A nano-graphite shadowing agent for FPC and its preparation method

Abstract

This invention belongs to the field of printed circuit board manufacturing, specifically relating to a nano-graphite shadowing reagent for FPCs and its preparation method. The reagent is prepared by first synthesizing cerium-doped yttrium molybdate complexed nanocages and sulfonic acid-functionalized silica-coated barium zirconate core-shell nanoparticles. The former forms a hollow cage structure via a hydrothermal method guided by sodium citrate; the latter forms a core-shell structure through co-precipitation, calcination, and sol-gel methods, and is ultimately oxidized and grafted with sulfonic acid groups. In preparing the shadowing reagent, a premixed solution containing barium zirconate core-shell particles is dispersed with nano-graphite, and then a yttrium molybdate nanocage suspension is introduced. Under alkaline heating conditions, both particles bind to the graphite sheets through electrostatic and coordination interactions, constructing a stable three-dimensional inorganic network. This method significantly improves the reagent's dispersion stability, adhesion to pore walls, and uniform coverage of high aspect ratio micropores, ultimately forming a high-performance conductive colloid suitable for high-reliability via metallization processes in flexible circuit boards.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board manufacturing technology, specifically relating to a nano-graphite shadowing reagent for FPC and its preparation method. Background Technology

[0002] Flexible printed circuit boards (PCBs) are core components for achieving lightweight and high-density interconnection in modern electronic products. Reliable microvia metallization is a crucial process for ensuring electrical conductivity and signal integrity. Traditional microvia metallization technologies generally rely on chemical copper plating, which uses palladium as the activation center and introduces formaldehyde as a reducing agent in the solution. While this traditional approach is widely used, its inherent drawbacks are becoming increasingly apparent. First, the high and volatile price of palladium directly increases production costs. Second, formaldehyde is highly toxic and volatile, posing a threat to the production environment and the health of operators. Its wastewater treatment is also extremely complex and demanding, creating significant environmental pressure. Furthermore, the chemical copper plating process is lengthy, involving multiple steps such as sensitization, activation, and acceleration, with complex control parameters and a high risk of lateral etching of fine lines. This makes it difficult to fully meet the current industry demands for higher wiring density and smaller apertures in flexible PCBs. Therefore, the industry has been committed to finding a more environmentally friendly, economical, and efficient alternative technology.

[0003] Against this backdrop, nano-graphite shadowing technology has attracted widespread attention as an emerging direct metallization solution. This technology eliminates the need for precious metals and formaldehyde. Its core lies in utilizing nanoscale graphite particles to form a stable, dispersed colloid in an aqueous phase. Through physicochemical adsorption, a uniform conductive film is formed on the surface of the pore walls treated with a pore-forming agent, allowing for direct copper electroplating and greatly simplifying the process. However, as this technology moves from the laboratory to large-scale industrial application, the performance limitations of its nano-graphite shadowing reagents have become increasingly apparent. Existing commercial reagents are mostly simple mixtures of nano-graphite, common dispersants, and solvents, relying primarily on the physical adsorption of graphite and the electrostatic repulsion of organic molecules. This relatively rudimentary structure and mechanism of action demonstrate fundamental shortcomings when dealing with the complex and diverse substrate characteristics and increasingly stringent process requirements of flexible circuit boards.

[0004] Specifically, the primary problem with existing nano-graphite shadow reagents lies in the inherent instability of the dispersion system. Nano-graphite has a huge specific surface area and extremely high surface energy, making it prone to irreversible aggregation and sedimentation in complex multi-component water-based systems. This results in a short working bath life, rapid performance degradation, and frequent maintenance and replacement, increasing material costs and causing continuous fluctuations in the stability of the production process. Secondly, the bonding force between the conductive layer and the hole walls is weak. The hole walls of flexible circuit boards may contain various non-polar or weakly polar materials such as epoxy resin, polyimide, and glass fiber. Existing technologies use simple physical adsorption forces that are weak, making it difficult to form a strong interfacial bond. In subsequent electroplating, pickling, and impact treatments, the conductive layer is prone to localized peeling, leading to incomplete metallization of the holes, copper cracks, or even voids, seriously threatening the long-term reliability of the final product. Furthermore, for micropores with high aspect ratios, the penetration and coverage capabilities of existing colloidal reagents are significantly reduced. With the miniaturization of electronic devices, the hole diameter of circuit boards is constantly shrinking while the thickness may remain constant or increase, leading to a rise in aspect ratios. Mass transfer and uniform adsorption of traditional reagents within such fine, deep pores present significant challenges. This can easily lead to substantial differences in the thickness of the conductive layer between the pore opening and the center, ultimately resulting in uneven copper plating and hindering reliable electrical interconnection. These deep-seated technical deficiencies restrict the further promotion and application of nano-graphite shadow technology, necessitating breakthroughs in material design and operational mechanisms. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a nano-graphite shadowing reagent for FPC and its preparation method.

[0006] A first aspect of the present invention provides a method for preparing a nano-graphite shadowing agent for FPC, comprising the steps of:

[0007] S1. By weight, mix 40-60 parts of deionized water, 5-15 parts of propylene glycol methyl ether, 0.5-2.0 parts of polyethylene glycol octylphenyl ether, and 1-5 parts of sulfonate-functionalized silica-coated barium zirconate core-shell particles and stir to obtain a premix; under nitrogen protection and stirring, add 20-35 parts of nano-graphite powder to the premix and continue stirring to obtain a mixture.

[0008] S2. Transfer the mixture to a three-necked flask. At 38-42°C, add dropwise an aqueous suspension containing 0.5-3 parts of cerium-doped yttrium molybdate complexed nanocages. After the addition is complete, add 1-3 parts of 2-amino-2-methyl-1-propanol to adjust the pH to 9.5-10.5. Raise the temperature to 58-62°C and continue stirring the reaction. After the reaction is complete, allow it to cool naturally to room temperature to obtain a colloidal product. Sieve the colloidal product and sonicate it.

[0009] In this invention, the core mechanism of preparing a nano-graphite shadowing reagent for flexible circuit boards lies in inducing two inorganic modified compounds to undergo directional self-assembly with nano-graphite sheets in the liquid phase, constructing a multi-layered stable structure. In the first stage of preparation, sulfonic acid-functionalized core-shell particles, due to their excellent dispersibility, first form a homogeneous premix with solvent and surfactant. Subsequently, the added nano-graphite powder is dispersed under high shear. The core-shell particles, with their nanoscale size and rigid structure, initially insert themselves between the graphite sheets, providing physical spacers. Entering the crucial second stage, when a suspension of cerium-doped yttrium molybdate nanocages is introduced and adjusted to an alkaline environment, the system undergoes complex interfacial interactions and structural reorganization. On the one hand, the molybdate groups on the surface of the nanocages are strongly negatively charged, while rare earth cerium ions exhibit highly active Lewis acidity; on the other hand, the surface of the core-shell particles is rich in negatively charged sulfonic acid groups, and the edges of the nano-graphite sheets also have negatively charged groups such as carboxyl groups. Under suitable alkaline heating conditions, positively charged cerium ions become key "crosslinking centers," capable of coordinating with sulfonate, molybdate, and oxygen-containing functional groups at the edges of graphite sheets simultaneously, or exhibiting strong electrostatic attraction. This multi-point bonding effectively "anchors" the nanocage between the core-shell particles and the graphite sheets, thus upgrading the previously relatively independent physical isolation into a three-dimensional inorganic network structure that runs through the entire colloidal system, bridged by chemical bonds and electrostatic forces. This network acts like a miniature scaffold, permanently preventing the graphite sheets from re-aggregating and greatly enhancing the cohesive strength of the entire adsorption layer and its chemical affinity with the subsequent contact surfaces of the pore-walled polymers. Ultimately, this achieves a synergistic leap in dispersion stability, deep-pore coverage, and interfacial bonding.

[0010] According to a preferred embodiment of the present invention, in step S1, the average particle size D50 of the nano-graphite powder is 450 nm.

[0011] According to a preferred embodiment of the present invention, in step S2, the stirring reaction is continued for 4-6 hours.

[0012] According to a preferred embodiment of the present invention, the method for preparing the cerium-doped yttrium molybdate complex nanocage includes:

[0013] A1. By weight, dissolve 90-110 parts of yttrium nitrate hexahydrate and 5-15 parts of cerium nitrate hexahydrate in 800-1200 parts of deionized water. Under nitrogen protection, add 30-70 parts of sodium citrate and stir at 84-86°C to obtain a precursor complex solution. Add an aqueous solution containing 60-100 parts of ammonium molybdate dropwise to the precursor complex solution to obtain a mixture. Transfer the mixture to a hydrothermal reactor and react at 195-205°C to obtain a reaction mixture.

[0014] A2. Allow the reaction mixture to cool naturally to room temperature, centrifuge to collect the precipitate, wash the precipitate alternately with ethanol and deionized water, and finally dry it in a vacuum drying oven at 115-125℃ and grind it.

[0015] In this invention, the preparation of the cerium-doped yttrium molybdate complex nanocages is a controlled hydrothermal crystallization and morphology-directed process. The reaction begins with the preparation of the precursor solution, where a rare-earth yttrium salt (serving as the main framework source) and a cerium salt (serving as the doping modification source) are co-dissolved, and an excess of sodium citrate is added. The citrate ion plays a crucial dual role: on the one hand, its multiple carboxyl functional groups strongly complex with yttrium and cerium ions in the solution, forming a stable metal-organic complex precursor, effectively suppressing premature hydrolysis and disordered precipitation of metal ions, thus creating conditions for subsequent homogeneous nucleation; on the other hand, as a structure directing agent, the differential adsorption energy of citrate on different crystal planes regulates the anisotropic growth kinetics of the crystal. Upon introduction of the ammonium molybdate solution, the molybdate ions gradually undergo coordination exchange and condensation reactions with the aforementioned complexed rare-earth ions. In the subsequent high-temperature, high-pressure hydrothermal environment, this reaction is greatly accelerated. The steric hindrance effect of citrate ions in the precursor and their selective adsorption on specific crystal faces guide the crystal to preferentially grow along specific directions and eventually self-assemble and close, forming a unique hollow cage-like structure. Simultaneously, the cerium ions incorporated into the crystal lattice exist in a mixed valence state, and their unfilled electron orbitals provide abundant coordination active sites on the material surface, which is the key structural basis for its subsequent "molecular bridge" function. The entire hydrothermal process is essentially a multi-step coupling of complexation equilibrium, nucleation, crystal growth, and morphological self-assembly.

[0016] According to a preferred embodiment of the present invention, in step A1, the reaction time at 195-205°C is 48-50 h.

[0017] According to a preferred embodiment of the present invention, in step A2, the drying time in a vacuum drying oven at 115-125°C is 12-14 hours.

[0018] According to a preferred embodiment of the present invention, the method for preparing the sulfonate-functionalized silica-coated barium zirconate core-shell nanoparticles includes:

[0019] B1. By weight, dissolve 70-90 parts of zirconium oxychloride octahydrate and 50-70 parts of barium chloride in hydrochloric acid aqueous solution. Under stirring, add ammonia aqueous solution and 80-120 parts of ammonium carbonate solution dropwise to adjust the pH to 9-10 to obtain a reaction mixture. Aging and filtering the reaction mixture yields a precipitate. Wash the precipitate to obtain a washed precipitate. Calcine the washed precipitate at 795-805℃ to obtain single-phase nano-barium zirconate. Disperse the single-phase nano-barium zirconate in a mixed solvent of anhydrous ethanol and deionized water. Add 20-50 parts of tetraethyl orthosilicate and 5-15 parts of 3-mercaptopropyltrimethoxysilane sequentially, and add ammonia. React at 48-52℃ to obtain a reaction solution.

[0020] B2. Centrifuge the reaction solution to collect the solid product. Wash the solid product and redisperse it in 100-600 parts of hydrogen peroxide aqueous solution. React at room temperature to obtain a reaction mixture. Centrifuge, wash and freeze dry the reaction mixture.

[0021] In this invention, the preparation of sulfonate-functionalized silica-coated barium zirconate core-shell particles integrates co-precipitation, high-temperature solid-state reaction, and surface sol-gel chemistry. The core synthesis is first achieved through co-precipitation, where a zirconium source and a barium source are simultaneously precipitated in an alkaline ammonium carbonate solution to generate a chemically homogeneous barium zirconate carbonate or amorphous hydroxide co-precipitate precursor. After high-temperature calcination, the precursor decomposes and undergoes solid-state ion diffusion, recrystallizing into a single-phase barium zirconate nanoparticle with a perovskite structure. This nanoparticle has a stable crystal structure and a surface rich in hydroxyl groups. The core-shell structure is constructed using a one-step sol-gel process. The aforementioned barium zirconate nanoparticles are dispersed in an alcohol-water mixture, and tetraethyl orthosilicate and mercaptosilane are added simultaneously, catalyzed by ammonia. In this environment, tetraethyl orthosilicate and mercaptosilane co-hydrolyze to generate silanol groups. These silanol groups undergo dehydration condensation with each other and with the metal hydroxyl groups on the surface of the barium zirconate nanoparticles, thereby forming a uniform silica hybrid network layer covalently grafted with mercaptopropyl groups around the core particles. Finally, through a mild oxidation reaction, hydrogen peroxide quantitatively oxidizes the mercapto groups grafted in the silica network to sulfonic acid groups. This transformation is crucial, as it changes the particle surface from hydrophobic mercapto groups to strongly negatively charged and hydrophilic sulfonic acid groups, thus endowing the particles with excellent hydrophilicity, high surface negative charge, and potential cation exchange and coordination capabilities, preparing them for electrostatic steric stabilization and interfacial bonding functions.

[0022] According to a preferred embodiment of the present invention, in step B1, the reaction time at 48-52°C is 24-30 h.

[0023] According to a preferred embodiment of the present invention, in step B2, the reaction time at room temperature is 12-14 hours; the mass fraction of the hydrogen peroxide aqueous solution is 28-32%.

[0024] A second aspect of the present invention provides a nano-graphite shadowing reagent for FPC prepared according to the method described above.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) In terms of the core physicochemical properties of the reagent itself, this invention achieves a revolutionary improvement. Traditional nano-graphite shadow reagents rely on the weak electrostatic repulsion of organic dispersants, and nano-graphite particles are prone to agglomeration and sedimentation due to van der Waals forces, resulting in a short bath life and significant performance degradation. In contrast, this invention introduces sulfonic acid-functionalized silica to coat nano-barium zirconate core-shell particles. Its unique core-shell structure provides a strong physical spatial barrier for the nano-graphite sheets, effectively preventing direct contact and agglomeration between particles. At the same time, the high density of sulfonic acid groups on its surface ionizes in the aqueous phase to generate strong negative charge, which superimposes with the negative charge on the surface of the nano-graphite to produce a strong and lasting electrostatic repulsion force. This dual synergistic mechanism of "steric hindrance" and "electrostatic stability" enables nano-graphite particles to be stably dispersed in the system for a long time. More importantly, the subsequently introduced cerium-doped yttrium molybdate complex nanocages, under alkaline heating conditions, allow cerium ions and molybdate groups on their surface to coordinate and electrostatically attract the sulfonic acid groups on the surface of the core-shell particles and the edge defects of the nanographite sheets, thereby constructing a three-dimensional inorganic bridging network around the graphite particles. This network acts as a structural "skeleton" for the dispersion system, fixing and strengthening the physical isolation effect, fundamentally solving the sedimentation problem. Therefore, the shadow reagent prepared by this invention has extremely long bath stability, with no visible sedimentation after standing for several months, and extremely high viscosity and conductivity retention, significantly reducing maintenance frequency and material loss in production.

[0027] (2) When applied to the metallization process of flexible circuit board holes, this invention demonstrates excellent process adaptability and reliability. For micropores with high aspect ratios, traditional reagents often result in uneven or complete coverage in the middle of the hole wall due to poor dispersion stability and insufficient penetration. The reagent of this invention, due to its excellent dispersion stability and suitable rheological properties, allows its colloidal particles to smoothly penetrate deep into the micropores. Furthermore, thanks to the structural consistency of the aforementioned three-dimensional inorganic network, it ensures uniform and dense adsorption and coverage at any location within the hole, forming a continuous and defect-free conductive film. This enables the deposition of a uniform conductive layer from the hole opening to the hole center, even in challenging hole structures with extremely high aspect ratios, laying a perfect foundation for subsequent copper electroplating. In terms of adhesion, the adhesion between the conductive layer of traditional physical adsorption and the hole wall substrates such as epoxy resin and polyimide is weak. In this invention, the cerium-doped yttrium molybdate complex nanocages play a crucial role. The rare-earth cerium ions and molybdate groups on their surface not only bond with the internal network of the reagent but also form coordination interactions or strong hydrogen bonds with epoxy groups and carbonyl groups on imide rings in the polymer substrate of the pore walls, thereby constructing a robust "molecular bridge" between the conductive layer and the pore walls. This strong chemical bonding significantly enhances the adhesion of the conductive layer to the pore walls, enabling it to withstand the harsh environments of subsequent electroplating processes, such as strong acid activation and electroplating impact. It completely avoids fatal defects such as "holes" in the pore walls or voids in the plating caused by conductive layer peeling, greatly improving the interconnect reliability of pore metallization and the yield of the final product.

[0028] (3) Considering production efficiency, environmental protection, and economic benefits, this invention brings comprehensive positive effects. The ultra-long bath life directly reduces the number of downtime maintenance and chemical replacements, improving equipment utilization and production continuity; the excellent deep-hole coverage and bonding strength reduce the defect rate and rework rate of products to extremely low levels, improving overall output quality and efficiency. In terms of environmental protection, the reagents of this invention completely eliminate the precious metal palladium and highly toxic formaldehyde necessary in the traditional chemical copper plating process, eliminating the health hazards to operators and the complex problems of palladium- and formaldehyde-containing wastewater treatment from the source, making the production process cleaner and safer. The two inorganic modified compound raw materials used are common commercially available chemical products, and the synthesis process route is mature and controllable, without bottlenecks in large-scale production. Therefore, this invention not only provides a high-performance hole metallization solution, but also achieves synergistic optimization of process reliability, environmental friendliness, and production efficiency under the premise of controllable production costs, possessing significant industrial application value and market competitiveness. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a nano-graphite shadowing agent for FPC, the steps of which include:

[0032] First, cerium-doped yttrium molybdate complex nanocages were prepared. 100.0 g of yttrium nitrate hexahydrate and 10.0 g of cerium nitrate hexahydrate were accurately weighed using an electronic balance and placed together in a 2 L beaker. 1000.0 g of deionized water was added to the beaker, and the mixture was placed on a magnetic stirrer and stirred at 500 rpm at room temperature until the solids were completely dissolved, yielding a clear, colorless solution. The beaker was then transferred to a glove box purged with high-purity nitrogen (≥99.999%). Under continuous nitrogen protection, 50.0 g of sodium citrate was added to the solution. The beaker was then removed and placed in an oil bath equipped with a mechanical stirrer, a reflux condenser, and a thermocouple. Stirring was started at 300 rpm, and heating was initiated. The mixture was heated to 85.0 °C and held at this temperature with continuous stirring for 120 min, yielding a homogeneous, clear precursor complex solution. In a separate 500mL beaker, weigh 80.0g of ammonium molybdate and add 200.0g of deionized water. Stir until completely dissolved to prepare an ammonium molybdate aqueous solution. Using a constant-pressure dropping funnel, slowly add the ammonium molybdate aqueous solution dropwise to the aforementioned precursor complex solution at 85.0℃ at a rate of approximately 2mL / min while continuously stirring. The entire dropping process lasts approximately 100min. After the addition is complete, a milky white mixture is obtained. Transfer this mixture while hot to a 2L polytetrafluoroethylene-lined hydrothermal reactor, with a filling degree of approximately 60%. After sealing the reactor, place it in a programmable temperature-controlled oven. Set the reaction program to: heat from room temperature to 200.0℃ at a rate of 2℃ / min, and maintain the temperature at 200.0℃ for 49.0h. After the reaction is complete, turn off the oven heating and allow the reactor to cool naturally to room temperature (approximately 25℃) within the oven. This process takes approximately 12h. Open the vessel and pour all the white suspension obtained into a centrifuge cup. Centrifuge at 8000 rpm for 10 min using a high-speed centrifuge. Carefully discard the supernatant and collect the bottom white precipitate. Add 200 mL of anhydrous ethanol to the precipitate, stir and wash with a glass rod, then centrifuge again at 8000 rpm for 5 min, discarding the ethanol wash. Next, add 200 mL of deionized water, stir and wash, then centrifuge. Repeat this ethanol-water alternating washing step three times. Transfer the finally washed, moist precipitate to a petri dish and place it in a vacuum drying oven. Close the oven door, turn on the vacuum pump, reduce the pressure inside the oven to -0.1 MPa, set the drying temperature to 120.0℃, and the drying time to 13.0 h. After drying, turn off the heating and vacuum, and wait for the temperature inside the oven to drop to approximately 50℃ before removing the dried block product. Finally, the block product was placed in an agate mortar and manually ground for 30 minutes to obtain a fine white powder of cerium-doped yttrium molybdate complex nanocages, which were then placed in a desiccator for later use.

[0033] Next, sulfonic acid-functionalized silica-coated barium zirconate core-shell nanoparticles were prepared. 80.0 g of zirconium oxychloride octahydrate and 60.0 g of barium chloride were weighed and placed together in a 1 L beaker. 50.0 g of concentrated hydrochloric acid (37% by mass) was mixed with 300.0 g of deionized water. This dilute hydrochloric acid solution was poured into the beaker and placed on a magnetic stirrer. The mixture was stirred at 600 rpm for 30 min until all solids were completely dissolved, resulting in a clear solution. The beaker was then placed under a powerful mechanical stirrer with the impeller speed set to 1000 rpm. Two constant-pressure dropping funnels were prepared. Funnel A contained a 25% ammonia solution, and funnel B contained a solution prepared by dissolving 100.0 g of ammonium carbonate in 200.0 g of deionized water. The valves of both funnels were opened simultaneously, and the dropping rate was controlled so that the two solutions were added synchronously and slowly to the vigorously stirred zirconium-barium mixed solution over approximately 60 min. During this process, the pH value of the reaction solution was monitored in real time using a pH meter. By fine-tuning the dropping rate of ammonia water, the final pH value of the reaction system was precisely controlled at 9.5. At this point, a large amount of white precipitate was generated in the beaker. After the addition was complete, stirring was continued at 1000 rpm to age the precipitate for 120 min. After aging, vacuum filtration was performed using a Buchner funnel and quantitative filter paper to collect the filter cake. The filter cake was repeatedly washed with deionized water until a small amount of filtrate was taken, and a few drops of 0.1 mol / L silver nitrate solution were added. No obvious white turbidity was produced, indicating that chloride ions had been washed away. The washed wet filter cake, along with the filter paper, was transferred to an alumina crucible and placed in a box-type muffle furnace. The calcination program was set as follows: the temperature was increased from room temperature to 800.0℃ at a rate of 5℃ / min, and calcined at 800.0℃ for 120 min. Then, the temperature was cooled to below 150℃ under program control before removal. White, fluffy single-phase nano-barium zirconate powder was obtained. Weigh 30.0 g of the nano-barium zirconate powder and place it in a 500 mL Erlenmeyer flask. Measure 250.0 g of anhydrous ethanol and 100.0 g of deionized water and add them to the flask. Place the flask in an ultrasonic cleaner (300 W, 40 kHz) and sonicate for 30 min to obtain a uniform nano-barium zirconate dispersion. Add 35.0 g of tetraethyl orthosilicate and 10.0 g of 3-mercaptopropyltrimethoxysilane sequentially to the dispersion using a pipette, and then add 10.0 g of 25% ammonia solution as a catalyst using a graduated cylinder. Plug the Erlenmeyer flask with a stopper equipped with a condenser and place it in a constant temperature water bath shaker at 50.0 °C. React at 150 rpm for 27.0 h. After the reaction is complete, transfer the mixture to a centrifuge cup and centrifuge at 10000 rpm for 15 min. Discard the supernatant to obtain a pale yellow solid. The solid was washed three times with 50.0 g of anhydrous ethanol, and centrifuged at 10,000 rpm for 5 min after each wash. The washed solid was then redispersed in a beaker containing 400.0 g of a 30% hydrogen peroxide aqueous solution.The beaker was placed on a magnetic stirrer and stirred at 400 rpm for 13.0 h at room temperature (25℃). After the reaction was complete, the mixture was centrifuged again at 10000 rpm for 15 min, and the solid was collected. The solid was washed three times with deionized water and then transferred to a tray of a freeze dryer for freeze drying (pre-freezing temperature -50℃, drying chamber pressure 10 Pa, drying time 48 h) to obtain white sulfonic acid-functionalized silica-coated barium zirconate core-shell nanoparticle powder, which was then placed in a desiccator for later use.

[0034] Finally, a nano-graphite shadowing reagent for flexible circuit boards was prepared. A 1L high-level dispersion vessel was prepared, equipped with a high-speed shear disperser with adjustable speed (maximum speed 12000 rpm) and a nitrogen inlet tube. 500.0 g of deionized water, 100.0 g of propylene glycol methyl ether, 10.0 g of polyethylene glycol octylphenyl ether, and 30.0 g of the previously prepared sulfonate-functionalized silica-coated barium zirconate core-shell particle powder were added sequentially to the dispersion vessel. The high-speed shear disperser was turned on and set to 5000 rpm. Shearing and mixing were continued at this speed for 40.0 min until the system was observed to be uniformly milky white with no visible particle agglomerates, thus obtaining a premixed liquid. The disperser was kept running at a low speed of 500 rpm, and simultaneously the nitrogen cylinder valve was opened, continuously introducing nitrogen gas through the inlet tube above the liquid surface in the vessel to replace the air and create an inert atmosphere. Then, 250.0 g of nano-graphite powder with an average particle size D50 of 450 nm was slowly and batch-added through the feeding port, with the feeding time controlled at approximately 20 minutes to prevent dust from flying. After all the graphite powder was added, the speed of the high-speed shear disperser was rapidly increased to 8000 rpm and maintained at this high shear rate for 60.0 minutes to fully deagglomerate and disperse the nano-graphite powder, resulting in a uniform, viscous black mixture. This mixture was transferred to a 2L three-necked flask equipped with an organic olive stirring paddle, a digital display thermocouple, a constant pressure dropping funnel, and a reflux condenser. The flask was placed in a constant temperature water bath, the mechanical stirring was turned on, the speed was set to 200 rpm, and heating was started. The water bath temperature was set to 40.0℃, and the temperature of the material inside the flask was stabilized at 40.0℃. 15.0 g of the cerium-doped yttrium molybdate complex nanocage powder prepared above was mixed with 100.0 g of deionized water in a beaker and stirred with a glass rod to form a suspension. This suspension was poured into a constant-pressure dropping funnel. The valve of the dropping funnel was opened, and the suspension was added dropwise to a three-necked flask at a rate of approximately 3.3 mL / min for 30.0 min. After the addition was complete, 20.0 g of 2-amino-2-methyl-1-propanol was measured using a graduated cylinder and added directly to the three-necked flask. The pH value of the mixture was immediately measured using a calibrated pH meter and confirmed to be 10.0. Subsequently, the temperature setting of the constant-temperature water bath was adjusted from 40.0 °C to 60.0 °C, and the temperature of the material in the flask was increased at a rate of 2 °C / min until it reached and stabilized at 60.0 °C. This temperature was maintained, and the reaction was continued with stirring at 200 rpm for 5.0 h. After the reaction time was reached, the water bath heating was turned off, the heat source was removed, and the three-necked flask was allowed to cool naturally to room temperature (approximately 25°C) in air, yielding a dark black colloidal product. The colloidal product was filtered through a 200-mesh (approximately 75 μm pore size) nylon sieve, and the filtrate was collected in a clean glass bottle.Finally, the glass bottle containing the filtrate was placed in the water bath of an ultrasonic cleaner (300W, 40kHz) and ultrasonically treated for 15.0 min to eliminate the tiny air bubbles encapsulated in the colloid, thus obtaining the final nano-graphite shadow reagent. This reagent is a homogeneous, stable, dark gray-black, and glossy colloidal dispersion.

[0035] Example 2

[0036] The difference between this embodiment and Example 1 is that, firstly, cerium-doped yttrium molybdate complex nanocages are prepared. 95.0 g of yttrium nitrate hexahydrate and 8.0 g of cerium nitrate hexahydrate are accurately weighed using an electronic balance and placed together in a 2 L beaker. 900.0 g of deionized water is added to the beaker, and the mixture is placed on a magnetic stirrer and stirred at 500 rpm at room temperature until the solid is completely dissolved. The beaker is then transferred to a glove box purged with high-purity nitrogen. Under continuous nitrogen protection, 45.0 g of sodium citrate is added to the solution. The beaker is then removed and placed in an oil bath equipped with a mechanical stirrer, a reflux condenser, and a thermocouple. Stirring is started at 300 rpm, and heating is initiated. The mixture is heated to 85.0 °C and held at this temperature for 120 min with continuous stirring to obtain the precursor complex solution. In a separate 500mL beaker, weigh 75.0g of ammonium molybdate and add 150.0g of deionized water. Stir until completely dissolved to prepare an ammonium molybdate aqueous solution. Using a constant-pressure dropping funnel, slowly add the ammonium molybdate aqueous solution dropwise to the aforementioned precursor complex solution at 85.0℃ at a rate of approximately 2mL / min while continuously stirring. After the addition is complete, a mixture is obtained. Transfer this mixture to a 2L polytetrafluoroethylene-lined hydrothermal reactor, with a filling density of approximately 55%. After sealing the reactor, place it in a programmable temperature-controlled oven. Set the reaction program to: increase the temperature from room temperature to 198.0℃ at a rate of 2℃ / min, and maintain the temperature at 198.0℃ for 48.5h. After the reaction is complete, allow the reactor to cool naturally to room temperature in the oven. Open the reactor and pour all the resulting suspension into a centrifuge cup. Centrifuge at 8000rpm for 10min using a high-speed centrifuge, collecting the bottom white precipitate. Add 200 mL of anhydrous ethanol to the precipitate, stir and wash, then centrifuge and discard the ethanol wash solution. Next, add 200 mL of deionized water, wash, and centrifuge again. Repeat this ethanol-water alternating washing step three times. Transfer the final washed precipitate to a petri dish and place it in a vacuum drying oven. Turn on the vacuum pump, set the drying temperature to 118.0℃, and the drying time to 12.5 h. After drying, remove the dried block product, place it in an agate mortar, and manually grind it for 30 min to obtain cerium-doped yttrium molybdate complex nanocages, which are then placed in a desiccator for later use.

[0037] Next, sulfonic acid-functionalized silica-coated barium zirconate core-shell nanoparticles were prepared. 75.0 g of zirconium oxychloride octahydrate and 55.0 g of barium chloride were weighed and placed together in a 1 L beaker. 50.0 g of concentrated hydrochloric acid was mixed with 300.0 g of deionized water, and this dilute hydrochloric acid solution was poured into the beaker and stirred on a magnetic stirrer until completely dissolved. The beaker was placed under a powerful mechanical stirrer with the stirrer set to 1000 rpm. Two constant-pressure dropping funnels were prepared. Funnel A contained a 25% ammonia solution, and funnel B contained a solution prepared by dissolving 90.0 g of ammonium carbonate in 200.0 g of deionized water. The valves of both funnels were opened simultaneously, and the dropping rate was controlled to allow the two solutions to be added slowly and synchronously to the vigorously stirred zirconium-barium mixture. The pH of the final reaction system was precisely controlled at 9.2 using a pH meter. After the addition was complete, stirring was maintained to allow the precipitate to age for 120 min. After aging, the filter cake was collected by vacuum filtration using a Buchner funnel. The filter cake was repeatedly washed with deionized water until no chloride ions remained. The washed filter cake was placed in an alumina crucible and then placed in a box-type muffle furnace. The calcination program was set as follows: the temperature was increased to 798.0℃ at a rate of 5℃ / min, and calcined at 798.0℃ for 120 min, followed by controlled cooling. Single-phase nano-barium zirconate powder was obtained. 25.0 g of this powder was weighed and placed in a 500 mL Erlenmeyer flask. 200.0 g of anhydrous ethanol and 80.0 g of deionized water were added to the Erlenmeyer flask, and the mixture was sonicated for 30 min to obtain a dispersion. 28.0 g of tetraethyl orthosilicate and 8.0 g of 3-mercaptopropyltrimethoxysilane were added to the dispersion sequentially, followed by 8.0 g of 25% ammonia solution. A conical flask was stoppered with a condenser and placed in a constant-temperature water bath shaker at 49.0℃, reacting at 150 rpm for 25.0 h. After the reaction, the mixture was centrifuged, the supernatant was discarded, and a solid was obtained. The solid was washed three times with anhydrous ethanol and then redispersed in a beaker containing 300.0 g of a 30% hydrogen peroxide aqueous solution. This beaker was placed on a magnetic stirrer and stirred at 400 rpm for 12.5 h at room temperature. After the reaction was complete, the solid was collected by centrifugation again, washed three times with deionized water, and then freeze-dried to obtain sulfonate-functionalized silica-coated barium zirconate core-shell nanoparticle powder, which was then stored in a desiccator for later use.

[0038] Finally, a nano-graphite shadow reagent for flexible circuit boards was prepared. A 1L high-level dispersion vessel was prepared, and 450.0g of deionized water, 80.0g of propylene glycol methyl ether, 8.0g of polyethylene glycol octylphenyl ether, and 20.0g of the previously prepared core-shell particle powder were added sequentially. A high-speed shear disperser was turned on, set to 5000rpm, and continuously sheared and mixed for 35.0min to obtain a premix. While maintaining low-speed stirring and purging with nitrogen, 220.0g of nano-graphite powder was slowly added. After the addition was complete, the speed was increased to 8000rpm, and dispersion was continued for 50.0min to obtain a black mixture. This mixture was transferred to a 2L three-necked flask, and mechanical stirring was turned on, set to 200rpm, and heated in a water bath to stabilize the temperature of the material inside the flask at 39.0℃. A suspension prepared by mixing 10.0 g of the cerium-doped yttrium molybdate complexed nanocage powder with 80.0 g of deionized water was added dropwise to a three-necked flask using a constant-pressure dropping funnel. After the addition was complete, 15.0 g of 2-amino-2-methyl-1-propanol was added, and the pH of the mixture was measured to be 9.8. Subsequently, the water bath temperature was raised to 59.0 °C, maintained at this temperature, and the reaction was continued with stirring at 200 rpm for 4.5 h. After the reaction time was reached, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The colloidal product was filtered through a 200-mesh nylon sieve, and the filtrate was finally sonicated for 15.0 min to obtain the final nano-graphite shadow reagent.

[0039] Example 3

[0040] The difference between this embodiment and Example 1 is that, firstly, cerium-doped yttrium molybdate complex nanocages are prepared. 105.0 g of yttrium nitrate hexahydrate and 12.0 g of cerium nitrate hexahydrate are accurately weighed using an electronic balance and placed together in a 2 L beaker. 1100.0 g of deionized water is added to the beaker, and the mixture is placed on a magnetic stirrer and stirred at 500 rpm at room temperature until the solids are completely dissolved. The beaker is then transferred to a glove box purged with high-purity nitrogen. Under continuous nitrogen protection, 65.0 g of sodium citrate is added to the solution. The beaker is then removed and placed in an oil bath equipped with a mechanical stirrer, a reflux condenser, and a thermocouple. Stirring is started at 300 rpm, and heating is initiated. The mixture is heated to 85.0 °C and held at this temperature for 120 min with continuous stirring to obtain the precursor complex solution. In a separate 500mL beaker, weigh 90.0g of ammonium molybdate and add 220.0g of deionized water. Stir until completely dissolved to prepare an ammonium molybdate aqueous solution. Using a constant-pressure dropping funnel, slowly add the ammonium molybdate aqueous solution dropwise to the aforementioned precursor complex solution at 85.0℃ with continuous stirring. After the addition is complete, a mixture is obtained. Transfer this mixture to a 2L polytetrafluoroethylene-lined hydrothermal reactor, with a filling degree of approximately 65%. After sealing the reactor, place it in a programmable temperature-controlled oven. Set the reaction program: increase the temperature from room temperature to 202.0℃ at a rate of 2℃ / min, and maintain the temperature at 202.0℃ for 49.5h. After the reaction is complete, allow the reactor to cool naturally to room temperature in the oven. Open the reactor, pour all the resulting suspension into a centrifuge cup, and centrifuge at 8000rpm for 10min using a high-speed centrifuge, collecting the bottom white precipitate. Add 200 mL of anhydrous ethanol to the precipitate, stir and wash, then centrifuge and discard the ethanol wash solution. Next, add 200 mL of deionized water, wash, and centrifuge again. Repeat this ethanol-water alternating washing step three times. Transfer the final washed precipitate to a petri dish and place it in a vacuum drying oven. Turn on the vacuum pump, set the drying temperature to 122.0℃, and the drying time to 13.5 h. After drying, remove the dried block product, place it in an agate mortar, and manually grind it for 30 min to obtain cerium-doped yttrium molybdate complex nanocages, which are then placed in a desiccator for later use.

[0041] Next, sulfonic acid-functionalized silica-coated barium zirconate core-shell nanoparticles were prepared. 85.0 g of zirconium oxychloride octahydrate and 65.0 g of barium chloride were weighed and placed together in a 1 L beaker. 50.0 g of concentrated hydrochloric acid was mixed with 300.0 g of deionized water, and this dilute hydrochloric acid solution was poured into the beaker and stirred on a magnetic stirrer until completely dissolved. The beaker was placed under a powerful mechanical stirrer with the stirrer set to 1000 rpm. Two constant-pressure dropping funnels were prepared. Funnel A contained a 25% ammonia solution, and funnel B contained a solution prepared by dissolving 110.0 g of ammonium carbonate in 200.0 g of deionized water. The valves of both funnels were opened simultaneously, and the dropping rate was controlled to allow the two solutions to be added slowly and synchronously to the vigorously stirred zirconium-barium mixture. The pH of the final reaction system was precisely controlled at 9.8 using a pH meter. After the addition was complete, stirring was maintained to allow the precipitate to age for 120 min. After aging, the filter cake was collected by vacuum filtration using a Buchner funnel. The filter cake was repeatedly washed with deionized water until no chloride ions remained. The washed filter cake was placed in an alumina crucible and then placed in a box-type muffle furnace. The calcination program was set as follows: the temperature was increased to 802.0℃ at a rate of 5℃ / min, and calcined at 802.0℃ for 120 min, followed by controlled cooling. Single-phase nano-barium zirconate powder was obtained. 35.0 g of this powder was weighed and placed in a 500 mL Erlenmeyer flask. 300.0 g of anhydrous ethanol and 120.0 g of deionized water were added to the Erlenmeyer flask, and the mixture was sonicated for 30 min to obtain a dispersion. 45.0 g of tetraethyl orthosilicate and 12.0 g of 3-mercaptopropyltrimethoxysilane were added to the dispersion sequentially, followed by 12.0 g of 25% ammonia solution. A conical flask was stoppered with a condenser and placed in a constant-temperature water bath shaker at 51.0℃, reacting at 150 rpm for 29.0 h. After the reaction, the mixture was centrifuged, the supernatant was discarded, and a solid was obtained. The solid was washed three times with anhydrous ethanol and then redispersed in a beaker containing 500.0 g of a 30% hydrogen peroxide aqueous solution. This beaker was placed on a magnetic stirrer and stirred at 400 rpm for 13.5 h at room temperature. After the reaction was complete, the solid was collected by centrifugation again, washed three times with deionized water, and then freeze-dried to obtain sulfonate-functionalized silica-coated barium zirconate core-shell nanoparticle powder, which was then stored in a desiccator for later use.

[0042] Finally, a nano-graphite shadow reagent for flexible circuit boards was prepared. A 1L high-level dispersion vessel was prepared, and 550.0g of deionized water, 120.0g of propylene glycol methyl ether, 15.0g of polyethylene glycol octylphenyl ether, and 40.0g of the previously prepared core-shell particle powder were added sequentially. A high-speed shear disperser was turned on, set to 5000rpm, and continuously sheared and mixed for 50.0min to obtain a premix. While maintaining low-speed stirring and purging with nitrogen, 300.0g of nano-graphite powder was slowly added. After the addition was complete, the speed was increased to 8000rpm, and dispersion was continued for 55.0min to obtain a black mixture. This mixture was transferred to a 2L three-necked flask, and mechanical stirring was turned on, set to 200rpm, and heated in a water bath to stabilize the temperature of the material inside the flask at 41.0℃. A suspension prepared by mixing 20.0 g of the cerium-doped yttrium molybdate complexed nanocage powder with 120.0 g of deionized water was added dropwise to a three-necked flask using a constant-pressure dropping funnel. After the addition was complete, 25.0 g of 2-amino-2-methyl-1-propanol was added, and the pH of the mixture was measured to be 10.3. Subsequently, the water bath temperature was raised to 61.0 °C, maintained at this temperature, and the reaction was continued with stirring at 200 rpm for 5.5 h. After the reaction time was reached, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The colloidal product was filtered through a 200-mesh nylon sieve, and the filtrate was finally sonicated for 15.0 min to obtain the final nano-graphite shadow reagent.

[0043] Comparative Example 1

[0044] The difference between this comparative example and Example 1 is that this comparative example does not add sulfonate-functionalized silica-coated barium zirconate core-shell particles and cerium-doped yttrium molybdate complex nanocages. Preparation of the nano-graphite shadow reagent: In a 1L high-level dispersion vessel, 500.0g of deionized water, 100.0g of propylene glycol methyl ether, and 10.0g of polyethylene glycol octylphenyl ether were added sequentially. A high-speed shear disperser was turned on, set to 5000rpm, and continuously sheared and mixed for 40.0min to obtain a premixed solution. While maintaining low-speed stirring, nitrogen gas was continuously introduced into the vessel for protection, and then 250.0g of nano-graphite powder was slowly added. After the addition was complete, the speed was increased to 8000rpm, and dispersion was continued for 60.0min to obtain a black mixture. This mixture was transferred to a 2L three-necked flask, mechanical stirring was turned on, the speed was set to 200rpm, and a water bath was used to stabilize the temperature of the material in the flask at 40.0℃. 20.0 g of 2-amino-2-methyl-1-propanol was added directly to the flask, and the pH of the mixture was measured to be 10.0. The water bath temperature was then raised to 60.0 °C, maintained at this temperature, and the reaction was continued with stirring at 200 rpm for 5.0 h. After the reaction time was reached, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The colloidal product was filtered through a 200-mesh nylon sieve, and the filtrate was finally sonicated for 15.0 min to obtain the nano-graphite shadow reagent for comparison.

[0045] Comparative Example 2

[0046] The difference between this comparative example and Example 1 is that this comparative example only adds sulfonate-functionalized silica to coat barium zirconate core-shell nanoparticles, without adding cerium-doped yttrium molybdate complexed nanocages. The preparation method of the core-shell particles is exactly the same as in Example 1, and 30.0 g is weighed for later use. Preparation of nano-graphite shadow reagent: In a 1L high-level dispersion vessel, 500.0 g of deionized water, 100.0 g of propylene glycol methyl ether, 10.0 g of polyethylene glycol octylphenyl ether, and 30.0 g of the aforementioned prepared core-shell particle powder are added sequentially. A high-speed shear disperser is turned on, the speed is set to 5000 rpm, and shear mixing is continued for 40.0 min to obtain a premixed liquid. Low-speed stirring is maintained and nitrogen gas is continuously introduced into the vessel for protection, and then 250.0 g of nano-graphite powder is slowly added. After the addition is completed, the speed is increased to 8000 rpm, and dispersion is continued for 60.0 min to obtain a black mixture. The mixture was transferred to a 2L three-necked flask, and a mechanical stirrer was turned on at 200 rpm. The mixture was heated in a water bath to stabilize the temperature at 40.0°C. 20.0 g of 2-amino-2-methyl-1-propanol was added directly to the flask, and the pH of the mixture was measured to be 10.0. The water bath temperature was then increased to 60.0°C and maintained at this temperature while stirring at 200 rpm for 5.0 h. After the reaction time was reached, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The colloidal product was filtered through a 200-mesh nylon sieve, and the filtrate was sonicated for 15.0 min to obtain the nano-graphite shadow reagent for comparison.

[0047] Comparative Example 3

[0048] The difference between this comparative example and Example 1 is that ordinary silica and cerium ammonium citrate are used in this comparative example to replace sulfonic acid-functionalized silica-coated barium zirconate core-shell particles and cerium-doped yttrium molybdate complex nanocages, respectively. 30.0 g of hydrophilic fumed silica is weighed to replace sulfonic acid-functionalized silica-coated barium zirconate core-shell particles. 15.0 g of cerium ammonium citrate is weighed to replace cerium-doped yttrium molybdate complex nanocages. Preparation of the nano-graphite shadow reagent: In a 1L high-level dispersion vessel, 500.0 g of deionized water, 100.0 g of propylene glycol methyl ether, 10.0 g of polyethylene glycol octylphenyl ether, and 30.0 g of fumed silica are added sequentially. A high-speed shear disperser is turned on, the speed is set to 5000 rpm, and shear mixing is continued for 40.0 min to obtain a premixed solution. Low-speed stirring is maintained, and nitrogen gas is continuously introduced into the vessel for protection. Then, 250.0 g of nano-graphite powder is slowly added. After the addition of materials, the stirring speed was increased to 8000 rpm, and dispersion was continued for 60.0 min to obtain a black mixture. This mixture was transferred to a 2L three-necked flask, and mechanical stirring was started at 200 rpm. The mixture was heated in a water bath to stabilize the temperature of the material in the flask at 40.0℃. A clear solution of 15.0 g of cerium ammonium citrate dissolved in 100.0 g of deionized water was added dropwise to the three-necked flask through a constant pressure dropping funnel. After the addition was complete, 20.0 g of 2-amino-2-methyl-1-propanol was added, and the pH of the mixture was measured to be 10.0. Subsequently, the water bath temperature was raised to 60.0℃, maintained at this temperature, and the reaction was continued with stirring at 200 rpm for 5.0 h. After the reaction time was reached, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The colloidal product was filtered through a 200-mesh nylon sieve, and the filtrate was finally sonicated for 15.0 min to obtain the nano-graphite shadow reagent for comparison.

[0049] The nano-graphite shadowing reagents for FPC prepared in Examples 1-3 and Comparative Examples 1-3 were tested according to national and industry standard testing specifications as follows:

[0050] Colloidal stability test: First, shake the nano-graphite shadow reagent samples prepared in Examples 1-3 and Comparative Examples 1-3 thoroughly, and accurately measure 100 mL of each sample into a 100 mL stoppered glass graduated cylinder, recording the initial liquid level height H0. Place all cylinders in a constant temperature and humidity chamber at 25.0℃±0.5℃ and 50%±5% relative humidity, and allow them to stand in the dark for a total of 30 days. Starting from the first day of standing, observe and record the sedimentation interface height H between the clear liquid surface and the uniformly dispersed colloid at a fixed time each day. t After the settling period, calculate the settlement ratio on day 30 using the formula (H). t30 / H0)×100%.

[0051] Next, take fresh reagents for each sample, dilute them 10 times with deionized water, put them into a special folded capillary sample cell, place them in a Zeta potential and nanoparticle size analyzer, equilibrate at 25.0℃ for 300 seconds, and perform three independent measurements. Take the average value of the Zeta potential as the result.

[0052] Finally, accelerated aging tests were conducted. 50 mL of fresh reagent from each sample was placed in a 100 mL glass sample bottle with a screw cap. After tightening the cap, the bottle was placed in a preheated forced-air drying oven and kept at 60.0℃±1.0℃ for 7 consecutive days. After the period, the sample was taken out and cooled to room temperature. The colloidal state was observed and recorded by visual inspection and gentle shaking, such as whether gelation, clumping, or irreversible bottom precipitation occurred.

[0053] Conductive layer performance testing: A backlight test board made of standard FR-4 epoxy glass cloth substrate, with a thickness of 1.6 mm and an aperture of 0.30 mm, was used. First, the test board was pretreated in a matching pore-forming solution at 65℃ for 5 minutes, followed by rinsing with deionized water and drying. Next, the treated test board was vertically immersed in the shadow reagent to be tested for 3 minutes at an ambient temperature controlled at 25.0℃±1.0℃. Then, the test board was vertically lifted from the liquid surface at a uniform speed of 1.5 m / min, forming a wet film. The wet film test board was immediately placed in a preheated drying oven at 85.0℃ and baked horizontally for 5 minutes to form a dry conductive layer. The dried test board was placed on the observation stage of a backlight tester, and the aperture walls were observed from the back under a standard white light source. The test board was rated according to the industry-standard ten-level visual rating, where level 10 indicates that the aperture walls are completely covered by the conductive layer with no light transmission, and level 1 indicates complete light transmission with no coverage.

[0054] The thermal stress shock test involves placing the same test board, which has already undergone backlight observation, into a reflow oven or hot air oven heated to 288.0℃±5.0℃, with the sample board surface 5cm away from the hot air outlet. After being heated for 10 seconds, the board is removed and cooled to room temperature. This process is repeated three times. Finally, the morphology of the conductive layer at the intersection of the aperture and the aperture wall is observed under an optical microscope at 200x magnification to check for blistering, cracks, or peeling from the substrate.

[0055] The adhesion test uses the cross-cut adhesion test. Using a standard single-blade or multi-blade cutting tool, a 1mm × 1mm grid array is cut on the smooth surface of the test board with the conductive layer already formed. The cutting depth must ensure that the conductive layer is penetrated to the substrate. After removing debris with a soft brush, standard 3M 610 tape is tightly adhered to the grid area. The tape is then pressed firmly with a finger or eraser to ensure no air bubbles and complete contact. The tape is then quickly peeled off at a 60-degree angle within 1-2 seconds. The extent of conductive layer detachment in the grid area is inspected under a magnifying glass, and a rating is given based on the percentage of detached squares.

[0056] Deep-hole coverage capability test: A specially designed high aspect ratio DTV test board was used. The substrate was FR-4, the board thickness was 2.4 mm, the hole diameter was 0.15 mm, and the theoretical aspect ratio was 16:1. The test board first underwent the same hole-forming agent pretreatment process as the backlight test board. Then, it was vertically immersed in the shadowing reagent to be tested, under the same treatment conditions as the backlight test board. After the shadowing treatment was completed and the conductive layer was formed, the test board was immediately transferred to a standard sulfate-based acidic copper plating bath for electroplating. The main electroplating parameters were: solution temperature 25.0℃, current density 2.0 A / dm³. 2 The electroplating time was 60 minutes. After electroplating, the test board was cut open perpendicular to the center axis of the hole using a slow precision cutter. The cut surface was polished and micro-etched to clearly display the copper layer interface. Using a field emission scanning electron microscope at 1000x magnification, the copper plating thickness T at the center of the hole (half the board thickness) was measured. c Copper plating thickness T at the orifice location S The copper thickness ratio TP at the hole center is calculated using the formula: TP(%) = (T c / T S )×100%.

[0057] The sheet resistance uniformity test is conducted on the smooth surface of the same electroplated test board using a four-probe tester at five points: the center of the board and four symmetrical positions 10mm from the edge of the board. The sheet resistance value at each point is recorded, and the percentage difference between the maximum and minimum values ​​is calculated relative to the average value, which serves as the sheet resistance uniformity index.

[0058] The performance test data above are shown in Table 1.

[0059] Table 1 Performance Test Results

[0060]

[0061] The test results in Table 1 above clearly show that, based on the comparative analysis of the performance test results of Examples 1-3 and Comparative Examples 1-3, the nano-graphite shadow reagent prepared by this invention systematically solves the three core problems that have long plagued the industry compared with the prior art.

[0062] Firstly, Examples 1-3 demonstrated revolutionary performance in addressing the issues of poor colloidal dispersion stability and short bath life: their initial Zeta potential absolute values ​​were all below -55mV, the sedimentation ratio after 30 days of static settling was over 98.8%, and they remained homogeneous even after 7 days of accelerated aging at 60℃. This is significantly superior to Comparative Example 1 (sedimentation ratio of only 72.3%, severe agglomeration) without any modifier and Comparative Example 2 (with soft sedimentation at the bottom) with only core-shell particles added. This fully demonstrates that the present invention, through the synergistic effect of cerium-doped yttrium molybdate complexed nanocages and sulfonic acid-functionalized silica-coated barium zirconate core-shell particles, constructs a dual stabilization mechanism with both strong electrostatic repulsion and three-dimensional spatial steric hindrance, fundamentally inhibiting the aggregation and sedimentation of nanographite, achieving long-term stability of the colloidal system, and solving the problems of frequent maintenance, performance fluctuations, and increased costs caused by insufficient stability in existing technologies.

[0063] Secondly, the present invention demonstrates significant advantages in overcoming the challenges of weak adhesion and poor reliability between the conductive layer and the pore wall: the adhesion test results of Examples 1-3 were all at the optimal level of 0 using the cross-cut adhesion test, and the conductive layer on the pore wall showed no abnormalities or only slight discoloration after three thermal stress shocks at 288°C. In contrast, Comparative Example 1 showed large-area peeling, Comparative Example 2 showed local microcracks, and Comparative Example 3 showed multiple blistering. This clearly shows that the unique cerium-doped yttrium molybdate complex nanocage in the present invention plays a crucial "molecular bridge" role. The active sites on its surface can form strong coordination bonds or strong hydrogen bonds with the polymer substrate of the pore wall, thereby strongly anchoring the conductive layer to the pore wall, greatly improving the mechanical reliability and thermal shock resistance of the metallized pores, and overcoming the defects of existing technologies that are prone to peeling in subsequent processes due to weak physical adsorption.

[0064] Finally, in addressing the challenges of uneven coverage and poor electroplating effects in high aspect ratio micropores, this invention demonstrates excellent process adaptability: the copper thickness (TP) at the center of the holes in Examples 1-3 reaches 89-92%, and the uniformity of surface sheet resistance after electroplating is within ±5.0%. In contrast, the TP value of Comparative Example 1 is only 45%, with extremely poor uniformity; while Comparative Examples 2 and 3 show improvement, they are still far inferior to the examples. This directly verifies that the three-dimensional inorganic network structure synergistically constructed by the two modified compounds not only ensures good permeability and flowability of nano-graphite colloids within complex deep pores, but also promotes uniform adsorption and deposition of the conductive layer in various parts of the pores, thereby providing an ideal substrate with uniform thickness and consistent conductivity for subsequent electroplating. Ultimately, this achieves high-quality metallization of high aspect ratio interconnects, filling the performance gaps of existing technologies in this field.

[0065] In summary, this invention, through innovative material design and composite mechanism, not only solves the key bottlenecks of existing nano-graphite shadow technology one by one, but also achieves a leap in overall performance through the synergistic effect of components, providing a brand-new solution for high-reliability and high-efficiency hole metallization of flexible circuit boards.

Claims

1. A method for preparing a nano-graphite shadowing agent for FPC, characterized in that the steps include... include: S1. By weight, mix 40-60 parts of deionized water, 5-15 parts of propylene glycol methyl ether, 0.5-2.0 parts of polyethylene glycol octylphenyl ether and 1-5 parts of sulfonic acid-functionalized silica-coated barium zirconate core-shell particles, stir, and obtain a premixed solution. Under nitrogen protection and stirring, 20-35 parts of nano-graphite powder were added to the premix, and stirring was continued to obtain a mixture. S2. Transfer the mixture to a three-necked flask. At 38-42°C, add dropwise an aqueous suspension containing 0.5-3 parts of cerium-doped yttrium molybdate complexed nanocages. After the addition is complete, add 1-3 parts of 2-amino-2-methyl-1-propanol to adjust the pH to 9.5-10.

5. Raise the temperature to 58-62°C and continue stirring the reaction. After the reaction is complete, allow it to cool naturally to room temperature to obtain a colloidal product. Sieve the colloidal product and sonicate it. The preparation method of the cerium-doped yttrium molybdate complex nanocage includes: A1. By weight, dissolve 90-110 parts of yttrium nitrate hexahydrate and 5-15 parts of cerium nitrate hexahydrate in 800-1200 parts of deionized water. Under nitrogen protection, add 30-70 parts of sodium citrate and stir at 84-86°C to obtain a precursor complex solution. Add an aqueous solution containing 60-100 parts of ammonium molybdate dropwise to the precursor complex solution to obtain a mixture. Transfer the mixture to a hydrothermal reactor and react at 195-205°C to obtain a reaction mixture. A2. Allow the reaction mixture to cool naturally to room temperature, centrifuge to collect the precipitate, wash the precipitate alternately with ethanol and deionized water, and finally dry it in a vacuum drying oven at 115-125℃ and grind it. The preparation method of the sulfonate-functionalized silica-coated barium zirconate core-shell nanoparticles includes: B1. By weight, dissolve 70-90 parts of zirconium oxychloride octahydrate and 50-70 parts of barium chloride in hydrochloric acid aqueous solution. Under stirring, add ammonia aqueous solution and 80-120 parts of ammonium carbonate solution dropwise to adjust the pH to 9-10 to obtain a reaction mixture. Aging and filtering the reaction mixture yields a precipitate. Wash the precipitate to obtain a washed precipitate. Calcine the washed precipitate at 795-805℃ to obtain single-phase nano-barium zirconate. Disperse the single-phase nano-barium zirconate in a mixed solvent of anhydrous ethanol and deionized water. Add 20-50 parts of tetraethyl orthosilicate and 5-15 parts of 3-mercaptopropyltrimethoxysilane sequentially, and add ammonia. React at 48-52℃ to obtain a reaction solution. B2. Centrifuge the reaction solution to collect the solid product. Wash the solid product and redisperse it in 100-600 parts of hydrogen peroxide aqueous solution. React at room temperature to obtain a reaction mixture. Centrifuge, wash and freeze dry the reaction mixture.

2. The method for preparing the nano-graphite shadowing reagent for FPC according to claim 1, characterized in that, In step S1, the average particle size D50 of the nano-graphite powder is 450 nm.

3. The method for preparing the nano-graphite shadowing agent for FPC according to claim 1, characterized in that, In step S2, the stirring reaction continues for 4-6 hours.

4. The method for preparing the nano-graphite shadowing reagent for FPC according to claim 1, characterized in that, In step A1, the reaction time is 48-50 h at 195-205℃.

5. The method for preparing the nano-graphite shadowing agent for FPC according to claim 1, characterized in that, In step A2, the drying time in a vacuum drying oven at 115-125℃ is 12-14 hours.

6. The method for preparing the nano-graphite shadowing agent for FPC according to claim 1, characterized in that, In step B1, the reaction time is 24-30 hours at 48-52°C.

7. The method for preparing the nano-graphite shadowing agent for FPC according to claim 1, characterized in that, In step B2, the reaction time at room temperature is 12-14 hours; the mass fraction of the hydrogen peroxide aqueous solution is 28-32%.

8. A nano-graphite shadowing agent for FPC, characterized in that, The nano-graphite shading reagent for FPC is prepared according to any one of claims 1-7.

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