Flexible circuit board preparation method, flexible circuit board and rigid-flex board

Abstract

According to the preparation method of the flexible circuit board, the flexible circuit board and the rigid-flex board, the kerfs are formed in the first flexible copper-clad plate on the inner layer in advance, and after lamination, no matter how many layers of flexible copper-clad plates exist in the air layer area, actually, only the second flexible copper-clad plate on the outermost layer needs to be cut, so that the cutting difficulty is greatly reduced, and the production efficiency is improved. And laser with lower energy can be adopted for cutting, so that carbon black is avoided, and the reliability of a product is improved. Due to the fact that the cutting thickness is small, when a grinding tool is adopted for punching and mechanical milling, the base material cannot be pulled, burrs cannot be generated, and the size precision of the product is improved.

Description

Technical Field

[0001] The present invention relates to printed circuit board processing technology, and in particular to a method for preparing a flexible printed circuit board, a flexible printed circuit board, and a rigid-flex printed circuit board. Background Art

[0002] A flexible printed circuit board (FPC) is a printed circuit board made of a flexible substrate, which has high flexibility and bendability and is widely used in many fields.

[0003] As the number of layers of the FPC increases, the bending performance of the FPC becomes worse. Setting an air gap between the FPC layers can make the FPC have better bending performance. Figure 1 As a process flow chart of a method for manufacturing an air gap of a flexible printed circuit board, as Figure 1 shown, currently, for the production of the air gap: the adhesive layer 11 in the air gap area A is removed in advance, and then the flexible plates 12 of each layer are laminated together through the adhesive layer 11 and pressed, and finally the end position of the air gap area A is cut by laser cutting or mechanical milling to process the size width required by the specification.

[0004] As the number of layers of the flexible plate 12 increases, the overall thickness of the FPC reaches 1 mm - 2 mm, or even thicker. Using a laser to cut the end position of the air gap area A requires high energy and multiple processing times. It not only wastes the production capacity of the equipment, but also generates serious carbon black and adheres to the side walls, seriously affecting the reliability of the product. And because the flexible plate 12 uses a flexible substrate, using mechanical milling to cut the end position of the air gap area A will pull the substrate and generate burrs, affecting the dimensional accuracy of the FPC and subsequent assembly. Summary of the Invention

[0005] The present invention provides a method for preparing a flexible printed circuit board, a flexible printed circuit board, and a rigid-flex printed circuit board, which can avoid the generation of carbon black during laser cutting, improve the reliability of the product, avoid pulling the substrate and generating burrs when using die punching and mechanical milling, and improve the dimensional accuracy of the product.

[0006] In a first aspect, the present invention provides a method for preparing a flexible printed circuit board, including:

[0007] providing a plurality of adhesive sheets and a plurality of first flexible copper clad laminates, wherein the air gap areas are provided at the same positions of the adhesive sheets and the first flexible copper clad laminates, and the first flexible copper clad laminates have circuits extending in a first direction;

[0008] forming a window on the adhesive sheet, and the air gap area is located within the window;

[0009] Form slits on the first flexible copper clad laminate, where the slits are located at two opposite edges of the air layer region in the second direction, and the first direction and the second direction are perpendicular to each other in the plane of the first flexible copper clad laminate;

[0010] Stack the adhesive sheet and the first flexible copper clad laminate alternately, attach a second flexible copper clad laminate without circuits on the outermost adhesive sheets on both sides, and then press them together to obtain a laminated structure. The openings in the adhesive sheets between adjacent two flexible copper clad laminates form air layers;

[0011] Form circuits on the second flexible copper clad laminate;

[0012] Cut at the same positions of the slits on the second flexible copper clad laminate, and remove the areas on both sides of the slits to obtain a flexible printed circuit board.

[0013] Optionally, the first flexible copper clad laminate and the second flexible copper clad laminate are also provided with non-functional regions and bonding regions. The bonding regions are located on both sides of the air layer region in the first direction. There are circuits extending from the air layer region to the bonding regions in the first direction. The bonding regions are used for bonding rigid printed circuit boards, and the non-functional regions are located on both sides of the air layer region in the second direction.

[0014] Optionally, forming circuits on the second flexible copper clad laminate includes:

[0015] Form circuits in the air layer region and the bonding regions on the second flexible copper clad laminate, and form bonding pads and metal vias connecting different flexible copper clad laminates in the bonding regions on the second flexible copper clad laminate.

[0016] Optionally, the width of the opening along the second direction is greater than the width of the air layer region along the second direction.

[0017] Optionally, the distance between the two slits in the second direction is less than the width of the air layer region along the second direction.

[0018] Optionally, the distances between the two slits on at least two first flexible copper clad laminates in the second direction are different.

[0019] Optionally, the width range of the slit along the second direction is 0.2 mm - 0.5 mm.

[0020] Optionally, the methods for forming the opening, the slit, and cutting at the same positions of the slit on the second flexible copper clad laminate include laser cutting, die punching, and mechanical routing.

[0021] In a second aspect, the present invention also provides a flexible printed circuit board, which is prepared by using the method for preparing a flexible printed circuit board provided in the first aspect of the present invention.

[0022] In a third aspect, the present invention also provides a rigid-flex printed circuit board, which includes the flexible printed circuit board provided in the second aspect of the present invention.

[0023] In the method for preparing a flexible printed circuit board provided by the present invention, slits are formed in advance on the first flexible copper clad laminate of the inner layer. After lamination, regardless of the number of flexible copper clad laminates in the air layer region, in fact, only the outermost second flexible copper clad laminate needs to be cut, which greatly reduces the cutting difficulty. Laser with lower energy can be used for cutting, avoiding the generation of carbon black and improving the reliability of the product. Since the cutting thickness is small, when using a die punch and mechanical milling, the substrate will not be pulled and burrs will not be generated, improving the dimensional accuracy of the product. Description of the Drawings

[0024] The present invention will be further described in detail below with reference to the drawings and embodiments.

[0025] Figure 1 It is a top view of the adhesive sheet and the first flexible copper clad laminate provided by the present invention;

[0026] Figure 2 It is a schematic diagram after windowing the adhesive sheet of the present invention;

[0027] Figure 3 It is a schematic diagram after slitting the first flexible copper clad laminate of the present invention;

[0028] Figure 4 It is a schematic diagram of the laminated structure after lamination provided by the present invention;

[0029] Figure 5 It is a schematic diagram of cutting the second flexible copper clad laminate provided by the present invention;

[0030] Figure 6 It is a schematic diagram of the structure of a flexible printed circuit board provided by the present invention. Detailed Embodiments

[0031] To make the technical problems solved, the technical solutions adopted, and the technical effects achieved by the present invention clearer, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0032] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connected", "connected to", and "fixed" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0033] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "above and to the upper side", and "on the upper surface" of the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "below and to the lower side", and "on the lower surface" of the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature. In addition, the terms "first" and "second" are only used for distinction in description and have no special meanings.

[0034] The present invention provides a method for preparing a flexible printed circuit board, and the method for preparing the flexible printed circuit board includes:

[0035] S101. Provide a plurality of bonding sheets and a plurality of first flexible copper clad laminates. Air layer regions are provided at the same positions of the bonding sheets and the first flexible copper clad laminates, and the first flexible copper clad laminate has a circuit extending in a first direction.

[0036] Figure 1 is a top view of the bonding sheet and the first flexible copper clad laminate provided by the present invention. As Figure 1 shown, air layer regions AA are provided at the same positions of the bonding sheet 110 and the first flexible copper clad laminate 120. Among them, the same position means the position where the vertical projections completely coincide after the bonding sheet 110 and the first flexible copper clad laminate 120 are laminated. That is, after the bonding sheet 110 and the first flexible copper clad laminate 120 are laminated, the vertical projections of the air layer regions AA of each layer completely coincide. Exemplarily, the first flexible copper clad laminate 120 includes a flexible substrate and a copper foil attached to the flexible substrate, and the copper foil is subjected to a patterning process to form a circuit extending in a first direction X. The material of the flexible substrate may include, but is not limited to, polyimide film (PI) and polyester film (PET). The material of the bonding sheet 110 may include, but is not limited to, FR4, PPE, PI, MPI, LCP, PTFE, and hydrocarbon resin, etc., and the present invention does not make any limitations here.

[0037] In some embodiments of the present invention, as Figure 1As shown, the first flexible copper clad laminate 120 is further provided with a non-functional area A1 and a bonding area A2. The bonding area A2 is located on both sides of the air layer area AGA in the first direction X. A circuit extending to the bonding area A2 in the first direction X is provided in the air layer area AGA. The bonding area A2 is used for bonding a rigid circuit board. The non-functional area A1 is located on both sides of the air layer area AGA in the second direction Y, and no circuit is provided in the non-functional area A1.

[0038] S102. Form a window opening on the adhesive sheet, and the air layer area is located within the window opening.

[0039] Figure 2 This is a schematic diagram of the adhesive sheet after window opening according to the present invention. As Figure 2 shown, a window opening 111 is formed on the adhesive sheet 110, and the air layer area AA is located within the window opening 111.

[0040] Exemplarily, the method for forming a window opening on the adhesive sheet includes, but is not limited to, laser cutting, die punching, and mechanical routing.

[0041] S103. Form a slit on the first flexible copper clad laminate. The slit is located at two opposite edges of the air layer area in the second direction. The first direction and the second direction are perpendicular to each other within the plane of the first flexible copper clad laminate.

[0042] Figure 3 This is a schematic diagram of the first flexible copper clad laminate after slitting according to the present invention. As Figure 3 shown, a slit 121 is formed on the first flexible copper clad laminate 120. The slit 121 is located at two opposite edges of the air layer area AGA in the second direction Y. The first direction X and the second direction Y are perpendicular to each other within the plane of the first flexible copper clad laminate 120. In some embodiments of the present invention, the width range of the slit 121 in the second direction Y is 0.2 mm - 0.5 mm.

[0043] Exemplarily, in some embodiments of the present invention, the sum of the widths of the two slits 121 in the second direction Y and the width of the air layer area AGA in the second direction Y is equal to the width of the window opening 111 in the second direction Y.

[0044] Exemplarily, in some embodiments of the present invention, the distances H between the two slits 121 on at least two first flexible copper clad laminates 120 in the second direction Y are different, that is, the distances H between the two slits 121 on each first flexible copper clad laminate 120 in the second direction Y can be separately designed and controlled as needed.

[0045] Exemplarily, the method for forming a slit on the first flexible copper clad laminate includes, but is not limited to, laser cutting, die punching, and mechanical routing.

[0046] S104. Alternately stack the adhesive sheet and the first flexible copper clad laminate, attach the second flexible copper clad laminate without circuitry on the outermost adhesive sheets on both sides, and then perform lamination to obtain a laminated structure. An air layer is formed by the opening of the adhesive sheet between adjacent two flexible copper clad laminates.

[0047] Figure 4 FIG. is a schematic diagram of the laminated structure after lamination provided by the present invention. As Figure 4 shown, alternately stack the adhesive sheet 110 after opening and the first flexible copper clad laminate 120 after slitting in the Z direction (the Z direction is the direction perpendicular to the plane of the flexible copper clad laminate), attach the second flexible copper clad laminate 130 without circuitry on the outermost adhesive sheets 110 on both sides, and then perform lamination by means of thermal lamination to obtain a laminated structure. An air layer Airgap is formed by the opening of the adhesive sheet 110 between adjacent two flexible copper clad laminates. The second flexible copper clad laminate 130 includes a flexible substrate and a copper foil attached to the flexible substrate, and the copper foil is not patterned. It should be noted that Figure 4 the number of layers of the flexible copper clad laminate and the adhesive sheet in [FIG.] is an exemplary illustration rather than a limitation of the present invention.

[0048] Exemplarily, during the process of alternately stacking the adhesive sheet 110 and the first flexible copper clad laminate 120, methods such as riveting, binding, and hot melting can be used for interlayer fixation to ensure the interlayer alignment accuracy.

[0049] Exemplarily, during the lamination process, conformal materials such as kraft paper, HDPE, aluminum sheet, and buffer pads can be provided on the surface of the second flexible copper clad laminate 130 to avoid damage to the copper foil of the second flexible copper clad laminate 130. At the same time, it is convenient for the peeling of the conformal material after lamination.

[0050] S105. Form circuitry on the second flexible copper clad laminate.

[0051] After lamination, perform patterning on the second flexible copper clad laminate 130 to form circuitry on the second flexible copper clad laminate. Exemplarily, the process of patterning includes but is not limited to film pasting, exposure, development, and etching; the equipment involved includes but is not limited to circuitry equipment for printed circuit boards such as a film pasting machine, a vacuum film pasting machine, an LDI exposure machine, an etching line, and a vacuum etching line.

[0052] In the embodiment of the present invention, the second flexible copper clad laminate 130 is also provided with a non-functional area A1 and a bonding area A2, and is set at the same position as the first flexible copper clad laminate 120. Forming circuitry on the second flexible copper clad laminate includes:

[0053] On the air layer region AGA and the bonding region A2 on the second flexible copper clad laminate 130, circuits are formed, and on the bonding region A2 on the second flexible copper clad laminate 130, bonding pads and metal vias connecting different flexible copper clad laminates are formed. Among them, the bonding pads are used to achieve electrical connection with the rigid circuit board.

[0054] S106. Cut at the same positions of the slits on the second flexible copper clad laminate, and remove the regions on both sides of the slits to obtain a flexible circuit board.

[0055] Figure 5 It is a schematic diagram of cutting the second flexible copper clad laminate provided by the present invention. As Figure 5 shown, cut at the same positions of the slit 121 on the second flexible copper clad laminate 130, and remove the regions on both sides of the slit 121 to obtain a flexible circuit board 100. Exemplarily, the methods for cutting at the same positions of the slit 121 on the second flexible copper clad laminate 130 include but are not limited to laser cutting, die punching, and mechanical routing. Since the inner first flexible copper clad laminate 120 is pre-formed with the slit 121, no matter how many layers of flexible copper clad laminates there are in the air layer region AA, in fact, only the outermost second flexible copper clad laminate 130 needs to be cut, which greatly reduces the cutting difficulty. Laser with lower energy can be used for cutting, avoiding the generation of carbon black and improving the reliability of the product. Since the cutting thickness is small, die punching and mechanical routing will not cause pulling on the substrate and generation of burrs, improving the dimensional accuracy of the product.

[0056] In the embodiment of the present invention, as Figure 2 shown, the width W1 of the opening 111 along the second direction Y is greater than the width W2 of the air layer region AGA along the second direction Y, so as to control the amount of overflow glue of the adhesive sheet 110 during the lamination process and avoid the molten overflow of the adhesive sheet 110 during the lamination process and block the slit 121. Exemplarily, in a specific embodiment of the present invention, the width W1 of the opening 111 along the second direction Y is 0.2 mm larger than the width W2 of the air layer region AGA along the second direction Y.

[0057] In some embodiments of the present invention, the distance H between the two slits 121 in the second direction Y is less than the width W2 of the air layer region AGA along the second direction Y to avoid poor Airgap size caused by interlayer misalignment after lamination. The specific size of the distance H between the two slits 121 in the second direction Y can be adjusted according to the actual interlayer alignment ability. Exemplarily, in a specific embodiment of the present invention, the distance H between the two slits 121 in the second direction Y is 0.05 mm - 0.1 mm smaller than the width W2 of the air layer region AGA along the second direction Y.

[0058] The flexible printed circuit board manufacturing method provided by the present invention forms slits on the first flexible copper clad laminate of the inner layer in advance. After lamination, no matter how many layers of flexible copper clad laminates there are in the air layer region, in fact, only the second flexible copper clad laminate of the outermost layer needs to be cut, greatly reducing the cutting difficulty. A laser with lower energy can be used for cutting, avoiding the generation of carbon black and improving the reliability of the product. Since the cutting thickness is small, when using a die punching and mechanical milling, it will not cause pulling on the substrate and generate burrs, improving the dimensional accuracy of the product.

[0059] The present invention also provides a flexible printed circuit board, which is prepared by using the flexible printed circuit board manufacturing method provided in any of the foregoing embodiments of the present invention. Figure 6 As shown in the structural schematic diagram of a flexible printed circuit board provided by the present invention, Figure 6 As shown, the flexible printed circuit board 100 includes an air layer region AGA and bonding regions A2 on both sides of the air layer region AGA. The flexible printed circuit board 100 includes multiple layers of alternately stacked flexible circuit layers (including the first flexible copper clad laminate inside and the second flexible copper clad laminate outside) and adhesive sheets. The part of the adhesive sheet corresponding to the air layer region AGA is opened to form an air layer Airgap. Circuits are formed on the flexible circuit layers in the air layer region AGA and extend to the bonding regions A2. Bonding pads and metal vias connecting different flexible copper clad laminates are formed in the bonding regions A2. Among them, the bonding pads are used to achieve electrical connection with the rigid printed circuit board. Specifically, the specific structure of the air layer region AGA has been described in detail in the foregoing embodiments, and the present invention will not elaborate here.

[0060] The present invention also provides a flexible printed circuit board, including the flexible printed circuit board provided in the foregoing embodiments of the present invention.

[0061] In the description herein, it should be understood that the orientation or positional relationships such as "upper", "lower", "left", "right", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0062] In the description of this specification, the description referring to terms such as "one embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example.

[0063] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0064] The technical principles of the present invention have been described above in conjunction with specific embodiments. These descriptions are only for explaining the principles of the present invention and cannot be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art can readily conceive of other specific embodiments of the present invention without creative efforts, and these embodiments will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible printed circuit board, characterized in that, Including: Providing a plurality of adhesive sheets and a plurality of first flexible copper clad laminates, wherein air layer regions are provided at the same positions of the adhesive sheets and the first flexible copper clad laminates, and circuits extending in a first direction are provided on the first flexible copper clad laminates; Forming openings in the adhesive sheets, with the air layer regions located within the openings; Forming slits in the first flexible copper clad laminates, the slits being located at two opposite edges of the air layer regions in a second direction, the first direction and the second direction being perpendicular to each other within the plane of the first flexible copper clad laminate; Alternately stacking the adhesive sheets and the first flexible copper clad laminates, and attaching second flexible copper clad laminates without circuits on the outermost adhesive sheets on both sides, and then pressing to obtain a laminated structure, with the openings in the adhesive sheets between adjacent two flexible copper clad laminates forming air layers; Forming circuits on the second flexible copper clad laminates; Cutting at the same positions of the slits on the second flexible copper clad laminates, and removing the regions on both sides of the slits to obtain a flexible printed circuit board.

2. The method for preparing a flexible printed circuit board according to claim 1, wherein The first flexible copper clad laminate and the second flexible copper clad laminate are also provided with non-functional regions and bonding regions, the bonding regions being located on both sides of the air layer region in the first direction, and circuits extending in the first direction to the bonding regions being provided within the air layer region, the bonding regions being used for bonding rigid printed circuit boards, and the non-functional regions being located on both sides of the air layer region in the second direction.

3. The method for preparing a flexible printed circuit board according to claim 2, wherein Forming circuits on the second flexible copper clad laminates includes: Forming circuits in the air layer regions and bonding regions on the second flexible copper clad laminates, and forming bonding pads and metal vias connecting different flexible copper clad laminates in the bonding regions on the second flexible copper clad laminates.

4. The method for manufacturing a flexible printed circuit board according to claim 1, wherein, The width of the openings in the second direction is greater than the width of the air layer regions in the second direction.

5. The method for preparing a flexible printed circuit board according to claim 1, wherein The distance between the two slits in the second direction is less than the width of the air layer regions in the second direction.

6. The method for preparing a flexible printed circuit board according to claim 1, wherein, The distances between the two slits in the second direction on at least two of the first flexible copper clad laminates are different.

7. The method for preparing a flexible printed circuit board according to claim 1, wherein The width of the slits in the second direction ranges from 0.2 mm to 0.5 mm.

8. The method for preparing a flexible printed circuit board according to claim 1, wherein, The methods for forming the openings, the slits, and cutting at the same positions of the slits on the second flexible copper clad laminates include laser cutting, die punching, and mechanical routing.

9. A flexible printed circuit board, characterized in that, Prepared and formed by using the flexible printed circuit board preparation method according to any one of claims 1-8.

10. A rigid-flex printed circuit board, characterized in that, Including the flexible printed circuit board according to claim 9.

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