Polytetrafluoroethylene emulsion, composite material, copper-clad plate and preparation method thereof

Abstract

The invention discloses a polytetrafluoroethylene emulsion, a composite material, a copper-clad plate and a preparation method thereof, the polytetrafluoroethylene emulsion is an emulsion formed by taking polytetrafluoroethylene as matrix resin to act with a functional filler, and the functional filler comprises silicon nitride and silicon dioxide modified boron nitride with a core-shell structure. According to the system, the contradiction among heat conduction, bonding performance and dielectric loss is solved; and the performance requirements of high thermal conductivity, high adhesion and low dielectric loss of the copper-clad plate are met.

Description

Technical Field

[0001] This invention relates to the technical field of polymer composite material processing, specifically to a polytetrafluoroethylene emulsion, a composite material, a copper-clad laminate, and a method for preparing the same. Background Technology

[0002] With the advent of the 5G era, electronic products are increasingly trending towards miniaturization, lower frequency, and greater functionality. This has significantly impacted traditional copper-clad laminates (CCLs), placing higher demands on their thermal conductivity, dielectric properties, and adhesion. Polytetrafluoroethylene (PTFE) possesses extremely low dielectric constant and dielectric loss, making it an ideal substrate for CCLs in high-frequency applications such as 5G and millimeter-wave radar. However, PTFE's low thermal conductivity and poor adhesion limit its application in the CCL field. Currently, the industry primarily addresses this by introducing inorganic fillers with high thermal conductivity and low dielectric properties to improve PTFE's thermal conductivity.

[0003] Invention application CN111993720A discloses a high-thermal-conductivity polytetrafluoroethylene (PTFE) high-frequency copper-clad laminate, which comprises two copper layers and a high-thermal-conductivity PTFE board in between. The high-thermal-conductivity PTFE board material is obtained by modifying PTFE with hydroxylated boron nitride (BN), followed by hot pressing with fillers of silica, yttrium oxide, and alumina. Although the thermal conductivity of the copper-clad laminate prepared by this method is improved (3.1 W / m·K), the dielectric loss is relatively high. CN113930026A provides a high-thermal-conductivity, low-dielectric-conductivity resin composition based on spherical boron nitride filler and a method for preparing prepregs and copper-clad laminates using this composition. This method, by adding fillers such as octadecylamine-grafted spherical boron nitride and modified fused silica, achieves a maximum thermal conductivity of 3 W / m·K, but the peel strength is only 0.65 N / mm.

[0004] Currently, the biggest challenge in developing high-performance copper-clad laminates is how to systematically resolve the contradiction between thermal conductivity, adhesion performance, and dielectric loss. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this application is to provide a polytetrafluoroethylene composite material that systematically solves the contradiction between thermal conductivity and adhesion performance and dielectric loss; and meets the performance requirements of high thermal conductivity, high adhesion and low dielectric loss of copper clad laminate.

[0006] To solve the above problems, the technical solution adopted in this application is as follows:

[0007] This application provides a polytetrafluoroethylene emulsion, which is an emulsion formed by the interaction of polytetrafluoroethylene as the main resin and functional fillers. The functional fillers include silicon nitride and silicon dioxide modified boron nitride with a core-shell structure.

[0008] As a further preferred embodiment, the polytetrafluoroethylene emulsion described in this application comprises the following components in parts by weight:

[0009] 40-60 parts of polytetrafluoroethylene

[0010] 10-50 parts of silica-modified boron nitride

[0011] 10-30 parts of silicon nitride

[0012] 10-30 parts of auxiliary filler.

[0013] As a further preferred embodiment, the polytetrafluoroethylene emulsion described in this application embodiment further includes a thickener, the amount of which is 0.5-1.0 parts by weight; the auxiliary filler is silica and / or titanium dioxide; by weight, the amount of titanium dioxide is 0-10 parts and the amount of silica is 10-20 parts.

[0014] As a further preferred embodiment, the silica-modified boron nitride described in this application is a core-shell structure formed by coating boron nitride with silica; the modified boron nitride is prepared by the sol-gel method, including the following steps:

[0015] PVP and boron nitride were added to ethanol solutions separately and stirred until homogeneous. Ammonia and tetraethyl orthosilicate (TEOS) mixture were then added and stirred to react and obtain a sol-gel mixture.

[0016] The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and tetraethyl orthosilicate (TEOS), and the resulting wet product was dried in an oven to obtain silica-modified boron nitride.

[0017] This application also provides a method for preparing polytetrafluoroethylene composite material, including the following steps:

[0018] Preparation of silica-modified boron nitride: Polyvinylpyrrolidone (PVP) and boron nitride were added separately to an ethanol solution and stirred until homogeneous. A mixture of ammonia and tetraethyl orthosilicate (TEOS) was added and stirred to obtain a sol-gel mixture. The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and tetraethyl orthosilicate (TEOS). The resulting wet product was dried in an oven to obtain silica-modified boron nitride.

[0019] Preparation of dispersion slurry: Polytetrafluoroethylene, silica-modified boron nitride, silicon nitride, titanium dioxide, and silicon dioxide are mixed in proportion, deionized water is added, and the mixture is stirred evenly to obtain dispersion slurry;

[0020] Preparation of polytetrafluoroethylene composite emulsion: Add thickener to dispersion slurry, mix and degas to obtain polytetrafluoroethylene mixed emulsion.

[0021] This application also provides a polytetrafluoroethylene composite material, which is a semi-cured sheet obtained by coating a film with the mixed emulsion described in this application and then drying and sintering it.

[0022] This application also provides a method for preparing polytetrafluoroethylene composite material, which involves coating a mixed emulsion into a film, and then drying and sintering it to obtain a polytetrafluoroethylene composite prepreg.

[0023] As a further preferred embodiment, in the preparation method described in the embodiments of this application, the coating thickness is 0.15-0.30 mm during coating film formation; the drying temperature is 50-150℃ and the drying time is 5-10 min during drying; and the sintering temperature is 360-385℃ and the time is 15-30 min during sintering.

[0024] This application also provides a polytetrafluoroethylene (PTFE) copper-clad laminate, comprising the PTFE composite prepreg layer described in this application embodiment and copper foil layers covering the upper and lower surfaces of the PTFE composite prepreg layer; the PTFE copper-clad laminate has a thermal conductivity greater than 2.8 W / mK, a dielectric loss less than 0.0008, and a peel strength greater than 1.8 N / mm.

[0025] This application also provides a method for preparing polytetrafluoroethylene copper-clad laminate. The polytetrafluoroethylene composite prepreg is arranged neatly, and copper foil is covered on both the top and bottom sides. Then it is placed in a vacuum press for pressing. The pressing procedure is as follows: hot pressing pressure 70-90 kgf, hot pressing vacuum degree -98 kPa, hot pressing temperature 370-390℃, and heat preservation and pressure holding time 2-4 h.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The polytetrafluoroethylene emulsion described in this application uses silicon nitride and core-shell structured silica-modified boron nitride as functional fillers. The hydrophilic surface of silica-modified boron nitride matches the polytetrafluoroethylene emulsion, improving the dispersibility of boron nitride in the aqueous phase of polytetrafluoroethylene emulsion, avoiding sedimentation, preventing filler agglomeration, ensuring the continuity of the thermal / dielectric network, and reducing the amount of thickener.

[0028] 2. Ordinary boron nitride repels the molecular chains of non-polar polytetrafluoroethylene (PTFE), leading to filler agglomeration, interfacial gaps, increased interfacial thermal resistance, and stress concentration. The PTFE emulsion described in this application uses silicon nitride and core-shell silica-modified boron nitride as functional fillers. The silica-modified boron nitride forms a silica coating layer on the surface of the boron nitride, providing a large number of hydroxyl groups (-OH), which form a hydrogen bond network with the fluorine atoms at the ends of the PTFE chains. This effectively improves the interfacial bonding energy, promotes uniform filler dispersion, and, when applied to copper-clad laminates, effectively improves the peel strength of the copper-clad laminate.

[0029] 3. In the polytetrafluoroethylene composite material described in this application, the addition of silica-modified boron nitride prevents direct contact between boron nitride and polytetrafluoroethylene through a silica coating layer, inhibiting interfacial reactions at high temperatures and increasing the decomposition temperature of the composite material; the silica coating reduces the polarity of boron nitride, inhibits interfacial polarization loss, and reduces dielectric loss.

[0030] The present invention will be further described in detail below with reference to specific embodiments. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] The term "comprising" and other equivalent descriptive terms used in the specification and claims of this application are intended to cover a non-exclusive inclusion, which includes both the contents explicitly described in the specification and claims and steps or units that are not described in the specification and claims but are inherent in the product, method or structure.

[0033] This application provides a polytetrafluoroethylene (PTFE) emulsion, which is formed by the interaction of PTFE as the main resin and functional fillers. The functional fillers include silicon nitride and silica-modified boron nitride with a core-shell structure. Boron nitride itself has high thermal conductivity and low dielectric constant, but its surface polarity is strong, resulting in poor compatibility with the non-polar PTFE emulsion, which easily leads to uneven filler dispersion and weak interfacial bonding. In the core-shell structured silica-modified boron nitride, the silica shell forms a nanoscale rough structure on the boron nitride surface to provide more active sites and improve the interfacial bonding ability with PTFE. The silica surface is rich in hydroxyl groups (-OH), which can form hydrogen bonds or van der Waals forces with the fluorine atoms at the ends of the PTFE molecular chains, and its chemical inertness is more compatible with PTFE, which can significantly improve interfacial bonding. In the PTFE emulsion, the boron nitride core of the functional filler can provide high thermal conductivity, improving the thermal conductivity of the material.

[0034] In this application, polytetrafluoroethylene (PTFE) is used as the main resin. Insufficient PTFE content leads to decreased film-forming properties of the emulsion and easy cracking during sintering. To ensure the continuity of the emulsion film, avoid excessive filler causing mechanical property collapse, and reserve sufficient space for functional fillers to ensure the construction of a thermally conductive / reinforcing network, the amount of PTFE in the specific embodiment is 40-60 parts by weight. In this application, the silica coating layer in the silica-modified boron nitride acts as an interface compatibilizer, reducing interfacial thermal resistance and shielding the polar surface of boron nitride to reduce dielectric loss, while the boron nitride core constructs a continuous heat dissipation path. To fully cover the PTFE / filler interface, improve interfacial peel strength, and prevent boron nitride agglomeration, the silica-modified boron nitride in the embodiments of this application is 10-50 parts by weight, preferably 20-35 parts by weight. The polytetrafluoroethylene (PTFE) emulsion described in this application embodiment further includes silicon nitride. During the PTFE film formation process, silicon nitride serves two purposes: firstly, it forms a rigid framework, providing the film's hardness and flexural strength; secondly, its low coefficient of thermal expansion reduces the PTFE's coefficient of thermal expansion, allowing the PTFE film's coefficient of thermal expansion to match that of the copper foil, thus meeting the application's performance requirements. In specific embodiments, the amount of silicon nitride used is 10-30 parts by weight. The PTFE emulsion described in this application embodiment further includes auxiliary fillers; these auxiliary fillers are selected from, but are not limited to, one or more mixtures of titanium dioxide, silicon dioxide, alumina, and barium carbonate; wherein the addition of titanium dioxide can improve the dielectric constant to meet impedance matching requirements, silicon dioxide can reduce the coefficient of thermal expansion and improve the emulsion's rheological properties, alumina is used to enhance arc resistance, and barium carbonate can absorb high-frequency vibrations and suppress resonance peaks.

[0035] In this application, due to the improved core-shell structure of silica-modified boron nitride (SiO2@BN) and its interfacial bonding with polytetrafluoroethylene (PTFE), and the high hardness of silicon nitride (Si3N4) providing mechanical support, in some preferred embodiments, the thermal conductivity and mechanical properties of the PTFE composite material can be balanced by controlling the mass ratio of silica-modified boron nitride to silicon nitride. When the mass ratio of silica-modified boron nitride to silicon nitride is 0.5-3, a PTFE composite material with excellent thermal conductivity and mechanical properties can be obtained.

[0036] As a further preferred embodiment, the polytetrafluoroethylene (PTFE) emulsion described in this application also includes a thickener, which increases the emulsion viscosity through molecular chain entanglement and hydration, inhibits the sedimentation of high-density fillers, and ensures the stability of the coating process. Preferably, the thickener used in this application embodiment is hydroxyethyl cellulose, which has good water solubility and thickening effect, and good compatibility with PTFE emulsion. In addition, sodium carboxymethyl cellulose (CMC) or hydroxypropyl methyl cellulose (HPMC) can also be used to replace hydroxyethyl cellulose, but experiments have shown that hydroxyethyl cellulose is the optimal choice in the embodiments of this application. The amount of thickener has a significant impact on the viscosity of the emulsion and the degree of crosslinking during film formation. Too little thickener results in insufficient viscosity of the PTFE emulsion, causing accelerated filler sedimentation; too much thickener leads to excessive crosslinking of the PTFE emulsion, causing stringing during coating, embrittlement of the sintered film, and coating or film defects. To avoid uneven coating thickness, edge thickening, or coating defects caused by improper viscosity control, the amount of thickener added in this application is controlled at 0.5-1.0 parts by weight.

[0037] Preferably, in this embodiment of the application, silica-modified boron nitride is prepared using the sol-gel method, and the specific preparation method includes the following steps:

[0038] Polyvinylpyrrolidone (PVP) and boron nitride were added separately to an ethanol solution and stirred at 500-800 rpm for 1-2 hours until homogeneous. A mixture of ammonia and tetraethyl orthosilicate (TEOS) was then added and stirred for 10-15 hours to obtain a sol-gel mixture.

[0039] The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and tetraethyl orthosilicate (TEOS), and the resulting wet product was dried in an oven at 50-75°C to obtain silica-modified boron nitride.

[0040] In this embodiment, silica-modified boron nitride is prepared using the sol-gel method. During the reaction, PVP acts as a dispersing stabilizer. The long chains of PVP adsorb onto the surface of boron nitride, forming hydrogen bonds that anchor the boron nitride and create a steric hindrance effect, preventing boron nitride agglomeration and forming a uniformly dispersed suspension. PVP also acts as a surface modifier, further reducing the contact angle of the boron nitride surface, promoting the wetting and adsorption of the TEOS / ammonia mixture at the boron nitride interface, and increasing the number of silica coating binding sites. Furthermore, PVP can regulate the thickness uniformity of the silica coating layer, achieving continuous nanoscale coating. During the modification process, 20%-30% ammonia water is used to catalyze the hydrolysis of TEOS to generate Si-OH, which preferentially condenses at the boron nitride interface, effectively avoiding coating layer thickness deviations. The silica layer thickness is linearly adjusted by controlling the ratio of ammonia water to TEOS (3:6):1) and the reaction time (2-12h), controlling the coating layer thickness within the range of 10-80nm. The low surface tension of the ethanol solvent allows the sol to penetrate the pores of boron nitride, forming a full surface coverage and avoiding blind spots in the coating layer. On the other hand, it can strengthen the interfacial bonding force. The BN bonds on the boron nitride surface are partially hydrolyzed into B-OH and NH groups after ammonia treatment, which combine with the Si-OH of silica through covalent bonds (Si-OB) and hydrogen bonds, effectively improving the interfacial bonding energy. This improves the thermal conductivity of copper-clad laminates made of polytetrafluoroethylene composites, reduces dielectric loss, and increases the peel strength of copper foil.

[0041] Furthermore, in the above-mentioned process of preparing silica-modified boron nitride, this application embodiment also provides a method for preparing polytetrafluoroethylene composite material, including the following steps:

[0042] Preparation of silica-modified boron nitride: PVP and boron nitride were added separately to an ethanol solution and stirred at 500-800 rpm for 1-2 hours until homogeneous. Ammonia and TEOS mixture were added and stirring was continued for 10-15 hours to obtain a sol-gel mixture. The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and TEOS. The wet product was dried in an oven at 50-75℃ to obtain silica-modified boron nitride.

[0043] Preparation of dispersion slurry: Polytetrafluoroethylene, silica-modified boron nitride, silicon nitride, titanium dioxide, and silicon dioxide are mixed in proportion, deionized water is added, and the mixture is stirred for 1-3 hours to obtain dispersion slurry;

[0044] Preparation of polytetrafluoroethylene composite emulsion: Add thickener to dispersion slurry, mix and degas for 10-20 min to obtain polytetrafluoroethylene mixed emulsion.

[0045] This application also provides a polytetrafluoroethylene composite material, which is a semi-cured sheet obtained by coating a film with the mixed emulsion described in this application and then drying and sintering it.

[0046] This application also provides a method for preparing a polytetrafluoroethylene (PTFE) composite material, which involves coating a mixed emulsion into a film, followed by drying and sintering to obtain a PTFE composite prepreg. In this preparation method, the coating thickness is 0.15-0.30 mm; the drying temperature is 50-150°C, and the drying time is 5-10 min. During sintering, a relatively low sintering temperature is used, 360-385°C, for 15-30 min, depending on the coating thickness; this allows the PTFE molecular chains to penetrate into the boron nitride interlayer, forming a mechanical interlock.

[0047] This application also provides a polytetrafluoroethylene (PTFE) copper-clad laminate, including the PTFE composite prepreg layer described in this application and copper foil layers covering the upper and lower surfaces of the PTFE composite prepreg.

[0048] This application also provides a method for preparing polytetrafluoroethylene copper-clad laminate. Two polytetrafluoroethylene composite prepregs are placed neatly, and copper foil is covered on both sides. Then they are placed in a vacuum press for pressing. The pressing procedure is as follows: hot pressing pressure 70-90 kgf, hot pressing vacuum degree -98 kPa, hot pressing temperature 370-390℃, and heat preservation and pressure holding time 2-4 h.

[0049] The following are some of the embodiments listed in this application.

[0050] Example 1

[0051] This embodiment provides a silica-modified boron nitride, which is prepared by the following method: 0.4g PVP and 5g boron nitride are added to 80mL of ethanol solution respectively, and stirred at 600 rpm for 2 hours until homogeneous. Then, a mixture of 10mL ammonia and TEOS (the volume ratio of ammonia to TEOS is 4:1, and the concentration of ammonia is 25%) is added, and the mixture is stirred for another 12 hours at room temperature to obtain a sol-gel mixture. The sol-gel mixture is washed with ultrapure water to remove unreacted ammonia and TEOS. The resulting wet product is dried in an oven at 60°C to obtain silica-modified boron nitride.

[0052] Example 2

[0053] This application provides a polytetrafluoroethylene composite material, prepared by the following method:

[0054] Preparation of dispersion slurry: 50g polytetrafluoroethylene, 10g silica-modified boron nitride obtained in Example 1, 20g silicon nitride, 8g titanium dioxide, 12g silica and 20g deionized water were mixed and stirred at 2000 rpm for 2 hours to obtain dispersion slurry;

[0055] Preparation of polytetrafluoroethylene composite emulsion: 1g of hydroxymethyl cellulose was added to the dispersion slurry, stirred evenly at 2000 rpm and defoamed for 20 min to obtain polytetrafluoroethylene mixed emulsion;

[0056] Coating to form a film: The polytetrafluoroethylene mixed emulsion is coated to form a composite film with a coating thickness of 0.25 mm. The composite film is then placed in an oven and dried at 80°C.

[0057] Sintering: The dried composite film is placed in a high-temperature oven at 380℃ and sintered for 30 minutes to obtain a polytetrafluoroethylene semi-cured sheet.

[0058] Example 3

[0059] This embodiment provides a polytetrafluoroethylene (PTFE) copper-clad laminate, which is obtained by stacking two PTFE prepreg sheets obtained in Example 2 above, covering both sides with 18μm thick copper foil, and then placing them under a vacuum press with a vacuum degree of -98kPa for high-temperature pressing. The hot pressing pressure is 80kgf, the hot pressing temperature is 380℃, and the heat and pressure holding time is 3 hours to obtain the PTFE copper-clad laminate.

[0060] The properties of the polytetrafluoroethylene copper-clad laminate obtained in Example 3 were tested. The dielectric properties were tested using method 2.5.5.5 of section 2.5 of the IPC-TM-650 standard; the thermal conductivity was tested using the ASTM D5470 standard; the peel strength was tested using method 2.4.8 of the IPC-TM-650 standard; and the coefficient of thermal expansion was tested using method 2.4.41 of the IPC-TM-650 standard. The test results are shown in Table 1.

[0061] Table 1: Test results of polytetrafluoroethylene copper clad laminate in Example 3

[0062] performance Example 3 Dielectric constant (10GHz) 3.18 Dielectric loss (10GHz) 0.00079 Thermal conductivity (W / m·K) 2.82 Peel strength (N / mm) 1.93 Coefficient of thermal expansion (ppm / ℃) 40

[0063] Based on Example 3 above, in order to investigate the effect of the polytetrafluoroethylene resin dosage ratio on the performance of polytetrafluoroethylene copper clad laminate, different dosages were used for verification. Other conditions were the same as in Example 3, and the specific conditions and performance test results are shown in Table 2.

[0064] Table 2: Effect of PTFE dosage ratio on the performance of PTFE copper clad laminate

[0065]

[0066] As shown in Table 2, reducing the amount of polytetrafluoroethylene (PTFE) in the system leads to an increase in the content of other components, reducing dielectric loss and coefficient of thermal expansion, and improving thermal conductivity. However, this results in poor peel strength and unsatisfactory overall performance. Conversely, increasing the amount of PTFE reduces the content of other components, leading to increased dielectric loss and coefficient of thermal expansion, and decreased thermal conductivity and peel strength of the copper-clad laminate. Similarly, it is impossible to obtain a copper-clad laminate material that combines high thermal conductivity, low dielectric loss, and high peel strength. Therefore, considering all factors, the optimal amount of PTFE in this patent is 50g to obtain a copper-clad laminate with better overall performance.

[0067] Furthermore, based on Example 3 above, in order to investigate the effect of the ratio of silica-modified boron nitride to silicon nitride on the performance of polytetrafluoroethylene copper clad laminate, different mass ratios were used for verification. The total amount of silica-modified boron nitride and silicon nitride remained constant at 30g, only the ratio between the two was changed. Other conditions were the same as in Example 3, and the specific conditions and performance test results are shown in Table 3.

[0068] Table 3: Effect of the ratio of silica-modified boron nitride to silicon nitride on the properties of polytetrafluoroethylene copper clad laminate

[0069]

[0070] The data in Table 3 show that increasing the ratio of silicon dioxide-modified boron nitride to silicon nitride will increase the thermal conductivity of copper-clad laminate and reduce its peel strength, while having little effect on dielectric properties and coefficient of thermal expansion.

[0071] Furthermore, based on Example 3 above, in order to explore the effect of silica-modified boron nitride prepared by using ammonia and TEOS with different volume ratios on the performance of polytetrafluoroethylene copper clad laminate, the volume ratio of ammonia and TEOS was changed (the total volume of the mixture was 10 mL), while other conditions were the same as in Example 3. The specific conditions and performance test results are shown in Table 4.

[0072] Table 4: Effect of the volume ratio of ammonia to TEOS on the properties of polytetrafluoroethylene copper clad laminate

[0073]

[0074] Table 4 shows that a high ammonia ratio leads to excessive catalysis of silica formation, resulting in a decrease in dielectric properties, thermal conductivity, and peel strength. A low ammonia ratio, due to insufficient hydrolysis and resulting in a less dense silica coating, also leads to a decrease in dielectric properties, thermal conductivity, and peel strength.

[0075] Furthermore, based on Example 3 above, in order to explore the effect of sintering temperature on the performance of polytetrafluoroethylene copper-clad laminate during the preparation of polytetrafluoroethylene composite material, the sintering temperature was changed, while other conditions remained the same as in Example 3. The specific conditions and performance test results are shown in Table 5.

[0076] Table 5: Effect of sintering temperature on the properties of polytetrafluoroethylene copper clad laminate

[0077]

[0078] The data in Table 5 show that sintering temperature has a certain impact on the peel strength of copper clad laminate. Both lower and higher sintering temperatures will cause a decrease in peel strength, while the impact on dielectric properties, thermal conductivity and coefficient of thermal expansion is relatively small.

[0079] Example 4

[0080] This application provides a polytetrafluoroethylene (PTFE) copper-clad laminate. The raw materials for the PTFE prepreg are 50g PTFE resin, 20g deionized water, 15g silica-modified boron nitride from Example 1, 15g silicon nitride, 8g titanium dioxide, and 12g silicon dioxide. The preparation method of the PTFE prepreg is the same as that of Example 2, and the preparation method of the PTFE copper-clad laminate is the same as that of Example 3.

[0081] Example 5

[0082] This application provides a polytetrafluoroethylene (PTFE) copper-clad laminate. The raw materials for the PTFE prepreg are 50g PTFE resin, 20g deionized water, 20g silica-modified boron nitride, 10g silicon nitride, 8g titanium dioxide, and 12g silicon dioxide. The preparation method of the PTFE prepreg is the same as in Example 2, and the preparation method of the PTFE copper-clad laminate is the same as in Example 3.

[0083] Comparative Example 1

[0084] A polytetrafluoroethylene (PTFE) copper-clad laminate is provided. The raw materials for the PTFE prepreg are 50g PTFE resin, 20g deionized water, 10g boron nitride, 20g silicon nitride, 8g titanium dioxide, and 12g silicon dioxide. The method for preparing the prepreg is the same as in Example 2, and the method for preparing the PTFE copper-clad laminate is the same as in Example 3.

[0085] Comparative Example 2

[0086] A polytetrafluoroethylene (PTFE) copper-clad laminate is provided. The raw materials for the PTFE prepreg are 50g PTFE resin, 20g deionized water, 30g silica-modified boron nitride, 8g titanium dioxide, and 12g silica. The method for preparing the prepreg is the same as in Example 2, and the method for preparing the PTFE copper-clad laminate is the same as in Example 3.

[0087] Performance testing

[0088] The properties of the polytetrafluoroethylene copper-clad laminates obtained in Examples 4-5 and Comparative Examples 1-2 were tested. Dielectric properties were tested using method 2.5.5.5 of section 2.5 of the IPC-TM-650 standard; thermal conductivity was tested using ASTM D5470; peel strength was tested using method 2.4.8 of the IPC-TM-650 standard; and the coefficient of thermal expansion was tested using method 2.4.41 of the IPC-TM-650 standard. The test results are shown in Table 1.

[0089] Table 6: Performance Test Results

[0090] performance Example 4 Example 5 Comparative Example 1 Comparative Example 2 Dielectric constant (10GHz) 3.15 3.12 3.17 3.20 Dielectric loss (10GHz) 0.00081 0.00080 0.00089 0.00080 Thermal conductivity (W / m·K) 3.04 3.27 1.13 2.32 Peel strength (N / mm) 1.89 1.84 1.53 0.89 Coefficient of thermal expansion (ppm / ℃) 38 35 43 41

[0091] As can be seen from the table, the copper-clad laminates of Examples 3-5 exhibit excellent dielectric properties, thermal conductivity, and adhesion. By varying the amounts of silica-modified boron nitride and silicon nitride used in Examples 3-5, it can be observed that the thermal conductivity of the final copper-clad laminate increases with the increasing proportion of silica-modified boron nitride. Comparing Comparative Example 1 and Example 3, the difference lies in the use of silica-modified boron nitride in Example 3 and boron nitride in Comparative Example 1. With the content of each component remaining constant, the copper-clad laminate prepared with silica-modified boron nitride exhibits significantly higher thermal conductivity. Comparing Examples 3-5 with Comparative Example 2, it was found that the addition of silicon nitride effectively improves the peel performance between the polytetrafluoroethylene (PTFE) composite material and the copper foil, and the combination of silica-modified boron nitride and silicon nitride significantly enhances the thermal conductivity of the PTFE composite material.

[0092] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A polytetrafluoroethylene emulsion, characterized in that, It is an emulsion formed by the interaction of polytetrafluoroethylene as the main resin and functional fillers, wherein the functional fillers include silicon nitride and silicon dioxide modified boron nitride with a core-shell structure.

2. The polytetrafluoroethylene emulsion according to claim 1, characterized in that, Includes the following components in parts by weight: 40-60 parts of polytetrafluoroethylene 10-50 parts of silica-modified boron nitride 10-30 parts of silicon nitride 10-30 parts of auxiliary filler.

3. The polytetrafluoroethylene emulsion according to claim 2, characterized in that, It also includes a thickener, the amount of which is 0.5-1.0 parts by weight, and the thickener is one or a mixture of two or more of hydroxyethyl cellulose, carboxymethyl cellulose, and hydroxypropyl methyl cellulose; the auxiliary filler is one or a mixture of two or more of titanium dioxide, silicon dioxide, alumina, and barium carbonate.

4. The polytetrafluoroethylene emulsion according to claim 1, characterized in that, The silicon dioxide modified boron nitride is a core-shell structure formed by coating boron nitride with silicon dioxide. The core-shell structure includes a boron nitride core and a silicon dioxide shell layer continuously coated on the surface of the boron nitride core. The average thickness of the silicon dioxide shell layer is 10nm-100nm. The modified boron nitride was prepared by the sol-gel method, including the following steps: Polyvinylpyrrolidone and boron nitride were added separately to an ethanol solution and stirred until homogeneous. A mixture of ammonia and tetraethyl orthosilicate was then added and stirred to react, resulting in a sol-gel mixture. The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and TEOS, and the resulting wet product was dried in an oven to obtain modified boron nitride.

5. A method for preparing the polytetrafluoroethylene composite material as described in any one of claims 1-4, characterized in that, Includes the following steps: Preparation of silica-modified boron nitride: Polyvinylpyrrolidone and boron nitride were added to ethanol solution and stirred until homogeneous. Ammonia and tetraethyl orthosilicate mixture were added and stirred to react to obtain sol-gel mixture. The sol-gel mixture was washed with ultrapure water to remove unreacted ammonia and tetraethyl orthosilicate. The wet product was dried in an oven to obtain silica-modified boron nitride. Preparation of dispersion slurry: Polytetrafluoroethylene, silica-modified boron nitride, silicon nitride, titanium dioxide, and silicon dioxide are mixed in proportion, deionized water is added, and the mixture is stirred evenly to obtain dispersion slurry; Preparation of polytetrafluoroethylene composite emulsion: Add thickener to dispersion slurry, mix and degas to obtain polytetrafluoroethylene mixed emulsion.

6. A polytetrafluoroethylene composite material, characterized in that, It is a semi-cured sheet obtained by coating a film with the mixed emulsion described in any one of claims 1-4 and then drying and sintering it.

7. A method for preparing the polytetrafluoroethylene composite material as described in claim 6, characterized in that, The mixed emulsion is coated into a film, and after drying and sintering, a polytetrafluoroethylene composite semi-cured sheet is obtained.

8. The method for preparing the polytetrafluoroethylene composite material according to claim 7, characterized in that, When coating to form a film, the coating thickness is 0.15-0.30 mm; when drying, the temperature is 50-150℃ and the drying time is 5-10 min; when sintering, the sintering temperature is 360-385℃ and the time is 15-30 min.

9. A polytetrafluoroethylene copper-clad laminate, characterized in that, It includes the polytetrafluoroethylene composite prepreg layer as described in claim 6 and the copper foil layer covering the upper and lower surfaces of the polytetrafluoroethylene composite prepreg layer, wherein the thermal conductivity of the polytetrafluoroethylene copper clad laminate is greater than 2.8 W / mK, the dielectric loss is less than 0.0008, and the peel strength is greater than 1.8 N / mm.

10. A method for preparing a polytetrafluoroethylene copper-clad laminate as described in claim 9, characterized in that, Arrange the polytetrafluoroethylene composite prepreg neatly, cover both sides with copper foil, and then place it in a vacuum press for pressing. The pressing procedure is as follows: hot pressing pressure 70-90 kgf, hot pressing vacuum degree -98 kPa, hot pressing temperature 370-390℃, and heat preservation and pressure holding time 2-4 hours.

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