Production method of multi-layer FPC (Flexible Printed Circuit) control board for manufacturing display device

Abstract

The invention relates to the technical field of display device manufacturing and the like, and provides a production method of a multi-layer FPC control board for display device manufacturing, and the method comprises the steps: achieving the high-precision alignment of functional layers on a reference jig through a mechanical positioning hole and an optical target, and forming an initial laminated body containing a plurality of functional layers; windowing along a preset folding axis by adopting a controlled mold, removing the third copper-clad layer, the second polyimide insulating layer and the AD pure adhesive layer, exposing the back surface of the second copper-clad layer and forming a local thinning area; differential thermocompression bonding is carried out in the mode that main pressure is applied to the non-windowing side and auxiliary pressure is applied to the windowing side, so that a flexible structure is formed in the windowing area, and the non-windowing area keeps the original thickness and rigidity characteristic; and finally, curing and shaping are completed by adopting a preset cooling curve. By means of the method, high-precision interlayer alignment, controllable local windowing, regional difference pressing and rigid-flexible integrated forming can be achieved, and the reliability, consistency and manufacturing efficiency of the FPC control panel in the folding display device are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical fields of display device manufacturing, multilayer FPC control board production and the like, and in particular to a production method of a multilayer FPC control board for display device manufacturing. BACKGROUND

[0002] Flexible Printed Circuit (FPC) has been widely used in the field of display device manufacturing due to its good flexibility, thin structure and excellent space wiring capability, especially in folding display modules, wearable devices and high-integration portable terminals. In order to meet the needs of functional diversification and space integration, multilayer FPC control boards have gradually become the mainstream structure. However, the existing multilayer FPC control boards often need to have rigid support areas and flexible folding areas in the structure design. In the traditional manufacturing method, the whole board is usually stacked uniformly, and then the local rigid material is removed through subsequent laser cutting, mechanical milling and other methods to form a bendable flexible window area. Such methods have the following outstanding technical problems: first, large interlayer alignment error: in the traditional stacking process, the functional layers only rely on rough positioning and pressing for fixation, lacking high-precision positioning control, which leads to easy deviation from the predetermined area during subsequent windowing, affecting the integrity of the conductive layer. Second, insufficient windowing control precision: most traditional windowing methods use uniform depth cutting, which is difficult to accurately control the removal sequence and termination position of different levels of materials, often causing internal copper layer scratches, fractures or residual glue cleaning quality problems. Third, uneven flexible window structure strength: after local windowing, different area stress distribution is not regulated in combination with the pressing process, which is easy to form thickness unevenness, resin accumulation or bulging phenomenon, eventually causing wrinkles, cracking or electrical performance failure in the flexible folding area.

[0003] In summary, the existing production technology of multilayer FPC control boards has the technical problems of large interlayer alignment error, insufficient windowing control precision, and uneven flexible window structure strength. SUMMARY

[0004] In view of the above-mentioned deficiencies of the prior art, the present application provides a production method of a multilayer FPC control board for display device manufacturing, which has high-precision interlayer alignment, controllable local windowing, regional differential pressing and rigid-flex integrated forming functions, and can improve the reliability, consistency and manufacturing efficiency of the FPC control board in the folding display device.

[0005] The production method of a multilayer FPC control board for display device manufacturing provided by the present application comprises: The functional layers are aligned in sequence on a reference fixture by mechanical positioning holes and optical targets to form an initial stack; the initial stack comprises, from top to bottom, a first copper cladding layer, a first polyimide insulating layer, a second copper cladding layer, an AD pure glue bonding layer, a second polyimide insulating layer, and a third copper cladding layer; A controlled mold is used to open a window along a preset folding axis from the third copper cladding layer, and the corresponding window materials of the third copper cladding layer, the second polyimide insulating layer, and the AD pure glue bonding layer are sequentially removed until the back surface of the second copper cladding layer is exposed without causing mechanical damage, so as to form a thickness reduction area in the initial stack; A hard pressing plate is laid on the side without the window, and a soft cushion is laid on the side with the window; a main pressure P1 is applied from the side without the window, and a secondary pressure P2 is applied from the side with the window, and P1 is greater than P2; the initial stack is integrally hot-pressed by differential pressure, so that the window area remains bendable due to the overall thickness reduction and lower back pressure, while the non-window area remains rigid due to the original thickness and higher back pressure; After the pressing pressure is maintained until the AD pure glue bonding layer is cured, the temperature is lowered to a safe temperature according to a preset cooling curve, the pressure is released, and an integrated multi-layer FPC control panel containing a flexible window area and a rigid area is obtained.

[0006] Compared with the prior art, the present application has the following advantages: The present application provides a production method of a multi-layer FPC control panel for display device manufacturing, which comprises: aligning the functional layers in sequence on a reference fixture by mechanical positioning holes and optical targets to form an initial stack; the initial stack comprises, from top to bottom, a first copper cladding layer, a first polyimide insulating layer, a second copper cladding layer, an AD pure glue bonding layer, a second polyimide insulating layer, and a third copper cladding layer; a controlled mold is used to open a window along a preset folding axis from the third copper cladding layer, and the corresponding window materials of the third copper cladding layer, the second polyimide insulating layer, and the AD pure glue bonding layer are sequentially removed until the back surface of the second copper cladding layer is exposed without causing mechanical damage, so as to form a thickness reduction area in the initial stack; a hard pressing plate is laid on the side without the window, and a soft cushion is laid on the side with the window; a main pressure P1 is applied from the side without the window, and a secondary pressure P2 is applied from the side with the window, and P1 is greater than P2; the initial stack is integrally hot-pressed by differential pressure, so that the window area remains bendable due to the overall thickness reduction and lower back pressure, while the non-window area remains rigid due to the original thickness and higher back pressure; after the pressing pressure is maintained until the AD pure glue bonding layer is cured, the temperature is lowered to a safe temperature according to a preset cooling curve, the pressure is released, and an integrated multi-layer FPC control panel containing a flexible window area and a rigid area is obtained. The method of the present application has the functions of high-precision interlayer alignment, controllable local windowing, regional differential pressing, and rigid-flex integrated forming, and can improve the reliability, consistency, and manufacturing efficiency of the FPC control panel in the folding display device. Attached Figure Description

[0007] 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: Fig. 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; Fig. 2 This is a schematic diagram of a multilayer FPC control board according to an embodiment of the present invention; Fig. 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

[0008] 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.

[0009] See Figs. 1-3 This embodiment provides a method for manufacturing a multilayer FPC control board for display device manufacturing, including the following steps: 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.

[0010] 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. S103, laying a hard pressing plate on the non-windowing side and laying a soft cushion on the windowing side; applying a main pressure P1 from the non-windowing side and applying a secondary pressure P2 from the windowing side, and P1 is greater than P2; the initial stack is integrally hot-pressed by differential pressure, so that the windowing area remains bendable due to the total thickness thinning and lower back pressure, while the non-windowing area maintains the original thickness and remains rigid due to the higher back pressure; S104, after the curing of the AD pure glue bonding layer is completed, the pressure is released after the temperature is lowered to a safe temperature according to a preset cooling curve, and an integrated multi-layer FPC control panel containing a flexible window area and a rigid area is obtained.

[0011] In this embodiment, the mechanical positioning hole and the optical target on the reference jig are used to align each functional layer in turn to form an initial stack, which can solve the technical problem of large alignment error between layers in the traditional layering process of multi-layer FPC, and realize high-precision and repeatable spatial positioning of each functional layer, laying a precise foundation for subsequent local windowing and differential pressing. The controlled mold starts from the third copper-clad layer and opens a window along the preset folding axis, sequentially removes the corresponding window materials of the third copper-clad layer, the second polyimide insulating layer and the AD pure glue bonding layer, and exposes the back of the second copper-clad layer without causing mechanical damage, which can solve the technical problems of insufficient windowing control precision and easy scratching of internal copper layers in traditional processes, and realize layered controllable removal and end-point self-passivation, ensuring the integrity of internal conductive layers and the thickness consistency of the window. Lay a hard pressing plate on the non-windowing side and lay a soft cushion on the windowing side; apply a main pressure P1 from the non-windowing side and apply a secondary pressure P2 from the windowing side, and the main pressure is greater than the secondary pressure, which can solve the technical problems of uneven stress distribution between the flexible window area and the rigid area after local windowing, thickness imbalance and bulging of the non-windowing area to the windowing area, and realize rigid and flexible collaborative pressing under differential pressure, so that the windowing area remains bendable and the non-windowing area maintains high rigidity, effectively avoiding the bulging of the non-windowing area to the windowing area. After the curing of the AD pure glue bonding layer is completed, the temperature is lowered to a safe temperature according to a preset cooling curve, and the pressure is released, and an integrated multi-layer FPC control panel containing a flexible window area and a rigid area is obtained, which can solve the technical problems of uneven curing shrinkage and residual stress concentration in conventional hot pressing processes, realize controlled synchronization of the curing-cooling process, further improve the durability of the folding area and the dimensional stability of the whole panel, realize seamless transition of rigid support and flexible folding in a single panel, and improve the assembly efficiency and long-term reliability of the folding display module.

[0012] It should be noted that after the cooling of the hot pressing, the completed integrated multi-layer FPC control panel can be scanned and compared by using a high-speed multi-spectral AOI system integrated at the outlet position of the hot pressing device, to detect the thickness of the flexible window area, the flatness of the non-windowed area and the interface residual bubble distribution data in real time; the detection data is returned to the hot pressing controller through the industrial Ethernet, and the parameter optimization model based on the convolutional neural network is used to online iterative correction of the current batch of pressing temperature-pressure-time curve, and adaptive compensation values are given to P1, P2 and cooling rate of the next panel, to solve the quality fluctuation and rework problem caused by traditional artificial sampling inspection, and to improve the process stability and production rhythm of large-scale folding display FPC control panel.

[0013] Preferably, the alignment of the initial stack includes: presetting a plurality of positioning pins and through holes corresponding to the functional layer process reference on the reference jig, and setting a vacuum adsorption platform with a flatness of not greater than 0.02 mm to provide an interlayer reference plane; placing the first copper-clad layer on the reference jig, and after rough positioning by fitting the reference hole with the positioning pin, recognizing the optical target of the layer by the upper visual system, correcting the movement and rotation deviation by the micro-displacement platform and starting local vacuum adsorption fixation; placing 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 in turn, each layer is first positioned by hanging on the positioning pin through the corresponding mechanical positioning hole to complete the initial positioning, then the optical target of each layer is recognized by the upper visual system, the feature of the target of the previous fixed layer is compared, the micro-displacement platform is driven to automatically eliminate the movement and rotation deviation between layers, and vacuum adsorption is used to complete the fixation; after all the functional layers are aligned and fixed, the vacuum ring around the jig is used to remove the residual air between the layers at one time, and the initial stack that can directly enter the subsequent windowing process is obtained.

[0014] In this embodiment, a plurality of positioning pins and through holes corresponding to the functional layer process reference are preset on the reference jig, and a vacuum adsorption platform with a flatness of not greater than 0.02 mm is arranged to provide an interlayer reference plane, which can solve the problems of interlayer overall misplacement and large positioning error caused by insufficient flatness of the reference platform and non-uniform mechanical reference in the traditional FPC lamination process, realize the collimation operation of each layer on the same high-precision reference plane, and improve the alignment consistency and positioning accuracy of the whole board. After the first copper-clad layer is placed on the reference jig and the reference hole is sleeved with the positioning pin to complete the rough positioning, the optical target of the layer is recognized by the upper visual system, the rotation deviation is corrected and moved by the micro-displacement platform, and the local vacuum adsorption is started, which can solve the problems of low manual positioning accuracy, uncontrollable position adjustment, and difficulty in realizing accurate fixation of the initial reference layer, realize precise correction and adsorption locking of the position error after rough positioning, and provide a stable initial reference for subsequent multi-layer stacking. Each layer is first positioned by the corresponding mechanical positioning hole to complete the initial positioning, then the optical target is recognized by the upper visual system, the features of the target are compared with those of the target of the previous fixed layer, the micro-displacement platform is automatically driven to eliminate the interlayer movement and rotation deviation, and the vacuum adsorption method is used to complete the fixation, which can solve the problems of large cumulative error between layers in traditional manual or single reference positioning and difficulty in layer-by-layer correction, realize automatic precise correction and adsorption fixation layer by layer, ensure the accurate alignment of interlayer targets, and improve the configuration accuracy and product consistency of the whole lamination. After all the functional layers are aligned and fixed, the vacuum ring around the jig is used to remove the residual air between the layers at one time, and the initial lamination body that can directly enter the subsequent windowing process is obtained, which can solve the problems of local blistering, interlayer non-adhesion and forming defects caused by air inclusion in the traditional lamination process, realize the full adhesion and exhaust between layers, improve the uniformity and stability of the whole lamination body, realize high-precision, high-efficiency and no rework in the front-end process, and provide a reliable premise for the preparation of the integrated rigid-flex structure of the FPC control board.

[0015] Preferably, the controlled mold is a stepped limit knife edge metal hard mold or a UV laser-mechanical composite mold; the windowing process of the controlled mold is performed according to two-stage depth control: the first stage uses a rough machining knife edge or a high-power laser to quickly remove the preset window material of the third copper-clad layer and the second polyimide insulating layer; the second stage switches to a fine machining micro-knife edge or a low-power pulsed laser, and is monitored in real time by the lower dead point limit or the reflected light intensity to ensure that the termination position stays within ±10µm of the top of the AD pure adhesive bonding layer, thereby obtaining a window bottom surface with a flatness Ra≤4µm.

[0016] In this embodiment, the controlled mold is a stepped limiting knife edge metal hard mold or a UV laser-mechanical composite mold, which can solve the problem of traditional single cutting mode in multi-layer heterogeneous material processing that cannot balance efficiency and precision, and realize high adaptability of layered cutting control in different materials such as rigid copper layer and flexible resin layer, etc., to improve the universality and controllability of window processing. The windowing process is performed according to two-stage depth control, which can solve the problem of overcutting or undercutting caused by one-time cutting in the existing FPC windowing process, and it is difficult to accurately terminate, realizing the processing mode of coarse-fine separation and segmented control, balancing the cutting efficiency while considering the windowing precision and interlayer safety. The first stage uses a coarse machining knife edge or a high-power laser to quickly remove the preset window material of the third copper layer and the second polyimide insulating layer, which can solve the problem of low efficiency and high time cost of windowing by using single fine machining method, realize the rapid stripping of the upper layer of thick and hard material, and greatly shorten the windowing period and reserve the finishing allowance. The second stage switches to fine machining micro-knife edge or low-power pulsed laser, and monitors in real time through the lower dead point limiting or reflected light intensity to ensure that the termination position stays within ±10 µm of the top of the AD pure adhesive bonding layer, thereby obtaining a window bottom surface with a flatness Ra≤4 µm. It can solve the problem of large position deviation of the window bottom surface caused by traditional depth control relying on manual experience or time control, and the rough surface, uneven residual glue and subsequent bulging of the flexible window of multi-layer FPC after opening, and realize real-time monitoring and automatic limiting termination to improve the depth control precision and avoid damaging the lower layer of conductive copper layer, providing structural protection for subsequent differential pressing and stability of flexible functional area.

[0017] It should be noted that the UV laser-mechanical composite mold integrates a variable diffracted beam shaping unit and a copper layer back reflectivity real-time monitoring module during the second stage fine machining process; the beam shaping unit dynamically adjusts the pulsed energy density distribution according to the window corner curvature radius and local adhesive film thickness, so that the laser spot size is in the range of 12 µm–40 µm with gradient transition; the reflectivity monitoring module collects the second harmonic signal reflected from the AD glue-copper interface through the double-channel photodiode integrated in the focusing head sidewall, and judges the critical exposure point of the copper layer and sends a stop command to the numerical control system through the adaptive threshold algorithm, thereby improving the termination depth control accuracy to ±5 µm, reducing the maximum roughness Ra of the window bottom surface to below 3 µm, and the copper layer surface scratch defect rate is less than 0.5 %, effectively solving the process problem of overcutting-undercutting coexistence of micro windows.

[0018] Preferably, the preset window is linearly arranged 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 multi-folding requirement, multiple windows are arranged in an equidistant or staggered manner, and the center distance between adjacent windows is ≥ 1.5 W.

[0019] In this embodiment, the preset window is linearly arranged along the folding axis, and the window length is 90%-100% of the effective length of the folding axis, which can solve the problem of unreasonable size setting of the traditional flexible window, which fails to cover the complete folding area, resulting in local bending stress concentration and structural fatigue, and realize continuous and uniform coverage of the flexible area on the entire effective folding section, thereby improving the 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, which can solve the problem of insufficient mechanical strength caused by excessively wide window or excessively high bending stiffness caused by excessively narrow window in the existing window design, realize the optimal balance between flexibility and structural integrity in the window geometry, and ensure smooth folding and long-term failure-free. When there are multiple folding requirements, multiple windows are arranged in an equidistant or staggered manner, which can solve the problem of uneven stress distribution of the flexible area in the multiple folding scenario, which is prone to local fatigue cracks, realize the spatial optimization of the window structure and the discrete distribution of the folding path, and improve the reliability of the multiple folding of the whole plate. The center distance between adjacent windows is ≥ 1.5 W, which can solve the problem of structural weakening and thermal stress superposition caused by excessively dense arrangement of multiple windows, realize reasonable redundancy and stress buffering between window areas, and balance the continuity of the flexible area and the mechanical strength of the whole plate.

[0020] It should be noted that the window width W can be designed in a gradient manner along the folding axis direction: taking the folding center as the symmetry axis, gradually widening or narrowing to both sides at a linear gradient of 0.05 mm / 10 mm, and setting a tapered transition section at the folding end point, the transition section length accounting for 5%-8% of the total window length; at the same time, a circular arc buffer zone with a radius of R / 2 is added at both ends of the folding axis, and the circular arc buffer zone and the linear window are smoothly connected through a third-order Bezier curve; the gradient-circular arc composite window is iteratively optimized by finite element thermal-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.

[0021] Preferably, before the window is opened by the controlled mold, a hollow area with a four-side margin of 0.2 mm-0.4 mm is formed in the first polyimide insulating layer corresponding to the window projection area, and the hollow edge adopts a round corner transition structure to limit the lateral flow of the resin in the subsequent pressing and inhibit the window bulging.

[0022] In this embodiment, a hollow area with a 0.2 mm-0.4 mm margin is formed in the first polyimide insulating layer corresponding to the window projection area. This can solve the problem of uneven thickness and local resin accumulation in the flexible window area caused by the unconstrained flow of resin in the window area during the traditional lamination process. The resin filling boundary can be effectively guided by the local material pre-reserved cavity, and the diffusion of the resin to the central area is limited, thereby obtaining a flexible area with uniform thickness and stable structure. The round corner transition structure of the hollow edge can solve the problem of stress concentration caused by sharp corners or sudden changes in the hollow edge, and can prevent cracks, wrinkles or thermal stress peeling at the window boundary after lamination. The stress continuity and smooth transition of the interface during the lamination process of the resin are realized, and the interfacial bonding strength and thermal mechanical stability of the flexible window area are improved.

[0023] Preferably, the hard pressing plate is an aluminum plate with a thickness of 0.2 mm-0.4 mm and an anodized hard film, and the soft cushion is a silicone pad with a Shore A hardness of 35-55 and a thickness of 0.6 mm-1.5 mm. The surface of the hard pressing plate and the soft cushion is covered with a PTFE release film. The differential pressure ΔP = P1-P2 is controlled by a pressure sensor array in a closed loop, and ΔP is positively correlated with the window width W and the total thickness H of the non-windowed area, so as to form a controllable stress release band at the window boundary and reduce the stress concentration at the folding point.

[0024] In this embodiment, the hard pressing plate is an aluminum plate with a thickness of 0.2 mm-0.4 mm and an anodized hard film, and the soft cushion is a silicone pad with a Shore A hardness of 35-55 and a thickness of 0.6 mm-1.5 mm. The surface of the hard pressing plate and the soft cushion is covered with a PTFE release film, which can solve the problems of uneven heat pressing, interface contamination and pressing plate residual marks caused by material mismatching or adhesion during the traditional lamination process, and realize the collaborative lamination of high-strength rigid support and flexible cushioning. At the same time, the PTFE release film can prevent material adhesion and ensure the surface quality of the window area and the non-window area. The differential pressure ΔP = P1-P2 is controlled by a pressure sensor array in a closed loop, which can solve the problems of pressure fluctuation and uneven regional stress caused by manual pressure adjustment or single-point pressure measurement in the conventional lamination process, realize accurate differential pressure adjustment based on multi-point feedback, and improve the controllability and repeatability of the lamination process. The differential pressure ΔP = P1-P2 is controlled by a pressure sensor array in a closed loop, which can solve the problems of pressure fluctuation and uneven regional stress caused by manual pressure adjustment or single-point pressure measurement in the conventional lamination process, realize accurate differential pressure adjustment based on multi-point feedback, and improve the controllability and repeatability of the lamination process. ΔP is positively correlated with the window width W and the total thickness H of the non-windowed area, which can solve the problems of stress mutation and edge folding point failure caused by the difference in structural thickness between the window area and the non-windowed area, realize dynamic matching of the lamination differential pressure according to the structural geometric parameters, and construct a gradual stress release band at the window boundary to reduce the risk of rupture and stress fatigue accumulation at the folding initial point.

[0025] Preferably, after the windowing is completed, an annular cover film with a width of 0.3 mm-0.6 mm and a thickness of 18 µm-25 µm is attached to the surface of the first polyimide insulating layer around the window, which is used to block the lateral flow of the AD pure adhesive bonding layer resin into the window area during the pressing process, to ensure the uniform thickness of the window area.

[0026] In this embodiment, an annular cover film with a width of 0.3 mm-0.6 mm and a thickness of 18 µm-25 µm is attached to the surface of the first polyimide insulating layer around the window, which is used to block the lateral flow of the AD pure adhesive bonding layer resin into the window area during the pressing process, to solve the problem of glue accumulation, thickness unevenness and interface mutation caused by lateral disordered flow of resin during hot pressing, and to achieve effective physical barrier band construction at the edge of the flexible window, guiding the resin to solidify in the non-window area during the pressing stage, ensuring the thickness and structure uniformity of the window area.

[0027] Preferably, the process of hot pressing the initial stack as a whole includes a vacuum exhaust stage, a temperature rising and glue exhausting stage, a constant temperature curing stage and a controlled cooling stage; the temperature-pressure curve of each stage is parameterized set according to the curing characteristics of the AD pure adhesive bonding layer, and closed-loop control of temperature-pressure is used to ensure the interlayer bonding strength and the flatness of the board.

[0028] In this embodiment, the process of hot pressing the initial stack as a whole includes a vacuum exhaust stage, a temperature rising and glue exhausting stage, a constant temperature curing stage and a controlled cooling stage, which can solve the problems of extensive traditional hot pressing process and uncontrollable heat-pressure coupling process, resulting in residual gas between layers, incomplete glue exhausting or incomplete curing, and achieve phased management of resin flow, gas exhausting and structure curing throughout the process, improving the interlayer bonding uniformity and structure stability of FPC stack. The temperature-pressure curve of each stage is parameterized set according to the curing characteristics of the AD pure adhesive bonding layer, which can solve the problem of insufficient universality of fixed heating or pressure curve in existing pressing, and achieve personalized hot pressing parameters for the adhesive material used, to ensure its full crosslinking and curing at the optimal reaction temperature and time. Closed-loop control of temperature-pressure is used to ensure the interlayer bonding strength and the flatness of the board, which can solve the problem of lack of feedback adjustment mechanism in traditional open pressing process, resulting in significant impact of temperature or pressure fluctuation on pressing quality, and achieve real-time monitoring and accurate adjustment of process conditions during the whole hot pressing process, to stabilize the interlayer glue film state and improve the consistency of bonding firmness and flatness of the final board.

[0029] Preferably, a water-soluble release agent is pre-applied to the interface between the second copper-clad layer and the AD pure adhesive bonding layer, and when the controlled mold cutting or laser beam touches the interface, the reflected signal changes abruptly, triggering the windowing termination by the signal processing module in time, to avoid scratching the second copper-clad layer.

[0030] In this embodiment, the water-soluble release agent is pre-applied at the interface between the second copper-clad layer and the AD pure adhesive bonding layer. This can solve the problem of lack of effective physical or optical interface identification means in the traditional delamination cutting process, leading to difficulty in accurately determining the termination depth during the cutting process. It can construct an intermediate layer with identifiable signal characteristics at the key interface, providing a stable and controllable termination reference point for subsequent processing. When the controlled mold cutting or laser beam reaches the interface, the reflected signal changes abruptly, triggering the window termination immediately by the signal processing module. This can solve the problem of scratches, fractures or reliability reduction of the second copper-clad layer caused by overcutting or delayed shutdown in existing processes. It realizes a real-time identification mechanism based on the abrupt change of the reflected signal, triggers a high-response termination instruction, and accurately controls the window termination depth.

[0031] Preferably, a V-shaped micro-notch with a depth of 4-8 pm, a power of ≤5 W, a wavelength of 355 nm, and a distance of 0.15-0.25 mm from the window edge is formed on the surface of the second polyimide insulating layer on both sides of the long side of the window to release micro-stress and reduce circumferential stress concentration during folding.

[0032] In this embodiment, a V-shaped micro-notch with a depth of 4-8 pm, a power of ≤5 W, a wavelength of 355 nm, and a distance of 0.15-0.25 mm from the window edge is formed on the surface of the second polyimide insulating layer on both sides of the long side of the window. This can solve the problem of circumferential stress concentration, material cracking or micro-wrinkling in the folding area of the multi-layer FPC during hot pressing and long-term bending. It can construct a structural micro-release zone around the window edge to effectively buffer and disperse stress during folding, thereby improving the mechanical stability and fatigue life of the flexible area. The UV laser with a power of ≤5 W and a wavelength of 355 nm can process a depth of 4-8 pm. This can solve the problem of large damage to the surface of polyimide, edge coking or uncontrollable micro-cracks caused by conventional mechanical or high-power laser processing. It can achieve high-precision, low-heat-affected shallow notch processing without damaging the underlying functional layer, ensuring structural integrity and process safety. The V-shaped micro-notch with a distance of 0.15-0.25 mm from the window edge can solve the problem of structural weakening or ineffective stress release caused by improper notch position setting. It can establish a directional stress unloading path in the key area near the stress concentration, optimize the stress distribution characteristics of the boundary area, and prevent material damage or functional failure at the folding point.

[0033] Preferably, when the same FPC control board needs to form multiple flexible regions, differentiated windowing depths are performed for different folding regions: the first region only removes the third copper-clad layer; the second region removes the third copper-clad layer and the second polyimide insulating layer; the third region further removes the AD pure adhesive bonding layer; and the pressing temperature, pressure and holding time are independently set for each region according to a preset pressing parameter table, so as to integrate multiple flexible folding levels on one board.

[0034] In the embodiment, when the same FPC control board needs to form multiple flexible regions, differentiated windowing depths are performed for different folding regions, which can solve the problem that multiple bending performance requirements cannot be realized on a single FPC board in the existing process, leading to the problems of multiple board combination, complex structure and inconvenient assembly for similar products, and realize flexible configuration of different flexible level regions in the same control board to meet the differentiated requirements of folding radius, thickness and flexibility at different positions in complex display structures. The first region only removes the third copper-clad layer, the second region removes the third copper-clad layer and the second polyimide insulating layer; and the third region further removes the AD pure adhesive bonding layer, which can solve the problem that the traditional window opening process cannot accurately peel off different structural layers, which easily leads to window uniformity and cannot form multi-level flexible windows, and realize the formation of thinning regions with different thicknesses and mechanical responses by controlling the number of removed layers to construct multi-level flexible characteristics from the structural level. The pressing temperature, pressure and holding time are independently set for each region according to a preset pressing parameter table, which can solve the problem of local overpressure or underpressure caused by uniform hot pressing parameters in the traditional hot pressing process, leading to inconsistent performance of different flexible regions, and realize fine parameter matching according to the thickness difference and material response characteristics of the region, so that each flexible level region obtains optimal pressing quality and structural morphology.

[0035] It should be noted that after the multi-level flexible region pressing is completed, a CO2 laser scanning head with a center wavelength of 10.6 µm is used to perform surface heating on the third region according to a preset thermal field distribution, so that the AD pure adhesive bonding layer is locally heated to 110 °C and maintained for 25 seconds to release the pressing residual stress; at the same time, clean nitrogen at a temperature of 18 °C is blown into the second region to form a thermal gradient barrier, preventing the thermal influence from diffusing to the second region and the first region, thereby further reducing the interface residual stress of the multi-level flexible region.

[0036] Preferably, when the number of copper-clad layers of the multi-layer FPC control board is N, N ≥ 3, the kth layer and all functional layers below it are selected from the bottom copper-clad layer upwards to implement through windowing, 1 ≤ k < N–1; and during pressing, the reverse layering strategy is adopted, the hard pressing plate and the main pressure are located on the non-windowed side, and the soft buffer pad and the auxiliary pressure are located on the windowed side, so as to ensure the forming consistency of the multi-level folding region.

[0037] In the embodiment, when the number of copper-clad layers of the multi-layer FPC control board is N, N ≥ 3, according to the target folding topography, the kth layer and all functional layers below it are selected from the bottom copper-clad layer upwards to implement through windowing, 1 ≤ k < N-1, which can solve the problem that the traditional FPC only partially opens windows on the top layer or the middle layer, and is difficult to meet the complex or large-angle folding requirements, and realizes accurate control of the windowing level in the structural depth according to the target folding curvature and deformation requirement, realizes the through thinning of the flexible area from the surface layer to the deep layer, and thus supports the application scenarios of larger folding radius or higher bending frequency. During pressing, the reverse layering strategy is adopted, the hard pressing plate and the main pressure are located on the non-windowing side, and the soft buffer pad and the auxiliary pressure are located on the windowing side, which can solve the problem of uneven pressure in the multi-stage windowing area, easy bulging or collapse of the flexible area in the conventional pressing layout, and realize the reverse distribution of the structure, utilize the rigid pressing plate to provide high-pressure shaping and suppress the warping of the non-windowing area, and at the same time utilize the buffer pad to form a soft fit in the windowing area, effectively control the local topography change.

[0038] It should be noted that the above embodiments are only preferred specific embodiments of the present application, and the protection scope of the present application is not limited thereto. Any changes or replacements within the technical range disclosed by the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application. The protection scope of the present application 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, The method comprises the following steps: aligning each functional layer in sequence on a reference fixture by 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 glue bonding layer, a second polyimide insulating layer, and a third copper-clad layer; adopting a controlled mold to open a window along a preset folding axis from the third copper-clad layer, sequentially removing the corresponding window materials of the third copper-clad layer, the second polyimide insulating layer, and the AD pure glue bonding layer, until the back surface of the second copper-clad layer is exposed without causing mechanical damage thereto, to form a thickness-reduced area in the initial stack; laying a hard press plate on the side without the window and a soft cushion on the side with the window; applying a main pressure P1 from the side without the window and a secondary pressure P2 from the side with the window, with P1 being greater than P2; and thermally pressing the initial stack as a whole by differential pressure, so that the windowed area remains bendable due to the overall thickness reduction and lower back pressure, while the non-windowed area remains rigid due to the original thickness and higher back pressure; after the pressing pressure is maintained until the AD pure glue bonding layer is cured, cooling to a safe temperature according to a preset cooling curve, releasing the pressure, and obtaining an integrated multi-layer FPC control panel containing both a flexible windowed area and a rigid area.

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 comprises: presetting a plurality of positioning pins and through holes corresponding to the process reference of the functional layer on the reference fixture, and setting a vacuum adsorption platform with a flatness of not greater than 0.02 mm to provide an interlayer reference plane; placing the first copper-clad layer on the reference fixture, allowing its reference hole to be sleeved with the positioning pin to complete coarse positioning, then recognizing the optical target of the layer by the upper visual system, correcting the movement and rotation deviation by the micro-displacement platform, and starting local vacuum adsorption fixation; placing the first polyimide insulating layer, the second copper-clad layer, the AD pure glue bonding layer, the second polyimide insulating layer, and the third copper-clad layer in sequence, each layer first being hung on the positioning pin by the corresponding mechanical positioning hole to complete preliminary positioning, then the optical target of each layer being recognized by the upper visual system, and the features of the target being compared with those of the target of the previously fixed layer to automatically eliminate the interlayer movement and rotation deviation by driving the micro-displacement platform, and then being fixed by vacuum adsorption; after all the functional layers are aligned and fixed, the fixture peripheral vacuum ring is used to one-time extract the residual air between the layers to obtain the initial stack which can directly enter the subsequent windowing process.

3. The production method of a multilayer FPC control board for display device manufacturing according to claim 1, characterized by, The controlled mold is a stepped limiting knife edge metal hard mold or a UV laser-mechanical composite mold; the windowing process of the controlled mold is performed according to two-stage depth control: the first stage uses a rough machining knife edge or a high-power laser to quickly remove the preset window materials of the third copper-clad layer and the second polyimide insulating layer; the second stage switches to a fine machining micro-knife edge or a low-power pulsed laser, and the termination position is ensured to stay within ±10 µm of the top of the AD pure glue bonding layer by real-time monitoring through lower dead point limiting or reflected light intensity, thereby obtaining a window bottom surface with a flatness Ra≤4 µm.

4. The production method of a multi-layer FPC control board for display device manufacturing according to claim 1, characterized by, The preset window is linearly arranged along the folding axis, the window length is 90%-100% of the effective length of the folding axis, the window width W satisfies 0.4 mm ≤ W ≤ 2.5 mm and W ≤ the target minimum bending radius R; when there is a multi-folding requirement, a plurality of windows are arranged in an equidistant or staggered manner, and the center distance between adjacent windows is ≥ 1.5 W.

5. The production method of a multi-layer FPC control board for display device manufacturing according to claim 1, characterized by, Before the controlled mold is opened, a hollow area with a 0.2 mm-0.4 mm margin is formed in the first polyimide insulating layer corresponding to the window projection area, and the hollow edge adopts a round corner transition structure to limit the lateral flow of resin in the subsequent pressing and suppress the window bulging.

6. The production method of a multilayer FPC control board for display device manufacturing according to any one of claims 1 to 5, characterized in that, The hard pressing plate is an aluminum plate with a thickness of 0.2 mm-0.4 mm and an anodized hard film treatment, 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, and the surface of the hard pressing plate and the soft buffer pad is covered with a PTFE release film; The differential pressure ΔP = P1-P2 is controlled by a pressure sensor array, and ΔP is positively correlated with the window width W and the total thickness H of the unopened window area, so as to form a controllable stress release belt at the window boundary and reduce the stress concentration at the folding point.

7. The production method of a multilayer FPC control board for display device manufacturing according to claim 6, characterized by, After the window is opened, a ring-shaped cover film with a width of 0.3 mm-0.6 mm and a thickness of 18 µm-25 µm is pasted on the surface of the first polyimide insulating layer around the window, which is used to block the lateral flow of AD pure glue bonding layer resin into the window area during pressing, so as to ensure the uniform thickness of the window area.

8. The production method of a multilayer FPC control board for display device manufacturing according to any one of claims 1 to 5, characterized in that, The process of hot pressing the initial stack as a whole includes: vacuum exhaust stage, temperature rising and degassing stage, constant temperature curing stage and controlled cooling stage; the temperature-pressure curve of each stage is parameterized set according to the curing characteristics of AD pure glue bonding layer, and is controlled by temperature-pressure closed loop to ensure the interlayer bonding strength and the flatness of the plate surface.

9. The production method of a multi-layer FPC control board for display device manufacturing according to any one of claims 1 to 5, characterized in that, A water-soluble release agent is pre-coated on the interface between the second copper-clad layer and the AD pure glue bonding layer, when the controlled mold cutting or laser beam touches the interface, the reflected signal changes suddenly, and the window opening is terminated immediately by the signal processing module, avoiding scratching the second copper-clad layer.

10. The production method of a multilayer FPC control board for display device manufacturing according to any one of claims 1 to 5, characterized in that, A V-shaped micro notch with a power ≤ 5 W and a wavelength of 355 nm is engraved on the surface of the second polyimide insulating layer on both sides of the window long side, with a depth of 4 µm-8 µm and a distance of 0.15 mm-0.25 mm from the window edge, to release micro stress and reduce the folding circumferential stress concentration.

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