Special-shaped FPC and manufacturing method thereof

Abstract

According to the special-shaped FPC and the manufacturing method thereof, the pre-formed special-shaped flexible base material layer is arranged, the shape of the pre-formed special-shaped flexible base material layer is directly matched with the special-shaped surface of a target installation space, and a circuit layer, an insulation covering layer and a special-shaped supporting layer are all attached to the special-shaped surface of the special-shaped flexible base material layer, so that the FPC does not need to be forcibly bent, twisted or stretched subsequently, and the production efficiency is improved. The problems of circuit breakage and delamination caused by stress concentration are fundamentally avoided, the structural stability of the FPC is improved, and the service life of the FPC is prolonged. The flexible circuit board is used for solving the technical problem that in order to achieve special-shaped layout, the plane of an existing flexible circuit board generally needs to be forcibly bent, twisted or stretched.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board technology, specifically to an irregularly shaped FPC and its manufacturing method. Background Technology

[0002] Flexible printed circuit boards (FPCs) are widely used in consumer electronics, automotive electronics, and medical devices due to their bendability, thinness, and ability to perform three-dimensional wiring. As product designs increasingly pursue miniaturization, high integration, and irregular spatial layouts, higher requirements are being placed on the shape and structure of FPCs.

[0003] To achieve irregularly shaped layouts, existing flexible circuit boards typically require forced bending, twisting, or stretching of their planes. This causes a sharp concentration of stress at local sharp angles or curved surfaces, easily leading to micro-cracks in the copper foil, delamination of the cover film, and even circuit breakage. This mechanically forced deformation is uncontrollable and unsustainable. During use, stress relaxation or environmental temperature changes can cause shape rebound and poor contact, severely affecting the electrical reliability and durability of the product during long-term operation in a compact three-dimensional space. Summary of the Invention

[0004] The purpose of this invention is to provide an irregularly shaped FPC and its manufacturing method, so as to solve the technical problem that existing flexible circuit boards usually need to be forcibly bent, twisted or stretched to achieve irregular layouts.

[0005] The technical solution of this invention is implemented as follows:

[0006] On one hand, the present invention provides an irregularly shaped FPC, comprising an irregularly shaped flexible substrate layer, a circuit layer, an insulating cover layer and an irregularly shaped support layer stacked sequentially;

[0007] The irregularly shaped flexible substrate layer includes a pre-formed irregularly shaped structure whose shape matches the irregularly shaped surface of the target installation space;

[0008] The circuit layer is fabricated on the upper surface of the irregularly shaped flexible substrate layer and is attached to the irregularly shaped surface of the irregularly shaped flexible substrate layer; the insulating cover layer covers the upper surface of the circuit layer; the irregularly shaped support layer is fabricated on the lower surface of the irregularly shaped flexible substrate layer and matches the irregularly shaped surface of the irregularly shaped flexible substrate layer.

[0009] A further technical solution is that the irregular structure includes at least one of arc shape, stepped shape, wavy shape or irregular curved surface, with a thickness of 0.02-0.1mm.

[0010] A further technical solution is that the circuit layer is made of copper foil with a thickness of 0.01-0.05mm, a line width of 0.03-0.1mm, and a line spacing of 0.03-0.1mm.

[0011] A further technical solution is that an opening is provided on the insulating cover layer at the position of the pad corresponding to the circuit layer, and the shape of the opening matches the pad.

[0012] A further technical solution is that the irregular support layer is provided with a number of uniformly distributed weight-reducing holes, the diameter of which is 0.5-2mm and the spacing between adjacent weight-reducing holes is 2-5mm.

[0013] On the other hand, the present invention provides a method for manufacturing irregularly shaped FPCs, comprising the following steps:

[0014] Step S1: Design the irregular mold according to the irregular surface parameters of the target installation space;

[0015] Step S2: Deposit a copper layer on the upper surface of the irregular flexible substrate layer, and then form a circuit pattern through photoresist coating, exposure, development and etching processes;

[0016] Step S3: Use screen printing technology to print photosensitive solder resist ink onto the upper surface of the circuit layer, and then perform pre-baking, exposure, development and curing processes;

[0017] Step S4: Coat the lower surface of the irregular flexible substrate layer with flexible epoxy resin composite material, place it in the molding mold and press and cure it to generate an irregular FPC model;

[0018] Step S5: Cut, polish, and clean the irregular FPC model to obtain the finished product.

[0019] A further technical solution is that step S1 specifically includes:

[0020] Step S11: Obtain the three-dimensional parameters of the irregular surface of the target installation space, and clarify the curvature, size and boundary contour of the irregular surface;

[0021] Step S12: Based on the three-dimensional parameters, perform structural design of the irregular mold to determine the matching of the mold cavity shape and the irregular surface;

[0022] Step S13: Simulate and verify the designed mold structure;

[0023] Step S14: Fabricate irregular-shaped molds according to the verified design scheme;

[0024] Step S15: The polyimide or polyester substrate is formed in a shaped mold by hot pressing. The hot pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 30-60min. After forming, it is naturally cooled to room temperature.

[0025] A further technical solution is that step S2 specifically includes:

[0026] Step S21: Clean the upper surface of the irregular flexible substrate layer to remove surface impurities and oxide layer, and deposit a copper layer on the pretreated substrate surface using vacuum sputtering or chemical copper plating process to form a uniform conductive substrate.

[0027] Step S22: Coat the photoresist and pre-bake it to evenly cover the irregular surface with the photoresist;

[0028] Step S23: After aligning and bonding the circuit pattern mask with the photoresist layer, expose the image to transfer the circuit pattern to the photoresist layer.

[0029] Step S24: The unexposed photoresist is removed by development, the exposed copper layer is removed by etching, and the residual photoresist is stripped off to form a preset circuit pattern.

[0030] A further technical solution is that step S3 specifically includes:

[0031] Step S31: Use screen printing technology to print photosensitive solder resist ink onto the upper surface of the circuit layer, covering the non-pad area;

[0032] Step S32: Pre-baking the printed photosensitive solder resist ink, aligning and bonding the window pattern mask with the ink layer, and then exposing it. After development, the unexposed ink is removed to expose the solder pad area.

[0033] Step S33: Curing the ink layer to form an insulating covering layer.

[0034] A further technical solution is that step S4 specifically includes:

[0035] S41. Clean and pre-treat the lower surface of the irregularly shaped flexible substrate layer;

[0036] S42. Apply flexible epoxy resin composite material to the lower surface of the pretreated substrate;

[0037] S43. Place the coated substrate into the matching molding die and position it.

[0038] S44. Press the mold together.

[0039] S45. Maintain the pressed state and carry out curing treatment. After curing, demold to obtain the irregular support layer.

[0040] The beneficial effects of this invention are as follows:

[0041] 1. The irregularly shaped FPC of the present invention has a pre-formed irregularly shaped flexible substrate layer whose shape directly matches the irregular surface of the target installation space. The circuit layer, insulation cover layer and irregularly shaped support layer are all attached to the irregular surface of the irregularly shaped flexible substrate layer. There is no need to forcibly bend, twist or stretch the FPC afterward, which fundamentally avoids the problems of circuit breakage and delamination caused by stress concentration, and improves the structural stability and service life of the FPC.

[0042] 2. The irregularly shaped FPC of the present invention has each layer structure that fits the irregularly shaped surface, which can achieve a close fit with the installation space, avoid the problems of misalignment and loosening, ensure the stability of electrical connection, and improve the reliability of electronic equipment.

[0043] 3. The manufacturing method of the present invention directly prepares the irregular flexible substrate layer through hot pressing and other processes. The subsequent preparation processes of each layer are adapted to the irregular substrate, eliminating the need for additional bending and twisting processing steps, reducing production steps, tooling equipment and labor costs, and each process parameter is controllable, with high processing accuracy, which is conducive to mass production.

[0044] 4. The irregular support layer enhances the structural strength and shape retention of the irregular FPC, while the weight-reducing hole design reduces the product weight while ensuring strength, meeting the development needs of miniaturization and lightweight electronic devices; the insulating cover layer uses photosensitive solder resist ink and is formed by screen printing process, which can cover the circuit layer, has good insulation protection effect, and is highly compatible with irregular structures. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of an irregularly shaped FPC structure according to the present invention;

[0046] Figure 2 This is a step diagram illustrating an irregularly shaped FPC and its manufacturing method according to the present invention.

[0047] In the figure, 1 is the irregularly shaped flexible substrate layer; 2 is the circuit layer; 3 is the insulating covering layer; and 4 is the irregularly shaped support layer. Detailed Implementation

[0048] To better understand the technical content of this invention, specific embodiments are provided below, and the invention will be further described in conjunction with the accompanying drawings.

[0049] See Figure 1 The present invention provides an irregularly shaped FPC, comprising an irregularly shaped flexible substrate layer 1, a circuit layer 2, an insulating cover layer 3, and an irregularly shaped support layer 4 stacked sequentially.

[0050] In this embodiment, the irregularly shaped flexible substrate layer 1 is an arc-shaped structure (adapting to the arc-shaped installation space of a wearable device), made of polyimide material with a thickness of 0.05mm, and has good flexibility and shape retention capabilities; the circuit layer 22 is made of copper foil with a thickness of 0.03mm, formed by laser etching process, with a circuit width of 0.05mm and a circuit spacing of 0.05mm, and is tightly attached to the upper surface of the irregularly shaped flexible substrate layer 1; the insulating cover layer 3 is made of photosensitive solder resist ink and covers the upper surface of the circuit layer 2, with openings corresponding to the pads of the circuit layer 2, and the shape of the openings matching the pads; the irregularly shaped support layer 4 is made of flexible epoxy resin composite material with 15wt% glass fiber powder added, with a thickness of 0.1mm, and is attached to the lower surface of the irregularly shaped flexible substrate layer 1, with weight-reducing holes of 1mm diameter and 3mm spacing evenly arranged on it.

[0051] like Figure 2 As shown, this embodiment also provides a method for manufacturing the above-mentioned irregular-shaped FPC, including the following steps:

[0052] Step S1: Design the irregular mold according to the irregular surface parameters of the target installation space;

[0053] Specifically, based on the core requirement that irregularly shaped FPC products need to be compatible with the target installation space, a mold structure with corresponding irregular contours is constructed by extracting and transforming the key parameters of the irregular surface of the installation space, so as to provide a stable structural benchmark and positioning guarantee for the subsequent molding process of irregularly shaped FPCs.

[0054] Specifically, the first step is to obtain complete parameters of the irregular surface of the target installation space through 3D scanning and mapping, including key information such as the contour curve, curvature change, dimensional tolerance, and assembly interface position of the irregular surface. This ensures that the extracted parameters are complete and reflect the actual structural requirements of the installation space. Then, the extracted irregular surface parameters are converted into technical parameters for mold design. Professional design software such as CAD is used to model the core structure of the mold cavity and mold core, ensuring a proper fit between the inner surface contour of the mold cavity and the irregular surface contour of the target installation space. Simultaneously, the molding processability of the mold is considered, such as setting reasonable draft angles and guiding structures to ensure the smooth implementation of subsequent pressing and curing processes. Finally, the designed irregular mold provides structural constraints for the subsequent coating, pressing, and curing of flexible epoxy resin composite materials. This allows the flexible substrate and composite material to cure under the limiting and shaping action of the mold, forming a structural shape that perfectly matches the irregular surface of the installation space. This ensures from the source that the final irregular FPC product can be embedded into the target installation space and meet assembly size requirements.

[0055] Furthermore, step S1 specifically includes:

[0056] Step S11: Obtain the three-dimensional parameters of the irregular surface of the target installation space, and clarify the curvature, size and boundary contour of the irregular surface;

[0057] Step S12: Based on three-dimensional parameters, design the structure of the irregular mold and determine the matching of the mold cavity shape and the irregular surface;

[0058] Step S13: Simulate and verify the designed mold structure;

[0059] Step S14: Fabricate irregular-shaped molds according to the verified design scheme;

[0060] Step S15: The polyimide or polyester substrate is formed in a shaped mold by hot pressing. The hot pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 30-60min. After forming, it is naturally cooled to room temperature.

[0061] Specifically, key geometric feature parameters of the irregular surface of the target installation space are captured through 3D scanning, mapping, and other technologies. This ensures that the acquired parameters are complete and reflect the actual structural requirements of the installation space, providing original data support for subsequent mold design and avoiding mismatch between the mold and the installation space due to parameter deviations. The acquired 3D parameters are then converted into a mold model, which is constructed using professional design software such as CAD. This ensures that the inner surface contour of the mold cavity complements the irregular surface of the target installation space, while also considering the mold's manufacturability and the convenience of subsequent substrate molding. Finite element simulation and other technologies are used to simulate the stress state of the mold, cavity deformation, and the fit between the substrate and the cavity during the subsequent hot pressing process of the substrate. This allows for the early detection of potential defects in the mold structure design, such as stress concentration and poor fit. Simulation optimizes the mold structure parameters, ensuring the mold's structural stability and molding reliability. Based on the design scheme that has passed simulation verification, precision machining processes such as CNC machining and EDM are used to process the mold blank into a solid mold that meets the design requirements. This ensures that the mold cavity dimensions and contours meet the design standards, providing a structural constraint for the irregular substrate molding. Utilizing the thermoplastic properties of polyimide or polyester substrates, under set hot-pressing parameters, the substrate softens upon heating and then tightly conforms to the mold cavity contour under pressure. Heat preservation and pressure holding ensure the substrate is fully shaped, followed by natural cooling to room temperature to maintain its final irregular shape. The precisely defined hot-pressing temperature, pressure, and heat preservation / pressure holding time parameters are determined based on the substrate's thermal properties and molding requirements. This ensures that the substrate has structural stability after molding, is free from warping or deformation, and matches the mold cavity, ultimately resulting in an irregularly shaped flexible substrate adapted to the target installation space, providing a support foundation for subsequent processes such as circuit pattern fabrication.

[0062] Step S2: Deposit a copper layer on the upper surface of the irregular flexible substrate layer 1, and then form a circuit pattern through photoresist coating, exposure, development and etching processes;

[0063] First, a copper layer is deposited on the upper surface of the irregularly shaped flexible substrate layer 1. Conventional and mature technologies in the field, such as physical vapor deposition (e.g., sputtering, evaporation), chemical vapor deposition, or electroless plating, are used to ensure that copper atoms are uniformly and densely attached to the upper surface of the irregularly shaped substrate, forming a continuous conductive copper layer. During the deposition process, process parameters (e.g., deposition temperature, rate, and time) need to be controlled to ensure that the copper layer has good adhesion to the surface of the irregularly shaped substrate, while ensuring that the conductivity of the copper layer itself is stable and can adapt to the deformation characteristics of the flexible substrate, so as to avoid problems such as copper layer peeling or breakage during subsequent processes or use. The process then proceeds sequentially with photoresist coating, exposure, and development. The core principle is to utilize the photochemical sensitivity of photoresist to delineate the circuit area: First, a coating process (such as spin coating or roll coating) is used to uniformly cover the copper layer surface with photoresist, forming a photoresist film of uniform thickness. The coating process must adapt to the irregular contour of the substrate to ensure that the film layer is free of defects such as missed coating or bubbles. Then, the pre-made circuit pattern mask is aligned with the photoresist film layer, and the alignment reference is adjusted according to the contour characteristics of the irregular substrate. Subsequently, exposure processing is performed to cause specific photochemical reactions in the exposed areas of the photoresist (positive photoresist is soluble in the developer after exposure, while negative photoresist is insoluble in the developer after exposure). Next, the development process is carried out using the corresponding type of developer to remove the photoresist areas that have not undergone the expected photochemical reaction. Finally, the copper layer areas corresponding to the lines that need to be retained are completely covered and protected by photoresist, while the copper layers in non-line areas are completely exposed. Finally, an etching process is performed, which uses the chemical dissolution reaction between the etching solution (such as acidic etching solution or alkaline etching solution) and copper to selectively remove the exposed redundant copper layer. During the etching process, the etching time, temperature and etching solution concentration must be controlled to ensure that the redundant copper layer is completely removed without damaging the copper layer of the circuit protected by the photoresist or destroying the structural integrity of the irregular flexible substrate.

[0064] Furthermore, step S2 specifically includes:

[0065] Step S21: Clean the upper surface of the irregular flexible substrate layer 1 to remove surface impurities and oxide layer, and deposit a copper layer on the pretreated substrate surface using vacuum sputtering or chemical copper plating process to form a uniform conductive substrate.

[0066] Step S22: Coat the photoresist and pre-bake it to evenly cover the irregular surface with the photoresist;

[0067] Step S23: After aligning and bonding the circuit pattern mask with the photoresist layer, expose the image to transfer the circuit pattern to the photoresist layer.

[0068] Step S24: The unexposed photoresist is removed by development, the exposed copper layer is removed by etching, and the residual photoresist is stripped off to form a preset circuit pattern.

[0069] Specifically, the pre-treatment cleaning removes oil, dust, and oxide layers from the substrate surface through plasma cleaning, solvent wiping, etc., improving the surface activity of the substrate and the adhesion of the subsequent copper layer, and avoiding insufficient adhesion and deterioration of conductivity of the copper layer due to impurities or oxide layers. Vacuum sputtering or chemical copper plating processes use physical or chemical actions to uniformly and densely deposit copper atoms on the surface of the pre-treated irregular substrate. Vacuum sputtering uses high-energy particles to bombard the copper target to cause copper atoms to escape and deposit, while chemical copper plating uses an oxidation-reduction reaction to reduce and deposit copper ions on the substrate surface. Both processes can adapt to the curved contours of irregular substrates, ensuring the uniformity of copper layer thickness and conductivity stability, and finally forming a continuous conductive substrate that meets the requirements of subsequent circuit etching. Coating methods such as roller coating and spraying, adapted to irregularly shaped surfaces, are used to evenly spread the photoresist on the copper layer surface. Pre-baking (typically 80-120℃) removes the solvent from the photoresist, improving the dryness and adhesion of the photoresist film. This prevents film peeling and deformation during subsequent exposure and development, while ensuring complete adhesion between the photoresist film and the irregular substrate surface, free from defects such as bubbles and missed coatings, laying the foundation for subsequent pattern transfer. Pattern transfer is achieved by utilizing the photochemical sensitivity of the photoresist: First, an alignment reference is established based on the contour characteristics of the irregular substrate, ensuring that the preset lines on the circuit pattern mask are aligned with the irregular contour of the substrate. During exposure, the photoresist in the light-transmitting areas of the mask undergoes photopolymerization or photodecomposition reactions (depending on the type of photoresist), while the photoresist in the light-blocking areas retains its original properties. This transfers the preset circuit pattern to the photoresist layer in the form of "photochemical reaction difference regions." The developing process uses a developer solution adapted to the photoresist type to selectively dissolve and remove photoresist areas that did not undergo the expected photochemical reaction, thus protecting the copper layer areas corresponding to the lines to be retained, while exposing the copper layer in non-line areas. The etching process utilizes the chemical dissolution reaction between the etching solution and copper to remove the exposed redundant copper layer. During the etching process, etching parameters (temperature, time, etching solution concentration) must be controlled to avoid over-etching and damaging the copper layer of the protected areas and the irregularly shaped substrate. The residual photoresist is removed from the surface of the copper layer of the lines by solvent stripping or plasma stripping, ultimately obtaining a line pattern that is completely consistent with the preset design, with precise dimensions and stable conductivity. This line pattern provides the core carrier for the electrical signal transmission of the irregularly shaped FPC.

[0070] Step S3: The photosensitive solder resist ink is printed onto the upper surface of the circuit layer 2 using a screen printing process, followed by pre-baking, exposure, development, and curing.

[0071] Specifically, utilizing the selective penetration characteristics of screen printing mesh, combined with printing fixtures and parameter control adapted to the surface contour of the irregularly shaped circuit layer 2, photosensitive solder resist ink is uniformly transferred to the upper surface of circuit layer 2 through the mesh of the screen. During the printing process, the squeegee pressure, printing speed, and the distance between the screen and the substrate need to be adjusted according to the irregular curved surface of circuit layer 2 to ensure that the ink completely covers the non-soldering areas of circuit layer 2, while avoiding conductive areas such as solder pads that need to be reserved, and that the ink layer thickness is uniform and consistent, without defects such as missed printing, ink overflow, or bubbles. Subsequently, a pre-baking treatment is performed, in which the solvent components in the photosensitive solder resist ink are removed by heating at a low temperature (usually 70-90℃), improving the dryness and adhesion of the ink layer, avoiding ink layer peeling or displacement during subsequent exposure and development, and preventing the evaporation of solvents in the ink from interfering with subsequent photochemical reactions. Next, exposure processing is performed. Utilizing the photopolymerization properties of photosensitive solder resist ink, the photomask with the pre-set solder resist pattern is aligned with the ink layer (the alignment reference must be adapted to the irregular contour of the substrate to ensure the solder resist area matches the circuit layer 2). During exposure, the photosensitive solder resist ink in the light-transmitting area of ​​the photomask undergoes a photopolymerization reaction, and the molecular chains cross-link and solidify to form a stable structure insoluble in the developer. The ink in the light-blocking area of ​​the photomask remains uncured, thus defining the effective area of ​​the solder resist layer. Afterwards, development processing is performed using a developer adapted to the photosensitive solder resist ink. The uncured ink that has not undergone photopolymerization is selectively dissolved and removed, fully exposing the reserved soldering area while retaining the cured solder resist ink area, ensuring the solder resist layer pattern matches the design requirements. Finally, curing processing is performed. High temperature (usually 150-180℃) is used to further induce a deep cross-linking reaction in the developed solder resist ink layer, forming a stable solder resist layer with a dense structure, high temperature and humidity resistance, and excellent insulation properties. During the curing process, temperature and holding time must be controlled to ensure the ink layer is completely cured and forms a good bond with the circuit layer 2 and the substrate.

[0072] Furthermore, step S3 specifically includes:

[0073] Step S31: Use screen printing technology to print photosensitive solder resist ink onto the upper surface of circuit layer 2, covering the non-pad area;

[0074] Step S32: Pre-baking the printed photosensitive solder resist ink, aligning and bonding the window pattern mask with the ink layer, and then exposing it. After development, the unexposed ink is removed to expose the solder pad area.

[0075] Step S33: Curing the ink layer to form an insulating covering layer 3.

[0076] Specifically, by utilizing the selective penetration characteristics of screen printing mesh and combining it with a printing fixture adapted to the curved contour of irregularly shaped circuit layer 2, the photosensitive solder resist ink is evenly transferred to the upper surface of circuit layer 2 by adjusting the squeegee pressure, printing speed, and the bonding distance between the screen and circuit layer 2. During the printing process, the ink viscosity and printing parameters must be strictly controlled to ensure that the ink completely covers all non-solder pad areas while avoiding the solder pad areas, forming an initial ink coverage layer, which lays the structural foundation for subsequent solder pad reservation and insulation protection. Next, a three-step progressive method is used: Pre-baking treatment involves heating at a low temperature (usually 70-90℃) to remove solvent components from the ink, improve the adhesion between the ink layer and the circuit layer 2, and prevent ink layer peeling or displacement during subsequent exposure and development; In the exposure stage, the photopolymerization characteristics of photosensitive solder resist ink are utilized to achieve alignment between the windowed pattern mask and the ink layer using a positioning reference adapted to the contour of the irregular substrate (the windowed area of ​​the mask matches the pad area). During exposure, the ink in the light-transmitting area of ​​the mask (corresponding to the ink above the pad) remains soluble because it has not undergone photopolymerization, while the ink in the light-blocking area of ​​the mask (corresponding to the ink above the non-pad) undergoes photopolymerization to form a stable structure; In the development stage, a developer adapted to the type of photosensitive solder resist ink is used to selectively dissolve and remove the unexposed soluble ink area, thereby exposing the pad area, while retaining the cured ink layer in the non-pad area to ensure that the solder resist coverage is completely consistent with the design requirements. By heating at high temperatures (usually 150-180℃) or curing with ultraviolet light, the ink layer remaining after development undergoes a deep cross-linking reaction, forming a stable insulating cover layer 3 with a dense structure, excellent insulation properties, high temperature and humidity resistance, and strong adhesion. During the curing process, the curing temperature and the heat preservation (or irradiation) time need to be controlled to ensure that the ink layer is completely cured, while avoiding damage to the irregularly shaped substrate and the circuit layer 2 caused by high temperature. Finally, the insulating cover layer 3 effectively protects the non-pad areas of the circuit layer 2, prevents circuit oxidation and short circuits, and ensures the solderability of the pad areas.

[0077] Step S4: Coat the lower surface of the irregular flexible substrate layer 1 with flexible epoxy resin composite material, place it in the molding mold and press and cure it to generate an irregular FPC model.

[0078] Specifically, by utilizing the properties of flexible epoxy resin composites that combine adhesion and structural strength after curing, coating processes such as spraying and scraping are used to adapt to the contours of irregularly shaped lower surfaces, so that the composite material can uniformly and densely cover the lower surface of the substrate. During the coating process, it is necessary to control the coating thickness and uniformity to ensure that the composite material can fully fill the gaps in the irregular contours of the lower surface of the substrate, laying a supporting foundation for subsequent enhancement of the structural stability of the substrate and improvement of the load-bearing capacity of irregular shapes. The coated substrate is then placed in a molding die for pressing and curing. The core principle consists of two parts: First, the positioning and constraint function of the molding die. This die has the same structure as the irregular mold designed in step S1, and its cavity contour matches the shape of the target irregular FPC. It can provide irregular positioning for the coated substrate and prevent the substrate from shifting or deforming during the pressing process. Second, the synergistic effect of pressing and curing. During the pressing process, a preset pressure is applied to make the flexible epoxy resin composite material and the lower surface of the substrate fit tightly together, eliminating interface gaps and ensuring a strong bond between the two. During the curing process, process parameters such as temperature and holding time are controlled (e.g., curing temperature of 80-150℃ and holding time of 30-60min adapted to the properties of epoxy resin) to promote the cross-linking polymerization reaction of epoxy resin, transforming it from a flexible state to a structurally stable cured state. Finally, the substrate and the cured epoxy resin composite material form an integrated irregular structure, i.e., the irregular FPC model.

[0079] Furthermore, step S4 specifically includes:

[0080] S41. Clean and pre-treat the lower surface of the irregular flexible substrate layer 1;

[0081] S42. Apply flexible epoxy resin composite material to the lower surface of the pretreated substrate;

[0082] S43. Place the coated substrate into the matching molding die and position it.

[0083] S44. Press the mold together.

[0084] S45. Maintain the pressed state and perform curing treatment. After curing, demold to obtain irregular support layer 4.

[0085] Specifically, by using cleaning methods adapted to irregular curved surfaces, such as plasma cleaning and solvent wiping, oil, dust, oxide layers, and process residues on the substrate's lower surface are removed. This improves the substrate's surface activity and compatibility with subsequent composite materials, preventing impurities from causing weak bonding and peeling defects between the composite material and the substrate, thus laying a reliable interface foundation for subsequent coating processes. Utilizing the adhesive, flexible, and post-cured structural strength properties of flexible epoxy resin composites, coating processes adapted to the irregular lower surface contours of the substrate, such as spraying and scraping, are employed. With controlled coating parameters (such as paint viscosity, coating speed, and scraper pressure), the composite material uniformly and densely covers the substrate's lower surface, while fully filling the gaps in the irregular contours, ensuring consistent coating thickness and guaranteeing the structural uniformity of the support layer. Using a molding die that matches the shape of the target irregular FPC (adapted to the structure of the initial irregular mold), the coated substrate is aligned and placed using positioning reference structures within the mold (such as positioning pins and limiting grooves). This ensures that the irregular contour of the substrate completely fits the contour of the mold cavity, preventing substrate displacement or deformation during subsequent pressing and curing processes, and guaranteeing that the final shape of the support layer matches the design requirements. By applying a preset pressure to the mold, the flexible epoxy resin composite material is further pressed tightly against the lower surface of the substrate, eliminating tiny gaps between the two interfaces. Simultaneously, the composite material better adapts to the irregular contours of the substrate and the mold under pressure, improving the integrity of the material filling. Under the constraint of continuous pressing, by controlling process parameters such as curing temperature and holding time (e.g., curing temperature of 80-150℃ and holding time of 30-60min for flexible epoxy resin), the epoxy resin is promoted to undergo cross-linking polymerization reaction, transforming from a flowable flexible state to a structurally stable and high-strength cured state. After curing, the mold is demolded. Since the mold cavity contour is consistent with the target irregular shape, the cured composite material forms an irregular support layer 4 that matches the irregular contour of the substrate and is firmly bonded to the substrate. This support layer can effectively enhance the overall structural strength and deformation resistance of the irregular FPC, ensuring its morphological stability during installation and use.

[0086] Step S5: Cut, polish, and clean the irregular FPC model to obtain the finished product.

[0087] Specifically, based on the design dimensions of the irregularly shaped FPC, laser cutting or precision die-cutting processes are used to adapt to the irregular contours, removing excess edges, overflow, and other redundant structures from the model's edges. This ensures that the finished product's dimensions perfectly match the target installation space requirements, while avoiding damage to the model's main body's circuit layer 2, solder mask layer, and support layer during the cutting process, thus guaranteeing the integrity of the core functional structure. For any burrs, flash, or unevenness that may exist on the surface of the finished product after cutting, fine grinding tools (such as sandpaper and grinding wheels) combined with grinding methods suitable for irregular curved surfaces are used to lightly grind the defective areas, eliminating surface irregularities and improving the smoothness and regularity of the finished product's surface. At the same time, excessive grinding is avoided to prevent damage to the substrate or functional layer structure. By employing methods such as ultrasonic cleaning, solvent wiping, or compressed air purging, debris, dust, and residual oil and chemical reagents from previous processes are removed from the surface of the finished product, ensuring a clean and contaminant-free surface. Ultrasonic cleaning utilizes the cavitation effect of ultrasonic waves to efficiently remove impurities from tiny crevices, while solvent wiping uses specialized solvents that do not damage the finished product material, ensuring effective cleaning while avoiding corrosion or damage to circuitry, solder mask, etc. Through this synergistic process of cutting, polishing, and cleaning, a precisely sized, uniformly shaped, and contaminant-free irregularly shaped FPC product is ultimately obtained. This product fully adapts to the structural requirements of the target installation space, possesses stable electrical performance and excellent appearance quality, and meets the needs of practical application scenarios.

[0088] This invention replicates the irregular contour of the installation space using a mold structure, providing a fundamental guarantee for the adaptation of the final product to the installation space. Next, utilizing the photosensitive properties of photoresist, the conductive areas to be retained are defined through exposure and development. Then, the copper layer in the non-contact areas is removed by etching, thereby forming a circuit layer 2 on the flexible substrate that meets the electrical connection requirements. Subsequently, a uniform coating of solder resist ink is achieved through screen printing. With the help of the photocuring properties of the photosensitive solder resist ink, a solder resist layer is formed after a series of processes, which provides insulation protection for the non-soldering areas of circuit layer 2, preventing circuit oxidation and short circuits, while ensuring the solderability of the soldering areas. Then, utilizing the adhesive and curing properties of flexible epoxy resin composite materials, the composite material is pressed into the lower surface of the substrate through mold pressing and is formed according to the irregular contour of the mold. At the same time, the curing reaction enhances the overall structural strength and irregular shape stability of the substrate, ultimately generating an irregular FPC model that combines irregular structure and electrical circuits. Finally, the excess corners of the model are trimmed to make the finished product size match the installation requirements. Surface burrs and defects are removed by grinding to improve structural regularity. Impurities and oil stains remaining from the process are removed by cleaning to ensure the appearance quality and reliability of the finished product, ultimately obtaining an irregular FPC finished product that meets the design requirements. The entire process, from structural adaptation and electrical function construction to protection reinforcement and molding optimization, fully realizes the preparation of irregular-shaped FPCs.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An irregularly shaped FPC, characterized in that, It includes an irregularly shaped flexible substrate layer, a circuit layer, an insulating cover layer, and an irregularly shaped support layer stacked in sequence; The irregularly shaped flexible substrate layer includes a pre-formed irregularly shaped structure whose shape matches the irregularly shaped surface of the target installation space; The circuit layer is fabricated on the upper surface of the irregularly shaped flexible substrate layer and is attached to the irregularly shaped surface of the irregularly shaped flexible substrate layer; the insulating cover layer covers the upper surface of the circuit layer; the irregularly shaped support layer is fabricated on the lower surface of the irregularly shaped flexible substrate layer and matches the irregularly shaped surface of the irregularly shaped flexible substrate layer.

2. The irregularly shaped FPC according to claim 1, characterized in that, The irregular structure includes at least one of arc shape, stepped shape, wavy shape or irregular curved surface, with a thickness of 0.02-0.1 mm.

3. The irregularly shaped FPC according to claim 1, characterized in that, The circuit layer is made of copper foil with a thickness of 0.01-0.05 mm, a line width of 0.03-0.1 mm, and a line spacing of 0.03-0.1 mm.

4. The irregularly shaped FPC according to claim 1, characterized in that, The insulating cover layer has a window at the position of the pad corresponding to the circuit layer, and the shape of the window matches the pad.

5. The irregularly shaped FPC according to claim 1, characterized in that, The irregular support layer is provided with a number of evenly distributed weight-reducing holes, the diameter of which is 0.5-2mm and the spacing between adjacent weight-reducing holes is 2-5mm.

6. The method for manufacturing the irregular-shaped FPC according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Design the irregular mold according to the irregular surface parameters of the target installation space; Step S2: Deposit a copper layer on the upper surface of the irregular flexible substrate layer, and then form a circuit pattern through photoresist coating, exposure, development and etching processes; Step S3: Use screen printing technology to print photosensitive solder resist ink onto the upper surface of the circuit layer, and then perform pre-baking, exposure, development and curing processes; Step S4: Coat the lower surface of the irregular flexible substrate layer with flexible epoxy resin composite material, place it in the molding mold and press and cure it to generate an irregular FPC model; Step S5: Cut, polish, and clean the irregular FPC model to obtain the finished product.

7. A method for manufacturing an irregularly shaped FPC according to claim 6, characterized in that, Step S1 specifically includes: Step S11: Obtain the three-dimensional parameters of the irregular surface of the target installation space, and clarify the curvature, size and boundary contour of the irregular surface; Step S12: Based on the three-dimensional parameters, perform structural design of the irregular mold to determine the matching of the mold cavity shape and the irregular surface; Step S13: Simulate and verify the designed mold structure; Step S14: Fabricate irregular-shaped molds according to the verified design scheme; Step S15: The polyimide or polyester substrate is formed in a shaped mold by hot pressing. The hot pressing temperature is 180-220℃, the pressure is 2-5MPa, and the holding time is 30-60min. After forming, it is naturally cooled to room temperature.

8. A method for manufacturing an irregularly shaped FPC according to claim 6, characterized in that, Step S2 specifically includes: Step S21: Clean the upper surface of the irregular flexible substrate layer to remove surface impurities and oxide layer, and deposit a copper layer on the pretreated substrate surface using vacuum sputtering or chemical copper plating process to form a uniform conductive substrate. Step S22: Coat the photoresist and pre-bake it to evenly cover the irregular surface with the photoresist; Step S23: After aligning and bonding the circuit pattern mask with the photoresist layer, expose the image to transfer the circuit pattern to the photoresist layer. Step S24: The unexposed photoresist is removed by development, the exposed copper layer is removed by etching, and the residual photoresist is stripped off to form a preset circuit pattern.

9. A method for manufacturing an irregularly shaped FPC according to claim 6, characterized in that, Step S3 specifically includes: Step S31: Use screen printing technology to print photosensitive solder resist ink onto the upper surface of the circuit layer, covering the non-pad area; Step S32: Pre-baking the printed photosensitive solder resist ink, aligning and bonding the window pattern mask with the ink layer, and then exposing it. After development, the unexposed ink is removed to expose the solder pad area. Step S33: Curing the ink layer to form an insulating covering layer.

10. A method for manufacturing an irregularly shaped FPC according to claim 6, characterized in that, Step S4 specifically includes: S41. Clean and pre-treat the lower surface of the irregularly shaped flexible substrate layer; S42. Apply flexible epoxy resin composite material to the lower surface of the pretreated substrate; S43. Place the coated substrate into the matching molding die and position it. S44. Press the mold together. S45. Maintain the pressed state and carry out curing treatment. After curing, demold to obtain the irregular support layer.

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