Circuit board manufacturing method and circuit board

Abstract

The invention relates to the field of circuit board manufacturing, in particular to a circuit board manufacturing method and a circuit board, and the circuit board manufacturing method comprises the following steps: S1, manufacturing at least two daughter boards, manufacturing first through holes for interlayer interconnection on the daughter boards, and manufacturing connection pads electrically connected with the first through holes on the pressing surfaces of the daughter boards; s2, manufacturing at least one middle connecting plate with a conductive column, wherein the position of the conductive column corresponds to the connecting bonding pad on the adjacent daughter board; and S3, alternately laminating and pressing the daughter boards and the middle connecting boards, so that the conductive columns are aligned with the connecting bonding pads and are electrically connected with the connecting bonding pads. According to the method, the ultra-thick board which cannot be manufactured is decomposed into a plurality of sub-boards which can be conventionally processed, and then the sub-boards are integrated through the middle connecting board, so that the physical limitation of the traditional equipment on the thickness of a single board is ingeniously avoided, the manufacturing of an ultra-thick circuit board which is far beyond the capacity of the current equipment becomes possible, and the production yield can be improved.

Description

Technical Field

[0001] This invention relates to the field of circuit board manufacturing, and more specifically, to a method for manufacturing a circuit board and a circuit board. Background Technology

[0002] Traditional manufacturing processes for ultra-thick circuit boards follow a typical linear workflow of "laminated first, then interconnected and externally processed." Specifically, after the fabrication and browning of multiple sub-boards are completed, they are first laminated into a single structure. To achieve electrical interconnection between layers, the formed ultra-thick board must be mechanically or laser-drilled to open all layers. Then, a series of complex processes, such as copper plating, vacuum filling, and secondary copper plating, are used to establish metallized connections within the holes. Finally, surface treatments such as outer layer pattern transfer, etching, solder mask application, immersion gold plating, and character printing are performed.

[0003] However, this traditional process has the following drawbacks when manufacturing high-thickness circuit boards: First, when the board thickness reaches 21.5 mm, it far exceeds the physical limits of horizontal electroplating and developing equipment, making it impossible to carry out key processes such as pattern transfer and film exposure normally; Second, it is extremely difficult to drill high aspect ratio through holes and achieve reliable hole wall metallization on such ultra-thick boards. Because the chemical solutions are difficult to exchange effectively in deep holes, defects such as no copper or thin copper in the holes are easily caused, which seriously damages the reliability of vertical electrical interconnection; In addition, when performing outer layer surface treatment on the formed ultra-thick boards, it is also difficult to guarantee the treatment quality due to chemical exchange and process compatibility issues. Summary of the Invention

[0004] The present invention aims to overcome at least one of the defects (deficiencies) of the prior art and provide a method for manufacturing a circuit board and a circuit board, solving the problems that existing PCB manufacturing methods cannot perform pattern transfer and film exposure on ultra-thick boards, and cannot guarantee the reliability of their vertical electrical interconnections.

[0005] The technical solution adopted by this invention is a method for manufacturing a circuit board, comprising the following steps:

[0006] S1. Fabricate at least two sub-boards, wherein the sub-boards have first through-holes for interlayer interconnection, and the mating surfaces of the sub-boards have connection pads electrically connected to the first through-holes. S2. Fabricate at least one intermediate connecting plate with conductive pillars, the positions of which correspond to the connecting pads on the adjacent sub-plates; S3. Alternately stack and press the sub-board and intermediate connecting board together so that the conductive post is aligned with the connecting pad and electrically connected; Step S2 includes the following steps: S21. Prepregs are paired, and copper foil is applied to both sides of the prepregs respectively; S22. Pre-curing and pressing the prepreg and copper foil together to make the prepreg have both processability and fluidity and adhesion. S23. Drill a second through hole on the prepreg covered with copper foil, the position of the second through hole corresponding to the position of the first through hole on the adjacent sub-board; S24. The second through hole is subjected to a hole wall metallization treatment to form a metallized hole wall; S25. An annular groove is formed on the copper foil at both ends of the second through hole. The annular groove forms a hole ring at both ends of the second through hole that is connected to the metallized hole wall. The annular groove isolates the hole ring from the surrounding copper foil. S26. Fill the second through hole with conductive material and pre-bake it to form a conductive pillar; S27. Remove the copper foil from both sides of the prepreg.

[0007] By breaking down unmanufacturable ultra-thick circuit boards into multiple conventionally processable sub-boards, and then integrating them through intermediate connecting boards, this method cleverly bypasses the physical limitations of traditional equipment on single-board thickness, making it possible to manufacture ultra-thick circuit boards far exceeding the capabilities of current equipment. Secondly, the complex manufacturing process of ultra-thick circuit boards is decomposed into three relatively independent and more controllable modules: sub-board fabrication, intermediate board fabrication, and integration and lamination. Each module can be performed under optimal process parameters, reducing the overall process difficulty and significantly improving production yield and product consistency. Particularly for vertical electrical interconnects, this manufacturing method results in smaller thicknesses for each sub-board and intermediate connecting board, lower cross-sectional area ratios for vias, and utilizes mature and reliable conventional processes. The chemicals can flow and exchange fully, ensuring high-quality metallization of the via walls. More importantly, by filling the second through hole of the intermediate connecting plate with conductive material to form a solid conductive pillar, a vertical interconnection channel with mechanical strength and conductive reliability far exceeding that of traditional electroplated copper layers is established. This fundamentally eliminates the defects common in high aspect ratio deep holes, such as no copper or thin copper, and achieves the ultimate reliability of interlayer electrical interconnection in ultra-thickness circuit boards.

[0008] The fabrication process of the intermediate interconnect board ensures excellent interlayer interconnect reliability. Through prepreg pairing and pre-curing lamination, the intermediate interconnect board achieves an optimal balance between processability and final lamination bonding. Pre-curing lamination provides the prepreg with the necessary rigidity, ensuring dimensional stability and processability during subsequent processes such as drilling, metallization, and filling. Precisely controlled pre-curing parameters result in only partial cross-linking, retaining an appropriate amount of uncured resin. During final lamination, this resin can remelt and flow, exhibiting flowability and adhesion comparable to ordinary prepregs, thus perfectly filling the circuit pattern and forming a strong chemical bond with adjacent sub-boards, ensuring the integrity of the lamination and the reliability of interlayer insulation. The synergistic effect of via wall metallization and conductive material filling constructs a robust and reliable vertical interconnect structure. The conductive material filling the second through-hole forms a solid conductive pillar. During final lamination, this conductive pillar achieves strong physical contact and bonding with the connection pads on the adjacent sub-boards under high temperature and pressure, forming the core channel for vertical electrical connections. Metallization of the via walls creates a rigid metal support bushing between the prepreg substrate and the internal conductive pillars. The prepreg itself has limited rigidity after pre-curing. If the via walls are not metallized, the soft substrate may not provide sufficient radial support for the internal conductive pillars under the immense pressure of final lamination. This could lead to displacement, deformation, or even breakage of the conductive pillars due to pressure instability, resulting in interconnect failure. The presence of metallized via walls significantly enhances the overall compressive strength and mechanical stability of the second via, ensuring the structural integrity of the conductive pillars during lamination and within the finished product. Metallized via walls also form an isolation barrier, preventing molten prepreg resin from flowing into the second via during final lamination, encroaching on the conductive material space and causing decreased interconnect reliability or even open-circuit failure. Simultaneously, it prevents conductive material from being squeezed out into the insulating layer, leading to interlayer short circuit risks. During the final lamination of the sub-board and intermediate connecting board, the hole rings at both ends of the second via correspond to the connection pads on the adjacent sub-board, increasing the contact area and making the connection more stable. In addition, when removing the copper foil from both sides of the prepreg, the hole rings remain on both sides of the prepreg to prevent the conductive posts in the second through hole from being removed or carried out along with the copper foil.

[0009] In step S25, a dry film is first applied to the copper foil surface of the copper-clad prepreg. Then, the dry film is exposed and developed to form a patterned window of an annular groove region around the second via. Next, the copper foil in the annular groove region is removed using an etching process, forming the annular groove. Finally, the remaining dry film on the copper foil surface is removed. The annular groove forms a ring at both ends of the second via that connects to the metallized hole wall within the second via, isolating the ring from the surrounding copper foil. This ensures that the ring remains on both sides of the prepreg when the surrounding copper foil is removed subsequently. Using exposure and etching to create the ring allows for the production of very fine and precisely positioned patterned windows, ensuring that the final ring is concentric with the second via and has the same width. Furthermore, the processing efficiency is high; regardless of the number of second vias, all annular groove patterns can be defined synchronously and consistently through a single exposure and development process.

[0010] In step S3, during the final pressing of the sub-board and the intermediate connecting board, the core of the process lies in simultaneously achieving the final molding and reliable bonding of two different pre-cured materials (prepreg for structural bonding and conductive material for electrical interconnection). However, the curing characteristics of these two materials differ; therefore, this invention employs a two-stage stepped curing pressing process. This process provides optimal reaction conditions through two specific temperatures and times: sufficient flow, venting, and complete curing of the prepreg, and interface fusion and curing of the conductive material. This ensures that a stable overall structural bond and reliable vertical electrical interconnection are achieved simultaneously after final pressing. Specifically, the first stage of curing pressing is performed at a temperature of 180-200°C for 45-80 minutes and a pressure of 530-580 psi. Maintaining the temperature of 180-200°C for 45-80 minutes aims to provide the pre-baked conductive material with an optimal "flow-bond-final curing" window. Under these conditions, the conductive material can flow fully and complete the final curing and cross-linking, forming a stable conductive network. The core function of the 530-580 psi pressure is to apply sufficient pressure while the conductive material is in a molten and flowing state, ensuring a tight physical contact and reliable bond between the conductive material and the bonding pads of the upper and lower sub-boards, thus guaranteeing the reliability of the electrical connection. The second stage of curing and pressing involves a temperature of 210-230℃, a time of 90-150 minutes, and a pressure of 530-580 psi. Maintaining a higher temperature of 210-230℃ for 90-150 minutes ensures that the pre-cured prepreg resin system flows fully and cross-links completely (final curing), achieving its final mechanical and insulating properties. The core function of the 530-580 psi pressure is to ensure that the prepreg flows fully during the molten stage, completely filling the interlayer circuitry and expelling all gases, effectively preventing the formation of defects such as voids and insufficient adhesive, and ensuring the density and reliability of the interlayer bond. It is particularly important to note that pressure control during the pressing process is crucial and must be maintained within the precise range of 530-580 psi. If the pressure is too low, it will not be able to effectively drive the interfacial bonding of the conductive material and the flow and filling of the prepreg, resulting in insufficient interlayer adhesion and filling. If the pressure is too high, even though the hole wall of the second through hole has been metallized, the huge pressure may still cause microscopic deformation of the intermediate connecting plate substrate, causing the internal conductive pillars to break under stress and form an open circuit failure.

[0011] In step S22, setting the pre-curing pressing temperature to 110-130℃ achieves the optimal balance between "rigidity" and "adhesion." The prepreg exhibits ideal flowability and adhesion within the temperature range of 110-165℃. Below 110℃, its flowability and adhesion are poor. The upper temperature limit must consider the flowability and adhesion of the prepreg during both the pre-curing pressing and the final lamination pressing. When the pre-curing pressing temperature is between 130℃ and 165℃, although the prepreg still possesses relatively ideal flowability and adhesion, it may significantly reduce these properties during the final lamination pressing of the sub-board and intermediate connecting board. Reduced flowability prevents the intermediate connecting board from tightly bonding with the circuit patterns on the adjacent sub-board surface as designed, and also hinders the effective expulsion of air between layers. This easily leads to defects such as resin-filled voids and interface delamination, severely compromising the mechanical strength and insulation reliability of the multilayer board. Decreased adhesion prevents the formation of a strong chemical bond between the intermediate connecting board and the sub-board, leading to a sharp drop in interlayer bonding strength and creating a risk of delamination in the entire multilayer structure. Therefore, the upper limit temperature for pre-curing lamination is limited to 130℃ to ensure that the prepreg retains ideal flowability and adhesion during the final lamination process, enabling a stable connection between the intermediate connecting board and the sub-board and filling in the circuit pattern.

[0012] In step S26, the conductive material filled in the second through-hole is conductive copper paste. While ensuring excellent conductivity and high current-carrying capacity of the vertical conductive pillars, it significantly reduces raw material costs compared to precious metal pastes (such as silver paste), providing economic feasibility for the large-scale commercial production of ultra-thickness circuit boards. The pre-baking process is a shaping process aimed at giving the conductive copper paste sufficient initial mechanical strength to ensure it is stably fixed within the second through-hole in subsequent processes, eliminating the risk of sagging, displacement, or deformation. Therefore, the pre-baking temperature should not be too low, and the time should not be too short. Simultaneously, the pre-baked conductive copper paste should still retain fluidity and adhesion under the high temperature and pressure of final bonding, enabling closer physical contact with the connection pads of adjacent sub-boards. Therefore, the pre-baking temperature should also not be too high, and the time should not be too long. In summary, the pre-baking temperature is set to 80-100℃, and the time is set to 20-40 minutes.

[0013] In step S23, the diameter of the drilled second through hole is 6-10 mil. The diameter of the second through hole needs to take into account the metallization of the hole wall and the filling of conductive material. If the diameter of the second through hole is too small (less than 6 mil), it may lead to difficulties in the metallization of the hole wall and the filling of conductive material, affecting the quality of metallization or filling. In addition, if the diameter is too small, the conductive post will also be too thin, its cross-sectional area will be too small, and its current capacity will be limited, resulting in insufficient current carrying capacity. On the other hand, if the diameter of the second through hole is too large (greater than 10 mil), it will occupy valuable wiring space, limit the design density of the circuit board, and at the same time, an excessively large hole will weaken the mechanical strength of the intermediate connecting board.

[0014] In step S25, the outer diameter of the formed via ring is 4-8 mil larger than the diameter of the second through hole. The via ring increases the connection area, provides an alignment reference, and ensures precise alignment with the connection pads on adjacent daughterboards during final lamination, achieving excellent electrical connection. The via ring should not be too large or too small. A via ring that is too small will lead to insufficient alignment tolerance, poor connection reliability, and low production yield. A via ring that is too large will unreasonably occupy wiring space, restrict the design density of the circuit board, and may affect signal integrity. The outer diameter of the via ring should not be greater than the outer diameter of the connection pads on adjacent daughterboards.

[0015] In step S24, the thickness of the metallized hole wall formed by the hole wall metallization treatment of the second through hole is 0.2-0.4 mil. The thickness of the metallized hole wall should not be too thick or too thin. If the thickness of the metallized hole wall is too thick (greater than 0.4 mil), the effective filling diameter for filling conductive material will be reduced, making subsequent filling of conductive material difficult, and the production cost will also increase sharply. If the copper layer thickness is too thin (less than 0.2 mil), the mechanical strength and current carrying capacity of the hole wall will be insufficient, and cracks will easily occur under thermal stress, posing a reliability hazard. Therefore, this solution limits the thickness of the metallized hole wall formed by the hole wall metallization treatment to 0.2-0.4 mil.

[0016] The circuit board manufactured using the manufacturing method described in claims 1-9 has excellent interlayer alignment accuracy, ultra-high reliability vertical interconnection, and high-quality outer layer processing.

[0017] Compared with existing technologies, the advantages of this invention are as follows: By decomposing unmanufacturable ultra-thickness circuit boards into multiple conventionally processable sub-boards, and then integrating them through intermediate connecting boards, this method cleverly bypasses the physical limitations of traditional equipment on the thickness of a single board, making it possible to manufacture ultra-thickness circuit boards far exceeding the capabilities of current equipment. The complex manufacturing process of ultra-thickness circuit boards is decomposed into three modules: sub-board fabrication, intermediate connecting board fabrication, and lamination. Each module can be performed under optimal process parameters, reducing the overall process difficulty and improving production yield. In particular, for vertical electrical interconnections, the individual thickness of each module is significantly reduced, allowing the aspect ratio of its internal vias to be controlled within the ideal range of mature processes. Therefore, the metallization of the first and second through holes can be achieved through existing, mature, and high-yield conventional processes, resulting in a uniform, defect-free, and highly reliable metallization layer. This fundamentally avoids the industry's technical bottlenecks encountered when drilling high aspect ratio deep holes on ultra-thickness circuit boards, such as difficulties in chemical exchange, uneven copper plating, and the tendency to produce holes without copper or with thin copper. This provides a solid and reliable foundation for vertical interconnection in ultra-thickness circuit boards. After the two outermost sub-boards are fabricated, the outer layer is treated first, and then they are laminated. This eliminates the lengthy and unreliable steps of drilling, copper plating, and hole filling on thick boards, greatly simplifying the process. In the fabrication of the intermediate interconnect board, prepregs are first paired, and copper foil is applied to both sides of the prepregs. Then, the copper-clad prepregs are pre-cured and pressed at 110-130℃ to give them a certain rigidity, ensuring dimensional stability and machinability in subsequent processes. Simultaneously, during final pressing, they possess flowability and adhesion comparable to ordinary prepregs, effectively filling the circuit pattern and forming a strong bond with adjacent sub-boards, ensuring the integrity of the lamination and the reliability of interlayer insulation. After pre-curing and pressing the copper-clad prepregs, a second through-hole is drilled using a laser. The position of the second through-hole corresponds to the connection pads on the sub-board and is used to fill conductive material, achieving vertical interconnection of the sub-boards. The diameter of the second through-hole is 6-10 mil. This avoids the problems of excessively small hole diameters leading to difficulties in metallization of the hole walls and filling of conductive material, as well as excessively thin conductive pillars resulting in insufficient current capacity. Conversely, excessively large hole diameters do not weaken the mechanical strength of the intermediate interconnect board, nor occupy wiring space and limit the design density of the circuit board. The second through-hole undergoes a metallization process to form a metallized wall with a thickness of 0.2-0.4 mil. This metallization enhances the overall compressive strength and mechanical stability of the second through-hole, preventing displacement, deformation, or breakage of the conductive pillars within the through-hole due to the immense pressure during final lamination, thus avoiding interconnect failure. It also prevents molten prepreg resin from flowing into the second through-hole and encroaching on the conductive material space during final lamination, and prevents the conductive material from being squeezed out into the insulating layer.A thickness of 0.2-0.4 mil provides sufficient mechanical strength while ensuring smooth subsequent filling of conductive material. Annular slots are formed on the copper foil at both ends of the second via using exposure and etching processes. These slots form rings that connect to the metallized hole walls within the second via, and the slots isolate the rings from the surrounding copper foil, allowing the rings to remain on the prepreg when the surrounding copper foil is removed. Exposure and etching can simultaneously create all annular slots, resulting in high processing efficiency and accurate positioning of the rings, concentric with the second via and of consistent width. The rings increase the connection area, providing an alignment reference and ensuring precise alignment with the connection pads on adjacent sub-boards during final lamination, achieving excellent electrical connections. The outer diameter of the rings is 4-8 mil larger than the diameter of the second via, ensuring that it is neither too small (leading to insufficient alignment tolerance and poor connection reliability) nor too large (resulting in unreasonable occupation of wiring space and limiting the design density of the circuit board). After filling with conductive copper paste, it undergoes pre-baking to form conductive pillars. The pre-baking temperature is 80-100℃ for 20-40 minutes, ensuring the conductive copper paste acquires sufficient initial mechanical strength. This guarantees the pre-baked conductive copper paste will be stably fixed within the second through-hole in subsequent processes. Simultaneously, it retains fluidity and adhesion under the high temperature and pressure of final lamination, enabling tight bonding with the connection pads on adjacent sub-boards. When laminating the sub-boards with the intermediate connecting board, a two-stage stepped curing and lamination process is used to simultaneously achieve the final molding and reliable bonding of two different pre-cured materials (prepreg and conductive material). The first stage of curing and lamination is performed at 180-200℃ for 45-80 minutes and at a pressure of 530-580 psi, allowing the conductive material to flow fully and complete final curing and cross-linking, achieving effective contact and reliable bonding with the connection pads on the upper and lower sub-boards. The second stage of curing and bonding involves a temperature of 210-230℃, a time of 90-150 minutes, and a pressure of 530-580 psi. This allows the prepreg to flow fully and cross-link completely, filling the interlayer circuitry and connecting with the upper and lower sub-boards. The pressure of 530-580 psi ensures effective connection between the sub-board and the intermediate board while preventing excessive pressure from causing the conductive pillars to break and creating an open circuit. Attached Figure Description

[0018] Figure 1 The diagram shows the structure of the first and second sub-boards fabricated in Example 1.

[0019] Figure 2 This is a flowchart of the manufacturing process for the intermediate connecting plate.

[0020] Figure 3 This is a schematic diagram showing the two sides of the prepreg covered with copper foil.

[0021] Figure 4This is a schematic diagram showing the second through hole drilled on a copper-clad prepreg.

[0022] Figure 5 A schematic diagram showing the second through hole after the hole wall has been metallized.

[0023] Figure 6 This is a schematic diagram showing the annular grooves formed on the copper foil at both ends of the second through hole.

[0024] Figure 7 This is a schematic diagram showing the second through-hole after it has been filled with conductive material.

[0025] Figure 8 This is a schematic diagram after removing the copper foil from both sides of the prepreg.

[0026] Figure 9 The dynamic viscosity curve of EM-896K3 prepreg.

[0027] Figure 10 This diagram illustrates how excessively high pre-curing and pressing temperatures on prepregs can lead to voids during final pressing.

[0028] Figure 11 This is a schematic diagram showing the failure to metallize the second through hole, which led to the breakage of the conductive post during final pressing.

[0029] Figure 12 This is a schematic diagram of the stacking process in Example 1.

[0030] Figure 13 This is a schematic diagram of the first rivet hole.

[0031] Figure 14 This is a schematic diagram of a two-stage stepped curing and pressing process used in the final pressing stage.

[0032] Figure 15 This is a partial cross-sectional schematic diagram of a circuit board manufactured according to the manufacturing method of the present invention.

[0033] Figure 16 The diagram shows the structure of the first sub-board, the second sub-board, and the third sub-board fabricated for Example 2.

[0034] Figure 17 This is a schematic diagram of the annular grooves formed on the copper foil at both ends of the second through hole in Example 2.

[0035] Figure 18 The diagram shows the structure of the first intermediate connecting plate and the second intermediate connecting plate fabricated for Example 2.

[0036] Figure 19 This is a schematic diagram of the stacking process in Example 2. Detailed Implementation

[0037] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate the following embodiments, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0038] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. These terms are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0039] Example 1 This embodiment provides a method for manufacturing a circuit board integrating two sub-boards and one intermediate connecting board, including the following steps: S1. The first sub-board 100 and the second sub-board 200 are manufactured respectively. The manufacturing method includes: S11. Inner layer circuit formation: Following the sequence of material cutting, inner layer pattern transfer, inner layer etching, and inner layer testing, the preset inner layer circuit pattern is fabricated on the copper-clad board (core board). S12, Inner layer browning treatment: The core board with completed inner layer circuitry is subjected to browning treatment to generate a uniform, dense oxide layer with micro-roughness on the copper surface. This is intended to significantly increase the bonding force between the copper surface and the prepreg during subsequent lamination and prevent delamination between layers.

[0040] S13, Lamination and Drilling: The browned inner core board and prepreg (PP) are laminated according to a predetermined structure and pressed under high temperature and pressure to form a complete sub-board substrate with the required number of layers. Subsequently, through holes for electrical interconnection and first alignment holes for subsequent overall alignment are drilled on the laminated sub-board. The through holes include first through holes 110 and blind / buried holes. The first alignment holes include multiple first pin holes and first rivet holes. In this embodiment, there are 12 first rivet holes.

[0041] S14. Hole wall metallization and outer layer circuit formation: The first through-holes 110 and blind / buried vias drilled on each sub-board for electrical interconnection are metallized to form a copper layer on the hole wall, realizing electrical interconnection between circuits of different layers. Subsequently, through processes such as outer layer pattern transfer and outer layer etching, the outer layer pattern of the sub-board is formed. During this process, connection pads 120 electrically connected to the copper layer in the first through-hole 110 are formed on the lamination surface of the first sub-board 100 and the second sub-board 200.

[0042] S15. Perform outer layer treatment on the first sub-board 100 and the second sub-board 200. The outer layer treatment includes green solder mask, immersion gold plating, and character printing.

[0043] At this point, the first sub-board 100 and the second sub-board 200 are completed. First alignment holes for interlayer alignment are machined on both the first sub-board 100 and the second sub-board 200, and connecting pads 120 electrically connected to the first through-hole 110 are formed on the mating surfaces. The resulting first sub-board 100 and second sub-board 200 are as follows: Figure 1 As shown.

[0044] S2. Fabricate the intermediate connecting plate 400, the fabrication method is as follows: Figure 2 As shown, it includes the following steps: S21. Prepregs are paired, and 1 oz copper foil 402 is coated onto each of the two sides of the prepreg 401, with the smooth side of the copper foil 402 facing the prepreg, to obtain a copper-coated prepreg. Figure 3 As shown. The prepreg 401 is made of a relatively soft material with poor processability. Applying copper foil 402 to it can increase its processability.

[0045] S22. Pre-curing and laminating the prepreg 401 and copper foil 402. The pre-curing and laminating temperature in this step is 110-130℃. This step aims to give the copper-clad prepreg a certain rigidity, ensuring sufficient machinability and dimensional stability to support subsequent precision processes such as drilling, hole wall metallization, and conductive material filling. Simultaneously, it retains the flowability and adhesion required for final lamination to complete the filling of the circuit pattern and form a strong bond with the sub-board.

[0046] The temperature range of 110-130℃ is a precisely designed process window. This embodiment takes EM-896K3 prepreg as an example. EM-896K3 prepreg is an ultra-low loss prepreg with an extremely low dielectric loss factor (Df) and a stable dielectric constant (Dk), making it suitable for high-end PCB manufacturing such as 5G communication and AI servers. Figure 9 The dynamic viscosity curve of EM-896K3 prepreg is shown below. Figure 9It can be seen that at a heating rate of 2.0℃ / min, the minimum viscosity of the prepreg is 4283 Pa·s, and the minimum viscosity temperature is 166℃; at a heating rate of 3.0℃ / min, the minimum viscosity of the prepreg is 4027 Pa·s, and the minimum viscosity temperature is 172℃; at a heating rate of 4.0℃ / min, the minimum viscosity of the prepreg is 3933 Pa·s, and the minimum viscosity temperature is 172℃. The specific comparison table is shown in Table 1.

[0047] Table 1

[0048] like Figure 9 As shown, within the temperature range of 80-170℃ (below the red dotted line), the prepreg possesses basic flowability and adhesion; while within the temperature range of 110-165℃ (within the red box), its flowability and adhesion reach the ideal range, which is most conducive to circuit filling and bonding. If the pre-curing temperature is below 110℃, the resin cross-linking degree is insufficient, resulting in insufficient rigidity, flowability, and adhesion of the prepreg, failing to meet the manufacturing requirements of this invention. To ensure that the prepreg still has sufficient flowability and adhesion during final lamination, this invention sets the upper limit of the pre-curing temperature to 130℃. This aims to avoid the reduction in flowability and adhesion of the prepreg 401 during final lamination due to over-curing, thereby causing defects such as insufficient resin flowability, incomplete filling, and the formation of interlayer voids. Figure 10 This demonstrates that when the temperature exceeds 130°C during pre-curing and pressing, the semi-cured sheet lacks fluidity and adhesion during final pressing, resulting in voids.

[0049] Furthermore, due to the relatively low pre-curing pressing temperature (110-130℃), the process window for the prepreg resin to maintain optimal fluidity is relatively short. Therefore, during the pre-curing pressing process, when the resin reaches its lowest melt viscosity, i.e., the stage where its fluidity and adhesion are most ideal, pressure should be applied in a timely manner to utilize this brief high fluidity window to achieve sufficient interlayer bonding and avoid weak adhesion due to decreased fluidity.

[0050] After pre-curing and lamination, the copper-clad prepreg is cut into preset standard sizes, such as 18-inch × 24-inch boards, to obtain a flat and regular processing shape.

[0051] S221. Machining positioning system holes: Drill multiple second alignment holes and positioning holes on a PL machine after pre-curing and laminating the copper-clad semi-cured sheet. The positions of the second alignment holes correspond to the positions of the first alignment holes on the first sub-board 100 and the second sub-board 200, and are used to align the first sub-board 100, the intermediate connecting plate 400 and the second sub-board 200 during lamination and lamination. In traditional multilayer board manufacturing processes, prepreg is used to bond the circuitry of two adjacent core boards and filler core boards, without involving pattern alignment or requiring alignment control. However, in this invention, a second through-hole 430 needs to be drilled on the pre-cured copper-clad prepreg and filled with conductive material. After the first sub-board 100, intermediate connecting board 400, and second sub-board 200 are finally laminated, it is necessary to ensure that the conductive material filled in the second through-hole 430 is connected to the connecting pads 120 on the lamination surfaces of the first sub-board 100 and the second sub-board 200. Therefore, a second alignment hole needs to be processed, which includes multiple second pin holes and second rivet holes. In this embodiment, there are 12 second rivet holes, whose positions correspond to the positions of the first rivet holes. The positioning holes are used to provide a positioning reference for the drilling equipment during subsequent drilling.

[0052] S23. Drill a second through hole 430 on the copper-clad prepreg, the position of the second through hole 430 corresponding to the position of the first through hole 110 on the first sub-board 100 and the second sub-board 200. For example... Figure 4 As shown, in this step, a laser drilling process is used to drill a second through-hole 430 on the pre-cured copper-clad prepreg after lamination. The position and number of the second through-hole 430 precisely correspond to the position and number of the first through-hole 110 on the first daughterboard 100 and the second daughterboard 200, to ensure that during the subsequent final lamination, the conductive posts 420 on the intermediate connecting board 400 can form a precise electrical interconnection with the connecting pads 120 on the first daughterboard 100 and the second daughterboard 200. The aperture D of the second through-hole 430 is preferably 6-10 mil. The aperture D of the second through-hole 430 is related to the diameter of the conductive post 420. If the aperture D of the second through-hole 430 is too small, the subsequently formed conductive post 420 will be too thin, resulting in insufficient current carrying capacity. Furthermore, an excessively small second through-hole 430 will also lead to difficulties in metallization of the hole wall and filling of conductive material. On the other hand, if the aperture D of the second through-hole 430 is too large, it will occupy wiring space, limit the design density of the circuit board, and weaken the mechanical strength of the intermediate connecting board.

[0053] Laser drilling is used because the pre-cured copper-clad prepreg has limited mechanical strength and is soft. Compared with mechanical drilling, laser drilling has the characteristics of a small heat-affected zone and no contact stress, which can effectively avoid mechanical stress damage or delamination to the surface and internal structure of the pre-cured copper-clad prepreg. At the same time, it can avoid the resin residue problem caused by mechanical drilling, thus providing a solid foundation for obtaining clean and highly adhesive metallized hole walls.

[0054] S24. The second through hole 430 is subjected to a hole wall metallization treatment to form a metallized hole wall 410. For example... Figure 5 As shown, after cleaning and activating the hole wall of the second through-hole 430, a continuous chemical copper layer is deposited on the hole wall of the second through-hole 430 through a chemical copper plating process. Then, a thickening process is applied to the chemical copper layer through electroplating to form a metallized hole wall 410 that meets the requirements. The prepreg 401 has limited rigidity. If the hole wall is not metallized, under the enormous pressure applied during final pressing, the prepreg 401 may not be able to provide sufficient radial support for the internal conductive pillars 420, causing the conductive pillars 420 to shift, deform, or even break due to pressure instability, resulting in interconnect failure. The presence of the metallized hole wall 410 greatly enhances the overall compressive strength and mechanical stability of the second through-hole 430, ensuring the structural integrity of the conductive pillars 420 during pressing and within the finished product. Figure 11 As shown, step S24 (hole wall metallization) was not performed, causing the conductive post 420 to break during final pressing. The thickness B of the metallized hole wall 410 is 0.2-0.4 mil, which is neither too thick and occupy too much space in the second through hole 430, making it difficult to fill with conductive material later, nor too thin and causing the hole wall to have too low mechanical strength, thus posing a reliability hazard.

[0055] S25. An annular groove 440 is formed on the copper foil at both ends of the second through hole 430. The annular groove 440 forms a hole ring 450 at both ends of the second through hole 430 that connects to the metallized hole wall 410, and the annular groove 440 isolates the hole ring 450 from the surrounding copper foil. Figure 6 As shown. Step S25 includes: S251. Apply a dry film to the surface of the copper foil 402 of the copper-clad prepreg; S252. Expose and develop the dry film to form a graphic window of an annular grooved area around the second through hole 430. S253. Remove the copper foil in the annular slotted area by etching process to form the annular slotted area 440; S254. Remove the remaining dry film from the surface of copper foil 402.

[0056] Without the annular ring 450, after final lamination, only the conductive post 420 contacts the connecting pad 120. With the annular ring 450, both the annular ring 450 and the conductive post 420 can contact the connecting pad 120. The annular ring 450 increases the connection area, provides an alignment reference, and ensures precise alignment with the connecting pads 120 on the first daughterboard 100 and the second daughterboard 200 during final lamination, achieving excellent electrical connection. Because the annular slot 440 isolates the annular ring 450 from the surrounding copper foil, it will remain on the prepreg 401 when the surrounding copper foil is subsequently removed. The conductive post 420 within the second through-hole 430 will also not be removed or carried out during copper foil removal. The outer diameter D1 of the via ring 450 is 4-8 mil larger than the diameter D of the second through hole 430. This ensures that it is neither too small, leading to insufficient alignment tolerance and poor connection reliability, nor too large, resulting in unreasonable occupation of wiring space and restriction of the circuit board design density. Preferably, the outer diameter D1 of the via ring 450 is not larger than the outer diameter D2 of the connecting pad 120. This dimensional relationship provides the necessary alignment tolerance for lamination and also ensures that the via ring 450 does not exceed the range of the connecting pad 120 and contact other surrounding conductors or copper surfaces.

[0057] The annular slot 440 and the hole ring 450 are manufactured using an exposure and development process because of its high processing efficiency. All annular slots 440 and hole rings 450 can be manufactured simultaneously, and the hole ring 450 is accurately positioned, concentric with the second through hole 430, and has the same width.

[0058] In step S25, a ring-shaped positioning copper ring concentric with the second rivet hole is simultaneously fabricated. The outer diameter of the positioning copper ring is 8-12 mil larger than the diameter of the second rivet hole. The positioning copper ring is used to increase the rigidity of the second rivet hole to facilitate subsequent positioning.

[0059] S26. Fill the second through hole 430 with conductive material and pre-bake to form the conductive pillar 420. For example... Figure 7 As shown, conductive copper paste is filled into the metallized second through-hole 430 under vacuum to ensure dense filling and no air bubbles. Subsequently, it is pre-baked to form conductive pillars 420. The pre-baking temperature is 80-100℃, and the time is 20-40 minutes. This pre-baking step aims to achieve two key objectives: first, to solidify the conductive copper paste into conductive pillars 420, providing sufficient initial mechanical strength to ensure stable fixation within the second through-hole 430 during subsequent handling and final lamination; second, to allow the conductive pillars 420 to remelt and regain necessary fluidity and adhesive activity at the high temperature of the final lamination, thereby achieving sufficient interfacial bonding and reliable electrical interconnection with the connection pads 120 of the first daughterboard 100 and the second daughterboard 200.

[0060] In this embodiment, conductive copper paste is used as the conductive material. It is understood that the conductive material is not limited to this. For example, conductive silver paste or other conductive pastes with similar functions can also be used and fall within the scope of protection of this invention. Similarly, regarding the method of filling the second through hole 430 with conductive material, although this embodiment uses vacuum filling as an example to ensure a dense and bubble-free filling, other feasible filling processes (such as scraping, printing pressure filling, etc.) are also applicable to this invention.

[0061] S27. Remove the copper foil 402 from both sides of the prepreg 401 to form an intermediate connecting plate 400 with conductive posts 420. In this step, due to the formation of the annular slot 440, the hole ring 405 will remain on the prepreg 401 when the copper foil 402 is removed. Similarly, the positioning copper ring will also remain on the prepreg 401. Simultaneously, the conductive posts 420 within the second through hole 430 will not be removed or carried out, but will remain within the second through hole 430. Figure 8 As shown. At this point, the intermediate connecting plate 400 is complete.

[0062] S3. The first sub-board 100, the intermediate connecting plate 400, and the second sub-board 200 are laminated together. Before lamination, the copper surfaces (covering the copper foil area and the connecting pads 120) of the lamination surfaces of the first sub-board 100 and the second sub-board 200 are browned to increase their surface roughness and chemical activity. This not only greatly enhances the bonding strength and durability between the prepreg resin and the lamination surface, thereby improving interlayer bonding and effectively preventing delamination, but also provides a better interface for the bonding of the conductive post 420 and the connecting pads 120, making the contact between the two tighter and the bonding more stable, fundamentally ensuring the long-term reliability of the vertical electrical interconnection.

[0063] like Figure 12 As shown, the prepared first sub-board 100, intermediate connecting board 400, and second sub-board 200 are stacked and assembled. Specifically, an alternating stacking sequence of "first sub-board 100 - intermediate connecting board 400 - sub-board 200" is adopted, and precise alignment is performed through the first alignment hole and the second alignment hole to ensure that each conductive post 420 on the intermediate connecting board 400 is precisely aligned with the corresponding connecting pad 120 on the pressing surface of the first sub-board 100 and the second sub-board 200.

[0064] The stacking and alignment process of the first sub-board 100, the intermediate connecting board 400, and the second sub-board 200 is as follows: Step 1: Place the second sub-board 200 on the pressing platform with its pressing surface facing upwards, and insert the first pin hole on it into the positioning pin pre-set on the pressing platform; at the same time, arrange the 6 rivets diagonally ( Figure 13The six first rivet holes indicated by the middle arrow are inserted into their corresponding first rivet holes from below the second sub-board 200, as shown in the image. Figure 13 As shown.

[0065] Step 2: Place the intermediate connecting plate 400 on the second sub-plate 200, and insert the positioning pin and the 6 rivets into the corresponding second pin holes and second rivet holes respectively.

[0066] Step 3: Place the first sub-plate 100 on the intermediate connecting plate 400 with the pressing surface facing down, so that the corresponding first pin hole and first rivet hole on it are respectively fitted with the positioning pin and 6 rivets.

[0067] Step 4: Insert the remaining six rivets from above the first sub-plate 100 into its unused first rivet holes. This ensures that the entire "second sub-plate 200 - intermediate connecting plate 400 - first sub-plate 100" stacked structure forms a strong mechanical interlock in the vertical direction through the rivets, providing stable alignment for subsequent pressing.

[0068] During the alignment process of this stack, the positioning copper ring on the intermediate connecting plate 400 can improve the rigidity of the second rivet hole and effectively prevent the second rivet hole from deforming or tearing due to force, thereby ensuring the alignment stability of the entire stack structure.

[0069] Subsequently, as Figure 14 As shown, a two-stage stepped curing and pressing process is used to press the laminated structure: The first stage of curing and pressing involves controlling the heating rate to rapidly and uniformly heat the laminated structure consisting of the intermediate connecting plate 400, the first sub-plate 100, and the second sub-plate 200 to 180-200°C. This temperature is maintained for 45-80 minutes while applying a pressure of 530-580 psi. The core objective of this stage is to ensure that the pre-baked conductive material in the intermediate connecting plate 400 can fully flow, fuse at the interface, and complete the final curing and cross-linking, thereby achieving a low-resistance, reliable electrical bond with the connecting pads 120 on the first sub-plate 100 and the second sub-plate 200. The perforated ring 450 on the intermediate connecting plate 400 increases the contact area with the connecting pads 120, achieving excellent electrical connection.

[0070] The second stage of bonding involves raising the temperature to 200-250°C and maintaining it for 90-150 minutes, while keeping the pressure at 530-580 psi. The core purpose of this stage is to allow the prepreg resin to flow fully and completely fill the interlayer circuit pattern, and to fully crosslink (completely cure) at this temperature, thereby achieving a strong bond and reliable interlayer insulation between the first sub-board 100 and the second sub-board 200.

[0071] The pressure range of 530-580 psi is precisely designed to provide sufficient pressure to drive the interfacial bonding of conductive materials and the flow and filling of resin, while preventing the fragile conductive pillars 420 inside the intermediate connecting plate 400 from being crushed or broken due to excessive pressure, thereby preventing open circuit failure.

[0072] At this point, the circuit board product, which consists of two sub-boards and one intermediate connecting board, has been manufactured as a whole using this manufacturing method. Figure 15 This is a partial cross-sectional view of a circuit board manufactured according to the method of the present invention. After final lamination, the conductive pillars 420 are complete and tightly connected to the connecting pads 120, enabling ultra-high reliability vertical interconnection. The lines on the lamination surfaces of the first sub-board 100 and the second sub-board 200 are completely filled without any voids. It should be emphasized that since the first sub-board 100 and the second sub-board 200 have undergone outer layer treatments including solder mask, immersion gold plating, and character printing during the sub-board manufacturing stage (step S15), the finished board does not require any additional surface treatment processes after lamination and can directly proceed to the final routing and electrical testing stages before shipment.

[0073] Example 2 This embodiment provides a method for manufacturing a circuit board integrating a three-layer sub-board and two intermediate connecting boards, including the following steps: S1. The manufacturing methods for the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a are as follows: S11. Inner layer circuit formation: Following the sequence of material cutting, inner layer pattern transfer, inner layer etching, and inner layer testing, the preset inner layer circuit pattern is fabricated on the copper-clad board (core board). S12, Inner layer browning treatment: The core board with completed inner layer circuitry is subjected to browning treatment to generate a uniform, dense oxide layer with micro-roughness on the copper surface. This is intended to significantly increase the bonding force between the copper surface and the prepreg during subsequent lamination and prevent delamination between layers.

[0074] S13, Lamination and Drilling: The browned inner core board and prepreg (PP) are laminated according to a predetermined structure and pressed under high temperature and pressure to form a complete sub-board substrate with the required number of layers. Subsequently, through holes for interlayer communication and first alignment holes for subsequent overall alignment are drilled on the laminated sub-board. The through holes include first through holes 110a and blind / buried holes. The first alignment holes include multiple first pin holes and first rivet holes. In this embodiment, there are 12 first rivet holes.

[0075] S14. Hole Wall Metallization and Outer Layer Circuit Formation: The first through-hole 110a and blind / buried vias drilled on each sub-board for electrical interconnection are metallized to form a copper layer on the hole wall, realizing electrical interconnection between circuits of different layers. Subsequently, through processes such as outer layer pattern transfer and outer layer etching, the outer layer pattern of each sub-board is formed. During this process, connection pads 120a that are electrically connected to the copper layer in the first through-hole 110a are formed on the lamination surface of the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a.

[0076] S15. Perform outer layer treatment on the first sub-board 100a and the third sub-board 300a. The outer layer treatment includes green solder mask, immersion gold plating, and character printing.

[0077] At this point, the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a are completed. First alignment holes for interlayer alignment are machined on each of the three sub-boards, and connecting pads 120a are formed on the mating surfaces. The resulting first sub-board 100a, second sub-board 200a, and third sub-board 300a are as follows... Figure 16 As shown.

[0078] S2. Fabricate the first intermediate connecting plate 400a and the second intermediate connecting plate 500a. The fabrication methods for both are the same, as follows: Figure 2 As shown, it includes the following steps: S21. Prepregs are paired by applying 1oz copper foil 402a to each of the two sides of the prepreg 401a, with the smooth side of the copper foil 402a facing the prepreg 401a, thus obtaining a copper-clad prepreg. The prepreg 401a is made of a relatively soft material with poor processability; applying copper foil 402a increases its processability.

[0079] S22. Pre-curing and laminating the prepreg 401a and copper foil 402a. The pre-curing and laminating temperature in this step is 110-130℃. This step aims to give the copper-clad prepreg a certain rigidity, ensuring sufficient machinability and dimensional stability to support subsequent precision processes such as drilling, hole wall metallization, and conductive material filling, while retaining the flowability and adhesion required for final lamination to complete the filling of the circuit pattern and form a firm bond with the sub-board.

[0080] The temperature range of 110-130℃ is a precisely designed process window. This embodiment takes EM-896K3 prepreg as an example. EM-896K3 prepreg is an ultra-low loss prepreg with an extremely low dielectric loss factor (Df) and a stable dielectric constant (Dk), making it suitable for high-end PCB manufacturing such as 5G communication and AI servers. Figure 9The dynamic viscosity curve of EM-896K3 prepreg is shown below. Figure 9 It can be seen that at a heating rate of 2.0℃ / min, the minimum viscosity of the prepreg is 4283 Pa.s and the minimum viscosity temperature is 166℃; at a heating rate of 3.0℃ / min, the minimum viscosity of the prepreg is 4027 Pa.s and the minimum viscosity temperature is 172℃; at a heating rate of 4.0℃ / min, the minimum viscosity of the prepreg is 3933 Pa.s and the minimum viscosity temperature is 172℃. For specific comparisons, please refer to Table 1 above.

[0081] like Figure 9 As shown, within the temperature range of 80-170℃ (below the red dotted line), the prepreg possesses basic fluidity and adhesion; while within the temperature range of 110-165℃ (within the red box), its fluidity and adhesion reach the ideal range, which is most conducive to circuit filling and bonding. If the pre-curing temperature is below 110℃, the resin cross-linking degree is insufficient, resulting in insufficient rigidity, fluidity, and adhesion of the prepreg, failing to meet the manufacturing requirements of this invention. To ensure that the prepreg still possesses sufficient fluidity and adhesion during final lamination, this invention sets the upper limit of the pre-curing temperature to 130℃. This aims to avoid the reduction in fluidity and adhesion of the prepreg 401a during final lamination due to over-curing, thereby causing defects such as insufficient resin fluidity, incomplete filling, and the formation of interlayer voids. Figure 10 This demonstrates that due to a pre-curing temperature exceeding 130°C, the prepreg 401a lacks fluidity and adhesion during final pressing, resulting in voids.

[0082] Furthermore, due to the relatively low pre-curing pressing temperature (110-130℃), the process window for the prepreg resin to maintain optimal fluidity is relatively short. Therefore, during the pre-curing pressing process, when the resin reaches its lowest melt viscosity, i.e., the stage where its fluidity and adhesion are most ideal, pressure should be applied in a timely manner to utilize this brief high fluidity window to achieve sufficient interlayer bonding and avoid weak adhesion due to decreased fluidity.

[0083] After pre-curing and lamination, the copper-clad prepreg is cut into preset standard sizes, such as 18-inch × 24-inch boards, to obtain a flat and regular processing shape.

[0084] S221. Machining positioning system holes: Drill multiple second alignment holes and positioning holes on a PL machine after pre-curing and pressing the semi-cured sheet. The positions of the second alignment holes correspond to the positions of the first alignment holes on the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a, and are used to align the first sub-board 100a, the first intermediate connecting plate 400a, the second sub-board 200a, the second intermediate connecting plate 500a, and the third sub-board 300a during lamination and pressing. In traditional multilayer board manufacturing processes, prepreg is used to bond the circuitry of two adjacent core boards and filler core boards, without involving pattern alignment or requiring alignment control. However, in this invention, a second through-hole 430a needs to be drilled on the pre-cured copper-clad prepreg after lamination, and conductive material is filled into the second through-hole 430a. After the first sub-board 100a, the first intermediate connecting board 400a, the second sub-board 200a, the second intermediate connecting board 500a, and the third sub-board 300a are finally laminated, it is necessary to ensure that the conductive material filled in the second through-hole 430a connects to the connecting pads 120a on the lamination surfaces of the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a. Therefore, a second alignment hole needs to be machined, which includes multiple second pin holes and second rivet holes. In this embodiment, there are 12 second rivet holes, whose positions correspond to the positions of the first rivet holes. The positioning holes provide a positioning reference for the drilling equipment during subsequent drilling.

[0085] S23. Drill a second through-hole 430a on the copper-clad prepreg, the position of which corresponds to the position of the first through-hole 110a on the adjacent sub-board. In this step, laser drilling is used to drill the second through-hole 430a on the pre-cured and laminated copper-clad prepreg. The position and number of the second through-hole 430a precisely correspond to the position and number of the first through-hole 110a on the adjacent sub-board to ensure that, during the subsequent final lamination, the conductive posts 420a on the first intermediate connecting plate 400a and the second intermediate connecting plate 500a can form a precise electrical interconnection with the connecting pads 120a on the adjacent sub-board. The diameter d of the second through-hole 430a is preferably 6-10 mil. The diameter d of the second through hole 430a is related to the diameter of the conductive post 420a. If the diameter d of the second through hole 430a is too small, the subsequently formed conductive post 420a will be too thin, resulting in insufficient current carrying capacity. Furthermore, an excessively small second through hole 430a will also make it difficult to metallize the hole wall and fill the conductive material. On the other hand, if the diameter d of the second through hole 430a is too large, it will occupy wiring space, limit the design density of the circuit board, and weaken the mechanical strength of the intermediate connection board.

[0086] Laser drilling is used because the pre-cured copper-clad prepreg has limited mechanical strength and is soft. Compared with mechanical drilling, laser processing has the characteristics of a small heat-affected zone and no contact stress, which can effectively avoid mechanical stress damage or delamination to the surface and internal structure of the pre-cured copper-clad prepreg. At the same time, it can avoid the problem of resin residue caused by mechanical drilling, thus providing a solid foundation for obtaining a clean and highly adhesive metallized layer on the hole wall.

[0087] S24. The second through-hole 430a undergoes a hole wall metallization process to form a metallized hole wall 410a. After cleaning and activation treatment of the hole wall of the second through-hole 430a, a continuous chemical copper layer is deposited on the hole wall of the second through-hole 430a through a chemical copper plating process. Then, a thickening process is applied to the chemical copper layer through electroplating to form a metallized hole wall 410a that meets the requirements. The prepreg 401a has limited rigidity. If the hole wall is not metallized, under the huge pressure applied during final pressing, the prepreg 401a may not be able to provide sufficient radial support for the internal conductive pillar 420a, causing the conductive pillar 420a to shift, deform, or even break due to pressure instability, resulting in interconnect failure. The presence of the metallized hole wall 410a greatly enhances the overall compressive strength and mechanical stability of the second through-hole 430a, ensuring the structural integrity of the conductive pillar 420a during the pressing process and inside the finished product. Figure 11 As shown, step S24 (hole wall metallization) was not performed, causing the conductive post 420a to break during final pressing. The thickness b of the metallized hole wall 410a is 0.2-0.4 mil, which is neither too thick and occupy too much space in the second through hole 430a, making it difficult to fill with conductive material later, nor too thin and have too low mechanical strength, posing a reliability hazard.

[0088] S25. An annular groove 440a is formed on the copper foil 402a at both ends of the second through hole 430a. The annular groove 440a forms a hole ring 450a at both ends of the second through hole 430a that connects to the metallized hole wall 410a. The annular groove 440a isolates the hole ring 450a from the surrounding copper foil 402a. Figure 17 As shown. Step S25 includes: S251. Apply a dry film to the surface of the copper foil 402a of the copper-clad prepreg. S252. Expose and develop the dry film to form a graphic window of an annular grooved area around the second through hole 430a. S253. Remove the copper foil in the annular slotted area by etching process to form the annular slotted area 440a; S254. Remove the remaining dry film from the surface of copper foil 402a.

[0089] Without the annular ring 450a, after final lamination, the conductive post 420a only contacts the connecting pad 120a. However, with the annular ring 450a, both the annular ring 450a and the conductive post 420a can make tight contact with the connecting pad 120a. The annular ring 450a increases the contact area, provides an alignment reference, and ensures precise alignment with the connecting pad 120a on the adjacent sub-board during final lamination, achieving excellent electrical connection. Since the annular slot 440a isolates the annular ring 450a from the surrounding copper foil, it will remain on the prepreg 401a when the surrounding copper foil is subsequently removed. The conductive post 420a within the second through-hole 430a will also not be removed or carried out during copper foil removal. The outer diameter d1 of the via ring 450a is 4-8 mil larger than the diameter d of the second through hole 430a. This ensures that it is neither too small, leading to insufficient alignment tolerance and poor connection reliability, nor too large, resulting in unreasonable occupation of wiring space and limiting the design density of the circuit board. Preferably, the outer diameter d1 of the via ring 450a is not greater than the outer diameter d2 of the connecting pad 120a. This dimensional relationship provides the necessary alignment tolerance for lamination and also ensures that the via ring 450a does not exceed the range of the connecting pad 120a and contact other surrounding conductors or copper surfaces.

[0090] The annular slot 440a and the hole ring 450a are manufactured using an exposure and development process because of its high processing efficiency. All annular slots 440a and hole rings 450a can be manufactured simultaneously, and the hole ring 450a is accurately positioned, concentric with the second through hole 430a, and has the same width.

[0091] In step S25, a ring-shaped positioning copper ring concentric with the second rivet hole is simultaneously fabricated. The outer diameter of the positioning copper ring is 8-12 mil larger than the diameter of the second rivet hole. The positioning copper ring is used to increase the rigidity of the second rivet hole to facilitate subsequent positioning.

[0092] S26. Fill the second through-hole 430a with conductive material and pre-bake to form a conductive pillar 420a. Under vacuum, fill the metallized second through-hole 430a with conductive copper paste to ensure a dense, bubble-free filling. Then, pre-bake it to form the conductive pillar 420a at a temperature of 80-100℃ for 20-40 minutes. This pre-baking step aims to achieve two key objectives: first, to solidify the conductive copper paste into a conductive pillar 420, providing sufficient initial mechanical strength to ensure stable fixation within the second through-hole 430a during subsequent handling and final lamination; second, to allow the conductive pillar 420 to remelt and regain necessary fluidity and adhesive activity at the high temperature of the final lamination, thereby achieving sufficient interfacial bonding and reliable electrical interconnection with the connection pads 120a of adjacent sub-boards.

[0093] In this embodiment, conductive copper paste is used as the conductive material. It is understood that the conductive material is not limited to this. For example, conductive silver paste or other conductive pastes with similar functions can also be used and fall within the scope of protection of this invention. Similarly, regarding the method of filling the second through hole 430a with conductive material, although this embodiment uses vacuum filling as an example to ensure a dense and bubble-free filling, other feasible filling processes (such as scraping, printing pressure filling, etc.) are also applicable to this invention.

[0094] S27. Remove the copper foil 402a from both sides of the prepreg 401a to form a first intermediate connecting plate 400a and a second intermediate connecting plate 500a with conductive posts 420a. In this step, due to the formation of the annular slot 440a, the hole ring 405a will remain on the prepreg 401a when the copper foil 402a is removed. Similarly, the positioning copper ring will also remain on the prepreg 401a. At the same time, the conductive posts 420a within the second through hole 430a will not be removed or carried out, but will remain within the second through hole 430a. Figure 18 As shown. At this point, the first intermediate connecting plate 400a and the second intermediate connecting plate 500a are complete.

[0095] S3. The first sub-board 100a, the second sub-board 200a, the third sub-board 300a, the first intermediate connecting plate 400a, and the second intermediate connecting plate 500a are laminated and pressed together. Before lamination and pressing, the copper surfaces (covering the copper foil area and the connecting pad 120a) of the lamination surfaces of the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a are subjected to a browning treatment to increase their surface roughness and chemical activity. This not only greatly enhances the bonding strength and durability between the prepreg resin and the lamination surface, thereby improving the interlayer bonding force and effectively preventing delamination, but also provides a better interface for the bonding of the conductive post 420a and the connecting pad 120a, making the contact between the two tighter and the bonding more stable, fundamentally ensuring the long-term reliability of the vertical electrical interconnection.

[0096] The prepared first sub-board 100a, second sub-board 200a, third sub-board 300a, first intermediate connecting plate 400a, and second intermediate connecting plate 500a are stacked and assembled. Specifically, as follows... Figure 19As shown, an alternating stacking sequence of "first sub-board 100a - first intermediate connecting board 400a - sub-board 200a - second intermediate connecting board 500a - third sub-board 300a" ​​is adopted, and precise alignment is performed through the first alignment hole and the second alignment hole to ensure that each conductive post 420a on the first intermediate connecting board 400a and the second intermediate connecting board 500a is precisely aligned with the corresponding connecting pad 120a on the pressing surface of the first sub-board 100a, the second sub-board 200a and the third sub-board 300a.

[0097] The stacking and alignment process of the first sub-board 100a, the second sub-board 200a, the third sub-board 300a with the first intermediate connecting plate 400a and the second intermediate connecting plate 500a is as follows: Step 1: Place the third sub-board 300a on the pressing platform with its pressing surface facing upwards, and insert the first pin hole on it into the positioning pin pre-set on the pressing platform; at the same time, arrange the 6 rivets diagonally ( Figure 13 The six first rivet holes indicated by the middle arrow are inserted from below the third sub-board 300a into their corresponding six first rivet holes, as shown in the image. Figure 13 As shown.

[0098] Step 2: Place the second intermediate connecting plate 500a on the third sub-plate 300a, and insert the positioning pin and the 6 rivets into the corresponding second pin holes and second rivet holes respectively.

[0099] Step 3: Place the second sub-plate 200a on the second intermediate connecting plate 500a, and insert the positioning pin and the 6 rivets into the corresponding first pin hole and first rivet hole, respectively.

[0100] Step 4: Place the first intermediate connecting plate 400a on the second sub-plate 200a, and insert the positioning pin and the 6 rivets into the corresponding second pin holes and second rivet holes, respectively.

[0101] Step 5: Place the first sub-plate 100a on the first intermediate connecting plate 400a with the pressing surface facing down, so that the corresponding first pin hole and first rivet hole on it are respectively fitted with the positioning pin and 6 rivets.

[0102] Step 6: Insert the remaining six rivets from above the first sub-plate 100a into the remaining unoccupied first rivet holes, so that the entire laminated structure forms a firm mechanical interlock in the vertical direction through the rivets, providing a stable alignment guarantee for subsequent pressing.

[0103] During the stacking alignment process, the positioning copper rings on the first intermediate connecting plate 400a and the second intermediate connecting plate 500a can improve the rigidity of the second rivet hole and effectively prevent the second rivet hole from deforming or tearing due to force, thereby ensuring the alignment stability of the entire stacked structure.

[0104] Subsequently, as Figure 14 As shown, a two-stage stepped curing and pressing process is used to press the laminated structure: The first stage of curing and pressing involves controlling the heating rate to rapidly and uniformly heat the laminated structure consisting of the first intermediate connecting plate 400a, the second intermediate connecting plate 500a, the first sub-plate 100a, the second sub-plate 200a, and the third sub-plate 300a to 180-200°C. This temperature is maintained for 45-80 minutes while applying a pressure of 530-580 psi. The core objective of this stage is to allow the pre-baked conductive material in the first intermediate connecting plate 400a and the second intermediate connecting plate 500a to flow fully, fuse at the interface, and complete the final curing and cross-linking. This achieves a low-resistance, reliable electrical bond with the connecting pads 120a on the first sub-plate 100a, the second sub-plate 200a, and the third sub-plate 300a. The perforated rings 450a on the first intermediate connecting plate 400a and the second intermediate connecting plate 500a increase the contact area with the connecting pads 120a, resulting in excellent electrical connection.

[0105] The second stage of bonding involves raising the temperature to 200-250°C and maintaining it for 90-150 minutes, while keeping the pressure at 530-580 psi. The core objective of this stage is to allow the prepreg resin to flow fully and completely fill the interlayer circuit pattern, and to achieve full cross-linking (complete curing) at this temperature, thereby achieving a strong bond and reliable interlayer insulation between the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a.

[0106] The pressure range of 530-580 psi is precisely designed to provide sufficient pressure to drive the interfacial bonding of conductive materials and the flow and filling of resin, while avoiding crushing or breakage of the fragile conductive pillars 420a within the first intermediate connecting plate 400a and the second intermediate connecting plate 500a due to excessive pressure, thereby preventing open circuit failure.

[0107] At this point, the circuit board product, which integrates three sub-boards and two intermediate connecting boards, has been manufactured as a whole using this manufacturing method. Figure 15This is a partial cross-sectional view of a circuit board manufactured according to the method of the present invention. After final lamination, the conductive pillars 420a are complete and tightly connected to the connecting pads 120a, enabling ultra-high reliability vertical interconnection. The lines on the lamination surfaces of the first sub-board 100a, the second sub-board 200a, and the third sub-board 300a are completely filled without any voids. It should be emphasized that since the first sub-board 100a and the third sub-board 300a, which are the outermost layers, have undergone outer layer treatment including solder mask, immersion gold plating, and character printing during the sub-board manufacturing stage (step S15), the finished board does not require any additional surface treatment process after lamination and can directly proceed to the final routing (shape processing) and electrical testing stages before shipment.

[0108] Understandably, this method can be used to manufacture high-thickness circuit boards with any number of layers and intermediate connecting boards.

[0109] Example 3 This embodiment provides a circuit board, which is manufactured using the manufacturing method described in Embodiment 1 or Embodiment 2.

[0110] Thanks to the manufacturing method described above, the circuit board features excellent interlayer alignment accuracy, ultra-high reliability vertical interconnects, and high-quality outer layer processing, making it particularly suitable for AI computing boards, high-power power modules, and high-end communication equipment with extremely stringent performance and reliability requirements.

[0111] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for manufacturing a circuit board, comprising the following steps: S1. Fabricate at least two sub-boards, wherein the sub-boards have first through-holes for interlayer interconnection, and the mating surfaces of the sub-boards have connection pads electrically connected to the first through-holes. S2. Fabricate at least one intermediate connecting plate with conductive pillars, the positions of which correspond to the connecting pads on the adjacent sub-plates; S3. Alternately stack and press the sub-board and intermediate connecting board together so that the conductive post is aligned with the connecting pad and electrically connected; Its features are, Step S2 includes the following steps: S21. Prepregs are paired, and copper foil is applied to both sides of the prepregs respectively; S22. Pre-curing and pressing the prepreg and copper foil together to make the prepreg have both processability and fluidity and adhesion. S23. Drill a second through hole on the prepreg covered with copper foil, the position of the second through hole corresponding to the position of the first through hole on the adjacent sub-board; S24. The second through hole is subjected to a hole wall metallization treatment to form a metallized hole wall; S25. An annular groove is formed on the copper foil at both ends of the second through hole. The annular groove forms a hole ring at both ends of the second through hole that is connected to the metallized hole wall. The annular groove isolates the hole ring from the surrounding copper foil. S26. Fill the second through hole with conductive material and pre-bake it to form a conductive pillar; S27. Remove the copper foil from both sides of the prepreg.

2. The method for manufacturing a circuit board according to claim 1, characterized in that, Step S25 includes: S251. Apply a dry film to the copper foil surface of the copper-clad prepreg. S252. Expose and develop the dry film to form a graphic window of an annular grooved area around the second through hole; S253. Remove the copper foil in the annular slotted area by etching process to form an annular slot; S254. Remove any remaining dry film from the surface of the copper foil.

3. The method for manufacturing a circuit board according to claim 1, characterized in that, In step S3, a two-stage stepped curing pressing process is used during pressing.

4. The method for manufacturing a circuit board according to claim 3, characterized in that, The two-stage stepped curing and pressing process includes a first-stage curing and pressing and a second-stage curing and pressing. The temperature of the first-stage curing and pressing is 180-200℃, the time is 45-80min, and the pressure is 530-580psi. The temperature of the second-stage curing and pressing is 200-250℃, the time is 90-150min, and the pressure is 530-580psi.

5. The method for manufacturing a circuit board according to claim 4, characterized in that, In step S22, the pre-curing and pressing temperature is 110-130℃.

6. The method for manufacturing a circuit board according to claim 4, characterized in that, In step S26, the conductive material is conductive copper paste, and the pre-baking temperature is 80-100℃ for 20-40 minutes.

7. The method for manufacturing a circuit board according to claim 1, characterized in that, In step S23, the diameter of the second through hole is 6-10 mil.

8. The method for manufacturing a circuit board according to claim 1, characterized in that, In step S25, the outer diameter of the formed annular hole is 4-8 mil larger than the diameter of the second through hole.

9. The method for manufacturing a circuit board according to claim 1, characterized in that, In step S24, the thickness of the metallized hole wall is 0.2-0.4 mil.

10. A circuit board, characterized in that, It is manufactured using the method described in any one of claims 1-9.

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