Flexible circuit board and manufacturing method thereof

Abstract

The invention provides a flexible circuit board and a manufacturing method thereof. The flexible circuit board comprises a circuit substrate and two protective layers. The circuit substrate comprises a flexible insulating layer, two circuit layers respectively located on two opposite sides of the flexible insulating layer, and a plurality of via holes. The via holes are arranged in the soft insulating layer, and each via hole passes through the soft insulating layer from one circuit layer and extends to the other circuit layer so as to be electrically connected with the circuit layers. One end face of the via hole is exposed out of the surface of the circuit layer, and the end face does not protrude out of the surface. The two protection layers are respectively arranged on the circuit layer and cover the surface of the circuit layer and the end faces of the via holes, and the circuit substrate is located between the two protection layers. Therefore, when the flexible circuit board is dynamically bent, damage or cracks caused by inconsistent copper lattices between the via holes and the circuit layer can be reduced.

Description

Technical Field

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

[0002] As the application scope of flexible printed circuits (FPCs) continues to expand, the demand for higher circuit density is also increasing to meet the demands of various applications. During the FPC manufacturing process, circuit layers can be formed using additive, semi-additive, or subtractive methods. Generally speaking, dry film photoresist is used during these processes to mask the metal layer to be patterned, enabling selective etching or selective plating.

[0003] However, the adhesion between dry film photoresist and the metal layer is affected by the surface roughness of the metal layer. When the metal layer's surface is too rough, the dry film photoresist cannot adhere smoothly to the metal layer and may even fall off the metal layer, making the circuit etching process more difficult. In addition, the narrower the line pitch of the circuit layer, the more difficult it is to strip the dry film photoresist, which greatly increases the possibility of short circuits or open circuits in the circuit layer. Summary of the Invention

[0004] Therefore, the present invention provides a flexible circuit board and a manufacturing method thereof to improve the process yield of the flexible circuit board.

[0005] At least one embodiment of the present invention provides a method for manufacturing the flexible printed circuit board.

[0006] A flexible printed circuit board provided in one embodiment of the present invention includes a first circuit substrate and two protective layers. The first circuit substrate includes a flexible insulating layer, two circuit layers located on opposite sides of the flexible insulating layer, and a plurality of first vias. The first vias are disposed in the flexible insulating layer, and each first via extends from one circuit layer through the flexible insulating layer to the other circuit layer to electrically connect the circuit layers. One end face of the first via is exposed to the surface of the circuit layer and does not protrude from the surface. Two protective layers are disposed on the circuit layer, respectively, and cover the surface of the circuit layer and the end faces of the first vias, with the first circuit substrate located between the two protective layers.

[0007] In at least one embodiment of the present invention, an end surface of the first conducting hole is flush with a surface of the circuit layer.

[0008] In at least one embodiment of the present invention, the flexible printed circuit board further includes two bonding layers and two cover layers. The two bonding layers are respectively disposed on the protective layer and cover the circuit layer and the protective layer. The two cover layers are respectively disposed on the bonding layers, with the first circuit substrate, the protective layer, and the bonding layer located between the two cover layers.

[0009] In at least one embodiment of the present invention, the flexible printed circuit board further includes a plurality of openings disposed in the cover layer, each of the openings corresponding to the at least one first conductive via, with the end surface of the at least one first conductive via exposed at the bottom surface of the opening. The flexible printed circuit board further includes a plurality of soldering materials disposed on the first conductive vias corresponding to the openings. The flexible printed circuit board further includes a plurality of metal blocks disposed on the soldering materials, and electronic components disposed on the metal blocks. The electronic components are connected to the soldering materials via the metal blocks, and the electronic components are electrically connected to the first circuit substrate via the metal blocks and the soldering materials.

[0010] In at least one embodiment of the present invention, the flexible printed circuit board further includes two second circuit substrates, each disposed within the bonding layer. The first circuit substrate is positioned between the two second circuit substrates, and each second circuit substrate includes a plurality of second conductive vias. These second conductive vias are disposed on the circuit layer of the first circuit substrate and are connected to at least one first conductive via. Each second conductive via extends through the bonding layer and the protective layer to the first circuit substrate, and the second circuit substrates are electrically connected to the first circuit substrate via the second conductive vias.

[0011] In at least one embodiment of the present invention, the thickness of the protective layer is in a range from 2 μm to 6 μm.

[0012] The present invention also provides a method for manufacturing a flexible circuit board, comprising providing a substrate, the substrate comprising a soft insulating layer and two metal layers, wherein the soft insulating layer is located between the metal layers; disposing two initial protective layers on the substrate, wherein the substrate is located between the initial protective layers; removing a portion of the substrate and a portion of the initial protective layer to form a plurality of openings on the initial protective layer, wherein the openings extend from one metal layer through the soft insulating layer to the other metal layer and are exposed to the initial protective layer; depositing a conductive material in each opening to form a via, wherein one end face of the via is exposed to the initial protective layer and the end face does not protrude from the surface of the metal layer, and the metal layers are electrically connected to each other through the via; after depositing the conductive material, disposing a protective material on the initial protective layer, wherein the protective material covers the initial protective layer and the end face of the via; after disposing the protective material, patterning the initial protective layer and the protective material to expose the metal layer and form a protective layer; and after forming the protective layer, patterning the metal layer to form two circuit layers.

[0013] In at least one embodiment of the present invention, the method further comprises laminating two bonding layers on the circuit layer after forming the circuit layer, wherein the circuit layer is located between the two bonding layers, and the bonding layers respectively cover the protective layers; and after laminating the bonding layers, laminating two cover layers on the bonding layer, wherein the bonding layers are located between the two cover layers.

[0014] In at least one embodiment of the present invention, the above method further includes removing a portion of the covering layer and a portion of the bonding layer after laminating the covering layer to form a plurality of openings on the covering layer, wherein the bottom surface of each opening exposes the conductive hole; after forming the openings, disposing a plurality of welding materials on the conductive holes exposed by the bottom surface of the openings; disposing metal blocks on the welding materials respectively; and disposing electronic components on the metal blocks so that the electronic components are connected to the welding materials through the metal blocks.

[0015] In at least one embodiment of the present invention, at least one opening communicates with two opposite sides of the substrate.

[0016] Based on the above, the end faces of the vias in flexible printed circuits are recessed or flush with the surface of the circuit layer, and the surface of the circuit layer and the end faces of the vias are covered with a protective layer. This eliminates the presence of a copper layer formed by electroplating between the circuit layer and the bonding layer, thereby reducing the risk of damage or cracks caused by copper lattice misalignment between the vias and the circuit layer during dynamic bending of the flexible printed circuit board. Furthermore, since dry film photoresist is not used in the flexible printed circuit board manufacturing process, the impact of dry film photoresist on the circuit board manufacturing process can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be understood from the following detailed description and the accompanying drawings. It should be noted that various features are not drawn to scale as is standard in industry practice. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion.

[0018] Figure 1 A cross-sectional view of a flexible printed circuit board according to an embodiment of the present invention is shown.

[0019] Figure 2 A cross-sectional view of a flexible printed circuit board according to another embodiment of the present invention is shown.

[0020] Figures 3A to 3H A cross-sectional view is shown of a method for manufacturing a flexible printed circuit board according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described in detail with reference to the following examples. It should be noted that the following descriptions of the embodiments of the present invention are provided for illustrative purposes only and are not intended to be exhaustive or to limit the specific embodiments of the present invention. For example, the description of "a first feature formed on a second feature" encompasses various embodiments, including the first feature directly contacting the second feature and the additional feature formed between the first feature and the second feature so that the two do not directly contact each other. Furthermore, the same reference numbers used in the drawings and the specification will, whenever possible, represent identical or similar elements.

[0022] Spatially relative terms, such as "lower," "below," "beneath," "above," and related terms, are used herein to simply describe the relationship of an element or feature as shown in the figures to another element or feature. These spatially relative terms encompass not only the orientations depicted in the figures, but also various orientations during use or operation of the device. Furthermore, when an element is rotatable (90 degrees or other angles), the spatially relative descriptors used herein should be interpreted accordingly.

[0023] In the following text, in order to clearly present the technical features of this case, the dimensions (such as length, width, thickness and depth) of the elements (such as layers, films, substrates and regions, etc.) in the drawings will be magnified in unequal proportions. Therefore, the description and explanation of the embodiments below are not limited to the dimensions and shapes presented by the elements in the drawings, but should cover the dimensions, shapes and deviations thereof caused by actual processes and / or tolerances. For example, the flat surfaces shown in the drawings may have rough and / or nonlinear features, and the acute angles shown in the drawings may be replaced with obtuse angles. Therefore, the elements presented in the drawings of this case are mainly for illustration and are not intended to accurately depict the actual shapes of the elements, nor are they intended to limit the claims of this case.

[0024] The present invention provides a flexible printed circuit board 100. Please refer to Figure 1 Flexible printed circuit board 100 includes a circuit substrate 110, protective layers 120a and 120b, bonding layers 140a and 140b, and cover layers 160a and 160b. Circuit substrate 110 includes a flexible insulating layer 112, circuit layers 114a and 114b, and a plurality of vias 116. Circuit layers 114a and 114b are located on opposite sides of flexible insulating layer 112. Flexible insulating layer 112 may be made of an insulating material such as an organic resin (e.g., epoxy resin), or the like.

[0025] Vias 116 are disposed in the flexible insulating layer 112, and the material of vias 116 may include copper. Each via 116 extends from circuit layer 114a through the flexible insulating layer 112 to circuit layer 114b, electrically connecting circuit layers 114a and 114b. Vias 116 have an end surface 116e, while circuit layers 114a and 114b each have a surface 114s. Vias 116's end surface 116e is exposed on surface 114s of circuit layer 114a.

[0026] In this embodiment, the circuit substrate 110 further includes a plurality of vias 118. The function of vias 118 in the circuit substrate 110 is similar to that of vias 116. In other words, since vias 118 also extend from the circuit layer 114a through the soft insulating layer 112 and to the circuit layer 114b, the circuit layer 114a can also be electrically connected to the circuit layer 114b through vias 118. However, the difference between vias 118 and 116 is that vias 116 are conductive buried vias (BVHs) in the circuit substrate 110, while vias 118 are conductive through holes (PTHs) in the circuit substrate 110. Therefore, vias 118 have two end surfaces 118e, which are exposed on the surfaces 114s of the circuit layers 114a and 114b, respectively.

[0027] It is particularly noted that in various embodiments of the present invention, the end surface 116e does not protrude from the surface 114s. For example, in this embodiment, the end surface 116e of the via 116 may be flush with the surface 114s of the circuit layer 114a. That is, the end surface 116e and the surface 114s may be substantially planar and coplanar with each other. However, in other embodiments, the end surface 116e of the via 116 may be recessed from the surface 114s of the circuit layer 114a.

[0028] Protective layers 120a and 120b are disposed on circuit layers 114a and 114b of circuit substrate 110, respectively, and cover surfaces 114s of circuit layers 114a and 114b, as well as end faces 116e of vias 116. Circuit substrate 110 is located between protective layers 120a and 120b. Protective layers 120a and 120b can be made of an insulating material such as epoxy resin, with a thickness T1 of protective layer 120a (or a thickness T1 of protective layer 120b) ranging from 2 μm to 6 μm.

[0029] The bonding layers 140a and 140b of the flexible printed circuit board 100 are disposed on the protective layers 120a and 120b, respectively, and cover the circuit layers 114a and 114b and the protective layers 120a and 120b of the circuit substrate 110. Specifically, the bonding layer 140a is disposed on the protective layer 120a and covers the circuit layer 114a and the protective layer 120a, while the bonding layer 140b is disposed on the protective layer 120b and covers the circuit layer 114b and the protective layer 120b. The bonding layers 140a and 140b may include a bonding material such as epoxy resin.

[0030] Covering layers 160a and 160b of flexible printed circuit board 100 are disposed on bonding layers 140a and 140b, respectively. Circuit substrate 110, protective layers 120a and 120b, and bonding layers 140a and 140b are located between covering layers 160a and 160b. In this embodiment, covering layers 160a and 160b may be solder masks, and thus, the covering layers 160a and 160b may be made of an insulating material such as resin.

[0031] In this embodiment, the flexible printed circuit board 100 further includes a plurality of openings 130, which are disposed on the cover layer (e.g., the cover layer 160a). Each opening 130 corresponds to at least one via 116. Specifically, one opening 130 is disposed on one via 116, and the end surface 116e of the via 116 is exposed to the bottom surface 130s of the opening 130, while at least one via 116 is not exposed by the opening 130. Figure 1 For example, the plurality of vias 116 are not exposed by the opening 130. Figure 1 Two openings 130 are shown as an example, but the present invention is not limited thereto. The number of the openings 130 may be more than one (eg, three).

[0032] In addition, flexible printed circuit board 100 includes a plurality of solder materials 150, each disposed on a via 116 corresponding to opening 130. Because end surfaces 116e of via 116 are exposed to bottom surface 130s of opening 130, solder materials 150 are in direct contact with via 116. Furthermore, flexible printed circuit board 100 includes a plurality of metal blocks 170, each disposed on and in direct contact with solder materials 150.

[0033] In some embodiments, the metal blocks 170 may be disposed one-to-one on the solder material 150, but the present invention is not limited thereto. More than one metal block 170, for example, two metal blocks 170, may be disposed on one solder material 150. In this embodiment, the metal blocks 170 are solder bumps and may include metal materials such as copper and tin.

[0034] The flexible printed circuit board 100 further includes an electronic component 190 disposed on the metal block 170 . The electronic component 190 is connected to the solder material 150 through the metal block 170 . Therefore, the electronic component 190 is electrically connected to the circuit substrate 110 through the metal block 170 and the solder material 150 .

[0035] In this embodiment, only one electronic component 190 is shown, and this electronic component 190 is disposed on one side of the circuit substrate 110 (i.e., on the circuit layer 114a), but the present invention is not limited to this. For example, the flexible printed circuit board 100 may include more than one electronic component 190, such as two, and these electronic components 190 may also be disposed on opposite sides of the circuit substrate 110 (i.e., on the circuit layers 114a and 114b). In various embodiments of the present invention, the electronic component 190 may include an active component (e.g., a transistor) or a passive component (e.g., a capacitor).

[0036] Please refer to Figure 2 In another embodiment, flexible printed circuit board 200 is similar to flexible printed circuit board 100. Specifically, flexible printed circuit board 200 also includes circuit substrate 110, protective layers 120a and 120b, and cover layers 160a and 160b. Notably, flexible printed circuit board 200 also includes bonding layers 240a and 240b, which are similar to bonding layers 140a and 140b of flexible printed circuit board 100.

[0037] In addition, the difference between the flexible printed circuit board 200 and the flexible printed circuit board 100 is that the flexible printed circuit board 200 further includes circuit substrates 201a and 201b. The circuit substrates 201a and 201b are respectively disposed in the bonding layers 240a and 240b, and the circuit substrate 110 is located between the circuit substrates 201a and 201b.

[0038] In particular, each of the circuit substrates 201a and 201b includes a plurality of vias 206. These vias 206 are disposed on the circuit layers 114a and 114b of the circuit substrate 110 and are connected to at least one via 116 of the circuit substrate 110. Figure 2 For example, some vias 116 are connected to the via 206 , while some vias 116 are not connected to the via 206 .

[0039] Each via 206 extends through bonding layers 240a and 240b and protective layers 120a and 120b to circuit substrate 110. Specifically, via 206 on circuit substrate 201a extends through bonding layer 240a and protective layer 120a to via 116 on circuit substrate 110. Meanwhile, via 206 on circuit substrate 201b extends through bonding layer 240b and protective layer 120b to via 116 on circuit substrate 110. Thus, circuit substrates 201a and 201b can be electrically connected to circuit substrate 110 via via 206.

[0040] In some embodiments, the flexible printed circuit board 200 further includes protective layers 202a and 202b. The protective layers 202a and 202b are respectively disposed on the circuit substrates 201a and 201b, and the circuit substrates 201a and 201b are located between the protective layers 202a and 202b.

[0041] At least one embodiment of the present invention provides a method for manufacturing a flexible printed circuit board. Taking the flexible printed circuit board 100 as an example, the manufacturing method may include the following steps: Figures 3A to 3H Several steps are shown. First, please refer to Figure 3A , providing a substrate 310, the substrate 310 includes a soft insulating layer 112, a metal layer 313a and a metal layer 313b.

[0042] In various embodiments of the present invention, substrate 310 may be a conventional flexible copper clad laminate (FCCL), wherein flexible insulating layer 112 is located between metal layers 313a and 313b. Metal layers 313a and 313b may be deposited on flexible insulating layer 112, and the material of metal layers 313a and 313b may include copper.

[0043] Next, initial protective layers 320a and 320b are formed on substrate 310, for example, by thermal lamination or coating, with substrate 310 positioned between the initial protective layers 320a and 320b. The initial protective layers 320a and 320b cover the metal layers 313a and 313b, respectively, thereby isolating the metal layers 313a and 313b from the outside air and preventing them from contacting the outside air and accelerating oxidation. In this embodiment, the thickness t1 of the initial protective layers 320a and 320b can be in the range of 1 μm to 3 μm.

[0044] Please refer to Figure 3B A portion of the substrate 310 and a portion of the initial protection layers 320a and 320b can be removed by, for example, laser drilling or mechanical drilling to form a plurality of openings 305 in the initial protection layers 320a and 320b. These openings 305 extend from the metal layer 313a through the soft insulating layer 112 to the metal layer 313b, and expose the initial protection layer (including the initial protection layers 320a and 320b).

[0045] It is worth noting that in this embodiment, some openings 305 connect only to one side of the substrate 310, that is, these openings 305 are exposed only to the surface 320s of the initial protective layer 320a. On the other hand, at least one opening 305 connects to opposite sides of the substrate 310, that is, at least one opening 305 is exposed to the surfaces 320s of both the initial protective layers 320a and 320b. In other words, some openings 305 are blind holes, while others are through holes.

[0046] Please refer to Figure 3C Then, a conductive material (not shown) is deposited in each opening 305 by electroplating to form a via 116. The end surface 116e of the via 116 is exposed to the initial protection layer (including the initial protection layers 320a and 320b) and does not protrude from the surface 313s of the metal layer (including the metal layers 313a and 313b). In detail, for the blind hole opening 305, the end surface 116e of the via 116 is exposed to the initial protection layer 320a and does not protrude from the surface 313s of the metal layer 313a. For the through hole opening 305, the via (refer to Figure 1 The end surface 118e of the via 118 is exposed to the initial protection layers 320a and 320b and does not protrude from the surface 313s of the metal layers 313a and 313b. The metal layers 313a and 313b are electrically connected to each other through the via 116.

[0047] Please refer to Figure 3D After depositing the conductive material, a protective material 322 can be applied onto the initial protective layers 320a and 320b. The protective material 322 covers the initial protective layers 320a and 320b and the end surface 116e of the via 116, isolating the via 116 from the outside air. It is worth noting that a portion of the protective material 322 can fill the through-hole opening 305 and connect opposite sides of the substrate 310. In this embodiment, the thickness t2 of the protective material 322 can range from 1 μm to 5 μm.

[0048] Please refer to Figure 3E After the protective material 322 is provided, the initial protective layers 320a and 320b and the protective material 322 are patterned by, for example, laser ablation to expose the metal layers 313a and 313b (indicated at Figure 3D ). In this way, the Figure 1 After forming the protective layers 120a and 120b, the metal layers 313a and 313b may be patterned by, for example, chemical etching to form circuit layers 114a and 114b.

[0049] Please refer to Figure 3F After forming circuit layers 114a and 114b, bonding layers 140a and 140b can be attached to circuit layers 114a and 114b, for example, by thermal compression bonding. Circuit layers 114a and 114b are positioned between bonding layers 140a and 140b, and bonding layers 140a and 140b cover protective layers 120a and 120b, respectively. Specifically, bonding layers 140a and 140b cover initial protective layers 320a and 320b, as well as protective material 322.

[0050] After the bonding layers 140a and 140b are bonded, cover layers 160a and 160b may be bonded onto the bonding layers 140a and 140b, respectively, by, for example, thermal compression bonding. The bonding layers 140a and 140b (and the protective layers 120a and 120b) are located between the cover layers 160a and 160b.

[0051] Please refer to Figure 3G After the cover layers 160a and 160b are bonded together, a portion of the cover layer 160a and a portion of the bonding layer 140a can be removed by, for example, laser ablation to form a plurality of openings 130 in the cover layer 160a. The bottom surface 130s of each opening 130 exposes a portion of the via 116 and the circuit layer 114a.

[0052] Please refer to Figure 3H After forming the opening 130, a plurality of solder materials 150 can be deposited on the vias 116 exposed by the bottom surface 130s of the opening 130, for example, by printing. The solder material 150 can include solder paste. Although not shown in the figures, in some embodiments, the manufacturing steps of the flexible printed circuit board 100 further include forming a metal layer on the circuit layer 114a exposed by the bottom surface 130s of the opening 130 using an electroless nickel immersion gold (ENIG) process.

[0053] Next, metal blocks 170 can be placed on the soldering material 150 using surface mount technology (SMT), and electronic components 190 can be placed on the metal blocks 170 so that the electronic components 190 are connected to the soldering material 150 through the metal blocks 170. At this point, the flexible printed circuit board 100 of this embodiment is substantially completed.

[0054] In summary, the end faces of the vias in the flexible printed circuit board are recessed or flush with the surface of the circuit layer (e.g., circuit layers 114a and 114b), and the surface of the circuit layer and the end faces of the vias are covered by a protective layer. This eliminates the presence of a copper layer formed by electroplating between the circuit layer and the bonding layer, thereby reducing the risk of damage or cracks caused by copper lattice misalignment between the vias and the circuit layer during dynamic bending of the flexible printed circuit board.

[0055] Furthermore, since the flexible printed circuit (FPCB) manufacturing process does not use dry film photoresist, nor does it require the associated steps (e.g., exposure, development, and stripping), it not only reduces the impact of dry film photoresist on PCB manufacturing yield (e.g., short circuits in the circuit layer caused by incomplete dry film photoresist stripping), but also helps reduce the environmental pollution caused by the FPCB manufacturing process.

[0056] Although the embodiments of the present invention have been disclosed above, they are not intended to limit the embodiments of the present invention. Any person skilled in the art may make slight changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, the scope of protection of the embodiments of the present invention shall be determined by the appended claims.

[0057]

Explanation of symbols

[0058] 100,200: Flexible printed circuit board

[0059] 110, 201a, 201b: Circuit board

[0060] 112: Soft insulation layer

[0061] 114a, 114b: circuit layer

[0062] 114s, 313s, 320s: surface

[0063] 116,118,206: vias

[0064] 116e,118e: End face

[0065] 120a, 120b, 202a, 202b: protective layer

[0066] 130: Opening

[0067] 130s: Bottom

[0068] 140a, 140b, 240a, 240b: bonding layer

[0069] 160a, 160b: Covering layer

[0070] 150: welding materials

[0071] 170:Metal Block

[0072] 190: Electronic components

[0073] 305: Opening

[0074] 310:Substrate

[0075] 313a, 313b: Metal layer

[0076] 320a, 320b: Initial protective layer

[0077] 322: Protective Materials

[0078] T1, t1, t2: thickness.

Claims

1. A flexible printed circuit board, characterized in that: Include: The first circuit substrate comprises: soft insulation layer; Two circuit layers, located on opposite sides of the soft insulating layer; and a plurality of first conductive vias disposed in the soft insulating layer, wherein each of the first conductive vias passes through one of the circuit layers and extends to the other of the circuit layers to electrically connect the circuit layers, wherein an end surface of the first conductive via is exposed to a surface of the circuit layer and does not protrude from the surface; as well as Two protective layers are respectively arranged on the circuit layer and cover the surface of the circuit layer and the end surface of the first conducting hole, wherein the first circuit substrate is located between the two protective layers.

2. The flexible printed circuit board according to claim 1, wherein The end surface of the first conducting hole is flush with the surface of the circuit layer.

3. The flexible printed circuit board according to claim 1, wherein Also includes: Two bonding layers, respectively disposed on the protective layer and covering the circuit layer and the protective layer; and Two covering layers are respectively arranged on the bonding layer, wherein the first circuit substrate, the protection layer and the bonding layer are located between the two covering layers.

4. The flexible printed circuit board according to claim 3, wherein: Also includes: a plurality of openings disposed on the cover layer, wherein the openings respectively correspond to at least one of the first conductive holes, and the end surface of at least one of the first conductive holes is exposed to the bottom surface of the opening; a plurality of welding materials, respectively disposed on the first conducting holes corresponding to the openings; a plurality of metal blocks, respectively disposed on the welding material; as well as An electronic component is disposed on the metal block, wherein the electronic component is connected to the soldering material through the metal block, and the electronic component is electrically connected to the first circuit substrate through the metal block and the soldering material.

5. The flexible printed circuit board according to claim 3, wherein: Also includes: Two second circuit substrates are respectively disposed in the bonding layer, wherein the first circuit substrate is located between the two second circuit substrates, and each of the second circuit substrates includes: A plurality of second vias are arranged on the circuit layer of the first circuit substrate and connect at least one of the first vias, wherein each of the second vias extends to the first circuit substrate through the bonding layer and the protective layer, and the second circuit substrate is electrically connected to the first circuit substrate through the second vias.

6. The flexible printed circuit board according to claim 1, wherein The thickness of the protective layer ranges from 2 μm to 6 μm.

7. A method for manufacturing a flexible circuit board, characterized in that: Include: Providing a substrate, the substrate comprising a soft insulating layer and two metal layers, wherein the soft insulating layer is located between the metal layers; On the substrate, two initial protective layers are provided, wherein the substrate is located between the initial protective layers; removing a portion of the substrate and a portion of the initial protective layer to form a plurality of openings on the initial protective layer, wherein the openings extend from one of the metal layers through the soft insulating layer to the other metal layer and are exposed to the initial protective layer; Depositing a conductive material in each of the openings to form a plurality of vias, wherein one end surface of the via is exposed to the initial protection layer and the end surface does not protrude from the surface of the metal layer, and the metal layers are electrically connected to each other through the vias; After depositing the conductive material, providing a protective material on the initial protective layer, wherein the protective material covers the initial protective layer and the end surface of the via hole; After providing the protective material, patterning the initial protective layer and the protective material to expose the metal layer and form a protective layer; as well as After forming the protection layer, the metal layer is patterned to form two circuit layers.

8. The method according to claim 7, characterized in that Also includes: After forming the circuit layer, laminating two bonding layers on the circuit layer, wherein the circuit layer is located between the two bonding layers, and the bonding layers respectively cover the protective layers; and After the bonding layer is bonded, two covering layers are bonded on the bonding layer respectively, wherein the bonding layer is located between the two covering layers.

9. The method according to claim 8, characterized in that Also includes: After attaching the cover layer, removing a portion of the cover layer and a portion of the bonding layer to form a plurality of openings on the cover layer, wherein a bottom surface of each of the openings exposes the via hole; After forming the opening, disposing a plurality of welding materials on the via hole exposed by the bottom surface of the opening; placing metal blocks on the welding materials respectively; as well as An electronic component is disposed on the metal block so that the electronic component is connected to the soldering material through the metal block.

10. The method according to claim 7, characterized in that At least one of the openings communicates with two opposite sides of the substrate.

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