Low-dielectric and low-loss halogen-free epoxy plastic packaging material and preparation method thereof

Abstract

The present application relates to the technical field of high polymer materials, and particularly relates to a low-dielectric low-loss halogen-free epoxy plastic packaging material and a preparation method thereof; the present application adopts naphthalene type epoxy resin as a main body resin, cooperates with active ester curing agent and benzoxazine prepolymer as a modified auxiliary agent, and adds porous mullite microspheres with a double-layer coating of polydopamine and silicon dioxide on the surface as inorganic fillers; the benzoxazine prepolymer takes magnolol as a skeleton, is modified by a phosphorus flame-retardant group and is siloxane functionalized, introduces efficient halogen-free flame-retardant elements phosphorus and silicon, participates in the epoxy curing reaction through the benzoxazine ring, and the siloxane segment can improve the filler dispersibility; the porous mullite microspheres contain a large number of pores inside, and the external coating layer is dense and closed, so that the dielectric constant and thermal conductivity of the material can be effectively reduced without sacrificing the processability and reliability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a low dielectric, low loss, halogen-free epoxy molding compound and its preparation method. Background Technology

[0002] With the development of high-frequency and high-speed applications such as 5G communication, millimeter-wave radar, and high-speed data centers, increasingly stringent requirements are being placed on the signal integrity and transmission efficiency of semiconductor packaging materials. The dielectric constant of the packaging material directly determines the signal transmission speed and characteristic impedance, while dielectric loss affects signal attenuation and heat generation. Both must be kept at extremely low levels to ensure effective transmission of high-frequency signals. Furthermore, in system-in-package (SiP), the molding compound often serves directly as the substrate for redistribution layers or as the antenna dielectric. This requires the material to not only possess excellent dielectric properties but also a low coefficient of thermal expansion, low moisture absorption, and high reliability. Simultaneously, for environmental and safety reasons, the molding compound must meet halogen-free flame-retardant requirements.

[0003] Currently, the main approaches to reducing the dielectric constant and dielectric loss of epoxy molding compounds include selecting low-polarity epoxy resins, using reactive ester curing systems to eliminate secondary hydroxyl groups, and adding low-dielectric inorganic fillers. For example, naphthalene-type epoxy resins, due to their low carbon-hydrogen skeleton polarizability, are often used as the main resin in low-dielectric formulations; reactive ester curing agents react with epoxy groups to form ester bonds, avoiding the problem of generating a large number of polar alcohol hydroxyl groups in traditional phenolic curing, thus effectively reducing losses. Regarding fillers, molten spherical silica is currently the mainstream inorganic filler due to its low intrinsic dielectric constant and good flowability. To meet halogen-free flame retardant requirements, phosphorus- or nitrogen-containing flame retardants are typically used to replace traditional bromine-based flame retardants, such as introducing phosphaphenanthrene heterocyclic compounds into the resin backbone or adding phosphazene flame retardants.

[0004] However, existing technologies still have the following shortcomings. First, the reduction in dielectric constant by simply modifying resin is limited; the dielectric constant of pure resin systems is typically difficult to lower than 2.8, and the excessive use of large-volume groups or flexible segments in pursuit of low loss often leads to a decrease in heat resistance. Second, the intrinsic dielectric constant of traditional spherical silica is approximately 3.8, and its thermal conductivity is approximately 1.4 W / m·K. Even after introducing epoxy molding compounds, the thermal conductivity may still be too high for applications such as antenna packaging where heat dissipation is not required, thus causing unnecessary thermal crosstalk. Furthermore, existing halogen-free flame retardants, such as those simply containing phosphate esters or phosphazene compounds, often exhibit poor compatibility with resins, migration and precipitation, or negatively impact dielectric properties. Therefore, developing a halogen-free epoxy molding compound that combines low dielectric constant, low dielectric loss, low thermal conductivity, high flame retardancy, and high reliability remains a pressing issue in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a low-dielectric-loss, low-loss halogen-free epoxy molding compound and its preparation method. This invention uses naphthalene-type epoxy resin as the main resin, combined with an active ester curing agent and benzoxazine prepolymer as modifying agents, and adds porous mullite microspheres with a surface double-layer coating of polydopamine and silica as inorganic fillers. The benzoxazine prepolymer uses magnolol as its backbone, modified with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and functionalized with siloxanes. This introduces highly efficient halogen-free flame-retardant elements phosphorus and silicon, and allows the benzoxazine ring to participate in the epoxy curing reaction. Simultaneously, its siloxane segments improve filler dispersibility. The porous mullite microspheres contain numerous pores, and the external coating layer is tightly sealed, effectively reducing the dielectric constant and thermal conductivity of the material without sacrificing processability and reliability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound, comprising the following steps: Step S1: Weigh the following raw materials in parts by weight: 60 parts of naphthalene-type epoxy resin, 45-50 parts of reactive ester curing agent, 10-15 parts of benzoxazine prepolymer, 40-50 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent and 1 part of curing accelerator. Step S2: Mix naphthalene-type epoxy resin, reactive ester curing agent, benzoxazine prepolymer and curing accelerator, mix at 90°C for 15 min, then add mold release agent, low dielectric and low thermal conductivity microspheres and spherical silica and continue mixing for 20 min, then transfer to an extruder, melt extrude at 180°C, and cure to obtain low dielectric and low loss halogen-free epoxy molding compound.

[0007] The benzoxazine prepolymer was prepared by the following steps: Step A1: Magnolol and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were mixed and reacted under nitrogen protection at a stirring rate of 150 rpm and a temperature of 160 °C for 24 h. The mixture was washed with ethanol / deionized water and dried to obtain the magnolol intermediate. Step A2: Mix magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and toluene, stir at 300 rpm at room temperature for 30 min, then heat to 85 °C and react for 6 h, rotary evaporate, and distill under reduced pressure to obtain benzoxazine prepolymer. Furthermore, in step A1, the ratio of magnolol to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 26.6g:47.5g; In step A2, the ratio of magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and toluene is 6.9-7 g: 1.24 g: 4.5 mL: 20 mL.

[0008] The low-dielectric and low-thermal-conductivity microspheres are prepared by the following steps: Step B1: Mix aluminum sec-butoxide, tetraethyl orthosilicate, ethyl acetoacetate and n-octanol, and stir at 300 rpm at room temperature for 60 min. Then add Span-80 and polyvinylpyrrolidone, and continue stirring for 20 min to obtain an oil phase aluminum silica sol. Mix sodium dodecyl sulfate, OP-10 and deionized water, and stir at 500 rpm at 40°C for 30 min to obtain an aqueous phase. Furthermore, in step B1, the ratio of aluminum sec-butoxide, ethyl orthosilicate, ethyl acetoacetate, n-octanol, Span-80, and polyvinylpyrrolidone is 2.2-2.3g:0.65g:1.2g:5mL:0.3g:0.25g, and the ratio of sodium dodecyl sulfate, OP-10, and deionized water is 2g:4g:200mL.

[0009] Step B2: Pour the oil phase aluminum silica sol into the aqueous phase, stir for 24 hours at a stirring rate of 600-1000 rpm and room temperature, centrifuge, filter, wash with deionized water / ethanol, and dry to obtain precursor microspheres. Place the precursor microspheres in a tube furnace, heat from room temperature to 350℃ at 0.5℃ / min and hold for 2 hours in an air atmosphere, then heat to 1200℃ at 2℃ / min and hold for 3 hours. Cool, sieve, and obtain porous mullite microspheres. Step B3: Porous mullite microspheres and Tris-HCl buffer were mixed and ultrasonically dispersed. Dopamine hydrochloride was added while stirring at 150 rpm and room temperature. The mixture was stirred for 12 h, centrifuged, filtered, washed, and dried to obtain dopamine-coated microspheres. The dopamine-coated microspheres were mixed with an ethanol solution, and ammonia solution was added to adjust the pH to 9. The mixture was stirred at 300 rpm and room temperature, and a mixture of tetraethyl orthosilicate and ethanol was added. The mixture was reacted for 6 h, centrifuged, filtered, washed, and dried. The mixture was then heat-treated at 175 °C for 2 h under a nitrogen atmosphere to obtain low dielectric and low thermal conductivity microspheres. Furthermore, in step B3: the ratio of porous mullite microspheres, Tris-HCl buffer, and dopamine hydrochloride is 1.5-1.8g:50mL:1.3g, wherein the pH of the Tris-HCl buffer is 8.5 and the molar concentration is 0.01mol / L; the ratio of dopamine-coated microspheres, ethanol aqueous solution, tetraethyl orthosilicate, and ethanol is 3g:40mL:0.3-0.5g:5mL, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 4:1.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a low dielectric and low loss halogen-free epoxy molding compound and its preparation method; the present invention uses naphthalene-type epoxy resin as the main resin, combined with an active ester curing agent and benzoxazine prepolymer as modifying agents, and adds porous mullite microspheres with a surface double-layer coating of polydopamine and silica as inorganic fillers; the benzoxazine prepolymer uses magnolol as the backbone, and is modified by DOPO and functionalized with siloxane, which not only introduces the highly efficient halogen-free flame retardant elements phosphorus and silicon, but also participates in the epoxy curing reaction through the benzoxazine ring, while its siloxane segments can improve the dispersibility of the filler; the porous mullite microspheres contain a large number of pores inside, and the outer coating layer is tightly sealed, which can effectively reduce the dielectric constant and thermal conductivity of the material without sacrificing processability and reliability.

[0011] In the preparation process of the benzoxazine prepolymer of this invention, magnolol is used as the backbone. Magnolol itself contains a biphenyl structure. The biphenyl group has a symmetrical electron cloud and low polarizability, which provides crosslinking sites and flame retardant function without significantly increasing the dielectric constant of the system. The benzoxazine ring undergoes ring-opening polymerization upon heating, forming a semi-interpenetrating crosslinked structure with the epoxy resin and reactive ester curing network. This not only eliminates the secondary alcohol hydroxyl groups caused by traditional phenolic curing, but also reduces curing internal stress and further improves dielectric loss due to the absence of small molecule release and near-zero shrinkage during ring opening. The siloxane groups on the prepolymer side chains can be hydrolyzed and condensed into a micro-crosslinked siloxane network, or partially grafted onto the filler surface, effectively improving the dispersion uniformity of low-dielectric microspheres in the epoxy matrix and reducing interfacial polarization and loss caused by filler agglomeration. At the same time, the introduction of silicon has a synergistic flame retardant effect, working together with the phosphorus provided by DOPO to form a dense phosphorus-silicon char layer during combustion, with flame retardant efficiency far superior to a single flame retardant mechanism.

[0012] The low-dielectric and low-thermal-conductivity microspheres utilize mullite as the matrix. Mullite itself has a dielectric constant of approximately 6.5-7 and exhibits excellent mechanical strength and a low coefficient of thermal expansion. Through a sol-emulsion template method combined with calcination, numerous nanoscale isolated closed pores filled with air are generated within the microspheres. These closed pores, acting as a low-dielectric phase, are uniformly dispersed within the mullite framework, effectively reducing the equivalent dielectric constant and thermal conductivity of the microspheres. A double-layer shell of polydopamine and silica is then sequentially coated onto the surface: the polydopamine layer is closely adhered to the mullite. The surface seals off any remaining semi-open pores and provides a uniform anchoring surface for the silica shell. The outer silica layer forms a dense encapsulation layer, which can further form covalent bonds with epoxy resin through a coupling agent. This "organic-inorganic covalent bridging" completely suppresses the interfacial polarization between the filler and the resin, which is the most important contribution to low dielectric loss. At the same time, the complete encapsulation prevents resin from penetrating into the inner cavity, ensuring that the dielectric effect of the closed pores is not annihilated, and also enabling the microspheres to withstand the high pressure of transfer molding without changing their structural integrity.

[0013] In the overall formulation, the all-carbon-hydrogen bridged ring skeleton of naphthalene-type epoxy gives it an extremely low molecular polarizability, and the active ester curing avoids the appearance of secondary hydroxyl groups. In combination with the curing accelerator, it maximizes the reduction of electrical loss from the source of the resin phase. The low dielectric microspheres, through the physical introduction of air cavities and interface passivation, enable the composite material to achieve a lower dielectric constant at a lower filling density than traditional silica, while maintaining low thermal conductivity. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the reaction of the benzoxazine prepolymer proposed in this invention. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] In the following preparation examples, embodiments, and comparative examples, the polyvinylpyrrolidone used was PVP K30, the naphthalene-type epoxy resin was EBA-65, the active ester curing agent was EPICLON HPC-8000-65T, the spherical silica was Degussa R-202, the mold release agent was Honeywell AC-325, and the curing accelerator was DMP-30.

[0017] Preparation Example 1: The benzoxazine prepolymer was prepared by the following steps: Step A1: Magnolol and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were mixed and reacted under nitrogen protection at a stirring rate of 150 rpm and a temperature of 160 °C for 24 h. The mixture was washed with ethanol / deionized water and dried to obtain the magnolol intermediate. Step A2: Mix magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and toluene, stir at 300 rpm at room temperature for 30 min, then heat to 85 °C and react for 6 h, rotary evaporate, and distill under reduced pressure to obtain benzoxazine prepolymer. Furthermore, in step A1, the ratio of magnolol to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 26.6g:47.5g; In step A2, the ratio of magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane, and methyl is 7g:1.24g:4.5mL:20mL.

[0018] Preparation Example 2: Compared with Preparation Example 1, the ratio of magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and methyl in step A2 was adjusted to 6.9g:1.24g:4.5mL:20mL, while the other steps were the same.

[0019] Preparation Example 3: Compared with Preparation Example 1, in step A1, the ratio of magnolol to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was adjusted to 26.6g:23.7g, while the other steps were the same.

[0020] Preparation Example 4: The low-dielectric and low-thermal-conductivity microspheres were prepared by the following steps: Step B1: Mix aluminum sec-butoxide, tetraethyl orthosilicate, ethyl acetoacetate and n-octanol, and stir at 300 rpm at room temperature for 60 min. Then add Span-80 and polyvinylpyrrolidone, and continue stirring for 20 min to obtain an oil phase aluminum silica sol. Mix sodium dodecyl sulfate, OP-10 and deionized water, and stir at 500 rpm at 40°C for 30 min to obtain an aqueous phase. Furthermore, in step B1, the ratio of aluminum sec-butoxide, ethyl orthosilicate, ethyl acetoacetate, n-octanol, Span-80, and polyvinylpyrrolidone is 2.3g:0.65g:1.2g:5mL:0.3g:0.25g, and the ratio of sodium dodecyl sulfate, OP-10, and deionized water is 2g:4g:200mL.

[0021] Step B2: Pour the oil phase aluminum silica sol into the aqueous phase, stir at a stirring rate of 1000 rpm at room temperature for 24 h, centrifuge, filter, wash with deionized water / ethanol, dry to obtain precursor microspheres, place the precursor microspheres in a tube furnace, in an air atmosphere, heat from room temperature to 350℃ at 0.5℃ / min and hold for 2 h, then heat to 1200℃ at 2℃ / min and hold for 3 h, cool, sieve to obtain porous mullite microspheres; Step B3: Porous mullite microspheres and Tris-HCl buffer were mixed and ultrasonically dispersed. Dopamine hydrochloride was added while stirring at 150 rpm and room temperature. The mixture was stirred for 12 h, centrifuged, filtered, washed, and dried to obtain dopamine-coated microspheres. The dopamine-coated microspheres were mixed with an ethanol solution, and ammonia solution was added to adjust the pH to 9. The mixture was stirred at 300 rpm and room temperature, and a mixture of tetraethyl orthosilicate and ethanol was added. The mixture was reacted for 6 h, centrifuged, filtered, washed, and dried. The mixture was then heat-treated at 175 °C for 2 h under a nitrogen atmosphere to obtain low dielectric and low thermal conductivity microspheres. Furthermore, in step B3: the ratio of porous mullite microspheres, Tris-HCl buffer, and dopamine hydrochloride is 1.8g:50mL:1.3g, wherein the pH of the Tris-HCl buffer is 8.5 and the molar concentration is 0.01mol / L; the ratio of dopamine-coated microspheres, ethanol aqueous solution, tetraethyl orthosilicate, and ethanol is 3g:40mL:0.5g:5mL, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 4:1.

[0022] Preparation Example 5: Compared with Preparation Example 4, Preparation Example 5 adjusts the ratio of aluminum sec-butoxide, tetraethyl orthosilicate, ethyl acetoacetate, n-octanol, Span-80 and polyvinylpyrrolidone in step B1 to 2.2g:0.65g:1.2g:5mL:0.3g:0.25g, while the other steps are the same.

[0023] Preparation Example 6: Compared with Preparation Example 4, in Preparation Example 6, the stirring speed in step B2 was adjusted to 600 rpm, while the other steps were the same.

[0024] Preparation Example 7: Compared with Preparation Example 4, Preparation Example 7 adjusts the ratio of porous mullite microspheres, Tris-HCl buffer and dopamine hydrochloride in step B3 to 1.5g:50mL:1.3g, while keeping the other steps the same.

[0025] Preparation Example 8: Compared with Preparation Example 4, the ratio of dopamine-coated microspheres, aqueous ethanol solution, tetraethyl orthosilicate and ethanol in step B3 was adjusted to 3g:40mL:0.3g:5mL, while the other steps were the same.

[0026] Comparative Preparation Example 1: Compared to Preparation Example 4, in step B1, the ratio of aluminum sec-butoxide, tetraethyl orthosilicate, ethyl acetoacetate, n-octanol, Span-80 and polyvinylpyrrolidone was adjusted to 1.6g:1.3g:1.2g:5mL:0.3g:0.25g, while the other steps remained the same.

[0027] Comparative Preparation Example 2: Compared to Preparation Example 4, in Comparative Preparation Example 2, the stirring speed in step B2 was adjusted to 300 rpm, while the other steps remained the same.

[0028] Example 1: A method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound, comprising the following steps: Step S1: Weigh the following raw materials in parts by weight: 60 parts of naphthalene-type epoxy resin, 50 parts of reactive ester curing agent, 15 parts of benzoxazine prepolymer, 50 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent and 1 part of curing accelerator. Step S2: Mix naphthalene-type epoxy resin, reactive ester curing agent, benzoxazine prepolymer and curing accelerator, mix at 90°C for 15 min, then add mold release agent, low dielectric and low thermal conductivity microspheres and spherical silica and continue mixing for 20 min, then transfer to an extruder, melt extrude at 180°C, and cure to obtain low dielectric and low loss halogen-free epoxy molding compound.

[0029] Example 2: In Example 2, the benzoxazine prepolymer was replaced with that obtained in Preparation Example 2, while the other steps were the same.

[0030] Example 3: In Example 3, the benzoxazine prepolymer was replaced with that obtained in Preparation Example 3, while the other steps were the same.

[0031] Example 4: In Example 4, the low dielectric and low thermal conductivity microspheres were replaced with those prepared in Preparation Example 5, while the other steps were the same.

[0032] Example 5: Compared with Example 1, Example 5 replaces the low dielectric and low thermal conductivity microspheres with those prepared in Preparation Example 6, while the other steps are the same.

[0033] Example 6: In Example 6, the low dielectric and low thermal conductivity microspheres were replaced with those prepared in Example 7, while the other steps were the same.

[0034] Example 7: In Example 7, the low dielectric and low thermal conductivity microspheres were replaced with those prepared in Example 8, while the other steps were the same.

[0035] Example 8: Compared with Example 1, Example 8 uses the following raw materials in parts by weight: 60 parts of naphthalene-type epoxy resin, 45 parts of reactive ester curing agent, 10 parts of benzoxazine prepolymer, 40 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent and 1 part of curing accelerator, and the other steps are the same.

[0036] Example 9: Compared to Example 1, Example 8 uses the following raw materials in parts by weight: 60 parts of naphthalene-type epoxy resin, 50 parts of reactive ester curing agent, 15 parts of benzoxazine prepolymer, 40 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent, and 1 part of curing accelerator. The other steps are the same.

[0037] Comparative Example 1: Compared with Example 1, the low dielectric and low thermal conductivity microspheres in Comparative Example 1 were replaced with those prepared in Comparative Preparation Example 1, while the other steps were the same.

[0038] Comparative Example 2: Compared with Example 1, the low dielectric and low thermal conductivity microspheres in Comparative Example 2 were replaced with those prepared in Comparative Preparation Example 2, while the other steps were the same.

[0039] Comparative Example 3: Compared with Example 1, Comparative Example 3 replaced the following raw materials by weight: 60 parts of naphthalene-type epoxy resin, 50 parts of reactive ester curing agent, 5 parts of benzoxazine prepolymer, 50 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent and 1 part of curing accelerator, while the other steps were the same.

[0040] The low-dielectric-loss, low-loss halogen-free epoxy molding compounds obtained from the examples and comparative examples were subjected to performance testing: 1) Referring to ISO 179-1:2026, the impact strength was measured at room temperature using an XJUD-5 electronic pendulum impact testing machine; 2) Dry the sample with dimensions of 30mm×5mm×2mm at 80℃ for 24h, then soak it in water for 120h, and measure its water absorption rate. Water absorption rate = (weight after soaking - original weight) / original weight * 100%; 3) The thermal conductivity of the sample was tested at room temperature using an LFA 447 laser thermal conductivity meter. The sample was a cylindrical sample with a diameter of 12.5 mm and a thickness of 1 mm. 4) The dielectric constant and dielectric loss of the sample were tested using a Concept 80 broadband dielectric spectrum analyzer. The sample size was 40mm×40mm×1cm, the test electrode size was Φ25mm×1mm, the test frequency was 10kHz-1MHz, and the test temperature was room temperature. 5) The flame retardant performance of the sample was tested using the UL94 vertical burning method. The sample size was 125mm×13mm×1.6mm.

[0041] The test results are shown in the table below: Table 1. Results of Comprehensive Performance Testing of Samples Table 2. Results of Sample Dielectric Constant and Dielectric Loss Tests The test results shown in the table demonstrate the performance comparison between the examples and the comparative examples: Example 1 uses the benzoxazine prepolymer from Preparation Example 1 and the low-dielectric- and low-thermal-conductivity microspheres from Preparation Example 4 as core functional components. The benzoxazine prepolymer uses magnolol as its backbone, and its biphenyl structure has symmetrical electron clouds and low polarizability, which introduces crosslinking and flame-retardant functions without significantly increasing the dielectric constant of the system. The DOPO group provides phosphorus, which releases PO· radicals during combustion to capture H· and HO· to ​​interrupt the combustion chain reaction and achieve gas-phase flame retardancy. The siloxane side chains hydrolyze to generate silanol groups during mixing, which can react with the low-dielectric microspheres. The silica shell on the surface undergoes condensation to form Si-O-Si covalent bridges, improving the dispersion uniformity of microspheres in the epoxy matrix and reducing local interfacial polarization caused by filler agglomeration. At the same time, silicon elements migrate to the surface during combustion to participate in the formation of a dense phosphorus-silicon carbon layer, achieving synergistic flame retardancy of the condensed phase. The benzoxazine ring undergoes thermal ring-opening polymerization during extrusion at 180℃, forming an interpenetrating cross-linked network with naphthalene-type epoxy resin and reactive ester curing agent. The ring-opening process has no small molecule release and the curing shrinkage is almost zero, reducing the curing internal stress. The low-dielectric microspheres contain a large number of isolated closed pores, which uniformly disperse air as a low-dielectric phase within the mullite framework, effectively reducing the equivalent dielectric constant and thermal conductivity of the microspheres. The outer polydopamine layer seals the semi-open pores remaining on the surface after calcination and provides a uniform anchoring base for the outer silica shell. Through subsequent silanol condensation with siloxane benzoxazine and silane coupling with epoxy resin, a covalently bonded bridging layer is formed at the filler-resin interface, completely suppressing interfacial polarization. The synergistic effect of each component enables Example 1 to achieve a balance among various properties.

[0042] In Example 2, compared to Example 1, the benzoxazine prepolymer was replaced with Preparation Example 2. In Preparation Example 2, the amount of magnolol intermediate was reduced from 7g to 6.9g in step A2, while the amounts of paraformaldehyde and γ-aminopropyltriethoxysilane remained unchanged. The slight reduction in the amount of intermediate slightly decreased the amount of benzoxazine rings formed, and the proportion of benzoxazine networks participating in interpenetrating crosslinking in the system slightly decreased, resulting in a slight reduction in crosslinking density. Due to the extremely small change, the performance data were basically the same as in Example 1. This indicates that small fluctuations in the amount of intermediate during the preparation of benzoxazine prepolymer do not cause significant degradation in the final performance, and the process window has a certain tolerance.

[0043] Compared to Example 1, Example 3 replaced the benzoxazine prepolymer with Preparation Example 3. In Preparation Example 3, the amount of DOPO in step A1 was reduced from 47.5g to 23.7g, about half, so that only about half of the two allyl groups of magnolol were added by DOPO. Since the DOPO group contains a highly polar P=O bond, the introduction of a large amount of DOPO will increase the total density of polar groups in the system, which will have a certain negative impact on the dielectric constant and dielectric loss. After the amount of DOPO in Example 3 was halved, the density of P=O bonds in the system decreased, the contribution of dipole polarization decreased, and it showed better dielectric properties than Example 1. However, DOPO is the most important source of phosphorus-based flame retardant element in the system, and its halving led to a significant decrease in flame retardant efficiency, and the flame retardant rating dropped from V-0 to V-1. This change reveals the competitive relationship between flame retardant performance and dielectric performance formed by the amount of DOPO: increasing DOPO is beneficial to flame retardancy but detrimental to dielectric properties, while reducing DOPO has the opposite effect, and a balance needs to be made according to the target application scenario.

[0044] Compared to Example 1, Example 4 replaced the low dielectric and low thermal conductivity microspheres with Preparation Example 5. In Preparation Example 5, the amount of aluminum sec-butoxide was reduced from 2.3g to 2.2g in step B1, and the aluminum-silicon molar ratio was slightly shifted from the 3:1 stoichiometric ratio of mullite towards the lower aluminum direction. The slight reduction in aluminum source resulted in the formation of trace amounts of silicon-rich amorphous phase in the crystalline phase of mullite after calcination, and the purity of mullite decreased slightly. The intrinsic dielectric constant of the silicon-rich amorphous phase is slightly higher than that of pure mullite, and its mechanical strength is lower than that of crystalline mullite.

[0045] Compared to Example 1, Example 5 replaced the low-dielectric, low-thermal-conductivity microspheres with those from Preparation Example 6. In Preparation Example 6, the emulsification stirring rate was reduced from 1000 rpm to 600 rpm in step B2. The reduced stirring rate decreased the shear force on the oil-phase droplets. According to droplet breakup theory, the equilibrium diameter of a droplet under a given interfacial tension is inversely proportional to the shear rate. Therefore, the droplet size increased and the particle size distribution broadened. This resulted in an increased and less uniform final microsphere particle size, leading to more resin-rich areas and stress concentration points during stacking in the epoxy matrix, and a decrease in impact strength to 7.1 kJ / m. 2 Larger microspheres also exhibit increased pore size, and some pores, due to their excessive size, merged before fully closing during calcination, reducing pore integrity and increasing water absorption to 0.50%. Simultaneously, the uneven distribution of the filler-resin interface area due to the non-uniform particle size of the microspheres indicates that the emulsification stirring rate is a key process parameter for controlling the microsphere particle size and final properties.

[0046] Compared to Example 1, Example 6 replaced the low-dielectric, low-thermal-conductivity microspheres with Preparation Example 7. In Preparation Example 7, the amount of porous mullite microspheres was reduced from 1.8g to 1.5g in step B3, while the amount of dopamine hydrochloride remained unchanged at 1.3g, meaning the amount of dopamine per unit surface area of ​​the microspheres increased. With the amount of microspheres reduced and the amount of dopamine unchanged, the polydopamine coating layer obtained on the surface of each microsphere was thicker and more uniform, resulting in a more thorough sealing effect on the semi-open pores on the surface. Furthermore, the thicker polydopamine organic layer, acting as a flexible buffer layer, could more effectively absorb the interfacial stress caused by the difference in thermal expansion coefficients between the filler and the resin matrix. A more complete coating meant more thorough interfacial passivation and further suppression of interfacial polarization, with the dielectric constant and dielectric loss at their lowest levels across the entire test frequency range. This demonstrates that the integrity and thickness of the polydopamine coating layer have a certain impact on the interfacial dielectric properties.

[0047] Compared to Example 1, Example 7 replaced the low-dielectric, low-thermal-conductivity microspheres with Preparation Example 8. In Preparation Example 8, the amount of tetraethyl orthosilicate was reduced from 0.5g to 0.3g in step B3, resulting in a corresponding reduction in the thickness of the outer silica shell. The thinner silica shell weakens the mechanical protection of the internal closed pores and polydopamine layer. Under the high-shear environment of subsequent mixing and twin-screw extrusion, the shell of some microspheres may break, exposing the internal closed pores as open pores. The unpassivated interfaces exposed by the broken shell and the penetration of open pores... The resin in the pores undergoes severe interfacial polarization under an electric field, leading to a sharp deterioration in dielectric loss in the low-frequency region. On the other hand, a thinner silica shell reduces the shell's contribution to the equivalent dielectric constant of the microspheres, and the air cavity in the damaged microspheres is in direct contact with the resin, resulting in an even lower local effective dielectric constant. This contradictory trend indicates that there is an optimal range for the thickness of the silica shell: if it is too thin, the coating is incomplete and the loss deteriorates; if it is too thick, the contribution of the shell's intrinsic dielectric constant increases, and the equivalent dielectric constant of the microspheres rises.

[0048] Compared to Example 1, Example 8 reduced the benzoxazine prepolymer to 10 parts, the low-dielectric- and low-thermal-conductivity microspheres to 40 parts, and the reactive ester curing agent to 45 parts. This reduction in total filler content increased the proportion of the continuous phase in the resin matrix, improved the overall toughness of the cured product, and increased the impact strength to 9.1 kJ / m. 2 The closed-cell insulation effect inside the low dielectric and low thermal conductivity microspheres is weakened, and the thermal conductivity increases to 0.56 W / m·K.

[0049] Compared to Example 1, Example 9 reduced the low-dielectric microspheres to 40 parts while maintaining 15 parts of benzoxazine prepolymer and 50 parts of active ester curing agent. Compared to Example 8, the amount of benzoxazine prepolymer was greater, the interpenetrating network formed by the ring-opening of benzoxazine was more complete, and the siloxane side chains improved the dispersion uniformity of the remaining microspheres. Compared to Example 1, the dielectric constant and thermal conductivity increased due to the reduced amount of low-dielectric microspheres, but were still within acceptable ranges. This example shows that there is a synergistic effect between the benzoxazine prepolymer and the low-dielectric microspheres: the siloxane side chains of the benzoxazine prepolymer improve the filler dispersion through chemical bridging, compensating for the risk of interfacial polarization caused by the reduction in filler content.

[0050] Compared to Example 1, Comparative Example 1 replaced the low-dielectric microspheres with the filler prepared in Comparative Example 1. In Comparative Example 1, the aluminum-silicon molar ratio was adjusted to approximately 1.8:1, significantly deviating from the 3:1 stoichiometric ratio of mullite, resulting in a severe excess of silicon. Under calcination conditions at 1200°C, the excess silicon dioxide formed a large amount of silicon-rich amorphous phase. This amorphous phase easily undergoes viscous flow at high temperatures, filling and eliminating pores, leading to a significant reduction in the closed-pore rate inside the microspheres. Simultaneously, due to insufficient aluminum content, a complete mullite crystalline framework could not be formed, resulting in a severe decrease in mechanical strength. Due to the lack of a closed-pore structure supported by the mullite crystalline phase, a large number of nano-air cavities inside the microspheres collapsed and disappeared, causing a sharp reduction in the volume of the low-dielectric phase. The strength of the silicon-rich amorphous framework was far lower than that of the mullite crystalline phase, with the impact strength dropping to 5.6 kJ / m². 2 The cracks and openings generated during the densification process increased the water absorption rate to 0.93%. Water and resin seeped into the microspheres through the openings, forming severe interfacial polarization under an electric field. This demonstrates that maintaining the mullite stoichiometry is crucial for achieving a stable closed-cell structure; deviations in the aluminum-silicon molar ratio will lead to microsphere structural collapse and overall performance degradation.

[0051] Compared to Example 1, Comparative Example 2 replaced the low-dielectric microspheres with the filler prepared in Comparative Example 2. In Comparative Example 2, the emulsification stirring rate was drastically reduced from 1000 rpm to 300 rpm. The shear force was insufficient to effectively break the oil phase into micron-sized droplets. At the same time, the excessively low stirring rate resulted in poor emulsion stability, ultimately forming large particles with large and highly irregular morphologies instead of uniform microspheres. Due to the lack of good dispersibility and regular stacking guaranteed by the uniform microsphere morphology, the large particles became severe stress concentration defects in the epoxy matrix, and the impact strength dropped to 5.2 kJ / m. 2The irregular particle surface has a large number of interconnected openings and cracks, and the water absorption rate soars to 1.22%. The large number of interconnected openings allows resin and water to fully penetrate into the particle interior, resulting in a very serious interfacial polarization effect. At the same time, there are almost no effective closed pores inside the large particles, and the thermal conductivity rises to 0.73 W / m·K. This proves that a sufficient stirring rate is a prerequisite for obtaining the desired microsphere size and morphology. Insufficient stirring rate will lead to emulsification failure and the product morphology will completely deviate from the design target.

[0052] Compared to Example 1, Comparative Example 3 reduced the amount of benzoxazine prepolymer from 15 parts to 5 parts. Since benzoxazine prepolymer is the main carrier of phosphorus and silicon in the system, its significant reduction in amount resulted in a substantial decrease in both phosphorus and silicon content in the system. The two links in the phosphorus-silicon synergistic flame retardant mechanism, namely gas-phase free radical capture and condensed phase char formation, were severely weakened. During combustion, an effective phosphorus-silicon protective char layer could not be formed, and the flame retardant rating plummeted from V-0 to V-2. At the same time, the proportion of benzoxazine interpenetrating crosslinking network was significantly reduced, and the active ester-epoxy crosslinking structure dominated the cured network. The lack of additional crosslinking anchor points provided by the benzoxazine network and the filler dispersion promoting effect of siloxane side chains led to a decrease in the strength and uniformity of the filler-resin interface bonding and an increase in interface polarization. This demonstrates that benzoxazine prepolymer plays an indispensable role in maintaining flame retardant and dielectric properties, and its amount needs to ensure the minimum threshold of phosphorus-silicon synergistic flame retardancy.

[0053] In Comparative Example 4, compared to Example 1, all low-dielectric, low-thermal-conductivity microspheres were replaced with an equal mass of spherical silica. Due to the absence of porous mullite microspheres containing internally isolated closed pores, the air-based low-dielectric phase was no longer present in the composite material, and the dielectric constant of all fillers was above 3.8. The dielectric constant at 1 MHz increased to 3.8, 0.9 higher than in Example 1. The spherical silica itself has a thermal conductivity of approximately 1.4 W / m·K, and with a filler volume of 130 parts, the filler volume fraction approached the maximum packing density, forming continuous phonon transport paths between filler particles, increasing the thermal conductivity to 1.32 W / m·K, completely eliminating the low thermal conductivity characteristics. Although the spherical silica bonded well with the epoxy matrix, the impact strength reached 10.5 kJ / m. 2 While the water absorption rate is only 0.23%, the dielectric and thermal conductivity properties are far inferior to those of Example 1 due to the lack of the closed-cell structure and interface passivation design of the low-dielectric- and low-thermal-conductivity microspheres. This fully demonstrates that the low-dielectric- and low-thermal-conductivity microsphere filler of the present invention plays an irreplaceable role in achieving low dielectric constant and low thermal conductivity. Traditional spherical silica alone cannot meet the dual requirements of dielectric and thermal conductivity for high-frequency, low-loss encapsulation.

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound, characterized in that: Includes the following steps: Step S1: Weigh the following raw materials in parts by weight: 60 parts of naphthalene-type epoxy resin, 45-50 parts of reactive ester curing agent, 10-15 parts of benzoxazine prepolymer, 40-50 parts of low dielectric and low thermal conductivity microspheres, 80 parts of spherical silica, 5 parts of release agent and 1 part of curing accelerator. Step S2: Mix naphthalene-type epoxy resin, reactive ester curing agent, benzoxazine prepolymer and curing accelerator, mix at 90°C for 15 min, then add mold release agent, low dielectric and low thermal conductivity microspheres and spherical silica and continue mixing for 20 min, then transfer to an extruder, melt extrude at 180°C, and cure to obtain low dielectric and low loss halogen-free epoxy molding compound.

2. The method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound according to claim 1, characterized in that: The benzoxazine prepolymer was prepared by the following steps: Step A1: Magnolol and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were mixed and reacted under nitrogen protection at a stirring rate of 150 rpm and a temperature of 160 °C for 24 h. The mixture was washed with ethanol / deionized water and dried to obtain the magnolol intermediate. Step A2: Mix magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and toluene, stir at 300 rpm at room temperature for 30 min, then heat to 85 °C and react for 6 h, rotary evaporate, and distill under reduced pressure to obtain benzoxazine prepolymer.

3. The method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound according to claim 2, characterized in that: In step A1, the ratio of magnolol to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 26.6g:47.5g. In step A2, the ratio of magnolol intermediate, paraformaldehyde, γ-aminopropyltriethoxysilane and toluene is 6.9-7 g: 1.24 g: 4.5 mL: 20 mL.

4. The method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound according to claim 1, characterized in that: The low-dielectric and low-thermal-conductivity microspheres are prepared by the following steps: Step B1: Mix aluminum sec-butoxide, tetraethyl orthosilicate, ethyl acetoacetate and n-octanol, and stir at 300 rpm at room temperature for 60 min. Then add Span-80 and polyvinylpyrrolidone, and continue stirring for 20 min to obtain an oil phase aluminum silica sol. Mix sodium dodecyl sulfate, OP-10 and deionized water, and stir at 500 rpm at 40°C for 30 min to obtain an aqueous phase. Step B2: Pour the oil phase aluminum silica sol into the aqueous phase, stir for 24 hours at a stirring rate of 600-1000 rpm and room temperature, centrifuge, filter, wash with deionized water / ethanol, and dry to obtain precursor microspheres. Place the precursor microspheres in a tube furnace and heat them in an air atmosphere from room temperature to 350℃ at 0.5℃ / min and hold for 2 hours, then heat them to 1200℃ at 2℃ / min and hold for 3 hours. Cool, sieve, and obtain porous mullite microspheres. Step B3: Porous mullite microspheres and Tris-HCl buffer were mixed and ultrasonically dispersed. Dopamine hydrochloride was added while stirring at 150 rpm and room temperature. The mixture was stirred for 12 h, centrifuged, filtered, washed, and dried to obtain dopamine-coated microspheres. The dopamine-coated microspheres were mixed with an ethanol solution, and ammonia solution was added to adjust the pH to 9. The mixture was stirred at 300 rpm and room temperature, and a mixture of tetraethyl orthosilicate and ethanol was added. The mixture was reacted for 6 h, centrifuged, filtered, washed, and dried. The mixture was then heat-treated at 175 °C for 2 h under a nitrogen atmosphere to obtain low dielectric and low thermal conductivity microspheres.

5. The method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound according to claim 4, characterized in that: In step B1: the ratio of aluminum sec-butoxide, ethyl orthosilicate, ethyl acetoacetate, n-octanol, Span-80 and polyvinylpyrrolidone is 2.2-2.3g:0.65g:1.2g:5mL:0.3g:0.25g, and the ratio of sodium dodecyl sulfate, OP-10 and deionized water is 2g:4g:200mL.

6. The method for preparing a low-dielectric- and low-loss halogen-free epoxy molding compound according to claim 4, characterized in that: In step B3: the ratio of porous mullite microspheres, Tris-HCl buffer, and dopamine hydrochloride is 1.5-1.8 g: 50 mL: 1.3 g, wherein the pH of the Tris-HCl buffer is 8.5 and the molar concentration is 0.01 mol / L; the ratio of dopamine-coated microspheres, ethanol aqueous solution, tetraethyl orthosilicate, and ethanol is 3 g: 40 mL: 0.3-0.5 g: 5 mL, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 4:

1.

7. A low-dielectric- and low-loss halogen-free epoxy molding compound, characterized in that: It is prepared according to any one of the preparation methods described in claims 1-6.

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