A pure copper circuit board and a method for manufacturing the same

Abstract

The application discloses a pure copper circuit board and a preparation method thereof, and belongs to the technical field of circuit board manufacturing. The preparation method comprises the following steps: attaching photoresist on the front and back surfaces of a pure copper foil respectively; exposing the first surface of the pure copper foil with the target pattern, and blank exposing the second surface opposite to the first surface; and sequentially developing, etching and removing the film of the exposed pure copper foil to obtain the pure copper circuit board with the target pattern. The photoresist is arranged on the front and back surfaces of the pure copper foil, and a layer of photoresist is attached to the bottom layer, so that the pure copper foil can be supported. During exposure, the photoresist on the front surface is exposed with the target pattern, and the photoresist on the back surface is blank exposed, so that the photoresist on the back surface used for supporting in the subsequent process is not etched, and the pure copper foil is effectively supported. Since the front and back surfaces are both made of photoresist material, the photoresist on the front and back surfaces can be removed at the same time, the preparation efficiency is improved, and the problem that the product is not flat and curled after the supporting film is debonded and formed does not exist.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing technology, and in particular to a pure copper circuit board and its preparation method. Background Technology

[0002] In the field of circuit board fabrication, there are scenarios where it is necessary to fabricate microvias with a diameter of 50μm on a 12μm thick pure copper foil. The main fabrication processes for such ultrathin pure copper FPCs (Flexible Printed Circuits) include laser ablation and substrate etching.

[0003] Laser hole-forming process: A laser is used to cut 50μm diameter micro-holes in a 12μm thick pure copper foil substrate. Advantages: Non-contact hole forming, simple process, smooth and non-curling product after forming, excellent hole shape consistency. Disadvantages: Residual carbon black from laser burning remains at the hole opening and on the hole wall; the product is too thin, making it impossible to remove carbon black from the hole wall and surface; carbon black contamination after product assembly at the customer end; low laser processing efficiency.

[0004] Carrier film etching process: A 12μm thick pure copper foil substrate is bonded to a carrier film to increase support and complete the circuit fabrication. The main process includes: single-sided carrier film bonding—single-sided photoresist bonding—single-sided exposure—development—etching—film removal—carrier film unbonding. Advantages: Good hole pattern consistency in mass production, no carbon black residue at the hole openings. Disadvantages: After carrier film unbonding and molding, the product is uneven and curled, making customer assembly difficult. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a pure copper circuit board and a method for preparing the same, so as to avoid the problems of contamination during the preparation process and the difficulties of subsequent assembly.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a pure copper circuit board, comprising:

[0008] Photoresist is applied to both sides of the pure copper foil.

[0009] The first side of the bonded pure copper foil is exposed with a target pattern, while the second side opposite the first side is exposed blank.

[0010] The exposed material is then sequentially developed, etched, and stripped to obtain a pure copper circuit board with the target pattern.

[0011] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is as follows:

[0012] A pure copper circuit board is prepared by the steps described above in the preparation method of a pure copper circuit board.

[0013] The beneficial effects of this invention are as follows: by providing photoresist on both sides of the pure copper foil and attaching a layer of photoresist to the bottom, the pure copper foil can be supported; during exposure, the photoresist on the front side is exposed with the target pattern, while the photoresist on the back side is exposed blank, so that the photoresist used for support on the back side will not be etched in subsequent processes, thus effectively supporting the pure copper foil; since both sides are photoresist materials, the photoresist on both sides can be removed simultaneously during film removal, without the need for separate removal, improving the preparation efficiency; at the same time, since no carrier film is used, there is no problem of unevenness and curling of the product after the carrier film is unbonded and formed. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the steps of a method for preparing a pure copper circuit board according to an embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram of the process steps of a method for preparing a pure copper circuit board according to an embodiment of the present invention;

[0016] Figure 3 This is a schematic diagram of the second side exposure of a method for preparing a pure copper circuit board according to an embodiment of the present invention;

[0017] Label Explanation:

[0018] 1. Pure copper foil; 2. Photoresist. Detailed Implementation

[0019] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0020] In related technologies, when fabricating patterns on a 12μm thick pure copper foil, the thinness of the copper foil makes the substrate very flexible, making contact processing impossible without a support. Existing methods, such as bonding the pure copper foil substrate to a carrier film, suffer from unevenness and curling of the product after the carrier film is unbonded, leading to difficulties in customer assembly. If a laser-burning process (non-contact) is used, there is a problem of residual carbon black from the laser burning at the hole openings and walls.

[0021] Therefore, to address the aforementioned technical problems, this technical solution provides a pure copper circuit board and its fabrication method, specifically:

[0022] Please refer to Figure 1 A method for preparing a pure copper circuit board, comprising:

[0023] Photoresist is applied to both sides of the pure copper foil.

[0024] The first side of the bonded pure copper foil is exposed with a target pattern, while the second side opposite the first side is exposed blank.

[0025] The exposed pure copper foil is sequentially developed, etched, and stripped to obtain a pure copper circuit board with the target pattern.

[0026] As described above, the beneficial effects of this invention are as follows: by providing photoresist on both sides of the pure copper foil and attaching a layer of photoresist to the bottom, the pure copper foil can be supported; during exposure, the photoresist on the front side is exposed with the target pattern, while the photoresist on the back side is exposed blank, so that the photoresist on the back side used for support will not be etched in subsequent processes, thus effectively supporting the pure copper foil; since both sides are photoresist materials, the photoresist on both sides can be removed simultaneously during film removal, without the need for separate removal, improving preparation efficiency; at the same time, since no carrier film is used, there is no problem of unevenness and curling of the product after the carrier film is unbonded and formed.

[0027] Furthermore, the exposure of the first side of the bonded pure copper foil with the target pattern includes:

[0028] The photoresist on the first surface is exposed using a dense aperture pattern.

[0029] As described above, by exposing the photoresist with a dense aperture pattern, the photoresist on the first side forms a dense aperture pattern, which enables the formation of pre-defined through-holes on the pure copper foil in subsequent processes.

[0030] Furthermore, the exposure of the photoresist on the first surface using a dense aperture pattern includes:

[0031] Holes of a predetermined diameter are formed on the exposed film, and the distance between the holes is the same as the diameter of the holes;

[0032] The photoresist is exposed using the exposure film at a preset exposure energy.

[0033] As described above, by forming holes of a preset diameter on the exposed film, and ensuring that the distance between the holes is the same as the diameter of the holes, the holes are evenly distributed while avoiding situations such as holes breaking due to excessively small distances between them.

[0034] Further, the blank exposure of the second surface opposite to the first surface includes:

[0035] The pure copper foil and the pure copper foil adjacent to it are subjected to overlapping exposure.

[0036] As described above, by overlapping exposure of pure copper foil and its adjacent pure copper foil, it is possible to ensure that the photoresist at the inter-wafer connection of adjacent pure copper foil protects the copper from being etched during etching, thus ensuring the continuity of the entire roll of pure copper foil.

[0037] Further, etching the exposed pure copper foil includes:

[0038] The traction belt is connected to the front end of the pure copper foil, and the traction belt is flush with the pure copper foil;

[0039] The pure copper foil is pulled by the traction belt, so that the pure copper foil comes into contact with the etching solution.

[0040] As described above, by connecting the traction belt flush with the front end of the pure copper foil, the traction belt must be flush with the product when it enters the etching line, and this will prevent the tension from being different at different positions due to the misalignment of the connection position.

[0041] Further, the stripping of the exposed pure copper foil includes:

[0042] Adjust the tension of the uncoating and collecting machine on the pure copper foil according to the thickness of the pure copper foil;

[0043] The pure copper foil is stripped using adjusted tension.

[0044] As described above, adjusting the tension of the uncoating and collecting machine on the pure copper foil according to its thickness can avoid the risk of product breakage due to excessive tension caused by a mismatch between the tension and the thickness of the pure copper foil, as well as the risk of product wrinkling due to insufficient tension.

[0045] Furthermore, when the thickness of the pure copper foil is 12-18μm, the tension of the uncoating and collecting machine is adjusted to 3±0.5kgf.

[0046] As described above, when the thickness of pure copper foil is 12-18μm, setting the tension of the stripping and collecting machine to 3±0.5kgf can effectively strip pure copper foil with a thickness of 12-18μm.

[0047] Furthermore, when the thickness of the pure copper foil is 18μm, the tension of the uncoating and collecting machine is adjusted to 5±0.5kgf.

[0048] As described above, when the thickness of pure copper foil is greater than 18μm, setting the tension of the stripping and collecting machine to 5±0.5kgf can effectively strip pure copper foil with a thickness greater than 18μm.

[0049] Furthermore, the step of bonding photoresist to both sides of the pure copper foil includes:

[0050] The pure copper foil is bonded with photoresist using a roll-to-roll method;

[0051] When bonding the photoresist, a wet bonding method is used, with a pressure of 5.5 ± 0.5 kg / cm². 2 The film application speed is 1.3±0.3m / min.

[0052] As described above, pure copper foil is laminated with photoresist using a roll-to-roll method, with a pressure of 5.5 ± 0.5 kg / cm². 2 Wet bonding, performed at a bonding speed of 1.3±0.3m / min, can effectively attach photoresist to pure copper foil.

[0053] Another embodiment of the present invention provides a pure copper circuit board, which is prepared by the various steps of the preparation method of a pure copper circuit board as described above.

[0054] As described above, the pure copper circuit board with the target pattern prepared by the above-described method does not have the problem of residual carbon black from laser burning at the hole opening and wall compared with the laser burning process; and it does not have the problem of unevenness and curling of the product after the carrier film is debonded and formed compared with the carrier film etching process. This makes the pure copper circuit board have better performance and is more conducive to the assembly of pure copper foil.

[0055] The pure copper circuit board and its preparation method provided by this invention can be applied to the preparation of pure copper circuit boards, and are particularly suitable for the preparation of thin pure copper foil circuit boards. The following detailed embodiments illustrate this:

[0056] Please refer to Figure 1 as well as Figure 2 A method for preparing a pure copper circuit board, comprising:

[0057] S0. Prepare pure copper foil 1.

[0058] S1. Photoresist 2 is bonded to both sides of the pure copper foil 1. For example... Figure 2 As shown in step S1, photoresist 2 is bonded to both sides of the pure copper foil 1. In this embodiment, the pure copper circuit board is fabricated using a roll-to-roll (RTR) method; taking the fabrication of a 12μm circuit as an example, a layer of photoresist 2 is bonded to both sides of the pure copper foil 1; when bonding the photoresist 2, a wet lamination method is used, with a pressure of 5.5±0.5 kg / cm². 2 The film application speed is 1.3 ± 0.3 m / min. For example, apply the film to the first side first, and then apply it to the second side after completing the application of the first side. During the application process, it is necessary to ensure that no wrinkles or melting of the film occur.

[0059] S2. Expose the first side of the bonded pure copper foil 1 with the target pattern, and expose the second side opposite the first side as blank. During exposure, a roll-to-roll single-sided exposure method is used to expose the photoresist 2 on the first side and the photoresist 2 on the second side sequentially.

[0060] When exposing the first surface: a dense aperture pattern is used to expose the photoresist 2 on the first surface; wherein, holes of a preset diameter are formed on the exposure film, and the distance between the holes is the same as the diameter of the holes; the photoresist 2 is exposed through the exposure film at a preset exposure energy. For example, the exposure film is a film with a hole diameter of 45μm, a hole spacing of 45μm, and is exposed at an exposure energy of 5 divisions.

[0061] When exposing the second side: the pure copper foil 1 and the pure copper foil 1 adjacent to it are subjected to overlapping exposure; the overlapping exposure means that adjacent areas are exposed twice during roll-to-roll exposure, that is, through the overlapping exposure between the front and back films, the exposure areas of the photoresist 2 are connected together to achieve the purpose of uninterrupted exposure. Figure 3 As shown, if the effective size of the product is 300mm and the width of the overlapping exposure area is 3mm, then the material conveying width is 297mm, so that the overlapping exposure area of ​​the product is exposed twice during the material conveying process, thereby ensuring that the photoresist 2 at the inter-wafer connection protects the copper from being etched during etching, and achieving the continuity of the entire roll of products.

[0062] S3. The exposed pure copper foil 1 is sequentially developed, etched, and stripped to obtain a pure copper circuit board with the target pattern. Specifically:

[0063] S31. Perform a development operation on the exposed pure copper foil 1; wherein, after exposure, the product is allowed to stand for a preset time before development, for example, 30 minutes after exposure before development, and the circuit fabrication of the exposed product is completed within 24 hours. Figure 2 In step S31, after development, part of the photoresist 2 on the first surface is removed, thus exposing the copper foil surface.

[0064] S32. Etching the exposed pure copper foil 1: Connect the traction belt to the front end of the pure copper foil 1, and make the traction belt flush with the pure copper foil 1; pull the pure copper foil 1 with the traction belt to bring the pure copper foil 1 into contact with the etching solution. Figure 2 In step S32, holes are formed by etching the developed copper foil.

[0065] S33. Remove the film from the exposed pure copper foil 1: Adjust the tension of the film removal and collection machine on the pure copper foil 1 according to its thickness; remove the film from the pure copper foil 1 using the adjusted tension. For example, when the thickness of the pure copper foil 1 is 12-18 μm, adjust the tension of the film removal and collection machine to 3 ± 0.5 kgf. If the thickness of the pure copper foil 1 is 18 μm, adjust the tension of the film removal and collection machine to 5 ± 0.5 kgf. Figure 2 In step S33, the photoresist 2 on the first surface and the photoresist 2 on the second surface are simultaneously removed, thereby forming a pure copper circuit board with the target pattern.

[0066] S4. Outline punching: According to the design requirements, the rolled pure copper circuit board is punched into the preset size using a mold.

[0067] Another embodiment of the present invention provides a pure copper circuit board, which is prepared by the above-described method for preparing a pure copper circuit board.

[0068] In summary, the pure copper circuit board and its fabrication method provided by this invention, by applying photoresist to both sides of the pure copper foil and by attaching a layer of photoresist to the bottom layer, increases the product's thickness, providing support for the pure copper foil and improving the product's tensile strength, while protecting the copper on the back side from oxidation and scratches; during exposure, the photoresist on the front side is exposed with the target pattern, while the photoresist on the back side is exposed blank, and by overlapping exposures, it can be ensured that the photoresist at the inter-wafer connection of adjacent pure copper foils protects the copper from etching during etching, thus preventing the back side from being used for support photoresist in subsequent processes. The photoresist is etched to effectively support the pure copper foil. Since both sides are made of photoresist material, the photoresist on both sides can be removed simultaneously during stripping, eliminating the need for separate removal and improving manufacturing efficiency. Furthermore, by using photoresist instead of a carrier film, and ensuring that the photoresist separates from the product in the stripping tank after etching, the problem of product curling during carrier film separation is avoided. It also eliminates carbon black contamination caused by laser sintering at the hole edges. This RTR process is mature, stable, and highly efficient, producing uniform hole shapes and consistent quality, making it suitable for mass production.

[0069] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a pure copper circuit board, characterized in that, include: Photoresist is applied to both sides of the pure copper foil. The first side of the bonded pure copper foil is exposed with a target pattern, while the second side opposite the first side is exposed blank. The exposed pure copper foil is sequentially developed, etched, and stripped to obtain a pure copper circuit board with the target pattern. The blank exposure of the second side opposite to the first side includes: overlapping exposure of the pure copper foil and the pure copper foil adjacent to the pure copper foil; the overlapping exposure means that adjacent areas are exposed twice in the roll-to-roll exposure process, and the photoresist exposure areas are connected together to achieve the purpose of uninterrupted exposure through the overlapping exposure between the front and back films; The photoresist removal process removes the photoresist on both the first and second surfaces simultaneously.

2. The method for preparing a pure copper circuit board according to claim 1, characterized in that, The step of exposing the first side of the bonded pure copper foil with the target pattern includes: The photoresist on the first surface is exposed using a dense aperture pattern.

3. The method for preparing a pure copper circuit board according to claim 2, characterized in that, The step of exposing the photoresist on the first surface using a dense aperture pattern includes: Holes of a predetermined diameter are formed on the exposed film, and the distance between the holes is the same as the diameter of the holes; The photoresist is exposed using the exposure film at a preset exposure energy.

4. The method for preparing a pure copper circuit board according to claim 1, characterized in that, Etching the exposed pure copper foil includes: The traction belt is connected to the front end of the pure copper foil, and the traction belt is flush with the pure copper foil; The pure copper foil is pulled by the traction belt, so that the pure copper foil comes into contact with the etching solution.

5. The method for preparing a pure copper circuit board according to claim 1, characterized in that, The stripping process for the exposed pure copper foil includes: Adjust the tension of the uncoating and collecting machine on the pure copper foil according to the thickness of the pure copper foil; The pure copper foil is stripped using adjusted tension.

6. The method for preparing a pure copper circuit board according to claim 5, characterized in that, When the thickness of the pure copper foil is 12-18μm, the tension of the uncoating and collecting machine is adjusted to 3±0.5kgf.

7. The method for preparing a pure copper circuit board according to claim 5, characterized in that, When the thickness of the pure copper foil is 18μm, the tension of the film removal and collection machine is adjusted to 5±0.5kgf.

8. The method for preparing a pure copper circuit board according to claim 1, characterized in that, The process of bonding photoresist to both sides of a pure copper foil includes: The pure copper foil is bonded with photoresist using a roll-to-roll method; When bonding the photoresist, a wet bonding method is used, with a pressure of 5.5 ± 0.5 kg / cm². 2 The film application speed is 1.3±0.3m / min.

9. A pure copper circuit board, characterized in that, It is prepared by each step of the method for preparing a pure copper circuit board as described in any one of claims 1-8.

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