Method for producing a multilayer fpc control board for display device manufacturing

Abstract

The application relates to the technical field of display device manufacturing, and provides a production method of a multilayer FPC control plate for display device manufacturing, which comprises the following steps: realizing high-precision alignment of functional layers by mechanical positioning holes and optical targets on a reference jig to form an initial laminated body containing multiple functional layers; adopting a controlled mold to open a window along a preset folding axis, remove a third copper-clad layer, a second polyimide insulating layer and an AD pure glue bonding layer, expose the back of a second copper-clad layer and form a local thinning area; performing differential hot pressing by applying a main pressure on the non-windowed side and a secondary pressure on the windowed side, so that the windowed area forms a flexible structure, and the non-windowed area maintains the original thickness and rigidity characteristics; and finally adopting a preset cooling curve to complete solidification and shaping. The method can realize high-precision interlayer alignment, controllable local windowing, regional differential pressing and rigid-flex integrated forming, and improves the reliability, consistency and manufacturing efficiency of the FPC control plate in the folding display device.

Description

Technical Field

[0001] This invention relates to the technical fields of display device manufacturing and multilayer FPC control board production, and in particular to a method for producing a multilayer FPC control board for display device manufacturing. Background Technology

[0002] Flexible printed circuit boards (FPCs) have been widely used in display device manufacturing due to their excellent flexibility, thin and light structure, and superior spatial wiring capabilities, especially in foldable display modules, wearable devices, and highly integrated portable terminals. To meet the needs of functional diversity and spatial integration, multi-layer FPC control boards have gradually become the mainstream structural form. However, existing multi-layer FPC control boards often require both rigid support areas and flexible folding areas in their structural design. In traditional manufacturing methods, a whole board is usually homogeneously stacked, and then local rigid materials are removed by laser cutting, mechanical milling, etc., in an attempt to form a flexible window area that can be bent. This type of method has the following prominent technical problems: First, large interlayer alignment errors: In the traditional stacking process, functional layers are fixed only by coarse positioning and pressing, lacking high-precision positioning control, which makes it easy to deviate from the predetermined area when opening windows, affecting the integrity of the conductive layer. Second, insufficient precision in window opening control: Traditional window opening methods mostly use uniform depth cutting, making it difficult to precisely control the removal sequence and termination position of different layers of material. This often leads to quality problems such as scratches, breakage, or residual adhesive in the internal copper layer due to over-cutting or under-cutting. Third, uneven strength of the flexible window structure: If the stress distribution in different areas is not controlled in conjunction with the pressing process after partial window opening, it is easy to form uneven thickness, resin accumulation, or bulging, ultimately causing wrinkles, cracks, or electrical performance failure in the flexible folding area.

[0003] In summary, the existing production technology of multilayer FPC control boards has technical problems such as large interlayer alignment errors, insufficient window opening control precision, and uneven strength of flexible window structures. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a method for manufacturing a multilayer FPC control board for display device manufacturing. This method features high-precision interlayer alignment, controllable local windowing, regional differential pressing, and rigid-flexible integrated molding, which can improve the reliability, consistency, and manufacturing efficiency of the FPC control board in foldable display devices.

[0005] The present invention provides a method for manufacturing a multilayer FPC control board for display device manufacturing, comprising:

[0006] On a reference fixture, each functional layer is sequentially aligned using mechanical positioning holes and optical targets to form an initial stack; the initial stack comprises, from top to bottom, a first copper-clad layer, a first polyimide insulating layer, a second copper-clad layer, an AD pure adhesive layer, a second polyimide insulating layer, and a third copper-clad layer.

[0007] Using a controlled mold, windows are opened along a preset folding axis starting from the third copper-clad layer. The corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure adhesive layer are removed in sequence until the back of the second copper-clad layer is exposed without causing mechanical damage to it, so as to form a thickness reduction zone in the initial stack.

[0008] A rigid pressure plate is laid on the side without windows, and a soft cushioning pad is laid on the side with windows. A main pressure P1 is applied to the side without windows, and a secondary pressure P2 is applied to the side with windows, with P1 being greater than P2. The initial laminate is thermally pressed together by differential pressure, so that the window area remains flexible due to the reduction in total thickness and the lower back pressure, while the unwindowed area maintains its original thickness and remains rigid due to the higher back pressure.

[0009] Maintain the pressing pressure until the AD pure adhesive layer has cured, then cool it to a safe temperature according to the preset cooling curve, release the pressure, and obtain an integrated multi-layer FPC control board that includes both flexible window areas and rigid areas.

[0010] Compared with the prior art, the beneficial effects of this invention are as follows:

[0011] This invention provides a method for manufacturing a multilayer FPC control board for display device manufacturing. The method includes: aligning functional layers sequentially on a reference fixture using mechanical positioning holes and an optical target to form an initial stack; the initial stack comprises, from top to bottom, a first copper-clad layer, a first polyimide insulating layer, a second copper-clad layer, an AD pure adhesive layer, a second polyimide insulating layer, and a third copper-clad layer; using a controlled mold, opening windows along a preset folding axis starting from the third copper-clad layer, and sequentially removing the corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure adhesive layer until the back of the second copper-clad layer is exposed without causing mechanical damage. Mechanical damage is removed to create a thickness reduction zone in the initial laminate. A rigid pressure plate is laid on the unwindowed side, and a soft cushioning pad is laid on the windowed side. A main pressure P1 is applied to the unwindowed side, and a secondary pressure P2 is applied to the windowed side, with P1 being greater than P2. The initial laminate is thermally pressed together by differential pressure, so that the windowed area remains flexible due to the reduced total thickness and lower back pressure, while the unwindowed area retains its original thickness and remains rigid due to higher back pressure. The pressing pressure is maintained until the AD pure adhesive layer is cured, and then the temperature is lowered to a safe temperature according to a preset cooling curve. The pressure is then released to obtain an integrated multilayer FPC control board that simultaneously includes a flexible window area and a rigid area. The method of this invention has high-precision interlayer alignment, controllable local windowing, regional differential pressing, and rigid-flexible integrated molding functions, which can improve the reliability, consistency, and manufacturing efficiency of FPC control boards in foldable display devices. Attached Figure Description

[0012] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. Some specific embodiments of the invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0013] Figure 1 This is a schematic flowchart of a method for manufacturing a multilayer FPC control board for display device manufacturing according to an embodiment of the present invention;

[0014] Figure 2 This is a schematic diagram of a multilayer FPC control board according to an embodiment of the present invention;

[0015] Figure 3 This is a schematic diagram of a pressing process during the overall hot pressing of the initial stacked body in an embodiment of the present invention. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are merely 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 should fall within the scope of protection of the present invention.

[0017] See Figures 1-3 This embodiment provides a method for manufacturing a multilayer FPC control board for display device manufacturing, including the following steps:

[0018] S101. Using mechanical positioning holes and optical targets, the functional layers are sequentially aligned on the reference fixture to form an initial stack; the initial stack includes, from top to bottom, a first copper-clad layer, a first polyimide insulating layer, a second copper-clad layer, an AD pure adhesive bonding layer, a second polyimide insulating layer, and a third copper-clad layer; wherein, the polyimide insulating layer can be abbreviated as PI layer.

[0019] S102. Using a controlled mold, windows are opened along a preset folding axis starting from the third copper-clad layer. The corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure adhesive layer are removed in sequence until the back of the second copper-clad layer is exposed without causing mechanical damage to it, so as to form a thickness reduction zone in the initial stack.

[0020] S103. Lay a rigid pressure plate on the side without windows and a soft cushioning pad on the side with windows. Apply a main pressure P1 to the side without windows and a secondary pressure P2 to the side with windows, with P1 being greater than P2. The initial laminated body is thermally pressed together by differential pressure, so that the windowed area remains flexible due to the reduction in total thickness and the lower back pressure, while the unwindowed area maintains its original thickness and remains rigid due to the higher back pressure.

[0021] S104. After the AD pure adhesive layer has cured, maintain the pressing pressure until it is cooled to a safe temperature according to the preset cooling curve, release the pressure, and obtain an integrated multi-layer FPC control board that includes both flexible window area and rigid area.

[0022] In this embodiment, mechanical positioning holes and optical targets are used on a reference fixture to align each functional layer sequentially to form an initial stack. This solves the technical problem of large interlayer alignment errors in the traditional multilayer FPC stacking process, achieving high-precision and repeatable spatial positioning of each functional layer, and laying a precise reference for subsequent local windowing and differential pressing. A controlled mold is used to open windows along a preset folding axis starting from the third copper-clad layer. The corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure adhesive layer are removed sequentially until the back of the second copper-clad layer is exposed without causing mechanical damage. This solves the technical problems of insufficient windowing control precision and easy scratching of the internal copper layer in the traditional process, achieving controllable layered removal and self-blunt stop at the endpoint, ensuring the integrity of the internal conductive layer and the consistency of the window thickness. A rigid pressure plate is laid on the side without windows, and a soft buffer pad is laid on the side with windows. A main pressure P1 is applied to the side without windows, and a secondary pressure P2 is applied to the side with windows, with the main pressure being greater than the secondary pressure. This solves the technical problems of uneven stress distribution, thickness imbalance, and bulging of the unopened area towards the opened area after partial window opening. It achieves rigid-flexible co-pressing under differential pressure, keeping the opened area flexible while maintaining high rigidity in the unopened area, effectively preventing bulging of the unopened area towards the opened area. The pressing pressure is maintained until the AD pure adhesive layer is cured, and then the temperature is lowered to a safe temperature according to the preset cooling curve. The pressure is then released, resulting in an integrated multi-layer FPC control board that includes both flexible and rigid areas. This solves the technical problems of uneven curing shrinkage and residual stress concentration in conventional hot pressing processes, achieving controlled synchronization of the curing-cooling process. This further improves the durability of the folding area and the overall dimensional stability of the board, achieving a seamless transition between rigid support and flexible folding within the single board, and improving the assembly efficiency and long-term reliability of the folding display module.

[0023] It should be noted that after hot pressing and cooling, a high-speed multispectral AOI system integrated at the outlet of the hot pressing device can be used to scan and compare the integrated multilayer FPC control board that has completed the pressing and cooling process. This system can detect the thickness of the flexible window area, the flatness of the unopened window area, and the distribution of residual bubbles at the interface in real time. The detection data is then transmitted back to the hot pressing controller via an industrial Ethernet network. A parameter optimization model based on a convolutional neural network performs online iterative correction on the pressing temperature-pressure-time curve of the current batch and provides adaptive compensation values ​​for P1, P2, and cooling rate of the next board. This solves the quality fluctuation and rework problems caused by traditional manual sampling inspection and improves the process stability and production cycle of FPC control boards used in large-scale foldable displays.

[0024] Preferably, the alignment of the initial stack includes: pre-setting a plurality of positioning pins and through holes corresponding to the process reference of the functional layers on the reference fixture, and setting a vacuum adsorption platform with a flatness of no more than 0.02 mm to provide an interlayer reference plane; placing the first copper-clad layer on the reference fixture, and after coarse positioning by fitting its reference hole with the positioning pin, the upper vision system identifies the optical target of the layer, calibrates the movement and rotation deviations by the micro-displacement platform, and starts local vacuum adsorption fixation; the first polyimide insulating layer, the second copper-clad layer, the AD pure adhesive bonding layer, the second polyimide insulating layer, and the third copper-clad layer are placed in sequence, and each layer is first initially positioned by attaching the positioning pin with the corresponding mechanical positioning hole, and then the upper vision system identifies its optical target, compares the features with the target of the previous fixed layer, drives the micro-displacement platform to automatically eliminate the interlayer movement and rotation deviations, and uses vacuum adsorption to complete the fixation; after all functional layers are aligned and fixed, the vacuum ring around the fixture is used to remove the residual air between the layers in one go, and an initial stack that can directly enter the subsequent window opening process is obtained.

[0025] In this embodiment, a number of positioning pins and through holes corresponding to the process reference of the functional layer are preset on the reference fixture, and a vacuum adsorption platform with a flatness of no more than 0.02 mm is set to provide an interlayer reference plane. This can solve the problems of overall misalignment and large positioning errors between layers caused by insufficient flatness of the reference platform and inconsistent mechanical references in the traditional FPC stacking process. It enables each layer to complete the alignment operation on the same high-precision reference plane, improving the alignment consistency and positioning accuracy of the entire board. After the first copper-clad layer is placed on the reference fixture and its reference hole is fitted with the positioning pin to complete the coarse positioning, the optical target of the layer is identified by the upper vision system. The movement and rotation deviations are calibrated by the micro-displacement platform and local vacuum adsorption fixation is initiated. This can solve the problems of low accuracy of manual positioning, uncontrollable position adjustment, and difficulty in accurately holding the initial reference layer. It can achieve precise correction and adsorption locking of position errors after coarse positioning, providing a stable initial reference for subsequent multilayer stacking. Each layer is initially positioned by attaching to the positioning pins through corresponding mechanical positioning holes. Then, the upper vision system identifies its optical target and compares its features with the target of the previously fixed layer. This drives a micro-displacement platform to automatically eliminate interlayer movement and rotational deviations, and vacuum adsorption is used for fixation. This solves the problem of large cumulative errors between layers and difficulty in layer-by-layer correction in traditional manual or single-reference positioning, achieving automatic layer-by-layer fine calibration and adsorption fixation. This ensures precise alignment of interlayer targets, improving the overall structural accuracy and product consistency of the laminate. After all functional layers are aligned and fixed, the vacuum ring around the fixture is used to remove residual air between layers in one go, resulting in an initial laminate that can directly enter the subsequent windowing process. This solves the problems of localized bubbling, incomplete layer bonding, and molding defects caused by air inclusions in traditional lamination processes. It achieves full bonding and air removal between layers, improving the uniformity and stability of the overall laminate. This enables a high-precision, high-efficiency, and rework-free front-end process, providing a reliable prerequisite for the integrated rigid-flexible structure fabrication of the FPC control board.

[0026] Preferably, the controlled mold is a stepped-limiting blade metal hard mold or a UV laser-mechanical composite mold; the window opening process of the controlled mold is executed according to a two-stage depth control: the first stage uses a roughing blade or a high-power laser to quickly remove the preset window material between the third copper-clad layer and the second polyimide insulating layer; the second stage switches to a fine-machining micro-blade or a low-power pulsed laser, and ensures that the termination position is within ±10µm of the top of the AD pure adhesive layer by limiting the bottom dead center or monitoring the reflected light intensity in real time, thereby obtaining a window bottom surface with a flatness Ra≤4µm.

[0027] In this embodiment, the controlled mold is a stepped-limiting cutting edge metal hard mold or a UV laser-mechanical composite mold, which can solve the problem that traditional single cutting methods cannot balance efficiency and precision in multi-layer heterogeneous material processing. It achieves highly adaptable layered cutting control in different materials such as rigid copper layers and flexible resin layers, improving the versatility and controllability of window processing. The window opening process is executed according to two-stage depth control, which can solve the problems of overcutting or undercutting and difficulty in precise termination caused by one-time cutting in the existing FPC window opening process. It realizes a processing mode of roughing and finishing separation and segmented control, which ensures cutting efficiency while taking into account window opening accuracy and interlayer safety. The first stage uses a roughing cutting edge or high-power laser to quickly remove the preset window material of the third copper-clad layer and the second polyimide insulating layer. This can solve the problems of low efficiency and high time cost of window opening using a single finishing method, and achieve rapid peeling of thicker and harder upper layers of material, significantly shortening the window opening cycle and reserving finishing allowance. The second stage switches between precision micro-blade machining or low-power pulsed laser, and uses bottom dead center limiting or real-time monitoring of reflected light intensity to ensure that the termination position stops within ±10µm of the top of the AD pure adhesive layer. This results in a window bottom surface with a flatness Ra≤4µm, which solves the problems of large window bottom surface position deviation caused by traditional depth control relying on manual experience or time control, resulting in surface roughness, uneven residual adhesive, and subsequent lamination bulging after opening the multi-layer FPC flexible window. Real-time monitoring and automatic limit termination improve the accuracy of depth control, avoid damage to the underlying conductive copper layer, and provide structural protection for subsequent differential lamination and the stability of the flexible functional area.

[0028] It should be noted that the UV laser-mechanical composite module integrates a variable diffraction beam shaping unit and a real-time copper layer back reflectivity monitoring module during the second stage of finishing. The beam shaping unit dynamically adjusts the pulse energy density distribution according to the window corner curvature radius and local adhesive film thickness, so that the laser spot size transitions in a gradient within the range of 12 µm–40 µm. The reflectivity monitoring module collects the second harmonic signal reflected from the AD adhesive-copper interface through a dual-channel photodiode integrated on the side wall of the focusing head, and determines the critical exposure point of the copper layer by combining it with an adaptive threshold algorithm and sends a stop command to the CNC system, thereby improving the termination depth control accuracy to ±5 µm, reducing the maximum roughness Ra of the bottom surface of the window to below 3 µm, and reducing the copper layer surface scratch defect rate to less than 0.5%, effectively solving the process problem of coexisting overcutting and undercutting of the micro-window.

[0029] Preferably, the preset windows are arranged linearly along the folding axis, the window length is 90%–100% of the effective length of the folding axis, and the window width W satisfies 0.4 mm ≤ W ≤ 2.5 mm and W ≤ the target minimum bending radius R; when there is a need for multiple folds, multiple windows are arranged in an equidistant or staggered manner, and the center distance between adjacent windows is ≥ 1.5 W.

[0030] In this embodiment, the preset windows are arranged linearly along the folding axis, and the window length is 90%–100% of the effective length of the folding axis. This solves the problem of unreasonable size settings of traditional flexible windows, which fail to cover the entire folding area, leading to local bending stress concentration and structural fatigue. It achieves continuous and uniform coverage of the entire effective folding section by the flexible area, improving folding durability and structural consistency. The window width W satisfies 0.4 mm ≤ W ≤ 2.5 mm and W ≤ the target minimum bending radius R. This solves the problem in existing window designs where excessively wide windows result in insufficient mechanical strength, or excessively narrow windows result in excessively high bending stiffness. It achieves the optimal balance between window geometry and structural integrity, ensuring smooth folding and long-term non-failure. When there are multiple folding requirements, multiple windows are arranged at equal intervals or in a staggered manner. This solves the problem of uneven distribution of repeated stress in the flexible area and the tendency for local fatigue cracks to occur in multi-folding scenarios. It achieves spatial optimization of the window structure and discrete distribution of the folding path, improving the reliability of multiple folds of the entire plate. With a center-to-center distance of ≥ 1.5 W between adjacent windows, the problem of structural weakening and thermal stress superposition caused by excessively dense arrangement of multiple windows can be solved, achieving reasonable redundancy and stress buffering between window areas, while taking into account the continuity of flexible areas and the mechanical strength of the overall board.

[0031] It should be noted that the window width W can be designed with a gradual change along the folding axis: with the folding center as the axis of symmetry, it gradually widens or narrows towards both sides with a linear gradient of 0.05 mm / 10 mm, and a tapered transition section is set at the folding end, with the length of the transition section accounting for 5%–8% of the total window length; at the same time, a circular arc buffer with a radius of R / 2 is added at both ends of the folding axis, and the circular arc buffer is smoothly connected to the linear window through a third-order Bezier curve; the gradient-circular arc composite window is iteratively optimized using finite element thermo-mechanical coupling simulation, so that the maximum equivalent stress is reduced by more than 18%, and the resistance drift of the flexible area is ≤3% after 200,000 bending cycles, thereby further reducing the risk of folding wrinkling and copper wire fatigue fracture.

[0032] Preferably, before opening the window using a controlled mold, a hollow area with a perimeter of 0.2 mm–0.4 mm is pre-formed in the first polyimide insulating layer corresponding to the window projection area, and the hollow edge adopts a rounded corner transition structure to restrict the lateral flow of resin during subsequent pressing and suppress window bulging.

[0033] In this embodiment, a hollow area with a perimeter of 0.2 mm–0.4 mm is pre-formed in the first polyimide insulating layer corresponding to the window projection area. This solves the problem of uneven thickness and local resin accumulation in the flexible window caused by unrestrained resin flow in the window area during traditional pressing. It effectively guides the resin to fill the boundary by pre-reserving cavities in the local material, limiting its diffusion to the central area, thereby obtaining a flexible area with uniform thickness and stable structure. The hollow edges adopt a rounded transition structure, which can solve the problem of stress concentration caused by sharp corners or abrupt changes in the hollow edges, resulting in cracks, wrinkles, or thermal stress peeling at the window boundary after pressing. This achieves stress continuity and smooth interface transition of the resin during the pressing process, improving the interfacial bonding strength and thermomechanical stability of the flexible window area.

[0034] Preferably, the rigid pressure plate is an aluminum plate with a thickness of 0.2 mm–0.4 mm and anodized hard film treatment, and the soft cushioning pad is a silicone pad with a Shore A hardness of 35–55 and a thickness of 0.6 mm–1.5 mm. The surfaces of the rigid pressure plate and the soft cushioning pad are covered with a PTFE release film.

[0035] The differential pressure ΔP = P1–P2 is controlled in a closed loop by a pressure sensor array, and ΔP is positively correlated with the window width W and the total thickness H of the unopened area, so as to form a controllable stress relief zone at the window boundary and reduce the stress concentration at the inflection point.

[0036] In this embodiment, the rigid pressure plate is an aluminum plate with a thickness of 0.2 mm–0.4 mm and anodized hard film treatment, and the soft buffer pad is a silicone pad with a Shore A hardness of 35–55 and a thickness of 0.6 mm–1.5 mm. The surfaces of the rigid pressure plate and the soft buffer pad are covered with a PTFE release film, which can solve the problems of uneven heat pressing, interface contamination, and residual marks on the pressure plate caused by material mismatch or adhesion in the traditional pressing process. It achieves synergistic pressing of high-strength rigid support and flexible buffer, and at the same time, the PTFE release film avoids material adhesion and ensures consistent surface quality in the window area and non-window area. The differential pressure ΔP = P1–P2 is controlled by a closed loop of pressure sensor array, which can solve the problems of pressure fluctuation and regional stress unevenness caused by manual pressure adjustment or single-point pressure measurement in conventional pressing. It realizes precise differential pressure adjustment based on multi-point feedback, improves the controllability and repeatability of the pressing process, and provides stable process assurance for complex structure FPCs. ΔP is positively correlated with the window width W and the total thickness H of the unopened window area. It can solve problems such as stress abrupt changes and edge folding point failure caused by the difference in structural thickness between the window area and the unopened window area. It can realize dynamic matching of pressure differential according to structural geometric parameters, build a gradual stress relief zone at the window boundary, and reduce the risk of breakage and stress fatigue accumulation at the initial folding point.

[0037] Preferably, after the window is opened, an annular cover film with a width of 0.3 mm–0.6 mm and a thickness of 18 µm–25 µm is applied to the surface of the first polyimide insulating layer around the window to prevent the resin of the AD pure adhesive layer from flowing laterally into the window area during the pressing process, so as to ensure that the thickness of the window area is uniform.

[0038] In this embodiment, an annular covering film with a width of 0.3 mm–0.6 mm and a thickness of 18 µm–25 µm is applied to the surface of the first polyimide insulating layer around the window. This film is used to prevent the resin of the AD pure adhesive layer from flowing laterally into the window area during the pressing process. This can solve the problems of resin accumulation, uneven thickness, and abrupt interface changes caused by disordered lateral flow of resin during hot pressing. It can also create an effective physical barrier at the edge of the flexible window, guide the resin to remain in the non-window area for curing during the pressing stage, and ensure that the thickness of the window area is controlled and the structure is uniform.

[0039] Preferably, the process of hot-pressing the initial laminate as a whole includes: a vacuum degassing stage, a heating and adhesive removal stage, a constant temperature curing stage, and a controlled cooling stage; the temperature-pressure curves of each stage are parameterized according to the curing characteristics of the AD pure adhesive layer, and the temperature-pressure closed-loop control is used to ensure the interlayer bonding strength and the flatness of the board surface.

[0040] In this embodiment, the process of hot-pressing the initial laminate as a whole includes: a vacuum degassing stage, a heating and adhesive removal stage, a constant-temperature curing stage, and a controlled cooling stage. This solves the problems of traditional hot-pressing processes being crude and lacking control over the heat-pressure coupling process, leading to residual gas between layers, insufficient removal of adhesive layers, or incomplete curing. It achieves staged management of resin flow, gas removal, and structural curing throughout the entire process, improving the internal bonding uniformity and structural stability of the FPC laminate. The temperature-pressure curves for each stage are parameterized according to the curing characteristics of the AD pure adhesive layer. This addresses the lack of versatility in existing pressing processes that use fixed heating or pressure curves, failing to adapt to different adhesive layer characteristics. It allows for customized hot-pressing parameters tailored to the adhesive materials used, ensuring full cross-linking and curing at the optimal reaction temperature and time. By using closed-loop temperature-pressure control to ensure interlayer bonding strength and board surface flatness, the problem of lack of feedback adjustment mechanism in traditional open pressing processes, which leads to significant impact of temperature or pressure fluctuations on pressing quality, can be solved. This enables real-time monitoring and precise adjustment of process conditions throughout the hot pressing process, stabilizing the interlayer adhesive film state and improving the bonding strength and flatness consistency of the final board.

[0041] Preferably, a water-soluble stripping agent is pre-applied at the interface between the second copper-clad layer and the AD pure adhesive layer. When the controlled mold cuts or the laser beam touches the interface, the reflected signal changes abruptly, and the signal processing module immediately triggers the window opening termination to avoid scratching the second copper-clad layer.

[0042] In this embodiment, a water-soluble stripping agent is pre-coated at the interface between the second copper-clad layer and the AD pure adhesive bonding layer. This solves the problem in traditional layered cutting processes where there is a lack of effective physical or optical interface identification methods, making it difficult to accurately determine the termination depth during the cutting process. This allows for the construction of an intermediate layer with identifiable signal characteristics at the critical interface, providing a stable and controllable termination reference point for subsequent processing. When the controlled mold cuts or the laser beam touches this interface, a sudden change in the reflected signal is triggered, and the signal processing module immediately triggers window termination. This solves the risk of scratches, breakage, or decreased reliability of the second copper-clad layer caused by overcutting or delayed shutdown in existing processes. It achieves a real-time identification mechanism based on the sudden change in the reflected signal, triggering a highly responsive termination command and precisely controlling the window termination depth.

[0043] Preferably, a V-shaped micro-scratches with a power ≤ 5 W, a wavelength of 355 nm, a UV laser is used to etch the surface of the second polyimide insulating layer on both sides of the window. The micro-scratches have a depth of 4 µm–8 µm and a distance of 0.15 mm–0.25 mm from the edge of the window, so as to release micro-stress and reduce the stress concentration in the circumferential direction of the fold.

[0044] In this embodiment, V-shaped micro-markings with a power ≤ 5W, a wavelength of 355nm, and a depth of 4µm–8µm are etched on the surface of the second polyimide insulating layer on both sides of the long side of the window, with a distance of 0.15mm–0.25mm from the window edge. This solves the problem of circumferential stress concentration, material cracking, or micro-wrinkling that easily occurs in the folded area of ​​multilayer FPC during hot pressing and long-term bending. It realizes the construction of a structural micro-release zone around the window edge, so that the stress during folding is effectively buffered and dispersed, thereby improving the mechanical stability and fatigue life of the flexible area. The UV laser etching depth of 4µm–8µm with a power ≤ 5W and a wavelength of 355nm can solve the problems of large damage to the polyimide surface and uncontrollable edge charring or micro-cracks caused by conventional mechanical or high-power laser processing methods. It achieves high-precision, low-thermal-affect shallow marking processing with low-power UV laser without damaging the underlying functional layer, ensuring structural integrity and process safety. V-shaped micro-scratches with a spacing of 0.15mm–0.25mm from the window edge can solve the problem of structural weakening or ineffective stress release caused by improper scratch placement. It can establish a directional stress unloading path near the critical area of ​​stress concentration, optimize the stress distribution characteristics of the boundary area, and prevent material damage or functional failure at the inflection point.

[0045] Preferably, when a multi-level flexible area needs to be formed on the same FPC control board, different windowing depths are executed for different folding areas: only the third copper-clad layer is removed in the first area; the third copper-clad layer and the second polyimide insulating layer are removed in the second area; the AD pure glue bonding layer is further removed in the third area; and the lamination temperature, pressure, and holding time are independently set for each area according to a preset lamination parameter table, so as to integrate multiple flexible folding levels on one board.

[0046] In this embodiment, when a multi-level flexible area needs to be formed on the same FPC control board, different windowing depths are executed for different folding areas, which can solve the problem that multiple bending performance requirements cannot be achieved on a single FPC board in the existing process, resulting in the need for multi-board combination, complex structure, and inconvenient assembly for similar products. It realizes the flexible configuration of different flexible grade areas within the same control board to meet the different requirements for folding radius, thickness, and flexibility at different positions in complex display structures. Only the third copper-clad layer is removed in the first area, the third copper-clad layer and the second polyimide insulating layer are removed in the second area; the AD pure glue bonding layer is further removed in the third area, which can solve the problem that the traditional windowing process cannot accurately peel different structural layers, easily leading to windowing uniformity and the inability to form multi-level flexible windows. It realizes the formation of thinning areas with different thicknesses and mechanical responses by controlling the number of removed layers, and constructs multi-level flexible characteristics from the structural level. The lamination temperature, pressure, and holding time are independently set for each area according to a preset lamination parameter table, which can solve the problem that local overpressure or underpressure occurs due to the unified lamination parameters for the whole board in the traditional hot pressing process, resulting in inconsistent performance of different flexible areas. It realizes fine parameter matching according to the regional thickness difference and material response characteristics, so that each flexible grade area can obtain the optimal lamination quality and structural morphology.

[0047] It should be noted that after the lamination of the multi-level flexible area is completed, a CO2 laser scanner with a central wavelength of 10.6 µm is used to perform planar heating on the third area according to a preset thermal field distribution, so that the AD pure glue bonding layer is locally heated to 110 °C and maintained for 25 seconds to release the residual stress of lamination; at the same time, clean nitrogen gas at a temperature of 18 °C is blown into the second area synchronously to form a thermal gradient barrier to prevent the heat influence from spreading to the second area and the first area, thereby further reducing the residual stress at the interface of the multi-level flexible area.

[0048] Preferably, when the number of copper-clad layers of the multi-layer FPC control board is N, N ≥ 3, the k-th layer and all the following functional layers are selected from the bottom copper-clad layer upward to implement through-windowing according to the target folding morphology, 1 ≤ k < N–1; when laminating, a reverse layering strategy is adopted, with the hard pressing plate and the main pressure on the non-windowed side, and the soft cushion and the secondary pressure on the windowed side, to ensure the forming consistency of the multi-level folding area.

[0049] In this embodiment, when the number of copper-clad layers of the multi-layer FPC control board is N, where N ≥ 3, starting from the bottom copper-clad layer upwards, the k-th layer and all the functional layers below it are selected according to the target folding morphology for through-windowing, where 1 ≤ k < N–1. This can solve the problem that traditional FPCs only perform local windowing on the top layer or intermediate layer, making it difficult to meet the requirements of complex or large-angle folding. It enables precise control of the windowing level in terms of structural depth according to the target folding curvature and deformation requirements, achieving through-thinning of the flexible area from the surface layer to the deep layer, thereby supporting application scenarios with a larger folding radius or a higher bending frequency. When pressing, a reverse layering strategy is adopted, with the hard pressing plate and the main pressure on the non-windowed side, and the soft cushion and the auxiliary pressure on the windowed side. This can solve the problem of uneven pressure in the multi-stage windowing area and the easy bulging or collapse of the flexible area in the conventional pressing layout. It enables, through reverse structural distribution, the use of the rigid pressing plate to provide high-pressure shaping and suppress warping in the non-windowed area, while using the cushion to form a compliant fit in the windowed area, effectively controlling local morphological changes.

[0050] It should be noted that the above embodiments are only preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A production method for a multilayer FPC control board for display device manufacturing, characterized by, Includes the following steps: On a reference fixture, each functional layer is sequentially aligned using mechanical positioning holes and optical targets to form an initial stack; the initial stack comprises, from top to bottom, a first copper-clad layer, a first polyimide insulating layer, a second copper-clad layer, an AD pure adhesive layer, a second polyimide insulating layer, and a third copper-clad layer. Using a controlled mold, windows are opened along a preset folding axis starting from the third copper-clad layer. The corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure adhesive layer are removed in sequence until the back of the second copper-clad layer is exposed without causing mechanical damage to it, so as to form a thickness reduction zone in the initial stack. A rigid pressure plate is laid on the side without windows, and a soft cushioning pad is laid on the side with windows. A main pressure P1 is applied to the side without windows, and a secondary pressure P2 is applied to the side with windows, with P1 being greater than P2. The initial laminate is thermally pressed together by differential pressure, so that the window area remains flexible due to the reduction in total thickness and the lower back pressure, while the unwindowed area maintains its original thickness and remains rigid due to the higher back pressure. Maintain the pressing pressure until the AD pure adhesive layer has cured, then cool it to a safe temperature according to the preset cooling curve, release the pressure, and obtain an integrated multi-layer FPC control board that includes both flexible window areas and rigid areas.

2. The production method of a multilayer FPC control board for display device manufacturing according to claim 1, characterized by, The alignment of the initial stack includes: pre-setting several positioning pins and through holes corresponding to the process reference of the functional layers on the reference fixture, and setting a vacuum adsorption platform with a flatness of no more than 0.02 mm to provide an interlayer reference plane; placing the first copper-clad layer on the reference fixture, and after coarse positioning by fitting its reference hole with the positioning pin, the upper vision system identifies the optical target of the layer, calibrates the movement and rotation deviations through the micro-displacement platform, and starts local vacuum adsorption fixation; the first polyimide insulating layer, the second copper-clad layer, the AD pure adhesive layer, the second polyimide insulating layer, and the third copper-clad layer are placed in sequence. Each layer is first initially positioned by attaching the positioning pin through the corresponding mechanical positioning hole, and then its optical target is identified by the upper vision system. The feature is compared with the target of the previous fixed layer, and the micro-displacement platform is driven to automatically eliminate the interlayer movement and rotation deviations, and the vacuum adsorption method is used to complete the fixation; after all functional layers are aligned and fixed, the vacuum ring around the fixture is used to remove the residual air between the layers in one go, resulting in an initial stack that can directly enter the subsequent window opening process.

3. The production method of a multi-layer FPC control board for display device manufacturing according to claim 1, characterized by, The controlled mold is a stepped-limiting blade metal hard mold or a UV laser-mechanical composite mold; the window opening process of the controlled mold is executed in two stages of depth control: the first stage uses a roughing blade or a high-power laser to quickly remove the preset window material between the third copper-clad layer and the second polyimide insulating layer; the second stage switches to a fine-machining micro-blade or a low-power pulsed laser, and ensures that the termination position is within ±10µm of the top of the AD pure adhesive layer by limiting the bottom dead center or monitoring the reflected light intensity in real time, thereby obtaining a window bottom surface with a flatness Ra≤4µm.

4. The production method of a multi-layer FPC control board for display device manufacturing according to claim 1, characterized by, Before opening the window using a controlled mold, a hollow area with a perimeter of 0.2 mm–0.4 mm is pre-formed in the first polyimide insulating layer corresponding to the window projection area, and the hollow edges adopt a rounded transition structure to restrict the lateral flow of resin during subsequent pressing and suppress window bulging.

5. The method for producing a multilayer FPC control board for manufacturing a display device according to any one of claims 1-4, characterized in that, The rigid pressure plate is an aluminum plate with a thickness of 0.2 mm–0.4 mm and anodized hard film treatment, and the soft cushioning pad is a silicone pad with a Shore A hardness of 35–55 and a thickness of 0.6 mm–1.5 mm. The surfaces of the rigid pressure plate and the soft cushioning pad are covered with PTFE release film. The differential pressure ΔP = P1–P2 is controlled in a closed loop by a pressure sensor array, and ΔP is positively correlated with the window width W and the total thickness H of the unopened area, so as to form a controllable stress relief zone at the window boundary and reduce the stress concentration at the inflection point.

6. The method for producing a multilayer FPC control board for manufacturing display devices according to claim 5, characterized in that, After the window is opened, an annular cover film with a width of 0.3 mm–0.6 mm and a thickness of 18 µm–25 µm is applied to the surface of the first polyimide insulation layer around the window. This film is used to prevent the resin of the AD pure adhesive layer from flowing laterally into the window area during the pressing process, so as to ensure that the thickness of the window area is uniform.

7. The method for producing a multilayer FPC control board for manufacturing a display device according to any one of claims 1-4, characterized in that, The process of hot-pressing the initial laminate as a whole includes: vacuum degassing stage, heating and adhesive removal stage, constant temperature curing stage and controlled cooling stage; the temperature-pressure curves of each stage are parameterized according to the curing characteristics of AD pure adhesive layer, and temperature-pressure closed-loop control is used to ensure interlayer bonding strength and board surface flatness.

8. The method for producing a multilayer FPC control board for manufacturing a display device according to any one of claims 1-4, characterized in that, A water-soluble stripping agent is pre-applied at the interface between the second copper-clad layer and the AD pure adhesive layer. When the controlled mold cuts or the laser beam touches this interface, the reflected signal changes abruptly, and the signal processing module immediately triggers the window opening termination to avoid scratching the second copper-clad layer.

9. The method for producing a multilayer FPC control board for manufacturing a display device according to any one of claims 1-4, characterized in that, On the surface of the second polyimide insulating layer on both sides of the long side of the window, a V-shaped micro-scribing depth of 4 µm–8 µm and a distance of 0.15 mm–0.25 mm from the window edge is made by UV laser with power ≤ 5 W and wavelength 355 nm to release micro-stress and reduce stress concentration in the circumferential direction of the fold.

Images