outer surface of the overall circuit board model through the 2D mesh, and then generating its 3D geometric entity from the geometric outer surface of the overall circuit board model, using the geometric entity of the overall circuit board model to perform Boolean operations on the geometric model of the area in the inner cavity model of the hot air reflow furnace, and then performing tetrahedral mesh division on the area in the inner cavity model of the hot air reflow furnace where the Boolean operation is performed, to obtain a mesh model of the inner cavity of the hot air reflow furnace with the built-in finite element model of the overall circuit board equipped with components, and outputting an MSH format mesh model file calculated in the Fluent software;

[0049] In this step, a mesh model of the inner cavity of the hot air reflow furnace of the finite element model of the entire circuit board equipped with components is obtained while avoiding mesh overlap.

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

[0051] S27: Generate UDF and TUI pre-processing scripts of Fluent software through Python scripts, solve in Fluent software, and obtain temperature curve, such as Figure 2 As shown, the hot air reflow process parameters are adjusted according to the temperature curve. The UDF file defines the speed of the entire circuit board and loads it into the boundary conditions, and the TUI file contains the material information of the components and loads it into the material properties of the corresponding circuit board and components in the MSH file.

[0052] In this embodiment, each component and its material information is read by searching for keywords in S26.

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

[0054] The obtained process parameters of hot air reflow soldering include the wind speed and temperature of each of the 10 temperature zones in the inner cavity model of the hot air reflow oven, and the speed at which the entire circuit board moves in the inner cavity model of the hot air reflow oven, with a total of 21 parameters.

[0055] The hot air reflow soldering process analysis method provided in this embodiment obtains the temperature curve of the process by simulating the temperature and speed during the process, and thus adjusts the hot air reflow soldering process parameters according to the temperature curve, thereby improving the soldering quality.

[0056] Compared with the click operation through the software interface, this embodiment uses a python script to create a pre-processing TCL script for the hypermesh software, and the operation process is simple and fast.

[0057] The simulation model for simulating the environment in the hot air reflow furnace can use the method described in the patent document with the publication number CN116151067A.

[0058] This embodiment also provides an implementation method for obtaining an INP file of a finite element model of an entire circuit board equipped with components, including:

[0059] S11: Establish a database of finite element mesh model I NP files of various components;

[0060] Use the scripts provided in the hypermesh software to perform some operations, including:

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

[0062] S13: Using a 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 mesh model INP file of the components;

[0063] S14: Use Python script to create the pre-processing TCL script of HyperMesh software, use the "rotate" function, select the origin of the component, rotate α 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), move the component from plane (P1, P2, P3) to plane (P4, P5, P6); according to the design position, rotate and move the local coordinate system of each component accordingly; realize placing the model of each component on the circuit board model according to the design position;

[0064] S15: renaming the materials and local coordinate systems of different components respectively according to the order of reading the components, realizing automatic assembly of the components, and outputting a finite element model I NP file of the whole circuit board assembled with the components.

[0065] When the above implementation method performs circuit board assembly based on the hypermesh software, Python is used to read information from the I NP format file, and then the internal script of the hypermesh software is written. The circuit board assembly process is fast and convenient, and can handle the assembly of multiple components.

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

[0067] The position information of the component takes 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 located as the coordinate origin, and takes the length and width directions of the circuit board as the X and Y axes, respectively. Figure 3 shown.

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

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

[0071] In S14 of this embodiment, rotating and moving the local coordinate system of each component according to the designed position includes:

[0072] Use the "rotate" function to select the origin of the component and rotate it α degrees around the Z axis;

[0073] Use the "position" function to create 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), and move the components from plane (P1, P2, P3) to plane (P4, P5, P6).

[0074] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "circumferential", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying 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 specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the technical solution.

[0075] In this technical solution, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this technical solution can be understood according to specific circumstances.

[0076] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present technical solution. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0077] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for obtaining a temperature curve of hot air reflow soldering, characterized in that: Include: S21: Create an inner cavity model of a hot air reflow oven; S22: Select the INP file of the entire inner cavity model of the hot air reflow furnace; 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 entire inner cavity model of the hot air reflow furnace; S24: Use Python script to create a pre-processing TCL script for HyperMesh software, and calculate the midpoint (X1, Y1, Z1) through the maximum and minimum values ​​of the X coordinates, Y coordinates, and Z coordinates of the inner cavity model of the hot air reflow 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), and P12 (X2, Y2+1, Z2), among which the plane (P10, P11, P12) is the initial welding position of the hot air reflow furnace; Move the finite element model of the entire circuit board with components assembled from plane (P7, P8, P9) to plane (P10, P11, P12); S25: Generate a 2D grid from the grid of the overall circuit board in the INP file of the finite element model of the overall circuit board equipped with components, generate a geometric outer surface of the overall circuit board model through the 2D grid, and then generate its 3D geometric entity from the geometric outer surface of the overall circuit board model, use the geometric entity of the overall circuit board model to perform Boolean operation on the geometric model of the area in the inner cavity model of the hot air reflow furnace, and then perform tetrahedral mesh division on the area in the inner cavity model of the hot air reflow furnace where the Boolean operation is performed, obtain a grid model of the inner cavity of the hot air reflow furnace with the built-in finite element model of the overall circuit board equipped with components, and output the grid model file calculated in the Fluent software; S26: The python script reads each component and its material information to obtain the process parameters of hot air reflow soldering; S27: Generate UDF and TUI pre-processing scripts of Fluent software through Python scripts, solve them in Fluent software, and obtain the temperature curve.

2. The temperature curve acquisition method according to claim 1, characterized in that: In S26, each component and its material information is read by searching for keywords.

3. The temperature curve acquisition method according to claim 1, characterized in that: In S26: After reading each component and its material information, save the component's name, density, thermal conductivity, and specific heat capacity; The obtained process parameters of hot air reflow soldering include the wind speed and temperature of each temperature zone in the inner cavity model of the hot air reflow oven, and the speed at which the entire circuit board moves in the inner cavity model of the hot air reflow oven.

4. The temperature curve acquisition method according to claim 1, characterized in that: The UDF file defines the speed of the entire circuit board movement and loads it into the boundary conditions. The TUI file contains the material information of the components and loads it into the corresponding material properties of the circuit board and components.

5. The temperature curve acquisition method according to claim 1, characterized in that: The method for obtaining the INP file of the finite element model of the whole circuit board equipped with components in S24 includes: S11: Establish a database of finite element mesh model INP files of various components; S12: Select the finite element mesh model INP file of the circuit board and establish a coordinate system; S13: Using a 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 mesh model INP file of the components; S14: Use Python script to create a pre-processing TCL script for the hypermesh software, and rotate and move the local coordinate system of each component according to the design position; S15: renaming the materials and local coordinate systems of different components respectively according to the order of reading the components, realizing automatic assembly of the components, and outputting an INP file of a finite element model of the entire circuit board assembled with the components.

6. The temperature curve acquisition method according to claim 5, characterized in that: The database of the finite element mesh model INP file of the component contains the material information and location information of the component; The position information of the component takes the bottom center of the component as the coordinate origin.

7. The temperature curve acquisition method according to claim 5, characterized in that: 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 curve acquisition method according to claim 7, characterized in that: In S13, the absolute value of the difference between the maximum value and the minimum value of the Z coordinate is used as the height of the component.

9. The temperature curve acquisition method according to claim 5, characterized in that: In S14, the local coordinate system of each component is rotated and moved according to the design position, including: Use the "rotate" function to select the origin of the component and rotate it α degrees around the Z axis; Use the "position" function to create 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), and move the component from plane (P1, P2, P3) to plane (P4, P5, P6).

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