Methods for establishing and simulation models of the internal environment of hot blast reflux furnaces

Abstract

This invention discloses a method for establishing a simulation model of the environment inside a hot air reflow oven. The oven is divided into static and dynamic regions. The components to be soldered are located within the grid of the dynamic region. A layer-by-layer method is used to update the grid within the dynamic region, simulating the components being moved by a conveyor device through different temperature zones, consistent with the movement of the components within the hot air reflow oven, thus simulating the environment inside the oven. Furthermore, the layer-by-layer method for updating the grid has high computational efficiency, improving the feasibility of the simulation model establishment method. The simulation model obtained by this method can simulate the flow field state in the hot air reflow oven. By observing changes in the flow field, parameters such as the inlet velocity and conveyor belt speed can be adjusted to optimize the process parameters for reflow soldering integrated circuit boards within the hot air reflow oven.

Description

Technical Field

[0001] This invention relates to the field of computer-aided design technology, and in particular to a method for establishing a simulation model of the internal environment of a hot blast reflux furnace and a simulation model thereof. Background Technology

[0002] Hot air reflow soldering is a soldering method that uses convection jet nozzles or heat-resistant fans to force airflow circulation, thereby heating the workpiece. This type of equipment began to emerge in the 1990s. Because this heating method brings the temperature of the printed circuit board (PCB) and components close to the gas temperature of a given heating zone, it completely overcomes the localized temperature differences and shielding effects of infrared reflow soldering, and is therefore widely used. Soldering defects are caused by unreasonable reflow soldering process parameters. Current reflow soldering process parameter design involves repeatedly passing physical PCB assemblies through a reflow oven with the required process parameters, and then collecting temperature curves using tools such as oven temperature testers. This "trial and error" method is used to gradually approach the ideal (or acceptable) target curve, thus achieving the desired reflow oven process parameter settings.

[0003] By establishing a virtual model of the hot air reflow oven using the finite element 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. This enables virtual simulation with computer assistance. Furthermore, finite element models can be established for printed circuit board components in different states and imported into the designed virtual model of the hot air reflow oven, achieving low-cost and efficient parameter settings for the hot air reflow oven.

[0004] In existing technologies, the finite element simulation models of hot air reflow ovens are often based on calculations performed under ideal conditions, without simulating the circuit board traversing different temperature zones on the conveyor belt. While these calculations are highly efficient, they are not based on the parameters of a real reflow oven, so the results are of little significance for optimizing process parameters, especially the control parameters of the reflow oven. Summary of the Invention

[0005] To simulate a more realistic environment inside a hot air reflux furnace and provide a reliable basis for optimizing the control parameters of the hot air reflux path, this invention provides a method for establishing a simulation model of the environment inside a hot air reflux furnace and a simulation model thereof.

[0006] The invention aims to achieve its objective through the following technical solutions.

[0007] The method for establishing a simulation model of the internal environment of a hot blast reflux furnace includes:

[0008] Establish the geometric model of the hot blast reflux furnace;

[0009] The geometric model of the hot air reflow oven is divided into a static region and a moving region;

[0010] The grid of the motion region moves along the direction of movement of the component to be welded, and the component to be welded is located in the grid of the motion region.

[0011] The mesh in the motion region is updated using a layer-layout method to obtain a finite element model;

[0012] Based on the finite element model, fluid dynamics calculations were performed to obtain a simulation model of the environment inside the hot air reflux furnace.

[0013] Preferably, the stationary area is provided above and below the moving area.

[0014] Preferably, a rectangular air outlet is used instead of the circular nozzle air outlet of the hot air reflux furnace, and one rectangular air outlet covers all the circular nozzle air outlets within a temperature zone.

[0015] Preferably, the two ends of the mesh in the motion region are hexahedral meshes; the space between the hexahedral meshes at the two ends is a tetrahedral mesh.

[0016] The component to be soldered is located in the tetrahedral grid of the motion region;

[0017] When the tetrahedral mesh is at one end of the motion region, the mesh stops updating.

[0018] Preferably, the hexahedral mesh and the tetrahedral mesh share a common node at their junction.

[0019] Preferably, the hexahedrons in the hexahedral mesh are cuboids;

[0020] The cross-section at the junction of the hexahedral mesh and the tetrahedral mesh is rectangular, and the side length of the rectangle is equal to the side length of the junction of the tetrahedral mesh and the tetrahedral mesh.

[0021] This application also provides a simulation model of the internal environment of a hot air reflux furnace, which is obtained through the simulation model establishment method.

[0022] This application also provides a design method for an integrated circuit board, wherein the integrated circuit board is reflow soldered in a hot air reflow oven, comprising simulating the integrated circuit board in the design stage as a component to be soldered in the simulation model, and adjusting the structure of the integrated circuit board according to the simulation results.

[0023] This application also provides a method for correcting reflow soldering process parameters. By applying the principle of heat transfer, the temperature curve of the component to be soldered during the reflow soldering process is obtained by changing the air velocity and temperature at the air inlet and the translation speed of the moving area in the simulation model.

[0024] The simulation model was used to obtain the wind speed and temperature distribution map of the fluid domain inside the hot air reflux furnace;

[0025] The reflow soldering process parameters are corrected based on the temperature curve, wind speed distribution map, and temperature distribution map.

[0026] This application also provides a welding defect analysis method, which uses the principle of heat transfer to obtain the temperature curve of the component to be welded during the reflow soldering process by changing the wind speed and temperature of the air inlet and the translation speed of the moving area in the simulation model.

[0027] The temperature curve is used as input parameters to analyze welding defects.

[0028] This invention discloses a method for establishing a simulation model of the internal environment of a hot blast reflow oven. The oven is divided into static and dynamic regions. The component to be soldered is located in the mesh of the dynamic region. A layer-by-layer method is used to update the mesh within the dynamic region, simulating the component being moved by a conveyor device through different temperature zones, consistent with the movement of the component within the hot blast reflow oven, thus simulating the internal environment of the oven. Furthermore, the layer-by-layer method for updating the mesh offers high computational efficiency, improving the feasibility of the simulation model establishment method.

[0029] The simulation model obtained by this method can simulate the flow field state in the hot air reflow oven. By observing the changes in the flow field, parameters such as the air inlet velocity and the conveyor belt speed can be changed, thereby optimizing the process parameters for reflow soldering integrated circuit boards in the hot air reflow oven.

[0030] For integrated circuit boards that require reflow soldering in a hot air reflow oven, the integrated circuit board in the design stage is used as the component to be soldered in the simulation model during the design phase. The structure of the integrated circuit board is adjusted according to the simulation results to improve the reliability of the design.

[0031] By applying the principles of heat transfer, the temperature curve of the component to be soldered during the reflow soldering process is obtained by changing the air velocity at the air inlet and the translation speed of the moving area in the simulation model; the air velocity and temperature distribution map of the fluid domain inside the hot air reflow oven is obtained through the simulation model; the reflow soldering process parameters are corrected based on the temperature curve, air velocity distribution map and temperature distribution map to shorten the production time.

[0032] By changing the airflow speed at the air inlet and the translation speed of the moving area in the simulation model, the temperature curve of the component to be soldered during the reflow soldering process is obtained; using the temperature curve as input parameters, welding defects are analyzed to identify the areas where problems occur in the product and make improvements. Attached Figure Description

[0033] Figure 1 A schematic diagram showing the positions of the stationary and moving regions in the simulation model of the simulation model establishment method for the internal environment of the hot air reflux furnace provided in Embodiment 1 of the present invention;

[0034] Figure 2 A schematic diagram of the mesh of the moving region in the simulation model of the simulation model establishment method for the internal environment of the hot air reflux furnace provided in Embodiment 1 of the present invention;

[0035] Figure 3 A schematic diagram of a rectangular air outlet in the simulation model of the simulation model establishment method for the internal environment of the hot air reflux furnace provided in Embodiment 1 of the present invention;

[0036] Figure 4a This is a comparison chart of the experimental and simulated temperature curves at position one in Embodiment 1 of the present invention;

[0037] Figure 4b The figure shows a comparison of the experimental and simulated temperature curves at position two in Embodiment 1 of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The principles and features of the present invention are described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. Example

[0039] This embodiment first provides a method for establishing a simulation model of the internal environment of a hot blast reflow furnace, including:

[0040] The internal dimensions of the actual hot air reflow oven were measured to establish a geometric model of the hot air reflow oven;

[0041] The geometric model of the hot blast reflow oven is divided into a static region and a moving region. The larger the moving region, the greater the computational load of the finite element model established by this method. However, such a finite element model is closer to the internal environment of the hot blast reflow oven.

[0042] The grid of the moving area moves along the direction of movement of the component to be welded, and the component to be welded is located in the grid of the moving area; that is to say, the moving area must at least include a device for conveying the component to be welded and the component to be welded.

[0043] The motion region uses a layer-layout method to update the mesh, such as Figure 1 As shown, the interfaces at the left and right ends A and B of the motion area are set as stationary surfaces. The mesh of the motion area is set as rigid body motion, and the speed and direction are set to be consistent with the speed and direction of the components to be welded in the hot air reflow oven to obtain the finite element model.

[0044] Based on the finite element model, fluid dynamics calculations were performed to obtain a simulation model of the environment inside the hot air reflux furnace.

[0045] The simulation model establishment method for the internal environment of the hot air reflow oven provided in this embodiment divides the area inside the hot air reflow oven into a static area and a moving area. The component to be soldered is located in the grid of the moving area. The grid in the moving area is updated by the layer-laying method to simulate the component to be soldered being driven by the conveying device to pass through different temperature zones, which is consistent with the movement of the component to be soldered in the hot air reflow oven, and basically completely simulates the internal environment of the hot air reflow oven.

[0046] The layer-based mesh update method can produce highly structured meshes, meaning the meshes are arranged in a regular and orderly manner. Since dynamic meshing requires re-meshing in each time increment step, the orderly structured mesh is the most efficient and computationally efficient method when repeatedly performing mesh update operations.

[0047] The preferred embodiment provided in this example is as follows: Figure 1 As shown, stationary regions 1 are set above and below the moving region 2. Circular nozzle outlets are set above and below the hot air recirculation furnace. The stationary regions are symmetrically arranged with respect to the moving region 1, consistent with the fluid state within the hot air recirculation path. Furthermore, in the simulation model, insulation region 3 is set to simulate the insulation areas between different temperature zones in the hot air recirculation furnace.

[0048] This embodiment provides a preferred solution for simulating the circular nozzle outlet in a hot blast reflow oven. (Refer to...) Figure 3 Taking the top or bottom surface of the hot air recirculation path as an example, a rectangular air outlet 40 replaces the circular nozzle air outlet 4 of the hot air recirculation furnace. One rectangular air outlet 40 covers all the circular nozzle air outlets 4 within a temperature zone. First, the flow rates of all the circular nozzle air outlets 4 within a temperature zone are equivalent to the flow rates of the rectangular air outlet 40, resulting in the equivalent air velocity of the rectangular air outlet 40, as shown in the formula. ,in The equivalent wind speed of all circular nozzle outlets 4 in the previous temperature zone; This is the equivalent wind speed of 40 for the second rectangular air outlet. This refers to the total area of ​​all circular nozzle outlets 4 within a temperature zone. This is the area of ​​the equivalent rectangular air outlet of size 40.

[0049] For the mesh in the motion region, this embodiment provides a preferred implementation method, referring to... Figure 1 and Figure 2 The two ends of the mesh in motion region 2 are hexahedral meshes 22; the space between the two ends of the hexahedral meshes 22 is a tetrahedral mesh 21; the component to be welded is located in the tetrahedral mesh 21 of motion region 2, and when the tetrahedral mesh 21 is at one end of motion region 2 (in... Figure 1When the right end of the tetrahedral mesh 21 moves to end B, the mesh stops updating.

[0050] The size of the tetrahedral mesh 21 region is determined by whether it can completely enclose the component to be soldered.

[0051] The mesh in motion region 2 is updated through layering, so that the mesh in motion region 2 moves from A to B. The hexahedral mesh 22 split after being stretched at end A can generate a neat mesh, and the hexahedral mesh 22 merged after being compressed at end B can also be neatly merged without affecting the mesh quality of motion region 2.

[0052] Hexahedral meshes cannot be used to divide the geometry of the component to be soldered. While tetrahedral meshes have lower precision than hexahedral meshes, they are universal for any geometric shape. Using tetrahedral meshes in the middle of motion region 2 is more suitable for simulating the structure of irregularly shaped components to be soldered.

[0053] Where the hexahedral mesh 22 and the tetrahedral mesh 21 meet, they share nodes. The boundary conditions for the hexahedral mesh 22 and the tetrahedral mesh 21 at their junctions are shared. This method is simpler than setting their respective boundary conditions first and then setting the contact conditions, and it makes the motion region 2 a unified whole.

[0054] The hexahedrons in the hexahedral mesh 22 are cuboids; the cross-sections at the junctions of the hexahedral mesh 22 and the tetrahedral mesh 21 are all rectangular, and the side length of the rectangle is equal to the side length of the tetrahedral mesh at the junction, sharing nodes.

[0055] Based on the simulation model establishment method for the internal environment of a hot blast reflow furnace provided in this embodiment, a simulation model of the internal environment of a hot blast reflow furnace is obtained, referring to... Figure 1 and Figure 2 As shown.

[0056] Thermocouples are attached to designated locations on the components to be soldered, such as integrated circuit boards, using insulating tape. Temperature curves at these designated locations are obtained. A simulation model of the hot air reflow oven environment is then obtained using the simulation model establishment method provided in this embodiment. The experimental parameters obtained by fitting the thermocouples to the simulation model are compared. The two curves at designated location one are shown below. Figure 4a As shown in the figure, the two curves at the specified position two are as follows: Figure 4b As shown in the figure, the usability and correctness of the simulation model establishment method for the internal environment of the hot air reflux furnace provided in this embodiment are verified.

[0057] This embodiment also provides a design method for an integrated circuit board, wherein the integrated circuit board is reflow soldered in a hot air reflow oven, including simulating the integrated circuit board in the design stage as a component to be soldered in the simulation model, and adjusting the structure of the integrated circuit board according to the simulation results.

[0058] This embodiment also provides a method for correcting reflow soldering process parameters. By applying the principle of heat transfer, the temperature curve of the component to be soldered during the reflow soldering process is obtained by changing the air velocity, temperature of the air inlet and the translation speed of the moving area in the simulation model.

[0059] The simulation model was used to obtain the wind speed and temperature distribution map of the fluid domain inside the hot air reflux furnace;

[0060] The reflow soldering process parameters are corrected based on the temperature curve, wind speed distribution map, and temperature distribution map.

[0061] This embodiment also provides a welding defect analysis method, which uses the principle of heat transfer to obtain the temperature curve of the component to be welded during the reflow soldering process by changing the wind speed, temperature and translation speed of the moving area at the air inlet in the simulation model.

[0062] The temperature curve is used as input parameters to analyze welding defects.

[0063] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0064] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0065] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0066] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0067] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for establishing a simulation model of the internal environment of a hot blast reflux furnace, characterized in that, Include: Establish the geometric model of the hot blast reflux furnace; The geometric model of the hot air reflow oven is divided into a static region and a moving region, with the static region located above and below the moving region. The mesh of the moving region moves along the direction of movement of the component to be welded. The two ends of the mesh of the moving region are hexahedral meshes, and the space between the two hexahedral meshes is a tetrahedral mesh. The hexahedral mesh and the tetrahedral mesh share a common node at their junction. The hexahedrons in the hexahedral mesh are cuboids. The cross-section at the junction of the hexahedral mesh and the tetrahedral mesh is a rectangle. The side length of the rectangle is equal to the side length of the junction of the hexahedral mesh and the tetrahedral mesh. The component to be welded is located in the tetrahedral mesh of the moving region. The moving region uses a layer-layout method to update the mesh and obtain a finite element model. When the tetrahedral mesh is at one end of the moving region, the mesh update stops. Based on the finite element model, fluid dynamics calculations were performed to obtain a simulation model of the environment inside the hot air reflux furnace.

2. The simulation model establishment method according to claim 1, characterized in that, The circular nozzles of the hot air reflux furnace are replaced with rectangular air outlets, and one rectangular air outlet covers all the circular nozzles within a temperature zone.

3. A simulation model of the internal environment of a hot blast reflux furnace, characterized in that, Obtained by the simulation model establishment method described in claim 1 or 2.

4. A method for designing an integrated circuit board, wherein the integrated circuit board is reflow soldered in a hot air reflow oven, characterized in that, The method includes simulating the integrated circuit board in the design phase as a component to be soldered in the simulation model described in claim 3, and adjusting the structure of the integrated circuit board based on the simulation results.

5. A method for correcting reflow soldering process parameters, characterized in that, Using the principles of heat transfer, the temperature curve of the component to be soldered during the reflow soldering process is obtained by changing the air velocity and temperature at the air inlet and the translation speed of the moving area in the simulation model described in claim 3. The wind speed and temperature distribution map of the fluid domain inside the hot air reflux furnace is obtained through the simulation model described in claim 3; The reflow soldering process parameters are corrected based on the temperature curve, wind speed distribution map, and temperature distribution map.

6. A method for analyzing welding defects, characterized in that, Using the principles of heat transfer, the temperature curve of the component to be soldered during the reflow soldering process is obtained by changing the air velocity and temperature at the air inlet and the translation speed of the moving area in the simulation model described in claim 3. The temperature curve is used as input parameters to analyze welding defects.

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