A multilayer board

Abstract

The embodiment of the present invention provides a multilayer board, including a first circuit substrate and a second circuit substrate; the first circuit substrate includes a base film layer, a first conductive layer and a first dielectric layer, the first conductive layer and the first dielectric layer are sequentially arranged on one side of the base film layer, and the first dielectric layer is provided with a first through hole; the second circuit substrate includes a first adhesive film layer and a second conductive layer arranged in a stacked manner, the first adhesive film layer is arranged on a side of the first dielectric layer away from the first conductive layer; a first protruding structure is provided on one side of the metal layer in the second conductive layer, the first protruding structure pierces the first adhesive film layer, and passes through the first through hole to connect with the metal layer in the first conductive layer. The multilayer board of the present invention greatly reduces the overall thickness of the multilayer board, enhances the bending resistance of the multilayer board, and improves the reliability and convenience of the multilayer board assembly, so that the multilayer board is suitable for high-frequency signal transmission.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a multilayer board. Background Art

[0002] With the rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightweight, multifunctionality and high-density assembly. Flexible circuit boards are widely used in electronic products due to their advantages such as small size, light weight and high flexibility.

[0003] In order to meet the development needs of high-frequency and high-speed digital signal transmission and ensure the normal operation of electronic products, the design and material selection of the multi-layer flexible circuit board must be optimized. At present, the existing flexible circuit boards usually use a dielectric layer with low dielectric loss, or reduce the dielectric constant, or change the thickness and material of the dielectric layer to reduce the fluctuation of the characteristic impedance, so as to ensure that the requirements of high-frequency and high-speed digital signal transmission are met under the normal operation of electronic products. However, due to the thick thickness of the multi-layer flexible circuit board itself, its bending performance is poor and the space utilization rate is low, thus limiting the application of flexible circuit boards in high-frequency signal transmission. Summary of the invention

[0004] The purpose of the embodiment of the present invention is to provide a multilayer board, which can reduce the overall thickness of the circuit board, enhance the bending resistance of the circuit board, and be effectively used in high-frequency signal transmission.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a multilayer board, including a first circuit substrate and a second circuit substrate;

[0006] The first circuit substrate comprises a base film layer, a first conductive layer and a first dielectric layer, wherein the first conductive layer and the first dielectric layer are sequentially arranged on one side of the base film layer, and the first dielectric layer is provided with at least one first through hole for exposing the metal layer in the first conductive layer;

[0007] A second circuit substrate is provided on a side of the first circuit substrate close to the first dielectric layer; the second circuit substrate includes a first adhesive film layer and a second conductive layer which are stacked, the first adhesive film layer being provided on a side of the first dielectric layer away from the first conductive layer; a first protruding structure is provided on a side of the metal layer in the second conductive layer facing the first adhesive film layer, the first protruding structure pierces the first adhesive film layer, and passes through the first through hole to be connected to the metal layer in the first conductive layer.

[0008] As an improvement of the above scheme, there are multiple second circuit substrates arranged on the side of the first circuit substrate close to the first dielectric layer; wherein a second dielectric layer is arranged between any two adjacent second circuit substrates, and at least one second through hole is opened on each second dielectric layer; in any two adjacent second circuit substrates, the first protruding structure of the second circuit substrate away from the first circuit substrate pierces the first adhesive film layer and passes through the second through hole, thereby connecting with the metal layer in the second conductive layer of the second circuit substrate close to the first circuit substrate.

[0009] As an improvement of the above scheme, there are multiple first circuit substrates, and the multiple first circuit substrates are stacked in sequence; wherein, a first connecting hole is provided on any two adjacent first circuit substrates, and a conductive medium for connecting the metal layer of the first conductive layer in the two adjacent first circuit substrates is provided in the first connecting hole.

[0010] As an improvement of the above scheme, the multilayer board also includes a third circuit substrate, the third circuit substrate includes a third conductive layer and a third dielectric layer which are stacked, the third dielectric layer is arranged on a side of the second conductive layer away from the first adhesive film layer, and a second connecting hole is provided on the third dielectric layer, and a conductive medium connecting the metal layer in the third conductive layer and the metal layer in the second conductive layer is provided in the second connecting hole.

[0011] As an improvement of the above solution, the first circuit substrate further includes a fourth conductive layer and a fourth dielectric layer, and the fourth conductive layer and the fourth dielectric layer are sequentially arranged on the other surface of the base film layer.

[0012] As an improvement of the above solution, at least one third through hole is provided on the fourth dielectric layer to expose the metal layer in the fourth conductive layer;

[0013] The second circuit substrate is also provided on the side of the first circuit substrate close to the fourth dielectric layer, and a plurality of the second circuit substrates are symmetrically arranged on both sides of the first circuit substrate or a plurality of the second circuit substrates are asymmetrically arranged on both sides of the first circuit substrate; wherein the first protruding structure of the second circuit substrate close to the fourth dielectric layer pierces the first adhesive film layer of the second circuit substrate and passes through the third through hole to be connected to the metal layer in the fourth conductive layer.

[0014] As an improvement of the above scheme, there are multiple second circuit substrates arranged on the side of the first circuit substrate close to the fourth dielectric layer; wherein a second dielectric layer is arranged between any two adjacent second circuit substrates, and at least one second through hole is opened on each second dielectric layer; in any two adjacent second circuit substrates, the first protruding structure of the second circuit substrate away from the first circuit substrate pierces the first adhesive film layer and passes through the second through hole, thereby connecting with the metal layer in the second conductive layer of the second circuit substrate close to the first circuit substrate.

[0015] As an improvement of the above solution, a plurality of third connection holes arranged at intervals are provided on the base film layer, and a conductive medium connecting the metal layer in the first conductive layer and the metal layer in the fourth conductive layer is provided in the third connection holes.

[0016] As an improvement of the above solution, the metal layer in the second conductive layer includes a first surface, the first surface is a non-flat surface, and the first surface constitutes the first protruding structure; or,

[0017] The metal layer in the second conductive layer includes a first surface, on which conductor particles are arranged, and the first surface and the conductor particles constitute the first protruding structure.

[0018] As an improvement of the above solution, the height of the first protruding structure is 0.2 μm-30 μm.

[0019] As an improvement of the above solution, the first adhesive film layer includes an adhesive layer that does not contain conductive particles.

[0020] As an improvement of the above scheme, the metal layer in the first conductive layer, the metal layer in the second conductive layer and the metal layer in the fourth conductive layer are respectively made of any one or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0021] Compared with the prior art, the multilayer board provided in the embodiment of the present invention has a first through hole on the first dielectric layer of the first circuit substrate to expose the metal layer in the first conductive circuit layer, and at the same time, the first adhesive film layer in the second circuit substrate is arranged on the side of the first dielectric layer away from the first conductive layer, and a first protruding structure is arranged on the side of the metal layer of the second conductive layer in the second circuit substrate facing the first adhesive film layer, so that the first protruding structure pierces the first adhesive film layer and passes through the first through hole to connect with the metal layer of the first conductive layer, thereby realizing internal conduction of the multilayer board; the multilayer board of the present invention replaces the impedance control layer and the first covering film layer of the outer layer of the traditional multilayer circuit board with the second circuit substrate, avoiding the arrangement of the impedance control layer and the first covering film layer, thereby greatly reducing the overall thickness of the multilayer board, enhancing the bending resistance of the multilayer board, and improving the reliability and convenience of the multilayer board assembly, so that the multilayer board is suitable for high-frequency signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a multilayer board in Embodiment 1 of the present invention;

[0023] Figure 2 is a schematic structural diagram of another multilayer board in Embodiment 1 of the present invention;

[0024] Figure 3 is a structural schematic diagram of another multilayer board in the first embodiment of the present invention;

[0025] Figure 4 is a structural schematic diagram of another multilayer board in the first embodiment of the present invention;

[0026] Figure 5 is a structural schematic diagram of another multilayer board in the first embodiment of the present invention;

[0027] Figure 6 is a schematic diagram of the structure of a multilayer board in Embodiment 2 of the present invention;

[0028] Figure 7 is a schematic diagram of the structure of a multilayer board in Embodiment 3 of the present invention;

[0029] Figure 8 is a schematic diagram of the structure of a multilayer board in a fourth embodiment of the present invention;

[0030] Fig. 9 It is a structural schematic diagram of a multilayer board in Embodiment 5 of the present invention;

[0031] Fig.10 is a schematic structural diagram of another multilayer board in Embodiment 5 of the present invention;

[0032] Fig.11 is a schematic diagram of the structure of a multilayer board in Embodiment 6 of the present invention;

[0033] Fig.12 is a schematic structural diagram of another multilayer board in Embodiment 6 of the present invention;

[0034] Fig.13 is a schematic diagram of the structure of a multilayer board in Embodiment 7 of the present invention;

[0035] Fig.14 It is a schematic flow chart of the method for preparing a multilayer board in the eighth embodiment of the present invention.

[0036] Among them, 1, first circuit substrate; 11, base film layer; 111, third connection hole; 12, first conductive layer; 121, metal layer in the first conductive layer; 122, insulating layer in the first conductive layer; 13, first dielectric layer; 131, first through hole; 14, first connection hole; 15, fourth conductive layer; 151, metal layer in the fourth conductive layer; 152, insulating layer in the fourth conductive layer; 16, fourth dielectric layer; 161, third through hole;

[0037] 2. second circuit substrate; 21. first adhesive film layer; 22. second conductive layer; 221. metal layer in the second conductive layer; 222. insulating layer in the second conductive layer; 223. first protruding structure; 224. conductor particles; 3. second dielectric layer; 31. second through hole; 4. conductive medium;

[0038] 5. Third circuit substrate; 51. Third conductive layer; 511. Metal layer in the third conductive layer; 512. Insulating layer in the third conductive layer; 52. Third dielectric layer; 521. Second connecting hole; 6. First insulating protective layer; 7. Second insulating protective layer. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Embodiment 1

[0041] Combination Figures 1 to 5 As shown, a multilayer board according to an embodiment of the present invention comprises a first circuit substrate 1 and a second circuit substrate 2;

[0042] The first circuit substrate 1 comprises a base film layer 11, a first conductive layer 12 and a first dielectric layer 13, wherein the first conductive layer 12 and the first dielectric layer 13 are sequentially arranged on one surface of the base film layer 11, and the first dielectric layer 13 is provided with at least one first through hole 131 for exposing the metal layer 121 in the first conductive layer;

[0043] A second circuit substrate 2 is provided on the side of the first circuit substrate 1 close to the first dielectric layer 13; the second circuit substrate 2 includes a first adhesive film layer 21 and a second conductive layer 22 which are stacked, and the first adhesive film layer 21 is provided on a side of the first dielectric layer 13 away from the first conductive layer 12; a first protruding structure 223 is provided on a side of the metal layer 221 in the second conductive layer which faces the first adhesive film layer 21, and the first protruding structure 223 pierces the first adhesive film layer 21 and passes through the first through hole 131 to be connected to the metal layer 121 of the first conductive layer.

[0044] In an embodiment of the present invention, a first through hole 131 is opened on the first dielectric layer 13 of the first circuit substrate 1 to expose the metal layer 121 in the first conductive layer, and the first adhesive film layer 21 in the second circuit substrate 2 is arranged on the side of the first dielectric layer 13 away from the first conductive layer 12, and a first protruding structure 223 is arranged on the side of the metal layer 221 of the second conductive layer in the second circuit substrate 2 facing the first adhesive film layer 21, so that the first protruding structure 223 pierces the first adhesive film layer 21 and passes through the first through hole 131 to connect with the metal layer 121 of the first conductive layer, thereby realizing internal conduction of the multilayer board; the multilayer board of the present invention replaces the impedance control layer and the first covering film layer of the outer layer of the traditional multilayer circuit board with the second circuit substrate 2, avoiding the arrangement of the impedance control layer and the first covering film layer, thereby greatly reducing the overall thickness of the multilayer board, enhancing the bending resistance of the multilayer board, and improving the reliability and convenience of the multilayer board assembly, so that the multilayer board is suitable for high-frequency signal transmission. In addition, the multilayer board provided by the embodiment of the present invention does not need to use metallized through holes to achieve electrical connection between layers in the multilayer board, avoiding manufacturing processes such as drilling and hole metallization, thereby simplifying the manufacturing process of the multilayer board and reducing the manufacturing cost of the multilayer board.

[0045] In the embodiment of the present invention, the type of the base film layer 11 can be set according to actual use requirements; specifically, the base film layer 11 can be set as a single base film layer, such as a single hard resin layer or a single flexible resin layer; the base film layer 11 can also be set as a composite base film layer, such as composed of multiple different types of hard resin layers, composed of multiple different types of flexible resin layers, or composed of a hard resin layer and a flexible resin layer; wherein the hard resin layer is specifically epoxy resin, glass fiber cloth, etc., and the flexible resin layer is specifically polyimide (PI), polyethylene terephthalate (PET), polytetrafluoroethylene (Teflon), polythiamine (Polyamide), polymethylmethacrylate (Polymethylmethacrylate), polycarbonate (Polycarbonate) or polyimide-polyethylene-terephthalate copolymer (Polyamide polyethylene-terephthalate copolymer), etc.

[0046] In the embodiment of the present invention, the first conductive layer 12 can be set as a circuit layer; it should be noted that in the process of manufacturing the circuit board, after etching, a plurality of metal layers are formed on the circuit layer, and there are gaps between the metal layers. In the subsequent process of laminating the circuit board, these gaps will be filled with glue to form an insulating layer; specifically, Figure 1 As shown, when the first conductive layer 12 is a circuit layer, during the lamination process of the high transmission layer plate, the gaps between the metal layers 121 in each of the first conductive layers in the first conductive layer 12 will be filled by the adjacent first dielectric layer 13, thereby forming an insulating layer 122 in the first conductive layer; therefore, when the first conductive layer 12 is a circuit layer, the first conductive layer 12 is composed of a plurality of metal layers 121 in the first conductive layers and a plurality of insulating layers 122 in the first conductive layers, and the metal layers 121 in the first conductive layers and the insulating layers 122 in the first conductive layers are staggered and connected, so that the metal layers 121 in each of the first conductive layers are independent of each other, as shown in FIG. Figure 1 In addition, the number of the metal layers 121 in the first conductive layer can also be set according to actual conditions; preferably, there are multiple metal layers 121 in the first conductive layer, and the metal layers 121 in each first conductive layer are independent of each other.

[0047] In addition, the first conductive layer 1 can also be set as a metal layer, that is, it is not etched. Figure 3As shown. Similarly, the second conductive layer 2 can also be set as a circuit layer or a metal layer; when the second conductive layer 2 is a circuit layer, during the lamination process of the multilayer board, the gaps between the metal layers 221 in each second conductive layer in the second conductive layer 2 will be filled by the adjacent first insulating protection layer 6, thereby forming an insulating layer 222 in the second conductive layer; therefore, when the second conductive layer 2 is a circuit layer, the second conductive layer 2 is composed of a plurality of metal layers 221 in the second conductive layer and a plurality of insulating layers 222 in the second conductive layer; in addition, the number of metal layers 221 in the second conductive layer can be set according to actual conditions; preferably, there are a plurality of metal layers 221 in the second conductive layer, and the metal layers 221 in each second conductive layer are independent of each other.

[0048] In the embodiment of the present invention, the number and position of the first through holes 131 provided on the first dielectric layer 13 can also be set according to actual use conditions. It is understandable that the first through holes 131 can be provided only on the first dielectric layer 13 at positions corresponding to the metal layer 221 in the second conductive layer and the metal layer 121 in the first conductive layer to be electrically connected, so that the first protruding structure 223 on the metal layer 221 in the second conductive layer can pierce the first adhesive film layer 21 and pass through the provided first through holes 131 to connect with the corresponding metal layer 121 in the first conductive layer, such as Figure 2 shown.

[0049] In addition, the type of the first dielectric layer 13 can also be set according to actual use requirements. Specifically, the first dielectric layer 13 can be set as a single dielectric layer, such as a glue film layer or a resin film layer; the first dielectric layer 13 can also be set as a composite dielectric layer, such as a composite dielectric layer including PI (Polyimide) and a binder.

[0050] In addition, in an embodiment of the present invention, the first circuit substrate 1 may further include at least one RCC (ResinCoated Copper Foil) board, one of the RCC boards being arranged on a side of the first dielectric layer 13 away from the first conductive layer 12, and / or another of the RCC boards being arranged on a side of the base film layer 11 away from the first conductive layer 12.

[0051] Specifically, the RCC board includes a copper layer and a second adhesive film layer stacked, when one of the RCC boards is arranged on the side of the first dielectric layer 13 away from the first conductive layer 12, the second adhesive film layer of the RCC board is arranged on the side of the first dielectric layer 13 away from the first conductive layer 12, and the copper layer is electrically connected to the first conductive layer 12 through a through hole, a blind hole or a buried hole; the second circuit substrate 2 is arranged on the side of the first circuit substrate close to the RCC board, specifically: the first adhesive film layer 21 of the second circuit substrate 2 is arranged on the side of the copper layer away from the second adhesive film layer, the metal layer 221 in the second conductive layer is provided with a first protruding structure 223 on the side facing the first adhesive film layer 21, and the first protruding structure 223 pierces the first adhesive film layer 21, thereby being electrically connected to the copper layer. In addition, when another of the RCC boards is arranged on the side of the base film layer 11 away from the first conductive layer 12, the second adhesive film layer of the RCC board is arranged on the side of the base layer 11 away from the first conductive layer 12.

[0052] like Figure 1 As shown, in order to enable the first protruding structure 223 to pierce the first adhesive film layer 21 and pass through the first through hole 131 to connect with the metal layer 121 of the first conductive layer, in a preferred embodiment, the metal layer 221 in the second conductive layer includes a first surface, the first surface is a non-flat surface, and the first surface constitutes the first protruding structure 223.

[0053] In another preferred embodiment, the metal layer 221 in the second conductive layer includes a first surface, on which conductive particles 224 are disposed, and the first surface and the conductive particles 224 constitute the first protruding structure 223. Figure 4 By arranging the conductor particles 224 on the first surface to form the first protruding structure 223, the penetration force of the first protruding structure 223 is enhanced, thereby further ensuring that the first protruding structure 223 can penetrate the first adhesive film layer 21 and pass through the first through hole 31 to connect with the metal layer 121 in the first conductive layer. It should be noted that when the conductor particles 224 are arranged on the first surface, the first surface can be a non-flat surface or a flat surface.

[0054] In the embodiment of the present invention, when the first surface is a non-flat surface, the first surface can be set as a regular non-flat surface, or as an irregular non-flat surface. Specifically, when the first surface is a regular non-flat surface, the non-flat surface is a periodically undulating structure, and the amplitude of the undulations and the interval of the undulations on the non-flat surface are the same; when the first surface is an irregular non-flat surface, the non-flat surface is a non-periodically undulating structure, and the amplitude of the undulations and the interval of the undulations on the non-flat surface are different.

[0055] In addition, the metal layer 221 in the second conductive layer also includes a second surface arranged opposite to the first surface, and the second surface is in contact with the first insulating protective layer 6; the second surface can be a surface of any shape, for example, a flat surface, or a non-flat surface matching the first surface, or other rough surfaces. The drawings of the present invention only illustrate the second surface as a flat surface, and second surfaces of any other shapes are within the protection scope of the present invention.

[0056] In the embodiment of the present invention, when the first surface is a non-flat surface, the first surface includes a plurality of convex parts and concave parts; when the first convex structure 223 is composed of the first surface and the conductor particles 224, the conductor particles 224 are preferably concentrated on the convex parts, so that the first convex structure 223 is more likely to pierce the first adhesive film layer 21 during the lamination process, thereby ensuring the conduction inside the multilayer board. In addition, the conductor particles 224 can also be distributed at other positions of the first surface, not only on the convex parts, such as Figure 4 Of course, the conductor particles 224 may also be distributed only on the protrusions.

[0057] In a specific implementation, the second conductive layer 22 may be formed first, and then the conductor particles 224 may be formed on the first surface of the metal layer 221 in the second conductive layer by other processes. Of course, the metal layer 221 and the conductor particles 224 in the second conductive layer may also be an integral structure formed by a one-time molding process.

[0058] Based on the above structure, when the first surface is a non-flat surface, during the lamination process, the first adhesive film layer 21 will squeeze the adhesive on the convex part of the first surface into the concave part of the first surface, thereby avoiding the phenomenon of board explosion caused by small amount of adhesive, and further causing the connection failure between the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer; at the same time, the conductor particles 224 with a certain height are formed on the first surface, which can ensure that the first protruding structure 223 can smoothly pierce the first adhesive film layer 21 during the lamination process, and has strong practicality.

[0059] In the embodiment of the present invention, the height of the conductor particles 224 can be set according to actual use conditions; preferably, in the embodiment, the height of the conductor particles 224 is 0.1 μm-30 μm. In addition, the conductor particles 224 can be at a certain distance from the outer surface of the first adhesive film layer 21, or can be in contact with the outer surface of the first adhesive film layer 21 or extend out of the outer surface of the first adhesive film layer 21.

[0060] In an embodiment of the present invention, the conductor particles 224 include one or more of metal particles, carbon nanotube particles and ferrite particles. In addition, the metal particles include single metal particles and / or alloy particles; wherein the single metal particles are made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy particles are made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. It should be noted that the conductor particles 224 may be the same material as the metal layer 221 in the second conductive layer, or may be different.

[0061] In addition, the shape of the conductor particles 224 shown in the figure is only exemplary. Due to differences in process means and parameters, the conductor particles 224 can also be in other shapes such as clusters, hanging ice, stalactites, and dendrites. In addition, the conductor particles 224 in the present invention are not limited to the shapes shown in the figure and above. As long as they are conductor particles with piercing and conductive functions, they are within the protection scope of the present invention.

[0062] In the embodiment of the present invention, in order to ensure that the first protruding structure 223 can pierce the first adhesive film layer 21 and pass through the first through hole 131 to connect with the metal layer 121 in the first conductive layer, the height of the first protruding structure 223 in this embodiment is 0.2μm-30μm. Preferably, the height of the first protruding structure 223 is 0.5μm-5μm. It should be noted that the height of the first protruding structure 223 is the distance D1 between the highest point and the lowest point of the first protruding structure 223, such as Figure 5 shown.

[0063] In addition, in the embodiment of the present invention, the first protruding structure 223 may also be provided on the side of the metal layer 221 in the second conductive layer away from the first adhesive film layer 21 , which will not be further elaborated herein.

[0064] In the embodiment of the present invention, in order to reduce the overall thickness of the circuit board and ensure that the metal layer 221 in the second conductive layer can be connected to the metal layer 121 in the first conductive layer through the first protruding structure 223, the thickness of the second conductive layer 22 in the present embodiment is 0.1 μm-9 μm; preferably, the thickness of the second conductive layer 22 is 0.2 μm-5 μm. In addition, in the present embodiment, the thickness of the first conductive layer 12 is 0.1 μm-9 μm; preferably, the thickness of the first conductive layer 12 is 0.2 μm-5 μm.

[0065] In the embodiment of the present invention, the materials of the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer can be set according to actual use conditions. In order to simplify the design and structure and reduce the cost, in this embodiment, the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer are respectively made of any one or more materials selected from aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0066] In the embodiment of the present invention, it should be noted that the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer in the attached drawings of this embodiment can be a single-layer structure or a multi-layer structure; specifically, one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold can be used as the main body, and then one or more of the metals other than the main body are formed on the surface of the main body by one or more of the methods of electroplating, chemical plating, physical vapor deposition, chemical vapor deposition, etc., thereby forming a multi-layer structure. In this embodiment, the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer are preferably a multilayer structure with copper as the main body, and one or more metals of nickel, chromium, silver, and gold formed on the copper surface. This is because the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer, which are only composed of copper, are easily oxidized or worn, and the nickel, chromium, silver, and gold formed on the copper surface can improve the corrosion resistance and wear resistance of the metal layer 121 in the first conductive layer and the metal layer 221 in the second conductive layer, thereby improving the conductive performance of the multilayer board and extending the service life of the multilayer board. In addition, according to the needs of actual production and application, the first conductive layer 12 and the second conductive layer 22 in the drawings of this embodiment can be set to a grid shape, a foamed shape, etc.

[0067] In the embodiment of the present invention, the first adhesive film layer 21 includes an adhesive layer without conductive particles. By making the first adhesive film layer 21 include an adhesive layer without conductive particles, the first adhesive film layer 21 has a bonding effect, so that the second conductive layer 22 and the first dielectric layer 13 are tightly bonded; in addition, since the first adhesive film layer 21 does not contain conductive particles, a large amount of charge accumulation is effectively avoided, resulting in eddy current loss, thereby reducing the insertion loss of the multilayer board during use, and enabling the multilayer board to withstand a larger current, thereby ensuring that the multilayer board is suitable for the transmission of high-frequency and high-speed signals, and can ensure the integrity of high-frequency signal transmission, and in addition, the bending resistance of the multilayer board can be improved.

[0068] In the embodiment of the present invention, in order to ensure that the first conductive layer 12 and the first dielectric layer 13 can be tightly bonded through the first adhesive film layer 21, while ensuring that the first protruding structure 223 can pierce the first adhesive film layer 21, the thickness of the first adhesive film layer 21 in this embodiment is 1μm-25μm; preferably, the thickness of the first adhesive film layer 21 is 1μm-8μm. In addition, the material used for the first adhesive film layer 21 is selected from the following: modified epoxy resin, acrylic acid, modified rubber, and modified thermoplastic polyimide. In addition, it should be noted that the outer surface of the first adhesive film layer 21 can be a flat surface without undulations, or a non-flat surface with gentle undulations.

[0069] In the embodiment of the present invention, it should be noted that the impedance control layer of the outer layer of the traditional multilayer board generally includes a first adhesive layer, a PI (Polyimide) substrate and a copper substrate; wherein the thickness of the first adhesive layer is 20μm-25μm; the thickness of the PI substrate is 12.5μm-50μm; the thickness of the copper substrate is 9μm-18μm; and the first covering film layer of the outer layer of the traditional multilayer board includes a second adhesive layer and a PI first covering film layer; wherein the thickness of the second adhesive layer is 20μm-25μm; The thickness of the PI first covering film layer is 12.5μm-50μm; the thickness of the second conductive layer 22 in the second circuit substrate 2 of the embodiment of the present invention is 0.1μm-9μm, and the thickness of the first adhesive film layer 21 is 1μm-25μm; therefore, the multilayer board of this embodiment greatly reduces the overall thickness of the multilayer board and enhances the bending resistance of the multilayer board by replacing the impedance control layer and the first covering film layer of the outer layer of the traditional multilayer board with the second circuit substrate 2, thereby realizing an ultra-thin circuit board with high flexibility.

[0070] like Figure 1As shown, in order to protect the multilayer board, the multilayer board in this embodiment further includes a first insulating protective layer 6, and the first insulating protective layer 6 is arranged on a side of the second conductive layer 22 away from the first adhesive film layer 21. By providing the first insulating protective layer 6, a good isolation protection effect is achieved, and the second conductive layer 22 is effectively prevented from contacting with other conductive bodies and causing interference.

[0071] Among them, the thickness of the first insulating protective layer 6 is 1μm-25μm; preferably, the thickness of the first insulating protective layer 6 is 3μm-20μm. In addition, the first insulating protective layer 6 can be set to a PPS film layer, a PEN film layer, a PET film layer, a PI film layer, a PA film layer, a film layer formed after epoxy resin ink is cured, a film layer formed after polyurethane ink is cured, a film layer formed after modified acrylic resin is cured, or a film layer formed after polyimide resin is cured. Of course, the type of the first insulating protective layer 6 can be set according to actual use requirements, and it only needs to ensure that the first insulating protective layer 6 can play an insulating and protective role in the multilayer board, and no further elaboration is made here.

[0072] Embodiment 2

[0073] like Figure 6 As shown, the multilayer board in this embodiment is different from that in the first embodiment in that the number of the second circuit substrates 2 arranged on the side of the first circuit substrate 1 close to the first dielectric layer 13 is multiple; wherein a second dielectric layer 3 is arranged between any two adjacent second circuit substrates 2, and each second dielectric layer 3 is provided with at least one second through hole 31; in any two adjacent second circuit substrates 2, the first protruding structure 223 of the second circuit substrate 2 away from the first circuit substrate 1 pierces the first adhesive film layer 21 and passes through the second through hole 31, thereby connecting with the metal layer 121 in the second conductive layer of the second circuit substrate 1 close to the first circuit substrate 1.

[0074] In the embodiment of the present invention, the number and position of the second through holes 31 provided on the second dielectric layer 3 can be set according to actual use conditions. It can be understood that the second through holes 31 can be provided on the second dielectric layer 3 at positions corresponding to the metal layers 221 in two adjacent second conductive layers that need to be electrically connected, so that the first protruding structure 223 on the metal layer 221 in the second conductive layer far from the first circuit substrate 1 in the metal layers 221 in the two adjacent second conductive layers pierces the first adhesive film layer 21 and passes through the provided second through holes 31, thereby connecting with the metal layer 221 in the corresponding second conductive layer close to the first circuit substrate 1.

[0075] In the embodiment of the present invention, the type of the second dielectric layer 3 can be set according to actual use. Specifically, the second dielectric layer 3 can be set as a single dielectric layer, such as a glue film layer or a resin film layer; the second dielectric layer 3 can also be set as a composite dielectric layer, such as a composite dielectric layer including PI (Polyimide) and a binder.

[0076] It should be noted that Figure 6 The number of the second circuit substrates 2 of the multilayer board shown is 3, which is merely exemplary. The number of the second circuit substrates 2 in this embodiment can be set according to actual use requirements, so other embodiments in which the number of the second circuit substrates 2 is adjusted are also within the protection scope of the present invention. In addition, the other structures and working principles of the multilayer board of this embodiment are the same as those of the first embodiment, and no further description is given here.

[0077] Embodiment 3

[0078] like Figure 7 As shown, the multilayer board in this embodiment is different from embodiments one and two in that the number of the first circuit substrates 1 is multiple, and the multiple first circuit substrates 1 are stacked in sequence; wherein, a first connecting hole 14 is provided on any two adjacent first circuit substrates 1, and a conductive medium 4 for connecting the metal layer 121 of the first conductive layer in the two adjacent first circuit substrates 1 is provided in the first connecting hole 14.

[0079] In the embodiment of the present invention, the conductive medium 4 is attached to the hole wall of the first connection hole 14, thereby forming a conductive hole. The conductive hole formed may be a through hole, a buried hole or a blind hole. Figure 7 Of course, the operator can also choose to fill the entire first connection hole 14 with the conductive medium 4, that is, not to form a conductive hole. The purpose of doing so is to prevent the etching solution from entering the conductive hole and protect the conductive medium 4 in the first connection hole 14 from being etched, thereby ensuring the internal conduction of the multilayer board.

[0080] In the embodiment of the present invention, the number and position of the first connection holes 14 can be set according to actual use. It can be understood that the first connection holes 14 can be set at the positions corresponding to the metal layers 121 in the two adjacent first conductive layers that need to be electrically connected, so that the metal layers 121 in the first conductive layers of the two adjacent first circuit elements 1 can be electrically connected through the conductive medium 4 in the first connection holes 14.

[0081] In the embodiment of the present invention, during the lamination process of the multilayer board, the first dielectric layer 13 flows to the first connecting hole 14 and the first through hole 131 provided on the first dielectric layer 13, so that the first connecting hole 14 and the first through hole 131 are filled with the first dielectric layer 13. Figure 7 As shown; of course, Figure 7 It is merely exemplary, and the first connection hole 14 and the first through hole 131 may be completely filled with the first dielectric layer 13 , or may be partially filled, and the present invention is not limited thereto.

[0082] In addition, it should be noted that Figure 7 The number of the first circuit substrates 1 of the multilayer board shown is 3, which is merely exemplary. The number of the first circuit substrates 1 in this embodiment can be set according to actual use requirements, so other embodiments in which the number of the first circuit substrates 1 is adjusted are also within the protection scope of the present invention. In addition, the other structures and working principles of the multilayer board of this embodiment are the same as those of embodiments 1 and 2, and no further description is given here.

[0083] Embodiment 4

[0084] like Figure 8 As shown, the multilayer board in this embodiment is different from the first and third embodiments in that the multilayer board also includes a third circuit substrate 5, the third circuit substrate 5 includes a third conductive layer 51 and a third dielectric layer 52 which are stacked, the third dielectric layer 52 is arranged on a side of the second conductive layer 22 away from the first adhesive film layer 21, and the third dielectric layer 52 is provided with a second connecting hole 521, and the second connecting hole 521 is provided with a conductive medium 4 connecting the metal layer 511 in the third conductive layer and the metal layer 221 in the second conductive layer.

[0085] In an embodiment of the present invention, the third conductive layer 51 can be set as a circuit layer or a metal layer; when the third conductive layer 51 is a circuit layer, during the lamination process of the multilayer board, the gaps between the metal layers 511 in each third conductive layer in the third conductive layer 51 will be filled with the adjacent first insulating protection layer 6, thereby forming an insulating layer 512 in the third conductive layer; therefore, when the second conductive layer 2 is a circuit layer, the third conductive layer 51 is composed of a plurality of metal layers 511 in the third conductive layers and a plurality of insulating layers 512 in the third conductive layers, and the metal layers 511 in the third conductive layers and the insulating layers 512 in the third conductive layers are staggered and connected, so that the metal layers 511 in each third conductive layer are independent of each other, such as Figure 8The number of the metal layers 511 in the third conductive layer can be set according to actual conditions. Preferably, in this embodiment, there are multiple metal layers 511 in the third conductive layer, and the metal layers 511 in each third conductive layer are independent of each other.

[0086] In the embodiment of the present invention, the thickness of the third conductive layer 51 is 0.1 μm-9 μm; preferably, the thickness of the third conductive layer 51 is 0.2 μm-5 μm. In addition, the material of the metal layer 511 in the third conductive layer can be set according to the actual use. In order to simplify the design and structure and reduce the cost, the metal layer 511 in the third conductive layer in this embodiment is made of any one or more materials selected from aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0087] It should be noted that the metal layer 511 in the third conductive layer of the drawings of this embodiment can be a single-layer structure or a multi-layer structure; specifically, it can be a material selected from aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold as the main body, and then one or more of the metals other than the main body are formed on the surface of the main body by electroplating, chemical plating, physical vapor deposition, chemical vapor deposition, etc., thereby forming a multi-layer structure. In this embodiment, the metal layer 511 in the third conductive layer is preferably a multi-layer structure with copper as the main body and one or more metals selected from nickel, chromium, silver, and gold formed on the copper surface. This is because the metal layer 511 in the third conductive layer composed only of copper is easily oxidized or worn, and the nickel, chromium, silver, and gold formed on the copper surface can improve the corrosion resistance and wear resistance of the metal layer 511 in the third conductive layer, thereby improving the conductive performance of the multilayer board and extending the service life of the multilayer board. In addition, according to the needs of actual production and application, the third conductive layer 51 in the drawings of this embodiment can be set to a grid shape, a foamed shape, etc.

[0088] In the embodiment of the present invention, the conductive medium 4 is attached to the hole wall of the second connection hole 521, thereby forming a conductive hole. Of course, the operator can also choose to fill the entire second connection hole 521 with the conductive medium 4, that is, not forming a conductive hole. The purpose of doing so is to prevent the etching solution from entering the conductive hole, protect the conductive medium 4 in the second connection hole 521 from being etched, thereby ensuring internal conduction of the multilayer board.

[0089] In the embodiment of the present invention, the number and position of the second connection holes 521 provided on the third dielectric layer 52 can be set according to actual use conditions. It can be understood that the second connection holes 521 can be provided at positions corresponding to the metal layer 511 in the third conductive layer and the metal layer 221 in the second conductive layer where electrical connection needs to be achieved, so that the metal layer 511 in the third conductive layer is electrically connected to the corresponding metal layer 221 in the second conductive layer through the conductive medium 4 in the provided second connection holes 521.

[0090] In the embodiment of the present invention, the type of the third dielectric layer 52 can be set according to actual use. Specifically, the third dielectric layer 52 can be set as a single dielectric layer, such as a glue film layer or a resin film layer; the third dielectric layer 52 can also be set as a composite dielectric layer, such as a composite dielectric layer including PI (Polyimide) and a binder.

[0091] like Figure 8 As shown, in order to protect the multilayer board, the multilayer board in this embodiment further includes a first insulating protective layer 6, which is disposed on a side of the third conductive layer 51 away from the third dielectric layer 52. By providing the first insulating protective layer 6, a good isolation protection effect is achieved, and the third conductive layer 51 is effectively prevented from interfering with other conductive bodies. The structure of the first insulating protective layer 6 can refer to the first embodiment, and no further description is given here.

[0092] In addition, it should be noted that the number of the third circuit substrates 5 in this embodiment can be set according to actual use requirements, so other embodiments in which the number of the third circuit substrates 5 is adjusted are also within the protection scope of the present invention. In addition, the other structures and working principles of the multilayer board in this embodiment are the same as those in the first and third embodiments, and no further details are given here.

[0093] Embodiment 5

[0094] Combination Fig. 9 and Fig.10 As shown, the multilayer board in this embodiment is different from embodiments one, two and four in that the first circuit substrate 1 also includes a fourth conductive layer 15 and a fourth dielectric layer 16, and the fourth conductive layer 15 and the fourth dielectric layer 16 are sequentially arranged on the side of the base film layer 11 away from the first conductive layer 12.

[0095] In an embodiment of the present invention, the fourth conductive layer 15 can be set as a circuit layer or a metal layer; when the fourth conductive layer 15 is a circuit layer, during the lamination process of the multilayer board, the gaps between the metal layers 151 in each fourth conductive layer in the fourth conductive layer 15 will be filled by the adjacent fourth dielectric layer 16, thereby forming an insulating layer 152 in the fourth conductive layer; therefore, when the fourth conductive layer 15 is a circuit layer, the fourth conductive layer 15 is composed of a plurality of metal layers 151 in the fourth conductive layers and a plurality of insulating layers 152 in the fourth conductive layers, and the metal layers 151 in the fourth conductive layers and the insulating layers 152 in the fourth conductive layers are staggeredly connected, so that the metal layers 151 in each fourth conductive layer are independent of each other, such as Fig. 9 The number of the metal layers 151 in the fourth conductive layer can be set according to actual conditions. Preferably, there are multiple metal layers 151 in the fourth conductive layer, and the metal layers 151 in each fourth conductive layer are independent of each other.

[0096] In the embodiment of the present invention, the thickness of the fourth conductive layer 15 is 0.1 μm-9 μm; preferably, the thickness of the fourth conductive layer 15 is 0.2 μm-5 μm. In addition, the material of the metal layer 511 in the fourth conductive layer can be set according to the actual use situation. Preferably, the metal layer 511 in the fourth conductive layer in this embodiment is made of any one or more materials selected from aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

[0097] It should be noted that the metal layer 151 in the fourth conductive layer of the drawings of this embodiment can be a single-layer structure or a multi-layer structure; specifically, it can be a material selected from aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold as the main body, and then one or more of the metals other than the main body are formed on the surface of the main body by electroplating, chemical plating, physical vapor deposition, chemical vapor deposition, etc., thereby forming a multi-layer structure. In this embodiment, the metal layer 151 in the fourth conductive layer is preferably a multi-layer structure with copper as the main body and one or more metals selected from nickel, chromium, silver, and gold formed on the copper surface. This is because the metal layer 151 in the fourth conductive layer composed only of copper is easily oxidized or worn, and the nickel, chromium, silver, and gold formed on the copper surface can improve the corrosion resistance and wear resistance of the metal layer 151 in the fourth conductive layer, thereby improving the conductivity of the multilayer board and extending the service life of the multilayer board. In addition, according to the needs of actual production and application, the fourth conductive layer in the drawings of this embodiment can be set to a grid shape, a foamed shape, etc.

[0098] like Fig.10As shown, in a preferred embodiment, a plurality of third connection holes 111 are provided on the base film layer 11 and a conductive medium 4 connecting the metal layer 121 in the first conductive layer and the metal layer 151 in the fourth conductive layer is provided in the third connection holes 111 .

[0099] In the embodiment of the present invention, the conductive medium 4 is attached to the hole wall of the third connection hole 111, thereby forming a conductive hole. Specifically, the third connection hole 111 can be drilled on the base film layer 11 by drilling technology, and then a layer of conductive medium is plated on the insulating hole wall by chemical plating and electroplating methods to form a conductive hole. Of course, the operator can also choose to fill the entire third connection hole 111 with the conductive medium 4, that is, not forming a conductive hole. The purpose of doing so is to prevent the etching solution from entering the conductive hole, protect the conductive medium 4 from being etched, and thus ensure the internal conduction of the multilayer board.

[0100] It should be noted that in the process of forming the conductive holes, when the multilayer board becomes thicker and the hole diameter decreases, it becomes increasingly difficult for the chemical solution to enter the depth of the hole. Although the electroplating equipment can use vibration, pressurization and other methods to allow the chemical solution to enter the center of the hole, the concentration difference still cannot avoid the thin center coating. At this time, the drilling layer will be slightly open. When the voltage is increased or the multilayer board is impacted under various harsh conditions, it is easy to cause the circuit of the multilayer board to be broken and unable to work normally. The multilayer board in this embodiment, because the conductive holes are only set on the base film layer 11, effectively avoids drilling holes on the thicker multilayer board, and thus effectively avoids the problem of circuit breaking of the multilayer board, thereby ensuring the normal operation of the multilayer board.

[0101] In addition, in the embodiment of the present invention, the number of the third connection holes 111 provided on the base film layer 11 can be set according to actual usage. It can be understood that the third connection holes 111 can be provided on the base film layer 11 at positions corresponding to the metal layer 121 in the first conductive layer and the metal layer 151 in the fourth conductive layer that need to be electrically connected, so that the metal layer 121 in the first conductive layer is electrically connected to the metal layer 151 in the fourth conductive layer through the conductive medium 4 in the third connection holes 111.

[0102] In the embodiment of the present invention, the type of the fourth dielectric layer 16 can be set according to actual use conditions. Specifically, the fourth dielectric layer 16 can be set as a single dielectric layer, such as a glue film layer or a resin film layer; the fourth dielectric layer 16 can also be set as a composite dielectric layer, such as a composite dielectric layer including PI (Polyimide) and a binder.

[0103] In addition, in an embodiment of the present invention, the first circuit substrate 1 may further include at least one RCC board, one of the RCC boards being arranged on a surface of the first dielectric layer 13 away from the first conductive layer 12, and / or another of the RCC boards being arranged on a surface of the fourth dielectric layer 16 away from the fourth conductive layer 15.

[0104] Specifically, the RCC board includes a copper layer and a second adhesive film layer stacked, when one of the RCC boards is arranged on the side of the first dielectric layer 13 away from the first conductive layer 12, the second adhesive film layer of the RCC board is arranged on the side of the first dielectric layer 13 away from the first conductive layer 12, and the copper layer is electrically connected to the first conductive layer 12 through a through hole, a blind hole or a buried hole; the second circuit substrate 2 is arranged on the side of the first circuit substrate 1 close to the RCC board, specifically: the first adhesive film layer 21 of the second circuit substrate 2 is arranged on the side of the copper layer away from the second adhesive film layer, the metal layer 221 in the second conductive layer is provided with a first protruding structure 223 on the side facing the first adhesive film layer 21, and the first protruding structure 223 pierces the first adhesive film layer 21, thereby being electrically connected to the copper layer. In addition, when another of the RCC boards is arranged on the side of the fourth dielectric layer 16 away from the fourth conductive layer 15, the second adhesive film layer of the RCC board is arranged on the side of the fourth dielectric layer 16 away from the fourth conductive layer 15. The other structures and working principles of the multilayer board of this embodiment are the same as those of embodiments 1, 2 and 4, and will not be further described here.

[0105] Embodiment 6

[0106] Combination Fig.11 and Fig.12 As shown, the multilayer board in this embodiment is different from the fifth embodiment in that at least one third through hole 161 is provided on the fourth dielectric layer 16 to expose the metal layer 151 in the fourth conductive layer;

[0107] The second circuit substrate 2 is also provided on the side of the first circuit substrate 1 close to the fourth dielectric layer 16, and a plurality of the second circuit substrates 2 are symmetrically arranged on both sides of the first circuit substrate 1 or a plurality of the second circuit substrates 2 are asymmetrically arranged on both sides of the first circuit substrate 1; wherein, the second circuit substrate 2 close to the fourth dielectric layer 16 of the first circuit substrate 1, its second dielectric layer 21 is arranged on the side of the first dielectric layer 16 away from the first conductive layer 12, and its first protruding structure 223 pierces the first adhesive film layer 21 of the second circuit substrate 2, and passes through the third through hole 161 to be connected to the metal layer 151 in the fourth conductive layer.

[0108] It should be noted that the number of the second circuit substrates 2 disposed on one side of the first dielectric layer 13 of the first circuit substrate 1 and the number of the second circuit substrates 2 disposed on one side of the fourth dielectric layer 16 of the first circuit substrate 1 can be set according to actual use requirements. Fig.11 As shown, when the number of the second circuit substrates 2 arranged on one side of the first dielectric layer 13 of the first circuit substrate 1 is equal to the number of the second circuit substrates 2 arranged on one side of the fourth dielectric layer 16 of the first circuit substrate 1, the plurality of second circuit substrates 2 are symmetrically arranged on both sides of the first circuit substrate 1 with the first circuit substrate 1 as the center. It can be understood that in the multilayer board, the first protruding structure 223 of the second circuit substrate 2 close to the first dielectric layer 13 of the first circuit substrate 1 pierces the first adhesive film layer 21 of the second circuit substrate 2 and passes through the first through hole 131 to connect with the metal layer 121 in the first conductive layer; and the first protruding structure 223 of the second circuit substrate 2 close to the fourth dielectric layer 16 of the first circuit substrate 1 pierces the first adhesive film layer 21 of the second circuit substrate 2 and passes through the third through hole 161 to connect with the metal layer 151 in the fourth conductive layer.

[0109] like Fig.12 As shown, when the number of the second circuit substrates 2 arranged on one side of the first dielectric layer 13 of the first circuit substrate 1 is not equal to the number of the second circuit substrates 2 arranged on one side of the fourth dielectric layer 16 of the first circuit substrate 1, a plurality of the second circuit substrates 2 are asymmetrically arranged on both sides of the first circuit substrate 1.

[0110] Among them, when the number of the second circuit substrates 2 arranged on the side of the first circuit substrate 1 close to the first dielectric layer 13 is multiple, and / or when the number of the second circuit substrates 2 arranged on the side of the first circuit substrate 1 close to the fourth dielectric layer 16 is multiple, a second dielectric layer 3 is provided between any two adjacent second circuit substrates 2, and at least one second through hole 31 is opened on each second dielectric layer 3; in any two adjacent second circuit substrates 2, the first protruding structure 223 of the second circuit substrate 2 away from the first circuit substrate 1 pierces the first adhesive film layer 21 and passes through the second through hole 31, thereby connecting with the metal layer 221 in the second conductive layer of the second circuit substrate 2 close to the first circuit substrate 1.

[0111] Combination Fig.11 and Fig.12As shown, in order to protect the multilayer board, the multilayer board in this embodiment further includes a second insulating protective layer 7, and the second insulating protective layer 7 is provided on the outermost second circuit substrate 2 located on one side of the fourth dielectric layer 16 of the first circuit substrate 1; specifically, the second insulating protective layer 7 is provided on the side of the first adhesive film layer 21 of the second circuit substrate 2 away from the second conductive layer 22 of the second circuit substrate 2. By providing the second insulating protective layer 7, a good isolation and protection effect is achieved, which effectively avoids the phenomenon that the second conductive layer 22 of the outermost second circuit substrate 2 located on one side of the fourth dielectric layer 16 of the first circuit substrate 1 contacts with other conductive bodies and causes interference.

[0112] Among them, the thickness of the second insulating protective layer 7 is 1μm-25μm; preferably, the thickness of the second insulating protective layer 9 is 3μm-20μm. In addition, the second insulating protective layer 7 can be set to a PPS film layer, a PEN film layer, a PET film layer, a PI film layer, a PA film layer, a film layer formed after the epoxy resin ink is cured, a film layer formed after the polyurethane ink is cured, a film layer formed after the modified acrylic resin is cured, or a film layer formed after the polyimide resin is cured. Of course, the type of the second insulating protective layer 7 can be set according to the actual use requirements, and it is only necessary to ensure that the second insulating protective layer 7 can play an isolating and protective role in the multilayer board. In addition, the other structures and working principles of the multilayer board of this embodiment are the same as those of Example 5, and no further details are given here.

[0113] Embodiment 7

[0114] like Fig.13 As shown, the multilayer board in this embodiment is different from the embodiment 6 in that a third circuit substrate 5 is further provided on the second circuit substrate 2 located on one side of the fourth dielectric layer 16 of the first circuit substrate 1. Specifically, the third circuit substrate 5 includes a third conductive layer 51 and a third dielectric layer 52 which are stacked, the third dielectric layer 52 being provided on a side of the second conductive layer 22 of the second circuit substrate 2 away from the first adhesive film layer 21 of the second circuit substrate 2, and the third dielectric layer 52 being provided with a second connection hole 521, and the second connection hole 521 being provided with a conductive medium 4 for connecting the metal layer 511 in the third conductive layer with the metal layer 221 in the second conductive layer of the second circuit substrate 2.

[0115] In the embodiment of the present invention, the specific structure of the third circuit substrate 5 can be found in the fourth embodiment, and no further details are given here.

[0116] like Fig.13As shown, when the outermost layer on one side of the fourth dielectric layer 16 of the first circuit substrate 1 is the third circuit substrate 5, in order to protect the multilayer board, the multilayer board in this embodiment further includes a second insulating protective layer 7, and the outermost third circuit substrate 5 on one side of the fourth dielectric layer 16 of the first circuit substrate 1 is provided with the second insulating protective layer 7; specifically, the second insulating protective layer 7 is provided on the side of the third conductive layer 51 of the third circuit substrate 5 away from the third dielectric layer 52 of the third circuit substrate 5. By providing the second insulating protective layer 7, a good isolation protection effect is achieved, which effectively avoids the third conductive layer 51 of the third circuit substrate 5 on the outermost layer on one side of the fourth dielectric layer 16 of the first circuit substrate 1 from contacting with other conductive bodies and causing interference. Among them, the specific structure of the second insulating protective layer 7 can refer to the sixth embodiment, and no further description is given here.

[0117] In addition, it should be noted that the number of the third circuit substrates 5 in this embodiment can be set according to actual use requirements, so other embodiments that adjust the number of the third circuit substrates 5 are also within the protection scope of the present invention. In addition, the other structures and working principles of the multilayer board in this embodiment are the same as those in the sixth embodiment, and no further details are given here.

[0118] Embodiment 8

[0119] like Fig.14 As shown, a schematic diagram of a process for preparing a multilayer board provided by an embodiment of the present invention is shown. The method is suitable for preparing the multilayer board described in the first embodiment above, and comprises the following steps:

[0120] S1. forming a second conductive layer; wherein the second conductive layer comprises a metal layer, and a first protrusion structure is formed on one side of the metal layer in the second conductive layer;

[0121] In an embodiment of the present invention, one of the methods for forming the second conductive layer specifically includes the steps of:

[0122] S11, coating a first insulating protective layer on the release film;

[0123] Specifically, ink is coated on one side of the release film to form a first insulating protective layer;

[0124] Among them, the release film is a PET (Polyethylene terephthalate) release film, and the thickness of the release film is 25μm-150μm, and the width is 100mm-1000mm; the material of the ink is any one of epoxy resin ink, polyurethane ink or polyimide; the thickness of the first insulating protective layer formed is 1μm-25μm, and the preferred thickness is 3μm-20μm.

[0125] S12, forming a second conductive layer on a side of the first insulating protective layer away from the release film;

[0126] Specifically, a second conductive layer is formed on a side of the first insulating protective layer away from the release film by using any one of chemical plating, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), evaporation, sputtering or electroplating or any combination thereof.

[0127] In an embodiment of the present invention, another method of forming the second conductive layer specifically includes the steps of:

[0128] S13, forming a second conductive layer with a carrier and being strippable;

[0129] S14, attaching the second conductive layer with a carrier and being removable to a protective transfer layer, thereby transferring the second conductive layer to the protective transfer layer;

[0130] S15, tearing off the carrier, and forming a first insulating protection layer on the surface of the second conductive layer;

[0131] Specifically, after tearing off the carrier, ink is applied on the side of the second conductive layer away from the protective transfer layer; after the ink is cured, the first insulating protective layer is formed on the side of the second conductive layer away from the protective transfer layer; wherein the material of the ink is any one of epoxy resin ink, polyurethane ink or polyimide; the thickness of the formed first insulating protective layer is 1μm-25μm, and the preferred thickness is 3μm-20μm.

[0132] S16, tearing off the protective transfer layer.

[0133] In an embodiment of the present invention, the first protruding structure on the metal layer in the second conductive layer is specifically formed by roughening the metal layer in the second conductive layer;

[0134] Specifically, one of the ways to roughen the metal layer in the second conductive layer is: using a circuit board micro-etching method to first roughen at least one side of the metal layer in the second conductive layer, then solidify, and finally passivate, thereby forming a first protruding structure on the metal layer in the second conductive layer;

[0135] In addition, another way to roughen the metal layer in the second conductive layer is: using a circuit board micro-etching method to first roughen at least one side of the metal layer in the second conductive layer, and then passivate it, thereby forming a first protruding structure on the metal layer in the second conductive layer; wherein the height of the first protruding structure is 0.2μm-30μm; preferably, the height of the first protruding structure is 0.5μm-5μm.

[0136] S2, forming a first adhesive film layer on a side of the second conductive layer having the first protruding structure formed thereon, thereby obtaining a second circuit substrate;

[0137] Specifically, in one embodiment, a first adhesive film layer is formed on a side of the second conductive layer having the first protruding structure, so as to obtain a second conductive substrate, specifically:

[0138] A first adhesive film layer is coated on the release film, and the first adhesive film layer is transferred by lamination to a side of the second conductive layer where the first protruding structure is formed.

[0139] In another embodiment, a first adhesive film layer is formed on a side of the second conductive layer having the first protruding structure, thereby obtaining a second circuit substrate, specifically:

[0140] A first adhesive film layer is coated on a side of the second conductive layer where the first protrusion structure is formed.

[0141] Specifically, a modified epoxy resin, a modified acrylic resin, a modified rubber or a modified thermoplastic polyimide is coated on the side of the second conductive layer where the first protruding structure is formed, and a drying process is performed, thereby forming the first adhesive film layer on the side of the second conductive layer where the first protruding structure is formed, and then obtaining the second circuit substrate;

[0142] Wherein, the thickness of the formed first adhesive film layer is 1 μm-25 μm; preferably, the thickness of the first adhesive film layer is 1 μm-8 μm.

[0143] S3, forming a first conductive layer, wherein the first conductive layer includes a metal layer;

[0144] The specific method for forming the first conductive layer may refer to the method for forming the second conductive layer, and no further details will be given here.

[0145] S4, forming a first dielectric layer on one side of the first conductive layer, and forming a first through hole on the first dielectric layer to expose the metal layer in the first conductive layer, thereby obtaining a first circuit substrate;

[0146] The number of the first through holes can be set according to actual usage.

[0147] S5. Press the side of the second circuit substrate provided with the first adhesive film layer to the side of the first circuit substrate provided with the first dielectric layer, so that the first protruding structure pierces the first adhesive film layer and passes through the first through hole to connect with the metal layer in the first conductive layer.

[0148] Specifically, a heat pressing method is adopted to press the side of the second circuit substrate provided with the first adhesive film layer onto the side of the first circuit substrate provided with the first dielectric layer.

[0149] In addition, it should be noted that the method for preparing the circuit board provided in this embodiment is only an example of preparing the multilayer board described in the first embodiment. The multilayer board described in the first embodiment can also be made by other preparation methods, for example, the first circuit substrate can be formed first, and then the second circuit substrate can be formed, and finally pressed together. In addition, the preparation methods of the multilayer boards described in the second to seventh embodiments can be specifically referred to the preparation methods of the circuit board provided in this embodiment, and no further description will be given here.

[0150] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A multilayer board, characterized in that: including a first circuit substrate and a second circuit substrate; The first circuit substrate comprises a base film layer, a first conductive layer and a first dielectric layer, wherein the first conductive layer and the first dielectric layer are sequentially arranged on one side of the base film layer, and the first dielectric layer is provided with at least one first through hole for exposing the metal layer in the first conductive layer; A second circuit substrate is provided on a side of the first circuit substrate close to the first dielectric layer; the second circuit substrate includes a first adhesive film layer and a second conductive layer which are stacked, the first adhesive film layer being provided on a side of the first dielectric layer away from the first conductive layer; a first protruding structure is provided on a side of the metal layer in the second conductive layer facing the first adhesive film layer, the first protruding structure pierces the first adhesive film layer, and passes through the first through hole to be connected to the metal layer in the first conductive layer.

2. The multilayer board according to claim 1, characterized in that There are multiple second circuit substrates arranged on the side of the first circuit substrate close to the first dielectric layer; wherein a second dielectric layer is arranged between any two adjacent second circuit substrates, and at least one second through hole is opened on each second dielectric layer; in any two adjacent second circuit substrates, the first protruding structure of the second circuit substrate away from the first circuit substrate pierces the first adhesive film layer and passes through the second through hole, thereby connecting with the metal layer in the second conductive layer of the second circuit substrate close to the first circuit substrate.

3. The multilayer board according to claim 1, characterized in that There are multiple first circuit substrates, and the multiple first circuit substrates are stacked in sequence; wherein, any two adjacent first circuit substrates are provided with a first connecting hole, and the first connecting hole is provided with a conductive medium for connecting the metal layer of the first conductive layer in the two adjacent first circuit substrates.

4. The multilayer board according to claim 1, characterized in that The multilayer board also includes a third circuit substrate, which includes a third conductive layer and a third dielectric layer stacked in layers, wherein the third dielectric layer is disposed on a side of the second conductive layer away from the first adhesive film layer, and a second connecting hole is disposed on the third dielectric layer, wherein a conductive medium connecting the metal layer in the third conductive layer and the metal layer in the second conductive layer is disposed in the second connecting hole.

5. The multilayer board according to any one of claims 1 to 4, characterized in that: The first circuit substrate further includes a fourth conductive layer and a fourth dielectric layer, and the fourth conductive layer and the fourth dielectric layer are sequentially arranged on the other surface of the base film layer.

6. The multilayer board according to claim 5, characterized in that The fourth dielectric layer is provided with at least one third through hole for exposing the metal layer in the fourth conductive layer; The second circuit substrate is also provided on the side of the first circuit substrate close to the fourth dielectric layer, and a plurality of the second circuit substrates are symmetrically arranged on both sides of the first circuit substrate or a plurality of the second circuit substrates are asymmetrically arranged on both sides of the first circuit substrate; wherein the first protruding structure of the second circuit substrate close to the fourth dielectric layer pierces the first adhesive film layer of the second circuit substrate and passes through the third through hole to be connected to the metal layer in the fourth conductive layer.

7. The multilayer board according to claim 6, characterized in that There are multiple second circuit substrates arranged on the side of the first circuit substrate close to the fourth dielectric layer; wherein a second dielectric layer is arranged between any two adjacent second circuit substrates, and at least one second through hole is opened on each second dielectric layer; in any two adjacent second circuit substrates, the first protruding structure of the second circuit substrate away from the first circuit substrate pierces the first adhesive film layer and passes through the second through hole, thereby connecting with the metal layer in the second conductive layer of the second circuit substrate close to the first circuit substrate.

8. The multilayer board according to claim 5, characterized in that The base film layer is provided with a plurality of third connection holes which are arranged at intervals, and a conductive medium which connects the metal layer in the first conductive layer and the metal layer in the fourth conductive layer is provided in the third connection holes.

9. The multilayer board according to any one of claims 1 to 4, characterized in that: The metal layer in the second conductive layer includes a first surface, the first surface is a non-flat surface, and the first surface constitutes the first protruding structure; or, The metal layer in the second conductive layer includes a first surface, on which conductor particles are arranged, and the first surface and the conductor particles constitute the first protruding structure.

10. The multilayer board according to claim 9, characterized in that The height of the first protrusion structure is 0.2 μm-30 μm.

11. The multilayer board according to any one of claims 1 to 4, characterized in that: The first adhesive film layer includes an adhesive layer without conductive particles.

12. The multilayer board according to claim 8, characterized in that The metal layer in the first conductive layer, the metal layer in the second conductive layer and the metal layer in the fourth conductive layer are respectively made of any one or more materials selected from the group consisting of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold.

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