Flexible circuit board and manufacturing method thereof

Abstract

The invention discloses a flexible circuit board and a manufacturing method thereof. The manufacturing method of the flexible circuit board comprises the following steps: providing a first conductive layer as a base material; forming a first photosensitive insulating layer on the first conductive layer, and exposing and developing the first photosensitive insulating layer to form a first conduction hole for conduction; electroplating on the surface of the first photosensitive insulating layer and in the first via hole to form a second conductive layer; dry films are pressed on the first conducting layer and the second conducting layer respectively, exposed, developed and etched to form circuits, then the dry films are removed, and a first layer circuit and a second layer circuit are formed respectively; forming a second photosensitive insulating layer on the surface, opposite to the first photosensitive insulating layer, of the first conductive layer, and forming a third photosensitive insulating layer on the surface, opposite to the first photosensitive insulating layer, of the second conductive layer; wherein the photosensitive insulating layer on the outermost layer of the flexible circuit board is used as a protective layer.

Description

Technical Field

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

[0002] With the advancement of technology, the demand for high-frequency, high-speed flexible circuit boards is increasing. This requires the circuit board insulation layer to have a low dielectric constant and dielectric loss. Traditional polyimide is difficult to meet, and modified polyimide, liquid crystal polymer, and fluororesin are needed. Due to the high cost of these materials, high-frequency, high-speed flexible circuit boards have so far maintained a low market share in the domestic market.

[0003] In addition, traditional processes have problems such as deviations in multiple alignments between laser and exposure, and low precision in punching out protective films, which are not conducive to the production of high-density circuit boards. Summary of the Invention

[0004] In view of this, the present invention provides a flexible circuit board and a method for manufacturing the same to solve the problems of the conventional process in the prior art, such as deviations in the multiple alignments between laser and exposure, low precision in punching the protective film, and difficulty in manufacturing high-density circuit boards.

[0005] The present invention provides a method for manufacturing a flexible circuit board, the method comprising:

[0006] providing a first conductive layer as a substrate;

[0007] forming a first photosensitive insulating layer on the first conductive layer, and exposing and developing the first photosensitive insulating layer to form a first conducting hole for conducting;

[0008] forming a second conductive layer by electroplating on the surface of the first photosensitive insulating layer and in the first via hole;

[0009] Laminating dry films on the first conductive layer and the second conductive layer respectively, exposing and developing and etching out the circuits, and then removing the dry films to form a first layer circuit and a second layer circuit respectively;

[0010] forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer;

[0011] Wherein, the photosensitive insulating layer located on the outermost layer of the flexible circuit board serves as a protective layer.

[0012] Preferably, in the method for manufacturing the flexible circuit board, the step of forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer, comprises:

[0013] forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a second conductive hole and / or a first inner layer opening after exposing and developing the second photosensitive insulating layer; forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer, and forming a third conductive hole and / or a second inner layer opening after exposing and developing the third photosensitive insulating layer;

[0014] The first conductive layer, the second conductive layer, and the photosensitive insulating layer form an inner layer circuit board.

[0015] Preferably, in the method for manufacturing the flexible circuit board, after the step of forming the first conductive layer, the second conductive layer, and the photosensitive insulating layer into an inner layer circuit board, the method further comprises:

[0016] Repeat the process of forming a circuit layer and a photosensitive insulating layer on the photosensitive insulating layer on both sides of the inner circuit board in sequence, until the flexible circuit boards are stacked to form a flexible circuit board with a target number of layers.

[0017] Preferably, in the method for manufacturing the flexible circuit board, only the openings of the inner circuit board and / or the outer circuit board are exposed on the outermost photosensitive insulating layer after exposure and development.

[0018] Preferably, in the method for manufacturing the flexible circuit board, the dielectric constant of the photosensitive insulating layer is less than 3.5, and the dielectric loss is less than 0.005.

[0019] Preferably, in the method for manufacturing the flexible circuit board, the step of forming the second conductive layer by electroplating on the surface of the first photosensitive insulating layer and in the first via hole includes:

[0020] Performing metallization treatment on the surface of the first photosensitive insulating layer and in the first via hole to form a seed layer for plating a conductive layer;

[0021] A second conductive layer is plated on the surface of the metallized structure.

[0022] Preferably, in the method for manufacturing the flexible circuit board, the step of performing metallization treatment on the surface of the first photosensitive insulating layer and in the first via hole to form a seed layer for plating the conductive layer includes:

[0023] A 30nm-60nm thick chromium metal is first vacuum sputtered on the surface of the first photosensitive insulating layer and in the first conducting hole, and then a layer of metal copper is vacuum sputtered as a seed layer. The thickness of the seed layer is 300-500nm.

[0024] Preferably, in the method for manufacturing the flexible circuit board, the step of plating a second conductive layer on the surface of the metallized structure includes:

[0025] A second conductive layer is electroplated on the surface of the metallized first photosensitive insulating layer and in the first conducting hole throughout the entire board to make the second conductive layer conductive with the first conductive layer.

[0026] Preferably, in the method for manufacturing the flexible circuit board, the first photosensitive insulating layer is a liquid photosensitive material or a film material;

[0027] When the first photosensitive insulating layer is a liquid photosensitive material, the first photosensitive insulating layer is coated on the first conductive layer through a coating process;

[0028] When the first photosensitive insulating layer is a film material, the first photosensitive insulating layer is pressed onto the first conductive layer through a pressing process.

[0029] In order to achieve the above object, the present invention further provides a flexible circuit board, which is manufactured using the above-mentioned method for manufacturing a flexible circuit board.

[0030] The present invention has at least the following beneficial effects:

[0031] The present invention realizes the production of high-precision flexible circuit boards by providing a photosensitive insulating layer and forming conductive holes by exposing and developing the photosensitive insulating layer without using laser.

[0032] Furthermore, conventional methods use lasers to create via holes, then remove the conductive layer and perform exposure. Since the laser and conductive layer plating are performed using different equipment, they need to be aligned separately. Repeated focus and alignment can lead to significant differences in accuracy. However, the present invention does not use lasers, but only uses a single exposure to create the via holes, followed by the conductive layer removal. Multiple focus and alignment are not required, and the conductive layer and via holes are formed simultaneously. Therefore, the present invention significantly improves accuracy by using a photosensitive insulating layer.

[0033] Furthermore, the present invention uses exposure and development of a photosensitive insulating layer to form conductive holes and openings, gradually stacking from the inner layer and gradually increasing, and finally forming a circuit board with a target number of layers; the intermediate processes are all repetitive processes, the manufacturing difficulty is reduced, and it is convenient for industrial production.

[0034] Furthermore, the laser process usually takes a long time (for example, 10 minutes), while the present invention takes a shorter time by using a photosensitive insulating layer. Processing the same product usually takes less than half the time of the laser process (for example, the laser process takes 10 minutes, while the present invention takes less than 5 minutes).

[0035] Furthermore, the laser process in the prior art is a laser method, which is a physical processing method, while the present invention uses a photosensitive insulating layer in a chemical method, utilizing the imaging function of the photosensitive insulating layer to form the via holes and opening positions.

[0036] Furthermore, the present invention uses photosensitive insulating materials with graphic functions, and realizes metallization and subsequent electroplating by vacuum sputtering, replacing traditional laser drilling and window opening, lamination, protective film and ink processes, thereby shortening the process route and improving efficiency.

[0037] Furthermore, the process route after using the photosensitive material in the present invention is basically a repetitive process, and multiple circuit layers are formed by repeated superposition, which is more conducive to controlling the quality of the process and realizing automated and intelligent production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0039] Figure 1 A flow chart showing a method for manufacturing a flexible circuit board according to an embodiment of the present invention is shown;

[0040] Figure 2 Shown Figure 1 A cross-sectional view of an embodiment after the first photosensitive insulating layer is covered on the first conductive layer;

[0041] Figure 3 Shown in Figure 2 A cross-sectional view of an embodiment of metallization treatment of the surface of the first photosensitive insulating layer and the inside of the first via hole;

[0042] Figure 4 Shown in Figure 3 A cross-sectional view of an embodiment of the surface of the first photosensitive insulating layer after the metallization treatment and the second conductive layer electroplated on the entire board in the first via hole;

[0043] Figure 5 Shown in Figure 4 A cross-sectional view of an embodiment in which the first conductive layer and the second conductive layer are laminated, and the dry film is exposed and developed to reveal the conductive layer to be etched;

[0044] Figure 6 Indicated in Figure 5 A cross-sectional view of an embodiment of the present invention when the dry film is removed after etching the circuit;

[0045] Figure 7 Indicated in Figure 6 A cross-sectional view of an embodiment in which the first conductive layer and the second conductive layer cover the second photosensitive insulating layer and the third photosensitive insulating layer respectively;

[0046] Figure 8 Indicated the Figure 7 A cross-sectional view of an embodiment in which the second photosensitive insulating layer and the third photosensitive insulating layer respectively form circuit layers;

[0047] Figure 9 A schematic diagram of an embodiment of a multi-layer flexible circuit board is shown.

[0048] The description of each reference numeral is as follows:

[0049] 1-first conductive layer, 1a-first circuit layer, 2-first photosensitive insulating layer, 21-first via hole, 3-seed layer, 4-second conductive layer, 41-second circuit layer, 5-second photosensitive insulating layer, 51-second via hole, 6-third photosensitive insulating layer, 61-third via hole, 62-second inner layer opening, 7-third circuit layer, 8-fourth circuit layer, 9-fourth photosensitive insulating layer, 91-outer layer opening, 10-fifth photosensitive insulating layer, 10a-inner layer opening, 11-dry film. DETAILED DESCRIPTION

[0050] The technical solutions of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments. It should be noted that the embodiments of the present invention and the features therein may be combined with each other unless there is a conflict.

[0051] In embodiments of the present invention, the term "and / or" describes the association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0052] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0053] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0054] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity direction; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above directional words are not used to limit the present invention.

[0055] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in the embodiments of the present invention, many technical details are provided to enable the reader to better understand the present invention. However, even without these technical details and the various changes and modifications based on the following embodiments, the technical solutions claimed in the present invention can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with each other and referenced to each other under the premise that there is no contradiction.

[0056] The manufacturing method of multi-layer circuit boards in the prior art generally includes laser, hole metallization, dry film lamination, exposure, development, inner layer pattern electroplating, film stripping, inner layer circuit, adhesive film auxiliary film lamination, adhesive film punching, outer layer material punching, pre-lamination, lamination, baking and curing, outer layer laser, hole metallization, dry film lamination, exposure, development, outer layer pattern electroplating, film stripping, outer layer circuit, picosecond, uncovering, protective film punching, protective film pre-lamination, fast pressing, baking and curing, ink printing, pre-baking, exposure, development, curing, etc.

[0057] Due to the problems of multiple alignment deviations between laser and exposure, low precision of protective film punching, etc. in traditional processes, it is not conducive to the production of high-density circuit boards.

[0058] To address this issue, the present invention utilizes a photosensitive insulating material with patterning capabilities, and achieves metallization through vacuum sputtering followed by electroplating, replacing the traditional laser drilling and windowing, lamination, protective film, and ink processes, thus simplifying the manufacturing process. Furthermore, the patterning capabilities of the photosensitive insulating material allow for a single patterning process, avoiding the issues of multiple alignment errors between the laser and exposure process and the low precision of protective film punching found in traditional processes, making it more suitable for the production of high-density circuit boards.

[0059] Specifically, the present invention provides a method for manufacturing a flexible circuit board, such as Figure 1 As shown, Figure 1 The figure shows a schematic diagram of the method for manufacturing the flexible circuit board provided by the present invention.

[0060] At S110, a first conductive layer 1 is provided as a substrate. The first conductive layer 1 may be, but is not limited to, copper foil; in some other embodiments, the first conductive layer 1 may also be made of other conductive materials. The selection of other conductive layers in the present invention can also refer to the first conductive layer 1 and will not be described in detail here.

[0061] At S120, a first photosensitive insulating layer 2 is formed on the first conductive layer 1, and a first conductive hole 21 for conduction is formed after exposing and developing the first photosensitive insulating layer 2. The first photosensitive insulating layer 2 can be a liquid photosensitive material or a film material, and is not specifically limited here. When the first photosensitive insulating layer 2 is a liquid photosensitive material, the first photosensitive insulating layer 2 can be coated on the first conductive layer 1 through a coating process. When the first photosensitive insulating layer 2 is a film material, the first photosensitive insulating layer 2 is pressed on the first conductive layer 1 through a pressing process. In some embodiments, the first photosensitive insulating layer 2 is photosensitive polyimide; in some other embodiments, the first photosensitive insulating layer 2 can also be a photosensitive material of other materials, such as benzocyclobutene, epoxy resin, polybenzoxazole, and aromatic fluorine-containing polymer.

[0062] It is worth noting that the materials and processes of other photosensitive insulating layers (e.g., second photosensitive insulating layer 5, third photosensitive insulating layer 6, ...) in the present invention can also refer to the description of the first photosensitive insulating layer 2 above and will not be described in detail here. The dielectric constant of the photosensitive insulating layer is less than 3.5, and the dielectric loss is less than 0.005.

[0063] The first photosensitive insulating layer 2 formed on the first conductive layer 1 must maintain a uniform thickness to avoid compromising overall quality. After forming the first photosensitive insulating layer 2 on the first conductive layer 1, heating can be used to remove the chemical organic solvent within the photosensitive insulating material, transforming the liquid into a solid film, facilitating subsequent operations, depending on the properties of the photosensitive insulating material. Alternatively, other methods, such as infrared heating, can be used.

[0064] The first photosensitive insulating layer 2 is exposed, developed and cured so that the first photosensitive insulating layer 2 is patterned and has good bonding with the first conductive layer 1. After the first conductive hole 21 is formed by exposing and developing the first photosensitive insulating layer 2, heating can be selected for baking and curing according to the characteristics of the photosensitive insulating material. The specific baking time and temperature need to be determined according to the thickness of the first photosensitive insulating layer 2 and the specific material. For example, curing can be performed at 200°C for 2 hours. By baking and curing, the photosensitive insulating material can achieve the preset material properties. In other embodiments, curing can also be performed by other means, such as ultraviolet light.

[0065] The position and size of the first conductive hole 21 can be determined according to design data, and the first conductive hole 21 can realize the conduction of circuits in different layers.

[0066] Figure 2 The diagram shows a schematic diagram of an embodiment of the method for manufacturing a flexible circuit board provided by the present invention when the first photosensitive insulating layer 2 is covered on the first conductive layer 1. Figure 2Taking the first conductive layer 1 as copper foil as an example, the first photosensitive insulating layer 2 is coated or laminated on the copper foil, and the first conductive hole 21 is formed after exposure and development, and then cured by baking at 200° C. for 2 hours.

[0067] S130 is a step of electroplating the surface of the first photosensitive insulating layer 2 and the interior of the first via 21 to form a second conductive layer 4. In some embodiments, a metallization treatment is performed on the surface of the first photosensitive insulating layer 2 and the interior of the first via 21 to form a seed layer 3 for plating a conductive layer; and the second conductive layer 4 is plated on the surface of the metallized structure. The seed layer 3 may be, but is not limited to, one or both of chromium metal and copper metal. In some other embodiments, the metallization treatment may also be a step of first sputtering a base layer such as chromium, titanium, or nickel-chromium, followed by sputtering copper.

[0068] Figure 3 Indicated in Figure 2 Schematic diagram of an embodiment of metallization treatment of the surface of the first photosensitive insulating layer 2 and the inside of the first conductive hole 21. Figure 3 In some embodiments, the seed layer 3 for plating the conductive layer is formed by metallization treatment on the surface of the first photosensitive insulating layer 2 and in the first conductive hole 21. The chromium metal with a thickness of 30nm-60nm is first vacuum sputtered on the surface of the first photosensitive insulating layer 2 and in the first conductive hole 21, and then a layer of metal copper is vacuum sputtered as the seed layer 3. The thickness of the seed layer 3 is 300-500nm.

[0069] Figure 4 Indicated in Figure 3 Schematic diagram of an embodiment of electroplating the second conductive layer 4 on the surface of the first photosensitive insulating layer 2 after the metallization treatment and in the first via hole 21. Figure 4 In some embodiments, the second conductive layer 4 is plated on the surface of the metallized structure, but is not limited to being plated on the surface of the metallized first photosensitive insulating layer 2 and within the first conductive hole 21, so that the second conductive layer 4 and the first conductive layer 1 are electrically conductive. The second conductive layer 4 can be, but is not limited to, a copper layer; in some other embodiments, the second conductive layer 4 can also be made of other conductive materials, such as silver. Taking the second conductive layer 4 as a copper layer as an example, copper is electroplated to a thickness of 10-20 microns to form a double-sided board structure. At the first conductive hole 21, the first conductive layer 1 and the second conductive layer 4 are electrically conductive.

[0070] At S140 , a dry film 11 is laminated onto the first conductive layer 1 and the second conductive layer 4 , exposed to light, developed, and etched to form circuits. The dry film 11 is then removed to form first and second circuit layers, respectively. The dry film 11 is laminated onto the first and second conductive layers 1 and 4 , exposed to light, developed, and etched to form circuits for signal transmission.

[0071] Figure 5 The diagram shows an embodiment in which the dry film 11 is pressed against the first conductive layer 1 and the second conductive layer 4 and then exposed and developed to reveal the conductive layer to be etched. Figure 6 Schematic diagram of an embodiment of removing the dry film 11 after etching the circuit. Figure 5 and Figure 6 , the conductive layer that needs to be etched is developed by exposure, and then the circuit is formed by etching to obtain the first layer circuit and the second layer circuit, completing the production of the inner layer circuit.

[0072] At S150, a second photosensitive insulating layer 5 is formed on the surface opposite to the first conductive layer 1 and the first photosensitive insulating layer 2, and a third photosensitive insulating layer 6 is formed on the surface opposite to the second conductive layer 4 and the first photosensitive insulating layer 2; wherein the photosensitive insulating layer located on the outermost layer of the flexible circuit board serves as a protective layer.

[0073] It should be noted that if the flexible circuit board is a two-layer board, the second photosensitive insulating layer 5 and the third photosensitive insulating layer 6 serve as protective films. If the flexible circuit board has three or more layers, the photosensitive insulating layer can be repeatedly exposed and developed to form vias and / or openings, gradually stacking the layers starting from the inner layer, until the target number of layers is achieved. The outermost photosensitive insulating layer, after exposure and development, may be an opening that only exposes the inner and / or outer layers of the circuit board.

[0074] In some embodiments, when the target number of layers is greater than three, the first circuit layer 1a and the second circuit layer 41 serve as inner circuit layers. Specifically, S150 includes forming a second photosensitive insulating layer 5 on the surface of the first conductive layer 1 opposite to the first photosensitive insulating layer 2, and forming a second via 51 and / or a first inner layer opening after exposing and developing the second photosensitive insulating layer 5; forming a third photosensitive insulating layer 6 on the surface of the second conductive layer 4 opposite to the first photosensitive insulating layer 2, and forming a third via 61 and / or a second inner layer opening 62 after exposing and developing the third photosensitive insulating layer 6; the first conductive layer, the second conductive layer, and the photosensitive insulating layer form an inner circuit board.

[0075] The outer circuit layer is formed by laminating the inner circuit board sequentially through the photosensitive insulating layer. In some embodiments, the outer circuit layer can be formed by repeatedly forming the circuit layer and the photosensitive insulating layer on the photosensitive insulating layer on both sides of the inner circuit board until the flexible circuit board has a target number of layers.

[0076] Of course, in some embodiments, the layers can be added by repeatedly forming a circuit layer and a photosensitive insulating layer on the photosensitive insulating layer on one side of the inner circuit board, until the flexible circuit board is stacked to form a flexible circuit board with a target number of layers.

[0077] For example, after forming a double-layer circuit board through steps 110 to 150, a circuit layer and a photosensitive insulating layer can be sequentially formed on both sides of the double-layer circuit board to obtain a four-layer circuit board; a circuit layer and a photosensitive insulating layer can be sequentially formed on both sides of the four-layer circuit board to obtain a six-layer circuit board; and so on. By repeating the operation, the number of layers can be gradually increased until the flexible circuit board with the target number of layers is reached.

[0078] Of course, in some embodiments, after forming a double-layer circuit board through steps 110 to 150, a circuit layer and a photosensitive insulating layer can be sequentially formed on one side of the double-layer circuit board to obtain a three-layer circuit board; a circuit layer and a photosensitive insulating layer can be sequentially formed on one side of the three-layer circuit board to obtain a four-layer circuit board; and so on. The operation can be repeated to gradually increase the layers until the target number of layers of the flexible circuit board is reached.

[0079] In some other embodiments, after forming a double-layer circuit board through steps 110 to 150, a circuit layer and a photosensitive insulating layer may be sequentially formed on one side or both sides of the formed double-layer circuit board. The specific method of adding layers can be selected according to actual needs.

[0080] It should be noted that the photosensitive insulating layer referred to in the present invention is not limited to the first photosensitive insulating layer 2, the second photosensitive insulating layer 5, and the third photosensitive insulating layer 6. Any photosensitive insulating layer can be used. The photosensitive insulating layer mentioned in the present invention can be a liquid or film material. In some other embodiments, the photosensitive insulating layer can also be a photosensitive material of other materials.

[0081] The method for manufacturing the flexible circuit board provided by the present invention is described below by taking a flexible circuit board having four layers as an example.

[0082] S1, providing a first conductive layer 1 as a substrate. For example, the first conductive layer 1 is a copper foil.

[0083] S2, forming a first photosensitive insulating layer 2 on the first conductive layer 1, and exposing and developing the first photosensitive insulating layer 2 to form a first conductive hole 21 for conduction. Figure 2 As shown, taking the first conductive layer 1 as copper foil as an example, a first photosensitive insulating layer 2 is coated or laminated on the copper foil, and a first conductive hole 21 is formed after exposure and development, and then cured by baking at 200° C. for 2 hours.

[0084] S3, metallizing the surface of the first photosensitive insulating layer 2 and the first via hole 21 to form a seed layer 3 for plating a conductive layer. Figure 3As shown, a 30-nanometer-thick chromium layer is first vacuum-sputtered on the surface of the first photosensitive insulating layer 2 and in the first conductive hole 21 , and then a 300-nanometer-thick copper layer is sputtered as a seed layer 3 for electroplating.

[0085] S4, forming a second conductive layer 4 by electroplating on the surface of the first photosensitive insulating layer 2 and in the first conducting hole 21. Figure 4 As shown, a second conductive layer 4 (such as copper) is electroplated on the surface of the first photosensitive insulating layer 2 and in the first conducting hole 21 .

[0086] S5, respectively pressing the dry film 11 on the first conductive layer 1 and the second conductive layer 4, exposing and developing to expose the conductive layer to be etched. Figure 5 As shown, taking the first conductive layer 1 and the second conductive layer 4 as copper as an example, after the dry film 11 is pressed between the first conductive layer 1 and the second conductive layer 4, the copper that needs to be etched can be exposed.

[0087] S6, after etching out the circuit, remove the dry film 11, and form the first layer circuit and the second layer circuit respectively. Figure 6 As shown, at this time, circuits are formed on the first conductive layer 1 and the second conductive layer 4 respectively, completing the production of the inner layer circuits.

[0088] S7, forming a second photosensitive insulating layer 5 on the surface of the first conductive layer 1 opposite to the first photosensitive insulating layer 2, forming a third photosensitive insulating layer 6 on the surface of the second conductive layer 4 opposite to the first photosensitive insulating layer 2, and forming a second conductive hole 51 and a first inner layer opening required to expose the inner layer in the second photosensitive insulating layer 5 after exposure and development; forming a third conductive hole 61 and a second inner layer opening 62 required to expose the inner layer in the third photosensitive insulating layer 6 after exposure and development. Figure 7 As shown, after exposure and development, a second conductive hole 51 and a first inner layer opening where the inner layer needs to be exposed are formed in the second photosensitive insulating layer 5; after exposure and development, a third conductive hole 61 and a second inner layer opening 62 where the inner layer needs to be exposed are formed in the third photosensitive insulating layer 6, and the layers are cured by baking at 200°C for 2 hours.

[0089] S8, forming the third circuit layer 7 and the fourth circuit layer 8 in sequence on the second photosensitive insulating layer 5 and the third photosensitive insulating layer 6 on both sides of the inner circuit board, and realizing the conduction between the outer layer and the inner layer. Figure 8 As shown, the outer layer circuits are made by a semi-additive process to obtain the third circuit layer 7 and the fourth circuit layer 8.

[0090] S9, finally forming a fourth photosensitive insulating layer 9 on the surface of the third circuit layer 7 opposite to the second photosensitive insulating layer 5, and forming a fifth photosensitive insulating layer 10 on the surface of the fourth circuit layer 8 opposite to the third photosensitive insulating layer 6, the fourth photosensitive insulating layer 9 and the fifth photosensitive insulating layer 10 respectively serving as protective films. Figure 9As shown, the fourth photosensitive insulating layer 9 and the fifth photosensitive insulating layer 10 are coated or laminated as protective films, and the outer layer opening 91 and the inner layer opening 10a are exposed after exposure and development, and then cured by baking at 200°C for 2 hours.

[0091] It is worth noting that when the target number of layers of the circuit board is greater than four, S7 and S8 can be repeated after S8 until the target number of layers is reached, and then S9 is executed.

[0092] The present invention also provides a flexible circuit board. An embodiment of the flexible circuit board includes an embodiment of the manufacturing method of the flexible circuit board. The beneficial effects of the manufacturing method of the flexible circuit board can be applied to the flexible circuit board.

[0093] The flexible circuit board provided by the present invention is provided with a photosensitive insulating layer, and the conductive holes are formed by exposing and developing the photosensitive insulating layer without using laser, thereby realizing the production of a high-precision flexible circuit board;

[0094] Furthermore, conventional methods use lasers to create vias, then de-plating the conductive layer and exposing the vias. Since the laser and conductive layer plating are performed using separate equipment, they require separate alignment. Repeated focus and alignment can lead to significant differences in precision. However, the present invention eliminates the use of lasers and uses only a single exposure to create the vias. De-plating the conductive layer eliminates the need for multiple focus and alignment cycles, allowing the conductive layer and vias to be formed simultaneously. Consequently, the present invention significantly improves precision through the use of a photosensitive insulating layer.

[0095] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for manufacturing a flexible circuit board, characterized in that: include: providing a first conductive layer as a substrate; forming a first photosensitive insulating layer on the first conductive layer, and exposing and developing the first photosensitive insulating layer to form a first conducting hole for conducting; forming a second conductive layer by electroplating on the surface of the first photosensitive insulating layer and in the first via hole; Laminating dry films on the first conductive layer and the second conductive layer respectively, exposing and developing and etching out the circuits, and then removing the dry films to form a first layer circuit and a second layer circuit respectively; forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer; Wherein, the photosensitive insulating layer located on the outermost layer of the flexible circuit board serves as a protective layer.

2. The method for manufacturing a flexible circuit board according to claim 1, wherein: The step of forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer, comprises: forming a second photosensitive insulating layer on a surface of the first conductive layer opposite to the first photosensitive insulating layer, and forming a second conductive hole and / or a first inner layer opening after exposing and developing the second photosensitive insulating layer; forming a third photosensitive insulating layer on a surface of the second conductive layer opposite to the first photosensitive insulating layer, and forming a third conductive hole and / or a second inner layer opening after exposing and developing the third photosensitive insulating layer; The first conductive layer, the second conductive layer, and the photosensitive insulating layer form an inner layer circuit board.

3. The method for manufacturing a flexible circuit board according to claim 2, wherein: After the step of forming the first conductive layer, the second conductive layer, and the photosensitive insulating layer into an inner layer circuit board, the method further includes: Repeat the process of forming a circuit layer and a photosensitive insulating layer on the photosensitive insulating layer on both sides of the inner circuit board in sequence, until the flexible circuit boards are stacked to form a flexible circuit board with a target number of layers.

4. The method for manufacturing a flexible circuit board according to claim 3, wherein: After exposure and development, only the openings of the inner layer circuit board and / or the outer layer circuit board are exposed on the outermost photosensitive insulating layer.

5. The method for manufacturing a flexible circuit board according to any one of claims 1 to 4, wherein: The dielectric constant of the photosensitive insulating layer is less than 3.5, and the dielectric loss is less than 0.

005.

6. The method for manufacturing a flexible circuit board according to claim 1, wherein: The step of forming a second conductive layer by electroplating on the surface of the first photosensitive insulating layer and in the first via hole comprises: Performing metallization treatment on the surface of the first photosensitive insulating layer and in the first via hole to form a seed layer for plating a conductive layer; A second conductive layer is plated on the surface of the metallized structure.

7. The method for manufacturing a flexible circuit board according to claim 6, wherein: The step of performing metallization treatment on the surface of the first photosensitive insulating layer and in the first via hole to form a seed layer for plating a conductive layer includes: A 30nm-60nm thick chromium metal is first vacuum sputtered on the surface of the first photosensitive insulating layer and in the first conducting hole, and then a layer of metal copper is vacuum sputtered as a seed layer. The thickness of the seed layer is 300-500nm.

8. The method for manufacturing a flexible circuit board according to claim 6, wherein: The step of plating a second conductive layer on the surface of the metallized structure comprises: A second conductive layer is electroplated on the surface of the metallized first photosensitive insulating layer and in the first conducting hole throughout the entire board to make the second conductive layer conductive with the first conductive layer.

9. The method for manufacturing a flexible circuit board according to claim 1, wherein: The first photosensitive insulating layer is a liquid photosensitive material or a film material; When the first photosensitive insulating layer is a liquid photosensitive material, the first photosensitive insulating layer is coated on the first conductive layer through a coating process; When the first photosensitive insulating layer is a film material, the first photosensitive insulating layer is pressed onto the first conductive layer through a pressing process.

10. A flexible circuit board, characterized in that: The invention is manufactured by the manufacturing method according to any one of claims 1 to 9.

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