Preparation method of crossed and overlapped rigid-flex printed circuit board

Abstract

The invention discloses a preparation method of a crossed and overlapped rigid-flexible combined board, which relates to the technical field of printed circuit boards and comprises the steps of S1, judging whether a crossed and overlapped structure exists in a flexible area according to a drawing, S2, manufacturing a flexible core board and only performing laser milling on a crossed position of the flexible area, S3, laminating the flexible core board and a part of rigid layers to manufacture an auxiliary board, and S4, manufacturing the flexible core board. S4, carrying out browning treatment on the auxiliary board pasted with the protective adhesive tape; S5, carrying out circuit manufacturing on the pressed main board; and S6, carrying out appearance milling and dispensing treatment on the board subjected to laser processing. According to the invention, by changing the lamination design, modifying the laser data of the flexible core board, and splitting the laser milling holes at the crossed and overlapped positions into a manufacturing mode of respectively carrying out laser on the crossed position and the overlapped position, the product yield, reliability and manufacturing efficiency of the crossed and overlapped rigid-flexible combined board are improved, the dependence on the experience of operators is reduced, and the production cost is reduced. And the cost of repeated trial and error and repair in the traditional process is avoided.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board technology, and in particular to a method for preparing a cross-overlapping rigid-flex board. Background Technology

[0002] Due to the rapid development of high technology, rigid-flexible composite plates have emerged. As time goes by, the market is no longer satisfied with rigid-flexible composite plates with ordinary structures, but is developing towards a variety of structures.

[0003] Traditional manufacturing processes involve separately fabricating two rigid-flex boards and then laminating them together to complete the product. The main process design is as follows: inner layer laser milling holes—lamination of the rigid layer—opening the cover—applying adhesive tape—browning—lamination of the main rigid area. In this design, the inner flexible core board must be formed first. However, the browning process before laminating the main rigid area is prone to chemical contamination, which can lead to coating film contamination. Therefore, the traditional manufacturing process, which involves a bifurcated and overlapping structure and is formed in one step, can no longer meet current requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a cross-overlapping rigid-flexural bonded plate to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a cross-overlapping rigid-flexible composite plate, comprising the following steps: S1: Based on the drawings, determine whether there are overlapping structures in the flexible area and decide to use a step-by-step laser forming process; S2: Fabricate flexible core board, only laser milling is performed at the intersection of the flexible area, and no laser processing is performed at the overlapping area; S3: The flexible core board is laminated with a part of the rigid board to make a sub-board. After the sub-board circuit is made and the cover is opened by laser, protective tape is applied at the intersection. S4: The sub-board with protective tape is browned and then laminated with the main rigid laminate. S5: Perform circuit fabrication, solder mask imaging and surface treatment on the laminated motherboard, and then perform laser milling on the overlapping positions of the flexible area; S6: Perform milling and glue application on the laser-processed panels, and finally inspect them.

[0006] Preferably, step S2 includes the following steps: S21: Cutting: Cutting the flexible copper-clad laminate substrate to obtain a flexible core board blank of specified dimensions; S22: Circuit fabrication. On a flexible core board blank, unwanted copper layers are removed through pattern transfer, exposure, development and etching processes to form inner layer circuit patterns. S23: Applying a cover film: A polyimide cover film is pressed onto the surface of the flexible core board with the completed circuit pattern using a hot-pressing process. S24: Laser milling, using laser equipment to precisely mill the flexible core board that has been covered with a film.

[0007] Preferably, step S24 includes the following steps: Laser processing data processing and path planning: Receive and parse the customer's original file containing the flexible area design, identify the independent layer data that defines the intersection and overlap positions, and generate two independent laser processing paths based on this data: one for performing contour cutting paths on the area within the intersection position layer, and the other for generating skip instructions on the area within the overlap position layer. Laser equipment parameter setting and calibration: Based on the material properties of the flexible cover film and the substrate, set the corresponding laser power, pulse frequency, cutting speed and focusing position process parameters on the laser processing equipment, and perform positioning calibration on the laser optical path and processing platform; Selective milling is performed, and the flexible core board with the cover film already pressed is fixed on the processing platform. The generated laser processing program is loaded and executed. The laser beam scans and irradiates according to the path planned for the intersection position, completely vaporizing and removing the cover film and the flexible substrate below it in the irradiation area, forming a clear and through window. At the same time, the program controls the laser beam to completely skip the overlapping area and not irradiate it, so that the cover film and the substrate in that area remain in their original physical seal. Online processing quality inspection measures the opening size and contour accuracy of the processed intersections during and after milling, and verifies the surface integrity of the overlapping areas to ensure compliance with preset standards. The processing results are recorded and linked with the data, binding and recording the actual parameters and test results of this laser processing with the unique identifier of the flexible core board.

[0008] Preferably, the laser processing data processing and path planning includes: The design data reception and parsing process involves receiving the original design files provided by the client, which contain layered information. The CAM software then parses these files, clearly identifying the specific layers representing the intersections of the flexible areas and the overlapping areas of the flexible areas, and naming these layers FLEX_CROSS and FLEX_OVERLAP respectively. Processing strategy allocation and path generation: For all closed graphic contours within the FLEX_CROSS layer, corresponding laser cutting paths are generated. The path parameters are preset according to the material and laser characteristics. For the FLEX_OVERLAP layer, no cutting paths are generated. Instead, a processing restricted area logical identifier associated with the graphic range of that layer is generated. Before outputting the final machining program, the simulation function of the CAM software and an independent verification program are used to simulate the generated path to ensure that no laser cutting path passes through the area defined by the FLEX_OVERLAP layer, and at the same time ensure that the cutting path of the FLEX_CROSS layer is completely within its defined contour. If the verification fails, an alarm is triggered and a prompt is made to check the original design data and layer definition rules.

[0009] Preferably, step S3 includes the following steps: S31: Sub-plate lamination: The flexible core board obtained in step S2 is aligned and laminated with the specified outer rigid substrate, and then pressed together by a hot press to form a sub-plate structure with partial rigidity. S32: Sub-board circuit fabrication. On the surface of the rigid layer of the laminated sub-board, an outer layer circuit pattern transfer process is performed, including film application, exposure, development, etching and film removal, to form the outer layer circuit required for the sub-board. S33: Laser opening. Using laser equipment, according to a pre-programmed procedure, the portion of the rigid layer of the sub-plate corresponding to the lower flexible cross position and the flexible area that needs to be exposed in the future is precisely milled to form a window, so that the lower flexible area is exposed. S34: Tape protection pretreatment: Before applying the tape, prepare polyimide tape that matches the shape and size of the openings at the intersections that need to be protected; S35: Precisely apply protective tape, align the pre-treated tape and apply it to the intersection area within the opened window.

[0010] Preferably, step S4 includes the following steps: S41: Sub-board browning treatment: The sub-board that has completed step S3 is sent to the browning production line for processing. S42: Pressing with the main rigid layer: After the sub-board has been browned, cleaned and dried, it is aligned and laminated with the remaining main rigid layer material, and then sent to a vacuum hot press to press it into a whole multi-layer rigid-flex board.

[0011] Preferably, step S5 includes the following steps: S51: On the surface of the laminated motherboard, the outer layer circuit pattern is formed by dry film lamination, exposure and development, and then formed by acid etching. S52: Solder resist ink is applied to the motherboard surface using a spraying process, and then ultraviolet exposure and sodium carbonate solution development are used to form a solder resist pattern. S53: Perform electroless nickel plating on the solder pad area that needs to be soldered and cover it with an immersion gold layer to complete the surface solderability treatment; S54: Use ultraviolet laser equipment to perform three-dimensional path milling on the overlapping positions of the flexible area to completely remove the cover film and flexible substrate, forming the final flexible structure.

[0012] Preferably, step S54 includes the following steps: Call the independent layer data in the design file to generate the laser cutting path, perform path optimization and anti-collision checks, and verify that the path does not overlap with the pre-processing area and is within the specified boundary. Identify the optical positioning target on the motherboard surface, calculate and compensate for deformation and displacement deviations based on the target coordinates, and map the theoretical cutting path to the physical coordinate system of the motherboard. Set the laser parameters, control the laser beam to perform layered scanning along the calibrated path, remove residue, determine the processing depth by the preset number of scans, until the cover film and flexible substrate are removed and the underlying copper foil is exposed; Photograph the processing area, measure the cutting contour dimensions and compare them with the design values, check the bottom residue and sidewall condition, and record the inspection results.

[0013] Preferably, the preset number of scans is a fixed number calculated based on the total thickness of the cover film and the flexible substrate, and the single scan removal depth calibrated through process experiments.

[0014] Preferably, during the layer scanning process, the plasma emission spectrum generated during laser processing is monitored simultaneously, and the processing is determined to be complete when a characteristic signal characterizing the lower copper foil material is detected.

[0015] The technical effects and advantages of this invention are as follows: This invention improves the yield, reliability, and manufacturing efficiency of cross-overlapping rigid-flex boards by modifying the laminated design and refining the laser milling of the flexible core board. This involves splitting the laser milling of the overlapping holes into separate laser processes for each intersection and overlap, thus enhancing the product yield, reliability, and manufacturing efficiency of the cross-overlapping rigid-flex boards. On one hand, step-by-step laser processing and localized protection eliminate defects such as delamination and blistering of the cover film caused by chemical contamination, ensuring the electrical integrity and long-term bending reliability of the flexible area. On the other hand, based on clear layer data and standardized processes, it reduces reliance on operator experience, avoids the costs of repeated trial and error and rework in traditional processes, and achieves high-quality, repeatable, large-scale production, meeting the market demand for highly reliable complex rigid-flex boards. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the preparation method of the cross-overlapping rigid-flex plate of the present invention; Figure 2 This is a schematic diagram of the stacking structure of the method for preparing the cross-overlapping rigid-flexible plate of the present invention; Figure 3 This is one of the schematic diagrams of the rigid-flexible plate stack of the present invention; Figure 4 This is the second schematic diagram of the rigid-flexible plate stack of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides, for example Figures 1-4 The method for preparing a cross-overlapping rigid-flexible composite plate, as shown, includes the following steps: S1: Based on the drawings, determine whether there are overlapping structures in the flexible area and decide to use a step-by-step laser forming process; S2: Fabricate flexible core board, only laser milling is performed at the intersection of the flexible area, and no laser processing is performed at the overlapping area; S3: The flexible core board is laminated with a part of the rigid board to make a sub-board. After the sub-board circuit is made and the cover is opened by laser, protective tape is applied at the intersection. S4: The sub-board with protective tape is browned and then laminated with the main rigid laminate. S5: Perform circuit fabrication, solder mask imaging and surface treatment on the laminated motherboard, and then perform laser milling on the overlapping positions of the flexible area; S6: Perform milling and glue application on the laser-processed panels, and finally inspect them.

[0019] like Figure 3 and Figure 4 As shown, the flexible regions of the two rigid-flex boards have an overlapping structure. First, during the flexible core board stage, only the overlapping areas are laser-cut while preserving their integrity. After the sub-boards are pressed together, the overlapping areas are locally protected with adhesive tape. After browning and main pressing are completed to ensure no contamination risk, the overlapping areas are finally laser-cut, resulting in the final product shown below. Figure 2 The complete cross-overlapping rigid-flexible plate shown is an example. This method not only fundamentally eliminates chemical contamination and significantly improves product reliability and yield, but also reduces trial-and-error costs and process dependence through standardized procedures.

[0020] Step S2 includes the following steps: S21: Cutting: Cutting the flexible copper-clad laminate substrate to obtain a flexible core board blank of specified dimensions; S22: Circuit fabrication. On a flexible core board blank, unwanted copper layers are removed through pattern transfer, exposure, development and etching processes to form inner layer circuit patterns. S23: Applying a cover film: A polyimide cover film is pressed onto the surface of the flexible core board with the completed circuit pattern using a hot-pressing process. S24: Laser milling, using laser equipment to precisely mill the flexible core board that has been covered with a film.

[0021] By sequentially executing material cutting, inner layer circuit fabrication, cover film lamination, and critical selective laser milling, windowing processing was achieved only at the cross-section stage of the flexible core board. At the same time, it ensured that the cover film at the overlapping position remained completely sealed to the substrate. This created a precise operating window for subsequent tape protection at the cross-section and established an endogenous barrier against browning agent contamination in the overlapping area. Thus, the overall strategy of step-by-step laser and time-delay processing was precisely initiated with repeatable standardized operations, ensuring the reliability and manufacturing feasibility of complex rigid-flex boards from the source.

[0022] Step S24 includes the following steps: Laser processing data processing and path planning receives and parses the customer's original file containing the flexible area design, identifies the independent layer data that defines the intersection and overlap positions, and generates two independent laser processing paths based on this data: one for performing contour cutting paths on the area within the intersection position layer, and the other for generating skip instructions on the area within the overlap position layer. This realizes the digitization and precise programming of processing intentions, ensuring from the source that the laser equipment can understand and differentiate between the two functional areas, avoiding human identification errors. It is the logical basis for selective processing and ensures the high accuracy and repeatability of the process. Laser equipment parameter setting and calibration involves setting the corresponding laser power, pulse frequency, cutting speed, and focusing position process parameters on the laser processing equipment based on the material characteristics of the flexible cover film and the substrate. The laser optical path and processing platform are then positioned and calibrated. Through targeted parameter setting, the cutting effect can be optimized, avoiding incomplete cutting due to insufficient energy or overburning and carbonization due to excessive energy. Precision calibration ensures the positional accuracy of the cutting contour and prevents processing errors caused by equipment deviation, which is the physical guarantee for achieving high-precision processing. Selective milling is performed, fixing the flexible core board with the cover film already pressed onto the processing platform. The generated laser processing program is loaded and executed. The laser beam scans and irradiates according to the path planned for the intersection position, completely vaporizing and removing the cover film and the flexible substrate below it in the irradiation area, forming a clear and continuous window. At the same time, the program controls the laser beam to completely skip the overlapping position area, without irradiating it, so that the cover film and the substrate in this area remain in their original physical seal. Through one clamping and program operation, the two opposite operation goals of precise processing of the intersection position and good preservation of the overlapping position are completed simultaneously. The production efficiency is high and secondary alignment errors are avoided. The good preservation of the overlapping position creates the necessary conditions for it to serve as a natural sealing layer in the subsequent browning process. Online quality inspection measures the opening dimensions and contour accuracy of the machined intersections during and after milling, and verifies the surface integrity of overlapping areas to ensure compliance with preset standards. Through real-time process quality control and feedback, processing anomalies (such as poor cutting or accidental damage) can be detected immediately, preventing defective semi-finished products from flowing into subsequent expensive processes and reducing scrap costs. Furthermore, confirming the integrity of the overlapping area provides direct evidence that this step has successfully achieved its process objective (i.e., selective protection), ensuring the reliability of the overall process route. The processing results are recorded and linked with the data. The actual parameters and test results of this laser processing are bound to the unique identifier of the flexible core board and recorded. Through electronic recording, the original data of the laser processing can be traced back when any board has problems in subsequent processes, which facilitates root cause analysis and process improvement.

[0023] Laser processing data processing and path planning include: The design data reception and parsing process receives original design files from the client, which contain layered information. CAM software parses these files, clearly identifying specific layers representing the intersections and overlaps of flexible areas. These layers are named FLEX_CROSS and FLEX_OVERLAP, respectively. The client's design intent is transformed into structured data objects that can be recognized and processed by a computer. Through clear layer identification and naming, an unambiguous data bridge is established between design and manufacturing, fundamentally avoiding confusion and errors that may occur with manual identification. This provides an accurate and reliable data source for subsequent selective processing.

[0024] The processing strategy allocation and path generation generate corresponding laser cutting paths for all closed graphic contours within the FLEX_CROSS layer. The path parameters are preset according to the material and laser characteristics. For the FLEX_OVERLAP layer, no cutting path is generated. Instead, a processing exclusion zone logic identifier associated with the graphic range of that layer is generated. This identifier will be used to guide subsequent equipment to prohibit laser output within this area. By directly converting design information into action and prohibition instructions that can be executed by the equipment, it is ensured that the processing intention is accurately translated into control code, so that subsequent physical processing can strictly distinguish different areas, providing a program logic guarantee for achieving step-by-step forming and area protection. Before outputting the final machining program, the simulation function of the CAM software and an independent verification program are used to simulate the generated path to ensure that no laser cutting path passes through the area defined by the FLEX_OVERLAP layer. At the same time, it is ensured that the cutting path of the FLEX_CROSS layer is completely within its defined contour. If the verification fails, an alarm is triggered and the user is prompted to check the original design data and layer definition rules. Through virtual simulation, potential machining accident risks (such as accidental cutting of overlapping areas) caused by design errors, data parsing deviations, or improper parameter settings are identified in advance. This improves the first-piece success rate and production safety, reduces material waste and downtime for debugging, and ensures the robustness of complex processes.

[0025] Step S3 includes the following steps: S31: Sub-plate lamination: The flexible core board obtained in step S2 is aligned and laminated with the specified outer rigid substrate, and then pressed together by a hot press to form a sub-plate structure with partial rigidity. S32: Sub-board circuit fabrication. On the surface of the rigid layer of the laminated sub-board, an outer layer circuit pattern transfer process is performed, including film application, exposure, development, etching and film removal, to form the outer layer circuit required for the sub-board. S33: Laser opening. Using laser equipment, according to a pre-programmed procedure, the portion of the rigid layer of the sub-plate corresponding to the lower flexible cross position and the flexible area that needs to be exposed in the future is precisely milled to form a window, so that the lower flexible area is exposed. S34: Tape protection pretreatment: Before applying the tape, prepare polyimide tape that matches the shape and size of the openings at the intersections that need to be protected; S35: Precisely apply protective tape, align the pre-treated tape and apply it to the intersection area within the opened window.

[0026] First, a laser is used to remove material from the corresponding area of ​​the rigid layer of the sub-plate, fully exposing the pre-processed flexible cross positions below. Then, a special polyimide tape is precisely applied to cover the exposed cross areas, creating a physical barrier for the subsequent browning process. By opening windows in the rigid layer, specific flexible areas are exposed at designated points. Then, by applying high-precision chemical-resistant tape, local sealing protection is provided for the processed flexible cross positions during the browning process, ensuring that the risk of chemical contamination is strictly isolated. At the same time, this protective measure is easy to remove after the subsequent main pressing, achieving a balance between protective effect and process operability.

[0027] Step S4 includes the following steps: S41: Sub-board browning treatment: The sub-board that has completed step S3 is sent to the browning production line for processing. S42: Pressing with the main rigid layer: After the sub-board has been browned, cleaned and dried, it is aligned and laminated with the remaining main rigid layer material, and then sent to a vacuum hot press to press it into a whole multi-layer rigid-flex board.

[0028] Step S4 involves browning the partially protected sub-board to form a rough oxide layer with high adhesion on its exposed copper surface. This is then vacuum-heat-pressed with the main rigid layer to achieve complete interlayer bonding. The phased lamination and browning sequence cleverly avoids the inherent risks of traditional processes. Furthermore, because the flexible cross-sections on the sub-board are meticulously protected with tape before browning, and the forming process for the flexible overlap area is proactively delayed, the possibility of browning chemicals contaminating the flexible cover film is completely eliminated. Simultaneously, the orderly pressing sequence ensures the strength and reliability of the interlayer bonding, laying the foundation for safely completing the remaining flexible area processing on the clean main board.

[0029] Step S5 includes the following steps: S51: On the surface of the laminated motherboard, the outer layer circuit pattern is formed by dry film lamination, exposure and development, and then formed by acid etching. S52: Solder resist ink is applied to the motherboard surface using a spraying process, and then ultraviolet exposure and sodium carbonate solution development are used to form a solder resist pattern. S53: Perform electroless nickel plating on the solder pad area that needs to be soldered and cover it with an immersion gold layer to complete the surface solderability treatment; S54: Use ultraviolet laser equipment to perform three-dimensional path milling on the overlapping positions of the flexible area to completely remove the cover film and flexible substrate, forming the final flexible structure.

[0030] Step S5 sequentially completes the outer layer circuit fabrication, solder mask protection, and surface treatment. Finally, the core laser process is performed, which uses an ultraviolet laser to precisely mill the previously intact flexible overlap area, completely removing its cover film and substrate to form the final flexible window. Since all chemical treatment processes that may cause contamination (such as etching and browning) are completed before step S54, the final laser processing of the overlap area completely avoids any risk of chemical contamination. This ensures the interface cleanliness and electrical reliability of this critical flexible area from the source, achieving high-quality and high-yield manufacturing of complex rigid-flex boards.

[0031] Step S54 includes the following steps: The process involves calling independent layer data from the design file to generate a laser cutting path, performing path optimization and anti-collision checks, verifying that the path does not overlap with the pre-processed area and is within the specified boundary. Path optimization improves processing efficiency, and anti-collision checks logically eliminate the risk of damaging the already formed intersecting area due to data errors. Boundary verification ensures the size and positional accuracy of the final flexible window, which is the data foundation for achieving high-precision, zero-interference forming. The optical positioning target on the motherboard surface is identified, and deformation and displacement deviations are calculated and compensated based on the target coordinates. The theoretical cutting path is mapped to the physical coordinate system of the motherboard. Through dynamic compensation, the precise fitting of the theoretical cutting path and the physical motherboard is ensured. Even if there is a slight deformation in the board, the absolute precision of laser processing at the overlapping position can be guaranteed. Laser parameters are set, and the laser beam is controlled to perform layer-by-layer scanning along the calibrated path to remove residue. The processing depth is determined by the preset number of scans until the cover film and flexible substrate are removed and the underlying copper foil is exposed. After setting parameters such as laser power and frequency according to material characteristics, the laser head performs layer-by-layer scanning according to the compensated path, vaporizing the material layer by layer. After each layer is scanned, processing residue is removed to avoid affecting the processing of the next layer. The number of scans calibrated in advance based on the total material thickness and the amount removed in a single scan is used as the criterion for the processing endpoint. The laser is controlled to stop when all the cover film and substrate are removed and the underlying copper foil is exposed. Layer-by-layer scanning avoids thermal damage caused by excessive energy in a single scan, and residue removal ensures processing quality and consistency. The preset number of scans is used as a depth control method to ensure that the target depth is accurately reached in each processing, forming a clean and vertical cutting surface that perfectly exposes the underlying conductor. The processing area is photographed, the cutting contour dimensions are measured and compared with the design values, the bottom residue and sidewall condition are detected, and the test results are recorded. Online inspection can detect and remove defective products in the first instance, preventing defects from flowing into subsequent processes. The test results are digitally recorded, and a complete processing file is established for each product, which facilitates quality traceability, process analysis and continuous improvement.

[0032] The preset number of scans is a fixed number calculated based on the total thickness of the cover film and the flexible substrate, as well as the single scan removal depth calibrated through process experiments. By transforming the key quality attribute of processing depth into a simple and repeatable engineering parameter that is directly related to the total material thickness and the calibrated removal rate, the control of complex precision processing becomes standardized and predictable. This reduces the reliance on expensive online detection sensors, simplifies equipment and operational requirements, and is especially suitable for batch production with known material thicknesses, ensuring that each product achieves highly consistent processing results, thus improving process stability and production efficiency.

[0033] During the layered scanning process, the plasma emission spectrum generated during laser processing is monitored simultaneously. When a characteristic signal representing the underlying copper foil material is detected, the processing is considered complete. By monitoring the plasma spectrum generated when the laser interacts with the material, the system can directly sense the type of material being removed. When the spectral signal changes from representing the organic capping film / substrate to representing the underlying copper metal, the system can instantly and automatically determine that the processing is complete and stop the laser, avoiding over-processing that damages the copper foil or under-processing that results in residue. This provides an optimal endpoint control solution for applications requiring extreme precision and versatility in materials.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a cross-overlapping rigid-flexible composite plate, characterized in that, Includes the following steps: S1: Based on the drawings, determine whether there are overlapping structures in the flexible area and decide to use a step-by-step laser forming process; S2: Fabricate flexible core board, only laser milling is performed at the intersection of the flexible area, and no laser processing is performed at the overlapping area; S3: The flexible core board is laminated with a part of the rigid board to make a sub-board. After the sub-board circuit is made and the cover is opened by laser, protective tape is applied at the intersection. S4: The sub-board with protective tape is browned and then laminated with the main rigid laminate. S5: Perform circuit fabrication, solder mask imaging and surface treatment on the laminated motherboard, and then perform laser milling on the overlapping positions of the flexible area; S6: Perform milling and glue application on the laser-processed panels, and finally inspect them.

2. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 1, characterized in that, Step S2 includes the following steps: S21: Cutting: Cutting the flexible copper-clad laminate substrate to obtain a flexible core board blank of specified dimensions; S22: Circuit fabrication. On a flexible core board blank, unwanted copper layers are removed through pattern transfer, exposure, development and etching processes to form inner layer circuit patterns. S23: Applying a cover film: A polyimide cover film is pressed onto the surface of the flexible core board with the completed circuit pattern using a hot-pressing process. S24: Laser milling, using laser equipment to precisely mill the flexible core board that has been covered with a film.

3. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 2, characterized in that, Step S24 includes the following steps: Laser processing data processing and path planning: Receive and parse the customer's original file containing the flexible area design, identify the independent layer data that defines the intersection and overlap positions, and generate two independent laser processing paths based on this data: one for performing contour cutting paths on the area within the intersection position layer, and the other for generating skip instructions on the area within the overlap position layer. Laser equipment parameter setting and calibration: Based on the material properties of the flexible cover film and the substrate, set the corresponding laser power, pulse frequency, cutting speed and focusing position process parameters on the laser processing equipment, and perform positioning calibration on the laser optical path and processing platform; Selective milling is performed, and the flexible core board with the cover film already pressed is fixed on the processing platform. The generated laser processing program is loaded and executed. The laser beam scans and irradiates according to the path planned for the intersection position, completely vaporizing and removing the cover film and the flexible substrate below it in the irradiation area, forming a clear and through window. At the same time, the program controls the laser beam to completely skip the overlapping area, without irradiating it, so that the cover film and the substrate in that area remain in their original physical seal. Online processing quality inspection measures the opening size and contour accuracy of the processed intersections during and after milling, and verifies the surface integrity of the overlapping areas to ensure compliance with preset standards. The processing results are recorded and linked with the data, binding and recording the actual parameters and test results of this laser processing with the unique identifier of the flexible core board.

4. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 3, characterized in that, The laser processing data processing and path planning include: The design data reception and parsing process involves receiving the original design files provided by the client, which contain layered information. The CAM software then parses these files, clearly identifying the specific layers representing the intersections of the flexible areas and the overlapping areas of the flexible areas, and naming these layers FLEX_CROSS and FLEX_OVERLAP respectively. Processing strategy allocation and path generation: For all closed graphic contours within the FLEX_CROSS layer, corresponding laser cutting paths are generated. The path parameters are preset according to the material and laser characteristics. For the FLEX_OVERLAP layer, no cutting paths are generated. Instead, a processing restricted area logical identifier associated with the graphic range of that layer is generated. Before outputting the final machining program, the simulation function of the CAM software and an independent verification program are used to simulate the generated path to ensure that no laser cutting path passes through the area defined by the FLEX_OVERLAP layer, and at the same time ensure that the cutting path of the FLEX_CROSS layer is completely within its defined contour. If the verification fails, an alarm is triggered and a prompt is made to check the original design data and layer definition rules.

5. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 1, characterized in that, Step S3 includes the following steps: S31: Sub-plate lamination: The flexible core board obtained in step S2 is aligned and laminated with the specified outer rigid substrate, and then pressed together by a hot press to form a sub-plate structure with partial rigidity. S32: Sub-board circuit fabrication. On the surface of the rigid layer of the laminated sub-board, an outer layer circuit pattern transfer process is performed, including film application, exposure, development, etching and film removal, to form the outer layer circuit required for the sub-board. S33: Laser opening. Using laser equipment, according to a pre-programmed procedure, the portion of the rigid layer of the sub-plate corresponding to the lower flexible cross position and the flexible area that needs to be exposed in the future is precisely milled to form a window, so that the lower flexible area is exposed. S34: Tape protection pretreatment: Before applying the tape, prepare polyimide tape that matches the shape and size of the openings at the intersections that need to be protected; S35: Precisely apply protective tape, align the pre-treated tape and apply it to the intersection area within the opened window.

6. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 1, characterized in that, Step S4 includes the following steps: S41: Sub-board browning treatment: The sub-board that has completed step S3 is sent to the browning production line for processing. S42: Pressing with the main rigid layer: After the sub-board has been browned, cleaned and dried, it is aligned and laminated with the remaining main rigid layer material, and then sent to a vacuum hot press to press it into a whole multi-layer rigid-flex board.

7. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 1, characterized in that, Step S5 includes the following steps: S51: On the surface of the laminated motherboard, the outer layer circuit pattern is formed by dry film lamination, exposure and development, and then formed by acid etching. S52: Solder resist ink is applied to the motherboard surface using a spraying process, and then ultraviolet exposure and sodium carbonate solution development are used to form a solder resist pattern. S53: Perform electroless nickel plating on the solder pad area that needs to be soldered and cover it with an immersion gold layer to complete the surface solderability treatment; S54: Use ultraviolet laser equipment to perform three-dimensional path milling on the overlapping positions of the flexible area to completely remove the cover film and flexible substrate, forming the final flexible structure.

8. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 7, characterized in that, Step S54 includes the following steps: Call the independent layer data in the design file to generate the laser cutting path, perform path optimization and anti-collision checks, and verify that the path does not overlap with the pre-processing area and is within the specified boundary. Identify the optical positioning target on the motherboard surface, calculate and compensate for deformation and displacement deviations based on the target coordinates, and map the theoretical cutting path to the physical coordinate system of the motherboard. Set the laser parameters, control the laser beam to perform layered scanning along the calibrated path, remove residue, determine the processing depth by the preset number of scans, until the cover film and flexible substrate are removed and the underlying copper foil is exposed; Photograph the processing area, measure the cutting contour dimensions and compare them with the design values, check the bottom residue and sidewall condition, and record the inspection results.

9. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 8, characterized in that, The preset number of scans is a fixed number calculated based on the total thickness of the cover film and the flexible substrate, as well as the single scan removal depth determined through process experiments.

10. The method for preparing a cross-overlapping rigid-flexible composite plate according to claim 8, characterized in that, During the layer scanning process, the plasma emission spectrum generated during laser processing is monitored simultaneously. When a characteristic signal characterizing the lower copper foil material is detected, the processing is determined to be complete.

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