CN113597084A

CN113597084A - Flexible circuit board and manufacturing method thereof

Info

Publication number: CN113597084A
Application number: CN202010366126.6A
Authority: CN
Inventors: 沈芾云; 郭宏艳; 何明展
Original assignee: Avary Holding Shenzhen Co Ltd; Qing Ding Precision Electronics Huaian Co Ltd
Current assignee: Avary Holding Shenzhen Co Ltd; Qing Ding Precision Electronics Huaian Co Ltd
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2021-11-02
Anticipated expiration: 2040-04-30
Also published as: CN113597084B

Abstract

The application provides a flexible circuit board, wherein a first circuit layer comprises a first signal transmission line, a second signal transmission line and a first grounding circuit; the second circuit layer comprises a third signal transmission line, a first signal transmission terminal, a second signal transmission terminal, a third signal transmission terminal and a fourth signal transmission terminal, wherein two ends of the first signal transmission line are electrically connected with the first signal transmission terminal and the second signal transmission terminal, two ends of the second signal transmission line are electrically connected with the third signal transmission terminal and the fourth signal transmission terminal, and two ends of the third signal transmission line are electrically connected with the second signal transmission terminal and the third signal transmission terminal; a first transmission area, a second transmission area and a bending area are defined, a first signal transmission line is arranged in the first transmission area, a second signal transmission line is arranged in the second transmission area, a third signal transmission line is arranged in the bending area, and a first grounding circuit is arranged in the bending area. The application also provides a manufacturing method of the flexible and foldable circuit board.

Description

Flexible circuit board and manufacturing method thereof

Technical Field

The application relates to the technical field of circuit boards, in particular to a flexible circuit board and a manufacturing method thereof.

Background

The multi-morphism of electronic products makes the high bending performance of circuit boards become a demand, especially wearable electronic products. Meanwhile, with the advent of the 5G era, higher frequency and efficiency requirements for wireless transmission have been made. Therefore, a transmission line having high bending and bending properties and capable of high-frequency transmission is becoming a popular research in the industry.

In the prior art, for a circuit board applied to a wearable electronic device, a signal transmission line is usually designed in a band shape, the signal transmission line is disposed in a middle layer of the circuit board, upper and lower sides of the signal transmission line are ground layers, two ends of the signal transmission line extend to an outer layer of the circuit board through conductive holes, and the signal transmission line is disposed in a dielectric layer. The bending of the circuit board can be realized through the structure, and the signal loss is avoided through the dielectric layer. However, in the process of high-frequency transmission, the larger the thickness of the dielectric layer is, the less the signal loss is, the larger the thickness of the dielectric layer is, the greater the bending difficulty of the circuit board is, and the circuit board is more likely to be broken after being bent for many times.

How to solve the above problems needs to be considered by those skilled in the art.

Disclosure of Invention

In view of the above, the present application provides a flexible printed circuit board, including:

a first circuit layer including a first signal transmission line, a second signal transmission line, and a first ground line, the first ground line being spaced apart from the first signal transmission line and the second signal transmission line, the first ground line being disposed between the first signal transmission line and the second signal transmission line;

a second circuit layer including a third signal transmission line, a first signal transmission terminal, a second signal transmission terminal, a third signal transmission terminal, and a fourth signal transmission terminal, wherein both ends of the first signal transmission line are electrically connected to the first signal transmission terminal and the second signal transmission terminal through conductive holes, both ends of the second signal transmission line are electrically connected to the third signal transmission terminal and the fourth signal transmission terminal through conductive holes, and both ends of the third signal transmission line are electrically connected to the second signal transmission terminal and the third signal transmission terminal through conductive holes, respectively; and

a first transmission area, a second transmission area and a bending area are defined, the first signal transmission line is arranged in the first transmission area, the second signal transmission line is arranged in the second transmission area, at least part of the third signal transmission line is arranged in the bending area, and the first grounding line is arranged in the bending area.

In an embodiment, the first transmission area is connected to the bending area, the second transmission area is connected to the bending area, the first transmission area and the second transmission area are located on two sides of the bending area, the first signal transmission terminal and the second signal transmission terminal are disposed in the first transmission area, and the third signal transmission terminal and the fourth signal transmission terminal are disposed in the second transmission area.

In an embodiment, the second circuit layer further includes a second ground circuit and a third ground circuit, the flexible circuit board further includes a third circuit layer, the second circuit layer and the third circuit layer are disposed on two opposite sides of the first circuit layer, the third circuit layer is disposed in the first transmission area and the second transmission area, the third circuit layer includes a fourth ground circuit and a fifth ground circuit, the second ground circuit and the fourth ground circuit are disposed in the first transmission area, and the third ground circuit and the fifth ground circuit are disposed in the second transmission area.

In an embodiment, the second ground line and the fourth ground line are disposed on opposite sides of the first signal transmission line, and the third ground line and the fifth ground line are disposed on opposite sides of the second signal transmission line.

In an embodiment, the second circuit layer further includes a second dielectric layer, the third signal transmission line, the first signal transmission terminal, the second signal transmission terminal, the third signal transmission terminal and the fourth signal transmission terminal are disposed on a surface of the second dielectric layer away from the first circuit layer, the third circuit layer further includes a third dielectric layer, the fourth ground line and the fifth ground line are disposed on a surface of the third dielectric layer away from the first circuit layer, and a thickness of the third dielectric layer is greater than a thickness of the second dielectric layer.

In one embodiment, the conductive via is formed by filling a conductive paste or electroplating.

In an embodiment, the printed circuit board further includes a first opening, the first opening is disposed in the bending region, and the first opening is disposed on a side of the first circuit layer away from the second circuit layer.

In an embodiment, the first circuit layer includes a first dielectric layer, the first signal transmission line, the second signal transmission line and the first ground line are disposed on a surface of the first dielectric layer, the first dielectric layer is disposed on a side of the first circuit layer away from the second circuit layer, and at least a portion of the side of the first dielectric layer away from the first ground line is exposed by the first opening.

In an embodiment, the display device further includes an electrostatic shielding layer disposed on a side of the second circuit layer away from the first circuit layer, and a projection of the electrostatic shielding layer in the bending region coincides with projections of the third signal line and the first ground line in the bending region.

In an embodiment, the second ground line includes at least two connection terminals, the electrostatic shielding layer is electrically connected to the second ground line through one of the connection terminals, and the electrostatic shielding layer is electrically connected to the third ground line through another connection terminal.

In an embodiment, the second circuit layer further includes at least four ground terminals, the first ground circuit and the second ground circuit are electrically connected to the ground terminals, and the flexible printed circuit board further includes a solder mask layer covering a surface of the ground terminal away from the first circuit layer.

In an embodiment, in the first transmission region and the second transmission region, the first ground line, the second ground line, the third ground line, the fourth ground line, and the fifth ground line are electrically connected through at least one via, and the via is not disposed in the bending region.

In an embodiment, the first ground line is a solid copper or a grid-shaped copper layer, and a copper exposure rate of the grid-shaped copper layer is greater than 50%.

The application also provides a manufacturing method of the flexible circuit board, which comprises the following steps:

providing a first single-sided copper-clad plate, and etching the first single-sided copper-clad plate through an image transfer process to obtain a first circuit layer;

providing a second single-sided copper-clad plate and a third single-sided copper-clad plate, and laminating the second single-sided copper-clad plate and the third single-sided copper-clad plate to two sides of the first circuit layer which are opposite to each other;

the first signal transmission line and the second signal transmission line are electrically connected with the second single-sided copper-clad plate through the conductive holes; and

and processing the second single-sided copper-clad plate through an image transfer process to obtain the second circuit layer, and processing the third single-sided copper-clad plate through an image transfer process to obtain the third circuit layer.

In one embodiment, the method further comprises the following steps:

providing a protective layer, wherein the protective layer is arranged on at least partial surfaces of the second circuit layer and the third circuit layer far away from the first circuit layer;

providing a solder mask layer, wherein the second circuit layer comprises a plurality of second grounding terminals, and the solder mask layer covers the second grounding terminals; and

and providing an electrostatic shielding layer, wherein the electrostatic shielding layer is arranged corresponding to the bending area, the second circuit layer comprises at least two connecting terminals, and the connecting terminals are electrically connected with the electrostatic shielding layer.

In one embodiment, the conductive via is first formed by laser or mechanical drilling to form a blind via, and then filled with conductive paste or plated to form the conductive via.

Compared with the prior art, the flexible circuit board and the manufacturing method thereof enable the flexible circuit board to comprise the bending area and the transmission area, the first signal transmission line and the second signal transmission line are arranged in the first transmission area and the second transmission area, the third signal transmission line is at least partially arranged in the bending area, the first signal transmission line, the second signal transmission line and the third signal transmission line are electrically connected through the conductive hole, the conductive hole is not arranged in the bending area, and two sides of the first signal transmission line, the second signal transmission line and the third signal transmission line are protected by the grounding circuit and the electrostatic shielding structure. (1) The flexible circuit board adopts a flexible material as a base material layer, a bending area is arranged between the first transmission area and the second transmission area, and the bending area of the transmission circuit board only comprises an electrostatic shielding layer, a third signal transmission line, a first grounding circuit, a second dielectric layer and a first dielectric layer, so that the transmission circuit board has good dynamic bending capability, and the service life of the transmission circuit board is prolonged. (2) The first grounding circuit and the electrostatic shielding layer are grounded, and are grounded while the shielding effect is achieved, so that signal backflow can be avoided, and the shielding effect is improved. (3) The electrostatic shielding layer is attached to the second circuit layer, so that the height offset is avoided, and the problem of breakage of the electrostatic shielding layer is solved.

Drawings

Fig. 1 is a schematic cross-sectional view of a flexible printed circuit according to an embodiment of the present disclosure.

Fig. 2 is a schematic top view of a portion of a flexible printed circuit according to an embodiment of the present application.

Fig. 3 is a schematic top view of a portion of a flexible printed circuit according to an embodiment of the present application.

Fig. 4 is a schematic top view of a portion of a flexible printed circuit according to an embodiment of the present application.

Fig. 5 is a schematic view of a manufacturing process of a flexible printed circuit board according to an embodiment of the present disclosure.

Fig. 6 is a schematic view of a manufacturing process of a flexible printed circuit according to an embodiment of the present disclosure.

Fig. 7 is a schematic view illustrating a manufacturing process of a flexible printed circuit according to an embodiment of the present disclosure.

Fig. 8 is a schematic view of a manufacturing process of a flexible printed circuit according to an embodiment of the present disclosure.

Fig. 9 is a schematic view of a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Fig. 10 is a schematic view of a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Fig. 11 is a schematic view illustrating a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Fig. 12 is a schematic view illustrating a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Fig. 13 is a schematic view illustrating a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Fig. 14 is a schematic view illustrating a manufacturing process of a flexible printed circuit according to an embodiment of the present application.

Description of the main elements

Flexible circuit board 1

First transmission area 101

Second transmission area 102

Bending zone 103

First wiring layer 11

First dielectric layer 110

First signal transmission line 111

Second signal transmission line 112

First ground line 113

First ground terminal 114

Second wiring layer 12

Second dielectric layer 120

First signal transmission terminal 121

Second signal transmission terminal 122

Third signal transmission terminal 123

Fourth signal transmission terminal 124

Third signal transmission line 125

Second ground line 126

Third ground line 127

Second ground terminal 128

Connecting terminal 129

Third wiring layer 13

Third dielectric layer 130

Fourth ground line 131

Fifth ground line 132

Protective layer 14

First protective layer 141

Second protective layer 142

Electrostatic shielding layer 15

Conductive vias 16

Blind hole 161

Via 165

First opening 17

Solder mask layer 18

First single-sided copper-clad plate 191

Second Single-sided copper-clad plate 192

Third single-sided copper-clad plate 193

Glue 194

The following detailed description will further illustrate the present application in conjunction with the above-described figures.

Detailed Description

The following description will refer to the accompanying drawings to more fully describe the present disclosure. There is shown in the drawings exemplary embodiments of the present application. This application may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. These exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals designate identical or similar components.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, as used herein, the terms "comprises," "comprising," "includes" and/or "including" or "having" and/or "having," integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Furthermore, unless otherwise defined herein, terms such as those defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present application and will not be interpreted in an idealized or overly formal sense.

The following description of exemplary embodiments refers to the accompanying drawings. It should be noted that the components depicted in the referenced drawings are not necessarily shown to scale; and the same or similar components will be given the same or similar reference numerals or similar terms.

Embodiments of the present application will now be described in further detail with reference to the accompanying drawings.

First embodiment

As shown in fig. 1 to 4, the present application provides a flexible printed circuit 1, which includes a first circuit layer 11, a second circuit layer 12, a third circuit layer 13, a protective layer 14 and an electrostatic shielding layer 15. The second circuit layer 12 and the third circuit layer 13 are disposed on two opposite sides of the first circuit layer 11, at least a portion of the protection layer 14 is disposed on a surface of the second circuit layer 12 away from the first circuit layer 11, at least a portion of the protection layer 14 is disposed on a surface of the third circuit layer 13 away from the first circuit layer 11, and the electrostatic shielding layer 15 covers a portion of the protection layer 14 and is electrically connected to the second circuit layer 12.

The first circuit layer 11 includes a first dielectric layer 110, a first signal transmission line 111, a second signal transmission line 112, a first ground line 113, and at least two first ground terminals 114. The first signal transmission line 111, the second signal transmission line 112 and the first ground line 113 are disposed on the same surface of the first dielectric layer 110. The first ground line 113 is disposed at a distance from the first signal transmission line 111 and the second signal transmission line 112, and the first ground line 113 is disposed between the first signal transmission line 111 and the second signal transmission line 112. At least one first ground terminal 114 is provided on the side of the first signal transmission line 111 away from the first ground line 113, and at least one first ground terminal 114 is provided on the side of the second signal transmission line 112 away from the first ground line 113.

The second circuit layer 12 includes a second dielectric layer 120, a first signal transmission terminal 121, a second signal transmission terminal 122, a third signal transmission terminal 123, a fourth signal transmission terminal 124, a third signal transmission line 125, a second ground line 126, a third ground line 127, at least four second ground terminals 128, and at least two connection terminals 129. The first signal transmission terminal 121, the second signal transmission terminal 122, the third signal transmission terminal 123, the fourth signal transmission terminal 124, the third signal transmission line 125, the second ground line 126, the third ground line 127, at least four second ground terminals 128, and at least two connection terminals 129 are disposed on the second dielectric layer 120 on the side away from the first circuit layer 11. Both ends of the first signal transmission line 111 are electrically connected to the first signal transmission terminal 121 and the second signal transmission terminal 122, both ends of the second signal transmission line 112 are electrically connected to the third signal transmission terminal 123 and the fourth signal transmission terminal 124, and both ends of the third signal transmission line 125 are electrically connected to the second signal transmission terminal 122 and the third signal transmission terminal 123, respectively.

In an embodiment, the flexible printed circuit board 1 further includes a plurality of conductive vias 16, two ends of the first signal transmission line 111 are electrically connected to the first signal transmission terminal 121 and the second signal transmission terminal 122 through one conductive via 16, and two ends of the second signal transmission line 112 are electrically connected to the third signal transmission terminal 123 and the fourth signal transmission terminal 124 through one conductive via 16.

The third circuit layer 13 includes a third dielectric layer 130, a fourth ground line 131 and a fifth ground line 132, wherein the fourth ground line 131 and the fifth ground line 132 are disposed on a side of the third dielectric layer 130 away from the first circuit layer 11.

In an embodiment, the thickness of the third dielectric layer 130 is greater than that of the second dielectric layer 120, which is beneficial to the bending performance of the bending circuit board 1 and the reduction of the transmission performance loss of the transmission line.

The flexible circuit board 1 defines a first transmission area 101, a second transmission area 102 and a bending area 103, the first transmission area 101 is connected with the bending area 103, the second transmission area 102 is connected with the bending area 103, and the first transmission area 101 and the second transmission area 102 are located on two sides of the bending area 103.

The third circuit layer 13 is disposed in the first transmission region 101 and the second transmission region 102, the first signal transmission line 111, the second ground line 126, and the fourth ground line 131 are disposed in the first transmission region 101, and the second signal transmission line 112, the third ground line 127, and the fifth ground line 132 are disposed in the second transmission region 102. The second ground line 126 and the fourth ground line 131 are disposed on opposite sides of the first signal transmission line 111, and the third ground line 127 and the fifth ground line 132 are disposed on opposite sides of the second signal transmission line 112.

The flexible circuit board 1 further includes a first opening 17, the first opening 17 is disposed in the bending region 103, the first opening 17 is disposed on a side of the first circuit layer 11 away from the second circuit layer 12, the first dielectric layer 110 is disposed on a side of the first circuit layer 11 away from the second circuit layer 12, and at least a portion of a side of the first dielectric layer 110 away from the first grounding circuit 113 is exposed by the first opening 17. In an embodiment, the composition of the first dielectric layer 110 includes, but is not limited to, polyimide, the first dielectric layer 110 can provide protection for the conductive traces of the first trace layer 11 in the bending region 103, and the first dielectric layer 110 located in the bending region 103 has good bending performance.

In an embodiment, the first signal transmission terminal 121 and the second signal transmission terminal 122 are disposed in the first transmission region 101, the third signal transmission terminal 123 and the fourth signal transmission terminal 124 are disposed in the second transmission region 102, the plurality of conductive vias 16 are disposed in the first transmission region 101 and the second transmission region 102, and the conductive vias 16 are not disposed in the bending region 103, so as to prevent a conductive material (e.g., copper) in the conductive vias 16 from being broken or damaged during the bending process of the flexible circuit board 1.

The passivation layer 14 covers the surfaces of the fourth ground line 131 and the fifth ground line 132 away from the third dielectric layer 130 to protect the third circuit layer 13, and the passivation layer 14 covers the surfaces of the second ground line 126 and the third ground line 127 away from the second dielectric layer 120 to protect the second circuit layer 12.

In an embodiment, the passivation layer 14 includes a first passivation layer 141 and a second passivation layer 142, the first passivation layer 141 is disposed on at least a portion of the surface of the second circuit layer 12 away from the first circuit layer 11, and the second passivation layer 142 is disposed on at least a portion of the surface of the third circuit layer 13 away from the first circuit layer 11.

At least part of the third signal transmission line 125 is disposed in the bending region 103, at least part of the first ground line 113 is disposed in the bending region 103, the electrostatic shielding layer 15 is disposed on the second circuit layer 12 far away from the first circuit layer 11, and a projection of the electrostatic shielding layer 15 on the bending region 103 covers a projection of the third signal transmission line 125 and the first ground line 113 on the bending region 103.

In an embodiment, the electrostatic shielding layer 15 is electrically connected to the second ground trace 126 through one connection terminal 129, the electrostatic shielding layer 15 is electrically connected to the third ground trace 127 through another connection terminal 129, the electrostatic shielding layer 15 is electrically connected to the second ground trace 126 and the third ground trace 127 to form an electrostatic shielding structure, and the electrostatic shielding layer 15 and the first ground trace 113 are disposed on two opposite sides of the third signal transmission line 125 for shielding signal interference outside the third signal transmission line 125.

In one embodiment, the first ground line 113 may be a solid copper or a grid copper layer, and the copper exposure rate of the grid copper layer is greater than 50%.

In an embodiment, in the first transmission region 101 and the second transmission region 102, the first ground line 113, the second ground line 126, the third ground line 127, the fourth ground line 131, and the fifth ground line 132 are electrically connected through at least one via 165, and the via 165 is not disposed in the bending region. In an embodiment, the number of the vias 165 may be multiple, and the multiple vias 165 may be uniformly spaced in the first transmission region 101 and the second transmission region 102.

In an embodiment, the electrostatic shielding layer 15 may be a multi-layer structure, and the electrostatic shielding layer 15 may include a conductive adhesive layer, a metal thin film layer and a protective layer, which are stacked, where the metal thin film layer may be copper or silver, and when the metal thin film layer is silver, the thickness of the metal thin film layer ranges from 0.1 μm to 0.5 μm. The electrostatic shielding layer 15 may cover at least a portion of the first protection layer 141, and when the electrostatic shielding layer 15 is disposed on the outermost portion of the winding circuit board 1, the metal thin film layer in the electrostatic shielding layer 15 may be prevented from being damaged.

The flex circuit board 1 further includes a solder mask layer 18, and the solder mask layer 18 covers the surfaces of the second ground terminals 128 far from the first circuit layer 11.

At the first opening 17 of the bending region 103, the first dielectric layer 110 can be used as a circuit protection structure, and the protection structure does not need to be attached, so that the overall thickness of the bending region 103 is reduced, and the electrostatic shielding layer 15 is smoothly attached to the surface of the first protection layer 141 far away from the second circuit layer 12, thereby avoiding the problem of filling offset.

The application also provides a manufacturing method of the flexible circuit board 1, which comprises the following steps:

step S1: as shown in fig. 5 and 6, a first single-sided copper-clad plate 191 is provided, and the first single-sided copper-clad plate 191 is etched by an image transfer process to obtain a first circuit layer 11.

Step S2: as shown in fig. 7, a second single-sided copper-clad plate 192 and a third single-sided copper-clad plate 193 are provided, and the second single-sided copper-clad plate 192 and the third single-sided copper-clad plate 193 are laminated to the two opposite sides of the first circuit layer 11.

In one embodiment, the second single-sided copper-clad plate 192 and the third single-sided copper-clad plate 193 can be bonded to the first circuit layer 11 by an adhesive 194, or can be directly bonded by a hot-press bonding method in other embodiments. In one embodiment, during the lamination process, the copper layers of the second single-sided copper-clad plate 192 and the third single-sided copper-clad plate 193 are disposed on the side away from the first circuit layer 11.

In one embodiment, the third single-sided copper-clad plate 193 is disposed in the first transmission region 101 and the second transmission region 102. In an embodiment, the third single-sided copper-clad plate 193 is fished to obtain the first opening 17, the first opening 17 is disposed in the bending region 103, and the first opening 17 may be formed before or after the pressing.

Step S3: as shown in fig. 8 and 9, the first signal transmission line 111 and the second signal transmission line 112 are electrically connected to the second single-sided copper-clad plate 192 through conductive vias.

In one embodiment, as shown in fig. 8, the blind via 161 is formed by laser or mechanical drilling, and the blind via 161 penetrates through the second single-sided copper-clad laminate 192 to be exposed to the first circuit layer 11; as shown in fig. 9, the blind via 161 is filled with conductive paste or plated to form a conductive via 16, so that the first circuit layer 11 is electrically connected to the second single-sided copper-clad plate 192.

In an embodiment, as shown in fig. 2 to 4, while the first signal transmission line 111 and the second signal transmission line 112 are electrically connected to the second single-sided copper-clad plate 192, a via hole 165 is formed in the first transmission area 101 and the second transmission area 102, so that the first ground line 113, the second ground line 126, the third ground line 127, the fourth ground line 131, and the fifth ground line 132 are electrically connected through the via hole 165.

Step S4: as shown in fig. 10, the second single-sided copper-clad plate 192 is processed by an image transfer process to obtain a second circuit layer 12, and the third single-sided copper-clad plate 193 is processed by an image transfer process to obtain a third circuit layer 13.

The second circuit layer 12 includes a second ground line 126, a third ground line 127, a third signal transmission line 125, a first signal transmission terminal 121, a second signal transmission terminal 122, a third signal transmission terminal 123, a fourth signal transmission terminal 124, at least four second ground terminals 128, and at least two connection terminals 129, wherein two ends of the first signal transmission line 111 are electrically connected to the first signal transmission terminal 121 and the second signal transmission terminal 122, two ends of the second signal transmission line 112 are electrically connected to the third signal transmission terminal 123 and the fourth signal transmission terminal 124, and two ends of the third signal transmission line 125 are electrically connected to the second signal transmission terminal 122 and the third signal transmission terminal 123. The first signal transmission terminal 121 and the fourth signal transmission terminal 124 are each electrically insulated from a ground line.

Step S5: as shown in fig. 11, a protective layer 14 is provided, and the protective layer 14 is provided on at least a part of the surface of the second wiring layer 12 and the third wiring layer 13 away from the first wiring layer 11.

Step S6: as shown in fig. 12, the solder mask layer 18 is provided such that the solder mask layer 18 covers the plurality of second ground terminals 128.

Step S7: as shown in fig. 13, the first signal transmission terminal 121, the fourth signal transmission terminal 124, and the connection terminal 129 are subjected to nickel-gold surface treatment.

Step S8: as shown in fig. 14, the electrostatic shielding layer 15 is provided, the electrostatic shielding layer 15 is disposed corresponding to the bending region 103, the electrostatic shielding layer 15 covers a portion of the first protection layer 141 disposed in the bending region 103, and the connection terminal 129 is electrically connected to the electrostatic shielding layer 15.

Hereinbefore, specific embodiments of the present application are described with reference to the drawings. However, those skilled in the art will appreciate that various modifications and substitutions can be made to the specific embodiments of the present application without departing from the spirit and scope of the application. Such modifications and substitutions are intended to be within the scope of the present application.

Claims

1. A flexible circuit board is characterized by comprising:

2. The flexible printed circuit board of claim 1, wherein the first transmission area is connected to the bending area, the second transmission area is connected to the bending area, the first transmission area and the second transmission area are located on two sides of the bending area, the first signal transmission terminal and the second signal transmission terminal are disposed in the first transmission area, and the third signal transmission terminal and the fourth signal transmission terminal are disposed in the second transmission area.

3. The flexible printed circuit board of claim 1, wherein the second circuit layer further includes a second ground line and a third ground line, the flexible printed circuit further includes a third circuit layer, the second circuit layer and the third circuit layer are disposed on opposite sides of the first circuit layer, the third circuit layer is disposed in the first transmission area and the second transmission area, the third circuit layer includes a fourth ground line and a fifth ground line, the second ground line and the fourth ground line are disposed on opposite sides of the first signal transmission line in the first transmission area, and the third ground line and the fifth ground line are disposed on opposite sides of the second signal transmission line in the second transmission area.

4. The flexible printed circuit board of claim 3, wherein the second circuit layer further comprises a second dielectric layer, the third signal transmission line, the first signal transmission terminal, the second signal transmission terminal, the third signal transmission terminal and the fourth signal transmission terminal are disposed on a surface of the second dielectric layer away from the first circuit layer, the third circuit layer further comprises a third dielectric layer, the fourth ground line and the fifth ground line are disposed on a surface of the third dielectric layer away from the first circuit layer, and a thickness of the third dielectric layer is greater than a thickness of the second dielectric layer.

5. The flex circuit board of claim 1, wherein the conductive vias are formed by filling conductive paste or plating.

6. The flexible printed circuit board of claim 1, further comprising a first opening disposed in the bending region, wherein the first opening is disposed on a side of the first circuit layer away from the second circuit layer.

7. The FPC as claimed in claim 6, wherein the first circuit layer includes a first dielectric layer, the first signal transmission line, the second signal transmission line and the first ground line are disposed on a surface of the first dielectric layer, the first dielectric layer is disposed on a side of the first circuit layer away from the second circuit layer, and at least a portion of the side of the first dielectric layer away from the first ground line is exposed by the first opening.

8. The flex circuit board of claim 3, further comprising an electrostatic shielding layer disposed on a side of the second circuit layer away from the first circuit layer, wherein a projection of the electrostatic shielding layer on the bending region covers projections of the third signal line and the first ground line on the bending region.

9. The flexible printed circuit board of claim 8, wherein the second ground trace includes at least two connection terminals, the electrostatic shielding layer is electrically connected to the second ground trace through one of the connection terminals, and the electrostatic shielding layer is electrically connected to the third ground trace through the other connection terminal.

10. The flexible printed circuit board of claim 1, wherein the second circuit layer further includes at least four second ground terminals, the first ground circuit and the second ground circuit are electrically connected to the second ground terminals, and the flexible printed circuit board further includes a solder mask layer covering a surface of the second ground terminal away from the first circuit layer.

11. The flexible printed circuit board of claim 3, wherein the first ground trace, the second ground trace, the third ground trace, the fourth ground trace, and the fifth ground trace are electrically connected by at least one via in the first transmission region and the second transmission region, and the via is not disposed in the bending region.

12. The flexible printed circuit board of claim 1, wherein the first ground trace is a solid copper or a copper grid, and the copper exposure rate of the copper grid is greater than 50%.

13. A method for manufacturing a flex circuit board according to any one of claims 1 to 12, comprising the steps of:

14. The method for manufacturing a flex circuit board according to claim 13, further comprising the steps of:

15. The method of claim 13, wherein the conductive vias are formed by laser or mechanical drilling, filling conductive paste or electroplating.