PCB buried hole circuit layer wet ink process

Abstract

The invention provides a PCB buried hole circuit layer wet ink process which comprises the following steps: selecting a PCB substrate with a preset buried hole, and soaking the PCB substrate in a self-assembly monomolecular layer precursor solution to obtain a surface activated substrate; the preparation method comprises the following steps: blending polylactic acid and a polymer modifier, melting and processing to prepare a wet ink matrix, adding a self-healing microcapsule and an alkoxy silane interfacial agent into the wet ink matrix to obtain a wet ink composition, injecting the wet ink composition into a preset buried hole of a surface activated substrate to obtain a filling intermediate, and pasting a flexible transfer film on the surface of the filling intermediate to obtain the surface activated substrate. A laminated structure is obtained, a mask pattern is arranged on the laminated structure, the laminated structure is exposed and developed, then the flexible transfer film is stripped, and a graphical wet ink circuit structure is obtained; and placing the graphical wet ink circuit structure in a temperature and humidity box for heat and humidity activation treatment to obtain a prefabricated plate, and electroplating the prefabricated plate to obtain a finished product of the PCB buried hole circuit board with the metal path. And high adhesiveness of wet ink on the inner wall of the buried hole is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of circuit board process, and particularly relates to a PCB buried hole circuit layer wet ink process. BACKGROUND

[0002] The PCB buried hole circuit wet ink process refers to a processing technology that uses wet-state photosensitive ink (i.e., "wet ink") as a conductive or pattern forming material in the process of manufacturing an inner layer or an intermediate layer circuit with a buried hole structure on a printed circuit board (PCB). It combines wet ink filling, pattern transfer, exposure and development, and electroplating conduction, and is suitable for the manufacturing of high-density interconnection (HDI) and flexible circuit boards. In traditional PCB manufacturing, a buried hole (Buried Via) is a micro hole structure connecting the circuits of inner layers, and the wet ink process refers to the use of unsolidified liquid photosensitive ink in the manufacturing of these buried hole circuits, which is filled by pouring or coated on the buried hole or substrate surface, and then subjected to exposure, development and solidification to form a patterned circuit structure.

[0003] In related technologies, on the one hand, the PCB buried hole structure usually has a high aspect ratio, typically reaching 1:3 or even 1:5 or more, which exacerbates the difficulty of capillary penetration of liquid ink in the hole. If the viscosity of the wet ink is high, the surface tension is large, and the wetting angle is not suitable for the hole wall material, then air bubbles are likely to be trapped and the ink is likely to retract during ink injection, resulting in virtual filling or ink suspension without adhesion at the bottom of the hole. On the other hand, on the PCB substrate that has not been surface modified, especially the glass fiber reinforced epoxy resin substrate, the surface is usually a low polarity or inert functional group structure. There is a lack of sufficient hydrogen bonding or van der Waals force adsorption between this surface and the polar groups (such as carboxyl and hydroxyl) in the conventional wet ink, resulting in the inability of the wet ink to effectively adhere to the hole wall surface. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a PCB buried hole circuit layer wet ink process, which aims to solve the problem of insufficient filling of wet ink in the buried hole and poor adhesion to the hole wall, resulting in virtual filling, ink dropping or falling off in subsequent processing.

[0005] To solve the above technical problems, the present application is implemented as follows, a PCB buried hole circuit layer wet ink process is proposed, the steps comprising: S1, selecting a PCB substrate with a preset buried hole, immersing the PCB substrate in a self-assembled monolayer precursor solution for 5-10 minutes, and then drying at 80°C for 10 minutes to obtain a surface-activated substrate, wherein the self-assembled monolayer precursor solution comprises a silane monomer and an organic solvent; S2, melt process after blending polylactic acid and polymer modifier, obtain wet ink matrix, add self-healing microcapsule and alkoxysilane interface active agent in wet ink matrix, obtain wet ink composition, inject wet ink composition into preset embedded hole of surface activated substrate, obtain filling intermediate, paste flexible transfer film on surface of filling intermediate, obtain laminated structure, set mask pattern on laminated structure and expose laminated structure, peel off flexible transfer film after development, obtain patterned wet ink line structure, wherein, self-healing microcapsule comprises metal matrix and degradable copolymer; S3, heat and humidity activation treatment is performed on the patterned wet ink line structure in a temperature and humidity box, the temperature is set to 85°C, the relative humidity is 95%, and the treatment time is 1-2 hours, to obtain a preformed plate, and the preformed plate is electroplated to obtain a PCB embedded hole circuit board product with metal vias.

[0006] In some embodiments, step S1 comprises: S1.1, immerse the PCB substrate with preset embedded holes in acetone, isopropyl alcohol, and deionized water three-step solvent cleaning tanks in sequence, each for 5 minutes, then place in a plasma reaction chamber, input oxygen, adjust the plasma power to 150W, the environmental pressure to 50Pa, and treat for 90-120 seconds; S1.2, weigh the silane monomer into an organic solvent, stir at a stirring speed of 300rpm for 5 minutes to obtain a self-assembled monolayer precursor solution, vertically fix the treated PCB substrate on a polytetrafluoroethylene support, completely immerse in the self-assembled monolayer precursor solution, stand at room temperature for 5-10 minutes, take out and place in an 80°C hot air drying oven for drying for 10 minutes, to obtain a surface activated substrate.

[0007] In some embodiments, in step S1, the silane monomer comprises at least one of 3-aminopropyl triethoxysilane, undecyltrichlorosilane, 3-mercaptopropyl trimethoxysilane, and octyltrichlorosilane, and the organic solvent comprises at least one of anhydrous n-hexane, anhydrous ethanol solution, anhydrous cyclohexane solution, and anhydrous toluene solution.

[0008] In some embodiments, step S2 comprises: S2.1, mix polylactic acid and polymer modifier, put into a double screw blending extrusion device, melt and plasticize under partition heating condition with temperature set to 190-220°C, and mix for 5 minutes to obtain a wet ink matrix; S2.2, disperse the metal matrix in a mixture of ethylene glycol and polyvinylpyrrolidone solution to obtain a conductive liquid, add degradable copolymer to the conductive liquid, emulsify with a high-speed emulsifier at a speed of 10000rpm for 3-5 minutes, then cool and solidify, centrifuge and dry to obtain self-healing microcapsules; S2.3, put the wet ink matrix granules into a melt kneader, set the heating temperature to 200°C, the stirring speed to 40 rpm, then add the self-healing microcapsule powder, and continue stirring for 5-10 minutes, then add the interfacial active agent dropwise, to obtain a wet ink composition; S2.4, place the surface-activated substrate in a vacuum chamber, vacuumize to -0.05 MPa, and pour the wet ink composition into the surface-activated substrate at 60°C, with a pouring duration of 90-120 seconds, restore the normal pressure, and cool to room temperature, to obtain a filled intermediate; S2.5, perform plasma surface treatment on the flexible transfer film, then adhere it to the surface of the filled intermediate, to obtain a laminated structure, and send the laminated structure into an exposure platform, expose the laminated structure to green visible light with a wavelength of 530 nm and an intensity of 150 mW / cm² for 20-30 seconds, develop, and peel off the flexible transfer film, to obtain a patterned wet ink line structure.

[0009] In some embodiments, step S2.2 comprises: S2.2.1, add the metal matrix to a mixed solution composed of ethylene glycol and polyvinylpyrrolidone, with a mass ratio of ethylene glycol: polyvinylpyrrolidone = 4: 1, stir on a magnetic stirrer at a stirring speed of 300 rpm for 30 minutes, to obtain a conductive liquid; S2.2.2, dissolve the degradable copolymer in dichloromethane to form an oil phase solution, slowly add the conductive liquid to part 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; S2.2.3, add the oil-in-water primary emulsion mixture to another part of the oil phase solution, and perform emulsification in an emulsifier at a stirring speed of 10000 rpm for 3-5 minutes, to obtain an oil-in-oil-in-water emulsion; S2.2.4, add the oil-in-oil-in-water emulsion to an aqueous phase solution, and perform emulsification in an emulsifier at a stirring speed of 10000 rpm for 3-5 minutes, to obtain a multiple emulsion; S2.2.5, transfer the multiple emulsion to an ice water bath and stand for 30 minutes, centrifuge at a speed of 8000 rpm, wash the precipitate with anhydrous ethanol and deionized water three times respectively, to obtain solid microcapsules, and place the solid microcapsules in a vacuum drying oven, dry at 50°C for 6 hours, to obtain self-healing microcapsules.

[0010] In some embodiments, in step S2, the high molecular modifier comprises at least one of polycaprolactam-polyether block copolymer, maleic anhydride grafted ethylene-octene copolymer, modified polycaprolactam, the metal matrix comprises at least one of silver nanoparticles, copper nanosheet, bismuth tin alloy, indium tin alloy, and the degradable copolymer comprises at least one of polylactic acid-glycolic acid copolymer, polycaprolactone-polylactic acid block copolymer, and polylactic acid-polyglycolic acid block copolymer.

[0011] In some embodiments, step S3 comprises: S3.1, using pure nitrogen to blow the patterned wet ink line structure, and then sending it into a high-precision constant temperature and humidity test box, setting the temperature to 85°C, the relative humidity to 95%, the processing time to 1-2 hours, the temperature rising rate to 2-5°C / min, and the humidity rising rate to 3-10% / min, to obtain a preformed plate; S3.2, placing the preformed plate at room temperature for 10 minutes, then washing it with deionized water at 40-50°C, and then electroplating the preformed plate, the electroplating solution comprising copper sulfate, sulfuric acid, brightener and wetting agent, the current density being 1.5-2.5 A / dm2, the temperature being 25-30°C, and the electroplating time being 30-60 minutes, and after electroplating, sequentially performing water washing, acid pickling to remove scale, and drying, to obtain a PCB buried hole line board product with metal vias.

[0012] In some embodiments, in step S3.2, the brightener comprises at least one of bis(3-sulfopropyl) disulfide, mercaptodiacetic acid, and polyethylene glycol propargyl ether, and the wetting agent comprises at least one of Yons green B, polyethyleneimine, and alkyl polyether sulfonate.

[0013] Compared with the prior art, the wet ink process for a PCB buried hole line layer in the present application has the following beneficial effects: The present application introduces a self-assembled monolayer precursor solution to perform interface activation treatment on a PCB substrate with a pre-set buried hole, significantly enhancing the interface affinity between the hole wall and the subsequent wet ink, improving the wettability and chemical anchoring ability. The wet ink composition uses a blend of polylactic acid and a high molecular modifier to construct a viscoelastic matrix, and adds multi-shell microcapsules with conductive self-healing function and an alkyl silane surfactant, which improves the filling fluidity while taking into account long-term stability and mechanical cushioning performance. Combined with flexible transfer film exposure technology and thermal and humidification activation treatment, a complete and clear wet ink line pattern can be obtained under complex graphic structures, and finally a stable and reliable metal via construction is realized through a low current density electroplating process. The overall process has the advantages of high filling integrity, high adhesion stability, strong line crack resistance, good ecological degradability, etc., and is particularly suitable for the preparation needs of high-reliability green electronic products and flexible degradable line boards. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flowchart of a PCB buried hole circuit layer wet ink process in an embodiment of the present application. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0016] Please refer to Figure 1 The present application provides a PCB buried hole circuit layer wet ink process, comprising the following steps: S1, selecting a PCB substrate with a preset buried hole, immersing the PCB substrate in a self-assembled monolayer precursor solution for 5-10 minutes, and then taking it out and drying it at 80°C for 10 minutes to obtain a surface-activated substrate, wherein the self-assembled monolayer precursor solution comprises silane monomers and an organic solvent.

[0017] A PCB substrate with a preset buried hole structure is selected as the initial carrier for wet ink hole filling treatment. In order to achieve surface interface activation, a stable self-assembled monolayer needs to be constructed on the PCB substrate. This monolayer not only improves the wettability and uniformity of the wet ink composition, but also gives the pattern structure higher adhesion strength and precision by adjusting the surface energy.

[0018] Step S1 comprises: S1.1, immersing the PCB substrate with the preset buried hole in three-step solvent cleaning tanks of acetone, isopropyl alcohol and deionized water in sequence, each for 5 minutes, and then placing it in a plasma reaction chamber, inputting oxygen, adjusting the plasma power to 150W and the environmental pressure to 50Pa, and processing for 90-120 seconds.

[0019] First, immerse the PCB substrate with the preset buried hole in three-step solvent cleaning tanks of acetone, isopropyl alcohol and deionized water in sequence, and control the immersion cleaning time of each step to be 5 minutes. This process can effectively remove organic matter, grease and particulate contamination on the surface of the substrate, providing a clean surface for subsequent reactions. Then, place the cleaned substrate in a plasma reaction chamber, input pure oxygen as the reaction gas, set the plasma power to 150W and the environmental pressure to 50Pa, and process for 90-120 seconds. Through the bombardment of oxygen plasma, the surface of the PCB is activated, the content of hydroxyl groups is significantly increased, and a nanoscale surface structure is formed through micro-roughening treatment, which is beneficial to the subsequent directional adsorption and chemical anchoring reaction of silane monomers, thereby enhancing the binding strength and uniformity of the self-assembled monolayer S1.2, the silane monomer is weighed into an organic solvent, stirred at a stirring speed of 300 rpm for 5 minutes to obtain a self-assembled monolayer precursor solution, the treated PCB substrate is vertically fixed on a polytetrafluoroethylene support, completely immersed in the self-assembled monolayer precursor solution, and left to react at room temperature for 5-10 minutes, and then taken out and placed in an 80°C hot air drying oven for drying for 10 minutes to obtain a surface-activated substrate.

[0020] Subsequently, a certain amount of silane monomer is injected into the selected organic solvent and stirred at a speed of 300 rpm for 5 minutes to fully dissolve and uniformly form a stable and transparent self-assembled monolayer precursor solution. The activated PCB substrate is vertically clamped in a polytetrafluoroethylene support and immersed in the precursor solution, and left 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 form an intermediate R-Si(OH)3, and then condense with the hydroxyl groups on the surface of the PCB to form a covalent bond, completing surface anchoring. At the same time, an ordered organic tail chain structure is arranged at the interface, and a dense and ordered monolayer is constructed. After that, the treated substrate is taken out and placed in an 80°C hot air drying oven for drying for 10 minutes to remove the residual solvent and unreacted small molecules on the surface, and finally a surface-activated substrate is obtained.

[0021] In step S1, the silane monomer includes at least one of 3-aminopropyl triethoxysilane, undecyltrichlorosilane, 3-mercaptopropyl trimethoxysilane, and octyltrichlorosilane, and the organic solvent includes at least one of anhydrous n-hexane, anhydrous ethanol solution, anhydrous cyclohexane solution, and anhydrous toluene solution.

[0022] S2, the wet ink matrix is prepared by blending polylactic acid and a polymer modifier and melt processing, the self-healing microcapsules and the alkoxysilane-based interfacial active agent are added to the wet ink matrix to obtain a wet ink composition, the wet ink composition is injected into the preset embedded hole 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 laminated structure, a mask pattern is arranged on the laminated structure and the laminated structure is exposed, and after development, the flexible transfer film is peeled off to obtain a patterned wet ink line structure, wherein the self-healing microcapsules include a metal matrix and a degradable copolymer.

[0023] 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 nanoplates, bismuth-tin alloy, and indium-tin alloy, and the degradable copolymer includes at least one of polylactic acid-glycolic acid copolymer, polycaprolactone-polylactic acid block copolymer, and polylactic acid-polyglycolic acid block copolymer.

[0024] Step S2 includes: S2.1, mixing polylactic acid and high polymer modifier, putting into double screw blending extrusion equipment, melting and plasticizing under the condition of partition heating with temperature setting at 190~220℃, and mixing for 5 minutes to obtain wet ink matrix.

[0025] This step realizes the performance control of the wet ink matrix by melt blending polylactic acid (PLA) and high polymer modifier. Polylactic acid has good film-forming property and biodegradability, but it has high brittleness and weak interfacial adhesion. The introduction of high polymer modifiers such as polycaprolactam-polyether block copolymer (PA-b-PEO), maleic anhydride grafted ethylene-octene copolymer (POE-g-MAH) or maleic anhydride grafted polycaprolactam (PA-g-MAH) can form hydrogen bonds or ester exchange reactions between the polar groups and the PLA molecular chain, thereby improving the flexibility, adhesion and compatibility of the polymer, especially for avoiding cracking or delamination in the subsequent wet ink hole injection process. Using a double screw extruder and setting 190~220℃ partition heating can ensure uniform dispersion of the modifier and obtain a stable wet ink matrix granule.

[0026] S2.2, dispersing the metal matrix in a mixed solution of ethylene glycol and polyvinylpyrrolidone to obtain a conductive liquid, then adding a degradable copolymer, emulsifying with a high-speed emulsifier at a speed of 10000 rpm for 3~5 minutes, and then cooling, solidifying, centrifuging and drying to obtain self-healing microcapsules.

[0027] Step S2.2 includes: S2.2.1, adding the metal matrix to a mixed solution composed of ethylene glycol and polyvinylpyrrolidone with a mass ratio of ethylene glycol:polyvinylpyrrolidone=4:1, stirring on a magnetic stirrer at a stirring speed of 300 rpm for 30 minutes to obtain a conductive liquid.

[0028] The metal matrix (such as silver nanoparticles, copper nanosheets, bismuth-tin alloy or indium-tin alloy) is dispersed in a mixed system composed of ethylene glycol and polyvinylpyrrolidone (PVP) to form a conductive liquid. This system not only provides a uniform medium, but also PVP can effectively inhibit agglomeration by coordination with the surface of the metal particles through its carbonyl group, forming a stable colloidal dispersion. Ethylene glycol as a high-boiling hydrophilic solvent can enhance the wettability during the emulsification process and participate in the nucleation and condensation of the subsequent shell structure.

[0029] S2.2.2, dissolving the degradable copolymer in dichloromethane to form an oil phase solution, slowly adding the conductive liquid to part of the oil phase solution, and stirring in the emulsifier at a stirring speed of 5000 rpm for 3~5 minutes to obtain an oil-in-water mixture.

[0030] The conductive liquid is slowly added to the dichloromethane oil phase containing degradable copolymers (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. In this process, the conductive liquid as the inner phase is encapsulated in the oil phase under emulsification shear to preliminarily build the first shell layer of the self-healing microcapsule. This layer is usually designed as a polymer structure that is more sensitive to wet heat stimulation, which can be broken to release the conductive core liquid when subjected to electrical aging or crack stimulation, thereby playing a self-repairing function.

[0031] S2.2.3, the oil-in-water primary emulsion mixture is again dropped into another part of the oil phase solution, and emulsified in an emulsifier at a stirring speed of 10000 rpm for 3-5 minutes to obtain an oil-in-oil-in-water emulsion.

[0032] The oil-in-water primary emulsion mixture is dropped into another part of the oil phase containing degradable copolymers, and further emulsified to form an oil-in-oil system to build the second layer of the oil-in-oil shell. This layer functions to provide mechanical barrier and delayed release properties, and is particularly suitable for using copolymers such as PCL-b-PLA having a crystalline-amorphous dual-phase structure, which can effectively regulate the sensitivity of the microcapsule to time-temperature-humidity, and realize a multi-stage self-healing response mechanism.

[0033] S2.2.4, the oil-in-oil-in-water emulsion is added to the aqueous phase solution, and emulsified in an emulsifier at a stirring speed of 10000 rpm for 3-5 minutes to obtain a multiple emulsion.

[0034] The double emulsion system is introduced into the external aqueous phase, and a surface modifier (such as chitosan, sodium carboxymethyl cellulose) can be added to the aqueous phase to form a multiple emulsion (W / O / O / W) with a three-phase structure. The shell layer of the external aqueous phase has good hydrophilicity and electrolyte stability, and also provides biodegradability, which helps the uniform distribution and interfacial integration of the microcapsule in the wet ink system. The finally formed multi-layer coated structure helps to improve the mechanical stability and storage period of the microcapsule, and also enhances the precision of its environmental stimulus response.

[0035] S2.2.5, the multiple emulsion is transferred to an ice water bath and allowed to stand for 30 minutes, centrifuged at a speed of 8000 rpm, and the precipitate is washed with anhydrous ethanol and deionized water three times respectively to obtain solid microcapsules. The solid microcapsules are placed in a vacuum drying oven and dried at 50°C for 6 hours to obtain self-healing microcapsules.

[0036] The inner and outer shell polymers were coagulated by placing the multiple emulsion system in an ice water bath for 30 minutes. Subsequently, centrifugal separation was performed at 8000 rpm to remove the free phase solvent, and the resulting precipitate was washed with absolute ethanol and deionized water three times each to effectively remove residual small molecules and unreacted substances. Finally, the resulting precipitate was placed in a vacuum dryer at 50°C for 6 hours to obtain self-healing microcapsules with clear structure and uniform particle size, which can be stably added to the subsequent wet ink system.

[0037] S2.3, The wet ink matrix granules were placed in a melt kneader, the heating temperature was set to 200°C, the stirring speed was 40 rpm, the self-healing microcapsule powder was added, and the stirring was continued for 5-10 minutes, then the interfacial active agent was added dropwise to obtain the wet ink composition.

[0038] In this step, the pre-prepared wet ink matrix granules were melted at 200°C, and the self-healing microcapsules were slowly added, and the stirring was maintained at 40 rpm to make the microcapsules uniformly dispersed in the high viscosity system. After stirring for 5-10 minutes, the alkoxysilane interfacial active agent (such as trimethoxyoctylsilane, alkyltriethoxysilane) was added dropwise to reduce the surface tension of the ink system through interfacial adjustment, improve its wettability and adhesion to the surface activated substrate, and enhance the uniformity of the distribution between the microcapsules and the matrix. Finally, a wet ink composition with good printability and self-healing performance was obtained.

[0039] S2.4, The surface activated substrate was placed in a vacuum chamber, vacuumed to -0.05 MPa, and the wet ink composition was injected into the surface activated substrate at 60°C, the injection duration was 90-120 seconds, the normal pressure was restored, and the temperature was cooled to room temperature to obtain the filled intermediate.

[0040] To ensure that the wet ink composition is fully filled in the hole without generating bubbles or voids, a reduced pressure injection strategy is used in this step. The surface activated substrate is placed in a vacuum chamber, vacuumed to -0.05 MPa, and the preheated wet ink composition at 60°C is injected into the PCB hole using the external atmospheric pressure difference, and maintained for 90-120 seconds. The temperature control in this stage helps to reduce the viscosity of the ink and improve the flowability. After the injection is completed, the normal pressure is restored and the temperature is cooled to room temperature to obtain a filled intermediate with a full structure and a dense interface.

[0041] S2.5, The flexible transfer film was subjected to plasma surface treatment, and then was attached to the surface of the filled intermediate to obtain a layered structure. The layered structure was sent to an exposure platform, a mask pattern was set on the layered structure, and the layered structure was exposed to green visible light with a wavelength of 530 nm and an intensity of 150 mW / cm² for 20-30 seconds. After development, the flexible transfer film was peeled off to obtain a patterned wet ink line structure.

[0042] To realize high-resolution pattern transfer, the surface of the flexible transfer film is first treated by plasma to improve its surface energy and ink affinity, then it is tightly attached to the surface of the filled intermediate to form a complete laminated structure. In the exposure platform, the mask pattern is set on the surface of the laminated structure, and green light with a wavelength of 530 nm and an intensity of 150 mW / cm² is used for exposure for 20-30 seconds. The light-sensitive components in the wet ink undergo cross-linking reaction and the pattern is developed. Finally, the transfer film is peeled off to obtain a patterned wet ink line structure with clear outline and firm combination, which provides high-precision guidance for subsequent electroplating to build metal vias.

[0043] S3, the patterned wet ink line structure is placed in a temperature and humidity chamber for heat and humidity activation treatment, the temperature is set to 85°C, the relative humidity is 95%, and the treatment time is 1-2 hours to obtain a preformed board. The preformed board is electroplated to obtain a finished PCB blind via circuit board with metal vias.

[0044] Step S3 includes: S3.1, the patterned wet ink line structure is blown with pure nitrogen gas, then it is sent into a high-precision constant temperature and humidity test chamber, the temperature is set to 85°C, the relative humidity is 95%, the treatment time is 1-2 hours, the temperature rising rate is 2-5°C / min, and the humidity rising rate is 3-10% / min to obtain a preformed board.

[0045] This step further improves the compactness and functional responsiveness of the surface layer structure of the patterned wet ink line structure by heat and humidity activation treatment. First, pure nitrogen gas is used to blow the surface, which can effectively remove residual micro-particles, water vapor and volatile residues on the patterned surface, providing a clean initial state for subsequent processing. Then it is sent into a high-precision constant temperature and humidity test chamber, and under the conditions of a set temperature of 85°C and a relative humidity of 95%, it is kept for 12 hours, so that the residual degradable copolymer or interfacial component in the wet ink line structure undergoes micro-crosslinking or structural reconstruction. Precise control of the temperature rising rate and the humidity rising rate (25°C / min and 3-10% / min, respectively) helps to avoid film layer cracking or interface peeling caused by thermal stress or moisture swelling stress. In this environment, the shell material of the self-healing microcapsule may swell slightly, promoting the interface fusion of the capsule and the surrounding wet ink, improving the overall structure density and thermal and humidity stability, and finally forming a preformed board with good mechanical properties, heat resistance and humidity resistance.

[0046] S3.2, the preformed board is placed at room temperature for 10 minutes, then it is rinsed with deionized water at 40-50°C, and then electroplated. The electroplating solution includes copper sulfate, sulfuric acid, brightener and wetting agent, the current density is 1.5-2.5 A / dm², the temperature is 25-30°C, and the electroplating time is 30-60 minutes. After electroplating, water washing, acid pickling and drying are performed in sequence to obtain a finished PCB blind via circuit board with metal vias.

[0047] In step S3.2, the brightener includes at least one of bis(3-sulfopropyl) disulfide, mercaptodiacetic acid, and polyethylene glycol propargyl ether, and the wetting agent includes at least one of Yons green B, polyethyleneimine, and alkyl polyether sulfonate.

[0048] After the heat and humidity treatment, the pre-processed board is left at room temperature for 10 minutes, which helps the system slowly recover from the excited state to the stable state, reducing internal stress accumulation. Using deionized water at 40-50°C for rinsing can gently remove low molecular weight by-products that may have been precipitated during the heat and humidity treatment, improving the cleanliness of the metal plating interface. In the subsequent electroplating process, the copper sulfate and sulfuric acid in the electroplating 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 propargyl ether can regulate the nucleation and growth rate of the grains during metal deposition, making the copper layer dense, smooth, and having good ductility by selectively adsorbing on the copper deposition surface; at the same time, wetting agents such as Yons green B, polyethyleneimine, or alkyl polyether sulfonate can reduce the surface tension of the liquid, enhance the wettability of the plating solution to micro-pores and pattern structures, especially in complex buried hole structures, to avoid electroplating dead angles and bubble residues, thereby obtaining a metal via structure with uniform thickness and strong adhesion. Finally, through steps such as water washing, acid cleaning, and drying, residual electrolytes and impurities are removed, and finally a PCB buried hole circuit board product with good conductivity and structural integrity is obtained.

[0049] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

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. 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 layers 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. The wet ink process for PCB buried via circuit layer according to claim 4, characterized in that, Step S2.2 includes: 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. 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. 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. 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; 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.

6. 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.

7. The wet ink process for PCB buried via circuit layers 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. 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.

8. The wet ink process for PCB buried via circuit layer according to claim 7, 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.

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