A method and system for optimizing holding time in a printed circuit board pressing process

Abstract

The present invention provides a holding time optimization method and system for a printed circuit board press molding process. Based on simulation conditions, the holding time of the press molding process is adjusted, and numerical simulation of the printed circuit board press molding process is performed to determine the relative warping deformation and warping deformation cloud map of the simulation model under different holding times; the relative warping deformation and warping deformation cloud map of the printed circuit board are compared and analyzed, and a sensitivity curve of the warping deformation of the printed circuit board to the holding time is established to determine the optimal holding time under the current temperature and pressure. The present invention does not need to add new preparation equipment or overly complicate the preparation process. The finite element simulation method is used to continuously adjust the holding time of the hot pressing process under high temperature and high pressure, so that the warping deformation at the end of the press molding of the printed circuit board is minimized, the flatness of the printed circuit board is improved, the scrap rate is reduced, and the cost investment is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of printed circuit board manufacturing, and in particular relates to a holding time optimization method and system for a printed circuit board pressing and forming process. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Printed Circuit Boards (PCB) are the main components of most electronic products and the carriers for the electrical connection of electronic components. Their main function is to connect various electronic components to form a predetermined circuit, play a role in relay transmission, and are the key electronic connectors of electronic products. They are widely used and play an important role in smart terminals, wearable devices, computers, communication electronic equipment, military weapon systems, mobile medical equipment, automobiles and other fields.

[0004] The production process of printed circuit boards generally includes design, manufacturing, assembly and testing. The lamination process in the manufacturing process is an important part of ensuring the quality of multi-layer PCBs. The lamination process refers to the process of sending fixed copper foil, prepreg, core board and other raw materials into a vacuum hot press for lamination. The high temperature and high pressure soften and flow the uncured resin in the prepreg, and at the same time, a curing reaction occurs, turning it into a cured sheet, thereby bonding one or more inner layer boards and copper foil into a multi-layer integral board. In this process, due to the asymmetry of the PCB lamination structure or the uneven distribution of the circuit pattern, the large difference in the thermal expansion coefficients of the resin and the reinforcing material, the resin and copper, and the shrinkage effect of the curing reaction of the resin, the PCB will produce greater internal stress. Compared with a single copper clad laminate, the PCB is thicker, the pattern distribution is more complex, and the number of cured sheets is more, so the thermal stress generated will also be greater and more difficult to eliminate. The internal stress in the PCB is reflected in the subsequent process flows such as drilling, surface etching or baking, causing the PCB to further warp and deform, directly affecting the surface assembly of components on the PCB. On the automated surface mounting line, the unevenness of the circuit board can cause inaccurate positioning, that is, the pins of the components cannot be accurately inserted into the vias of the circuit board or fit the surface solder joints, and may even damage the automatic mounting machine; the circuit board with components installed bends after welding; the electronic components and the printed circuit board solder joints have poor contact, etc. At the same time, during the processing of PCB, various processes such as high temperature, mechanical cutting, and wet processing will also have an important impact on PCB deformation.

[0005] In summary, the reasons that may cause PCB deformation are complex and varied. According to the inventors, the current methods to prevent PCB deformation and warping are mainly to control the humidity of the inventory environment, ensure the reasonable design of the circuit of the printed circuit board, eliminate the stress inside the substrate, and increase the leveling process. However, these methods require a lot of manpower and equipment, which increases the cost and complicates the entire manufacturing process. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a method and system for optimizing the holding time of a printed circuit board press molding process. The present invention does not require the addition of manufacturing equipment, nor does it require the complication of the manufacturing process. The finite element simulation method is used to continuously adjust the holding time of the hot pressing process under high temperature and high pressure, so that the warping deformation at the end of the press molding of the printed circuit board is minimized or controllable as needed, thereby improving the flatness of the printed circuit board, reducing the scrap rate, and saving costs.

[0007] According to some embodiments, the present invention adopts the following technical solutions:

[0008] A method for optimizing the holding time of a printed circuit board press molding process comprises the following steps:

[0009] Establish geometric model of printed circuit board;

[0010] According to the material performance parameters of the pressing process, the actual mechanical constraints and loads of the printed circuit board, the initial conditions and boundary conditions of heat transfer, the material performance parameters, mechanical boundary conditions, initial conditions and boundary conditions of heat transfer in the simulation model of the hot pressing process are set;

[0011] Based on the conditions, the holding time of the pressing process is adjusted, a numerical simulation of the pressing process of the printed circuit board is performed, and a relative warping deformation amount and a warping deformation cloud diagram of the simulation model under different holding times are determined;

[0012] The relative warping deformation and the warping deformation cloud map of the printed circuit board are compared and analyzed, a sensitivity curve of the warping deformation of the printed circuit board to the holding time is established, and the optimal holding time under the current temperature and pressure is determined.

[0013] As an optional implementation method, the specific process of establishing the geometric model of the printed circuit board includes: using a partitioning and layering method to perform geometric modeling on the printed circuit board, and in the thickness direction, according to the dimensions and stacking order of the copper foil-resin mixed layer, the substrate layer of the copper clad laminate, and the prepreg layer in the thickness direction, geometric modeling is performed layer by layer;

[0014] Each layer model is partitioned, and the copper content of each partition is identified and assigned according to the wiring diagram of the printed circuit board, and the material performance parameters of each partition are equivalently processed.

[0015] As an optional implementation method, after establishing the geometric model of the printed circuit board, the material properties of the model are defined, specifically including: establishing a series of copper-resin mixed unit cell models under different copper content partitions of the wiring layer, establishing periodic boundary conditions based on the position characteristics of the unit cell model in the printed circuit board simulation model, calculating the equivalent material performance parameters of the unit cell models with different copper contents, and assigning material properties to each partition.

[0016] As a further limitation, the material performance parameters include at least one of density, specific heat capacity, thermal conductivity, chemical reaction heat release per unit mass, chemical reaction kinetic order, pre-exponential factor, chemical reaction activation energy, thermal expansion coefficient, chemical contraction coefficient, modulus and Poisson's ratio.

[0017] As an optional implementation, a rigid plate model is added above and below the geometric model for calculating the stress and strain field of the printed circuit board, and the lower plate model is fixed. The pressing force of the pressing process in production is applied to the upper plate model to reflect the mechanical boundary.

[0018] As an optional implementation, the specific process of performing the numerical simulation of the printed circuit board pressing process includes:

[0019] Calculate the temperature field during the lamination process of the printed circuit board, and simulate the heat transfer process of the printed circuit board with the heat released by the curing reaction of the prepreg as the internal heat source during the lamination process;

[0020] The simulated temperature field results are imported as predefined fields of stress and strain fields of printed circuit boards to calculate stress, strain and displacement during the pressing process of printed circuit boards;

[0021] Simulate the shrinkage of printed circuit boards due to curing reactions, thermal expansion and contraction, and mechanical response under pressure.

[0022] As an optional implementation, the specific process of determining the relative warpage deformation amount and the warpage deformation cloud map of the simulation model at different holding times includes:

[0023] Only the holding time of the hot pressing stage is changed, the temperature field of the printed circuit board is calculated and used as the predefined field for stress-strain calculation. The stress, strain and displacement in the thickness direction of the printed circuit board when the mold is opened and cooled to room temperature are calculated. The influence of the holding time under the current highest temperature and maximum pressure on the warping deformation of the printed circuit board after pressing is analyzed, and the sensitivity curve of the warping deformation of the printed circuit board to the holding time is established.

[0024] A holding time optimization system for a printed circuit board press molding process, comprising:

[0025] A geometric model building module is configured to build a geometric model of a printed circuit board;

[0026] A parameter acquisition module is configured to set material performance parameters, mechanical boundary conditions, heat transfer initial conditions and boundary conditions in a thermal pressing process simulation model according to material performance parameters of the pressing process, actual mechanical constraints and loads of the printed circuit board, and heat transfer initial conditions and boundary conditions;

[0027] A numerical simulation module is configured to adjust the holding time of the pressing process based on the conditions, perform numerical simulation of the pressing process of the printed circuit board, and determine the relative warping deformation amount and warping deformation cloud map of the simulation model under different holding times;

[0028] The parameter optimization module is configured to compare and analyze the relative warpage deformation and the warpage deformation cloud map, establish a sensitivity curve of the warpage deformation of the printed circuit board to the holding time, and determine the optimal holding time under the current maximum temperature and maximum pressure.

[0029] An electronic device comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps in the above method are completed.

[0030] A computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, the steps in the above method are completed.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The invention reduces the warping deformation in the process of pressing and forming the printed circuit board by changing the process conditions, thereby improving the product yield and the reliability and stability in the process of using the product.

[0033] The present invention adopts a thermal-chemical-mechanical coupling method and a multi-scale simulation method, organically integrates and applies knowledge such as micromechanics, curing reaction kinetics, structural mechanics, viscoelastic mechanics, and heat transfer, establishes a finite element analysis model of the printed circuit board pressing process, simulates the printed circuit board pressing process, and can determine the optimal time value for controlling the warping deformation during the printed circuit board pressing and molding process as needed, which is helpful for actual production.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 It is a schematic diagram of the general multi-layer PCB laminated structure and copper clad plate structure;

[0037] Figure 2 It is an optimized design technology route for holding time under high temperature and high pressure during PCB pressing and forming process;

[0038] Figure 3 is a schematic diagram of a PCB geometric model involved in a specific implementation method;

[0039] Figure 4 It is a schematic diagram of the partitioning of the PCB geometric model involved in the specific implementation method;

[0040] Figure 5 is a curve of temperature and resin curing degree changing with time obtained by PCB simulation involved in Example 1;

[0041] Figure 6 It is the pressure boundary condition in the PCB simulation process involved in the first embodiment;

[0042] Figure 7 are the temperature results of the five groups of simulation examples involved in the first embodiment;

[0043] Figure 8 are the curing degree results of the five groups of examples involved in the first embodiment;

[0044] Fig. 9 The simulation results and experimental results of reducing the holding time and relative warping deformation of the PCB under high temperature and high pressure involved in the first embodiment;

[0045] Fig.10 The temperature and curing degree of the important process stage at different holding times under high temperature and high pressure compared with the reference value involved in Example 1;

[0046] Fig.11 are the temperature results of the twelve groups of simulation examples involved in the second embodiment;

[0047] Fig.12 are the curing degree results of the twelve groups of simulation examples involved in the second embodiment;

[0048] Fig.13 The simulation results and experimental results of the relative warping deformation of the PCB under extended high temperature and high pressure as mentioned in the second embodiment;

[0049] Fig.14 It is the temperature and curing degree of the important process stage under the high temperature and high pressure involved in Example 2 at different holding times compared with the reference value.

[0050] Among them, 101-aluminum template; 102-kraft paper; 103-mirror stainless steel plate; 104-copper clad laminate; 105-CCL substrate; 106-prepreg; 107-resin; 108-glass fiber cloth; 109-copper foil. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0052] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0053] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0054] A method for determining the process time for minimizing or controlling the warpage deformation amount in the press-molding process of a printed circuit board as needed, taking the press-molding process of the PCB as the research object, by continuously adjusting the holding time of the hot pressing process under high temperature and high pressure, and by means of a finite element simulation method, the warpage deformation amount at the end of the press-molding of the PCB is minimized or controlled as needed, thereby obtaining reasonable hot pressing process conditions, improving the flatness of the PCB, reducing the scrap rate, and saving costs.

[0055] The above-mentioned pressing process includes hot pressing, cold pressing and mold opening and cooling to room temperature. The temperature, time, pressure and other settings of these stages will affect the warping deformation of the PCB at the end of pressing.

[0056] The finite element simulation method mentioned above refers to a method of simulating the PCB pressing process using a thermal-chemical-mechanical coupling method, which mainly includes:

[0057] First, establish the geometric model of PCB layering and partitioning;

[0058] According to the material performance parameters of the pressing process, the actual mechanical constraints and loads of the PCB, the initial conditions and boundary conditions of heat transfer, the material performance parameters, mechanical boundary conditions, initial conditions and boundary conditions of heat transfer in the simulation model of the PCB thermal pressing process are set;

[0059] Conduct finite element simulation and data analysis of PCB lamination process;

[0060] Adjust the holding time of the hot pressing process under high temperature and high pressure, establish a sensitivity curve of PCB warpage to holding time, and minimize or control the warpage at the end of PCB pressing.

[0061] The whole method specifically includes the following steps:

[0062] (1) Geometric model construction: According to the actual size of the PCB, the geometric model is directly constructed through the graphical user interface, or the geometric model is established using geometric modeling software, the data file is generated and then imported into the finite element simulation software.

[0063] Since the geometric features of an actual PCB are relatively complex, including a laminated structure, copper lines with different routing directions in the wiring layer, solder joints, and a large copper foil area for subsequent connection with electronic components, it is unrealistic to completely restore these geometric features during modeling. Therefore, the present invention adopts a simplified method of partitioning and layering to model the PCB.

[0064] Specifically: in the thickness direction, modeling is carried out layer by layer according to the dimensions and stacking order of the copper foil-resin mixed layer, the substrate layer of the copper clad laminate (CCL), and the prepreg layer in the thickness direction; each layer model is partitioned, the copper content of different partitions is identified and assigned according to the wiring diagram of the PCB, and the material performance parameters of each partition are equivalently processed.

[0065] (2) Parameter acquisition: For the different copper content partitions of the wiring layer, a series of copper-resin mixed unit cell models with different copper contents are established. According to the position characteristics of the unit cell model in the PCB macro finite element model, periodic boundary conditions are established, and the equivalent material performance parameters of the unit cell model with various copper contents are calculated. The material properties are assigned to each partition of the wiring layer.

[0066] The simulation analysis of the PCB manufacturing process in the present invention mainly involves heat transfer, curing reaction molding, thermal expansion and contraction, chemical shrinkage, and viscoelastic deformation processes. The related material performance parameters include: density, specific heat capacity, thermal conductivity, chemical reaction heat release per unit mass, chemical reaction kinetics order, pre-exponential factor, chemical reaction activation energy, thermal expansion coefficient, chemical shrinkage coefficient, modulus, Poisson's ratio. Of course, in different embodiments, the above parameters can be deleted, added, replaced or adjusted.

[0067] Parameter acquisition also includes the acquisition of boundary conditions: in the actual production process, each hot press has multiple press plates, and two adjacent press plates form a group. Each group of press plates uses multiple mirror stainless steel plates to press multiple PCBs. The heat of the PCB ultimately comes from the heat medium oil circulating in the upper and lower press plates. The PCB closest to the press plate not only involves heat exchange with the press plate, but also involves heat exchange with other PCBs, and its thermal boundary conditions are relatively complex.

[0068] In the PCB simulation of the present invention, the temperature field model does not establish a pressure plate structure, but simplifies the calculation by applying a thermal convection boundary. In the stress field model, in order to truly reflect the mechanical boundary of the PCB in the thickness direction, a rigid plate is added to the upper and lower parts of the PCB, the lower plate is fixed, and the pressing force of the pressing process in production is applied to the upper plate.

[0069] (3) Numerical simulation: Using the thermal-chemical-mechanical coupling method, the resin curing reaction kinetic model and the viscoelastic mechanical constitutive model are called. First, the temperature field during the PCB pressing process is calculated, and the heat transfer process of the entire PCB with the heat released by the curing reaction of the semi-cured sheet as the internal heat source during the pressing process is simulated; then the simulated temperature field results are imported as the predefined field of the PCB stress-strain field, and the stress, strain and displacement during the PCB pressing process are calculated. The curing reaction shrinkage, thermal expansion and contraction, and viscoelastic mechanical deformation behaviors of the PCB, such as stress state, strain state, and PCB warping deformation state, are simulated.

[0070] To facilitate understanding by those skilled in the art, an example is now given to illustrate that in a certain embodiment, the pressing process includes a hot pressing process of 12600s, a cold pressing process of 3800s, and a process of opening the mold and air cooling to room temperature after pressing for 3000s.

[0071] (4) Parameter optimization: Change the holding time under high temperature and high pressure in the hot pressing stage, first calculate the temperature field of the PCB, and then use it as the predefined field for stress and strain calculation, so as to calculate and output the displacement distribution and size in the thickness direction of the PCB when the mold is opened and cooled to room temperature, analyze the influence of the holding time under high temperature and high pressure on the warpage deformation of the PCB after pressing, and establish the sensitivity curve of the warpage deformation of the printed circuit board to the holding time, so as to optimize the temperature-time and pressure-time curves of the pressing process in actual production, and minimize or control the warpage deformation of the PCB after pressing as needed.

[0072] Likewise, in different embodiments, the high temperature and high pressure may be different, but as long as in a certain embodiment, the temperature and pressure remain consistent.

[0073] To facilitate understanding by those skilled in the art, an example is now given to illustrate. In a certain embodiment, the high temperature in the PCB pressing process is 200° C., the highest temperature of the PCB surface layer in the hot pressing stage during the simulation process; the high pressure in the PCB pressing process is 2.89 MPa, the highest pressure of the PCB in the hot pressing stage during the simulation process; when the PCB surface layer reaches the highest temperature and the applied pressure is the highest pressure, the curing degree of the surface resin is above 96%; changing the holding time of the high temperature and high pressure during the pressing process is specifically to keep the heat transfer boundary conditions and the process parameters of the cold pressing stage unchanged when the PCB surface temperature is the highest temperature and the pressure is the highest pressure, and only change the process time of the hot pressing stage.

[0074] Correspondingly, the optimization design system for holding time under high temperature and high pressure during PCB pressing and forming includes the following contents:

[0075] The geometric model building module is used to build the geometric model of PCB simulation. The geometric model can be directly built through the graphical user interface or imported through the geometric model data file.

[0076] A parameter acquisition module is used to obtain material performance parameters of the PCB lamination process, mechanical boundary conditions, heat transfer boundary conditions and initial conditions in the actual PCB production process, and input the parameters through a graphical user interface;

[0077] The numerical simulation module is used to numerically simulate the pressing and mold opening processes based on the mathematical model of the PCB pressing process, and obtain the simulation results of the warping deformation amount and the warping deformation cloud map of the PCB after hot pressing, cold pressing, and mold opening and cooling to room temperature; in the numerical simulation module, the mathematical model of the PCB pressing process includes a PCB geometric model, a material performance parameter model, mechanical boundary conditions, heat transfer boundary conditions and initial conditions, a resin curing reaction kinetic model, and a viscoelastic mechanics constitutive model, which is used to numerically simulate the curing reaction, thermal expansion and contraction, and curing reaction shrinkage process in the PCB pressing and molding process, and complete the operation through a graphical user interface.

[0078] The parameter optimization module is used to perform single-objective optimization of minimizing or controlling the warpage deformation of PCB pressing and molding on demand by changing the holding time under high temperature and high pressure during the PCB pressing and molding process, or to perform multi-objective optimization of controlling the warpage deformation and manufacturing cost of PCB pressing and molding on demand, and to complete the operation by establishing a sensitivity curve of the warpage deformation of the printed circuit board to the holding time through a graphical user interface.

[0079] Embodiment 1:

[0080] This embodiment uses a PCB of an electronic product as a research object. The outer contour size of the PCB is 260 mm×160 mm, and there are 8 wiring layers, namely copper foil-resin mixed layers (hereinafter referred to as mixed layers). Figure 3 Schematic diagram of the PCB simulation model of this embodiment; Figure 4 Schematic diagram of the PCB simulation model partitioning of this embodiment.

[0081] In the finite element software, the geometric model is established by partitioning and layering according to the actual size of the PCB, that is, the mixed layer is divided into 5×4 equal parts according to the outer contour size, and at the same time, according to the number and size of its wiring layers, a PCB model with 8 mixed layers and 160 partitions is established in the three-dimensional software, and then it is imported into the finite element simulation software, and the material parameters of each partition are defined respectively, and then the temperature field and stress field of the pressing process (the whole process in this embodiment is 19400s) are calculated. In the heat transfer analysis, the PCB temperature change curve obtained by simulation over time is made close to the actual process temperature curve by applying convection boundaries and adjusting the convection heat transfer coefficient. Since the warping deformation of the PCB involves the shrinkage process of the curing reaction of the resin, the dynamic curing process of the semi-cured sheet resin needs to be calculated. Figure 5 The temperature and resin curing degree change curves over time obtained by PCB simulation.

[0082] The temperature field results and curing degree results obtained from the PCB simulation are imported as predefined fields into the calculation of the stress field. A rigid plate is added to the upper and lower sides of the PCB in the thickness direction (the plate is set as a rigid body in the finite element simulation software). The lower plate is completely fixed, and the pressing force of the pressing process in production is applied to the upper plate (pressure boundary conditions that vary with time), thereby truly reflecting the mechanical boundary of the PCB in the thickness direction. Figure 6 It is the pressure boundary condition during PCB simulation.

[0083] The PCB simulation calculation can obtain the warping deformation amount and warping deformation morphology of the PCB after the pressing. Several representative nodes are taken on the PCB surface, and their temperature and curing degree results are derived respectively. It can be seen that the time when the PCB is under high temperature and high pressure is 2204s. At 9300s, the curing degree of the PCB surface layer reaches more than 96%, and 9300s is a certain time when the PCB is under high temperature and high pressure during the pressing process (2000s in this embodiment). Therefore, 9300s is selected as the benchmark to reduce the holding time of constant temperature (200°C in this embodiment) and constant pressure (2.89MPa in this embodiment), and the warping deformation during the PCB pressing process is simulated and optimized. This embodiment designs five groups of calculation examples, which respectively reduce the holding time of PCB under high temperature and high pressure by 100s, 200s, 300s, 400s, and 500s, that is, the time that PCB is under high temperature and high pressure during the pressing process is 2104s, 2004s, 1904s, 1804s, and 1704s. Only the process time of the hot pressing stage is changed, and the mechanical boundary conditions, heat transfer boundary conditions, and process parameters of the cold pressing stage are not modified. The temperature field of the PCB is first calculated, and then used as a predefined field for stress and strain calculation, so as to calculate and output the displacement distribution in the thickness direction of the PCB when the mold is opened and cooled to room temperature. The simulation results of the PCB are compared with the experimental results, and the actual pressing molding process is improved to reduce production costs and improve the yield rate. Figure 7 The temperature results of the five simulation examples are shown below. Figure 8 The curing degree of five sets of simulation examples is shown in the figure. The holding time is used as the code for each example curve. Fig. 9 Simulation and experimental results to reduce the holding time and relative warpage deformation of PCB under high temperature and high pressure. Fig.10 The results of the temperature and curing degree of the important process stages under different holding times compared with the benchmark value under high temperature and high pressure are shown in Table 1. The timetable corresponding to each stage of different examples is shown in Table 1.

[0084] Table 1 Corresponding timetables for each stage of different examples

[0085]

[0086] It can be seen from the above results that when the resin curing degree of the PCB reaches or exceeds 96%, the holding time is reduced under high temperature and high pressure, and the warping deformation of the PCB after the mold is opened and cooled to room temperature shows a certain regularity, and the temperature and curing degree at different process stages also have certain differences as the holding time decreases. At the end of hot pressing and cold pressing, as the holding time decreases, the surface temperature of the PCB increases to a certain extent. When the mold is opened and cooled to room temperature, the temperature of the PCB in these examples is cooled to room temperature (25°C in this embodiment).

[0087] Depend on Fig. 9It can be seen that when the holding time is less than 0s compared to the baseline value, the warpage of the PCB shows a downward trend as the holding time under high temperature and high pressure decreases. From the current simulation results, the effect of the reduction in PCB internal stress caused by the reduction in resin curing degree is significantly greater than the effect of residual stress caused by the viscoelastic relaxation effect of internal stress at high temperature. As a result, the warpage of the PCB is reduced when the pressure is released and the mold is opened and cooled to room temperature. Among them, when the holding time is reduced by 200s, the warpage of the PCB is small. In the simulation calculation, due to the slight difference in model data or the error in calculation, the calculation results may be somewhat singular, but the error is within the range of 1μm and has little effect on the results. Simulation results and Fig. 9 The experimental results are consistent with that shown in Figure 2. As the holding time under high temperature and high pressure decreases, the warpage of the PCB tends to decrease.

[0088] In summary, appropriately reducing the holding time under high temperature and high pressure during the thermal pressing stage has a certain effect on reducing the warpage deformation in the thickness direction of the PCB. Reducing the holding time under high temperature and high pressure will result in a lower degree of curing of the resin when the mold is opened and cooled to room temperature. When the PCB is heated to above 200°C for reflow soldering, the resin may continue to solidify. The shrinkage effect of the curing reaction may cause fluctuations in the warpage morphology and warpage deformation of the PCB.

[0089] Embodiment 2:

[0090] This embodiment uses the same model as that of the first embodiment as the research object, and its modeling scheme, material parameter definition, etc. are the same. Subsequent calculations are performed based on the warpage deformation amount and warpage deformation cloud map of the PCB after lamination calculated in the first embodiment. 9300s is selected as the reference time, and the holding time of constant temperature (200°C in this embodiment) and constant pressure (2.89MPa in this embodiment) is increased to simulate and optimize the warpage deformation during the PCB lamination process. In this embodiment, twelve groups of calculation examples are designed, in which the holding time of the PCB under high temperature and high pressure is increased by 100s, 300s, 400s, 500s, 550s, 600s, 650s, 700s, 750s, 800s, 1800s, and 3600s, respectively. That is, the time that the PCB is under high temperature and high pressure during the pressing process is 2304s, 2504s, 2604s, 2704s, 2754s, 2804s, 2854s, 2904s, 2954s, 3004s, 4004s, and 5804s. Only the process time of the hot pressing stage is changed, and the mechanical boundary conditions, heat transfer boundary conditions, and process parameters of the cold pressing stage are not modified. The temperature field of the PCB is first calculated, and then used as a predefined field for stress and strain calculation. The displacement distribution in the thickness direction of the PCB when the mold is opened and cooled to room temperature is further calculated and output, and the warpage deformation of the PCB when the mold is opened and cooled to room temperature is obtained.

[0091] According to the simulation results of PCB, the actual pressing and forming process is improved to reduce the production cost and improve the quality stability of PCB. Fig.11 The temperature results of the twelve simulation examples are shown below. Fig.12 These are the curing degree results of twelve sets of simulation examples. The holding time is used as the code for each example curve. Fig.13 The simulation and experimental results of the relative warping deformation of PCB to extend the holding time under high temperature and high pressure. Fig.14 The results of temperature and curing degree of important process stages under different holding times compared with the benchmark value under high temperature and high pressure are shown in Table 2. The timetable corresponding to each stage of different examples is shown in Table 2.

[0092] Table 2 Timetable corresponding to each stage of different examples

[0093]

[0094] Continued

[0095]

[0096] It can be seen from the above results that when the resin curing degree of the PCB reaches or exceeds 96%, the holding time under high temperature and high pressure is extended, and the warping deformation of the PCB after the mold is opened and cooled to room temperature shows a certain regularity, and the temperature and curing degree at different process stages also have certain differences with the increase of holding time. At the end of hot pressing and cold pressing, as the holding time under high temperature and high pressure is extended, the surface temperature of the PCB decreases to a certain extent. When the mold is opened and cooled to room temperature, the temperature of the PCB in these examples is cooled to room temperature (25°C in this embodiment) due to the long air cooling time (3000s in this embodiment).

[0097] Depend on Fig.14It can be seen that when the holding time is greater than 0s compared with the benchmark value, as the holding time under high temperature and high pressure increases, the PCB warpage deformation shows a trend of first decreasing and then increasing. The simulation results are consistent with the experimental results. When the holding time under high temperature and high pressure is less than 600s, the effect of the residual stress reduction caused by the viscoelastic relaxation effect of the internal stress under high temperature is greater than the effect of the increase in the internal stress of the PCB caused by the increase in the curing degree. Therefore, the warpage deformation of the PCB when it is unloaded and opened to cool to room temperature is reduced to a certain extent; among them, the PCB warpage deformation when it is kept under high temperature and high pressure for 300s is the smallest. When the holding time under high temperature and high pressure is greater than 600s, as the PCB is placed under high temperature and high pressure for an increasing time, the resin curing degree increases, the curing reaction is also ongoing, and the stress caused by the shrinkage of the curing reaction is continuously generated. The extension of the holding time at high temperature causes the viscoelastic relaxation effect of the internal stress of the PCB to reduce the residual stress. Therefore, it should be a comprehensive process of new stress generation and existing stress relaxation. At this time, the increase in the internal stress of the PCB caused by the increase in the resin curing degree occupies a dominant position, so the PCB warpage deformation increases when the pressure is released and the mold is opened. Since the curing degree of the resin cannot reach 100% in the actual production process, the rate of increase of the curing degree decreases when the curing degree is high, or even the curing degree stops increasing. Fig.14 It can be seen that the slope of the curing degree has decreased.

[0098] In summary, the optimization design of PCB warpage can be performed by appropriately extending the holding time under high temperature and high pressure in the hot pressing stage. However, extending the holding time under high temperature and high pressure too much will not only fail to improve the warpage of the PCB, but also increase the process cost. Therefore, it is not advisable to extend the time too much in the actual production process. From the above results, it can be seen that the solution of reducing the warpage of the PCB during the pressing process by appropriately improving the holding time under high temperature and high pressure in the hot pressing stage is feasible, and the warpage of the PCB can be improved according to this optimization design system and method.

[0099] Of course, the above embodiments are only examples, and the various parameters therein can be adjusted or changed as needed in the application or other embodiments.

[0100] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for optimizing the holding time of a printed circuit board press molding process, characterized in that: The following steps are involved: Establish geometric model of printed circuit board; According to the material performance parameters of the pressing process, the actual mechanical constraints and loads of the printed circuit board, the initial conditions and boundary conditions of heat transfer, the material performance parameters, mechanical boundary conditions, initial conditions and boundary conditions of heat transfer in the simulation model of the hot pressing process are set; Based on the conditions, the holding time of the pressing process is adjusted, a numerical simulation of the pressing process of the printed circuit board is performed, and a relative warping deformation amount and a warping deformation cloud diagram of the simulation model under different holding times are determined; Comparing and analyzing the relative warpage deformation and the warpage deformation cloud map of the printed circuit board, establishing a sensitivity curve of the warpage deformation of the printed circuit board to the holding time, and determining the optimal holding time under the current temperature and pressure; The specific process of numerical simulation of printed circuit board lamination process includes: Calculate the temperature field during the lamination process of the printed circuit board, and simulate the heat transfer process of the printed circuit board with the heat released by the curing reaction of the prepreg as the internal heat source during the lamination process; The simulated temperature field results are imported as predefined fields of stress and strain fields of printed circuit boards to calculate stress, strain and displacement during the pressing process of printed circuit boards; Simulate the shrinkage of printed circuit boards due to curing reactions, thermal expansion and contraction, and mechanical response under pressure.

2. The method for optimizing the holding time of a printed circuit board press molding process according to claim 1, characterized in that: The specific process of establishing the geometric model of the printed circuit board includes: using the partitioning and layering method to perform geometric modeling on the printed circuit board, and in the thickness direction, according to the dimensions and stacking order of the copper foil-resin mixed layer, the substrate layer of the copper clad laminate, and the prepreg layer in the thickness direction, perform geometric modeling layer by layer; Each layer model is partitioned, and the copper content of each partition is identified and assigned according to the wiring diagram of the printed circuit board, and the material performance parameters of each partition are equivalently processed.

3. The method for optimizing the holding time of a printed circuit board press molding process according to claim 1, characterized in that: After establishing the geometric model of the printed circuit board, the material properties of the model are defined, including: establishing a copper-resin mixed unit cell model with different copper contents for the different copper content partitions of the wiring layer; establishing periodic boundary conditions based on the position characteristics of the unit cell model in the printed circuit board simulation model; calculating the equivalent material performance parameters of the unit cell model with different copper contents, and assigning material properties to each partition.

4. A method for optimizing the holding time of a printed circuit board press molding process as claimed in claim 3, characterized in that: The material performance parameters include at least one of density, specific heat capacity, thermal conductivity, chemical reaction heat release per unit mass, chemical reaction kinetic order, pre-exponential factor, chemical reaction activation energy, thermal expansion coefficient, chemical contraction coefficient, modulus and Poisson's ratio.

5. The method for optimizing the holding time of a printed circuit board press molding process according to claim 1, characterized in that: A rigid plate model is added above and below the geometric model for calculating the stress and strain field of the printed circuit board, and the lower plate model is fixed. The pressing force of the pressing process in production is applied to the upper plate model to reflect the mechanical boundary.

6. The method for optimizing the holding time of a printed circuit board press molding process according to claim 1, characterized in that: The specific process of determining the relative warpage deformation and warpage deformation cloud diagram of the simulation model at different holding times includes: Only the holding time of the hot pressing stage is changed, the temperature field of the printed circuit board is calculated and used as the predefined field for stress-strain calculation. The stress, strain and displacement in the thickness direction of the printed circuit board when the mold is opened and cooled to room temperature are calculated. The influence of the holding time under the current highest temperature and maximum pressure on the warping deformation of the printed circuit board after pressing is analyzed, and the sensitivity curve of the warping deformation of the printed circuit board to the holding time is established.

7. A holding time optimization system for a printed circuit board press molding process, characterized by: include: A geometric model building module is configured to build a geometric model of a printed circuit board; A parameter acquisition module is configured to set material performance parameters, mechanical boundary conditions, heat transfer initial conditions and boundary conditions in a thermal pressing process simulation model according to material performance parameters of the pressing process, actual mechanical constraints and loads of the printed circuit board, and heat transfer initial conditions and boundary conditions; A numerical simulation module is configured to adjust the holding time of the pressing process based on the conditions, perform numerical simulation of the pressing process of the printed circuit board, and determine the relative warping deformation amount and warping deformation cloud map of the simulation model under different holding times; A parameter optimization module is configured to compare and analyze the relative warpage deformation and the warpage deformation cloud map, establish a sensitivity curve of the warpage deformation of the printed circuit board to the holding time, and determine the optimal holding time under the current temperature and pressure; Among them, the specific process of numerical simulation of printed circuit board pressing process includes: Calculate the temperature field during the lamination process of the printed circuit board, and simulate the heat transfer process of the printed circuit board with the heat released by the curing reaction of the prepreg as the internal heat source during the lamination process; The simulated temperature field results are imported as predefined fields of stress and strain fields of printed circuit boards to calculate stress, strain and displacement during the pressing process of printed circuit boards; Simulate the shrinkage of printed circuit boards due to curing reactions, thermal expansion and contraction, and mechanical response under pressure.

8. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the steps of the method according to any one of claims 1 to 6.

9. An electronic device, characterized in that: The method comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps in the method according to any one of claims 1 to 6 are completed.

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