Anti-static automobile central control screen flexible circuit board

Abstract

The one or more embodiments of the specification provide an anti-static automobile central control screen flexible circuit board, comprising: a flexible circuit board, a plurality of parallel arranged conductor grooves are arranged in the flexible circuit board, a plurality of parallel arranged or braided arranged wire cores are arranged in the conductor grooves; a protective layer is arranged on at least one side surface of the flexible circuit board; a mesh isolation layer is arranged on the surface of the protective layer or embedded in the groove on the surface of the protective layer; and a grounding structure is electrically connected with the mesh isolation layer, for connecting the mesh isolation layer to an external grounding end; by arranging the mesh isolation layer on the surface of the protective layer, the excellent conductivity and the mesh braided structure of copper material can effectively absorb and reflect external electromagnetic waves, and the anti-electromagnetic interference ability of the component is significantly enhanced. Compared with the whole copper foil, the mesh structure of the copper wire mesh has better flexibility while maintaining good shielding effect.

Description

Technical Field

[0001] This invention relates to the field of electronic components and connectors, and in particular to an anti-static flexible circuit board for automotive central control screens. Background Technology

[0002] With the miniaturization, weight reduction, and high-frequency development of electronic devices, flexible printed circuit boards (FPCs) are widely used in mobile phones, tablets, automotive electronics, aerospace, medical devices, and other fields due to their advantages such as bendability, light weight, and small size. As a key component for signal and power transmission, the performance of flexible printed circuit boards directly affects the reliability and stability of the entire electronic system.

[0003] However, existing flexible circuit boards often face the following two main problems in complex usage environments: Firstly, there is insufficient physical protection. The wire cores of flexible circuit boards are relatively fragile. When subjected to external pressure, bending, or friction, the insulation layer is easily damaged or the wire cores break, affecting the reliability of signal transmission. Especially in applications with high vibration, such as automotive applications, flexible circuit boards need to withstand long-term mechanical stress.

[0004] Secondly, the electromagnetic shielding effectiveness is poor. In high-frequency circuits or complex electromagnetic environments, flexible circuit boards are susceptible to external electromagnetic interference (EMI), leading to problems such as signal crosstalk and data packet loss. Although some flexible circuit boards have external shielding layers, traditional shielding layers often have the following shortcomings: (1) Poor grounding of the shielding layer. In the prior art, some shielding layers lack effective grounding design, resulting in the shielding layer being in a "floating ground" state. A shielding layer without proper grounding not only cannot effectively discharge static electricity and electromagnetic interference signals, but may also become a new source of interference due to coupling with external noise, which directly violates the original intention of setting up the shielding layer.

[0005] (2) The shielding layer is not positioned properly. To achieve the best shielding effect, the shielding layer should be as close as possible to the signal line. However, in the existing scheme, some shielding layers are placed in the outermost protective layer, separated by a thick insulating layer, which significantly weakens the shielding effect.

[0006] (3) Complex manufacturing process. Some solutions attempt to achieve shielding function by machining grooves on the protective layer and embedding copper mesh. However, the process of precisely machining grooves on soft insulating materials and embedding copper mesh is complex and costly. Furthermore, the copper mesh embedded in the grooves is prone to separation or breakage during repeated bending.

[0007] (4) Grounding method has the risk of ground loop. In the existing scheme, the shielding layer is often directly connected to the system ground wire. A closed conductive loop may be formed between the large area shielding layer and the ground wire layer. In the alternating electromagnetic field, this loop is prone to inducing interference current, which will deteriorate the electromagnetic compatibility performance of the system.

[0008] Therefore, there is an urgent need to provide a flexible circuit board assembly that is compact, has good protection, high shielding efficiency, reliable grounding, and can effectively avoid the risk of ground loops. Summary of the Invention

[0009] In view of this, the purpose of one or more embodiments of this specification is to provide an anti-static automotive central control screen flexible circuit board, which solves the technical problems of existing flexible circuit boards lacking effective grounding of the shielding layer, insufficient shielding effectiveness, complex manufacturing process, weak physical protection, and grounding method that is prone to introducing ground loop interference.

[0010] To achieve the above objectives, one or more embodiments of this specification provide a flexible wire board assembly with electromagnetic shielding function, comprising: A flexible wire board, wherein the flexible wire board has a plurality of wire grooves arranged in parallel, and the wire grooves have a plurality of wire cores arranged in parallel or braided arrangement. A protective layer covers at least one surface of the flexible wire plate; A mesh isolation layer is disposed on the surface of the protective layer or embedded in a groove on the surface of the protective layer; and A grounding structure, electrically connected to the mesh isolation layer, is used to connect the mesh isolation layer to an external grounding terminal.

[0011] Furthermore, the mesh isolation layer is composed of a mesh structure woven from copper wires, wherein the mesh units of the mesh structure are arranged in rhombuses, rectangles, or hexagons; the diameter of the copper wires in the mesh isolation layer is 0.05 mm to 0.5 mm, and the mesh number of the mesh isolation layer is 10 to 200 meshes.

[0012] Furthermore, the grounding structure is a grounding pin, grounding plate, or conductive connection terminal extending from the mesh isolation layer, and the grounding structure is electrically connected to the ground of the mesh isolation layer; The mesh isolation layer is electrically connected to the flexible wire plate through conductive adhesive, and the surface of the mesh isolation layer is also covered with an insulating protective layer.

[0013] Furthermore, the protective layer is made of a flexible insulating material, and the mesh isolation layer is disposed on the surface of the protective layer facing the flexible wire board. The mesh isolation layer and the protective layer are fixedly connected by bonding or pressing. The protective layer is made of any one of the flexible insulating materials selected from polyimide, polyethylene terephthalate, polyethylene naphthalate, liquid crystal polymer or polytetrafluoroethylene.

[0014] Furthermore, the surface of the protective layer is recessed inward to form a groove, and the mesh isolation layer is embedded in the groove, with the upper surface of the mesh isolation layer not higher than the surface of the protective layer; The depth of the groove is greater than or equal to the thickness of the mesh isolation layer, and the outline shape of the groove is adapted to the shape of the mesh isolation layer.

[0015] Furthermore, the cross-section of the groove is an inverted trapezoidal structure, the angle between the side wall and the bottom wall of the inverted trapezoidal structure is 100° to 150°, and a rounded corner with a radius of 0.05mm to 0.2mm is provided at the junction of the bottom wall and the side wall of the inverted trapezoidal structure. After the mesh isolation layer is embedded in the groove, it is fixed by hot pressing. The heating area of ​​the hot pressing mold corresponds only to the edge of the groove within a range of 0.5mm to 2mm, so that the material of the protective layer is partially melted and only wraps the outermost edge of the mesh isolation layer within a range of 0.5mm to 2mm. The internal mesh area of ​​the mesh isolation layer is not penetrated by the molten material.

[0016] Furthermore, the groove is not provided in the bending area of ​​the flexible wire plate, but is only provided in the non-bending area of ​​the flexible wire plate or in the area with a bending radius greater than 10mm.

[0017] Furthermore, a resistor-capacitor network or ferrite bead is connected in series between the grounding structure and the mesh isolation layer. The resistor-capacitor network consists of a resistor and a capacitor connected in parallel. The resistance of the resistor is 0 ohms to 1000 ohms, and the capacitance of the capacitor is 10pF to 100nF. A transient voltage suppression diode is also connected in parallel between the grounding structure and the grid isolation layer. The transient voltage suppression diode is connected in parallel with the RC network or ferrite bead. That is, one end of the transient voltage suppression diode and the input end of the RC network or ferrite bead are connected to the grounding structure, and the other end of the transient voltage suppression diode and the output end of the RC network or ferrite bead are connected to the grid isolation layer.

[0018] Furthermore, the capacitance value of the capacitor is greater than 10 times the junction capacitance of the transient voltage suppression diode, and the peak pulse power of the transient voltage suppression diode is not less than 200W.

[0019] Furthermore, the flexible circuit board is a flat flexible circuit board, the protective layer is attached to at least one side surface of the flexible circuit board, and the thickness of the protective layer is 0.01mm to 0.5mm.

[0020] Compared with the prior art, the technical solution of the present invention has the following advantages: 1. Excellent electromagnetic shielding effect. By setting a mesh isolation layer on the surface of the protective layer, and utilizing the excellent conductivity of copper and the mesh woven structure, external electromagnetic waves can be effectively absorbed and reflected, significantly enhancing the component's anti-electromagnetic interference capability. Compared to a solid copper foil, the mesh structure of the copper wire mesh has better flexibility while maintaining good shielding effect.

[0021] 2. Grounding design ensures shielding effectiveness. By setting up a grounding structure electrically connected to the mesh isolation layer, the shielding layer can be effectively grounded, avoiding the "floating ground" phenomenon. The grounding structure ensures that static electricity and electromagnetic interference signals can be conducted to the ground through the shortest path, fully leveraging the protective function of the shielding layer.

[0022] 3. Effectively avoids ground loop interference. By placing an RC network or ferrite bead between the grounding structure and the ground layer, the ground loop effect formed between the large-area mesh isolation layer and the ground layer is effectively suppressed. In alternating electromagnetic fields, this RC network or ferrite bead can block or attenuate induced currents, preventing the shielding layer itself from becoming a new source of interference, further improving the electromagnetic compatibility performance of the system, especially suitable for strong electromagnetic interference environments such as vehicle-mounted systems. A single-point grounding method is preferred, connecting the mesh isolation layer to the ground layer through only one grounding structure, thus avoiding the formation of multiple closed loops from the source.

[0023] 4. Reliable and non-interfering electrostatic discharge. By incorporating a transient voltage suppressor diode (TVS diode) in the grounding structure and connecting it in parallel with an RC network or ferrite bead, its picosecond-level fast response and low clamping voltage provide an independent fast discharge path during electrostatic discharge events. The TVS diode and the RC network or ferrite bead form two independent parallel branches. When the capacitance is more than 10 times the junction capacitance of the TVS diode, the effect of the TVS diode junction capacitance on the RC parameters of the RC network is negligible. The two have clearly defined roles: the RC network or ferrite bead is responsible for suppressing steady-state ground loop interference, while the TVS diode is responsible for transient electrostatic discharge, ensuring no interference between them and balancing the dual requirements of improved electromagnetic compatibility and electrostatic protection.

[0024] 5. Maintains good flexibility. Using a copper wire mesh instead of a solid copper foil as the shielding layer, the mesh structure offers excellent bending performance and is less prone to breakage during repeated bending. The mesh structure of the insulating layer allows stress release during bending of the flexible board, avoiding the loss of flexibility caused by a solid metal layer.

[0025] 6. Simple structure and low manufacturing cost. The mesh insulating layer can be fixedly connected to the protective layer by bonding or pressing, which is simple and yields a high quality. The groove structure can be selectively set as needed, further optimizing the product's appearance and reliability. Compared to the complex solution of precisely machining grooves on soft insulating materials, the manufacturing cost of this invention is significantly reduced. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in one or more embodiments of this specification or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one or more embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the present invention; Figure 2 This is a schematic diagram of the protective layer structure of the present invention; Figure 3 This is a schematic diagram of the mesh isolation layer structure of the present invention; Figure 4 For the present invention Figure 3 A magnified structural diagram of region A in the middle.

[0028] In the diagram: 1. Flexible wire board; 11. Conductor groove; 12. Wire core; 2. Protective layer; 21. Groove; 22. Mesh isolation layer; 221. Warp; 222. Weft; 23. Grounding structure. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0030] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of this specification should have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar words used in one or more embodiments of this specification do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0031] Example 1 Basic structure: such as Figure 1 and Figure 2 As shown, the present invention provides a flexible wire board assembly with electromagnetic shielding function, which mainly includes a flexible wire board 1, a protective layer 2, a mesh isolation layer 22, and a grounding structure 23.

[0032] The flexible circuit board 1 is in the shape of a flat strip or band, and contains evenly spaced conductor grooves 11 inside. The conductor grooves 11 are provided with conductor cores 12 for transmitting electrical signals or power. The flexible circuit board 1 can adopt a conventional flexible printed circuit board (FPC) structure and has the characteristics of being resistant to bending.

[0033] In this embodiment, the flexible circuit board 1 is a single-sided flexible circuit board, the wire core 12 is a copper foil circuit, and the protective layer 2 is provided with a mesh isolation layer 22, which is distributed inside the protective layer 2.

[0034] The protective layer 2 covers at least one side surface of the flexible wire plate 1. The protective layer 2 is made of flexible insulating material and has the characteristics of bending resistance and aging resistance. It can provide effective mechanical protection for the internal wire groove 11 and prevent damage caused by external sharp objects or long-term friction.

[0035] The mesh isolation layer 22 is disposed on the surface of the protective layer 2 facing the flexible wire plate 1, and is fixedly connected to the protective layer 2 by bonding or pressing. The mesh isolation layer 22 is made of multiple fine copper wires interwoven and woven into a mesh structure (e.g., Figure 2 As shown in the figure, its thickness is relatively thin and will not significantly increase the overall thickness of the component. The mesh isolation layer 22 can serve as an electromagnetic shielding layer to block the intrusion of external electromagnetic waves, and it can also serve as an electrostatic discharge layer to discharge accumulated electrostatic charges.

[0036] The grounding structure 23 is electrically connected to the mesh isolation layer 22, and grounding pins, grounding plates or conductive connection terminals extend from the mesh isolation layer 22.

[0037] In practical applications, the grounding structure 23 connects the mesh isolation layer 22 to the ground layer of the flexible board 1 or the equipment system ground, providing a low-impedance discharge path for electrostatic and electromagnetic interference signals and ensuring that the shielding layer can work effectively.

[0038] Grounding method selection, single-point grounding and multi-point grounding: In this invention, the mesh isolation layer 22 is preferably grounded by a single-point grounding method, that is, the mesh isolation layer 22 is grounded by only one grounding structure 23. Single-point grounding can effectively avoid the formation of multiple closed conductive loops, fundamentally reducing the risk of ground loop interference.

[0039] Specifically, when the size of the mesh isolation layer 22 is small (length less than 50mm) or the operating frequency is low (below 10MHz), a single-point grounding method is preferred. At this time, the potential difference between different areas of the copper wire mesh can be ignored, and single-point grounding is sufficient to ensure the potential balance of different areas of the shielding layer.

[0040] The selection of the above size and frequency thresholds is based on the following: the relationship between the wavelength λ and frequency f of electromagnetic waves is λ = c / f (where c is the speed of light, approximately 3 × 10⁻⁶). 8m / s).

[0041] When the size of the shielding layer is less than 1 / 20 of the wavelength corresponding to the operating frequency, the potential difference between different areas of the shielding layer can be ignored, and single-point grounding is sufficient to ensure potential balance. For 10MHz, the wavelength is 30m, and 1 / 20 of it is 1.5m, which is much larger than 50mm. Therefore, single-point grounding is fully applicable below 10MHz. Even if the length of the copper wire mesh reaches 50mm, its size is still much smaller than 1.5m, and no significant potential difference will be generated.

[0042] When the size of the shielding layer 22 is large (length greater than 100mm) or the operating frequency is high (higher than 100MHz), in order to ensure the potential balance of each area of ​​the shielding layer, a multi-point grounding method can be adopted. The distance between adjacent grounding points shall not exceed 50mm, and each grounding point shall be connected in series with an independent RC network or ferrite bead to suppress the induced current that may be generated in each loop.

[0043] For 100MHz, the wavelength is 3m, and 1 / 20 of that is 0.15m (150mm). When the length of the copper wire mesh is greater than 100mm, it is close to this scale. Using multiple grounding points can ensure that the potential of each area is balanced. If the length of the copper wire mesh is between 50mm and 100mm and the operating frequency is between 10MHz and 100MHz, single-point grounding or multi-point grounding can be selected according to the actual situation. It is preferable to determine the best grounding method through experimental testing.

[0044] Working principle: In actual use, the conductor groove 11 of the flexible board 1 is responsible for transmitting electrical signals or power. The protective layer 2 covers the surface of the flexible board 1 to prevent the external physical environment from damaging the wire core. The mesh isolation layer 22 is connected to the external grounding terminal through the grounding structure 23 to form a complete electromagnetic shielding and electrostatic discharge path.

[0045] When external electromagnetic interference signals reach the isolation layer 22, they will be absorbed by the copper mesh and conducted to the ground through the grounding structure. The mesh structure of the copper wire mesh can reflect and absorb electromagnetic waves. Its shielding effectiveness is closely related to the mesh count, the diameter of the copper wire, and the shape of the mesh. Generally speaking, the higher the mesh count and the thicker the copper wire diameter, the better the shielding effect, but the flexibility will decrease accordingly.

[0046] When electrostatic charge accumulates on the surface of the component, it will also be discharged to the ground through the mesh isolation layer 22 and the grounding structure 23. The discharge path of electrostatic charge is: component surface → mesh isolation layer 22 → grounding structure 23 → grounding layer of flexible board 1 → system grounding terminal → earth. The lower the impedance of this path, the faster the electrostatic discharge, and the better the protection effect on the internal circuit.

[0047] Material selection The protective layer 2 is preferably made of polyimide (PI). Polyimide has excellent heat resistance (long-term operating temperature can reach above 260℃), good flexibility and excellent insulation properties, and is one of the most commonly used insulation materials in the field of flexible circuit boards. The mesh isolation layer 22 is woven from pure copper wire with a purity of not less than 99.9% to ensure good conductivity.

[0048] The adhesive layer uses acrylic or epoxy adhesives, which have good bonding strength and heat resistance, and can maintain a stable bonding effect in a temperature range of -40℃ to 150℃.

[0049] Example 2: The groove embedding structure and material-process adaptation are as follows: In one embodiment of the present invention, the surface of the protective layer 2 can be recessed inward to form a groove 21, and the mesh isolation layer 22 is embedded in the groove 21 so that the mesh isolation layer 22 is not higher than the surface of the protective layer 2, and the overall outer surface remains flat.

[0050] The depth of the groove 21 is not less than the thickness of the mesh isolation layer 22, and the shape of the groove 21 is adapted to the shape of the mesh isolation layer 22. In this embodiment, the depth of the groove 21 is 0.1mm to 0.3mm, which is slightly greater than the thickness of the mesh isolation layer 22 (0.08mm to 0.25mm) to ensure that the mesh isolation layer 22 can be completely embedded in the groove 21.

[0051] After the mesh isolation layer 22 is embedded in the groove 21, its surface is flush with or slightly lower than the surface of the protective layer 2. The advantages of this structure are: First, the mesh isolation layer 22 is embedded inside the protective layer 2 and is protected by the protective layer 2, making it less susceptible to external friction and scratches, thus improving the durability and reliability of the shielding layer.

[0052] Secondly, the overall outer surface is flat, which is conducive to the installation and wiring of flexible wire board components in narrow spaces, and avoids poor appearance caused by protruding copper wire mesh or interference with other components.

[0053] Third, the mesh isolation layer 22 is limited by the side wall of the groove 21, making it less prone to displacement or detachment when the flexible wire plate is repeatedly bent, thus improving the reliability of the product.

[0054] Different protective layer materials have different physical and chemical properties, making them suitable for different groove processing methods and copper wire mesh fixing methods.

[0055] The table below summarizes the preferred process solutions for various commonly used protective layer materials:

[0056] For polyimide and polyester protective layer materials, laser engraving is the preferred method for processing grooves. The laser power is 5W to 20W and the scanning speed is 100mm / s to 500mm / s. Laser engraving can precisely control the depth and contour shape of the grooves, and the processing speed is fast with a small heat-affected zone.

[0057] For thermotropic liquid crystal materials such as liquid crystal polymers, mold forming is preferred, which forms grooves while the protective layer is hot-pressed, resulting in high production efficiency and low cost.

[0058] For polytetrafluoroethylene (PTFE) materials, which have low surface energy and are difficult to bond, it is preferable to use plasma surface treatment (power 100W to 300W, time 30 seconds to 120 seconds) before bonding or pressing to improve the bonding force between the protective layer and the mesh isolation layer. Since PTFE does not have thermoplastic melt flow characteristics, it is not suitable for hot pressing and wrapping processes.

[0059] After the mesh isolation layer 22 is embedded in the groove 21, it is fixedly connected to the bottom surface and side wall of the groove 21 by adhesive or pressing. The adhesive is preferably conductive adhesive, which can not only fix the mesh isolation layer 22 in the groove 21, but also provide a certain conductive path, which is conducive to the uniform distribution and discharge of static electricity.

[0060] Example 3: The inverted trapezoidal groove anti-detachment structure and rounded corner transition, such as Figure 2 As shown, in another embodiment of the present invention, the cross-section of the groove 21 is an inverted trapezoidal structure, that is, the opening width of the groove 21 is smaller than the width of the bottom of the groove 21, the included angle α between the side wall and the bottom wall of the inverted trapezoidal structure is 100° to 150°, and a rounded transition with a radius of 0.05mm to 0.2mm is provided at the junction of the bottom wall and the side wall.

[0061] The design principle of the inverted trapezoidal structure is that when the mesh isolation layer 22 is embedded in the groove 21, since the opening width of the groove 21 is smaller than the internal width, the side wall of the groove forms a mechanical locking effect on the mesh isolation layer 22.

[0062] When the flexible wire plate assembly is subjected to shear stress during bending, the mesh isolation layer 22 tends to come out of the groove 21. However, due to the narrow opening of the groove 21, the mesh isolation layer 22 is blocked by the side wall and cannot come out easily.

[0063] The purpose of rounded corner transitions is that, under the fatigue load of repeated bending of flexible wire plates, sharp corner geometry will lead to significant stress concentration, becoming the starting point for crack initiation.

[0064] By setting a rounded transition with a radius of 0.05mm to 0.2mm, the stress concentration factor can be reduced by 30% to 50%, effectively preventing the protective layer 2 from developing cracks at the bottom corners and propagating to the entire thickness of the protective layer under long-term bending fatigue.

[0065] After the mesh isolation layer 22 is embedded in the inverted trapezoidal groove 21, it is further fixed by hot pressing. During the hot pressing process, the material of the protective layer 2 (such as polyimide) partially melts or softens under high temperature and pressure. The flowing protective layer material only wraps the outermost edge of the mesh isolation layer 22 within a range of 0.5mm to 2mm under pressure. After cooling, the protective layer material is re-cured and forms a tight fusion with the edge of the mesh isolation layer 22.

[0066] The design principle of only covering the outermost edge: The goal of hot pressing is to ensure that the molten protective layer material only covers the outermost edge of the mesh isolation layer 22 (within the range of 0.5mm to 2mm), without penetrating into the internal mesh area. The technical significance of this design is: First, the conductivity of the mesh isolation layer 22 depends on the mutual contact between the intersections of the warp threads 221 and the weft threads 222 in the copper wire braid structure. If the molten insulating polyimide material penetrates into the braid intersection and forms an insulating isolation layer on the surface of the copper wire, the mesh conductivity path in the penetration area will be blocked, weakening the shielding effect. Only wrapping the outermost edge can ensure the conductivity integrity of the internal mesh area.

[0067] Secondly, by controlling the wrapping area, the contact area between the molten material and the copper wire is reduced, thereby lowering the risk of oxidation of the copper wire at high temperatures.

[0068] Third, the outermost wrapping is sufficient to provide anti-peel anchoring force, without the need for material to penetrate into the inner mesh.

[0069] To achieve this effect, the upper mold of the hot pressing mold is provided with a raised heating head in the area corresponding to the groove 21. The shape of the heating head matches the groove 21, but the heating area of ​​the heating head only corresponds to the edge area of ​​the groove (width is 0.5mm to 2mm), and the center area of ​​the groove is not heated or the heating temperature is low.

[0070] During hot pressing, only the edge area of ​​the groove is heated and pressurized to the melting temperature, while the central area remains at a lower temperature (below Tg) and does not melt. In this way, the molten protective layer material only wraps the outermost edge of the mesh isolation layer 22 and does not penetrate into the inner mesh area.

[0071] Mass production compatibility notes: In roll-to-roll continuous production, to ensure precise control of the wrapping width from 0.5mm to 2mm, the width tolerance of the heating head of the hot pressing mold should be controlled within ±0.1mm, and the uniformity of the pressing temperature should be controlled within ±3℃. It is recommended to set up an online visual inspection system on the production line to monitor the wrapping width in real time. Products exceeding the range of 1mm to 2mm should be marked as unqualified. Through the above measures, stable wrapping width control can be achieved in mass production, and the yield rate can reach over 95%.

[0072] In this embodiment, the hot pressing process parameters and inert gas protection are as follows: the hot pressing temperature is preferably 300°C to 380°C, the pressure is preferably 1MPa to 5MPa, and the holding time is preferably 5 seconds to 30 seconds. The specific process parameters can be adjusted according to the material type of the protective layer 2.

[0073] For polyimide materials, the hot pressing temperature needs to be higher than its glass transition temperature (Tg is approximately 280°C to 350°C, depending on the specific grade) to ensure that the material softens and flows sufficiently to wrap the edges of the copper wire mesh, but at the same time it needs to be lower than its decomposition temperature (usually higher than 450°C) to avoid thermal degradation of the material. Therefore, a hot pressing temperature of 300°C to 380°C can ensure the material's fluidity while avoiding thermal damage.

[0074] Selection of high thermal stability protective layer materials Considering that the flexible circuit board assembly needs to undergo lead-free reflow soldering in the subsequent surface mount technology (SMT) process, and the peak temperature of reflow soldering is usually 240°C to 260°C, in order to ensure that the protective layer material after hot pressing does not undergo secondary softening and performance degradation during reflow soldering, the protective layer 2 preferably uses a polyimide grade with higher thermal stability, with a glass transition temperature Tg≥350°C and a thermal decomposition temperature Td≥500°C. After hot pressing at 300°C to 380°C, the microstructure and mechanical properties of this type of high-performance PI remain stable, and no significant secondary softening or performance degradation will occur during the subsequent reflow soldering process at 260°C.

[0075] After hot-pressing, the flexible wire plate assembly underwent a reflow soldering test at 260℃ (three reflow soldering tests according to J-STD-020 standard). The peel strength between the mesh isolation layer 22 and the protective layer 2 was not less than 90% of the initial value after hot pressing, which verified its thermal stability.

[0076] To prevent surface oxidation of the copper wires in the mesh isolation layer 22 during the high-temperature hot pressing process (copper will rapidly form an oxide layer in air above 300°C, leading to a decrease in conductivity), the hot pressing process is carried out in an inert gas protective atmosphere.

[0077] Specifically, the flexible wire board assembly to be heat-pressed is placed in a sealed heat-pressing chamber, and nitrogen or argon is introduced into the chamber to reduce the oxygen concentration in the chamber to below 1000 ppm. Then, the heat-pressing operation is performed. The inert gas protection can effectively suppress the high-temperature oxidation of the copper wire and ensure the conductivity and grounding reliability of the mesh isolation layer 22.

[0078] Grounding structure lead-out method and transition boundary treatment After the inverted trapezoidal groove 21 is embedded in the mesh isolation layer 22 and its edges are wrapped by the heat-pressed protective layer 2 material, the grounding structure 23 is led out from the groove 21.

[0079] Specifically, an unwrapped copper wire mesh edge lead-out area is provided at one or both ends of the groove 21. The wire mesh isolation layer 22 in the lead-out area is not wrapped by the molten protective layer material and remains exposed. The grounding structure 23 extends out of the groove 21 from the lead-out area so as to connect with the external grounding terminal.

[0080] Alternatively, a notch can be pre-set at the edge of the groove 21, from which the grounding structure 23 of the mesh isolation layer 22 extends. The width of the notch is 2mm to 8mm, and the depth is the same as the depth of the groove 21. During the hot pressing process, the notch area is shielded by a mask or partially depressurized to prevent the protective layer material from melting and flowing into the notch area, thus ensuring that the grounding structure 23 can extend smoothly.

[0081] Handling the transition boundary between the leading and enclosing regions: At the transition boundary between the wrapping area and the lead-out area, in order to avoid the protective layer material partially covering the copper wire surface of the lead-out area and forming a thin insulating layer, the thin insulating layer that may remain is removed by laser cleaning or plasma cleaning after hot pressing, so as to ensure reliable electrical contact between the mesh isolation layer 22 and the grounding structure 23.

[0082] The process parameters for laser cleaning are: pulsed laser energy density 0.5 J / cm². 2 Up to 1.5 J / cm 2 0.8 J / cm is preferred. 2 Up to 1.2 J / cm 2 To avoid melting or ablation of the copper wire surface, the plasma cleaning process parameters are: oxygen plasma, power 100W to 300W, time 30 seconds to 120 seconds. After cleaning, the surface roughness Ra value of the copper wire should be less than 0.8μm to ensure the reliability of welding or conductive adhesive bonding.

[0083] Alternatively, a peelable, high-temperature resistant mask material (such as polyimide tape) can be pre-coated in the lead-out area, and the mask material can be peeled off after heat pressing to keep the copper wire surface clean.

[0084] This dual-fixation mechanism (mechanical locking + material fusion) has the following significant advantages compared to fixing methods that rely solely on adhesives: First, it has stronger shear resistance. Adhesives are prone to fatigue peeling under repeated bending shear stress, while the mechanical locking and material fusion of the inverted trapezoidal structure do not depend on the adhesive strength of the adhesive, thus greatly improving shear resistance.

[0085] Second, it has higher long-term reliability. Even after tens of thousands of bends, the mesh isolation layer 22 is still firmly fixed in the groove 21 and will not lift or fall off.

[0086] Third, no additional adhesive is needed, which simplifies the manufacturing process and avoids the problem of decreased adhesion due to adhesive aging.

[0087] Example 4: The groove arrangement area is limited. In a preferred embodiment of the present invention, the groove 21 is not provided in the bending area of ​​the flexible wire plate 1, and the groove 21 is only provided in the non-bending area of ​​the flexible wire plate 1 or in the area where the bending radius is greater than 10mm.

[0088] Design principles: In practical applications, the flexible wire plate 1 has specific bending areas (i.e., areas that need to be repeatedly bent during use) and non-bending areas (i.e., areas that remain straight or only undergo minor bending during use). Within the bending areas, the flexible wire plate 1 is subjected to repeated bending stress and shear stress.

[0089] The inverted trapezoidal groove 21 forms a geometric abrupt change area on the protective layer 2 (suddenly recessed from a flat surface). Although a rounded transition is provided at the junction of the bottom wall and the side wall to reduce stress concentration, the superposition effect of bending stress and the stress concentration of the groove itself still exists in the bending area. Placing the groove 21 in the non-bending area or in the area with a bending radius greater than 10mm (i.e., the area with a very small degree of bending) can fundamentally avoid the superposition of bending stress and the stress concentration of the groove, ensuring the long-term reliability of the flexible wire plate 1 under repeated bending conditions.

[0090] In practical applications, those skilled in the art can determine the positions of the bending and non-bending areas by analyzing the installation form and movement trajectory of the flexible wire plate 1 in the final product, and set the groove 21 only in the non-bending area.

[0091] Example 5: Double-sided protective layer structure, such as Figure 4 As shown, in another embodiment of the present invention, both sides of the flexible wire plate 1 are covered with protective layers 2, and each protective layer 2 is provided with a mesh isolation layer 22.

[0092] Specifically, the upper surface of the flexible wire plate 1 is covered with a first protective layer 2a, and a first mesh isolation layer 22a is provided on the side of the first protective layer 2a facing the flexible wire plate 1; the lower surface of the flexible wire plate 1 is covered with a second protective layer 2b, and a second mesh isolation layer 22b is provided on the side of the second protective layer 2b facing the flexible wire plate 1.

[0093] The first isolation layer 22a and the second isolation layer 22b are respectively connected to the grounding layer or system grounding terminal of the flexible board 1 through their respective grounding structures.

[0094] The advantages of a double-sided protective layer structure are: First, the upper and lower double-layer mesh isolation layers form a structure similar to a "shielding cavity", which wraps the wire groove 11 of the flexible wire board 1 between the double-layer shielding layers, achieving full-enclosure electromagnetic shielding. Compared with the single-sided shielding structure, the double-sided shielding structure has a good suppression effect on electromagnetic interference from all directions, and the shielding effectiveness can be improved by more than 10dB.

[0095] Secondly, the double protective layer provides more comprehensive physical protection for the flexible board 1. No matter how the flexible board is bent or installed, its exposed surface is protected by the protective layer.

[0096] Third, the double-layer isolation layer can be connected to different grounding terminals respectively, or they can be connected to the same grounding terminal after being interconnected. This design provides greater flexibility in scenarios that require differential signal transmission or require shielding different signal areas separately.

[0097] In this embodiment, the first mesh isolation layer 22a and the second mesh isolation layer 22b can be electrically connected through conductive connectors provided on the edge of the flexible wire plate 1 or through through holes in the flexible wire plate 1. The inner wall of the through holes is plated with a copper layer to conduct the upper and lower mesh isolation layers, forming a complete shielding circuit.

[0098] Example 6: Mesh structure design and parameter-performance relationship of the mesh isolation layer, such as Figure 3 , Figure 4 As shown, the mesh isolation layer 22 is woven from warp threads 221 and weft threads 222 to form a regular mesh structure.

[0099] In this invention, the shape of the mesh unit can be rhomboid, rectangular, or hexagonal. Different mesh unit shapes have different effects on electromagnetic shielding effectiveness and flexibility. Rhombus mesh: When subjected to stretching or bending, the shape of the rhombus mesh can deform to absorb stress, exhibiting optimal flexibility. The shielding effect of the rhombus mesh is related to the acute angle of the mesh; the smaller the angle, the better the shielding effect, but the weaving difficulty also increases accordingly. Preferably, the acute angle of the rhombus mesh is 30° to 60°.

[0100] Rectangular mesh: The weaving process of rectangular mesh is the simplest and the lowest cost. Rectangular mesh has different mechanical properties in the warp and weft directions. The tensile strength in the warp direction is higher, while the flexibility in the weft direction is better. In practical applications, the arrangement direction of the rectangular mesh can be selected according to the bending direction of the flexible wire sheet, so that the long side of the mesh is consistent with the bending direction to obtain the best bending performance.

[0101] Hexagonal mesh: Hexagonal mesh has isotropic mechanical properties, with relatively balanced flexibility and strength in all directions. The shielding effect of hexagonal mesh is between that of rhomboid mesh and rectangular mesh, making it a good choice with good overall performance.

[0102] Quantitative relationship between mesh parameters of the shielding layer and shielding effectiveness: The mesh count of the mesh isolation layer 22 directly affects the shielding effect and flexibility. Mesh count refers to the number of meshes per inch of length. The higher the mesh count, the denser the mesh, and the better the shielding effect, but the amount of copper wire used increases and the flexibility decreases. The lower the mesh count, the sparser the mesh, and the better the flexibility, but the shielding effect decreases.

[0103] The shielding effectiveness and bending life under different combinations of mesh count and copper wire diameter were verified by experiments, as shown in the table below:

[0104] (Note: The above data are illustrative experimental data; actual values ​​may vary depending on the specific material batch and testing conditions.) Based on the above data, when the mesh count of the shielding layer 22 is 10 to 200 meshes and the copper wire diameter is 0.05 mm to 0.5 mm, a good balance can be achieved between shielding effect and flexibility. For general consumer electronics applications, 50 to 100 meshes are preferred; for wearable device applications with higher flexibility requirements, 10 to 50 meshes are preferred; and for automotive or industrial applications with higher shielding effect requirements, 100 to 200 meshes are preferred.

[0105] The diameter of the copper wire in the mesh isolation layer 22 also affects the shielding effect and flexibility. The larger the copper wire diameter, the better the shielding effect and the higher the mechanical strength, but the flexibility decreases and the overall thickness of the component increases. Preferably, the copper wire diameter is 0.05mm to 0.5mm. For most application scenarios, the overall performance is best when the copper wire diameter is 0.1mm to 0.2mm.

[0106] Example 7: Various ways to implement grounding structures, such as Figure 4 As shown, the grounding structure 23 can be implemented in a variety of different ways to adapt to different application scenarios and installation requirements.

[0107] Method 1: The grounding pin is a strip conductor extending outward from the edge of the mesh isolation layer 22. It is integrally braided with the mesh isolation layer 22 or connected by welding. The width of the grounding pin is 1mm to 5mm and the length is 3mm to 15mm.

[0108] During installation, the grounding pin can be directly inserted into the connector slot of the flexible board 1 and contact the grounding terminal inside the connector; it can also be soldered onto the grounding pad of the flexible board 1; or it can be fixed to the grounding terminal of the equipment by screws or clips.

[0109] The advantages of grounding pins are simple structure and convenient connection, making them suitable for scenarios that require quick plugging and unplugging.

[0110] Method 2: The grounding plate is a sheet-like conductor that extends outward from the surface of the mesh isolation layer 22. It has a large area and is usually square or round. The grounding plate is connected to the mesh isolation layer 22 by bonding or welding with conductive adhesive.

[0111] The larger area of ​​the grounding plate helps to reduce contact resistance and improve grounding reliability. The grounding plate can be glued to the grounding surface of the equipment with conductive adhesive or pressed onto the grounding terminal with screws.

[0112] The advantages of grounding plates are large contact area and low grounding resistance, making them suitable for scenarios with high requirements for grounding reliability.

[0113] Method 3: Conductive connection terminal The conductive connection terminal is a conductive terminal set on the edge or surface of the mesh isolation layer 22. It has a standard interface form, such as pin type, socket type, snap type, etc. The conductive connection terminal can be plugged into the matching connector to achieve a fast and reliable grounding connection.

[0114] The advantages of conductive connectors are high standardization, reliable connection, suitability for mass production, and applicability to large-scale production of consumer electronics products.

[0115] Regardless of the implementation method, the conduction resistance between the grounding structure 23 and the ground layer of the flexible board 1 should be controlled within 1 ohm to ensure that static electricity and electromagnetic interference signals can be discharged quickly.

[0116] Example 8: Parallel connection of RC network, ferrite bead and TVS diode In a preferred embodiment of the present invention, a resistor-capacitor network or a ferrite bead is connected in series between the grounding structure 23 and the grid isolation layer 22. At the same time, a transient voltage suppressor diode (TVS diode) is also connected in parallel between the grounding structure 23 and the grid isolation layer 22.

[0117] Connection topology: Grid isolation layer 22 → grounding structure 23 → node A, node A is connected to two parallel branches to grid isolation layer 22: Branch 1: RC network (resistor and capacitor in parallel) or ferrite bead; Branch 2: Transient voltage suppressor diode (TVS diode).

[0118] That is, one end of the transient voltage suppressor diode is connected to the ground structure 23 (node ​​A) together with the input terminal of the RC network or ferrite bead, and the other end of the transient voltage suppressor diode is connected to the grid isolation layer 22 together with the output terminal of the RC network or ferrite bead.

[0119] The RC network consists of a resistor and a capacitor connected in parallel. The resistance is 0 ohms to 1000 ohms, preferably 100 ohms to 500 ohms, and the capacitance is 10pF to 100nF, preferably 100pF to 10nF.

[0120] Resistor selection requirements: Surge-resistant resistors should be selected with a rated power of not less than 0.1W, preferably 0.25W to 0.5W, to ensure that they are not damaged or have a drifting resistance when subjected to transient high voltage during electrostatic discharge events.

[0121] Capacitor selection requirements: The rated voltage of the capacitor should not be lower than 100V, preferably 200V to 500V, to ensure that it will not be broken down under the high voltage generated by electrostatic discharge.

[0122] Ceramic capacitors are preferred due to their advantages of fast response and good high-frequency characteristics.

[0123] Analysis of the influence of TVS junction capacitance on RC parameters: In a two-parallel branch topology, the junction capacitance Cj of the TVS diode and the capacitance in the RC network are electrically connected in parallel and superimposed, with a total capacitance of C. total =C242+Cj, the junction capacitance of a TVS diode is typically tens to hundreds of pF (typically 50 pF to 300 pF), while C242 is typically 100 pF to 10 nF.

[0124] When C242 has a large value (e.g., 10nF), Cj (e.g., 100pF) accounts for only 1% of the total capacitance, and its effect on the RC cutoff frequency is negligible.

[0125] However, when C242 is small (e.g., 100pF), Cj being 100pF will increase the total capacitance by 100%, and the RC cutoff frequency will shift significantly.

[0126] To ensure that the influence of the TVS junction capacitance on the RC network parameters is within an acceptable range, the capacitance value should be more than 10 times the TVS junction capacitance, i.e., C242≥10×Cj.

[0127] Under these conditions, the total capacitance deviation does not exceed 10%, and the cutoff frequency deviation of the RC network does not exceed 5%, which is negligible in engineering. Preferably, when C242 is 1nF to 10nF, it is compatible with the junction capacitance of most TVS transistors (≤100pF), ensuring the stability of the RC cutoff frequency.

[0128] The working principle of the RC network is as follows: For DC or low-frequency signals (such as the low-frequency components of electrostatic discharge), capacitors exhibit high impedance, while resistors provide a DC path to ensure that electrostatic charges can be smoothly discharged to ground.

[0129] For high-frequency interference signals (such as radio frequency interference), the resistor has a high impedance, while the capacitor exhibits a low impedance. The high-frequency interference signal is coupled to the ground structure 23 through the capacitor for discharge.

[0130] In an alternating electromagnetic field, the large-area mesh isolation layer 22 may form a closed conductive loop. Under the action of an external alternating magnetic field, this loop will generate an induced electromotive force, thereby forming a circulating current. The circulating current will generate a voltage drop on the grounding structure 23, which will be superimposed on the signal ground, causing ground bounce noise and deteriorating the electromagnetic compatibility performance of the system. The resistor and capacitor of the RC network are connected in parallel and then in series in the grounding path, which increases the high-frequency impedance of the ground loop and effectively attenuates the induced circulating current, thereby preventing the shielding layer itself from becoming a new source of interference.

[0131] A ferrite bead is a high-frequency attenuation device. At low frequencies, it exhibits low impedance (close to 0 ohms), ensuring that electrostatic charges can be discharged smoothly. At high frequencies, it exhibits high impedance (typically hundreds to thousands of ohms), effectively suppressing high-frequency induced currents.

[0132] The impedance of the ferrite bead is preferably between 100Ω and 1000Ω (tested at 100MHz), the rated current is preferably not less than 2A, the DC resistance is preferably less than 0.5 ohms, and the rated current of the ferrite bead must meet the requirements of the ESD peak current in order to avoid magnetic saturation and loss of high-frequency impedance characteristics during electrostatic discharge.

[0133] A transient voltage suppressor diode connected in parallel with an RC network or a ferrite bead forms an independent ESD discharge branch. TVS diodes have the following characteristics: (1) Fast response speed: The response time of TVS tube is in the picosecond range (usually 1ps to 5ps), which can quickly conduct at the moment of electrostatic discharge, much faster than the response speed of RC network or ferrite bead.

[0134] (2) Low clamping voltage: The clamping voltage of TVS tubes is usually 5V to 30V (depending on the selection), which can clamp the electrostatic high voltage at a safe level and protect the subsequent circuits.

[0135] (3) Bidirectional conduction: For AC signals or bipolar electrostatic pulses, a bidirectional TVS tube is selected, which can provide protection in both positive and negative directions.

[0136] (4) Automatic recovery: After the electrostatic discharge event ends, the TVS tube automatically recovers to a high-resistance state, which does not affect the suppression effect of the RC network or the ferrite bead on ground loop interference.

[0137] The selection parameters for TVS diodes include: reverse working voltage (V RWM The voltage should not be lower than the operating voltage of the flexible board 1 (usually 3.3V, 5V or 12V), and the breakdown voltage (V) should be no less than the operating voltage of the flexible board 1. BR Slightly higher than the operating voltage, clamping voltage (V) C The peak pulse power (P) is lower than the maximum withstand voltage of the protected circuit. PPM Not less than 200W (for 8kV contact discharge level).

[0138] Advantages of parallel connection: When a TVS diode is connected in parallel with an RC network or a ferrite bead, it forms two independent parallel branches, which has the following significant advantages: First, the junction capacitance Cj of the TVS diode is superimposed in parallel with the capacitance in the RC network. However, when C242≥10×Cj, the influence of the junction capacitance of the TVS diode on the RC network parameters can be ignored, ensuring that the ground loop suppression effect is not significantly shifted due to the addition of the TVS diode.

[0139] Secondly, the TVS diode forms an independent ESD discharge branch, and its conduction characteristics are not affected by the RC network parameters, thus ensuring the reliability of ESD discharge.

[0140] Third, the two branches have a clear division of functions: the RC network or ferrite bead is responsible for suppressing steady-state ground loop interference, while the TVS diode is responsible for transient electrostatic discharge, and they do not interfere with each other.

[0141] Division of labor between RC networks / ferrite beads and TVS diodes: An RC network or ferrite bead is responsible for suppressing steady-state ground loop interference (continuous alternating magnetic field interference), while a TVS diode is responsible for transient electrostatic discharge (sudden high-voltage electrostatic pulses). The two are connected in parallel without interfering with each other, thus meeting the dual requirements of improving electromagnetic compatibility and electrostatic protection.

[0142] The advantages of using a TVS diode + RC network (or ferrite bead) parallel connection scheme are: compared with using an RC network or ferrite bead alone, the TVS diode provides an independent ESD discharge channel, avoiding the problem of incomplete ESD discharge caused by improper selection of RC network parameters, and improving the reliability of electrostatic protection.

[0143] Example 9: In some embodiments of the present invention, the surface of the mesh isolation layer 22 is also covered with an insulating protective layer to ensure insulation protection and connection reliability.

[0144] The insulating protective layer is made of materials with good insulating properties, such as polyimide film, polyester film, or insulating varnish. The thickness of the insulating protective layer is 0.005mm to 0.05mm, which can provide effective insulation protection without significantly increasing the overall thickness of the component.

[0145] The functions of the insulating protective layer include: First, it prevents the mesh isolation layer 22 from accidentally coming into contact with other conductors (such as adjacent electronic components, metal casings, etc.) and causing short circuits, thereby improving the safety of the product.

[0146] Secondly, the protective mesh isolation layer 22 is protected from oxidation and corrosion. Copper is easily oxidized in the air. The surface resistance of oxidized copper increases, which will affect the shielding effect and grounding performance. The insulating protective layer can isolate air and moisture and slow down the oxidation process of the copper wire mesh.

[0147] Third, improve the mechanical strength of the mesh isolation layer 22 to prevent the copper wire from breaking during repeated bending.

[0148] The insulating protective layer can be covered on the surface of the mesh isolation layer 22 by means of coating, bonding or spraying. For solid insulating materials such as polyimide film, hot pressing is preferred; for liquid insulating materials such as insulating varnish, spraying or dipping is preferred and then curing is preferred.

[0149] Long-term reliability of conductive adhesive and welded joints: The mesh isolation layer 22 and the flexible wire plate 1 can be electrically connected by conductive adhesive or welding. The long-term reliability comparison of different connection methods is as follows: Samples connected with conductive adhesive showed a grounding resistance change rate of no more than 20% after 100,000 bending tests (bending radius 5mm, frequency 60 times / minute, angle 180°). This method is suitable for applications in non-bending areas or with fewer bending cycles. Conductive adhesive connection has the advantages of low process temperature (usually <200℃) and minimal thermal damage to the FPC, but attention should be paid to adhesive layer fatigue in bending areas.

[0150] Samples using welded connections showed no cracking at the weld joints after 100,000 bending tests, and the grounding resistance change rate did not exceed 5%, demonstrating superior long-term reliability. The disadvantage of welded connections is the higher process temperature (peak temperature of lead-free welding is 240-260℃), resulting in greater thermal shock to the FPC substrate.

[0151] Preferably, the flexible wire plate 1 is connected by welding in the bending area, and conductive adhesive can be used to connect in the non-bending area to reduce the process cost. For applications with high reliability requirements, such as automotive, it is preferable to use welding for all connections.

[0152] Example 10: In-vehicle display applications The flexible wire board assembly of the present invention is particularly suitable for automotive display modules.

[0153] The vehicle display module includes a display screen and a system ground terminal. One end of the flexible board assembly is connected to the drive circuit of the display screen, and the other end is connected to the control unit of the vehicle electronic system.

[0154] The electromagnetic environment in a vehicle is extremely complex. Electric motors, ignition systems, and wireless communication devices all generate strong electromagnetic interference.

[0155] Meanwhile, vehicle displays are usually installed in prominent locations such as the dashboard, and their flexible wiring boards need to go through a long wiring path, making them susceptible to various interference sources along the way.

[0156] In addition, the problem of static electricity in the vehicle environment should not be ignored. Static electricity generated when people get in and out of the vehicle may be transmitted to the internal circuitry through the touch screen.

[0157] The advantages of the flexible wire board assembly of the present invention in automotive display applications are as follows: First, the mesh isolation layer 22 is connected to the system grounding terminal of the vehicle electronic system through the grounding structure 23, which can effectively suppress electromagnetic radiation from strong interference sources such as engines and motors, and ensure stable transmission of image signals from the display screen.

[0158] Secondly, the mesh structure of the mesh isolation layer 22 has good flexibility, which can adapt to repeated bending and wiring operations during the installation of the vehicle display screen and is not easy to break.

[0159] Third, the protective layer 2 provides physical protection for the flexible circuit board, preventing it from being scratched or worn during vehicle vibration or maintenance.

[0160] Fourth, through a reasonable grounding design, the mesh isolation layer 22 can quickly discharge the static charge accumulated in the vehicle environment to the ground, protecting sensitive components such as the display driver IC from electrostatic damage.

[0161] Fifth, by setting up an RC network or ferrite beads and a TVS diode in parallel between the grounding structure 23 and the system grounding terminal, interference currents are effectively prevented from being induced in the closed loop formed by the strong alternating electromagnetic field in the vehicle environment in the mesh isolation layer 22, preventing the shielding layer itself from becoming a new source of radiation or conducted interference. At the same time, the TVS diode ensures reliable discharge of ESD events, further improving the electromagnetic compatibility performance and electrostatic protection capability of the vehicle display screen.

[0162] In actual installation, the grounding structure 23 of the flexible circuit board assembly can be fixed to the metal housing of the vehicle display module with screws, or connected to the system grounding terminal via a connector. To ensure grounding reliability, conductive grease can be applied or anti-loosening washers can be added to the grounding connection.

[0163] Example 11: Manufacturing method: The manufacturing method of the flexible wire plate assembly of the present invention includes the following steps: Step 1: Fabrication of flexible wire plate 1 A flexible insulating substrate is provided, and the required circuit pattern, including wire groove 11, is formed on the surface of the substrate through processes such as copper plating and etching.

[0164] The circuit pattern can be formed using processes known in the art, such as subtractive (etching), additive (electroplating), or semi-additive methods.

[0165] For multilayer flexible circuit boards, it is also necessary to laminate the multilayer circuits together through a lamination process and achieve electrical connection between each layer through through-holes.

[0166] Step 2: Prepare the mesh isolation layer 22 Pure copper wire is braided into a mesh structure using a braiding machine to form a mesh isolation layer 22. During the braiding process, the shape of the mesh (diamond, rectangle, or hexagon), the mesh count (10 to 200 mesh), and the diameter of the copper wire (0.05 mm to 0.5 mm) can be adjusted as needed.

[0167] After weaving, the mesh isolation layer 22 is cut to match its dimensions with those of the protective layer 2 or the groove 21.

[0168] Optionally, the copper wire surface of the mesh isolation layer 22 may be tin-plated, silver-plated, or gold-plated to improve solderability, oxidation resistance, and conductivity.

[0169] Step 3: Prepare the protective layer 2 The flexible insulating material is cut to a size and shape that matches the flexible wire plate 1. If a groove 21 is required, it is machined into the corresponding position on the protective layer 2 by means of laser engraving, mechanical milling, or mold forming.

[0170] For inverted trapezoidal groove structures, laser engraving is preferred. By adjusting the incident angle of the laser beam and the engraving trajectory, an inverted trapezoidal cross-section with inclined sidewalls is formed.

[0171] The rounded corner transition at the junction of the bottom and side walls can be achieved by adjusting the radius of the arc at the corner of the laser engraving path, or by rounding it through subsequent micro-discharge machining. Alternatively, a mold forming method can be used to directly form an inverted trapezoidal groove structure with rounded corner transition during the hot pressing of the protective layer 2.

[0172] For polyimide and polyester protective layer materials, laser engraving is preferred for processing grooves, with a laser power of 5W to 20W and a scanning speed of 100mm / s to 500mm / s.

[0173] For thermotropic liquid crystal materials such as liquid crystal polymers, a mold forming method is preferred, in which grooves are formed simultaneously with the hot pressing of the protective layer.

[0174] For polytetrafluoroethylene (PTFE) materials, it is preferable to use plasma surface treatment (power 100W to 300W, time 30 seconds to 120 seconds) before subsequent bonding or pressing processes.

[0175] Step 4: Determine the groove layout area Based on the installation form and movement trajectory of the flexible board 1 in the final product, determine the positions of the bending area and the non-bending area, and set the groove 21 in the non-bending area. Avoid setting the groove 21 in the bending area. If the groove 21 must be set near the bending area, ensure that the bending radius of the area where the groove 21 is located is greater than 10mm.

[0176] Step 5: Composite mesh isolation layer 22 and protective layer 2 The mesh isolation layer 22 is placed on the surface of the protective layer 2 or embedded in the groove 21, and the two are fixedly connected by bonding or pressing.

[0177] For the inverted trapezoidal groove structure, after the mesh isolation layer 22 is embedded into the groove 21, it is subjected to hot pressing. The hot pressing temperature is 300℃ to 380℃, the pressure is 1MPa to 5MPa, and the holding time is 5 seconds to 30 seconds.

[0178] The hot pressing process is carried out in an inert gas protective atmosphere: the components to be hot pressed are placed in a sealed chamber, and nitrogen or argon is introduced to reduce the oxygen concentration to below 1000 ppm before hot pressing is performed.

[0179] The upper mold of the hot pressing mold has a raised heating head in the area corresponding to the groove 21. The shape of the heating head matches the groove 21, but the heating area of ​​the heating head only corresponds to the edge area of ​​the groove (width is 0.5mm to 2mm), and the center area of ​​the groove is not heated or the heating temperature is low.

[0180] During hot pressing, only the edge area of ​​the groove is heated and pressurized to the melting temperature, while the central area remains at a lower temperature (below Tg) and does not melt. In this way, the molten protective layer material only wraps the outermost edge of the mesh isolation layer 22 and does not penetrate into the internal mesh area.

[0181] In roll-to-roll continuous production, the width tolerance of the heating head of the hot pressing mold should be controlled within ±0.1mm, and the uniformity of the pressing temperature should be controlled within ±3℃. It is recommended to set up an online visual inspection system on the production line to monitor the width of the package in real time. Products exceeding 1mm to 2mm should be marked as unqualified products.

[0182] The specific process curve for hot pressing is as follows: In the preheating stage, the temperature is increased from room temperature to 150°C to 200°C at a rate of 5°C / s to 10°C / s, and held for 10 to 30 seconds to remove moisture and volatiles from the material; in the heating stage, the temperature is increased to 300°C to 380°C at a rate of 3°C / s to 5°C / s; in the pressure holding stage, a pressure of 1 MPa to 5 MPa is applied at the target temperature and held for 5 to 30 seconds; in the cooling stage, the temperature is cooled to room temperature at a rate of 5°C / s to 10°C / s, and the pressure is maintained during the cooling process until the temperature drops below 200°C.

[0183] Step 6: Set up grounding structure 23 and lead-out area A grounding structure 23, such as a grounding pin, grounding plate, or conductive connection terminal, is provided at an appropriate location on the mesh isolation layer 22. The grounding structure 23 and the mesh isolation layer 22 are electrically connected by means of braiding, welding, or bonding with conductive adhesive.

[0184] For the inverted trapezoidal groove structure, a lead-out area is preset at one or both ends of the groove 21. During the hot pressing process, the protective layer material will not wrap the edge of the copper wire mesh in this area by means of masking or partial non-pressure, so that the grounding structure 23 remains exposed so as to connect with the external RC network, ferrite bead, TVS tube or grounding structure 23.

[0185] At the transition boundary between the lead-out area and the wrapping area, any remaining thin insulating layer is removed by laser cleaning or plasma cleaning.

[0186] The laser cleaning parameters are: pulsed laser energy density 0.5 J / cm². 2 Up to 1.5 J / cm 2 0.8 J / cm is preferred. 2 Up to 1.2 J / cm 2 .

[0187] The plasma cleaning parameters are: oxygen plasma, power 100W to 300W, time 30 seconds to 120 seconds, and the surface roughness Ra value of the copper wire after cleaning should be less than 0.8μm.

[0188] Alternatively, a peelable, high-temperature resistant mask material can be pre-coated in the lead-out area, and then the mask material can be peeled off after hot pressing.

[0189] Step 7: Set up the resistor-capacitor network, ferrite bead, and TVS diode. A resistive-capacitive network or ferrite bead is connected in series between the grounding structure 23 and the grid isolation layer 22, and a TVS diode is connected in parallel at both ends (i.e., one end of the TVS diode is connected to the grounding structure 23 together with the input end of the resistive-capacitive network or ferrite bead, and the other end of the TVS diode is connected to the grid isolation layer 22 together with the output end of the resistive-capacitive network or ferrite bead).

[0190] The resistors in the RC network should be surge-resistant resistors with a rated power of not less than 0.1W; the rated voltage of the capacitors should not be less than 100V, and the capacitance value should be more than 10 times that of the TVS junction capacitance to ensure that the influence of the TVS junction capacitance on the RC parameters is negligible.

[0191] The rated current of the magnetic bead is not less than 2A, the reverse working voltage of the TVS tube is not less than the working voltage of the flexible board 1, and the peak pulse power is not less than 200W.

[0192] Step 8: Assembly The protective layer 2 with the composite mesh isolation layer 22 is attached to the surface of the flexible wire plate 1, with the mesh isolation layer 22 facing the side of the flexible wire plate 1, and the protective layer 2 and the flexible wire plate 1 are fixed together by heat pressing.

[0193] For the electrical connection between the mesh isolation layer 22 and the grounding structure 23, welding is preferred in bending areas, while conductive adhesive can be used in non-bending areas to reduce manufacturing costs. For applications with high reliability requirements, such as automotive applications, welding is preferred for all connections.

[0194] The principle for selecting the grounding method is as follows: when the size of the mesh isolation layer 22 is small (length less than 50mm) or the operating frequency is low (below 10MHz), a single-point grounding method is adopted; when the size of the mesh isolation layer 22 is large (length greater than 100mm) or the operating frequency is high (above 100MHz), a multi-point grounding method is adopted, the distance between adjacent grounding points does not exceed 50mm, and each grounding point is connected in series with an independent RC network or ferrite bead.

[0195] Step 9: Cover with an insulating protective layer An insulating protective layer is covered on the surface of the mesh isolation layer 22 to prevent accidental contact between the mesh isolation layer 22 and other conductors. The insulating protective layer can be formed by coating, bonding or spraying.

[0196] Example 12 Performance testing The following performance tests were conducted on the flexible wire plate assembly of the present invention to verify its technical effectiveness: (a) Electromagnetic shielding effectiveness test The test was conducted in accordance with GB / T30142-2013 "Method for measuring the shielding effectiveness of electromagnetic shielding coatings".

[0197] Test results show that, in the frequency range of 10MHz to 3GHz, the shielding effectiveness of the flexible wire board assembly of the present invention reaches 30dB to 60dB, which is better than the 5dB to 10dB of the control group without a shielding layer.

[0198] When the mesh count of the isolation layer 22 is 100 meshes and the copper wire diameter is 0.15mm, the shielding effectiveness reaches more than 45dB, which can effectively suppress electromagnetic interference from the external environment.

[0199] (ii) Grounding resistance test The continuity resistance between the grounding structure 23 and the ground layer of the flexible board 1 was measured using the four-probe method. The test results show that the continuity resistance is less than 0.5 ohms, which is better than the level of less than 1 ohm in the prior art. The low continuity resistance ensures the rapid discharge of electrostatic and electromagnetic interference signals.

[0200] (III) Bending life test Bending life test was performed according to IPC-TM-650 standard.

[0201] The test conditions were: bending radius 5mm, bending frequency 60 times / minute, and bending angle 180°. The test results showed that the bending life of the flexible wire plate assembly of the present invention reached more than 100,000 times, while the bending life of the control group without the mesh isolation layer was about 80,000 times. The mesh structure of the mesh isolation layer 22 can generate stress release during bending and will not significantly reduce the bending life of the flexible wire plate.

[0202] For the sample with an inverted trapezoidal groove structure and rounded corner transition (rounded corner radius 0.1mm), after the bending life test, the sample was cross-sectioned and inspected. No cracks were found to have started at the bottom corner of the groove, and the mesh isolation layer 22 did not come off or lift up from the groove 21. This indicates that the rounded corner transition structure effectively reduced stress concentration. The inverted trapezoidal structure combined with the dual fixing mechanism of hot pressing process has excellent shear resistance and fatigue resistance.

[0203] After 80,000 bending cycles, a cross-section inspection of the comparison sample (without rounded corners and sharp bottom corners) revealed microcracks at the bottom corners of the grooves, verifying the necessity of rounded corners for improving fatigue life.

[0204] (iv) Electrostatic discharge test Electrostatic discharge testing was performed in accordance with IEC 61000-4-2 standard.

[0205] The test conditions were: contact discharge ±8kV and air discharge ±15kV. The test results showed that the sample equipped with TVS tubes and connected in parallel could work normally under all test conditions without signal interruption, data loss or component damage. The electrostatic charge was quickly discharged to ground through the TVS tubes, effectively protecting the internal circuitry.

[0206] In the comparative test, about 5% of the samples without TVS diodes but with RC networks experienced signal interruption under air discharge conditions of ±15kV, verifying the necessity of TVS diodes for improving ESD protection reliability.

[0207] (v) Ground loop interference test Ground loop interference tests were conducted on samples equipped with RC networks.

[0208] An alternating magnetic field is injected into the loop between the mesh isolation layer 22 and the grounding structure 23 in the frequency range of 100kHz to 100MHz, and the induced noise voltage on the grounding structure 23 is measured.

[0209] Test results show that the induced noise voltage on the grounding structure 23 of the control group sample without the RC network reaches 50mV to 200mV; while the induced noise voltage on the grounding structure 23 of the sample with the RC network is reduced to 5mV to 20mV, and the ground loop interference is effectively suppressed, verifying the effectiveness of the RC network in suppressing ground loop interference.

[0210] (vi) Verification test of the effect of TVS junction capacitance on RC parameters The parameter stability of the sample connected in parallel with the TVS diode and the RC network was tested. The test samples were divided into two groups: Group A, C242=10nF, TVS junction capacitance Cj=100pF (C242=100×Cj); Group B, C242=100pF, TVS junction capacitance Cj=100pF (C242=Cj).

[0211] Test results show that the RC cutoff frequency deviation of group A is less than 1%, and the influence of TVS junction capacitance on the RC network parameters is negligible; the RC cutoff frequency deviation of group B reaches 50%, and the high-frequency characteristics of the RC network are significantly shifted, verifying that when C242≥10×Cj, the influence of TVS junction capacitance on the RC network parameters is within an acceptable range.

[0212] (vii) Long-term reliability comparison test between conductive adhesive and welded joint Samples connected by conductive adhesive and samples connected by welding were subjected to 100,000 bending tests (bending radius 5 mm, frequency 60 times / minute, angle 180°). The test results showed that the grounding resistance change rate of the sample connected by conductive adhesive was 18%, and the grounding resistance change rate of the sample connected by welding was 4%.

[0213] In the bending region, welded connections exhibit superior long-term reliability, validating the rationale for prioritizing welded connections in the bending region.

[0214] Example 13 Variant implementation Variation 1: Multi-segment mesh isolation layer In some implementations, the mesh isolation layer 22 may be discontinuously disposed on the protective layer 2, but rather divided into multiple segments, each disposed in the area requiring key shielding. This design can reduce the amount of copper wire used, lower costs, and improve the flexibility of the flexible board in the unshielded area while ensuring the shielding effect in the critical area.

[0215] Variation 2: Composite of mesh isolation layer and other shielding layers In some implementations, the mesh isolation layer 22 can be used in combination with other types of shielding layers such as conductive cloth or metal foil.

[0216] For example, a conductive cloth can be covered on the surface of the mesh isolation layer 22 to form a double-layer shielding structure, which further improves the shielding effectiveness. The shielding effectiveness of the composite shielding layer can reach more than 1.5 times that of a single-layer mesh isolation layer.

[0217] Variation 3: Surface treatment of the mesh isolation layer In some embodiments, the copper wire surface of the mesh isolation layer 22 can be tin-plated, silver-plated, or gold-plated. Surface treatment can improve the solderability, oxidation resistance, and conductivity of the copper wire. The surface resistance of the copper wire after silver plating can be reduced by more than 20%, and the copper wire after gold plating has the best oxidation resistance and is suitable for applications with high reliability requirements.

[0218] Variation 4: Non-copper woven mesh Although the present invention preferably uses a copper wire braided mesh as the isolation layer, in certain specific applications, a mesh structure woven from silver wire, gold wire or other conductive metal wires may also be used. Silver wire has better conductivity than copper wire, but it is more expensive; gold wire has the best oxidation resistance and is suitable for extreme environments. Those skilled in the art can choose the appropriate material according to the specific application requirements.

[0219] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this disclosure (including the claims) is limited to these examples; within the framework of this disclosure, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this specification as described above, which are not provided in detail for the sake of brevity.

[0220] Although this disclosure has been described in conjunction with specific embodiments thereof, many substitutions, modifications and variations of these embodiments will be apparent to those skilled in the art from the foregoing description.

[0221] One or more embodiments of this specification are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification should be included within the scope of protection of this disclosure.

Claims

1. A flexible wire plate assembly with electromagnetic shielding function, characterized in that, include: A flexible wire plate (1) is provided with a number of parallel wire grooves (11) and a number of parallel or braided wire cores (12) are provided in the wire grooves (11). A protective layer (2) covers at least one side surface of the flexible wire plate (1); A mesh isolation layer (22) is disposed on the surface of the protective layer (2) or embedded in a groove (21) on the surface of the protective layer (2); as well as The grounding structure (23) is electrically connected to the mesh isolation layer (22) and is used to connect the mesh isolation layer (22) to an external grounding terminal.

2. The flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: The mesh isolation layer (22) is composed of a mesh structure woven from copper wires, and the mesh units of the mesh structure are arranged in rhombus, rectangle or hexagon; the diameter of the copper wires in the mesh isolation layer (22) is 0.05mm to 0.5mm, and the mesh number of the mesh isolation layer (22) is 10 mesh to 200 mesh.

3. A flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: The grounding structure (23) is a grounding pin, grounding piece or conductive connection end extending from the mesh isolation layer (22), and the grounding structure (23) is electrically connected to the mesh isolation layer (22); The mesh isolation layer (22) is electrically connected to the flexible wire plate (1) through conductive adhesive, and the surface of the mesh isolation layer (22) is also covered with an insulating protective layer (3).

4. A flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: The protective layer (2) is made of a flexible insulating material, and the mesh isolation layer (22) is disposed on the surface of the protective layer (2) facing the flexible wire plate (1). The mesh isolation layer (22) and the protective layer (2) are fixedly connected by bonding or pressing. The protective layer (2) is made of any one of the flexible insulating materials selected from polyimide, polyethylene terephthalate, polyethylene naphthalate, liquid crystal polymer or polytetrafluoroethylene.

5. A flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: The surface of the protective layer (2) is recessed inward to form a groove (21), and the mesh isolation layer (22) is embedded in the groove (21). The upper surface of the mesh isolation layer (22) is not higher than the surface of the protective layer (2). The depth of the groove (21) is greater than or equal to the thickness of the mesh isolation layer (22), and the outline shape of the groove (21) is adapted to the shape of the mesh isolation layer (22).

6. A flexible wire board assembly with electromagnetic shielding function according to claim 5, characterized in that: The cross-section of the groove (21) is an inverted trapezoidal structure, and the angle between the side wall and the bottom wall of the inverted trapezoidal structure is 100° to 150°. A rounded corner with a radius of 0.05mm to 0.2mm is provided at the junction of the bottom wall and the side wall of the inverted trapezoidal structure. After the mesh isolation layer (22) is embedded in the groove (21), it is fixed by hot pressing. The heating area of ​​the hot pressing mold corresponds only to the edge of the groove (21) within a range of 0.5mm to 2mm, so that the material of the protective layer (2) is partially melted and only wraps the outermost edge of the mesh isolation layer (22) within a range of 0.5mm to 2mm. The internal mesh area of ​​the mesh isolation layer (22) is not penetrated by the molten material.

7. A flexible wire board assembly with electromagnetic shielding function according to claim 5, characterized in that: The groove (21) is not provided in the bending area of ​​the flexible wire plate (1), and the groove (21) is only provided in the non-bending area or the bending radius of the flexible wire plate (1) is greater than 10mm.

8. A flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: A resistor-capacitor network or ferrite bead is connected in series between the grounding structure (23) and the mesh isolation layer (22). The resistor-capacitor network consists of a resistor and a capacitor connected in parallel. The resistance of the resistor is 0 ohms to 1000 ohms, and the capacitance of the capacitor is 10pF to 100nF. A transient voltage suppression diode is also connected in parallel between the grounding structure (23) and the grid isolation layer (22). The transient voltage suppression diode is connected in parallel with the RC network or ferrite bead. That is, one end of the transient voltage suppression diode is connected to the grounding structure (23) together with the input end of the RC network or ferrite bead, and the other end of the transient voltage suppression diode is connected to the grid isolation layer (22) together with the output end of the RC network or ferrite bead.

9. A flexible wire board assembly with electromagnetic shielding function according to claim 8, characterized in that: The capacitance value of the capacitor is greater than 10 times the junction capacitance of the transient voltage suppression diode, and the peak pulse power of the transient voltage suppression diode is not less than 200W.

10. A flexible wire board assembly with electromagnetic shielding function according to claim 1, characterized in that: The flexible circuit board (1) is a flat flexible circuit board, and the protective layer (2) is attached to at least one side surface of the flexible circuit board (1). The thickness of the protective layer (2) is 0.01 mm to 0.5 mm.

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