A wet ink process for PCB buried via circuit layers

Abstract

This invention proposes a wet ink process for PCB buried via circuit layers. The steps include: selecting a PCB substrate with pre-set buried vias; immersing the PCB substrate in a self-assembly monolayer precursor solution to obtain a surface-activated substrate; melting and processing a mixture of polylactic acid and a polymer modifier to obtain a wet ink matrix; adding self-healing microcapsules and alkoxysilane surfactants to the wet ink matrix to obtain a wet ink composition; injecting the wet ink composition into the pre-set buried vias of the surface-activated substrate to obtain a filling intermediate; attaching a flexible transfer film to the surface of the filling intermediate to obtain a stacked structure; setting a mask pattern on the stacked structure and exposing the stacked structure; peeling off the flexible transfer film after development to obtain a patterned wet ink circuit structure; placing the patterned wet ink circuit structure in a temperature and humidity chamber for thermal and humidity activation treatment to obtain a prefabricated board; electroplating the prefabricated board to obtain a finished PCB buried via circuit board with metal pathways. This process achieves high adhesion of the wet ink to the inner wall of the buried vias.

Description

Technical Field

[0001] This invention belongs to the field of circuit board technology, and particularly relates to a wet ink process for PCB buried via circuit layers. Background Technology

[0002] The wet ink process for PCB buried vias refers to a manufacturing process that uses wet photosensitive ink (i.e., "wet ink") as a conductive or pattern-forming material during the fabrication of inner or intermediate layer circuits with buried via structures on a printed circuit board (PCB). It integrates multiple steps such as wet ink injection, pattern transfer, exposure and development, and electroplating for conductivity, and is suitable for the manufacture of high-density interconnect (HDI) and flexible circuit boards. In traditional PCB manufacturing, buried vias are micro-hole structures connecting inner layers to inner layer circuits. The wet ink process refers to the use of uncured liquid photosensitive ink, applied by pouring or scraping onto the surface of the buried via or substrate, followed by exposure, development, and curing steps to form a patterned circuit structure.

[0003] In related technologies, on the one hand, PCB buried via structures typically have a high aspect ratio, with typical values ​​reaching 1:3 or even 1:5 or higher. This exacerbates the difficulty of capillary penetration of liquid ink within the vias. If the wet ink has high viscosity, high surface tension, and a wetting angle that is not compatible with the via wall material, air bubbles are prone to stagnation and ink retraction during ink injection, resulting in incomplete filling of the via bottom or ink suspension without adhesion. On the other hand, on PCB substrates that have not undergone surface modification, especially glass fiber reinforced epoxy resin substrates, the surface is mostly a low-polarity structure or rich in inert functional groups. Such surfaces lack sufficient hydrogen bonds or van der Waals adsorption between themselves and the polar groups (such as carboxyl and hydroxyl groups) in conventional wet inks, causing the wet ink to be unable to effectively adhere to the via wall surface. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a wet ink process for PCB buried via circuit layers, which aims to solve the problem of insufficient filling of wet ink in buried vias and poor adhesion to the via walls, resulting in incomplete filling, ink loss, or detachment during subsequent processing.

[0005] To solve the above-mentioned technical problems, this invention is implemented as follows: a wet ink process for PCB buried via circuit layers is proposed, comprising the following steps:

[0006] S1. Select a PCB substrate with a pre-set buried via, immerse the PCB substrate in a self-assembly monolayer precursor solution for 5-10 minutes, remove it and dry it at 80°C for 10 minutes to obtain a surface-activated substrate, wherein the self-assembly monolayer precursor solution includes silane monomers and organic solvents.

[0007] S2. Polylactic acid and a polymer modifier are blended and melt-processed to obtain a wet ink matrix. Self-healing microcapsules and alkoxysilane surfactants are added to the wet ink matrix to obtain a wet ink composition. The wet ink composition is injected into the pre-set buried holes of the surface-activated substrate to obtain a filling intermediate. A flexible transfer film is attached to the surface of the filling intermediate to obtain a stacked structure. A mask pattern is set on the stacked structure and the stacked structure is exposed. After development, the flexible transfer film is peeled off to obtain a patterned wet ink circuit structure. The self-healing microcapsules include a metal matrix and a biodegradable copolymer.

[0008] S3. The graphic wet ink circuit structure is placed in a temperature and humidity chamber for hot and humid activation treatment. The temperature is set at 85°C, the relative humidity is 95%, and the treatment time is 1 to 2 hours to obtain a prefabricated board. The prefabricated board is then electroplated to obtain a finished PCB buried via circuit board with metal channels.

[0009] In some embodiments, step S1 includes:

[0010] S1.1. Immerse the PCB substrate with the pre-set buried holes in the three-step solvent cleaning tank of acetone, isopropanol and deionized water in sequence for 5 minutes each. Then place it in the plasma reaction chamber, input oxygen, adjust the plasma power to 150W, the ambient pressure to 50Pa, and process for 90~120 seconds.

[0011] S1.2 Weigh the silane monomer and inject it into the organic solvent. Stir at 300 rpm for 5 minutes to obtain a self-assembled monolayer precursor solution. Vertically fix the treated PCB substrate on a polytetrafluoroethylene support and completely immerse it in the self-assembled monolayer precursor solution. Let it stand at room temperature for 5-10 minutes to react. After taking it out, place it in an 80°C hot air drying oven to dry for 10 minutes to obtain a surface-activated substrate.

[0012] In some embodiments, in step S1, the silane monomer includes at least one of 3-aminopropyltriethoxysilane, undecyltrichlorosilane, 3-mercaptopropyltrimethoxysilane, and octyltrichlorosilane, and the organic solvent includes at least one of anhydrous n-hexane, anhydrous ethanol solution, anhydrous cyclohexane solution, and anhydrous toluene solution.

[0013] In some embodiments, step S2 includes:

[0014] S2.1 Mix polylactic acid with a polymer modifier and put it into a twin-screw blending extruder. Melt and plasticize it under zone heating conditions with a temperature set to 190~220℃ and knead for 5 minutes to obtain a wet ink matrix.

[0015] S2.2 Disperse the metal matrix in a mixed solution of ethylene glycol / polyvinylpyrrolidone to obtain a conductive liquid. Add a biodegradable copolymer to the conductive liquid and emulsify it for 3-5 minutes at 10,000 rpm using a high-speed emulsifier. After cooling, solidification, centrifugation, and drying, obtain self-healing microcapsules.

[0016] S2.3. Add the wet ink matrix granules into the melting mixing kettle, set the heating temperature to 200℃, the stirring speed to 40rpm, then add the self-healing microcapsule powder, and continue stirring for 5~10 minutes. Then add the surfactant dropwise to obtain the wet ink composition.

[0017] S2.4 Place the surface-activated substrate in a depressurization chamber, evacuate to -0.05 MPa, and inject the wet ink composition into the surface-activated substrate while maintaining a temperature of 60°C for 90-120 seconds. After restoring to normal pressure and cooling to room temperature, a filled intermediate is obtained.

[0018] S2.5. Perform plasma surface treatment on the flexible transfer film, and then apply it to the surface of the filler intermediate to obtain a stacked structure. Send the stacked structure into the exposure platform, set a mask pattern on the stacked structure, and expose the stacked structure with green visible light with a wavelength of 530nm and a light intensity of 150mW / cm² for 20~30 seconds. After development, peel off the flexible transfer film to obtain a patterned wet ink circuit structure.

[0019] In some embodiments, step S2.2 includes:

[0020] S2.2.1 Add the metal matrix to a mixture of ethylene glycol and polyvinylpyrrolidone in a mass ratio of ethylene glycol:polyvinylpyrrolidone = 4:1. Stir the mixture at 300 rpm for 30 minutes on a magnetic stirrer to obtain a conductive liquid.

[0021] S2.2.2 Dissolve the biodegradable copolymer in dichloromethane to form an oil phase solution. Slowly add the conductive liquid dropwise to a portion of the oil phase solution and perform primary emulsification in an emulsifier at a stirring speed of 5000 rpm for 3-5 minutes to obtain an oil-in-water mixture.

[0022] S2.2.3. Then, the water-in-oil primary emulsion mixture is dripped into another part of the oil phase solution, and emulsified in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain a water-in-oil emulsion.

[0023] S2.2.4 Add the oil-in-water emulsion to the aqueous solution and emulsify it in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain a multi-phase emulsion;

[0024] S2.2.5. The multiple emulsions were transferred to an ice-water bath and allowed to stand for 30 minutes. They were then centrifuged at 8000 rpm and the precipitate was washed three times with anhydrous ethanol and deionized water, respectively, to obtain solid microcapsules. The solid microcapsules were placed in a vacuum drying oven and dried at 50°C for 6 hours to obtain self-healing microcapsules.

[0025] In some embodiments, in step S2, the polymer modifier includes at least one of polycaprolactam-polyether block copolymer, maleic anhydride-grafted ethylene-octene copolymer, and modified polycaprolactam; the metal matrix includes at least one of silver nanoparticles, copper nanosheets, bismuth-tin alloy, and indium-tin alloy; and the biodegradable copolymer includes at least one of polylactic acid-glycolic acid copolymer, polycaprolactone-polylactic acid block copolymer, and polylactic acid-polyglycolic acid block copolymer.

[0026] In some embodiments, step S3 includes:

[0027] S3.1. The graphic wet ink circuit structure is blown with pure nitrogen and then sent into a high-precision constant temperature and humidity test chamber. The temperature is set at 85°C, the relative humidity is 95%, the processing time is 1~2 hours, the heating rate is 2~5°C / min, and the humidity rate is 3~10% / min to obtain the precast board.

[0028] S3.2. Let the precast board stand at room temperature for 10 minutes, then rinse with deionized water at 40~50°C, and then electroplate the precast board. The electroplating solution includes copper sulfate, sulfuric acid, brightener and wetting agent. The current density is 1.5~2.5A / dm², the temperature is 25~30°C, and the electroplating time is 30~60 minutes. After electroplating, the board is washed with water, acid-washed to remove scale, and dried in sequence to obtain the finished PCB buried via circuit board with metal channels.

[0029] In some embodiments, in step S3.2, the brightener includes at least one of bis(3-sulfopropyl) disulfide, mercaptodiacetic acid, and polyethylene glycol propyne ether, and the wetting agent includes at least one of Jans Green B, polyethyleneimine, and alkyl polyether sulfonate.

[0030] Compared with existing technologies, the wet ink process for PCB buried via circuit layers in this invention has the following advantages:

[0031] This invention introduces a self-assembled monolayer precursor liquid to activate the interface of PCB substrates with pre-set buried vias, significantly enhancing the interfacial affinity between the via walls and subsequent wet ink, improving wettability and chemical anchoring capabilities. The wet ink composition utilizes a blend of polylactic acid and a polymer modifier to construct a viscoelastic matrix, incorporating multilayer shell microcapsules with conductive self-healing properties and alkoxysilane surfactants. This improves filling fluidity while maintaining long-term stability and mechanical buffering performance. Combined with flexible transfer film exposure technology and thermal-wet activation treatment, complete and clear wet ink circuit patterns can be obtained even under complex graphic structures. Finally, a stable and reliable metal pathway is constructed through a low-current-density electroplating process. The overall process offers significant advantages such as high filling integrity, high adhesion stability, strong circuit crack resistance, and good eco-degradability, making it particularly suitable for the fabrication of high-reliability green electronic products and flexible biodegradable circuit boards. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a wet ink process for a PCB buried via circuit layer according to an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Please refer to Figure 1 This invention proposes a wet ink process for PCB buried via circuit layers, the steps of which include:

[0035] S1. Select a PCB substrate with pre-set buried vias, immerse the PCB substrate in a self-assembly monolayer precursor solution for 5-10 minutes, remove it and dry it at 80°C for 10 minutes to obtain a surface-activated substrate. The self-assembly monolayer precursor solution includes silane monomers and organic solvents.

[0036] A PCB substrate with a pre-defined buried via structure was selected as the initial carrier for wet ink via filling. To achieve surface interface activation, a stable self-assembled monolayer was constructed on this PCB substrate. This monolayer not only improves the wettability and via filling uniformity of the wet ink composition, but also imparts higher adhesion strength and precision to the pattern structure by adjusting the surface energy.

[0037] Step S1 includes:

[0038] S1.1. Immerse the PCB substrate with pre-set buried holes in a three-step solvent cleaning tank of acetone, isopropanol and deionized water for 5 minutes each. Then place it in the plasma reaction chamber, input oxygen, adjust the plasma power to 150W, the ambient pressure to 50Pa, and process for 90~120 seconds.

[0039] First, the PCB substrate with pre-set buried vias is sequentially immersed in a three-step solvent cleaning bath consisting of acetone, isopropanol, and deionized water, with each step lasting 5 minutes. This process effectively removes residual organic matter, grease, and particulate contaminants from the substrate surface, providing a clean surface for subsequent reactions. The cleaned substrate is then placed in a plasma reaction chamber, with pure oxygen introduced as the reaction gas. The plasma power is set to 150W, the ambient pressure to 50Pa, and the treatment time to 90-120 seconds. Through the bombardment of oxygen plasma, the PCB surface is activated, significantly increasing the hydroxyl content. Simultaneously, the micro-roughening treatment forms a nanoscale surface structure, which is beneficial for the subsequent directional adsorption and chemical anchoring reactions of silane monomers, thereby enhancing the bonding strength and uniformity of the self-assembled monolayer.

[0040] S1.2 Weigh the silane monomer and inject it into the organic solvent. Stir at 300 rpm for 5 minutes to obtain a self-assembled monolayer precursor solution. Vertically fix the treated PCB substrate on the polytetrafluoroethylene support and immerse it completely in the self-assembled monolayer precursor solution. Let it stand at room temperature for 5-10 minutes to react. After taking it out, place it in an 80°C hot air drying oven to dry for 10 minutes to obtain a surface-activated substrate.

[0041] Subsequently, a certain amount of silane monomer was injected into the selected organic solvent and stirred at 300 rpm for 5 minutes to fully dissolve and homogenize, forming a stable and transparent self-assembled monolayer precursor solution. The activated PCB substrate was vertically clamped in a polytetrafluoroethylene (PTFE) support and immersed entirely in the precursor solution, allowing it to react at room temperature for 5-10 minutes. During this process, the hydrolyzable groups (Si–OR or Si–Cl) of the silane monomer first react with trace amounts of moisture in the environment to generate the intermediate R–Si(OH)3, which then condenses with hydroxyl groups on the PCB surface to form covalent bonds, completing surface anchoring. Simultaneously, an ordered organic tail chain structure is arranged at the interface, constructing a dense and ordered monolayer. Afterward, the processed substrate was removed and placed in an 80°C hot air drying oven for 10 minutes to remove residual solvent and unreacted small molecules from the surface, finally obtaining the surface-activated substrate.

[0042] In step S1, the silane monomer includes at least one of 3-aminopropyltriethoxysilane, undecyltrichlorosilane, 3-mercaptopropyltrimethoxysilane, and octyltrichlorosilane, and the organic solvent includes at least one of anhydrous n-hexane, anhydrous ethanol solution, anhydrous cyclohexane solution, and anhydrous toluene solution.

[0043] S2. Polylactic acid and a polymer modifier are blended and melt-processed to obtain a wet ink matrix. Self-healing microcapsules and alkoxysilane surfactants are added to the wet ink matrix to obtain a wet ink composition. The wet ink composition is injected into the pre-set buried holes of a surface-activated substrate to obtain a filling intermediate. A flexible transfer film is attached to the surface of the filling intermediate to obtain a stacked structure. A mask pattern is set on the stacked structure and the stacked structure is exposed. After development, the flexible transfer film is peeled off to obtain a patterned wet ink circuit structure. The self-healing microcapsules include a metal matrix and a biodegradable copolymer.

[0044] In step S2, the polymer modifier includes at least one of polycaprolactam-polyether block copolymer, maleic anhydride-grafted ethylene-octene copolymer, and modified polycaprolactam; the metal matrix includes at least one of silver nanoparticles, copper nanosheets, bismuth-tin alloy, and indium-tin alloy; and the biodegradable copolymer includes at least one of polylactic acid-glycolic acid copolymer, polycaprolactone-polylactic acid block copolymer, and polylactic acid-polyglycolic acid block copolymer.

[0045] Step S2 includes:

[0046] S2.1 Mix polylactic acid with a polymer modifier and put it into a twin-screw blending extruder. Melt and plasticize it under zoned heating conditions with a temperature set to 190~220℃, and knead for 5 minutes to obtain a wet ink matrix.

[0047] This step involves melt-blending polylactic acid (PLA) with a polymeric modifier to regulate the performance of the wet ink matrix. PLA exhibits good film-forming properties and biodegradability, but it is also brittle and has weak interfacial adhesion. Introducing polymeric modifiers such as polycaprolactam-polyether block copolymers (PA-b-PEO), maleic anhydride-grafted ethylene-octene copolymers (POE-g-MAH), or maleic anhydride-grafted polycaprolactam (PA-g-MAH) can improve the polymer's flexibility, adhesion, and compatibility through hydrogen bonding or transesterification between polar groups and PLA molecular chains. This is particularly beneficial for preventing cracking or delamination during subsequent wet ink injection. Using a twin-screw extruder with zoned heating at 190~220℃ ensures uniform dispersion of the modifier, resulting in stable wet ink matrix granules.

[0048] S2.2 Disperse the metal matrix in a mixed solution of ethylene glycol / polyvinylpyrrolidone to obtain a conductive liquid. Add a biodegradable copolymer to the conductive liquid and emulsify it for 3-5 minutes at 10,000 rpm using a high-speed emulsifier. After cooling, solidification, centrifugation, and drying, obtain self-healing microcapsules.

[0049] Step S2.2 includes:

[0050] S2.2.1 Add the metal matrix to a mixture of ethylene glycol and polyvinylpyrrolidone in a mass ratio of 4:1 and stir at 300 rpm for 30 minutes on a magnetic stirrer to obtain a conductive liquid.

[0051] Metal matrices (such as silver nanoparticles, copper nanosheets, bismuth-tin alloys, or indium-tin alloys) are dispersed in a mixture of ethylene glycol and polyvinylpyrrolidone (PVP) to form a conductive liquid. This system not only provides a homogeneous medium, but PVP, through the coordination of its carbonyl groups with the surface of the metal particles, can effectively inhibit agglomeration, forming a stable colloidal dispersion. Ethylene glycol, as a high-boiling-point hydrophilic solvent, enhances wettability during the emulsification process and participates in the subsequent nucleation and condensation of the shell structure.

[0052] S2.2.2 Dissolve the biodegradable copolymer in dichloromethane to form an oil phase solution. Slowly add the conductive liquid dropwise to a portion of the oil phase solution. Perform primary emulsification in an emulsifier at a stirring speed of 5000 rpm for 3-5 minutes to obtain an oil-in-water mixture.

[0053] The aforementioned conductive liquid is slowly added dropwise to a dichloromethane oil phase containing a biodegradable copolymer (such as polylactic acid-glycolic acid copolymer PLGA, polycaprolactone-polylactic acid block copolymer PCL-b-PLA, etc.) to form an oil-in-water (W / O) primary emulsion system. During this process, the conductive liquid, as the inner phase, is encapsulated within the oil phase under emulsification shear, initially constructing the first shell layer of the self-healing microcapsule. This layer is typically designed as a polymer structure sensitive to humid and heat stimuli, which can rupture and release the conductive core liquid upon electrical aging or cracking, thus exerting a self-repairing function.

[0054] S2.2.3. Then, drop the water-in-oil primary emulsion mixture into another part of the oil phase solution, and emulsify it in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain a water-in-oil emulsion.

[0055] The water-in-oil pre-emulsion mixture is dripped into another portion of the oil phase containing a biodegradable copolymer, and further emulsified to form a water-in-oil-in-oil system, constructing a second oil-in-shell layer. This layer provides mechanical barrier and delayed release properties, and is particularly suitable for copolymers with a crystalline-amorphous biphase structure, such as PCL-b-PLA, which can effectively control the sensitivity of microcapsules to time, temperature, and humidity, achieving a multi-stage self-healing response mechanism.

[0056] S2.2.4 Add the oil-in-water emulsion to the aqueous solution and emulsify it in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain a multiple emulsion.

[0057] A dual emulsion system is introduced into the external aqueous phase, to which surface modifiers (such as chitosan or sodium carboxymethyl cellulose) can be added, forming a three-phase multi-emulsion structure (W / O / O / W). The outer aqueous shell exhibits good hydrophilicity and electrolyte stability, while also providing biodegradability, which facilitates the uniform distribution and interfacial integration of microcapsules in the wet ink system. The resulting multi-layered encapsulation structure helps improve the mechanical stability and shelf life of the microcapsules, while also enhancing their precise response to environmental stimuli.

[0058] S2.2.5. Transfer the multiple emulsion to an ice-water bath and let it stand for 30 minutes. Centrifuge at 8000 rpm and wash the precipitate three times with anhydrous ethanol and deionized water respectively to obtain solid microcapsules. Place the solid microcapsules in a vacuum drying oven and dry them at 50°C for 6 hours to obtain self-healing microcapsules.

[0059] The inner and outer shell polymers were solidified and fixed by placing the multiple emulsion system in an ice-water bath for 30 minutes. Subsequently, centrifugation at 8000 rpm was performed to remove the free phase solvent, and the mixture was washed three times sequentially with anhydrous ethanol and deionized water to effectively remove residual small molecules and unreacted substances. Finally, the resulting precipitate was vacuum-dried at 50°C for 6 hours to obtain self-healing microcapsules with clear structures and uniform particle size, which can be stably added to subsequent wet ink systems.

[0060] S2.3. Add the wet ink matrix granules into the melting mixing kettle, set the heating temperature to 200℃ and the stirring speed to 40 rpm, then add the self-healing microcapsule powder and continue stirring for 5~10 minutes. Then add the surfactant dropwise to obtain the wet ink composition.

[0061] In this step, the pre-prepared wet ink matrix granules are melted at 200°C, while self-healing microcapsules are slowly added and stirred at 40 rpm to ensure uniform dispersion of the microcapsules in the high-viscosity system. After stirring for 5-10 minutes, alkoxysilane surfactants (such as trimethoxyoctylsilane and alkyltriethoxysilane) are added dropwise. This reduces the surface tension of the ink system through interface modulation, improving its wettability and adhesion to the surface-activated substrate, while also enhancing the uniformity of distribution between the microcapsules and the substrate. The final result is a wet ink composition with good printability and self-healing properties.

[0062] S2.4 Place the surface-activated substrate in a depressurization chamber and evacuate it to -0.05MPa. Inject the wet ink composition into the surface-activated substrate while keeping it at 60°C for 90-120 seconds. After restoring to normal pressure and cooling to room temperature, the filled intermediate is obtained.

[0063] To ensure the wet ink composition fully fills the buried vias without creating bubbles or voids, a depressurized injection strategy is employed in this step. The surface-activated substrate is placed in a depressurized chamber, and the pressure is evacuated to -0.05 MPa. The preheated (60°C) wet ink composition is injected into the PCB vias using the external atmospheric pressure difference and maintained for 90–120 seconds. Temperature control during this stage helps reduce ink viscosity and improve flowability. After injection, the pressure is restored to normal and cooled to room temperature, resulting in a well-structured and densely interfacial filled intermediate.

[0064] S2.5. Perform plasma surface treatment on the flexible transfer film, and then apply it to the surface of the filler intermediate to obtain a stacked structure. Send the stacked structure into the exposure platform, set a mask pattern on the stacked structure, and expose the stacked structure with green visible light with a wavelength of 530nm and a light intensity of 150mW / cm² for 20~30 seconds. After development, peel off the flexible transfer film to obtain a patterned wet ink circuit structure.

[0065] To achieve high-resolution pattern transfer, the surface of the flexible transfer film is first subjected to plasma treatment to improve its surface energy and ink affinity. Then, it is tightly adhered to the surface of the filler intermediate to form a complete stacked structure. In an exposure platform, a mask pattern is applied to the surface of the stacked structure, and exposure is performed for 20-30 seconds using green light with a wavelength of 530 nm and an intensity of 150 mW / cm². The photosensitive components in the wet ink undergo a cross-linking reaction, developing the pattern. Finally, the transfer film is peeled off, resulting in a clearly defined and firmly bonded patterned wet ink circuit structure, providing high-precision guidance for subsequent electroplating to construct metal pathways.

[0066] S3. The patterned wet ink circuit structure is placed in a temperature and humidity chamber for heat and humidity activation treatment. The temperature is set at 85℃, the relative humidity at 95%, and the treatment time is 1~2 hours to obtain a prefabricated board. The prefabricated board is then electroplated to obtain a finished PCB buried via circuit board with metal channels.

[0067] Step S3 includes:

[0068] S3.1. The graphic wet ink circuit structure is blown with pure nitrogen gas and then sent into a high-precision constant temperature and humidity test chamber. The temperature is set at 85°C, the relative humidity is 95%, the processing time is 1~2 hours, the heating rate is 2~5°C / min, and the humidity rate is 3~10% / min to obtain the precast board.

[0069] This step further enhances the density and functional responsiveness of the surface layer structure by performing a thermal and humid activation treatment on the patterned wet ink circuit structure. First, pure nitrogen is used to blow away residual microparticles, moisture, and volatile residues, providing a clean initial state for subsequent processing. Then, the surface is placed in a high-precision constant temperature and humidity chamber and maintained at 85°C and 95% relative humidity for 12 hours, allowing residual biodegradable copolymers or interfacial components in the wet ink circuit to undergo micro-crosslinking or structural reconstruction. Precise control of the heating and humidification rates (25°C / min and 3~10% / min, respectively) helps prevent film cracking or interfacial peeling caused by thermal or humidification stress. Under this environment, the shell material of the self-healing microcapsules may slightly swell, promoting interfacial fusion between the capsule and the surrounding wet ink, improving overall structural density and thermal and humid stability, ultimately forming a prefabricated board with good mechanical properties and heat and moisture resistance.

[0070] S3.2. Let the precast board stand at room temperature for 10 minutes, then rinse with deionized water at 40~50°C, and then electroplate the precast board. The electroplating solution includes copper sulfate, sulfuric acid, brightener and wetting agent. The current density is 1.5~2.5A / dm², the temperature is 25~30°C, and the electroplating time is 30~60 minutes. After electroplating, the board is washed with water, acid-washed to remove scale, and dried in sequence to obtain the finished PCB buried via circuit board with metal channels.

[0071] In step S3.2, the brightener includes at least one of bis(3-sulfopropyl) disulfide, mercaptodiacetic acid, and polyethylene glycol propyne ether, and the wetting agent includes at least one of Yangs Green B, polyethyleneimine, and alkyl polyether sulfonate.

[0072] After hot and wet treatment, allowing the precast slab to stand at room temperature for 10 minutes helps the system slowly recover from the excited state to the stable state, reducing internal stress accumulation. Rinsing with deionized water at 40-50°C gently removes low-molecular-weight byproducts that may precipitate during the hot and wet treatment, improving the cleanliness of the metal plating interface. In the subsequent electroplating process, copper sulfate and sulfuric acid in the plating solution provide the dominant source of metal ions and a conductive environment. The addition of brighteners, such as bis(3-sulfopropyl)disulfide, mercaptodiacetic acid, or polyethylene glycol propyne ether, can regulate the nucleation and growth rate of grains during metal deposition. Through selective adsorption on the copper deposition surface, the copper layer becomes dense, smooth, and has good ductility. Simultaneously, wetting agents such as Jans Green B, polyethyleneimine, or alkyl polyether sulfonates reduce the surface tension of the liquid, enhancing the plating solution's wetting ability for micropores and patterned structures. Especially in complex buried via structures, this avoids plating dead zones and bubble residues, resulting in a metal pathway structure with uniform thickness and strong adhesion. Finally, through steps such as water washing, acid pickling to remove scale, and drying, residual electrolytes and impurities are removed, and a finished PCB buried via circuit board with good conductivity and structural integrity is finally obtained.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wet ink process for PCB buried via circuit layers, characterized in that the steps include... include: S1. Select a PCB substrate with a pre-set buried via, immerse the PCB substrate in a self-assembly monolayer precursor solution for 5-10 minutes, remove it and dry it at 80°C for 10 minutes to obtain a surface-activated substrate, wherein the self-assembly monolayer precursor solution includes silane monomers and organic solvents. S2. Polylactic acid and a polymer modifier are blended and melt-processed to obtain a wet ink matrix. Self-healing microcapsules and alkoxysilane surfactants are added to the wet ink matrix to obtain a wet ink composition. The wet ink composition is injected into the pre-set buried holes of the surface-activated substrate to obtain a filling intermediate. A flexible transfer film is attached to the surface of the filling intermediate to obtain a stacked structure. A mask pattern is set on the stacked structure and the stacked structure is exposed. After development, the flexible transfer film is peeled off to obtain a patterned wet ink circuit structure. The self-healing microcapsules include a metal matrix and a biodegradable copolymer. The preparation steps of self-healing microcapsules include: The metal matrix was added to a mixture of ethylene glycol and polyvinylpyrrolidone in a mass ratio of 4:

1. The mixture was stirred at 300 rpm for 30 minutes on a magnetic stirrer to obtain a conductive liquid. The biodegradable copolymer is dissolved in dichloromethane to form an oil phase solution. The conductive liquid is slowly added dropwise to a portion of the oil phase solution, and primary emulsification is carried out in an emulsifier at a stirring speed of 5000 rpm for 3-5 minutes to obtain an oil-in-water mixture. The water-in-oil mixture is then added dropwise to another portion of the oil phase solution, and emulsified in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain an oil-in-water emulsion. The oil-in-water emulsion is added to an aqueous solution and emulsified in an emulsifier at a stirring speed of 10,000 rpm for 3 to 5 minutes to obtain a multi-phase emulsion. The multiple emulsions were transferred to an ice-water bath and allowed to stand for 30 minutes. They were then centrifuged at 8000 rpm and the precipitate was washed three times with anhydrous ethanol and deionized water, respectively, to obtain solid microcapsules. The solid microcapsules were placed in a vacuum drying oven and dried at 50°C for 6 hours to obtain self-healing microcapsules. S3. The graphic wet ink circuit structure is placed in a temperature and humidity chamber for hot and humid activation treatment. The temperature is set at 85°C, the relative humidity is 95%, and the treatment time is 1 to 2 hours to obtain a prefabricated board. The prefabricated board is then electroplated to obtain a finished PCB buried via circuit board with metal channels.

2. The wet ink process for PCB buried via circuit layer according to claim 1, characterized in that, Step S1 includes: S1.

1. Immerse the PCB substrate with the pre-set buried holes in the three-step solvent cleaning tank of acetone, isopropanol and deionized water in sequence for 5 minutes each. Then place it in the plasma reaction chamber, input oxygen, adjust the plasma power to 150W, the ambient pressure to 50Pa, and process for 90~120 seconds. S1.2 Weigh the silane monomer and inject it into the organic solvent. Stir at 300 rpm for 5 minutes to obtain a self-assembled monolayer precursor solution. Vertically fix the treated PCB substrate on a polytetrafluoroethylene support and completely immerse it in the self-assembled monolayer precursor solution. Let it stand at room temperature for 5-10 minutes to react. After taking it out, place it in an 80°C hot air drying oven to dry for 10 minutes to obtain a surface-activated substrate.

3. A wet ink process for PCB buried via circuit layers according to claim 1 or 2, characterized in that, In step S1, the silane monomer includes at least one of 3-aminopropyltriethoxysilane, undecyltrichlorosilane, 3-mercaptopropyltrimethoxysilane, and octyltrichlorosilane, and the organic solvent includes at least one of anhydrous n-hexane, anhydrous ethanol solution, anhydrous cyclohexane solution, and anhydrous toluene solution.

4. The wet ink process for PCB buried via circuit layer according to claim 1, characterized in that, Step S2 includes: S2.1 Mix polylactic acid with a polymer modifier and put it into a twin-screw blending extruder. Melt and plasticize it under zone heating conditions with a temperature set to 190~220℃ and knead for 5 minutes to obtain a wet ink matrix. S2.2 Disperse the metal matrix in a mixed solution of ethylene glycol / polyvinylpyrrolidone to obtain a conductive liquid. Add a biodegradable copolymer to the conductive liquid and emulsify it for 3-5 minutes at 10,000 rpm using a high-speed emulsifier. After cooling, solidification, centrifugation, and drying, obtain self-healing microcapsules. S2.

3. Add the wet ink matrix granules into the melting mixing kettle, set the heating temperature to 200℃, the stirring speed to 40rpm, then add the self-healing microcapsule powder, and continue stirring for 5~10 minutes. Then add the surfactant dropwise to obtain the wet ink composition. S2.4 Place the surface-activated substrate in a depressurization chamber, evacuate to -0.05 MPa, and inject the wet ink composition into the surface-activated substrate while maintaining a temperature of 60°C for 90-120 seconds. After restoring to normal pressure and cooling to room temperature, a filled intermediate is obtained. S2.

5. Perform plasma surface treatment on the flexible transfer film, and then apply it to the surface of the filler intermediate to obtain a stacked structure. Send the stacked structure into the exposure platform, set a mask pattern on the stacked structure, and expose the stacked structure with green visible light with a wavelength of 530nm and a light intensity of 150mW / cm² for 20~30 seconds. After development, peel off the flexible transfer film to obtain a patterned wet ink circuit structure.

5. A wet ink process for PCB buried via circuit layers according to claim 1 or 4, characterized in that, In step S2, the polymer modifier includes at least one of polycaprolactam-polyether block copolymer, maleic anhydride-grafted ethylene-octene copolymer, and modified polycaprolactam; the metal matrix includes at least one of silver nanoparticles, copper nanosheets, bismuth-tin alloy, and indium-tin alloy; and the biodegradable copolymer includes at least one of polylactic acid-glycolic acid copolymer, polycaprolactone-polylactic acid block copolymer, and polylactic acid-polyglycolic acid block copolymer.

6. The wet ink process for PCB buried via circuit layer according to claim 1, characterized in that, Step S3 includes: S3.

1. The graphic wet ink circuit structure is blown with pure nitrogen and then sent into a high-precision constant temperature and humidity test chamber. The temperature is set at 85°C, the relative humidity is 95%, the processing time is 1~2 hours, the heating rate is 2~5°C / min, and the humidity rate is 3~10% / min to obtain the precast board. S3.

2. Allow the precast panels to stand at room temperature for 10 minutes, then rinse with deionized water at 40-50°C. Next, electroplate the precast panels using a solution containing copper sulfate, sulfuric acid, brightener, and wetting agent, at a current density of 1.5-2.5 A / dm³. 2 The temperature is 25~30°C, the electroplating time is 30~60 minutes, and after electroplating, the circuit is washed with water, acid pickled to remove scale, and dried in sequence to obtain the finished PCB buried via circuit board with metal channels.

7. The wet ink process for PCB buried via circuit layer according to claim 6, characterized in that, In step S3.2, the brightener includes at least one of bis(3-sulfopropyl) disulfide, mercaptodiacetic acid, and polyethylene glycol propyne ether, and the wetting agent includes at least one of Yangs Green B, polyethyleneimine, and alkyl polyether sulfonate.

Images