A microwave composite dielectric substrate and its preparation method

Abstract

The present invention proposes a microwave composite dielectric substrate and a preparation method thereof, comprising: uniformly mixing ammonia water, deionized water, ethanol, and hexadecyltrimethylammonium bromide; adding tetraethyl orthosilicate to the mixed solution; stirring the mixture for reaction; and after completion of the reaction, centrifuging and drying to obtain a solid product; subjecting the solid product to high-temperature calcination to obtain micron-sized micro-mesoporous silica spheres; mixing the micron-sized micro-mesoporous silica spheres with a polytetrafluoroethylene emulsion to obtain an organic-inorganic blend; subjecting the organic-inorganic blend to calendering and forming using a calendering mixing process to obtain a composite pre-pressed sheet; and subjecting the composite pre-pressed sheet to vacuum hot pressing and sintering to obtain a microwave composite dielectric substrate. By forming micro-mesoporous silica spheres, a "pinning" physical interaction is formed with polytetrafluoroethylene molecular chains, which enables the composite material to have a low dielectric constant, dielectric loss, and thermal expansion coefficient.

Description

Technical Field

[0001] The present invention relates to the field of microwave dielectric technology, and in particular to a microwave composite dielectric substrate and a preparation method thereof. Background Art

[0002] With the increasing popularity of 5G internet and the future development and application of 6G, the development of functional information materials is increasingly moving towards higher device integration and higher frequencies. Application requirements, such as fast signal transmission rates and high signal quality, require high-frequency, high-speed substrate materials to possess excellent dielectric properties, namely, low dielectric constant and low dielectric loss. Furthermore, to avoid thermal failure caused by excessively high temperatures in actual operating environments, high-frequency, high-speed substrate materials require a low coefficient of thermal expansion.

[0003] Polytetrafluoroethylene is considered to be the most important material in high-frequency dielectric boards because of its inherent advantages of low dielectric constant and dielectric loss, as well as its high temperature stability at different frequencies. However, its high thermal expansion coefficient severely limits its practical application scenarios. Therefore, it is very important to obtain a polytetrafluoroethylene-based composite dielectric substrate with both low dielectric properties and low thermal expansion properties. In view of the problem of high thermal expansion coefficient of polytetrafluoroethylene resin, it can be improved by adding silica filler with low thermal expansion coefficient and low dielectric constant, thereby obtaining a silica / polytetrafluoroethylene composite material with excellent dielectric properties and low thermal expansion coefficient. However, the current preparation of composite dielectric substrates by mixing silica and polytetrafluoroethylene resin still has the following problems:

[0004] (1) Micro-mesoporous silica nanospheres are relatively easy to synthesize. The micro-mesoporous silica nanospheres can form a good physical interaction with the polytetrafluoroethylene resin, thus forming a good interface between the two phases. However, due to the large surface energy of nano-sized silica itself, it is very easy to agglomerate and difficult to disperse well in the polytetrafluoroethylene matrix. As a result, the interface between the two phases in the prepared composite dielectric substrate is full of holes, and the performance is poor and unstable.

[0005] (2) Although the smooth-surfaced micrometer-scale silica currently prepared commercially or reported in public literature is less likely to agglomerate than nanoscale silica, it is difficult for the smooth-surfaced silica to form an effective interaction force with the polytetrafluoroethylene matrix. As a result, the smooth-surfaced silica and polytetrafluoroethylene interface are poorly bonded, causing the composite dielectric substrate to rapidly increase its high-frequency dielectric loss while reducing the thermal expansion coefficient.

[0006] CN115610044B discloses a low-loss polytetrafluoroethylene-based microwave composite dielectric substrate and preparation method. The composite dielectric substrate is obtained by mixing, impregnating, coating, drying and hot pressing micrometer-scale silica, dispersant, coupling agent and polytetrafluoroethylene. Since the introduced filler is not silica with micro-mesoporous channels, the dielectric constant of the prepared composite material is relatively large (~2.98), and the work is to improve the bonding between the silica filler and the polytetrafluoroethylene matrix by modifying the filler surface. On the one hand, the modification process inevitably requires the introduction of a modifier containing small molecule polar bonds, which will rapidly increase the dielectric loss when used in higher frequency (>10GHz) scenarios; on the other hand, the addition of the modification step complicates the material preparation process. In addition, this work does not focus on the problem that the thermal expansion coefficient of the composite material is large, which will cause the material to fail thermally. Summary of the Invention

[0007] In view of this, the present invention proposes a microwave composite dielectric substrate and a preparation method thereof to solve the problems of large dielectric constant, dielectric loss and thermal expansion coefficient of the composite dielectric substrate prepared in the prior art.

[0008] The technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a microwave composite dielectric substrate, which specifically comprises the following steps:

[0009] S1. Mix ammonia water, deionized water, ethanol and cetyltrimethylammonium bromide, add tetraethyl orthosilicate to the mixed solution, stir and react, and after the reaction is completed, centrifuge and dry to obtain a solid product;

[0010] S2, calcining the solid product at high temperature to obtain micron-sized micro-mesoporous silica spheres;

[0011] S3, mixing the micron-sized micro-mesoporous silica spheres with a polytetrafluoroethylene emulsion to obtain an organic-inorganic blend;

[0012] S4, calendering the organic-inorganic blend using a calendering and mixing process to obtain a composite material pre-compressed tablet;

[0013] S5. Subjecting the composite material pre-pressed sheet to vacuum hot pressing and sintering to obtain a microwave composite dielectric substrate.

[0014] In the present invention, tetraethyl orthosilicate is used as a silicon source and ethanol is used as a solvent. The ethanol and tetraethyl orthosilicate are mixed to form a sol. The addition of deionized water can promote the hydrolysis of tetraethyl orthosilicate to generate silicic acid. The addition of ammonia water can adjust the pH value of the solution, promote the polymerization of silicic acid and the formation of gel. Hexadecyltrimethylammonium bromide, as a surfactant, can form a micelle structure in the sol, and tiny cavities are formed in the sol through the micelle structure. The joint action of ammonia water, deionized water and hexadecyltrimethylammonium bromide promotes the formation of micro-mesoporous silica spheres. Specifically, after the cetyltrimethylammonium bromide molecules form a micellar structure, the hydrophobic cetyl chains gather together, while the hydrophilic trimethylammonium bromide ions are located on the surface of the micelles. This micellar structure forms tiny cavities in the sol, which will be retained during the subsequent gel formation and high-temperature calcination treatment to form a mesoporous structure; ammonia water makes the solution alkaline, promotes the hydrolysis and polymerization of silicic acid, and further promotes the formation of gel and the development of mesoporous structure; at the same time, the amino ions in the ammonia water can interact with the surface of silicic acid, increasing the stability of the colloidal particles. On this basis, the combined action of ammonia water and cetyltrimethylammonium bromide can promote the formation of an ordered mesoporous structure inside the silica, thereby preparing micron-sized micro-mesoporous silica spheres.

[0015] Furthermore, micron-scale micro-mesoporous silica is less likely to agglomerate than nano-scale silica and is easier to disperse evenly in polytetrafluoroethylene. The presence of micro-mesoporous channels brings in some air with an extremely low dielectric constant (dielectric constant of 1.0), which makes micro-mesoporous silica / polytetrafluoroethylene have a lower dielectric constant, and the micro-mesopores form a "pinning" physical interaction with the polytetrafluoroethylene molecular chains. The micro-mesoporous silica / polytetrafluoroethylene has good interface bonding, which makes the prepared composite material have both low dielectric loss and thermal expansion coefficient, and is a potential low-dielectric and low-thermal expansion composite medium substrate material.

[0016] On the basis of the above technical solution, preferably, the molar ratio of tetraethyl orthosilicate, ammonia water, deionized water, ethanol and hexadecyltrimethylammonium bromide is 1: (18-20): (360-400): (210-240): (0.1-0.3). In the present invention, the ratio of ammonia water, deionized water, ethanol and hexadecyltrimethylammonium bromide is limited, and micron-sized micro-mesoporous silica can be prepared. If the proportion of ammonia water in the mixed solution is too large, it is difficult to synthesize micron-sized micro-mesoporous silica spheres. If the proportion of ammonia water in the mixed solution is too small, its hydrolysis and polymerization will be reduced, making it difficult to synthesize spherical silica. If the proportion of hexadecyltrimethylammonium bromide in the mixed solution is too large, it is difficult to synthesize monodisperse spherical micro-mesoporous silica. If the proportion of hexadecyltrimethylammonium bromide in the mixed solution is too small, it will affect the formation of micelle structure, making it difficult to synthesize silica with micro-mesoporous channels.

[0017] Based on the above technical solution, preferably, the silicon dioxide content in the tetraethyl orthosilicate is ≥28.4%, and the tetraethyl orthosilicate is added at a rate of 0.5 to 2.0 ml / min. Controlling the addition rate of the tetraethyl orthosilicate within 0.5 to 2.0 ml / min can better form micro-mesoporous silica. If the addition rate of the tetraethyl orthosilicate is too fast, it is difficult to synthesize micron-sized micro-mesoporous silica. If the addition rate is too slow, the synthesized silica will agglomerate, making it difficult to form monodisperse spherical micro-mesoporous silica.

[0018] On the basis of the above technical solution, preferably, the stirring reaction conditions in step S1 are: a mechanical stirring rate of 200 to 600 rpm, and a reaction temperature of 0 to 20°C in a water bath. If the mechanical stirring rate is too fast, tetraethyl orthosilicate will not have time to react in the mixed solution to form a spherical shape, that is, the reaction process will be interrupted; if the stirring rate is too slow, tetraethyl orthosilicate will over-react in the mixed solution, causing the synthesized silica to agglomerate into flakes, making it difficult to form spherical micro-mesoporous silica. If the reaction temperature is too high during the reaction process, it may affect the hydrolysis and condensation rate of tetraethyl orthosilicate and the concentration of the micelle structure formed by hexadecyltrimethylammonium bromide, thereby affecting the formation of micron-sized micro-mesoporous silica.

[0019] Based on the above technical solution, preferably, the high-temperature calcination temperature in step S2 is 650-850°C, and the high-temperature calcination time is 2-8 hours. Excessively high calcination temperatures may cause the mesoporous structure to be destroyed or collapsed; excessive temperatures may also lead to excessive sintering of the solid product, resulting in aggregation or agglomeration of the silica sphere particles, further affecting the dielectric loss and thermal expansion coefficient of the prepared microwave composite dielectric substrate.

[0020] Based on the above technical solution, preferably, the average particle size of the micron-sized micro-mesoporous silica spheres is 0.9 to 2.1 μm; the mesopore diameter of the micron-sized micro-mesoporous silica spheres is 2.5 to 3.5 nm, and the mesoporous structure is a columnar pore with directional arrangement. In the present invention, by forming mesopores with a certain pore size within the silica spheres, air can be introduced through the mesoporous structure when the silica spheres are mixed with polytetrafluoroethylene to prepare a composite material, thereby reducing the dielectric constant. At the same time, the formation of the mesoporous structure can increase the specific surface area, and the mesoporous structure can interact with the molecular chains of polytetrafluoroethylene, thereby increasing the interfacial bonding strength of the composite material.

[0021] Based on the above technical solution, preferably, in step S3, the amount of polytetrafluoroethylene emulsion added is 50-70 wt%, and the amount of micron-sized micro-mesoporous silica spheres added is 10-45 vol%. The polytetrafluoroethylene emulsion and the micro-mesoporous silica spheres are mixed 2-6 times, each mixing time being 1-3 minutes, to promote sufficient contact between the polytetrafluoroethylene and the micro-mesoporous silica spheres.

[0022] Based on the above technical solution, preferably, the thickness of the composite pre-compressed sheet is 0.8 to 1.5 mm. In the present invention, a three-roll calender is used to calender the organic-inorganic blend multiple times to form the composite pre-compressed sheet. The calendering method improves uniformity and further promotes uniform mixing of the polytetrafluoroethylene resin and micron-sized micro-mesoporous silica in the system.

[0023] On the basis of the above technical solution, preferably, the pressure of the hollow hot pressing in step S5 is 5-30 MPa, the hot pressing time is 2-6 hours, and the hot pressing temperature is 365-395°C.

[0024] In a second aspect, the present invention provides a microwave composite dielectric substrate, which is prepared by the above-mentioned preparation method of a microwave composite dielectric substrate, wherein the microwave composite dielectric substrate has a dielectric constant of 2.1 to 2.4 and a dielectric loss of 1.4×10 -3 ~2.5×10 -3 , the thermal expansion coefficient is 41~63ppm / ℃.

[0025] The microwave composite dielectric substrate and its preparation method of the present invention have the following advantages over the prior art:

[0026] (1) The present invention uses micron-scale micro-mesoporous silica and polytetrafluoroethylene emulsion to prepare a composite dielectric material. Compared with nano-scale silica, micron-scale micro-mesoporous silica is not easy to agglomerate and is easy to disperse evenly in polytetrafluoroethylene. The presence of micro-mesoporous channels brings in some air, so that the micro-mesoporous silica / polytetrafluoroethylene has a lower dielectric constant, and the micro-mesoporous and polytetrafluoroethylene molecular chains form a "pinning" physical interaction. The micro-mesoporous silica / polytetrafluoroethylene has a good interface bonding, which enables the composite material to have a lower dielectric constant while also having a lower dielectric loss and thermal expansion coefficient. It is a potential low-dielectric and low-thermal expansion composite dielectric substrate material.

[0027] (2) The present invention uses tetraethyl orthosilicate as a silicon source and ethanol as a solvent. The addition of deionized water can promote the hydrolysis of tetraethyl orthosilicate to produce silicic acid; the addition of ammonia water can adjust the pH value of the solution, promote the polymerization of silicic acid and the formation of gel; hexadecyltrimethylammonium bromide as a surfactant can form a micelle structure in the sol, and tiny cavities are formed in the sol through the micelle structure. Through the combined action of ammonia water, deionized water and hexadecyltrimethylammonium bromide, a mesoporous structure with a certain pore size can be formed in the silica sphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 TEM image of the micro-mesoporous silica spheres prepared in Example 1 of the present invention;

[0030] Figure 2 This is a TEM image of the smooth-surfaced silica spheres prepared in Comparative Example 1 of the present invention;

[0031] Figure 3 This is a TEM image of a slice of the microwave composite dielectric substrate prepared in Example 1 of the present invention;

[0032] Figure 4 This is a TEM image of a slice of a microwave composite dielectric substrate prepared in Comparative Example 1 of the present invention;

[0033] Figure 5 1 is a graph showing the specific surface area test results of the silica spheres of Example 1 and Comparative Example 1 of the present invention;

[0034] Figure 6This is a particle size diagram of the micro-mesoporous silica spheres prepared in Example 1 of the present invention;

[0035] Figure 7 This is a particle size diagram of the smooth-surfaced silica spheres prepared in Comparative Example 1 of the present invention;

[0036] Figure 8 The dielectric constant diagrams of the microwave composite dielectric substrates prepared in Examples 1 to 3 and Comparative Example 1 are shown;

[0037] Figure 9 The dielectric loss diagram of the microwave composite dielectric substrate prepared in Examples 1 to 3 and Comparative Example 1;

[0038] Figure 10 Graphs showing the thermal expansion coefficients of microwave composite dielectric substrates prepared in Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below with reference to specific examples. If the specific experimental conditions are not specified in the examples, they are usually based on conventional conditions or the conditions recommended by the reagent company: the reagents, consumables, etc. used in the following examples, unless otherwise specified, can be obtained through commercial channels.

[0041] Example 1

[0042] This embodiment provides a microwave composite dielectric substrate and a method for preparing the same, which specifically includes the following steps:

[0043] (1) A mixed solution of tetraethyl orthosilicate (calculated as silicon dioxide ≥ 28.4%), ammonia water (NH3 content 25.0-28.0%), deionized water, ethanol (analytical grade) and hexadecyltrimethylammonium bromide (analytical grade) was prepared in a molar ratio of 1:19:370:230:0.2. The tetraethyl orthosilicate was added at a rate of 1 ml / min. The mixture was stirred mechanically at 400 rpm in a water bath at 10°C for 2.5 h. After the reaction, the mixture was washed with deionized water and ethanol, centrifuged several times, dried at 80°C for 8 h, and then ground to obtain a white powder.

[0044] (2) The white powder was placed in a crucible and calcined in a muffle furnace to remove organic matter and some incompletely reacted intermediate impurities in the silica. The high temperature treatment temperature was 800°C and the time was 5 hours to obtain micron-scale micro-mesoporous silica spheres with an average particle size of 0.97 μm.

[0045] (3) adding the micron-sized micro-mesoporous silica spheres to a polytetrafluoroethylene resin having a solid content of 60 wt%, stirring the mixture 6 times for 3 min using a dual-center mixer to obtain an organic-inorganic blend having a micro-mesoporous silica content of 30 vol%;

[0046] (4) The organic-inorganic blend is formed by mixing and calendering, and a composite material pre-compressed sheet with a thickness of 1.0 mm is obtained by calendering multiple times using a calender;

[0047] (5) The composite material pre-pressed sheets were stacked (copper foils were placed on the top and bottom, and the pre-pressed sheet was placed in the middle) and subjected to vacuum hot pressing and sintering. The stacked substrate sheet was placed between two pressed steel plates and then hot pressed and sintered in a hot press. The vacuum hot pressing pressure was 15 MPa, the time was 2.5 h, and the temperature was 385 ° C. After cooling to room temperature (25 ° C), a microwave composite dielectric substrate was obtained.

[0048] Example 2

[0049] This embodiment provides a microwave composite dielectric substrate and a method for preparing the same, which specifically includes the following steps:

[0050] (1) A mixed solution of tetraethyl orthosilicate (calculated as silicon dioxide ≥ 28.4%), ammonia water (NH3 content 25.0-28.0%), deionized water, ethanol (analytical grade) and hexadecyltrimethylammonium bromide (analytical grade) was prepared in a molar ratio of 1:16:350:200:0.1. The tetraethyl orthosilicate was added at a rate of 0.5 ml / min. The mixture was stirred mechanically at 200 rpm in a 0°C water bath for 5 h. After the reaction, the mixture was washed with deionized water and ethanol, centrifuged several times, dried at 100°C for 5 h, and then ground to obtain a white powder.

[0051] (2) The white powder was placed in a crucible and calcined in a muffle furnace to remove organic matter and some incompletely reacted intermediate impurities in the silica. The high temperature treatment temperature was 650°C and the time was 8 hours to obtain micron-scale micro-mesoporous silica spheres with an average particle size of 2.1 μm.

[0052] (3) adding the micron-sized micro-mesoporous silica spheres to a polytetrafluoroethylene resin having a solid content of 50 wt%, stirring the mixture twice for 1 min using a dual-center mixer to obtain an organic-inorganic blend having a micron-sized micro-mesoporous silica content of 10 vol%;

[0053] (4) forming the organic-inorganic blend by mixing and calendering, and using a calender to calender multiple times to obtain a composite material pre-compressed sheet with a thickness of 0.8 mm;

[0054] (5) The composite material pre-pressed sheets were stacked (copper foils were placed on the top and bottom, and the pre-pressed sheet was placed in the middle) and subjected to vacuum hot pressing and sintering. The stacked substrate sheet was placed between two pressed steel plates and then hot pressed and sintered in a hot press. After cooling to room temperature, a microwave composite dielectric substrate was obtained. The vacuum hot pressing pressure was 10 MPa, the time was 6 h, and the temperature was 395 ° C.

[0055] Example 3

[0056] This embodiment provides a microwave composite dielectric substrate and a method for preparing the same, which specifically includes the following steps:

[0057] (1) Tetraethyl orthosilicate (calculated as silicon dioxide ≥ 28.4%), ammonia water (NH3 content 25.0-28.0%), deionized water, ethanol (analytical grade) and hexadecyltrimethylammonium bromide (analytical grade) were prepared in a molar ratio of 1:20:400:250:0.3 to form a mixed solution. The tetraethyl orthosilicate was added at a rate of 2 ml / min. The mixture was stirred mechanically at 600 rpm in a water bath at 20°C for 5 h. After the reaction, the mixture was washed with deionized water and ethanol, centrifuged several times, dried at 120°C for 3 h, and then ground to obtain a white powder.

[0058] (2) The white powder is placed in a crucible and calcined in a muffle furnace to remove organic matter and some incompletely reacted intermediate impurities in the silica. The high temperature treatment temperature is 850°C and the time is 2 hours to obtain micron-scale micro-mesoporous silica spheres with an average particle size of 0.9 μm.

[0059] (3) adding the micron-sized micro-mesoporous silica spheres to a polytetrafluoroethylene resin having a solid content of 70 wt%, stirring the mixture four times for 2 min using a dual-center mixer to obtain an organic-inorganic blend having a micron-sized surface porous silica content of 45 vol%;

[0060] (4) The organic-inorganic blend is formed by mixing and calendering, and the calendering machine is used to obtain a composite material pre-pressed sheet with a thickness of 1.5 mm after multiple calendering;

[0061] (5) The composite material pre-pressed sheets were stacked (copper foils were placed on the top and bottom, and the pre-pressed sheet was placed in the middle) and subjected to vacuum hot pressing and sintering. The stacked substrate sheet was placed between two pressed steel plates and then hot pressed and sintered in a hot press. After cooling to room temperature, a microwave composite dielectric substrate was obtained. The vacuum hot pressing pressure was 30 MPa, the time was 2 h, and the temperature was 375 °C.

[0062] Example 4

[0063] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that tetraethyl orthosilicate, ammonia water, deionized water, ethanol, and hexadecyltrimethylammonium bromide are prepared into a mixed solution in a molar ratio of 1:16:370:230:0.2.

[0064] Example 5

[0065] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that tetraethyl orthosilicate, ammonia water, deionized water, ethanol, and hexadecyltrimethylammonium bromide are prepared into a mixed solution in a molar ratio of 1:22:370:230:0.2.

[0066] Example 6

[0067] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that tetraethyl orthosilicate, ammonia water, deionized water, ethanol, and hexadecyltrimethylammonium bromide are prepared into a mixed solution in a molar ratio of 1:19:370:230:0.05.

[0068] Example 7

[0069] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that tetraethyl orthosilicate, ammonia water, deionized water, ethanol, and hexadecyltrimethylammonium bromide are prepared into a mixed solution in a molar ratio of 1:19:370:230:0.35.

[0070] Example 8

[0071] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that the dripping rate of tetraethyl orthosilicate is 0.3 ml / min.

[0072] Example 9

[0073] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that the dripping rate of tetraethyl orthosilicate is 2.5 ml / min.

[0074] Example 10

[0075] This embodiment provides a microwave composite dielectric substrate and a preparation method thereof. The specific operation steps are the same as those in Example 1, except that the reaction is performed in a water bath at 40°C.

[0076] Comparative Example 1

[0077] This comparative example provides a smooth-surfaced silicon dioxide / polytetrafluoroethylene composite dielectric substrate and a preparation method thereof. The specific steps are as follows:

[0078] (1) Adding micron-sized smooth silica spheres (average particle size of 0.95 μm) to a polytetrafluoroethylene resin with a solid content of 60 wt%, the mixture was fully mixed with a mixer for 6 times for 3 min to obtain an organic-inorganic blend with a micron-sized smooth silica content of 30 vol%. The micron-sized smooth silica spheres were prepared according to the English literature Synthesis of Monodisperse Silica Microspheres by a Modified The obtained product was prepared by the method disclosed in Method [Integrated Ferroelectrics, 2014, 154: (142-146)].

[0079] (2) the organic-inorganic blend is formed by calendering and kneading, and a composite material pre-compressed sheet with a certain thickness of 1.0 μm is obtained by multiple calendering using a three-roll calender;

[0080] (3) The composite material pre-pressed sheets were stacked (copper foils were placed on the top and bottom, and the pre-pressed sheet was placed in the middle) and subjected to vacuum hot pressing and sintering. The stacked substrate sheets were placed between two pressed steel plates and then hot pressed and sintered in a hot press. After cooling to room temperature, a microwave composite dielectric substrate was obtained. The vacuum hot pressing pressure was 15 MPa, the time was 2.5 h, and the temperature was 385 ° C.

[0081] Comparative Example 2

[0082] This comparative example provides a micron-level surface porous SiO2-based microwave composite dielectric substrate and a preparation method thereof. The specific steps are as follows:

[0083] (1) adding micron-sized surface porous silica spheres to a polytetrafluoroethylene resin having a solid content of 60 wt%, stirring the mixture 6 times for 3 min using a dual-center mixer to obtain an organic-inorganic blend having a micron-sized surface porous silica sphere content of 30 vol%, wherein the micron-sized surface porous silica spheres are prepared according to the method disclosed in Chinese patent CN114835987A;

[0084] (2) forming the organic-inorganic blend by mixing and calendering, and using a calender to calender multiple times to obtain a composite material pre-compressed sheet with a thickness of 1.0 mm;

[0085] (3) The composite material pre-pressed sheets were stacked (copper foils were placed on the top and bottom, and the pre-pressed sheet was placed in the middle) and subjected to vacuum hot pressing and sintering. The stacked substrate sheet was placed between two pressed steel plates and then hot pressed and sintered in a hot press. The vacuum hot pressing pressure was 15 MPa, the time was 2.5 h, and the temperature was 385 ° C. After cooling to room temperature (25 ° C), a microwave composite dielectric substrate was obtained.

[0086] Specific surface area detection

[0087] The specific surface areas and mesopore parameters of the silica spheres prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were tested, and the test results are shown in Table 1.

[0088] Table 1

[0089]

[0090] Performance testing

[0091] The microwave composite dielectric substrates prepared in Examples 1 to 10 and Comparative Examples 1 to 2 were subjected to dielectric constant and dielectric loss tests at a test frequency of 30 GHz, and the thermal expansion coefficient of the microwave composite dielectric substrates was tested. The test results are shown in Table 2.

[0092] Table 2

[0093]

[0094] Figure 1 The TEM image of the micro-mesoporous silica spheres prepared in Example 1 is shown, showing that the micron-sized micro-mesoporous silica has obvious pores, i.e., a mesoporous structure. Figure 2 The transmission electron microscope analysis image of the micron-sized smooth-surface silica spheres prepared in Comparative Example 1 is shown, and it can be seen that the smooth-surface silica has no microporous or mesoporous structure.

[0095] Figure 3 、 Figure 4 TEM images of the microwave composite dielectric substrates prepared in Example 1 and Comparative Example 1 are shown respectively. It can be seen that the interface bonding force between the micro-mesoporous silica spheres and polytetrafluoroethylene prepared in Example 1 is better, while in the microwave composite dielectric substrate prepared in Comparative Example 1, there is an obvious wide gap between the smooth-surfaced silica spheres and polytetrafluoroethylene, and the interface bonding is poor.

[0096] Figure 5The specific surface area test results of the silica spheres prepared in Example 1 and Comparative Example 1 are shown. It can be seen that the specific surface area of the micro-mesoporous silica spheres prepared in Example 1 is significantly larger than the specific surface area of the smooth-surfaced silica spheres prepared in Comparative Example 1.

[0097] Figure 6 The particle size diagram of the micro-mesoporous silica spheres prepared in Example 1 is shown. Figure 7 The particle size diagram of the smooth-surfaced silica spheres prepared in Comparative Example 1 is shown. It can be seen that the particle size distribution ranges of the smooth-surfaced silica spheres and the micro-mesoporous silica spheres are basically the same, with an average particle size of about 0.95 to 0.97 μm.

[0098] Figure 8 The dielectric constant diagram of the microwave composite dielectric substrates prepared in Examples 1 to 3 and Comparative Example 1 shows that the dielectric constants of the microwave composite dielectric substrates prepared in Examples 1 to 3 are significantly lower than that of Comparative Example 1. For Example 3, when the micro-mesoporous silica filler is added to 45 vol% (the addition amount is significantly higher than 30 vol% of smooth-surface silica), its dielectric constant is still slightly lower than that of Comparative Example 1. Figure 9 The dielectric loss diagrams of the microwave composite dielectric substrates prepared in Examples 1 to 3 and Comparative Example 1 are shown. It can be seen that the microwave composite dielectric substrate prepared from PTFE containing micro-mesoporous silica has lower dielectric loss than that of silica with a smooth surface. Figure 10 The thermal expansion coefficient diagrams of the microwave composite dielectric substrates prepared in Examples 1 to 3 and Comparative Example 1 are shown. Compared with silica with a smooth surface, the microwave composite dielectric substrate prepared from PTFE containing micro-mesoporous silica has a lower thermal expansion coefficient.

[0099] As shown in Table 1, a comparison of Examples 1-3 with Comparative Examples 1-2 shows that the micro-mesoporous silica spheres prepared by the technical solution of the present invention have well-developed mesoporous channels and a significantly increased specific surface area. A comparison of Example 1 with Examples 4-10 shows that the amount of ammonia added, the amount of hexadecyltrimethylammonium bromide added, the tetraethyl orthosilicate dropwise addition rate, and the water bath reaction temperature all affect the formation of monodisperse micro-mesoporous silica spheres.

[0100] As shown in Table 2, the microwave composite dielectric substrate prepared by the technical solution of the present invention has the characteristics of low dielectric constant, low dielectric loss and low thermal expansion coefficient. The dielectric constant is about 2.1 to 2.4, and the dielectric loss is about 1.6×10 -3 ~2.5×10 -3range, and the thermal expansion coefficient is in the range of 41 to 63 ppm / °C. When Examples 1 to 3 are compared with Comparative Examples 1 and 2, it can be seen that the micro-mesoporous silica spheres prepared by the technical solution of the present invention can further reduce the dielectric constant, dielectric loss and thermal expansion coefficient compared with smooth-surface silica and micron-scale surface porous silica spheres. The reason for the reduction in dielectric loss and thermal expansion coefficient is that the micro-mesoporous channels contained in the micro-mesoporous silica spheres produce effective physical adsorption on the matrix PTFE molecular chains, so that the polytetrafluoroethylene molecular chains form a pinning physical interaction with the micro-mesoporous silica spheres, thereby improving the interface bonding between the silica spheres and the polytetrafluoroethylene; the reduction in dielectric constant is attributed to the introduction of air with an extremely low dielectric constant (dielectric constant of 1.0) through the micro-mesoporous pore shell. Comparing Example 1 with Examples 4-9 shows that the amount of ammonia added, the amount of cetyltrimethylammonium bromide added, and the tetraethyl orthosilicate droplet addition rate all affect the formation of monodisperse micro-mesoporous silica spheres, and thus the performance of the resulting microwave composite dielectric substrate. Comparing Example 1 with Example 10 shows that excessively high water bath reaction temperatures prevent the synthesis of micron-sized micro-mesoporous silica, leading to higher dielectric constants, dielectric losses, and thermal expansion coefficients.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a microwave composite dielectric substrate, characterized in that: The specific steps include: S1. Mix ammonia water, deionized water, ethanol and cetyltrimethylammonium bromide, add tetraethyl orthosilicate to the mixed solution, stir and react, and after the reaction is completed, centrifuge and dry to obtain a solid product; S2, calcining the solid product at high temperature to obtain micron-sized micro-mesoporous silica spheres; S3, mixing the micron-sized micro-mesoporous silica spheres with a polytetrafluoroethylene emulsion to obtain an organic-inorganic blend; S4, calendering the organic-inorganic blend using a calendering and mixing process to obtain a composite material pre-compressed tablet; S5, subjecting the composite material pre-pressed sheet to vacuum hot pressing and sintering to obtain a microwave composite dielectric substrate; The molar ratio of tetraethyl orthosilicate, ammonia water, deionized water, ethanol and cetyltrimethylammonium bromide is 1: (18-20): (360-400): (210-240): (0.1-0.3); The content of silicon dioxide in the tetraethyl orthosilicate is ≥28.4%, and the dropping rate of the tetraethyl orthosilicate is 0.5-2.0 ml / min; The micron-sized micro-mesoporous silica spheres have a mesopore diameter of 2.5 to 3.5 nm, and a mesoporous structure with directional columnar pores. In step S2, the high temperature calcination temperature is 650-850°C, and the high temperature calcination time is 2-8 hours; The stirring reaction conditions in step S1 are: a mechanical stirring rate of 200 to 600 rpm, a reaction temperature of 0 to 20° C. in a water bath; The average particle size of the micron-sized micro-mesoporous silica spheres is 0.9 to 2.1 μm; In step S3, the amount of polytetrafluoroethylene emulsion added is 50-70 wt%, and the amount of micron-sized micro-mesoporous silica spheres added is 10-45 vol%; The thickness of the composite material pre-pressed sheet is 0.8 to 1.5 mm; In step S5, the pressure of the hollow hot pressing is 5-30 MPa, the hot pressing time is 2-6 hours, and the hot pressing temperature is 365-395°C.

2. A microwave composite dielectric substrate, characterized in that: The microwave composite dielectric substrate is prepared by the method for preparing the microwave composite dielectric substrate according to claim 1, wherein the dielectric constant of the microwave composite dielectric substrate is 2.1 to 2.4, and the dielectric loss is 1.4×10 -3 ~2.5×10 -3 , the thermal expansion coefficient is 41~63ppm / ℃.

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