An epoxy resin composition for multilayer PCB manufacturing and a method of preparing the same

Abstract

The application relates to the technical field of epoxy resin adhesive material preparation, and provides an epoxy resin composition for multilayer PCB manufacturing and a preparation method thereof. In the application, a complex solvent is used in sections, epoxy resin is first made into uniform resin liquid, nitrile rubber is added, and glue liquid state is adjusted to obtain base glue liquid; then part of the base glue liquid is taken as filler carrier liquid, a coupling agent, inorganic flame-retardant filler and organic phosphorus flame retardant are sequentially wetted and dispersed, and are combined with the remaining base glue liquid; then a curing agent is pre-dispersed in the remaining solvent, the flame-retardant glue liquid, an antioxidant and an ion capturing agent are sequentially added; finally, the composition is obtained through homogenization, standing and defoaming. Through the sectional feeding and pre-dispersion of the filler and the curing agent, the method reduces agglomeration, local thickening and bubble entrainment in the high-viscosity system, makes the components uniformly distributed, reduces particle, viscosity and flow fluctuation in the storage and coating process, and improves the processing stability of the interlayer bonding material of the multilayer PCB.

Description

Technical Field

[0001] This disclosure relates to the field of epoxy resin adhesive material preparation technology, and more specifically, to an epoxy resin composition for multilayer PCB manufacturing and its preparation method. Background Technology

[0002] Epoxy resin compositions for multilayer PCB manufacturing are polymeric materials that form interlayer bonding media after coating, drying, and thermosetting. They primarily serve to bond and fill gaps between the core board, copper foil, and insulating layers. As the number of layers and circuit density of multilayer PCBs increase, the uniformity and stability of the adhesive during preparation and storage affect subsequent coating thickness, lamination flow, and the interlayer structure after curing. Therefore, the state of the adhesive is fundamental to the processing reliability of this type of material.

[0003] Related technologies typically use methods such as mechanical stirring, high-speed shearing, cyclic dispersion, or grinding to prepare workable adhesives from raw materials with different physical states and surface properties. As the raw materials gradually enter the system, the viscosity and rheological state of the adhesive continuously change, and the transmission of mechanical forces within the adhesive can easily vary. Increasing shear strength or extending processing time to reduce local aggregation may cause local temperature rises, gas entrainment, and changes in the volatile state, resulting in fluctuations in the adhesive's state over processing time and between production batches.

[0004] Therefore, in the preparation process of existing epoxy resin compositions for multilayer PCBs, there is still a problem that the raw materials are difficult to maintain a uniform distribution under high viscosity conditions. This will cause local particles, viscosity changes and inconsistent flow states in the adhesive during storage and subsequent processing, which will affect the processing stability of the material and the quality of interlayer bonding.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure. Summary of the Invention

[0006] The main purpose of this application is to solve the technical problem of insufficient uniformity of the adhesive solution in the preparation process of existing epoxy resin compositions for multilayer PCBs.

[0007] To achieve this objective, the present application adopts the following technical solution: A method for preparing an epoxy resin composition for multilayer PCB manufacturing, comprising: S1. The compound solvent is divided into a first solvent part and a second solvent part. Epoxy resin is added to the first solvent part in batches to obtain an epoxy resin liquid. Nitrile rubber is added to the epoxy resin liquid in batches, and a portion of the second solvent part is added to obtain a nitrile rubber adhesive liquid. S2. Take a portion of the nitrile rubber liquid as the filler carrier liquid, disperse the coupling agent in the filler carrier liquid, and then add inorganic flame retardant filler and organic phosphorus flame retardant in sequence to obtain flame retardant filler slurry. Combine the flame retardant filler slurry with the remaining nitrile rubber liquid and homogenize to obtain flame retardant liquid. S3. Disperse the curing agent in the remaining second solvent to obtain a curing agent dispersion. Add the curing agent dispersion, antioxidant and ion scavenger to the flame retardant adhesive in sequence to obtain an epoxy resin adhesive. S4. The epoxy resin solution is allowed to stand to degas and then stirred to homogenize, thereby obtaining an epoxy resin composition.

[0008] This application also discloses an epoxy resin composition for the manufacture of multilayer PCBs, comprising epoxy resin, nitrile rubber, inorganic flame retardant filler, organophosphorus flame retardant, curing agent, antioxidant, ion scavenger, coupling agent and compound solvent. Based on 100 parts of epoxy resin, the composition includes 50-90 parts of nitrile rubber, 28-42 parts of inorganic flame retardant filler, 18-32 parts of organophosphorus flame retardant, 5-14 parts of curing agent, 0.5-3 parts of antioxidant, 0.5-4 parts of ion scavenger, 2-5 parts of coupling agent, and 310-400 parts of compound solvent.

[0009] Compared with the prior art, this application has the following beneficial effects: This application first disperses epoxy resin in a compound solvent, then adds nitrile rubber and adjusts the concentration of the adhesive solution to form a relatively uniform base adhesive solution, reducing local thickening caused by insufficient rubber dispersion. Next, a portion of the nitrile rubber adhesive solution is used as a filler carrier liquid. A coupling agent, inorganic flame-retardant filler, and organophosphorus flame retardant are added sequentially to a smaller volume of the adhesive solution, allowing the powder to gradually complete wetting and dispersion, reducing the likelihood of agglomeration and local enrichment when the powder enters the full volume of high-viscosity adhesive solution at once. After the flame-retardant filler slurry is combined and homogenized with the remaining nitrile rubber adhesive solution, the difference in filler concentration at different locations in the adhesive solution is reduced. The curing agent is first dispersed in the remaining solvent before being added to the flame retardant adhesive. This reduces the clumping and uneven distribution of curing agent particles when directly added to the high-viscosity adhesive. The antioxidant and ion scavenger are added after the adhesive is homogenized, which also helps them to be evenly distributed in the system. Through homogenization, filtration, settling and vacuum degassing, larger particles and air bubbles entrained during mixing are removed, reducing local concentration differences, viscosity fluctuations and residual air bubbles in the adhesive.

[0010] In summary, the epoxy resin composition prepared in this application has a more uniform material distribution and a more stable liquid state, which can reduce local particles, inconsistent flow, and batch fluctuations during storage and coating. Attached Figure Description

[0011] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic flowchart of a method for preparing an epoxy resin composition for multilayer PCB manufacturing according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the flame-retardant filler slurry preparation steps in a method for preparing an epoxy resin composition for multilayer PCB manufacturing according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the curing agent dispersion preparation steps in a method for preparing an epoxy resin composition for multilayer PCB manufacturing according to an embodiment of the present invention. Figure 4 This is a Fourier transform infrared spectrum of an epoxy film prepared in one embodiment of this application. Detailed Implementation

[0012] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0013] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0014] The block diagrams shown in the attached figures are merely functional entities and do not necessarily correspond to physically independent entities.

[0015] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0016] Unless otherwise specified, the preparation methods and materials used in the following examples are conventional methods; unless otherwise specified, the parts of the materials used in the following examples are calculated by mass, and all materials used are new materials purchased from the market.

[0017] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] refer to Figure 1-3 This application provides a method for preparing an epoxy resin composition for multilayer PCB manufacturing, comprising: S1. The compound solvent is divided into a first solvent part and a second solvent part. Epoxy resin is added to the first solvent part in batches to obtain an epoxy resin liquid. Nitrile rubber is added to the epoxy resin liquid in batches, and a portion of the second solvent part is added to obtain a nitrile rubber adhesive liquid. In step S1, the actual amounts of epoxy resin, nitrile rubber, and compounding solvent are calculated based on the batch mass of the epoxy resin composition to be prepared. Before feeding, the mixing equipment is cleaned and dried to ensure that the inner wall of the mixing vessel, the stirring paddle, the scraping mechanism, the feeding port, and the bottom discharge port are free of residues, cleaning fluid, or visible moisture from the previous batch. Preferably, the mixing equipment is a closed mixing vessel equipped with a temperature regulating jacket, a low-speed stirring mechanism, and a scraping mechanism. This ensures that material circulation is maintained at all locations as the viscosity gradually increases, and reduces the loss of volatile solvents during feeding and stirring. After the equipment inspection is completed, the compounded solvent is divided into a first solvent portion and a second solvent portion according to the predetermined usage order. For example, 80% of the total mass of the compounded solvent can be taken as the first solvent portion and the remaining 20% ​​as the second solvent portion. The first solvent portion is mainly used for the initial dissolution and dispersion of epoxy resin and nitrile rubber. The second solvent portion is used to adjust the flow state of the nitrile rubber solution and to prepare the curing agent dispersion for subsequent use. This avoids excessive dilution of the initial system, which would reduce the wetting ability of the subsequent fillers, and also avoids the difficulty in forming an overall circulation due to the high viscosity of the solution after the addition of nitrile rubber.

[0019] After adding the first solvent portion to the mixing vessel, close the feed port and activate the jacket temperature control to stabilize the solvent temperature at approximately 28°C. Simultaneously, stir at approximately 120 rpm for 5 minutes to ensure uniform mixing of different solvent types within the vessel and to achieve a relatively consistent temperature between the vessel body, the agitator, and the solvent. Once the solvent temperature has stabilized, begin adding the epoxy resin. The epoxy resin is pre-divided into three batches, with each batch added in increasing or approximately equal amounts. When adding the first batch of epoxy resin, adjust the stirring speed to approximately 150 rpm and allow the epoxy resin to slowly enter the solvent along the material circulation direction within the mixing vessel. Control the addition time for each batch to 5–10 minutes to prevent a large amount of resin from accumulating below the feed port and forming high-viscosity clumps. After all the resin from the first batch has been added, increase the stirring speed to approximately 200 rpm and continue stirring for 20 minutes. During this process, use the wall scraper to carry the resin adhering to the vessel wall and the back of the agitator back to the bulk liquid phase. Once no obvious resin clumps remain on the liquid surface and the material in the reactor can form a continuous circulation, add the second batch of epoxy resin. After adding the second batch, continue stirring at approximately 200 rpm for 20 minutes. Then add the third batch of epoxy resin, and continue stirring for 30 minutes after the third batch is added. After all the epoxy resin has been added, continue stirring at approximately 28°C for 40 minutes to ensure that the epoxy resin added at different times is in full contact with the first solvent and to make the resin concentration in the upper, middle, and bottom parts of the reactor more uniform.

[0020] After the preset stirring time, take small samples from the upper and near-bottom positions of the vessel and observe them on a transparent glass plate. When the color, transparency, and flow state of the two samples are basically the same, and there are no visible resin particles, gel lumps, or areas with significant localized stringing, the epoxy resin solution can be considered to have formed. If the bottom sample is significantly thicker, or if there is still unwetted resin in the upper sample, continue stirring at approximately 200 rpm for 10–20 minutes, rather than shortening the time by suddenly increasing the stirring speed, to avoid temperature rise and solvent evaporation due to localized high-speed shear. After the epoxy resin solution reaches a homogeneous state, pre-divide the nitrile rubber into three batches and add them one batch at a time while maintaining slow overall circulation of the resin solution. When adding the first batch of nitrile rubber, reduce the stirring speed to approximately 100 rpm and evenly spread the nitrile rubber on the surface of the epoxy resin solution, allowing it to be wetted by the resin and solvent first, rather than sinking directly to the bottom of the vessel to form lumps. After adding the first batch, stir at low speed for about 3 minutes, then stop stirring and let it stand in a sealed container for about 20 minutes to allow the solvent to gradually penetrate into the nitrile rubber, reducing the possibility of surface swelling while the interior remains dry during subsequent stirring.

[0021] After the first batch of nitrile rubber has completed its static wetting process, the rotation speed is increased to approximately 300 rpm and stirring is performed for 35 minutes. This allows the nitrile rubber, which has absorbed some solvent, to gradually depolymerize and distribute itself in the epoxy resin solution. Once no obvious floating lumps remain on the surface, the second batch of nitrile rubber is added in the same manner, and the process of low-speed wetting, closed static standing, and medium-speed dispersion is repeated sequentially. The third batch of nitrile rubber is then added, and the above process is repeated. After all the nitrile rubber has been added, the jacket temperature is adjusted to approximately 35°C, and stirring continues at approximately 300 rpm for 80 minutes to ensure that the nitrile rubber and epoxy resin solution form a uniform and continuous gel phase. During this stage, as the nitrile rubber gradually swells and disperses, the viscosity of the solution will increase significantly. Therefore, it is necessary to observe the operating current and torque of the stirring equipment, as well as the material circulation status within the vessel. If a thick layer of adhesive is found adhering to the vessel wall, the scraping mechanism should be activated to carry the adhesive back to the main gel solution, rather than simply increasing the rotation speed. If a deep vortex is found forming in the center of the solution, the rotation speed should be appropriately reduced to prevent air from being continuously drawn into the solution.

[0022] After the nitrile rubber is dispersed, approximately 40% of the solvent by mass is taken from the second solvent portion to adjust the current state of the adhesive solution. This portion of solvent is slowly added along the vessel wall over approximately 10 minutes, while the stirring speed is adjusted to approximately 150 rpm, allowing the solvent to immediately diffuse with the main flow upon entering the adhesive solution and preventing the formation of a low-viscosity solvent layer in certain areas. After all the solvent has been added, the stirring speed is adjusted to approximately 200 rpm and stirring continues for 20 minutes, thereby ensuring that the added solvent is evenly distributed in the upper, middle, and bottom parts of the adhesive solution. After this stage, samples can be taken from different heights to observe their flow state. When the flow velocity of samples at all locations is basically consistent at the same tilt angle, and there are no undispersed nitrile rubber particles in the glass plate coated sample, the nitrile rubber adhesive solution is obtained.

[0023] S2. Take a portion of the nitrile rubber liquid as the filler carrier liquid, disperse the coupling agent in the filler carrier liquid, and then add inorganic flame retardant filler and organic phosphorus flame retardant in sequence to obtain flame retardant filler slurry. Combine the flame retardant filler slurry with the remaining nitrile rubber liquid and homogenize to obtain flame retardant liquid. In step S2, the overall homogeneity of the nitrile rubber solution obtained in step S1 is confirmed. If there is no obvious stratification, sedimentation, or undispersed lumps, a portion of it is taken as the filler carrier liquid. In this embodiment, approximately 30% of the total mass of the nitrile rubber solution can be taken as the filler carrier liquid. The taken-out solution is transferred to a sealed dispersion container equipped with stirring, scraping, and shearing dispersion functions, while the remaining nitrile rubber solution remains in the original mixing vessel. To prevent localized concentration differences from forming in the remaining solution during filler slurry preparation, the original mixing vessel can be intermittently stirred at a low speed of approximately 60 rpm, for example, stirring at a low speed for 3-5 minutes after every 15 minutes of settling. This maintains the solution in a basically homogeneous state while avoiding excessive air entrainment caused by prolonged stirring. The purpose of separating the filler carrier liquid is not to reduce the resin or rubber content in the final adhesive, but to allow the inorganic flame retardant filler and organophosphorus flame retardant to be wetted and dispersed in a smaller volume of adhesive first, and then combined with the remaining adhesive after a uniform flame retardant filler slurry is formed. This avoids the formation of localized agglomerates that are difficult to eliminate when the powder directly enters the full volume of high-viscosity adhesive.

[0024] Before feeding the powder, quality control can be implemented for the inorganic flame-retardant filler. Specifically, the inorganic flame-retardant filler to be used is placed in a clean, dry shallow dish to maintain a uniform powder layer thickness, and dried at approximately 105°C for 3 hours. After drying, the high-temperature powder is not directly exposed to the production environment for cooling. Instead, it is cooled in a closed or dry environment, and transferred to a closed transfer container after the powder temperature drops below 30°C, thereby reducing the possibility of reabsorbing environmental moisture during the cooling process. For filler batches with a high risk of soluble ion release, a separate sample from the same batch can be taken for water extraction testing. The powder is mixed with deionized water at a preset mass ratio, and after shaking or stirring, the conductivity of the extract and the content of migratable ions such as chloride and sodium ions are tested. The test results are used as the basis for determining whether the powder can be used in production.

[0025] After adjusting the temperature of the separated filler carrier liquid to approximately 28°C, stir at approximately 120 rpm for 5 minutes to restore continuous flow of the liquid. Then, begin adding the coupling agent. The coupling agent should be added slowly, dropwise or in a thin stream, over approximately 5 minutes, and placed at a location where the liquid can circulate, preventing it from adhering to the top of the container or accumulating at the bottom. After the coupling agent is added, increase the stirring speed to approximately 200 rpm and continue stirring for 20 minutes, while simultaneously activating the wall scraping mechanism to ensure uniform distribution of the coupling agent in the carrier liquid. Only after the coupling agent has been thoroughly mixed with the carrier liquid should the inorganic flame-retardant filler be added. This ensures that the surface of the powder entering the system can immediately contact the liquid containing the coupling agent, reducing the likelihood of powder surfaces sticking together due to insufficient wetting.

[0026] The inorganic flame-retardant filler was pre-divided into five batches, each with essentially the same quality. When adding the first batch of inorganic flame-retardant filler, the stirring speed was adjusted to approximately 150 rpm, and the powder was evenly sprinkled in from near the liquid surface. The feeding time for each batch was controlled to be 5–8 minutes to reduce the possibility of powder falling from a height into the adhesive and being entrained by air or forming dust. After adding the first batch of powder, low-speed stirring continued for about 3 minutes to allow the adhesive to initially adhere to the powder surface. Then, high-intensity mixing was stopped, and the mixture was sealed and allowed to stand for about 10 minutes to allow the adhesive to gradually penetrate between the powder agglomerates. After standing, the mixture was stirred at approximately 250 rpm for 20 minutes to allow the wetted powder to form a complete circulation within the container. Then, it was sheared and dispersed at approximately 700 rpm for 20 minutes to further deagglomerate the powder agglomerates in the carrier liquid. After the first batch of powder was dispersed, the liquid surface, container walls, and bottom were observed for the presence of a dry powder layer, white powder rings, or hard deposits. The second batch of inorganic flame-retardant filler was added only after these phenomena had largely disappeared.

[0027] The second to fifth batches of inorganic flame-retardant fillers were processed in the following sequence: slow feeding, low-speed wetting, short-time settling, medium-speed circulation, and shear dispersion. Before adding each batch of powder, it was confirmed that the previous batch had been coated with the adhesive. If the previous batch of powder was not fully dispersed before adding more powder, the newly added powder could easily coat the existing agglomerates, forming composite particles with a wet outer layer and dry powder inside. Therefore, sufficient dispersion time should be allowed between batches. After all the inorganic flame-retardant fillers were added, dispersion continued at approximately 600 rpm for 40 minutes, and the slurry temperature was maintained below 35°C using jacket cooling. If the temperature continued to rise during dispersion, the jacket temperature should be reduced or shearing should be paused, rather than continuing to increase the rotation speed. When the inorganic flame-retardant filler slurry reaches the qualified state, it should exhibit a uniform color, no continuous floating powder on the surface, and no obvious coarse particle trails after the slurry is scraped into a thin layer.

[0028] The organophosphorus flame retardant was then divided into three batches and added sequentially after the inorganic flame retardant filler had been dispersed. When adding the first batch of organophosphorus flame retardant, the stirring speed was reduced to approximately 150 rpm, and the addition was completed slowly over approximately 5 minutes. After addition, the mixture was stirred at approximately 200 rpm for 15 minutes to ensure the organophosphorus flame retardant was fully coated by the existing slurry. Then, it was sheared and dispersed at approximately 600 rpm for 20 minutes. The second and third batches were added in the same manner. After all batches were added, they were dispersed at approximately 500 rpm for 40 minutes to ensure a uniformly distributed flame retardant slurry consisting of the inorganic flame retardant filler, organophosphorus flame retardant, coupling agent, and filler carrier. Because the organophosphorus flame retardant was added after the initial dispersion of the inorganic flame retardant filler, it could penetrate between the inorganic filler particles and was less likely to form aggregates with the unwetted inorganic filler. This also reduced the possibility of both powders entering the slurry at once, causing excessively high instantaneous viscosity.

[0029] After the flame-retardant filler slurry is prepared, the remaining nitrile rubber solution in the original mixing vessel is adjusted to approximately 28°C and stirred at approximately 150 rpm. The flame-retardant filler slurry is then added to the remaining nitrile rubber solution in three batches. For the first addition, approximately one-third of the total mass of the flame-retardant filler slurry is added, with a transfer time of 10 minutes, allowing the high-solids slurry to slowly enter the main solution along the vessel wall. After addition, stirring continues for 15 minutes, and the wall-scraping mechanism is activated to diffuse the flame-retardant filler slurry from the localized high-concentration area into the main solution. The second batch is added only after the solution no longer shows obvious color streaks. The second batch is mixed thoroughly before the third batch is added. After all the flame-retardant filler slurry has been added, the stirring speed is adjusted to approximately 250 rpm and continuous homogenization is performed for 60 minutes. During homogenization, the wall-scraping mechanism is used periodically to bring the high-viscosity solution near the vessel wall and bottom back to the main circulation area. After homogenization, samples are taken from the top, middle and bottom of the mixing vessel, and the samples are scraped onto the surface of a glass plate under the same conditions. When the color, flow state and particle distribution of the three samples are basically the same, and there are no continuous white spots, coarse particle streaks or local powder enrichment areas in the thin layer, the flame retardant adhesive is obtained.

[0030] S3. Disperse the curing agent in the remaining second solvent to obtain a curing agent dispersion. Add the curing agent dispersion, antioxidant and ion scavenger to the flame retardant adhesive in sequence to obtain an epoxy resin adhesive. In step S3, the unused second solvent portion from step S1 is transferred to a separate, sealed dispersion container, and the solvent temperature is adjusted to approximately 22°C. The curing agent is not directly added in powder form to the high-viscosity flame-retardant adhesive obtained in step S2. Instead, a curing agent dispersion is first prepared using the remaining second solvent portion. This ensures that the curing agent particles are sufficiently wetted and have a relatively uniform initial distribution before entering the main adhesive solution. This reduces the possibility of the curing agent rapidly wetting its surface while remaining dry powder internally in the high-viscosity adhesive solution, and prevents the curing agent from concentrating and adhering to the surface of the flame-retardant filler agglomerates. After adding the remaining second solvent portion to the dispersion container, it is pre-stirred at approximately 100 rpm for 5 minutes to ensure uniform solvent temperature and composition at all locations within the container. Then, the curing agent is pre-divided into three batches and added to the solvent sequentially.

[0031] When adding the first batch of curing agent, maintain a low stirring speed of approximately 100 rpm and slowly add the material over 3-5 minutes, allowing the curing agent to gradually enter the liquid phase along with the solvent circulation. After the first batch is added, increase the stirring speed to approximately 150 rpm and stir for 15 minutes. Add the second batch of curing agent only after there is no obvious dry powder on the liquid surface and container walls. Add the second and third batches of curing agent in the same manner, adding each batch only after the previous batch has been largely wetted and dispersed. After all three batches of curing agent have been added, adjust the stirring speed to approximately 180 rpm and continue stirring for 30 minutes, allowing any sediment that may have formed at the bottom of the container to gradually re-enter the bulk liquid phase. When the curing agent also contains a small amount of curing accelerator, a small amount of the already formed curing agent dispersion can be used to wet the curing accelerator into a flowing slurry before adding it to the dispersion container. Use a small amount of dispersion to rinse the feeding equipment, ensuring that any curing accelerator adhering to the equipment enters the system, reducing batch deviations caused by small amounts of material adhering to the equipment.

[0032] After adding the curing accelerator, continue stirring at approximately 180 rpm for 40 minutes, maintaining the dispersion temperature below 25°C. The goal at this stage is not complete transparency of the dispersion, but rather for the curing agent to form a stable and easily redispersible suspension or dispersion in the solvent. Specifically, after stopping stirring, allow it to stand for 5–10 minutes, then restart stirring at a low speed. If the bottom sediment can quickly re-enter the bulk liquid phase, and there are no large visible particles or hard lumps in the dispersion, the curing agent dispersion is considered complete. If a solid layer that is difficult to redisperse exists at the bottom of the container, continue stirring at approximately 180 rpm for 10–20 minutes, and check whether the curing agent has formed clumps containing dry powder due to excessively rapid addition. Throughout the preparation and waiting period for adding the curing agent dispersion, keep the container sealed to reduce solvent evaporation and the entry of moisture from the air into the dispersion.

[0033] After the curing agent dispersion is prepared, the temperature of the flame-retardant adhesive obtained in step S2 is adjusted to approximately 28°C, and stirred at approximately 150 rpm to maintain overall circulation. Then, the curing agent dispersion is divided into three portions and added sequentially to the flame-retardant adhesive. When adding the first portion, the dispersion is allowed to flow slowly along the inner wall of the mixing vessel, with each addition taking approximately 8 minutes, avoiding direct pouring into the center of the stirring shaft or a static area on the liquid surface. After the first portion is added, it is stirred at approximately 180 rpm for 25 minutes, while simultaneously activating the wall scraping mechanism to prevent localized enrichment of the curing agent dispersion on the vessel wall, the back of the impeller, or the bottom of the vessel. Once the color and flow state of the adhesive surface return to uniformity, the second portion is added, and the above stirring process is repeated, followed by the third portion. After the third portion of the curing agent dispersion is added, it is first stirred at approximately 180 rpm for 25 minutes, then the stirring speed is adjusted to approximately 250 rpm and homogenization continues for 50 minutes, allowing the curing agent to diffuse from the initial addition point into the entire flame-retardant adhesive.

[0034] During the mixing of the curing agent dispersion and the flame-retardant adhesive, the adhesive temperature and equipment operating load need to be continuously monitored. Since the curing agent and curing accelerator components have already entered the epoxy resin system, excessively high local temperatures may reduce the storage stability of the adhesive. Therefore, a jacket can be used to maintain the adhesive temperature below 30°C. When the temperature continues to rise, it should be adjusted by lowering the jacket medium temperature, rather than opening the kettle lid for heat dissipation, to avoid solvent evaporation causing changes in the solid content and viscosity of the adhesive. After the curing agent dispersion is complete, the antioxidant is added. The antioxidant can be pre-divided into two parts. The first part is added slowly at approximately 150 rpm, stirred for 20 minutes, and the material adhering to the upper part of the kettle wall is carried back into the adhesive using a scraper. The second part is then added, and stirring continues for another 20 minutes. Adding the antioxidant after the flame-retardant adhesive and curing agent have become basically homogeneous avoids localized encapsulation during the large-scale powder feeding stage and allows for a more uniform distribution within the continuous phase formed by the epoxy resin and nitrile rubber.

[0035] After the antioxidant is added, the ion scavenger is pre-divided into two portions and added to the adhesive solution sequentially. When adding the first portion of ion scavenger, maintain a stirring speed of approximately 150 rpm, allowing the ion scavenger to slowly enter the system from near the surface of the adhesive solution. Stir for 20 minutes after addition, then add the second portion and continue stirring for another 20 minutes. The addition of the ion scavenger should be carried out under closed or small-opening conditions to avoid prolonged exposure to humid air. After all the ion scavenger has been added, adjust the stirring speed to approximately 250 rpm and continue stirring for 40 minutes, while maintaining a stable temperature in the adhesive solution. The curing agent, antioxidant, and ion scavenger are added sequentially, rather than pre-mixed into a composite powder and added all at once. This is because the usage, particle state, and function of the three materials differ. If added simultaneously, smaller amounts of antioxidant and ion scavenger may adhere to curing agent clumps or the surface of flame-retardant fillers, resulting in uneven distribution.

[0036] After stirring, samples of the epoxy resin were taken from the top, middle, and near the bottom of the mixing vessel, and each sample was coated onto a glass plate with the same thickness for observation. When the color and flowability of the samples at each location were basically consistent, no visible curing agent particles, antioxidant white spots, or ion scavenger agglomerates were found in the coated thin layer, and the equipment torque remained stable during continuous operation, it could be considered that the components were uniformly distributed, thus obtaining the epoxy resin adhesive.

[0037] S4. The epoxy resin solution is allowed to stand to degas and then stirred to homogenize, thereby obtaining an epoxy resin composition.

[0038] In step S4, the epoxy resin solution is kept in a sealed mixing vessel, and the temperature of the solution is stabilized at approximately 25°C using a jacket. Since the curing agent, antioxidant, and ion trapping agent are added later in step S3, although the components have undergone initial dispersion, small localized areas with compositions different from the main solution may still exist on the vessel wall, the back of the agitator, the bottom of the vessel, and near the sampling port. Therefore, a general stirring and homogenization process is required before degassing. Specifically, the wall scraping mechanism is activated first, and then the main stirring speed is gradually increased to approximately 200 rpm, and stirring is performed continuously for 25 minutes. The speed is not increased directly from a stationary state to the set value; instead, it is first run at approximately 80 rpm for 2–3 minutes to allow the solution to begin moving as a whole, then increased to approximately 150 rpm for approximately 2 minutes, and finally adjusted to approximately 200 rpm. This reduces the risk of the high-viscosity solution suddenly being sheared, causing liquid surface turbulence and air entrapment.

[0039] During homogenization, the scraping mechanism continuously carries the adhesive adhering to the inner wall of the mixing vessel, the back of the stirring paddle, and the edge of the vessel bottom back to the main circulation area, allowing the material in these locations to repeatedly exchange with the adhesive in the central area of ​​the vessel. When a slight depression forms on the liquid surface and the adhesive can slowly circulate from the vessel wall to the center, stirring can be continued at approximately 200 rpm. After about 15 minutes of homogenization, a small amount of adhesive can be taken from the sampling port and scraped onto a glass plate for observation. If directional color streaks, local light-colored spots, or densely packed particle areas still exist in the thin layer, the preset homogenization time should be continued.

[0040] After approximately 25 minutes of medium-speed homogenization, the stirring speed is reduced to approximately 80 rpm and continued for 5 minutes. This allows the surface depressions created by medium-speed stirring to gradually recover, and the adhesive adhering to the impeller and scraper to smoothly fall back into the bulk liquid phase. Using a method of first homogenizing at medium speed and then finishing at low speed reduces large-scale flow within the adhesive after the redistribution of components, and creates a more stable initial state for subsequent settling and degassing. After low-speed stirring is completed, stirring is stopped, and the sampling port, feed port, and vent are immediately closed to keep the mixing vessel sealed. The vessel is then allowed to stand at approximately 25°C for 30 minutes. During the settling period, no equipment is moved, and the vessel lid is not repeatedly opened for inspection. Instead, the liquid level changes are observed through the observation window, allowing larger air bubbles entrained during stirring to gradually rise and burst under buoyancy, while simultaneously eliminating localized stress and flow differences caused by shearing.

[0041] The settling time should not be extended indefinitely because the adhesive contains inorganic flame-retardant fillers, organophosphorus flame retardants, and ion scavengers. Prolonged complete stillness may still cause slight sedimentation of solid components with different particle sizes. Therefore, in this embodiment, degassing under reduced pressure is performed directly after 30 minutes of settling, rather than re-stirring at high speed after settling. Before degassing under reduced pressure, it should be ensured that sufficient gas phase space is maintained in the mixing vessel, so that the actual volume of the adhesive does not exceed approximately 70% of the effective volume of the equipment, thereby preventing the adhesive from expanding and entering the vacuum pipeline during vacuuming. The decompression process is carried out in stages. First, the vacuum gauge pressure is slowly reduced to about -0.03 MPa and maintained for 3 minutes. At this time, the main observation is whether the surface of the adhesive expands rapidly and whether the bubble layer rises significantly. After the liquid surface is basically stable, the vacuum gauge pressure is reduced to about -0.06 MPa and maintained for 5 minutes to allow medium-sized bubbles inside the adhesive to continue to escape. Then, the vacuum gauge pressure is stabilized at about -0.08 MPa and maintained for 15 minutes to allow smaller bubbles remaining inside the high-viscosity adhesive to gradually migrate to the surface.

[0042] During degassing under reduced pressure, the jacket temperature is maintained at approximately 25°C, and the main stirring mechanism is not activated to reduce the formation of new gas-liquid interfaces under low pressure. Since the compound solvent contains highly volatile solvents, excessively rapid vacuuming may simultaneously cause foaming of the adhesive and solvent loss; therefore, the vacuum level should be gradually reduced. When the bubble layer rapidly approaches the vessel lid, continue evacuation and maintain the current pressure. After the bubble layer descends, slowly reduce the pressure. When only a small number of bubbles intermittently burst on the adhesive surface, maintain the final vacuum state. If a large number of strings of bubbles continue to appear after reaching the preset vacuum level, the holding time can be appropriately extended, but the adhesive temperature and condensation recovery should be observed simultaneously to avoid significant changes in the solvent composition due to excessively long degassing time. The criteria for determining the end of degassing are: the liquid level is basically stable, no more strings of bubbles appear continuously in the observation window, and the volume of the adhesive no longer changes significantly during the vacuum holding period.

[0043] After degassing, slowly introduce clean, dry gas to gradually restore the mixing vessel to atmospheric pressure within 3-5 minutes, thus preventing sudden airflow from impacting the liquid surface and re-entraining air. After restoring atmospheric pressure, continue to let it stand in a sealed environment for 10 minutes, then take small samples from the upper and lower sampling ports respectively. When the sample is scraped onto the glass plate surface, the adhesive should form a continuous thin layer without dense pinholes, continuous bubbles, or obvious particle streaks. The color, viscosity, and flow state of the upper and lower samples should be basically the same. If a small number of continuously rising microbubbles are still present in the sample, do not re-stir at high speed, but let it stand for another 10 minutes before supplementing with short-term degassing under reduced pressure. After confirming that the adhesive uniformity and degassing state meet the requirements, transfer the adhesive to a clean, dry, and solvent-resistant sealed container using a low-drop method. The outlet should be as close as possible to the inner wall or bottom of the receiving container to allow the adhesive to flow continuously along the container wall, avoiding secondary air entrainment caused by falling from a high position. Immediately after filling, the container is sealed, and the batch number, net weight, and preparation time are recorded to obtain an epoxy resin composition for use in the manufacture of multilayer PCBs.

[0044] Example 1: In this embodiment, approximately 1000.067 g of epoxy resin composition was prepared, comprising: 166.1 g of bisphenol A type epoxy resin, 102.595 g of nitrile rubber, 58.63 g of inorganic flame retardant filler, 43.970 g of organophosphorus flame retardant, 3.127 g of antioxidant, 4.690 g of ion scavenger, 15.63 g of primary curing agent, 1.563 g of curing accelerator, 5.374 g of coupling agent, 576.49 g of N,N-dimethylformamide, and 21.887 g of methyl ethyl ketone (MEK). In the preparation process, N,N-dimethylformamide and methyl ethyl ketone are mixed to form a compound solvent. The compound solvent is then divided into a first solvent portion and a second solvent portion according to the method used in step S1 above. Subsequently, the preparation of epoxy resin liquid, batch wetting and dispersion of nitrile rubber, preparation of flame retardant filler slurry, preparation of curing agent dispersion, and addition of antioxidant and ion scavenger are completed sequentially. Finally, after homogenization and degassing, an epoxy resin composition is obtained. In this embodiment, based on 100 parts by weight of epoxy resin, nitrile rubber is approximately 61.77 parts, inorganic flame retardant filler is approximately 35.30 parts, organophosphorus flame retardant is approximately 26.47 parts, main curing agent and curing accelerator combined are approximately 10.35 parts, antioxidant is approximately 1.88 parts, ion scavenger is approximately 2.82 parts, coupling agent is approximately 3.24 parts, and compound solvent is approximately 360.25 parts.

[0045] Example 2: This embodiment prepares approximately 996.1 g of epoxy resin composition, comprising: 15.6 g of first bisphenol A type epoxy resin, 99.7 g of second bisphenol A type epoxy resin, 45.3 g of dicyclopentadiene phenolic type epoxy resin, 105.7 g of nitrile rubber, 11.0 g of main curing agent, 1.2 g of curing accelerator, 3.2 g of antioxidant, 4.8 g of ion scavenger, 60.2 g of inorganic flame retardant filler, 45.6 g of organophosphorus flame retardant, 5.5 g of coupling agent, 582.5 g of methyl ethyl ketone (MEK), and 15.8 g of N,N-dimethylformamide. During preparation, MEK and N,N-dimethylformamide are first mixed to form a compound solvent. Since MEK constitutes the majority of the compound solvent in this embodiment, the risk of residual high-boiling-point polar solvents can be reduced during subsequent coating and drying processes. Three epoxy resins were added to the first solvent in batches, from low viscosity to high viscosity. Then, nitrile rubber was added to form a nitrile rubber adhesive. Subsequently, coupling agent, inorganic flame-retardant filler, organophosphorus flame retardant, curing agent, antioxidant, and ion scavenger were added sequentially according to steps S2 to S4, followed by homogenization and degassing. In this embodiment, the total mass of epoxy resin was 160.6 g. Based on 100 parts of total epoxy resin mass, approximately 65.82 parts of nitrile rubber, 37.48 parts of inorganic flame-retardant filler, 28.39 parts of organophosphorus flame retardant, approximately 7.60 parts of main curing agent and curing accelerator combined, approximately 1.99 parts of antioxidant, approximately 2.99 parts of ion scavenger, approximately 3.42 parts of coupling agent, and approximately 372.54 parts of compound solvent. This embodiment can be considered a preferred implementation of a low-residual solvent formulation.

[0046] Example 3: This embodiment uses two formulations to prepare epoxy resin compositions for multilayer PCB manufacturing. The first formulation prepares approximately 1068.1g of epoxy resin composition, wherein 195g of bisphenol A epoxy resin, 105g of nitrile rubber, 19g of diaminodiphenyl sulfone, 1.9g of curing accelerator, 60g of aluminum hydroxide, 45g of diethylaluminum hypophosphite, 3.9g of antioxidant, 5.85g of ion scavenger, 5.85g of coupling agent, 600g of methyl ethyl ketone, and 26.6g of N,N-dimethylformamide.

[0047] In the preparation process, methyl ethyl ketone (MEK) and N,N-dimethylformamide (NDM) are first mixed to form a compound solvent, which is then divided into a first solvent portion and a second solvent portion. Bisphenol A type epoxy resin is added to the first solvent portion in batches, and the mixture is stirred to obtain an epoxy resin solution. Nitrile rubber is then added to the epoxy resin solution in batches, along with a portion of the second solvent portion, to obtain a nitrile rubber adhesive. A portion of the nitrile rubber adhesive is then used as a filler carrier liquid, and a coupling agent is dispersed in the filler carrier liquid. Aluminum hydroxide and aluminum diethylphosphite are then added sequentially to obtain a flame-retardant filler slurry. The flame-retardant filler slurry is combined with the remaining nitrile rubber adhesive and homogenized to obtain a flame-retardant adhesive. Diaminodiphenyl sulfone and a curing accelerator are dispersed in the remaining second solvent portion to obtain a curing agent dispersion. The curing agent dispersion is then added to the flame-retardant adhesive, followed by the sequential addition of an antioxidant and an ion scavenger to obtain an epoxy resin adhesive. Finally, the epoxy resin adhesive is stirred and homogenized, filtered, allowed to stand, and degassed under vacuum to obtain an epoxy resin composition.

[0048] In the first formulation of this embodiment, based on 100 parts of bisphenol A epoxy resin, there are approximately 53.85 parts of nitrile rubber, approximately 30.77 parts of aluminum hydroxide, approximately 23.08 parts of diethyl aluminum hypophosphite, approximately 10.72 parts of diaminodiphenyl sulfone and curing accelerator combined, 2 parts of antioxidant, 3 parts of ion scavenger, 3 parts of coupling agent, and approximately 321.33 parts of compound solvent.

[0049] The second formulation prepares approximately 1024.8g of epoxy resin composition, comprising: 40g of bisphenol A type epoxy resin, 120g of dicyclopentadiene phenol type epoxy resin, 140g of nitrile rubber, 13.2g of diaminodiphenyl sulfone, 1.32g of curing accelerator, 52.8g of aluminum hydroxide, 35.2g of diethyl aluminum hypophosphite, 3.2g of antioxidant, 4.8g of ion scavenger, 4.8g of coupling agent, 591g of butanone, and 18.48g of N,N-dimethylformamide.

[0050] In the preparation process, butanone and N,N-dimethylformamide are mixed to form a compound solvent, which is then divided into a first solvent portion and a second solvent portion. Bisphenol A type epoxy resin and dicyclopentadiene phenol type epoxy resin are added to the first solvent portion in batches, and the mixture is stirred to obtain an epoxy resin solution. Nitrile rubber is then added to the epoxy resin solution in batches, and a portion of the second solvent portion is added to obtain a nitrile rubber adhesive solution. Subsequently, a portion of the nitrile rubber adhesive solution is used as a filler carrier liquid, and a coupling agent is dispersed in the filler carrier liquid. Aluminum hydroxide and aluminum diethylphosphite are then added in sequence to obtain a flame-retardant filler slurry. The flame-retardant filler slurry is combined with the remaining nitrile rubber adhesive solution and homogenized to obtain a flame-retardant adhesive solution. Diaminodiphenyl sulfone and a curing accelerator are dispersed in the remaining second solvent to obtain a curing agent dispersion. The curing agent dispersion is then added to a flame retardant adhesive, followed by the addition of an antioxidant and an ion scavenger to obtain an epoxy resin adhesive. Finally, the epoxy resin adhesive is stirred, homogenized, filtered, allowed to stand, and degassed under vacuum to obtain an epoxy resin composition.

[0051] In the second formulation of this embodiment, based on a total mass of 100 parts of bisphenol A epoxy resin and dicyclopentadiene phenolic epoxy resin, 87.5 parts of nitrile rubber, 33 parts of aluminum hydroxide, 22 parts of diethyl aluminum hypophosphite, approximately 9.08 parts of diaminodiphenyl sulfone and curing accelerator, 2 parts of antioxidant, 3 parts of ion scavenger, 3 parts of coupling agent, and approximately 380.93 parts of compound solvent.

[0052] In an optional embodiment, referring to Table 1, comparative examples were selected for performance testing. The raw material composition and dosage of each component in Comparative Example 1 were consistent with those in Example 1, and the raw material composition and dosage of each component in Comparative Example 2 were consistent with those in Example 2, thus ensuring that the differences in comparison mainly stemmed from the preparation process rather than the dosage of the formulation. After preparation, each adhesive solution was stored for 7 days under sealed conditions at 25±1℃. The initial viscosity and the viscosity after storage were measured at 25℃ using the same rotational viscometer, the same rotor, and a rotation speed of 20 rpm. The viscosity change rate was calculated as the percentage difference between the stored viscosity and the initial viscosity relative to the initial viscosity. The difference in solid content between the upper and lower layers was measured by sampling from the top and bottom of the storage container under the same drying conditions. The number of particles larger than 50 μm was determined by microscopic observation and counting of the retained particles after passing 100 g of adhesive solution through a filter medium of the corresponding pore size. When preparing the adhesive film, the adhesive solution was coated onto the same polyimide substrate with the same wet film thickness, and the process was carried out using… The film was dried under the same segmented drying conditions of 80℃ for 10 min, 120℃ for 10 min, and 150℃ for 15 min. The residual solvent in the dried film per unit mass was then determined by gas chromatography. The dried film and copper foil were pressed together at 180℃ and 2.0 MPa for 60 min. After cooling, the film was cut into 25 mm wide samples and a 180° peel test was performed at a test speed of 300 mm / min. At least three parallel samples were tested in each group and the average value was taken. The heat resistance test was performed in a molten tin bath at 290±5℃. Each immersion was for 10 s, followed by 30 s cooling before the next immersion. The number of cycles completed before bubbling, delamination, cracking, or obvious delamination was taken as the test result. The amount of adhesive overflow was measured by making a cross-section of the pressed sample and taking the average value at no less than three locations under a metallographic microscope. The conductivity of the water extract was tested by soaking the cured film and deionized water at a mass ratio of 1:10 at 25℃ for 24 h.

[0053] Comparative Example 1 uses a conventional method where raw materials in different physical states are directly added to the total volume of adhesive solution and mixed by long-term high-speed shearing. In this method, the compounding solvent is added almost all at once, and nitrile rubber, inorganic flame retardant filler, organophosphorus flame retardant, curing agent, and additives are added directly to the same mixing vessel in sequence. The filler carrier liquid is not separated, and the flame retardant filler slurry and curing agent dispersion are not prepared in advance. The shearing time is extended by a high rotation speed. Comparative Example 2, although epoxy resin and nitrile rubber base adhesive solutions are prepared first, inorganic flame retardant filler and organophosphorus flame retardant are directly added to the total volume of high-viscosity adhesive solution. At the same time, the curing agent is added directly in powder form. The pre-drying and ion release screening of the inorganic flame retardant filler are not performed. Only conventional homogenization and degassing are performed at the end. The comparative trends in the table show that Examples 1 and 2, by first forming a uniform epoxy resin-nitrile rubber base solution, then using a portion of the base solution to prepare a flame-retardant filler slurry, and pre-dispersing the curing agent in the remaining solvent, resulted in significantly lower viscosity change rate, upper and lower solid content difference, and large particle count after 7 days of storage compared to the two comparative examples. This indicates that segmented feeding and small-volume pre-dispersion are beneficial in reducing powder agglomeration, local thickening, and storage sedimentation. Example 2 uses a more volatile ketone solvent as the main solvent in the compounding process, therefore its solvent residue in the adhesive film is lower than that in Example 1. Furthermore, the adhesive distribution in both examples is more uniform. The material exhibits uniformity, minimal local flow differences during drying and pressing, high peel strength, low average adhesive overflow, and heat resistance capable of withstanding six 290°C tin dips without significant delamination or delamination. Furthermore, the inorganic flame-retardant filler undergoes moisture and ion release testing, pre-drying, and sealed transfer before being added to a filler carrier liquid containing a coupling agent, followed by the addition of an ion trapping agent. This results in a lower conductivity of the cured adhesive film water extract compared to the untreated comparative example. This demonstrates that this application is beneficial for improving adhesive uniformity and processing stability, and reducing the impact of moisture and migratable ions introduced by the powder on the interlayer insulation and bonding reliability of multilayer PCBs.

[0054] Table 1: In another embodiment, reference Figure 4 The epoxy resin composition obtained in Example 2 was uniformly coated onto a clean polyimide film surface using a scraping method. The compounded solvent was gradually evaporated by staged heating, followed by thermosetting to obtain a continuous epoxy film without visible bubbles or obvious particles. Samples suitable for testing were cut from the obtained epoxy film, and the adhesive layer side of the sample was attached to the surface of a diamond attenuated total reflectance test crystal of a Fourier transform infrared spectrometer. The test was performed at wavenumbers of 4000–500 cm⁻¹. -1 Infrared transmission spectra were collected within the range, and the resulting infrared spectra are as follows: Figure 4 As shown.

[0055] Depend on Figure 4It can be seen that the obtained epoxy film is at 3618.60 cm. -1 3523.92cm -1 3431.37cm -1 and 3369.99cm -1 A stretching vibration absorption band related to hydroxyl and nitrogen-containing groups appears nearby, at 2925.69 cm⁻¹. -1 An absorption peak for aliphatic carbon-hydrogen bond stretching vibrations appears nearby, at 1725.61 cm⁻¹. -1 A carbonyl-related absorption peak appears nearby, at 1605.89 cm⁻¹. -1 and 1508.27cm -1 An absorption peak for aromatic ring skeletal vibrations appears nearby, at 1453.32 cm⁻¹. -1 and 1361.61cm -1 An absorption peak for carbon-hydrogen bond bending vibrations appears nearby, and it reaches 1295.62 cm⁻¹. -1 1236.14cm -1 1181.89cm -1 1147.98cm -1 1106.00cm -1 1072.04cm -1 and 1021.30cm -1 Characteristic absorptions associated with ether bonds, phosphorus-oxygen bonds, and other oxygen-containing groups are observed in the vicinity. The film exhibits absorption at 967.53 cm⁻¹. -1 914.69cm -1 827.55cm -1 803.38cm -1 778.10cm -1 734.14cm -1 665.43cm -1 and 557.72cm -1 There are also multiple fingerprint region absorption peaks nearby. The above absorption peaks correspond to the infrared absorption characteristics of the functional groups contained in epoxy resin, nitrile rubber, organophosphorus flame retardant and curing system, indicating that the components can form a uniform epoxy film after the batch dispersion, merging and homogenization and curing treatment.

[0056] In one embodiment, step S1 includes: S1.1 Take 70% to 95% of the total mass of the compounded solvent as the first solvent portion, and the remainder as the second solvent portion. Adjust the temperature of the first solvent portion to 20 to 35°C. Add the epoxy resin to the first solvent portion in 2 to 5 batches. After each batch is added, stir at 100 to 300 rpm for 10 to 30 minutes. After all the resin has been added, continue stirring for 20 to 60 minutes to obtain the epoxy resin solution. S1.2 Add nitrile rubber to epoxy resin solution in 2 to 4 batches. After each batch is added, let it stand for 10 to 40 minutes, then stir at 150 to 500 rpm for 20 to 50 minutes. After all the nitrile rubber is added, continue stirring at 25 to 45°C for 40 to 120 minutes to obtain a pre-dispersion. S1.3 Add 20% to 60% of the total mass of the second solvent to the pre-dispersion liquid, and stir at 100 to 300 rpm for 10 to 30 minutes to obtain nitrile rubber solution.

[0057] In this embodiment, the compounded solvent is pre-divided into a first solvent portion and a second solvent portion. The first solvent portion is used for wetting and dissolving the epoxy resin and for the initial dispersion of the nitrile rubber. A portion of the second solvent portion is used for viscosity adjustment after the addition of the nitrile rubber, and the remainder is reserved for preparing the curing agent dispersion. By using the compounded solvent in stages, excessive dilution of the base adhesive caused by adding all the solvent at once can be avoided, as well as the curing agent being directly added to the high-viscosity adhesive due to insufficient reserved solvent.

[0058] The epoxy resin can be one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, dicyclopentadiene phenol type epoxy resin, or phenolic type epoxy resin. When using multiple epoxy resins, the epoxy resin with lower viscosity and easier dispersion should be added to the first solvent to form a base resin solution, and then the epoxy resin with higher viscosity or greater structural rigidity should be added to reduce local resin agglomerates. Nitrile rubber can be one or more of carboxyl-based nitrile rubber, hydroxyl-terminated nitrile rubber, or powdered nitrile rubber, and the batch feed rate should be adjusted according to the particle state and swelling rate of the nitrile rubber. For nitrile rubber that easily forms lumps, the batch feed rate should be reduced, and each batch of nitrile rubber should first complete surface wetting and internal liquid absorption before stirring and dispersion.

[0059] The compound solvents include polar solvents and ketone solvents. Polar solvents are used to improve the wetting and dispersion of epoxy resins, nitrile rubber, and curing agents, while ketone solvents are mainly used to adjust the flowability of the adhesive and evaporate during subsequent drying. When the goal is to reduce solvent residue, at least one of N,N-dimethylformamide and N,N-dimethylacetamide is preferred as the polar solvent, and at least one of butanone and acetone is preferred as the ketone solvent. It is more preferable to use ketone solvents as the main component of the compound solvent. N-methylpyrrolidone and γ-butyrolactone can also be used as feasible polar solvents. When the system requires high solubility, they can be used in combination with ketone solvents such as butanone, but they are not used as the main component of the compound solvent in low-residue embodiments.

[0060] In one embodiment, reference Figure 2 Step S2 includes: S2.1 Take 15% to 45% of the total mass of nitrile rubber liquid as filler carrier liquid, add coupling agent to filler carrier liquid, stir at 20 to 35℃ and 100 to 300 rpm for 10 to 40 min to obtain filler pre-dispersion liquid; S2.2 Add catechol-based reactants to the complexation base solution and continue stirring for 15-30 min under light-protected conditions to obtain the catechol complexation solution; S2.3 Add the organophosphorus flame retardant to the inorganic flame retardant filler slurry in 2 to 6 batches. After each batch is added, stir at 100 to 300 rpm for 10 to 25 minutes and shear and disperse at 300 to 900 rpm for 10 to 35 minutes. After all the batches are added, continue to disperse for 20 to 60 minutes to obtain the flame retardant filler slurry. S2.4. Combine the flame-retardant filler slurry with the remaining nitrile rubber solution and homogenize at 150-400 rpm for 30-90 min to obtain the flame-retardant solution.

[0061] In this embodiment, a portion of the nitrile rubber adhesive is separated as a filler carrier liquid. The amount separated is sufficient to completely wet the inorganic flame-retardant filler and organophosphorus flame retardant, while ensuring that the resulting slurry can still form an effective circulation in the dispersion equipment. The coupling agent is first added to the filler carrier liquid for dispersion, and then the inorganic flame-retardant filler is added. This allows the inorganic flame-retardant filler to immediately contact the liquid phase containing the coupling agent after entering the adhesive, reducing direct contact between powder particles and the formation of hard agglomerates. The coupling agent can be one or more of epoxy silane coupling agents, amino silane coupling agents, titanate coupling agents, or aluminate coupling agents. When the viscosity of the coupling agent is high, it can be pre-diluted with a small amount of filler carrier liquid before being added to the remaining filler carrier liquid.

[0062] Inorganic flame-retardant fillers can be one or more of aluminum hydroxide, magnesium hydroxide, boehmite, or zinc borate, while organophosphorus flame retardants can be one or more of diethylaluminum hypophosphite, melamine polyphosphate, triphenyl phosphate, or hexaphenoxycyclotriphosphazene. The inorganic flame-retardant filler is added first and wetted and dispersed before the organophosphorus flame retardant is added. This ensures the organophosphorus flame retardant is distributed between the inorganic flame-retardant filler particles, preventing the formation of aggregates after both types of flame retardants enter the adhesive simultaneously.

[0063] Because inorganic flame-retardant fillers easily absorb environmental moisture during storage and transportation and may release migratable ions such as chloride, sodium, and potassium ions, their moisture content and ion release status are controlled before formal feeding. Specifically, test samples are taken from the inorganic flame-retardant fillers to be used, and the moisture content of the samples is determined. The conductivity and migratable ion content of the extract are then measured using water extraction. The samples used for testing are not added to the adhesive solution, thus preventing the testing water from entering the formal production system. When the test results do not meet the preset raw material control requirements, the batch of inorganic flame-retardant filler is discontinued, rather than simply compensating by increasing the amount of ion scavenging agent.

[0064] For inorganic flame-retardant fillers that have passed inspection but contain adsorbed moisture, vacuum drying, hot air drying, or drying gas treatment can be used before feeding. The drying temperature and time should be set according to the type of inorganic flame-retardant filler, its initial moisture content, and thermal stability. After drying, the powder should be cooled in a closed or low-humidity environment and stored in a sealed container. The powder should be used as soon as possible after cooling to a suitable feeding temperature to prevent it from reabsorbing moisture in an open environment. For fillers with high hygroscopicity, batch weighing and immediate feeding can be used to keep unused powder in a sealed state.

[0065] The dried inorganic flame-retardant filler is added in batches to a filler carrier liquid containing a coupling agent. After each batch of powder is added, it is first slowly wetted to allow the adhesive to penetrate into the powder agglomerates, followed by shear dispersion. No subsequent batch of powder is added before the previous batch is fully wetted to avoid forming particles that are externally coated with adhesive but still contain dry powder and air inside. After the inorganic flame-retardant filler is completely dispersed, the organophosphorus flame retardant is added, and dispersion is achieved through batch addition or slow dropwise addition, depending on its physical state.

[0066] This embodiment reduces the risk of inorganic flame-retardant fillers introducing moisture and releasing migratable ions into the adhesive solution by detecting the moisture and ions in the raw materials, drying before feeding, sealing and cooling, pre-dispersing the coupling agent, and wetting the powder in batches.

[0067] In one embodiment, reference Figure 3 Step S3 includes: S3.1 Adjust the remaining second solvent to 15-30℃, add the curing agent to the remaining second solvent in 2-4 batches, stir at 80-250 rpm for 10-20 min after each batch is added, and continue stirring for 20-60 min after all the ingredients are added to obtain the curing agent dispersion. S3.2 Adjust the flame retardant adhesive liquid to 20-35℃, add the curing agent dispersion liquid to the flame retardant adhesive liquid in 2-5 batches, stir for 15-40 minutes after each batch is added, and continue stirring for 20-80 minutes after all batches are added to obtain the cured adhesive liquid; S3.3 Add the antioxidant to the curing adhesive in 1 to 3 batches, stirring for 10 to 30 minutes after each batch is added. Then add the ion scavenger to the curing adhesive in 1 to 3 batches, stirring for 10 to 30 minutes after each batch is added. After all the antioxidants are added, continue stirring at 150 to 400 rpm for 20 to 60 minutes to obtain the epoxy resin adhesive.

[0068] In this embodiment, the curing agent includes a primary curing agent and a curing accelerator. The primary curing agent can be one or more of dicyandiamide, diaminodiphenyl sulfone, diaminodiphenylmethane, or diaminodiphenyl ether. The curing accelerator can be one or more of 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, or triphenylphosphine. The primary curing agent is added in batches to the remaining second solvent portion, and the curing accelerator is added after it has formed a uniform dispersion. For curing accelerators used in small quantities, a small amount of curing agent dispersion can be used for pre-wetting to reduce material loss caused by its adhesion to the feeding device.

[0069] The curing agent dispersion does not need to form a completely transparent solution. The standard for completion is that there are no large particles or hard deposits visible to the naked eye, and that it can be restored to homogeneity by low-speed stirring after a short period of standing. The curing agent dispersion is added to the flame retardant adhesive in batches, allowing each batch to fully diffuse before adding the next batch, thereby reducing the accumulation of curing agent in localized areas.

[0070] Antioxidants are added after the curing agent has been basically homogenized. One or more of 2,6-di-tert-butyl-p-cresol, triphenyl phosphite, dilauryl thiodipropionate, or distearate thiodipropionate can be used. Ion scavengers are added after the antioxidants have dispersed. One or more of hydrotalcite, zirconium phosphate, or zeolite molecular sieves can be used; bismuth oxide is not used as an ion scavenger. The ion scavenger should be kept sealed and dry before use, and added in batches to ensure uniform distribution in the adhesive. By adding the ion scavenger after the inorganic flame-retardant filler and curing agent have been basically dispersed, its encapsulation by filler agglomerates can be reduced, ensuring sufficient contact between the ion scavenger and the migratable ions in the adhesive.

[0071] In one embodiment, step S4 includes: S4.1. Homogenize the epoxy resin solution at 100-300 rpm for 10-40 min, and then filter it using a filter with a pore size of 50-200 μm. S4.2. Let the filtered epoxy resin solution stand at 20-35℃ for 10-60 minutes, then degas it under a vacuum gauge pressure of -0.095 to -0.06 MPa for 5-30 minutes. After degassing, restore it to normal pressure and seal it to obtain the epoxy resin composition.

[0072] In this embodiment, after the epoxy resin solution has undergone final homogenization, it enters the filtration device through a closed delivery pipeline. The filter medium can be pre-wetted with a small amount of the same composition of resin solution to expel air from the filter media. During filtration, the resin solution is continuously passed through the filter medium to prevent interruption of the delivery pipeline or the resin solution from falling into the receiving container from a height. When the filtration pressure differential increases significantly, the filter medium is replaced; filtration is not forced by increasing the pressure, and the filtered residue is not returned to the resin solution.

[0073] The filtered adhesive solution is allowed to stand under sealed conditions, allowing larger air bubbles to rise naturally before vacuum degassing. The vacuum level is gradually reduced; if the bubble layer rises too quickly, the degassing process is paused, and vacuuming resumes only after the bubbles descend. During degassing, the adhesive solution temperature is kept stable, and high-speed stirring is avoided to minimize the loss of volatile solvents. After degassing, clean, dry gas is slowly introduced to restore atmospheric pressure, and a low-drop method is used to complete the discharge and sealing packaging.

[0074] This application also discloses an epoxy resin composition for multilayer PCB manufacturing, prepared by the above-described method. The epoxy resin composition includes epoxy resin, nitrile rubber, inorganic flame-retardant filler, organophosphorus flame retardant, curing agent, antioxidant, ion scavenger, coupling agent, and compounding solvent. The amounts of each component are configured according to the mass parts defined in claim 10. The epoxy resin serves as the main film-forming and bonding component of the composition. It can be a single epoxy resin or a blend of two or more epoxy resins. In a preferred embodiment, bisphenol A type epoxy resin and dicyclopentadiene phenol type epoxy resin are used to provide the basic bonding properties and processing fluidity of the adhesive, while the dicyclopentadiene phenol type epoxy resin is used to adjust the heat resistance and structural stability of the cured adhesive layer. The nitrile rubber is distributed in the continuous organic phase formed by the epoxy resin, used to adjust the flexibility and interlayer bonding state of the cured adhesive layer, and by pre-wetting and dispersing in the epoxy resin liquid, the formation of localized lumps of nitrile rubber in the composition is reduced.

[0075] The inorganic flame-retardant filler and the organophosphorus flame retardant together constitute a flame-retardant system. In a preferred embodiment, the inorganic flame-retardant filler is aluminum hydroxide, and the organophosphorus flame retardant is diethylaluminum hypophosphite. Before addition, the aluminum hydroxide undergoes moisture detection, soluble ion detection, and pre-drying treatment, and is cooled and stored under sealed or low-humidity conditions to reduce the risk of the inorganic flame-retardant filler introducing moisture into the composition and releasing migratable ions. Diethylaluminum hypophosphite is added after the aluminum hydroxide has completed wetting and initial dispersion, ensuring its distribution between the inorganic flame-retardant filler particles. By using the inorganic flame-retardant filler and the organophosphorus flame retardant in combination, a composite flame-retardant system can be formed while avoiding excessive dosage of a single flame retardant.

[0076] The coupling agent is preferably an epoxy-based silane coupling agent. The coupling agent is first dispersed in a filler carrier liquid formed from a portion of the epoxy resin and nitrile rubber, and then contacts the inorganic flame-retardant filler. This allows the surface of the inorganic flame-retardant filler to be wetted by the organic adhesive liquid containing the coupling agent before entering the main body of the composition, thereby improving the interfacial state between the inorganic flame-retardant filler and the continuous epoxy resin phase, and reducing the formation of hard agglomerates of powder in the adhesive liquid. The coupling agent is not added directly after the composition is prepared, but rather during the flame-retardant filler slurry formation stage, allowing it to be uniformly distributed throughout the composition along with the flame-retardant filler slurry.

[0077] The curing agent includes a primary curing agent and a curing accelerator. In a preferred embodiment, the primary curing agent is diaminodiphenyl sulfone, and the curing accelerator is an imidazole-based curing accelerator. The primary curing agent and the curing accelerator are pre-mixed with a portion of the compounded solvent to form a curing agent dispersion, which is then added to the adhesive solution after the flame-retardant filler dispersion has been completed. This prevents the curing agent powder from directly entering the high-viscosity composition and forming local agglomerates. The antioxidant is added after the curing agent is uniformly dispersed to reduce the impact of oxidation on the composition during preparation, drying, and subsequent heat treatment. The ion trap is added after the antioxidant, preferably one or more of hydrotalcite, zirconium phosphate, or zeolite molecular sieves, and bismuth oxide is not used as the ion trap. The ion trap is used to adsorb or fix a small amount of migratory ions that may be introduced by the epoxy resin, flame-retardant filler, curing agent, and other additives, and together with the low moisture and low ion intake control of the inorganic flame-retardant filler, it forms an ion control method that combines source control and back-end trapping.

[0078] The compound solvent includes polar solvents and ketone solvents. The polar solvents are used to improve the wetting and dispersing abilities of the epoxy resin, nitrile rubber, and curing agent, while the ketone solvents are used to adjust the viscosity, coating flowability, and subsequent drying and removal properties of the composition. In a preferred low-residue embodiment, the polar solvent is at least one of N,N-dimethylformamide and N,N-dimethylacetamide, and the ketone solvent is at least one of butanone and acetone, with the ketone solvent serving as the main component of the compound solvent. More preferably, the compound solvent is composed of N,N-dimethylformamide and butanone, allowing a small amount of N,N-dimethylformamide to meet the polar wetting requirements of the epoxy resin, nitrile rubber, and curing agent, while butanone is used to adjust the application viscosity and evaporation removal properties of the composition, thereby reducing the risk of residue caused by excessive use of polar solvents.

[0079] The above composition can be prepared according to the aforementioned steps S1 to S4, that is, firstly, epoxy resin, nitrile rubber and part of the compounded solvent are used to form a uniform nitrile rubber liquid, then a flame retardant filler slurry is prepared using part of the nitrile rubber liquid, the flame retardant filler slurry is combined with the remaining nitrile rubber liquid, then a pre-prepared curing agent dispersion, antioxidant and ion scavenger are added, and finally, after overall homogenization, filtration, standing and vacuum degassing, the epoxy resin composition is obtained.

[0080] The obtained epoxy resin composition is a homogeneous, fluid adhesive, in which epoxy resin and nitrile rubber form a continuous organic phase. Inorganic flame-retardant fillers, organophosphorus flame retardants, and ion scavengers exist in a dispersed state within the continuous organic phase. Curing agents, antioxidants, and coupling agents are uniformly distributed within the composition. After standing, the composition should not exhibit visible continuous layering, obvious powder deposition, or large-sized agglomerates. After application, the adhesive should not show obvious particle streaks or dense bubbles.

[0081] In use, the epoxy resin composition is applied to the surface of a substrate for multilayer PCB manufacturing, and the compounded solvent is gradually evaporated by drying to form an adhesive layer with certain bonding and flow capabilities; subsequently, the adhesive layer is heated and flows and cured during the multilayer PCB lamination process, thereby filling the local gaps between adjacent layers and forming an interlayer bonding structure between the core board, copper foil and insulating layer.

[0082] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0083] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing an epoxy resin composition for multilayer PCB manufacturing, characterized in that, include: S1. The compound solvent is divided into a first solvent part and a second solvent part. Epoxy resin is added to the first solvent part in batches to obtain an epoxy resin liquid. Nitrile rubber is added to the epoxy resin liquid in batches, and a portion of the second solvent part is added to obtain a nitrile rubber adhesive liquid. S2. Take a portion of the nitrile rubber liquid as the filler carrier liquid, disperse the coupling agent in the filler carrier liquid, and then add inorganic flame retardant filler and organic phosphorus flame retardant in sequence to obtain flame retardant filler slurry. Combine the flame retardant filler slurry with the remaining nitrile rubber liquid and homogenize to obtain flame retardant liquid. S3. Disperse the curing agent in the remaining second solvent to obtain a curing agent dispersion. Add the curing agent dispersion, antioxidant and ion scavenger to the flame retardant adhesive in sequence to obtain an epoxy resin adhesive. S4. The epoxy resin solution is allowed to stand to degas and then stirred to homogenize, thereby obtaining an epoxy resin composition.

2. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 1, characterized in that, Step S1 includes: S1.1 Take 70% to 95% of the total mass of the compounded solvent as the first solvent portion, and the remainder as the second solvent portion. Adjust the temperature of the first solvent portion to 20 to 35°C. Add the epoxy resin to the first solvent portion in 2 to 5 batches. After each batch is added, stir at 100 to 300 rpm for 10 to 30 minutes. After all the resin has been added, continue stirring for 20 to 60 minutes to obtain the epoxy resin solution. S1.2 Add nitrile rubber to epoxy resin solution in 2 to 4 batches. After each batch is added, let it stand for 10 to 40 minutes, then stir at 150 to 500 rpm for 20 to 50 minutes. After all the nitrile rubber is added, continue stirring at 25 to 45°C for 40 to 120 minutes to obtain a pre-dispersion. S1.3 Add 20% to 60% of the total mass of the second solvent to the pre-dispersion liquid, and stir at 100 to 300 rpm for 10 to 30 minutes to obtain nitrile rubber solution.

3. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 2, characterized in that, The epoxy resin includes at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, dicyclopentadiene phenol type epoxy resin, and phenolic type epoxy resin; the nitrile rubber includes at least one of carboxyl nitrile rubber, hydroxyl-terminated nitrile rubber, and powdered nitrile rubber; the compounding solvent includes polar solvents and ketone solvents, the polar solvent includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide, and the ketone solvent includes at least one of butanone, acetone, cyclohexanone, and methyl isobutyl ketone; based on 100 parts of epoxy resin, the nitrile rubber is 50-90 parts, and the compounding solvent is 310-400 parts.

4. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 1, characterized in that, Step S2 includes: S2.1 Take 15% to 45% of the total mass of nitrile rubber liquid as filler carrier liquid, add coupling agent to filler carrier liquid, stir at 20 to 35℃ and 100 to 300 rpm for 10 to 40 min to obtain filler pre-dispersion liquid; S2.2 Add the inorganic flame retardant filler to the filler pre-dispersion liquid in 3 to 8 batches. After each batch is added, let it stand for 5 to 20 minutes, then stir at 150 to 400 rpm for 10 to 30 minutes, and shear disperse at 400 to 1000 rpm for 10 to 40 minutes. After all the fillers are added, continue to disperse for 20 to 80 minutes to obtain the inorganic flame retardant filler slurry. S2.3 Add the organophosphorus flame retardant to the inorganic flame retardant filler slurry in 2 to 6 batches. After each batch is added, stir at 100 to 300 rpm for 10 to 25 minutes and shear and disperse at 300 to 900 rpm for 10 to 35 minutes. After all the batches are added, continue to disperse for 20 to 60 minutes to obtain the flame retardant filler slurry. S2.

4. Combine the flame-retardant filler slurry with the remaining nitrile rubber solution and homogenize at 150-400 rpm for 30-90 min to obtain the flame-retardant solution.

5. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 4, characterized in that, The inorganic flame-retardant filler includes at least one of aluminum hydroxide, magnesium hydroxide, boehmite, and zinc borate; the organophosphorus flame retardant includes at least one of aluminum diethylphosphite, melamine polyphosphate, triphenyl phosphate, and hexaphenoxycyclotriphosphazene; based on 100 parts of epoxy resin, the inorganic flame-retardant filler is 28-42 parts, and the organophosphorus flame retardant is 18-32 parts.

6. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 1, characterized in that, Step S3 includes: S3.1 Adjust the remaining second solvent to 15-30℃, add the curing agent to the remaining second solvent in 2-4 batches, stir at 80-250 rpm for 10-20 min after each batch is added, and continue stirring for 20-60 min after all the ingredients are added to obtain the curing agent dispersion. S3.2 Adjust the flame retardant adhesive liquid to 20-35℃, add the curing agent dispersion liquid to the flame retardant adhesive liquid in 2-5 batches, stir for 15-40 minutes after each batch is added, and continue stirring for 20-80 minutes after all batches are added to obtain the cured adhesive liquid; S3.3 Add the antioxidant to the curing adhesive in 1 to 3 batches, stirring for 10 to 30 minutes after each batch is added. Then add the ion scavenger to the curing adhesive in 1 to 3 batches, stirring for 10 to 30 minutes after each batch is added. After all the antioxidants are added, continue stirring at 150 to 400 rpm for 20 to 60 minutes to obtain the epoxy resin adhesive.

7. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 6, characterized in that, The curing agent includes a main curing agent and a curing accelerator; the curing agent includes at least one of dicyandiamide, diaminodiphenyl sulfone, diaminodiphenylmethane, and diaminodiphenyl ether; the curing accelerator includes at least one of 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and triphenylphosphine; the curing agent is 5 to 14 parts per 100 parts of epoxy resin.

8. The method for preparing an epoxy resin composition for multilayer PCB manufacturing according to claim 1, characterized in that, Step S4 includes: S4.

1. Homogenize the epoxy resin solution at 100-300 rpm for 10-40 min, and then filter it using a filter with a pore size of 50-200 μm. S4.

2. Let the filtered epoxy resin solution stand at 20-35℃ for 10-60 minutes, then degas it under a vacuum gauge pressure of -0.095 to -0.06 MPa for 5-30 minutes. After degassing, restore it to normal pressure and seal it to obtain the epoxy resin composition.

9. A method for preparing an epoxy resin composition for multilayer PCB manufacturing according to any one of claims 1 to 8, characterized in that, The antioxidant includes at least one of 2,6-di-tert-butyl-p-cresol, triphenyl phosphite, dilauryl thiodipropionate, and distearate thiodipropionate; the ion scavenger includes at least one of hydrotalcite, zirconium phosphate, and zeolite molecular sieve; the coupling agent includes at least one of epoxy silane coupling agent, amino silane coupling agent, titanate coupling agent, and aluminate coupling agent; based on 100 parts of epoxy resin, the antioxidant is 0.5-3 parts, the ion scavenger is 0.5-4 parts, and the coupling agent is 2-5 parts.

10. An epoxy resin composition for manufacturing multilayer PCBs, characterized in that, Including epoxy resin, nitrile rubber, inorganic flame retardant filler, organophosphorus flame retardant, curing agent, antioxidant, ion scavenger, coupling agent and compound solvent; Based on 100 parts of epoxy resin, the composition includes 50-90 parts of nitrile rubber, 28-42 parts of inorganic flame retardant filler, 18-32 parts of organophosphorus flame retardant, 5-14 parts of curing agent, 0.5-3 parts of antioxidant, 0.5-4 parts of ion scavenger, 2-5 parts of coupling agent, and 310-400 parts of compound solvent.

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