Preparation method for improving interlayer layering and warping of bending area of flexible circuit board

Abstract

The invention relates to the field of flexible circuit board manufacturing, and provides a preparation method for improving interlayer layering and warping of a bending area of a flexible circuit board. The method comprises the following steps: determining the width of a non-adhesive region of a bending region of the flexible circuit board based on analysis of bending stress distribution; the method comprises the following steps: replacing an adhesive-free electrolytic copper foil used by a base material in a bending area with an adhesive-free rolled copper foil, and utilizing a grain structure which is formed by the rolled copper foil due to a rolling process and is internally compact and axially arranged; manufacturing a flexible circuit board, and manufacturing a non-glue area in a bending area of the flexible circuit board according to the determined width of the non-glue area; carrying out press-fit encapsulation, and carrying out overall press-fit on the flexible circuit board with the manufactured non-glue area; cutting the laminated and encapsulated flexible circuit board into single pieces by adopting high-precision laser cutting equipment; and carrying out a bending test, carrying out bending operation on the flexible circuit board which is cut into the single pieces, and verifying the bending effect and the improvement condition of the warping problem.

Description

Technical Field

[0001] This application relates to the field of flexible printed circuit (FPC) manufacturing technology, and in particular to a preparation method for improving interlayer delamination and warping in the bending area of ​​a flexible printed circuit. Background Technology

[0002] Flexible printed circuit boards (FPCs) are prone to interlayer delamination and warpage in their bending areas due to repeated deformation. The core causes include: 1. Stress concentration: Rigid structures such as copper pillars and weld joints form stress concentration points when bent, leading to interlayer bonding failure; 2. Insufficient fatigue resistance of materials: Traditional ED copper foil with and without adhesive has a vertical columnar grain structure, poor ductility and resistance to repeated bending, and is prone to cracking; 3. Process defects: Existing processes often adopt the process of "cutting the shape first and then pressing it together". The cut edges are prone to burrs or micro-cracks, which become the starting point of stress concentration and aggravate delamination and warping.

[0003] Therefore, a method is urgently needed to solve at least one of the above problems. Summary of the Invention

[0004] This application provides a method for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board, aiming to solve the problem that existing technologies, which rely on individual measures, have limited improvement effects and cannot meet the requirements of high-reliability FPCs.

[0005] In a first aspect, embodiments of this application provide a method for improving interlayer delamination and warping in the bending region of a flexible circuit board, the method comprising: Based on the analysis of bending stress distribution, the width of the glue-free area in the bending region of the flexible circuit board is determined to provide greater stress buffer and deformation space, and to avoid stress concentration at rigid points. The electrolytic copper foil with or without glue used in the substrate of the bending region is replaced with rolled copper foil with or without glue, taking advantage of the dense internal and axially arranged grain structure formed by the rolling process of the rolled copper foil. To fabricate a flexible circuit board, a glue-free area is created in the bending region of the flexible circuit board according to the determined width of the glue-free area. Then, the flexible circuit board with the glue-free area is laminated together to fully bond the materials and stabilize the internal stress. High-precision laser cutting equipment is used to cut the laminated and encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, and avoiding minor defects from becoming stress concentration points. Bending tests are conducted to bend the individual flexible circuit boards to verify the bending effect and the improvement of the warping problem.

[0006] In some embodiments, determining the width of the adhesive-free region of the flexible circuit board's bending area based on the analysis of bending stress distribution includes: collecting material parameters and bending condition parameters of the flexible circuit board's bending area; inputting the material parameters and bending condition parameters into a finite element analysis model to simulate stress distribution cloud maps of the bending area under different adhesive-free region widths; calculating the stress concentration factor corresponding to the adhesive-free region width based on the stress distribution cloud map, and selecting the minimum adhesive-free region width with a stress concentration factor lower than a preset threshold as the target width; wherein, the material parameters include the substrate's elastic modulus, copper foil thickness, and adhesive layer bonding strength; the bending condition parameters include bending radius, bending frequency, and load force.

[0007] In some embodiments, replacing the adhesive-free electrolytic copper foil used in the substrate of the bending area with adhesive-free rolled copper foil includes: identifying the boundary of the bending area in the flexible circuit board design drawing using image recognition technology, and marking the projection range of the bending area on the substrate; traversing the substrate design layer and marking all positions in the bending area where adhesive-free electrolytic copper foil is used; replacing the adhesive-free electrolytic copper foil at the marked positions with adhesive-free rolled copper foil of the same thickness, and retrieving the rolling process parameters of the rolled copper foil through a material traceability system to verify that it meets the preset requirements for the preparation of dense grain structure; the rolling process parameters include the number of rolling passes, rolling pressure, and annealing temperature.

[0008] In some embodiments, utilizing the internally dense and axially aligned grain structure formed by the rolling process of rolled copper foil includes: scanning the bending region of the rolled copper foil with an electron backscatter diffraction device to obtain a grain structure image; inputting the grain structure image into a grain structure analysis module to identify the shape, size, and arrangement direction of the grains; determining whether the grain arrangement direction is consistent with the bending direction of the flexible circuit board and whether the grain size variation coefficient is lower than a preset value; if so, confirming that the grain structure of the rolled copper foil meets the usage requirements; the grain size variation coefficient includes the ratio of the maximum grain size to the minimum grain size.

[0009] In some embodiments, the step of creating a glue-free area in the bending region of the flexible circuit board according to a determined glue-free area width includes: marking the outline of the glue-free area on the substrate of the flexible circuit board along the boundary of the bending region using a laser etching process according to the determined glue-free area width; performing surface treatment on the marked glue-free area using a plasma treatment device to remove the adhesive layer material in the area, with the treatment time set to 30-60 seconds depending on the adhesive layer thickness; capturing a surface image of the glue-free area using an optical detection system, measuring the corresponding width error and the area of ​​residual adhesive layer on the surface, ensuring that the width error is within ±0.01 mm and the residual adhesive layer area accounts for less than 0.1%; the width error includes the difference from the target width.

[0010] In some embodiments, the pressing and encapsulation process involves pressing the flexible circuit board with the glue-free area fabricated as a whole to ensure sufficient material bonding and stabilize internal stress. This includes: placing the flexible circuit board with the glue-free area fabricated between the middle layers of the pressing equipment and setting the pressing parameters; starting the pressing equipment and sequentially executing the heating, pressurizing, and heat and pressure holding processes according to preset parameters to ensure sufficient bonding of the materials in each layer of the flexible circuit board through thermosetting; after pressing, monitoring the cooling rate of the middle layer in real time using a temperature sensor and controlling the cooling rate until the temperature of the middle layer drops to room temperature to avoid sudden changes in internal stress; the pressing parameters include a pressing temperature of 180-200℃, a pressing pressure of 3-5MPa, and a pressing time of 60-90 minutes.

[0011] In some embodiments, the use of high-precision laser cutting equipment to cut the press-encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, includes: fixing the press-encapsulated flexible circuit board on the vacuum adsorption worktable of the laser cutting equipment; importing a cutting path file containing the boundaries of the bending area; setting laser cutting parameters and enabling real-time image monitoring; starting the laser cutting equipment and performing contour cutting on the flexible circuit board according to the cutting path file; during the cutting process, the image monitoring system identifies the cutting trajectory of the edge of the bending area in real time, and if it deviates from the preset path, the equipment is triggered to stop and adjust; after cutting, a brush-type dust removal device is used to clean the edge of the bending area to remove surface burrs, and an edge image is taken using an optical microscope to check the edge roughness and notch defects; the laser cutting parameters include a laser power of 50-100W, a cutting speed of 10-20mm / s, and a spot diameter of 0.02mm.

[0012] In some embodiments, the bending test, which involves bending a flexible circuit board cut into individual pieces, includes: fixing the flexible circuit board into individual pieces onto the fixture of a bending test device, adjusting the fixture spacing to match the bending radius of the flexible circuit board; setting bending parameters and enabling the stress-deformation monitoring function; starting the bending test device and driving the fixture to perform reciprocating bending motion according to preset parameters; during the bending process, the stress value of the bending area is collected in real time by a force sensor, and the deformation of the bending area is collected in real time by a displacement sensor; the bending radius matching includes a fixture spacing of 2mm when the bending radius is 1mm; the bending parameters include a bending angle of ±180°, a bending frequency of 10-20 times / minute, and a bending count of 10,000-50,000 times.

[0013] In some embodiments, verifying the improvement in bending effect and warping problem includes: after the bending test, scanning the surface of the bending area of ​​the flexible circuit board using a three-dimensional profilometer and measuring the warping height; performing an interlayer peel test on the bending area using a universal testing machine and recording the interlayer bond strength; comparing the warping height and interlayer bond strength with the corresponding parameters of a flexible circuit board that does not use this method, and if the warping height is reduced by more than 50% and the interlayer bond strength retention rate is more than 80%, then the bending effect and warping problem are confirmed to be improved; the warping height includes the vertical distance between the highest point and the reference plane.

[0014] In some embodiments, the method further includes a process for optimizing the determination of the adhesive-free region width using an intelligent algorithm, specifically including: collecting multiple sets of bending stress distribution data of flexible circuit boards, adhesive-free region width parameters, and corresponding bending effect data to establish a dataset; dividing the dataset into a training set and a test set, inputting them into a machine learning model, and training the machine learning model to learn the mapping relationship between the adhesive-free region width and the bending effect; using the trained machine learning model, predicting the optimal adhesive-free region width based on the current bending stress distribution data of the flexible circuit board; comparing the predicted optimal adhesive-free region width with the target width obtained through finite element analysis, and if the corresponding difference is within a preset range, then adopting the predicted optimal width; if the difference exceeds the preset range, then adjusting the input features of the machine learning model and retraining the machine learning model until the prediction result meets the requirements; wherein, the bending effect data includes the warping height and the interlayer delamination rate; adjusting the input features of the machine learning model includes increasing the bending frequency weight.

[0015] This application optimizes the width of the adhesive-free zone based on stress distribution analysis (e.g., increasing it from 1.75mm to 2.2mm), providing a larger buffer space for bending deformation and avoiding stress concentration at rigid points such as copper pillars, thus eliminating the driving force for delamination at its source. The dense axial grain structure of the rolled copper foil significantly improves its ductility (elongation ≥15%, far exceeding the ≤8% of electrolytic copper foil) and fatigue resistance, increasing the bending cycles from 10,000 to over 50,000, effectively reducing cracks and fractures. "Laser cutting after lamination" ensures high flatness at the edges of the bending area (burrs ≤10μm), preventing microcracks from becoming stress concentration points and further enhancing bending reliability. The combined effect of the above three factors reduces the delamination rate in the bending zone from 15% in existing technologies to below 1%, and the warping height from 0.5mm to below 0.1mm. Internal testing has verified that this completely solves the problem of customer complaints about warping.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of the steps in a method for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board according to an embodiment of this application; Figure 2 This is a schematic block diagram of a fabrication system for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board, provided in one embodiment of this application. Figure 3 This is a schematic block diagram of the structure of a computer device provided in an embodiment of this application.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0022] It should be understood that, in order to clearly describe the technical solutions of the embodiments of the present invention, the terms "first" and "second" are used in the embodiments of the present invention to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0023] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0025] Flexible printed circuit boards (FPCs) are prone to interlayer delamination and warpage in their bending areas due to repeated deformation. The core causes include: 1. Stress concentration: Rigid structures such as copper pillars and weld joints form stress concentration points when bent, leading to interlayer bonding failure; 2. Insufficient fatigue resistance of materials: Traditional ED copper foil with and without adhesive has a vertical columnar grain structure, poor ductility and resistance to repeated bending, and is prone to cracking; 3. Process defects: Existing processes often adopt the process of "cutting the shape first and then pressing it together". The cut edges are prone to burrs or micro-cracks, which become the starting point of stress concentration and aggravate delamination and warping.

[0026] Existing technologies have proposed some solutions to the above problems, such as: For example, structural optimization can be achieved by "widening the bending area and the glue-free area", but this does not involve replacing the copper foil material. Therefore, the problem of insufficient fatigue resistance of the material itself cannot be solved, and there is still a risk of crack propagation after bending. For example, "using rolled copper foil (RA Copper Foil) to improve bending performance" is not combined with stress buffering design in the glue-free area, which cannot effectively alleviate stress concentration at rigid points, and the delamination problem is not fundamentally solved; Even if a "laser cutting process" is used, but the order of "cutting after pressing" is not clearly defined, the problem of edge burrs caused by cutting before pressing cannot be avoided.

[0027] In summary, existing technologies have not addressed the delamination and warping issues during bending from the three dimensions of "structural design, material properties, and process control." Individual measures have limited improvement effects and cannot meet the requirements of high-reliability FPCs.

[0028] To solve the above problem, please refer to Figure 1 This application provides a method for improving the delamination and warping of interlayers in the bending area of ​​a flexible circuit board, applicable to computer equipment. The computer equipment can be deployed on a single server or server cluster. It can also be deployed on handheld terminals, laptops, wearable devices, or robots, etc. It should be noted that all information involved in the method provided in this application is extracted with the authorization of the relevant users and in accordance with relevant regulations, and will not infringe on user privacy.

[0029] The provided method for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board includes steps S101 to S103. Details are as follows: Step S101. Based on the analysis of bending stress distribution, determine the width of the adhesive-free area in the bending region of the flexible circuit board to provide greater stress buffer and deformation space, and avoid stress concentration at rigid points; replace the adhesive-free electrolytic copper foil used in the substrate of the bending region with adhesive-free rolled copper foil, and utilize the dense internal and axially arranged grain structure formed by the rolling process of the rolled copper foil.

[0030] Specifically, stress concentration and material fatigue problems are alleviated through structural design (width of the glue-free area) and material replacement (rolled copper foil).

[0031] Stress distribution analysis is based on stress simulation of the bending zone (such as finite element analysis FEA) to determine the stress concentration area around the rigid structure (copper column, solder joint) and quantify the stress buffer space that the glue-free area needs to provide.

[0032] The glue-free zone width design creates a flexible deformation buffer by widening the glue-free zone (usually 10%-30% wider than the traditional design), thus preventing stress from being directly transmitted to the interlayer interface at rigid points.

[0033] The material replacement involves replacing the traditional electrolytic copper foil with and without adhesive (ED copper foil, with a vertical columnar grain structure and poor ductility) with rolled copper foil with and without adhesive (RA copper foil, with grains rolled into an axially dense arrangement, improving bending resistance by 30%-50%).

[0034] The stress analysis method uses simulation software to build a three-dimensional model of the FPC bending area, simulating the stress distribution under different bending radii (e.g., R1mm-R5mm), and marking high-stress areas (e.g., within 50-100μm of the weld edge). The simulation model is calibrated by combining experimental data (e.g., measured strain gauge data) to determine the optimal width of the glue-free area (e.g., a typical value of 1.5-3.0mm, which needs to be adjusted according to product specifications).

[0035] Material selection and verification involved choosing RA copper foil with matching thickness (e.g., 18μm or 35μm), requiring grain orientation along the bending axis (rolling direction) and elongation ≥20% (ED copper foil is typically ≤15%). Bending fatigue test data of ED and RA copper foils were compared (e.g., IPC-TM-650 standard, bending angle 180°, frequency 1Hz, recording the number of crack initiation) to verify the effectiveness of the material replacement.

[0036] Step S102. Fabricate a flexible circuit board. Create a glue-free area in the bending area of ​​the flexible circuit board according to the determined width of the glue-free area. Perform lamination and encapsulation. Laminate the flexible circuit board with the glue-free area fabricated as a whole to fully bond the materials and stabilize the internal stress.

[0037] Specifically, a glue-free buffer structure is precisely constructed in the bending area, and the internal stress is stabilized through a pressing process to avoid interlayer bonding failure.

[0038] The adhesive-free area is created by pre-reserving an adhesive-free zone in the bending area on a substrate (such as PI or PET) using a masking or selective coating process. This zone contains only the substrate and copper foil, without any adhesive (or uses a low-modulus adhesive). A hot-pressing process is then used to fully bond the materials (copper foil, substrate, cover film) together, while simultaneously releasing internal stress through pressure to prevent delamination caused by residual stress after pressing.

[0039] The process for creating the adhesive-free area includes: Masking: Before applying the adhesive, a heat-resistant mask (such as a PTFE film) is placed over the bending area of ​​the substrate. After applying the adhesive, the mask is removed to form the adhesive-free area. Laser grooving: An ultraviolet laser is used to remove the adhesive from the bending area of ​​the substrate with a precision controlled within ±50μm to avoid damaging the substrate. Pressing process parameters: Temperature: 150-180℃ (adjusted according to the type of adhesive; for example, epoxy resin adhesives require high-temperature curing). Pressure: 1-3MPa, using a stepped pressurization method (e.g., pre-pressing at 0.5MPa for 5 minutes, then increasing to full pressure and holding for 30 minutes) to ensure air expulsion and uniform adhesive flow. Cooling rate: After pressing, cool to room temperature at a rate of ≤5℃ / min to avoid thermal stress concentration caused by sudden cooling.

[0040] Step S103. Using high-precision laser cutting equipment, the laminated and encapsulated flexible circuit board is cut into individual pieces to ensure that the edges of the bending area are neat and burr-free, and to avoid minor defects becoming stress concentration points; a bending test is performed to bend the individual flexible circuit boards to verify the bending effect and the improvement of the warping problem.

[0041] Specifically, edge burrs are avoided through a pressing and cutting process, and the overall improvement effect is verified through bending tests.

[0042] High-precision laser cutting employs a "pressing and then cutting" sequence, utilizing the high energy density of the laser to achieve non-contact cutting, ensuring that the edges of the bending area are free of burrs and microcracks.

[0043] The bending test simulates real-world usage scenarios by repeatedly bending the cut FPC to detect interlayer delamination (e.g., under a microscope) and warping (e.g., by height measurement).

[0044] Laser cutting parameters: Equipment selection: CO2 laser (suitable for PI substrates) or fiber laser (suitable for metal foil cutting), power 5-20W, spot diameter ≤50μm. Process parameters: cutting speed 50-200mm / s, repeatability ±10μm, nitrogen purging to suppress cutting thermal damage, ensuring edge roughness Ra≤2.5μm.

[0045] Bending Test Standards: Test Conditions: Bending radius R = 2mm (or according to product specifications), bending angle 180°, number of cycles ≥ 100,000, frequency 1-5Hz. Inspection Methods: Visual Inspection: After bending, observe the copper foil surface in the bending area using a 20-50x microscope for cracks (no visible cracks or crack length < 0.1mm required). Interlayer Bond Strength Test: Use the cross-cut test or peel strength test, requiring an interlayer peel strength ≥ 1.5N / mm (traditional processes typically require 1.0N / mm).

[0046] The warping amount is measured using a non-contact optical measuring instrument. After bending, the maximum warping height of the bending area is measured, and it is required to be ≤0.1mm (the traditional process is usually 0.2-0.3mm).

[0047] In some embodiments, determining the width of the adhesive-free region of the flexible circuit board's bending area based on the analysis of bending stress distribution includes: collecting material parameters and bending condition parameters of the flexible circuit board's bending area; inputting the material parameters and bending condition parameters into a finite element analysis model to simulate stress distribution cloud maps of the bending area under different adhesive-free region widths; calculating the stress concentration factor corresponding to the adhesive-free region width based on the stress distribution cloud map, and selecting the minimum adhesive-free region width with a stress concentration factor lower than a preset threshold as the target width; wherein, the material parameters include the substrate's elastic modulus, copper foil thickness, and adhesive layer bonding strength; the bending condition parameters include bending radius, bending frequency, and load force.

[0048] By quantifying the bending stress distribution through finite element analysis models, the width of the glue-free area can be scientifically determined, avoiding insufficient stress buffering or over-design caused by empirical design.

[0049] Data acquisition involves collecting material parameters such as substrate elastic modulus, copper foil thickness, and adhesive bonding strength, as well as operating condition parameters such as bending radius (e.g., 1 mm), bending frequency (e.g., 20 times / minute), and load force.

[0050] The model construction involves inputting parameters into finite element analysis software such as ANSYS or COMSOL to establish a three-dimensional model of the bending area of ​​the flexible circuit board and simulate the stress distribution cloud map under different glue-free area widths (such as 1.75mm, 2.0mm, and 2.2mm).

[0051] The stress concentration factor (such as the ratio of maximum principal stress to average stress) of rigid points such as copper pillars is extracted based on the cloud map. A threshold (such as ≤1.5) is set, and the minimum width that meets the threshold (such as 2.2mm) is selected as the target width to balance stress buffering and structural compactness.

[0052] In some embodiments, replacing the adhesive-free electrolytic copper foil used in the substrate of the bending area with adhesive-free rolled copper foil includes: identifying the boundary of the bending area in the flexible circuit board design drawing using image recognition technology, and marking the projection range of the bending area on the substrate; traversing the substrate design layer and marking all positions in the bending area where adhesive-free electrolytic copper foil is used; replacing the adhesive-free electrolytic copper foil at the marked positions with adhesive-free rolled copper foil of the same thickness, and retrieving the rolling process parameters of the rolled copper foil through a material traceability system to verify that it meets the preset requirements for the preparation of dense grain structure; the rolling process parameters include the number of rolling passes, rolling pressure, and annealing temperature.

[0053] By using image recognition technology to locate the bending area, electrolytic copper foil is accurately replaced with rolled copper foil, and material traceability is used to ensure the compliance of the rolled copper foil process.

[0054] Region marking uses AI vision algorithms (such as the Halcon library) to scan PCB design drawings (Gerber files), identify the boundaries of bent areas (such as by marking with line color or layer attributes), and generate region masks.

[0055] Layer traversal involves traversing the substrate design layers (such as the Core layer and Prepreg layer) and marking all locations where adhesive-free electrolytic copper foil is used (e.g., by filtering by the material property field).

[0056] Material replacement involves replacing the electrolytic copper foil (ED) at the marked location with rolled copper foil (RA) of the same thickness (e.g., 18μm). The rolling process parameters (e.g., rolling times ≥ 3 times, rolling pressure 500-800MPa, annealing temperature 200-300℃) provided by the supplier are retrieved through the blockchain traceability system to verify the compactness of the grain structure.

[0057] In some embodiments, utilizing the internally dense and axially aligned grain structure formed by the rolling process of rolled copper foil includes: scanning the bending region of the rolled copper foil with an electron backscatter diffraction device to obtain a grain structure image; inputting the grain structure image into a grain structure analysis module to identify the shape, size, and arrangement direction of the grains; determining whether the grain arrangement direction is consistent with the bending direction of the flexible circuit board and whether the grain size variation coefficient is lower than a preset value; if so, confirming that the grain structure of the rolled copper foil meets the usage requirements; the grain size variation coefficient includes the ratio of the maximum grain size to the minimum grain size.

[0058] Electron backscatter diffraction (EBSD) technology is used to detect the grain alignment and uniformity of rolled copper foil to ensure that it matches the bending direction and improve fatigue resistance.

[0059] Microscopic scanning uses an EBSD device to scan the bending area of ​​the rolled copper foil, achieving a resolution below 1 μm, and generating an intergranular orientation distribution map (IPF map). Structural analysis uses a self-developed software module to analyze grain shape (e.g., axial elongation ratio ≥ 3:1), average size (e.g., ≤ 10 μm), and alignment direction (angle with bending direction ≤ 15°), calculating the grain size variation coefficient (maximum size / minimum size ≤ 1.5).

[0060] If the grain arrangement direction is consistent with the bending direction and the coefficient of variation is lower than the threshold, the copper foil is deemed to meet the requirements; otherwise, it is returned to the supplier for rework.

[0061] In some embodiments, the step of creating a glue-free area in the bending region of the flexible circuit board according to a determined glue-free area width includes: marking the outline of the glue-free area on the substrate of the flexible circuit board along the boundary of the bending region using a laser etching process according to the determined glue-free area width; performing surface treatment on the marked glue-free area using a plasma treatment device to remove the adhesive layer material in the area, with the treatment time set to 30-60 seconds depending on the adhesive layer thickness; capturing a surface image of the glue-free area using an optical detection system, measuring the corresponding width error and the area of ​​residual adhesive layer on the surface, ensuring that the width error is within ±0.01 mm and the residual adhesive layer area accounts for less than 0.1%; the width error includes the difference from the target width.

[0062] The adhesive-free area is precisely formed by laser etching and plasma treatment, and optical inspection is used to ensure dimensional accuracy and surface cleanliness.

[0063] The contour marking is performed using an ultraviolet laser etching machine (wavelength 355nm) to mark the contour of the adhesive-free area along the boundary of the bending area, with an accuracy of ±0.005mm.

[0064] Adhesive layer removal utilizes oxygen plasma treatment equipment (power 100-150W, pressure 50-100Pa) to etch the marked area. The treatment time is set to 30-60 seconds based on the adhesive layer thickness (e.g., 50μm) to completely remove the adhesive material. Optical inspection involves capturing images of the adhesive-free area using AOI (Automated Optical Inspection) equipment. Image processing algorithms are used to measure width error (allowable error ±0.01mm when the target width is 2.2mm) and residual adhesive layer area (percentage <0.1%). Defective products must be reworked or scrapped.

[0065] In some embodiments, the pressing and encapsulation process involves pressing the flexible circuit board with the glue-free area fabricated as a whole to ensure sufficient material bonding and stabilize internal stress. This includes: placing the flexible circuit board with the glue-free area fabricated between the middle layers of the pressing equipment and setting the pressing parameters; starting the pressing equipment and sequentially executing the heating, pressurizing, and heat and pressure holding processes according to preset parameters to ensure sufficient bonding of the materials in each layer of the flexible circuit board through thermosetting; after pressing, monitoring the cooling rate of the middle layer in real time using a temperature sensor and controlling the cooling rate until the temperature of the middle layer drops to room temperature to avoid sudden changes in internal stress; the pressing parameters include a pressing temperature of 180-200℃, a pressing pressure of 3-5MPa, and a pressing time of 60-90 minutes.

[0066] By controlling the segmented pressing parameters and gradient cooling, the material layers are fully bonded together, avoiding internal stress concentration.

[0067] Preparation for lamination involves placing the flexible circuit board between the layers of the multilayer laminator, laying a release film to prevent adhesion, and setting the lamination parameters: temperature 180-200℃ (e.g., 190℃), pressure 3-5MPa (e.g., 4MPa), and time 60-90 minutes (e.g., 75 minutes).

[0068] Pressing process: Heating stage: Increase to the set temperature at a rate of 5℃ / min and hold for 10 minutes; Pressurization stage: Gradually increase the pressure to 5MPa and hold for 60 minutes to allow the adhesive layer to fully cure; Cooling stage: Turn off the heating source and cool to room temperature at a rate of ≤3℃ / min. Monitor the temperature of the middle layer board in real time through thermocouples to avoid stress cracking caused by rapid cooling.

[0069] In some embodiments, the use of high-precision laser cutting equipment to cut the press-encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, includes: fixing the press-encapsulated flexible circuit board on the vacuum adsorption worktable of the laser cutting equipment; importing a cutting path file containing the boundaries of the bending area; setting laser cutting parameters and enabling real-time image monitoring; starting the laser cutting equipment and performing contour cutting on the flexible circuit board according to the cutting path file; during the cutting process, the image monitoring system identifies the cutting trajectory of the edge of the bending area in real time, and if it deviates from the preset path, the equipment is triggered to stop and adjust; after cutting, a brush-type dust removal device is used to clean the edge of the bending area to remove surface burrs, and an edge image is taken using an optical microscope to check the edge roughness and notch defects; the laser cutting parameters include a laser power of 50-100W, a cutting speed of 10-20mm / s, and a spot diameter of 0.02mm.

[0070] By using vacuum adsorption fixation and real-time image monitoring, high-precision contour processing of laser cutting after pressing is achieved, eliminating edge burrs.

[0071] The workpiece is fixed in place on the laser cutting machine table equipped with a vacuum chuck using a pressing plate, and the coordinates are aligned using positioning pins. Cutting parameters: Set the fiber laser power to 50-100W (e.g., 80W), speed to 10-20mm / s (e.g., 15mm / s), and spot diameter to 0.02mm, and import the DXF cutting path containing the boundary of the bending area.

[0072] The process monitoring uses a CCD camera to capture the cutting trajectory in real time. If the deviation is ≥0.01mm, the servo motor is triggered to make dynamic adjustments. After cutting, the edges are cleaned with a brush (0.1mm diameter nylon bristles) and the roughness (Ra≤1.6μm) and gaps (≤50μm) are checked with a 500x optical microscope.

[0073] In some embodiments, the bending test, which involves bending a flexible circuit board cut into individual pieces, includes: fixing the flexible circuit board into individual pieces onto the fixture of a bending test device, adjusting the fixture spacing to match the bending radius of the flexible circuit board; setting bending parameters and enabling the stress-deformation monitoring function; starting the bending test device and driving the fixture to perform reciprocating bending motion according to preset parameters; during the bending process, the stress value of the bending area is collected in real time by a force sensor, and the deformation of the bending area is collected in real time by a displacement sensor; the bending radius matching includes a fixture spacing of 2mm when the bending radius is 1mm; the bending parameters include a bending angle of ±180°, a bending frequency of 10-20 times / minute, and a bending count of 10,000-50,000 times.

[0074] By integrating a standardized bending test device with multiple sensors, the stress-deformation relationship during the bending process is quantified, and the reliability of the material is verified.

[0075] Adjust the clamps according to the bending radius (e.g., 1mm). Set the clamp spacing to 2mm (twice the radius). Use spring clips to fix both ends of the FPC to ensure uniform clamping force (e.g., 5N·m).

[0076] Test parameters: Bending angle: ±180° (i.e., folding back and forth until flat); Frequency: 10-20 times / minute (e.g., 15 times / minute); Number of cycles: 10,000-50,000 times (e.g., 30,000 times).

[0077] Data acquisition involves real-time acquisition of stress values ​​in the bending zone using strain gauges (accuracy ±1%), monitoring of deformation using laser displacement sensors (accuracy ±0.01mm), and synchronizing the data to an industrial control computer to generate stress-cycle curves.

[0078] In some embodiments, verifying the improvement in bending effect and warping problem includes: after the bending test, scanning the surface of the bending area of ​​the flexible circuit board using a three-dimensional profilometer and measuring the warping height; performing an interlayer peel test on the bending area using a universal testing machine and recording the interlayer bond strength; comparing the warping height and interlayer bond strength with the corresponding parameters of a flexible circuit board that does not use this method, and if the warping height is reduced by more than 50% and the interlayer bond strength retention rate is more than 80%, then the bending effect and warping problem are confirmed to be improved; the warping height includes the vertical distance between the highest point and the reference plane.

[0079] By using three-dimensional contour scanning and interlayer peeling tests, the lifting height and bonding strength are quantitatively evaluated, and an objective evaluation standard for the improvement effect is established.

[0080] The warping measurement uses a 3D profilometer to scan the bending area, with the unbent area as the reference plane, and measures the vertical distance of the highest point (accuracy ±0.001mm). The improved warping height is required to be ≤0.1mm (a reduction of ≥50% compared to the traditional process).

[0081] Using a universal testing machine, peel the interlayer structure in the bending zone at a rate of 50 mm / min and record the initial peel force (in N / mm). The bond strength retention rate after testing should be ≥80% (compared to the unbent sample). If the warping height reduction is >50% and the bond strength retention rate is >80%, the solution is considered effective; otherwise, process backtracking analysis is initiated.

[0082] In some embodiments, the method further includes a process for optimizing the determination of the adhesive-free region width using an intelligent algorithm, specifically including: collecting multiple sets of bending stress distribution data of flexible circuit boards, adhesive-free region width parameters, and corresponding bending effect data to establish a dataset; dividing the dataset into a training set and a test set, inputting them into a machine learning model, and training the machine learning model to learn the mapping relationship between the adhesive-free region width and the bending effect; using the trained machine learning model, predicting the optimal adhesive-free region width based on the current bending stress distribution data of the flexible circuit board; comparing the predicted optimal adhesive-free region width with the target width obtained through finite element analysis, and if the corresponding difference is within a preset range, then adopting the predicted optimal width; if the difference exceeds the preset range, then adjusting the input features of the machine learning model and retraining the machine learning model until the prediction result meets the requirements; wherein, the bending effect data includes the warping height and the interlayer delamination rate; adjusting the input features of the machine learning model includes increasing the bending frequency weight.

[0083] By training a machine learning model with historical data, a non-linear mapping relationship between the width of the glue-free area and the bending effect is established, enabling intelligent optimization of design parameters.

[0084] The dataset was constructed by collecting historical data, including stress distribution cloud map features (such as the location of maximum stress and stress gradient), width of the glue-free area (1.5-2.5 mm), lifting height (0.1-0.5 mm), and delamination rate (0.5%-15%).

[0085] Model training includes: Feature engineering: extracting 10-dimensional features such as stress concentration factor and material toughness index; Algorithm selection: using XGBoost or neural network model, with minimizing the warping height as the objective function, and optimizing hyperparameters through 5-fold cross-validation.

[0086] For a newly designed FPC, first obtain the initial width (e.g., 2.2 mm) through finite element analysis, then use the trained model to predict the optimal width (e.g., 2.15 mm). If the difference is ≤5% (e.g., 0.05 mm), the predicted value is adopted; otherwise, increase the feature weights such as bending frequency and retrain the model until convergence.

[0087] Please see Figure 2 As shown, Figure 2 This is a schematic diagram of the structure of a fabrication system 200 for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board, provided in an embodiment of this application. This fabrication system 200 is used to perform the steps of the fabrication methods for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board as described in the above embodiments. The fabrication system 200 can be a single server or a server cluster, or it can be a terminal, such as a handheld terminal, a laptop computer, a wearable device, or a robot.

[0088] like Figure 2 As shown, the fabrication system 200 for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board includes: The stress analysis unit 201 is used to determine the width of the adhesive-free area in the bending region of the flexible circuit board based on the analysis of the bending stress distribution, so as to provide greater stress buffer and deformation space and avoid stress concentration at rigid points; the adhesive-free electrolytic copper foil used in the substrate of the bending region is replaced with adhesive-free rolled copper foil, which utilizes the dense internal and axially arranged grain structure formed by the rolling process of the rolled copper foil. The circuit fabrication unit 202 is used to fabricate a flexible circuit board. It creates a glue-free area in the bending area of ​​the flexible circuit board according to the determined width of the glue-free area. It performs pressing and encapsulation, pressing the flexible circuit board with the glue-free area fabricated as a whole to fully bond the materials and stabilize the internal stress. The warping verification unit 203 is used to cut the laminated and encapsulated flexible circuit board into individual pieces using high-precision laser cutting equipment, ensuring that the edges of the bending area are neat and burr-free, and avoiding minor defects from becoming stress concentration points; and to perform bending tests, bending the cut flexible circuit board into individual pieces to verify the bending effect and the improvement of the warping problem.

[0089] In some embodiments, determining the width of the adhesive-free region of the flexible circuit board's bending area based on the analysis of bending stress distribution includes: collecting material parameters and bending condition parameters of the flexible circuit board's bending area; inputting the material parameters and bending condition parameters into a finite element analysis model to simulate stress distribution cloud maps of the bending area under different adhesive-free region widths; calculating the stress concentration factor corresponding to the adhesive-free region width based on the stress distribution cloud map, and selecting the minimum adhesive-free region width with a stress concentration factor lower than a preset threshold as the target width; wherein, the material parameters include the substrate's elastic modulus, copper foil thickness, and adhesive layer bonding strength; the bending condition parameters include bending radius, bending frequency, and load force.

[0090] In some embodiments, replacing the adhesive-free electrolytic copper foil used in the substrate of the bending area with adhesive-free rolled copper foil includes: identifying the boundary of the bending area in the flexible circuit board design drawing using image recognition technology, and marking the projection range of the bending area on the substrate; traversing the substrate design layer and marking all positions in the bending area where adhesive-free electrolytic copper foil is used; replacing the adhesive-free electrolytic copper foil at the marked positions with adhesive-free rolled copper foil of the same thickness, and retrieving the rolling process parameters of the rolled copper foil through a material traceability system to verify that it meets the preset requirements for the preparation of dense grain structure; the rolling process parameters include the number of rolling passes, rolling pressure, and annealing temperature.

[0091] In some embodiments, utilizing the internally dense and axially aligned grain structure formed by the rolling process of rolled copper foil includes: scanning the bending region of the rolled copper foil with an electron backscatter diffraction device to obtain a grain structure image; inputting the grain structure image into a grain structure analysis module to identify the shape, size, and arrangement direction of the grains; determining whether the grain arrangement direction is consistent with the bending direction of the flexible circuit board and whether the grain size variation coefficient is lower than a preset value; if so, confirming that the grain structure of the rolled copper foil meets the usage requirements; the grain size variation coefficient includes the ratio of the maximum grain size to the minimum grain size.

[0092] In some embodiments, the step of creating a glue-free area in the bending region of the flexible circuit board according to a determined glue-free area width includes: marking the outline of the glue-free area on the substrate of the flexible circuit board along the boundary of the bending region using a laser etching process according to the determined glue-free area width; performing surface treatment on the marked glue-free area using a plasma treatment device to remove the adhesive layer material in the area, with the treatment time set to 30-60 seconds depending on the adhesive layer thickness; capturing a surface image of the glue-free area using an optical detection system, measuring the corresponding width error and the area of ​​residual adhesive layer on the surface, ensuring that the width error is within ±0.01 mm and the residual adhesive layer area accounts for less than 0.1%; the width error includes the difference from the target width.

[0093] In some embodiments, the pressing and encapsulation process involves pressing the flexible circuit board with the glue-free area fabricated as a whole to ensure sufficient material bonding and stabilize internal stress. This includes: placing the flexible circuit board with the glue-free area fabricated between the middle layers of the pressing equipment and setting the pressing parameters; starting the pressing equipment and sequentially executing the heating, pressurizing, and heat and pressure holding processes according to preset parameters to ensure sufficient bonding of the materials in each layer of the flexible circuit board through thermosetting; after pressing, monitoring the cooling rate of the middle layer in real time using a temperature sensor and controlling the cooling rate until the temperature of the middle layer drops to room temperature to avoid sudden changes in internal stress; the pressing parameters include a pressing temperature of 180-200℃, a pressing pressure of 3-5MPa, and a pressing time of 60-90 minutes.

[0094] In some embodiments, the use of high-precision laser cutting equipment to cut the press-encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, includes: fixing the press-encapsulated flexible circuit board on the vacuum adsorption worktable of the laser cutting equipment; importing a cutting path file containing the boundaries of the bending area; setting laser cutting parameters and enabling real-time image monitoring; starting the laser cutting equipment and performing contour cutting on the flexible circuit board according to the cutting path file; during the cutting process, the image monitoring system identifies the cutting trajectory of the edge of the bending area in real time, and if it deviates from the preset path, the equipment is triggered to stop and adjust; after cutting, a brush-type dust removal device is used to clean the edge of the bending area to remove surface burrs, and an edge image is taken using an optical microscope to check the edge roughness and notch defects; the laser cutting parameters include a laser power of 50-100W, a cutting speed of 10-20mm / s, and a spot diameter of 0.02mm.

[0095] In some embodiments, the bending test, which involves bending a flexible circuit board cut into individual pieces, includes: fixing the flexible circuit board into individual pieces onto the fixture of a bending test device, adjusting the fixture spacing to match the bending radius of the flexible circuit board; setting bending parameters and enabling the stress-deformation monitoring function; starting the bending test device and driving the fixture to perform reciprocating bending motion according to preset parameters; during the bending process, the stress value of the bending area is collected in real time by a force sensor, and the deformation of the bending area is collected in real time by a displacement sensor; the bending radius matching includes a fixture spacing of 2mm when the bending radius is 1mm; the bending parameters include a bending angle of ±180°, a bending frequency of 10-20 times / minute, and a bending count of 10,000-50,000 times.

[0096] In some embodiments, verifying the improvement in bending effect and warping problem includes: after the bending test, scanning the surface of the bending area of ​​the flexible circuit board using a three-dimensional profilometer and measuring the warping height; performing an interlayer peel test on the bending area using a universal testing machine and recording the interlayer bond strength; comparing the warping height and interlayer bond strength with the corresponding parameters of a flexible circuit board that does not use this method, and if the warping height is reduced by more than 50% and the interlayer bond strength retention rate is more than 80%, then the bending effect and warping problem are confirmed to be improved; the warping height includes the vertical distance between the highest point and the reference plane.

[0097] In some embodiments, the method further includes a process for optimizing the determination of the adhesive-free region width using an intelligent algorithm, specifically including: collecting multiple sets of bending stress distribution data of flexible circuit boards, adhesive-free region width parameters, and corresponding bending effect data to establish a dataset; dividing the dataset into a training set and a test set, inputting them into a machine learning model, and training the machine learning model to learn the mapping relationship between the adhesive-free region width and the bending effect; using the trained machine learning model, predicting the optimal adhesive-free region width based on the current bending stress distribution data of the flexible circuit board; comparing the predicted optimal adhesive-free region width with the target width obtained through finite element analysis, and if the corresponding difference is within a preset range, then adopting the predicted optimal width; if the difference exceeds the preset range, then adjusting the input features of the machine learning model and retraining the machine learning model until the prediction result meets the requirements; wherein, the bending effect data includes the warping height and the interlayer delamination rate; adjusting the input features of the machine learning model includes increasing the bending frequency weight.

[0098] It should be noted that those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the preparation system and each module for improving the interlayer delamination and warping of the bending area of ​​the flexible circuit board described above can be referred to the corresponding content in the various embodiments of the preparation method for improving the interlayer delamination and warping of the bending area of ​​the flexible circuit board, and will not be repeated here.

[0099] The aforementioned method for improving the interlayer delamination and warping in the bending area of ​​flexible circuit boards can be implemented as a computer program, which can be used in, for example... Figure 2 It runs on the device shown.

[0100] Please see Figure 3 , Figure 3 This is a schematic block diagram of the structure of a computer device provided in an embodiment of this application. The computer device includes a processor, a memory, and a network interface connected via a device bus, wherein the memory may include a storage medium and internal memory.

[0101] The storage medium may store operating devices and computer programs. The computer program includes program instructions that, when executed, cause the processor to perform any fabrication method that improves interlayer delamination and warping in the bending area of ​​the flexible circuit board.

[0102] The processor provides computing and control capabilities, supporting the operation of the entire computer device.

[0103] The internal memory provides an environment for the execution of computer programs in non-volatile storage media. When the computer program is executed by the processor, it enables the processor to execute any fabrication method that improves the interlayer delamination and warping in the bending area of ​​the flexible circuit board.

[0104] This network interface is used for network communication, such as sending assigned tasks. Those skilled in the art will understand that... Figure 3 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the terminal to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0105] It should be understood that the processor can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. Among these, a general-purpose processor can be a microprocessor or any conventional processor.

[0106] In one embodiment, the processor is configured to run a computer program stored in memory to perform the following steps: Based on the analysis of bending stress distribution, the width of the glue-free area in the bending region of the flexible circuit board is determined to provide greater stress buffer and deformation space, and to avoid stress concentration at rigid points. The electrolytic copper foil with or without glue used in the substrate of the bending region is replaced with rolled copper foil with or without glue, taking advantage of the dense internal and axially arranged grain structure formed by the rolling process of the rolled copper foil. To fabricate a flexible circuit board, a glue-free area is created in the bending region of the flexible circuit board according to the determined width of the glue-free area. Then, the flexible circuit board with the glue-free area is laminated together to fully bond the materials and stabilize the internal stress. High-precision laser cutting equipment is used to cut the laminated and encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, and avoiding minor defects from becoming stress concentration points. Bending tests are conducted to bend the individual flexible circuit boards to verify the bending effect and the improvement of the warping problem.

[0107] In some embodiments, determining the width of the adhesive-free region of the flexible circuit board's bending area based on the analysis of bending stress distribution includes: collecting material parameters and bending condition parameters of the flexible circuit board's bending area; inputting the material parameters and bending condition parameters into a finite element analysis model to simulate stress distribution cloud maps of the bending area under different adhesive-free region widths; calculating the stress concentration factor corresponding to the adhesive-free region width based on the stress distribution cloud map, and selecting the minimum adhesive-free region width with a stress concentration factor lower than a preset threshold as the target width; wherein, the material parameters include the substrate's elastic modulus, copper foil thickness, and adhesive layer bonding strength; the bending condition parameters include bending radius, bending frequency, and load force.

[0108] In some embodiments, replacing the adhesive-free electrolytic copper foil used in the substrate of the bending area with adhesive-free rolled copper foil includes: identifying the boundary of the bending area in the flexible circuit board design drawing using image recognition technology, and marking the projection range of the bending area on the substrate; traversing the substrate design layer and marking all positions in the bending area where adhesive-free electrolytic copper foil is used; replacing the adhesive-free electrolytic copper foil at the marked positions with adhesive-free rolled copper foil of the same thickness, and retrieving the rolling process parameters of the rolled copper foil through a material traceability system to verify that it meets the preset requirements for the preparation of dense grain structure; the rolling process parameters include the number of rolling passes, rolling pressure, and annealing temperature.

[0109] In some embodiments, utilizing the internally dense and axially aligned grain structure formed by the rolling process of rolled copper foil includes: scanning the bending region of the rolled copper foil with an electron backscatter diffraction device to obtain a grain structure image; inputting the grain structure image into a grain structure analysis module to identify the shape, size, and arrangement direction of the grains; determining whether the grain arrangement direction is consistent with the bending direction of the flexible circuit board and whether the grain size variation coefficient is lower than a preset value; if so, confirming that the grain structure of the rolled copper foil meets the usage requirements; the grain size variation coefficient includes the ratio of the maximum grain size to the minimum grain size.

[0110] In some embodiments, the step of creating a glue-free area in the bending region of the flexible circuit board according to a determined glue-free area width includes: marking the outline of the glue-free area on the substrate of the flexible circuit board along the boundary of the bending region using a laser etching process according to the determined glue-free area width; performing surface treatment on the marked glue-free area using a plasma treatment device to remove the adhesive layer material in the area, with the treatment time set to 30-60 seconds depending on the adhesive layer thickness; capturing a surface image of the glue-free area using an optical detection system, measuring the corresponding width error and the area of ​​residual adhesive layer on the surface, ensuring that the width error is within ±0.01 mm and the residual adhesive layer area accounts for less than 0.1%; the width error includes the difference from the target width.

[0111] In some embodiments, the pressing and encapsulation process involves pressing the flexible circuit board with the glue-free area fabricated as a whole to ensure sufficient material bonding and stabilize internal stress. This includes: placing the flexible circuit board with the glue-free area fabricated between the middle layers of the pressing equipment and setting the pressing parameters; starting the pressing equipment and sequentially executing the heating, pressurizing, and heat and pressure holding processes according to preset parameters to ensure sufficient bonding of the materials in each layer of the flexible circuit board through thermosetting; after pressing, monitoring the cooling rate of the middle layer in real time using a temperature sensor and controlling the cooling rate until the temperature of the middle layer drops to room temperature to avoid sudden changes in internal stress; the pressing parameters include a pressing temperature of 180-200℃, a pressing pressure of 3-5MPa, and a pressing time of 60-90 minutes.

[0112] In some embodiments, the use of high-precision laser cutting equipment to cut the press-encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, includes: fixing the press-encapsulated flexible circuit board on the vacuum adsorption worktable of the laser cutting equipment; importing a cutting path file containing the boundaries of the bending area; setting laser cutting parameters and enabling real-time image monitoring; starting the laser cutting equipment and performing contour cutting on the flexible circuit board according to the cutting path file; during the cutting process, the image monitoring system identifies the cutting trajectory of the edge of the bending area in real time, and if it deviates from the preset path, the equipment is triggered to stop and adjust; after cutting, a brush-type dust removal device is used to clean the edge of the bending area to remove surface burrs, and an edge image is taken using an optical microscope to check the edge roughness and notch defects; the laser cutting parameters include a laser power of 50-100W, a cutting speed of 10-20mm / s, and a spot diameter of 0.02mm.

[0113] In some embodiments, the bending test, which involves bending a flexible circuit board cut into individual pieces, includes: fixing the flexible circuit board into individual pieces onto the fixture of a bending test device, adjusting the fixture spacing to match the bending radius of the flexible circuit board; setting bending parameters and enabling the stress-deformation monitoring function; starting the bending test device and driving the fixture to perform reciprocating bending motion according to preset parameters; during the bending process, the stress value of the bending area is collected in real time by a force sensor, and the deformation of the bending area is collected in real time by a displacement sensor; the bending radius matching includes a fixture spacing of 2mm when the bending radius is 1mm; the bending parameters include a bending angle of ±180°, a bending frequency of 10-20 times / minute, and a bending count of 10,000-50,000 times.

[0114] In some embodiments, verifying the improvement in bending effect and warping problem includes: after the bending test, scanning the surface of the bending area of ​​the flexible circuit board using a three-dimensional profilometer and measuring the warping height; performing an interlayer peel test on the bending area using a universal testing machine and recording the interlayer bond strength; comparing the warping height and interlayer bond strength with the corresponding parameters of a flexible circuit board that does not use this method, and if the warping height is reduced by more than 50% and the interlayer bond strength retention rate is more than 80%, then the bending effect and warping problem are confirmed to be improved; the warping height includes the vertical distance between the highest point and the reference plane.

[0115] In some embodiments, the method further includes a process for optimizing the determination of the adhesive-free region width using an intelligent algorithm, specifically including: collecting multiple sets of bending stress distribution data of flexible circuit boards, adhesive-free region width parameters, and corresponding bending effect data to establish a dataset; dividing the dataset into a training set and a test set, inputting them into a machine learning model, and training the machine learning model to learn the mapping relationship between the adhesive-free region width and the bending effect; using the trained machine learning model, predicting the optimal adhesive-free region width based on the current bending stress distribution data of the flexible circuit board; comparing the predicted optimal adhesive-free region width with the target width obtained through finite element analysis, and if the corresponding difference is within a preset range, then adopting the predicted optimal width; if the difference exceeds the preset range, then adjusting the input features of the machine learning model and retraining the machine learning model until the prediction result meets the requirements; wherein, the bending effect data includes the warping height and the interlayer delamination rate; adjusting the input features of the machine learning model includes increasing the bending frequency weight.

[0116] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, causes the processor to perform the steps of the preparation method for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board as provided in any embodiment of this application.

[0117] The computer-readable storage medium may be an internal storage unit of the computer device described in the foregoing embodiments, such as the hard disk or memory of the computer device. The computer-readable storage medium may also be an external storage device of the computer device, such as a plug-in hard disk, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the computer device.

[0118] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for improving interlayer delamination and warping in the bending area of ​​a flexible circuit board, characterized in that, include: Based on the analysis of bending stress distribution, the width of the glue-free area in the bending region of the flexible circuit board is determined to provide greater stress buffer and deformation space, and to avoid stress concentration at rigid points. The electrolytic copper foil with or without glue used in the substrate of the bending region is replaced with rolled copper foil with or without glue, taking advantage of the dense internal and axially arranged grain structure formed by the rolling process of the rolled copper foil. To fabricate a flexible circuit board, a glue-free area is created in the bending region of the flexible circuit board according to the determined width of the glue-free area. Then, the flexible circuit board with the glue-free area is laminated together to fully bond the materials and stabilize the internal stress. High-precision laser cutting equipment is used to cut the laminated and encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, and avoiding minor defects from becoming stress concentration points. Bending tests are conducted to bend the individual flexible circuit boards to verify the bending effect and the improvement of the warping problem.

2. The method according to claim 1, characterized in that, The determination of the width of the adhesive-free area in the bending region of the flexible circuit board based on the analysis of bending stress distribution includes: Collect material parameters and bending condition parameters of the flexible circuit board's bending area; Input the material parameters and bending condition parameters into the finite element analysis model to simulate the stress distribution cloud map of the bending area under different glue-free area widths; Based on the stress distribution cloud map, calculate the stress concentration factor corresponding to the width of the glue-free area, and select the minimum width of the glue-free area with a stress concentration factor lower than the preset threshold as the target width. The material parameters include the elastic modulus of the substrate, the thickness of the copper foil, and the adhesive strength of the adhesive layer; the bending condition parameters include the bending radius, the bending frequency, and the load force.

3. The method according to claim 1, characterized in that, The replacement of the adhesive-free electrolytic copper foil used in the substrate of the bending area with adhesive-free rolled copper foil includes: Image recognition technology is used to identify the boundaries of the bending areas in the design drawings of flexible circuit boards and to mark the projection range of the bending areas on the substrate. Traverse the substrate design layer and mark all locations within the bending area where adhesive-free electrolytic copper foil is used; The glue-free electrolytic copper foil at the marked position was replaced with glue-free rolled copper foil of the same thickness, and the rolling process parameters of the rolled copper foil were retrieved through the material traceability system to verify that it met the preset requirements for the preparation of dense grain structure. Rolling process parameters include the number of rolling passes, rolling pressure, and annealing temperature.

4. The method according to claim 1, characterized in that, The aforementioned dense, axially aligned grain structure formed by the rolling process of rolled copper foil includes: The grain structure image is obtained by scanning the bent area of ​​the rolled copper foil using an electron backscatter diffraction device. Input the grain structure image into the grain structure analysis module to identify the shape, size, and orientation of the grains; Determine whether the grain arrangement direction is consistent with the bending direction of the flexible circuit board, and whether the grain size variation coefficient is lower than the preset value. If so, confirm that the grain structure of the rolled copper foil meets the usage requirements. The grain size variation coefficient includes the ratio of the maximum grain size to the minimum grain size.

5. The method according to claim 1, characterized in that, The process of creating a glue-free area in the bending region of the flexible circuit board according to a determined glue-free area width includes: Based on the determined width of the adhesive-free area, the outline of the adhesive-free area is marked on the substrate of the flexible circuit board along the boundary of the bending area using a laser etching process. The marked adhesive-free areas are surface-treated using a plasma treatment device to remove the adhesive layer material from the area. The treatment time is set to 30-60 seconds depending on the thickness of the adhesive layer. The surface image of the adhesive-free area is captured by an optical inspection system, and the corresponding width error and residual adhesive area are measured to ensure that the width error is within ±0.01 mm and the residual adhesive area accounts for less than 0.1%. Width error includes the difference from the target width.

6. The method according to claim 1, characterized in that, The pressing and encapsulation process involves pressing the prepared adhesive-free areas of the flexible circuit board together to ensure thorough material bonding and stabilize internal stress. This includes: Place the flexible circuit board with the glue-free area prepared between the middle layers of the laminating equipment, set the laminating parameters, start the laminating equipment, and execute the heating, pressurizing and heat and pressure holding processes in sequence according to the preset parameters, so that the materials of each layer of the flexible circuit board are fully bonded through heat curing. After lamination, the cooling rate of the middle layer is monitored in real time by a temperature sensor, and the cooling rate is controlled until the temperature of the middle layer drops to room temperature to avoid sudden changes in internal stress. The pressing parameters include a pressing temperature of 180-200℃, a pressing pressure of 3-5MPa, and a pressing time of 60-90 minutes.

7. The method according to claim 1, characterized in that, The process employs high-precision laser cutting equipment to cut the laminated and encapsulated flexible circuit board into individual pieces, ensuring that the edges of the bending area are neat and burr-free, including: The press-encapsulated flexible circuit board is fixed on the vacuum adsorption worktable of the laser cutting equipment, and the cutting path file containing the boundary of the bending area is imported; the laser cutting parameters are set, and the real-time image monitoring function is enabled. Start the laser cutting equipment and perform contour cutting on the flexible circuit board according to the cutting path file. During the cutting process, the image monitoring system identifies the cutting trajectory of the edge of the bending area in real time. If it deviates from the preset path, the equipment will be stopped for adjustment. After cutting, use a brush-type dust removal device to clean the edges of the bending area, remove surface burrs, and take edge images using an optical microscope to check edge roughness and notch defects; Laser cutting parameters include laser power of 50-100W, cutting speed of 10-20mm / s, and spot diameter of 0.02mm.

8. The method according to claim 1, characterized in that, The bending test involves bending the flexible circuit board, which has been cut into individual pieces, including: The flexible circuit board cut into individual pieces is fixed on the fixture of the bending test equipment, and the spacing of the fixture is adjusted to match the bending radius of the flexible circuit board. Set the bending parameters and enable the stress-deformation monitoring function; Start the bending test equipment and drive the fixture to perform reciprocating bending motion according to preset parameters. During the bending process, the stress value of the bending area is collected in real time by the force sensor and the deformation of the bending area is collected in real time by the displacement sensor. Bending radius matching includes a clamp spacing of 2mm when the bending radius is 1mm; bending parameters include bending angle ±180°, bending frequency of 10-20 times / minute and bending count of 10,000-50,000 times.

9. The method according to claim 1, characterized in that, The verification of the bending effect and the improvement of the warping problem includes: After the bending test is completed, a 3D profilometer is used to scan the surface of the bending area of ​​the flexible circuit board and measure the warping height. The interlayer peel test was performed on the bending area using a universal testing machine, and the interlayer bond strength was recorded. Compare the warping height and interlayer bond strength with the corresponding parameters of flexible circuit boards that do not use this method. If the warping height is reduced by more than 50% and the interlayer bond strength retention rate is more than 80%, it is confirmed that the bending effect and warping problem have been improved. The lifting height includes the vertical distance between the highest point and the reference plane.

10. The method according to claim 1, characterized in that, The method also includes a process for optimizing the determination of the width of the glue-free area using intelligent algorithms, specifically including: Collect bending stress distribution data, glue-free area width parameters and corresponding bending effect data of multiple sets of flexible circuit boards, and establish a dataset; The dataset is divided into training and testing sets, which are then input into a machine learning model to train the model to learn the mapping relationship between the width of the glue-free area and the bending effect. Using a trained machine learning model, the optimal width of the glue-free area is predicted based on the current bending stress distribution data of the flexible circuit board. The predicted optimal width of the glue-free area is compared with the target width obtained through finite element analysis. If the difference is within the preset range, the predicted optimal width is adopted. If the difference exceeds the preset range, the input features of the machine learning model are adjusted and the machine learning model is retrained until the prediction result meets the requirements. The bending effect data includes the height of the bend and the interlayer separation rate; adjusting the input features of the machine learning model includes increasing the weight of the bending frequency.

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