Flexible circuit board and method of manufacturing the same

Abstract

A manufacturing method of a bending-resistant circuit board, comprising the steps of: providing a circuit substrate, the circuit substrate comprising a bending layer and a circuit structure arranged on one side of the bending layer, the circuit structure comprising a plurality of first conductive circuits, the plurality of first conductive circuits being arranged at intervals, and each adjacent two of the first conductive circuits having a first line-spacing groove therebetween; and arranging a first protective layer on the circuit structure, the first protective layer covering each of the first conductive circuits, part of the first protective layer being filled into the first line-spacing groove, and the thickness of the first protective layer being less than the depth of the first line-spacing groove. The manufacturing method of the bending-resistant circuit board provided by the application can improve the bending frequency and the bending angle. In addition, the application also provides a bending-resistant circuit board.

Description

Technical Field

[0001] This application relates to a bend-resistant circuit board and a method for manufacturing the same. Background Technology

[0002] In recent years, rollable or foldable electronic products have become increasingly popular. Flexible circuit boards used in such electronic products need to have excellent flexibility and high-frequency bending resistance.

[0003] Generally, flexible circuit boards need to have cavities inside to facilitate bending. However, the presence of these cavities not only hinders the installation of vias but also reduces the overall wiring density of the flexible circuit board. Summary of the Invention

[0004] To address the problems in the background art, this application provides a method for manufacturing a bend-resistant circuit board.

[0005] In addition, this application also provides a bend-resistant circuit board.

[0006] A method for manufacturing a bend-resistant circuit board includes the following steps: providing a circuit substrate, the circuit substrate including a flexural layer and a circuit structure disposed on one side of the flexural layer, the circuit structure including a plurality of first conductive lines, the plurality of first conductive lines being spaced apart, and a first spacing groove being provided between each adjacent pair of first conductive lines; providing a first protective layer on the circuit structure, the first protective layer covering each first conductive line, a portion of the first protective layer filling the first spacing groove, the thickness of the first protective layer being less than the depth of the first spacing groove.

[0007] Furthermore, the circuit structure further includes embedded circuitry and intermediate circuitry, the intermediate circuitry being disposed between the embedded circuitry and the first conductive circuitry, the embedded circuitry being disposed within the flexible layer, and the manufacturing method of the circuit substrate including the following steps:

[0008] A first copper foil layer is provided. A first photosensitive pattern and a second photosensitive pattern are respectively formed on two opposite surfaces of the first copper foil layer. The first photosensitive pattern is provided with a plurality of first grooves, and the second photosensitive pattern is provided with a plurality of second grooves. The first grooves and the second grooves are correspondingly arranged, and a portion of the first copper foil layer is exposed at the bottom of the first grooves and the second grooves. A first conductive line is formed in the first groove, and an embedded line is formed in the second groove. The first conductive line and the embedded line are correspondingly arranged. The first photosensitive pattern and the second photosensitive pattern are removed, so that a second spacing groove is formed between each two adjacent embedded lines. The first spacing groove and the second spacing groove are correspondingly arranged. A flexible layer is formed on the embedded line, and a portion of the flexible layer is filled into the second spacing groove. A portion of the first copper foil layer corresponding to the first spacing groove or the second spacing groove is removed to form the intermediate line, thereby obtaining the circuit substrate.

[0009] Further, the method includes the following steps: A second copper foil layer is disposed on the side of the flexural layer opposite to the first conductive line. An opening is made in the second copper foil layer, the opening penetrating both the second copper foil layer and the flexural layer, the opening corresponding to the embedded line, with a portion of the embedded line exposed at the bottom of the opening. An electroplated layer is disposed on the second copper foil layer, a portion of the electroplated layer filling the opening to form a conductor, the conductor electrically connecting the embedded line and the second copper foil layer. The electroplated layer and the second copper foil layer are then etched to form a plurality of second conductive lines, the second conductive lines being spaced apart, with a third spacing groove between each adjacent pair of second lines.

[0010] Furthermore, the method includes the steps of: depositing a photosensitive ink layer on the second conductive line, with a portion of the photosensitive ink layer filling the third line spacing groove; exposing a portion of the photosensitive ink layer outside the second conductive line to form a second protective layer; and removing the unexposed portion of the photosensitive ink layer, such that the second protective layer has a window corresponding to the area of ​​the third line spacing groove.

[0011] Further, the step "depositing a first protective layer on the circuit structure" includes: depositing a dry film solder resist layer on the first conductive line, the dry film solder resist layer covering the first conductive line, and a portion of the dry film solder resist layer filling the first line spacing groove. Exposing the portion of the dry film solder resist layer covering the first conductive line to obtain a portion of the protective layer. Removing the portion of the dry film solder resist layer within the first line spacing groove, and disposing of another portion of the dry film solder resist layer at the bottom of the first line spacing groove, with the portion of the dry film solder resist layer at the bottom of the first line spacing groove connected to the portion of the protective layer covering the first conductive line. Exposing the portion of the dry film solder resist layer at the bottom of the first line spacing groove to obtain the other portion of the protective layer.

[0012] Furthermore, the dry film solder resist layer comprises a polymerizable monomer with carboxyl groups, acrylate, adhesive, and photoinitiator.

[0013] A bend-resistant circuit board includes a circuit board substrate and a first protective layer. The circuit board substrate includes a flexural layer and a circuit structure disposed on one side of the flexural layer. The circuit structure includes a plurality of first conductive lines, which are spaced apart. A first spacing groove is provided between each pair of adjacent first conductive lines. The first protective layer covers each first conductive line, and a portion of the first protective layer is filled into the first spacing groove. The thickness of the first protective layer is less than the depth of the spacing groove.

[0014] Furthermore, the bend-resistant circuit board also includes a second protective layer, a conductor, and multiple second conductive lines. The circuit structure further includes embedded lines and intermediate lines, with the intermediate lines disposed between the embedded lines and the first conductive lines. The embedded lines are located within the bend layer. The second conductive lines are spaced apart on the side of the bend layer opposite to the first conductive lines. The conductor is located within the bend layer and electrically connects the embedded lines and the second conductive lines. The second protective layer covers the second conductive lines.

[0015] Furthermore, the flexural layer includes an adhesive layer and an insulating layer. The adhesive layer is disposed between the insulating layer and the second conductive line. A portion of the adhesive layer is filled between each pair of adjacent embedded lines. The second conductive line is disposed on the insulating layer.

[0016] Compared to existing technologies, the bend-resistant circuit board provided in this application has multiple first conductive lines spaced apart on one side of the flexural layer, with a first spacing groove between each pair of adjacent first conductive lines. When the bend-resistant circuit board is bent due to external force, the first spacing groove can reduce the compression between the first conductive lines, thereby significantly reducing the internal stress of the bend-resistant circuit board and increasing the number of bends and the bending angle of the bend-resistant circuit board. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the first copper foil layer provided in an embodiment of this application.

[0018] Figure 2 for Figure 1 The diagram shows the first copper foil layer after the first dry film and the second dry film are applied.

[0019] Figure 3 For exposure and development Figure 2 The diagram shows the first dry film and the second dry film.

[0020] Figure 4 for Figure 1 The diagram shows a first conductive line installed on the first copper foil layer.

[0021] Figure 5 To remove Figure 4 The diagram shows the first photosensitive pattern and the second photosensitive pattern.

[0022] Figure 6 In order to be in Figure 5 The diagram shows the embedded circuit after the installation of a flexural layer and a second copper foil layer.

[0023] Figure 7 A schematic diagram showing the second copper foil layer on the circuit board provided in this application.

[0024] Figure 8 for Figure 7 The diagram shows a circuit board with a dry film solder resist layer applied.

[0025] Figure 9 For exposure Figure 8 The diagram shows a portion of the dry film solder resist layer.

[0026] Figure 10 To remove Figure 9 The diagram shown is a schematic of the unexposed dry film solder resist layer located within the first line spacing groove.

[0027] Figure 11 for Figure 10 The diagram shown is a schematic of the first conductive line after it has been covered with the first protective layer.

[0028] Figure 12 Figure 11 The diagram shows the second copper foil layer after the opening is set.

[0029] Figure 13 Figure 12 The diagram shows the result of an electroplating layer being applied to the second copper foil layer.

[0030] Figure 14 for Figure 13 The diagram shows a second conductive line installed on the flexural layer.

[0031] Figure 15 for Figure 14 The diagram shows the second conductive line after a photosensitive ink layer has been applied.

[0032] Figure 16 For exposure Figure 15 The diagram shows a portion of the photosensitive ink layer.

[0033] Figure 17 A schematic diagram of the bend-resistant circuit board provided in this application.

[0034] Explanation of main component symbols

[0035] 100% Bend-resistant circuit board

[0036] Circuit board 10

[0037] Flexural layer 11

[0038] Adhesive layer 111

[0039] Insulation layer 112

[0040] Line Structure 12

[0041] First conductive line 121

[0042] Buried Line 122

[0043] Middle Line 123

[0044] First line spacing groove 124

[0045] Second line spacing groove 125

[0046] First copper foil layer 13

[0047] First dry film 131

[0048] Second dry film 132

[0049] First photosensitive pattern 133

[0050] Second photosensitive pattern 134

[0051] First groove 135

[0052] Second cable tray 136

[0053] First protective layer 20

[0054] Dry film solder resist layer 21

[0055] Second copper foil layer 30

[0056] Opening 31

[0057] Electroplating layer 32

[0058] Conductor 33

[0059] Second conductive line 40

[0060] Third line spacing groove 41

[0061] Photosensitive ink layer 42

[0062] Second protective layer 43

[0063] Window 431

[0064] Thickness D1, D3

[0065] Depth D2

[0066] The following detailed description, in conjunction with the accompanying drawings, will further illustrate this application. Detailed Implementation

[0067] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0068] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also exist in an intervening component. When a component is considered to be "set on" another component, it can be directly set on the other component or may also exist in an intervening component.

[0069] Please see Figures 1 to 17 This application provides a method for manufacturing a bend-resistant circuit board 100, comprising the following steps:

[0070] S1: Please see Figure 7 A circuit board 10 is provided, the circuit board 10 including a flexible layer 11 and a circuit structure 12. The circuit structure 12 includes a plurality of first conductive lines 121, a plurality of embedded lines 122 and a plurality of intermediate lines 123. The intermediate lines 123 are disposed between the embedded lines 122 and the first conductive lines 121. The embedded lines 122 are embedded in the flexible layer 11. The first conductive lines 121 and the intermediate lines 123 protrude from a surface of the flexible layer 11. A first spacing groove 124 is provided between each two adjacent first conductive lines 121.

[0071] In this embodiment, please refer to Figures 1 to 7The manufacturing method of the circuit board 10 includes the following steps:

[0072] S10: Please refer to Figure 1 Provides a first copper foil layer 13.

[0073] S11: Please refer to Figure 2 A first dry film 131 and a second dry film 132 are respectively disposed on opposite sides of the first copper foil layer 13.

[0074] S12: Please refer to Figure 3 The first dry film 131 is exposed and developed to form a first photosensitive pattern 133, and the second dry film 132 is exposed and developed to form a second photosensitive pattern 134. The first photosensitive pattern 133 is provided with a plurality of first grooves 135, and the second photosensitive pattern 134 is provided with a plurality of second grooves 136. A portion of the first copper foil layer 13 is exposed at the bottom of both the first grooves 135 and the second grooves 136, with the first grooves 135 and the second grooves 136 corresponding to each other.

[0075] S13: Please see Figure 4 Electroplating is performed in the first groove 135 to form the first conductive line 121, and electroplating is performed in the second groove 136 to form the embedded line 122. The first conductive line 121 and the embedded line 122 are correspondingly arranged. In other embodiments of this application, the first conductive line 121 and the embedded line 122 can also be formed by chemical plating or by applying conductive paste.

[0076] S14: Please see Figure 5 Remove the first photosensitive pattern 133 and the second photosensitive pattern 134 so that there is a second line spacing groove 125 between each two adjacent embedded lines 122, and the first line spacing groove 124 and the second line spacing groove 125 are correspondingly set.

[0077] S15: Please see Figure 6A flexible layer 11 is provided on the embedded circuit 122. The flexible layer 11 includes an adhesive layer 111 and an insulating layer 112. The adhesive layer 111 is disposed between the insulating layer 112 and the embedded circuit 122. The adhesive layer 111 fills the second line spacing groove 125, thereby increasing the bonding force between the embedded circuit 122 and the adhesive layer 111. The adhesive layer 111 is made of at least one of the following: thermoplastic resin (e.g., epoxy resin, phenolic resin, etc.), thermoplastic resin and PI (polyimide) composite, thermoplastic PI film (PI with specific flexible groups introduced), rubber adhesive, polyvinyl acetate copolymer (ethylene-vinyl acetate copolymer, etc.), acrylate, etc. The insulating layer 112 is made of materials including, but not limited to, liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), poly(ether-ether-ketone) (PEEK), polyphenylene oxyde (PPO), polyimide (PI), polyester resin (PET), and polyethylene naphthalate two-formicacid glycol ester (PEN). Preferably, the adhesive layer 111 is made of epoxy resin and the insulating layer 112 is made of polyimide, so that the flexural layer 11 has excellent bending resistance.

[0078] S16: A second copper foil layer 30 is provided on the insulating layer 112.

[0079] S17: Please see Figure 7 Remove a portion of the first copper foil layer 13 corresponding to the first line spacing groove 124 or the second line spacing groove 125 to form the intermediate line 123, thereby obtaining the circuit substrate 10.

[0080] In this embodiment, the manufacturing method further includes the step of:

[0081] S2: Please see Figure 11A first protective layer 20 is provided on the outside of the first conductive line 121. The first protective layer 20 covers each of the first conductive lines 121. Part of the first protective layer 20 is filled into the first line spacing groove 124. The thickness D1 of the first protective layer 20 is less than the depth D2 of the first line spacing groove 124. That is, the first protective layer 20 does not completely fill the first line spacing groove 124. The part of the first line spacing groove 124 that is not completely filled with the first protective layer 20 can reduce the internal stress on the first conductive line 121 during bending, thereby increasing the bending resistance of the first conductive line 121.

[0082] In this embodiment, step S2 specifically includes:

[0083] S21: Please see Figure 8 A dry film solder resist layer 21 is disposed on the first conductive line 121, the dry film solder resist layer 21 covering the first conductive line 121, and a portion of the dry film solder resist layer 21 filling the first line spacing groove 124. The thickness D3 of the dry film solder resist layer 21 is greater than the depth D2 of the first line spacing groove 124. The dry film solder resist layer 21 comprises a polymerizable monomer with carboxyl groups, a (meth)acrylate compound, an adhesive, and a photoinitiator. The dry film solder resist layer 21 can be exposed multiple times, and a predetermined thickness of the dry film solder resist layer 21 can be removed using chemicals.

[0084] S22: Please see Figure 9 A portion of the dry film solder resist layer 21 covering the first conductive line 121 is exposed to obtain a portion of the first protective layer 20.

[0085] S23: Please see Figure 10 The chemical etching removes a portion of the dry film solder resist layer 21 within the first line spacing groove 124, while another portion of the dry film solder resist layer 21 is attached to the bottom of the first line spacing groove 124. The portion of the dry film solder resist layer 21 attached to the bottom of the first line spacing groove 124 is connected to the portion of the first protective layer 20 covering the first conductive line 121.

[0086] S24: Please see Figure 11 The portion of the dry film solder resist layer 21 located at the bottom of the first line spacing groove 124 is exposed to obtain another portion of the first protective layer 20.

[0087] In this embodiment, the manufacturing method further includes the step of:

[0088] S3: Please see Figure 12An opening 31 is made in the second copper foil layer 30, and the opening 31 penetrates the second copper foil layer 30, the insulating layer 112, and the adhesive layer 111. The opening 31 is provided corresponding to the embedded circuit 122, and part of the embedded circuit 122 is exposed at the bottom of the opening 31.

[0089] S4: Please see Figure 13 An electroplated layer 32 is provided on the second copper foil layer 30, and part of the electroplated layer 32 is filled into the opening 31 to form a conductor 33. The conductor 33 electrically connects the embedded circuit 122 and the second copper foil layer 30.

[0090] S5: Please see Figure 14 The electroplated layer 32 and the second copper foil layer 30 are etched to form a plurality of second conductive lines 40, the second conductive lines 40 being spaced apart, and a third line spacing groove 41 being provided between each two adjacent second conductive lines 40.

[0091] S6: Please see Figure 15 A photosensitive ink layer 42 is provided on the second conductive line 40, and part of the photosensitive ink layer 42 is filled into the third line spacing groove 41. The photosensitive ink layer 42 can only be exposed once.

[0092] S7: Please see Figure 16 The photosensitive ink layer 42 on the outer side of the second conductive line 40 is exposed to form a second protective layer 43.

[0093] S8: Please see Figure 17 Remove the unexposed portion of the photosensitive ink layer 42, so that the area of ​​the second protective layer 43 corresponding to the third line spacing groove 41 has a window 431, thereby obtaining the bend-resistant circuit board 100.

[0094] Compared with the prior art, the manufacturing method of the bend-resistant circuit board 100 provided in this application has the following advantages:

[0095] (i) By spaced multiple first conductive lines 121 on one side of the flexible layer 11, and a first spacing groove 124 between each two adjacent first conductive lines 121, when the bendable circuit board 100 is bent due to external force, the first spacing groove 124 can reduce the compression between each first conductive line 121, thereby significantly reducing the internal stress of the bendable circuit board 100 and increasing the number of bends and the bending angle of the bendable circuit board 100.

[0096] (ii) By setting multiple embedded lines 122 within the flexural layer 11, and setting intermediate lines 123 on the embedded lines 122, and setting a first conductive line 121 on the intermediate lines 123, the embedded lines 122, intermediate lines 123 and the first conductive line 121 together constitute a circuit structure 12 with a large thickness. This not only enables the bending of the circuit structure 12 with a large thickness, but also makes it difficult for the circuit structure 12 to fall off the flexural layer 11 as a whole because part of the circuit structure 12 is embedded within the flexural layer 11. That is, the first conductive line 121 is not easy to fall off, thereby improving the reliability of the bend-resistant circuit board 100. At the same time, a conductor 33 can be set on the embedded lines 122 to further increase the density of the bend-resistant circuit board 100.

[0097] (iii) By setting a first protective layer 20, which covers the first conductive line 121, and the thickness D1 of the first protective layer 20 is less than the depth D2 of the first line spacing groove 124, and by setting a second protective layer 43, which covers the second conductive line 40, and the second protective layer 43 has an opening 431 that exposes the second line spacing groove 125, not only can the purpose of protecting the first conductive line 121 and the second conductive line 40 be achieved, but it is also beneficial to reduce the overall thickness of the bend-resistant circuit board 100.

[0098] Please see Figure 17 This application also provides a bend-resistant circuit board 100, which includes a circuit board 10 and a first protective layer 20. The circuit board 10 includes a flexible layer 11 and a circuit structure 12 disposed on one side of the flexible layer 11. The circuit structure 12 includes a plurality of first conductive lines 121, which are spaced apart. A first spacing groove 124 is provided between each two adjacent first conductive lines 121. The first protective layer 20 covers each first conductive line 121, and a portion of the first protective layer 20 is filled into the first spacing groove 124. The thickness D1 of the first protective layer 20 is less than the depth D2 of the first spacing groove 124 (see [link to relevant documentation]). Figure 11 ).

[0099] Please see Figure 17In this embodiment, the bend-resistant circuit board 100 further includes a second protective layer 43, a conductor 33, and a plurality of second conductive lines 40. The circuit structure 12 further includes an embedded line 122 and an intermediate line 123. The intermediate line 123 is disposed between the embedded line 122 and the first conductive line 121, and the embedded line 122 is disposed within the flexural layer 11. The second conductive lines 40 are spaced apart on the side of the flexural layer 11 opposite to the first conductive line 121. The conductor 33 is disposed within the flexural layer 11 and electrically connects the embedded line 122 and the second conductive lines 40. The second protective layer 43 covers the second conductive lines 40.

[0100] Please see Figure 17 In this embodiment, the flexural layer 11 includes an adhesive layer 111 and an insulating layer 112. The adhesive layer 111 is disposed between the insulating layer 112 and the second conductive line 40. Part of the adhesive layer 111 is filled into the second spacing groove 125 between each two adjacent embedded lines 122. The second conductive line 40 is disposed on the insulating layer 112.

[0101] The specific embodiments of this application have been described above with reference to the accompanying drawings. However, those skilled in the art will understand that various changes and substitutions can be made to the specific embodiments of this application without departing from the spirit and scope of this application. All such changes and substitutions fall within the scope defined by this application.

Claims

1. A method for manufacturing a bend-resistant circuit board, characterized in that, Including the following steps: A circuit board is provided, the circuit board including a flexible layer and a circuit structure disposed on one side of the flexible layer, the circuit structure including a plurality of first conductive lines, the plurality of first conductive lines being spaced apart, and a first line spacing groove being provided between each two adjacent first conductive lines. A first protective layer is provided on the circuit structure, the first protective layer covers each of the first conductive lines, a portion of the first protective layer is filled into the first line spacing groove, and the thickness of the first protective layer is less than the depth of the first line spacing groove. The step "setting a first protective layer on the circuit structure" includes: A dry film solder resist layer is provided on the first conductive line, the dry film solder resist layer covers the first conductive line, and a portion of the dry film solder resist layer is filled into the first line spacing groove. A portion of the dry film solder resist layer surrounding the first conductive line is exposed to obtain a portion of the protective layer. A portion of the dry film solder resist layer within the first line spacing groove is removed, and another portion of the dry film solder resist layer is disposed at the bottom of the first line spacing groove. The portion of the dry film solder resist layer disposed at the bottom of the first line spacing groove is connected to the portion of the protective layer covering the first conductive line. The portion of the dry film solder resist layer located at the bottom of the first line spacing groove is exposed to obtain another portion of the protective layer.

2. The manufacturing method as described in claim 1, characterized in that, The circuit structure further includes embedded circuits and intermediate circuits, the intermediate circuits being disposed between the embedded circuits and the first conductive circuit, the embedded circuits being disposed within the flexible layer, and the manufacturing method of the circuit substrate including the following steps: Provide a first copper foil layer; A first photosensitive pattern and a second photosensitive pattern are respectively provided on two opposite surfaces of the first copper foil layer. The first photosensitive pattern is provided with a plurality of first grooves, and the second photosensitive pattern is provided with a plurality of second grooves. The first grooves and the second grooves are provided correspondingly, and a portion of the first copper foil layer is exposed at the bottom of the first grooves and the second grooves. The first conductive line is provided in the first wire groove, and the embedded line is provided in the second wire groove, with the first conductive line and the embedded line being provided in a corresponding manner. Remove the first and second photosensitive patterns, so that a second spacing groove is formed between every two adjacent embedded lines, with the first and second spacing grooves correspondingly provided; and The flexural layer is provided on the embedded line, and a portion of the flexural layer is filled into the second line spacing groove. Remove a portion of the first copper foil layer corresponding to the first or second line spacing groove to form the intermediate circuit, thereby obtaining the circuit substrate.

3. The manufacturing method as described in claim 2, characterized in that, It also includes the following steps: A second copper foil layer is disposed on the side of the flexural layer opposite to the first conductive line; An opening is provided on the second copper foil layer, the opening penetrating the second copper foil layer and the flexural layer, and part of the embedded circuit is exposed at the bottom of the opening; An electroplated layer is provided on the second copper foil layer, and part of the electroplated layer is filled into the opening to form a conductor; as well as The electroplated layer and the second copper foil layer are etched to form a plurality of second conductive lines. The conductor electrically connects the second conductive lines and the embedded lines. The second conductive lines are spaced apart, and a third line spacing groove is provided between each two adjacent second conductive lines.

4. The manufacturing method as described in claim 3, characterized in that, It also includes the following steps: A photosensitive ink layer is disposed on the second conductive line, and a portion of the photosensitive ink layer is filled into the third line spacing groove; The photosensitive ink layer on the outer side of the second conductive line is exposed to form a second protective layer, which covers the second conductive line.

5. The manufacturing method as described in claim 4, characterized in that, It also includes the following steps: The unexposed portion of the photosensitive ink layer is removed, resulting in a window in the second protective layer, the window corresponding to the third line spacing groove.

6. The manufacturing method as described in claim 1, characterized in that, The dry film solder resist layer comprises polymer monomers, acrylates, adhesives, and photoinitiators.

7. A bend-resistant circuit board, characterized in that, It includes a circuit board, a first protective layer, a second protective layer, a conductor, and multiple second conductive lines. The circuit board includes a flexible layer and a circuit structure disposed on one side of the flexible layer. The circuit structure includes a plurality of first conductive lines, a plurality of embedded lines and a plurality of intermediate lines. The intermediate lines are disposed between the embedded lines and the first conductive lines. The embedded lines are spaced apart in the flexible layer. A second line spacing groove is provided between each two adjacent embedded lines. The intermediate lines are disposed in the embedded lines. The first conductive lines are disposed in the intermediate lines. Multiple first conductive lines are spaced apart, with a first spacing groove between each pair of adjacent first conductive lines. A first protective layer covers each first conductive line, with a portion of the first protective layer filling the first spacing groove. The thickness of the first protective layer is less than the depth of the spacing groove. The first protective layer is a dry film solder resist layer. The second conductive line is spaced apart on the side of the flexural layer opposite to the first conductive line. The conductor is disposed within the flexural layer and electrically connects the embedded line and the second conductive line. The second protective layer covers the second conductive line. The flexural layer includes an adhesive layer and an insulating layer. The adhesive layer is disposed between the insulating layer and the second conductive line. A portion of the adhesive layer is filled into the second line spacing groove. The second conductive line is disposed on the insulating layer.

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