Processing method of reinforcing steel sheet for flexible circuit board

Abstract

The invention discloses a processing method of a reinforcing steel sheet for a flexible circuit board, which comprises the following steps of: pasting a first pure adhesive film capable of being thermally cured on the surface of a target steel sheet, and performing hot-pressing curing on the pure adhesive film to form a body insulating layer; a second pure adhesive film is attached to the other surface of the target steel sheet to form an adhesion layer; and integrally cutting the target steel sheet comprising the body insulating layer and the adhesion layer according to a preset size to obtain the reinforcing steel sheet. According to the invention, the construction of the insulating layer and the forming process of the steel sheet are clearly separated, so that the reinforced steel sheet still keeps a stable and continuous exposed insulating interface after being formed, and the risk of short circuit between exposed metal of the steel sheet and a flexible circuit board circuit or an external device is reduced structurally; and the electrical safety and the long-term reliability of the reinforcing steel sheet in a complex assembly environment are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of flexible circuit board manufacturing technology, and in particular to a method for processing reinforcing steel sheets for flexible circuit boards. Background Technology

[0002] Flexible circuit boards (PCBs) are widely used in consumer electronics, communication equipment, and automotive electronics due to their flexibility, light weight, and adaptability to various spaces. During the manufacturing and assembly of PCBs, metal reinforcing sheets are typically placed on areas that need to withstand insertion / extraction forces or localized loads, such as connector mounting areas and chip carrier areas, to improve the mechanical strength and dimensional stability of these areas. These reinforcing sheets are often made of stainless steel or other metal materials, which possess high strength and rigidity.

[0003] Because metallic materials are conductive, when reinforcing steel sheets are used in flexible circuit boards, the exposed surfaces and edges of the reinforcing steel sheets can easily cause short circuits if they come into contact with the circuitry, pads, or surrounding electronic components of the flexible circuit board. Therefore, reliable insulation treatment is required for the reinforcing steel sheets. In existing technologies, insulation is often achieved by spraying or printing insulating coatings on the surface of the reinforcing steel sheets, or by attaching insulating tape or protective films to the surface of the steel sheets.

[0004] However, in actual processing and use, the above insulation methods still have shortcomings in terms of film uniformity, edge coverage integrity, and structural stability in subsequent punching or assembly processes. They are prone to forming weak points in insulation at the edges or cut areas of the steel sheet, affecting the electrical safety and long-term reliability of the reinforcing steel sheet in complex assembly environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a processing method for reinforcing steel sheets for flexible circuit boards, which enables the reinforcing steel sheets to maintain a stable and continuous exposed insulation interface after forming.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for processing reinforcing steel sheets for flexible circuit boards includes the following steps: S1. Apply a heat-curable first pure adhesive film to the surface of the target steel sheet, and heat-press the pure adhesive film to form a body insulation layer. S2. Apply a second pure adhesive film to the other surface of the target steel sheet to form an adhesive layer; S3. Cut the target steel sheet, including the main body insulation layer and the adhesive layer, into a whole according to the preset size to obtain the reinforcing steel sheet.

[0007] The beneficial effects of the present invention are as follows: a processing method for reinforcing steel sheets for flexible circuit boards is provided. By first applying and hot-pressing a first pure adhesive film to one surface of the target steel sheet to form a stable body insulation layer, and then applying a second pure adhesive film to the other surface to form an adhesion layer, and then cutting the whole structure after the double-layer structure is completed, the system optimization of the insulation structure and processing technology of the reinforcing steel sheet is achieved.

[0008] Because the main insulating layer has been thermo-cured before the overall cutting, it will not flow or deform during subsequent cutting, thus effectively resisting the shear and extrusion forces generated during cutting and preventing damage, cracking, or peeling of the insulating layer at the edges. Meanwhile, the adhesive layer only serves to bond with the flexible circuit board; its material state and mechanical properties do not affect the integrity of the main insulating layer.

[0009] By clearly separating the insulation layer construction from the steel sheet forming process, the reinforcing steel sheet maintains a stable and continuous exposed insulation interface after forming. This structurally reduces the risk of short circuits between the exposed metal of the steel sheet and the flexible circuit board circuit or external devices, significantly improving the electrical safety and long-term reliability of the reinforcing steel sheet in complex assembly environments. Attached Figure Description

[0010] Figure 1 The state of the insulation layer of the reinforcing steel sheet produced in the prior art; Figure 2 This is a flowchart illustrating a method for processing reinforcing steel sheets for flexible circuit boards according to an embodiment of the present invention. Figure 3 This refers to the state of the insulating layer of the reinforcing steel sheet produced by a processing method for a reinforcing steel sheet used in flexible circuit boards in this invention. Figure 4 This is a schematic diagram of the structure of a reinforcing steel sheet in an embodiment of the present invention; Label Explanation: 1. Target steel sheet; 2. Body insulation layer; 3. Adhesive layer. Detailed Implementation

[0011] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0012] Before detailing the embodiments of this application, some related concepts will first be explained: Pure adhesive film refers to a film-like material formed solely by the colloidal material itself, without any substrate, reinforcing fibers, or supporting film. This film exhibits good adhesion in its uncured state and forms a continuous, dense structural layer after curing. The material itself simultaneously undertakes both film formation and functional fulfillment.

[0013] The body insulation layer refers to the insulation structure layer formed by the insulation material itself and directly bonded to the surface of the target steel sheet after curing. This insulation structure layer exists as part of the reinforcing steel sheet structure, rather than an independently attached cover layer.

[0014] In existing technologies, the common methods are either "first punching and forming, then performing insulation treatment" or "simultaneously applying the insulation layer and adhesive layer before punching and forming." However, the process of punching and forming first, followed by insulation treatment, is relatively fragmented, which is not conducive to improving overall processing efficiency; for example... Figure 1 As shown, when the insulation layer and adhesive layer are simultaneously applied and then punched, the mechanical shearing and extrusion forces generated during the punching process will act on both the insulation layer and the adhesive layer. This can easily cause the insulation layer to be deformed by extrusion at the edge of the cut, generate micro-cracks, or partially peel off from the steel sheet substrate. This can create potential weak points in the insulation at the edge of the reinforcing steel sheet, affecting the electrical safety and reliability of the reinforcing steel sheet during subsequent assembly and long-term use.

[0015] To at least solve the above problems, please refer to Figures 2 to 4 This invention provides a method for processing reinforcing steel sheets for flexible circuit boards, including the following steps: S1. Apply a heat-curable first pure adhesive film to the surface of the target steel sheet, and heat-press the pure adhesive film to form a body insulation layer. S2. Apply a second pure adhesive film to the other surface of the target steel sheet to form an adhesive layer; S3. Cut the target steel sheet, including the main body insulation layer and the adhesive layer, into a whole according to the preset size to obtain the reinforcing steel sheet.

[0016] As can be seen from the above description, the beneficial effects of the present invention are as follows: by first applying and hot-pressing a first pure adhesive film to one surface of the target steel sheet to form a stable body insulation layer, and then applying a second pure adhesive film to the other surface to form an adhesion layer, and then cutting the whole structure after the double-layer structure is completed, the system optimization of the insulation structure and processing technology of the reinforced steel sheet is achieved.

[0017] Because the main insulating layer has been thermo-cured before the overall cutting, it will not flow or deform during subsequent cutting, thus effectively resisting the shear and extrusion forces generated during cutting and preventing damage, cracking, or peeling of the insulating layer at the edges. Meanwhile, the adhesive layer only serves to bond with the flexible circuit board; its material state and mechanical properties do not affect the integrity of the main insulating layer.

[0018] By clearly separating the insulation layer construction from the steel sheet forming process, the reinforcing steel sheet maintains a stable and continuous exposed insulation interface after forming. This structurally reduces the risk of short circuits between the exposed metal of the steel sheet and the flexible circuit board circuit or external devices, significantly improving the electrical safety and long-term reliability of the reinforcing steel sheet in complex assembly environments. In some embodiments, the heat-curable first pure adhesive film is an epoxy pure adhesive film.

[0019] As described above, defining the first pure adhesive film as an epoxy pure adhesive film provides a clear material system basis for the formed bulk insulating layer. The epoxy resin system, after curing, exhibits high dielectric strength, good heat resistance, and stable chemical properties, enabling it to withstand reflow soldering, hot-pressing, and other process conditions during flexible circuit board assembly and use without performance degradation.

[0020] By using a pure epoxy film instead of a sprayed coating or a composite film with a substrate, the resulting insulation layer is a continuous and dense colloidal structure, eliminating issues such as pinholes, insufficient edge coverage, or substrate delamination. This results in more uniform and reliable insulation performance on the exposed surface of the reinforcing steel sheet. Furthermore, this pure epoxy film can form a stable bonding interface with the steel sheet surface under hot-pressing conditions, which helps maintain the integrity of the insulation layer during subsequent machining and long-term service, thereby further enhancing the safety of the reinforcing steel sheet.

[0021] Specifically, the thickness of the epoxy pure adhesive film is less than 40 μm, preferably 15-35 μm. Within this thickness range, the epoxy pure adhesive film can form a continuous and stable insulating layer after curing, meeting the basic requirements for short circuit prevention on the exposed surface of the reinforcing steel sheet, while avoiding stress concentration during cutting or a decrease in molding accuracy due to excessive adhesive layer thickness.

[0022] In some embodiments, in step S1, the temperature range of hot pressing curing is 150-170°C, and the pressure range is 0.5-0.8 MPa.

[0023] As described above, the temperature and pressure range for the hot-pressing curing of the first epoxy pure adhesive film are limited, allowing the epoxy pure adhesive film to fully cure on the steel sheet surface and form a stable structure. Under these temperature and pressure conditions, the epoxy pure adhesive film can complete an effective cross-linking reaction, forming a dense and uniform bulk insulation layer, while avoiding problems such as adhesive layer aging, excessive internal stress, or steel sheet deformation caused by excessive temperature or pressure.

[0024] In some embodiments, in step S3, the target steel sheet, including the main insulating layer and the adhesive layer, is cut as a whole according to a preset size, specifically as follows: The reinforcing steel sheet, including the main insulating layer and the adhesive layer, is stamped with a mold according to a preset size.

[0025] As described above, limiting the overall cutting method to die stamping ensures high dimensional accuracy and processing efficiency in the forming process of the reinforcing steel sheet. Since the insulating layer is cured before stamping, it is less prone to deformation or peeling during the die stamping process, thus ensuring the continuity of the insulating layer at the edges of the steel sheet after stamping. Compared to punching with the insulating layer uncured, the above process effectively reduces the risk of edge insulation failure, enabling the highly efficient die stamping method to be stably applied to the mass production of reinforcing steel sheets, balancing processing efficiency and product reliability.

[0026] In some implementations, step S3 is followed by step S4: The adhesive layer of the reinforcing steel sheet is adhered to the target flexible circuit board.

[0027] As described above, the further step of adhering the reinforcing steel sheet to the target flexible circuit board via an adhesive layer creates a direct correspondence between the structural design of the reinforcing steel sheet and its final usage state. Since the adhesive layer and the main insulating layer are located on opposite sides of the steel sheet, the adhesive layer bears the main bonding and stress buffering role during the bonding process, while the main insulating layer does not participate in the bonding stress, thus avoiding the insulating layer being affected by compression or shearing during assembly.

[0028] In some embodiments, the thickness of the target steel sheet ranges from 0.15 to 0.25 mm.

[0029] As can be seen from the above description, the thickness of the target steel sheet is limited to 0.15–0.25 mm, so that the reinforcing steel sheet can meet the local support requirements of connectors, chip carrier areas, etc., while avoiding adverse effects on the bending performance and assembly space of the flexible circuit board due to excessive thickness of the steel sheet.

[0030] In some embodiments, the thickness of the second pure adhesive film ranges from 25 to 60 μm.

[0031] As described above, limiting the thickness of the second pure adhesive film to 25–60 μm ensures sufficient adhesive volume and cushioning capacity when bonding the flexible circuit board. This thickness range helps compensate for minor surface irregularities between the steel sheet and the flexible circuit board, improving the contact adequacy and bonding reliability of the bonding interface.

[0032] Please refer to Figure 3 and Figure 4 A reinforcing steel sheet, manufactured using a processing method for reinforcing steel sheets used in flexible circuit boards, comprising: Target steel sheet; The body insulation layer is applied to one surface of the target steel sheet and completely cured. An adhesive layer is applied to the other surface of the target steel sheet.

[0033] As described above, a reinforcing steel sheet manufactured by the aforementioned processing method is provided. In this structure, a body insulating layer and an adhesive layer are respectively disposed on both sides of the steel sheet, and the body insulating layer is in a fully cured state. This structure ensures that, in its final use state, the exposed surface of the reinforcing steel sheet is always covered by a stable insulating layer, while the side in contact with the flexible circuit board is reliably fixed by the adhesive layer.

[0034] Please refer to Figures 2 to 4 Embodiment 1 of the present invention is as follows: A method for processing reinforcing steel sheets for flexible circuit boards, the method being applicable to forming reinforcing structures at locations requiring localized enhancement of mechanical strength, such as connector mounting areas and chip carrier areas of flexible circuit boards.

[0035] In this embodiment, a target steel sheet is first provided. The target steel sheet can be made of stainless steel and its thickness is controlled within the range of 0.15–0.25 mm to ensure the reinforcement strength while avoiding adverse effects on the overall flexibility of the flexible circuit board.

[0036] During the processing, a heat-curable first pure adhesive film is first applied to one surface of the target steel sheet. This first pure adhesive film is preferably an epoxy pure adhesive film with a thickness ranging from 15 to 35 μm. Subsequently, the target steel sheet with the first pure adhesive film applied undergoes a hot-press curing treatment. The hot-press curing temperature is controlled within the range of 150–170°C, and the pressure range is controlled within the range of 0.5–0.8 MPa, allowing the first pure adhesive film to fully cure on the steel sheet surface, forming a stable, integral insulating layer bonded to the steel sheet surface.

[0037] After the main insulating layer has cured, a second pure adhesive film is applied to the other surface of the target steel sheet. This second pure adhesive film is used to form an adhesion layer for subsequent bonding with the flexible circuit board, and its thickness is preferably 25–60 μm. This adhesion layer remains in a partially cured state during the processing stage to provide good adhesion and stress buffering capabilities during subsequent bonding.

[0038] Subsequently, the target steel sheet, which simultaneously possesses both a body insulation layer and an adhesive layer, is cut as a whole according to a preset size to obtain a single reinforcing steel sheet. In this embodiment, the overall cutting method preferably employs die stamping, enabling the reinforcing steel sheet to achieve high processing efficiency while ensuring dimensional accuracy. Since the body insulation layer has already undergone hot-press curing before cutting, it is less prone to flow or peeling during the stamping process, thereby ensuring the continuity and integrity of the insulation layer in the edge area of ​​the reinforcing steel sheet.

[0039] Please refer to Figure 3 and Figure 4 Embodiment two of the present invention is as follows: This embodiment provides a reinforcing steel sheet, which is suitable for areas of flexible circuit boards that require localized structural strength enhancement, such as connector mounting areas and chip carrier areas.

[0040] In this embodiment, the reinforcing steel sheet includes a target steel sheet, a body insulating layer, and an adhesive layer.

[0041] The target steel sheet is a metal steel sheet, preferably made of stainless steel, specifically SUS304 stainless steel, with a thickness of about 0.2 mm and a hardness grade of H, so as to ensure the reinforcing strength while taking into account the overall flexibility requirements of the flexible circuit board.

[0042] The main insulating layer is disposed on one surface of the target steel sheet and is in a fully cured state. The main insulating layer is composed of a pure epoxy resin film, which contains no substrate carrier and is formed solely from colloids. Its thickness is less than 40 μm, preferably 15–35 μm. The main insulating layer is directly bonded to the surface of the target steel sheet, forming a continuous and dense insulating structure for electrical isolation of the exposed surface of the target steel sheet.

[0043] The adhesive layer is disposed on the other surface of the target steel sheet for bonding and fixing to the flexible circuit board. The adhesive layer is composed of a second pure adhesive film, which may be an acrylic pure adhesive film with a thickness ranging from 25 to 60 μm. The adhesive layer remains in an incompletely cured or semi-cured state while the reinforcing steel sheet is in its formed state, so as to provide good adhesion performance and stress buffering capacity when bonding to the flexible circuit board.

[0044] In the final use state of the reinforcing steel sheet, the main insulating layer exists as the exposed insulating structure of the reinforcing steel sheet, and the adhesive layer is in direct contact with the flexible circuit board and is fixed thereto, thereby reducing the risk of short circuit between the exposed metal of the steel sheet and the circuit of the flexible circuit board or external devices while ensuring the reinforcement effect.

[0045] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for processing a reinforcing sheet for a flexible circuit board, characterized by, The method comprises the steps of: S1, coating a heat-curable first pure adhesive film on the surface of a target steel sheet, and heat-pressing and curing the pure adhesive film to form a body insulating layer; S2, coating a second pure adhesive film on the other surface of the target steel sheet to form an adhesive layer; S3, cutting the target steel sheet including the body insulating layer and the adhesive layer according to a preset size to obtain a reinforcing steel sheet.

2. The method of claim 1, wherein the method further comprises the step of: The heat-curable first pure adhesive film is an epoxy pure adhesive film.

3. The method of claim 2, wherein the method further comprises the step of: The thickness of the epoxy pure adhesive film is less than 40 μm.

4. The method of claim 3, wherein the step of forming the reinforcing sheet is performed by a process of: The thickness of the epoxy pure adhesive film ranges from 15 μm to 35 μm. ​ 5. The method of claim 1-4, wherein the method is characterized by: In the step S1, the temperature for heat-pressing and curing ranges from 150 ℃ to 170 ℃, and the pressure ranges from 0.5 MPa to 0.8 MPa.

6. The method of claim 1, wherein the method further comprises the step of: In the step S3, the target steel sheet including the body insulating layer and the adhesive layer is cut according to a preset size, specifically: The reinforcing steel sheet including the body insulating layer and the adhesive layer is die-stamped according to a preset size.

7. The method of claim 1, wherein the method further comprises the step of: The step S3 further comprises a step S4: The adhesive layer of the reinforcing steel sheet is adhered to a target flexible circuit board.

8. The method of claim 1, wherein the method further comprises the step of: The thickness of the target steel sheet ranges from 0.15 mm to 0.25 mm.

9. The method of claim 1, wherein the method further comprises the step of: The thickness of the second pure adhesive film ranges from 25 μm to 60 μm.

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