Low-dielectric silica powder, resin composition containing the silica powder, and method for preparing the low-dielectric silica powder

Abstract

An object of the present invention is to provide a silica powder having a very small dielectric loss tangent and a resin composition containing the silica powder. Another object of the present invention is to provide a method for producing a silica powder having a low dielectric loss tangent and a strong adhesion at the interface with a resin. The present invention provides a low-dielectric silica powder, which is characterized in that its average particle size is 0.1 to 30 μm and its dielectric loss tangent (10 GHz) is 0.0005 or less.

Description

Technical Field

[0001] The present invention relates to a silica powder having a very small dielectric property, particularly a very small dielectric loss tangent in a high-frequency region, a method for producing the same, and a resin composition containing the silica powder. Background Art

[0002] Nowadays, with the high-performance and high-speed communication of information terminals such as smartphones, there is a strong demand for high densification, extreme thinning, and low dielectric property, particularly low dielectric loss tangent, of semiconductor sealing materials such as printed wiring boards and underfill materials used.

[0003] The transmission loss of a signal is as shown in the Edward A. Wolff formula: Transmission loss As shown, it is known that the smaller the dielectric constant (ε) and the dielectric loss tangent (tanδ) of a material, the more the loss is suppressed. In particular, according to the above formula, it can be seen that the dielectric loss tangent (tanδ) contributes more to the transmission loss.

[0004] As a method for reducing the dielectric loss tangent of semiconductor sealing materials such as printed wiring boards and underfill materials, a method of adding an inorganic powder having a dielectric loss tangent lower than that of the resin is common. However, an inorganic powder having a dielectric loss tangent of 0.0006 or less in a high-frequency region and a dielectric constant of 4.0 or less is rarely known.

[0005] Silica powder, which is one of the representative general inorganic powders, is a material having a small coefficient of thermal expansion, excellent insulation, and dielectric properties when added as an inorganic powder to a resin.

[0006] It is considered that if the dielectric property of silica powder, particularly the dielectric loss tangent, can be reduced to the level of fused silica, it will be possible to develop a wide range of uses as a sealing material for high-speed communication semiconductors, or a filler for high-speed communication substrates or antenna substrates, etc., which are expected to have great development in the future. However, such silica powder has not been found yet.

[0007] In Patent Document 1, although low-silanol silica was prepared by heat treatment in an atmosphere with a low water vapor partial pressure, only the reduction rate of the silanol group was mentioned, the amount of silanol in the treated silica was not measured, and the dielectric loss tangent was not mentioned.

[0008] In Patent Document 2, silica glass fibers prepared by a sol-gel method were heat-treated to prepare silica glass fibers having a water content of 1000 ppm or less. Although the water content of the silica glass fibers after heat treatment was described in Patent Document 2, the amount of silanol and the dielectric loss tangent were not mentioned.

[0009] In addition, although Patent Document 2 shows the relationship between the moisture content in silica glass fibers and the dielectric loss tangent, it does not describe the amount of silanol (Si-OH), and the dielectric loss tangent is a value obtained by measuring a printed circuit board using silica glass fibers and PTFE. Therefore, the relationship between the amount of silanol and the dielectric loss tangent of the glass fibers is not clear.

[0010] For fused silica, the amount of hydroxyl groups (OH groups) remaining in the glass is generally related to the dielectric loss tangent. In addition, it is known that by heat treatment, the hydroxyl groups decrease and the structure of the fused silica changes (Non-Patent Document 1). However, if a hydroxyl group-containing fused silica is heat-treated at a high temperature, the amount of strain increases, especially the strain on the glass surface increases (Non-Patent Document 2), and thus the strength is significantly reduced. Therefore, heat-treated silica powder that can be used as a filler crucial for the adhesion strength to a resin has not been practically applied.

[0011] Prior Art Documents

[0012] Patent Documents

[0013] Patent Document 1: Japanese Patent Laid-Open No. 2-289416

[0014] Patent Document 2: Japanese Patent Laid-Open No. 5-170483

[0015] Non-Patent Documents

[0016] Non-Patent Document 1: Change in OH Group Concentration in Silica Glass Accompanying Heat Treatment, Thesis for Master's Degree, Department of Engineering, Fukui University, February 2011

[0017] Non-Patent Document 2: Structural Change of Silica Glass Block by Heat Treatment, Thesis for Master's Degree, Department of Engineering, Fukui University, February 2005 Summary of the Invention

[0018] Technical Problem to be Solved by the Invention

[0019] The present invention has been completed to solve the above problems, and an object thereof is to provide a silica powder having a very small dielectric loss tangent and a resin composition containing the silica powder. Another object of the present invention is to provide a method for producing a silica powder having a low dielectric loss tangent and strong adhesion at the interface with a resin.

[0020] Technical Means for Solving the Technical Problem

[0021] To solve the above technical problem, the present invention provides a low-dielectric silica powder, characterized in that its average particle size is 0.1 to 30 μm and its dielectric loss tangent (10 GHz) is 0.0005 or less.

[0022] In the case of the above-mentioned silica powder, the tangent of the dielectric loss angle is very small, and thus it can be developed for a wide range of uses as a sealing material for semiconductors for high-speed communication, or as a filler for substrates for high-speed communication or antenna substrates.

[0023] At this time, it is preferable that: inside and on the surface of the low-dielectric silica powder, the metals selected from aluminum, magnesium, and titanium and / or their oxides are each 200 ppm or less in terms of the mass of the metal, and the alkali metals and alkaline earth metals are each 10 ppm or less in terms of mass.

[0024] In the case of the above-mentioned silica powder, it will not corrode the electrodes.

[0025] In addition, it is preferable that the content of hydroxyl groups (Si-OH) in the low-dielectric silica powder is 300 ppm or less.

[0026] In the case of the above-mentioned silica powder, the tangent of the dielectric loss angle is even lower.

[0027] Furthermore, it is preferable that the content of B is 1 ppm or less, the content of P is 1 ppm or less, and the contents of U and Th are each 0.1 ppb or less.

[0028] In the case of the above-mentioned silica powder, the dielectric properties become preferable, and in addition, failures caused by radiation can be prevented.

[0029] In addition, in the present invention, it is preferable that the maximum particle size of the low-dielectric silica powder is 100 μm or less.

[0030] Thus, it is preferable to remove coarse particles or agglomerated particles larger than 100 μm before use.

[0031] In addition, the present invention provides a resin composition containing a low-dielectric silica powder, which is characterized in that it is a mixture of the above-mentioned low-dielectric silica powder and a resin.

[0032] In the case of the above-mentioned resin composition containing a low-dielectric silica powder, a cured product with a very small tangent of the dielectric loss angle can be provided.

[0033] In addition, the present invention provides a method for preparing a low-dielectric silica powder, which is a method for preparing a low-dielectric silica powder, and is characterized in that the silica powder is heat-treated at a temperature of 500°C to 1500°C to make the tangent of the dielectric loss angle (10 GHz) of the silica powder 0.0005 or less, and then the surface of the heat-treated silica powder is etched with an etching solution.

[0034] If it is the method for preparing the low-dielectric silica powder as described above, it is possible to prepare a low-dielectric silica powder with a low dielectric loss tangent, high strength, and strong adhesion at the interface with the resin at a high production rate.

[0035] At this time, it is preferable to perform the heat treatment for 30 minutes to 72 hours.

[0036] By performing the heat treatment in this way, the dielectric loss tangent of the low-dielectric silica powder can be made an appropriate value.

[0037] In addition, as the etching solution, it is preferable to use an aqueous solution selected from aqueous hydrofluoric acid solution, aqueous ammonium fluoride solution, aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous sodium carbonate solution, ammonia water, and alkaline electrolyzed water.

[0038] From the viewpoints of the removal effect of the strain layer of the heat-treated silica powder and the improvement of the adhesion to the resin, the above etching solution is preferable.

[0039] At this time, as the etching solution, it is preferable to use an alkaline aqueous solution with a pH value of 11 or more. In addition, it is more preferable to use alkaline electrolyzed water with a pH value of 12 or more.

[0040] From the viewpoints of the etching effect of the silica powder and the improvement of the adhesion between the silica powder and the resin, the above etching solution is more preferable. From the viewpoints of the working environment or wastewater treatment, alkaline electrolyzed water with a pH value of 12 or more is further preferable.

[0041] It is preferable to further perform a coupling agent treatment on the surface of the silica powder after the etching treatment.

[0042] When the surface of the silica powder is covered with a silane coupling agent as described above and incorporated into a resin or the like, the adhesion between the resin and the powder surface can be made more firm.

[0043] Advantages of the Invention

[0044] As described above, if it is the low-dielectric silica powder of the present invention, the dielectric loss tangent is very small, and a cured product with a very small dielectric loss tangent can be provided for a resin composition containing the low-dielectric silica powder as a mixture of the low-dielectric silica powder and the resin. In addition, if it is the method for preparing the low-dielectric silica powder of the present invention, it is possible to prepare a silica powder with a low dielectric loss tangent, high strength, and strong adhesion at the interface with the resin at an excellent production rate. Brief Description of the Drawings

[0045] Figure 1 It is a chart showing the relationship between the silica filling amount and the dielectric loss tangent (10 GHz).

[0046] Figure 2Scanning electron microscope photograph of a fracture surface obtained by breaking the cured product of Example 5.

[0047] Figure 3 Scanning electron microscope photograph of a fracture surface obtained by breaking the cured product of Example 6.

[0048] Figure 4 Scanning electron microscope photograph of a fracture surface obtained by breaking the cured product of Comparative Example 4. Detailed Description of the Invention

[0049] As described above, it is required to develop a silica powder with a very small dielectric loss tangent.

[0050] The inventors of the present application repeatedly conducted in-depth research on the above technical problems, especially on low dielectric properties, and found that heating the silica powder to a temperature of 500°C to 1500°C is effective in reducing the dielectric loss tangent. In addition, by preparing an etched silica powder obtained by slightly etching the surface of the silica powder, the surface of the powder becomes firm, and the adhesion to the resin is improved, thus completing the present invention.

[0051] That is, the present invention relates to a low-dielectric silica powder, characterized in that its average particle size is 0.1 to 30 μm and its dielectric loss tangent (10 GHz) is 0.0005 or less.

[0052] In addition, the present invention relates to a method for preparing a low-dielectric silica powder, which is a method for preparing a low-dielectric silica powder, characterized in that the silica powder is heat-treated at a temperature of 500°C to 1500°C to make the dielectric loss tangent (10 GHz) of the silica powder 0.0005 or less, and then the surface of the heat-treated silica powder is etched with an etching solution.

[0053] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0054] The present invention relates to a silica powder having an average particle size of 0.1 to 30 μm and a dielectric loss tangent (10 GHz) of 0.0005 or less. In addition, it preferably relates to a silica powder in which the metals selected from aluminum, magnesium, and titanium and / or their oxides in the interior and on the surface of the silica powder are each 200 ppm or less in terms of metal mass, and the contents of alkali metals and alkaline earth metals are each 10 ppm or less in terms of mass. In addition, it relates to a silica powder having a hydroxyl group (Si-OH) content of 300 ppm or less. Further, it also relates to a silica powder having an average particle size of 0.1 to 30 μm and preferably a maximum particle size of 100 μm or less.

[0055] Furthermore, it relates to a method for preparing silica powder, which is heat-treated at a temperature of 500°C to 1500°C so that the tangent of the dielectric loss angle (10 GHz) of the silica powder is 0.0005 or less, preferably 0.0004 or less. Preferably, through the above heat treatment, the content of hydroxyl groups (Si-OH) contained in the silica powder becomes 300 ppm or less, more preferably 280 ppm or less, and further preferably 150 ppm or less, to form silica powder having the characteristic of a low tangent of the dielectric loss angle. This silica powder is suitable as a sealing material for semiconductors or a filler for substrates such as high-speed communication substrates and antenna substrates.

[0056] For the silica powder having the above excellent dielectric properties, a low-dielectric resin composition can be easily obtained by blending it into a resin. In addition, the low-dielectric silica powder can also be used as a filler for low-dielectric organic substrates.

[0057] As the silica powder used as the raw material for the low-dielectric silica powder of the present invention, the following silica powder can be used, but as long as it is silica powder, it can be used regardless of whether it is the following production method. The silica powder is: spherical molten silica powder obtained by pulverizing naturally occurring crystalline quartz to obtain powder and passing the powder through a high-temperature flame of about 2000°C; silica powder obtained by purifying water glass as a raw material, sintering it at a high temperature, and pulverizing it, etc. Generally, even if silica powder that is easily obtained as a filler for semiconductor sealing materials, etc., and has been treated at a high temperature of about 2000°C is used, it is impossible to obtain low-dielectric silica powder with a tangent of the dielectric loss angle meeting the target, that is, a tangent of the dielectric loss angle of 0.0005 or less.

[0058] According to the experimental results of the inventors of the present application, as long as the content of the metal or its metal oxide selected from aluminum, magnesium, and titanium is 200 ppm or less in terms of the mass of the metal inside or on the particle surface of the silica powder to be heat-treated, crystallization will not easily occur in the heat treatment process, and the target low-dielectric silica powder can be obtained. In addition, the content of each of the alkali metals and alkaline earth metals is preferably 10 ppm or less, more preferably 5 ppm or less. There is a problem that silica powder with a large amount of alkali metals and alkaline earth metals corrodes the electrodes of high-speed communication substrates or semiconductor elements. From the perspective of preventing corrosion, silica powder with less alkali metals and alkaline earth metals is also required. Further, it is preferable that the content of B (boron) is 1 ppm or less and the content of P (phosphorus) is 1 ppm or less. In order to prevent failures caused by radiation, it is further preferable that the content of U or Th in the silica powder is 0.1 ppb or less. Thus, by suppressing the impurity concentration to a low level, the dielectric properties and the like of the silica powder become more preferable. The concentration of the above impurities can be measured by atomic absorption spectrophotometry, inductively coupled plasma (ICP) emission spectrometry, or the like.

[0059] In addition, in the present invention, the alkali metals refer to lithium, sodium, potassium, rubidium, cesium, and francium among the elements belonging to Group 1 of the periodic table excluding hydrogen. In addition, the alkaline earth metals refer to calcium, strontium, barium, and radium among the elements belonging to Group 2 of the periodic table excluding beryllium and magnesium.

[0060] The average particle size of the silica powder of the present invention is 0.1 to 30 μm. In addition, since spherical powder can be highly filled in the resin, it is preferable as a sealing material for semiconductors, but powder with a broken shape can also be used. If the average particle size is less than 0.1 μm, the specific surface area is large and it cannot be highly filled in the resin. In addition, if the average particle size is greater than 30 μm, the filling property in narrow parts is poor, and problems such as non-filling will occur. Therefore, generally, powder with an average particle size of 0.5 μm to 20 μm and a maximum particle size of 100 μm or less is preferred.

[0061] When used as a filler for underfill materials or high-speed substrates, the average particle size is 0.1 to 5 μm and the maximum particle size is 20 μm or less, and more preferably the average particle size is 0.1 to 3 μm and the maximum particle size is 10 μm or less.

[0062] In order to improve the fluidity and processability and other properties of the low-dielectric silica powder, silica powders with different average particle sizes can be mixed.

[0063] In addition, in the present invention, the maximum particle size and the average particle size can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD-3100: manufactured by Shimadzu Corporation, etc.), and the mass average diameter D50 (i.e., the particle diameter at which the cumulative mass is 50% or the median diameter) in the particle size distribution measurement based on the laser diffraction method can be obtained and used as the average particle size.

[0064] In order to enable the low-dielectric silica powder of the present invention to have a wide range of uses as a sealing material for semiconductors for high-speed communication, or as a filler for substrates or antenna substrates for high-speed communication, the tangent of the dielectric loss angle (10 GHz) is made 0.0005 or less. Moreover, in order to achieve the above-mentioned tangent of the dielectric loss angle, the silica powder is heat-treated in advance.

[0065] The heating temperature desired for low dielectric constant is 500°C to 1500°C, more preferably 600°C to 1300°C, and further preferably 700°C to 1000°C. As the heating method, the silica powder is placed in an electric heating furnace, a muffle furnace, etc. and heat-treated at 500°C to 1500°C.

[0066] The heat treatment time of the silica powder varies depending on the heating temperature. From the perspective of practicality, it is preferably 30 minutes to 72 hours, more preferably 1 hour to 24 hours, and further preferably 2 hours to 12 hours.

[0067] In addition, the cooling from the heating temperature to room temperature can be slow cooling or rapid cooling. Since the molten silica sometimes partially crystallizes depending on the conditions, it is advisable to optimize the heating temperature or the cooling conditions.

[0068] As the heating atmosphere, it can be in air, an inert gas such as nitrogen, and can be under normal pressure, in a vacuum or under reduced pressure, without particular limitation. However, considering the cost, it is usually carried out under normal pressure and in air.

[0069] The hydroxyl content of the heat-treated silica powder is analyzed by infrared spectrophotometry, whereby it is possible to confirm whether the desired dielectric properties have been achieved.

[0070] It is known that in the GHz frequency band, the dipoles based on polarization respond to the electric field and cause dielectricity. Therefore, the key to low dielectric properties in the GHz frequency band lies in reducing the polarization in the structure.

[0071] The dielectric constant is expressed by the following Clausius-Mossotti equation, with the molar polarizability and the molar volume as factors. From this, it can be seen that the key to reducing the dielectric constant lies in reducing the polarization and increasing the molar volume.

[0072] Dielectric constant = [1 + 2(ΣPm / ΣVm)] / [1 - (ΣPm / ΣVm)]

[0073] (Pm: Molar polarizability of atomic group, Vm: Molar volume of atomic group)

[0074] In addition, the dielectric loss tangent (tanδ) is the delay of the dielectric response to an alternating current electric field. In the GHz frequency band, the main reason lies in the orientation relaxation of dipoles. Therefore, in order to reduce the dielectric loss tangent, a method of removing dipoles (forming a structure close to non-polar) can be considered.

[0075] In summary, as a method for low dielectric property of silica particles in the GHz frequency band, in the present invention, the concentration of hydroxyl groups (silanols) as polar groups is suppressed to be low.

[0076] From the above perspective, in the present invention, it is preferable that the concentration of hydroxyl groups (Si-OH) in the heat-treated silica powder is in the above range. In addition, in the etching treatment described later, in order to dissolve and remove the strain layer on the surface of the silica powder, the lower the concentration of hydroxyl groups in the heat-treated silica powder, the better.

[0077] Thereby, silica powder with a lower dielectric loss tangent can be obtained. The concentration of hydroxyl groups in the finally obtained silica powder is preferably 300 ppm or less, more preferably 280 ppm or less, and further preferably 150 ppm or less.

[0078] As described later, the concentration of hydroxyl groups (Si-OH) in the silica powder can be quantified by measuring the transmittance of the peak near 3680 cm -1 Due to the infrared absorption near 3680 cm -1 attributing to internal silanols (refer to Patent Document 1), based on this characteristic absorption band, silanols as polar groups that affect the dielectric loss tangent are determined and quantified. Thereby, the degree of reduction of the dielectric loss tangent can be estimated more specifically. In addition, since the infrared absorption (refer to Patent Document 1) of isolated silanols near 3740 cm -1 is negligible in the present invention, as described above, as long as the transmittance of the peak near 3680 cm -1 is measured, the reduction of the dielectric loss tangent can be sufficiently estimated.

[0079] As described above, the transmission loss of the signal is as in the Edward A. Wolff formula: Transmission loss As shown, the smaller the dielectric constant (ε) and the tangent of the dielectric loss angle (tanδ) of a material, the more the loss is suppressed. Especially for transmission loss, the contribution of the tangent of the dielectric loss angle (tanδ) is relatively large. Therefore, a lower tangent of the dielectric loss angle is required.

[0080] Through the heat treatment of the present invention, the tangent of the dielectric loss angle can be at the original level of the quartz powder, that is, 0.0005 or less. More preferably, it is 0.0004 or less, and further preferably, it is 0.0002 or less.

[0081] Since there may be silica powder partially fused due to the treatment temperature in the silica powder obtained by heat treatment, after pulverization using a pulverizing device such as a ball mill, the coarse particles or agglomerated particles larger than 100 μm are removed by a sieve and then used. The removal of the above-mentioned coarse particles can be carried out using a 150-mesh sieve.

[0082] However, since treatment at high temperature tends to form a strain layer on the surface of the silica powder, the strength of the cured product of the resin composition filled with such silica powder is likely to decrease. Regarding the removal of the strain layer on the surface of the silica powder, the strain layer can be easily removed by immersion in an etching solution or the like.

[0083] As the etching solution, acidic aqueous solutions such as hydrofluoric acid aqueous solution, and basic aqueous solutions selected from ammonium fluoride aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, ammonia water, basic electrolyzed water, etc. can be used. As the acidic aqueous solution, acidic ammonium fluoride (NH4F·HF) aqueous solution, acidic potassium fluoride (KHF2) aqueous solution can also be used. From the viewpoints of the working environment or wastewater treatment, a basic aqueous solution is more preferable, and among them, basic electrolyzed water is more preferable.

[0084] Regarding the etching treatment conditions of the silica powder after heat treatment, the temperature is preferably room temperature (23°C) to 100°C, and more preferably 40°C to 80°C. Since the treatment time depends on the etching rate on the silica surface according to the treatment temperature (for example, room temperature to 90°C, preferably 40°C to 80°C), there is no particular limitation. The lower the temperature of the etching solution, the less etching can be carried out, and the higher the temperature, the faster the etching rate. However, for practicality, a temperature at which the treatment can be completed within a treatment time of 10 minutes or more to 168 hours is preferred. The treatment time is preferably 1 hour to 72 hours, and more preferably 10 hours to 24 hours. In addition, the treatment can be carried out within the above temperature and time ranges even under atmospheric pressure or in a pressurized atmosphere.

[0085] As long as the strain layer can be removed, there is no particular limitation on the pH value of the etching solution, and it can be adjusted by adding an acid or a base as needed.

[0086] As an alkaline solution, as long as the pH value is 8.0 or higher, the etching effect of the silica powder is sufficient, and the adhesion improvement between the resin and the surface of the etched silica powder can be confirmed. The pH value is preferably 10.0 to 13.5, and more preferably 11.0 to 13.0.

[0087] As the alkaline etching solution, an alkaline aqueous solution with a pH value of 11 or higher is preferably used, and alkaline electrolyzed water with a pH value of 12 or higher is more preferably used.

[0088] In addition, in powders with insufficient crushing or spheroidization, sharp edges on the powder surface, etc. will be reduced by etching, so it is effective for high filling or reduction of local stress.

[0089] After the etching is completed, the silica powder is separated by means such as filtration, and further washed repeatedly with ion-exchanged water or pure water until the washing water becomes neutral. After washing, the silica powder is separated by filtration or centrifugation, etc., and dried at a temperature of 100°C to 200°C to remove moisture. Usually, since the silica powder will aggregate due to the drying of moisture, a pulverizing device such as a ball mill is used for pulverization. When the aggregation caused by drying is strong, it can be washed with an alcohol such as methanol after washing with ion-exchanged water, and the silica powder is separated by filtration or centrifugation, etc. and then dried to prevent aggregation.

[0090] For the low dielectric silica powder obtained in this way, after removing coarse particles or aggregated particles larger than 100 μm using a sieve (for example, a 150-mesh sieve), it is used.

[0091] The coupling agent treatment is an optional process, which is a process of treating the surface of the silica powder with a coupling agent or the like. The coupling agent is not particularly limited, and a silane coupling agent is preferred.

[0092] The reason is that when preparing a resin composition or the like by covering the surface of the low dielectric silica powder that has been subjected to high-temperature treatment and etching treatment with a silane coupling agent after washing and drying, the surface treatment with the silane coupling agent makes the adhesion between the resin and the surface of the low dielectric silica powder firm.

[0093] As the silane coupling agent, known silane coupling agents can be used, but alkoxysilanes are preferred, and more preferably one or more selected from the group consisting of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, and trifluoropropyltrimethoxysilane.

[0094] Regarding the concentration of the above-mentioned silane coupling agent, it is usually used in the form of a dilute solution between 0.1% by mass and 5% by mass, and is particularly effective when used between 0.1% by mass and 1% by mass. Thereby, the above-mentioned silane coupling agent adheres uniformly, bringing a more uniform protective effect to the surface of the silica powder and being easy to handle. In addition, it can also be uniformly and without deviation incorporated into the resin used when manufacturing substrates and the like.

[0095] The silica powder after the above-mentioned low dielectric loss tangent treatment can be incorporated as a filler into thermosetting resins or thermoplastic resins such as epoxy resins, silicone resins, polyimide resins, Teflon (registered trademark) resins, maleimide resins, and polyphenylene ether resins.

[0096] The resin composition containing low dielectric silica powder as a mixture of the above-mentioned low dielectric silica powder and resin can provide a cured product with a very small dielectric loss tangent. In particular, by incorporating the silica powder subjected to etching treatment (etched silica powder), the strain on the surface of the silica powder is removed and high strength is achieved, and the adhesion strength between the resin and the silica powder can be further improved.

[0097] The low dielectric silica powder obtained in the above manner is a useful material for sealing materials for high-speed communication semiconductor devices and the like, or fillers for low dielectric organic substrates such as servers or antennas, etc., which are expected to have great development in the future.

[0098] Examples

[0099] Hereinafter, examples and comparative examples will be given to specifically illustrate the present invention, but the present invention is not limited thereto.

[0100] In addition, in this specification, the values of the dielectric loss tangent and the hydroxyl content of the silica powder prepared in the examples or comparative examples are the values obtained by the following methods.

[0101] <Method for measuring dielectric loss tangent>

[0102] Taking silica powder A1 (untreated product of RS8225) as an example, the method for measuring the dielectric loss tangent will be described.

[0103] Mix, disperse, and dissolve the silica powder in anisole solvent containing SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a low dielectric maleimide resin and dicumyl peroxide (PERCUMYL D: manufactured by NOF CORPORATION) as a curing agent and a free radical polymerization initiator in the proportion shown in Table 1 below to prepare a varnish.

[0104] Silica powder was added to the resin so that it was 0%, 11.1%, 33.3%, and 66.7% by volume. It was extended to a thickness of 200 mm using a bar coater and placed in a dryer at 80°C for 30 minutes to remove the anisole solvent, thereby preparing an uncured maleimide resin composition.

[0105] [Table 1]

[0106]

[0107] The prepared uncured maleimide resin composition was placed in a mold of 60 mm × 60 mm × 100 μm, cured at 180°C, 10 minutes, and 30 MPa using a hand press, and then completely cured at 180°C for 1 hour using a dryer to produce a resin cured sheet. The resin cured sheet was cut into a size of 50 mm × 50 mm, and the split post dielectric resonators (SPDR) for dielectric constant measurement were used to separate the dielectric resonator frequency of 10 GHz (manufactured by Keysight Technologies Co., Ltd.) to measure the tangent of the dielectric loss angle at 10 GHz.

[0108] Regarding the obtained values of the tangent of the dielectric loss angle, as Figure 1 shown, a graph was obtained with the volume % of silica powder as the horizontal axis and the measured tangent of the dielectric loss angle as the vertical axis, and a straight line of volume % of silica powder vs. tangent of the dielectric loss angle was plotted based on this graph. This straight line was extrapolated, and the tangent of the dielectric loss angle of 100% silica powder was taken as the value of the tangent of the dielectric loss angle of silica powder.

[0109] Although there are measuring instruments capable of directly measuring silica powder, since the measurement is carried out by filling silica powder in a pot, it is difficult to remove the air mixed in. Especially for silica powder with a relatively large specific surface area, it is more affected by the mixed air, so it is even more difficult. Therefore, in order to eliminate the influence of the mixed air and obtain a value in a state close to the actual use form, in the present invention, the tangent of the dielectric loss angle of silica powder is obtained by the above measurement method.

[0110] <Measurement method of hydroxyl group (Si-OH) content>

[0111] A sample was prepared by filling silica powder until it filled an aluminum pan with a thickness of 1.5 mm. For the infrared absorption spectrum of this sample, using a Fourier transform infrared spectrophotometer (IRAffinity-1S) and a diffuse reflection measurement device (DRS-8000A), the 3680 cm -1Transmittance T of the nearby peak. Based on the obtained transmittance values, the absorbance A is calculated by applying the Lambert-Beer law shown below.

[0112] · Absorbance A = -Log 10 T

[0113] T = 3680 cm -1 Nearby transmittance

[0114] Next, based on the absorbance calculated using the above formula, the molar concentration C (mol / L) of the hydroxyl group is calculated using the following formula.

[0115] · C = A / εL

[0116] ε: Molar extinction coefficient (molar extinction coefficient of the hydroxyl group ε = 77.5 dm 3 / mol·cm)

[0117] C: Molar concentration (mol / L)

[0118] L: Thickness of the sample (optical path length) (1.5 mm)

[0119] Based on the obtained absorbance A, the molar concentration C is calculated using the above formula.

[0120] Using the obtained molar concentration C, the content (ppm) of the hydroxyl group in the silica powder is calculated using the following formula.

[0121] · Content of the hydroxyl group (ppm) = {(C × M) / (d × 1000)} × 10 6

[0122] Specific gravity d of the silica powder = 2.2 g / cm 3

[0123] Molecular weight M of the hydroxyl group (Si-OH) = 45 g / mol

[0124] [Examples 1-4, Comparative Examples 1-3]

[0125] The resin composition was prepared in the following manner, and the dielectric loss tangent of the cured product of the obtained resin composition was measured. The results are shown in Tables 2 and 3.

[0126] (Example 1)

[0127] 5 kg of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.) with an average particle size of 15 μm, a dielectric loss tangent of 0.0006, and a hydroxyl content of 370 ppm was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900 °C for 5 hours, and then cooled to room temperature over 6 hours. The heat-treated silica powder was placed in a plastic container containing 20 liters of alkaline electrolyzed water (pH value of 13), heated to 60 °C while stirring for 2 hours to remove the strain layer on the particle surface. Then, the silica powder was separated using a centrifugal separator, washed with methanol, and dried. The dried silica powder was pulverized with a ball mill, and the silica powder LK-1 with coarse particles removed using a 150-mesh sieve had a reduced hydroxyl content of 270 ppm and a dielectric loss tangent of 0.0002.

[0128] (Example 2)

[0129] 5 kg of silica powder B (SO-E5 manufactured by Admatechs) with an average particle size of 1.5 μm, a dielectric loss tangent of 0.0011, and a hydroxyl content of 290 ppm was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900 °C for 12 hours, and then cooled to room temperature over 6 hours. The heat-treated silica powder was placed in a plastic container containing 20 liters of alkaline electrolyzed water (pH value of 13), heated to 60 °C while stirring for 2 hours to remove the strain layer on the particle surface. Then, the silica powder was separated using a centrifugal separator, washed with methanol, and dried to obtain silica powder LK-2. The dielectric loss tangent of this silica powder was 0.0003 and the hydroxyl content was 240 ppm.

[0130] (Example 3)

[0131] Using silica powder C (EMIX-100 manufactured by TATSUMORI LTD.) with an average particle size of 0.1 μm, a dielectric loss tangent of 0.0053, and a hydroxyl content of 475 ppm, 5 Kg of this silica powder C was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900 °C for 12 hours, and then cooled to room temperature over 6 hours. The heat-treated silica powder was placed in a plastic container containing 20 liters of alkaline electrolyzed water (pH value of 13), heated to 60 °C while stirring for 2 hours, thereby removing the strain layer on the particle surface. Then, the silica powder was separated using a centrifugal separator, washed with methanol, and dried to obtain silica powder LK-3. The dielectric loss tangent of this silica powder was 0.0004 and the hydroxyl content was 135 ppm.

[0132] (Example 4)

[0133] 5 Kg of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.) with an average particle size of 15 μm and a dielectric loss tangent of 0.0006 was placed in an alumina container and heat-treated in a muffle furnace (manufactured by AS ONE Corporation) at the temperatures, times, and atmospheres recorded in Table 3. After heating, it was cooled to room temperature over 6 hours to obtain silica powders LK-4, LK-5, LK-6, LK-7, and LK-8 (Examples 4-1 to 4-5). For each silica powder obtained by pulverizing the heat-treated silica powder with a ball mill and removing the coarse particles with a 150-mesh sieve, the dielectric loss tangent (10 GHz) and the hydroxyl content were measured and shown in Table 3.

[0134] (Comparative Example 1)

[0135] 5 Kg of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.) with an average particle size of 15 μm and a dielectric loss tangent of 0.0006 was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 400 °C for 12 hours, and then cooled to room temperature over 6 hours. The heat-treated silica powder was placed in a plastic container containing 20 liters of alkaline electrolyzed water (pH value of 13), heated to 60 °C while stirring for 2 hours, thereby removing the strain layer on the particle surface. Then, the silica powder was separated using a centrifugal separator, washed with methanol, and dried. The dried silica powder was pulverized with a ball mill and the coarse particles were removed with a 150-mesh sieve. The dielectric loss tangent of this silica powder was 0.0006, and no improvement in the dielectric loss tangent was observed. The hydroxyl content was 355 ppm.

[0136] (Comparative Example 2)

[0137] 5 kg of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.) with an average particle size of 15 μm and a dielectric loss tangent of 0.0006 was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 1600°C for 12 hours, and then cooled to room temperature over 6 hours. The silica powder after the heat treatment was partially fused and could not be pulverized.

[0138] (Comparative Example 3)

[0139] 5 kg of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.) with an average particle size of 15 μm and a dielectric loss tangent of 0.0006 was placed in an alumina container and heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900°C for 10 minutes, and then cooled to room temperature over 6 hours. The dielectric loss tangent of this silica powder was 0.0006, and no improvement in the dielectric loss tangent was observed. The hydroxyl group content was 365 ppm.

[0140] [Table 2]

[0141]

[0142] [Table 3]

[0143]

[0144] [Examples 5 - 7, Comparative Example 4]

[0145] A resin composition was prepared in the following manner, and the dielectric loss tangent of the cured product of the obtained resin composition was measured. The results are shown in Table 4.

[0146] (Example 5)

[0147] 65 parts by mass of cresol novolak type epoxy resin (EOCN1020, manufactured by Nippon Kayaku Co., Ltd.), 35 parts by mass of phenol novolak resin (H-4, manufactured by Gunei Chemical Industry Co., Ltd.), 400 parts by mass of LK-1 (heated + etched silica powder) of Example 1, 0.2 parts by mass of catalyst TPP (triphenylphosphine, manufactured by HOKKO CHEMICAL INDUSTRY CO., LTD.), and 0.5 parts by mass of silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) were thoroughly mixed, then heat-kneaded using a continuous kneading device, pelletized, and cooled. The pellets were crushed to form granular powder, and a thermosetting resin composition formed from epoxy resin was obtained.

[0148] Under the curing condition of 175 °C, the composition was subjected to transfer molding for 2 minutes to cure it. Further, it was post-cured at 180 °C for 2 hours to obtain a cured product. The cured product was broken and the interface between silica and resin on the fracture surface was observed ( Figure 2 ). As a result, since the resin and the silica powder were firmly bonded, no silica powder was observed on the fracture surface, and there were many fractures in the resin part. The dielectric loss tangent of the cured product was 0.004, which was good.

[0149] (Example 6)

[0150] 65 parts by mass of cresol novolak type epoxy resin (EOCN1020, manufactured by Nippon Kayaku Co., Ltd.), 35 parts by mass of phenol novolak resin (H-4, manufactured by Gunei Chemical Industry Co., Ltd.), 400 parts by mass of LK-6 (silica powder that was heat-treated but not etched) of Example 4, 0.2 parts by mass of catalyst TPP (triphenylphosphine, manufactured by HOKKO CHEMICAL INDUSTRY CO., LTD.), and 0.5 parts by mass of silane coupling agent (KBM403, manufactured by Shin-Etsu Chemical Co., Ltd.) were thoroughly mixed, then heat-kneaded using a continuous kneading device, pelletized, and cooled. The pellets were crushed to form granular powder, and a thermosetting resin composition formed from epoxy resin was obtained.

[0151] Under the curing condition of 175 °C, the composition was subjected to transfer molding for 2 minutes to cure it. Further, it was post-cured at 180 °C for 2 hours to obtain a cured product. The cured product was broken and the interface between the silica powder and resin on the fracture surface was observed ( Figure 3) As a result, there is no resin adhesion on the surface of the silica powder, and breakage occurs at the interface between the silica powder and the resin. The tangent of the dielectric loss angle of the cured product is 0.004, which is good.

[0152] (Example 7)

[0153] 100 parts by mass of SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.) of a low-dielectric maleimide resin, 400 parts by mass of LK-6 of Example 4, and 2 parts by mass of dicumyl peroxide (PERCUMYL D: manufactured by NOF CORPORATION), which is a curing agent and a radical polymerization initiator, were mixed in 150 parts by mass of anisole solvent, dispersed and dissolved therein to prepare a maleimide resin composition varnish. Then, it was spread to a thickness of 200 μm using a bar coater and placed in a dryer at 80 °C for 30 minutes to remove the anisole solvent, thereby preparing an uncured maleimide resin composition.

[0154] The prepared uncured maleimide resin composition was placed in a mold of 60 mm × 60 mm × 100 μm, cured using a manual press at 180 °C for 10 minutes under 30 MPa, and then completely cured at 180 °C for 1 hour using a dryer to produce a resin cured sheet. The tangent of the dielectric loss angle of the cured product was measured. The tangent of the dielectric loss angle of the cured product was 0.0007, which was better than that of the untreated silica powder A1 admixture.

[0155] (Comparative Example 4)

[0156] 65 parts by mass of a cresol novolac type epoxy resin (EOCN1020 manufactured by Nippon Kayaku Co., Ltd.), 35 parts by mass of a phenol novolac resin (H-4 manufactured by Gunei Chemical Industry Co., Ltd.), 400 parts by mass of silica powder A1 (unheated-treated silica powder: RS8225 manufactured by TATSUMORI LTD.), 0.2 parts by mass of a catalyst TPP (triphenylphosphine manufactured by HOKKO CHEMICAL INDUSTRY CO., LTD.), and 0.5 parts by mass of a silane coupling agent (KBM403 manufactured by Shin-Etsu Chemical Co., Ltd.) were thoroughly mixed using a high-speed mixing device, then heat-kneaded using a continuous kneading device, pelletized, and cooled. The pellet was pulverized to form a granular powder, and a thermosetting resin composition formed from an epoxy resin was obtained.

[0157] Under the curing condition of 175 °C, the composition was subjected to transfer molding for 2 minutes to cure it. Further, it was post-cured at 180 °C for 2 hours to obtain a cured product. The cured product was broken and the interface between silica and resin on the fracture surface was observed ( Figure 4 ), and as a result, cohesive failure of the resin occurred at the interface between silica and resin. The dielectric loss tangent of the cured product was 0.005, which was inferior to that of the present invention (Examples 5 and 6).

[0158] (Comparative Example 5)

[0159] 100 parts by mass of SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.), a low dielectric malimide resin, 400 parts by mass of silica powder A1 (RS8225 manufactured by TATSUMORI LTD.), and 2 parts by mass of dicumyl peroxide (PERCUMYL D: manufactured by NOF CORPORATION), a curing agent and a radical polymerization initiator, were mixed in 150 parts by mass of anisole solvent, dispersed and dissolved to prepare a malimide resin composition varnish. Then, it was spread to a thickness of 200 mm using a bar coater and placed in a dryer at 80 °C for 30 minutes to remove the anisole solvent, thereby preparing an uncured malimide resin composition.

[0160] The prepared uncured malimide resin composition was placed in a mold of 60 mm × 60 mm × 100 μm, cured at 180 °C, 10 minutes, and 30 MPa using a manual press, and then completely cured at 180 °C for 1 hour using a dryer to produce a resin cured sheet. The dielectric loss tangent of the cured product was measured using this resin cured sheet. The dielectric loss tangent of the cured product was 0.001, which was inferior to that of the present invention (Example 7).

[0161] [Table 4]

[0162]

[0163] The blending amounts of the respective components in the table are parts by mass.

[0164] As can be seen from Tables 2 and 3, the tangent of the dielectric loss angle (tanδ) of the silica powder of the present invention (Examples 1-3, 1-5 of Example 4) is significantly reduced compared with the untreated silica powder. On the other hand, improvement in the tangent of the dielectric loss angle was not observed when the heat treatment temperature was low (Comparative Example 1) or when the heat treatment was insufficient (short treatment time) (Comparative Example 3). In addition, if the heat treatment temperature is too high, partial fusion and inability to be pulverized occur (Comparative Example 2). Whether the atmosphere of the heat treatment is air or nitrogen, the tangent of the dielectric loss angle is improved, but if high-temperature treatment is carried out in a nitrogen atmosphere, there is a tendency for the amount of hydroxyl groups in the powder to further decrease (4, 5 of Example 4). Thus, by subjecting the silica powder to a suitable heat treatment, a silica powder with a desired low tangent of the dielectric loss angle can be obtained.

[0165] As can be seen from the results of Example 1 (LK-1) and 3 of Example 4 (LK-6), the tangent of the dielectric loss angle and the amount of hydroxyl groups of the powder hardly changed before and after the etching treatment. On the other hand, when the cured product of the composition obtained by blending each powder into the resin was broken and the fracture surface was observed, in the former (Example 5), since the resin and the silica powder were firmly bonded, more fractures than the resin part were observed, while in the latter (Example 6), fractures occurred at the interface between the silica powder and the resin. From this, it can be known that the etching treatment hardly affects the tangent of the dielectric loss angle of the powder after heat treatment and has the effect of improving the adhesion strength with the resin.

[0166] Moreover, as can be seen from Examples 6 and 7, by using a resin composition in which the low-dielectric silica powder of the present invention is blended in a low-dielectric resin, the tangent of the dielectric loss angle of the cured product can be easily reduced.

[0167] In addition, by observing the results of Example 6 and Comparative Example 4, and Example 7 and Comparative Example 5: by using a resin composition blended with heat-treated low-dielectric silica particles, the tangent of the dielectric loss angle of the cured product can be easily reduced.

[0168] It has been known that low-silanol silica can be obtained by heat treatment, but it is considered that if the silica powder is treated at a high temperature, a strain layer will be formed on the surface, and the strength of the cured product of the resin composition filled with the heat-treated silica powder will decrease. Therefore, heat-treated silica powder that can be used as a filler crucial for the adhesion strength with the resin has not been actually used.

[0169] However, according to the research of the inventors of the present application, it was first discovered that even when the resin composition obtained by blending heat-treated silica particles into the resin is cured, it has sufficient strength. Moreover, it was also discovered that the dielectric loss tangent of the cured product can be easily reduced by heat treatment. Further, according to the further research of the inventors of the present application, it was first discovered that by immersing in the etching solution as described above, the strain layer on the surface of the silica powder can be easily removed. By combining heat treatment and etching treatment, the selection range of the raw material silica powder becomes wider, which helps to reduce costs. At the same time, silica powder (etched silica powder) with a low dielectric loss tangent and good adhesion to the resin can be efficiently prepared. Thus, since the method for preparing low-dielectric silica of the present invention can prepare silica powder with a low dielectric loss tangent and strong adhesion at the interface with the resin at a high productivity, it has high industrial utilization value.

[0170] In addition, the present invention is not limited to the above-described embodiments. The above-described embodiments are illustrative, and technical solutions having substantially the same constitution as the technical concept described in the claims of the present invention and achieving the same effects are all included in the protection scope of the present invention.

Claims

1. A low-dielectric silica powder, characterized in that, Its average particle size is 0.1 to 30 μm, the tangent of the dielectric loss angle at 10 GHz is 0.0005 or less, and the Si-OH content attributable to internal silanols in the low-dielectric silica powder is 300 ppm or less.

2. The low-dielectric silica powder according to claim 1, characterized in that, Inside and on the surface of the low-dielectric silica powder, metals selected from aluminum, magnesium, and titanium and / or their oxides are each 200 ppm or less in terms of the mass of the metal, and alkali metals and alkaline earth metals are each 10 ppm or less in terms of mass.

3. The low-dielectric silica powder according to claim 1, wherein The content of boron is 1 ppm or less, the content of phosphorus is 1 ppm or less, and the contents of uranium and thorium are each 0.1 ppb or less.

4. The low-dielectric silica powder according to claim 2, wherein The content of boron is 1 ppm or less, the content of phosphorus is 1 ppm or less, and the contents of uranium and thorium are each 0.1 ppb or less.

5. The low-dielectric silica powder according to any one of claims 1 to 4, characterized in that The maximum particle size of the low-dielectric silica powder is 100 μm or less.

6. A resin composition containing low-dielectric silica powder, characterized in that, It is a mixture of the low-dielectric silica powder according to any one of claims 1 to 5 and a resin.

7. A method for preparing a low-dielectric silica powder, which is the method for preparing the low-dielectric silica powder according to claim 1, characterized in that the silica powder is heat-treated at a temperature of 500°C to 1500°C so that the tangent of the dielectric loss angle of the silica powder at 10 GHz is 0.0005 or less, and then the surface of the heat-treated silica powder is etched with an etching solution.

8. The preparation method of the low-dielectric silica powder according to claim 7, characterized in that, The heat treatment is carried out for 30 minutes to 72 hours.

9. The preparation method of the low-dielectric silica powder according to claim 7, characterized in that, As the etching solution, an aqueous solution selected from hydrofluoric acid aqueous solution, ammonium fluoride aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, ammonia water, and alkaline electrolyzed water is used.

10. The preparation method of the low-dielectric silica powder according to claim 8, characterized in that, As the etching solution, an aqueous solution selected from hydrofluoric acid aqueous solution, ammonium fluoride aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, ammonia water, and alkaline electrolyzed water is used.

11. The preparation method of the low-dielectric silica powder according to claim 7, characterized in that, As the etching solution, an alkaline aqueous solution with a pH value of 11 or more is used.

12. The method for preparing the low-dielectric silica powder according to claim 8, wherein As the etching solution, an alkaline aqueous solution with a pH value of 11 or more is used.

13. The preparation method of the low-dielectric silica powder according to claim 9, characterized in that, As the etching solution, an alkaline aqueous solution with a pH value of 11 or more is used.

14. The preparation method of the low-dielectric silica powder according to claim 10, characterized in that, As the etching solution, an alkaline aqueous solution with a pH value of 11 or more is used.

15. The preparation method of the low-dielectric silica powder according to any one of claims 11 to 14, characterized in that As the alkaline aqueous solution, alkaline electrolyzed water with a pH value of 12 or more is used.

16. The preparation method of the low-dielectric silica powder according to any one of claims 7 to 14, characterized in that, The surface of the silica powder after the etching treatment is further subjected to a coupling agent treatment.

17. The preparation method of the low-dielectric silica powder according to claim 15, characterized in that, The surface of the silica powder after the etching treatment is further subjected to a coupling agent treatment.

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