High-thermal-conductivity and low-dielectric composite material capable of being dynamically repaired as well as preparation method and application of high-thermal-conductivity and low-dielectric composite material

Abstract

The invention relates to a high-thermal-conductivity and low-dielectric composite material capable of being dynamically repaired and a preparation method and application thereof, and belongs to the technical field of electronic advanced packaging and high-frequency substrate thermal management materials. According to the invention, a traditional hydroxyl-containing binder is abandoned, and a boron-oxygen-six-ring-crosslinked 3D boron nitride bidirectional orientation skeleton is constructed in situ by using a self-condensation reaction of a boric acid precursor under bidirectional freeze concentration; meanwhile, novel polysiloxane with a discotic liquid crystal side chain and a dynamic borate network is synthesized; a vacuum-pressure alternating auxiliary impregnation process is utilized to induce the disc-shaped liquid crystal to be assembled on the surface of a framework in an epitaxial manner, and in-situ addition curing without byproducts is carried out. According to the invention, the industrial pain points that the traditional packaging material cannot give consideration to Z-axis high thermal conductivity, high-frequency ultralow dielectric loss and unreworkable property after curing are overcome, and the packaging material is especially suitable for the fields of 5G / 6G high-frequency communication and 2.5 D / 3D Chiplet advanced system-level packaging.

Description

Technical Field

[0001] This invention relates to the field of advanced electronic packaging and high-frequency substrate thermal management materials, and particularly to a dynamically repairable high thermal conductivity, low dielectric composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of fifth-generation (5G) and even sixth-generation (6G) mobile communication technologies, high-frequency millimeter-wave bands (typically referring to 30GHz to 300GHz) have become the core frequency bands for improving data transmission rates and system capacity. Simultaneously, to overcome the physical and economic limits of Moore's Law, chip-based heterogeneous integration technologies, such as TSMC's CoWoS (Chip-on-Wafer-on-Substrate) and InFO (Integrated Fan-Out) advanced three-dimensional stacked packaging solutions, have become the mainstream path for achieving system-level integration of high-performance processors and high-bandwidth memory (HBM). The convergence of these two technological trends has led to an exponential increase in heat flux density within the package structure. In particular, the tight stacking of multiple high-performance bare chips (dies) in the vertical direction (Z-axis) results in a highly concentrated heat source, with heat primarily conducted along the thickness direction (Z-axis), creating a severe "thermal accumulation" effect within the package. This places unprecedentedly stringent requirements on the vertical thermal conductivity of the materials.

[0003] Currently, mainstream thermal conductive materials for electronic packaging mostly employ composite material systems that blend organosilicon or epoxy resin with highly thermally conductive inorganic fillers (such as alumina, boron nitride, and silicon nitride). However, when facing the dual challenges of 5G / 6G millimeter-wave communication and chiplet 3D stacking, traditional blending systems reveal three fatal flaws: First, the filler particles are distributed randomly and disordered in a "sea-island" structure within the resin matrix, making it difficult to form a continuous and efficient thermal conduction path along the crucial Z-axis. This results in the composite material's Z-axis thermal conductivity being far lower than the theoretical value, failing to meet the rapid heat dissipation requirements of 3D stacked structures. Second, the high filler content strategy pursued for high thermal conductivity inevitably leads to a large number of interfacial micropores between the resin matrix and filler particles, as well as between the filler particles themselves. Under the influence of a high-frequency alternating electric field, space charge accumulates at these defective interfaces, triggering a significant Maxwell-Wagner interfacial polarization effect. This effect drastically degrades the high-frequency dielectric properties of materials, specifically manifested as a significant increase in the dielectric constant (Dk) and dielectric loss factor (Df). This not only leads to severe delays and attenuation of millimeter-wave signals during transmission but also generates additional heat due to dielectric loss, creating a positive feedback loop of thermoelectric performance degradation, severely restricting its application prospects in 6G and higher frequency bands. Third, and most critically, once traditional thermally conductive fillers and encapsulating resins (such as epoxy resin) undergo a thermosetting cross-linking reaction, a permanent and irreversible three-dimensional chemical network is formed. This means the entire package becomes a dense, integrated structure. In expensive heterogeneous integrated packaging modules (such as CPU / GPU packages containing HBM), if a single chip fails, the entire package, worth thousands or even tens of thousands of dollars, will be scrapped because the packaging material cannot be removed without damage to expose the underlying chip for repair or replacement, resulting in huge economic losses and resource waste. This "non-repairable" characteristic runs counter to the high-yield and high-value reuse principles pursued in high-end chip manufacturing.

[0004] To address the shortcomings of traditional systems, the industry has explored various modification methods. For example, liquid crystal epoxy resins have been used to replace ordinary epoxy resins to improve thermal conductivity and mechanical properties in a single direction (such as the Z-axis). Low-polarity functional groups or mesoporous materials have been introduced to reduce the dielectric constant and loss of the system. However, the intrinsic polarity of existing liquid crystal epoxy resins remains relatively high, making it difficult to meet the requirements of extremely low dielectric loss (Df < 0.002) for the 6G millimeter-wave band. More importantly, both traditional epoxy resins and modified liquid crystal epoxy resins are essentially thermosetting systems; once cross-linked and cured, they cannot be dissolved or melted, and the aforementioned "non-repairable" problem has remained unresolved.

[0005] Therefore, developing a new generation of electronic packaging materials that can simultaneously achieve the three major characteristics of "Z-axis oriented high thermal conductivity", "ultra-low dielectric loss" and "intelligent repairability" has become a key technical bottleneck that urgently needs to be solved in this field. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a dynamic, reworkable high thermal conductivity, low dielectric composite material, its preparation method and application, in order to solve the problem that existing electronic packaging composite materials cannot simultaneously achieve the three major characteristics of "Z-axis oriented high thermal conductivity", "ultra-low dielectric loss" and "intelligent reworkability".

[0007] In a first aspect, the present invention provides a method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material, comprising the following steps: S1. Two-dimensional boron nitride (2D-BN) nanosheets and boric acid precursor are dispersed in deionized water to form a slurry. The slurry is placed in a bidirectional temperature gradient mold for directional freezing. After freeze drying and thermal annealing, a 3D-BN sponge skeleton is formed. S2. Using 2,3,6,7,10,11-hexahedoxybenzotriphenylene (HAT6) as a precursor, a disc-shaped liquid crystal monomer with a single-ended alkenyl flexible tail was prepared by controlled cleavage and etherification reaction. S3. Dissolve polymethylhydrosiloxane (PMHS), the disc-shaped liquid crystal monomer described in step S2, and the diene dynamic borate crosslinking agent in an organic solvent, add a platinum complex catalyst, and prepare a disc-shaped liquid crystal organosilicon impregnation solution. S4. The disk-shaped liquid crystal silicone impregnation liquid is injected into the 3D-BN sponge skeleton. After the impregnation is saturated by vacuum-pressure alternating process, the 3D-BN sponge skeleton is taken out and left to stand at room temperature for 1-2 hours. Then, it is heated and cured to obtain the dynamic repairable high thermal conductivity and low dielectric composite material. The boric acid precursor is one or more of 1,4-phenyldiboronic acid (BDBA), 4,4'-biphenyldiboronic acid, and 1,4-naphthalenediboronic acid.

[0008] This invention abandons traditional hydroxyl-containing adhesives and utilizes 1,4-phenylenediboric acid, 4,4'-biphenylenediboric acid, or 1,4-naphthalenediboric acid as precursors in a self-condensation reaction under bidirectional freeze-concentration to construct in situ a 3D boron nitride bidirectional oriented framework crosslinked with "boroxine". At the same time, a novel polysiloxane with disc-shaped liquid crystal side chains and a dynamic borate ester network is synthesized. Using a vacuum-pressure alternating assisted impregnation process, the disc-shaped liquid crystal is induced to epitaxially assemble on the surface of the framework and undergo in situ addition curing without byproducts. The resulting composite material overcomes the industry pain points of traditional electronic packaging materials, which cannot simultaneously achieve high thermal conductivity along the Z-axis, ultra-low dielectric loss at high frequencies, and the inability to be repaired and reworked after curing. The material has a Z-axis thermal conductivity of 2.70~6.80 W / m·K and a dielectric loss of ≤0.0022 at 10 GHz. Furthermore, it has the ability to intelligently deconstruct and repair and recycle fillers without damage within 15~40 minutes in a specific synergistic liquid, making it particularly suitable for 5G / 6G high-frequency communication and 2.5D / 3D Chiplet advanced system-in-package (SiP) applications.

[0009] Further, in step S1, the mass fraction of the two-dimensional boron nitride nanosheets in the slurry is 10~20 wt.%; the amount of boric acid precursor added is 2~10 wt.% of the total mass of the two-dimensional boron nitride nanosheets; more preferably, the amount of boric acid precursor added is 3 wt.% of the total mass of the two-dimensional boron nitride nanosheets. And / or, the freeze-drying conditions are: temperature -50°C, absolute pressure <10 Pa, and drying time not less than 48 h; And / or, the heating and annealing method is as follows: heating to 110-150°C at a rate of 1-5°C / min and holding at that temperature for 2-4 hours.

[0010] More preferably, the heating and annealing method is as follows: heating to 120°C at a rate of 2°C / min and holding at that temperature for 2 hours.

[0011] Only a small amount of boric acid precursor is needed to generate a dynamic valence-supported crosslinking network composed of boron-oxygen hexacyclic rings in situ through its self-condensation dehydration reaction. This avoids the deterioration of high-frequency dielectric loss caused by the introduction of traditional hydroxyl-containing adhesives (such as polyvinyl alcohol), fundamentally eliminates the polarization defects of residual hydroxyl groups, and ensures extremely low intrinsic dielectric loss of the backbone.

[0012] Further, in step S2, the method for synthesizing the disk-shaped liquid crystal monomer is as follows: 2,3,6,7,10,11-hexahedoxybenzotriphenylene and boron tribromide are subjected to a cleavage reaction at a molar ratio of 1:1.1~1.5 to obtain a monohydroxy intermediate; the monohydroxy intermediate is subjected to an etherification reaction with 11-bromo-1-undecene or 6-bromo-1-hexene at a molar ratio of 1:1.2~2.0 to obtain the disk-shaped liquid crystal monomer.

[0013] Specifically, the solvent for the cleavage reaction can be one or more of dichloromethane, 1,2-dichloroethane, and chloroform; the solvent for the etherification reaction can be one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and dimethyl sulfoxide.

[0014] Further, in step S3, the diene-based dynamic borate crosslinking agent is prepared by a dehydration condensation reaction of a diboronic acid compound and an alkenyl-containing diol compound; the diboronic acid compound includes one or more of 1,4-phenyldiboronic acid and 4,4'-biphenyldiboronic acid; the alkenyl-containing diol compound includes one or more of propyleneoxypropylene glycol and 5-ethylene-1,2-diol; the molar ratio of the diboronic acid compound to the alkenyl-containing diol compound is 1:2~2.1.

[0015] Specifically, the solvent for the dehydration condensation reaction of diboronic acid compounds with alkenyl-containing diol compounds can be one or more of toluene, xylene, and cyclohexane.

[0016] Furthermore, in step S3, the raw material ratio of the disc-shaped liquid crystal organosilicon impregnation solution is controlled to be 1:0.2~0.6:0.4~0.8, where the molar ratio of Si-H bonds:disc-shaped liquid crystal monomer double bonds:crosslinking agent double bonds is 1:0.2~0.6:0.4~0.8.

[0017] Further, in step S4, the operation method of the vacuum-pressure alternating process is as follows: first, the 3D-BN sponge skeleton is evacuated to an absolute pressure ≤50 mbar and maintained for 20~45 min, then the disk-shaped liquid crystal silicone impregnation liquid is injected, and a positive pressure of 0.1~0.6 MPa is applied and maintained for 20~240 min.

[0018] Further, in step S4, the reaction conditions for the heating and curing are as follows: heating to 60-80℃ at a rate of 1-5℃ / min and holding for 2-4 h; then heating to 120-150℃ and holding for 2-4 h.

[0019] More preferably, the heating and curing reaction conditions are as follows: heating to 80°C at a rate of 1~5°C / min and holding at that temperature for 2 hours; then heating to 150°C and holding at that temperature for 4 hours.

[0020] Furthermore, the composite material can be degraded into a gel state by heating with a composite synergistic repair solution. After rinsing, the waste liquid is centrifuged and washed to recover two-dimensional boron nitride. The composite synergistic repair solution is composed of a good solvent and a dynamic bond-breaking agent in a volume ratio of 1 to 3:1. The good solvent is one or more of toluene and D-limonene. The dynamic bond-breaking agent is one or more of ethylene glycol and 1,3-propanediol. The heating treatment is performed at a temperature of 60~80℃ for 15~40 min; the centrifugal washing speed is ≥3000 rpm.

[0021] Secondly, this invention provides a dynamically repairable high thermal conductivity and low dielectric composite material, prepared by the above-mentioned method; the composite material has a dual dynamic covalent interpenetrating network structure of "inorganic boron-oxygen hexacyclic crosslinked bidirectional 3D-BN sponge skeleton / organic borate ester crosslinked disc-shaped liquid crystal polysiloxane"; under a filler load of 10~20 wt.%, the Z-axis thermal conductivity of the composite material is 2.70~6.80 W / m·K; at a frequency of 10 GHz, the dielectric constant is 2.82~3.05, the dielectric loss is ≤0.0022; the coefficient of thermal expansion is 80~135 ppm / ℃; and it can complete intelligent gel decomposition within 15~40 min in a composite synergistic repair solution at 60~80 ℃.

[0022] Thirdly, the present invention also provides an application of a dynamically repairable high thermal conductivity, low dielectric composite material, which is used as an electronic packaging composite material in the fields of 5G / 6G high-frequency communication and 2.5D / 3D Chiplet advanced system-in-package.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. Order-of-magnitude leap in Z-axis thermal conductivity: This invention abandons traditional polymer binders, such as polyvinyl alcohol (PVA), which easily introduce polar impurities. Instead, it utilizes only the self-condensation of boric acid precursors under freeze concentration to construct an in-situ 3D-BN sponge framework cross-linked with boron-oxygen hexacyclic rings. During impregnation, the disk-shaped liquid crystal groups, due to their high geometric similarity to the surface of the 2D-BN nanosheets constituting the pore walls of the 3D framework, spontaneously adhere to the pore wall surface through π-π interactions, achieving rapid and seamless Z-axis phonon transmission. This invention, through bidirectional freeze casting and epitaxial assembly of disk-shaped liquid crystals, completely eliminates the scattering of heat conduction by horizontal grain boundaries and the micro-gaps at the resin interface, achieving a leap in Z-axis thermal conductivity with extremely low filler ratios.

[0024] 2. Solving the Pain Point of High-Frequency Dielectric Loss: This invention innovatively synthesizes polysiloxanes with disc-shaped liquid crystal groups such as benzotriphenylene on the side chains. The main chain provides extremely low intrinsic polarizability, and the disc-shaped liquid crystal groups self-assemble to form a highly dense "columnar phase" during curing. The strong steric hindrance "physically freezes" the residual polar groups in the siloxane network, giving the resin matrix extremely low high-frequency dielectric loss. In the preparation of the 3D-BN sponge skeleton of this invention, PVA and other binders containing highly polar hydroxyl groups are completely eliminated. The freeze-concentration effect drives the boric acid precursor to self-condense and dehydrate to form hydroxyl-free boron-oxygen hexagons. Combined with the polar steric freezing effect of the disc-shaped liquid crystal organosilicon, polarization defects are fundamentally eliminated. The material has extremely low dielectric constant and dielectric loss at 10 GHz and even millimeter-wave frequencies.

[0025] 3. Green and Non-destructive Collaborative Repair and Recycling Mechanism: This invention endows thermosetting encapsulation materials with unprecedented intelligent deconstruction capabilities. Dynamic covalent bonds are introduced into both the inorganic framework (boron-oxygen hexacyclic rings) and the organic resin (dynamic diene borate esters). At room temperature, it exhibits a highly reliable solid state. Under the stimulation of a specific repair solution, the dual network undergoes chemical deconstruction, enabling non-destructive disassembly of expensive chips and green recycling of inorganic fillers. During the repair process, a good solvent first breaks the π-π physical stacking of the disk-shaped liquid crystal, causing the matrix to swell. Subsequently, a small-molecule diol penetrates deep into the network, targeting and severing the borate ester crosslinking bonds in the organosilicon network and the boron-oxygen hexacyclic ring points of the 3D-BN sponge framework. Based on the synergistic destruction of physical swelling and dual chemical bond breaking, the high-strength solid material rapidly degrades into a gel state. This not only enables the mechanical stress-free rescue of chip modules costing tens of thousands of dollars, but also allows for the closed-loop recycling of expensive 2D-BN fillers through low-speed centrifugation, significantly reducing the economic and environmental costs of advanced manufacturing.

[0026] 4. "Softness Overcoming Hardness" Thermal Stress Dissipation Mechanism: This invention creatively controls the coefficient of thermal expansion (CTE) of the composite material within a golden buffer range of 80~150 ppm / °C. This range not only reflects the effective physical constraint of the 3D-BN sponge skeleton on the high-expansion organosilicon (original value >220 ppm / °C), but also perfectly preserves the intrinsic low-modulus flexibility of the matrix, thus constructing a "softness overcoming hardness" thermal stress dissipation mechanism, while providing the necessary free volume for the dynamic deconstruction and repair of the polymer.

[0027] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained through the specific points highlighted in the description. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention.

[0029] With the rapid evolution of 5G / 6G millimeter-wave communication and advanced chip packaging (such as CoWoS technology), the three-dimensional stacking of multiple high-performance bare chips leads to an exponential increase in heat flux density, with heat mainly concentrated in the thickness direction (Z-axis). Traditional silicone and thermally conductive filler blends have three major drawbacks: First, the filler is randomly arranged in the resin, making it difficult to construct efficient Z-axis heat dissipation channels; second, high filler content leads to severe interfacial microporosity, causing Maxwell-Wagner interface polarization under high-frequency alternating electric fields, resulting in a sharp deterioration of the material's dielectric constant (Dk) and dielectric loss (Df); third, once the traditional thermally conductive bottom filler or encapsulation resin is thermally cured and cross-linked, it forms an irreversible three-dimensional dead network. If a single chip in the encapsulation module is damaged, the entire encapsulation, worth tens of thousands of dollars, cannot be disassembled and reworked.

[0030] To address the shortcomings of traditional systems, the industry has explored various modification schemes. For example, replacing ordinary epoxy resins with liquid crystal epoxy resins leverages the self-assembly capability of their liquid crystal units to induce molecular chain orientation to some extent, thereby improving thermal and mechanical properties in a single direction (such as the Z-axis). Simultaneously, some studies have introduced low-polarity functional groups or mesoporous materials to reduce the dielectric constant and loss of the system. However, the intrinsic polarity of existing liquid crystal epoxy resins remains relatively high; ester bonds and rigid mesocrystalline units in their molecular structure still exhibit significant dipole polarization at high frequencies, making it difficult to meet the requirements of ultra-low dielectric loss (Df) in the 6G millimeter-wave band. More importantly, both traditional epoxy resins and modified liquid crystal epoxy resins are essentially thermosetting systems; once cross-linked and cured, they cannot dissolve or melt, and the aforementioned "irreparable" problem has remained unresolved.

[0031] Therefore, the present invention provides a method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material, comprising the following steps: S1. 2D-BN nanosheets and boric acid precursor are dispersed in deionized water to form a slurry. The slurry is placed in a two-way temperature gradient mold for directional freezing. After freeze drying and thermal annealing, a 3D-BN sponge skeleton is formed. S2. Using 2,3,6,7,10,11-hexahedoxybenzotriphenylene (HAT6) as a precursor, a disc-shaped liquid crystal monomer with a single-ended alkenyl flexible tail was prepared by controlled cleavage and etherification reaction. S3. Dissolve polymethylhydrosiloxane (PMHS), the disc-shaped liquid crystal monomer from step S2, and the diene dynamic borate crosslinking agent in an organic solvent, add a platinum complex catalyst, and prepare a disc-shaped liquid crystal organosilicon impregnation solution. S4. Inject the disc-shaped liquid crystal silicone impregnation solution into the 3D-BN sponge skeleton. After saturation by vacuum-pressure alternating process, take out the 3D-BN sponge skeleton and let it stand at room temperature for 1~2 h. Then, heat up to cure it to obtain a dynamic repairable high thermal conductivity and low dielectric composite material. Specifically, in step S1, the boric acid precursor is one or more of 1,4-phenyldiboronic acid (BDBA), 4,4'-biphenyldiboronic acid, and 1,4-naphthalenediboronic acid.

[0032] It should be noted that, to avoid the deterioration of high-frequency dielectric loss caused by the introduction of traditional hydroxyl-containing binders (such as PVA), this invention introduces only a trace amount of boric acid precursor into the slurry. Taking BDBA as an example, BDBA is used as a single precursor without the addition of any aliphatic polyols. The mixed slurry is placed in a bidirectional temperature gradient mold for directional freezing. During the subsequent vacuum drying and sublimation dehydration process, the complete escape of water disrupts the chemical equilibrium. The escape of water causes the solute to concentrate in the interface region of BN nanosheets and initially drives the self-condensation reaction of BDBA molecules enriched at the BN grain boundaries. Subsequently, the vacuum is released, and a step-by-step programmed temperature heating annealing treatment is performed under inert gas purging. This confined annealing process further promotes the dehydration reaction, generating in situ a dynamic covalent cross-linked network composed of "boron-oxygen hexacyclic rings". This step not only "softly bridges" the 2D-BN nanosheets into a high-strength 3D oriented framework, but also fundamentally eliminates the polarization defects of residual hydroxyl groups, ensuring extremely low intrinsic dielectric loss of the framework.

[0033] Specifically, in step S1, a wedge-shaped pad is provided at the bottom of the bidirectional temperature gradient mold, and the material of the wedge-shaped pad is polydimethylsiloxane (PDMS).

[0034] Specifically, in step S1, the mass fraction of 2D-BN nanosheets in the slurry is 10~20 wt.%, for example: 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%; the amount of boric acid precursor added is 2~10 wt.% of the total mass of the two-dimensional boron nitride nanosheets (for example: 2 wt%, 3 wt.%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%). More preferably, the amount of boric acid precursor added is 3 wt.% of the total mass of the two-dimensional boron nitride nanosheets. With the increase of the amount of 2D-BN nanosheets added, a denser bidirectional oriented 3D-BN sponge skeleton can be obtained, and the Z-axis thermal conductivity increases accordingly.

[0035] Specifically, in step S1, the freeze-drying conditions are: temperature -50℃, absolute pressure <10 Pa, and drying time not less than 48 h.

[0036] Specifically, in step S1, the heating and annealing method is as follows: the temperature is increased to 110~150℃ (e.g., 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min) at a rate of 1~5℃ / min (e.g., 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃) and held for 2~4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h).

[0037] More preferably, the method of heating and annealing is as follows: heating to 120 °C at a rate of 2 °C / min and holding at that temperature for 2 h.

[0038] Specifically, the size range of the 2D-BN nanosheets of this invention can be selected as follows: average sheet diameter of 2~15 μm and thickness of 10~20 nm. When 2D-BN nanosheets with an average sheet diameter of 2~5 μm are selected, the cost can be effectively controlled while obtaining a composite material that simultaneously considers thermal conductivity, dielectric properties and coefficient of thermal expansion, which can meet the needs of conventional application scenarios. When ultra-large 2D-BN nanosheets with an average sheet diameter of 10~15 μm are selected, a "high-speed" 3D-BN sponge skeleton with larger porosity and fewer grain boundaries can be produced, significantly improving the Z-axis thermal conductivity. However, the material cost increases, making it suitable for special scenarios with higher requirements for thermal conductivity.

[0039] Specifically, in step S2, the method for synthesizing the disk-shaped liquid crystal monomer is as follows: 2,3,6,7,10,11-hexahexoxybenzotriphenylene and boron tribromide are subjected to a cleavage reaction at a molar ratio of 1:1.1~1.5 to obtain a monohydroxy intermediate; the monohydroxy intermediate is subjected to an etherification reaction with 11-bromo-1-undecene or 6-bromo-1-hexene at a molar ratio of 1:1.2~2.0 to obtain the disk-shaped liquid crystal monomer.

[0040] It should be noted that, using HAT6 as the initial precursor, boron tribromide was used in an anhydrous environment for controlled local molecular cleavage to remove the single hexyl group and expose the phenolic hydroxyl group, thus preparing monohydroxy pentahexyloxybenzotriphenylene. Subsequently, taking 11-bromo-1-undecene as an example, under alkaline catalytic conditions, it was subjected to a Williamson etherification reaction with 11-bromo-1-undecene to synthesize a disc-shaped liquid crystal monomer with a flexible tail of a specific carbon chain length, namely 2-(10-undecenoxy)-3,6,7,10,11-pentahexyloxybenzotriphenylene.

[0041] Specifically, the solvent for the cleavage reaction can be one or more of dichloromethane, 1,2-dichloroethane, and chloroform; the solvent for the etherification reaction can be one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0042] It should be noted that in the cleavage reaction, the molar ratio of HAT6 to boron tribromide is 1:1.1~1.5, for example: 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5. In the etherification reaction, the molar ratio of the monohydroxy intermediate to 11-bromo-1-undecene or 6-bromo-1-hexene is 1:1.2~2.0, for example: 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0.

[0043] Specifically, in step S3, the diene dynamic borate crosslinking agent is prepared by a dehydration condensation reaction of a diboronic acid compound and an alkenyl-containing diol compound; the diboronic acid compound includes one or more of 1,4-phenyldiboronic acid and 4,4'-biphenyldiboronic acid; the alkenyl-containing diol compound includes one or more of propyleneoxypropanediol and 5-ethylene-1,2-diol; the molar ratio of the diboronic acid compound to the alkenyl-containing diol compound is 1:2 to 2.1, for example: 1:2, 1:2.05, 1:2.1.

[0044] Specifically, the solvent for the dehydration condensation reaction of diboronic acid compounds with alkenyl-containing diol compounds can be one or more of toluene, xylene, and cyclohexane.

[0045] It should be noted that the diene dynamic borate ester crosslinking agent is a crosslinking agent with double bonds at both ends and a dynamic borate ester ring inside. The diene dynamic borate ester crosslinking agent can also be prepared using other conventional synthetic methods in the prior art, such as reacting a diboronic acid compound (e.g., 4,4'-biphenyl diboronic acid) with a diol containing crosslinkable double bonds (e.g., trimethylolpropane monoallyl ether). In this case, the molar ratio of 4,4'-biphenyl diboronic acid to trimethylolpropane monoallyl ether is 1:2.05.

[0046] Specifically, in step S3, the raw material ratio of the disc-shaped liquid crystal silicone impregnation solution is controlled to be 1:0.2~0.6:0.4~0.8, for example: 1:0.2:0.8, 1:0.3:0.7, 1:0.4:0.6, 1:0.5:0.5, 1:0.6:0.4. The organic solvent can be any one of toluene, xylene, and cyclohexane, and the solid content of the disc-shaped liquid crystal silicone impregnation solution is controlled to be within the range of 40%~60%.

[0047] It should be noted that in the formulation of the disk-shaped liquid crystal silicone impregnation solution: increasing the grafting ratio of disk-shaped liquid crystal monomers, that is, sacrificing some mechanical crosslinking in exchange for a denser columnar liquid crystal network stack; if the proportion of diene-based dynamic borate ester crosslinking agent is significantly increased, a high-density reversible network rich in dynamic ester exchange sites can be constructed.

[0048] This invention innovatively synthesizes polysiloxanes with disc-shaped liquid crystal groups such as benzotriphenylene (TP) on the side chains. The main chain provides extremely low intrinsic polarizability; the disc-shaped liquid crystal groups self-assemble into a highly dense "columnar phase" during curing, and the strong steric hindrance "physically freezes" the residual polar groups in the siloxane network, giving the resin matrix extremely low high-frequency dielectric loss.

[0049] Specifically, in step S4, the operation method of the vacuum-pressure alternating process is as follows: first, the 3D-BN sponge skeleton is evacuated to an absolute pressure ≤50 mbar and maintained for 20~45 min; after injecting the disk-shaped liquid crystal silicone impregnation liquid, a positive pressure of 0.1~0.6 MPa is applied and maintained for 20~240 min.

[0050] It should be noted that a vacuum-pressure alternating impregnation process is used to inject the impregnation solution into the 3D-BN sponge skeleton. Negative pressure is used to eliminate air in the pores, and epitaxial assembly is induced under capillary force and liquid crystal π-π coupling. Specifically, in the above steps, the absolute pressure of the vacuum can be controlled to ≤30 mbar, ≤35 mbar, ≤40 mbar, or ≤45 mbar; the holding time can be selected as: 20 min, 22 min, 25 min, 28 min, 30 min, 33 min, 35 min, 38 min, 40 min, or 45 min. After injecting the disk-shaped liquid crystal silicone impregnation solution, the applied positive pressure can be selected as: 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, or 0.6 MPa; the holding time can be selected as: 20 min, 60 min, 80 min, 100 min, 140 min, 160 min, 180 min, 200 min, 220 min, or 240 min. Understandably, the higher the BN concentration, the lower the porosity of the material, and the longer the silicon impregnation time. Meanwhile, to avoid instantaneous pressure causing the framework to crack, a gradual pressure application method is adopted.

[0051] Specifically, in step S4, the reaction conditions for the heating and curing are as follows: heating to 60-80℃ (e.g., 60℃, 65℃, 70℃, 75℃, 80℃) at a rate of 1-5℃ / min (e.g., 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min) and holding at that temperature for 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h); then heating to 120-150℃ (e.g., 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃) and holding at that temperature for 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h, 4 h).

[0052] It should be noted that the saturated 3D-BN sponge skeleton is placed in a programmable temperature-controlled environment for stepwise heating, and cured by in-situ crosslinking via hydrosilylation to obtain the composite material of the present invention.

[0053] This invention utilizes the freeze-concentration effect to drive the self-condensation and dehydration of BDBA to form a hydroxyl-free boron-oxygen hexacyclic ring; combined with the polar space freezing effect of disk-shaped liquid crystal organosilicon, polarization defects are fundamentally eliminated, and the material has extremely low dielectric constant and dielectric loss at 10 GHz and even millimeter wave frequencies.

[0054] Specifically, the composite material of the present invention can be degraded into a gel state by heat treatment with a composite synergistic repair solution. After rinsing, the waste liquid is centrifuged and washed to recover two-dimensional boron nitride. The composite synergistic repair solution is composed of a good solvent and a dynamic bond-breaking agent in a volume ratio of 1 to 3:1, for example: 1:1, 1.5:1, 2:1, 2.5:1, 3:1. The good solvent is one or more of toluene and D-limonene. The dynamic bond-breaking agent is one or more of ethylene glycol and 1,3-propanediol. The heat treatment temperature is 60 to 80°C, for example: 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C. The time is 15 to 40 min, for example: 15 min, 18 min, 20 min, 23 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min. The centrifugal washing speed is ≥3000 rpm.

[0055] It should be noted that the composite material obtained by this invention has reworkable characteristics. When rework is required, the packaged module to be repaired, which is attached to the composite material, is placed in a composite synergistic repair liquid. Through heat treatment, the material is degraded into a gel state through the synergistic effect of physical swelling and chemical bond breaking. The device can be separated without damage by solvent rinsing, and the waste liquid can be collected and the 2D-BN filler can be recovered by centrifugal washing.

[0056] This invention endows thermosetting encapsulation materials with unprecedented intelligent deconstruction capabilities. During the rework process, a good solvent first breaks the π-π physical stacking of the disk-shaped liquid crystal, causing the matrix to swell. Subsequently, a small-molecule diol penetrates deep into the network, targeting and severing the boron ester crosslinks in the organosilicon network and the boron-oxygen six-link points of the 3D-BN sponge skeleton. Based on the synergistic destruction of physical swelling and dual chemical bond breaking, the high-strength solid material rapidly degrades into a gel state. This not only enables the mechanical stress-free rescue of chip modules costing tens of thousands of dollars, but also allows for the closed-loop recycling of expensive 2D-BN fillers through low-speed centrifugation, greatly reducing the economic and environmental costs of advanced manufacturing.

[0057] This invention also provides a dynamically repairable high thermal conductivity, low dielectric composite material, prepared by the above-described method. This composite material possesses a dual dynamic valence-donating interpenetrating network structure: an inorganic boron-oxygen hexacyclic crosslinked bidirectional 3D-BN sponge skeleton and an organic borate ester crosslinked disc-shaped liquid crystal polysiloxane. With a filler loading of 10–20 wt.%, the composite material exhibits a Z-axis thermal conductivity of 2.70–6.80 W / m·K; a dielectric constant of 2.82–3.05 at 10 GHz, and a dielectric loss ≤0.0022; a coefficient of thermal expansion of 80–135 ppm / ℃; and intelligent gelation and decomposition can be completed within 15–40 minutes in a composite synergistic repair solution at 60–80 ℃.

[0058] The present invention also provides an application of a dynamically repairable high thermal conductivity, low dielectric composite material, which is used as an electronic packaging composite material in the fields of 5G / 6G high frequency communication and 2.5D / 3D Chiplet advanced system-in-package.

[0059] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0060] The two-dimensional boron nitride (2D-BN) nanosheets used in Examples 1-5 and Comparative Examples 1-2 below have an average sheet diameter of 2-5 μm and a thickness of 10-20 nm; the polymethylhydrosiloxane (PMHS) used in the examples and comparative examples below has a hydrogen content of 0.5-1.5 wt%; other reagents, methods, instruments, and equipment are conventional in the art. Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0061] Example 1 A method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material includes the following steps: S1. 2D-BN nanosheets were dispersed in deionized water to prepare a 10 wt.% slurry, and 1,4-phenylenediboric acid (BDBA) was added. The amount of BDBA added was 3 wt.% of the total mass of the 2D-BN nanosheets. The slurry was poured into a high thermal conductivity copper plate mold with PDMS wedge-shaped pads at the bottom (to create a bidirectional temperature gradient), and then subjected to liquid nitrogen for directional freezing. After complete freezing, it was freeze-dried at -50℃ and <10 Pa for 48 h. Subsequently, under inert gas purging, the temperature was increased to 120℃ at a rate of 2℃ / min and held for 2 h to obtain a Z-axis highly oriented 3D-BN sponge skeleton cross-linked with boron-oxygen hexacyclic rings.

[0062] S2. Synthesis of disk-shaped liquid crystal monomer (TP monomer): Under nitrogen protection, 1.0 mol of HAT6 was dissolved in anhydrous dichloromethane and placed in an ice bath at 0°C. 1.2 mol of boron tribromide dichloromethane solution was slowly added dropwise, followed by a reaction at room temperature for 2-3 hours. The reaction solution was quenched with ice water, extracted, and separated by silica gel column chromatography to obtain a monohydroxy pentahexyloxybenzotriphenylene intermediate. 1.0 mol of the above monohydroxy intermediate and 1.5 mol of 11-bromo-1-undecene were dissolved in anhydrous N,N-dimethylformamide (DMF), and 3.0 mol of anhydrous potassium carbonate was added as an acid-binding agent and a trace amount of potassium iodide catalyst. The mixture was heated under reflux at 85°C for 24 hours. The reaction product was washed with water, extracted with dichloromethane, and finally purified by column chromatography to obtain the final disc-shaped liquid crystal monomer—2-(10-undecenooxy)-3,6,7,10,11-pentahexyloxybenzotriphenylene.

[0063] S3: 1,4-Phenylated diboronic acid and allyloxypropylene glycol were added to a flask equipped with a water separator at a molar ratio of 1:2.05. The mixture was heated under reflux for 12 hours using toluene as the solvent, continuously separating the water generated during the reaction. After the reaction was completed, the solvent was removed by rotary evaporation and the mixture was purified to obtain a diene dynamic borate crosslinking agent. PMHS, TP monomer, and diene dynamic borate crosslinking agent were dissolved in anhydrous toluene, with the molar ratio of Si-H bonds: TP monomer double bonds: crosslinking agent double bonds strictly controlled at 1:0.4:0.6. 15 ppm of castalin catalyst was added, and the mixture was ultrasonically degassed for 30 min to obtain a low-viscosity disc-shaped liquid crystal silicone impregnation solution with a solid content of approximately 50%.

[0064] S4: Place the 3D-BN sponge skeleton in a sealed container, evacuate to an absolute pressure ≤50 mbar and maintain for 30 min. After injecting the impregnation liquid, apply a positive pressure of 0.3 MPa and maintain for 30 min to ensure that the impregnation liquid completely penetrates the pores. Remove the 3D-BN sponge skeleton impregnation body, allow it to stand at room temperature for 1 h to evaporate the solvent, then heat it to 80℃ at a rate of 2℃ / min and hold for 2 h, followed by heating to 150℃ and holding for 4 h to complete the addition curing.

[0065] Example 2 The preparation process of Example 2 is largely the same as that of Example 1, except that in Example 2, 2D-BN nanosheets are prepared as a 12 wt.% slurry in step S1.

[0066] The 3D-BN sponge skeleton was evacuated to an absolute pressure of ≤50 mbar and held for 30 min. After injecting the impregnation solution, in order to overcome the capillary resistance caused by the decrease in porosity, a positive pressure of 0.5 MPa was applied and the holding time was extended to 45 min to achieve full wetting.

[0067] Example 3 The preparation process of Example 3 is largely the same as that of Example 1, except that in Example 3, 2D-BN nanosheets are prepared as a slurry of 15 wt.% in step S1.

[0068] After the air is removed and the impregnation liquid is injected, a positive pressure of 0.6 MPa is applied and maintained for 80 min. The low viscosity resin is forcibly pressed into the depth of the micro-nano channels by using the long-term high pressure difference.

[0069] Example 4 The preparation process of Example 4 is largely the same as that of Example 1, except that in Example 4, 2D-BN nanosheets are prepared as a slurry of 18 wt.% in step S1.

[0070] Apply 0.6 MPa and maintain for 150 min to ensure thorough impregnation.

[0071] Example 5 The preparation process of Example 5 is largely the same as that of Example 1, except that in Example 5: in step S1, 2D-BN nanosheets are prepared into a 20 wt.% slurry; in step S4, the 3D-BN sponge skeleton is placed in a sealed container, vacuumed to an absolute pressure ≤30 mbar and maintained for 30 min, and after the impregnation liquid is injected, a positive pressure of 0.6 MPa is applied and maintained for 240 min to ensure that the impregnation liquid completely penetrates the pores.

[0072] Example 6 The preparation process of Example 6 is largely the same as that of Example 3, except that the ratio of the disk-shaped liquid crystal silicone impregnation solution in Example 6 is adjusted to: the molar ratio of Si-H bond: TP monomer double bond: crosslinking agent double bond is 1: 0.6: 0.4.

[0073] Example 7 The preparation process of Example 7 is largely the same as that of Example 3, except that the ratio of the disk-shaped liquid crystal organosilicon impregnation solution in Example 7 is adjusted to: the molar ratio of Si-H bond: TP monomer double bond: crosslinking agent double bond is 1: 0.5: 0.5.

[0074] Example 8 The preparation process of Example 8 is largely the same as that of Example 3. The difference is that in Example 8, the ratio of the disk-shaped liquid crystal organosilicon impregnation solution is adjusted to: the molar ratio of Si-H bond: TP monomer double bond: crosslinking agent double bond is 1: 0.3: 0.7.

[0075] Example 9 The preparation process of Example 9 is largely the same as that of Example 3, except that the ratio of the disk-shaped liquid crystal silicone impregnation solution in Example 9 is adjusted to: the molar ratio of Si-H bond: TP monomer double bond: crosslinking agent double bond is 1: 0.2: 0.8.

[0076] Example 10 Example 10 is prepared in a similar manner to Example 1, except that “11-bromo-1-undecene” is replaced with “6-bromo-1-hexene”. After reacting with the monohydroxy intermediate, a disc-shaped liquid crystal monomer (2-(5-hexenoxy)-3,6,7,10,11-pentahexoxybenzotriphenylene) with a shorter terminal alkenyl carbon chain is synthesized.

[0077] Example 11 Example 11 was prepared in a similar manner to Example 1, except that ultra-large two-dimensional boron nitride (2D-BN) nanosheets with an average diameter of 10-15 μm and a thickness of 10-20 nm were used in Example 11 to prepare a slurry of 15 wt.%. In step S4, the 3D-BN sponge framework was placed in a sealed container, evacuated to ≤50 mbar and maintained for 20 min, and then the impregnation solution was injected. After that, a positive pressure of 0.2 MPa was applied for 20 min.

[0078] The composite materials prepared in Examples 1-11 were subjected to rework tests: the cured composite material modules were immersed in a synergistic rework solution of ethylene glycol / toluene (volume ratio 1:1) at 80°C, and the degelation time is shown in Table 1; then the modules were removed and the softened gel on the surface was rinsed with isopropanol to separate the device; the waste liquid generated from rinsing was collected, centrifuged at 3000 rpm for 10 minutes, the bottom precipitate was collected, washed with anhydrous ethanol and vacuum dried at 80°C to obtain the recovered 2D-BN powder.

[0079] Comparative Example 1 Traditional disordered blend thermosetting system S1. Weigh out 10 wt.% of two-dimensional boron nitride (2D-BN) nanosheets, the same mass fraction as in Example 1, and add them directly to a mixed matrix of conventional polydimethylsiloxane (PDMS, without disc-shaped liquid crystal side chains) and polymethylhydrosiloxane (PMHS). Add an equimolar amount of a conventional irreversible crosslinking agent (divinyltetramethyldisiloxane, without borate bonds) and 15 ppm of caster platinum catalyst, the same amount as in Example 1.

[0080] S2. Add an appropriate amount of toluene to adjust the viscosity. After 60 minutes of high-speed mechanical stirring and ultrasonic vacuum degassing, remove interfacial bubbles. Cast the high-viscosity slurry into a polytetrafluoroethylene mold. After allowing the solvent to evaporate at room temperature for 1 hour, perform the same curing procedure as in Example 1: heat to 80°C at 2°C / min and hold for 2 hours, then heat to 150°C and hold for 4 hours to obtain a common powder blend composite material. At this point, the BN inside the material is randomly distributed.

[0081] S3. Immerse the thermocured powder blend composite material sample block in an ethylene glycol / toluene (volume ratio 1:1) synergistic repair solution at 80℃ for 48 hours, then remove and observe and record the sample condition.

[0082] Comparative Example 2 unidirectional 3D-BN system of liquid crystal epoxy resin / PVA adhesive S1. Disperse 10 wt.% of 2D-BN nanosheets in deionized water and add 0.5 wt.% of polyvinyl alcohol (PVA) as a cryogenic binder. Pour the mixture into a flat-bottomed ordinary unidirectional cryogenic mold (without wedge-shaped pads), and freeze it with liquid nitrogen and then freeze-dry it under vacuum to obtain a unidirectional multi-domain 3D-BN sponge skeleton physically bonded by PVA.

[0083] S2. Select the currently advanced bisphenol A cyanate and liquid crystal epoxy resin (LCER) with rod-shaped mesocrystalline groups and mix them according to the standard curing ratio. Add an appropriate amount of butanone as a solvent to prepare an epoxy impregnation solution (without dynamic covalent bond design).

[0084] S3. Vacuum impregnation: Using the same vacuum-pressure alternating impregnation process as in Example 1 (vacuuming to ≤50mbar and applying 0.3 MPa positive pressure), the epoxy impregnation solution is injected into the unidirectional 3D-BN sponge skeleton containing PVA residue.

[0085] S4. High-temperature thermal curing: After the solvent evaporates, the epoxy resin is subjected to step-high-temperature cross-linking according to the standard curing curve (120℃ for 2 h, 180℃ for 2 h, 200℃ for 2 h) to obtain liquid crystal epoxy composite material.

[0086] S5. Immerse the thermocured liquid crystal epoxy composite material sample block in an ethylene glycol / toluene (volume ratio 1:1) synergistic repair solution at 80℃ for 48 hours. After removal, observe and record the sample status.

[0087] Performance testing The composite materials prepared in Examples 1-11 and Comparative Examples 1-2 were comprehensively evaluated according to the following test standards: 1. Z-axis thermal conductivity: The thermal diffusivity in the thickness direction of the sample was measured and the thermal conductivity was calculated using the laser flare method (LFA, according to ASTM E1461 standard); 2. Dielectric properties (Dk and Df): Measured at a high frequency of 10 GHz using a microwave resonant cavity method combined with a vector network analyzer (IPC-TM-650 2.5.5.5 standard). 3. Coefficient of thermal expansion (CTE): The linear expansion coefficient in the thickness direction of the material was measured using a thermomechanical analyzer (TMA) within the temperature range of 25℃ to 150℃ (according to IPC-TM-650 2.4.24 standard). 4. Synergistic liquid repair degelation time: A cured sample with a size of 10×10×1 mm was completely immersed in an ethylene glycol / toluene (volume ratio 1:1) synergistic repair liquid at 80℃, and the time required for it to completely lose its mechanical strength and transform into a low-viscosity flowable gel state was recorded.

[0088] The test results are shown in the table.

[0089] Table 1 Performance test results of Examples 1-11 and Comparative Examples 1-2

[0090] Based on Examples 1-11 and Comparative Examples 1-2, and referring to Table 1, it can be seen that the composite material prepared by this invention has a Z-axis thermal conductivity of 2.70-6.80 W / m·K; at a frequency of 10 GHz, the dielectric constant (Dk) is 2.82-3.05, the dielectric loss (Df) is ≤0.0022, and the coefficient of thermal expansion (CTE) is 80-135 ppm / ℃; and it can complete intelligent gelation and decomposition within 15-40 minutes in a composite synergistic repair solution at 60-80℃. The composite materials prepared by Comparative Examples 1 and 2 using conventional processes do not possess repairable characteristics.

[0091] Based on the test data in Table 1, the composite material exhibits the best overall performance, especially when the amount of 2D-BN nanosheets added is 12 wt.%~15 wt.% and the impregnation solution ratio is controlled within the range of 1:0.3~0.6:0.4~0.7.

[0092] In summary, the dynamically repairable high thermal conductivity, low dielectric composite material obtained through the method of this invention possesses extremely high Z-axis thermal conductivity, ultra-low dielectric loss at millimeter-wave high frequencies, and a low coefficient of thermal expansion that matches the underlying silicon chip. In particular, its unprecedented "intelligent and controllable rework and filler closed-loop recycling" capability effectively solves the industry challenges of traditional advanced packaging materials in simultaneously achieving vertical high-speed heat dissipation, high-frequency signal fidelity, and the inability to disassemble and rework after thermosetting. It has extremely broad application prospects and commercial value in high-end microelectronics manufacturing fields such as 5G / 6G high-frequency communication substrates and 2.5D / 3D Chiplet advanced system-in-package (SiP) bottom fillers for high-computing chips.

[0093] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention (such as adjusting the length of the side chains of the disc-shaped liquid crystal, changing the filler sheet diameter, or fine-tuning the ratio of the dynamic crosslinking agent, etc.) should all be within the scope of protection of the present invention.

Claims

1. A method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material, characterized in that, Includes the following steps: S1. Two-dimensional boron nitride nanosheets and boric acid precursor are dispersed in deionized water to form a slurry. The slurry is placed in a bidirectional temperature gradient mold for directional freezing. After freeze drying and thermal annealing, a 3D-BN sponge skeleton is formed. S2. Using 2,3,6,7,10,11-hexahedoxybenzotriphenylene as a precursor, a disc-shaped liquid crystal monomer with a single-ended alkenyl flexible tail was prepared by controlled cleavage and etherification reaction. S3. Dissolve polymethylhydrosiloxane, the disc-shaped liquid crystal monomer mentioned in step S2 and diene dynamic borate crosslinking agent in an organic solvent, add platinum complex catalyst, and prepare a disc-shaped liquid crystal organosilicon impregnation solution. S4. The disk-shaped liquid crystal silicone impregnation liquid is injected into the 3D-BN sponge skeleton. After the impregnation is saturated by vacuum-pressure alternating process, the 3D-BN sponge skeleton is taken out and left to stand at room temperature for 1-2 hours. Then, it is heated and cured to obtain the dynamic repairable high thermal conductivity and low dielectric composite material. The boric acid precursor is one or more of 1,4-phenyldiboronic acid, 4,4'-biphenyldiboronic acid, and 1,4-naphthalenediboronic acid.

2. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S1, the mass fraction of the two-dimensional boron nitride nanosheets in the slurry is 10-20 wt.%; the amount of the boric acid precursor added is 2-10 wt.% of the total mass of the two-dimensional boron nitride nanosheets. And / or, the freeze-drying conditions are: temperature -50°C, absolute pressure <10 Pa, and drying time not less than 48 h; And / or, the heating and annealing method is as follows: heating to 110-150°C at a rate of 1-5°C / min and holding at that temperature for 2-4 hours.

3. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S2, the method for synthesizing the disk-shaped liquid crystal monomer is as follows: 2,3,6,7,10,11-hexahexoxybenzotriphenylene and boron tribromide are subjected to a cleavage reaction at a molar ratio of 1:1.1~1.5 to obtain a monohydroxy intermediate; the monohydroxy intermediate is subjected to an etherification reaction with 11-bromo-1-undecene or 6-bromo-1-hexene at a molar ratio of 1:1.2~2.0 to obtain the disk-shaped liquid crystal monomer.

4. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S3, the diene-based dynamic borate ester crosslinking agent is prepared by a dehydration condensation reaction of a diboronic acid compound and an alkenyl-containing diol compound; the diboronic acid compound includes one or more of 1,4-phenyldiboronic acid and 4,4'-biphenyldiboronic acid; the alkenyl-containing diol compound includes one or more of propyleneoxypropylene glycol and 5-ethylene-1,2-diol; the molar ratio of the diboronic acid compound to the alkenyl-containing diol compound is 1:2 to 2.

1.

5. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S3, the raw material ratio of the disc-shaped liquid crystal organosilicon impregnation solution is controlled to be 1:0.2~0.6:0.4~0.8, where the molar ratio of Si-H bond:disc-shaped liquid crystal monomer double bond:crosslinking agent double bond is 1:0.2~0.6:0.4~0.

8.

6. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S4, the operation method of the vacuum-pressure alternating process is as follows: first, the 3D-BN sponge skeleton is evacuated to an absolute pressure ≤50 mbar and maintained for 20~45 min. After injecting the disk-shaped liquid crystal silicone impregnation liquid, a positive pressure of 0.1~0.6 MPa is applied and maintained for 20~240 min.

7. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, In step S4, the reaction conditions for heating and curing are as follows: heating to 60-80℃ at a rate of 1-5℃ / min and holding for 2-4 hours; then heating to 120-150℃ and holding for 2-4 hours.

8. The method for preparing a dynamically repairable high thermal conductivity, low dielectric composite material according to claim 1, characterized in that, The composite material can be degraded into a gel state by heating with a composite synergistic repair solution. After rinsing, the waste liquid is centrifuged and washed to recover two-dimensional boron nitride. The composite synergistic repair solution is composed of a good solvent and a dynamic bond-breaking agent in a volume ratio of 1 to 3:

1. The good solvent is one or more of toluene and D-limonene. The dynamic bond-breaking agent is one or more of ethylene glycol and 1,3-propanediol. The heating treatment is performed at a temperature of 60~80℃ for 15~40 min; the centrifugal washing speed is ≥3000 rpm.

9. A dynamically repairable composite material with high thermal conductivity and low dielectric constant, characterized in that, The composite material is prepared by the method described in any one of claims 1 to 8, which describes a dynamic, reworkable, high thermal conductivity, and low dielectric composite material. The composite material has a dual dynamic covalent interpenetrating network structure of "inorganic boron-oxygen hexacyclic crosslinked bidirectional 3D-BN sponge skeleton / organic borate ester crosslinked disc-shaped liquid crystal polysiloxane". Under a filler loading of 10–20 wt.%, the composite material has a Z-axis thermal conductivity of 2.70–6.80 W / m·K; a dielectric constant of 2.82–3.05 at 10 GHz, a dielectric loss ≤0.0022; a coefficient of thermal expansion of 80–135 ppm / ℃; and can complete intelligent gel decomposition within 15–40 min in a composite synergistic repair solution at 60–80 ℃.

10. The application of a dynamically repairable high thermal conductivity, low dielectric composite material, characterized in that, Application of the composite material according to claim 9 in 5G / 6G high-frequency communication and 2.5D / 3D Chiplet advanced system-in-package.

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