A method for preparing a modified epoxy resin material for printed circuit boards

Abstract

The present application relates to the technical field of printed circuit board preparation, in particular to a preparation method of modified epoxy resin material for printed circuit board, comprising the following steps: activating surface hydroxyl of porous nano-SiO2 with hydrochloric acid, then wrapping nano-Al2O3 and GO on the outer surface in sequence to prepare single-core double-shell filler, which replaces single inorganic heat-conducting filler to mix with epoxy resin to modify the epoxy resin; the present application takes low-dielectric porous nano-SiO2 as core to reduce the dielectric constant of the whole modified epoxy resin material; thin-shell Al2O3 and GO are used to construct heat-conducting path, GO can form continuous heat-conducting network through stacking and lapping between layers under low addition amount, and the high heat-conducting coefficient of Al2O3 and GO can improve the heat-conducting performance of the printed circuit board under the condition of ensuring low dielectric constant; the Al-O-Si covalent bond and amide bond of the single-core double-shell filler are not easy to break at high temperature, thus solving the problem of easy peeling of the shell layer at high temperature caused by physical wrapping and adsorption, and maintaining stable dielectric constant.

Description

Technical Field

[0001] This invention relates to the field of printed circuit board manufacturing technology, specifically to a method for preparing a modified epoxy resin material for printed circuit boards. Background Technology

[0002] Printed circuit boards (PCBs) are the support structures for electronic components. They consist of an insulating substrate and copper foil covering the insulating substrate. The mainstream PCB types include: 1. Epoxy fiberglass cloth substrate; 2. Metal substrate; 3. High-frequency and high-speed substrate. Among them, the metal substrate usually has a three-layer structure: the top layer is a copper foil circuit layer, the middle layer is a highly thermally conductive insulating dielectric layer, and the bottom layer is a metal base layer. The highly thermally conductive insulating dielectric layer is made of epoxy resin filled with thermally conductive filler.

[0003] Currently, fillers with good thermal conductivity, such as boron nitride (BN), aluminum nitride (AlN), aluminum oxide (Al2O3), and magnesium oxide (MgO), are used to modify epoxy resins. Without affecting the original excellent properties of epoxy resins, they can improve their thermal conductivity to a certain extent.

[0004] Furthermore, with the increasing frequency and higher transmission speed of electronic devices, there are requirements for lower dielectric constant, dielectric loss, and higher thermal conductivity of high-frequency printed circuit boards. However, when only alumina or aluminum nitride is used as thermally conductive filler to fill epoxy resin, although the thermal conductivity can be improved, the dielectric constant will increase, resulting in higher dielectric loss of the printed circuit board. In other words, the thermal conductivity and low dielectric constant of the printed circuit board cannot achieve a better balance.

[0005] Graphene oxide (GO) is a derivative of graphene, possessing advantages such as a two-dimensional sheet structure and high specific surface area. GO inherently has a high thermal conductivity; compared to traditional inorganic fillers, the thermal conductivity of composite materials can be significantly improved even with lower GO loading levels. Furthermore, at low addition levels, graphene oxide can form a nano-barrier layer, which can reduce the ingress of water molecules to some extent and lower the dielectric constant of the insulating dielectric layer; however, this method has limited effect on reducing the dielectric constant.

[0006] Existing technologies combine hollow silica spheres with graphene oxide. The hollow silica spheres are uniformly attached to the surface of graphene oxide. The hollow structure of the silica spheres can introduce more air into the epoxy resin to further reduce the dielectric constant. However, the silica spheres are only attached to the graphene oxide sheets, and the interfacial force between the two is weak. Under the exothermic curing conditions of epoxy resin (around 150°C) and the high temperature conditions of PCB soldering (above 260°C), interfacial separation, particle shedding and agglomeration are prone to occur, resulting in problems such as interruption of the thermal conductivity path of the composite material, deterioration of dielectric properties and decrease in insulation reliability.

[0007] Existing technologies also include core-shell hybrid structures with silicon dioxide as the core and graphene oxide as the shell. These core-shell hybrid structures are introduced into epoxy polymer matrices as new fillers. However, ordinary physical coating methods can cause the shell to fall off and disintegrate at high temperatures, resulting in unstable dielectric constants.

[0008] Therefore, the present invention provides a modified epoxy resin that can maintain high thermal conductivity and low dielectric constant of printed circuit boards under high temperature conditions. Summary of the Invention

[0009] To solve the above problems, the present invention provides a method for preparing modified epoxy resin material for printed circuit boards, comprising the following steps: S1, pretreatment of porous nano-SiO2: porous nano-SiO2 is dispersed in deionized water, then concentrated hydrochloric acid is added, and the mixture is stirred at 60-80℃ for 2-4 hours, cooled, washed until neutral, and vacuum dried at 120℃ for 4 hours to obtain activated porous nano-SiO2.

[0010] Porous nano-SiO2 with a porosity of 50% was selected. A large amount of air phase was introduced into the porous nano-SiO2. The dielectric constant of air is about 1. Compared with solid nano-SiO2, the dielectric constant is significantly reduced. When the porosity is 50%, the dielectric constant of porous nano-SiO2 is about 2.8, which is much lower than the dielectric constant of dense SiO2 (specific value is 3.9), providing a low dielectric substrate for the subsequent thermally conductive shell.

[0011] The porous nano-SiO2, after being activated by hydrochloric acid, provides abundant surface hydroxyl groups, which provide a large number of nucleation sites for the hydrolysis and deposition of aluminum nitrate. This makes the aluminum oxide shell uniform and firm, rather than simply adsorbed and wrapped. Under subsequent high-temperature environments, the shell is not easy to fall off or agglomerate, and the dielectric constant is more stable.

[0012] S2. Primary Encapsulation of Porous Nano-SiO2: Activated porous nano-SiO2 was dispersed in deionized water. Aluminum nitrate solution was slowly added dropwise at 40-50℃ with stirring at 300 rpm. Dilute ammonia was added dropwise to maintain the pH of the system at 7.5-8.5. After the addition was complete, stirring was continued for 2 hours. The mixture was centrifuged, washed until neutral, and dried at 80℃ for 12 hours. Then, it was calcined in a muffle furnace at 500-600℃ for 2 hours with a heating rate of 5-10℃ / min to obtain porous nano-SiO2-Al2O3 composite particles.

[0013] High-temperature calcination causes Al2O3 to react with the surface hydroxyl groups of porous nano-SiO2 to form Al-O-Si covalent bonds. The inner shell and core are no longer adsorbed and wrapped, but are firmly bonded by covalent bonds, avoiding the phenomenon of physical coating falling off at high temperatures.

[0014] By wrapping nano-Al2O3 around porous nano-SiO2, the thermal conductivity bottleneck caused by the hollow structure of porous nano-SiO2 is avoided.

[0015] S3, Porous nano-SiO2 secondary encapsulation: Graphene oxide is encapsulated on the outside of porous nano-SiO2-Al2O3 composite particles to form a single-core double-shell filler.

[0016] Single nano-Al2O3 or nano-SiO2 tends to form isolated hot spots in epoxy resin. During heat transfer, it needs to cross the resin interface multiple times. By coating the outer layer of porous nano-SiO2-Al2O3 composite particles with graphene oxide, the particles are connected by a layered structure to form a continuous heat-conducting network, thereby improving the thermal conductivity.

[0017] S4. Preparation of epoxy resin adhesive:

[0018] S41. Pretreatment of packing material: Vacuum dry the mononuclear double-shell packing material at 120℃ for 4 hours, add 1-3% of silane coupling agent by weight of the mononuclear double-shell packing material, stir at 1000-1500 rpm for 10-15 minutes, ultrasonically treat for 30 minutes, and then dry at 80℃ for 1 hour.

[0019] The silane coupling agent KH550 hydrolyzes in the aqueous phase to generate silanol groups, which undergo a condensation reaction with the hydroxyl groups on the surface of the mononuclear double-shell filler to form Si-O-Si covalent bonds. At the same time, the terminal amino group of KH55 forms a covalent bond with the epoxy group of the epoxy resin, thereby achieving chemical coupling between the mononuclear double-shell filler and the epoxy resin, further reducing the interfacial thermal resistance and improving the thermal conductivity.

[0020] S42. Preparation of adhesive solution: Mix epoxy resin and reactive diluent at a weight ratio of 100:(10-20), preheat in a 60℃ water bath for 30 min, add dispersant, and stir at 300 rpm for 10 min; add mononuclear double-shell filler to epoxy resin in batches while stirring, stir at 1500 rpm for 10 min, ultrasonic frequency 20-40 kHz, ultrasonic power 300-500 W, and sonicate for 15 min; cool, add defoamer and curing agent, stir at 500 rpm for 10 min, then extrude accelerator, stir for 5 min, and degas under vacuum for 15-20 min to obtain modified epoxy resin adhesive solution.

[0021] By adding fillers with porous nano-SiO2 as the core, nano-alumina as the inner shell, and graphene oxide as the outer shell to epoxy resin, the modified epoxy resin material is guaranteed to have a lower dielectric constant and higher thermal conductivity.

[0022] Preferably, the mass ratio of the porous nano-SiO2, deionized water, and concentrated hydrochloric acid is 1:(4-8):(0.2-0.4).

[0023] Preferably, the mass ratio of the activated porous nano-SiO2, deionized water, and aluminum nitrate is 1:50:(0.3-0.5), and the concentration of the aluminum nitrate solution is 0.2-0.3 mol / L.

[0024] By introducing a small amount of aluminum nitrate, the resulting Al2O3 shell is thin, thus avoiding an increase in dielectric constant caused by excessive Al2O3.

[0025] Preferably, step S3, the secondary encapsulation process of porous nano-SiO2, includes: S31, coupling treatment: mixing silane coupling agent with deionized water, stirring and hydrolyzing for 15 min to obtain hydrolysate.

[0026] Porous nano-SiO2-Al2O3 composite particles were dispersed in anhydrous ethanol to obtain a dispersion. Then, the hydrolysate was added dropwise to the dispersion, and the mixture was stirred at 70℃ and 400 rpm for 4 h. After centrifugation, washing, and vacuum drying at 80℃ for 6 h, aminated porous nano-SiO2-Al2O3 composite particles were obtained.

[0027] S32. Activation treatment of graphene oxide: Sonicate a 2 g / L aqueous dispersion of graphene oxide for 1 h at an ultrasonic frequency of 20-40 kHz and an ultrasonic power of 300-500 W. Add EDC·HCl and NHS to the aqueous dispersion of graphene oxide and stir for 30 min to obtain an activated aqueous dispersion of graphene oxide.

[0028] S33. Encapsulation treatment: Aminated porous nano-SiO2-Al2O3 composite particles were added to the activated graphene oxide aqueous dispersion and stirred at 300 rpm for 24 h to allow the amino groups to react with the activated carboxyl groups to form amide bonds. The graphene oxide was then encapsulated on the outer surface of the porous nano-SiO2-Al2O3 composite particles to form a secondary encapsulation. After centrifugation and washing, the particles were vacuum dried at 60 °C for 12 h to obtain a single-core double-shell packing material.

[0029] Preferably, during the coupling process, the mass ratio of porous nano-SiO2-Al2O3 composite particles, anhydrous ethanol, and silane coupling agent is 1:(15-20):0.0125, the mass ratio of silane coupling agent to deionized water is 1:(5-10), and the silane coupling agent is KH550.

[0030] Preferably, in the graphene oxide activation treatment, the mass ratio of graphene oxide, EDC·HCl, and NHS is 1:(0.2-0.3):(0.1-0.15).

[0031] Preferably, in the encapsulation process, the mass ratio of aminated porous nano-SiO2-Al2O3 composite particles to graphene oxide is 1:(0.015-0.03).

[0032] Preferably, the modified epoxy resin adhesive comprises, by weight, 100 parts epoxy resin, 15-30 parts mononuclear double-shell filler, 10-20 parts reactive diluent, 1-3 parts dispersant, 0.5-1 part defoamer, 80-85 parts curing agent, and 1-2 parts accelerator, wherein the amount of graphene oxide added in the mononuclear double-shell filler is 0.3% of the weight of epoxy resin.

[0033] Preferably, the reactive diluent is one of propylene oxide butyl ether and diglycidyl ether; the dispersant is one of silane dispersant and polycarboxylate dispersant; the defoamer is one of organosilicon defoamer and polyether defoamer; the curing agent is one of methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride; and the accelerator is benzyl dimethylamine.

[0034] Preferably, the epoxy resin is one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene ring type epoxy resin, alicyclic epoxy resin, and fluorinated epoxy resin.

[0035] This invention has at least one of the following technical effects:

[0036] 1. This invention uses low-dielectric porous nano-SiO2 as the core to reduce the overall dielectric constant of the modified epoxy resin material; it constructs a thermally conductive path with thin-shell Al2O3 and GO. GO can form a continuous thermally conductive network through the stacking and overlapping of layers even with a low addition amount. Combined with the high thermal conductivity of Al2O3 and GO, the thermal conductivity of the printed circuit board is improved while ensuring a low dielectric constant.

[0037] 2. This invention uses Al-O-Si covalent bonds to tightly bind the Al2O3 shell to the SiO2 core. By activating GO, the amino groups react with the activated carboxyl groups to form amide bonds, making the chemical bonds of the single-core double-shell filler less prone to breakage at high temperatures. This solves the problem of easy shell detachment at high temperatures caused by physical encapsulation and adsorption, and maintains a stable dielectric constant.

[0038] 3. This invention forms a dense nano barrier layer through GO sheets, which prevents water molecules, oxygen molecules and other media from penetrating the thermally conductive insulating film, thereby reducing dielectric loss and improving high-temperature insulation stability. Attached Figure Description

[0039] Figure 1 A physical image of the mononuclear double-shell packing material prepared in Example 1. Detailed Implementation

[0040] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0041] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0042] Preparation example of single-core double-shell packing

[0043] Preparation Example 1

[0044] S1. Pretreatment of porous nano-SiO2: 200g of porous nano-SiO2 was dispersed in 1kg of deionized water, then 40g of concentrated hydrochloric acid was added, and the mixture was stirred at 70℃ for 3h. After cooling and washing until neutral, the mixture was dried under vacuum at 120℃ for 4h to obtain activated porous nano-SiO2.

[0045] S2. Primary Encapsulation of Porous Nano-SiO2: 200g of activated porous nano-SiO2 was dispersed in 10kg of deionized water. At 40-50℃, 60g of 0.25mol / L aluminum nitrate solution was slowly added dropwise while stirring at 300rpm. Simultaneously, dilute ammonia was added dropwise to maintain the pH of the system at 7.5-8.5. After the addition was complete, stirring was continued for 2h. The mixture was centrifuged and washed until neutral. It was dried at 80℃ for 12h and then calcined in a muffle furnace at 500-600℃ for 2h at a heating rate of 10℃ / min to obtain porous nano-SiO2-Al2O3 composite particles.

[0046] S3, Porous nano-SiO2 secondary encapsulation: Graphene oxide is encapsulated on the outside of porous nano-SiO2-Al2O3 composite particles to form a single-core double-shell filler;

[0047] S31. Coupling treatment: Mix 2.5g KH550 with 20g deionized water, stir and hydrolyze for 15min to obtain hydrolysate;

[0048] 200g of porous nano-SiO2-Al2O3 composite particles were dispersed in 4kg of anhydrous ethanol to obtain a dispersion. Then, the hydrolysate was added dropwise to the dispersion. The mixture was stirred at 70℃ and 400rpm for 4h, centrifuged, washed, and vacuum dried at 80℃ for 6h to obtain aminated porous nano-SiO2-Al2O3 composite particles.

[0049] S32. Activation treatment of graphene oxide: Take 2L of 2g / L graphene oxide aqueous dispersion, sonicate for 1h, sonic frequency 20kHz, sonic power 300W, add 0.8g EDC·HCl and 0.4g NHS to the graphene oxide aqueous dispersion, stir for 30min to obtain activated graphene oxide aqueous dispersion.

[0050] S33. Encapsulation Treatment: Add 200g of aminated porous nano-SiO2-Al2O3 composite particles to 2L of activated graphene oxide aqueous dispersion, stir at 300rpm for 24h, allowing the amino groups to react with the activated carboxyl groups to form amide bonds. Graphene oxide encapsulates the outer surface of the porous nano-SiO2-Al2O3 composite particles, forming a secondary encapsulation. Centrifuge, wash, and vacuum dry at 60℃ for 12h to obtain a single-core double-shell packing material, as shown in the attached diagram. Figure 1 As shown, it appears as a white to light gray powder.

[0051] Preparation Example 2

[0052] The difference from Preparation Example 1 is that: in this preparation example, the amount of concentrated hydrochloric acid added is 60g, the amount of aluminum nitrate added is 80g, the amount of EDC·HCl added is 0.8g, the amount of NHS added is 0.6g, and the amount of aminated porous nano-SiO2-Al2O3 composite particles added is 150g.

[0053] Preparation Example 3

[0054] The difference from Preparation Example 1 is that the amount of concentrated hydrochloric acid added in this preparation example is 80g, the amount of aluminum nitrate added is 100g, the amount of EDC·HCl added is 1.2g, the amount of NHS added is 0.6g, and the amount of aminated porous nano-SiO2-Al2O3 composite particles added is 200g.

[0055] Preparation Example 4

[0056] The difference from Preparation Example 1 is that this preparation example does not perform primary encapsulation treatment, but only secondary encapsulation treatment. In the secondary encapsulation treatment, 200g of activated porous nano-SiO2 is dispersed in 4kg of anhydrous ethanol to form a dispersion.

[0057] Examples of modified epoxy resin solutions

[0058] Example 1

[0059] S4. Preparation of epoxy resin materials:

[0060] S41. Pretreatment of packing material: Take 75g of the single-core double-shell packing material prepared in Example 1, vacuum dry at 120℃ for 4h, add 1.5g of KH550, stir at 1200rpm for 10min, sonicate for 30min, and then dry at 80℃ for 1h.

[0061] S42. Preparation of adhesive solution: Mix 0.5 kg of bisphenol A type epoxy resin with 50 g of diglycidyl ether, preheat in a 60°C water bath for 30 min, add 5 g of silane dispersant, and stir at 300 rpm for 10 min.

[0062] 75g of single-core double-shell filler was added to the epoxy resin in batches while stirring. The mixture was stirred at 1500rpm for 10min, and the ultrasonic frequency was 30kHz with an ultrasonic power of 400W for 15min.

[0063] Cool to room temperature, add 2.5g of silicone defoamer and 400g of methylhexahydrophthalic anhydride, stir at 500rpm for 10min, then add 5g of benzyl dimethylamine, stir for 5min, and degas under vacuum for 20min to obtain modified epoxy resin solution.

[0064] Example 2

[0065] The difference from Example 1 is that in this example, the amount of diglycidyl ether mixture added is 100g, the amount of silane dispersant added is 15g, the amount of mononuclear double shell filler added is 150g, the amount of organosilicon defoamer added is 5g, methylhexahydrophthalic anhydride is 425g, and benzyl dimethylamine is 10g.

[0066] Example 3

[0067] The difference from Example 1 is that in this example, the added mononuclear double-shell packing material is the mononuclear double-shell packing material prepared in Example 2.

[0068] Example 4

[0069] The difference from Example 2 is that in this example, the added mononuclear double-shell packing material is the mononuclear double-shell packing material prepared in Example 2.

[0070] Example 5

[0071] The difference from Example 1 is that in this example, the added mononuclear double-shell packing material is the mononuclear double-shell packing material prepared in Preparation Example 3.

[0072] Example 6

[0073] The difference from Example 2 is that in this example, the added mononuclear double-shell packing material is the mononuclear double-shell packing material prepared in Preparation Example 3.

[0074] Comparative Example 1

[0075] The difference from Example 1 is that the single-core double-shell filler prepared in Example 1 was replaced with an equal amount of nano-alumina.

[0076] Comparative Example 2

[0077] The difference from Example 2 is that the single-core double-shell filler obtained in Preparation Example 1 was replaced with an equal amount of nano-alumina.

[0078] Comparative Example 3

[0079] The difference from Example 1 is that the mononuclear double-shell packing material prepared in Example 1 is used instead of the mononuclear double-shell packing material prepared in Example 4.

[0080] Comparative Example 4

[0081] The difference from Example 1 is that the amount of mononuclear double-shell filler added is 160g, in order to investigate the effect of slightly over-addition of mononuclear double-shell filler on the dielectric constant and thermal conductivity of the modified epoxy resin.

[0082] The modified epoxy resin solutions prepared in Examples 1-6 and Comparative Examples 1-4 were coated onto PET release films and then placed in an oven at 100-150°C to dry, forming a semi-cured film. The prepared semi-cured film was cut according to the target substrate size, ensuring neat edges and no burrs. Multiple semi-cured films were stacked together and placed into a stainless steel mold of a laminator. High-temperature resistant polytetrafluoroethylene films were laid on top and bottom. High-temperature sealing strips were attached to the edges of the mold to ensure vacuum sealing during lamination. The lamination was performed using a vacuum hot press to finally obtain an insulating substrate, which is a thermally conductive insulating film.

[0083] The lamination process uses existing lamination technology, which will not be described in detail here.

[0084] The thermal conductivity and dielectric constant of the thermally conductive insulating films subsequently prepared in Examples 1-6 and Comparative Examples 1-4 were tested. The thermal conductivity was tested using the laser flare method, and the dielectric constant was tested using the resonant cavity method. The test results are shown in Table 1.

[0085] Table 1 shows the thermal conductivity and dielectric constant of the thermally conductive insulating films corresponding to Examples 1-6 and Comparative Examples 1-4.

[0086]

[0087] As shown in Table 1, the thermally conductive insulating films made from the modified epoxy resin materials prepared in Examples 1-6 have a thermal conductivity of 1.81-2.70 W / (m·K) and a dielectric constant of only 3.2-3.5 without high-temperature treatment. After high-temperature treatment at 260℃, the thermal conductivity only decreases slightly, and the dielectric constant changes by ≤0.3, which is far superior to the thermal conductivity of the nano-Al2O3 filler in Comparative Examples 1-2 (0.35-0.42 W / (m·K)). Furthermore, the dielectric constant of Comparative Examples 1-2 is 4.8-5.0, and the performance deteriorates significantly after high temperature. This demonstrates the significant advantages of single-core double-shell fillers in terms of thermal conductivity and dielectric constant compared to single inorganic thermally conductive fillers.

[0088] A comparison of Example 1 and Comparative Example 3 shows that, at high temperatures, the dielectric constant of the mononuclear double-shell filler changes less. Both the inner and outer shells are chemically bonded to the porous nano-SiO2 core, making the shells less prone to detachment and dispersion at high temperatures. This demonstrates stronger stability compared to the conventional SiO2-GO core-shell structure (physical coating). Furthermore, due to the additional alumina shell layer, the thermal conductivity of Example 1 is significantly improved compared to Comparative Example 3.

[0089] When the amount of single-core double-shell filler added exceeds the upper limit, although the thermal conductivity of the thermally conductive insulating film increases slightly, the dielectric constant also increases slightly. In practice, the appropriate proportion of single-core double-shell filler added can be selected according to the acceptable upper limit of dielectric constant.

[0090] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0091] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a modified epoxy resin material for printed circuit boards, characterized in that, Includes the following steps: S1. Pretreatment of porous nano-SiO2: Disperse porous nano-SiO2 in deionized water, then add concentrated hydrochloric acid, stir at 60-80℃ for 2-4 hours, cool, wash, and dry to obtain activated porous nano-SiO2. S2. Primary encapsulation of porous nano-SiO2: Activated porous nano-SiO2 is dispersed in deionized water, and aluminum nitrate solution is slowly added dropwise at 40-50℃ while stirring. At the same time, dilute ammonia water is added dropwise to maintain the pH of the system at 7.5-8.

5. After the addition is completed, stirring is continued for 2 hours. After centrifugation, washing, drying, and calcination, porous nano-SiO2-Al2O3 composite particles are obtained. S3, Porous nano-SiO2 secondary encapsulation: Graphene oxide is encapsulated on the outside of porous nano-SiO2-Al2O3 composite particles to form a single-core double-shell filler; S4. Preparation of epoxy resin adhesive: S41. Pretreatment of packing material: Vacuum dry the mononuclear double shell packing material at 120℃ for 4 hours, add 1-3% of silane coupling agent by mass of the mononuclear double shell packing material, stir at high speed, sonicate for 30 minutes, and then dry at 80℃ for 1 hour. S42. Preparation of adhesive solution: Mix epoxy resin with reactive diluent, preheat in a water bath, add dispersant, and stir for 10 minutes; The single-core double-shell filler was added to the epoxy resin in batches while stirring, and ultrasonic treatment was assisted. Cool, add defoamer and curing agent and stir for 10 minutes, then add accelerator and stir for 5 minutes. Degas under vacuum for 15-20 minutes to obtain modified epoxy resin solution.

2. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... The mass ratio of the porous nano-SiO2, deionized water, and concentrated hydrochloric acid is 1:(4-8):(0.2-0.4).

3. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... The mass ratio of activated porous nano-SiO2, deionized water, and aluminum nitrate is 1:50:(0.3-0.5), and the concentration of the aluminum nitrate solution is 0.2-0.3 mol / L.

4. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that, Step S3, the secondary encapsulation process of porous nano-SiO2, includes: S31. Coupling treatment: Mix the silane coupling agent with deionized water and stir for 15 minutes to hydrolyze, and obtain the hydrolysate. Porous nano-SiO2-Al2O3 composite particles were dispersed in anhydrous ethanol to obtain a dispersion. Then, the hydrolysate was added dropwise to the dispersion. The mixture was stirred at 70℃ and 400 rpm for 4 h, centrifuged, washed, and vacuum dried at 80℃ for 6 h to obtain aminated porous nano-SiO2-Al2O3 composite particles. S32. Activation treatment of graphene oxide: Sonicate 2 g / L of graphene oxide aqueous dispersion for 1 h, ultrasonic frequency 20-40 kHz, ultrasonic power 300-500 W, add EDC・HCl and NHS to graphene oxide aqueous dispersion, stir for 30 min to obtain activated graphene oxide aqueous dispersion. S33. Encapsulation treatment: Aminated porous nano-SiO2-Al2O3 composite particles were added to the activated graphene oxide aqueous dispersion and stirred at 300 rpm for 24 h to allow the amino groups to react with the activated carboxyl groups to form amide bonds. The graphene oxide was then encapsulated on the outer surface of the porous nano-SiO2-Al2O3 composite particles to form a secondary encapsulation. After centrifugation and washing, the particles were vacuum dried at 60 °C for 12 h to obtain a single-core double-shell packing material.

5. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 4, characterized in that... During the coupling process, the mass ratio of porous nano-SiO2-Al2O3 composite particles, anhydrous ethanol, and silane coupling agent was 1:(15-20). 0.0125, the mass ratio of silane coupling agent to deionized water is 1:(5-10), and the silane coupling agent is KH550.

6. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 4, characterized in that... : In the graphene oxide activation treatment, the mass ratio of graphene oxide, EDC·HCl, and NHS is 1:(0.2-0.3):(0.1-0.15).

7. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... In the encapsulation process, the mass ratio of aminated porous nano-SiO2-Al2O3 composite particles to graphene oxide is 1:(0.015-0.03).

8. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... : The modified epoxy resin adhesive comprises, by weight, 100 parts epoxy resin, 15-30 parts mononuclear double-shell filler, 10-20 parts reactive diluent, 1-3 parts dispersant, 0.5-1 part defoamer, 80-85 parts curing agent, and 1-2 parts accelerator. The amount of graphene oxide added in the mononuclear double-shell filler is 0.3% of the weight of epoxy resin.

9. The method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... The reactive diluent is one of propylene oxide butyl ether and diglycidyl ether. The dispersant is one of silane dispersants or polycarboxylate dispersants; The defoamer is one of the following: silicone defoamer or polyether defoamer. The curing agent is one of methylhexahydrophthalic anhydride or methyltetrahydrophthalic anhydride, and the accelerator is benzyldimethylamine.

10. A method for preparing a modified epoxy resin material for printed circuit boards according to claim 1, characterized in that... The epoxy resin is one of the following: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene ring type epoxy resin, alicyclic epoxy resin, and fluorinated epoxy resin.

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