Ceramic substrate and ceramic green sheet

Abstract

A ceramic substrate according to the present disclosure comprises an insulating layer. The insulating layer contains hollow inorganic particles. The median diameter d50 of the hollow inorganic particles is 0.1 to 10 μm. The percentage of hollow inorganic particles contained in the total insulating layer is 5 to 70 vol%.

Description

Ceramic substrates and ceramic green sheets

[0001] The present disclosure relates to a ceramic substrate and a ceramic green sheet.

[0002] Ceramic substrates have advantages over resin substrates, such as superior heat resistance, heat dissipation, and moisture resistance, and no outgassing, and are used in high-frequency applications such as telecommunications, automobiles, and military applications including radar. However, ceramic substrates tend to have higher dielectric constants than resin substrates. Therefore, ceramic substrates have been disclosed in which hollow inorganic particles, such as hollow silica particles, are dispersed in a ceramic raw material matrix in order to lower the dielectric constant of the ceramic substrate (e.g., Patent Documents 1 and 2).

[0003] JP-A-59-111345 JP-A-5-243423

[0004] Since hollow inorganic particles have a lower dielectric constant than solid inorganic particles, adding hollow inorganic particles to the insulating layer of a ceramic substrate makes it easier to obtain an insulating layer with a low dielectric constant. However, adding hollow inorganic particles to lower the dielectric constant may reduce the bending strength of the insulating layer. Furthermore, depending on the hollow inorganic particles added, adding them to the insulating layer may not significantly reduce the dielectric constant.

[0005] An object of one embodiment of the present disclosure is to provide a ceramic substrate having an insulating layer that has both a low dielectric constant and high bending strength. Another object of one embodiment of the present disclosure is to provide a ceramic green sheet from which a ceramic substrate having an insulating layer that has both a low dielectric constant and high bending strength can be obtained.

[0006] Means for solving the above problems include the following aspects: <1> A ceramic substrate including an insulating layer, wherein the insulating layer contains hollow inorganic particles, the hollow inorganic particles have a median diameter d50 of 0.1 to 10 μm, and the content of the hollow inorganic particles in the entire insulating layer is 5 to 70 volume %. <2> The density of the hollow inorganic particles determined by a constant volume expansion method is 0.35 to 2.00 g / cm ３<3> The ceramic substrate according to <1> or <2>, wherein the hollow inorganic particles have a 20% breakdown pressure of 120 MPa or more as measured by mercury intrusion porosimetry. <4> The ceramic substrate according to <1> or <2>, wherein the 20% breakdown pressure of the hollow inorganic particles is 120 MPa or more as measured by mercury intrusion porosimetry. ２ The ceramic substrate according to any one of <1> to <3>, wherein the content of the hollow inorganic particles is 99% by mass or more. <5> The ceramic substrate according to any one of <1> to <4>, wherein the hollow inorganic particles are treated with a coupling agent. <6> The ceramic substrate according to any one of <1> to <5>, wherein the insulating layer further contains glass and alumina particles other than the hollow inorganic particles. <7> The ceramic substrate according to any one of <1> to <6>, wherein the insulating layer has a relative dielectric constant of 5.5 or less at a frequency of 10 GHz. <8> The ceramic substrate according to any one of <1> to <7>, wherein the ceramic substrate is a low-temperature fired ceramic substrate. <9> A ceramic green sheet containing hollow inorganic particles, wherein the hollow inorganic particles have a median diameter d50 of 0.1 to 10 μm, and the content of the hollow inorganic particles relative to the entire ceramic green sheet is 5 to 70% by volume. <10> The density of the hollow inorganic particles determined by a constant volume expansion method is 0.35 to 2.00 g / cm ３ <11> The ceramic green sheet according to <9> or <10>, wherein the hollow inorganic particles have a 20% burst pressure of 120 MPa or more as measured by mercury intrusion porosimetry. <12> The ceramic green sheet according to <9> or <10>, wherein the 20% burst pressure of the hollow inorganic particles is 120 MPa or more as measured by mercury intrusion porosimetry. <13> The ceramic green sheet according to <9> or <10>, wherein the 20% burst pressure of the hollow inorganic particles is 120 MPa or more as measured by mercury intrusion porosimetry. ２<13> The ceramic green sheet according to any one of <9> to <12>, wherein the hollow inorganic particles are treated with a coupling agent. <14> The ceramic green sheet according to any one of <9> to <13>, further containing glass and alumina particles other than the hollow inorganic particles. <15> The ceramic green sheet according to any one of <9> to <14>, further containing a resin. <16> The ceramic green sheet according to any one of <9> to <15>, which is for a low-temperature fired ceramic substrate.

[0007] According to one embodiment of the present disclosure, there is provided a ceramic substrate having an insulating layer that has both a low dielectric constant and high bending strength. Also, according to one embodiment of the present disclosure, there is provided a ceramic green sheet from which a ceramic substrate having an insulating layer that has both a low dielectric constant and high bending strength can be obtained.

[0008] Hereinafter, modes for carrying out embodiments of the present disclosure will be described in detail. However, the embodiments of the present disclosure are not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the embodiments of the present disclosure.

[0009] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be contained. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, "hollow inorganic particles" refers to a group of multiple hollow inorganic particles, unless otherwise specified. In the present disclosure, "sphericity" refers to the average value of the ratio (DS / DL) of the minimum diameter (DS) to the maximum diameter (DL) calculated by measuring the maximum diameter (DL) and the minor diameter (DS) perpendicular to the maximum diameter (DL) of each of 100 particles in a photographic projection obtained by photographing with a scanning electron microscope (SEM).

[0010] [Ceramic Substrate] A ceramic substrate according to one embodiment of the present disclosure is a ceramic substrate including an insulating layer. The insulating layer contains hollow inorganic particles, the hollow inorganic particles having a median diameter d50 of 0.1 to 10 μm, and the hollow inorganic particles are present at a volumetric content of 5 to 70% of the entire insulating layer. Hereinafter, hollow inorganic particles having a median diameter d50 of 0.1 to 10 μm are also referred to as "specific hollow particles." Ceramic substrates generally offer advantages over resin substrates, such as superior heat resistance, heat dissipation, and moisture resistance, and the absence of outgassing. They are therefore used in high-frequency applications such as telecommunications, automobiles, and military applications, including radar. Therefore, ceramic substrates are required to have a low dielectric constant and high strength. In the ceramic substrate according to this embodiment, the specific hollow particles are incorporated into the insulating layer at the above-mentioned content, thereby achieving both a low dielectric constant and high bending strength in the insulating layer. The reason for this is presumed to be as follows.

[0011] Compared to insulating layers containing hollow inorganic particles with a median diameter d50 greater than the above range (hereinafter also referred to as "large-diameter hollow particles"), insulating layers containing specific hollow particles are less susceptible to a decrease in insulating layer strength due to cracking caused by hollow particles, reducing the impact of hollow inorganic particles on insulating layer strength and increasing bending strength. Furthermore, specific hollow particles are less susceptible to cracking and crushing than large-diameter hollow particles. When hollow inorganic particles crack or crush within the insulating layer, the volume of the voids decreases, resulting in a state similar to that of solid inorganic particles, thereby increasing the dielectric constant of the entire insulating layer. Therefore, it is presumed that insulating layers containing specific hollow particles suppress the increase in dielectric constant due to crushing of hollow inorganic particles compared to insulating layers containing large-diameter hollow particles, resulting in a low dielectric constant. Additionally, in this embodiment, the specific hollow particles are contained in the insulating layer at a content of 5 to 70 volume% of the entire insulating layer. Therefore, when the content is equal to or greater than the lower limit, the specific hollow particles can reduce the dielectric constant of the insulating layer, while when the content is equal to or less than the upper limit, the specific hollow particles can prevent a decrease in the bending strength of the insulating layer. For these reasons, it is presumed that the present embodiment can achieve both a low dielectric constant and high bending strength in the insulating layer.

[0012] The ceramic substrate according to this embodiment may include at least an insulating layer, and may be a single-layer substrate of an insulating layer, or a multilayer substrate including layers other than the insulating layer. The layer other than the insulating layer is not particularly limited, and examples thereof include a wiring layer including wiring made of a conductor. Here, the insulating layer is a layer having insulating properties. Furthermore, the term "insulating" refers to a layer having a volume resistivity of 1.0×10 in a normal state. ６ The volume resistivity is a value measured as follows. Specifically, a test piece is prepared in accordance with JIS C 6481:1996, and the resistance between circuits is measured in a normal state (specifically, after leaving the test piece to stand in air at a constant temperature and humidity of 20°C and a relative humidity of 65% for 96 hours).

[0013] The ceramic substrate according to this embodiment is preferably a low-temperature fired ceramic substrate. The ceramic substrate can be obtained, for example, by forming a ceramic-containing composition into a sheet, drying the resulting ceramic green sheet, and laminating it with other sheets as needed. The low-temperature fired ceramic substrate is a fired body obtained by firing the ceramic green sheet at a relatively low temperature (e.g., 1000°C or less). By firing the ceramic green sheet at a low temperature, even when the wiring layer and the insulating layer are co-fired, low-resistance conductors such as silver and copper can be used as the conductor material for the wiring layer, resulting in a low-temperature co-fired ceramic substrate (i.e., LTCC) with low resistance loss. The firing temperature is, for example, 1000°C or less. From the viewpoint of expanding the selection of conductors that can be used and enabling the production of a ceramic substrate with low resistance loss, 1000°C or less is preferred, 950°C or less is more preferred, and 900°C or less is even more preferred. The insulating layer of the ceramic substrate according to this embodiment will now be described.

[0014] <Insulating Layer> The insulating layer contains at least specific hollow particles and may contain other components as necessary. Examples of other components include inorganic particles other than hollow inorganic particles (hereinafter also referred to as "solid inorganic particles"), glass, ceria, zirconia, titania, yttria, etc. In particular, among ceramic substrates, the insulating layer of a low-temperature fired ceramic substrate preferably contains glass as another component. The inclusion of glass facilitates firing at low temperatures. Furthermore, the insulating layer more preferably contains solid inorganic particles in addition to glass as another component from the viewpoint of improving bending strength, and even more preferably contains glass and alumina particles, which are solid inorganic particles, from the viewpoint of improving bending strength and ease of processing. When the insulating layer contains glass and solid inorganic particles as other components, the total content of the specific hollow particles, glass, and solid inorganic particles is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may even be 100% by mass, based on the entire insulating layer. Hereinafter, an insulating layer containing specific hollow particles, glass, and solid inorganic particles will be described as an example of an insulating layer contained in a ceramic substrate.

[0015] (Specific Hollow Particles) The insulating layer contains hollow inorganic particles having a median diameter d50 of 0.1 to 10 μm, i.e., specific hollow particles. The insulating layer may contain only one type of specific hollow particle, or two or more types. Here, hollow inorganic particles refer to particles having a shell layer containing an inorganic component and having a space inside the shell layer. The space can be confirmed by observation with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like. In the present disclosure, "having a space inside the shell layer" means that, when a cross section of a single hollow inorganic particle is observed, a hollow state exists in which the shell layer surrounds a single space. The shell layer may have a single-layer structure or a multi-layer structure of two or more layers.

[0016] The inorganic components contained in the shell layer of the specific hollow particles include SiO ２ , Al ２ O ３ , B ２ O ３, CaO, MgO, Na ２ O.K. ２ O, Li ２ The shell layer of the specific hollow particles contains SiO as an inorganic component from the viewpoint of realizing a low dielectric constant of the specific hollow particles and a high bending strength of the insulating layer. ２ It is preferable that the inorganic component contains SiO ２ Examples of hollow inorganic particles containing SiO include hollow silica particles and hollow aluminosilicate particles. ２ The content of SiO is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and extremely preferably 99% by mass or more. The upper limit of the content is 100% by mass, but may be 99.99% by mass. In other words, the SiO content relative to the total amount of the specific hollow particles is ２ From the viewpoint of realizing a low dielectric constant of the specific hollow particles, the content of SiO is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and extremely preferably 99% by mass or more. ２ The content may be 100% by mass or less, or may be 99.99% by mass or less.

[0017] In particular, when the insulating layer further contains glass, the SiO ２ The content of SiO relative to the total amount of the specific hollow particles is preferably 99% by mass or more. ２ When the content of SiO is within the above range, the eutectic formation of the glass frit and the specific hollow particles due to the influence of the low-melting-point component from the glass frit is suppressed in the process of forming the insulating layer, and the hollow structure of the specific hollow particles is easily maintained. ２ The content of the SiO in the shell layer is preferably 99% by mass or more, more preferably 99.9% by mass or more, and even more preferably 99.95% by mass or more. ２The content of is measured by ICP atomic emission spectrometry, flame atomic absorption spectrometry, etc. Specifically, perchloric acid and hydrofluoric acid are added to the specific hollow particles, and the mixture is ignited to remove the silicon, which is the main component, and then the content is measured by ICP-AES (inductively coupled plasma atomic emission spectrometry) using an ICPE-9000 (manufactured by Shimadzu Corporation).

[0018] The average thickness of the shell layer of the specific hollow particles is preferably 0.01 to 0.3, where the diameter of the primary particles of the specific hollow particles is 1. When the average thickness of the shell layer is equal to or greater than the above lower limit when the diameter of the primary particles is 1, the strength of the specific hollow particles is improved. From this perspective, when the diameter of the primary particles is 1, the average thickness of the shell layer is more preferably 0.02 or greater, and even more preferably 0.03 or greater. When the diameter of the primary particles is 1, the average thickness of the shell layer is equal to or less than the above upper limit, making it easier to obtain properties due to the hollow shape, such as improved dielectric properties. From this perspective, when the diameter of the primary particles is 1, the average thickness of the shell layer is more preferably 0.2 or less, and even more preferably 0.1 or less. The average thickness of the shell layer is the average value of the shell layer thicknesses of 20 hollow inorganic particles measured by TEM observation.

[0019] As described above, the median diameter d50 of the specific hollow particles is 0.1 to 10 μm. When the median diameter d50 of the specific hollow particles is equal to or less than the upper limit, the insulating layer can have high bending strength and a low dielectric constant. Furthermore, the improved smoothness of the insulating layer also improves adhesion to wiring and the like. From these viewpoints, the median diameter d50 of the specific hollow particles is preferably 6 μm or less, more preferably 3 μm or less, even more preferably 2.5 μm or less, particularly preferably 2 μm or less, and extremely preferably 1 μm or less. When the median diameter d50 of the specific hollow particles is equal to or greater than the lower limit, an increase in the dielectric loss tangent due to moisture absorption is less likely to occur. From this viewpoint, the median diameter d50 of the specific hollow particles is preferably 0.2 μm or more, more preferably 0.3 μm or more. The median diameter d50 of the specific hollow particles is 0.1 to 10 μm, preferably 0.1 to 6 μm, more preferably 0.1 to 3 μm, even more preferably 0.1 to 2.5 μm, particularly preferably 0.2 to 2 μm, and extremely preferably 0.3 to 2 μm. The median diameter d50 of hollow inorganic particles such as specific hollow particles is the volume-based cumulative 50% diameter of the hollow inorganic particles determined using a laser diffraction particle size distribution analyzer (e.g., the "MT3300EXIIJ" manufactured by Microtrac-Bell Corporation). That is, the particle size distribution is measured using a laser diffraction / scattering method, a cumulative curve is determined with the total volume of the hollow inorganic particles set to 100%, and the particle diameter is the point on the cumulative curve where the cumulative volume is 50%. Note that in the present disclosure, the median diameter d50 of the hollow inorganic particles is measured in a state including primary particles and secondary particles.

[0020] The average primary particle diameter of the specific hollow particles is preferably 10 nm to 10 μm, more preferably 20 nm to 7 μm, even more preferably 50 nm to 5 μm, particularly preferably 70 nm to 3 μm, and most preferably 100 nm to 2.5 μm. The average primary particle size of hollow inorganic particles such as specific hollow particles is determined by directly observing the particle diameter (diameter, or the average of the long and short sides if the particle is not spherical) using SEM observation. Specifically, the primary particle sizes of 100 hollow inorganic particles are measured using SEM images, and the value at which the cumulative distribution of the primary particle sizes obtained by averaging these is 50% is estimated to be the average primary particle diameter of all primary particles.

[0021] The BET specific surface area of ​​the specific hollow particles is 1.0 to 100.0 m ２ The BET specific surface area of ​​the hollow inorganic particles is preferably 1.0 m / g. ２ On the other hand, by having the BET specific surface area be equal to or less than the upper limit, the resolution by exposure is improved. From this viewpoint, the BET specific surface area is set to be 50 m ２ / g or less is more preferable, and 20m ２ / g or less is more preferable, and 15m ２ The BET specific surface area can be measured by a multipoint method using nitrogen gas after pre-treatment, such as drying the hollow inorganic particles at 230°C to 50 mTorr, using a specific surface area measuring device (for example, "Tristar II3020" manufactured by Shimadzu Corporation).

[0022] From the viewpoint of further reducing the dielectric constant, the density of the specific hollow particles determined by a constant volume expansion method using Ar gas and a dry pycnometer is 0.35 to 2.00 g / cm ３ is preferably 0.35 to 1.50 g / cm ３ More preferably, 0.40 to 1.00 g / cm ３ When the insulating layer contains two or more types of specific hollow particles, the density of the specific hollow particles is determined by calculating a weighted average of the densities of the individual specific hollow particles. As the dry pycnometer, an AccuPycII 1340 manufactured by Micromeritics or an equivalent device can be used.

[0023] From the viewpoint of further reducing the relative dielectric constant, the porosity of the specific hollow particles is preferably 30 to 90%, more preferably 40 to 90%, and even more preferably 50 to 85%. The porosity of the specific hollow particles is calculated by dividing the density of the specific hollow particles by the true density of the specific hollow particles and multiplying the result by 100. The true density of the specific hollow particles can be measured using He gas with a Micromeritics AccuPycII 1340 or an equivalent device.

[0024] The shape of each specific hollow particle contained in the specific hollow particles is not particularly limited and may be spherical or non-spherical. From the viewpoint of the fluidity of the composition, the shape of each specific hollow particle is preferably spherical. From the viewpoint of the fluidity of the composition, the sphericity of the specific hollow particles is preferably 0.75 or more, more preferably 0.90 or more, even more preferably 0.93 or more, and particularly preferably 1.00. Furthermore, from the viewpoint of improving the bending strength of the insulating layer, the specific hollow particles are preferably non-porous particles.

[0025] The 20% breakdown pressure of the specific hollow particles measured by mercury porosimetry is preferably 120 MPa or more, more preferably 150 MPa or more, more preferably 200 MPa or more, and even more preferably 250 MPa or more, from the viewpoint of improving the bending strength of the insulating layer. Hereinafter, the 20% breakdown pressure measured by mercury porosimetry will also be simply referred to as "breakdown pressure." The upper limit of the breakdown pressure of the specific hollow particles is not particularly limited, and the breakdown pressure can be, for example, 600 MPa or less. Herein, the breakdown pressure refers to the breakdown pressure measured by mercury porosimetry, and is the minimum pressure that shows a 20% decrease in capacity from the maximum integrated capacity when pressure is applied from 0 to 400 MPa by mercury porosimetry. The burst pressure of the specific hollow particles is measured in accordance with ASTM D 3102-78 using a mercury intrusion porosimeter (e.g., AutoPore IV 9500 manufactured by MICROMERITICS INSTRUMENT Co., Ltd.) Examples of methods for controlling the burst pressure of the specific hollow particles include a method in which the shell layer described below is made dense by incorporating at least one element selected from the group consisting of alkali metals and alkaline earth metals into the shell layer, and then the burst pressure is controlled by adjusting the average thickness and median diameter d50 of the shell layer.

[0026] The specific hollow particles may contain at least one element selected from the group consisting of alkali metals belonging to Group 1 of the periodic table and alkaline earth metals belonging to Group 2 of the periodic table. Among alkali metals and alkaline earth metals, the specific hollow particles preferably contain one or more metals M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. The inclusion of metal M in the specific hollow particles acts as a flux during firing, reducing the specific surface area and the dielectric loss tangent. From the standpoint of ease of availability, the specific hollow particles preferably contain one or more metals M selected from the group consisting of Na, K, Mg, Ca, and Sr, more preferably one or more metals selected from the group consisting of Na, Mg, and Ca, and even more preferably Na.

[0027] In the production of the specific hollow particles, the metal M is incorporated between the reaction step and the washing step. For example, when the specific hollow particles are hollow silica particles, the metal M can be incorporated into the hollow silica particles by adding a metal salt of the metal M to a reaction solution used in forming a silica shell layer in the reaction step of the hollow silica particle production process, or by washing the hollow silica precursor with a solution containing metal ions of the metal M before sintering.

[0028] When the specific hollow particles are hollow silica particles, the concentration of metal M contained in the hollow silica particles is preferably 5 mass ppm or more and 1 mass % or less. If the total concentration of metal M is 5 mass ppm or more, the flux effect during firing promotes condensation of bonded silanol groups, reducing the remaining silanol groups and thereby reducing the dielectric loss tangent. If the concentration of metal M is too high, the amount of components that react with silica to form silicate increases, which may worsen the hygroscopicity of the hollow silica particles, so it is preferable to contain it at 1 mass % or less. The concentration of metal M is more preferably 5 mass ppm or more, even more preferably 10 mass ppm or more, and preferably 1 mass % or less, more preferably 500 mass ppm or less, and most preferably 300 mass ppm or less.

[0029] The sodium extraction amount of the specific hollow particles in water at 90°C is preferably 10 ppm by mass or less. Hereinafter, the sodium extraction amount in water at 90°C will also be simply referred to as the "sodium extraction amount." When the sodium extraction amount is equal to or less than the above upper limit, an insulating layer with high insulation properties can be obtained. From this viewpoint, the sodium extraction amount is more preferably 5 ppm by mass or less, and even more preferably 2 ppm by mass or less. From the viewpoint of obtaining a high breakdown pressure and a low electrostatic dissipation factor by making the shell layer dense, the sodium extraction amount is preferably 0.01 ppm by mass or more, and more preferably 0.02 ppm by mass or more.

[0030] The sodium extraction amount of the specific hollow particles is measured as follows. Specifically, the specific hollow particles to be measured are added to water in an amount 10 times the mass of the specific hollow particles, placed in a plastic container, sealed with a lid, and left in a thermostatic chamber at 90°C for 24 hours to obtain extracted water in which the sodium ions contained in the specific hollow particles have been extracted. The resulting extracted water is filtered, and the sodium ion concentration contained in the extracted water is determined using atomic absorption flame spectroscopy with the absolute calibration curve method. This is multiplied by 10, and the total value is multiplied by the specific gravity measured with an Ar pycnometer and divided by the true density measured with a He pycnometer to determine the sodium extraction amount of the specific hollow particles. For example, when the specific hollow particles are hollow silica particles, the sodium extraction amount of the specific hollow particles can be controlled by the composition of the silica source used in synthesizing the hollow silica particles, the method for washing the hollow silica particles, the method for washing the precursor of the hollow silica particles, etc. Examples of silica sources used in synthesizing hollow silica particles include alkoxysilanes such as tetramethoxysilane and tetraethoxysilane; sodium silicate; etc. The hollow silica particles and their precursors are preferably washed with an inorganic acid such as hydrochloric acid, sulfuric acid, or nitric acid; water; or the like.

[0031] From the viewpoint of obtaining an insulating layer with a low dielectric constant, the specific hollow particles preferably have a relative dielectric constant of less than 3.0 at a frequency of 1 GHz, more preferably 2.5 or less, and even more preferably 2.0 or less. The lower limit of the relative dielectric constant of the specific hollow particles at 1 GHz is not particularly limited. The specific hollow particles may have a relative dielectric constant of 1 GHz of 1.5 or more. The dielectric dissipation factor of the specific hollow particles is preferably 0.0001 to 0.05 at a frequency of 1 GHz. By having the dielectric dissipation factor at 1 GHz equal to or less than the above upper limit, an insulating layer with a low dielectric dissipation factor can be obtained. From this viewpoint, the dielectric dissipation factor at 1 GHz is more preferably 0.01 or less, even more preferably 0.005 or less, even more preferably 0.003 or less, and particularly preferably 0.002 or less. It is substantially difficult to synthesize hollow inorganic particles with a dielectric dissipation factor of less than 0.0001 at 1 GHz. The dielectric loss tangent at 1 GHz may be 0.0002 or more, or may be 0.0003 or more.

[0032] The dielectric constant and dielectric loss tangent of hollow inorganic particles such as specific hollow particles are measured using a dedicated device (e.g., Keycom Corporation's "Vector Network Analyzer E5063A") using a perturbation resonator method. Specifically, measurements are performed at a test frequency of 1 GHz, a test temperature of approximately 24°C, a humidity of approximately 45%, and three measurements. The measurement sample is prepared by vacuum-drying the obtained hollow inorganic particles at 150°C, and then filling a PTFE (polytetrafluoroethylene) tube with the hollow inorganic particle powder while thoroughly tapping. The dielectric constant of the entire container is measured, and then converted to a dielectric loss tangent using the filling rate of the powder in the container.

[0033] Each specific hollow particle may be treated with a coupling agent. By treating the surface of the specific hollow particle with a coupling agent, the elution of the components constituting the specific hollow particle in the insulating layer is suppressed. Therefore, an increase in the dielectric constant and a decrease in the bending strength of the insulating layer due to elution are suppressed, making it easier to achieve both a low dielectric constant and high bending strength in the insulating layer. Examples of coupling agents include silane coupling agents, titanate coupling agents, zirconate coupling agents, and aluminate coupling agents.

[0034] Examples of silane coupling agents include aminosilane coupling agents, methacrylsilane silane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, and organosilazane compounds. Examples of vinylsilane coupling agents include vinyltrialkoxysilanes such as vinyltrimethoxysilane. Examples of organosilazane compounds include hexaalkyldisilazanes such as 1,1,1,3,3,3-hexamethyldisilazane. Examples of titanate coupling agents include alkoxytitanate coupling agents. Examples of zirconate coupling agents include alkoxyzirconate coupling agents. Examples of alkoxyzirconate coupling agents include zirconium alkoxides such as zirconium isopropoxide. Examples of aluminate coupling agents include alkoxyaluminate coupling agents. Examples of alkoxyaluminate coupling agents include aluminum alkoxides such as aluminum isopropoxide.

[0035] One type of coupling agent may be used, or two or more types may be used in combination. From the viewpoint of achieving a low dielectric constant and high bending strength in the insulating layer, the specific hollow particles are preferably treated with at least one selected from the group consisting of silane coupling agents, zirconate coupling agents, and aluminate coupling agents, and more preferably treated with at least one selected from the group consisting of vinylsilane coupling agents, organosilazane compounds, alkoxyzirconate coupling agents, and alkoxyaluminate coupling agents. The amount of coupling agent attached is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 5 parts by mass, and even more preferably 0.10 to 2 parts by mass, per 100 parts by mass of the specific hollow particles. Treatment of the surfaces of the specific hollow particles with a coupling agent can be confirmed by detecting peaks due to the substituents of the coupling agent using IR. The amount of coupling agent attached can also be measured by the carbon content.

[0036] The specific hollow particles may be commercially available or may be prepared by a conventional method. For example, hollow silica particles prepared by the methods described in International Publication No. 2019 / 131658 and International Publication No. 2021 / 172294 can be used.

[0037] The content of the specific hollow particles relative to the entire insulating layer is 5 to 70 volume %, and from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer, it is preferably 10 to 60 volume %, more preferably 15 to 50 volume %, and even more preferably 20 to 40 volume %. When the insulating layer contains glass, the content of the specific hollow particles is preferably 0.1 to 5 times the content of the glass, more preferably 0.2 to 2 times, and even more preferably 0.2 to 1.5 times, by volume, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer. When the insulating layer contains solid inorganic particles, the content of the specific hollow particles is preferably 15 to 60 volume %, more preferably 20 to 55 volume %, and even more preferably 30 to 55 volume %, based on the total amount of inorganic particles including the specific hollow particles and solid inorganic particles, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer.

[0038] (Glass) The insulating layer may contain glass as needed. The insulating layer may contain only one type of glass, or may contain two or more types of glass. Examples of glass include borosilicate glass, quartz glass, soda glass, etc. Among these, from the viewpoint of the insulating reliability of the insulating layer, alkali-free glass is preferred, and borosilicate glass is more preferred. Examples of borosilicate glass include SiO ２ , Al ２ O ３ , and B ２ O ３ Examples of borosilicate glass include glass containing ZnO, CaO, Na ２ O.K. ２ O may also be contained. SiO in borosilicate glass ２ The content of Al in borosilicate glass is, for example, 75 to 90 mol %, preferably 80 to 90 mol %, and more preferably 80 to 85 mol %. ２ O ３The content of B in borosilicate glass is, for example, 1 to 10 mol %, preferably 1 to 8 mol %, and more preferably 1 to 5 mol %. ２ O ３ The content of is, for example, 9 to 18 mol %, preferably 10 to 17 mol %, and more preferably 12 to 16 mol %.

[0039] The glass content of the entire insulating layer is preferably 15 to 60% by volume, more preferably 20 to 55% by volume, and most preferably 30 to 55% by volume, from the viewpoint of achieving both a low dielectric constant and high bending strength in the insulating layer.

[0040] (Solid inorganic particles) The insulating layer may contain inorganic particles other than hollow inorganic particles, i.e., solid inorganic particles, as needed. The insulating layer may contain only one type of glass, or may contain two or more types. Examples of solid inorganic particles include ceramic particles such as alumina, titania, silica, zirconia, magnesia, mullite, aluminum nitride, silicon nitride, silicon carbide, forsterite, cordierite, and yttria. Among these, from the viewpoint of improving the bending strength and ease of processing of the insulating layer, particles such as alumina, titania, and zirconia are preferred as solid inorganic particles, and alumina particles are more preferred.

[0041] The median diameter d50 of the solid inorganic particles is not particularly limited and may be, for example, 0.001 to 50 μm. From the viewpoint of obtaining high bending strength while suppressing the surface roughness of the LTCC substrate, it is preferably 0.1 to 80 μm, more preferably 0.1 to 50 μm. The BET specific surface area of ​​the solid inorganic particles is not particularly limited and may be, for example, 0.1 to 100 m. ２ / g, and from the viewpoint of high bending strength, 0.1 to 80 m ２ / g is preferred, and 0.2 to 30m ２ The dielectric constant of the solid inorganic particles is not particularly limited and may be, for example, 3 to 20 at a frequency of 1 GHz, and from the viewpoint of reducing dielectric loss, it is preferably 3 to 10, more preferably 3 to 8. The median diameter d50, BET specific surface area, and dielectric constant of the solid inorganic particles are determined by the same methods as those for the median diameter d50, BET specific surface area, and dielectric constant of the hollow inorganic particles described above, respectively.

[0042] The content of the solid inorganic particles in the entire insulating layer is preferably 15 to 60% by volume, more preferably 20 to 55% by volume, and most preferably 30 to 55% by volume, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer. When the insulating layer contains glass, the content of the solid inorganic particles is preferably 0.2 to 3 times, more preferably 0.3 to 2 times, and even more preferably 0.5 to 1.5 times the content of the glass on a volume basis, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer.

[0043] (Characteristics of the insulating layer) The thickness of the insulating layer is not particularly limited and may be, for example, 50 to 1,000 μm, or may be 75 to 700 μm or 100 to 500 μm. From the viewpoint of reducing transmission loss, the relative dielectric constant of the insulating layer is preferably 3.0 to 5.5, more preferably 3.0 to 5.0, at a frequency of 10 GHz. From the viewpoint of reducing transmission loss, the dielectric dissipation factor of the insulating layer is preferably 0.001 or less, more preferably 0.0009 or less, and even more preferably 0.0008 or less, at a frequency of 10 GHz. The relative dielectric constant and dielectric dissipation factor of the insulating layer are values ​​measured using a split post dielectric resonator (SPDR) at a temperature of 25° C. and a frequency of 10 GHz.

[0044] <Production of Ceramic Substrate> In the production of a ceramic substrate in this embodiment, first, a ceramic green sheet that will become an insulating layer after firing is produced. The resulting ceramic green sheet is then laminated with other sheets as necessary and fired. The ceramic substrate may be produced by firing a ceramic green sheet alone, firing a laminate of multiple ceramic green sheets, or firing a laminate of a ceramic green sheet and another sheet (e.g., a sheet that will become a wiring layer after firing). The firing temperature may be, for example, 700 to 1000°C. From the viewpoint of easily maintaining the shape of the specific hollow particles during firing, it is preferably 1000°C or less, more preferably 950°C or less, and even more preferably 900°C or less. By keeping the firing temperature below the above upper limit, the shape of the specific hollow particles is easily maintained during firing. The firing time may be, for example, 30 to 300 minutes, and the firing atmosphere may be, for example, atmospheric pressure. Hereinafter, a ceramic green sheet used in the production of a ceramic substrate and a method for producing the ceramic green sheet will be described.

[0045] (Ceramic Green Sheet) The ceramic green sheet is a sheet that becomes the aforementioned insulating layer upon firing and contains at least the components that constitute the insulating layer. That is, the ceramic green sheet contains at least hollow inorganic particles having a median diameter d50 of 0.1 to 10 μm, i.e., specific hollow particles. Details of the specific hollow particles are the same as those of the specific hollow particles contained in the insulating layer described above. The content of the specific hollow particles relative to the entire ceramic green sheet is 5 to 70% by volume, and from the viewpoint of achieving both a low dielectric constant and high bending strength in the insulating layer obtained by firing the ceramic green sheet, it is preferably 10 to 60% by volume, more preferably 15 to 50% by volume, and even more preferably 20 to 40% by volume.

[0046] When the ceramic green sheet contains glass, the content of the specific hollow particles is preferably 0.1 to 5 times, more preferably 0.2 to 2 times, and even more preferably 0.2 to 1.5 times the content of the glass on a volume basis, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer. When the ceramic green sheet contains solid inorganic particles, the content of the specific hollow particles is preferably 15 to 60% by volume, more preferably 20 to 55% by volume, and even more preferably 30 to 55% by volume, based on the total amount of inorganic particles including the specific hollow particles and solid inorganic particles, from the viewpoint of achieving both a low dielectric constant and high bending strength of the insulating layer obtained by firing the ceramic green sheet.

[0047] When the components constituting the insulating layer obtained by firing include glass, the ceramic green sheet for forming the insulating layer also contains glass. For example, when the ceramic green sheet is for a low-temperature fired ceramic substrate, the ceramic green sheet preferably contains glass in addition to specific hollow particles, more preferably glass and solid inorganic particles, and even more preferably glass and alumina particles, which are solid inorganic particles. The type of glass contained in the ceramic green sheet is the same as the type of glass contained in the insulating layer described above. Glass may be contained in the ceramic green sheet as particulate glass particles. The median diameter d50 of the glass particles is not particularly limited and may be, for example, 0.5 to 20 μm. From the viewpoint of uniformity of the green sheet, 0.5 to 10 μm is preferred, and 0.5 to 7 μm is more preferred. The median diameter d50 of the glass particles is determined by the same method as the median diameter d50 of the hollow inorganic particles described above. The glass content of the entire ceramic green sheet is preferably 10 to 55% by volume, more preferably 15 to 50% by volume, and even more preferably 25 to 50% by volume, from the viewpoint of achieving both a low dielectric constant and high bending strength in the insulating layer obtained by firing the ceramic green sheet.

[0048] When the components constituting the insulating layer obtained by firing include inorganic particles other than hollow inorganic particles, i.e., solid inorganic particles, the ceramic green sheet for forming the insulating layer contains solid inorganic particles. Details of the solid inorganic particles are the same as those of the solid inorganic particles contained in the insulating layer described above. The content of the solid inorganic particles relative to the entire ceramic green sheet is preferably 10 to 55% by volume, more preferably 15 to 50% by volume, and even more preferably 25 to 50% by volume, from the viewpoint of achieving both a low dielectric constant and high bending strength in the insulating layer obtained by firing the ceramic green sheet.

[0049] The ceramic green sheet may further contain components other than the components constituting the insulating layer. Examples of components other than the components constituting the insulating layer include components that are removed from the ceramic green sheet by firing, such as resins, plasticizers, surfactants, etc. Note that the components that are removed from the ceramic green sheet by firing may be at least partially removed by firing, and some of the components may remain in the insulating layer, or reaction products of the components may remain in the insulating layer.

[0050] Examples of resins include polyvinyl butyral resin and polyvinyl alcohol, with polyvinyl butyral resin being preferred from the viewpoints of flexibility and ease of decomposition. When ceramic green sheets contain resin, they are less likely to fall off during the manufacturing process, thereby improving productivity. From the viewpoint of minimizing residual decomposition products, the resin content relative to the entire ceramic green sheet is preferably 3 to 40 mass%, more preferably 5 to 35 mass%, and even more preferably 10 to 30 mass%. Examples of plasticizers include dioctyl phthalate, with dioctyl phthalate being preferred from the viewpoint of compatibility. When ceramic green sheets contain a plasticizer, they are advantageously flexible, making them easier to handle and improving productivity. From the viewpoint of minimizing residual decomposition products, the plasticizer content relative to the entire ceramic green sheet is preferably 0.2 to 5 mass%, more preferably 0.5 to 4 mass%, and even more preferably 1.0 to 3 mass%.

[0051] The surfactant is commercially available, for example, BYK (registered trademark)-R606, BYK (registered trademark)-405, BYK (registered trademark)-R605, BYK (registered trademark)-R607, BYK (registered trademark)-410, BYK (registered trademark)-411, BYK (registered trademark)-415, BYK (registered trademark)-430, BYK (registered trademark)-431, BYK (registered trademark)-7410ET, and BYK (registered trademark)-7411E. S (all manufactured by BYK Japan), TALEN 1450, TALEN 2000, TALEN 2200A, TALEN 7200-20, TALEN 8200-20, TALEN 8300-20, TALEN 8700-20, TALEN BA-600, FLOWNON SH-290, FLOWNON SH-295S, FLOWNON SH-350, FLOWNON HR-2, FLOWNON HR-4AF (all manufactured by Kyoeisha Chemical Co., Ltd.).

[0052] The surfactant is preferably contained in the green sheet in a range of 0.01 to 5% by mass. A surfactant content of 0.01% by mass or more can suppress aggregation of constituent particles in the dispersion during the process, thereby increasing the bending strength of the LTCC. Furthermore, a surfactant content of 5% by mass or less in the green sheet can suppress residue in the LTCC after firing, thereby reducing the impact on the physical properties of the resin composition. The surfactant content in the green sheet is more preferably 0.02% by mass or more, even more preferably 0.04% by mass or more, particularly preferably 0.05% by mass or more, and more preferably 4% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2.5% by mass or less.

[0053] (Method for manufacturing ceramic green sheets) In the production of ceramic green sheets, first, a composition is prepared containing the components constituting the insulating layer described above, components other than the components constituting the insulating layer described above, and, if necessary, a solvent. Specifically, for example, when producing a ceramic green sheet for obtaining an insulating layer containing specific hollow particles, glass, and solid inorganic particles, a composition containing the specific hollow particles, glass, solid inorganic particles, a resin, a plasticizer, and a solvent is prepared. Examples of solvents include methyl ethyl ketone and methyl isobutyl ketone, and methyl ethyl ketone is preferred from the viewpoint of easy volatility. The amount of solvent added is not particularly limited, and it is sufficient to add an amount of solvent that gives the composition a viscosity that allows it to be molded into a sheet. The method for preparing the composition is not particularly limited, and the composition may be prepared by stirring and mixing the components.

[0054] Next, the obtained composition is formed into a sheet and dried to obtain a ceramic green sheet. The method for forming the composition is not particularly limited, and examples thereof include a doctor blade method and die coating. Examples of methods for drying the sheet-formed composition include drying in a gear oven and drying in a hot air oven. The drying temperature is, for example, 30 to 200°C, and the drying time is, for example, 1 to 100 minutes. The thickness of the obtained ceramic green sheet may be approximately the same as the thickness of the desired insulating layer, and specifically, for example, 50 to 1,200 μm, but may also be 75 to 850 μm or 100 to 650 μm.

[0055] Next, embodiments of the present disclosure will be described in detail using examples, but the embodiments of the present disclosure are not limited to these examples. Examples 1 to 10 are examples, and Examples 11 to 14 are comparative examples.

[0056] [Preparation of Inorganic Particles A] (Solid Silica 1) Solid silica particles (product name: TS-6021, manufactured by Micron Corporation, median diameter d50: 10 μm, relative dielectric constant at a frequency of 1 GHz: 4.0, dielectric dissipation factor at a frequency of 1 GHz: 0.001, BET specific surface area: 3.5 m) ２ / g, shape: spherical) was prepared.

[0057] (Preparation of Specific Hollow Particles 2) 4 g of EO-PO-EO block copolymer (Pluronic F68 manufactured by ADEKA Corporation) was added to 1,250 g of pure water and stirred until dissolved. 42 g of an n-decane solution prepared by dissolving 4 g of sorbitan acid monooleate (IONET S-80 manufactured by Sanyo Chemical Industries, Ltd.) in n-decane was added to this aqueous solution, and the mixture was stirred using an IKA homogenizer until the entire solution became uniform, producing a coarse emulsion. This coarse emulsion was emulsified using a high-pressure emulsifier (LAB1000 manufactured by SMT Corporation) at a pressure of 50 bar to produce a fine emulsion with an emulsion diameter of 1 μm. The resulting fine emulsion was allowed to stand at 40°C for 12 hours to produce a post-aging emulsion.

[0058] 1300 g of the obtained emulsion after aging was diluted with an aqueous sodium silicate solution (SiO ２ Concentration 10.4% by mass, Na ２ 23 g of 2M hydrochloric acid (O concentration 3.6% by mass) was added and stirred thoroughly while maintaining the temperature at 30°C. 1M aqueous sodium hydroxide solution was slowly added dropwise to this solution while stirring thoroughly to adjust the pH to 6, thereby obtaining an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was maintained at 30°C for 10 minutes and aged. The entire amount of the aged oil core-silica shell particle dispersion was heated to 70°C, and 1M aqueous NaOH solution was slowly added while stirring to adjust the pH to 9. Next, a diluted aqueous sodium silicate solution (SiO ２ Concentration 10.4% by mass, Na ２ 330 g of a solution of 1,000 sachets (3.6% by mass) was gradually added together with 0.5 M hydrochloric acid to adjust the pH to 9. The suspension was kept at 80° C. for 1 day and then cooled to room temperature (25° C.) to obtain a hollow silica precursor dispersion.

[0059] The entire hollow silica precursor dispersion was adjusted to pH 2 with 2M hydrochloric acid and then filtered using a quantitative filter paper 5C. Then, 350 ml of 80°C ion-exchanged water was added and pressure filtered again to wash the hollow silica cake. The filtered cake was dried under a nitrogen atmosphere at 100°C for 1 hour and then at 400°C for 2 hours (heating rate 10°C / min) to remove organic components and obtain a hollow silica precursor. The obtained hollow silica precursor was calcined at 1000°C for 1 hour (heating rate 10°C / min) to sinter the shell layer and obtain hollow silica calcined particles. 10 g of the hollow silica calcined particles, 150 ml of isopropanol, and 0.1 g of vinyltrimethoxysilane were added to a 200 ml glass beaker and refluxed at 100°C for 1 hour. The mixture was then filtered under reduced pressure using a hydrophobic PTFE membrane filter, washed with 20 ml of isopropanol, and vacuum dried for 2 hours in a vacuum dryer adjusted to 150°C to obtain surface-treated hollow silica particles, designated as Hollow Particles 2. The average thickness of the shell layer of Hollow Particles 2 was 40 nm, and the BET specific surface area of ​​Hollow Particles 2 was 12 m. ２ / g, the shape of the specific hollow particles 2 was spherical, and the porosity of the specific hollow particles 2 was 70%.

[0060] (Preparation of specific hollow particles 3) Specific hollow particles 3 were obtained under the same conditions as specific hollow particles 2, except that the amount of EO-PO-EO block copolymer (Pluronic F68 manufactured by ADEKA Corporation) added was changed to 2 g, the amount of sorbitan acid monooleate (IONET S-80 manufactured by Sanyo Chemical Industries, Ltd.) added was changed to 2 g, and the amount of diluted sodium silicate aqueous solution was changed from 330 g to 240 g. The average thickness of the shell layer of specific hollow particles 3 was 40 nm, and the BET specific surface area of ​​specific hollow particles 3 was 12 m. ２ / g, the shape of the specific hollow particles 3 was spherical, and the porosity of the specific hollow particles 3 was 70%.

[0061] (Preparation of specific hollow particles 4) As raw material compounds, colloidal silica, tetraethyl orthosilicate, aluminum nitrate nonahydrate, magnesium nitrate hexahydrate, calcium nitrate tetrahydrate, sodium nitrate, and, as needed, boric acid, potassium nitrate, and lithium nitrate were used. ２ O ３16.8% by mass, SiO ２ 54.5% by mass, B ２ O ３ 8.5% by mass, CaO8.3% by mass, MgO5.8% by mass, Na ２ O2.8% by mass, K ２ O 1.5 mass%, and Li ２ The raw material compounds were dissolved in tap water to prepare an aqueous solution of the raw material compounds, with a concentration of 0.4 mol / L and a total mass of 1.5% by mass of O. The aqueous solution of the raw material compounds was sprayed into a spray pyrolysis furnace using a two-fluid nozzle and fired at 1000°C to obtain specific hollow particles 4, which are inorganic oxide hollow particles.

[0062] (Hollow Inorganic Particles 5) Hollow inorganic particles (product name: iM16K, manufactured by 3M Company) were prepared and used as hollow inorganic particles 5.

[0063] (Preparation of specific hollow particles 6) Specific hollow particles 6 were obtained under the same conditions as specific hollow particles 2, except that the amount of diluted sodium silicate aqueous solution was changed from 330 g to 660 g. The average thickness of the shell layer of specific hollow particles 6 was 100 nm, and the BET specific surface area of ​​specific hollow particles 6 was 8 m. ２ / g, the shape of the specific hollow particles 6 was spherical, and the porosity of the specific hollow particles 6 was 70%.

[0064] (Specific hollow particles 7) Specific hollow particles 7 were obtained under the same conditions as specific hollow particles 2, except that the following treatment was carried out instead of performing the surface treatment with vinyltrimethoxysilane. 10 g of the hollow calcined silica particles and 100 ml of toluene were added to a 200 ml glass beaker, and while mixing and stirring, 0.1 g of zirconium isopropoxide was added and refluxed at 100° C. for 1 hour. The resulting solid was then filtered under reduced pressure using a hydrophobic PTFE membrane filter, and heated and dried for 2 hours in a vacuum dryer adjusted to 200° C. to produce zirconia-coated specific hollow particles 7.

[0065] (Specific hollow particles 8) Specific hollow particles 8 were obtained under the same conditions as specific hollow particles 2, except that the following treatment was carried out instead of performing the surface treatment with vinyltrimethoxysilane. 10 g of the hollow calcined silica particles and 100 ml of toluene were added to a 200 ml glass beaker, and while mixing and stirring, 0.1 g of aluminum isopropoxide was added and refluxed at 100° C. for 1 hour. The resulting solid was then filtered under reduced pressure using a hydrophobic PTFE membrane filter, and heated and dried for 2 hours in a vacuum dryer adjusted to 200° C. to produce aluminum-coated specific hollow particles 8.

[0066] (Specific Hollow Particles 9) Specific hollow particles 9 were obtained under the same conditions as specific hollow particles 2, except that the following treatment was carried out instead of performing the surface treatment with vinyltrimethoxysilane. 10 g of the hollow calcined silica particles and 100 ml of toluene were added to a 200 ml glass beaker, and while mixing and stirring, 0.1 g of 1,1,1,3,3,3-hexamethyldisilazane was added and refluxed at 100°C for 1 hour. The resulting solid was then filtered under reduced pressure using a hydrophobic PTFE membrane filter, and heated and dried for 2 hours in a vacuum dryer adjusted to 200°C, thereby producing trimethylsilyl-treated specific hollow particles 9.

[0067] (Measurement of Inorganic Particles A) For the inorganic particles A, the relative permittivity at a frequency of 1 GHz ("relative permittivity" in the table), the dielectric loss tangent at a frequency of 1 GHz ("dielectric loss tangent" in the table), the breakdown pressure ("breakdown pressure (MPa)" in the table), and the SiO content relative to the total inorganic particles were measured by the above-mentioned method. ２ Content of (in the table "SiO ２ Purity (mass%)), median diameter d50 ("Median diameter d50 (μm)" in the table), and density determined by constant volume expansion method ("Density (g / cm ３ The results of the measurements are shown in Table 1. In Table 1, "-" means that the measurement was omitted.

[0068]

[0069] [Preparation of Ceramic Green Sheet] (Preparation of Composition) As raw material powder for the glass ceramic substrate, the above-mentioned inorganic particles A and SiO ２ , B ２ O ３ , and Al ２ O ３ The borosilicate glass particles, which are mainly composed of SiO 2 , and the solid inorganic particles, alumina particles, were prepared. In addition, polyvinyl butyral resin was prepared as a binder for forming the sheet, dioctyl phthalate (DOP) was prepared as a plasticizer, and methyl ethyl ketone (MEK) was prepared as a solvent.

[0070] The borosilicate glass particles have a median diameter d50 of 4.0±0.5 μm and a SiO ２ Content: 83 mol%, Al ２ O ３ Content: 3 mol%, B ２ O ３ The alumina particles used had a median diameter d50 of 3 μm and a specific surface area of ​​1.6 m. ２ / g was prepared.

[0071] (Preparation of Green Sheet) The above-mentioned inorganic particles A, borosilicate glass particles ("glass particles" in Table 2), and alumina particles were weighed and placed in an alumina pot in a total amount of 1 L in the proportions shown in Table 2 below. In Example 11, the borosilicate glass particles and alumina particles were placed in a total amount of 1 L in the proportions shown in Table 2 below.

[0072] Furthermore, 120 g of the polyvinyl butyral resin was placed in a pot, along with the solvent (MEK) and plasticizer (DOP) in amounts necessary to provide an appropriate slurry viscosity and sheet strength, and the mixture was mixed in the pot for 5 hours to obtain a ceramic slurry composition.

[0073] Next, a 0.15 mm thick composition layer was prepared using this ceramic slurry composition by a doctor blade method. The resulting ceramic green sheet was dried for 10 minutes in a gear oven at 100°C to obtain a ceramic green sheet. The polyvinyl butyral resin content relative to the entire ceramic green sheet was 20 mass% and the DOP content relative to the entire ceramic green sheet was 2 mass%.

[0074] [Preparation and Evaluation of Ceramic Substrates] (Dielectric Constant and Dielectric Loss Tangent) The obtained ceramic green sheets were fired individually at 900°C under atmospheric pressure for 1 hour without being stacked to obtain glass ceramic substrates for measuring dielectric constant and dielectric loss tangent. The obtained glass ceramic substrates included insulating layers formed by firing the aforementioned ceramic green sheets. The obtained glass ceramic substrates were cut into test pieces measuring 10 cm x 5 cm x 0.12 μm. The obtained test pieces were used to measure the dielectric constant and dielectric loss tangent at a temperature of 25°C and a frequency of 10 GHz using a split post dielectric resonator (SPDR). The results are shown in Table 2.

[0075] (Three-point bending strength) Eight of the obtained ceramic green sheets were stacked and fired at 900°C under atmospheric pressure for 1 hour to obtain a glass ceramic substrate for measuring three-point bending strength. The obtained glass ceramic substrate was a substrate including an insulating layer which was a fired body of the above-mentioned ceramic green sheet. The obtained glass ceramic substrate was cut to obtain test pieces of 80 mm x 10 mm x 1 mm. A three-point bending test was performed using the obtained test pieces in accordance with JIS K7171. The result of Example 11 was set to 100, and comparisons were made based on relative strength. The results are shown in Table 2. In Table 2, "-" means that the corresponding component was not contained.

[0076]

[0077] As shown in Table 2, it can be seen that the insulating layers of the ceramic substrates of Examples 1 to 10 have both a low dielectric constant and a high bending strength compared to the insulating layers of the ceramic substrates of Examples 11 to 14. It is presumed that the relative dielectric constant of Example 14 was not reduced due to cracks in the hollow inorganic particles.

[0078] The disclosure of Japanese Patent Application No. 2023-200933, filed on November 28, 2023, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A ceramic substrate including an insulating layer, wherein the insulating layer contains hollow inorganic particles, the median diameter d50 of the hollow inorganic particles is 0.1 to 10 μm, and the content of the hollow inorganic particles in the entire insulating layer is 5 to 70 volume %.

2. The density of the hollow inorganic particles, as determined by a constant volume expansion method, is 0.35 to 2.00 g / cm ３ The ceramic substrate according to claim 1 , 3. The ceramic substrate according to claim 1, wherein the hollow inorganic particles have a 20% breakdown pressure of 120 MPa or more as measured by mercury intrusion porosimetry.

4. SiO relative to the entire hollow inorganic particles ２ The ceramic substrate according to claim 1 , wherein the content of is 99 mass % or more.

5. The ceramic substrate according to claim 1, wherein the hollow inorganic particles are treated with a coupling agent.

6. The ceramic substrate according to any one of claims 1 to 5, wherein the insulating layer further contains glass and alumina particles other than the hollow inorganic particles.

7. The ceramic substrate according to any one of claims 1 to 5, wherein the insulating layer has a relative dielectric constant of 5.5 or less at a frequency of 10 GHz.

8. The ceramic substrate according to any one of claims 1 to 5, which is a low-temperature fired ceramic substrate.

9. A ceramic green sheet containing hollow inorganic particles, wherein the median diameter d50 of the hollow inorganic particles is 0.1 to 10 μm, and the content of the hollow inorganic particles in the entire ceramic green sheet is 5 to 70 volume %.

10. The density of the hollow inorganic particles, as determined by a constant volume expansion method, is 0.35 to 2.00 g / cm ３ The ceramic green sheet according to claim 9 .

11. The ceramic green sheet according to claim 9, wherein the hollow inorganic particles have a 20% burst pressure of 120 MPa or more as measured by mercury intrusion porosimetry.

12. SiO relative to the entire hollow inorganic particles ２ The ceramic green sheet according to claim 9, wherein the content of is 99 mass% or more.

13. The ceramic green sheet according to claim 9, wherein the hollow inorganic particles are treated with a coupling agent.

14. The ceramic green sheet according to any one of claims 9 to 13, further comprising glass and alumina particles other than the hollow inorganic particles.

15. The ceramic green sheet according to claim 14, further comprising a resin.

16. The ceramic green sheet according to any one of claims 9 to 13, which is for use in a low-temperature fired ceramic substrate.

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