Method for drilling through holes in multi-layer board through carbon dioxide laser

Abstract

The invention discloses a method for drilling a multilayer board through hole by carbon dioxide laser, which comprises the following steps of: etching and removing a copper layer corresponding to all drilling positions when an inner layer circuit is manufactured on a core board, and manufacturing a hole ring arranged around the drilling positions on an inner layer needing to be connected with a hole wall copper layer; coating the surface of the hole ring of the core plate with a layer of alkali-soluble light-cured printing ink with the outer diameter larger than that of the drilling position, curing the alkali-soluble light-cured printing ink, and filling the hollow window of the hole ring with the alkali-soluble light-cured printing ink to form a printing ink disc; the core plate and the outer layer copper foil are laminated according to the lamination sequence through PP and then are pressed to form a production plate; etching and windowing are carried out on the drilling positions on the outer layer copper foil of the production board; a through hole is drilled in the position, corresponding to the drilling position, of the production board through laser, and the ink disc in the inner layer forms an ink ring; and dissolving and removing the ink ring on the hole wall by adopting an alkaline solution so as to expose the hole ring on the inner layer. The method can solve the problem that the carbon dioxide laser cannot ablate the copper foil, and the purpose of drilling the through holes in the multi-layer board through the carbon dioxide laser is achieved.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a method for drilling through holes in multilayer boards using a carbon dioxide laser. Background Technology

[0002] Circuit board drilling is a key process for interconnecting circuits between layers. As electronic devices become smaller and denser, traditional mechanical drilling can no longer meet the processing requirements of small holes. Laser drilling technology for multilayer boards has been widely used due to its advantages such as high precision and high flexibility.

[0003] There are significant differences between mechanical drilling and laser drilling for through holes in multilayer boards in terms of key indicators such as production efficiency, cost, and processing accuracy. A detailed comparative analysis is as follows: (a) Comparison of production efficiency The production efficiency of mechanical drilling of through holes in multilayer boards exhibits a "hole diameter dependent" characteristic: for conventional through holes with a diameter ≥ 0.2 mm, mechanical drilling can be carried out in batches by multi-axis drilling machines, with a short processing time per hole and high batch production efficiency; however, when the hole diameter is reduced to below 0.15 mm, the rigidity of the mechanical drill bit decreases significantly. In order to avoid drill bit breakage, the drilling speed and feed rate need to be reduced, the processing time per hole is significantly extended, and the production efficiency drops sharply.

[0004] Laser drilling is better suited for machining micro-diameter holes: for micro-through holes of 0.05-0.15mm, lasers can directly ablate the substrate through non-contact processing, eliminating the need to consider tool rigidity issues, and enabling high-speed scanning drilling, reducing single-hole processing time to the millisecond level. However, for large through holes with a diameter ≥0.2mm, laser drilling requires multiple scans to expand the hole diameter, making the processing time longer than mechanical drilling, thus negating its efficiency advantage. Furthermore, laser drilling can achieve multi-layer penetration processing in a single step, while mechanical drilling requires drilling layer by layer for multi-layer boards, further widening the efficiency gap in micro-diameter hole machining scenarios.

[0005] (II) Cost Comparison The core cost of mechanically drilling through holes in multilayer boards lies in the cutting tools and equipment maintenance: the initial purchase cost of mechanical drilling equipment is relatively low, but its core consumable is the drill bit. The manufacturing difficulty of small-diameter drill bits is high and their lifespan is short (usually they need to be replaced after drilling hundreds of holes). Moreover, drill bit replacement and debugging require production time, resulting in a high unit cost for small-batch, small-diameter processing. However, in the case of large-batch, conventional-diameter processing, the cost of cutting tools can be reduced through economies of scale, resulting in a significant advantage in unit cost.

[0006] The core cost of laser drilling lies in the initial investment in equipment: the initial purchase cost of laser drilling equipment (especially high-precision ultraviolet laser drilling machines) is 3-5 times that of mechanical drilling machines, and the equipment consumes electricity and laser source consumables (such as CO2 laser tubes and fiber laser modules) during operation, and the maintenance cost is also relatively high; however, in the scenario of small-batch, high-precision micro-diameter hole processing, laser drilling does not require frequent replacement of consumables, and can reduce unit costs by reducing debugging time and improving processing qualification rate, which is more economical.

[0007] (III) Accuracy Comparison The accuracy of mechanically drilled through holes in multilayer boards is limited by the cutting tools and mechanical structure: the hole diameter accuracy is usually ±0.02-0.05mm, and the hole position accuracy is affected by the spindle runout of the drilling machine, the accuracy of the guide rail, and the wear of the drill bit, which can easily lead to defects such as hole position misalignment, hole wall roughness, and burrs. For multilayer board processing, the interlayer alignment accuracy of mechanical drilling depends on the positioning pins, which is difficult to meet the ±0.01mm hole position accuracy requirements of high density interconnect (HDI) circuit boards.

[0008] Laser drilling offers significant precision advantages thanks to its non-contact processing and high-precision positioning system: the hole diameter accuracy can reach ±0.005-0.02mm, and the hole position accuracy is guaranteed by a laser positioning system (such as CCD vision positioning), achieving high-precision positioning at the ±0.005mm level; at the same time, the hole walls of laser drilling are smooth, with no burrs generated, and the heat-affected zone can be controlled at the micron level, without causing damage to the surrounding substrate, making it fully compatible with the processing requirements of HDI circuit boards.

[0009] Furthermore, in the precision machining of multilayer circuit boards, laser drilling technology demonstrates significantly superior interlayer alignment accuracy compared to traditional mechanical drilling methods. This is primarily due to the non-contact processing mechanism of laser drilling, which completely avoids interlayer alignment deviations caused by a series of physical factors during mechanical drilling, such as continuous drill wear, equipment vibration, and spindle misalignment. Therefore, laser processing can ensure a high degree of consistency and repeatability in the position of drilled holes in each layer of the circuit board, thereby better meeting the stringent technical requirements of modern high-precision, high-density interconnect circuit boards for via placement.

[0010] This superior precision control capability makes laser drilling irreplaceable in the manufacturing of high-end electronic devices. Especially as electronic products continue to move towards thinner, lighter, and more integrated designs, circuit board designs are becoming increasingly complex, with single boards typically containing over 100,000 holes, and the requirements for hole diameter and spacing are constantly shrinking. Against this backdrop, traditional mechanical drilling, limited by inherent technological bottlenecks, is increasingly unable to meet the demands of high-difficulty processing such as micro-holes and blind / buried vias. Therefore, adopting high-precision, high-efficiency laser drilling technology has become an inevitable trend in the industry.

[0011] To select the appropriate laser wavelength, the absorption rates of different laser types on various components of the substrate were compared as follows: The circuit board substrate is mainly composed of copper foil, glass fiber (reinforcing material), and resin (adhesive). Different types of lasers (carbon dioxide laser, fiber laser, UV laser) have different wavelengths, resulting in significantly different absorption rates on the substrate components, thus affecting the drilling effect and quality. Specific absorption characteristics are as follows: (a) Carbon dioxide laser (wavelength 10.6μm) Carbon dioxide lasers are mid-infrared lasers, and their wavelengths have a high degree of matching with the molecular vibration frequencies of resins and glass fibers. Therefore, they have extremely high absorption rates (≥90%) for resins and glass fibers, which can quickly dissolve resins and glass fibers, achieving efficient drilling. However, copper foil has extremely low absorption rates for mid-infrared lasers (≤5%), and the laser energy is difficult for copper foil to absorb. It cannot directly dissolve copper foil, and the copper foil at the drilling location must be removed first by etching or other methods before laser drilling can be performed. Otherwise, the laser energy will be reflected, unable to penetrate the substrate, and may even damage the equipment. Currently, in the process of circuit board manufacturing, the use of carbon dioxide laser technology for blind hole drilling is a very mature and widely used technology, but it has not yet been widely applied to through-hole drilling.

[0012] (ii) Fiber laser (wavelength 1.06μm) Fiber lasers are near-infrared lasers, which significantly improve the absorption rate of copper foil (≥85%), and can directly ablate copper foil without prior etching to create windows, making them suitable for drilling scenarios where copper foil needs to be preserved. However, fiber lasers have moderate absorption rates for resin and glass fiber (resin ≈60%, glass fiber ≈40%), and their ablation efficiency is lower than that of carbon dioxide lasers. Furthermore, the laser energy is easily absorbed by the substrate, resulting in a large heat-affected zone, which may lead to defects such as resin carbonization and glass fiber delamination, affecting the drilling quality.

[0013] (iii) UV laser (wavelength 266nm / 355nm) UV lasers, being ultraviolet light, have the shortest wavelength and the highest photon energy. They exhibit a "balanced" absorption rate across the substrate components: approximately 70% for copper foil, 95% for resin, and 80% for glass fiber. This allows for efficient simultaneous ablation of copper foil, resin, and glass fiber without prior etching. More importantly, UV lasers destroy the substrate's molecular bonds through "photochemical ablation," rather than thermal ablation. The heat-affected zone can be controlled within 5μm, virtually eliminating defects such as resin carbonization and glass fiber delamination, resulting in optimal drilling quality. However, UV laser equipment is the most expensive and has relatively low ablation efficiency, making it suitable for high-precision, high-quality high-end circuit board processing. Summary of the Invention

[0014] To address the aforementioned shortcomings of existing technologies, this invention provides a method for drilling through-holes in multilayer boards using a carbon dioxide laser. By pre-etching windows into the copper layers at corresponding drilling locations in the inner and outer layers, the method solves the problem that some lasers (such as carbon dioxide lasers) cannot melt copper foil, thereby achieving the goal of drilling through-holes in multilayer boards using a carbon dioxide laser.

[0015] To address the aforementioned technical problems, this invention provides a method for drilling through-holes in multilayer boards using a carbon dioxide laser, which is carried out according to the following steps based on a conventional multilayer board production process: S1. When fabricating inner layer circuits on the core board, the copper layer at all corresponding drill holes is etched away, and a hole ring is fabricated around the drill hole on the inner layer that needs to be connected to the copper layer of the hole wall. S2. Coat the surface of the hole ring of the core board with an alkali-soluble photocurable ink with an outer diameter larger than the outer diameter of the drilled hole, and fill the inner empty window of the hole ring with the alkali-soluble photocurable ink. Expose and cure the alkali-soluble photocurable ink with UV light to form an ink disk. S3. The core board and the outer copper foil are stacked and pressed together in the stacking order using PP to form the production board; S4. Apply film to the production board, and after exposure and development, open windows at all corresponding drill holes. Then, remove the copper layer at the corresponding drill holes in the outer layer by etching, and then remove the film. S5. A carbon dioxide laser is used to drill through holes at the corresponding drilling positions on the production board, and the ink disk in the inner layer forms an ink ring surrounding the through hole. S6. Finally, use an alkaline solution to dissolve and remove the ink ring on the hole wall to expose the inner hole ring.

[0016] Furthermore, in step S2, the ink disk includes an inner filling portion that fills the open window inside the hole ring and an outer covering portion that covers the surface of the hole ring, so that the ink disk is formed into a stepped structure with a larger outer diameter and a smaller inner diameter. The outer diameter of the outer covering portion is 0.01-0.05 mm larger than the outer diameter of the drilled hole, and the ink thickness on the surface of the hole ring is greater than the ink width on one side.

[0017] Furthermore, in step S5, when laser drilling, a double-sided drilling method is used to drill through holes. That is, a carbon dioxide laser is first used to perform the first drilling process at the drilling position on one surface of the production board. After flipping the production board, a second drilling process is performed at the drilling position on the other surface of the production board. The depth of the first drilling process and the second drilling process are both greater than or equal to half the thickness of the production board. After the two drilling processes, a through hole is formed by drilling from top to bottom.

[0018] Furthermore, in step S6, the production plate is immersed in a sodium hydroxide solution at 60-70 degrees Celsius for 30-120 minutes; and the mass percentage of the solute in the sodium hydroxide solution is 10%-20%.

[0019] Furthermore, after step S6, the following steps are also included: S7. The production board is sequentially subjected to copper plating and electroplating to metallize the through holes and form conductive holes.

[0020] Furthermore, after the through-hole electroplating, an outer layer is formed, and the following steps are included after step S7: S8. The through holes are filled with resin and cured, and then the resin protruding from the plate surface is ground flat by grinding plate. S9. Apply a film to the production board and create a window at at least one end of the corresponding via through exposure and development to expose the top surface of the copper layer on the wall of the via at least one end. S10. The exposed copper layer on the hole wall is etched to isolate the copper inside the hole from the outer layer. S11. After removing the film, resin ink is used to fill the eroded part of the copper layer on the hole wall and then cured to form a structure that separates the copper layer on the hole wall from the outer layer. Then, the resin protruding from the board surface is ground flat by a grinding plate.

[0021] Furthermore, to achieve the inner layer separation of the through hole, in step S2, the ink disk includes an inner filling part that fills the open window inside the hole ring and an outer covering part that covers the surface of the hole ring, so that the ink disk is formed into a stepped structure with a larger outer diameter and a smaller inner diameter. The outer diameter of the outer covering part is 0.2-0.5 mm larger than the outer diameter of the drilled hole, and the thickness of the outer covering part is 5-50 μm. The ink width:thickness ratio on one side of the hole ring surface is >3:1.

[0022] Furthermore, in step S3, at least two ink trays are provided in the inner layer of the production board at the corresponding drilling positions.

[0023] Furthermore, after step S6, the following steps are also included: S7. The via is metallized by copper plating and electroplating, while the etched areas and isolation bands are not plated with copper. An isolation band is formed between every two etched areas, forming an internally isolated via.

[0024] Furthermore, the electroplating in step S7 specifically includes the following steps: S71. The production board is subjected to DC flash plating, but no copper layer is plated at the etched areas. S72. Then, pulse electroplating is performed on the production board to remove the copper layer on the hole wall of the isolation strip. S73. Finally, the production board is subjected to DC electroplating to isolate the inside of the through holes into through holes with at least two conductive sections.

[0025] Compared with the prior art, the present invention has the following beneficial effects: In this invention, by pre-etching windows into the copper layers at corresponding drilling locations in the inner and outer layers, the problem of some lasers (such as CO2 lasers) being unable to ablate copper foil is solved, achieving the purpose of CO2 laser drilling through-holes in multilayer boards. Laser drilling offers high precision, high efficiency, and good processing stability, avoiding interlayer alignment deviations caused by drill bit wear and equipment vibration during mechanical drilling. This ensures the accuracy and repeatability of the drilling position, effectively improving the quality and consistency of through-hole processing and significantly reducing the defect rate in the production process, thereby increasing the overall yield and production efficiency. However, after lamination into the production board, due to positioning deviations and material expansion and contraction, a certain degree of vertical deviation is inevitable. That is, there will be a certain vertical deviation in the windows formed at the drilling locations in the inner and outer layers. When the vertical deviation exceeds... Currently, laser-cut holes may deviate from the vertical channel of the copper foil hole ring outside the window, and some laser energy is blocked by the inner copper foil hole ring, resulting in localized resin residue in the inner layer. This residual resin can cause open circuits in the inner layer connections. Therefore, this application sprays an ink pad formed by alkaline-soluble photocurable ink on the outer side of the copper foil hole ring and at the window. After drilling, the ink pad between the hole wall and the inner copper foil hole ring is removed by an alkaline solution, without causing secondary damage to the circuit board. This creates an etching effect on the hole wall, exposing the entire inner wall of the copper foil hole ring. Subsequently, after copper plating and electroplating, a three-dimensional connection is formed between the copper layer on the hole wall and the inner copper foil hole ring, making the connection between the two more robust. This improves the reliability of the electrical connection between the inner and outer layers. This etching method is simple to operate, low in cost, and can be well integrated into existing circuit board manufacturing processes.

[0026] Secondly, double-sided drilling is used during laser drilling. By precisely positioning the windowed areas on both surfaces, the laser drilling direction is accurately aligned during the two drilling operations on the production board. This ensures that the holes formed during the first and second drilling operations are precisely aligned vertically, guaranteeing that the vertical accuracy of the through holes meets the requirements, with a vertical deviation of ≤0.025mm. Attached Figure Description

[0027] Figure 1 These are schematic diagrams showing the ink trays fabricated on the two-core board in Examples 1 and 2; Figure 2 This is a schematic diagram of the production plate after being pressed together in the embodiment; Figure 3 This is a schematic diagram showing the windowed area etched onto the outer layer of the production board in the embodiment. Figure 4 This is a schematic diagram showing the process of laser drilling through holes in a multilayer board on a production board, as described in the embodiment. Figure 5 This is a schematic diagram of the etched surface on the production board in the embodiment. Figure 6This is a schematic diagram showing the copper plating and electroplating processes on the production board in the embodiment. Figure 7 This is a schematic diagram of the resin-filled holes on the production board in Example 2; Figure 8 This is a schematic diagram showing the recessed area etched on the production board in Example 2; Figure 9 This is a schematic diagram of the process in Example 2 where the recessed areas on the production board are filled with resin ink. Figure 10 This is a schematic diagram of the copper plating layer formed on the outer layer of the production board in Example 2; Figure 11 This is a schematic diagram of the ink tray fabricated on the two-core board in Example 3; Figure 12 This is a schematic diagram of the etching process on the production board in Example 3; Figure 13 This is a schematic diagram of the copper plating and electroplating process on the production board in Example 3. Detailed Implementation

[0028] To better understand the technical content of this invention, the technical solution of this invention will be further introduced and explained below in conjunction with specific embodiments.

[0029] Example 1 This embodiment illustrates a method for manufacturing a circuit board, which includes a process of drilling through-holes in a multilayer board using a carbon dioxide laser, comprising the following processing steps in sequence: (1) Cutting: Cut two core boards according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the copper layer thickness on both surfaces of the core board is 0.5oz. The core board has drilling positions, which are the positions where drilling is required in subsequent processing.

[0030] (2) Inner layer circuit fabrication (negative film process): Inner layer pattern transfer, photosensitive film is coated using a vertical coating machine, and the film thickness of the photosensitive film is controlled at 8μm. The inner layer circuit is exposed using a fully automatic exposure machine with 5-6 exposure rulers (21 exposure rulers). After development, the inner layer circuit pattern is formed; Inner layer etching, the inner layer circuit is etched out on the core board after exposure and development. The inner layer line width is measured to be 3mil; Inner layer AOI, and then the inner layer circuit is inspected for defects such as open circuits, short circuits, line gaps, and line pinholes. Defective products are scrapped, and defect-free products are sent to the next process.

[0031] In the process of fabricating the inner layer circuitry, a copper foil hole ring is fabricated on one surface of the two-core board to surround the drilled hole position. This involves etching the copper layer of the copper foil hole ring to create a copper-free window. The other surface of the two-core board forms a copper-free area at the drilled hole position, and no copper foil hole ring is fabricated around the drilled hole position.

[0032] Fabrication of the ink tray: A layer of alkali-soluble UV-curable ink with an outer diameter larger than the outer diameter of the drilled hole is sprayed onto the copper foil etched window surface of the two-core board. The alkali-soluble UV-curable ink fills the window of the hole ring, and is then exposed and cured by UV light to form ink tray 1 (e.g., Figure 1 (As shown).

[0033] Among them, such as Figure 1 As shown, the ink tray 1 includes an inner filling part 10 that fills the opening of the copper foil hole ring and an outer covering part 11 that covers the surface of the copper foil hole ring, so that the ink tray is formed into a stepped columnar structure with a larger outer diameter and a smaller inner diameter. The outer diameter of the outer covering part is 0.01-0.05 mm larger than the hole diameter of the drilled hole, that is, the ring width of the overlapping area between the outer covering part and the hole ring is 0.005-0.025 mm, and the ink thickness on the surface of the hole ring is greater than the ink width on one side, that is, the ink thickness of the outer covering part is greater than the ring width of the overlapping area between the outer covering part and the hole ring.

[0034] In one embodiment, the outer diameter of the outer cover is 0.05 mm larger than the outer diameter of the drilled hole, that is, the circumference of the overlapping area between the outer cover and the hole ring is 0.025 mm, and the ink thickness of the outer cover is 38 micrometers.

[0035] (4) Lamination: The browning speed is based on the thickness of the bottom copper layer. The two-core board, PP and outer copper foil are laminated in sequence as required. The two-core boards with copper foil hole rings and ink tray 1 are arranged adjacently on one side (e.g. Figure 2 As shown in the figure), then according to the Tg of the board material, appropriate lamination conditions are selected to press the laminated board to form a production board; and in the inner layer of the production board, two adjacent ink trays are provided at the corresponding drilling positions.

[0036] (5) Windowing: Dry film is applied to both surfaces of the production board. After exposure and development, windows are made at the corresponding drilling positions. Then, the copper layer at the window opening is etched to form the windowed area 2 (e.g., Figure 3 (As shown), then remove the dry film.

[0037] (6) Drilling: Use a carbon dioxide laser to drill through holes 3 at the corresponding drilling positions on the production board (e.g., Figure 4 As shown), the two ink disks in the inner layer form an ink ring surrounding the through hole, and the ink thickness is greater than the width of the ink ring.

[0038] Specifically, due to the limited depth of laser drilling, a double-sided drilling method is used to drill through holes. First, a carbon dioxide laser is used to drill a hole at the drilling position on one side of the production board. After flipping the production board, a second drilling is performed at the drilling position on the other side of the production board. The depth of both the first and second drilling processes is greater than or equal to half the thickness of the production board. After the two drilling processes, a through hole is formed by drilling from top to bottom.

[0039] Etching: Immerse the production board in a sodium hydroxide solution at 60-70 degrees Celsius for 30-120 minutes to dissolve and remove all ink rings on the hole walls, forming etched sites 4 (e.g., Figure 5 As shown in the figure, the inner layer of perforated copper foil is exposed.

[0040] In one embodiment, the concentration of the sodium hydroxide solution is 10%-20%, that is, the mass percentage of the solute (i.e., sodium hydroxide) in the sodium hydroxide solution is 10%-20%, and the remainder is water.

[0041] (8) Copper plating: A thin layer of copper is deposited on the board surface and hole walls using chemical copper plating. The backlight test is level 10, and the copper plating thickness in the hole is 0.3μm.

[0042] (9) Electroplating: Perform full-board electroplating on the production board according to design requirements, forming a copper layer 5 on the hole walls (e.g., Figure 6 (As shown), to metallize the through hole.

[0043] (10) Fabrication of outer layer circuits (positive film process): outer layer pattern transfer, using a fully automatic exposure machine and positive film circuit film, the outer layer circuit is exposed with 5~7 exposure rulers (21 exposure rulers), after development, the outer layer circuit pattern is formed on the multilayer board; outer layer pattern electroplating, and then copper and tin plating are performed on the production board respectively. The electroplating parameters are set according to the required copper thickness. Copper plating is performed with a current density of 1.8ASD for 60 minutes, and tin plating is performed with a current density of 1.2ASD for 10 minutes, with a tin thickness of 3~5μm; then the film is removed, etched and tin is removed in sequence, and the outer layer circuit is etched on the production board; outer layer AOI, using an automatic optical inspection system, by comparing with CAM data, to detect whether there are defects such as open circuits, gaps, incomplete etching, and short circuits in the outer layer circuit.

[0044] (11) Solder resist and screen printing: After screen printing solder resist ink on the surface of the production board, it undergoes pre-curing, exposure, development and heat curing treatments in sequence to cure the solder resist ink into a solder resist layer; specifically, the solder resist ink on the TOP side and the characters on the TOP side are added with the "UL mark", thereby coating a layer on the lines and substrates that do not need to be soldered to prevent bridging between lines during soldering, provide a permanent electrical environment and chemical corrosion resistance, and at the same time play a role in beautifying the appearance. (12) Surface treatment (immersion nickel and gold): The copper surface of the solder pads of the solder mask opening position is uniformly deposited with a nickel layer and a gold layer of a certain required thickness through chemical principle. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

[0045] (13) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0046] (14) Molding: Based on existing technology and design requirements, the circuit board is made with a shape tolerance of + / -0.05mm.

[0047] (15) FQC: In accordance with the customer's acceptance standards and the applicant's inspection standards, inspect the appearance of the circuit board, and repair any defects in a timely manner to ensure excellent quality control for the customer.

[0048] (16) FQA: Re-test the appearance of the circuit board, the thickness of the copper in the holes, the thickness of the dielectric layer, the thickness of the solder mask, the thickness of the inner copper layer, etc. to see if they meet the customer's requirements.

[0049] (17) Packaging: The circuit boards are sealed according to the packaging method and quantity required by the customer, and desiccant and humidity card are placed in the packaging before shipment.

[0050] Example 2 This embodiment provides a method for manufacturing a circuit board, the purpose of which is to isolate the outer layer of the through-hole. The manufacturing method is basically the same as that of Embodiment 1, except that the following steps are included between steps (9) and (10): a. First resin plugging: The through holes are plugged with resin and cured (e.g.) Figure 7 (as shown), and then the resin protruding from the plate surface is ground flat using a grinding plate.

[0051] b. Etching: A dry film is applied to the production board, and then exposed and developed to create a window at the break point of the corresponding via, exposing the top surface of the copper layer on the via wall at the break point. Then, etching is used to etch the exposed copper layer on the via wall to form a recessed position (e.g., 6) below the substrate surface (the dielectric layer). Figure 8 As shown in the figure, the copper layer on the hole wall at the disconnected end is disconnected from the outer copper layer.

[0052] c. Second resin plugging: After film removal, use resin ink 7 to fill and cure the recessed areas (e.g. Figure 9 As shown in the figure, a structure is formed that separates the copper layer on the hole wall from the outer layer, and then the resin protruding from the plate surface is ground flat by a grinding plate.

[0053] d. Forming the copper plating layer: A copper plating layer is formed on the filled resin surface through copper immersion and electroplating (electroplating using POFV process) 8 (e.g. Figure 10 (As shown).

[0054] Example 3 This embodiment provides a method for manufacturing a circuit board, the purpose of which is to isolate the inner layer through holes. The manufacturing method is basically the same as that in Embodiment 1, except for steps (3), (7) and (9), as follows: like Figure 11As shown, the ink disk 1 produced in step (3) includes an inner filling part 10 filling the opening of the copper foil hole ring and an outer covering part 11 covering the surface of the copper foil hole ring, so that the ink disk is formed into a stepped columnar structure with a larger outer diameter and a smaller inner diameter; the outer diameter of the outer covering part is 0.2-0.5 mm larger than the outer diameter of the drilled hole, that is, the ring width of the overlapping area between the outer covering part and the hole ring is 0.1-0.25 mm, the thickness of the outer covering part is 5-50 μm, and the ink width on one side of the hole ring surface is greater than the thickness by 3:1, that is, the ring width of the overlapping area between the outer covering part and the hole ring is greater than the ink thickness of the outer covering part by 3:1.

[0055] In one embodiment, the outer diameter of the ink disk is 0.5 mm larger than the outer diameter of the drilled hole (0.25 mm on one side), that is, the ring width of the overlapping area between the outer cover and the hole ring is 0.25 mm, and the thickness of the outer cover is 50 micrometers. The ratio of the ring width of the overlapping area between the outer cover and the hole ring to the thickness of the outer cover is 5:1.

[0056] like Figure 12 As shown, the depth of the etched position 4 formed in step (6) is 0.1-0.25 mm and the height is 5-50 μm. Preferably, the depth of the etched position is 0.25 mm and the height is 50 μm. The ratio between the depth and thickness of the etched position is 5:1. The conductivity of the etched position is very poor under this ratio, which can ensure that no copper layer will be deposited at the etched position during the later chemical copper deposition.

[0057] In step (9) of electroplating, the production board is first subjected to DC flash plating, and no copper layer is plated at the etched areas; then, the production board is subjected to pulse electroplating to remove the copper layer on the hole wall of the isolation strip; finally, the production board is subjected to DC electroplating to divide the inside of the through hole into a through hole with multiple conductive segments (such as...). Figure 13 (As shown).

[0058] Specifically, the current density during DC flash plating is 0.8-1.5 ASD, and the time is 3-6 minutes; DC flash plating thickens the copper layer on the hole wall by 1-5 micrometers.

[0059] In one embodiment, the total pulse electroplating time is 6 minutes, and the current density of the forward pulse electroplating in each cycle is 3 ASD and the time is 10 ms, while the current density of the reverse pulse electroplating is 9 ASD and the time is 10 ms.

[0060] In one embodiment, the copper thickness of the hole is increased by 30 micrometers during DC electroplating.

[0061] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for drilling through holes in a multilayer board using a carbon dioxide laser, characterized in that, Follow these steps: S1. When fabricating inner layer circuits on the core board, the copper layer at all corresponding drill hole positions is etched away, and a hole ring is fabricated around the drill hole position on the inner layer that needs to be connected to the copper layer of the hole wall. S2. Coat the surface of the hole ring of the core board with an alkali-soluble photocurable ink with an outer diameter larger than the outer diameter of the drilled hole, and fill the inner empty window of the hole ring with the alkali-soluble photocurable ink. Expose and cure the alkali-soluble photocurable ink with UV light to form an ink disk. S3. The core board and the outer copper foil are stacked and pressed together in the stacking order using PP to form the production board; S4. Apply film to the production board, and after exposure and development, open windows at all corresponding drill holes. Then, remove the copper layer at the corresponding drill holes in the outer layer by etching, and then remove the film. S5. A carbon dioxide laser is used to drill through holes at the corresponding drilling positions on the production board, and the ink disk in the inner layer forms an ink ring surrounding the through hole. S6. Finally, use an alkaline solution to dissolve and remove the ink ring on the hole wall to expose the inner hole ring.

2. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to claim 1, characterized in that, In step S2, the ink disk includes an inner filling portion that fills the open window inside the hole ring and an outer covering portion that covers the surface of the hole ring, so that the ink disk is formed into a stepped structure with a larger outer diameter and a smaller inner diameter. The outer diameter of the outer covering portion is 0.01-0.05 mm larger than the outer diameter of the drilled hole, and the ink thickness on the surface of the hole ring is greater than the ink width on one side.

3. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to claim 1, characterized in that, In step S5, when laser drilling, a double-sided drilling method is used to drill through holes. That is, a carbon dioxide laser is first used to drill holes at the drilling positions on one surface of the production board. After flipping the production board, a second drilling is performed at the drilling positions on the other surface of the production board. The depth of the first and second drilling is ≥ half the thickness of the production board. After the two drillings, a through hole is formed from top to bottom.

4. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to claim 1, characterized in that, In step S6, the production plate is immersed in a sodium hydroxide solution at 60-70 degrees Celsius for 30-120 minutes; and the mass percentage of the solute in the sodium hydroxide solution is 10%-20%.

5. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to any one of claims 1-4, characterized in that, Step S6 is followed by the following steps: S7. The production board is sequentially subjected to copper plating and electroplating to metallize the through holes and form conductive holes.

6. The method for drilling through holes in a multilayer board using a carbon dioxide laser according to claim 5, characterized in that, After through-hole electroplating, an outer layer partition is applied. Following step S7, the following steps are also included: S8. The through holes are filled with resin and cured, and then the resin protruding from the plate surface is ground flat by grinding plate. S9. Apply a film to the production board and create a window at at least one end of the corresponding via through exposure and development to expose the top surface of the copper layer on the hole wall at at least one end of the via. S10. The exposed copper layer on the hole wall is etched to isolate the copper inside the hole from the outer layer. S11. After the film is removed, resin ink is used to fill the eroded part of the copper layer on the hole wall and then cured to form a structure that separates the copper layer on the hole wall from the outer layer. Then, the resin protruding from the board surface is ground flat by a grinding plate.

7. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to claim 1, characterized in that, To achieve internal layer isolation in the through hole, in step S2, the ink disk includes an inner filling portion that fills the open window inside the hole ring and an outer covering portion that covers the surface of the hole ring, so that the ink disk forms a stepped structure with a larger outer diameter and a smaller inner diameter. The outer diameter of the outer covering portion is 0.2-0.5 mm larger than the outer diameter of the drilled hole, and the thickness of the outer covering portion is 5-50 μm. The ink width:thickness ratio on one side of the hole ring surface is greater than 3:

1.

8. The method for drilling through holes in multilayer boards using a carbon dioxide laser according to claim 7, characterized in that, In step S3, at least two ink trays are provided in the inner layer of the production board at the corresponding drilling positions.

9. The method for drilling through holes in a multilayer board using a carbon dioxide laser according to claim 8, characterized in that, Step S6 is followed by the following steps: S7. The via is metallized by copper plating and electroplating, while the etched areas and isolation bands are not plated with copper. An isolation band is formed between every two etched areas, forming an internally isolated via.

10. The method for drilling through holes in a multilayer board using a carbon dioxide laser according to claim 9, characterized in that, The electroplating in step S7 specifically includes the following steps: S71. The production board is subjected to DC flash plating, but no copper layer is plated at the etched areas. S72. Then, pulse electroplating is performed on the production board to remove the copper layer on the hole wall of the isolation strip. S73. Finally, the production board is subjected to DC electroplating to isolate the inside of the through holes into through holes with at least two conductive sections.

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