A method for pre-metallization activation of thick copper PCB board holes using a dispersant-free graphene pre-copper plating activation solution.

Abstract

This application provides a method for activating thick copper PCB holes using a dispersant-free graphene pre-copper plating activation solution. The method involves slowly adding a graphene oxide nanosheet dispersion to the graphene nanosheet dispersion. The graphene oxide, rich in carboxyl and hydroxyl functional groups, forms π-π adsorption with the graphene, thus hydrophilically modifying the graphene. This results in a dispersant-free graphene pre-copper plating activation solution, which is used for the pre-metallization activation of PCB holes. This eliminates the need for a dispersant, requires less graphene oxide, exhibits stronger conductivity, reduces the likelihood of bubble blockage, and allows for the formation of an activation layer with superior overall performance on the hole walls of the PCB holes.

Description

Technical Field

[0001] This invention relates to the field of PCB board hole activation technology before metallization, and in particular to a method for activating thick copper PCB board holes before metallization using a dispersant-free graphene copper plating pre-activation solution. Background Technology

[0002] Currently, PCB hole metallization refers to the process of plating a layer of conductive metal onto the insulating hole walls of printed conductors on each layer using chemical plating and electroplating methods, enabling reliable interconnection. PCB hole metallization technology is one of the key technologies in printed PCB manufacturing. Metallized holes refer to the process of chemically plating a thin layer of copper onto the inner wall of the hole between the top and bottom layers, thus connecting the top and bottom layers of the printed circuit board. PCB hole metallization relies on the stability of palladium paste. The traditional process flow is: alkaline degreasing → two or three-stage countercurrent rinsing → roughening (micro-etching) → two-stage countercurrent rinsing → pre-immersion → activation → two-stage countercurrent rinsing → desmearing → two-stage countercurrent rinsing → copper plating → two-stage countercurrent rinsing → acid immersion → alkaline degreasing.

[0003] Furthermore, there are three main processes for PCB hole metallization:

[0004] The first method involves forming a conductive layer using graphite or carbon black. However, the conductive layer formed by graphite or carbon black has poor conductivity, and due to the large particle size, it is difficult to adhere when the through-hole size is small.

[0005] The second method involves using a layer of palladium as a seed layer, but palladium is difficult to mass-produce due to its high cost.

[0006] The third method involves polymerizing pyrrole, thiophene, furan, and aniline on the pore walls to form a conductive polymer layer. While this is currently the most widely used pore metallization process, its polymerization process requires oxidation treatment with potassium permanganate solution, which causes some environmental pollution. Furthermore, the conductivity of the resulting polymer conductive layer is relatively limited.

[0007] To address the aforementioned issues, the latest generation of PCB board hole metallization pre-activation technology has emerged. This technology primarily utilizes novel carbon materials such as graphene and carbon nanotubes. However, due to their hydrophobic properties, graphene and carbon nanotubes present dispersion difficulties, requiring the addition of suitable dispersants, and the dispersion effect is generally limited. The aforementioned hole metallization pre-activation process also involves chemical circulation and stirring, aeration, and ultrasonication. Because the added surfactants and other additives can easily cause small bubbles to form on the hole walls, leading to hole blockage during copper plating and a decrease in yield.

[0008] Furthermore, Chinese patent application No. 202210331517.3, "A Method for Metallizing Graphene Oxide Holes in Flexible Copper-Clad Laminates," discloses a method of immersing graphene in an aqueous solution with a concentration of 18-24 wt% before chemical copper plating (activation process) and then performing hole metallization. The graphene oxide microstructure is sheet-like, and when dispersed in the solution, the sheet-like graphene oxide readily adsorbs onto the surface of the copper hole walls due to its strong electrostatic adsorption force, completely adsorbing the entire hole wall. As the hole metallization time increases, i.e., the black hole time of the flexible copper-clad laminate in the graphene oxide solution increases, the carboxyl groups in the graphene oxide molecules undergo a complexation reaction with copper to form intermetallic complexes. At this point, the hole walls and the graphene oxide layer directly form strong molecular bonds, preventing detachment during subsequent copper plating. After copper plating, the hole walls are smooth and flat, without defects, and there is no problem of incomplete plating. In addition, compared with other hole metallization processes, graphene oxide hole metallization has a thinner conductive layer, making it more suitable for high-frequency circuit board manufacturing.

[0009] However, the aforementioned patents still have the following problems:

[0010] Compared to graphene, graphene oxide has strong hydrophilicity but poor electrical conductivity, resulting in a high concentration of graphene oxide aqueous solution used in the aforementioned patent application. Generally speaking, this high-concentration graphene oxide aqueous solution still requires the use of a small amount of dispersant as an auxiliary dispersant. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for activating thick copper PCB holes using a dispersant-free graphene pre-copper plating activation solution that eliminates the need for dispersants, uses less graphene oxide, has stronger conductivity, is less prone to bubble blockage, and forms an activation layer with better overall performance on the hole walls of the PCB.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A method for activating thick copper PCB board holes before metallization using a dispersant-free graphene pre-copper plating activation solution includes the following steps:

[0014] A first suspension with a solid content of 0.1% to 1% was prepared by mixing expanded graphite with pure water, and then the suspension was exfoliated using a high-pressure homogenizer to obtain a graphene nanosheet dispersion; wherein the graphene nanosheet dispersion contained graphene with a sheet size of 500 nm to 1 μm.

[0015] A second suspension with a solid content of 0.1% to 0.5% was prepared by mixing graphene oxide with pure water, and then subjected to ultrasonic emulsification and high-pressure homogenization to obtain a graphene oxide nanosheet dispersion; wherein the graphene oxide in the graphene oxide nanosheet dispersion has a sheet size of less than 200 nm.

[0016] The graphene oxide nanosheet dispersion was slowly added to the graphene nanosheet dispersion. The graphene oxide, which is rich in carboxyl and hydroxyl functional groups, formed π-π adsorption with the graphene to perform hydrophilic modification, thus obtaining a graphene activation solution without dispersant before copper plating.

[0017] The graphene copper plating pre-activation solution is injected into the activation tank, and the PCB board is mounted on the rotating body. The PCB board is immersed in the graphene copper plating pre-activation solution in the activation tank. The rotating body is controlled to drive the PCB board to rotate in one direction, so that the graphene copper plating pre-activation solution continuously washes the hole walls of the PCB board. The air bubbles on the hole walls of the PCB board are discharged based on the washing force of the graphene copper plating pre-activation solution and the centrifugal force generated by the rotation of the PCB board itself.

[0018] The holes in the PCB board are coated with an activation layer in the pre-copper activation solution before the graphene is plated with copper.

[0019] In one embodiment, the expansion ratio of the expanded graphite is >250.

[0020] In one embodiment, during the stripping operation of the high-pressure homogenizer, the operating parameters of the high-pressure homogenizer are as follows:

[0021] The homogenization pressure was 150–300 MPa, the flow rate was 30 L / min, and the homogenization time was 1–2 h.

[0022] In one embodiment, the oxygen content of the graphite oxide is 40% to 60%.

[0023] In one embodiment, the ultrasonic emulsification operation specifically involves placing the second suspension into an ultrasonic tank for emulsification and dispersion for 30 minutes to 2 hours.

[0024] In one embodiment, during the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the volume ratio of the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion is 1:(1~1.5).

[0025] In one embodiment, the volume of both the graphene oxide nanosheet dispersion and the graphene nanosheet dispersion is 100 mL.

[0026] In the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the slow addition rate is 5-20 ml / min.

[0027] In one embodiment, the rotating body includes a gantry frame, a motor, a bushing, a stirring shaft, a stirring paddle, a clamping ring, and a clamping member. The gantry frame is mounted on the activation tank, the motor is mounted on the gantry frame, the bushing is mounted on the motor, one end of the stirring shaft passes through the bushing and is connected to the rotating shaft of the motor, the stirring paddle is fixed to the other end of the stirring shaft, the clamping ring is clamped to the outside of the stirring shaft, the clamping member is fixed to the clamping ring, the clamping member is used to clamp the PCB board, and the motor operates to drive the PCB board to rotate around the stirring shaft as the rotation axis.

[0028] In one embodiment, the clamping member includes multiple connecting rods and multiple clamps, wherein the number of connecting rods is the same as the number of clamps;

[0029] One end of the connecting rod is fixed to the clamping ring, and the other end of the connecting rod is fixed to the plate clamp, which is used to hold the PCB board.

[0030] In one embodiment, each of the clamping members is centrally symmetrically distributed with respect to the stirring shaft as the axis, and each of the PCB boards is centrally symmetrically distributed with respect to the stirring shaft as the axis.

[0031] Compared with the prior art, the present invention has at least the following advantages:

[0032] 1. This invention uses graphene oxide as a hydrophilic functional modification group with a smaller sheet size, adsorbed onto graphene with a larger sheet size. The resulting graphene pre-copper plating activation solution modifies the originally hydrophobic graphene, thus acquiring strong hydrophilicity. Furthermore, graphene oxide can be used as a hydrophilic functional modification group with a smaller sheet size, adsorbed onto graphene with a larger sheet size. Thus, the resulting graphene pre-copper plating activation solution modifies the originally hydrophobic graphene, thus acquiring strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of a dispersant, and it also possesses the advantage of strong conductivity. Compared to traditional technologies that require simply using graphene oxide with poor conductivity as the activation solution for the conductive material, the graphene pre-copper plating activation solution of this invention also significantly reduces the amount of graphene oxide used, while also achieving stronger conductivity.

[0033] 2. Compared with traditional methods that use novel carbon materials, such as graphene and carbon nanotubes, the present invention addresses the problem that graphene and carbon nanotubes, due to their hydrophobic properties, are difficult to disperse and require the addition of suitable dispersants, with generally poor dispersion results. The graphene pre-copper plating activation solution of this invention uses graphene oxide as a hydrophilic functional modification group with a smaller sheet size adsorbed onto graphene with a larger sheet size. In this way, the obtained graphene pre-copper plating activation solution modifies the original hydrophobic graphene, thereby possessing strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of dispersants, resulting in the graphene pre-copper plating activation solution with a stable dispersion system.

[0034] 3. This invention mounts a PCB board onto a rotating body, immersing the PCB board in the pre-copper activation solution of the graphene plating tank. The rotating body is controlled to drive the PCB board in a unidirectional rotation, causing the pre-copper activation solution to continuously flush the walls of the drilled holes in the PCB board. Because the PCB board has a flat surface structure, when it rotates and impacts the pre-copper activation solution, the PCB board experiences significant resistance from the solution. This resistance forces the pre-copper activation solution to flow through the drilled holes in the PCB board, which on the one hand increases the... The interaction between the graphene pre-copper plating activation solution and the hole walls of the PCB board improves the adsorption and deposition efficiency and quality of graphene oxide-modified graphene on the hole walls of the PCB board, thus better forming the activation layer. On the other hand, the graphene pre-copper plating activation solution will flush the hole walls of the PCB board, thereby breaking or flushing away air bubbles on the hole walls of the PCB board, so that the hole walls of the PCB board can fully contact and interact with the graphene pre-copper plating activation solution, improving the adsorption quality of graphene oxide-modified graphene on the hole walls of the PCB board, and thus improving the overall quality of the activation layer. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of a method for activating thick copper PCB holes using a dispersant-free graphene copper plating pre-activation solution according to an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the structure of a rotating body according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of a rotating body according to another embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the graphene nanosheet dispersion (GO) and graphene oxide nanosheet dispersion prepared in Example 1 of the present invention.

[0040] Figure 5 This is an enlarged view of the hole wall of the PCB board after the hole metallization process in Embodiment 1 of the present invention. Detailed Implementation

[0041] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0042] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] This application provides a method for activating thick copper PCB board holes before metallization using a dispersant-free graphene pre-copper plating activation solution, comprising the following steps: preparing a first suspension with a solid content of 0.1% to 1% using expanded graphite and pure water, and performing a peeling operation using a high-pressure homogenizer to obtain a graphene nanosheet dispersion; wherein the graphene in the graphene nanosheet dispersion has a sheet size of 500 nm to 1 μm; preparing a second suspension with a solid content of 0.1% to 0.5% using graphene oxide and pure water, and sequentially performing an ultrasonic emulsification operation and a high-pressure homogenizer peeling operation to obtain an oxide graphene nanosheet dispersion; wherein the graphene in the oxide graphene nanosheet dispersion has a sheet size of less than 200 nm; slowly adding the oxide graphene nanosheet dispersion to the graphene nanosheet dispersion, and then... Graphene oxide rich in carboxyl and hydroxyl functional groups forms π-π adsorption with graphene to perform hydrophilic modification, resulting in a graphene pre-copper plating activation solution without dispersant. This activation solution is injected into an activation tank, and a PCB board is mounted on a rotating body, immersed in the activation solution. The rotating body is controlled to rotate the PCB board unidirectionally, causing the activation solution to continuously flush the walls of the drilled holes in the PCB board. Air bubbles on the hole walls are expelled by the flushing force of the activation solution and the centrifugal force generated by the PCB board's rotation. An activation layer adheres to the hole walls in the activation solution.

[0045] To better understand the method of using the dispersant-free graphene pre-copper plating activation solution for pre-metallization activation of holes in thick copper PCB boards, the following further explanation is provided:

[0046] Please see Figure 1 One embodiment of the method for activating thick copper PCB board holes using a dispersant-free graphene pre-copper plating activation solution includes the following steps:

[0047] S110: A first suspension with a solid content of 0.1% to 1% is prepared by mixing expanded graphite with pure water, and the suspension is then subjected to a peeling operation using a high-pressure homogenizer to obtain a graphene nanosheet dispersion; wherein the graphene nanosheet dispersion contains graphene with a sheet size of 500 nm to 1 μm.

[0048] In one embodiment, the expansion ratio of the expanded graphite is >250, thus enabling the preparation of a graphene nanosheet dispersion with fewer defects.

[0049] In one embodiment, during the exfoliation operation of the high-pressure homogenizer, the operating parameters of the high-pressure homogenizer are as follows: homogenization pressure of 150-300 MPa, flow rate of 30 L / min, and homogenization time of 1-2 h, thereby preparing the graphene nanosheet dispersion with fewer defects.

[0050] S120: A second suspension with a solid content of 0.1% to 0.5% is prepared by mixing graphene oxide with pure water, and then subjected to ultrasonic emulsification and high-pressure homogenization to obtain a graphene oxide nanosheet dispersion; wherein the graphene oxide in the graphene oxide nanosheet dispersion has a sheet size of less than 200 nm.

[0051] In one embodiment, the oxygen content of the graphene oxide is 40% to 60%, which makes the graphene oxide nanosheet dispersion rich in more carboxyl and hydroxyl functional groups. When it is used to modify the graphene in the graphene nanosheet dispersion, it can improve the hydrophilicity of graphene and reduce the amount of graphene oxide, that is, reduce the amount of graphene oxide in the graphene activation solution before copper plating.

[0052] In one embodiment, the ultrasonic emulsification operation specifically involves placing the second suspension into an ultrasonic tank for emulsification and dispersion for 30 min to 2 h, thereby preparing the graphene oxide nanosheet dispersion with fewer defects.

[0053] S130: The graphene oxide nanosheet dispersion is slowly added to the graphene nanosheet dispersion. The graphene oxide, which is rich in carboxyl and hydroxyl functional groups, forms π-π adsorption with the graphene to perform hydrophilic modification, thereby obtaining a graphene pre-copper plating activation solution without dispersant.

[0054]

[0055] It should be noted that the graphene oxide in the graphene oxide nanosheet dispersion contains many carboxyl and hydroxyl functional groups, which enables the graphene oxide to be better dispersed in the aqueous solution to form a more stable dispersion system. Furthermore, the graphene oxide rich in carboxyl and hydroxyl functional groups forms π-π adsorption with the graphene, significantly improving the hydrophobic properties of the graphene. Therefore, by combining this method with the control of the sheet size—specifically, the sheet size of the graphene in the graphene nanosheet dispersion is 500 nm to 1 μm, and the sheet size of the graphene oxide in the graphene oxide nanosheet dispersion is less than 200 nm—this approach allows for better control of the graphene oxide nanosheet dispersion. In this way, graphene oxide can be adsorbed onto graphene with a smaller sheet size as a hydrophilic functional modification group, resulting in a graphene pre-copper plating activation solution that, by modifying the originally hydrophobic graphene, possesses strong hydrophilicity. Furthermore, graphene oxide can be adsorbed onto graphene with a smaller sheet size as a hydrophilic functional modification group, resulting in a graphene pre-copper plating activation solution that, by modifying the originally hydrophobic graphene, possesses strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of dispersants, and it also possesses the advantage of strong conductivity. Compared to traditional technologies that require simply using graphene oxide, which has poor conductivity, as an activation solution for conductive materials, the graphene pre-copper plating activation solution in this case also significantly reduces the amount of graphene oxide used, while also achieving stronger conductivity.

[0056] Furthermore, compared to traditional methods using novel carbon materials, such as graphene and carbon nanotubes, which suffer from the difficulty of dispersion due to their hydrophobic properties and the need for suitable dispersants, the graphene pre-copper plating activation solution of this invention uses graphene oxide as a hydrophilic functional modification group with a smaller sheet size adsorbed onto graphene with a larger sheet size. In this way, the obtained graphene pre-copper plating activation solution modifies the original hydrophobic graphene, thereby acquiring strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of dispersants, resulting in the graphene pre-copper plating activation solution with a stable dispersion system.

[0057] In one embodiment, during the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the volume ratio of the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion is 1:(1-1.5); further, the volumes of both the nanosheet dispersion and the graphene nanosheet dispersion are 100 mL; further, during the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the dropping rate of the slow addition is 5-20 mL / min. This allows the graphene oxide rich in carboxyl and hydroxyl functional groups to more fully form π-π adsorption with graphene, better enabling the graphene oxide to be adsorbed as a hydrophilic functional modification group with a smaller sheet size onto the graphene with a larger sheet size.

[0058] S140: The graphene pre-copper plating activation solution is injected into the activation tank, and the PCB board is mounted on the rotating body. The PCB board is immersed in the graphene pre-copper plating activation solution in the activation tank. The rotating body is controlled to drive the PCB board to rotate in one direction, so that the graphene pre-copper plating activation solution continuously washes the hole walls of the PCB board. The air bubbles on the hole walls of the PCB board are discharged based on the washing force of the graphene pre-copper plating activation solution and the centrifugal force generated by the rotation of the PCB board itself.

[0059] It is understood that in the activation tank, in order to improve the dispersibility of the graphene pre-copper plating activation solution and to allow the hydrophilic modified graphene oxide in the pre-copper plating activation solution to better and more fully contact the hole walls of the PCB board, so as to better adsorb onto the hole walls of the PCB board, operations such as circulation stirring, aeration, and ultrasonication are usually performed simultaneously to achieve the expected goal. However, these operations will cause small air bubbles to form on the hole walls of the PCB board. These small air bubbles often make it difficult for the hydrophilic modified graphene oxide to adhere to the local hole walls where these air bubbles adhere (i.e., the hole clogging problem commonly known in the industry). As a result, the activation layer formed during the activation process is unstable in terms of continuity and uniformity due to air bubbles, which in turn leads to quality problems in the copper plating layer formed in the subsequent copper plating process, resulting in a decrease in yield.

[0060] This invention mounts a PCB board onto a rotating body, immersing the PCB board in the pre-copper activation solution of the graphene in the activation tank. The rotating body is controlled to drive the PCB board in a unidirectional rotation, causing the pre-copper activation solution to continuously flush the walls of the drilled holes in the PCB board. Because the PCB board has a flat surface structure, when it rotates and impacts the pre-copper activation solution, the PCB board experiences significant resistance from the solution. This resistance forces the pre-copper activation solution to flow through the drilled holes in the PCB board, which on the one hand increases the risk of graphene plating failure. The interaction between the graphene pre-copper plating activation solution and the hole walls of the PCB board improves the adsorption and deposition efficiency and quality of graphene oxide-modified graphene on the hole walls of the PCB board, thus better forming the activation layer. On the other hand, the graphene pre-copper plating activation solution will flush the hole walls of the PCB board, thereby breaking or flushing away air bubbles on the hole walls of the PCB board, so that the hole walls of the PCB board can fully contact and interact with the graphene pre-copper plating activation solution, improving the adsorption quality of graphene oxide-modified graphene on the hole walls of the PCB board, and thus improving the overall quality of the activation layer. Furthermore, when the PCB board rotates due to the rotation of the rotating body, the pores on the hole walls of the drilled holes on the PCB board are also affected by centrifugal force. In addition, the adhesion of the bubbles to the hole walls of the drilled holes on the PCB board is relatively small. Thus, the bubbles on the hole walls of the drilled holes on the PCB board are expelled or broken into smaller bubbles and dispersed into the graphene copper plating pre-activation liquid due to the combined effect of the scouring force of the graphene copper plating pre-activation liquid and the centrifugal force generated by the rotation of the PCB board itself. This state is real-time and dynamic, continuously solving the problem of bubble blockage. This ensures that the hole walls of the drilled holes on the PCB board maintain a relatively large degree of contact and interaction with the graphene copper plating pre-activation liquid passing through the holes, so as to achieve the effect of forming an activation layer with better overall performance on the hole walls of the drilled holes on the PCB board.

[0061] It should be noted that, regarding the activation method of the graphene pre-copper plating activation solution based on dispersant-free graphene for pre-metallization of holes in thick copper PCB boards, the PCB board is a thick copper PCB board with a thickness-to-diameter ratio of the drilled holes greater than 12:1. The resistance to the discharge of air bubbles from the drilled holes of the thick copper PCB board is relatively large. The activation method of this case can achieve great adaptability.

[0062] To better adapt to the PCB board being a thick copper PCB board, the thickness-to-diameter ratio of the drilled holes in the thick copper PCB board is greater than 12:1. This allows air bubbles on the hole walls of the PCB board to be expelled or broken into smaller bubbles and dispersed into the pre-copper activation solution due to the combined effects of the scouring force of the graphene copper plating pre-activation solution and the centrifugal force generated by the rotation of the PCB board itself. This process is real-time and dynamic, continuously addressing the problem of air bubble blockage. This ensures that the hole walls of the PCB board maintain a relatively high degree of contact and interaction with the graphene copper plating pre-activation solution passing through the holes, thereby achieving the effect of forming an activation layer with better overall performance on the hole walls of the PCB board. In one embodiment, please refer to... Figure 2 The rotating body 100 includes a gantry frame (not shown), a motor 110, a bushing 120, a stirring shaft 130, a stirring paddle 140, a clamping ring 150, and a clamping member 160. The gantry frame is mounted on the activation tank, the motor is mounted on the gantry frame, the bushing is mounted on the motor, one end of the stirring shaft passes through the bushing and is connected to the rotating shaft of the motor, the stirring paddle is fixed to the other end of the stirring shaft, the clamping ring is clamped to the outside of the stirring shaft, and the clamping member is fixed to the clamping ring. The clamping member is used to clamp the PCB board, and the motor operates to drive the PCB board to rotate around the stirring shaft as the rotation axis, thus better adapting to the PCB board. The PCB is a thick copper board with a hole thickness-to-diameter ratio greater than 12:1. This allows air bubbles on the hole walls to be expelled or broken into smaller bubbles and dispersed into the pre-copper activation solution due to the combined effects of the scouring force of the graphene pre-copper activation solution and the centrifugal force generated by the rotation of the PCB itself. This process is real-time and dynamic, continuously addressing the problem of air bubble blockage. This ensures that the hole walls of the PCB maintain a relatively high degree of contact and interaction with the graphene pre-copper activation solution passing through the holes, thereby achieving the effect of forming an activation layer with better overall performance on the hole walls of the PCB.

[0063] Furthermore, the clamping component includes multiple connecting rods and multiple plate clamps, the number of connecting rods being the same as the number of plate clamps; one end of each connecting rod is fixed to the clamping ring, and the other end of each connecting rod is fixed to the plate clamp, which is used to clamp the PCB board; even further, each clamping component is centrally symmetrically distributed with the stirring shaft as the axis, and each PCB board is centrally symmetrically distributed with the stirring shaft as the axis, thus enabling the concentrated batch processing of multiple PCB boards for pre-hole metallization activation.

[0064] Furthermore, the distance between the top edge of the PCB board and the static liquid surface of the graphene copper plating pre-activation solution in the activation tank is greater than 30 cm, and the rotation speed of the rotating body is 30-60 rpm. In this way, when each PCB board rotates around the stirring shaft, the graphene copper plating pre-activation solution at the top of the activation tank can be better filled into the gaps between the rotating PCB boards, thereby better realizing the pre-activation process of hole metallization in a concentrated batch of multiple PCB boards.

[0065] It is understandable that, relative to the parallel arrangement of the PCBs and their perpendicular placement to the liquid surface, when each PCB is vertically inserted into the pre-copper graphene activation solution in the activation tank, the PCBs, due to their large surface area, experience significant resistance when rotating within the solution. This causes excessive turbulence in the activation solution, resulting in large air bubbles. Simultaneously, due to the clamping of the PCBs at certain locations, the PCBs may bend backward at both ends when overcoming the resistance of the activation solution, and may even vibrate. This affects the structural performance of the PCBs themselves and, moreover, the adhesion quality of the activation layer.

[0066] To reduce the travel resistance encountered during the PCB rotation activation process, the backward bending of the PCB ends, and potential vibration issues, in one embodiment, please refer to... Figure 3 The clamping mechanism includes two clamping plates. The PCB board is clamped by the two clamping plates, which are arranged parallel to each other. The extending direction of the clamping plates is not perpendicular to the extending direction of the stirring shaft. Specifically, the extending direction of the clamping plates forms an acute angle with the extending direction of the stirring shaft, with the acute angle ranging from 15 to 45 degrees. This ensures that the plane of the PCB board is not perpendicular to the extending direction of the stirring shaft. Furthermore, the spacing between each pair of PCB boards is equal. The clamping plates of each clamping component are spirally distributed around the stirring shaft, and the PCB boards are also spirally distributed around the stirring shaft. This reduces the travel resistance encountered by the PCB board during the rotational activation process, reduces the problem of the PCB board bending backward at both ends, and minimizes potential vibration issues.

[0067] Furthermore, in order to ensure that each PCB board can be uniformly clustered without interference and laid on the stirring shaft by each board clamp, the board clamps of each clamping member are spirally distributed around the stirring shaft as the axis, and the acute angle formed by the plane of each PCB board and the extension direction of the stirring shaft is not the same. In this way, the first distance between two adjacent PCB boards in the lower part of the activation tank is greater than the second distance between two adjacent PCB boards in the upper part of the activation tank. This can make the inflow resistance of the stirring shaft smaller and the outflow resistance larger when the stirring shaft rotates, forcing an increase in flow rate and strengthening the interaction between the board and the liquid.

[0068] S150: The hole walls of the PCB board are coated with an activation layer in the pre-copper activation solution before the graphene is plated with copper.

[0069] The hole walls of the PCB board after activation through step S150 can be coated with a high-quality conductive activation layer, which is more conducive to the subsequent hole metallization process of the PCB board.

[0070] Compared with the prior art, the present invention has at least the following advantages:

[0071] 1. This invention uses graphene oxide as a hydrophilic functional modification group with a smaller sheet size, adsorbed onto graphene with a larger sheet size. The resulting graphene pre-copper plating activation solution modifies the originally hydrophobic graphene, thus acquiring strong hydrophilicity. Furthermore, graphene oxide can be used as a hydrophilic functional modification group with a smaller sheet size, adsorbed onto graphene with a larger sheet size. Thus, the resulting graphene pre-copper plating activation solution modifies the originally hydrophobic graphene, thus acquiring strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of a dispersant, and it also possesses the advantage of strong conductivity. Compared to traditional technologies that require simply using graphene oxide with poor conductivity as the activation solution for the conductive material, the graphene pre-copper plating activation solution of this invention also significantly reduces the amount of graphene oxide used, while also achieving stronger conductivity.

[0072] 2. Compared with traditional methods that use novel carbon materials, such as graphene and carbon nanotubes, the present invention addresses the problem that graphene and carbon nanotubes, due to their hydrophobic properties, are difficult to disperse and require the addition of suitable dispersants, with generally poor dispersion results. The graphene pre-copper plating activation solution of this invention uses graphene oxide as a hydrophilic functional modification group with a smaller sheet size adsorbed onto graphene with a larger sheet size. In this way, the obtained graphene pre-copper plating activation solution modifies the original hydrophobic graphene, thereby possessing strong hydrophilicity. Therefore, good dispersion performance can be obtained without the use of dispersants, resulting in the graphene pre-copper plating activation solution with a stable dispersion system.

[0073] 3. This invention mounts a PCB board onto a rotating body, immersing the PCB board in the pre-copper activation solution of the graphene plating tank. The rotating body is controlled to drive the PCB board in a unidirectional rotation, causing the pre-copper activation solution to continuously flush the walls of the drilled holes in the PCB board. Because the PCB board has a flat surface structure, when it rotates and impacts the pre-copper activation solution, the PCB board experiences significant resistance from the solution. This resistance forces the pre-copper activation solution to flow through the drilled holes in the PCB board, which on the one hand increases the... The interaction between the graphene pre-copper plating activation solution and the hole walls of the PCB board improves the adsorption and deposition efficiency and quality of graphene oxide-modified graphene on the hole walls of the PCB board, thus better forming the activation layer. On the other hand, the graphene pre-copper plating activation solution will flush the hole walls of the PCB board, thereby breaking or flushing away air bubbles on the hole walls of the PCB board, so that the hole walls of the PCB board can fully contact and interact with the graphene pre-copper plating activation solution, improving the adsorption quality of graphene oxide-modified graphene on the hole walls of the PCB board, and thus improving the overall quality of the activation layer.

[0074] The following are examples, but it should be noted that the following examples do not exhaust all possible situations, and the materials used in the following examples are commercially available unless otherwise specified.

[0075] Example 1

[0076] ① Preparation of defect-free graphene nanosheet dispersion (GO): Expanded graphite with an expansion ratio >250 was used as the raw material. 100 mL of a suspension with a solid content of 1% was prepared by mixing expanded graphite with pure water. The suspension was then exfoliated by a high-pressure homogenizer at a pressure of 250 MPa, a flow rate of 30 L / min, and a homogenization time of 2 h to obtain a graphene nanosheet dispersion with a size of 500 nm to 1 μm.

[0077] ② Preparation of graphene oxide nanosheet dispersion: The raw material is graphene oxide with an oxygen content of 40% to 60%. 100 mL of graphene oxide and pure water are mixed to form a suspension with a solid content of 0.5%. The suspension is placed in an ultrasonic tank for emulsification and dispersion for 2 h. The dispersion is then exfoliated by a high-pressure homogenizer at a homogenization pressure of 250 MPa and a flow rate of 30 L / min for 2 h to obtain a graphene oxide nanosheet dispersion with a size of less than 200 nm.

[0078] ③ Preparation of stable and dispersed graphene nano-dispersion (graphene activation solution before copper plating): The graphene oxide nano-dispersion is slowly added dropwise to the graphene nano-dispersion while stirring. The dropwise addition rate is controlled at 15 ml / min, and finally a graphene nano-dispersion (graphene activation solution before copper plating) without dispersant is obtained.

[0079] The graphene nanosheet dispersion (GO) and graphene oxide nanosheet dispersion prepared in Example 1 can be found in [reference needed]. Figure 4 .

[0080] A stable, dispersed graphene nano-dispersion (graphene pre-copper plating activation solution) is injected into the activation tank and fixed to the stirring shaft of a rotating motor. The propeller-type three-bladed paddle effectively creates a vortex in the solution, ensuring uniform dispersion of graphene within the tank. Rotation ensures that the holes on the PCB board are thoroughly wetted by the pretreatment alkaline solution and graphene dispersion, preventing clogging during the copper plating stage caused by surfactants or uneven graphene dispersion.

[0081] After activation, the PCB board undergoes copper plating and immersion copper processes in sequence to complete the hole metallization process.

[0082] For an example of a PCB board after hole metallization, please refer to [reference needed]. Figure 5 ,from Figure 5 It can be seen that the copper layer on the hole wall is relatively uniform in thickness.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for activating thick copper PCB board holes before metallization using a dispersant-free graphene pre-copper plating activation solution, characterized in that, Includes the following steps: A first suspension with a solid content of 0.1% to 1% was prepared by mixing expanded graphite with pure water, and then the suspension was exfoliated using a high-pressure homogenizer to obtain a graphene nanosheet dispersion; wherein the graphene nanosheet dispersion contained graphene with a sheet size of 500 nm to 1 μm. A second suspension with a solid content of 0.1% to 0.5% was prepared by mixing graphene oxide with pure water, and then subjected to ultrasonic emulsification and high-pressure homogenization to obtain a graphene oxide nanosheet dispersion; wherein the graphene oxide in the graphene oxide nanosheet dispersion has a sheet size of less than 200 nm. The graphene oxide nanosheet dispersion was slowly added to the graphene nanosheet dispersion. The graphene oxide, which is rich in carboxyl and hydroxyl functional groups, formed π-π adsorption with the graphene to perform hydrophilic modification, thus obtaining a graphene activation solution without dispersant before copper plating. The graphene copper plating pre-activation solution is injected into the activation tank, and the PCB board is mounted on the rotating body. The PCB board is immersed in the graphene copper plating pre-activation solution in the activation tank. The rotating body is controlled to drive the PCB board to rotate in one direction, so that the graphene copper plating pre-activation solution continuously washes the hole walls of the PCB board. The air bubbles on the hole walls of the PCB board are discharged based on the washing force of the graphene copper plating pre-activation solution and the centrifugal force generated by the rotation of the PCB board itself. The holes in the PCB board are coated with an activation layer in the pre-copper activation solution before the graphene is plated with copper.

2. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, The expansion ratio of the expanded graphite used is >250.

3. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, During the stripping operation in the high-pressure homogenizer, the operating parameters of the high-pressure homogenizer are as follows: The homogenization pressure was 150–300 MPa, the flow rate was 30 L / min, and the homogenization time was 1–2 h.

4. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, The oxygen content of the graphite oxide is 40% to 60%.

5. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, The ultrasonic emulsification operation specifically involves placing the second suspension into an ultrasonic tank for emulsification and dispersion for 30 minutes to 2 hours.

6. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, In the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the volume ratio of the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion is 1:(1~1.5).

7. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 6, characterized in that, The volume of both the graphene oxide nanosheet dispersion and the graphene nanosheet dispersion is 100 mL. In the operation of slowly adding the graphene oxide nanosheet dispersion to the graphene nanosheet dispersion, the slow addition rate is 5-20 ml / min.

8. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 1, characterized in that, The rotating body includes a gantry frame, a motor, a bushing, a stirring shaft, a stirring paddle, a clamping ring, and a clamping component. The gantry frame is mounted on the activation tank, the motor is mounted on the gantry frame, the bushing is mounted on the motor, one end of the stirring shaft passes through the bushing and is connected to the rotating shaft of the motor, the stirring paddle is fixed to the other end of the stirring shaft, the clamping ring is clamped to the outside of the stirring shaft, and the clamping component is fixed to the clamping ring. The clamping component is used to clamp the PCB board, and the motor operates to drive the PCB board to rotate around the stirring shaft as the rotation axis.

9. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 8, characterized in that, The clamping component includes multiple connecting rods and multiple plate clamps, wherein the number of connecting rods is the same as the number of plate clamps; One end of the connecting rod is fixed to the clamping ring, and the other end of the connecting rod is fixed to the plate clamp, which is used to hold the PCB board.

10. The method for activating thick copper PCB board holes using the dispersant-free graphene pre-copper plating activation solution according to claim 9, characterized in that, Each of the clamping components is centrally symmetrically distributed with respect to the stirring shaft as the axis, and each of the PCB boards is centrally symmetrically distributed with respect to the stirring shaft as the axis.

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