Circuit board

Abstract

The utility model discloses a circuit board, which relates to the technical field of printed circuit boards and comprises a substrate, a first circuit layer, a second circuit layer and a conductive connecting part. The base material comprises a first surface and a second surface which are oppositely arranged, and one or more connecting holes for communicating the first surface with the second surface; the first circuit layer is arranged on the first surface; the second circuit layer is arranged on the second surface; and the conductive connecting part is arranged in the connecting hole and is electrically connected with the first circuit layer and the second circuit layer, and the conductive connecting part and the second circuit layer are integrally formed. Since the conductive slurry and the second circuit layer are integrated, the resistance at the joint of the conductive slurry and the first circuit layer is small, the connection is more reliable, the electrical performance is better, and the bending resistance of the manufactured circuit board is better.

Description

Technical Field

[0001] The utility model relates to the technical field of printed circuit boards, in particular to a circuit board. Background Art

[0002] Currently, printed circuit boards (PCBs) are mostly manufactured using a copper-clad laminate substrate and chemical etching. After years of development, this technology has become highly mature and boasts high production yields. However, it still suffers from complex processes and environmental pollution.

[0003] Traditional chemical etching is a subtractive process, meaning the raw material is a complete copper-clad laminate. A chemical solution is used to etch away the unwanted portions, leaving only the desired circuitry. This inevitably results in a cumbersome process. Furthermore, as the chemical solution etches away the unwanted copper foil, a large amount of wastewater is generated that requires treatment, creating pressure on environmental regulations and potentially causing environmental pollution.

[0004] Based on the above problems and driven by industry demand, conductive paste printed circuit boards were born. The production principle is to use conductive paste to directly print the required circuits on a blank substrate. This is what the industry calls the incremental method.

[0005] A process for printing double-layer circuit boards with conductive paste is as follows: Figure 11 First, the circuit layer 90 is printed on both surfaces of the substrate 9, and then a hole 91 is punched on the substrate. After that, the conductive silver paste 92 is poured into the hole 91. The circuit layers 90 on both surfaces of the substrate 9 are electrically connected through the conductive silver paste 92. In order to achieve reliable contact between the circuit layer 90 and the conductive silver paste 92, the two end portions 920 of the conductive silver paste 92 need to cover the top of the circuit layer near the hole 91 to form a raised structure. If the upper surface of the conductive silver paste 92 is set to be flush with the nearby circuit layer 90, then the contact area between the conductive silver paste 92 and the circuit layer is the contact area between the peripheral side wall of the conductive silver paste 92 and the inner side wall of the hole of the circuit 90. Since the thickness of the circuit layer is very thin, the contact surface between the circuit layer 90 and the conductive silver paste 92 is particularly small, which can easily lead to poor contact and increase resistance, affecting reliability of use.

[0006] The above content is only used to help understand the technical solution of this application and does not constitute an admission that the above is prior art. Utility Model Content

[0007] The purpose of the utility model is to provide a circuit board with better electrical performance.

[0008] To achieve the above-mentioned purpose of the utility model, the utility model proposes a circuit board, comprising:

[0009] A substrate comprising a first surface and a second surface disposed opposite to each other and a connecting hole connecting the first surface and the second surface;

[0010] A first circuit layer is provided on the first surface;

[0011] A second circuit layer is provided on the second surface; and

[0012] The conductive connecting portion is disposed in the connecting hole and is electrically connected to the first circuit layer and the second circuit layer. The conductive connecting portion and the second circuit layer are integrally formed.

[0013] Furthermore, the conductive connection portion and the first circuit layer are provided separately, and an end portion of the conductive connection portion contacts a surface of the first circuit layer exposed in the connection hole.

[0014] Furthermore, the total area of the contact regions between the first circuit layer and all the conductive connection portions is greater than or equal to 0.126 square millimeters.

[0015] Furthermore, a portion of the circuit board corresponding to the conductive connecting portion does not have a protruding structure.

[0016] Furthermore, the thickness of the substrate is less than or equal to 80 micrometers, and the thickness of the second circuit layer is 1 to 25 micrometers.

[0017] Furthermore, the cross section of the connecting hole is circular, polygonal, pentagonal or petal-shaped, the corners of the pentagonal star are arc-shaped, and the petal-shaped includes three to six arc-shaped parts.

[0018] Furthermore, the cross section of the connecting hole is circular, and the diameter of the narrowest part thereof ranges from 0.02 to 1 mm.

[0019] Furthermore, the diameter of the narrowest part of the connecting hole ranges from 0.05 to 0.5 mm.

[0020] Furthermore, the connection hole is in a column shape connecting the first surface and the second surface; or,

[0021] The connecting hole is tapered and connects the first surface and the second surface; or

[0022] The connection hole includes a columnar portion communicating with the first surface and a tapered portion connected between the second surface and the columnar portion.

[0023] Furthermore, the first circuit layer, the second circuit layer and the conductive connection portion are made of silver, copper, tin or carbon.

[0024] Compared with the prior art, the present invention has the following beneficial effects: in the circuit board provided by the present invention, since the conductive paste and the second circuit layer are integrated, the resistance at the connection between the conductive paste and the first circuit layer is small, the electrical performance is better, the connection between the conductive paste and the second circuit layer is more reliable, and the circuit board has better anti-bending performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the manufacturing method of the circuit board in the utility model.

[0026] Figure 2 It is a cross-sectional schematic diagram when the first circuit layer is provided on the first surface of the first substrate in the present invention.

[0027] Figure 3a yes Figure 2 The schematic diagram shown is when a single connection hole is opened on the circuit board.

[0028] Figure 3b yes Figure 3a The schematic diagram of the circuit board shown is when the second circuit layer is set.

[0029] Figure 4a yes Figure 2 The schematic diagram shown is a circuit board with multiple connection holes.

[0030] Figure 4b yes Figure 4a The schematic diagram of the circuit board shown is when the second circuit layer is set.

[0031] Figure 5 This is a schematic diagram of an embodiment of the present invention in which the cross section of the connecting hole is in the shape of a five-pointed star.

[0032] Figure 6 This is a schematic diagram of an embodiment of the present invention in which the cross section of the connecting hole is petal-shaped.

[0033] Figure 7 This is a cross-sectional view of a circuit board in an embodiment of the present invention when the second circuit layer is not connected. In the figure, the connection hole is in the shape of a cone hole.

[0034] Figure 8 This is a cross-sectional view of a circuit board in an embodiment of the present invention when the second circuit layer is not connected. In the figure, the connection hole includes a tapered portion and a columnar portion.

[0035] Figure 9 This is a schematic diagram of laminating a second substrate with a first circuit layer to a first substrate according to an embodiment of the present invention.

[0036] Figure 10aThis is a structural schematic diagram of a circuit board in an embodiment of the present invention. In the figure, the circuit board includes a second substrate, and the local connection structure includes a single conductive connection part.

[0037] Figure 10b This is a structural schematic diagram of a circuit board in an embodiment of the present invention. In the figure, the circuit board includes a second substrate, and the local connection structure includes a plurality of conductive connection parts.

[0038] Figure 11 It is a structural diagram of the circuit board described in the background technology part of this utility model. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the accompanying drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0040] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0041] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0042] like Figures 1 to 4b As shown, the utility model proposes a method for manufacturing a circuit board, comprising the following steps:

[0043] S1. Provide a first substrate 1 , wherein the first substrate 1 includes a first surface 101 and a second surface 102 that are opposite to each other.

[0044] The material of the first substrate 1 can be, for example, a pi film first substrate. The required material thickness of the first substrate 1 can be comprehensively selected based on the product thickness and cost requirements.

[0045] S2. References Figure 2 , forming a first circuit layer 2 on the first surface 101 of the first substrate 1 .

[0046] The method for forming the first circuit layer 2 is not limited. For example, the first circuit layer 2 can be formed by an incremental method in the prior art.

[0047] S3. References Figure 3a and Figure 4a One or more connection holes 103 are opened on the second surface 102 of the first substrate 1. For example, one, two or more connection holes 103 can be opened. The first circuit layer 2 is partially exposed in the connection holes 103, and the connection holes 103 do not penetrate the first circuit layer 2. That is, the connection holes 103 are in the shape of blind holes, which penetrate the first substrate 1 but do not penetrate the connection holes 103.

[0048] S4. References Figure 3b and Figure 4b , a conductive paste is used to form a second circuit on the second surface 102 , and part of the conductive paste fills the connection hole 103 and connects it to the first circuit layer 2 .

[0049] The conductive paste can be, for example, silver paste or copper paste, and of course other conductive pastes (such as tin paste and carbon paste with conductive functions, etc.) can also be used. It can be understood that since the conductive paste is liquid and fluid when it is not solidified, it can automatically fill into the connecting hole 103 and contact the first circuit layer 2 to achieve electrical conduction with the first circuit layer 2.

[0050] S5. The conductive paste on the second surface 102 is cured to solidify the second circuit to form a second circuit layer 4. The conductive paste in the connection hole 103 is solidified to form a conductive connection portion 3. The first circuit layer 2 and the second circuit layer 4 are electrically connected via the conductive connection portion 3, thereby realizing the circuit layer manufacturing on both sides of the first substrate 1.

[0051] The curing method varies depending on the conductive paste material, and for example, heat curing or UV curing may be used.

[0052] It is understood that the conductive connection portion 3 and the second circuit layer 4 are integrally formed, and the bulk resistance between them is much smaller than the contact resistance between the conductive paste and the circuit layer in the preparation method described in the background technology section (typically, the bulk resistance is one order of magnitude smaller than the contact resistance). In addition, the contact area between the conductive connection portion 3 and the first circuit layer 2 depends on the cross-sectional area of the conductive connection portion 3 (or the connection hole 103). Therefore, the contact area between the two is larger than the contact area of the sidewall contact structure, making the connection more secure, the resistance lower, and the overall electrical performance and reliability better. At the same time, the end of the conductive connection portion 3 does not need to protrude from the circuit layer, and the surface of the circuit layer can be made flat. That is, the portion of the circuit board corresponding to the conductive connection portion 3 does not have an external protrusion, which makes it easier to assemble and solder electronic components on the circuit board. Furthermore, due to the large contact and connection area between the conductive connection portion 3 and the first circuit layer 2, the resulting circuit board also has better bending performance and is less likely to have poor contact due to bending.

[0053] It will be appreciated that this article uses a single local connection structure between first circuit layer 2 and second circuit layer 4 as an example. At this local connection, one or more connection holes 103 may be provided, thereby forming one or more conductive connection portions 3 connecting first circuit layer 2 and second circuit layer 4. In other words, the local connection structure includes one or more connection holes 103 and conductive connection portions 3 formed within connection holes 103. Multiple similar local connection structures may be present throughout the entire circuit board, and their number and location may be determined based on the desired circuit structure.

[0054] Figure 3a shows a schematic structural diagram of a local connection structure including a single connection hole 103, Figure 3b It shows a structural schematic diagram when the conductive connection part 3 is formed in a single connection hole 103. Figure 4a shows a schematic structural diagram when the local connection structure includes multiple connection holes 103, Figure 4b It shows a structural schematic diagram when the conductive connection parts 3 are formed in the plurality of connection holes 103 .

[0055] In the above-described preparation method, the second circuit layer 4 is produced using a conductive paste. This differs from conventional etching methods in that it eliminates the need to corrode the copper layer, thus minimizing environmental impact and preventing copper waste, thereby reducing production costs. Furthermore, this method enables incremental production of circuit boards, significantly expanding the application scope of incremental production. It can also effectively replace some applications of circuit boards produced using conventional etching methods, significantly contributing to environmental protection.

[0056] In step S3, second surface 102 is an unprinted circuit layer, and connection holes 103 are drilled from the unprinted circuit layer of first substrate 1 toward the printed circuit layer. However, the depth of the holes must be controlled to extend to the first circuit layer 2, i.e., they are blind holes relative to the entire circuit board. Optionally, the depth of connection holes 103 is the same as the thickness of first substrate 1 to avoid damaging first circuit layer 2. Connection holes 103 can be drilled by mechanical drilling or laser drilling, or other blind hole drilling methods.

[0057] As a feasible embodiment, when forming the second circuit in step S4, a conductive paste is printed onto the second surface 102 using a printer in conjunction with a stencil. The stencil has a hollow structure in the area corresponding to the second circuit. In this way, the conductive paste is printed from the hollow area onto the second surface 102 in the same shape as the second circuit, forming the second circuit. The printer can be an automatic or semi-automatic printer to improve printing efficiency. The stencil used includes, but is not limited to, steel mesh, nylon mesh, or stencils made of other materials. The stencil is selected based on the required circuit precision. Generally, a stencil with a higher mesh count, made of the same material, will achieve higher printing precision.

[0058] The cross-sectional shape of the connection hole 103 is not limited, and can be, for example, circular, polygonal, star-shaped or petal-shaped, etc. Figure 5 The five-pointed star connecting hole 103 has five corners 1033, referring to Figure 6 The petal-shaped connection hole 103 includes at least three arcuate portions 1034 to facilitate the full filling of the conductive paste into the connection hole 103. Non-circular connection holes 103 increase the contact area between the conductive paste and the hole wall, enhancing the connection strength and further improving the circuit board's bending performance. For ease of processing, the connection hole 103 can be circular. Unless otherwise specified, the cross-section of the connection hole 103 is circular.

[0059] As a preferred embodiment, Figure 3a 、 Figure 7 and Figure 8 As shown, the diameter D of a single connection hole 103 at its narrowest point ranges from 0.02 to 1 mm. Preferably, the diameter D of the connection hole 103 at its narrowest point ranges from 0.05 to 0.5 mm, which can facilitate efficient filling of the conductive paste in the connection hole 103, reduce gaps, and reduce the risk of poor filling. At the same time, the diameter of the connection hole 103 is not too large, which is conducive to saving materials.

[0060] Optionally, the thickness of the first substrate 1 is 80 μm or less, and the thickness of the second circuit layer 4 is 1 to 25 μm, further optionally 5 to 15 μm, for example, 8 μm. It is understood that the thickness of the circuit layer is substantially consistent with the thickness of the conductive paste during printing. Taking an 8-μm conductive paste as an example, if the thickness of the first substrate 1 is greater than 100 μm, it will be very difficult for an 8-μm thick silver paste to be poured through the connection holes 103. When the thickness of the first substrate 1 is between 80 μm and 100 μm, while an 8-μm thick silver paste can be poured into the connection holes 103 and contact the first circuit layer 2, the conductive effect will be poor, potentially leading to conductivity issues. A thickness of 80 μm or less for the first substrate 1 is more conducive to ensuring conductive quality. Furthermore, the thickness of the first substrate 1 can range from 10 to 80 μm, further optionally 20 to 50 μm, for example, 20 μm, 25 μm, 35 μm, 40 μm, 45 μm, and 50 μm.

[0061] Optionally, the first circuit layer 2 and the second circuit layer 4 have the same thickness.

[0062] In some embodiments, as Figure 3a As shown, the connection hole 103 is in a column shape connecting the first surface 101 and the second surface 102, which facilitates the opening of the connection hole 103; in other embodiments, such as Figure 7 As shown, the connection hole 103 is in a cone shape connecting the first surface 101 and the second surface 102, which is conducive to guiding the conductive paste to fill into the connection hole 103 and improve the filling effect; in other embodiments, such as Figure 8 As shown, the connection hole 103 includes a columnar portion communicating with the first surface 101 and a tapered portion 1032 connected between the second surface 102 and the columnar portion 1031. It is understood that the shape of the conductive connection portion 3 corresponds to the shape of the connection hole 103.

[0063] Optionally, the contact area between all conductive connection portions 3 and the first circuit layer 2 is greater than or equal to 0.126 square millimeters, ensuring sufficient contact area between the conductive connection portions 3 and the first circuit layer 2 to ensure connection and conduction. In some embodiments, the local connection structure includes only a single connection hole 103 and a conductive connection portion 3, and the diameter of the portion of the connection hole 103 near the first circuit layer 2 can be set to greater than or equal to 0.2 mm. In other embodiments, the local connection structure includes multiple connection holes 103 and conductive connection portions 3, and the total area of the portions of the multiple connection holes 103 near the first circuit layer 2 is greater than or equal to 0.126 square millimeters.

[0064] As described above, the first circuit layer 2 can be formed in any manner, and both the incremental method and the subtractive method in the prior art can form the first circuit layer 2. In some embodiments, step S2 includes the following steps:

[0065] S20. Forming a first circuit on the first surface 101 using a conductive paste;

[0066] S21 . Curing the conductive paste to cure the first circuit to form a first circuit layer 2 .

[0067] In step S20 , the first circuit can also be prepared by printing the conductive paste onto the first surface 101 using a printer in conjunction with a stencil. The stencil is provided with a hollow structure in the area corresponding to the second circuit to form the first circuit.

[0068] In other embodiments, reference Figure 9 , step S2 includes the following steps:

[0069] S20. Provide a second substrate 5, wherein a first circuit layer 2 is provided on the surface of the second substrate 5; in this step, the first circuit layer 2 on the surface of the second substrate 5 can be self-provided, for example, the second substrate 5 with the first circuit layer 2 can be directly purchased, or the first circuit layer 2 can be molded on the second substrate 5, and the molding method can refer to the method of molding the first circuit layer 2 on the first substrate 1.

[0070] S21. Connect the second substrate 5 to the first substrate 1 so that the first circuit layer 2 is attached to the first surface 101 of the first substrate 1. For example, the first substrate 1 and the second substrate 5 can be bonded face to face. In this way, the first surface 101 of the first circuit layer 2 can be formed into the first circuit layer 2. Subsequently, steps S3, S4 and S5 can be performed to form the following: Figure 10a or Figure 10b The circuit board shown.

[0071] The step S3 of opening a connection hole on the second surface of the first substrate includes the following steps:

[0072] S30. A hole is punched by a drilling device, the depth of the hole being equal to the thickness of the first substrate 1;

[0073] S31 . Start the drilling device to perform a drilling process on the first substrate 1 to form the connection hole 103 , and the waste generated during the drilling process is automatically absorbed by the drilling device.

[0074] The drilling equipment can be mechanical or laser, primarily suitable for drilling primary substrates like PI and PET. It requires minimal power and won't penetrate metal. Simply enter the desired drilling depth into the drilling system, and it also features a built-in negative pressure chip suction feature. The drilling surface is porous and negatively pressurized, automatically absorbing any debris generated during drilling, achieving a self-cleaning effect.

[0075] The conductive paste of the printed circuit layer can be silver paste or copper paste, and of course other conductive pastes (such as tin paste and carbon paste with conductive functions) can also be used. It is understood that the materials of the first circuit layer 2, the second circuit layer 4 and the conductive connection part 3 are the same as the material of the conductive paste used.

[0076] Optionally, the temperature during the curing treatment of the conductive paste is 100 to 260°C, and the time is 3 to 90 minutes, so that the conductive paste can be reliably cured. In some embodiments, when the conductive paste is silver paste, the temperature during the curing treatment is 185 to 195°C, and the time is 25 to 35 minutes, for example, the temperature is 190°C, the time is 30 minutes, or the temperature is 185°C, the time is 35 minutes, or the temperature is 195°C, the time is 25 minutes; in other embodiments, when the conductive paste is copper paste, the temperature during the curing treatment is 195 to 205°C, and the time is 5 to 15 minutes, for example, the temperature is 200°C, the time is 10 minutes, or the temperature is 195°C, the time is 15 minutes, or the temperature is 205°C, the time is 5 minutes. By setting the appropriate temperature and baking time, the conductive paste on the surface of the first substrate and the conductive paste in the connection hole 103 can be reliably cured, thereby improving the reliability of the circuit board. The curing process is usually based on the curing conditions of the conductive material used. The printed circuit is baked at a specific temperature and time. Its purpose is to cure the conductive paste used for circuit printing. The baking equipment can use conventional baking equipment such as an oven or IR oven.

[0077] The manufacturing method of the circuit board also includes the back-end process. The back-end process of the printed circuit board of this scheme is the same as that of the circuit board made by the traditional method, including but not limited to solder mask, text printing and electrical testing, etc.

[0078] like Figure 3b and Figure 4b As shown, the present invention further proposes a circuit board, which includes: a first substrate 1, a first circuit layer 2, a second circuit layer 4 and a conductive connecting portion 3.

[0079] The first substrate 1 includes a first surface 101 and a second surface 102 opposite to each other and one or more connecting holes 103 connecting the first surface 101 and the second surface 102 .

[0080] The first circuit layer 2 is disposed on the first surface 101 .

[0081] The second circuit layer 4 is disposed on the second surface 102 .

[0082] The conductive connection portion 3 is disposed in the connection hole 103 and is electrically connected to the first circuit layer 2 and the second circuit layer 4 , so that electrical signals can be transmitted between the first circuit layer 2 and the second circuit layer 4 .

[0083] The circuit board can be prepared by the above-mentioned circuit board manufacturing method, and of course can also be prepared by other methods.

[0084] It can be understood that the second circuit layer 4 and the conductive connection part 3 of the circuit board are integrally formed.

[0085] Furthermore, the conductive connection portion 3 is provided separately from the first circuit layer 2 , and the end portion 30 of the conductive connection portion 3 is in contact with the surface of the first circuit layer 2 exposed in the connection hole 103 .

[0086] In some embodiments, the area of the contact region between the first circuit layer 2 and all the conductive connection portions 3 is greater than or equal to 0.126 square millimeters.

[0087] In some embodiments, the portion of the prepared circuit board corresponding to the conductive connecting portion 3 does not have a protruding structure.

[0088] In some embodiments, reference Figure 3b and Figure 4b The thickness D1 of the first substrate 1 is less than or equal to 50 micrometers, and the thickness D2 of the second circuit layer 4 is 1 to 25 micrometers, and can further be 5 to 25 micrometers.

[0089] In some embodiments, the cross section of the connection hole 103 is circular, polygonal, pentagonal or petal-shaped. Figure 6 When the connecting hole 103 is in a petal shape, the petal shape includes three to six arc-shaped parts.

[0090] In some embodiments, as Figure 3a 、 Figure 7 and Figure 8 As shown, the cross section of the connecting hole 103 is circular, and the diameter D at the narrowest point thereof ranges from 0.02 to 1 mm, and can further be selected to be 0.05 to 0.5 mm.

[0091] In some embodiments, as Figure 3a As shown, the connection hole 103 is in a column shape connecting the first surface 101 and the second surface 102, which facilitates the opening of the connection hole 103; in other embodiments, such as Figure 5 As shown, the connection hole 103 is in a cone shape connecting the first surface 101 and the second surface 102, which is conducive to guiding the conductive paste to fill into the connection hole 103 and improve the filling effect; in other embodiments, such as Figure 6 As shown, the connection hole 103 includes a columnar portion communicating with the first surface 101 and a tapered portion 1032 connected between the second surface 102 and the columnar portion 1031. It is understood that the shape of the conductive connection portion 3 corresponds to the shape of the connection hole 103.

[0092] In some embodiments, the materials of the first circuit layer 2 , the second circuit layer 4 and the conductive connection portion 3 are silver, copper, tin or carbon.

[0093] In some embodiments, reference Figure 10a and Figure 10b The circuit board further includes a second substrate 5 connected to the first substrate 1 , and the first circuit layer 2 is located between the first substrate 1 and the second substrate 5 .

[0094] The above is only a specific implementation of the present invention, and any other improvements made based on the concept of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A circuit board, characterized in that: include: A first substrate comprising a first surface and a second surface opposite to each other and one or more connecting holes connecting the first surface and the second surface; A first circuit layer is provided on the first surface; A second circuit layer is provided on the second surface; and The conductive connecting portion is disposed in the connecting hole and is electrically connected to the first circuit layer and the second circuit layer. The conductive connecting portion and the second circuit layer are integrally formed.

2. The circuit board according to claim 1, wherein: The conductive connection portion is provided separately from the first circuit layer, and an end portion of the conductive connection portion contacts a surface of the first circuit layer exposed in the connection hole.

3. The circuit board according to claim 2, wherein: The total area of the contact regions between the first circuit layer and all the conductive connection portions is greater than or equal to 0.126 square millimeters.

4. The circuit board according to claim 1, wherein: The portion of the circuit board corresponding to the conductive connection portion does not have a protruding structure.

5. The circuit board according to claim 1, wherein: The thickness of the first substrate is less than or equal to 80 micrometers, and the thickness of the second circuit layer is 1 to 25 micrometers.

6. The circuit board according to any one of claims 1 to 5, characterized in that: The cross section of the connecting hole is circular, polygonal, star-shaped or petal-shaped, and the petal-shaped portion includes at least three arc-shaped portions.

7. The circuit board according to any one of claims 1 to 5, characterized in that: The cross section of the connecting hole is circular, and the diameter of the narrowest part thereof ranges from 0.02 to 1 mm.

8. The circuit board according to claim 7, wherein: The diameter of the narrowest part of the connecting hole ranges from 0.05 to 0.5 mm.

9. The circuit board according to any one of claims 1 to 5, characterized in that: The connection hole is in a column shape connecting the first surface and the second surface; or, The connecting hole is in a tapered shape connecting the first surface and the second surface; or The connection hole includes a columnar portion communicating with the first surface and a tapered portion connected between the second surface and the columnar portion.

10. The circuit board according to any one of claims 1 to 5, characterized in that: The first circuit layer, the second circuit layer and the conductive connection portion are made of silver, copper, tin or carbon.

11. The circuit board according to any one of claims 1 to 5, characterized in that: It also includes a second substrate connected to the first substrate, and the second circuit layer is located between the first substrate and the second substrate.

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