Bending-resistant circuit board and preparation method thereof

Abstract

The invention provides a bending-resistant circuit board and a preparation method thereof. The bending-resistant circuit board comprises an inner-layer circuit board and an outer-layer circuit layer. The inner layer circuit board comprises a first circuit layer, an insulating layer and a cavity. The bonding layer covers part of the first circuit layer, and the cavity is formed in the insulating layer. The cavity is defined by a first magnetic layer, a second magnetic layer, a third magnetic layer and a fourth magnetic layer, and the polarities of the surfaces, facing the cavity, of the magnetic layers are the same. The outer circuit layer is located on the surface of the insulating layer. By constructing the cavity formed by the magnetic material, the internal circuit of the circuit board is always in a suspended state, so that the bending stress influence can be reduced, and the bending resistance of the circuit board is improved. A certain repulsive force exists in the cavity formed by the magnetic material, so that the shape of the cavity can be maintained, and the problems that the cavity in the prior art is sunken and the circuit board is uneven can be solved. A circuit layer can also be formed on the surface of the cavity, so that the wiring density is improved.

Description

Bending-resistant circuit board and preparation method thereof Technical Field

[0001] The present application relates to the technical field of circuit boards, and in particular to a bending-resistant circuit board and a preparation method thereof. Background Art

[0002] Foldable electronic products, such as foldable phones, often use flexible printed circuits (FPCs) as connectors at the folds. In recent years, as the functional requirements of electronic products have evolved, the requirements for the number of FPC layers at the bends, the copper thickness of the circuit network, and the number of bends (>500,000) have become increasingly stringent.

[0003] To reduce the thickness of the FPC and mitigate the effects of bending stress during bending, an air gap (cavity) is typically created within the FPC. However, due to the lack of internal support in the air gap area, there is a risk of the board sinking. Furthermore, multiple air gaps in a multilayer board can reduce the board's signal transmission capacity and reliability.

[0004] Summary of the Invention

[0005] In view of this, the present application proposes a bending-resistant circuit board and a manufacturing method thereof to solve at least one of the above-mentioned problems.

[0006] One embodiment of the present application provides a bend-resistant circuit board, comprising an inner circuit board and an outer circuit layer. The inner circuit board comprises a first circuit layer, an insulating layer, and a cavity. The cavity is formed within the insulating layer and contains a portion of the first circuit layer. The cavity is formed by a first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer, wherein the second magnetic layer and the fourth magnetic layer are arranged relative to each other along the thickness direction of the inner circuit board. The polarity of the surfaces of the first magnetic layer, the second magnetic layer, the third magnetic layer, and the fourth magnetic layer facing the cavity is the same. The outer circuit layer is arranged on the surface of the insulating layer facing away from the first circuit layer.

[0007] In one embodiment, a magnetic material is provided on a surface of the first circuit layer in the cavity, and the polarity of a surface of the magnetic material facing away from the first circuit layer is the same as the polarity of a surface of the first magnetic layer facing the cavity.

[0008] In one embodiment, the inner circuit board further includes a second circuit layer, the second circuit layer being located on a surface of the second magnetic layer facing away from the first circuit layer. The inner circuit board further includes a third circuit layer, the third circuit layer being located on a surface of the fourth magnetic layer facing away from the first circuit layer. The third circuit layer is disposed opposite the second circuit layer.

[0009] In one embodiment, the bending-resistant circuit board further includes a conductive structure that electrically connects the outer circuit layer and the first circuit layer, the outer circuit layer and the second circuit layer, and the outer circuit layer and the third circuit layer.

[0010] In one embodiment, the bending-resistant circuit board has a groove, the groove is connected to the cavity, and the groove penetrates the fourth magnetic layer and at least partially penetrates the insulating layer along the thickness direction of the bending-resistant circuit board.

[0011] One embodiment of the present application provides a method for preparing a bending-resistant circuit board, which includes the following steps:

[0012] A first magnetic layer is provided on a substrate, wherein the substrate includes a base material layer and a first circuit layer provided on a surface of the base material layer, the first magnetic layer covers a portion of the surface of the first circuit layer, and the first magnetic layer has a gap along an extension direction of the substrate;

[0013] Disposing a first sacrificial layer on the substrate, the first sacrificial layer covering a portion of the surface of the first magnetic layer and covering the gap, wherein a surface of the first sacrificial layer facing away from the base layer is flush with a surface of the remaining portion of the first magnetic layer facing away from the base layer;

[0014] Disposing a second magnetic layer on the surface of the first magnetic layer and the first sacrificial layer away from the substrate layer, and forming a second circuit layer on the surface of the second magnetic layer away from the first sacrificial layer;

[0015] removing the base material layer of the substrate;

[0016] A third magnetic layer is provided on a surface of the first magnetic layer facing away from the second magnetic layer, wherein the third magnetic layer is provided corresponding to the first magnetic layer;

[0017] Disposing a second sacrificial layer on a surface of the first sacrificial layer facing away from the second magnetic layer, wherein a surface of the second sacrificial layer facing away from the first sacrificial layer is higher than a surface of the third magnetic layer facing away from the first magnetic layer;

[0018] A fourth magnetic layer is disposed on a surface of the third magnetic layer facing away from the first magnetic layer and on a surface of the second sacrificial layer facing away from the first sacrificial layer, and a portion of the first magnetic layer, the third magnetic layer, the second magnetic layer, and the fourth magnetic layer enclose a cavity; and surfaces of the first magnetic layer, the second magnetic layer, the third magnetic layer, and the fourth magnetic layer facing the cavity have the same polarity;

[0019] removing the first sacrificial layer and the second sacrificial layer in the cavity;

[0020] forming a third circuit layer on a surface of the fourth magnetic layer facing away from the third magnetic layer;

[0021] A first outer circuit layer is formed on the surface of the second circuit layer away from the second magnetic layer, and a second outer circuit layer is formed on the surface of the third circuit layer away from the fourth magnetic layer to obtain the bending-resistant circuit board.

[0022] In one embodiment, the step of forming a first outer circuit layer on the surface of the second circuit layer facing away from the first circuit layer includes: laminating at least a copper-clad laminate on the side of the second circuit layer facing away from the second magnetic layer, the copper-clad laminate including a substrate layer and a copper foil layer, the substrate layer being located between the copper foil layer and the second circuit layer; and forming the copper foil layer into the first outer circuit layer.

[0023] In one embodiment, the preparation method further includes: manufacturing a conductive structure on the bend-resistant circuit board so that the first outer circuit layer is electrically connected to the first circuit layer and the second circuit layer respectively.

[0024] In one embodiment, the step of forming a second outer circuit layer on the surface of the third circuit layer facing away from the first circuit layer includes: laminating at least a copper clad laminate on the side of the third circuit layer facing away from the fourth magnetic layer, the copper clad laminate including a substrate layer and a copper foil layer, the substrate layer being located between the copper foil layer and the third circuit layer; and forming the copper foil layer into the second outer circuit layer.

[0025] In one embodiment, the preparation method further includes: manufacturing a conductive structure on the bend-resistant circuit board to electrically connect the second outer circuit layer to the third circuit layer.

[0026] The present application utilizes the principle that like poles of magnetic materials repel each other, and constructs a cavity formed of magnetic material inside the circuit board, so that the internal circuit of the circuit board is always in a suspended state when the circuit board is in a bent / unbent state, thereby reducing the impact of bending stress and improving the bending resistance of the circuit board. After bending, the internal circuit of the circuit board is still in a suspended state, and the electrical function is not affected. The cavity formed of magnetic material in the present application has a certain repulsive force inside, which can enable the cavity to maintain its shape, thereby solving the problem of depression and uneven circuit board caused by lack of supporting force in the cavity of the prior art. In addition, the surface of the cavity of the present application can also form a circuit layer, which not only improves the space utilization of the cavity, but also increases the wiring density, so that the cavity has electrical functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a cross-sectional view of a copper clad laminate provided in one embodiment of the present application.

[0028] FIG2 is a cross-sectional view of a substrate formed by manufacturing the copper clad laminate shown in FIG1 .

[0029] FIG. 3 is a cross-sectional view showing a structure in which a first magnetic layer is provided on the structure shown in FIG. 2 .

[0030] FIG. 4 is a cross-sectional view of a structure shown in FIG. 3 in which a first sacrificial layer is provided.

[0031] FIG. 5 is a cross-sectional view showing a process of disposing a second magnetic layer and forming a second circuit layer on the structure shown in FIG. 4 .

[0032] FIG6 is a cross-sectional view of the adhesive layer and the copper clad laminate laminated on the outer side of the second circuit layer of the structure shown in FIG5.

[0033] FIG. 7 is a cross-sectional view of the structure shown in FIG. 6 with the substrate layer removed.

[0034] FIG. 8 is a cross-sectional view showing a structure in which a third magnetic layer is provided on the surface of the structure shown in FIG. 7 .

[0035] FIG9 is a cross-sectional view of disposing a second sacrificial layer on the surface of the first sacrificial layer of the structure shown in FIG8 .

[0036] FIG. 10 is a cross-sectional view showing a fourth magnetic layer provided on the surface of the structure shown in FIG. 9 .

[0037] FIG. 11 is a cross-sectional view of the structure shown in FIG. 10 after the first sacrificial layer and the second sacrificial layer are removed.

[0038] FIG. 12 is a cross-sectional view showing a structure in which a third circuit layer is formed on the surface of the fourth magnetic layer.

[0039] FIG13 is a cross-sectional view of the adhesive layer and the copper clad laminate laminated on the outside of the third circuit layer of the structure shown in FIG12 .

[0040] FIG. 14 is a cross-sectional view showing a blind hole formed in the structure shown in FIG. 13 .

[0041] FIG15 is a cross-sectional view of copper plating in the blind hole and on the surface of the copper clad laminate of the structure shown in FIG14 .

[0042] FIG. 16 is a cross-sectional view of a bend-resistant circuit board obtained by forming an outer circuit layer by the copper foil layer of the structure shown in FIG. 15 in one embodiment.

[0043] Description of Main Component Symbols: Flex-Resistant Circuit Board 100, Copper Clad Laminate 10a, Base Layer 11, Copper Foil Layer 12, Substrate 10, First Circuit Layer 13, Second Circuit Layer 14, Third Circuit Layer 15, Outer Circuit Layer 16, First Outer Circuit Layer 17, Second Outer Circuit Layer 18, Magnetic Material 20, First Magnetic Layer 21, Second Magnetic Layer 22, Third Magnetic Layer 23, Fourth Magnetic Layer 24, First Sacrificial Layer 31, Second Sacrificial Layer 32, Adhesive Layer 40, Thin Copper Layer 50, Conductive Structure 60, Inner Circuit Board 70, Insulation Layer 71, Cavity 101, Blind Via 102, Groove 103, Gap 210, Opening240, 401

[0044] The following specific implementation methods will further illustrate the embodiments of the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the art of the present application. The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0046] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0047] It will be understood that when a layer is referred to as being “on” another layer, it can be directly on the other layer or intervening layers may be present therebetween. In contrast, when a layer is referred to as being “directly on” another layer, there are no intervening layers present.

[0048] In addition, the terms "first," "second," and so on, used in this application are for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0049] The embodiments of the present application are described herein with reference to cross-sectional views, which are schematic diagrams of idealized embodiments (and intermediate configurations) of the present application. Thus, it is foreseeable that the shapes of the diagrams may differ due to manufacturing processes and / or tolerances. Therefore, the embodiments of the present application should not be interpreted as being limited to the specific shapes of the regions illustrated herein, but should include deviations in shapes, such as those resulting from manufacturing. The regions shown in the figures are merely schematic, and their shapes are not intended to represent the actual shapes of the illustrated devices and are not intended to limit the scope of the present application.

[0050] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features of the embodiments may be combined with each other.

[0051] 1 to 16 , the first aspect of the present application provides a method for preparing a bending-resistant circuit board 100 , which includes steps S10 to S100 . It is understood that the numbering of the steps is intended to clarify the specific preparation method and does not limit the order of the steps.

[0052] Please refer to FIG. 1 to FIG. 3 , in step S10 , a first magnetic layer 21 is disposed on a substrate 10 .

[0053] As shown in Figures 1 and 2, in some embodiments, the substrate 10 can be prepared from a copper clad laminate 10a. The copper clad laminate 10a includes a base material layer 11 and a copper foil layer 12 provided on the surface of the base material layer 11. In this embodiment, the copper clad laminate 10a is a single-sided copper clad laminate, that is, the base material layer 11 has a copper foil layer 12 on only one surface. The copper foil layer 12 can be formed into a first circuit layer 13 by steps such as exposure, development, etching, and film stripping to obtain the substrate 10. Steps such as exposure, development, etching, and film stripping are commonly used technical means in the field and will not be repeated here. It can be understood that a portion of the surface of the base material layer 11 close to the first circuit layer 13 can be exposed from the first circuit layer 13.

[0054] In some embodiments, the material of the substrate layer 11 may be, but is not limited to, a flexible substrate such as polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate diformic acid glycol ester (PEN), polydimethylsiloxane (PDMS), or liquid crystal polymer (LCP). In this embodiment, the material of the substrate layer 11 is PI.

[0055] As shown in Figure 3, a magnetic material can be deposited on substrate 10 to form a first magnetic layer 21 through processes such as, but not limited to, printing, vacuum evaporation, electrodeposition, and sputtering. The first magnetic layer 21 covers a portion of the surface of the first circuit layer 13. Specifically, the first magnetic layer 21 may cover the surface of the circuit pattern located in the central region of the first circuit layer 13. That is, except for the surface near the base layer 11, the rest of the surface of the circuit pattern in the central region of the first circuit layer 13 is covered by the first magnetic layer 21. Furthermore, the first magnetic layer 21 is not continuous but discontinuous along the extension direction of the substrate 10. That is, along the extension direction of the substrate 10 (which can be the length direction or the width direction of the substrate 10), the first magnetic layer 21 has gaps 210. The number of gaps 210 can be adjusted as the circuit pattern of the first circuit layer 13 changes, and this application does not impose any restrictions.

[0056] As shown in Figure 3, in this embodiment, the height of the first magnetic layer 21 (i.e., the distance along the thickness of the substrate 10) is not uniform. The height of the first magnetic layer 21 in the edge region is higher than that of the first magnetic layer 21 in the center region. The first magnetic layer 21 in the edge region can be directly disposed on the substrate layer 11 without covering the circuit pattern of the first circuit layer 13. The first magnetic layer 21 in the center region covers the circuit pattern of the first circuit layer 13.

[0057] In some embodiments, the magnetic material forming the first magnetic layer 21 may be a strong magnetic (ferromagnetic and ferrimagnetic) magnetic film material. The magnetic film material may be, but is not limited to, ferrite, spinel, garnet ferrite thin films, etc. The thickness of the first magnetic layer 21 may be 1 μm to 5 μm.

[0058] Please refer to FIG. 4 , in step S20 , a first sacrificial layer 31 is disposed on the substrate 10 .

[0059] As shown in Figure 4, the first sacrificial layer 31 covers part of the first magnetic layer 21 (i.e., the first magnetic layer 21 with a lower height in Figure 4) and the gap 210 in the first magnetic layer 21, and the surface of the first sacrificial layer 31 facing away from the substrate layer 11 is flush with the surface of the remaining part of the first magnetic layer 21 (i.e., the first magnetic layer 21 with a higher height in Figure 4) facing away from the substrate layer 11.

[0060] 5 , in step S30 , a second magnetic layer 22 is disposed on the surfaces of the first magnetic layer 21 and the first sacrificial layer 31 facing away from the substrate layer 11 , and a second circuit layer 14 is formed on the surface of the second magnetic layer 22 facing away from the first sacrificial layer 31 .

[0061] As shown in FIG5 , in some embodiments, the second magnetic layer 22, the first magnetic layer 21 located higher in the edge area, and the substrate layer 11 together form a receiving space, and the first sacrificial layer 31 is located in the receiving space. The cross-section of the receiving space is roughly rectangular. The second magnetic layer 22 can be formed by, but not limited to, a printing process, a vacuum evaporation method, an electroplating method, a sputtering method, and the like. The magnetic material forming the second magnetic layer 22 can be a ferromagnetic (ferromagnetic and ferrimagnetic) magnetic film material, and its magnetic material can be the same as or different from that of the first magnetic layer 21, and this application does not impose any restrictions. Along the extension direction of the substrate 10, the height of the second magnetic layer 22 (that is, the distance along the thickness direction of the substrate 10) can remain unchanged.

[0062] In some embodiments, the second wiring layer 14 can be formed using, but not limited to, a printed web process or a selective metallization process. As shown in Figure 5 , a portion of the surface of the second magnetic layer 22 can be exposed from the second wiring layer 14. The thickness and line width and spacing of the second wiring layer 14 can be adjusted based on actual needs and are not limited in this application. Forming the second wiring layer 14 on the second magnetic layer 22 can increase wiring density, overcoming the drawback of prior art that reduces wiring density due to the presence of air gaps.

[0063] Referring to Figure 6 , in some embodiments, after step S30, step S101 may be performed: laminating an adhesive layer 40 and the copper-clad laminate 10a on the side of the second circuit layer 14 facing away from the second magnetic layer 22. The adhesive layer 40 covers the substrate 10 (i.e., the surface of the first circuit layer 13 and the surface of the base material layer 11 exposed from the first circuit layer 13) and the surface of the second magnetic layer 22 exposed from the second circuit layer 14. The adhesive layer 40 may be, but is not limited to, AD glue (acrylic hot melt glue).

[0064] As shown in FIG6 , in some embodiments, a copper-clad laminate 10a includes a substrate layer 11 and a copper foil layer 12 disposed on a surface of the substrate layer 11. The substrate layer 11 is disposed between the copper foil layer 12 and an adhesive layer 40. The adhesive layer 40 can be made of the same material as the substrate layer 11; both can be thermoplastic dielectric materials. The adhesive layer and the substrate layer 11 can together form an insulating layer 71.

[0065] In other embodiments, the adhesive layer 40 can be omitted, and only the copper-clad laminate 10a can be laminated to the side of the second circuit layer 14 facing away from the second magnetic layer 22. The copper-clad laminate 10a also includes a base layer 11 and a copper foil layer 12 located on the surface of the base layer 11. The base layer 11 is located between the substrate 10 and the copper foil layer 12. The base layer 11 covers the surface of the first circuit layer 13, the surface of the base layer 11 exposed from the first circuit layer 13, and the surface of the second magnetic layer 22 exposed from the second circuit layer 14. When the adhesive layer 40 is omitted, the base layer 11 can be made of a thermoplastic insulating material, and the base layer 11 also serves as the insulating layer 71.

[0066] Please refer to FIG. 7 , in step S40 , the base material layer 11 of the substrate 10 is removed.

[0067] In some embodiments, the base material layer 11 of the substrate 10 can be removed by, but not limited to, chemical etching. For example, the base material layer 11 of the substrate 10 can be immersed in an etching solution to cause a chemical reaction with the etching solution. The etching solution can include sodium hydroxide, hydrofluoric acid, and acidic hydrogen peroxide.

[0068] Referring to FIG8 , step S50, a third magnetic layer 23 is disposed on a surface of the first magnetic layer 21 facing away from the second magnetic layer 22. The third magnetic layer 23 is disposed correspondingly to the first magnetic layer 21. The corresponding arrangement means that the orthographic projection of the first magnetic layer 21 and the orthographic projection of the third magnetic layer 23 completely overlap.

[0069] As shown in Figure 8, the circuit pattern of the first circuit layer 13, which is covered by the first magnetic layer 21, has a surface that was previously covered by the base layer 11 of the substrate 10, but is now covered by the third magnetic layer 23. Like the first magnetic layer 21, the third magnetic layer 23 is discontinuous along the extension direction (which can be the length or width direction) of the copper-clad laminate 10a. A portion of the third magnetic layer 23 covers the first circuit layer 13 and the surface of the first magnetic layer 21 facing away from the second magnetic layer 22, while the remaining portion of the third magnetic layer 23 covers the surface of the first magnetic layer 21 facing away from the second magnetic layer 22. In this embodiment, the portion of the first magnetic layer 21 near the center, and the portion of the third magnetic layer 23 near the center, completely cover the surface of the first circuit layer 13 near the center.

[0070] In some embodiments, the third magnetic layer 23 can be formed by, but is not limited to, printing, vacuum evaporation, electrodeposition, sputtering, or other processes. The magnetic material forming the third magnetic layer 23 can be a ferromagnetic (ferromagnetic or ferrimagnetic) magnetic film material. The magnetic material can be the same as or different from that of the first magnetic layer 21, and this is not a limitation of the present application. The height of the third magnetic layer 23 (i.e., the distance along the thickness direction of the copper-clad laminate 10a) can remain constant along the extension direction of the copper-clad laminate 10a.

[0071] Referring to FIG. 9 , step S60, a second sacrificial layer 32 is disposed on the surface of the first sacrificial layer 31 facing away from the second magnetic layer 22. The second sacrificial layer 32 completely fills the gaps within the third magnetic layer 23. Furthermore, the surface of the second sacrificial layer 32 facing away from the first sacrificial layer 31 is higher than the surface of the third magnetic layer 23 facing away from the first magnetic layer 21. The second sacrificial layer 32 also covers the surface of the third magnetic layer 23 near the center facing away from the first magnetic layer 21.

[0072] Referring to FIG. 10 , step S70, a fourth magnetic layer 24 is disposed on the surface of the third magnetic layer 23 facing away from the first magnetic layer 21 and on the surface of the second sacrificial layer 32 facing away from the first sacrificial layer 31. A portion of the first magnetic layer 21, a portion of the third magnetic layer 23, the entire second magnetic layer 22, and the entire fourth magnetic layer 24 enclose a cavity 101, which has a generally rectangular cross-section. The first and second sacrificial layers 31 and 32 are contained within the cavity 101, along with portions of the first magnetic layer 21, portions of the third magnetic layer 23, and portions of the first circuit layer 13. The surfaces of the first, second, third, and fourth magnetic layers 21, 22, 23, and 24 facing the cavity 101 have the same polarity.

[0073] As shown in FIG10 , in some embodiments, the first side of the rectangular shape is composed of the first magnetic layer 21, the third magnetic layer 23, and the fourth magnetic layer 24. The second side, parallel to the first side, is also composed of the first magnetic layer 21, the third magnetic layer 23, and the fourth magnetic layer 24. The third side is composed of the second magnetic layer 22, and the fourth side, parallel to the third side, is composed of the fourth magnetic layer 24. Each side of the rectangular shape is equidistant from the parallel magnetic layer within the cavity 101, and the gaps between adjacent magnetic layers within the cavity 101 (i.e., the magnetic layer located in the aforementioned central region) are also equidistant. This balances the repulsive forces between the magnetic layers, thereby maintaining the shape of the cavity 101 and preventing it from sag or collapse. This, in turn, reduces the impact of bending stress on the circuit board during bending, enhancing the circuit board's bending resistance.

[0074] As shown in FIG10 , in some embodiments, the fourth magnetic layer 24 has an opening 240 extending through the fourth magnetic layer 24 along its thickness. The opening 240 is located approximately in the center of the fourth magnetic layer 24 , and a portion of the surface of the second sacrificial layer 32 facing away from the first sacrificial layer 31 is exposed through the opening 240 .

[0075] Please refer to FIG. 11 , in step S80 , the first sacrificial layer 31 and the second sacrificial layer 32 in the cavity 101 are removed.

[0076] In some embodiments, the first sacrificial layer 31 and the second sacrificial layer 32 can be removed by dry etching. A fluorine-containing gas (typically XeF2 or HF) is introduced into the cavity 101. The active species in the generated plasma chemically react with the first sacrificial layer 31 and the second sacrificial layer 32 to form products such as volatile compounds. The products can then be drawn out of the cavity 101 through the opening 240, thereby completing the removal of the first sacrificial layer 31 and the second sacrificial layer 32.

[0077] Referring to FIG. 12 , step S90 , a third wiring layer 15 is formed on the surface of the fourth magnetic layer 24 facing away from the third magnetic layer 23 . The thickness and line width and spacing of the third wiring layer 15 can be adjusted based on actual needs and are not limited in this application. Forming the third wiring layer 15 on the fourth magnetic layer 24 increases wiring density, overcoming the drawback of prior art where wiring density is reduced due to the presence of air gaps.

[0078] In some embodiments, the third circuit layer 15 can be formed by, but not limited to, a printing network process or a selective metal sputtering process. As shown in FIG12 , a portion of the surface of the fourth magnetic layer 24 can be exposed from the third circuit layer 15 .

[0079] Referring to Figures 13 to 15 , in step S100, first outer circuit layer 17 is formed on the surface of second circuit layer 14 facing away from second magnetic layer 22, and second outer circuit layer 18 is formed on the surface of third circuit layer 15 facing away from fourth magnetic layer 24, thereby obtaining flex-resistant circuit board 100. Step S100 may include steps S101 to S105. Step S101 (compression-bonding adhesive layer 40 and copper-clad laminate 10a on the side of second circuit layer 14 facing away from first circuit layer 13) is performed after step S30.

[0080] As shown in Figure 13, in some embodiments, in step S102, an adhesive layer 40 and a copper-clad laminate 10a are laminated together on the side of the third circuit layer 15 facing away from the fourth magnetic layer 24. The adhesive layer 40 may cover a portion of the surface of the first circuit layer 13, the surface of the fourth magnetic layer 24 exposed from the third circuit layer 15, and the surface of the third circuit layer 15. The adhesive layer 40 may have an opening 401 extending through the adhesive layer 40 along its thickness, and the opening 401 is connected to the opening 240. The opening 401 and the opening 240 together form a groove 103. The groove 103 reduces bending stress during flexing of the circuit board, thereby improving the circuit board's flex resistance. The copper-clad laminate 10a includes a substrate layer 11 and a copper foil layer 12, with the substrate layer 11 positioned between the copper foil layer 12 and the adhesive layer 40. The adhesive layer 40 may be, but is not limited to, AD adhesive. The adhesive layer 40 may be made of the same material as the substrate layer 11; both may be thermoplastic dielectric materials. The adhesive layer 40 and the base layer 11 may together form an insulating layer 71 .

[0081] In other embodiments, only the copper-clad laminate 10a may be laminated onto the side of the third circuit layer 15 facing away from the fourth magnetic layer 24, and the adhesive layer 40 may be omitted. The copper-clad laminate 10a similarly includes a substrate layer 11 and a copper foil layer 12 located on the surface of the substrate layer 11. The substrate layer 11 covers the surfaces of the first circuit layer 13 and the third circuit layer 15, and also covers the surface of the fourth magnetic layer 24 exposed from the third circuit layer 15. When the adhesive layer 40 is omitted, the substrate layer 11 may be made of a thermoplastic insulating material. The substrate layer 11 also serves as the insulating layer 71, and the groove 103 serves as the opening 240.

[0082] As shown in FIG14 , in some embodiments, step S103 may involve forming blind vias 102 in the copper clad laminate 10a and the adhesive layer 40 by, but not limited to, laser or mechanical drilling. The blind vias 102 may penetrate the copper clad laminate 10a (the upper copper clad laminate 10a in FIG14 ) and the adhesive layer 40 along the thickness direction, with a portion of the surface of the first circuit layer 13 exposed through the blind vias 102. The blind vias 102 may penetrate the copper clad laminate 10a (the upper copper clad laminate 10a in FIG14 ) and a portion of the adhesive layer 40 along the thickness direction, with a portion of the surface of the second circuit layer 14 exposed through the blind vias 102. The blind vias 102 may penetrate the copper clad laminate 10a (the lower copper clad laminate 10a in FIG14 ) and a portion of the adhesive layer 40 along the thickness direction, with a portion of the surface of the third circuit layer 15 exposed through the blind vias 102.

[0083] It is understandable that when the adhesive layer 40 is omitted, the blind hole 102 penetrates the copper clad board 10a along the thickness direction, and part of the surface of the first circuit layer 13 and part of the surface of the third circuit layer 15 can be exposed from the blind hole 102.

[0084] As shown in FIG. 15 , in some embodiments, step S104 may include electroplating a thin copper layer 50 within the blind via 102 to form a conductive structure 60. The conductive structure 60 may be, but is not limited to, a conductive via. It will be appreciated that during electroplating, the outer surfaces of the upper and lower copper-clad laminates 10a will also be plated with a thin copper layer 50.

[0085] As shown in FIG. 16 , in some embodiments, in step S105 , the upper copper foil layer 12 (and the thin copper layer 50 on its surface) is formed into a first outer circuit layer 17, and the lower copper foil layer 12 (and the thin copper layer 50 on its surface) is formed into a second outer circuit layer 18. The first outer circuit layer 17 and the second outer circuit layer 18 can be formed by lamination, exposure, development, etching, and film stripping. The first outer circuit layer 17 and the first circuit layer 13 can be electrically connected via a conductive structure 60, the first outer circuit layer 17 and the second circuit layer 14 can be electrically connected via a conductive structure 60, and the second outer circuit layer 18 and the third circuit layer 15 can be electrically connected via a conductive structure 60.

[0086] Please refer to FIG. 16 . A second aspect of the present application provides a bending-resistant circuit board 100 prepared by the above method, which includes an inner circuit board 70 and an outer circuit layer 16 .

[0087] As shown in FIG16 , the inner circuit board 70 includes a first circuit layer 13, an insulating layer 71, and a cavity 101. Cavity 101 is formed within the insulating layer 71 and contains a portion of the first circuit layer 13, so that the first circuit layer 13 within the cavity 101 is suspended (i.e., not in direct contact with the substrate layer 11 or the insulating layer 71). Cavity 101 is formed by a first magnetic layer 21, a second magnetic layer 22, a third magnetic layer 23, and a fourth magnetic layer 24. The second magnetic layer 22 and the fourth magnetic layer 24 are arranged opposite each other along the thickness direction of the inner circuit board 70 (i.e., the vertical direction in FIG16 ). The first magnetic layer 21, the second magnetic layer 22, the third magnetic layer 23, and the fourth magnetic layer 24 have the same polarity toward the inner surface of the cavity 101, thereby generating a repulsive force, thereby maintaining the shape of the cavity 101 and preventing collapse. In some embodiments, the cross-sectional shape of the cavity 101 is generally rectangular.

[0088] As shown in FIG16 , outer circuit layer 16 is disposed on the surface of insulating layer 71 facing away from first circuit layer 13. In this embodiment, there are two outer circuit layers 16: a first outer circuit layer 17 disposed on the upper surface of first circuit layer 13 and a second outer circuit layer 18 disposed on the lower surface of first circuit layer 13.

[0089] As shown in Figure 16, in some embodiments, a magnetic material 20 is provided on the surface of the first circuit layer 13 within the cavity 101. The polarity of the surface of the magnetic material 20 facing away from the first circuit layer 13 is the same as the polarity of the surface of the first magnetic layer 21 facing the cavity 101. The magnetic material 20 completely covers the surface of the first circuit layer 13 within the cavity 101. The magnetic layer formed by the magnetic material 20 within the cavity 101 may be discontinuous. Each side of the cavity 101 is equidistant from the magnetic layer formed by the magnetic material 20 parallel to it within the cavity 101, and the distances between adjacent gaps within the magnetic layer within the cavity 101 are also equidistant. This balances the repulsive forces between the magnetic layers, maintaining the shape of the cavity 101 and preventing it from sag or collapse. This, in turn, reduces the impact of bending stress on the circuit board during bending, enhancing the circuit board's bending resistance.

[0090] As shown in FIG16 , in some embodiments, inner circuit board 70 further includes a second circuit layer 14. Second circuit layer 14 is located on the surface of second magnetic layer 22 facing away from first circuit layer 13. Forming second circuit layer 14 on second magnetic layer 22 can increase wiring density, overcoming the disadvantage of prior art where wiring density is reduced due to the presence of cavities.

[0091] As shown in FIG16 , in some embodiments, inner circuit board 70 further includes a third circuit layer 15. Third circuit layer 15 is located on the surface of fourth magnetic layer 24 facing away from first circuit layer 13. Third circuit layer 15 and second circuit layer 14 are arranged opposite each other along the thickness of inner circuit board 70 (i.e., the vertical direction in FIG16 ). Forming third circuit layer 15 on fourth magnetic layer 24 improves wiring density, overcoming the drawback of prior art where wiring density is reduced due to the presence of cavities.

[0092] As shown in FIG16 , in some embodiments, the bend-resistant circuit board 100 further includes a conductive structure 60. The conductive structure 60 electrically connects the outer circuit layer 16 to the first circuit layer 13, the outer circuit layer 16 to the second circuit layer 14, and the outer circuit layer 16 to the third circuit layer 15. The conductive structure 60 may be, but is not limited to, a conductive via.

[0093] As shown in Figure 16 , in some embodiments, insulating layer 71 includes adhesive layer 40 and substrate layer 11. Substrate layer 11 is positioned between outer circuit layer 16 and adhesive layer 40. Substrate layer 11 and adhesive layer 40 can be made of the same thermoplastic dielectric material. In other embodiments, adhesive layer 40 can be omitted from insulating layer 71 , in which case insulating layer 71 serves as substrate layer 11.

[0094] As shown in FIG16 , in some embodiments, the bend-resistant circuit board 100 has a groove 103, which passes through at least the fourth magnetic layer 24 along the thickness direction of the bend-resistant circuit board 100. The groove 103 can reduce the bending stress when the circuit board is bent, thereby improving the bend resistance of the circuit board. In this embodiment, the groove 103 passes through the fourth magnetic layer 24 and the adhesive layer 40 located on the surface of the fourth magnetic layer 24 along the thickness direction of the bend-resistant circuit board 100. The groove 103 is connected to the cavity 101, and the side walls of the groove 103 are the fourth magnetic layer 24 and the adhesive layer 40, and the bottom wall is the substrate layer 11. In other embodiments, when the insulating layer 71 does not include the adhesive layer 40, the groove 103 passes through the fourth magnetic layer 24 along the thickness direction of the bend-resistant circuit board 100 and is connected to the cavity 101.

[0095] The present application utilizes the principle that like poles of magnetic materials repel each other, and constructs a cavity 101 formed of magnetic material inside the circuit board, so that the internal circuit of the circuit board is always in a suspended state when the circuit board is in a bent / unbent state, thereby reducing the impact of bending stress and improving the bending resistance of the circuit board. After bending, the internal circuit of the circuit board is still in a suspended state, and the electrical function is not affected. The cavity 101 formed of magnetic material in the present application has a certain repulsive force inside, which can enable the cavity 101 to maintain its shape, thereby solving the problem of depression and uneven circuit board caused by lack of supporting force in the cavity of the prior art. In addition, the surface of the cavity 101 of the present application can also form a circuit layer, which not only improves the space utilization rate of the cavity 101, but also increases the wiring density, so that the cavity 101 has electrical functions.

[0096] The above description is some specific implementation methods of the present application, but in actual application, it is not limited to these implementation methods. For ordinary technicians in this field, other variations and changes made according to the technical concept of the present application should fall within the scope of protection of the present application.

Claims

1. A bend-resistant circuit board, characterized in that, it includes: an inner-layer circuit board, including a first circuit layer, an insulating layer, and a cavity. The cavity is formed within the insulating layer and includes part of the first circuit layer. The cavity is surrounded by a first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer. The second magnetic layer and the fourth magnetic layer are oppositely arranged along the thickness direction of the inner-layer circuit board. The polarities of the surfaces of the first magnetic layer, the second magnetic layer, the third magnetic layer, and the fourth magnetic layer facing the cavity are the same; and an outer-layer circuit layer, which is arranged on the surface of the insulating layer facing away from the first circuit layer.

2. The bend-resistant circuit board according to claim 1, characterized in that, a magnetic material is provided on the surface of the first circuit layer located within the cavity, and the polarity of the surface of the magnetic material facing away from the first circuit layer is the same as the polarity of the surface of the first magnetic layer facing the cavity.

3. The bend-resistant circuit board according to claim 1, characterized in that, the inner-layer circuit board further includes a second circuit layer, and the second circuit layer is located on the surface of the second magnetic layer facing away from the first circuit layer; the inner-layer circuit board further includes a third circuit layer, and the third circuit layer is located on the surface of the fourth magnetic layer facing away from the first circuit layer, and the third circuit layer is oppositely arranged with the second circuit layer.

4. The bend-resistant circuit board according to claim 3, characterized in that, the bend-resistant circuit board further includes a conductive structure, and the conductive structure electrically connects the outer-layer circuit layer and the first circuit layer, electrically connects the outer-layer circuit layer and the second circuit layer, and electrically connects the outer-layer circuit layer and the third circuit layer.

5. The bend-resistant circuit board according to claim 1, characterized in that, the bend-resistant circuit board has a groove, the groove communicates with the cavity, and the groove penetrates through the fourth magnetic layer and at least partially penetrates through the insulating layer along the thickness direction of the bend-resistant circuit board.

6. A method for manufacturing a bend-resistant circuit board, characterized in that, the manufacturing method includes the following steps: providing a first magnetic layer on a substrate, wherein the substrate includes a base material layer and a first circuit layer provided on the surface of the base material layer, the first magnetic layer covers part of the surface of the first circuit layer, and along the extending direction of the substrate, the first magnetic layer has a gap; providing a first sacrificial layer on the substrate, the first sacrificial layer covers part of the surface of the first magnetic layer and covers the gap, and the surface of the first sacrificial layer facing away from the base material layer is flush with the surface of the remaining part of the first magnetic layer facing away from the base material layer; providing a second magnetic layer on the surface of the first magnetic layer and the first sacrificial layer facing away from the base material layer, and forming a second circuit layer on the surface of the second magnetic layer facing away from the first sacrificial layer; removing the base material layer of the substrate; providing a third magnetic layer on the surface of the first magnetic layer facing away from the second magnetic layer, and the third magnetic layer is correspondingly arranged with the first magnetic layer; A second sacrificial layer is disposed on the surface of the first sacrificial layer facing away from the second magnetic layer, and the surface of the second sacrificial layer facing away from the first sacrificial layer is higher than the surface of the third magnetic layer facing away from the first magnetic layer; A fourth magnetic layer is disposed on the surface of the third magnetic layer facing away from the first magnetic layer and the surface of the second sacrificial layer facing away from the first sacrificial layer, and a cavity is formed by enclosing a part of the first magnetic layer, the third magnetic layer, the second magnetic layer, and the fourth magnetic layer; the polarities of the surfaces of the first magnetic layer, the second magnetic layer, the third magnetic layer, and the fourth magnetic layer facing the cavity are the same; The first sacrificial layer and the second sacrificial layer in the cavity are removed; A third circuit layer is formed on the surface of the fourth magnetic layer facing away from the third magnetic layer; A first outer circuit layer is formed on the surface of the second circuit layer facing away from the second magnetic layer, and a second outer circuit layer is formed on the surface of the third circuit layer facing away from the fourth magnetic layer to obtain the flexible circuit board.

7. The manufacturing method according to claim 6, wherein, The step of forming the first outer circuit layer on the surface of the second circuit layer facing away from the first circuit layer includes: At least laminating a copper clad laminate on the side of the second circuit layer facing away from the second magnetic layer, the copper clad laminate includes a substrate layer and a copper foil layer, and the substrate layer is located between the copper foil layer and the second circuit layer; The copper foil layer is fabricated to form the first outer circuit layer.

8. The manufacturing method according to claim 7, wherein, The manufacturing method further includes: fabricating a conductive structure on the flexible circuit board to electrically connect the first outer circuit layer to the first circuit layer and the second circuit layer respectively.

9. The manufacturing method according to claim 6, wherein, The step of forming the second outer circuit layer on the surface of the third circuit layer facing away from the first circuit layer includes: At least laminating a copper clad laminate on the side of the third circuit layer facing away from the fourth magnetic layer, the copper clad laminate includes a substrate layer and a copper foil layer, and the substrate layer is located between the copper foil layer and the third circuit layer; The copper foil layer is fabricated to form the second outer circuit layer.

10. The manufacturing method according to claim 9, wherein, The manufacturing method further includes: fabricating a conductive structure on the flexible circuit board to electrically connect the second outer circuit layer to the third circuit layer.

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