An interlayer insulating adhesive for a multilayer printed circuit board

Abstract

The present application relates to the technical field of printed circuit board, and discloses an interlayer insulating adhesive for multilayer printed circuit board, which is composed of a composite material system of modified polyimide resin 40-60 parts, epoxy resin 20-30 parts, boron nitride nanosheet activated by argon plasma 10-20 parts, silane coupling agent 3-8 parts, coated flame retardant 5-12 parts and leveling agent 0.5-2 parts.The dielectric constant of the adhesive is 3.2-3.5 and the loss tangent value is less than 0.005 at a frequency of 10GHz, the peel strength is greater than 0.8kN / m, and the insulation resistance retention rate is more than 95% after 1000 hours of damp heat aging, while realizing the synergistic optimization of UL94 V-0 level flame retardation and the thermal expansion coefficient less than 25ppm / ℃, improving the signal transmission reliability and long-term service stability of high-frequency circuit board, improving the mechanical impact resistance of the circuit board, and reducing the high-frequency signal transmission distortion rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printed circuit board, in particular to an interlayer insulating adhesive for multilayer printed circuit board. BACKGROUND

[0002] Printed circuit board, also known as printed circuit board and printed wiring board, is often abbreviated as PCB, which is an important electronic component, a support for electronic components and a provider of electronic component circuit connection. Since it is made by electronic printing technology, it is called "printed" circuit board. Before the emergence of printed circuit board, the interconnection between electronic components was directly connected by wires to form a complete circuit, and the circuit panel only existed as an effective experimental tool. Printed circuit board has become the absolute dominant position in the electronic industry. The interlayer insulating adhesive of multilayer printed circuit board is a key basic material for the miniaturization of modern electronic equipment, and its performance directly affects the high-frequency signal transmission reliability and long-term service stability of the circuit board, which is one of the core laminated media for realizing high-density interconnection structure.

[0003] At present, due to the multiple technical bottlenecks of the interlayer insulating adhesive, when the pressing process of the multilayer printed circuit board is implemented, the resin matrix of the conventional adhesive cannot inhibit the thermal stress mismatch at the interface between the filler and the resin during the high-temperature curing stage. If the interface delamination phenomenon is not controlled in time, it may cause the interlayer peeling strength to decrease, which seriously affects the mechanical reliability of the circuit board.

[0004] Therefore, the present application provides an interlayer insulating adhesive for multilayer printed circuit board to solve the above problems. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides an interlayer insulating adhesive for multilayer printed circuit board to solve the problems raised in the background art.

[0006] To achieve the above purpose, the present application provides the following technical solution: An interlayer insulating adhesive for multilayer printed circuit board is prepared from the following raw materials by weight:

[0007] Modified polyimide resin 40-60 parts, epoxy resin 20-30 parts, boron nitride nanosheet 10-20 parts, silane coupling agent 3-8 parts, flame retardant 5-12 parts and leveling agent 0.5-2 parts;

[0008] The preparation process comprises the following steps:

[0009] Step one: pretreatment, place the boron nitride nanosheet in a vacuum plasma treatment device, treat it under argon atmosphere at a power of 200-500W for 10-30 minutes to obtain activated boron nitride;

[0010] Step two: resin matrix preparation, modified polyimide resin and epoxy resin are added to the reaction kettle, control the temperature 25-35℃, stirring at 300-600r / min for 15-25 minutes;

[0011] Step three: dispersion treatment, activated boron nitride, silane coupling agent is added to the mixture obtained in step two, heated to 50-70℃, high speed dispersion at 800-1200r / min for 30-50 minutes;

[0012] Step four: blending modification, flame retardant and leveling agent are added to the product of step three, maintain the temperature 40-60℃, stirring at 400-800r / min for 20-40 minutes, to obtain homogeneous insulation adhesive.

[0013] Further, the modified polyimide resin is prepared by the following method:

[0014] 4,4'-diamino diphenyl ether and pyromellitic dianhydride are added to N-methyl pyrrolidone solvent in a molar ratio of 1:1.02-1.05, under nitrogen protection at 0-5℃ for 2-4 hours, then 1-3% of the total amount of nano titanium dioxide is added, heated to 80-100℃ and continue to react for 3-5 hours, after cooling, precipitate in deionized water, vacuum drying to obtain modified polyimide resin, its intrinsic viscosity is 0.65-0.75dL / g.

[0015] Further, the thickness of the boron nitride nanosheet is 50-200nm, the lateral size is 1-5μm, and the vacuum degree is controlled at 1×10 -2 ~5×10 -3 Pa, argon flow rate is 20-80sccm.

[0016] Further, the silane coupling agent is at least one of γ-aminopropyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane, which needs to be diluted to 10-20% concentration with anhydrous ethanol before adding.

[0017] Further, the flame retardant is prepared by the following method:

[0018] Aluminum hydroxide, ammonium polyphosphate and organic montmorillonite are mixed in a mass ratio of 5:3:1, added to a high-speed pulverizer and pulverized at 15000-20000r / min for 10-15 minutes, and then passed through an 800-1000 mesh screen. The powder obtained is coated with 1-2% of the total amount of polysiloxane in a fluidized bed.

[0019] Further, the high-speed dispersion in step three uses a disc type disperser, the ratio of the diameter of the dispersion disc to the diameter of the kettle body is 1:3-1:5, and the shear rate is 5000-8000s -1 .

[0020] Further, the application method of the insulating adhesive comprises:

[0021] The adhesive is applied to the surface of the copper foil of the circuit board, the coating thickness is controlled to be 20-50 mu m, preheating is performed at 80-100 DEG C for 3-5 minutes, then it is laminated with the adjacent insulating layer, and curing is performed in a vacuum hot press at a pressure of 0.5-1.5 MPa and a temperature of 160-180 DEG C for 30-60 minutes.

[0022] Further, the coating adopts a slot die coating head, the coating speed is 5-15 m / min, the back roll temperature is set to be 40-60 DEG C, and the coating gap accuracy is controlled to be ±2 mu m.

[0023] Further, the leveling agent is at least one of fluorocarbon modified polyacrylate and silicone polyether copolymer, and the molecular weight is 5000-10000 g / mol.

[0024] Further, the dielectric constant of the obtained insulating layer at a frequency of 10 GHz is 3.2-3.5, the dielectric loss tangent is less than 0.005, the thermal expansion coefficient is less than 25 ppm / DEG C, the peel strength is greater than 0.8 kN / m, and the flame retardant level reaches UL94 V-0 level.

[0025] Compared with the prior art, the application provides an interlayer insulating adhesive for a multilayer printed circuit board, which has the following beneficial effects:

[0026] 1. In the application, by setting the boron nitride plasma activation process, the chemical active site density on the surface of the boron nitride nanosheet is improved by performing argon atmosphere plasma treatment on the boron nitride nanosheet during the lamination of the multilayer circuit board, the uniformity of the filler in the resin matrix is improved, the local stress concentration phenomenon caused by the aggregation of the filler is reduced, the microstructure integrity of the interlayer interface is ensured, the interlayer peel strength is further improved, and the mechanical impact resistance of the circuit board is improved.

[0027] 2. In the application, by setting the polyimide-epoxy compound system, under high-temperature curing and high-frequency working conditions, the interpenetrating structure of the rigid segment of the modified polyimide and the flexible network of the epoxy resin is formed by regulation, the self-balancing mechanism of the dielectric constant and the thermal conductivity coefficient is constructed, the dielectric loss of the material under high frequency is stably controlled, and the thermal conductivity coefficient is maintained, the dielectric-thermal coupling distortion in high-speed signal transmission is inhibited in real time, the high-frequency signal transmission distortion rate is reduced, and the bit error rate of the 5G communication substrate is reduced.

[0028] 3. In the present application, by setting the segmented blending process, in the production process of the adhesive, by precisely controlling the order of raw material addition and process parameters in stages, the resin-filler stable interface is first established and then the functional additives are introduced, forming a dense organic-inorganic hybrid protective layer, which prolongs the water vapor permeation path and can block the electrochemical migration channel of copper ions in a humid environment, ensuring that the initial insulation resistance is maintained after environmental testing, breaking through the service life of the multilayer circuit board. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 A step flow chart of the interlayer insulating adhesive of the multilayer printed circuit board of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] Embodiment 1: An interlayer insulating adhesive for a multilayer printed circuit board, which is made of the following raw materials by weight:

[0032] 40 parts of modified polyimide resin, 20 parts of epoxy resin, 10 parts of boron nitride nanosheet, 3 parts of silane coupling agent, 5 parts of flame retardant, and 0.5 parts of leveling agent;

[0033] The preparation process comprises the following steps:

[0034] Step one: pretreatment, place the boron nitride nanosheet in a vacuum plasma treatment device, treat it in an argon atmosphere at a power of 200W for 10 minutes to obtain activated boron nitride;

[0035] Step two: resin matrix preparation, add modified polyimide resin and epoxy resin to a reaction kettle, control the temperature at 25℃, and stir at 300r / min for 15 minutes;

[0036] Step three: dispersion treatment, add activated boron nitride and silane coupling agent to the mixture obtained in step two, heat to 50℃, and disperse at a high speed of 800r / min for 30 minutes;

[0037] Step four: blending modification, add flame retardant and leveling agent to the product of step three, maintain the temperature at 40℃, and stir at 400r / min for 20 minutes to obtain a homogeneous insulating adhesive;

[0038] The modified polyimide resin is prepared by the following method:

[0039] The 4,4'-diaminodiphenyl ether and pyromellitic dianhydride are added in N-methyl pyrrolidone solvent in a molar ratio of 1:1.02, and reacted at 0℃ for 2 hours under nitrogen protection, then 1% of the total amount of nano titanium dioxide is added, and the temperature is raised to 80℃ for continuous reaction for 3 hours, and then cooled and precipitated in deionized water, and vacuum dried to obtain a modified polyimide resin with a specific viscosity of 0.65 dL / g;

[0040] The thickness of the boron nitride nanosheet is 50 nm, the lateral size is 1 μm, and the vacuum degree is controlled at 1×10 -2 Pa, and the argon flow rate is 20 sccm;

[0041] The silane coupling agent is at least one of γ-aminopropyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane, which is diluted to 10% concentration with anhydrous ethanol before being added;

[0042] The flame retardant is prepared by the following method:

[0043] The aluminum hydroxide, ammonium polyphosphate and organic montmorillonite are mixed in a mass ratio of 5:3:1, added into a high-speed pulverizer for pulverization at 15000 r / min for 10 minutes, and then screened through an 800 mesh screen, and the obtained powder is coated with 1% of the total amount of polysiloxane in a fluidized bed;

[0044] The high-speed dispersion in step three uses a disc disperser, the ratio of the diameter of the dispersion disc to the diameter of the kettle body is 1:3, and the shear rate is 5000 s -1 ;

[0045] The application method of the insulating adhesive includes:

[0046] The adhesive is coated on the surface of the copper foil of the circuit board, the coating thickness is controlled to be 20 μm, preheated at 80℃ for 3 minutes, then laminated with the adjacent insulating layer, and cured in a vacuum hot press at a pressure of 0.5 MPa and a temperature of 160℃ for 30 minutes;

[0047] The coating uses a slot die coater, the coating speed is 5 m / min, the back roll temperature is set to 40℃, and the coating gap accuracy is controlled to be ;

[0048] The leveling agent is at least one of fluorocarbon modified polyacrylate and organosilicon polyether copolymer, and the molecular weight is 5000 g / mol;

[0049] The obtained insulating layer has a dielectric constant of 3.2, a dielectric loss tangent value less than 0.005, a thermal expansion coefficient less than 25 ppm / ℃, a peel strength greater than 0.8 kN / m, and a flame retardant level reaching UL94 V-0 level.

[0050] Example 2: An interlayer insulating adhesive for a multilayer printed circuit board, made from the following raw materials in parts by weight:

[0051] Modified polyimide resin 50 parts, epoxy resin 25 parts, boron nitride nanosheet 15 parts, silane coupling agent 5.5 parts, flame retardant 8.5 parts and leveling agent 1.25 parts;

[0052] The preparation process comprises the following steps:

[0053] Step one: pretreatment, place the boron nitride nanosheet in a vacuum plasma treatment device, treat it in an argon atmosphere at a power of 350W for 20 minutes to obtain activated boron nitride;

[0054] Step two: resin matrix preparation, add modified polyimide resin and epoxy resin to the reaction kettle, control the temperature at 30℃, and stir at 450r / min for 20 minutes;

[0055] Step three: dispersion treatment, add activated boron nitride and silane coupling agent to the mixture obtained in step two, heat to 60℃, and disperse at a high speed of 1000r / min for 40 minutes;

[0056] Step four: blending modification, add flame retardant and leveling agent to the product of step three, maintain the temperature at 50℃, and stir at 600r / min for 30 minutes to obtain a homogeneous insulating adhesive;

[0057] The modified polyimide resin is prepared by the following method:

[0058] Add 4,4'-diamino diphenyl ether and pyromellitic dianhydride in a molar ratio of 1:1.035 to N-methyl pyrrolidone solvent, react under nitrogen protection at 2.5℃ for 3 hours, then add 2% of the total amount of nanometer titanium dioxide, heat to 90℃ and continue to react for 4 hours, cool and precipitate in deionized water, and vacuum dry to obtain modified polyimide resin with a specific viscosity of 0.70dL / g;

[0059] The thickness of the boron nitride nanosheet is 125nm, the lateral size is 3μm, and the vacuum degree is controlled at 7.5×10 -3 Pa, argon flow rate is 50sccm;

[0060] The silane coupling agent is at least one of γ-aminopropyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane, which needs to be diluted to 15% concentration with anhydrous ethanol before adding;

[0061] The flame retardant is prepared by the following method:

[0062] Aluminum hydroxide, ammonium polyphosphate and organic montmorillonite were mixed in a mass ratio of 5:3:1, added to a high-speed pulverizer and pulverized at 17500 r / min for 12.5 minutes, and then sieved through a 900-mesh screen. The obtained powder was coated with 1.5% of the total amount of polysiloxane in a fluidized bed;

[0063] The high-speed dispersion in step three was performed using a disc-type disperser with a ratio of the diameter of the dispersion disc to the diameter of the kettle body of 1:4 and a shear rate of 6500 s -1 ;

[0064] The application method of the insulating adhesive comprises:

[0065] The adhesive was coated on the surface of the copper foil of the circuit board, the coating thickness was controlled to be 35 μm, preheating was performed at 90°C for 4 minutes, then the adjacent insulating layer was laminated, and curing was performed in a vacuum hot press at a pressure of 1.0 MPa and a temperature of 170°C for 45 minutes;

[0066] The coating was performed using a slot-type coating head, the coating speed was 10 m / min, the back roll temperature was set to be 50°C, and the coating gap precision was controlled to be 0 μm;

[0067] The leveling agent was at least one of a fluorocarbon-modified polyacrylate and a silicone-polyether copolymer, and the molecular weight thereof was 7500 g / mol;

[0068] The obtained insulating layer had a dielectric constant of 3.35, a dielectric loss tangent value of less than 0.005, a thermal expansion coefficient of less than 25 ppm / °C, a peel strength of greater than 0.8 kN / m, and a flame retardant level of UL94 V-0 grade.

[0069] Example 3: An interlayer insulating adhesive for a multilayer printed circuit board was prepared from the following raw materials in parts by weight:

[0070] The modified polyimide resin was 60 parts, the epoxy resin was 30 parts, the boron nitride nanosheet was 20 parts, the silane coupling agent was 8 parts, the flame retardant was 12 parts, and the leveling agent was 2 parts;

[0071] The preparation process thereof included the following steps:

[0072] Step one: pretreatment, the boron nitride nanosheet was placed in a vacuum plasma treatment device, treated at a power of 500 W for 30 minutes in an argon atmosphere, and activated boron nitride was obtained;

[0073] Step two: preparation of the resin matrix, the modified polyimide resin and the epoxy resin were added to a reaction kettle, the temperature was controlled to be 35°C, and stirring was performed at 600 r / min for 25 minutes;

[0074] Step three: dispersion treatment, the activated boron nitride and the silane coupling agent were added to the mixture obtained in step two, the temperature was raised to 70°C, and high-speed dispersion was performed at 1200 r / min for 50 minutes;

[0075] Step four: blending modification, adding flame retardant and leveling agent to the product of step three, maintaining temperature at 60℃, stirring at 800r / min for 40 minutes, obtaining homogeneous insulating adhesive;

[0076] The modified polyimide resin is prepared by the following method:

[0077] 4,4'-diamino diphenyl ether and pyromellitic dianhydride are added to N-methyl pyrrolidone solvent in a molar ratio of 1:1.05, reacted at 5℃ for 4 hours under nitrogen protection, then 3% of nano titanium dioxide is added, and the temperature is raised to 100℃ for continuous reaction for 5 hours. After cooling, it is precipitated in deionized water and vacuum dried to obtain a modified polyimide resin with a specific viscosity of 0.75 dL / g;

[0078] The thickness of the boron nitride nanosheet is 200 nm, the lateral size is 5 μm, and the vacuum degree is controlled at 5×10⁻³ Pa during plasma treatment, and the argon flow rate is 80 sccm;

[0079] The silane coupling agent is at least one of γ-aminopropyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane, which is diluted to 20% concentration with anhydrous ethanol before use;

[0080] The flame retardant is prepared by the following method:

[0081] Aluminum hydroxide, ammonium polyphosphate and organic montmorillonite are mixed in a mass ratio of 5:3:1, added to a high-speed pulverizer at 20000r / min for 15 minutes, and sieved through a 1000 mesh screen. The obtained powder is coated with 2% of polysiloxane in a fluidized bed;

[0082] The high-speed dispersion in step three uses a disc-type disperser with a ratio of disperser disc diameter to kettle body diameter of 1:5 and a shear rate of 8000s -1 ;

[0083] The application method of the insulating adhesive includes:

[0084] The adhesive is coated on the surface of the copper foil of the circuit board, the coating thickness is controlled at 50 μm, preheated at 100℃ for 5 minutes, then laminated with the adjacent insulating layer, and cured in a vacuum hot press at a pressure of 1.5 MPa and a temperature of 180℃ for 60 minutes;

[0085] The coating uses a slot die coater, the coating speed is 15 m / min, the back roll temperature is set to 60℃, and the coating gap precision is controlled at 2 μm;

[0086] The leveling agent is at least one of fluorocarbon modified polyacrylate and organosilicon polyether copolymer, and its molecular weight is 10000 g / mol;

[0087] The dielectric constant of the obtained insulation layer at 10 GHz frequency is 3.5, the dielectric loss tangent is less than 0.005, the thermal expansion coefficient is less than 25 ppm / °C, the peel strength is greater than 0.8 kN / m, and the flame retardant level reaches UL94 V-0 level.

[0088] Comparative Example 1, the difference between this comparative example and Example 1 is that the argon plasma activation technology is not used in the filler treatment process.

[0089] Comparative Example 2, the difference between this comparative example and Example 2 is that a single polyimide resin is used in the resin matrix instead of the polyimide-epoxy compound system.

[0090] Comparative Example 3, the difference between this comparative example and Example 3 is that the polysiloxane coating process is omitted in the preparation of the flame retardant.

[0091] Comparative Example 4, the difference between this comparative example and Example 3 is that the one-step mixing method is used instead of the segmented blending process in the blending process.

[0092] The interlayer insulation adhesive of one of the multilayer printed circuit boards in Examples 1-3 and Comparative Examples 1-4 was tested for performance, and the test items and test methods are as follows:

[0093] High-frequency dielectric test: measure the dielectric constant and loss tangent at 10 GHz frequency.

[0094] Interlayer peel strength: measure the 90° peel strength using a universal material testing machine.

[0095] Hygrothermal aging test: detect the insulation resistance decay rate after 1000 hours in an 85°C / 85%RH environment.

[0096] Thermal mechanical property: measure the Z-direction thermal expansion coefficient using TMA method at a heating rate of 5°C / min.

[0097] Flame retardant safety: evaluate the flame retardant level according to the UL94 vertical burning standard.

[0098] The test data of the interlayer insulation adhesive of one of the multilayer printed circuit boards in Examples 1-3 and Comparative Examples 1-4 are recorded in Table 1 below:

[0099]

[0100] By comparing and analyzing the data in the table, it can be seen that the interlayer insulating adhesive of the multilayer printed circuit board in Examples 1-3 is obviously more excellent in performance than the interlayer insulating adhesive of the multilayer printed circuit board in Comparative Examples 1-4, which shows that by setting the boron nitride plasma activation process, when the multilayer circuit board is laminated and compounded, the chemical active site density of the boron nitride nanosheet is improved by argon atmosphere plasma treatment, the uniformity of the filler in the resin matrix is improved, the local stress concentration phenomenon caused by the agglomeration of the filler is reduced, the microstructure integrity of the interlayer interface is ensured, the interlayer peeling strength is further improved, the mechanical impact resistance of the circuit board is improved, by setting the polyimide-epoxy compound system, under high temperature curing and high frequency working conditions, the interpenetrating structure of the rigid segment of the modified polyimide and the flexible network of the epoxy resin is formed by adjusting, the self-balancing mechanism of the dielectric constant and the thermal conductivity coefficient is constructed, the dielectric loss of the material under high frequency is stably controlled, and the thermal conductivity coefficient is maintained, which can inhibit the dielectric-thermal coupling distortion in real time during high-speed signal transmission, ensure that the high-frequency signal transmission distortion rate is reduced, reduce the bit error rate of the 5G communication substrate, by setting the segmented blending process, in the adhesive production process, the raw material adding sequence and process parameters are accurately controlled in stages, the resin-filler stable interface is established, and then the functional additives are introduced, a dense organic-inorganic hybrid protective layer is formed, the water vapor permeation path is lengthened, the electrochemical migration channel of copper ions in a humid environment is blocked, and the initial insulating resistance is maintained after environmental testing, thereby breaking through the service life of the multilayer circuit board.

[0101] By comparing and analyzing the related data in the table, it can be seen that the interlayer insulating adhesive of the multilayer printed circuit board provided by the present application has achieved a breakthrough in the three core indicators of dielectric performance, mechanical strength and environmental stability. Therefore, the interlayer insulating adhesive of the multilayer printed circuit board provided by the present application has a broader market prospect and has great industrialization value in the trillion-level electronic information industry, and is more suitable for promotion.

[0102] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0103] The preferred embodiments of the application disclosed above are only to facilitate the elucidation of the application. The preferred embodiments do not describe all the details of the application and limit the application to the specific embodiments described. Obviously, many modifications and variations can be made in light of the teachings above. The description is chosen and described in order to best explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and get the best results from the application. The application is only limited by the claims and their full scope and equivalents.

Claims

1. An interlayer dielectric adhesive for a multilayer printed circuit board, characterized by: It is made from the following weight parts of raw materials: Modified polyimide resin 40-60 parts, epoxy resin 20-30 parts, boron nitride nanosheet 10-20 parts, silane coupling agent 3-8 parts, flame retardant 5-12 parts and leveling agent 0.5-2 parts; Its preparation process includes the following steps: Step one: pretreatment, the boron nitride nanosheet is placed in a vacuum plasma treatment equipment, treated at 200-500W power for 10-30 minutes in argon atmosphere to obtain activated boron nitride; Step two: resin matrix preparation, modified polyimide resin and epoxy resin are added to the reaction kettle, the temperature is controlled at 25-35℃, and stirring is carried out at 300-600r / min for 15-25 minutes; Step three: dispersion treatment, activated boron nitride and silane coupling agent are added to the mixture obtained in step two, heated to 50-70℃, and dispersed at high speed of 800-1200r / min for 30-50 minutes; Step four: blending modification, flame retardant and leveling agent are added to the product of step three, the temperature is maintained at 40-60℃, and stirring is carried out at 400-800r / min for 20-40 minutes to obtain homogeneous insulating adhesive; The flame retardant is prepared by the following method: Aluminum hydroxide, ammonium polyphosphate and organic montmorillonite are mixed in a mass ratio of 5:3:1, added to a high-speed pulverizer and pulverized at 15000-20000r / min for 10-15 minutes, then passed through an 800-1000 mesh screen, and the obtained powder is coated with 1-2% of polysiloxane in a fluidized bed; The high-speed dispersion in the step three adopts a disc disperser, the ratio of the diameter of the dispersion disc to the diameter of the kettle body is 1:3-1:5, and the shear rate is 5000-8000 s -1 .

2. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, characterized in that: The modified polyimide resin is prepared by the following method: 4,4'-diamino diphenyl ether and pyromellitic dianhydride are added to N-methyl pyrrolidone solvent in a molar ratio of 1:1.02-1.05, reacted at 0-5℃ for 2-4 hours under nitrogen protection, then 1-3% of nano titanium dioxide is added, the temperature is raised to 80-100℃, and the reaction is continued for 3-5 hours, then it is cooled and precipitated in deionized water, and vacuum dried to obtain modified polyimide resin with intrinsic viscosity of 0.65-0.75dL / g.

3. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, characterized in that: The thickness of the boron nitride nanosheet is 50-200 nm, the lateral size is 1-5 μm, and the vacuum degree is controlled at 1×10 -2 -3 Pa during the plasma treatment, and the argon flow rate is 20-80 sccm.​ 4. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, characterized in that: The silane coupling agent is at least one of γ-aminopropyl triethoxysilane and γ-glycidyl ether propyl trimethoxysilane, which needs to be diluted to 10-20% concentration with anhydrous ethanol before adding.

5. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, wherein: The application method of the insulating adhesive includes: The adhesive is coated on the surface of the copper foil of the circuit board, the coating thickness is controlled at 20-50μm, preheated at 80-100℃ for 3-5 minutes, then laminated with the adjacent insulating layer, and cured in a vacuum hot press at a pressure of 0.5-1.5MPa and a temperature of 160-180℃ for 30-60 minutes.

6. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 5, wherein: The coating is carried out by using a slot die coating head, the coating speed is 5-15m / min, the back roll temperature is set to 40-60℃, and the coating gap precision is controlled within ±2μm.

7. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, wherein: The leveling agent is at least one of fluorocarbon modified polyacrylate and organosilicon polyether copolymer, and its molecular weight is 5000-10000g / mol.

8. An interlayer die attach adhesive for a multilayer printed circuit board according to claim 1, characterized in that: The dielectric constant of the obtained insulation layer at 10GHz frequency is 3.2-3.5, the dielectric loss tangent is less than 0.005, the thermal expansion coefficient is less than 25ppm / ℃, the peeling strength is greater than 0.8kN / m, and the flame retardant level reaches UL94 V-0 level.

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