Circuit board hole wall modification method, circuit board, and hole wall metal layer preparation method

Abstract

The application provides a circuit board hole wall modification method, a circuit board and a preparation method of a hole wall conductive layer. The circuit board hole wall modification method comprises the following steps: providing a circuit board base body with a hole; attaching a mixture of a first photosensitive resin and a silane coupling agent to the hole wall of the hole of the circuit board base body, the first photosensitive resin comprising a first photosensitive prepolymer, and the silane coupling agent comprising an amino group in the molecular structure; performing a first curing treatment on the first photosensitive resin to crosslink and cure part of the first photosensitive resin; immersing the hole in a dispersion liquid containing graphene to make the graphene react with the silane coupling agent; and performing a second curing treatment on the first photosensitive prepolymer. The modification method of the circuit board hole wall can assist the graphene to spread and fix on the surface of the first photosensitive resin in a sheet layer form, form a stable conductive network, and further improve the conductive performance of the conductive layer formed by the graphene material.

Description

Technical Field

[0001] This application relates to the field of circuit board processing technology, specifically to a method for modifying the hole walls of a circuit board and a method for preparing a circuit board and a conductive layer on the hole walls. Background Technology

[0002] Hole metallization refers to the process of depositing a thin layer of metal on the walls of holes between multilayer circuit boards. It is an important step in the printed circuit board manufacturing process, mainly used to achieve electrical connections between multilayer circuit boards. Some related technologies propose to perform hole metallization of circuit boards using a black hole process. This technology mainly involves adsorbing carbon or graphite particles onto the hole walls to provide a certain conductivity, replacing the traditional chemical copper plating step, and then electroplating copper on the carbon film surface. However, most carbon or graphite particles are large-diameter particles, which have problems such as poor dispersibility, poor conductivity, and difficulty in adsorbing onto the hole walls. It is difficult to form a dense conductive layer on the hole walls, and neither the adhesion nor the conductivity is satisfactory.

[0003] Some related technologies propose using graphene, which has better conductivity, to replace carbon or graphite particles. However, problems still limit the further application of graphene materials. For example, the strong van der Waals forces between graphene sheets cause graphene materials to easily agglomerate in slurries, making it difficult to fully spread and adhere to the hole walls. This agglomeration problem also makes it difficult for graphene materials to form a structurally stable and continuous conductive network. Although the dispersibility of graphene oxide formed by oxidizing graphene can be improved, the problem of forming a structurally stable and continuous conductive network still exists when it adheres to the hole walls. Therefore, the conductivity of graphene conductive layers on circuit board hole walls needs further improvement. Summary of the Invention

[0004] Therefore, it is necessary to provide a method for metallizing circuit board holes. This preparation method can promote the spread of graphene material in a sheet-like morphology and form a stable conductive network structure, thereby improving the conductivity of the conductive layer formed by the graphene material.

[0005] Some embodiments of this application provide a method for modifying the wall of a circuit board hole, which includes the following steps:

[0006] Provide a circuit board substrate with holes;

[0007] A mixture of a first photosensitive resin and a silane coupling agent is attached to the hole wall of the circuit board substrate. The first photosensitive resin includes a first photosensitive prepolymer, and the silane coupling agent contains amino groups in its molecular structure.

[0008] The first photosensitive resin is subjected to a first curing treatment, which causes a portion of the first photosensitive resin to cross-link and cure.

[0009] The pores are immersed in a dispersion containing graphene, allowing the graphene to react with the silane coupling agent; and,

[0010] The first photosensitive prepolymer is subjected to a second curing process.

[0011] In some embodiments of this application, the dispersion further includes a second photosensitive resin, the second photosensitive resin comprising a second photosensitive prepolymer; the first photosensitive prepolymer is hydrophobic, the second photosensitive prepolymer is hydrophilic, and the solvent of the dispersion includes water and / or a hydrophilic solvent.

[0012] In the step of performing a second curing treatment on the first photosensitive prepolymer, both the first photosensitive prepolymer and the second photosensitive prepolymer are simultaneously cured.

[0013] In some embodiments of this application, the mass content of graphene in the dispersion is 1% to 10%, and the mass content of the second photosensitive prepolymer is 20% to 50%.

[0014] In some embodiments of this application, during the curing process of the first and second photosensitive prepolymers, ultraviolet light is used to irradiate the pore walls, and the intensity of the ultraviolet light is 100 mW / cm². 2 ~500mW / cm 2 The duration of illumination is 5 to 30 minutes.

[0015] In some embodiments of this application, in the step of immersing the pores in a dispersion containing graphene, the temperature of the dispersion is controlled at 50°C to 100°C, and the dispersion is subjected to ultrasonic vibration treatment to crosslink the graphene with the silane coupling agent.

[0016] In some embodiments of this application, the silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and bisaminosilane.

[0017] In some embodiments of this application, the step of attaching a mixture of a first photosensitive resin and a silane coupling agent to the hole walls of the circuit board substrate includes:

[0018] The pore wall is immersed in a mixed solution of the first photosensitive resin and the silane coupling agent and then removed; in the mixed solution, the mass content of the first photosensitive prepolymer is 40% to 70%, and the mass content of the silane coupling agent is 1% to 10%.

[0019] In some embodiments of this application, during the first curing process of the first photosensitive resin, ultraviolet light is used to irradiate the first photosensitive resin adhering to the hole wall, and the intensity of the ultraviolet light is 5mW / cm². 2 ~30mW / cm 2 The duration of illumination is 5 to 30 seconds;

[0020] After the first curing treatment of the first photosensitive resin, the degree of crosslinking of the first photosensitive resin is 30% to 70%.

[0021] Furthermore, this application also provides a method for preparing a metal layer on the wall of a circuit board hole, which includes the following steps:

[0022] The hole walls of the circuit board substrate are modified using the circuit board hole wall modification method described in any of the above embodiments to form graphene material on the hole walls of the circuit board substrate.

[0023] Based on the formed graphene material, a metal layer is electroplated on the hole wall of the circuit board substrate.

[0024] Furthermore, this application also provides a circuit board, the circuit board substrate of which is prepared by the method for preparing the metal layer of the circuit board hole wall as described in any of the above embodiments.

[0025] In at least one embodiment of the circuit board via wall modification method of this application, a first photosensitive resin and a silane coupling agent are first mixed and attached to the via wall of the circuit board substrate. Then, the first photosensitive resin undergoes a first curing treatment, causing some of the first photosensitive prepolymer in the first photosensitive resin to crosslink and cure. Controlling the partial crosslinking of the first photosensitive prepolymer allows the first photosensitive resin to be essentially formed, enabling it to support the silane coupling agent and serve as a support structure for subsequent graphene. Simultaneously, the incompletely crosslinked first photosensitive resin maintains the reactivity of the silane coupling agent, allowing the silane coupling agent molecules to fully react with graphene in subsequent processes. Furthermore, the amino groups on the surface of the silane coupling agent can hydrolyze to form cations, thus allowing the silane coupling agent to adsorb graphene through electrostatic interactions, assisting in the spreading and attachment of graphene to the surface of the first photosensitive resin. Both the siloxane groups and amino groups in the silane coupling agent can react with the oxygen-containing groups on the graphene surface, thereby fixing the graphene in a sheet-like form to the surface of the first photosensitive resin. In summary, the method for modifying the hole walls of this circuit board can help graphene spread and fix on the surface of the first photosensitive resin in a sheet-like form, forming a stable conductive network, thereby improving the conductivity of the conductive layer formed by the graphene material. Detailed Implementation

[0026] To facilitate understanding of this application, a more complete description will be provided below. Preferred embodiments of this application are given. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0027] 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 application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0029] This application provides a method for modifying the hole walls of a circuit board, which includes the following steps.

[0030] Step S1: Provide a circuit board substrate with holes.

[0031] In some embodiments of this application, the material of the circuit board substrate may include polymeric materials. For example, the material of the circuit board substrate may include one or more of epoxy resin, polytetrafluoroethylene, polyimide, and polyester. In some embodiments of this application, the material of the circuit board substrate may also include glass fiber.

[0032] In some embodiments of this application, the circuit board substrate is selected from single-layer boards, multilayer boards, or high-density interconnect boards.

[0033] In some embodiments of this application, the holes on the circuit board substrate are through holes or blind holes.

[0034] The method for preparing the graphene conductive layer of this application can be applied to holes with relatively small apertures. In some embodiments of this application, the aperture of the hole on the circuit board substrate is ≤0.8mm. Further, the aperture of the hole on the circuit board substrate is 0.05mm to 0.8mm. For example, the aperture of the hole on the circuit board substrate can be 0.05mm, 0.08mm, 0.1mm, 0.2mm, 0.3mm, 0.5mm, or 0.8mm, or the aperture of the hole on the circuit board substrate can be within any two of the above aperture ranges.

[0035] In some embodiments of this application, the aspect ratio of the holes on the circuit board substrate is 5:1 to 20:1. For example, the aspect ratio of the holes on the circuit board substrate is 5:1, 6:1, 8:1, 10:1, 12:1, 14:1, 15:1, 18:1, or 20:1. Alternatively, the aspect ratio of the holes on the circuit board substrate may be between any two of the above-mentioned aspect ratios.

[0036] Step S2: The mixture of the first photosensitive resin and the silane coupling agent is attached to the hole wall of the circuit board substrate.

[0037] The first photosensitive resin is in a liquid state. The first photosensitive resin includes a resin material capable of curing under ultraviolet light irradiation. In some embodiments, the first photosensitive resin includes a first photoinitiator and a first photosensitive prepolymer. The first photoinitiator is capable of initiating cross-linking and curing of the first photosensitive prepolymer under ultraviolet light irradiation.

[0038] In some embodiments, the first photosensitive prepolymer is hydrophobic or hydrophilic. In this embodiment, the first photosensitive prepolymer is hydrophobic. For example, the first photosensitive prepolymer may include one or more of a hydrophobic acrylated epoxy resin prepolymer, a hydrophobic polyurethane-type photosensitive prepolymer, and a hydrophobic unsaturated polyester prepolymer.

[0039] In some embodiments, the first photoinitiator is capable of initiating cationic polymerization under ultraviolet light irradiation. For example, the first photoinitiator includes materials such as iodonium salts and thiodonium salts that can generate active cations under ultraviolet light irradiation. The relatively slow curing rate of cationic polymerization is advantageous for controlling the degree of crosslinking in the subsequent first curing treatment.

[0040] In some embodiments, the silane coupling agent contains an amino group in its molecular structure. The amino group can hydrolyze to generate a positively charged amino cation, which adsorbs negatively charged graphene onto its surface via Coulomb forces, causing the graphene to adhere to the silane coupling agent surface in a sheet-like form. The amino group can also undergo a condensation reaction with carboxyl groups on the graphene surface to form amide bonds, thereby fixing the graphene sheet structure.

[0041] Meanwhile, the molecular structure of the silane coupling agent contains siloxane groups. Siloxane groups can hydrolyze to generate silanol groups, which can further undergo a condensation reaction with the hydroxyl groups on the graphene surface, thereby forming stable Si-OC bonds, which further fix the graphene sheets.

[0042] In some embodiments, the silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and diaminosilane.

[0043] In some embodiments, the step of attaching the mixture of the first photosensitive resin and the silane coupling agent to the hole walls of the circuit board substrate includes: immersing the hole walls in the mixed solution of the first photosensitive resin and the silane coupling agent and then removing them. This immersion process allows the mixed solution of the first photosensitive resin and the silane coupling agent to enter the holes of the circuit board substrate, enabling the first photosensitive resin and the silane coupling agent to adhere to the hole walls of the circuit board substrate. After the immersion process, the circuit board substrate is removed from the mixed solution of the first photosensitive resin and the silane coupling agent, leaving only the first photosensitive resin and the silane coupling agent adhered to the hole walls.

[0044] In some embodiments, before immersing the hole walls in the mixed solution of the first photosensitive resin and silane coupling agent, the method further includes the following steps: vacuuming the holes on the circuit board substrate; immersing the circuit board substrate in the mixed solution of the first photosensitive resin and silane coupling agent under negative pressure within the holes; and then releasing the pressure to push the mixed solution of the first photosensitive resin and silane coupling agent into the holes. For holes with a high aspect ratio, such as those with an aspect ratio greater than 10:1, the mixed solution of the first photosensitive resin and silane coupling agent is not easily able to fully and uniformly cover the hole walls. Vacuuming the holes on the circuit board substrate avoids air bubbles remaining inside the holes, and also allows the pressure to promote the full filling and complete coverage of the hole walls by the mixed solution of the first photosensitive resin and silane coupling agent.

[0045] In some embodiments, the mass content of the first photosensitive prepolymer in the mixed solution is 40% to 70%. For example, the mass content of the first photosensitive prepolymer is 40%, 45%, 50%, 55%, 60%, 65%, or 70%, or the mass content of the first photosensitive prepolymer may be between any two of the above mass contents.

[0046] In some embodiments, the mass content of the silane coupling agent in the mixed solution is 1% to 10%. For example, the mass content of the silane coupling agent is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or the content of the silane coupling agent may be between any two of the above mass contents. Using this mass content of silane coupling agent ensures sufficient adsorption of graphene in subsequent processes.

[0047] It is understood that the mixed solution also contains a solvent, which can be an organic solvent. In addition, the mixed solution may also include other additives.

[0048] Step S3: Perform a first curing treatment on the first photosensitive resin to crosslink and cure a portion of the first photosensitive resin.

[0049] It is understood that by controlling the intensity and irradiation time of ultraviolet light, the degree of crosslinking of the first photosensitive resin can be controlled, thus preventing complete curing of the first photosensitive resin. In some embodiments of this application, after the first curing treatment, the degree of crosslinking of the first photosensitive resin is 30% to 70%. For example, the degree of crosslinking of the first photosensitive resin can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, or it can be between any two of the above-mentioned degrees of crosslinking. The degree of crosslinking of the first photosensitive resin can be measured by DSC (differential scanning calorimetry).

[0050] In some embodiments, during the first curing process of the first photosensitive resin, the first photosensitive resin adhering to the hole wall is irradiated with ultraviolet light, and the intensity of the ultraviolet light is 5 mW / cm². 2 ~30mW / cm 2 The duration of illumination is 5 to 30 seconds.

[0051] In some embodiments, during the first curing process of the first photosensitive resin, an optical fiber is inserted into a hole in the circuit board substrate or placed at the opening of a hole in the circuit board substrate, and ultraviolet light is guided into the hole through the end of the optical fiber to irradiate the first photosensitive resin attached to the hole wall. By guiding ultraviolet light into the hole through the end of the optical fiber, the curing degree of the first photosensitive resin attached to different depths on the hole wall can be more uniform, avoiding situations where some parts are completely cured or completely uncured.

[0052] In this application, the purpose of attaching the first photosensitive resin to the pore walls and performing a first curing treatment is to form a structurally stable semi-cured network. This network uses the first photosensitive resin to limit the silane coupling agent and serves as a support structure for the subsequent graphene, preventing the first photosensitive resin and the silane coupling agent from being dissolved or washed away during subsequent processes. Furthermore, the insufficiently cured first photosensitive resin can cross-link and cure with the second photosensitive resin in subsequent processes. The resulting cross-linked network further fixes the graphene sheets and improves the adhesion between the graphene sheets and the first photosensitive resin.

[0053] Step S4: Immerse the pores in a dispersion containing graphene to allow the graphene to react with the silane coupling agent.

[0054] In some embodiments, the surface of the graphene contains oxygen-containing groups. The graphene may be reduced graphene oxide to provide better electrical conductivity.

[0055] In some embodiments, the dispersion further includes a second photosensitive resin, which comprises a resin material capable of curing under ultraviolet light irradiation. The second photosensitive resin and the first photosensitive resin may be made of the same or different materials. In some embodiments, the second photosensitive resin comprises a second photoinitiator and a second photosensitive prepolymer.

[0056] In some embodiments, the second photosensitive prepolymer is hydrophilic or hydrophobic. In some embodiments, the first photosensitive prepolymer is hydrophobic and the second photosensitive prepolymer is hydrophilic. In other embodiments, the first photosensitive prepolymer is hydrophilic and the second photosensitive prepolymer is hydrophobic. In this embodiment, the second photosensitive prepolymer is hydrophilic. For example, the second photosensitive prepolymer may include one or more of a hydrophilic modified acrylated epoxy resin prepolymer, a hydrophilic modified polyurethane-type photosensitive prepolymer, and a hydrophilic modified unsaturated polyester prepolymer.

[0057] Taking a first photosensitive prepolymer that is hydrophobic and a second photosensitive prepolymer that is hydrophilic as an example, after the first curing treatment, the first photosensitive resin forms a hydrophobic surface, which is beneficial for controlling the amount of second photosensitive resin attached to its surface, and thus controlling the thickness of the second photosensitive resin. The solid graphene, however, is largely unaffected and can still react and bind with the silane coupling agent. This helps prevent the second photosensitive resin from becoming too thick and significantly obscuring the graphene sheets, thereby improving the conductivity of the conductive layer formed by the graphene material.

[0058] In some embodiments, the second photoinitiator can initiate free radical polymerization under ultraviolet light irradiation. For example, the second photoinitiator includes materials such as benzophenone and / or benzophenone derivatives that can generate active free radicals under ultraviolet light irradiation. The curing speed of free radical polymerization is relatively fast, which is beneficial to ensure the full curing of the second photosensitive resin. Furthermore, by using a second photosensitive resin capable of undergoing free radical polymerization and a first photosensitive resin capable of undergoing cationic polymerization, ultraviolet light can simultaneously initiate the polymerization of the first and second photosensitive resins, forming an interpenetrating polymer network structure. This results in a UV-cured layer with higher adhesion after polymerization, firmly fixing the graphene material onto the UV-cured layer.

[0059] In some embodiments, the second photosensitive prepolymer is hydrophilic. Graphene has oxygen-containing functional groups on its surface, thus exhibiting hydrophilicity. The better compatibility between graphene and the hydrophilic second photosensitive prepolymer allows for more uniform mixing, resulting in a more uniform distribution of graphene on the surface of the UV-cured layer and improving the conductivity of the final conductive layer. Furthermore, the curing process of the second photosensitive prepolymer and part of the cured layer requires UV initiation. UV light can also simultaneously reduce the oxygen-containing functional groups on the graphene surface, further enhancing the conductivity of the graphene material.

[0060] In some embodiments, during the step of immersing the pores in a graphene-containing dispersion, the temperature of the dispersion is controlled at 50°C to 100°C, and the dispersion is subjected to ultrasonic vibration treatment to crosslink the graphene with the silane coupling agent. Ultrasonic vibration treatment of the dispersion promotes the movement of the graphene sheets within the dispersion. When the graphene adheres to the surface of the silane coupling agent in a sheet-like form, the graphene sheets are less likely to detach due to the Coulombic forces between the silane coupling agent and the graphene sheet surface. Therefore, ultrasonic vibration treatment facilitates the adhesion of graphene in a sheet-like form to the surfaces of the first photosensitive resin and the silane coupling agent. Controlling the temperature of the dispersion at 50°C to 100°C also helps to accelerate the reaction rate between the graphene and the silane coupling agent, thereby fixing the graphene in a sheet-like form to the surfaces of the first photosensitive resin and the silane coupling agent.

[0061] In some embodiments, the pores are immersed in a dispersion containing graphene and kept for 6 to 24 hours to allow for a fully reactive reaction between the graphene and the silane coupling agent.

[0062] In some embodiments, the mass content of the second photosensitive prepolymer in the dispersion is 20% to 50%. For example, the mass content of the second photosensitive prepolymer is 30%, 35%, 40%, 45%, or 50%, or the mass content of the second photosensitive prepolymer may be between any two of the above-mentioned mass contents.

[0063] In some embodiments, the graphene content in the dispersion is 1% to 10% by mass. For example, the graphene content is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by mass, or the graphene content may be between any two of the above-mentioned mass contents.

[0064] In some embodiments of this application, the dispersion further contains a solvent, including water and / or a hydrophilic solvent.

[0065] In some embodiments of this application, before immersing the holes in the graphene-containing dispersion, the following steps are also included: evacuating the holes on the circuit board substrate, immersing the circuit board substrate in the dispersion while the holes are under negative pressure, and then releasing the pressure to allow the dispersion to penetrate into the holes.

[0066] Step S5: Perform a second curing treatment on the first photosensitive prepolymer.

[0067] In some embodiments, the dispersion further includes a second photosensitive resin. During the second curing process of the first photosensitive prepolymer, both the first and second photosensitive prepolymers are simultaneously cured.

[0068] In some embodiments, in the step of curing the first photosensitive prepolymer and the second photosensitive prepolymer, the second photosensitive resin and the first photosensitive resin are completely cured, that is, the degree of crosslinking of the first photosensitive resin and the second photosensitive resin after curing is 100% or substantially 100%.

[0069] It is understood that after the curing process, the first photosensitive resin and the second photosensitive resin are cured to form a UV-curable layer. In some embodiments, the UV-curable layer may include a first cured sublayer and a second cured sublayer sequentially disposed on the pore walls. The first cured sublayer includes a first photosensitive resin, and the second cured sublayer includes a second photosensitive resin. At the interface between the first and second cured sublayers, the first and second photosensitive resins polymerize to form an interpenetrating polymer network structure. Graphene sheets are mainly located on the first cured sublayer, and some graphene sheets are also located inside the second cured sublayer.

[0070] In some embodiments of this application, during the curing process of the first and second photosensitive prepolymers, ultraviolet light is used to irradiate the pore walls, with an intensity of 100 mW / cm². 2 ~500mW / cm 2 The illumination time is 5 to 30 minutes. In particular, extending the illumination time of ultraviolet light can not only promote the complete curing of the first and second photosensitive resins, but also more fully reduce the oxygen-containing groups on the graphene surface, so as to obtain graphene materials with higher conductivity.

[0071] In some embodiments of this application, after the curing process, the following step is further included: removing residual solvent from the circuit board substrate. The method for removing residual solvent from the circuit board substrate may be drying.

[0072] It is understood that the circuit board hole wall modification method of this application embodiment can be completed through the above steps S1 to S5, and graphene material can be formed on the hole wall surface of the circuit board.

[0073] In the circuit board via wall modification method of this application, a first photosensitive resin and a silane coupling agent are first mixed and attached to the via wall of the circuit board substrate. Then, the first photosensitive resin undergoes a first curing treatment, causing some of the first photosensitive prepolymer in the first photosensitive resin to crosslink and cure. Controlling the partial crosslinking of the first photosensitive prepolymer allows the first photosensitive resin to be essentially formed, enabling it to support the silane coupling agent and serve as a support structure for subsequent graphene. Simultaneously, the incompletely crosslinked first photosensitive resin maintains the reactivity of the silane coupling agent, allowing the silane coupling agent molecules to fully react with graphene in subsequent processes. Furthermore, the amino groups on the surface of the silane coupling agent can hydrolyze to form cations, while the oxygen-containing groups on the surface of graphene can ionize to form anions. Therefore, the silane coupling agent can adsorb graphene through electrostatic interaction, assisting graphene spreading on the surface of the first photosensitive resin. Both the siloxane groups and amino groups in the silane coupling agent can react with the oxygen-containing groups on the surface of graphene, thereby fixing the graphene in a sheet-like form on the surface of the first photosensitive resin. In summary, the method for modifying the hole walls of this circuit board can help graphene spread and fix on the surface of the first photosensitive resin in a sheet-like form, forming a stable conductive network, thereby improving the conductivity of the conductive layer formed by the graphene material.

[0074] It is understandable that while some related technologies indicate that silane coupling agents can modify graphene oxide, the modification is usually achieved by directly mixing the silane coupling agent and graphene oxide in a solution, rather than by adsorbing and fixing the graphene oxide sheet onto the hole walls of the circuit board substrate using the silane coupling agent. This application found in experiments that the photosensitive resin can support the silane coupling agent even when it is not fully cured, and the silane coupling agent molecules still possess strong reactivity. This may be because the silane coupling agent molecules can maintain a certain migration ability in the incompletely cured photosensitive resin. The embodiments of this application propose that the silane coupling agent be first supported by a first photosensitive resin after a first curing treatment, preventing the silane coupling agent from being washed away by the dispersion in subsequent processes. Simultaneously, the silane coupling agent molecules can maintain their reactivity in the incompletely cured first photosensitive resin, allowing the silane coupling agent molecules to fully react with graphene in subsequent processes to adsorb and fix the graphene, enabling the graphene sheet to spread and adhere to the surface of the first photosensitive resin.

[0075] Furthermore, this application also provides a method for preparing a metal layer on the hole wall of a circuit board, which includes the following steps: modifying the hole wall of the circuit board substrate using the circuit board hole wall modification method of steps S1 to S5 above to form graphene material on the hole wall of the circuit board substrate; and then, electroplating a metal layer on the hole wall of the circuit board substrate based on the formed graphene material.

[0076] In some embodiments, the metal in the prepared metal layer includes copper. Because conductive graphene material is attached to the hole walls of the circuit board substrate, copper can be selectively deposited on the hole walls of the circuit board substrate.

[0077] In some embodiments, during the electroplating process to form a metal layer, the circuit board substrate can be immersed in an electroplating solution, and an electric current can be applied to the surface of the hole walls of the circuit board substrate to deposit metal material. The electroplating solution is a copper-ion-containing solution to prepare a metal layer containing metallic copper.

[0078] Furthermore, this application also provides a circuit board that can be manufactured by the aforementioned method of metallizing circuit board holes.

[0079] This application also provides the following embodiments and comparative examples to further illustrate the implementation and advantages of the circuit board hole wall modification method of this application.

[0080] Example 1

[0081] (1) A multilayer board test piece with through holes is used as the circuit board substrate. The test piece is 2mm thick and the hole diameter is 0.2mm.

[0082] (2) The circuit board substrate is immersed in a mixed solution of a first photosensitive resin and a silane coupling agent under negative pressure. The first photosensitive resin includes a hydrophobic acrylated epoxy resin prepolymer, and the silane coupling agent is 3-aminopropyltriethoxysilane. The mass content of the acrylated epoxy resin prepolymer in the mixed solution is 50%, and the mass content of the silane coupling agent is 5%. Simultaneously, ultrasonic dispersion is performed. After the circuit board substrate is immersed for 30 seconds, it is removed. Then, a light intensity of 10 mW / cm² is applied. 2 The circuit board substrate is irradiated with ultraviolet light for 10 seconds to perform a first curing treatment on the first photosensitive resin.

[0083] (3) The circuit board substrate was immersed in a dispersion containing a second photosensitive resin and reduced graphene oxide under negative pressure. The second photosensitive resin included a hydrophilically modified acrylated epoxy resin prepolymer. The mass content of the hydrophilically modified acrylated epoxy resin prepolymer in the dispersion was 30%, and the mass content of reduced graphene oxide was 5%. The dispersion was subjected to ultrasonic vibration treatment, and the temperature of the dispersion was controlled at 80℃ to promote the crosslinking of reduced graphene oxide and silane coupling agent. After the circuit board substrate was immersed in the dispersion and reacted for 12 hours, it was removed, the dispersion adhering to the surface was scraped off, and the second photosensitive resin and reduced graphene oxide adhering to the inner wall of the holes were retained. Then, a light intensity of 200mW / cm was used. 2 The circuit board substrate was irradiated with ultraviolet light for 10 minutes to allow the second photosensitive resin and the first photosensitive resin to fully cure.

[0084] (4) Immerse the circuit board substrate in a copper plating solution at a current density of 1 A / dm³. 2 The electroplating time is 10 minutes, and a copper metal layer is formed on the surface of the hole wall of the circuit board substrate.

[0085] Example 2

[0086] The difference between Example 2 and Example 1 is only that in step (2), a hydrophilic modified acrylate epoxy resin prepolymer is used as the photosensitive prepolymer in the first photosensitive resin.

[0087] Example 3

[0088] The difference between Example 3 and Example 1 is that in step (3), the dispersion contains only 5% by mass of reduced graphene oxide and does not contain the second photosensitive resin.

[0089] Example 4

[0090] The only difference between Example 4 and Example 1 is that in step (3), the temperature of the dispersion is controlled at 80°C and ultrasonic dispersion is not performed.

[0091] Comparative Example 1

[0092] The only difference between Comparative Example 1 and Example 1 is that in step (2), the circuit board substrate is immersed in the first photosensitive resin under negative pressure. The mass content of the acrylate epoxy resin prepolymer in the first photosensitive resin is 50%, and no silane coupling agent is added.

[0093] Comparative Example 2

[0094] The only difference between Comparative Example 2 and Example 1 is that in step (2), the circuit board substrate is immersed in a 5% silane coupling agent solution under negative pressure, and no first photosensitive resin is added to the solution.

[0095] Comparative Example 3

[0096] The only difference between Comparative Example 3 and Example 1 is that in step (2), the first photosensitive resin is not subjected to the first curing treatment, and step (3) is carried out directly.

[0097] Comparative Example 4

[0098] The only difference between Comparative Example 4 and Example 1 is that in step (2), a light intensity of 200 mW / cm² is used. 2 The circuit board substrate was irradiated with ultraviolet light for 10 minutes to allow the first photosensitive resin to fully cure.

[0099] Resistivity testing: After the photosensitive resins of each embodiment and comparative example were fully cured, the circuit board substrate was cut along the centerline of the through-hole, and the resistivity of the dry film on the hole wall surface was measured using the four-probe method. The results are shown in Table 1. A lower resistivity indicates better conductivity of the conductive layer formed by the graphene material.

[0100] Copper metal layer coverage test: After the circuit board substrates of each embodiment and comparative example were electroplated to form a copper metal layer, the circuit board substrate was cut along the centerline of the through hole, the copper metal layer was observed, and the coverage of the copper metal layer was calculated (coverage = surface area of ​​copper metal layer / total area of ​​hole wall). The results are shown in Table 1. The higher the coverage of the copper metal layer, the more fully the conductive layer formed by the graphene material covers the surface of the hole wall.

[0101] Adhesion performance test: After the copper metal layer was formed on the circuit board substrate of each embodiment and comparative example by electroplating, the plating layer was applied and pulled three times using pressure-sensitive tape, and it was observed whether there was any granular peeling off the tape surface.

[0102] Table 1

[0103] Resistivity (Ω·cm) Copper metal layer coverage Coating adhesion performance Example 1 2.67 99.5％ No particle shedding was observed. Example 2 5.75 98.4％ No particle shedding was observed. Example 3 3.24 99.0％ No particle shedding was observed. Example 4 4.47 98.8％ No particle shedding was observed. Comparative Example 1 6.26 96.5％ No granular shedding was observed. Comparative Example 2 150.83 38.4％ There is obvious granular shedding. Comparative Example 3 108.64 45.1％ There is obvious granular shedding. Comparative Example 4 81.72 55.8％ There is obvious granular shedding.

[0104] Referring to Table 1, in Examples 1 to 4, a first photosensitive resin and a silane coupling agent were first used and cured. Then, the pore walls were immersed in a dispersion containing reduced graphene oxide and subjected to heating and ultrasonic treatment, allowing the reduced graphene oxide to react with the silane coupling agent. The partially cured first photosensitive resin could be used to support the silane coupling agent to prevent its loss, thus enabling the silane coupling agent to adsorb and fix the reduced graphene oxide. The reduced graphene oxide could adhere to the surface of the first photosensitive resin in a sheet-like manner, forming a stable and complete conductive network. Therefore, the resistivity of the final reduced graphene oxide layer was significantly lower, and the electroplated copper metal layer also had high coverage and was not easily peeled off. The resistivity of Example 2 is higher than that of Example 1. This is mainly because Example 2 uses a hydrophilic modified acrylated epoxy resin prepolymer as the photosensitive prepolymer in the first photosensitive resin. Similarly, the hydrophilic modified second photosensitive resin is deposited more on the surface of the first photosensitive resin, resulting in a thicker insulating material formed after the second photosensitive resin is cured, which to some extent blocks the conductivity of the reduced graphene oxide. The resistivity of Example 3 is higher than that of Example 1. This is mainly because Example 3 does not use the second photosensitive resin, and the conductive network formed by the reduced graphene oxide lacks further fixation, which to some extent leads to a decrease in the conductivity of the reduced graphene oxide. The resistivity of Example 4 is higher than that of Example 1. This is mainly because ultrasonic dispersion was not performed in the process of step (3), resulting in relatively unevenness of the reduced graphene oxide sheets when they are adsorbed and fixed on the surface of the first photosensitive resin, which to some extent leads to a decrease in the conductivity of the reduced graphene oxide.

[0105] Referring to Table 1, compared to Example 1, the resistivity of Comparative Example 1 increased and the coverage of the copper metal layer decreased. This is mainly because the first photosensitive resin did not contain a silane coupling agent, and the reduced graphene oxide was stacked in a more random form during the subsequent process, resulting in a relatively incomplete conductive network. No particulate detachment occurred in Comparative Example 1. This is mainly because in step (3), the second photosensitive resin was attached to the first photosensitive resin and cured, fixing the reduced graphene oxide in situ on the surface or within the surface layer of the photosensitive resin, thereby improving the overall adhesion of the coating.

[0106] Referring to Table 1, compared to Example 1, Comparative Example 2 used only a silane coupling agent in step (2) without using the first photosensitive resin. However, the resistivity, copper metal layer coverage, and coating adhesion performance of Comparative Example 2 all showed significant deterioration. This is mainly because the silane coupling agent was not carried in the first photosensitive resin and was easily washed away by the dispersion in step (3). Moreover, after the silane coupling agent entered the dispersion, it reacted with the reduced graphene oxide crosslinking, which hindered the adhesion of the reduced graphene oxide to the pore walls. In Comparative Example 3, the first photosensitive resin was not subjected to the first curing treatment in step (2). Both the first photosensitive resin and the silane coupling agent were largely removed by the dispersion in step (3), resulting in a significantly higher resistivity in Comparative Example 3. Compared to Comparative Example 2, the first photosensitive resin remaining on the pore walls in Comparative Example 3 could play a certain role in fixing the reduced graphene oxide, so the resistivity of Comparative Example 3 was slightly lower than that of Comparative Example 2. In Comparative Example 4, the first photosensitive resin was completely cured in step (2), and the silane coupling agent therein essentially lost its reactivity. Therefore, in step (3), it could not effectively fix the reduced graphene oxide sheets, and the second photosensitive resin was also difficult to bond with the first photosensitive resin, resulting in poor fixation of the reduced graphene oxide. Consequently, in subsequent processes, the reduced graphene oxide in Comparative Example 4 accumulated in a relatively random manner, making it difficult to form a complete conductive network. Furthermore, Comparative Example 4 also exhibited significant particle detachment, indicating relatively poor coating adhesion.

[0107] The above detailed description is a specific description of the feasible embodiments of this application. These embodiments are not intended to limit the patent scope of this application. All equivalent implementations or modifications that do not depart from the scope of this application should be included in the patent scope of this application.

Claims

1. A method for modifying the wall of a circuit board hole, characterized in that, Includes the following steps: Provide a circuit board substrate with holes; A mixture of a first photosensitive resin and a silane coupling agent is attached to the hole wall of the circuit board substrate. The first photosensitive resin includes a first photosensitive prepolymer, and the silane coupling agent contains amino groups in its molecular structure. The first photosensitive resin is subjected to a first curing treatment, which causes a portion of the first photosensitive resin to cross-link and cure. The pores are immersed in a dispersion containing graphene, allowing the graphene to react with the silane coupling agent. The dispersion further includes a second photosensitive resin, which comprises a second photosensitive prepolymer. The first photosensitive prepolymer is hydrophobic, the second photosensitive prepolymer is hydrophilic, and the solvent of the dispersion includes water and / or a hydrophilic solvent. The first photosensitive prepolymer is subjected to a second curing treatment. In the step of performing the second curing treatment on the first photosensitive prepolymer, both the first photosensitive prepolymer and the second photosensitive prepolymer are simultaneously cured.

2. The circuit board hole wall modification method according to claim 1, characterized in that, In the dispersion, the mass content of graphene is 1% to 10%, and the mass content of the second photosensitive prepolymer is 20% to 50%.

3. The circuit board hole wall modification method according to claim 1, characterized in that, In the step of curing the first and second photosensitive prepolymers, the pore walls are irradiated with ultraviolet light at an intensity of 100 mW / cm². 2 ~500mW / cm 2 The duration of illumination is 5 to 30 minutes.

4. The method for modifying the hole wall of a circuit board according to any one of claims 1 to 3, characterized in that, In the step of immersing the pores in a dispersion containing graphene, the temperature of the dispersion is controlled at 50°C to 100°C, and the dispersion is subjected to ultrasonic vibration treatment to crosslink the graphene with the silane coupling agent.

5. The circuit board hole wall modification method according to claim 4, characterized in that, The silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and diaminosilane.

6. The method for modifying the hole wall of a circuit board according to any one of claims 1 to 3 and 5, characterized in that, The step of attaching the mixture of the first photosensitive resin and the silane coupling agent to the hole walls of the circuit board substrate includes: The pore wall is immersed in a mixed solution of the first photosensitive resin and the silane coupling agent and then removed; in the mixed solution, the mass content of the first photosensitive prepolymer is 40%~70%, and the mass content of the silane coupling agent is 1%~10%.

7. The circuit board hole wall modification method according to claim 6, characterized in that, In the first curing process of the first photosensitive resin, the first photosensitive resin adhering to the hole wall is irradiated with ultraviolet light at an intensity of 5 mW / cm². 2 ~30mW / cm 2 The duration of illumination is 5 to 30 seconds; After the first curing treatment of the first photosensitive resin, the degree of crosslinking of the first photosensitive resin is 30%~70%.

8. A method for preparing a metal layer on the wall of a circuit board hole, characterized in that, Includes the following steps: The circuit board hole wall modification method as described in any one of claims 1 to 7 is used to modify the hole wall of the circuit board substrate to form graphene material on the hole wall of the circuit board substrate. Based on the formed graphene material, a metal layer is electroplated on the hole wall of the circuit board substrate.

9. The method for preparing the metal layer on the circuit board hole wall according to claim 8, characterized in that, The metal in the prepared metal layer includes copper.

10. A circuit board, characterized in that, The circuit board substrate is prepared using the method for preparing the metal layer of the circuit board hole wall as described in claim 8 or 9.