Method for replacing back diamond with printing ink

Abstract

The invention discloses a method for replacing backdrilling with printing ink, which comprises the following steps of: providing a plurality of core boards which at least comprise a target core board; coating or pasting photosensitive alkali-soluble films on all the core boards, manufacturing an inner layer circuit through a negative film process, forming a copper disc with the outer diameter larger than the aperture at the drilling position of the target core board, and reserving an ink layer formed by the photosensitive alkali-soluble films after inner layer etching; spraying light-cured ink on the outer side of the ink layer at the copper disc position, and performing UV exposure curing to form a protective layer; removing the photosensitive alkali-soluble film which is not covered by the light-cured ink; pressing the core plate and the outer-layer copper foil into a production plate through a prepreg; and after drilling, carrying out concave etching on the photosensitive alkali-soluble film in the hole, and forming an isolating ring at the concave etching position after chemical copper plating and full-board electroplating, thereby realizing electrical isolation between the inner layer and the non-connecting layer. According to the method, isolation of the inner layer and the outer layer is achieved through the ink technology, back drilling is not needed in the mode, cost is low, machining is simple, and machining of removing the pile head of the high-frequency and high-speed circuit board can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method of using ink to replace back drilling. Background Art

[0002] As the integration of electronic systems continues to increase, circuit boards are becoming more and more integrated and functional, so it is inevitable that the design density of PCBs will become higher and higher. In addition, there are more and more applications of high-speed interconnection, and the requirements for high-speed signals of products will become higher and higher, such as 5G / 6G communications, supercomputing, high-performance computing, cloud computing, big data, etc.

[0003] As the application of high-frequency and high-speed products has increased significantly, new requirements have been put forward for the integrity of high-speed digital signals. The transmission lines of high-speed circuits have very high requirements for signal integrity under high-frequency and high-speed conditions. The control and implementation of signal integrity are strongly correlated with the impedance and insertion loss of the transmission line. When the high-speed rate exceeds 25Gbps, the impact of insertion loss on signal integrity becomes increasingly greater. The length of the extra stub at the high-speed via directly affects the size of the insertion loss. During signal transmission, this stub position will form an oscillation section, whether it is filtering or oscillation, which will damage the high-speed signal transmission and distort the signal. In order to obtain better high-speed signal integrity, the length of the stub needs to be controlled as small as possible.

[0004] In order to reduce the stub, the prior art uses a back-drilling process. Back-drilling is a method of secondary drilling of copper to remove the stub part that is not conducive to signal transmission in the PTH hole that has been electroplated. The shorter the length of the remaining stub after back-drilling, the better the signal. Generally, the length of the remaining stub needs to be controlled to be less than 7mil after back-drilling to avoid a major negative impact on the integrity of signal transmission.

[0005] At present, the common method to reduce the pile head is the back drilling process, that is, to remove the pile head part that is not conducive to signal transmission in the PTH hole that has been electroplated by secondary drilling. The back drilling process can improve signal integrity to a certain extent, but there are also many problems. The back drilling depth is difficult to accurately control the pile head size, and a slight deviation may lead to a decrease in signal quality; the back drilling equipment is expensive, which increases the production cost; the back drilling process is slow and the production efficiency is low. These problems limit the application of the back drilling process in large-scale production, and also prompt researchers to find more efficient and low-cost alternatives.

[0006] The previously disclosed patent CN117998752A - a method to replace back drilling, requires a film material that does not adhere to chemical copper and laser processing, the material cost is high, and the laser cutting process is time-consuming.

[0007] Another alternative to back drilling: ink composition, as a new type of material, has shown great potential in the field of circuit board manufacturing. By rationally designing the composition and structure of the ink composition, precise control of specific areas of the circuit board can be achieved, thereby achieving the purpose of replacing back drilling. For example, the ink composition of the previously disclosed patent document CN115558334B is to add a substance that can react with acid to produce gas to the alkali-soluble ink, so as to dissolve it with acid after chemical copper; the disadvantage is that it requires special materials and processing procedures: printing ink, alkali washing, acid washing; studying ink compositions and methods of replacing back drilling are of great significance for improving the signal integrity of circuit boards, reducing production costs, and improving production efficiency. It can not only meet the current demand for high-frequency and high-speed performance of electronic equipment, but also promote the innovative development of circuit board manufacturing technology, and provide strong support for the progress of the electronics industry. Summary of the invention

[0008] In view of the above-mentioned existing technical defects, the present invention provides a method of using ink instead of back drilling, and a method of isolating the inner layer and the outer layer through the ink process. This method does not require back drilling, has low cost and simple processing, can realize the processing of removing the pile head of high-frequency and high-speed circuit boards, and can accurately control the length of the pile head, or even eliminate the pile head.

[0009] In order to solve the above technical problems, the present invention provides a method of using ink to replace back drilling, comprising the following steps:

[0010] S1. Provide a plurality of core boards, including a first target core board and a second target core board. After coating or pasting a photosensitive alkali-soluble film on all the core boards, use a negative film process to produce inner circuits on the core boards, and respectively produce a first copper plate and a second copper plate with an outer diameter larger than the drilling position at positions corresponding to the drilling holes on one surface of the first target core board and the second target core board, and do not perform film stripping after etching;

[0011] S2, spraying a layer of light-curable ink covering the outside of the photosensitive alkali-soluble film at positions corresponding to the first copper plate and the second copper plate, and exposing and curing the light-curable ink by UV light;

[0012] S3, removing the photosensitive alkali-soluble films on the first target core board and the second target core board that are not covered by the photocurable ink;

[0013] S4, laminating a plurality of core boards and outer copper foils in a preset order through a prepreg sheet and then pressing them into a production board; one surface of the production board is a connection layer to be connected to the first copper disk of the inner layer, and the other surface is a non-connection layer not connected to the first copper disk of the inner layer; when pressing the arrangement of boards, the second copper disk on the second target core board is located at the second outer layer inside the non-connection layer;

[0014] S5. Drill through holes at corresponding drilling positions on the production board to expose the first copper plate, the second copper plate, the photosensitive alkali-soluble film and the photocurable ink on the wall of the through hole; after drilling, the photosensitive alkali-soluble film exposed in the hole is etched to form two etched positions; and then the through hole is metallized by chemical copper and full-board electroplating in turn. In the case of chemical copper, no copper layer is deposited at the two etched positions in the through hole, forming two isolation rings; in the case of full-board electroplating, the copper deposited layer on the wall between the two isolation rings will dissolve into the electroplating solution to form a copper-free isolation zone, so that the first copper plate of the inner layer is disconnected from the non-connected layer at the through hole.

[0015] Furthermore, in step S5, the depth of the recessed etching is at least 5 times the thickness of the photosensitive alkali-soluble film.

[0016] Furthermore, in step S1, the thickness of the photocurable ink is 10-30 micrometers, and the outer diameter of the photocurable ink is 0.2-0.5 mm larger than the hole diameter of the drilling position.

[0017] Furthermore, the photosensitive alkali-soluble film is a wet film or a dry film, and the thickness of the photosensitive alkali-soluble film is 10-40 microns.

[0018] Furthermore, when the photosensitive alkali-soluble film is a wet film with a thickness of 10 microns, the outer diameter of the photocurable ink is 0.2 mm larger than the hole diameter of the drilling position; and the depth of the concave etching is 50 microns.

[0019] Furthermore, when the photosensitive alkali-soluble film is a dry film with a thickness of 40 microns, the outer diameter of the photocurable ink is 0.5 mm larger than the hole diameter of the drilling position, and the depth of the concave etching is 200 microns.

[0020] In a second aspect, the present invention also provides another method of using ink to replace back drilling, comprising the following steps:

[0021] S1. Provide a plurality of core boards, including at least one target core board, coat or affix a photosensitive alkali-soluble film on all the core boards, and use a negative film process to produce inner-layer circuits on the core boards, and produce a copper disk having an outer diameter larger than the drilling position at a position corresponding to the drilling hole on one surface of the target core board, and do not perform film stripping after etching;

[0022] S2, spraying a layer of light-curing ink covering the outside of the photosensitive alkali-soluble film at the position corresponding to the copper disk, and exposing and curing the light-curing ink by UV light;

[0023] S3, removing the photosensitive alkali-soluble film on the target core board that is not covered by the photocurable ink;

[0024] S4, laminating and pressing a plurality of core boards and outer copper foils into a production board through a prepreg in a preset order; one surface of the production board is a connection layer to be connected to the inner copper disk, and the other surface is a non-connection layer not connected to the inner copper disk;

[0025] S5. Drill through holes at corresponding drilling positions on the production board to expose the first copper disk, the second copper disk, the photosensitive alkali-soluble film and the photocurable ink on the wall of the through hole; after drilling, the photosensitive alkali-soluble film exposed in the hole is etched back to form an etched position; and then a layer of copper is plated on the hole wall by chemical copper. During chemical copper, no copper layer is deposited at the etched position in the through hole to form an isolation ring; the hole opening is back-drilled at the non-connected layer to drill out the copper layer at the hole opening to disconnect the non-connected layer from the copper layer of the hole wall; finally, the production board is fully electroplated; during full-board electroplating, the copper deposited layer on the wall between the isolation ring and the non-connected layer will dissolve into the electroplating solution to form a copper-free isolation zone, so that the inner copper disk is disconnected from the non-connected layer at the through hole.

[0026] Furthermore, in step S5, the depth of the recessed etching is at least 5 times the thickness of the photosensitive alkali-soluble film.

[0027] Furthermore, in step S1, the thickness of the photosensitive alkali-soluble film is 10-40 microns, the thickness of the photocurable ink is 10-30 microns, and the outer diameter of the photocurable ink is 0.2-0.5 mm larger than the hole diameter of the drilling position.

[0028] Further, when the photosensitive alkali-soluble film is a wet film with a thickness of 10 microns, the outer diameter of the photocurable ink is 0.2 mm larger than the hole diameter of the drilling position; the depth of the concave etching is 50 microns;

[0029] When the photosensitive alkali-soluble film is a dry film with a thickness of 40 microns, the outer diameter of the photocurable ink is 0.5 mm larger than the hole diameter of the drilling position, and the depth of the concave etching is 200 microns.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] In the method of the present invention, a commonly used photosensitive alkali-soluble film (i.e., a wet film or a dry film) is used in the inner layer to form an alkali-soluble layer. After etching, the core board is not subjected to a film stripping treatment first, but a photocurable ink is first sprayed on the outer side of the photosensitive alkali-soluble film to form a protective layer, and then the film stripping is performed to remove the unnecessary photosensitive alkali-soluble film, thereby forming a double-layer ink structure consisting of a photosensitive alkali-soluble film and a photocurable ink at the drilling position. After drilling, an isolation ring without a copper layer is formed at the two photosensitive alkali-soluble films in the hole through a recessed etching process, and the wall between the two isolation rings is The copper layer on the surface will also dissolve into the plating solution during the subsequent full-board electroplating, thereby forming a copper-free isolation zone between the two isolation rings, that is, the pile head at this position is removed, so that the inner copper disk and the non-connected layer on the production board are disconnected at the through hole, thereby replacing the existing back drilling method to realize the processing of removing the pile head of high-frequency and high-speed circuit boards, and the length of the pile head can be accurately controlled, or even there is no pile head; in this way, the method of isolating the inner and outer layers is realized by a combination of two inks, and this method does not require back drilling, has low cost and simple processing.

[0032] Additional aspects and advantages of the present invention will be given in part in the following description, which will become obvious from the following description, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of etching on the first target core plate in Examples 1 and 2;

[0034] Figure 2 Schematic diagram of the second target core board after etching in Examples 1 and 2;

[0035] Figure 3 Schematic diagram of spraying photocurable ink on the first target core plate and stripping the film in Examples 1 and 2;

[0036] Figure 4 Schematic diagram of spraying photocurable ink on the second target core plate and stripping the film in Examples 1 and 2;

[0037] Figure 5 Schematic diagram of the production of the plate after press synthesis in Examples 1 and 2;

[0038] Figure 6 Schematic diagram of the production board after drilling in Examples 1 and 2;

[0039] Figure 7 Schematic diagram of copper deposition on the production board in Examples 1 and 2;

[0040] Figure 8 Schematic diagram of the whole plate electroplating on the production plate in Examples 1 and 2;

[0041] Fig. 9Schematic diagram of etching on the target core board in Examples 3 and 4;

[0042] Fig.10 Schematic diagram of spraying photocurable ink on a target core board and stripping the film in Examples 3 and 4;

[0043] Fig.11 Schematic diagram of the production of plates after press synthesis in Examples 3 and 4;

[0044] Fig.12 Schematic diagram of the production board after drilling in Examples 3 and 4;

[0045] Fig.13 Schematic diagram of copper deposition on the production board in Examples 3 and 4;

[0046] Fig.14 Schematic diagram of back drilling on the production board in Examples 3 and 4;

[0047] Fig.15 Schematic diagram of the production board after full-board electroplating in Examples 3 and 4. DETAILED DESCRIPTION

[0048] The following will be combined with 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 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.

[0049] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0050] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0051] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0052] Example 1

[0053] A method of using ink to replace back drilling shown in this embodiment includes the following processing steps in sequence:

[0054] (1) Cutting: Cut out a plurality of FR4 core boards according to the actual panel size during production, and the copper layer thickness on both surfaces of the core boards is 0.5 oz; the plurality of core boards include at least one first target core board 1 and one second target core board 2.

[0055] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, a wet film (i.e., photosensitive alkali-soluble film) is coated on the core board using a vertical coating machine, the film thickness of the wet film is controlled at 10 μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler), and the inner layer circuit pattern is formed after development; inner layer etching, the exposed and developed core board is etched to form the inner layer circuit, and the inner layer line width is measured to be 3 mi l. At the same time, one side surface of the first target core board and the second target core board is respectively made with a first copper plate 10 and a second copper plate 20 (such as a copper plate 10 and a copper plate 20) with an outer diameter larger than the drilling position at the corresponding drilling position. Figure 1 and Figure 2 As shown), the first copper disk is used for later connection with the outer layer circuit to connect the inner and outer layer circuits. The first target core board and the second target core board are not stripped after etching, that is, the wet film on the outside of the inner layer circuit layer is retained.

[0056] In one embodiment, the outer diameter of the copper disk is 0.2 mm larger than the hole diameter of the drilling position.

[0057] (3) Spraying protective layer: (such as Figure 3 to Figure 4 As shown in the figure, a layer of photocurable ink 12 covering the outside of the wet film 11 is sprayed at the positions corresponding to the first copper plate 10 and the second copper plate 20, and the photocurable ink 12 is exposed and cured by UV light to form a protective layer; then the wet films on the first target core plate and the second target core plate that are not covered by the photocurable ink are removed by a film stripping process, that is, the outer diameters of the retained wet film and the photocurable ink are the same as the outer diameters of the two copper plates, which are 0.2 mm larger than the hole diameters of the drilling positions.

[0058] In one embodiment, the thickness of the photocurable ink is preferably 20 microns.

[0059] (4) Inner layer AO I: Then check the inner layer circuit for defects such as open short circuits, circuit gaps, and circuit pinholes. Defective products will be scrapped, and non-defective products will be sent to the next process.

[0060] (5) Lamination: The browning speed is based on the bottom copper thickness. Multiple core boards (including two target core boards) and outer copper foils are laminated together through prepreg in a preset order. Then, appropriate lamination conditions are selected according to the Tg of the board material to laminate the laminated boards to form a production board (such as Figure 5As shown); one side surface of the production board is a connecting layer 13 that needs to be connected to the first copper disk 10 of the inner layer, and the other surface is a non-connecting layer 14 that is not connected to the first copper disk 10 of the inner layer, and the position between the non-connecting layer and the first copper disk is the position of the pile head that needs to be removed; in the pressed board before pressing, the second copper disk 20 on the second target core board 2 is located at the sub-outer layer inside the non-connecting layer 14, that is, the second copper disk 20 of the inner layer is adjacent to the non-connecting layer 14 of the outer layer.

[0061] (6) Drilling: According to the existing drilling technology, a through hole 15 (such as Figure 6 As shown), that is, the through hole passes through the middle of the photocurable ink, the wet film, the second copper plate and the first copper plate from top to bottom, so that the photocurable ink, the wet film, the second copper plate and the first copper plate are exposed on the wall of the through hole.

[0062] (7) Copper deposition: Figure 7 As shown, a thin layer of copper 16 is deposited on the board surface and the hole wall by chemical copper method to metallize the through hole. The backlight test is level 10, and the thickness of the copper deposited in the hole is 0.5μm. In the expansion section and the degumming section of the chemical copper production line, the two layers of wet film on the hole wall will be etched back to form two etched positions 17, so that when the chemical copper is applied behind the degumming section, the copper layer is not deposited at the two etched positions in the through hole, forming two isolation rings.

[0063] In one embodiment, the etch-back depth of the wet film is preferably 50 microns, so that the thickness-to-diameter ratio at the etch-back position is 5:1. This thickness-to-diameter ratio can ensure that no copper layer is deposited at the etch-back position during chemical copper deposition.

[0064] In another embodiment, the depth of the recessed etching may be at least 5 times the thickness of the photosensitive alkali-soluble film.

[0065] It is understandable that, in another specific implementation case, an etching process can be added between drilling and copper deposition, that is, the wet film in the hole is etched back using a sodium hydroxide solution; preferably, the concentration of the sodium hydroxide solution is 10%, and the solution temperature is controlled at 60-70 degrees Celsius during etching, and the time is at least half an hour.

[0066] (8) Full-board electroplating: According to the design requirements, the production board is subjected to full-board electroplating. Since the two concave etched positions are not deposited with a copper layer, the conductivity of the copper layer on the wall between the two isolation rings is very poor or even non-conductive. During full-board electroplating, the copper layer on the wall between the two isolation rings will dissolve into the electroplating solution to form a copper-free isolation zone 18 (such as Figure 8As shown), the first copper plate of the inner layer is disconnected from the non-connected layer at the through hole, that is, the pile head that originally needed to be removed by back drilling is directly removed in this way. This method replaces the existing back drilling method to realize the processing of removing the pile head of high-frequency and high-speed circuit boards, and the length of the pile head can be accurately controlled, or even there is no pile head; this method realizes the isolation of the inner layer and the outer layer by combining two inks. This method does not require back drilling, has low cost and simple processing.

[0067] In a specific embodiment, after completing the full-board electroplating in the above-mentioned step (8), other post-production processes are carried out in sequence on the production board according to the prior art, such as making outer layer circuits, making solder mask layers, surface treatment, molding, electrical testing, FQC, FQA and packaging, etc., to finally obtain the desired circuit board.

[0068] Example 2

[0069] The method of using ink instead of back drilling shown in this embodiment is basically the same as that in Embodiment 1, except that the photosensitive alkaline soluble film used to make the inner layer circuit on the core board is different. In this embodiment, the wet film is replaced with a dry film, and the inner layer circuit pattern is formed after exposure by sticking the dry film on the core board.

[0070] In this embodiment, the thickness of the dry film is preferably 40 microns.

[0071] In this embodiment, since the dry film is thick, in order to achieve the required thickness-to-diameter ratio after etching, the first copper plate, the second copper plate, the dry film retained after film stripping, and the photocurable ink are all 0.5 mm larger than the drilling position.

[0072] In this embodiment, the etch depth of the dry film in the later chemical copper stripping stage is preferably 200 microns, so that the thickness-to-diameter ratio at the etch position is 5:1. This thickness-to-diameter ratio can ensure that no copper layer is deposited at the etch position during chemical copper deposition.

[0073] Example 3

[0074] A method of using ink to replace back drilling shown in this embodiment includes the following processing steps in sequence:

[0075] (1) Cutting: Cut out multiple FR4 core boards according to the actual panel size during production, and the copper layer thickness on both surfaces of the core boards is 0.5 oz; the multiple core boards include a target core board 3.

[0076] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, a wet film 11 (i.e., a photosensitive alkali-soluble film) is coated on the core board using a vertical coating machine, and the film thickness of the wet film is controlled at 10 μm. A fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler), and the inner layer circuit pattern is formed after development; inner layer etching, the inner layer circuit is etched out of the exposed and developed core board, and the inner layer line width is measured to be 3 mi l. At the same time, a copper disk 31 (such as 31) with an outer diameter larger than the drilling position is made on one side of the surface of the target core board 3 at the corresponding drilling position Fig. 9 As shown), the copper plate 31 is used for the later connection with the outer layer circuit to connect the inner and outer layer circuits. The target core board is not subjected to film stripping treatment after etching, that is, the wet film on the outer side of the inner layer circuit layer is retained.

[0077] In one embodiment, the outer diameter of the copper disk is 0.2 mm larger than the hole diameter of the drilling position.

[0078] (3) Spraying protective layer: Fig.10 As shown, a layer of photocurable ink 12 covering the outside of the wet film 11 is sprayed at the position corresponding to the copper disk 31, and the photocurable ink 12 is exposed and cured by UV light to form a protective layer; then the wet film on the target core board that is not covered by the photocurable ink is removed through a film stripping process, that is, the outer diameters of the retained wet film and the photocurable ink are the same as the outer diameter of the copper disk 31, and are both 0.2 mm larger than the hole diameter of the drilling position.

[0079] In one embodiment, the thickness of the photocurable ink is preferably 20 microns.

[0080] (4) Inner layer AO I: Then check the inner layer circuit for defects such as open short circuits, circuit gaps, and circuit pinholes. Defective products will be scrapped, and non-defective products will be sent to the next process.

[0081] (5) Lamination: The browning speed is based on the bottom copper thickness. Multiple core boards (including the target core board) and outer copper foil are laminated together through the prepreg in a preset order. Then, the laminated boards are laminated under appropriate lamination conditions according to the Tg of the board material to form a production board (such as Fig.11 One side surface of the production board is a connection layer 13 that needs to be connected to the inner copper disk 31, and the other surface is a non-connection layer 14 that is not connected to the inner copper disk 31. The position between the non-connection layer and the copper disk is the position of the pile head that needs to be removed.

[0082] (6) Drilling: According to the existing drilling technology, a through hole 15 (such as Fig.12 As shown), that is, the through hole passes through the middle of the photocurable ink, the wet film and the copper disk from top to bottom, so that the photocurable ink, the wet film and the copper disk are exposed on the wall surface of the through hole.

[0083] (7) Copper deposition: Fig.13 As shown, a thin layer of copper 16 is deposited on the board surface and the hole wall by chemical copper method to metallize the through hole, and the backlight test is level 10, and the thickness of the copper deposited in the hole is 0.5μm; in the expansion section and the degumming section of the chemical copper production line, the wet film 11 on the hole wall will be etched back to form an etched position 17, so that when the chemical copper is applied behind the degumming section, the copper layer is not deposited at the etched position in the through hole, forming an isolation ring.

[0084] In one embodiment, the etch-back depth of the wet film is preferably 50 microns, so that the thickness-to-diameter ratio at the etch-back position is 5:1. This thickness-to-diameter ratio can ensure that no copper layer is deposited at the etch-back position during chemical copper deposition.

[0085] In another embodiment, the depth of the recessed etching may be at least 5 times the thickness of the photosensitive alkali-soluble film.

[0086] It is understandable that, in another specific implementation case, an etching process can be added between drilling and copper deposition, that is, the wet film in the hole is etched back using a sodium hydroxide solution; preferably, the concentration of the sodium hydroxide solution is 10%, and the solution temperature is controlled at 60-70 degrees Celsius during etching, and the time is at least half an hour.

[0087] (8) Drilling: Use a drill bit for drilling through holes or a drill bit slightly larger than the through hole and drill away the copper layer at the hole opening by back drilling (such as Fig.14 As shown in the figure, the back drilling thickness only needs to be controlled to drill away the chemical copper layer at the hole mouth, and there is no need to continue drilling inward to remove the copper layer on the hole wall, so as to disconnect the non-connected layer from the copper layer on the hole wall.

[0088] (9) Full-board electroplating: According to the design requirements, the production board is subjected to full-board electroplating. Since no copper layer is deposited on the etched area, and the non-connected layer and the hole wall copper layer are also disconnected, the conductivity of the copper layer on the wall between the etched area and the non-connected layer is very poor, or even non-conductive. During full-board electroplating, the copper layer on the wall between the etched area and the non-connected layer will dissolve into the electroplating solution to form a copper-free isolation zone 15 (such as Fig.15 As shown), the inner copper disk 31 is disconnected from the non-connection layer 14 at the through hole, that is, the pile head that originally needed to be removed by back drilling is directly removed in this way. This method replaces the existing back drilling method to realize the processing of removing the pile head of high-frequency and high-speed circuit boards, and the length of the pile head can be accurately controlled, or even there is no pile head; this method realizes the isolation of the inner layer and the outer layer through the combination of two inks + surface back drilling. This method does not require back drilling, has low cost and simple processing.

[0089] In a specific embodiment, after completing the full-board electroplating in the above-mentioned step (9), other post-production processes are carried out in sequence on the production board according to the prior art, such as making outer layer circuits, making solder mask layers, surface treatment, molding, electrical testing, FQC, FQA and packaging, etc., to finally obtain the desired circuit board.

[0090] Example 4

[0091] The method of using ink instead of back drilling shown in this embodiment is basically the same as that in Example 3, except that the photosensitive alkaline soluble film used to make the inner layer circuit on the core board is different. In this embodiment, the wet film is replaced by a dry film, and the inner layer circuit pattern is formed after exposure by sticking the dry film on the core board.

[0092] In this embodiment, the thickness of the dry film is preferably 40 microns.

[0093] In this embodiment, since the dry film is relatively thick, in order to achieve the required thickness-to-diameter ratio after etching, the copper plate, the dry film retained after film stripping, and the photocurable ink are all 0.5 mm larger than the drilling position.

[0094] In this embodiment, the etch depth of the dry film in the later chemical copper stripping stage is preferably 200 microns, so that the thickness-to-diameter ratio at the etch position is 5:1. This thickness-to-diameter ratio can ensure that no copper layer is deposited at the etch position during chemical copper deposition.

[0095] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method of using ink to replace back drilling, characterized in that: The following steps are involved: S1. Provide a plurality of core boards, including a first target core board and a second target core board. After coating or pasting a photosensitive alkali-soluble film on all the core boards, use a negative film process to produce inner circuits on the core boards, and respectively produce a first copper plate and a second copper plate with an outer diameter larger than the drilling position at positions corresponding to the drilling holes on one surface of the first target core board and the second target core board, and do not perform film stripping after etching; S2, spraying a layer of light-curable ink covering the outside of the photosensitive alkali-soluble film at positions corresponding to the first copper plate and the second copper plate, and exposing and curing the light-curable ink by UV light; S3, removing the photosensitive alkali-soluble films on the first target core board and the second target core board that are not covered by the photocurable ink; S4, laminating a plurality of core boards and outer copper foils in a preset order through a prepreg sheet and then pressing them into a production board; one surface of the production board is a connection layer to be connected to the first copper disk of the inner layer, and the other surface is a non-connection layer not connected to the first copper disk of the inner layer; when pressing the arrangement of boards, the second copper disk on the second target core board is located at the second outer layer inside the non-connection layer; S5. Drill through holes at corresponding drilling positions on the production board. After drilling, the photosensitive alkali-soluble film exposed in the hole is etched back to form two etched positions. The through holes are then metallized by chemical copper and full-board electroplating in sequence. During chemical copper, no copper layer is deposited at the two etched positions in the through hole, forming two isolation rings. During full-board electroplating, the copper deposited layer on the wall between the two isolation rings will dissolve into the electroplating solution to form a copper-free isolation zone, so that the first copper disk of the inner layer is disconnected from the non-connected layer at the through hole.

2. The method of using ink to replace back drilling according to claim 1, characterized in that: In step S5, the depth of the recessed etching is at least 5 times the thickness of the photosensitive alkali-soluble film.

3. The method of using ink to replace back drilling according to claim 1 or 2, characterized in that: In step S1, the thickness of the photocurable ink is 10-30 microns, and the outer diameter of the photocurable ink is 0.2-0.5 mm larger than the hole diameter of the drilling position.

4. The method of using ink to replace back drilling according to claim 3, characterized in that: The photosensitive alkali-soluble film is a wet film or a dry film, and the thickness of the photosensitive alkali-soluble film is 10-40 microns.

5. The method of using ink to replace back drilling according to claim 4, characterized in that: When the photosensitive alkali-soluble film is a wet film with a thickness of 10 microns, the outer diameter of the photocurable ink is 0.2 mm larger than the hole diameter of the drilling position; the depth of the concave etching is 50 microns.

6. The method of using ink to replace back drilling according to claim 5, characterized in that: When the photosensitive alkali-soluble film is a dry film with a thickness of 40 microns, the outer diameter of the photocurable ink is 0.5 mm larger than the hole diameter of the drilling position, and the depth of the concave etching is 200 microns.

7. A method of using ink to replace back drilling, characterized in that: The following steps are involved: S1. Provide a plurality of core boards, including at least one target core board, coat or affix a photosensitive alkali-soluble film on all the core boards, and use a negative film process to produce inner-layer circuits on the core boards, and produce a copper disk having an outer diameter larger than the drilling position at a position corresponding to the drilling hole on one surface of the target core board, and do not perform film stripping after etching; S2, spraying a layer of light-curing ink covering the outside of the photosensitive alkali-soluble film at the position corresponding to the copper disk, and exposing and curing the light-curing ink by UV light; S3, removing the photosensitive alkali-soluble film on the target core board that is not covered by the photocurable ink; S4, laminating and pressing a plurality of core boards and outer copper foils into a production board through a prepreg in a preset order; one surface of the production board is a connection layer to be connected to the inner copper disk, and the other surface is a non-connection layer not connected to the inner copper disk; S5. Drill through holes at corresponding drilling positions on the production board. After drilling, the photosensitive alkali-soluble film exposed in the hole is etched back to form an etched position. Then a layer of copper is plated on the hole wall by chemical copper. During chemical copper, no copper layer is deposited at the etched position in the through hole, forming an isolation ring. Then, the copper layer at the hole mouth is drilled out to disconnect the non-connected layer from the copper layer on the hole wall. Finally, the production board is fully electroplated. During full-board electroplating, the copper deposited layer on the wall between the isolation ring and the non-connected layer will dissolve into the electroplating solution to form a copper-free isolation zone, so that the inner copper disk is disconnected from the non-connected layer at the through hole.

8. The method of using ink to replace back drilling according to claim 7, characterized in that: In step S5, the depth of the recessed etching is at least 5 times the thickness of the photosensitive alkali-soluble film.

9. The method of using ink to replace back drilling according to claim 7 or 8, characterized in that: In step S1, the thickness of the photosensitive alkali-soluble film is 10-40 microns, the thickness of the photocurable ink is 10-30 microns, and the outer diameter of the photocurable ink is 0.2-0.5 mm larger than the hole diameter of the drilling position.

10. The method of using ink to replace back drilling according to claim 9, characterized in that: When the photosensitive alkali-soluble film is a wet film with a thickness of 10 microns, the outer diameter of the photocurable ink is 0.2 mm larger than the hole diameter of the drilling position; the depth of the concave etching is 50 microns; When the photosensitive alkali-soluble film is a dry film with a thickness of 40 microns, the outer diameter of the photocurable ink is 0.5 mm larger than the hole diameter of the drilling position, and the depth of the concave etching is 200 microns.

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