Electronic-grade hollow silicon dioxide microsphere as well as preparation method and application thereof

Abstract

The invention provides an electronic-grade hollow silicon dioxide microsphere as well as a preparation method and application thereof. The preparation method comprises the following steps: by taking synthesized hyperbranched polysiloxane with a side chain functional group structure as a precursor and a nonionic surfactant as a structure-directing agent, obtaining emulsion oil drops with different structures, adding alkali, and performing in-situ conversion to form a hollow silicon dioxide microsphere structure with high porosity; a shell layer with the characteristics of higher purity, higher density, adjustable thickness and the like is formed by a sol-gel in-situ shell layer deposition technology; the compact shell layer is added to prevent resin and a solvent from entering the microspheres, water adsorption in the microspheres is reduced, meanwhile, the flowability of the microspheres in the resin can be enhanced, and the excellent performance of the hollow silicon dioxide microspheres can be played to the maximum extent. The dielectric constant Dk (at) 10GHz is less than 1.7, and the dielectric loss Df (at) 10GHZ is less than 0.1%; the material can be used as a low-dielectric-constant material, a heat-insulating material, a density-reducing filler, an insulating material and other

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silica microspheres, and particularly relates to an electronic-grade hollow silica microsphere and a preparation method and application thereof. BACKGROUND

[0002] The spherical silica powder material is also commonly referred to as spherical silica powder or spherical silica; as a filler, the spherical silica powder is one of the key basic materials in the field of integrated circuit packaging, and plays a role in reducing the thermal expansion coefficient of the resin matrix material, improving high-temperature resistance, adjusting the dielectric constant, flame retardation, improving the mechanical strength of the substrate, reducing the cost of raw materials, and the like. At present, most of the spherical silica powder is solid powder material, and the dielectric constant (Dk) thereof is generally about 3.88. With the development and application of advanced communication technologies such as 5G, new electronic products are developing towards high frequency and high speed. In the high-frequency and high-speed application scenario, the packaging substrate material needs to have a lower dielectric constant and dielectric loss tangent (Df) to reduce the energy loss of the signal due to the dielectric conduction and polarization hysteresis effect in high-speed transmission, and to ensure the quality and stability of signal transmission. Since the Dk and Df values of air are much lower than those of most materials, the development of spherical silica powder with high porosity structure can greatly reduce the Dk and Df values of the composite material using it as a filler, and has become a research hotspot in the field of advanced packaging in high-frequency and high-speed application scenarios. Since achieving a low Dk value only requires a larger void space inside the microsphere, it is irrelevant how the void space is formed.

[0003] In 2021, 3M Company launched a hollow glass microsphere dedicated to the 5G field, which first applied its hollow filler product to the field of advanced packaging in high-frequency and high-speed application scenarios. The 4730 / 4725 packaging substrate of Rogers, USA, uses 3M hollow glass microspheres to reduce the dielectric constant and replace high-cost resin materials. However, the hollow glass microspheres of the company are only suitable for signal frequency bands below 6 GHz. The main reason is that the particle size of the 3M hollow glass microspheres is too large, with the smallest particle size being 15.3 microns, and most of the product particle sizes being above 30 microns. Compared with the particle size of 0.5-10 microns of traditional silica powder, the particle size is still too large, which limits its application. At the same time, the composition of the hollow glass microspheres is complex, containing a certain amount of alkali metal, and the water absorption rate is high, which makes it difficult to meet the demand of high-frequency and high-speed application scenarios in terms of dielectric loss, and it is not suitable for manufacturing fine lines and dense interlayer vias of high-frequency and high-speed copper-clad plates.

[0004] High purity hollow or porous silica microspheres synthesized by sol-gel wet chemical method have been reported more, mainly used as a carrier for drugs or catalysts, or as an adsorbent for separation and other applications. The internal hole space is composed of one or more shell layers and one or more internal cavity structures. Its preparation method has been studied a lot, mainly including hard template method, soft template method, double template method, self template method, etc. The microspheres synthesized by these methods have high purity, but are often synthesized under the condition of complex process, special organic solvent, special template material, high production cost, and are not suitable for industrial production. At the same time, compared with other fields, the hollow silica microspheres as fillers used in the field of advanced packaging have special requirements on mechanical strength, size control range, shell density, water absorption, dielectric constant and dielectric loss, etc. Overall, although the synthesis technology of hollow silica microspheres has been studied a lot at home and abroad, most of the products do not meet the standard requirements of electronic grade fillers. Therefore, the application of hollow silica microspheres synthesized by chemical method in high-frequency high-speed packaging substrate materials is rarely reported.

[0005] The hollow silica microspheres used as electronic grade fillers need to meet the requirements of low hydroxyl content, control of pore openness, particle size between 1-10 microns, good mechanical strength, low cost, etc. These special requirements make the low-cost synthesis of electronic grade hollow silica microspheres with high porosity still a challenging work, and the synthesis method and production process still need to be developed. SUMMARY

[0006] In order to overcome the shortcomings of the prior art and solve the problems existing in the prior art, the present application provides an electronic grade hollow silica microsphere and a preparation method and application thereof.

[0007] In a first aspect, the present application provides a preparation method of an electronic grade hollow silica microsphere, comprising the following steps:

[0008] S1: mixing a first silicon source, an alcohol solvent, deionized water and an acidic medium, heating and reacting to polymerize, and then distilling to remove reaction by-products and solvents, to obtain a hyperbranched polysiloxane;

[0009] S2: adding a structure directing agent to the hyperbranched polysiloxane and mixing uniformly; under stirring, adding to deionized water and continuing to stir, to obtain a stable emulsion dispersion;

[0010] S3: adding an alkaline medium to the emulsion dispersion as a catalyst, and preparing silica hollow microspheres by in-situ conversion through hydrolysis-crosslinking reaction;

[0011] S4: slowly adding the second silicon source into the reaction system of step S3, the second silicon source is hydrolyzed and cross-linked to deposit on the outer surface of the hollow silica microspheres to form a dense shell layer, thereby obtaining the hollow silica microspheres;

[0012] S5: the hollow silica microspheres obtained in step S4 are subjected to standing and sedimentation, washing and drying, thereby obtaining the hollow silica microsphere powder.

[0013] The preparation method of the present application uses a synthesized hyperbranched organopolysiloxane as a precursor, and under the help of a structure directing agent, self-assembles in water to form oil-in-water emulsion droplets as templates, and in-situ converts to synthesize hollow silica microspheres. The polysiloxane with a side chain functional group structure as a precursor has a strong hydrophobicity, and forms an oily droplet in water, and the hydrolysis and cross-linking speed is slow. At the same time, when the methoxy and ethoxy parts of the side chain are hydrolyzed, they will be converted into hydrophilic silanol, bringing about rich interfacial activity and diversity of microstructure changes; using a non-ionic surfactant as a structure directing agent, different structure emulsion droplets are obtained, and after adding alkali, high-porosity hollow silica microsphere structures are formed in-situ. The particle size, internal pore structure of the hollow silica microspheres are rationally controlled, and the particle size, porosity, pore size, pore distribution and pore structure type are controlled and synthesized. The second silicon source is used to form a shell layer by sol-gel in-situ shell deposition technology, which has the characteristics of higher purity, higher density, adjustable thickness, etc., increases the dense shell layer to prevent resin and solvent from entering the microsphere interior, reduces the water adsorption in the microsphere interior, and at the same time can enhance the flowability of the microspheres in the resin, and maximizes the excellent performance of the hollow silica microspheres.

[0014] The microspheres of the present application do not use special drying and washing processes during synthesis, the material has high porosity and high mechanical strength, the surface has a dense shell layer, the particle size and distribution obtained by one synthesis can meet the requirements of the filler, and there is no need for subsequent secondary screening to meet the particle size distribution requirements, and the comprehensive production cost can meet the cost control requirements of the filler.

[0015] In one embodiment, the method further comprises a post-processing step: the hollow silica microsphere powder is subjected to high-temperature calcination or microwave sintering to obtain electronic-grade hollow silica microspheres.

[0016] Through high-temperature calcination or microwave sintering, the cross-linking reaction of silanol can be promoted, and the strength of the microspheres is increased while the silanol is removed.

[0017] In one embodiment, in step S1:

[0018] The first silicon source is one or a combination of two or more of tetraethoxysilane, tetramethoxysilane, methyltriethoxysilane or dimethyldimethoxysilane, and a low molecular weight polymer with a SiO2 content of less than 50% obtained by pre-polymerization of the above-mentioned silicon source.

[0019] The hyperbranched organopolysiloxane precursor is prepared from the first silicon source, and polyethoxysiloxane (PEOS) synthesized from tetraethoxysilane (TEOS), polymethoxysiloxane (PMOS) synthesized from tetramethoxysilane (TMOS), and polysiloxane with complex side chain functional groups synthesized from methyl triethoxysilane, dimethyl dimethoxysilane, etc. The hyperbranched organopolysiloxane precursor has controllable molecular weight and branching degree, and has few by-products in the hydrolysis and polymerization reaction, thereby greatly reducing the production cost. The hyperbranched organopolysiloxane precursor has obvious advantages in the synthesis of silica materials with complex structures.

[0020] In an embodiment, the alcohol solvent is one or a combination of two or more of ethanol, methanol, propanol, isopropanol, or n-butanol. The alcohol has good solubility for the silicon source, and the alcohol can slow down the hydrolysis rate of the silicon source, so that the hydrolysis and crosslinking rate is slow, which is beneficial to the control of the morphology of the silica.

[0021] In an embodiment, the acidic medium is one or a combination of two or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, or acetic acid. The acidic medium as a catalyst can further regulate the hydrolysis process of the first silicon source.

[0022] In an embodiment, the mass ratio of the first silicon source to the alcohol solvent is (5-8):1.

[0023] In an embodiment, the mass ratio of the alcohol solvent to the deionized water is 50:(1-20).

[0024] In an embodiment, the molar ratio of the first silicon source to the acidic medium is 1:(0.02-0.2), and the pH of the solution after adding the acidic medium is 1-4. The first silicon source is hydrolyzed and polymerized under the catalysis of different water contents and acidic media, so that the polymerization rate and degree are controlled, and thus the hyperbranched polysiloxane with different polymerization degrees is obtained. By regulating the addition amount of water and the acidic medium, the molecular weight and branching degree of the hyperbranched polysiloxane are controllable. Moreover, the hyperbranched polysiloxane has few by-products in the hydrolysis and polymerization reaction, thereby greatly reducing the production cost.

[0025] In an embodiment, the heating reaction in step S1 is performed at a reaction temperature of 50-100°C for 1-4 hours.

[0026] In an embodiment, in step S2, the structure-directing agent is one or a combination of two or more of polyether-modified polyorganosiloxane, polyether-epoxy co-modified silicone oil, polyether-alkyl-modified silicone oil, polyether-modified silicone oil, polyethylene glycol, or lauryl alcohol polyoxyethylene ether.

[0027] The structure-directing agent is one or a combination of two or more of polyether-modified polyorganosiloxane, polyether-epoxy co-modified silicone oil, polyether-alkyl-modified silicone oil, polyether-modified silicone oil, polyethylene glycol, or lauryl alcohol polyoxyethylene ether.

[0028] The structure directing agent does not contain any heteroatom except carbon, hydrogen and oxygen, and the waste liquid is easy to handle. The structure directing agent does not have strong interaction with silica under alkaline conditions, and the preparation can be completed by subsequent conventional cleaning and drying without arranging complex template removal operation. The polymer beads as hard template for pore making are not needed, and the ultra-high porosity can be obtained. The technical problems such as high price, difficulty in template removal and trouble in waste liquid treatment caused by the conventional template method are solved.

[0029] In an embodiment, the molar ratio of the structure directing agent to the first silicon source is 1:(10-50);

[0030] In an embodiment, the molar ratio of the hyperbranched polysiloxane to the deionized water is 1:(5-12). The structure of the diverse hollow silica microspheres can be regulated by the molecular weight and viscosity of the hyperbranched polysiloxane, and the type and addition ratio of the structure directing agent.

[0031] In an embodiment, in step S3:

[0032] The alkaline substance is 25% concentration of ammonia or sodium hydroxide; and the pH of the solution after adding the alkaline medium is 10-12;

[0033] The molar ratio of the hyperbranched polysiloxane to the alkaline medium is 1:(0.5-2);

[0034] The temperature of the hydrolysis-crosslinking reaction is 20-30℃, and the reaction time is 2-10h.

[0035] In an embodiment, in step S4:

[0036] The second silicon source is one of tetraethoxysilane, tetramethoxysilane or tetrabutoxysilane or a combination of two or more thereof.

[0037] In an embodiment, the addition amount of the second silicon source is 1.0%-20% of the mass of the hyperbranched polysiloxane.

[0038] In an embodiment, the temperature of the hydrolysis-crosslinking deposition is 20-30℃, and the time is 2-10h. The shell formed by the sol-gel in-situ shell deposition technology has the characteristics of higher purity, higher density and adjustable thickness, the dense shell increases the resistance of the resin and solvent to enter the microspheres, reduces the water adsorption in the microspheres, and at the same time, can enhance the flowability of the microspheres in the resin, and maximizes the excellent performance of the hollow silica microspheres.

[0039] In an embodiment, in step S6:

[0040] The high-temperature calcination method is used, the high-temperature calcination temperature is 800-1050℃, and the high-temperature calcination reaction time is 5-7h.

[0041] In an embodiment, the microwave sintering method is used, the microwave sintering temperature is 700-1000℃, and the microwave sintering time is 5-7h. The microwave sintering technology uses the microwave thermal effect of silicon hydroxyl to promote the cross-linking reaction of silicon hydroxyl at a lower temperature, can effectively remove silicon hydroxyl and improve the strength of the microspheres through cross-linking reaction, and has self-limiting due to the weakening of the microwave thermal effect after the removal of silicon hydroxyl, and does not cause sintering agglomeration of the microsphere powder, can improve the strength of the microspheres while not sacrificing the porosity of the microspheres, and solves the problem that the traditional high-temperature calcination process causes the difficulty in coordinating the high strength and high porosity of the microspheres.

[0042] In a second aspect, the embodiments of the present application provide an electronic-grade hollow silica microsphere, which is prepared by the preparation method of the electronic-grade hollow silica microsphere.

[0043] In an embodiment, the electronic-grade hollow silica microsphere has a Dk@10GHz of <1.7, a Df@10GHz of <0.1%, an electrical conductivity of 5-50us / cm, a pH value of 6-9, a water content of ≤0.09%, and a particle size distribution D90 / D10 of ≤3.

[0044] In a third aspect, the embodiments of the present application provide an application of the electronic-grade hollow silica microsphere as a filler in advanced packaging and substrates.

[0045] In an embodiment, the substrate is a copper-clad plate, and the copper-clad plate has a thermal expansion coefficient of less than 200ppm / ℃, a dielectric constant of less than 2.40, a dielectric loss of less than 0.1%, and a thermal decomposition temperature of more than 500℃.

[0046] The above technical solutions have at least the following advantages or beneficial effects:

[0047] The electronic grade hollow silica microsphere preparation method of the present application takes the synthesized hyperbranched polysiloxane with side chain functional group structure as the precursor, takes the non-ionic surfactant as the structure directing agent, obtains different structure emulsion oil drops, and forms the high porosity hollow silica microsphere structure in situ after adding alkali; the structure of the diversity hollow silica microsphere can be obtained; including the porous microsphere with wormhole structure, the foam type porous microsphere densely packed by spherical holes with different sizes, and the hollow microsphere composed of porous shell layer and central large cavity; the shell layer with higher purity, higher density, and adjustable thickness is formed by the sol-gel in-situ shell deposition technology; the dense shell layer prevents the resin and solvent from entering the microsphere interior, reduces the water adsorption in the microsphere, and can enhance the flowability of the microsphere in the resin, and maximizes the excellent performance of the hollow silica microsphere.

[0048] The electronic grade hollow silica microsphere of the present application has high shell layer purity, high density, and adjustable thickness; the shell is the hollow silica microsphere structure with diverse porous structure; the obtained product has good dispersion, purity greater than 99.9%, porosity≥60%, particle size distribution D90 / D10≤3, pH value range 6-9, conductivity range 5-50 us / cm, moisture content≤0.09%, dielectric constant Dk@10GHz range<1.7, and dielectric loss Df@10GHZ<0.1%; and can be used as low dielectric constant material, heat insulation material, density reduction filler, and insulation material product.

[0049] The above summary is intended to illustrate only and is not intended to limit the application in any way. Further aspects, implementations, and features of the application will be apparent from a review of the drawings and the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0050] In the drawings, like reference numerals will be used to indicate like or similar elements throughout the several views. The drawings are not necessarily to scale. It should be understood that the drawings only depict some embodiments in accordance with the disclosure and should not be considered limiting of the scope of the disclosure.

[0051] Figure 1 The scanning electron microscope image of the electronic grade hollow silica microsphere of Example 1;

[0052] Figure 2 The particle size distribution graph of the electronic grade hollow silica microsphere of Example 1;

[0053] Figure 3 The shell deposition TEM graph of the microsphere before and after the hydrolysis crosslinking deposition of tetraethoxysilane of Example 1; wherein the left graph is the microsphere before deposition, and the right graph is the microsphere after deposition;

[0054] Figure 4 Scanning electron micrograph of the electronic grade hollow silica microspheres of Comparative Example 1;

[0055] Figure 5 Nitrogen desorption curve of the hollow silica microspheres of Example 1 and Comparative Example 1;

[0056] Figure 6 Pore size distribution of the hollow silica microspheres of Example 1 and Comparative Example 1;

[0057] Figure 7 Pore size distribution of the hollow silica microspheres of Example 1 and Comparative Example 1;

[0058] Figure 8 Mercury intrusion curve of the hollow silica microspheres of Example 1 and Comparative Example 1;

[0059] Figure 9 Pore size distribution of the hollow silica microspheres of Example 1 and Comparative Example 1 obtained by mercury intrusion test;

[0060] Figure 10 Cross-sectional SEM of the electronic grade hollow silica microspheres of Example 2;

[0061] Figure 11 Cross-sectional SEM of the electronic grade hollow silica microspheres of Example 3;

[0062] Figure 12 Cross-sectional SEM of the electronic grade hollow silica microspheres of Example 4. DETAILED DESCRIPTION

[0063] Hereinafter, only certain exemplary embodiments are described simply. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are considered to be exemplary in nature and not limiting.

[0064] Therefore, the application of the chemical method for synthesizing hollow silica microspheres in the field of high-frequency high-speed packaging substrate materials is rarely reported. The specific reasons are analyzed in detail as follows:

[0065] Firstly, the control of the content of silicon hydroxyl. There are a large number of internal pore surfaces in the hollow silica microspheres synthesized by chemical method. After the microspheres are synthesized at low temperature in solution, the internal and external surfaces contain a large number of silicon hydroxyl groups, and the silicon hydroxyl group density can even exceed 15 silicon hydroxyl groups per square nanometer of surface. When these hollow microspheres are used in the fields of biology, medicine, catalysis, separation, etc., a large number of surface silicon hydroxyl groups are beneficial to the dispersibility of the products and the grafting of various functional groups on the surface. However, these high-density silicon hydroxyl groups can greatly increase the water absorption rate and dielectric loss value (Df) of the material. Therefore, in the application of the electronic industry, it is necessary to reduce the content of silicon hydroxyl groups as much as possible. Therefore, after the hollow microspheres are synthesized by the ordinary chemical method, additional technical solutions are needed to reduce the content of silicon hydroxyl groups.

[0066] Secondly, the control of the openness of the pores. The hollow microspheres synthesized by chemical method are often of porous structure, generally have good openness, and there are a certain number of open channels between the internal space and the external environment. In subsequent applications in biology, medicine, catalysis, separation, etc., these open channels are needed as mass transfer channels and storage spaces for adsorbed substances. However, when used as fillers, it is necessary to avoid the entry of solvents and resins into the interior of the hollow microspheres as much as possible to maintain the empty space of the internal pores, so as to achieve the purposes of reducing the dielectric constant and reducing the amount of resin used. Therefore, the hollow silica microspheres used as electronic-grade fillers need a dense shell layer as a protective layer for the internal pore space to close the mass transfer channels between the internal and external spaces.

[0067] For example, the control of particle size. Most of the hollow microspheres used in biology and adsorption separation applications are in the sub-micron to nanometer size range. Or prepared into sub-millimeter particles. However, the size of the electronic-grade filler usually needs to be controlled in the range of 1-10 microns, and the high-end application needs to be controlled in the range of about 1-5 microns. Too small particle size will cause high viscosity of the material during processing, and even a small amount of too large particle size will cause a sharp decline in product performance. Electronic-grade filler materials have high requirements for particle size and particle size distribution.

[0068] In addition, when the hollow silica microspheres are used as fillers, they must have good mechanical strength to ensure that the microspheres do not break seriously in subsequent processing procedures. However, the hollow microspheres need high porosity to achieve lower dielectric constant (Dk) in order to reduce the dielectric constant of the composite substrate. High mechanical strength means that the porosity of the synthesized hollow microspheres cannot be too high, while low dielectric constant and dielectric loss tangent require the hollow microspheres to have high porosity, which is a certain contradiction. Coordination of the contradiction between high strength and high porosity is one of the main technical difficulties in the application of hollow silica microspheres in this field.

[0069] Finally, as a filler, the cost control of the hollow silica microspheres is also an important indicator. In the chemical synthesis of hollow silica material, it is necessary to avoid complex process, the use of special organic solvents, special drying process, and the production of waste liquid containing special heteroatoms as much as possible. For example, if centrifugal separation washing and supercritical drying are required, the production equipment and operating costs will increase significantly. If a surfactant containing bromide ions such as CTAB is selected, the waste liquid treatment cost will increase by more than ten times. The use of toxic organic solvents, chemical reagents containing sulfur and phosphorus heteroatoms, and metal ion-containing bases and silicon sources will greatly increase the subsequent washing and waste liquid treatment costs. It cannot meet the cost control requirements of the entire industry for fillers. Since particle size control is also an important requirement for high-performance fillers, in order to reduce costs, it is also necessary to be able to achieve once synthesis within the target range, and to avoid adjusting the particle size distribution range through slow settling, screening, centrifugal separation and other remedial measures as much as possible. Because the above operations will greatly increase the cost of the product, making it lose its product competitiveness

[0070] The hollow silica microspheres used as electronic grade fillers need to meet all the above requirements. Therefore, the present application provides an electronic grade hollow silica microsphere and a preparation method and application thereof.

[0071] Example 1

[0072] The present embodiment provides a preparation method of an electronic grade hollow silica microsphere, comprising the following steps:

[0073] 300 g of tetraethyl orthosilicate was added to a reaction kettle, stirred at 160 rpm, 50 g of ethanol, 10 g of deionized water were added to the reaction kettle, then 10 g of hydrochloric acid solution with a concentration of 4 mol / L was slowly added dropwise, then the temperature was raised to 85°C, and the stirring reaction was continued for 2 h, and then the ethanol and hydrochloric acid in the system were removed by distillation under reduced pressure to obtain 214 g of hyperbranched polysiloxane with a viscosity of 13 cp;

[0074] After breaking the vacuum, 11 g of polyether alkyl modified silicone oil (brand DY-ET200, the same in the following examples) was added under stirring at 120 rpm, and then added to 800 g of deionized water to obtain an emulsion dispersion;

[0075] Under the condition of stirring at 200 rpm, 80 g of ammonia water with a concentration of 25% was added to the emulsion dispersion, and after 6 h, 2% of tetraethoxysilane based on the mass of the hyperbranched polysiloxane was slowly added dropwise, and the stirring reaction was continued at room temperature for 6 h to obtain hollow silica microspheres;

[0076] Through washing, the unhydrolyzed silicon source, polyether silicone oil and ammonia water were removed, and after drying at 100°C, hollow silica microsphere powder was obtained;

[0077] Microwave (2450 MHZ) sintering 1050℃, 6h to obtain electronic grade hollow silica microspheres.

[0078] The scanning electron microscope of the electronic grade hollow silica microspheres obtained in this example is shown in Figure 1 The particle size distribution is shown in Figure 2 The post-deposition wall thickness increases, and the TEM image is shown in Figure 3

[0079] The obtained particle size distribution width is 0.5-7um, the average particle size is 2.09um, D90 / D10=2.98, and the purity is 99.99% for electronic grade hollow silica microspheres. The conductivity is 10us / cm, the pH is about 7.2, the moisture content is 0.05%, the dielectric constant @10GHz: 1.30, and the dielectric loss @10GHz: 0.08%(ccl, the same as the following examples).

[0080] Comparative Example 1

[0081] This comparative example 1 provides a method for preparing electronic grade spherical hollow silica, which is different from example 1 in that it does not use tetraethoxysilane for in-situ shell deposition technology, and the rest of the method steps are the same; Specifically:

[0082] Under the condition of stirring at 200rpm, 80g of 25% concentration of ammonia water was added to the emulsion dispersion, and after 6h, hollow silica microspheres were obtained.

[0083] The scanning electron microscope of the electronic grade spherical hollow silica obtained in this comparative example 1 is shown in Figure 4

[0084] As can be seen from the figure, since the comparative example 1 does not undergo in-situ shell deposition, some microspheres have holes.

[0085] Detection comparison:

[0086] (1) The electronic grade spherical hollow silica of example 1 and comparative example 1 was subjected to BET specific surface area detection (BET test method: the sample was previously degassed at 160℃ for 10 hours, and after cooling, N2 adsorption-desorption isotherm test was carried out at 77K); The N2 adsorption-desorption isotherm is shown in Figure 5 The pore size distribution is shown in Figure 6 and Figure 7 The results are shown in Table 1;

[0087] Table 1

[0088]

[0089]

[0090] ​​As can be seen from Table 1, compared with the comparative example 1 not using the in-situ shell deposition technology, the specific surface, micropore specific surface, pore volume and other values of the example 1 are obviously reduced compared with the product not subjected to shell deposition. It is illustrated that the shell deposition can indeed form a densified outer shell, and greatly reduce the number of open pores in the shell.

[0091] (2) Mercury intrusion test

[0092] The electronic grade spherical hollow silica of the example 1 and the comparative example 1 is subjected to the mercury intrusion test, and the test results are shown in Table 1, the mercury intrusion curve is shown in Figure 8 , and the pore size distribution is shown in Figure 9 .

[0093] It can be found from the pore size distribution that the comparative example 1 has three peaks, and the example 1 has two peaks, and the peak with the largest pore size is the hollow pore before and after the surface deposition, and the two small peaks disappear or move to a smaller pore size after the deposition. Since it is a hollow structure microsphere, the hollow and shell pore size values in the table can be obtained.

[0094] As can be seen from Table 1, compared with the comparative example 1, the pore volume, shell pore and porosity of the example 1 are better.

[0095] As shown in Figure 8 and Figure 9 , the mercury intrusion curve of the example 1 starts to rise at a higher pressure, indicating that there are more large pores; the mercury withdrawal curve slowly decreases at a high pressure, indicating that the pore structure is relatively closed; the mercury intrusion curve of the comparative example 1 starts to rise at a low pressure, indicating that there are a large number of small pores; the mercury withdrawal curve decreases rapidly at a high pressure, indicating that the pore structure is relatively open.

[0096] (3) Oil absorption value test

[0097] The electronic grade spherical hollow silica of the example 1 and the comparative example 1 is subjected to the oil absorption value test, about 2.0g of the silica microsphere powder is weighed and placed on a glass dish, and oil is slowly added, and the ink knife is carefully and fully mixed to make the oil and all silica microsphere powder particles evenly wet. Then, the oil is added while being pressed, and at the end point, the oil is added more slowly, and each drop needs to be fully pressed and mixed. When the sample and the oil are coagulated into a paste, and there is no oil on the glass dish, the titration end point is reached. The consumption of the silica microsphere powder and the oil is recorded respectively. All operations should be completed within 20-30min. The oil absorption value is expressed by the mass of the oil required per gram of silica microsphere. The mercury intrusion curve is shown in Figure 8 , the pore size distribution is shown in Figure 9 , and the results are shown in Table 1.

[0098] The porosities of Example 1 and Comparative Example 1 before microwave calcination are not much different, being 85.78% and 86.11% respectively, but the oil absorption values differ by more than three times. The reason is that during the mercury intrusion test, the shell layer is finally crushed by high pressure, and the pore volume tested includes the pore space inside the hollow microspheres. However, during the oil absorption value test, since no dense shell layer deposition is performed in Comparative Example 1, oil can enter the internal cavity, so a very high oil absorption value is tested. In Example 1, the shell densification operation is performed, so that the internal cavity is isolated from the external space, and during the oil absorption value test at normal pressure, oil cannot enter the internal cavity, but can only be adsorbed in the accumulated pores between the particles, so the value is small.

[0099] (4) The materials of Example 1 and Comparative Example 1 were used as fillers for copper-clad plates (CCL, the same as the following examples); the properties of the copper-clad plates are shown in Table 2:

[0100] Table 2

[0101]

[0102] The properties of the copper-clad plates are a thermal expansion coefficient less than 200 ppm / ℃, a dielectric constant less than 2.40, a dielectric loss less than 0.1%, and a thermal decomposition temperature higher than 500℃.

[0103] The materials of Example 1 and Comparative Example 1 were used as fillers for pure glue stacking: single + double (AS250FAPI + copper). The properties are shown in Table 3:

[0104] Table 3

[0105]

[0106]

[0107] Due to Comparative Example 1, without in-situ shell deposition, some of the spheres have holes, high oil absorption value, large shell pore, and large specific surface area, indicating that the shell is not dense enough, resulting in large dielectric loss and large dielectric constant in downstream applications, affecting the overall performance. Example 1 has undergone in-situ shell deposition treatment, which helps to densify the shell and helps to reduce the dielectric loss of downstream customers, greatly improving the performance.

[0108] Comparative Example 2

[0109] This example provides a method for preparing electronic-grade spherical hollow silica, which is different from Comparative Example 1 in that high-temperature sintering is used instead of microwave sintering, and the rest of the method steps are the same.

[0110] 1000℃ high-temperature calcination for 6h to obtain electronic-grade hollow silica microspheres.

[0111] After the electronic-grade hollow silica microspheres of Comparative Example 2 were calcined at 1000° C. and then ultrasonically dispersed in ethanol, it was clearly observed that a large number of large aggregates exceeding 100 μm in size were formed. The electronic-grade spherical hollow silica microspheres obtained in this example were hard agglomerated and could not be used.

[0112] Example 2

[0113] This embodiment provides a method for preparing electronic-grade spherical hollow silica, which differs from Example 1 in that trimethylchlorosilane is added dropwise (the addition amount is 1% of the mass of the hyperbranched polysiloxane) and high-temperature sintering technology is used in step S5. The remaining steps are the same.

[0114] Under stirring conditions at 200 rpm, 80 g of 25% aqueous ammonia was added to the emulsion dispersion. After 6 h, 1% trimethylchlorosilane by weight of the hyperbranched polysiloxane was slowly added dropwise. The mixture was stirred and reacted at room temperature for 6 h to obtain hollow silica microspheres.

[0115] Hollow electronic grade spherical silica was obtained by calcining at 1000℃ for 6h.

[0116] The scanning electron microscopy of the cross section of the electronic grade spherical hollow silica obtained in this example is as follows Figure 10 As shown, after calcining at 1000°C and ultrasonically dispersing the hollow silica microspheres in ethanol, the particle size distribution was tested. The test results showed that after calcining at 1000°C, the distribution was still unimodal, the average particle size was 2.02 μm, and the distribution width was 0.6-7.1 μm. Compared with before calcination, the distribution width did not widen, the average particle size was slightly reduced, and the difference in D90 / D10 was very small. Therefore, it can be considered that the electronic-grade spherical hollow silica microspheres obtained in this example are soft agglomerates, which have a porosity of 81%, an electrical conductivity of 11.us / cm, a pH of about 7.3, a moisture content of 0.04%, a dielectric constant @10 GHz: 1.31, and a dielectric loss @10 GHz: 0.08%.

[0117] The hollow silica microspheres in Comparative Example 2, which were not in situ hydrophobically modified, became hard agglomerates after calcination at 1000°C and were unusable. However, the hollow silica microspheres in Example 2, which were in situ hydrophobically modified and calcined at 1000°C, became soft agglomerates and could be opened and redispersed well. Example 1 and Comparative Example 1, which were microwave sintered without in situ hydrophobic modification, also dispersed well without agglomeration.

[0118] Example 3

[0119] This embodiment provides a method for preparing electronic-grade hollow silica microspheres, comprising the following steps:

[0120] Into a reaction kettle, 300 g of tetraethyl orthosilicate was added and stirred at 160 rpm. Then, 50 g of ethanol, 2 g of deionized water, and 10 g of hydrochloric acid solution with a concentration of 4 mol / L were added into the reaction kettle. After that, the temperature was raised to 85°C, and the reaction was continued for 2 h under stirring. Then, the ethanol and hydrochloric acid in the system were removed by distillation under reduced pressure to obtain 254 g of hyperbranched polysiloxane with a viscosity of 8 cp.

[0121] After breaking the vacuum, 11 g of polyether silicone oil (commercially available) was added under stirring at 120 rpm, and then added into 800 g of deionized water to obtain an emulsion dispersion.

[0122] Under stirring at 200 rpm, 80 g of ammonia water with a concentration of 25% was added into the emulsion dispersion. After 6 h, 2% of tetraethoxysilane by mass of the hyperbranched polysiloxane was slowly added dropwise, and the reaction was continued under stirring at room temperature for 6 h to obtain hollow silica microspheres.

[0123] By washing, the unhydrolyzed silicon source, polyether silicone oil, and ammonia water were removed. After drying at 100°C, hollow silica microsphere powder was obtained.

[0124] Microwave sintering was performed at 1050°C for 6 h to obtain electronic-grade hollow silica microspheres.

[0125] It was tested that the electronic-grade spherical hollow silica obtained in this embodiment 3 had the following properties: the cross-sectional SEM image thereof is shown in Figure 11 The average particle size was 1.52 um. The structure was a bicontinuous (vermicular) pore stack, which was a porous microsphere with a porosity of 62%. This may be because the viscosity of polysiloxane is small, the hydrolysis speed is fast, and the content part is easy to form a small core after the surface of the micelle is quickly solidified, thereby leading to the formation of a vermicular structure. The conductivity was 10.3 us / cm, the pH was about 6.8, the moisture content was 0.08%, the dielectric constant @ 10 GH was 1.45, and the dielectric loss @ 10 GH was 0.26%.

[0126] According to the test structure, the bicontinuous pore stack was not suitable for application in the field of advanced packaging, and was more suitable for applications requiring material transfer.

[0127] Embodiment 4

[0128] This embodiment provides a method for preparing electronic-grade spherical hollow silica, which comprises the following steps:

[0129] Into a reaction kettle, 150 g of tetraethyl orthosilicate and 150 g of tetramethyl orthosilicate were added and stirred at 160 rpm, 50 g of ethanol, 15 g of deionized water were added into the reaction kettle, then 10 g of hydrochloric acid solution with a concentration of 4 mol / L was slowly added dropwise, then the temperature was raised to 85°C, and the stirring was continued for 2 h, and then the ethanol and hydrochloric acid in the system were removed by distillation under reduced pressure to obtain 202 g of hyperbranched polysiloxane with a viscosity of 25 cp;

[0130] After breaking the vacuum, 18 g of polyether alkyl modified silicone oil was added under stirring at 120 rpm, and then added into 1200 g of deionized water to obtain an emulsion dispersion;

[0131] Under the condition of stirring at 200 rpm, 80 g of ammonia water with a concentration of 25% was added into the emulsion dispersion, and after 6 h, 2% of tetraethoxysilane by mass of the hyperbranched polysiloxane was slowly added dropwise, and the stirring was continued at room temperature for 6 h to obtain hollow silica microspheres;

[0132] By washing, the unhydrolyzed silicon source, polyether silicone oil and ammonia water were removed, and after drying at 100°C, hollow silica microsphere powder was obtained;

[0133] Microwave sintering was carried out at 1050°C for 6 h to obtain electronic grade hollow silica microspheres.

[0134] Test results: The cross-sectional SEM image of the electronic grade spherical hollow silica obtained in this embodiment is shown in Figure 12 The average particle size of the obtained microspheres is 8.41 um, D90 / 10 = 2.63, and has a honeycomb-shaped pore (foam) structure with a porosity of 64%, which may be due to the fact that the polysiloxane has a large viscosity, the mass transfer is slow, the polysiloxane in the inner part of the micelle surface is slowly solidified after rapid solidification, and a foam-like structure is formed due to phase separation. The conductivity is 12.3 us / cm, the pH is about 7.5, the moisture content is 0.06%, the dielectric constant @ 10 GHz is 1.68, and the dielectric loss @ 10 GHz is 0.06%.

[0135] By changing the mass of water added during the synthesis of hyperbranched polysiloxane, hyperbranched polysiloxanes with different viscosities were prepared, and the pore structure characteristics thereof at different viscosities were counted, and the results are shown in Table 4.

[0136] Table 4

[0137]

[0138] Therefore, in this application, electronic grade hollow silica microspheres with different pore structures can be prepared by adjusting the reaction conditions.

[0139] The application innovates the technology of forming the hollow silica microspheres by using the self-made hyperbranched polysiloxane as the precursor and the non-ionic surfactant as the structure directing agent, and the different structure emulsion oil droplets are obtained, and the high porosity hollow silica microsphere structure is formed in situ after adding the alkali.

[0140] The hyperbranched polysiloxane with side chain functional groups is synthesized as the precursor of silica, and the precursor has strong hydrophobicity, forms the oily droplets in water, and has slow hydrolysis and crosslinking speed. Meanwhile, the side chain methoxy and ethoxy parts are converted into the hydrophilic silanol when hydrolyzed, which brings the abundant interfacial activity and the diversity of microstructure changes, and shows the obvious advantages in the synthesis and preparation of the silica material with complex structure. The molecular weight and the branching degree of the hyperbranched polysiloxane precursor are controllable, the by-product of the hydrolysis and polymerization reaction is little, and the production cost is greatly reduced.

[0141] The structure directing agent does not contain any heteroatom except carbon, hydrogen and oxygen, and the waste liquid treatment is convenient. And the structure directing agent does not have strong interaction with the silica under the alkaline condition, and the preparation can be completed after the conventional cleaning and drying, and the complex template removal operation is not needed. The hyperporosity can be obtained without using the polymer small ball as the hard template for pore forming. The technical problems such as the high price, the difficulty in removing the template and the trouble in treating the waste liquid caused by the conventional template method are solved.

[0142] The structure of the hollow silica microspheres with the diversity can be regulated by the molecular weight and the viscosity of the hyperbranched polysiloxane, and the type and the adding proportion of the structure directing agent. The pore structure includes the porous microspheres with the wormhole structure formed by the accumulation of the silica sol particles, the foam type porous microspheres formed by the dense stacking of the spherical pores with different sizes, and the hollow microspheres composed of the porous shell layer and the central large cavity. The foam and wormhole microspheres can basically maintain the porosity even if they are broken, and the stability is good in the subsequent processing. The microspheres with the large cavity in the inside have the larger pore volume, and the pore volume can be further improved by adding the pore expander, and the dielectric constant is lower. The mass transfer of the wormhole microspheres is better, and the application needs the material transfer. The foam pore material is beneficial to the closed internal cavity and reduces the influence of the material transfer process.

[0143] The electronic grade hollow silica microspheres are directly synthesized once, and the particle size and the distribution of the obtained product are in the target range, and the variation coefficient (D90 / D10≤3). The particle size distribution range does not need to be adjusted by the remedial measures such as slow sedimentation, screening, centrifugal separation and the like. The shell layer formed by the sol-gel in situ shell deposition technology has the characteristics of higher purity, higher density and adjustable thickness, the dense shell layer prevents the resin and the solvent from entering the inside of the microspheres, reduces the water adsorption in the microspheres, and can enhance the fluidity of the microspheres in the resin, and the excellent performance of the hollow silica microspheres is maximized.

[0144] Microwave sintering technology is used to utilize the microwave thermal effect of silanol to promote the cross-linking reaction of silanol at a lower temperature. The silanol can be effectively removed and the strength of the microspheres can be improved through the cross-linking reaction. Moreover, since the microwave thermal effect is weakened after the removal of silanol, this technology is self-limiting and will not cause sintering and agglomeration of the microsphere powder. It can improve the strength of the microspheres without sacrificing the porosity of the microspheres, solving the problem of the contradiction between high strength and high porosity of microspheres caused by traditional high-temperature calcination process.

[0145] Finally, the raw materials are easy to purchase. Organic silanes such as tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methyltriethoxysilane or dimethyldimethoxysilane, polyether-modified silicone oil and polyethylene glycol from the first silicon source are widely used and are ready-made industrial products with a wide range of product models and specifications that can be directly purchased.

[0146] In the description of this specification, the reference terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0147] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0148] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various modifications or substitutions within the technical scope disclosed in this application, and such modifications or substitutions should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing electronic grade hollow silica microspheres, characterized in that: The following steps are involved: S1: mixing a first silicon source, an alcohol solvent, deionized water, and an acidic medium, heating to react and polymerize, and then distilling off reaction byproducts and the solvent to obtain a hyperbranched polysiloxane; S2: adding a structure directing agent to the hyperbranched polysiloxane and mixing uniformly; adding the mixture to deionized water while stirring, and continuing to stir to obtain a stable emulsion dispersion; S3: adding an alkaline medium to the emulsion dispersion as a catalyst to prepare hollow silica microspheres through in-situ conversion via a hydrolysis-crosslinking reaction; S4: slowly adding the second silicon source to the reaction system of step S3, and the second silicon source is hydrolyzed, cross-linked, and deposited on the outer surface of the hollow silica microspheres to form a dense shell layer, thereby obtaining hollow silica microspheres; S5: The hollow silica microspheres in step S4 are allowed to settle, washed and dried to obtain hollow silica microsphere powder.

2. The method for preparing electronic grade hollow silica microspheres according to claim 1, wherein The method also includes a post-processing step: high-temperature calcination or microwave sintering of the hollow silica microsphere powder to obtain electronic-grade hollow silica microspheres.

3. The method for preparing electronic grade hollow silica microspheres according to claim 1 or 2, characterized in that: In step S1: The first silicon source is one or a combination of two or more of tetraethoxysilane, tetramethoxysilane, methyltriethoxysilane or dimethyldimethoxysilane, and the low molecular weight polymer with an SiO2 content of less than 50% is obtained by prepolymerization of the above silicon sources; The alcohol solvent is one or a combination of two or more of ethanol, methanol, propanol, isopropanol or n-butanol; The acidic medium is one or a combination of two or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid or acetic acid; The molar ratio of the first silicon source to the acidic medium is 1:(0.02-0.2); the pH of the solution after adding the acidic medium is 1-4; The conditions for the heating reaction in step S1 are: reaction temperature 50° C.-100° C., and reaction time 1 h-4 h.

4. The method for preparing electronic grade hollow silica microspheres according to claim 1 or 2, characterized in that: In step S2: The structure directing agent is one or a combination of two or more of polyether-modified polyorganosiloxane, polyether epoxy co-modified silicone oil, polyether alkyl-modified silicone oil, polyether-modified silicone oil, polyethylene glycol or lauryl alcohol polyoxyethylene ether; The molar ratio of the structure directing agent to the first silicon source is 1:(10-50); The molar ratio of the hyperbranched polysiloxane to deionized water is 1:(5-12).

5. The method for preparing electronic grade hollow silica microspheres according to claim 1 or 2, characterized in that: In step S3: The alkaline substance is 25-30% ammonia water; the pH of the solution after adding the alkaline medium is 10-12; The molar ratio of the hyperbranched polysiloxane to the alkaline medium is 1:(0.5-2); The temperature of the hydrolysis-crosslinking reaction is 20-30° C., and the reaction time is 2-10 h.

6. The method for preparing electronic grade hollow silica microspheres according to claim 1 or 2, characterized in that: In step S4: The second silicon source is one or a combination of two or more of tetraethoxysilane, tetramethoxysilane or tetrabutoxysilane; The amount of the second silicon source added is 1.0%-20% of the mass of the hyperbranched polysiloxane; The temperature of hydrolysis cross-linking deposition is 20-30°C and the time is 2-10 hours.

7. The method for preparing electronic grade hollow silica microspheres according to claim 2, wherein: In step S6: The high temperature calcination method is adopted, the high temperature calcination temperature is 800℃-1050℃, and the high temperature calcination reaction time is 5h-7h; A microwave sintering method is adopted, the microwave sintering temperature is 700° C.-1000° C., and the microwave sintering time is 5 h-7 h.

8. An electronic grade hollow silica microsphere, characterized in that: The electronic-grade hollow silica microspheres are prepared by the preparation method of the electronic-grade hollow silica microspheres according to any one of claims 1 to 7.

9. The electronic grade hollow silica microspheres according to claim 8, characterized in that: The electronic-grade hollow silica microspheres have a Dk@10GHz value of <1.7, a Df@10GHz value of <0.1%, a conductivity of 5-50 us / cm, a pH value of 6-9, a moisture content of ≤0.09%, and a particle size distribution of D90 / D10 ≤3.

10. Use of the electronic-grade hollow silica microspheres according to claim 8 or 9 as fillers in advanced packaging and substrates.

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