Circuit board hole plugging method and circuit board

Abstract

The invention discloses a circuit board hole plugging method and a circuit board, and belongs to the technical field of circuit board manufacturing, and the method comprises the steps: carrying out the pretreatment of a substrate, and forming a first hole and a first circuit layer in the substrate; coating printing ink on the surface of the pre-treated substrate by using a roller, and filling partial space of the first hole with the printing ink; after filling is completed, the coated printing ink is cured; respectively stacking prepregs on the two sides of the cured substrate, stacking release films on the surfaces of the prepregs, heating and pressing to enable the molten prepregs to fill the residual space of the first hole, and cooling and curing; after hole plugging is completed, the release film is removed. Preliminary hole plugging is carried out through roller ink coating and curing, final hole plugging is completed by combining and utilizing the release film to press the prepreg, the process route is optimized, the product production period is prolonged, and the manufacturing cost and the product reliability risk are reduced through new process development on the premise that the product quality is met.

Description

Technical Field

[0001] The present application relates to the technical field of circuit board manufacturing, and in particular to a circuit board plugging method and a circuit board. Background Art

[0002] With the continuous advancement of mini-LED (Mini Light-Emitting Diode) technology, market penetration is increasing, and the demand for cost sensitivity in the supply chain is rising. On the one hand, as fine-pitch displays move towards higher resolutions, the costs of technologies such as mass transfer, packaging, and PCB (Printed Circuit Board) fabrication are rising. On the other hand, increasingly fierce market competition is further increasing cost pressures. To enhance product cost advantages, improvements can be made to existing PCB fabrication processes.

[0003] The existing circuit board manufacturing process primarily involves pre-processing the substrate; after pre-processing, via plugging is performed; and after via plugging, post-processing steps include circuit fabrication, lamination, target drilling, edge grinding, copper reduction by browning, and laser drilling. The primary purpose of via plugging is to prevent solder from flowing into the vias during soldering, which can cause quality issues such as cold solder joints and short circuits. It also improves the reliability and electrical performance of the PCB. The existing via plugging process involves five steps: material selection and characterization, resin via plugging, baking, ceramic grinding, and AOI (Automatic Optical Inspection) for the resin via plugging. This requires a high level of equipment and materials, resulting in high manufacturing costs. Furthermore, the existing lamination process primarily uses prepreg (PP) and copper foil to laminate multilayer substrates. The presence of copper foil on the substrate complicates laser drilling. In order to minimize the difficulty of laser drilling, additional steps such as targeting, edge grinding, and browning copper reduction are required before laser drilling. This increases the demand for equipment and materials, resulting in higher manufacturing costs. Moreover, this method has limited effect in reducing the difficulty of laser drilling and still affects the accuracy and consistency of laser drilling. Summary of the Invention

[0004] The purpose of this application is to provide a circuit board plugging method and a circuit board, which performs preliminary plugging by roller coating ink and curing, and combines the use of release film to press the semi-cured sheet to complete the final plugging, wherein: the roller coating ink and curing process replaces the traditional resin plugging process, and the ceramic grinding plate and resin plugging AOI process are eliminated; the release film replaces the copper foil in the traditional copper foil pressing process, and the shooting, edge grinding and browning copper reduction processes are eliminated, the process route is optimized, and the product production cycle is improved. Under the premise of meeting product quality, the new process development is used to reduce the manufacturing cost and product reliability risk.

[0005] To achieve the above objectives, the present application provides a circuit board via plugging method, comprising:

[0006] performing pre-processing on the substrate to form a first hole and a first circuit layer in the substrate;

[0007] Using a roller to apply ink on the surface of the pre-treated substrate so that the ink fills part of the space in the first hole;

[0008] After the filling is completed, the applied ink is cured;

[0009] Prepregs are stacked on both sides of the cured substrate, and release films are stacked on the surfaces of the prepregs, followed by heating and pressing to allow the melted prepregs to fill the remaining space of the first hole, and then cooled and solidified;

[0010] After the plugging is completed, the release film is removed.

[0011] Optionally, the pre-processing of the substrate to form the first hole and the first circuit layer in the substrate includes:

[0012] Cutting the substrate to obtain the substrate with a target size;

[0013] Drilling the substrate after the cutting process to form the first hole in the substrate;

[0014] depositing a copper layer on the surface of the drilled substrate and in the first hole;

[0015] Electroplating the copper layer on the surface of the substrate after the deposition process;

[0016] Laminating a photosensitive dry film on the surface of the substrate after the electroplating treatment;

[0017] exposing and developing the photosensitive dry film to form a patterned photosensitive dry film;

[0018] Etching the copper layer that is not covered by the patterned photosensitive dry film to form the first circuit layer;

[0019] Performing AOI inspection on the first circuit layer.

[0020] Optionally, the ink is a mixture of UV ink and a diluent;

[0021] The step of curing the applied ink comprises:

[0022] Pre-baking and curing the applied ink to allow the diluent to evaporate quickly, so that the remaining ink has viscosity;

[0023] UV curing the remaining ink, cross-linking macromolecules of the remaining ink, and obtaining the cured ink.

[0024] Optionally, the release film is a TPX release film.

[0025] The removing the release film comprises:

[0026] Tearing off the release film; or, dissolving the release film by using a film dissolving solution.

[0027] Optionally, after the removing the release film, the method further comprises:

[0028] Laser drilling the substrate covered with the prepreg, and forming a second hole in the substrate;

[0029] Depositing a copper layer on the surface of the substrate after the drilling and in the second hole;

[0030] Electroplating the copper layer in the second hole of the substrate after the depositing;

[0031] Bonding a photosensitive dry film on the surface of the substrate after the electroplating;

[0032] Exposing and developing the photosensitive dry film, and forming a patterned photosensitive dry film;

[0033] Etching the copper layer not covered by the patterned photosensitive dry film, and forming a second circuit layer;

[0034] Performing AOI inspection on the second circuit layer.

[0035] Optionally, the first circuit layer comprises a first pad and a second pad; the first pad is configured to be electrically connected with a first pin of a chip; and the second pad is configured to be electrically connected with a second pin of the chip.

[0036] After the removing the release film, the method further comprises:

[0037] Forming an insulating bridge on the surface of the substrate between the first pad and the second pad; the thickness of the insulating bridge is greater than the thickness of the first pad and greater than the thickness of the second pad.

[0038] Optionally, the insulating bridge is an ink bridge.

[0039] The forming the insulating bridge on the surface of the substrate between the first pad and the second pad comprises:

[0040] Performing inkjet printing on the surface of the substrate between the first pad and the second pad, and curing the non-polar ink layer by UV laser during the inkjet printing process to form the ink bridge;

[0041] Alternatively, a layer of the non-polar ink layer is screen-printed on the surface of the substrate between the first pad and the second pad, and the non-polar ink layer is cured after the screen printing is completed to form the ink bridge.

[0042] Optionally, after laser drilling is performed on the substrate covered with the prepreg to form a second hole in the substrate, the insulating bridge is formed on the surface of the substrate between the first pad and the second pad.

[0043] Optionally, before forming the insulating bridge on the substrate surface between the first pad and the second pad, the method further includes:

[0044] The prepreg covering the surface of the substrate is etched and roughened by using a chemical solution to remove residues formed in the second hole after laser drilling and to clean the surface of the substrate.

[0045] To achieve the above-mentioned purpose, the present application also provides a circuit board, including: a circuit board prepared by the above-mentioned circuit board plugging method.

[0046] Obviously, the circuit board plugging method provided by this application has the following advantages compared with the traditional circuit board plugging process:

[0047] (1) The process of "roller coating ink and curing" is used to replace the process of "resin plugging, baking plate, ceramic grinding plate and resin plugging AOI". Since the circuit production is completed before "roller coating ink", there is no need for ceramic grinding plate; and since ink is also a dielectric layer, it has no effect on the inner layer circuit and does not require AOI inspection, so the "ceramic grinding plate and resin plugging AOI" process can be cancelled. This greatly reduces the product's demand for equipment and materials, improves the product's pass rate and reduces manufacturing costs, completes the process transformation, reduces the product's manufacturing costs, and improves the product's core competitiveness in terms of cost;

[0048] (2) Pre-filling the holes with ink can eliminate most of the air and water vapor, and then using the release film to press the semi-cured sheet, and filling the remaining part of the hole with the melted semi-cured sheet, so that there are no quality risks in the entire pressing process. At the same time, the release film is used to replace the copper foil in the pressing process. The release film is used as an auxiliary material and can be removed after pressing, so as to obtain a PCB board without copper foil covering. Because there is no copper foil covering, the semi-cured sheet has a certain degree of permeability, which greatly improves the performance of the laser (including alignment and punching), reduces the difficulty of subsequent laser punching, and simultaneously improves the accuracy and consistency of laser punching, and achieves a breakthrough in the process capability from large holes (aperture 100μm) to small holes (aperture 70μm). In addition, there is no need to carry out the "targeting, edge grinding and browning copper reduction" process, which optimizes the process route and reduces the processing cost while improving quality and efficiency.

[0049] The present application also provides a circuit board having the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0051] Figure 1 This is a schematic diagram of the structure of a resin plug hole;

[0052] Figure 2 Schematic diagram of a conventional laminated structure to be pressed;

[0053] Figure 3 is a schematic diagram of laminating a laminated structure to be laminated;

[0054] Figure 4 A flow chart of a circuit board via plugging method provided in an embodiment of the present application;

[0055] Figure 5 A schematic structural diagram of a laminated structure to be laminated provided in an embodiment of the present application;

[0056] Figure 6 A schematic structural diagram of a copper foil-free pressed circuit board provided in an embodiment of the present application;

[0057] Figure 7 A schematic cross-sectional view of a circuit board provided in an embodiment of the present application.

[0058] The following are the descriptions of the reference numerals:

[0059] 1 - resin material; 2 - via hole; 3 - substrate; 31 - first circuit layer; 4 - copper foil; 5 - prepreg; 6 - to-be-pressed laminated structure; 7 - carrier plate; 8 - release film; 91 - first pad; 92 - second pad; 10 - insulating bridge; 11 - solder resist ink layer. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0061] The existing circuit board preparation process mainly includes:

[0062] Material preparation: substrate, plug hole resin, ink, drill bit, milling cutter, prepreg;

[0063] Inner layer process flow: sequentially perform cutting, drilling, copper plating, copper electroplating, hole plugging, dry film pressing, exposure, development, etching, inner layer AOI, and pressing;

[0064] Outer layer process flow: sequentially perform targeting, edge grinding, brown copper reduction, laser drilling, copper plating, hole filling electroplating, dry film pressing, exposure, development, etching, outer layer AOI, and post-processing technology.

[0065] Among them, the hole plugging process mainly includes five steps: material selection and characteristics, resin hole plugging, baking plate, ceramic grinding plate, and resin hole plugging AOI, and the specific principle is as follows:

[0066] Material selection and characteristics: usually select high molecular materials such as epoxy resin as the main material of hole plugging; such resins have good fluidity, adhesion and compatibility with substrate materials, can form a close bond with the substrate after curing, and also have certain electrical performance, heat resistance and chemical corrosion resistance;

[0067] Resin hole plugging: filling method is to fill resin material 1 into via hole 2 by means of vacuum pressure filling, pressure filling or screen printing equipment and process, as shown in Figure 1 Under vacuum or by applying a certain pressure, air in the via hole 2 can be effectively removed, so that the resin material 1 can fully fill every corner of the via hole 2, ensuring the density and fullness of the filling, and avoiding defects such as air bubbles;

[0068] A resin plugging method for PCB back-drilling mentioned in the related art uses a screen printing process to plug the holes, including placing a screen printing screen above the back-drilling hole on the PCB board; placing an aluminum sheet above the screen printing screen, and making the aluminum sheet window correspond to the back-drilling hole; filling resin on the aluminum sheet, and starting the scraper control device to keep the scraper at 6KG / CM 2 The resin is scraped twice on the aluminum sheet with a pressure of 20 Hz and a scraping frequency of 20 Hz, so that the resin enters the back-drilled hole along the window of the aluminum sheet and flows into the through hole below the back-drilled hole, filling the entire stepped through hole to ensure the saturation of the resin in the hole; the PCB board after the plugging is completed is placed in an oven and baked at 80 ℃ for 30 minutes, then at 90 ℃ for 30 minutes, and then at 150 ℃ for 60 minutes to complete the resin plugging of the PCB board;

[0069] Baking the board: After filling, the substrate is placed in a specific curing environment, such as an oven or UV (Ultraviolet) curing equipment, and operated according to the curing process parameters of the resin material. During the curing process, the resin material undergoes a chemical reaction, gradually transforming from a liquid to a solid state, forming a solid plug structure. The cured resin plug has good mechanical strength and chemical stability, and can withstand various stresses and environmental influences during subsequent processing and use.

[0070] Ceramic grinding plate: The surface of the resin plug hole after curing may not be flat enough, and requires post-processing such as grinding to make it flush with the substrate surface, forming a smooth and flat surface for subsequent copper plating and other processing; after copper plating on the hole surface, a good electrical connection and mechanical bond are formed between the resin plug hole and the metal copper, further improving the reliability and performance of the substrate;

[0071] Resin plug hole AOI: AOI is used to check the filling of holes (such as buried vias) after grinding, as well as quality abnormalities such as pits, and perform secondary repairs.

[0072] The lamination process mainly includes five steps: material preparation, laminate design and stacking, lamination operation (including pre-lamination and formal lamination), cooling and demoulding. The specific principles are as follows:

[0073] Material preparation: Prepare the required inner layer substrate (substrate after plugging), prepreg, copper foil and other materials. The substrate must ensure that the circuit pattern accuracy error is within ±5μm, there are no short circuits, open circuits, or pinhole defects with a diameter greater than 50μm, and the circuit conductivity is good. Prepreg products with appropriate performance parameters should be selected according to different application scenarios.

[0074] Layered design and stacking: Figure 2As shown, a multilayer substrate 3 (including a double layer of copper foil 4 on the surface) is laminated in accordance with electromagnetic compatibility principles, typically adopting a symmetrical structure of "signal layer - ground layer - power layer - bottom layer - signal layer". Prepreg 5 is stacked on both the front and back sides of each substrate 3. After the laminated structure of substrate 3 and prepreg 5 is obtained, copper foil 4 is stacked on the front and back sides of the laminated structure. A visual alignment system is used to position each layer of material, with an X / Y axis alignment accuracy of ±25μm. Auxiliary materials include high-temperature resistant polyimide release paper and glass fiber mat.

[0075] Pre-pressing: Figure 3 As shown, the laminated structure 6 to be laminated obtained in the above steps is placed on a carrier plate 7 of a laminating machine; preliminary lamination is performed at low temperature and low pressure to initially bond the interlayer materials in preparation for formal lamination; preheating and low pressure are used in this process to avoid excessive flow of the interlayer materials and to prevent the ingress of air and impurities;

[0076] Formal lamination: This is carried out in a high-temperature, high-pressure environment to allow the interlayer materials to fully flow and solidify, and ultimately the copper foil, prepreg, and inner substrate are laminated to form a solid multi-layer PCB board. Temperature control uses multi-zone temperature control technology, and the surface temperature difference of the laminated steel plate used is within the range of -1.5°C to 1.5°C. Taking the substrate as an example of an FR4 (epoxy resin glass fiber board) core board, its curing curve is divided into preheating, curing, and post-curing sections. Pressure control uses a servo hydraulic system, and the pressure gradient is controlled within 5psi / mm. Large-area panels require the use of a zoned pressure compensation function to ensure that the thickness uniformity error is within the range of -5μm to 5μm.

[0077] Cooling and demoulding: After the pressing is completed, gradient cooling is carried out first. First, it is naturally cooled to below 120℃ in the equipment, and then transferred to the air cooling tunnel to cool to room temperature.

[0078] Among them, target drilling: X-Ray (X-Radiation) is used to irradiate the inner target area, and then the drill bit is used to drill copper in this area to provide positioning and alignment reference for subsequent processing.

[0079] Among them, grinding: use tools such as gong machines or milling machines to trim the edges of multi-layer PCB boards.

[0080] Among them, browning reduces copper:

[0081] Improve laser absorption rate: Untreated copper foil has a very low absorption rate for CO2 laser. After browning treatment, an oxide layer is formed on the surface of the copper foil, and the color changes to brown-red or black. The absorption capacity of laser is significantly enhanced, which can more effectively convert laser energy into heat energy, thereby improving drilling efficiency.

[0082] Can enhance bonding strength: During the browning process, the copper foil surface forms a uniform honeycomb microstructure in the micro-etching reaction, which increases the specific surface area, so that the copper foil surface after pressing has good bonding strength with the resin material, which helps to prevent the copper foil and the substrate material from delamination during laser drilling, ensures the quality and stability of the hole wall, and reduces the occurrence of defects such as blistering;

[0083] It can reduce light reflectivity: the browned copper foil surface reflects less laser light, and its rough surface structure can also increase the diffuse reflection of light, further reducing the reflection loss of the laser, so that more laser energy can be used for material ablation, improving the accuracy and quality of drilling, while avoiding damage to the laser equipment by reflected light.

[0084] In addition, the conventional thickness of laminated copper foil is 12μm, and drilling such a thick copper foil requires sacrificing laser efficiency and drilling accuracy and quality. Therefore, the copper is reduced to 5μm-6μm to improve the consistency of drilling.

[0085] The existing plugging process mainly includes five steps: material selection and characteristics, resin plugging, baking plate, ceramic grinding plate, and resin plugging AOI. It has high requirements for equipment and materials, resulting in high manufacturing costs. In addition, the existing lamination process mainly uses semi-cured sheets and copper foil to press the multi-layer substrate. The copper foil covering the substrate increases the difficulty of laser drilling. In order to minimize the difficulty of laser drilling, additional steps such as targeting, edge grinding, and browning copper reduction are required before laser drilling. This increases the demand for equipment and materials, resulting in high manufacturing costs. Moreover, this method has limited effect on reducing the difficulty of laser drilling and still affects the accuracy and consistency of laser drilling.

[0086] Therefore, the present application provides a circuit board plugging method, which performs preliminary plugging by roller coating ink and curing, and combines the use of release film to press the semi-cured sheet to complete the final plugging, wherein: the roller coating ink and curing process replaces the traditional resin plugging process, and the ceramic grinding plate and resin plugging AOI process are eliminated; the release film replaces the copper foil in the traditional copper foil pressing process, and the targeting, edge grinding and browning copper reduction processes are eliminated, the process route is optimized, and the product production cycle is improved. Under the premise of meeting product quality, new process development is used to reduce manufacturing costs and product reliability risks.

[0087] Please refer to Figure 4 , Figure 4 A flowchart of a circuit board via plugging method provided in an embodiment of the present application may include:

[0088] S101: Pre-processing the substrate to form a first hole and a first circuit layer in the substrate.

[0089] This embodiment does not limit the specific type of the substrate used, which can be determined according to actual conditions. For example, the substrate can be an FR4 core board.

[0090] This embodiment does not limit the specific type of the first hole, which can be determined according to actual conditions. For example, the first hole can include a through hole and / or a blind hole.

[0091] This embodiment does not limit the specific method of pre-processing the substrate, as long as it is ensured that the first hole and the first circuit layer can be formed in the substrate. For example, the following method can be used:

[0092] Cutting the substrate to obtain a substrate with a target size;

[0093] Drilling the cut substrate to form a first hole in the substrate;

[0094] depositing a copper layer on the surface of the drilled substrate and in the first hole;

[0095] Electroplating a copper layer on the surface of the substrate after the deposition process;

[0096] Laminating a photosensitive dry film on the surface of the electroplated substrate;

[0097] Exposing and developing the photosensitive dry film to form a patterned photosensitive dry film;

[0098] Etching the copper layer not covered by the patterned photosensitive dry film to form a first circuit layer;

[0099] Perform AOI inspection on the first circuit layer.

[0100] It should be noted that after step S101 is completed, the first hole formed is a via hole.

[0101] S102: using a roller to apply ink on the surface of the pre-treated substrate so that the ink fills part of the space in the first hole.

[0102] It should be noted that the roller coating method used in this embodiment is more cost-effective and efficient than other processes, and can be applied to different products and a wider range of application scenarios. The ink used to fill the holes in this embodiment is more cost-effective, heat-resistant, and has a smaller shrinkage rate than other materials, making it more suitable for filling holes.

[0103] This embodiment does not limit the specific type of ink, which can be determined according to actual conditions. Preferably, the ink can be a mixture of UV ink and a diluent.

[0104] S103: After the filling is completed, the applied ink is cured.

[0105] This embodiment does not limit the specific curing method, as long as the ink can be cured. For example, when the ink is a mixture of UV ink and diluent, the following method can be used for curing:

[0106] Pre-bake and cure the applied ink to allow the diluent to evaporate quickly, making the remaining ink viscous;

[0107] The remaining ink is UV cured to cross-link the remaining ink macromolecules to obtain cured ink.

[0108] It should be noted that UV ink is an ink with a low expansion coefficient. In this embodiment, the low expansion coefficient UV ink is first subjected to a roller coating process to fill the pores with ink; then, the diluent in the ink mixture is rapidly evaporated through pre-baking and curing, thereby giving the ink a certain viscosity; finally, the macromolecules are cross-linked through UV curing to completely cure the ink.

[0109] S104: Prepregs are stacked on both sides of the cured substrate, and release films are stacked on the surfaces of the prepregs, followed by heating and pressing to allow the melted prepregs to fill the remaining space of the first hole, and then cooled and solidified.

[0110] This embodiment does not limit the specific type of release film, as long as it can be easily peeled off. Preferably, the release film can be TPX release film; TPX release film is a transparent heat-resistant polyolefin polymer material with polymethylpentene as the base material, with high light transmittance (over 90%), low density (0.83g / cm3) and high temperature resistance (melting point 230-240°C).

[0111] This embodiment does not limit the specific number of stacked substrates, which can be determined according to actual conditions. For example, one layer of substrate can be stacked, or at least two layers of substrates can be stacked. When stacking one layer of substrate, a layer of prepreg can be stacked on both sides of the cured substrate, and a layer of release film can be stacked on the surface of the prepreg (here refers to the side of the prepreg facing away from the substrate); when stacking at least two layers of substrate, a layer of cured substrate and a layer of prepreg can be stacked alternately, and the surface of the outermost substrate can be covered with a prepreg, and a layer of release film can be stacked on both sides of the obtained stacked structure. Figure 5 As shown (the prepreg between adjacent substrates is not shown in the figure), the release film 8 can be stacked in the order of a layer of prepreg, a layer of substrate 3 with a first circuit layer 31, a layer of prepreg 5, a layer of substrate 3 with a first circuit layer 31, a layer of prepreg 5, a layer of substrate 3 with a first circuit layer 31, a layer of prepreg 5, a layer of substrate 3 with a first circuit layer 31, a layer of prepreg 5, a layer of substrate 3 with a first circuit layer 31, a layer of release film 8.

[0112] S105: After the plugging is completed, the release film is removed.

[0113] It should be noted that if Figure 6 As shown, this embodiment replaces the laminated copper foil with a release film. The release film serves as an auxiliary material and can be removed after lamination, resulting in a PCB board without copper foil covering. Without copper foil interference, the laser equipment alignment system can directly capture the optical point of the inner layer circuit in the subsequent laser drilling process, reducing the drilling error of the target drilling machine and achieving more accurate alignment. The laser directly hits the prepreg without the reflection and absorption of the copper metal, resulting in better drilling accuracy, quality, and consistency. Simultaneously, the 100μm laser hole can be reduced to 70μm, and the alignment accuracy is improved from 50μm to 25μm, resulting in better overall performance.

[0114] This embodiment does not limit the specific method of removing the release film, as long as the release film can be peeled off from the surface of the prepreg, for example, the release film can be torn off; or the release film can be dissolved by a film-dissolving solution.

[0115] Furthermore, in order to achieve inter-layer interconnection, this embodiment may further include, after step S105:

[0116] performing laser drilling on the substrate covered with the prepreg to form a second hole in the substrate;

[0117] depositing a copper layer on the punched substrate surface and in the second hole;

[0118] electroplating a copper layer in the second hole of the substrate after the deposition process;

[0119] Laminating a photosensitive dry film on the surface of the electroplated substrate;

[0120] Exposing and developing the photosensitive dry film to form a patterned photosensitive dry film;

[0121] Etching the copper layer not covered by the patterned photosensitive dry film to form a second circuit layer;

[0122] Perform AOI inspection on the second circuit layer.

[0123] This embodiment does not limit the specific type of the second hole, which can be determined according to actual conditions. For example, the second hole can be a blind hole.

[0124] This embodiment does not limit the specific thickness of the deposited copper layer. For example, the thickness of the deposited copper layer may be 0.3 μm-0.5 μm, including both ends.

[0125] It should be noted that the purpose of electroplating in this embodiment is to thicken the copper layer so that the second hole is filled. This embodiment does not limit the specific thickness of the electroplated copper layer. For example, the thickness of the electroplated copper layer can be 18μm-20μm, including both ends.

[0126] It should be noted that, in this embodiment, after step S101 is completed; or after the second circuit layer is formed, the substrate having the first circuit layer and the second circuit layer is obtained as a PCB board.

[0127] Furthermore, in order to improve product quality, after performing AOI inspection on the second circuit layer, this embodiment may further include: post-processing the substrate after the circuit layer is manufactured (ie, the substrate having the first circuit layer and the second circuit layer).

[0128] This embodiment does not limit the specific manner of post-processing, which can be determined according to actual conditions. For example, post-processing may include:

[0129] Solder resist: Apply ink to the second circuit layer to form a solder resist ink layer;

[0130] Printing characters / baking board: Printing character ink on the solder mask ink layer and baking the board for curing;

[0131] CNC milling / dimension measurement: Use CNC (Computer Numerical Control) milling machines and milling cutters to process the shape of the PCB board after curing the baking board, and measure and monitor the dimensions required by the drawings;

[0132] Electrical testing / FQC: Electrical testing and FQC (Final Quality Control) are performed on PCB boards after the finished surface processing. Electrical testing includes functional testing, and FQC includes appearance inspection.

[0133] OSP: After the inspection, the PCB board is subjected to OSP (Organic Solderability Preservative) surface treatment to prevent the pad from oxidation;

[0134] Packaging: Packing the PCB boards after OSP surface treatment.

[0135] This application can be applied to any fine-pitch HDI (High-Density Interconnect) product, such as a fine-pitch LED display. Taking a fine-pitch LED display as an example, after the substrate is post-processed after the circuit layer is completed, it can also include: module patching and module testing, including:

[0136] (1) The film layer is mounted using the SMD (Surface Mount Device) mounting process, which may include:

[0137] Circuit board preparation: Clean, dry, and perform anti-static treatment on the PCB to remove impurities such as oil, dust, etc. on the surface of the PCB to ensure the quality of subsequent solder paste printing and component placement, while preventing static electricity from damaging the components;

[0138] Solder paste printing: Printing solder paste on the pads of the PCB board to provide a soldering medium for subsequent patch placement;

[0139] SMT: Use a SMT machine to accurately mount the packaged LED light-emitting unit to the corresponding position on the PCB board;

[0140] Reflow soldering: Place the PCB board with the LED light-emitting unit mounted on it into a reflow soldering oven. After preheating, heating, insulation and cooling, the solder paste melts and solidifies, completing the solder connection between the LED light-emitting unit and the PCB board.

[0141] Inspection: Use AOI, X-ray inspection and other equipment to inspect the assembled LED modules to check the quality of solder joints, whether there are any missing or misaligned components, and ensure that the electrical performance and reliability of the products meet the requirements;

[0142] Rework: For unqualified products or defective solder joints found during the inspection process, rework is carried out. During rework, it is usually necessary to first remove the defective components or solder joints, and then re-perform solder paste printing, patch and reflow soldering operations to repair the defects.

[0143] (2) Module testing may include:

[0144] Functional test: Perform functional tests on the assembled LED modules, including lighting tests and photoelectric parameter tests, to check whether the luminous color, brightness, wavelength, forward voltage, etc. meet the standards;

[0145] Aging test: The LED module is subjected to aging tests under certain conditions, usually including high temperature aging and constant current aging, to simulate the long-term working state during actual use, discover potential quality problems in advance, and screen out unqualified products.

[0146] It should be noted that the first circuit layer in this embodiment may include a first solder pad and a second solder pad; the first solder pad can be used to electrically connect to the first pin of the chip; the second solder pad can be used to electrically connect to the second pin of the chip; the chip can be an LED light-emitting unit; the first pin can be a P-pole pin; the first pin can be an N-pole pin.

[0147] It should be noted that the current flip-chip LED is soldered to the PCB board through solder paste printing. Since the distance between the P-pole pin and the N-pole pin is only 50μm, it will cause tin whisker growth and ionization migration, thus causing short circuit problems.

[0148] Furthermore, in order to reduce the tin whisker effect of the chiplet connection bridge, an insulating bridge can be used to raise the chiplet connection bridge to suppress the growth of tin whiskers. Specifically, after step S105, this embodiment may further include: forming an insulating bridge on the substrate surface between the first pad and the second pad; the thickness of the insulating bridge is greater than the thickness of the first pad and greater than the thickness of the second pad. Figure 7 As shown, a first solder pad 91 and a second solder pad 92 are provided on the surface of the substrate 3; the first solder pad 91 is used to electrically connect to the P-pole pin of the chip; the second solder pad 92 is used to electrically connect to the N-pole pin of the chip; an insulating bridge 10 is provided on the surface of the substrate 3 in the area between the first solder pad 91 and the second solder pad 92; in addition, other areas on the surface of the substrate 3 can be used to set a solder resist ink layer 11.

[0149] It should be noted that this embodiment sets an insulating bridge in the area between the P-pole pin and the N-pole pin of the chip, which can reduce the occurrence of abnormalities such as tin short circuit caused by the solder paste being too close during the solder paste printing process and the subsequent electrochemical growth, thereby improving the product's pass rate and overall yield.

[0150] This embodiment does not limit the specific type of the insulating bridge, as long as it has insulating properties. Preferably, the insulating bridge can be an ink bridge.

[0151] This embodiment does not limit the specific method of forming the insulating bridge, as long as it can be formed between the first pad and the second pad and the thickness is greater than the thickness of the first pad and the thickness of the second pad. For example, when the insulating bridge is an ink bridge, the insulating bridge can be formed in the following two ways:

[0152] An insulating bridge is formed on a surface of a substrate between a first pad and a second pad, comprising:

[0153] A non-polar ink layer is inkjet-printed on the surface of the substrate between the first pad and the second pad, and the non-polar ink layer is cured by UV laser during the inkjet printing process to form an ink bridge;

[0154] Alternatively, a non-polar ink layer is screen-printed on the substrate surface between the first pad and the second pad, and the non-polar ink layer is cured after the screen printing is completed to form an ink bridge.

[0155] It should be noted that, in this embodiment, the UV laser is used to print and cure the ink during the inkjet printing process, which can reduce the lateral flow of the ink.

[0156] This embodiment does not limit the specific width of the non-polar ink layer. For example, the width of the non-polar ink layer can be 40 μm-50 μm, inclusive. This embodiment does not limit the specific thickness of the non-polar ink layer. For example, the thickness of the non-polar ink layer can be 20 μm-25 μm, inclusive. This embodiment does not limit the specific distance of the self-advection of the non-polar ink layer. For example, the self-advection distance of the non-polar ink layer can be less than 2 μm.

[0157] This embodiment does not limit the specific time of forming the insulating bridge, but only ensures that it can be formed before printing the solder paste. Preferably, the substrate covered with the semi-cured sheet can be laser drilled to form a second hole in the substrate, and then an insulating bridge can be formed on the surface of the substrate between the first pad and the second pad.

[0158] It should be noted that, in the subsequent copper layer deposition process of this embodiment, the copper layer cannot be deposited at the insulating bridge position due to the obstruction of the non-polar ink layer.

[0159] Furthermore, before forming an insulating bridge on the substrate surface between the first solder pad and the second solder pad, this embodiment may also include: etching and roughening the semi-cured sheet covering the substrate surface with a solution to remove residues formed in the second hole after laser drilling, and cleaning the substrate surface.

[0160] It should be noted that, in this embodiment, the semi-cured sheet covering the surface of the substrate is etched and roughened by using a chemical solution, so that the residue formed in the second hole after laser drilling (including the carbon-based residue generated by the semi-cured sheet under the action of the laser, and the melted semi-cured sheet) can be removed, and the substrate surface can be cleaned at the same time, thereby improving the bonding strength between the insulating bridge and the semi-cured sheet.

[0161] It should be noted that, in this embodiment, there is no need to perform a step of removing residues before the subsequent copper layer deposition process.

[0162] Based on the above embodiments, the present application has the following advantages compared with the traditional circuit board plugging process:

[0163] (1) The process of "roller coating ink and curing" is used to replace the process of "resin plugging, baking plate, ceramic grinding plate and resin plugging AOI". Since the circuit production is completed before "roller coating ink", there is no need for ceramic grinding plate; and since ink is also a dielectric layer, it has no effect on the inner layer circuit and does not require AOI inspection, so the "ceramic grinding plate and resin plugging AOI" process can be cancelled. This greatly reduces the product's demand for equipment and materials, improves the product's pass rate and reduces manufacturing costs, completes the process transformation, reduces the product's manufacturing costs, and improves the product's core competitiveness in terms of cost;

[0164] (2) Pre-filling the holes with ink can eliminate most of the air and water vapor, and then using the release film to press the semi-cured sheet, and filling the remaining part of the hole with the melted semi-cured sheet, so that there are no quality risks in the entire pressing process. At the same time, the release film is used to replace the copper foil in the pressing process. The release film is used as an auxiliary material and can be removed after pressing, so as to obtain a PCB board without copper foil covering. Because there is no copper foil covering, the semi-cured sheet has a certain degree of permeability, which greatly improves the performance of the laser (including alignment and punching), reduces the difficulty of subsequent laser punching, and simultaneously improves the accuracy and consistency of laser punching, and achieves a breakthrough in the process capability from large holes (aperture 100μm) to small holes (aperture 70μm). In addition, there is no need to carry out the "targeting, edge grinding and browning copper reduction" process, which optimizes the process route and reduces the processing cost while improving quality and efficiency.

[0165] An embodiment of the present application further provides a circuit board, including: a circuit board prepared by the circuit board hole plugging method described above.

[0166] Based on the above embodiments, the present application is prepared by the above-mentioned circuit board plugging method and also has the above-mentioned beneficial effects.

[0167] The following is a specific example to illustrate the above circuit board preparation process. The process is as follows:

[0168] Material preparation: FR4 core board, ink, drill bit, milling cutter, TPX release film, prepreg;

[0169] Inner layer process flow:

[0170] 1. Pre-processing: cutting, drilling, copper deposition, copper electroplating, dry film pressing, exposure, development, etching, inner layer AOI;

[0171] 2. Ink roller coating: Use a roller to apply a mixture of low expansion coefficient UV ink and diluent on the surface of the pre-treated substrate, so that the ink mixture fills part of the space in the first hole;

[0172] 3. Pre-baking and curing: Pre-baking and curing allows the diluent in the ink mixture to evaporate quickly, thus giving the ink a certain viscosity.

[0173] 4. UV curing: Through pre-baking curing, the diluent in the ink mixture is quickly volatilized, so that the ink has a certain viscosity;

[0174] 5. Lamination: Place prepregs on both sides of the cured substrate, and place TPX release film on the surface of the prepregs. Heat and press them together to allow the melted prepregs to fill the remaining space in the first hole, and then cool and solidify.

[0175] Outer layer process flow:

[0176] 1. Film tearing / dissolving: tear off the release film; or, dissolve the release film by using film dissolving chemicals; without the interference of copper foil, the laser equipment alignment system can directly grab the optical points of the inner layer circuit in the subsequent laser drilling process, reducing the drilling error of the targeting machine, improving the alignment accuracy, directly drilling the prepreg, and without the reflection and absorption of copper metal, the drilling precision and quality are better, and the consistency is better;

[0177] 2. Laser drilling: laser drilling the substrate covered with prepreg to form a second hole in the substrate;

[0178] 3. Debinding: etching and roughening the prepreg on the surface of the substrate by using chemicals to remove the residues formed in the second hole after laser drilling (including carbon-based residues generated by the prepreg under the action of laser, and melted prepreg), and at the same time, clean the surface of the substrate to improve the bonding force between the insulating bridge and the prepreg;

[0179] 4. Bridge printing: inkjet printing a layer of non-polar ink layer on the surface of the substrate between the first pad and the second pad, and curing the non-polar ink layer by UV laser during the inkjet printing process to form an ink bridge; the side flow of the ink can be reduced by curing the non-polar ink layer by UV laser during the inkjet printing process;

[0180] Or, screen printing a layer of non-polar ink layer on the surface of the substrate between the first pad and the second pad, and curing the non-polar ink layer after the screen printing is completed to form an ink bridge;

[0181] Wherein, the width of the non-polar ink layer is controlled within the range of 40μm-50μm, the thickness of the non-polar ink layer is within the range of 20μm-25μm; the self-flowing distance of the non-polar ink layer is less than 2μm;

[0182] 5. Copper deposition (without debinding): depositing a copper layer with a thickness of 0.3μm-0.5μm on the surface of the substrate after drilling and in the second hole; the graphite bridge position is blocked by the non-polar ink layer and cannot deposit a copper layer.

[0183] 6. Hole filling electroplating: electroplating a copper layer in the second hole of the substrate after deposition to thicken the copper layer to 18μm-20μm to fill the second hole;

[0184] 7. Second circuit layer manufacturing: sequentially performing dry film, exposure, development, etching, and outer layer AOI;

[0185] 8. Post-processing: sequentially performing solder mask, character printing, plate baking, CNC milling of outer shape, dimension measurement, electrical measurement, FQC, OSP, and packaging.

[0186] The principles and implementation methods of the present application are described herein using specific examples, and the various embodiments are in a progressive relationship. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. The description of the above embodiments is only used to help understand the method and core ideas of the present application. For those of ordinary skill in the art, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

[0187] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

Claims

1. A circuit board plugging method, characterized in that: include: performing pre-processing on the substrate to form a first hole and a first circuit layer in the substrate; Using a roller to apply ink on the surface of the pre-treated substrate so that the ink fills part of the space in the first hole; After the filling is completed, the applied ink is cured; Prepregs are stacked on both sides of the cured substrate, and release films are stacked on the surfaces of the prepregs, followed by heating and pressing to allow the melted prepregs to fill the remaining space of the first hole, and then cooled and solidified; After the plugging is completed, the release film is removed.

2. The circuit board plugging method according to claim 1, wherein: The pre-processing of the substrate to form a first hole and a first circuit layer in the substrate includes: Cutting the substrate to obtain the substrate with a target size; Drilling the substrate after the cutting process to form the first hole in the substrate; depositing a copper layer on the surface of the drilled substrate and in the first hole; Electroplating the copper layer on the surface of the substrate after the deposition process; Laminating a photosensitive dry film on the surface of the substrate after the electroplating treatment; exposing and developing the photosensitive dry film to form a patterned photosensitive dry film; Etching the copper layer that is not covered by the patterned photosensitive dry film to form the first circuit layer; Performing AOI inspection on the first circuit layer.

3. The circuit board plugging method according to claim 1, wherein: The ink is a mixture of UV ink and a diluent; The step of curing the applied ink comprises: Pre-baking and curing the applied ink to allow the diluent to evaporate quickly, so that the remaining ink has viscosity; The remaining ink is UV cured to cause macromolecular cross-linking of the remaining ink to obtain the cured ink.

4. The circuit board plugging method according to claim 1, wherein: The release film is a TPX release film; The removing of the release film comprises: Tear off the release film; or, dissolve the release film with a film-dissolving solution.

5. The circuit board plugging method according to claim 1, wherein: After removing the release film, the method further comprises: performing laser drilling on the substrate covered with the prepreg to form a second hole in the substrate; depositing a copper layer on the surface of the punched substrate and in the second hole; electroplating the copper layer in the second hole of the substrate after the deposition process; Laminating a photosensitive dry film on the surface of the substrate after the electroplating treatment; exposing and developing the photosensitive dry film to form a patterned photosensitive dry film; Etching the copper layer that is not covered by the patterned photosensitive dry film to form a second circuit layer; Performing AOI inspection on the second circuit layer.

6. The circuit board plugging method according to any one of claims 1 to 5, characterized in that: The first circuit layer includes a first pad and a second pad; the first pad is used to be electrically connected to a first pin of the chip; the second pad is used to be electrically connected to a second pin of the chip; After removing the release film, the method further comprises: An insulating bridge is formed on the surface of the substrate between the first pad and the second pad; the thickness of the insulating bridge is greater than the thickness of the first pad and greater than the thickness of the second pad.

7. The circuit board plugging method according to claim 6, wherein: The insulating bridge is an ink bridge; The forming of an insulating bridge on the substrate surface between the first pad and the second pad comprises: Performing inkjet printing on the surface of the substrate between the first pad and the second pad, and curing the non-polar ink layer by UV laser during the inkjet printing process to form the ink bridge; Alternatively, a layer of the non-polar ink layer is screen-printed on the surface of the substrate between the first pad and the second pad, and the non-polar ink layer is cured after the screen printing is completed to form the ink bridge.

8. The circuit board plugging method according to claim 6, wherein: After laser drilling is performed on the substrate covered with the prepreg to form a second hole in the substrate, the insulating bridge is formed on the surface of the substrate between the first pad and the second pad.

9. The circuit board plugging method according to claim 8, wherein: Before forming the insulating bridge on the substrate surface between the first pad and the second pad, the method further includes: The prepreg covering the surface of the substrate is etched and roughened by using a chemical solution to remove residues formed in the second hole after laser drilling and to clean the surface of the substrate.

10. A circuit board, characterized in that: include: A circuit board prepared by the circuit board plugging method according to any one of claims 1 to 9.

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