TWI860187B - Bending resistant circuit board and reparation method thereof - Google Patents

Abstract

The present application provides a bending resistant circuit board and a preparation method thereof. The bending resistant circuit board includes an inner circuit board and an outer circuit layer. The inner circuit board includes a first circuit layer, an insulation layer, and a cavity. The cavity is formed within the insulation layer and includes a portion of the first circuit layer. The cavity is formed by enclosing a first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer, and the polarity of the magnetic layers towards the surface of the cavity is the same. The outer circuit layer is located on the surface of the insulation layer. By constructing the cavity formed by magnetic materials, the present application can reduce the influence of bending stress, maintain the shape of the cavity, and form a circuit layer on the surface of the cavity. Therefore, the bending resistance of the circuit board is improved, and the wiring density is increased.

Description

Bending resistant circuit board and preparation method thereof

The present application relates to the technical field of circuit boards, and more particularly to a bending-resistant circuit board and a preparation method thereof.

Foldable electronic products such as foldable mobile phones usually use flexible circuit boards (FPCs) as connectors at the folds. In recent years, as the functional requirements of electronic products change, 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 times) have become increasingly higher.

In order to reduce the thickness of the FPC and reduce the impact of bending stress when bending, an air gap (cavity) is generally formed inside the FPC. However, since the air gap area has no internal support, there is a risk of the circuit board sinking. At the same time, multiple air gaps in multi-layer boards will also reduce the signal transmission capability and reliability of the circuit board.

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

An embodiment of the present application provides a bending-resistant circuit board, which includes an inner circuit board and an outer circuit layer. The inner circuit board includes a first circuit layer, an insulating layer and a cavity. The cavity is formed in the insulating layer and contains part 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, and the second magnetic layer and the fourth magnetic layer are arranged opposite 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.

In one implementation, a magnetic material is disposed 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.

In one embodiment, the inner circuit board further includes a second circuit layer, which is 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, which is located on a surface of the fourth magnetic layer facing away from the first circuit layer. The third circuit layer is arranged opposite to the second circuit layer.

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

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

An embodiment of the present application provides a method for preparing a bending-resistant circuit board, which comprises the following steps:

A first magnetic layer is arranged on a substrate, wherein the substrate comprises a base material layer and a first circuit layer arranged 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;

A first sacrificial layer is disposed on the substrate, wherein the first sacrificial layer covers a portion of the surface of the first magnetic layer and the gap, and a surface of the first sacrificial layer facing away from the base layer is flush with a surface of the remaining first magnetic layer facing away from the base layer;

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;

removing the base material layer of the substrate;

A third magnetic layer is disposed on a surface of the first magnetic layer facing away from the second magnetic layer, and the third magnetic layer is disposed corresponding to the first magnetic layer;

A second sacrificial layer is disposed 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;

A fourth magnetic layer is disposed on a surface of the third magnetic layer facing away from the first magnetic layer and 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 surround a cavity; 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;

removing the first sacrificial layer and the second sacrificial layer in the cavity;

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

A first outer circuit layer is formed on a surface of the second circuit layer facing away from the second magnetic layer, and a second outer circuit layer is formed on a surface of the third circuit layer facing away from the fourth magnetic layer, thereby obtaining the bending-resistant circuit board.

In one implementation, the step of forming a first outer circuit layer on a surface of the second circuit layer facing away from the first circuit layer includes: at least pressing a copper-clad laminate on a 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 manufacturing the copper foil layer to form the first outer circuit layer.

In one implementation, 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.

In one implementation, the step of forming a second outer circuit layer on a surface of the third circuit layer facing away from the first circuit layer includes: at least pressing a copper-clad laminate on a 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 manufacturing the copper foil layer to form the second outer circuit layer.

In one implementation, 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.

This application uses the principle of magnetic material repulsion between like poles to construct 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 the circuit board is bent, its internal circuits are still in a suspended state, and the electrical function is not affected. The cavity formed by magnetic material in this 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 the lack of support force in the cavity of the prior art. In addition, a circuit layer can be formed on the surface of the cavity of this application, which not only improves the space utilization rate of the cavity, but also increases the wiring density, so that the cavity has electrical functions.

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

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

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.

In addition, the descriptions of "first", "second", etc. in this application are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Embodiments of the present application are described herein with reference to cross-sectional views, which are schematic views of idealized embodiments (and intermediate configurations) of the present application. As such, variations in the shapes illustrated due to manufacturing processes and/or tolerances are to be expected. Therefore, embodiments of the present application should not be construed as limited to the specific shapes of the regions illustrated herein, but should include deviations in shapes resulting, for example, from manufacturing. The regions illustrated in the figures are schematic in themselves, their shapes are not intended to illustrate the actual shapes of the devices, and are not intended to limit the scope of the present application.

The following is a detailed description of some implementations of the present application in conjunction with the attached drawings. In the absence of conflict, the following implementations and features in the implementations can be combined with each other.

Please refer to Figures 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 understandable that the numbering of the steps is intended to clearly describe the specific preparation method, and does not limit the order of the steps.

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

As shown in FIG. 1 and FIG. 2 , in some embodiments, the substrate 10 may be prepared from a copper-clad plate 10a. The copper-clad plate 10a includes a base material layer 11 and a copper foil layer 12 disposed on the surface of the base material layer 11. In this embodiment, the copper-clad plate 10a is a single-sided copper-clad plate, that is, the base material layer 11 has only one surface provided with the copper foil layer 12. The copper foil layer 12 may be formed into a first circuit layer 13 by steps of exposure, development, etching, and film stripping to obtain the substrate 10. Steps of exposure, development, etching, and film stripping are commonly used technical means in this field and will not be described in detail herein. It is understandable that a portion of the surface of the base material layer 11 close to the first circuit layer 13 may be exposed from the first circuit layer 13.

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

As shown in FIG3 , a magnetic material may be disposed on the substrate 10 by a process including but not limited to a printing process, a vacuum evaporation method, an electroplating method, a sputtering method, etc. to form a first magnetic layer 21. 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 area of the first circuit layer 13. That is, except for the surface close to the base material layer 11, the other surfaces of the circuit pattern in the central area of the first circuit layer 13 are covered by the first magnetic layer 21. Moreover, the first magnetic layer 21 is not continuous in the extension direction of the substrate 10, but is discontinuous. That is, along the extension direction of the substrate 10 (which may be the length direction of the substrate 10 or the width direction of the substrate 10), the first magnetic layer 21 has a gap 210. The number of the gaps 210 can be adjusted as the circuit pattern of the first circuit layer 13 changes, and the present application does not impose any limitation thereto.

As shown in FIG3 , in this embodiment, the height of the first magnetic layer 21 (i.e., the distance along the thickness direction of the substrate 10) is not uniform, and the height of the first magnetic layer 21 located in the edge region is higher than the height of the first magnetic layer 21 located in the center region. The first magnetic layer 21 in the edge region can be directly disposed on the base layer 11 without covering the circuit pattern of the first circuit layer 13, and the first magnetic layer 21 in the center region covers the circuit pattern of the first circuit layer 13.

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

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

As shown in FIG4 , 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 FIG4 ) 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 first magnetic layer 21 (i.e., the first magnetic layer 21 with a higher height in FIG4 ) facing away from the substrate layer 11 .

Referring to FIG. 5 , in step S30 , a second magnetic layer 22 is disposed on the surface 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 .

As shown in FIG5 , in some embodiments, the second magnetic layer 22, the first magnetic layer 21 located at a higher edge region, 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 strong magnetic (ferromagnetic and ferrimagnetic) magnetic film material, and the magnetic material can be the same as or different from the first magnetic layer 21, and the present 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.

In some embodiments, the second circuit layer 14 can be formed by, but not limited to, a printed network process or a selective sputtering metallization process. As shown in FIG5 , a portion of the surface of the second magnetic layer 22 can be exposed from the second circuit layer 14. The thickness and line width and line spacing of the second circuit layer 14 can be adjusted according to actual needs, and the present application does not impose any restrictions. Forming the second circuit layer 14 on the second magnetic layer 22 can improve the wiring density, overcoming the disadvantage of the prior art that the wiring density is reduced due to the presence of air gaps.

Please refer to FIG. 6 . In some embodiments, after step S30, step S101 may be further performed: an adhesive layer 40 and a copper-clad plate 10a are pressed on a side of the second circuit layer 14 away from the second magnetic layer 22. The adhesive layer 40 covers the substrate 10 (i.e., covers 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).

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

In other embodiments, the adhesive layer 40 may be omitted, and only the copper-clad laminate 10a may be pressed on the side of the second circuit layer 14 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, and 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, covers the surface of the base layer 11 exposed from the first circuit layer 13, and covers the surface of the second magnetic layer 22 exposed from the second circuit layer 14. When the adhesive layer 40 is omitted, the material of the base layer 11 may be a thermoplastic insulating material, and the base layer 11 is also the insulating layer 71.

Please refer to FIG. 7 , step S40 , removing the base material layer 11 of the substrate 10 .

In some embodiments, the base material layer 11 of the substrate 10 may be removed by, but not limited to, chemical etching. For example, the base material layer 11 of the substrate 10 may be immersed in an etching solution to chemically react with the etching solution. The etching solution may include sodium hydroxide, hydrofluoric acid, and acidic hydrogen peroxide.

Please refer to Fig. 8, step S50, the third magnetic layer 23 is disposed on the surface of the first magnetic layer 21 away from the second magnetic layer 22, and 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 can completely overlap.

As shown in FIG8 , the circuit pattern of the first circuit layer 13 covered by the first magnetic layer 21 has a surface that was previously covered by the base material layer 11 of the substrate 10, but is now covered by the third magnetic layer 23. Along the extension direction (which can be the length direction or the width direction) of the copper-clad plate 10a, the third magnetic layer 23 is discontinuous, like the first magnetic layer 21. Part of the third magnetic layer 23 covers the surface of the first circuit layer 13 and the first magnetic layer 21 that is away from the second magnetic layer 22, and the remaining part of the third magnetic layer 23 covers the surface of the first magnetic layer 21 that is away from the second magnetic layer 22. In this embodiment, the portion of the first magnetic layer 21 near the center located in the central area 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.

In some embodiments, the third magnetic layer 23 can be formed by, but not limited to, a printing process, a vacuum evaporation method, an electroplating method, a sputtering method, etc. The magnetic material forming the third magnetic layer 23 can be a strong magnetic (ferromagnetic and ferrimagnetic) magnetic film material, and the magnetic material can be the same as or different from the first magnetic layer 21, and the present application does not impose any restrictions. Along the extension direction of the copper-clad plate 10a, the height of the third magnetic layer 23 (i.e., the distance along the thickness direction of the copper-clad plate 10a) can remain unchanged.

Please refer 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 gap in the third magnetic layer 23, and 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, and the second sacrificial layer 32 covers the surface of the third magnetic layer 23 near the center facing away from the first magnetic layer 21.

Please refer 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 the surface of the second sacrificial layer 32 facing away from the first sacrificial layer 31. Part of the first magnetic layer 21 and part of the third magnetic layer 23, all of the second magnetic layer 22 and all of the fourth magnetic layer 24 surround a cavity 101, and the cross section of the cavity 101 is roughly rectangular. The first sacrificial layer 31 and the second sacrificial layer 32 are contained in the cavity 101, and part of the first magnetic layer 21, part of the third magnetic layer 23 and part of the first circuit layer 13 are also contained in the cavity 101. The surfaces of the first magnetic layer 21 , the second magnetic layer 22 , the third magnetic layer 23 and the fourth magnetic layer 24 facing the cavity 101 have the same polarity.

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 magnetic layer parallel to it in the cavity 101, and the distances between the gaps adjacent to the magnetic layers in the cavity 101 (i.e., the magnetic layers located in the central region mentioned above) are also equidistant. In this way, the repulsive forces between the magnetic layers are balanced, thereby maintaining the shape of the cavity 101 to prevent the cavity 101 from being dented or collapsed, thereby reducing the influence of the bending stress on the circuit board when bending, and enhancing the bending resistance of the circuit board.

As shown in FIG10 , in some embodiments, the fourth magnetic layer 24 has an opening 240 penetrating the fourth magnetic layer 24 along the thickness direction. The opening 240 is substantially located in the center region of the fourth magnetic layer 24 , and a portion of the surface of the second sacrificial layer 32 away from the first sacrificial layer 31 can be exposed through the opening 240 .

Please refer to FIG. 11 , step S80 , removing the first sacrificial layer 31 and the second sacrificial layer 32 in the cavity 101 .

In some embodiments, the first sacrificial layer 31 and the second sacrificial layer 32 can be removed by dry etching. Fluorine-containing gas (generally XeF2, HF) is introduced into the chamber 101, and the active substances in the generated plasma react with the first sacrificial layer 31 and the second sacrificial layer 32 to form products such as volatile compounds, which can then be drawn out of the chamber 101 through the opening 240, thereby completing the operation of removing the first sacrificial layer 31 and the second sacrificial layer 32.

Please refer to FIG. 12 , step S90, forming a third wiring layer 15 on the surface of the fourth magnetic layer 24 away from the third magnetic layer 23. The thickness and line width and line spacing of the third wiring layer 15 can be adjusted according to actual needs, and the present application does not limit it. Forming the third wiring layer 15 on the fourth magnetic layer 24 can improve the wiring density, overcoming the disadvantage of the prior art that the wiring density is reduced due to the existence of the air gap.

In some embodiments, the third circuit layer 15 may be formed by, but not limited to, a printed network process or a selective sputtering metallization process. As shown in FIG. 12 , a portion of the surface of the fourth magnetic layer 24 may be exposed from the third circuit layer 15 .

Referring to FIG. 13 to FIG. 15 , in step S100, a first outer circuit layer 17 is formed on the surface of the second circuit layer 14 facing away from the second magnetic layer 22, and a second outer circuit layer 18 is formed on the surface of the third circuit layer 15 facing away from the fourth magnetic layer 24, to obtain a bending-resistant circuit board 100. Step S100 may include steps S101 to S105. Step S101 (pressing the adhesive layer 40 and the copper-clad plate 10a on the side of the second circuit layer 14 facing away from the first circuit layer 13) has been performed after step S30.

As shown in FIG. 13 , in some embodiments, in step S102, an adhesive layer 40 and a copper-clad plate 10a are pressed together on a side of the third circuit layer 15 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 penetrating the adhesive layer 40 in the thickness direction, 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 can reduce the bending stress when the circuit board is bent, thereby improving the bending resistance of the circuit board. The copper clad laminate 10a includes a substrate layer 11 and a copper foil layer 12, wherein the substrate layer 11 is located between the copper foil layer 12 and the adhesive layer 40. The adhesive layer 40 may be, but is not limited to, AD glue. The material of the adhesive layer 40 may be the same as that of the substrate layer 11, and both may be thermoplastic dielectric materials. The adhesive layer 40 and the substrate layer 11 may form an insulating layer 71 together.

In other embodiments, the copper-clad laminate 10a may be pressed only on 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 also 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 covers the surface of the fourth magnetic layer 24 exposed from the third circuit layer 15. When the adhesive layer 40 is omitted, the material of the substrate layer 11 may be a thermoplastic insulating material, the substrate layer 11 is also the insulating layer 71, and the groove 103 is the opening 240.

As shown in FIG. 14 , in some embodiments, in step S103, a blind hole 102 may be formed on the copper clad laminate 10a and the adhesive layer 40 by, but not limited to, laser or mechanical drilling. The blind hole 102 may penetrate the copper clad laminate 10a (the copper clad laminate 10a on the upper side in FIG. 14 ) and the adhesive layer 40 along the thickness direction, and a portion of the surface of the first circuit layer 13 is exposed from the blind hole 102. The blind hole 102 may penetrate the copper clad laminate 10a (the copper clad laminate 10a on the upper side in FIG. 14 ) and a portion of the adhesive layer 40 along the thickness direction, and a portion of the surface of the second circuit layer 14 is exposed from the blind hole 102. The blind hole 102 can penetrate the copper clad laminate 10 a (the copper clad laminate 10 a on the lower side in FIG. 14 ) and a portion of the adhesive layer 40 along the thickness direction, and a portion of the surface of the third circuit layer 15 is exposed from the blind hole 102 .

It can be understood that when the adhesive layer 40 is omitted, the blind hole 102 penetrates the copper clad plate 10a along the thickness direction, and a portion of the surface of the first circuit layer 13 can be exposed from the blind hole 102, and a portion of the surface of the third circuit layer 15 can be exposed from the blind hole 102.

As shown in FIG. 15 , in some embodiments, in step S104, a thin copper layer 50 may be electroplated in the blind hole 102 by, but not limited to, electroplating to form a conductive structure 60. The conductive structure 60 may be, but not limited to, a conductive hole. It is understood that during electroplating, the outer surface of the upper and lower copper-clad plates 10a will also be plated with a thin copper layer 50.

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, stripping, and the like. The first outer circuit layer 17 and the first circuit layer 13 may be electrically connected through the conductive structure 60 , the first outer circuit layer 17 and the second circuit layer 14 may be electrically connected through the conductive structure 60 , and the second outer circuit layer 18 and the third circuit layer 15 may be electrically connected through the conductive structure 60 .

Please refer to FIG. 16 . The 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 .

As shown in FIG16 , the inner circuit board 70 includes a first circuit layer 13, an insulating layer 71 and a cavity 101. The cavity 101 is formed in the insulating layer 71 and includes a portion of the first circuit layer 13, so that the first circuit layer 13 in the cavity 101 is suspended (i.e., not in direct contact with the substrate layer 11 or the insulating layer 71). The cavity 101 is formed by the first magnetic layer 21, the second magnetic layer 22, the third magnetic layer 23 and the fourth magnetic layer 24. The second magnetic layer 22 and the fourth magnetic layer 24 are arranged opposite to each other along the thickness direction of the inner circuit board 70 (i.e., the vertical direction in FIG. 16 ), and 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 to form a repulsive force, thereby maintaining the shape of the cavity 101 to prevent collapse. In some embodiments, the cross-sectional shape of the cavity 101 is substantially rectangular.

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

As shown in FIG. 16 , in some embodiments, a magnetic material 20 is provided on the surface of the first circuit layer 13 in the cavity 101, and 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 in the cavity 101, and the magnetic layer formed by the magnetic material 20 in the cavity 101 may be discontinuous. Each side of the cavity 101 is equidistant from the magnetic layer formed by the magnetic material 20 in the cavity 101 and parallel thereto, and the distances between adjacent gaps in the magnetic layer in the cavity 101 are also equidistant. In this way, the repulsive forces between the magnetic layers are balanced, thereby maintaining the shape of the cavity 101 to prevent the cavity 101 from being dented or collapsed, thereby reducing the influence of the bending stress on the circuit board when bending, and enhancing the bending resistance of the circuit board.

As shown in FIG16 , in some embodiments, the inner circuit board 70 further includes a second circuit layer 14. The second circuit layer 14 is located on the surface of the second magnetic layer 22 away from the first circuit layer 13. Forming the second circuit layer 14 on the second magnetic layer 22 can improve the wiring density, overcoming the disadvantage of the prior art that the wiring density is reduced due to the presence of the cavity.

As shown in FIG. 16 , in some embodiments, the inner circuit board 70 further includes a third circuit layer 15. The third circuit layer 15 is located on the surface of the fourth magnetic layer 24 away from the first circuit layer 13, and the third circuit layer 15 and the second circuit layer 14 are arranged opposite to each other along the thickness direction (i.e., the vertical direction in FIG. 16 ) of the inner circuit board 70. Forming the third circuit layer 15 on the fourth magnetic layer 24 can improve the wiring density, overcoming the disadvantage of the prior art that the wiring density is reduced due to the presence of the cavity.

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

As shown in FIG. 16 , in some embodiments, the insulating layer 71 includes an adhesive layer 40 and a substrate layer 11. The substrate layer 11 is located between the outer circuit layer 16 and the adhesive layer 40. The substrate layer 11 and the adhesive layer 40 may be made of the same material, which is a thermoplastic dielectric material. In other embodiments, the adhesive layer 40 in the insulating layer 71 may be omitted, and in this case, the insulating layer 71 is the substrate layer 11.

As shown in FIG. 16 , in some embodiments, the bend-resistant circuit board 100 has a groove 103, and the groove at least penetrates 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, and improve the bend resistance of the circuit board. In this embodiment, the groove 103 penetrates 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 some other embodiments, when the insulating layer 71 does not include the adhesive layer 40 , the groove 103 penetrates the fourth magnetic layer 24 along the thickness direction of the bending resistant circuit board 100 and communicates with the cavity 101 .

The present application utilizes the principle of magnetic material repulsion between like poles to construct 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 influence of bending stress and improving the bending resistance of the circuit board. The internal circuit of the circuit board after bending 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 support force in the cavity of the prior art. Furthermore, a circuit layer can be formed on the surface of the cavity 101 of the present application, which not only improves the space utilization of the cavity 101, but also increases the wiring density, so that the cavity 101 has electrical functions.

The above descriptions are some specific implementations of this application, but in the actual application process, it cannot be limited to these implementations. For ordinary technical personnel in this field, other variations and changes made based on the technical concept of this application should all fall within the scope of protection of this application.

100: Bending-resistant circuit board 10a: Copper-clad board 11: Base material layer 12: Copper foil layer 10: Substrate 13: First circuit layer 14: Second circuit layer 15: Third circuit layer 16: Outer circuit layer 17: First outer circuit layer 18: Second outer circuit layer 20: Magnetic material 21: First magnetic layer 22: Second magnetic layer 23: Third magnetic layer 24: Fourth magnetic layer 31: First sacrificial layer 32: Second sacrificial layer 40: Adhesive layer 50: Thin copper layer 60: Conductive structure 70: Inner circuit board 71: Insulation layer 101: Cavity 102: Blind hole 103: Groove 210: Gap 240: Opening 401: Opening

FIG1 is a cross-sectional view of a copper-clad plate provided in an embodiment of the present application.

FIG. 2 is a cross-sectional view of a substrate formed by manufacturing the copper-clad plate shown in FIG. 1 .

FIG. 3 is a cross-sectional view showing a first magnetic layer disposed on the structure shown in FIG. 2 .

FIG. 4 is a cross-sectional view showing a first sacrificial layer disposed on the structure shown in FIG. 3 .

FIG. 5 is a cross-sectional view showing a second magnetic layer disposed on the structure shown in FIG. 4 and a second circuit layer formed.

FIG. 6 is a cross-sectional view of the adhesive layer and the copper-clad plate being pressed together outside the second circuit layer of the structure shown in FIG. 5 .

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

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 .

FIG. 9 is a cross-sectional view showing a structure shown in FIG. 8 in which a second sacrificial layer is disposed on the surface of the first sacrificial layer.

FIG10 is a cross-sectional view showing a fourth magnetic layer disposed on the surface of the structure shown in FIG9.

FIG. 11 is a cross-sectional view of the structure shown in FIG. 10 with the first sacrificial layer and the second sacrificial layer removed.

FIG. 12 is a cross-sectional view showing a third circuit layer formed on the surface of the fourth magnetic layer of the structure shown in FIG. 11 .

FIG. 13 is a cross-sectional view of the adhesive layer and the copper-clad plate being pressed together outside the third circuit layer of the structure shown in FIG. 12 .

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

FIG. 15 is a cross-sectional view of the copper plating in the blind hole and on the surface of the copper-clad plate of the structure shown in FIG. 14 .

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

100: Bending-resistant circuit board

11: Base material layer

13: First circuit layer

14: Second circuit layer

15: Third circuit layer

16: Outer circuit layer

17: First outer circuit layer

18: Second outer circuit layer

20: Magnetic materials

21: First magnetic layer

22: Second magnetic layer

23: The third magnetic layer

24: Fourth magnetic layer

40: Adhesive layer

60: Conductive structure

70: Inner circuit board

71: Insulation layer

101: Cavity

103: Groove

Claims (10)

A bending-resistant circuit board, which is improved in that it comprises: an inner circuit board, comprising a first circuit layer, an insulating layer and a cavity, wherein the cavity is formed in the insulating layer and contains part of the first circuit layer, wherein the cavity is formed by enclosing 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 opposite to each other along the thickness direction of the inner circuit board, and 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; and an outer circuit layer, wherein the outer circuit layer is arranged on the surface of the insulating layer facing away from the first circuit layer. A bend-resistant circuit board as described in claim 1, wherein a magnetic material is provided on the surface of the first circuit layer located in 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. A bend-resistant circuit board as described in claim 1, wherein the inner circuit board further includes a second circuit layer, the second circuit layer is located on the 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 is located on the surface of the fourth magnetic layer facing away from the first circuit layer, and the third circuit layer is arranged opposite to the second circuit layer. A bend-resistant circuit board as described in claim 3, wherein the bend-resistant circuit board further includes a conductive structure, wherein the conductive structure electrically connects the outer circuit layer and the first circuit layer, electrically connects the outer circuit layer and the second circuit layer, and electrically connects the outer circuit layer and the third circuit layer. A bend-resistant circuit board as described in claim 1, wherein the bend-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 bend-resistant circuit board. A method for preparing a bending-resistant circuit board, the improvement of which is that the preparation method comprises the following steps: A first magnetic layer is arranged on a substrate, wherein the substrate comprises a base material layer and a first circuit layer arranged on the 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 the extension direction of the substrate; A first sacrificial layer is arranged on the substrate, the first sacrificial layer covers a portion 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; A second magnetic layer is provided on the surface of the first magnetic layer and the first sacrificial layer facing away from the substrate layer, and a second circuit layer is formed on the surface of the second magnetic layer facing away from the first sacrificial layer; The substrate layer of the substrate is removed; A third magnetic layer is provided on the surface of the first magnetic layer facing away from the second magnetic layer, and the third magnetic layer is provided corresponding to the first magnetic layer; A second sacrificial layer is provided 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 provided on the surface of the third magnetic layer facing away from the first magnetic layer and on the 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 surround a cavity; 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 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 bending-resistant circuit board. The preparation method as described in claim 6, wherein the step of forming a first outer circuit layer on the surface of the second circuit layer facing away from the first circuit layer comprises: Pressing at least a copper-clad laminate on one side of the second circuit layer facing away from the second magnetic layer, the copper-clad laminate comprising a substrate layer and a copper foil layer, the substrate layer being located between the copper foil layer and the second circuit layer; Forming the copper foil layer into a first outer circuit layer. The preparation method as described in claim 7, wherein the preparation method further comprises: 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. The preparation method as described in claim 6, wherein the step of forming a second outer circuit layer on the surface of the third circuit layer facing away from the first circuit layer comprises: Pressing at least a copper-clad laminate on one side of the third circuit layer facing away from the fourth magnetic layer, the copper-clad laminate comprising a substrate layer and a copper foil layer, the substrate layer being located between the copper foil layer and the third circuit layer; Forming the copper foil layer into a second outer circuit layer. The preparation method as described in claim 9, wherein the preparation method further comprises: manufacturing a conductive structure on the bend-resistant circuit board to electrically connect the second outer circuit layer with the third circuit layer.

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