Flexible board manufacturing method and flexible board

Abstract

The invention provides a soft board manufacturing method and a soft board, and the method comprises the steps: solidifying first glue on a core board to form a filling layer, and the first glue is magnetic inactivation glue; a window is formed in the bonding sheet; stacking and pressing the core board and the bonding sheet to form a mother board, and filling the window with the filling layer; a groove is formed in the side face of the mother board, a notch is formed in the side face of the groove, and the notch partially exposes the filling layer; applying an alternating magnetic field to melt the first glue, and discharging the first glue through the notch to form a cavity; and closing the notch to form a dielectric layer. The manufacturing method of the flexible board can be used for manufacturing the flexible board with the cavity serving as the dielectric layer.

Description

Technical Field

[0001] The present application relates to the field of circuit boards, and in particular to a method for manufacturing a flexible circuit board and a flexible circuit board. Background Art

[0002] A soft board (also known as FPC or flexible circuit board) is a bendable circuit board that is widely used in various wearable smart terminals. In order to meet the transmission requirements of high-frequency and high-speed signals (such as 5G high-speed signals), the requirements for the dielectric properties of FPC are correspondingly increased.

[0003] Therefore, the related technology generally adopts low dielectric constant, low loss and high flow adhesive sheets to make circuit boards. However, in the application scenario of 224G high-speed products, it is difficult to meet the low-loss transmission requirements of signals even with high-speed materials.

[0004] Since the dielectric constant of air (DK=1.00053) is much lower than that of conventional resin materials, some related technologies make a closed cavity at the signal line position of the circuit board and use the cavity as a dielectric layer to meet the transmission requirements of high-speed signals. However, this process cannot be implemented in flexible circuit boards at present. Summary of the invention

[0005] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a method for manufacturing a flexible board and a flexible board, wherein the method for manufacturing a flexible board can manufacture a flexible board having a cavity as a dielectric layer.

[0006] The method for manufacturing a flexible board provided by the present application includes: curing a first glue on a core board to form a filling layer, wherein the first glue is a magnetically inactivated glue; opening a window on a bonding sheet; stacking and pressing the core board and the bonding sheet to form a mother board, wherein the filling layer fills the window; opening a groove on a side of the mother board, wherein the groove forms a notch on the side, wherein the notch partially exposes the filling layer; applying an alternating magnetic field to melt the first glue, and discharging the first glue through the notch to form a cavity; and closing the notch to form a dielectric layer.

[0007] According to the flexible board manufacturing method provided by the present application, at least the following technical effects are achieved: first, by providing a filling layer before lamination and removing it after lamination, the present application can produce a cavity of suitable size in the flexible board to meet the dielectric performance requirements of the dielectric layer; second, the present application uses magnetically inactivated glue as the raw material of the filling layer, and utilizes the fluidity of the magnetically inactivated glue to better fit the circuit layer, thereby eliminating the need to provide a covering film and also achieving the effect of avoiding indentations on the circuit layer; finally, the magnetically inactivated glue will melt under an alternating magnetic field, thereby enabling the magnetically inactivated glue to be discharged through a notch smaller than the filling layer, thereby facilitating the subsequent closure of the notch; therefore, the flexible board manufacturing method can manufacture a flexible board having a cavity as a dielectric layer.

[0008] According to some embodiments of the present application, the height of the filling layer is greater than or equal to the thickness of the bonding sheet.

[0009] According to some embodiments of the present application, curing the first glue on the core board includes applying a first tape having the same height as the filling layer to the core board to define an area corresponding to the cavity; applying the first glue to the area; and peeling off the first tape after the first glue is cured.

[0010] According to some embodiments of the present application, the first glue is applied to a level higher than the first tape, and then excess first glue is scraped off before curing.

[0011] According to some embodiments of the present application, an excess of glue of the bonding sheet is left between the window and the filling layer.

[0012] According to some embodiments of the present application, the length of the groove is less than or equal to one third of the length of the filling layer.

[0013] According to some embodiments of the present application, the grooves are opened on the side surfaces at both sides, and airflow is applied from the groove on one side toward the groove on the other side to promote the discharge of the first glue.

[0014] According to some embodiments of the present application, a second glue is applied to the groove to close the cavity.

[0015] According to some embodiments of the present application, before applying the second glue, a second tape is applied to the surface of the motherboard, and after applying the second glue, the second tape is peeled off.

[0016] The soft board provided in the present application is manufactured using the soft board manufacturing method provided in the present application.

[0017] The soft board provided in the present application is manufactured using the soft board manufacturing method provided in the present application, so the soft board correspondingly has the beneficial effects provided by the soft board manufacturing method, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide further understanding of the technical solution disclosed in the present application and constitute a part of the specification. Together with the embodiments disclosed in the present application, they are used to explain the technical solution disclosed in the present application and do not constitute a limitation on the technical solution disclosed in the present application.

[0019] Figure 1 It is a schematic diagram of the process of manufacturing a flexible circuit board according to an embodiment of the present application;

[0020] Figure 2 is a schematic diagram of the structure of the flexible board in an embodiment of the present application;

[0021] Figure 3 It is a structural schematic diagram of the method for manufacturing a flexible board according to an embodiment of the present application when a tape is applied to a sub-board;

[0022] Figure 4 is a structural schematic diagram of a method for manufacturing a flexible board according to an embodiment of the present application when a filler is formed on a sub-board;

[0023] Figure 5 It is a structural schematic diagram of the flexible circuit board manufacturing method of the embodiment of the present application when the boards are arranged and pressed;

[0024] Figure 6 is a schematic structural diagram of a motherboard after being processed by the flexible board manufacturing method of an embodiment of the present application;

[0025] Figure 7 This is a schematic diagram of the structure of the flexible circuit board manufacturing method of the embodiment of the present application when notching;

[0026] Figure 8 It is a structural schematic diagram of the flexible board manufacturing method of the embodiment of the present application when the notch is blocked.

[0027] Reference numerals:

[0028] The core board 110 , the circuit layer 111 , the substrate 112 , the bonding sheet 210 , the cavity 220 , the filling layer 310 , the first adhesive tape 320 , the groove 330 , and the second adhesive tape 340 . DETAILED DESCRIPTION

[0029] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0030] In the description of the present application, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0031] In the description of this application, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0032] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application based on the specific content of the technical solution.

[0033] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0034] In order to meet the signal requirements of high-frequency circuit boards, some related technologies make a cavity at the signal position of the circuit board and use the cavity as a dielectric layer. However, the current related technologies generally make the cavity on a hard board.

[0035] In related technologies, in order to improve the bending ability of flexible boards, an air layer structure (also called air-gap) is generally set between two layers of sub-boards. The conventional practice is to make a groove on the adhesive sheet before lamination, put a gasket in the groove, and then make a groove from the side after lamination to pull out the gasket to form an air layer.

[0036] The air layer structure has certain similarities with the cavity as a dielectric layer, but the present application notes that the air layer structure cannot use air as the dielectric layer.

[0037] On the one hand, the dielectric layer requires a closed cavity, while the sides of the air layer are generally not closed, and in order to remove the gasket, the size of the side groove is large (greater than or equal to the length of the gasket), which is often difficult to achieve even if it is desired to be closed.

[0038] On the other hand, since the shape of the gasket is fixed, in order to avoid the gasket directly contacting the circuit layer during pressing and causing indentations on the circuit layer, and to avoid oxidation of the exposed circuit layer, a covering film must be attached to the circuit layer for protection when making the air layer. However, the covering film, as a dielectric material, will have a negative impact on the dielectric properties.

[0039] To this end, the present application provides a method for manufacturing a flexible circuit board, which is suitable for manufacturing a flexible circuit board having a cavity as a dielectric layer in the present application.

[0040] Figure 1 The basic process of the flexible circuit board manufacturing method of the present application is shown. Figure 2Correspondingly, an embodiment of a soft board manufactured using the soft board manufacturing method of the present application is shown. It can be understood that in this embodiment, the soft board is composed of two layers of core boards 110 sandwiched by a layer of adhesive sheet 210, the surface of the core board 110 has a circuit layer 111, and the core board 110 also includes a substrate 112. A cavity 220 serving as a dielectric layer is formed between the two layers of core boards 110, but the soft board applicable to the present application is not limited to this, and the soft board may also have more layers of core boards 110.

[0041] The following is based on Figure 1 , combined with Figures 2 to 8 , the flexible circuit board manufacturing method of this application is introduced.

[0042] The method for manufacturing a flexible circuit board provided in the present application includes the following steps.

[0043] Step S110: curing the first glue on the core board 110 to form a filling layer 310, wherein the first glue is magnetically inactivated glue.

[0044] It is understood that the filling layer 310 is used to form the cavity 220 later. Figure 5 The filling layer 310 does not need to cover the entire core board 110 , and the filling layer 310 only needs to be selectively provided in a local area of ​​the core board 110 that has a higher signal requirement.

[0045] In addition, the flexible board has a multi-layer core board 110, and only the cavity 220 needs to be formed between the two core boards 110 with signal requirements. Therefore, not all core boards 110 need to form a filling layer 310. The present application can flexibly set the position of the filling layer 310 according to the signal requirements.

[0046] The magnetic deactivation glue is a polyurethane adhesive containing tiny iron oxide particles. After curing, the magnetic deactivation glue can be melted and debonded under a certain magnetic field strength, so as to facilitate removal. Since it is directly cured on the core board 110, the first glue can flow fully on the core board 110, fill the uneven parts on the substrate 110, compensate for the height difference between the circuit layer 111 and the substrate 112, and make the filling layer 310 better adapt to the shape change of the circuit layer 111.

[0047] Optionally, in some embodiments, the core board 110 may use a standard flexible copper-clad laminate, wherein the substrate 112 is polyimide to provide good bending performance, and the circuit layer 111 uses low-roughness rolled copper. Alternatively, the core board 110 may also use other flexible materials, such as PTFE as the substrate 112.

[0048] Obviously, before curing the first glue, it is also necessary to make a circuit pattern on the circuit layer 111 on the inner side of the core board 110 .

[0049] Optionally, in some embodiments, in order to precisely control the size of the filling layer 310 and meet the requirements of the dielectric layer for size parameters, when curing the first glue, tape or similar removable materials can be used to surround and define an area corresponding to the cavity 220 on the core board 110, and the first glue is applied to the area.

[0050] For example, refer to Figure 3 and Figure 4 In some embodiments, curing the first glue on the core board 110 includes: applying a first tape 320 at the same height as the core board 110 and the filling layer 310 to define an area corresponding to the cavity 220; applying the first glue in the area; and peeling off the first tape 320 after the first glue is cured.

[0051] In order to facilitate lamination and peeling, the width of the first adhesive tape 320 may be set to be greater than 2 mm, for example, any value between 2 mm and 3 mm.

[0052] Optionally, in some embodiments, the height of the first tape 320 is greater than the height of the target cavity 220. For example, the height of the first tape 320 can be set to be 0 mil to 1 mil greater than the height of the cavity 220, thereby leaving a certain margin to ensure that the filling layer 310 can fully contact the other core board 110 during subsequent pressing.

[0053] Furthermore, in order to make the height dimension of the filling layer 310 more accurate, in some embodiments, the first glue is applied to a height higher than the first adhesive tape 320 , and then the excess first glue is scraped off before curing.

[0054] Specifically, the first glue can be printed layer by layer in the area defined by the first adhesive tape 320 by silk-screen printing, and the printing height is appropriately higher than the first adhesive tape 320, which allows the first glue to flow and fully fill different positions in the area, and on the other hand, allows the first glue to be kept in the area under the action of surface tension and will not overflow. After waiting for a period of time, the first glue is scraped off to obtain a filling layer 310 with a flat top.

[0055] Step S111 : opening a window on the bonding sheet 210 .

[0056] Reference Figure 5 The bonding sheet 210 is used to bond the adjacent core plates 110. The height of the bonding sheet 210 determines the height of the dielectric layer to be formed subsequently. The window is used to avoid the filling layer 310. The window can be accurately formed by laser cutting.

[0057] Step S130: stack and press the core board 110 and the bonding sheet 210 to form a mother board, and fill the window with the filling layer 310.

[0058] Since the first glue flows on the surface of the core board 110 first and then solidifies, during pressing, the pressure can be more evenly transmitted to the core board 110 and the circuit layer 111 on the core board 110 through the filling layer 310. Even if no covering film is provided, it is not easy to produce indentations on the circuit layer 111, thereby improving the quality of the circuit layer 111 and satisfying the requirement that the dielectric layer cannot contain any medium other than air, thereby ensuring the dielectric properties of the dielectric layer.

[0059] It should be noted that in the flexible board, the bonding sheet 210 is usually made of pure epoxy resin material. The bonding sheet 210 has fluidity during lamination. In order to avoid the influence of the flow of glue on the signal position, in some embodiments, the bonding sheet 210 is preferably made of epoxy resin material. Figure 6 , a glue overflow margin of the bonding sheet 210 can be left between the window and the filling layer 310 .

[0060] Exemplarily, when the bonding sheet 210 is pure glue, a single-side margin of 0.05 mm to 1 mm may be used.

[0061] In order to enhance the lamination effect, during lamination, lamination can be performed on both sides, for example, a combination of PE film and aluminum sheet can be used for lamination.

[0062] Step S140 : a groove 330 is formed on the side of the motherboard, the groove 330 forms a notch on the side, and the notch partially exposes the filling layer 310 .

[0063] It is understandable that after the motherboard is formed by lamination, other processing steps of the flexible board can be performed, such as drilling holes, electroplating, making circuit patterns on the outer circuit layer 111, surface treatment, processing the shape of the flexible board, etc., which will not be described in detail here. Step S140 can be performed as a later process after the shape processing of the flexible board is completed.

[0064] In some embodiments, the groove 330 may be cut by laser so that the size of the groove 330 is more precise.

[0065] Step S150 : applying an alternating magnetic field to melt the first glue, and discharging the first glue through the notch to form a cavity 220 .

[0066] Reference Figure 7 Since the first glue can be melted and debonded under the action of the alternating magnetic field, the notch does not need to completely expose the filling layer 310, but only needs to partially expose the filling layer 310, that is, the first glue can be discharged from the notch and the filling layer 310 can be removed.

[0067] For example, in some embodiments, the length (L2) of the groove 330 is less than or equal to the length of the filling layer 310 (i.e. Figure 5 One third of L1).

[0068] Considering that the notch becomes smaller, a portion of the first glue may be retained in the cavity 220 and difficult to be discharged naturally. Therefore, some auxiliary means may be used to promote the discharge of the first glue.

[0069] It should also be pointed out that since the first glue is discharged after melting and has a certain fluidity, it is also suitable for making a filling layer 310 with various shapes to better match the position of the signal line. When a gasket is used to make an air layer structure in the related technology, it is limited by the removal method (the shape of the gasket must be able to be pulled out from the side), and the shape of the air layer structure is limited.

[0070] For example, in some embodiments, grooves 330 are opened on the sides of both sides, and airflow is applied from the groove on one side to the groove on the other side to promote the discharge of the first glue.

[0071] Step S160: closing the notch to form a dielectric layer.

[0072] Optionally, in some embodiments, a second glue may be applied to the groove 330 to close the cavity.

[0073] It should be noted that the flexible board needs to have a certain bending ability, so the second glue should be a glue with a certain elasticity after curing, such as epoxy glue of appropriate specifications. The second glue should also have a certain viscosity to reduce fluidity and prevent the second glue from flowing into the cavity 220 and affecting the dielectric properties.

[0074] Optionally, to ensure that the second glue does not contaminate other areas during coating, refer to Figure 8 In some embodiments, before applying the second glue, a second tape 340 may be applied to the surface of the core board 110 corresponding to the notch, and the second tape 340 plays a protective role. After applying the second glue, the second tape 340 may be peeled off.

[0075] For example, in some embodiments, the width (W2) of the second tape 340 is set to at least 3 times the width (W1) of the groove 330. Specifically, when the width of the groove 330 is 0.5 mm to 1 mm, the width of the second tape 340 can be set to 2 mm to 3 mm. The second tape 340 can be a high temperature resistant tape.

[0076] In summary, the flexible circuit board manufacturing method provided by this application has at least the following technical effects:

[0077] First, the present application can produce a cavity 220 of a suitable size in the flexible board by providing a filling layer 310 before lamination and removing it after lamination to meet the dielectric performance requirements of the dielectric layer.

[0078] Secondly, the present application uses magnetically inactivated glue as the raw material of the filling layer 310 , and utilizes the fluidity of the magnetically inactivated glue to better fit the circuit layer 111 , thereby eliminating the need for a covering film and also being able to achieve the effect of preventing indentations on the circuit layer 111 .

[0079] Finally, the magnetically inactivated glue will melt under the alternating magnetic field, so that the magnetically inactivated glue can be discharged through the slot smaller than the filling layer 310, which is helpful for closing the slot later. By applying magnetic force to discharge the first glue, it is also possible to avoid damaging the circuit layer 111 that is in direct contact with the first glue. On the contrary, if conventional ink is used as the filling layer 310, since the ink can only be washed off in an acid-base environment, the cleaning liquid will directly damage the circuit layer 111 that is not covered with a covering film.

[0080] Therefore, the flexible circuit board manufacturing method can manufacture a flexible circuit board having the cavity 220 as a dielectric layer.

[0081] In some selectable embodiments, the function / operation mentioned in the block diagram may not occur in the order mentioned in the operation diagram. For example, depending on the function / operation involved, the two boxes shown in succession can actually be executed substantially simultaneously or the boxes can sometimes be executed in reverse order. In addition, the embodiment presented and described in the flow chart of the application is provided by way of example, for the purpose of providing a more comprehensive understanding of technology. The disclosed method is not limited to the operation and logic flow presented herein. Selectable embodiments are expected, wherein the order of various operations is changed and the sub-operation of a part described as a larger operation is performed independently.

[0082] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for manufacturing a flexible circuit board, characterized in that: include: Curing a first glue on the core plate to form a filling layer, wherein the first glue is a magnetically inactivated glue; Opening a window on the bonding sheet; The core board and the bonding sheet are stacked and pressed together to form a mother board, and the filling layer fills the window; A groove is formed on a side of the motherboard, wherein the groove forms a notch on the side, and the notch partially exposes the filling layer; Applying an alternating magnetic field to melt the first glue, and discharging the first glue through the notch to form a cavity; The notch is closed to form a dielectric layer.

2. The method for manufacturing a flexible circuit board according to claim 1, characterized in that: The height of the filling layer is greater than or equal to the thickness of the bonding sheet.

3. The method for manufacturing a flexible circuit board according to claim 1 or 2, characterized in that: Curing the first glue on the core board includes: applying a first tape of the same height as the filling layer to the core board to define an area corresponding to the cavity; applying the first glue in the area; and peeling off the first tape after the first glue is cured.

4. The method for manufacturing a flexible circuit board according to claim 3, characterized in that: The first glue is applied to a level higher than the first adhesive tape, and then excess first glue is scraped off before curing.

5. The method for manufacturing a flexible circuit board according to claim 1, characterized in that: An excess amount of glue overflowing from the bonding sheet is left between the window and the filling layer.

6. The method for manufacturing a flexible circuit board according to claim 1, characterized in that: The length of the groove is less than or equal to one third of the length of the filling layer.

7. The method for manufacturing a flexible circuit board according to claim 1 or 6, characterized in that: The grooves are opened on the side surfaces at both sides, and airflow is applied from the groove on one side toward the groove on the other side to promote the discharge of the first glue.

8. The method for manufacturing a flexible circuit board according to claim 1, characterized in that: A second glue is applied to the groove to close the cavity.

9. The method for manufacturing a flexible circuit board according to claim 8, characterized in that: Before applying the second glue, a second adhesive tape is applied to the surface of the motherboard, and after applying the second glue, the second adhesive tape is peeled off.

10. A soft board, characterized in that: The soft board is manufactured by the soft board manufacturing method according to any one of claims 1 to 9.

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