Low-alpha radiation spheroid alumina / liquid crystal polymer 5g base station substrate material

Abstract

The application belongs to the field of high-frequency communication materials, and specifically discloses a Low-alpha ray spherical alumina / liquid crystal polymer 5G base station substrate material, which is characterized by containing a liquid crystal copolymer matrix and Ce 3+ doped spherical alumina fillers; the liquid crystal copolymer matrix comprises 60-68 mol% of p-hydroxybenzoic acid, 20-24 mol% of 5,5'-dithiobis(2-nitrobenzoic acid) and 12-16 mol% of 4-(5-amino-6-hydroxy-2-benzoxazolyl)-benzoic acid three kinds of comonomers; the Ce 3+ doped spherical alumina fillers are sequentially coated with Bi2Te 3‑x Se x topological insulating layer and phosphate silane grafting layer, wherein x=0.12-0.18. The Low-alpha ray spherical alumina / liquid crystal polymer 5G base station substrate material of the application has an alpha ray shielding rate of greater than or equal to 99.95%, a thermal conductivity of greater than or equal to 3.35 W / mK, and a dielectric loss factor tan delta of less than 0.00014 at 28 GHz, and can meet the high-frequency, high-reliability and other stringent requirements for the substrate in 5G millimeter wave antenna applications.

Description

Technical Field

[0001] This invention relates to the field of high-frequency communication materials technology, specifically to a Low-α ray spherical alumina / liquid crystal polymer 5G base station substrate material. Background Technology

[0002] As 5G communication upgrades to millimeter-wave bands (28 / 39GHz), base station substrates must simultaneously meet several core requirements: in the 28GHz band, the dielectric loss factor (tanδ) must be ≤0.0005 to reduce signal transmission attenuation; the thermal conductivity must be ≥3W / mK to solve the problem of local overheating caused by high-density chip packaging; the alpha ray shielding rate must be ≥99.9% to avoid high-energy alpha particles causing "soft errors" in the chip; and the dielectric loss change (Δtanδ) after 1000 hours of humid heat aging at 85℃ / 85%RH must be ≤+0.5% to adapt to outdoor base station environments.

[0003] Currently, among 5G base station substrate materials, ceramic-based materials (such as Al2O3 and AlN) have high thermal conductivity (AlN thermal conductivity ≥150W / mK) and excellent alpha-ray shielding performance (Al2O3 shielding rate ≥99.5%); however, they have high dielectric loss (tanδ@28GHz ≥0.0008), are brittle, and have high processing costs, making them difficult to adapt to flexible packaging. Low-alpha ray spherical alumina, based on ordinary ceramic-based materials, has advantages such as low alpha particle content, excellent insulation, adjustable particle size distribution, high sphericity, and low magnetic foreign matter content, but U / Th <5ppb needs to be controlled; however, radioactive element removal processes (such as acid washing) lead to a 40% decrease in surface hydroxyl density and a 30% weakening of interfacial bonding energy, increasing the risk of substrate delamination after damp heat aging and causing dielectric stability degradation Δtanδ >15%. In addition, the traditional spherical alumina particle size is not coupled with the 5G millimeter-wave wavelength, resulting in multiple reflections of electromagnetic waves at the filler interface and an insertion loss of -0.5dB / cm.

[0004] Polymer-based composite materials (such as liquid crystal polymers (LCP), glass fibers, etc.) have low intrinsic dielectric loss (tanδ@28GHz ≤ 0.0004 for LCP), but the addition of high thermal conductivity fillers (such as spherical Al2O3) can easily lead to interfacial polarization problems. When the filler content is ≥35wt%, the interfacial polarization causes the dielectric loss to increase sharply to tanδ≥0.0006, while the thermal conductivity can only reach 1.2~2.0W / mK, which cannot meet the high thermal conductivity requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a Low-α ray spherical alumina / liquid crystal polymer 5G base station substrate material.

[0006] To address the aforementioned technical problems, this invention provides a Low-α ray spherical alumina / liquid crystal polymer 5G base station substrate, comprising the following components based on a total substrate material mass of 100 wt%:

[0007] A 42-50 wt% liquid crystal copolymer matrix comprising the following molar percentages of carboxylic acid monomers copolymerized: 60-68 mol% p-hydroxybenzoic acid, 20-24 mol% 5,5'-dithiobis(2-nitrobenzoic acid), and 12-16 mol% 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid; wherein the 5,5'-dithiobis(2-nitrobenzoic acid) is pre-complexed with a cerium-containing compound before copolymerization;

[0008] 35-40 wt% Ce 3+ Doped spherical alumina filler, its surface is sequentially coated with: Bi2Te 3-x Se x A topological insulating layer and a phosphate ester silane graft layer, wherein x = 0.12 to 0.18;

[0009] 3-5 wt% bismaleimide, 2-4 wt% UV absorber and 5-9 wt% plasticizer.

[0010] It should be noted that 5,5'-dithiobis(2-nitrobenzoic acid) (pKa = 5.12) has a relatively low carboxyl group activity due to the electron-withdrawing effect of the nitro group; if the three monomers are directly copolymerized, local homopolymerization with preferential self-polymerization of p-hydroxybenzoic acid is likely to occur. After pre-complexation with cerium-containing compounds, the carboxyl group activity of 5,5'-dithiobis(2-nitrobenzoic acid) can be increased by 30%–40%, and its reactivity tends to be consistent with that of the other two monomers, ensuring uniform monomer reaction in the copolymerization system. Furthermore, Ce... 3+ The electronegativity of the carboxyl carbon is enhanced through coordination bonds, which significantly improves its reactivity with the hydroxyl groups in p-hydroxybenzoic acid and 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid, and reduces the activation energy of the esterification reaction.

[0011] Furthermore, the ultraviolet absorber is a hindered amine stabilizer, and the plasticizer is triethyl citrate;

[0012] The substrate material has an alpha-ray shielding rate of ≥99.95%, a thermal conductivity of ≥3.35 W / mK, a dielectric loss factor tanδ <0.00014 at 28 GHz, and Δtanδ ≤ +0.3% after 1000 h of humid heat aging at 85℃ / 85%RH.

[0013] Furthermore, the substrate material is prepared by a method comprising:

[0014] (1) Preparation of liquid crystal copolymer: 5,5'-dithiobis(2-nitrobenzoic acid) and cerium-containing compound according to carboxyl group: Ce3+ After pre-complexing at 50–65 °C for 2–3 h with a molar ratio of 1:1.2, it is then mixed with 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid and p-hydroxybenzoic acid; under a N2 atmosphere, at 385–405 nm and 30–40 mW / cm 2 Under LED light source irradiation, the mixture was heated in stages and polycondensed for 100–150 min to obtain a liquid crystal copolymer with a number-average molecular weight Mn ≥ 3.5 × 10⁻⁶. 4 g / mol, PDI≤1.6;

[0015] (2)Ce 3+ Preparation of doped spherical alumina filler: Using cerium nitrate-aluminum nitrate as a precursor, co-precipitation was carried out in an ammonia-ammonium carbonate mixture at pH 10.0 ± 0.2, followed by spray drying, freeze drying, and plasma-activated sintering to obtain Ce-doped alumina filler with γ-Al₂O₃ crystal phase. 3+ Doped spherical alumina; the Ce 3+ The doping amount is 1.5–2.8 mol%, based on the total moles of Al2O3;

[0016] (3) Double-layer coating modification of the filler: On the surface of the filler obtained in step (2), using bismuth-containing compounds, tellurium-containing compounds and selenium-containing compounds as precursors, atomic layer deposition is performed 200-250 times at 140-150℃ to grow Bi2Te. 3-x Se x A topological insulating layer was formed; then annealed at 300℃ in a N2 / Se = 95:5 mixture for 30–60 min, followed by rapid cooling with an inert gas; finally, grafting was performed using a phosphate ester silane coupling agent to obtain a double-layer coated Ce. 3+ Doped spherical alumina;

[0017] (4) Casting: The liquid crystal copolymer from step (1) and the double-layer coated Ce from step (3) are cast together. 3+ Doped spherical alumina filler and bismaleimide are sheared and mixed, and ultraviolet absorbers and plasticizers are added simultaneously to obtain a composite melt; it is then cast and molded at 280-290°C; it is then cooled in sections to 80°C and annealed at 120-140°C for 2-4 hours to obtain the substrate material.

[0018] Further, in step (1), the staged heating parameters are: 180℃ for 30-40 min, 220℃ for 60-90 min, and 240℃ for 30-50 min; tetrabutyl titanate catalyst and lithium borate are also added to the copolymerization system; the amount of tetrabutyl titanate is 0.06-0.09 wt%, and the amount of lithium borate is 0.1-0.2 wt%, both based on the total mass of the system.

[0019] It should be noted that in the above copolymerization process, the nitro group contained in 5,5'-dithiobis(2-nitrobenzoic acid) is generated by photo-induced free radicals under 385-405nm LED ultraviolet irradiation, which activates the carboxyl group and reduces the activation energy of the esterification reaction.

[0020] A. Photoinduced nitro radical generation: The energy of 385–405 nm ultraviolet light (3.22–3.48 eV) matches the n→π* transition energy (3.0–3.5 eV) of the nitro (-NO2) group, exciting the lone pair electrons of the nitro oxygen atom to transition to the antibonding orbital, weakening and breaking the C-NO2 bond, generating a ·NO2 radical. Furthermore, in the pre-complexation step, Ce... 3+ Ce-O-carboxyl complexes formed with carboxyl groups can stabilize NO2 free radicals;

[0021] B. Activating the carboxyl group and promoting ester bond formation: The highly oxidizing NO2 free radical can attack the hydroxyl (-OH) and carboxyl (-COOH) groups of p-hydroxybenzoic acid or 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid, abstracting H atoms to generate hydroxyl radicals (·OH) or acyl radicals (·COO). - This reduces the activation energy of the esterification reaction between carboxyl and hydroxyl groups, allowing polycondensation to occur without high temperatures.

[0022] Furthermore, the pre-complexed Ce-O-carboxyl chelate is formed via Ce 3+ The 4f electron cloud can couple with the π antibonding orbital of the nitro group, lowering the n→π transition energy barrier. Under LED light source irradiation at wavelengths of 385–405 nm, the nitro group is more easily broken to form ·NO2, and Ce... 3+ Through electron transfer (Ce 3+ →·NO2→Ce 4+ Stabilize free radicals and prevent them from prematurely quenching.

[0023] Further, in step (2), the inlet temperature of the spray drying is 200±10℃, and the freeze-drying temperature is -60~-50℃; the plasma activation sintering process is specifically as follows:

[0024] The freeze-dried particles were activated for 60–90 seconds using a magnetic rotating arc plasma torch with a power of 50–150 kW in a 95:5 Ar / H2 mixed atmosphere. They were then heated to 1050–1100 °C at a rate of 80–100 °C, and the axial pressure was applied in stages to 40–60 MPa for 6–10 min. The particles were then rapidly cooled with liquid nitrogen to a sintered body temperature of ≤200 °C. Finally, they were annealed at 800 °C in an N2 atmosphere for 30–40 min. The pulse activation mode was 60 ms on and 30 ms off.

[0025] In the above sintering process, the particle surface is activated by the instantaneous high temperature of plasma; rapid sintering can suppress the γ→α diffusion phase transformation. The rapid quenching step can avoid the γ→α phase transformation and Ce phase decay that occur in the 800–1000℃ range during slow cooling. 3+ The issue of migration. An annealing temperature of 800℃ is below the γ→α phase transformation threshold but above the recrystallization temperature (approximately 600℃), effectively releasing lattice distortion stress caused by rapid cooling and preventing substrate warping; the N2 atmosphere can prevent Ce... 3+ Oxidized to Ce 4+ .

[0026] Further, in step (3), the bismuth-containing compound is tris(2,2,6,6-tetramethyl-3,5-heptadecyl)bismuth(III), the tellurium-containing compound is bis(trimethylsilyl)tellurium, and the selenium-containing compound is di-tert-butylselenium; the atomic layer deposition is controlled by pulse feedback, and its parameters are:

[0027] Bismuth(III) tris(2,2,6,6-tetramethyl-3,5-heptadecane) pulsation for 0.20–0.30 s, followed by Ar purging with varying flow rate for 10 s;

[0028] Bis(trimethylsilyl)tellurium pulse 0.55–0.72 s, variable flow Ar purge 10 s;

[0029] Di-tert-butylselenide pulse for 0.30–0.45 s, followed by variable flow Ar purging for 10 s;

[0030] The Se:Te molar ratio is (6-9):(44-41).

[0031] The core of atomic layer deposition (ALD) is the self-limiting chemical reaction of the precursor on the substrate surface. Within each precursor pulse cycle, deposition ceases once the reactants reach surface saturation adsorption. The deposition rates of Se and Te are positively correlated with the pulse time (a saturation threshold exists). This scheme precisely controls the relative ratio of Se and Te by controlling the pulse time of the precursors bis(trimethylsilyl)tellurium and di-tert-butylselenium, and directly controls the Se / Te atomic ratio.

[0032] Further: In step (3), the grafting process is as follows: γ-aminopropyltriethoxysilane and tris(tert-butyldimethylsilyl)phosphite with a mass ratio of 1:1 to 2 are pre-hydrolyzed at pH=4.5 for 30 to 40 min; the filler is dispersed in it at a solid-liquid ratio of 1:10 to 15, and the temperature is raised to 60 to 85°C and refluxed for 6 to 8 h.

[0033] Further: In step (4), the melt flow rate of the casting process is 5±0.2g / 10min, the cooling rate of the segmented cooling process is 15~25℃ / min, and the heating rate of the annealing process is 5℃ / min.

[0034] In this invention, the double-layered Ce 3+ Bi2Te in doped spherical alumina 3-x Se x The topological insulating layer achieves low-dissipation electron transport through spin-momentum locking via a Dirac cone band structure. When coupled to a γ-Al₂O₃ substrate, the breaking of z-axis symmetry activates Raman forbidden modes, optimizing surface state stability. Quantum confinement (thickness 8–10 nm) suppresses bulk phonon scattering, reducing dielectric loss. Se doping compensates for Te vacancies (n-type defects) in Bi₂Te₃, reducing bulk carrier concentration and shifting the Fermi level toward the Dirac point. However, increasing x suppresses Te vacancies, further reducing bulk carrier concentration and bringing the Fermi level closer to the Dirac point. Furthermore, due to the lattice constant of Bi₂Te₃... ) and Bi2Se3 The mismatch reaches 6.4%, and increasing x will exacerbate the mismatch with γ-Al2O3 (lattice constant ~). The mismatch of ) . Therefore, the x value directly affects Bi2Te 3-x Se x Interfacial stress between the topological insulating layer and the alumina filler, and the performance of the substrate.

[0035] The harm caused by alpha rays stems from the "soft errors" in chips triggered when high-energy particles penetrate the substrate. This invention reduces alpha ray levels primarily through a three-pronged approach: reducing alpha ray source release, absorbing particle energy, and scattering particle motion paths.

[0036] (1) Ce doping 3+ This generates alpha particle "energy traps" and inhibits the release of radioactive impurities: the alpha rays in spherical alumina mainly originate from U and Th impurities in the raw materials. 3+ Ionic radius Greater than Al 3+ Replace Al 3+ Later, "vacancy-Ce" forms in the γ-Al₂O₃ lattice. 3+ "The defect pair, whose energy level (0.8–1.2 eV) matches the energy quantization level of the alpha particle, can absorb the kinetic energy of the alpha particle through transitions; in addition, Ce..." 3+ The 4f orbital can interact with U 6+ ,Th 4+ They form stable coordination compounds (Ce-UO, Ce-Th-O) to prevent impurity atoms from migrating with the humid and hot environment.

[0037] (2)Bi2Te 3-x Se x Insulating topological layers, surface state scattering, and energy dissipation in layered structures:

[0038] Topological surface state scattering of alpha particles: The Dirac cone surface states of the topological insulating layer have delocalized π electron clouds. Alpha particles interact with the π electron clouds through Coulomb repulsion, causing the particle's trajectory to be deflected / scattered.

[0039] Layered structures increase kinetic energy dissipation: Bi2Te 3-x Se x It has a hexagonal layered structure, and the coating thickness of 8-10 nm forms multiple scattering interfaces, which can guide the directional transport of phonons along the interlayer. As alpha particles penetrate the multiple topological layers to reach the resin matrix, scattering occurs, increasing the total path length and improving the kinetic energy dissipation rate.

[0040] (3) Phosphate silane coating, dense interface to block radiation source and particle transmission: sealing radioactive sites on the filler surface: phosphate groups-filler hydroxyl coordination bonds + amino-resin carboxyl covalent bonds form a dense coating layer, sealing the micropores of U and Th impurity radiation sites on the surface of spherical alumina, thus preventing the release of α rays; preventing Coulomb interaction to aid energy dissipation: negatively charged phosphate groups can interact with α particles (+2e) through long-range Coulomb attraction, further slowing down the particle's movement speed; at the same time, the Si-O bonds and CN bonds in the coating layer can absorb the energy of α particles through bond vibration, preventing energy transfer to the chip.

[0041] Beneficial effects:

[0042] The Low-α ray spherical alumina / liquid crystal polymer 5G base station substrate material provided by this invention has the following beneficial effects:

[0043] I. Ultra-low dielectric loss: The copolymer contains a rigid planar structure of benzoxazole, which enhances the molecular chain stacking density. The strong electron-withdrawing property of the oxazole epoxy atom effectively suppresses dipole polarization; combined with Bi2Te 3-x Se x The quantum confinement effect of the topological insulating layer results in a dielectric loss factor (tanδ) of <0.00014 for the substrate material in the 28GHz millimeter-wave band, which can significantly reduce the attenuation of high-frequency signal transmission and meet the high-speed data transmission requirements of 5G base stations.

[0044] II. High thermal conductivity and efficient alpha-ray shielding:

[0045] High thermal conductivity: Bi2Te 3-x Se x The Dirac cone band structure of the topological insulating layer has the characteristics of bulk insulation and surface conductivity, which can realize the scatter-free transmission of electrons. Its layered crystal structure can guide the directional transmission of phonons along the interlayer, reducing the disordered scattering of phonons. The rigid stacking of benzoxazole units further reduces phonon scattering, which further improves the thermal conductivity of the substrate, so as to realize the rapid heat conduction of 5G base station chips and avoid local overheating leading to performance degradation.

[0046] High-efficiency alpha ray shielding: Ce 3+ Doping can act as an electron trap to capture alpha particles; Bi2Te 3-x Se x The topological insulating layer extends the energy dissipation path through multiple scatterings; the phosphate coating blocks the source, reduces the release of alpha rays and assists in energy dissipation, making the alpha ray shielding rate exceed 99.95%, effectively reducing the risk of chip "soft errors" caused by alpha particles.

[0047] III. Environmental stability:

[0048] Stability during humid and hot aging: The phosphate ester silane grafted layer forms a dense interface through the coordination bond between the phosphate group and the filler hydroxyl group and the covalent bond between the amino group and the resin carboxyl group, which inhibits the penetration of moisture under humid and hot conditions and avoids delamination failure caused by interface hydrolysis.

[0049] UV aging stability: Bi2Te 3-x Se x The topological insulating layer can absorb ultraviolet light from 200 to 400 nm. Combined with hindered amine ultraviolet absorbers, it effectively inhibits the ultraviolet degradation of molecular chains. After ultraviolet aging, the yellowness index ΔE of the substrate is much lower than that without Bi2Te. 3-x Se x The substrate with topological insulation layer covering filler extends the service life of the substrate in outdoor base station environments.

[0050] IV. Strong interfacial bonding and excellent mechanical properties

[0051] Phosphate silane graft layer eliminates Ce 3+ The polarity difference between doped spherical alumina and liquid crystal copolymers, Ce 3+ Doping significantly improves the substrate peel strength, meeting the reliable connection requirements of 5G base station substrates with chips and metal wiring; it can be mass-produced through tape casting and is compatible with high-density packaging process requirements. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0053] Figure 1 To prepare Ce in Example 1 3+ Doped spherical alumina, Ce double-coated as in Examples 1 and 4-5 3+ Ce-doped spherical alumina, Ce-doped with phosphate ester silane graft layer (Comparative Example 3) 3+ XRD results of doped spherical alumina and pure spherical alumina filler with double-layer coating as in Comparative Example 4.

[0054] Figure 2 The double-layer coated Ce of Examples 1 and 4-53+ XRF spectrum of doped spherical alumina filler.

[0055] Figure 3 The double-layer coated Ce as in Examples 1 and 4-5 3+ Ce-doped spherical alumina and Ce-doped phosphate ester silane grafted layers in Comparative Example 3 3+ Two-dimensional dispersion plot of angle-resolved photoelectron spectroscopy for doped spherical alumina.

[0056] Figure 4 The infrared absorption spectra are those of the liquid crystal copolymers in Example 1 and Comparative Example 2, and the liquid crystal homopolymer in Comparative Example 1. Detailed Implementation

[0057] To more fully demonstrate the practical applications and technical advantages of the present invention, the following detailed description is provided through multiple embodiments and comparative examples. Those skilled in the art should understand that these embodiments are merely examples and do not constitute a limitation on the scope of protection of the present invention.

[0058] Unless otherwise specified, the experimental methods used in the specific implementation methods are all conventional methods; the materials and reagents used are all commercially available unless otherwise specified.

[0059] The properties and sources of some raw materials used in the examples and comparative examples are as follows:

[0060] Tris(dibenzylideneacetone)palladium(Pd2(dba)3), from Strem; cerium nitrate hexahydrate, tris(2,2,6,6-tetramethyl-3,5-heptadecyl)bismuth(III), from Sigma-Aldrich;

[0061] Tetrabutyl titanate, 3-aminopropyltriethoxysilane, and 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid are from Shanghai Yuanye Biotechnology Co., Ltd.

[0062] 5,5'-Dithio-bis(2-nitrobenzoic acid), bis(trimethylsilyl)tellurium, tri(tert-butyldimethylsilyl)phosphite (moisture content <0.1wt%), from Bailingwei Technology;

[0063] Di-tert-butylselenide, Shaanxi Didu Pharmaceutical Chemical Co., Ltd.; Tinuvin 770, Shenzhen Yoshida Chemical Co., Ltd.; Lithium borate, Hubei Yunmei Technology Co., Ltd.

[0064] Preparation Example 1

[0065] Ce 3+ Preparation of doped spherical alumina fillers.

[0066] Co-precipitation: Cerium nitrate (0.08 mol) and aluminum nitrate (2.44 mol) were dissolved in 500 mL of deionized water, and H2O2 (0.36 mol) was added and stirred for 30 min to obtain a metal salt solution; a 2 mol / L ammonia-ammonium carbonate mixture was prepared and the pH was adjusted to 10.0; under the assistance of 40 kHz ultrasound, the metal salt solution was added dropwise to the precipitant at 2 mL / min, maintaining the pH at 9.8 ± 0.2, and aged at 60 °C for 8 h.

[0067] Spray forming: Filter by suction, and wash the precipitate until neutral. Add 3wt% polyethylene glycol and stir to obtain a uniform slurry with a solid content of 20wt%. Use an LPG-5 centrifugal spray dryer (Changzhou Yibu Drying Equipment Co., Ltd.) with a feed rate of 50mL / min, an inlet temperature of 210℃, an outlet temperature of 90℃, and an atomization pressure of 0.4MPa for spray drying to obtain microspheres. Pour them into liquid nitrogen and freeze rapidly to -50℃. Transfer them to an LGJ-50F freeze dryer (Beijing Sihuan Scientific Instruments Co., Ltd.) and dry at a vacuum degree ≤10Pa and a cold trap temperature of -50℃ for 24h.

[0068] Sintering: Dry precursor powder was uniformly filled into a graphite mold and placed in an SPS-20T discharge plasma sintering furnace (Shanghai Chenxin Electric Furnace Co., Ltd., including pulse power supply and axial pressure module). A 95:5 volume ratio Ar / H2 mixture was introduced. The plasma arc power was set to 60kW (850A current, 50V voltage), and activation was performed for 90 seconds using a pulse mode of 60ms on / 30ms off. The temperature was rapidly increased to 1100℃ at a rate of 100℃ / min under an axial pressure of 40MPa, and then held at 50MPa axial pressure for 10min. The sintered body was then rapidly cooled with liquid nitrogen to a temperature ≤200℃ to lock in the γ phase and Ce phase. 3+ Site; Annealed at 800℃ for 30 min in an SX2-12-16 type box-type resistance furnace (Shanghai Yifeng Electric Furnace Co., Ltd.) under N2 atmosphere. Depressurized and demolded to obtain Ce. 3+ Doped spherical alumina filler.

[0069] Preparation Example 2

[0070] Preparation of pure spherical alumina filler: The difference from the preparation process in Example 2 is that in the co-precipitation process, cerium nitrate is not added to the metal salt solution used, while the rest of the process remains unchanged.

[0071] Relevant tests were performed on the packings obtained in Preparation Examples 1 and 2:

[0072] The particle size and particle size distribution width (SPAN = (D)) were measured using a Bettersize2000 intelligent laser particle size analyzer. 90 -D 10 ) / D 50 );

[0073] Specific surface area was measured using a Micromeritics TriStar II 3020 surface area analyzer (BET nitrogen adsorption method);

[0074] Its dielectric constant ε was measured using an Agilent E4980A LCR meter. r The tanδ@28GHz was tested using an Agilent N5249A vector network analyzer (with a WR-28 waveguide probe).

[0075] In addition, regarding the Ce prepared in Example 2 3+ Doped spherical alumina fillers are based on X-ray photoelectron spectroscopy (Thermo K-Alpha, Ce). 3+ Characteristic peak 882.6 eV, Ce 4+ The valence state of Ce was determined by the characteristic peak at 888.0 eV, and the Ce doping level was detected by an Agilent 7900 inductively coupled plasma mass spectrometer (ICP-MS, with Rh as the internal standard at 10 μg / L).

[0076] The test results are shown in Table 1.

[0077] Table 1

[0078] performance Preparation Example 1 Preparation Example 2 Particle size <![CDATA[D 50 =2.8μm;SPAN=1.02]]> <![CDATA[D 50 =2.9μm;SPAN=1.2]]> Specific surface area <![CDATA[220m 2 / g]]> <![CDATA[215m 2 / g]]> Ce doping 2.52 mol% / Ce price status <![CDATA[Ce 3+ / (What 3+ +What 4+ )≥95%]]> / <![CDATA[ε r ]]> 9.3 9.5 tanδ@28GHz ≤0.001 0.0012

[0079] Table 1 shows that the only difference in the preparation processes between the two is Ce. 3+ Doped with similar particle size distributions. The pure Al₂O₃ prepared in Example 3 was Ce-free. 3+ Due to the electron trapping effect, the dielectric loss is slightly higher.

[0080] Example 1

[0081] (1) Synthesis of liquid crystal copolymers:

[0082] Pre-complexation: 5,5'-dithiobis(2-nitrobenzoic acid) (22 mmol) and cerium nitrate (26.4 mmol) were dissolved in DMF / ethanol (v:v = 3:2) under ultrasonic-assisted stirring (300 W) to obtain a solution with a solid content of 20 wt%. The solution was then cooled to 50 °C and pre-complexed at 500 rpm for 3 h. After cooling to room temperature, the solution was filtered to obtain a pale yellow complex. The complex was transferred to a polymerization reactor, and 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid (14 mmol) and p-hydroxybenzoic acid (64 mmol) were added. The mixture was then mixed with anhydrous N-methylpyrrolidone (100 mL).

[0083] After introducing N2 into the polymerization reactor and purging it three times, the reactor was sealed. While stirring, the temperature was raised to 120°C and dehydrated under reduced pressure for 1 hour. Then, 0.08 wt% tetrabutyl titanate and 0.12 wt% lithium borate were added. The temperature was raised to 250°C, the pressure reduced to 0.1 MPa, and the reactor was stirred at 200 rpm. An external LED light source (385 nm, 35 mW / cm²) was installed. 2 The temperature was gradually increased, and the mixture was held successively at 180℃ for 30 min, 220℃ for 60 min, and 240℃ for 30 min (total polycondensation time was 120 min). Acetic anhydride was then added for end-capping. After the reaction was completed, excess acetic anhydride was removed by vacuum distillation at 200℃ and 0.09 MPa for 30 min. The mixture was cooled to room temperature, and the crude product was dissolved in chloroform (10% w / v). The insoluble matter was removed by filtration, and the filtrate was added dropwise to 10 times its volume of methanol to precipitate the product. The precipitate was washed with methanol (50 mL × 3), dried under vacuum at 120℃ for 24 h, and pulverized through a 100-mesh sieve to obtain a yellow liquid crystal copolymer powder with a yield of 78%.

[0084] The molecular weight of the liquid crystal copolymer was determined using a Waters 1515 gel permeation chromatography system (GPC, equipped with a Styragel HR4 / HR5 column). Test conditions: mobile phase was THF (flow rate 1 mL / min), column temperature 35℃, injection volume 100 μL (sample concentration 1 mg / mL); a standard curve was plotted using polystyrene standards, and the number-average molecular weight (Mn) and dispersity (PDI = (Mw / Mn)) were calculated. The test result was Mn = (4.15 ± 0.08) × 10⁻⁶. 4 g / mol, PDI = 1.48 ± 0.03.

[0085] (2)Ce 3+ Preparation of doped spherical alumina filler: The filler obtained in Example 1 was used;

[0086] (3) Double-layer coating modification of fillers:

[0087] Topological insulation layer coating: in Ce 3+Atomic layer deposition (ALD) of doped spherical alumina filler was performed using an ALD R-200 atomic layer deposition system (Guangzhou Jingying Scientific Instruments Co., Ltd.) with tris(2,2,6,6-tetramethyl-3,5-heptadecyl)bismuth(III) / bis(trimethylsilyl)tellurium / di-tert-butylselenium as precursors at 150 °C (x = 0.15). The pulse deposition parameters were as follows: tris(2,2,6,6-tetramethyl-3,5-heptadecyl)bismuth(III) pulse 0.25 s, variable flow Ar purge 10 s; bis(trimethylsilyl)tellurium pulse 0.66 s, flow Ar purge 10 s; di-tert-butylselenium pulse 0.38 s, flow Ar purge 10 s; 210 cycles. After annealing, the material was annealed for 40 minutes at 300℃ in a box-type resistance furnace with a N2 / Se (v:v = 95:5) mixture; then quenched with He gas to obtain Bi2Te with a thickness of 8.3 ± 0.5 nm and a uniformity (σ) of 4.8%. 2.85 Se 0.15 Topological insulating layer.

[0088] Phosphate ester silane coupling agent coating: γ-aminopropyltriethoxysilane and tris(tert-butyldimethylsilyl)phosphite were mixed in ethanol / water (v:v = 95:5) at a mass ratio of 1:1.5 and pre-hydrolyzed at pH = 4.5 for 30 min; then Bi2Te 2.85 Se 0.15 Encased Ce 3+ Doped spherical alumina filler was dispersed in the solution at a solid-liquid ratio of 1:10-15, and the solution was heated to 80℃ and stirred for 6.5 h. After centrifugation and washing, the solution was vacuum dried at 60℃ to obtain a double-layer coated Ce. 3+ Doped spherical alumina filler.

[0089] (4) The liquid crystal copolymer (45 wt%) from step (1) and the filler (40 wt%) obtained in step (3) were added to a twin-screw extruder. 5 wt% bismaleimide, 3 wt% Tinuvin 770 and 7 wt% triethyl citrate were added, and the mixture was melt-sheared and mixed at 285°C and 300 rpm to obtain a melt. The melt was then poured into a casting die. Casting was performed in a DL-LYJ-20MU240 film casting machine (Zhejiang Delong Technology Co., Ltd.): the casting temperature was set to 285°C, the cooling roller temperature was set to 80°C, and the melt flow rate was 5.0 g / 10 min. The temperature was lowered to 180°C at a rate of 15°C / min, and then further cooled to 80°C at a rate of 25°C / min. Unidirectional casting was performed to obtain a 0.3 mm thick sheet. The substrate material (100mm×100mm×1mm) was then annealed in a SX2-12-16 type box-type resistance furnace at a temperature of 5℃ / min to 140℃ for 4 hours to obtain the substrate material.

[0090] Example 2

[0091] The difference from the example is that in step (1), the molar percentages of 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid, p-hydroxybenzoic acid, and 5,5'-dithiobis(2-nitrobenzoic acid) are 12 mol%, 68 mol%, and 20 mol%, respectively. The Mn of the liquid crystal copolymer was determined by GPC to be (3.82 ± 0.12) × 10⁻⁶. 4 g / mol, PDI = 1.53 ± 0.05.

[0092] Example 3

[0093] The difference from Example 1 is that in step (1), the molar percentages of 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid, p-hydroxybenzoic acid, and 5,5'-dithiobis(2-nitrobenzoic acid) are 15 mol%, 62 mol%, and 23 mol%, respectively. GPC measured the Mn of the liquid crystal copolymer to be (4.41 ± 0.06) × 10⁻⁶. 4 g / mol, PDI = 1.45 ± 0.02.

[0094] Example 4

[0095] The difference from Example 1 is that in step (3), the atomic layer deposition parameters were adjusted as follows: bis(trimethylsilyl)tellurium pulse 0.72s, Ar purging flow rate 10s; di-tert-butylselenium pulse 0.32s, Ar purging flow rate 10s (x = 0.12); 205 cycles were performed to obtain Bi2Te with a thickness of 8.2 ± 0.2 nm and σ = 3.4%. 2.88 Se 0.12 Coating layer.

[0096] Example 5

[0097] The difference from Example 1 is that in step (3), the atomic layer deposition parameters were adjusted as follows: bis(trimethylsilyl)tellurium pulse 0.60s, Ar purging flow rate 10s; di-tert-butylselenium pulse 0.45s, Ar purging flow rate 10s (x = 0.18); 250 cycles were performed to obtain Bi2Te with a thickness of 8.1 ± 0.4 nm and σ = 6.6%. 2.82 Se 0.18 Coating layer.

[0098] Example 6

[0099] The difference from Example 1 is that in step (4), the liquid crystal polymer matrix and the double-layer coated Ce 3+ The mass ratios of the doped spherical alumina fillers were 48 wt% and 37 wt%, respectively.

[0100] Comparative Example 1

[0101] The difference from Example 1 is that in step (1), only p-hydroxybenzoic acid was used for homopolymerization to obtain a liquid crystal homopolymer before subsequent operations were performed. GPC measurements showed that the Mn of the liquid crystal homopolymer was (2.85 ± 0.14) × 10⁻⁶. 4 g / mol, PDI = 1.85 ± 0.05.

[0102] Comparative Example 2

[0103] The difference from Example 1 is that in step (1), 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid was not added, and the amounts of 5,5'-dithiobis(2-nitrobenzoic acid) and p-hydroxybenzoic acid were 25.6 mol% and 74.4 mol%, respectively. GPC measured the Mn of the liquid crystal copolymer to be (3.21 ± 0.1) × 10⁻⁶. 4 g / mol, PDI = 1.72 ± 0.04.

[0104] Comparative Example 3

[0105] The difference from Example 1 is that in step (3), Bi2Te is removed. 3-x Se x Topological insulation layer coating process, i.e. Ce 3+ The doped spherical alumina is only coated with a phosphate ester silane graft layer.

[0106] Comparative Example 4

[0107] The difference from Example 1 is that step (2) uses the pure spherical alumina filler obtained in Example 2, while the subsequent double-layer coating modification operation remains unchanged.

[0108] I. Structural characterization of the packing material:

[0109] (1) X-ray diffraction (XRD): XRD was used to analyze Ce in the preparation of Example 1. 3+ Doped spherical alumina fillers and the double-layer coated Ce in Examples 1, 4-5, and Comparative Examples 3-4 3+ XRD characterization of doped spherical alumina fillers was performed. The testing equipment was a FRINGECLASS desktop X-ray diffractometer (Nanjing Aocong Electronics Co., Ltd.), with Cu Kα radiation (λ = 0.15406 nm), tube voltage 40 kV, tube current 40 mA, and a scan rate of 2° / min. The step size was 0.02°. Grain size was calculated using the Scherrer equation (β = Kλ / (Dcosθ), K = 0.89, β is the full width at half maximum (FWHM), and θ is the diffraction angle). Results are shown below. Figure 1 The standard cards are labeled below the image (γ-Al2O3: PDF#00-010-0425, Bi2Se3: PDF#01-089-2008 and Bi2Te3: PDF#00-015-0803).

[0110] Figure 2 In the preparation of Ce in Example 1 3+ The doped spherical alumina is clearly a γ-Al2O3 phase: characteristic peaks include (111), (311), (400), and (440), with 37.6° (311) being the main peak. Ce 3+ Doping caused the 45.8° (400) peak to shift to the right (refer to the γ-Al2O3 standard card PDF#00-010-0425).

[0111] Example 1 shows Bi2Te 3-x Se x The characteristic peaks of the 17.7° (006) and 27.5° (015) crystal planes confirm that Bi2Te 2.85 Se 0.15 It has a hexagonal layered structure. The (006) crystal plane has a half-width at half-maximum of 1.8° and a grain size of 4.2 nm; the (015) crystal plane has a half-width at half-maximum of 0.32° and a grain size of 4.5 nm. Se doping causes the (015) peak to shift to the left (refer to Bi2Te3 standard card PDF#00-015-0803).

[0112] In Example 4, due to the decrease in Se content, the (006) crystal plane peak shifted to the left and the (015) crystal plane peak shifted to the right. In Example 5, the Se content was higher, the lattice mismatch increased, and the intensity of the (015) peak decreased by 10%; and because the atomic radius of Se (≈117 pm) is smaller than that of Te (≈142 pm), a selenium-rich region is easily formed when high Se doping occurs: therefore, a 32.5° selenium-rich phase peak appears (refer to Bi2Se3 standard card PDF#01-089-2008, 32.6° (101) crystal plane), but the intensity of this selenium-rich phase peak is ≤5%, which does not affect Bi2Te. 3-x Se x The main structure of the topological insulating layer. Further increasing the Se content leads to a further increase in lattice distortion, far exceeding that of Bi2Te. 3-x Se x The solid solution limit and severe phase separation lead to selenium atom segregation and the formation of Bi2Se3 nanophase, indicating that x = 0.18 is the upper limit.

[0113] Comparative Example 3 without Bi2Te 3-x Se x The characteristic peak, a sharp peak at 37.6° (311), indicates a grain size of 50 nm. Comparative Example 4 (Ce-free) 3+ The characteristic peak at 37.6° (311) shifts to the left (larger lattice) and the phase intensity at 45.8° (400) increases, indicating higher crystallinity.

[0114] (2) X-ray fluorescence spectroscopy (XRF): Characterization was performed using high-resolution XRF (Thermo Scientific ARLQuant's XED XRF spectrometer). Excitation source: Rh target X-ray tube (40kV / 50mA), detector: Si-PIN detector (resolution 145eV@MnKα). Testing was conducted in an atmospheric environment, with major element testing for 300s and trace element testing for 600s, ensuring a SeKα count rate >3000cps. Compton scattering internal standard method (I0.05) was used. Te Lα / I 总 To eliminate the influence of sample thickness, the atomic ratio was calculated using the fundamental parameter method (FP). Furthermore, the interference of Bi Mβ (9.8 keV) on Te Lβ needed to be corrected, with a correction factor k = 0.087 (correction formula is...). Table 2 and... Figure 2 The results are shown.

[0115] Table 2

[0116] Example Se doping level (x) Te / Bi atomic ratio TeLα / BiLα intensity ratio SeKα / BiLα intensity ratio 1 0.15 1.425 1.43±0.03 0.15±0.02 4 0.12 1.44 1.45±0.03 0.12±0.02 5 0.18 1.41 1.41±0.03 0.18±0.02

[0117] Figure 2 In Examples 1, 4, and 5, characteristic spectral lines of Bi Lα (10.84 keV), Te Lα (4.51 keV), and Se Kα (11.22 keV) were observed. In Example 1, the full width at half maximum (FWHM) of the Te Lα peak was 0.22 keV, and the Te Lα / Bi Lα intensity ratio was 1.43. In Example 4, the FWHM of the Te Lα peak was 0.21 keV, which was sharper than that of Example 1, with a slightly higher Te / Bi intensity ratio and a decreased intensity of the Se Kα characteristic peak. In Example 5, the intensity of the Te spectral line was lower than that of Example 1, the Te / Bi ratio decreased to 1.41, while the Se peak intensity increased. Table 2 also shows that the Te / Bi ratio decreased with increasing Se doping concentration.

[0118] (3) Topological Surface State (TSS) Analysis:

[0119] The topological surface states in the fillers of Examples 1, 4, and 5 were further verified using angle-resolved photoelectron spectroscopy (ARPES, Scienta Omicron, Shanghai Microway Semiconductor Technology Co., Ltd.). Plotting momentum kx (π / a) on the horizontal axis and energy (eV) on the vertical axis yielded... Figure 3 Two-dimensional dispersion maps of angle-resolved photoelectron spectroscopy for Examples 1, 4-5 and Comparative Example 3 are shown. Figure 3In the diagram, a black / white dashed line marks the location where the Fermi level (EF) is 0 eV: this is the absolute reference for ARPES analysis, used to determine the occupancy of electronic states (below which are occupied states, above which are unoccupied states); light and dark colors (blue-yellow-red) are used to visually represent the intensity of the photoelectric emission signal, i.e., the electronic state density in momentum space. A red pentagram clearly marks the vertex of the Dirac cone (i.e., the Dirac point).

[0120] In Bi2Te 3-x Se x In this system, the introduction of Se gradually pushes the Fermi level from the valence band peak (p-type) of Bi₂Te₃ towards the center of the band gap of Bi₂Se₃. Dirac cone linear dispersion was observed in Examples 1, 4, and 5, proving that Bi₂Te₃… 3-x Se x Successful encapsulation of the topological insulating layer. Its upward-opening "V" or "U" shaped dispersion band is a hallmark feature of the topological surface states.

[0121] Example 1 shows a clear Dirac cone dispersion, exhibiting a single, gapless topological surface state with a bulk band gap of ~0.15 eV; the Dirac point is located ~300 meV below the valence band apex. This confirms that appropriate Se doping achieves optimal bulk insulation, maximally suppressing bulk carrier interference on the signal.

[0122] In Example 4, due to insufficient Se (x = 0.12), a strong bulk electron signal appeared near the Fermi level (EF); surface states and bulk states were mixed. This indicates that even with low Se doping, the bulk phase still exhibits n-type semiconductor characteristics. The Fermi level penetrates the conduction band, and a large number of free bulk electrons annihilate the relatively weak topological surface state signal, resulting in insufficient clarity of the Dirac cone. In Example 5, the Dirac cone is clear, but the Dirac point is deeply embedded in the valence band (>400 meV), with no surface state channel at the Fermi level, leading to an increased bulk band gap. This indicates that although a large number of Se-doped topological surface states exist, they cause the Fermi level to be significantly pinned in the valence band, and its Dirac point is far from the Fermi level, failing to provide an effective electron transport channel. Therefore, the amount of Se doping (x) must be strictly controlled within the solid solution limit. If it is excessive (x > 0.18), it will cause the separation of the selenium-rich phase, resulting in lattice distortion and increased carrier scattering. The Dirac point is trapped in the valence band (EF ~ 0.5 eV), and surface state electrons need to overcome the energy barrier to participate in the transport, which leads to a decrease in mobility.

[0123] Comparative Example 3 without Bi2Te 3-x Se xTopological insulating layer coating, in essence, is a wide-bandgap insulator ceramic, lacking the crystal structure and symmetry of topological insulators, and therefore completely lacks topologically protected surface states. Consequently, its spectrum exhibits a featureless diffuse background or impurity states, without a Dirac cone dispersion relation; and while impurity states exist, they lack a band gap and manifest as metallic or defect states.

[0124] The above three characterization results indicate that x = 0.15 is the optimal solution.

[0125] II. Compositional analysis of liquid crystal copolymers / homomers:

[0126] Infrared spectroscopy was performed on the liquid crystal copolymers in Example 1 and Comparative Example 2, as well as the liquid crystal homopolymer of Comparative Example 1. Instrument: Nicolet iS50 FTIR spectrometer, KBr pellet method (sample: KBr = 1:100), resolution: 4 cm⁻¹ -1 Scanning range: 400-4000cm -1 The scan was performed 32 times, and the baseline was automatically corrected using OMNIC software. Wavenumbers (cm²) were used to measure the baseline. -1 Plotting absorbance (au) on the x-axis and absorbance (au) on the y-axis, we get... Figure 4 The infrared absorption spectrum.

[0127] Depend on Figure 4 Example 1 at 1730cm -1 (ester group) and 1710cm -1 (Imide) bimodal separation is clear; at 1595 cm⁻¹ -1 With 1350cm -1 The presence of both asymmetric and symmetric characteristic peaks of the nitro group confirms the successful copolymerization of 5,5'-dithiobis(2-nitrobenzoic acid); and the 510 cm⁻¹ peak further confirms this. -1 The disulfide bond peak indicates a complete disulfide bond structure. Benzooxazole ring (1620 cm⁻¹) -1 This also indicates the presence of 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid. The 1695 cm⁻¹ of Comparative Example 1... -1 Broad peak (unreacted carboxyl group) and 3440 cm⁻¹ -1 A strong peak (free hydroxyl group) indicates a low end-capping rate in the homopolymer; and the oxazole ring is missing (1620 cm⁻¹). -1 ), Nitro (1595cm) -1 Peak. Comparative Example 2 at 1700 cm⁻¹. -1 (imide) and 1728cm -1 (Ester group) partially overlaps.

[0128] 3. Performance characterization of substrate materials

[0129] The following tests were performed on all embodiments and comparative examples, and the results are summarized in Table 3.

[0130] The dielectric loss factor tanδ@28GHz was measured according to IEC 61189-2 at 28GHz and 23±0.5℃.

[0131] Thermal conductivity was tested using the laser flare method (ASTM E1461) with a Netzsch LFA467 HyperFlash laser flare meter: pulsed laser energy 10J, detection delay 10μs; at 25℃ in an N2 atmosphere.

[0132] Peel strength was tested according to ASTM D3167 using an INSTRON 5967 universal testing machine (5kN load cell). The ambient temperature was 23℃ and the humidity was 50%. The sample was a Type 1BA dumbbell type (150mm long, 25mm gauge length, 10mm width), with a tensile rate of 10mm / min. The test was repeated 5 times, and the average value was taken.

[0133] Alpha-ray shielding efficiency was measured according to ISO 18589-6:2020. The measurement was performed using an ORTEC alpha spectrometer (equipped with a PIPS detector, resolution 18 keV @ 5.486 MeV). The radiation source was... 241 Am (activity 100 kBq, energy 5.486 MeV), sample fixed between source and detector (distance 2 cm); background count was measured first for 30 min, then sample count for 3600 s. Alpha ray shielding efficiency = (1 - sample count / background count) × 100%

[0134] Carrier mobility was measured using a TeraView TPS Spectra 3000 terahertz time-domain spectrometer (THz-TDS). Test conditions: THz pulse frequency 0.3–3 THz, N2 atmosphere (humidity <5%), sample thickness 0.3 mm.

[0135] The UV aging yellowness index ΔE was determined by first aging the samples in a Q-Lab QUV / se UV aging chamber (using a UVB-313 lamp with an irradiance of 0.71 W / m²). 2 The sample was aged at 340nm for 1000 hours at 60℃; after vacuum drying at 60℃ for 2 hours, it was tested with a KonicaMinolta CM-700d colorimeter, and the average value of 5 measuring points was taken.

[0136] For damp heat aging Δtanδ, the sample was first aged in an ESPEC SH-241 constant temperature and humidity chamber at 85℃ / 85%RH for 1000h; tanδ was measured before and after damp heat aging at 28GHz, Δtanδ=(aged tanδ-initial tanδ) / initial tanδ×100%.

[0137] Table 3

[0138]

[0139] The 5G base station substrate material provided by this invention is based on liquid crystal copolymer-Ce 3+ The synergistic effect of doped filler and double-layer coating achieves a performance balance of ultra-low dielectric loss (tanδ < 0.00014), high thermal conductivity (≥ 3.35 W / mK), high alpha-ray shielding (≥ 99.95%), and high reliability (Δtanδ ≤ +0.3%). The rigid and electron-withdrawing 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid monomer in the liquid crystal copolymer matrix helps reduce tanδ and improve thermal conductivity; the synergistic effect of the phosphate-filler hydroxyl coordination bonds and the amino-resin carboxyl covalent bonds in the phosphate ester silane graft layer strengthens the interfacial bonding force, preventing moisture penetration in humid and hot environments.

[0140] The liquid crystal homopolymer / polymer raw materials of Comparative Examples 1 and 2 lacked 4-(5-amino-6-hydroxy-2-benzoxazole)-benzoic acid units, resulting in high molecular chain disorder and intensified dipole polarization. Their tanδ values ​​were 3.6 times and 3.5 times that of Example 1, respectively, and their thermal conductivity decreased to 1.20–2.80 W / mK.

[0141] Comparative Example 3 lacks Bi2Te 3-x Se x The dielectric modulation of the topological insulating layer enhances the polarization of the filler-resin interface, with tanδ being 2.14 times that of Example 1; the electronic thermal conductivity channel is lost, and the thermal conductivity drops to 3.10 W / mK; there is no ultraviolet absorption function, and ΔE increases to 8.0.

[0142] Ce doping 3+ It can generate lattice defects, enhancing Bi2Te 3-x Se x Adhesion of the topological insulating layer coating; Comparative Example 4 lacking Ce 3+ Therefore, the peel strength is the lowest, the double coating layer is easy to fall off, which leads to increased interfacial polarization, a significant increase in tanδ, and a sharp drop in α-ray shielding efficiency.

[0143] In summary, the substrate material provided by this invention, through the synergistic design of liquid crystal copolymer matrix, doped filler, and double-layer coating, can meet the core requirements of 5G millimeter-wave base station substrates for ultra-low dielectric loss, high thermal conductivity, and high reliability.

[0144] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low-alpha-ray spheroid alumina / liquid crystal polymer 5G base station substrate material characterized by, The substrate material comprises the following components, based on the total mass of the substrate material being 100 wt%: 42-50 wt% of a liquid crystalline copolymer matrix comprising the following molar percentages of carboxylic acid comonomers: 60-68 mol% of p-hydroxybenzoic acid, 20-24 mol% of 5,5'-dithiobis(2-nitrobenzoic acid) and 12-16 mol% of 4-(5-amino-6-hydroxy-2-benzoxazolyl)-benzoic acid; and the 5,5'-dithiobis(2-nitrobenzoic acid) needs to be pre-complexed with a cerium-containing compound before copolymerization; 35-40 wt% Ce 3+ Doped spherical alumina filler, whose surface is coated in turn: Bi2Te 3-x Se x Topological insulating layer and phosphonate silane grafting layer, where x = 0.12-0.18; 3-5 wt% of a bismaleimide, 2-4 wt% of an ultraviolet absorber and 5-9 wt% of a plasticizer.

2. The substrate material of claim 1, wherein: The ultraviolet absorber is a hindered amine light stabilizer, and the plasticizer is triethyl citrate; The substrate material has an alpha-ray shielding rate of ≥99.95%, a thermal conductivity of ≥3.35 W / mK, a dielectric loss factor tan δ of <0.00014 at a frequency of 28 GHz, and a Δtan δ of ≤+0.3% after 1000 hours of damp heat aging at 85°C / 85% RH.

3. The substrate material of claim 1, wherein, The substrate material is prepared by the following method: (1) Preparation of liquid crystal copolymer: 5,5'-dithiobis(2-nitrobenzoic acid) and cerium-containing compound are mixed according to carboxyl:Ce 3+ molar ratio = 1:1.2, pre-complexed at 50-65 ℃ for 2-3 h, mixed with 4-(5-amino-6-hydroxy-2-benzoxazolyl)-benzoic acid and p-hydroxybenzoic acid; under N2 atmosphere, irradiated by 385-405 nm, 30-40 mW / cm 2 of LED light source for 100-150 min in stages to obtain liquid crystal copolymer, wherein the number average molecular weight Mn of the liquid crystal copolymer is greater than or equal to 3.5 × 10 4 g / mol, and the PDI is less than or equal to 1.

6. (2) Ce 3+ Preparation of the doped spherical alumina filler: using cerium nitrate-aluminum nitrate as the precursor, co-precipitation was carried out in an ammonia water-ammonium carbonate mixed solution with pH = 10.0 ± 0.2, and then spray drying, freeze drying and plasma activation sintering processes were carried out to obtain Ce 3+ doped spherical alumina; the Ce 3+ The doping amount is 1.5-2.8 mol%, based on the total moles of Al2O3. (3) Double-layer coating modification of the filler: on the surface of the filler obtained in step (2), a bismuth-containing compound, a tellurium-containing compound and a selenium-containing compound are used as precursors, specifically tris(2,2,6,6-tetramethyl-3,5-heptanedione) bismuth(III) / bis(trimethylsilyl) tellurium / di-tert-butyl selenium, atomic layer deposition for 200-250 times at 140-150 ℃, growth of Bi2Te 3-x Se x topological insulating layer; and annealing at 300 ℃ under N2 / Se = 95:5 mixed gas for 30-60 min, inert gas quenching; finally, grafting with a phosphate silane coupling agent to obtain a double-layer coated Ce 3+ doped spherical alumina; (4) Casting: the liquid crystal copolymer of step (1), the double-layer coated Ce 3+ Shearing mixed the doped spherical alumina filler and bismaleimide, and synchronously added ultraviolet absorber and plasticizer to obtain a composite melt; sequentially casted at 280-290 ℃; and then subcooled to 80 ℃, and annealed at 120-140 ℃ for 2-4 h to obtain the substrate material.

4. The substrate material of claim 3, wherein, In step (1), the parameters of the staged temperature increase are: 180°C for 30-40 min, 220°C for 60-90 min, and 240°C for 30-50 min; a tetrabutyl titanate catalyst and lithium borate are further added to the copolymerization system; the amount of the tetrabutyl titanate catalyst is 0.06-0.09 wt%, and the amount of the lithium borate is 0.1-0.2 wt%, both based on the total mass of the system.

5. The substrate material of claim 3, wherein, In step (2), the inlet temperature of the spray drying is 200±10°C, and the freeze-drying temperature is -60--50°C.

6. The substrate material of claim 3, wherein, In step (2), the process of the plasma activation sintering is as follows: The freeze-dried particles are pulsed activated for 60-90 seconds by a magnetic rotating arc plasma torch under an Ar / H2 mixed atmosphere with a volume ratio of 95:5 at a power of 50-150 kW; then heated to 1050-1100°C at a rate of 80-100°C, and the axial pressure is loaded in stages to 40-60 MPa, and kept for 6-10 min; rapidly cooled to ≤200°C by liquid nitrogen; finally, annealed at 800°C in an N2 atmosphere for 30-40 min; the mode of the pulsed activation is on for 60 ms and off for 30 ms.

7. The substrate material of claim 3, wherein, In step (3), the bismuth-containing compound is tris(2,2,6,6-tetramethyl-3,5-heptanedione) bismuth(III), the tellurium-containing compound is bis(trimethylsilyl) tellurium, and the selenium-containing compound is di-tert-butyl selenium; the atomic layer deposition uses pulse feedback control, and the parameters are as follows: tris(2,2,6,6-tetramethyl-3,5-heptanedione) bismuth(III) pulse 0.20-0.30 s, variable flow Ar purge 10 s; bis(trimethylsilyl) tellurium pulse 0.55-0.72 s, variable flow Ar purge 10 s; di-tert-butyl selenium pulse 0.30-0.45 s, variable flow Ar purge 10 s; the Se:Te molar ratio is (6-9):(44-41).

8. The substrate material of claim 3, wherein: The grafting process in step (3) is: pre-hydrolyzing γ-aminopropyl triethoxysilane and tris (tert-butyl dimethyl silyl) phosphite in a mass ratio of 1:1-2 at pH=4.5 for 30-40 min; dispersing the filler in it at a solid-liquid ratio of 1:10-15, and refluxing at 60-85℃ for 6-8 h.

9. The substrate material of claim 3, wherein: In step (4), the melt flow rate of the casting forming is 5±0.2 g / 10 min, the temperature decreasing rate of the staged cooling is 15-25℃ / min, and the temperature increasing rate of the annealing treatment is 5℃ / min.

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