Low-temperature fired ceramic substrate

Abstract

A low-temperature fired ceramic substrate 1 comprises: a low-temperature fired ceramic 11 containing a fired glass component (A1) and an oxide (C1) of a ceramic crystal component; and pores 17. The oxide (C1) of the ceramic crystal component contains a ZnAl2O4 crystal. When subjected to measurement at 6 GHz by a perturbation method, the low-temperature fired ceramic substrate 1 demonstrates a relative dielectric constant of 3.8 or less and a Q value of 1500 or more.

Description

Low-temperature fired ceramic substrate

[0001] This invention relates to a low-temperature fired ceramic substrate.

[0002] As a ceramic material for ceramic multilayer wiring boards, glass ceramic materials (LTCC materials) that can be fired at low temperatures are known.

[0003] In the GHz-order frequency range, to handle higher frequencies, it is necessary to lower the relative permittivity of the LTCC substrate material and reduce dielectric loss (increase the Q value). Specifically, a relative permittivity of 3.8 or less and a Q value of 1500 or more at 6 GHz are required.

[0004] For example, Patent Document 1 discloses a method for reducing the dielectric constant by using a filler with internal voids, such as hollow silica, as a constituent component. Patent Document 2 also discloses a method for reducing dielectric loss in a glass ceramic containing glass containing Si, B, Al, and Zn, and aggregate, by optimizing the composition of Si, B, Al, and Zn in the glass.

[0005] International Publication No. 2018 / 083830, Patent No. 7494908

[0006] However, in Patent Document 1, the dielectric containing BaO as the main phase is a dense body with a high relative permittivity of about 7.0, so even if vacancies are formed, the relative permittivity is about 4.5, and even when an excessive number of vacancies are formed, the relative permittivity is about 3.9.

[0007] Patent Document 2 states that SiO ２ Although low dielectric constant glass and dielectric fillers, mainly consisting of [specific material], were used, no vacancies were formed, resulting in a relative permittivity of around 5.0, with the lowest being approximately 4.2. Furthermore, crystallization had not progressed sufficiently, and the Q-factor was around 500 to 1400 at 6 GHz.

[0008] This invention was made to solve the above problems and aims to provide a low-temperature fired ceramic substrate that can achieve both a low dielectric constant and a high Q value.

[0009] The low-temperature fired ceramic substrate of the present invention is a low-temperature fired ceramic substrate having a low-temperature fired ceramic containing a glass component (A1) and an oxide of a ceramic crystal component (C1) after firing, and pores, wherein the oxide of the ceramic crystal component (C1) is ZnAl ２ O ４ The above low-temperature fired ceramic substrate, which contains crystals, has a relative permittivity of 3.8 or less and a Q value of 1500 or more at 6 GHz, as measured by the perturbation method.

[0010] According to the present invention, it is possible to provide a low-temperature fired ceramic substrate that can achieve both a low relative permittivity and a high Q value.

[0011] Figure 1 is a schematic cross-sectional view showing an example of the low-temperature fired ceramic substrate of the present invention. Figure 2 is a schematic cross-sectional view showing another example of the low-temperature fired ceramic substrate of the present invention. Figure 3 is a schematic cross-sectional view showing another example of the low-temperature fired ceramic substrate of the present invention.

[0012] The low-temperature fired ceramic substrate of the present invention will be described below. However, the present invention is not limited to the configuration described below, and may be modified as appropriate without departing from the spirit of the invention. Furthermore, a combination of several of the preferred configurations described below also constitutes the present invention.

[0013] [Low-Temperature Fired Ceramic Substrate] The low-temperature fired ceramic substrate of the present invention is a low-temperature fired ceramic substrate having a low-temperature fired ceramic containing a glass component (A1) and an oxide of a ceramic crystal component (C1) after firing, and pores, wherein the oxide of the ceramic crystal component (C1) is ZnAl ２ O ４ The above low-temperature fired ceramic substrate, which contains crystals, has a relative permittivity of 3.8 or less and a Q value of 1500 or more at 6 GHz, as measured by the perturbation method.

[0014] Figure 1 is a schematic cross-sectional view showing an example of a low-temperature fired ceramic substrate of the present invention. The low-temperature fired ceramic substrate 1 comprises a low-temperature fired ceramic layer 10 having predetermined dimensions in the length direction (direction indicated by arrow X in Figure 1) and width direction (direction indicated by arrow Y in Figure 1), and having a first main surface 10a and a second main surface 10b facing each other in the thickness direction (direction indicated by arrow Z in Figure 1).

[0015] The low-temperature fired ceramic layer 10 has a low-temperature fired ceramic 11 and pores 17. Since the pores 17 are filled with a gas with a low dielectric constant (usually air), the dielectric constant of the low-temperature fired ceramic substrate 1 can be lowered.

[0016] Preferably, the void 17 is composed of hollow silica 16, which is a fired body of silica-coated resin beads.

[0017] The average diameter of the pores 17 is preferably 1 μm or more and 10 μm or less, and more preferably 1 μm or more and 3 μm or less. When the average diameter of the pores 17 is 1 μm or more and 10 μm or less, it is effective in reducing the dielectric constant, and it is possible to form micro-elements such as capacitors and coils in the ceramic. When the average diameter of the pores 17 is less than 1 μm, the effect of reducing the dielectric constant becomes difficult to achieve. Also, when the average diameter of the pores 17 exceeds 10 μm, the reliability between layers may decrease when the electrode spacing is narrow. When the average diameter of the pores 17 is 1 μm or more and 3 μm or less, it is possible to achieve a low dielectric constant without reducing the mechanical strength of the low-temperature fired ceramic.

[0018] The porosity (the ratio of the volume occupied by voids to the total volume of the low-temperature fired ceramic substrate) is preferably between 10% and 45%. If the porosity is less than 10%, the dielectric constant of the low-temperature fired ceramic substrate may not decrease sufficiently. If the porosity exceeds 45%, the proportion of voids becomes too high, which may reduce the mechanical strength of the low-temperature fired ceramic substrate.

[0019] The average diameter and porosity of pores in a low-temperature fired ceramic substrate can be determined by analyzing an enlarged image obtained by observing a cross-section of the low-temperature fired ceramic substrate with a scanning electron microscope (SEM). Specifically, five fields of view are randomly extracted from an enlarged image (magnification: 1000 times) of the cut surface of the low-temperature fired ceramic substrate imaged by SEM. For all the pores in the five fields of view, the pore area is calculated by image analysis, averaged, and the volume ratio (porosity) occupied by the pores can be calculated.

[0020] It is preferable that the pores 17 are not unevenly distributed in the thickness direction Z. For example, when the low-temperature fired ceramic layer 10 constituting the low-temperature fired ceramic substrate 1 is trisected in the thickness direction Z and is divided into the first layer, the second layer, and the third layer from the side of the first main surface 10a, the difference between the maximum value and the minimum value of the porosity is preferably 10% or less.

[0021] The low-temperature fired ceramic 11 is a fired body obtained by firing a low-temperature co-fired ceramic (LTCC) material, which is a glass-ceramic material that can be sintered at a firing temperature of 1000 °C or lower, and contains a glass component (A1) and an oxide (C1) of a ceramic crystal component after firing. In this specification, the fired body refers to a material in which the sintering of the glass-ceramic material has sufficiently progressed and has solidified. That is, even if the low-temperature co-fired ceramic (LTCC) material is heated, if the sintering between the glass-ceramic materials has not sufficiently progressed, it is not included in the low-temperature fired ceramic in this specification.

[0022] The glass component (A1) after firing preferably contains, for example, SiO ２ and B ２ O ３ When the glass component (A1) after firing contains SiO ２ and B ２ O ３ , low-temperature sintering at 1000 °C or lower is possible and it is chemically stable.

[0023] The glass component (A1) after firing more preferably further contains ZnO and / or Al ２ O ３ .

[0024] The proportion of ZnO and Al contained in the glass component (A1) after firing. ２ O ３ The proportions of each are preferably 0.1 mol% or more and 10 mol% or less, respectively. Also, the proportion of ZnO and Al contained in the glass component (A1) after firing. ２ O ３ The sum of the proportions is preferably 15 mol% or less.

[0025] The glass component (A1) after firing may further contain RO. RO is an alkaline earth metal oxide (MgO, CaO, SrO, and BaO).

[0026] The proportion of RO contained in the glass component (A1) after firing is preferably 0.1 mol% or more and 10 mol% or less.

[0027] Furthermore, the proportion of ZnO contained in the glass component (A1) after firing, and Al ２ O ３ The sum of the proportion of and the proportion of RO is preferably 15 mol% or less.

[0028] The proportion of RO, the proportion of ZnO, and Al contained in the glass component (A1) after firing. ２ O ３ When measuring the proportion of glass components from a sample of a fired product, the composition of the glass components can be determined by WDS (wavelength-dispersive X-ray fluorescence analysis) on the glass region identified by scanning transmission electron microscopy (STEM) and electron diffraction of the exfoliated sample. Furthermore, the presence of crystalline phases can be identified by electron diffraction.

[0029] SiO in the glass component (A1) after firing ２ The content is preferably 50 mol% or more and 80 mol% or less. SiO in the glass component (A1) after firing. ２ If the content is within the above range, insufficient sintering will not occur.

[0030] SiO in the glass component (A1) after firing ２The SiO content can be determined by performing WDS measurements on glass regions identified by STEM and electron diffraction. Specifically, the SiO content is measured at 10 randomly selected locations within the glass regions identified by combining STEM and electron diffraction. ２ The average value of the content (concentration) of the SiO of the post-fired glass component (A1) in the low-temperature fired ceramic substrate is used. ２ This refers to the content.

[0031] It is preferable that the post-fired glass component (A1) does not contain alkali metal oxides. By not including alkali metal oxides in the post-fired glass component (A1), a low-temperature fired ceramic with low dielectric loss can be obtained. If alkali metal oxides are included in the post-fired glass component (A1), it is preferable that the proportion of alkali metal oxides included in the post-fired glass component (A1) is 0.1 mol% or less.

[0032] The oxide (C1) component of the ceramic crystal is ZnAl ２ O ４ Contains crystals. ZnAl ２ O ４ Because the crystal itself exhibits a high Q value, the oxide (C1) of the ceramic crystal component is ZnAl ２ O ４ The presence of this substance increases the Q-value of low-temperature fired ceramics.

[0033] In this specification, the components contained in the oxide (C1) of the ceramic crystal component are also referred to as "~crystal" in order to distinguish them from the same components contained in the glass component (A1) after firing. For example, ZnAl contained in the oxide (C1) of the ceramic crystal component. ２ O ４ is ZnAl ２ O ４ Also called crystal. Similarly, SiO is contained in the oxide (C1) of the ceramic crystal component. ２ SiO ２ Also called crystals.

[0034] ZnAl in the oxide (C1) of ceramic crystal components ２ O ４The crystal content is preferably 10% by weight or more and 38% by weight or less. ZnAl ２ O ４ When the crystal content is within the above range, it is possible to achieve both a low dielectric constant and a high Q value in low-temperature fired ceramic substrates. ZnAl ２ O ４ If the crystal content is 10% by weight or less, ZnAl ２ O ４ In some cases, the Q-factor may not be sufficiently high due to an insufficient amount of crystals. (ZnAl) ２ O ４ If the crystal content exceeds 38% by weight, ZnAl ２ O ４ If the amount of crystals becomes too large, the dielectric constant will increase.

[0035] ZnAl ２ O ４ It is preferable that the crystals precipitate uniformly in the glass component (A1) after firing. ZnAl ２ O ４ If the crystals precipitate uniformly in the glass component (A1) after firing, the ZnAl crystals will be deposited into the glass component by firing. ２ O ４ It can be seen that crystals have precipitated. ZnAl ２ O ４ A high Q value can be obtained when the crystals precipitate uniformly in the glass component (A1) after firing. ２ O ４ Whether the crystals precipitated uniformly can be confirmed by STEM and electron diffraction. (Glass and ZnAl) ２ O ４ When crystals are mixed and fired, ZnAl is present in the glass raw material before firing. ２ O ４ The elements may aggregate or be unevenly distributed. In contrast, during firing, ZnAl is released from the glass. ２ O ４ When crystals precipitate, specific patterns such as aggregation as described above are not observed, and ZnAl ２ O ４ The crystals are arranged randomly. Therefore, the ZnAl in the glass component (A1) after firing. ２ O４ By checking the crystal arrangement, it is possible to distinguish whether the ZnAl ２ O ４ crystals are precipitated from the glass component during firing or are added as crystals.

[0036] The oxide (C1) of the ceramic crystal component may contain at least one selected from the group consisting of ZnAl ２ O ４ other than BaAl ２ Si ２ O ８ SiO ２ Zn ２ SiO ４ TiO ２ ２

[0037] The low-temperature fired ceramic 11 may further contain CuO and / or Cu. When the low-temperature fired ceramic 11 contains CuO and / or Cu, during firing, ZnO - Al ２ O ３ -B ２ O ３ -SiO ２ system glass (pre-fired glass) promotes the precipitation of ZnAl ２ O ４ Zn ２ SiO ４ crystals, and the amounts of ZnO and Al ２ O ３ in the post-fired glass component (A1) can be reduced. Also, when the glass (pre-fired glass) is a RO-ZnO-Al ２ O ３ -B ２ O ３ -SiO ２ system glass, it is also possible to promote the precipitation of BaAl ２ Si ２ O ４ crystals and reduce the amount of RO in the post-fired glass component (A1).

[0038] The sum of the proportions of CuO and Cu in the low-temperature fired ceramic 11 is preferably 1% by weight or less. The proportions of CuO and Cu in the low-temperature fired ceramic are obtained by fluorescent X-ray analysis. When the firing of the low-temperature fired ceramic is carried out in an air atmosphere, CuO is present in the low-temperature fired ceramic, and when the firing is carried out in a reducing atmosphere, Cu is present.

[0039] The ratio of post-fired glass components (A1) and oxides of ceramic crystalline components (C1) contained in the low-temperature fired ceramic 11 is not particularly limited. For example, the ratio of post-fired glass components (A1) contained in the low-temperature fired ceramic 11 can be 10% by weight or more and 55% by weight or less, and the ratio of oxides of ceramic crystalline components (C1) can be 45% by weight or more and 90% by weight or less.

[0040] The low-temperature fired ceramic substrate of the present invention has a relative permittivity of 3.8 or less at 6 GHz, as measured by the perturbation method. The low-temperature fired ceramic substrate of the present invention has a low relative permittivity because it contains low-temperature fired ceramic and voids. This relative permittivity is the relative permittivity of the entire low-temperature fired ceramic substrate (excluding the conductive layer, etc., described later) and includes voids. Therefore, the relative permittivity of the low-temperature fired ceramic constituting the low-temperature fired ceramic substrate may be greater than 3.8.

[0041] The low-temperature fired ceramic substrate of the present invention preferably has a relative permittivity of 3.3 or less at 6 GHz, as measured by the perturbation method.

[0042] The low-temperature fired ceramic substrate of the present invention has a Q value of 1500 or more at 6 GHz, as measured by the perturbation method. In the low-temperature fired ceramic substrate of the present invention, ZnAl is used in the low-temperature fired ceramic. ２ O ４ Because of the deposition of a certain material, the Q-factor is large. In other words, the dielectric loss is small.

[0043] The Q value at 6 GHz, measured by the perturbation method, is preferably 2000 or higher, more preferably 2500 or higher, and even more preferably 3000 or higher.

[0044] In the low-temperature fired ceramic substrate of the present invention, voids may be formed by the burning away of the carbon-based material.

[0045] Figure 2 is a schematic cross-sectional view showing another example of the low-temperature fired ceramic substrate of the present invention. The low-temperature fired ceramic substrate 2 comprises a low-temperature fired ceramic layer 13. The low-temperature fired ceramic layer 13 has a low-temperature fired ceramic 11 and voids 17. The voids 17 are formed by the burning away of the carbon-based material.

[0046] The low-temperature fired ceramic substrate of the present invention may consist of multiple layers of low-temperature fired ceramic having low-temperature fired ceramic and pores. Furthermore, the low-temperature fired ceramic layers constituting the low-temperature fired ceramic substrate of the present invention may be provided with internal wiring or the like.

[0047] An example of a low-temperature fired ceramic substrate in which multiple low-temperature fired ceramic layers are stacked will be explained with reference to Figure 3.

[0048] Figure 3 is a schematic cross-sectional view showing another example of the low-temperature fired ceramic substrate of the present invention.

[0049] The low-temperature fired ceramic substrate 3 shown in Figure 3 comprises a laminate 4 in which multiple low-temperature fired ceramic layers 10 are stacked in the thickness direction Z. The low-temperature fired ceramic layer 10 shown in Figure 3 is the same as the low-temperature fired ceramic layer 10 shown in Figure 1. Therefore, the low-temperature fired ceramic layer 10 shown in Figure 3 also has low-temperature fired ceramic 11 and pores 17, similar to Figure 1.

[0050] The laminate 4 may further have conductive layers. These conductive layers may constitute passive elements such as capacitors and inductors, or connecting wiring that provides electrical connections between elements. Such conductive layers include conductive layers 21, 22, 23 and via-hole conductive layer 24, as shown in Figure 3.

[0051] The conductor layers 21, 22, 23 and the via-hole conductor layer 24 preferably contain Ag or Cu as the main component. By using such low-resistance metals, the occurrence of signal propagation delay associated with the high frequency of electrical signals is prevented. Furthermore, since the low-temperature fired ceramic layer 10 is a fired body produced by firing low-temperature co-fired ceramic (LTCC) material, it can be formed by co-firing with Ag and Cu.

[0052] The low-temperature fired ceramic substrate of the present invention preferably incorporates Cu wiring, and more preferably incorporates Cu wiring formed by the co-firing of low-temperature co-fired ceramic (LTCC) material and Cu.

[0053] The conductive layer 21 is located inside the laminate 4. Specifically, the conductive layer 21 is located at the interface between the low-temperature fired ceramic layers 10.

[0054] The conductive layer 22 is located on one main surface of the laminate 4. The conductive layer 23 is located on the other main surface of the laminate 4.

[0055] The via-hole conductor layer 24 is arranged to penetrate the low-temperature fired ceramic layer 10 in the thickness direction Z, and plays a role in electrically connecting conductor layers 21 of different layers, electrically connecting conductor layers 21 and 22, and electrically connecting conductor layers 21 and 23.

[0056] In the low-temperature fired ceramic substrate of the present invention, the number of low-temperature fired ceramic layers is not particularly limited.

[0057] In this invention, chip components may be mounted on the low-temperature fired ceramic substrate in a state where they are electrically connected to the conductive layer. Examples of chip components include LC filters, capacitors, inductors, and the like.

[0058] The low-temperature fired ceramic substrate of the present invention may be mounted on a mounting substrate (e.g., a motherboard) so as to be electrically connected via a conductive layer.

[0059] The low-temperature fired ceramic substrate of the present invention is manufactured, for example, as follows.

[0060] (A) Preparation of glass composition B ２ O ３ SiO ２ ZnO, Al ２ O ３ A glass composition is prepared by mixing these in predetermined proportions. The glass composition may contain alkaline earth metal oxides (RO) or alkali metal oxides (R') as needed. ２ O) and other additives may be added.

[0061] (B) Preparation of glass powder The glass composition is melted, and the resulting molten material is rapidly cooled to produce cullet. The cullet is coarsely ground, and then further ground using a ball mill or the like to prepare glass powder having a predetermined particle size.

[0062] Glass powder with SiO ２ , B ２ O ３ ZnO, Al ２ O ３ By using a material containing ZnAl, low-temperature sintering becomes possible, and ZnAl is released from the glass during firing. ２ O ４ It becomes easier for it to precipitate.

[0063] Glass powder is SiO ２ 30% or more by weight, 75% or less by weight, B ２ O ３ 10% or more by weight, 30% or less by weight of ZnO, 5% or more by weight, 20% or less by weight of Al ２ O ３ It is preferable that it contains 5% or more and 20% or less by weight of [the substance].

[0064] The glass powder contains the aforementioned SiO ２ , B ２ O ３ ZnO, Al ２ O ３ Other components such as Cu and CuO may also be included.

[0065] (C) Preparation of low-temperature co-fired ceramic (LTCC) material: Low-temperature co-fired ceramic (LTCC) material is prepared by mixing glass powder and a pore-forming agent with fillers other than silica, which are added as needed.

[0066] As a pore-forming agent, resin beads coated with an inorganic material or carbon-based materials can be used. Silica is preferred as the inorganic material for coating the resin beads. In other words, silica-coated resin beads are preferred as the resin beads coated with an inorganic material. By adding resin beads coated with an inorganic material as a pore-forming agent, pores can be formed in the low-temperature fired ceramic substrate after firing. Furthermore, if the inorganic material is silica, the crystallization of the glass during firing can be promoted. The average particle size of the resin beads coated with an inorganic material is preferably 1 μm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0067] Examples of carbon-based materials include carbon blacks such as acetylene black, Ketjen black, and furnace black, as well as carbon particles. Among these, acetylene black is preferred. The average particle size of the carbon-based material is not particularly limited, but it is preferably 0.1 μm or less. The average particle size of the carbon-based material is preferably 0.001 μm or more and 0.1 μm or less, more preferably 0.005 μm or more and 0.08 μm or less, and even more preferably 0.01 μm or more and 0.05 μm or less. As the carbon-based material contained in the LTCC material burns away, voids are formed.

[0068] Furthermore, simple resin beads (resin beads not coated with inorganic materials such as silica) or hollow silica (balloon silica) cannot be used as pore-forming agents. When simple resin beads are used as pore-forming agents, pores are initially formed by the thermal decomposition of the resin beads due to heating (approximately 500°C), but when the temperature rises further (approximately 900°C), the pores may be filled by softened glass, making it difficult to control the pore formation.

[0069] Furthermore, when hollow silica (balloon silica) is used as a pore-forming agent, when preparing green sheets to obtain low-temperature fired ceramic substrates, the hollow silica (balloon silica) floats in the raw material paste, preventing the uniform formation of pores in the thickness direction, or the hollow silica is destroyed during lamination or pressurization of the green sheets.

[0070] Furthermore, in the preparation of low-temperature co-fired ceramic (LTCC) materials, the decrease in glass viscosity during heating is suppressed by not adding silica as a filler. As a result, ZnAl ２ O ４ Crystal precipitation is promoted. By adding silica, a low dielectric material, as a filler, it is expected that the dielectric constant of the low-temperature fired ceramic substrate will decrease. However, in reality, adding silica as a filler reduces the viscosity of the glass during heating. As a result, ZnAl ２ O ４ This inhibits crystallization, making it impossible to achieve both a low dielectric constant and a high Q-factor.

[0071] Furthermore, when a carbon-based material is used as a pore-forming agent, the combustion of the carbon-based material begins after the softening of the glass during the heating process described later. As a result, the generated gas is not released, and pores are formed.

[0072] Other fillers besides silica include, for example, alumina and forsterite.

[0073] The proportion of glass powder in low-temperature co-fired ceramic (LTCC) material is preferably 60% by weight or more and 95% by weight or less. If the proportion of glass powder in the low-temperature co-fired ceramic (LTCC) material is less than 60% by weight, the Q value may decrease. On the other hand, if the proportion of glass powder in the low-temperature co-fired ceramic (LTCC) material exceeds 95% by weight, the glass powder may melt during firing, making it impossible to maintain the shape of the green sheet.

[0074] The proportion of inorganic material-coated resin beads in low-temperature co-fired ceramic (LTCC) material is preferably 10% by volume or more and 45% by volume or less. If the proportion of inorganic material-coated resin beads in the low-temperature co-fired ceramic (LTCC) material is less than 10% by volume, the proportion of voids in the low-temperature fired ceramic substrate will decrease, and the dielectric constant may not decrease sufficiently. On the other hand, if the proportion of inorganic material-coated resin beads in the low-temperature co-fired ceramic (LTCC) material exceeds 45% by volume, the proportion of voids in the low-temperature fired ceramic substrate will become too high, and the mechanical strength of the low-temperature fired ceramic substrate may decrease.

[0075] The proportion of carbon-based material in low-temperature co-fired ceramic (LTCC) material is preferably 0.1% by weight or more and 10% by weight or less, and more preferably 0.1% by weight or more and 2% by weight or less. If the proportion of carbon-based material in the low-temperature co-fired ceramic (LTCC) material is less than 0.1% by weight, the proportion of voids in the low-temperature fired ceramic substrate will decrease, and the dielectric constant may not decrease sufficiently. On the other hand, if the proportion of carbon-based material in the low-temperature co-fired ceramic (LTCC) material exceeds 10% by weight, the proportion of voids in the low-temperature fired ceramic substrate will become too high, and the mechanical strength of the low-temperature fired ceramic substrate may decrease.

[0076] The proportion of fillers other than silica in low-temperature co-fired ceramic (LTCC) materials is preferably 1% by weight or more and 10% by weight or less. If the proportion of fillers other than silica in the low-temperature co-fired ceramic (LTCC) material is less than 1% by weight, the mechanical strength may be low. On the other hand, if the proportion of fillers other than silica in the low-temperature co-fired ceramic (LTCC) material exceeds 10% by weight, the dielectric constant may become too high or crystallization may be inhibited, lowering the Q value.

[0077] (D) Preparation of Green Sheets Low-temperature co-fired ceramic (LTCC) material is mixed with a binder, plasticizer, etc. to prepare a ceramic slurry. Then, the ceramic slurry is molded onto a base film (for example, polyethylene terephthalate (PET) film) and dried to produce a green sheet.

[0078] (E) Preparation of Laminated Green Sheets Laminated green sheets (unfired state) are prepared by laminating green sheets. The green sheets will become low-temperature fired ceramic substrates (low-temperature fired ceramic layers) after firing. A conductive layer may be formed on the laminated green sheets. The conductive layer can be formed using a conductive paste containing Ag or Cu by screen printing, photolithography, etc.

[0079] (F) Firing of the laminated green sheet The laminated green sheet is fired. As a result, a low-temperature fired ceramic substrate having a laminate as shown in Figure 3 is obtained.

[0080] The firing temperature of the laminated green sheet is not particularly limited as long as it is a temperature at which the low-temperature co-fired ceramic (LTCC) material constituting the green sheet can be sintered, and may be, for example, 1000°C or lower.

[0081] The firing atmosphere for the laminated green sheet is not particularly limited, but an air atmosphere is preferred when using a material that is difficult to oxidize, such as Ag, as the conductive layer, and a low-oxygen atmosphere such as a nitrogen atmosphere is preferred when using a material that is easily oxidized, such as Cu. Furthermore, the firing atmosphere for the laminated green sheet may also be a reducing atmosphere.

[0082] Furthermore, the green sheet and the laminated green sheet may be fired while sandwiched between restraining green sheets. The restraining green sheet is made of an inorganic material (for example, Al) that does not substantially sinter at the sintering temperature of the low-temperature co-fired ceramic (LTCC) material constituting the green sheet. ２ O ３It contains as its main component. Therefore, the restraining green sheet does not shrink during firing of the green sheet and acts to suppress shrinkage in the main plane direction relative to the green sheet. As a result, the dimensional accuracy of the resulting low-temperature fired ceramic layer (especially the conductive layer) is improved.

[0083] The following are examples that more specifically disclose the low-temperature fired ceramic substrate of the present invention. However, the present invention is not limited to these examples.

[0084] (Preparation of low-temperature fired ceramic substrates) (A) Preparation of glass Glass powders G1 to G5 were prepared by the following method. First, the glass raw material powder SiO was prepared to have the composition shown in Table 1. ２ , B ２ O ３ Al ２ O ３ A glass composition was obtained by mixing ZnO powder with the glass composition. The glass composition was placed in a Pt crucible and melted in an air atmosphere at 1600°C for more than 30 minutes. Then, the resulting molten material was rapidly cooled to produce cullet. After coarse grinding the cullet, it was placed in a container with ethanol and PSZ balls (diameter: 5 mm) and mixed in a ball mill. By adjusting the mixing time during mixing in the ball mill, glass powders G1 to G5 with a median particle size of 1.0 μm were obtained. Here, "median particle size" refers to the median particle size D50 measured by laser diffraction and scattering.

[0085]

[0086] (B) Preparation of the green sheet Next, glass powders G1 to G5 and Al as a filler are mixed according to the formulations shown in Tables 2 and 3. ２ O ３ (Alumina) (Average particle size: 1 μm) and / or SiO ２Silica (average particle size: 1 μm) and silica-coated resin beads (average particle size: 3 μm) or carbon-based materials [acetylene black (average particle size: 30 nm), carbon particle A (average particle size: 1 μm), carbon particle B (average particle size: 20 μm)] were placed in a toluene-ethanol mixed solvent and mixed in a ball mill. A binder solution of polyvinyl butyral dissolved in the toluene-ethanol mixed solvent and a dioctyl phthalate (DOP) solution, which is a plasticizer, were then mixed to form a slurry. The obtained slurry was molded onto a PET film using a doctor blade and dried at 40°C to obtain green sheets P1 to P18 with a thickness of 10 μm.

[0087] (C) Preparation of low-temperature fired ceramic substrates Green sheets P1 to P18 were cut to 50 mm x 50 mm and fired in a reducing atmosphere at 990°C for 60 minutes to obtain low-temperature fired ceramic (LTCC) substrates S1 to S18 having one low-temperature fired ceramic layer. However, in the case of low-temperature fired ceramic substrates S5 and S11, the green sheets melted instead of hardening during firing and could not maintain their shape.

[0088] [Measurement of Relative Permittivity and Q-factor] For the obtained low-temperature fired ceramic substrates S1-S4, S6-S10, and S12-S18, the relative permittivity and Q-factor (reciprocal of dielectric loss) were measured at 25°C and 6GHz using the perturbation method. The measurement conditions were as follows. The results are shown in Tables 2 and 3. [Measurement equipment and measurement conditions] Network analyzer: Keysight 8757D Signal generator: Keysight synthesized sweeper 83751 Resonator: Self-made jig (resonance frequency: 6GHz) Prior to the measurement, the network analyzer and signal generator were connected and the cable loss was measured. The resonator was calibrated using a standard substrate (quartz, relative permittivity: 3.73, Q-factor: 9091@3GHz, thickness: 0.636mm).

[0089] [Composition Analysis] Furthermore, the low-temperature fired ceramic substrates S1-S4, S6-S10, and S12-S18 were pulverized, and XRD measurements were performed with Si as the standard material at a scan speed of 0.2 deg / min. The internal standard method was used to determine ZnAl ２ O ４ Quantify ZnAl ２O ４ The crystal content was determined. The results are shown in Tables 2 and 3. Note that in Tables 2 and 3, the low-temperature fired ceramic substrates S4 to S7 and S11 to S13, indicated by *, are comparative examples that do not correspond to the low-temperature fired ceramic substrate of the present invention.

[0090] [Measurement of porosity and pore diameter] Porosity and pore diameter (average diameter of pores) were measured for low-temperature fired ceramic substrates S1-S4, S7-S10, and S13-S18 using the method described above. The results are shown in Tables 2 and 3.

[0091]

[0092]

[0093] From the results in Tables 2 and 3, it was confirmed that the low-temperature fired ceramic substrates S1 to S3 using silica-coated resin beads as a pore-forming agent, and the low-temperature fired ceramic substrates S8 to S10 and S14 to S18 using carbon-based materials as pore-forming agents, all had a low relative permittivity of 3.8 or less and a high Q value exceeding 1500.

[0094] From the results of low-temperature fired ceramic substrates S14 and S15, it was confirmed that even when using carbon particles with an average particle diameter of 1 μm or more, a low-temperature fired ceramic with a relative permittivity of 3.8 or less and a Q value exceeding 1500 can be obtained, although the pore size is larger than when using acetylene black with an average particle diameter of 30 nm. From the results of low-temperature fired ceramic substrates S8 to S10 and S16 to S18, it was confirmed that by adding acetylene black at a rate of 0.1% to 10% by weight, a low-temperature fired ceramic substrate with a relative permittivity of 3.8 or less and a Q value exceeding 1500 can be obtained. Furthermore, it was confirmed that there is a correlation between the amount of carbon-based material added and the pore size, and that the pore size increases as the amount of carbon-based material added increases.

[0095] In the low-temperature fired ceramic substrate S4, the dielectric constant was high and the Q value was low. This was because no pores were formed due to the absence of a pore-forming agent, and furthermore, because silica was added as a filler, ZnAl ２ O ４This is thought to be because the crystallization of was inhibited. The porosity of the low-temperature fired ceramic substrate S4 was substantially 0%, and the pore size of the few pores that were formed was less than 1.0 μm. In the low-temperature fired ceramic substrates S5 and S11, the green sheet melted instead of hardening during firing and could not maintain its shape. This is thought to be because the proportion of glass powder G3 was high at 96 wt%, causing the glass powder to completely melt during firing. In the low-temperature fired ceramic substrates S6 and S12, the green sheet did not sinter sufficiently during firing. This is thought to be because of the SiO in the glass powder G4. ２ It is thought that the sintering did not proceed sufficiently at 990°C because the proportion was high. The low-temperature fired ceramic substrate S6, in which sintering did not proceed sufficiently, had low mechanical strength and therefore could not be used as a low-temperature fired ceramic substrate. Also, because sintering did not proceed sufficiently, ZnAl ２ O ４ It is thought that the crystals did not precipitate sufficiently. The Q values ​​were low in the low-temperature fired ceramic substrates S7 and S13. This is because the glass powder G5 does not contain ZnO, so ZnAl precipitated during firing. ２ O ４ This is thought to be because crystals did not precipitate.

[0096] 1, 2, 3 Low-temperature fired ceramic substrate 4 Laminate 10, 13 Low-temperature fired ceramic layer 10a First main surface 10b Second main surface 11 Low-temperature fired ceramic 16 Hollow silica 17 Vacancies 21, 22, 23 Conductor layer 24 Via hole conductor layer

Claims

1. A low-temperature fired ceramic substrate having a low-temperature fired ceramic containing a glass component (A1) and an oxide of a ceramic crystal component (C1) after firing, and pores, wherein the oxide of the ceramic crystal component (C1) is ZnAl ２ O ４ A low-temperature fired ceramic substrate containing crystals, wherein the low-temperature fired ceramic substrate has a relative permittivity of 3.8 or less and a Q value of 1500 or more at 6 GHz as measured by the perturbation method.

2. The low-temperature fired ceramic substrate according to claim 1, wherein the voids are formed by the burning away of the carbon-based material.

3. The low-temperature fired ceramic substrate according to claim 2, wherein the average particle size of the carbon-based material is 0.1 μm or less.

4. The low-temperature fired ceramic substrate according to claim 2 or 3, wherein the carbon-based material is acetylene black.

5. The low-temperature fired ceramic substrate according to claim 1, wherein the voids are composed of hollow silica, which is a fired body of silica-coated resin beads.

6. The glass component (A1) after firing is SiO ２ and B ２ O ３ A low-temperature fired ceramic substrate according to any one of claims 1 to 5, including the above.

7. The aforementioned ZnAl ２ O ４ The low-temperature fired ceramic substrate according to any one of claims 1 to 6, wherein the crystals are uniformly precipitated in the post-fired glass component (A1).

8. A low-temperature fired ceramic substrate according to any one of claims 1 to 7, wherein the porosity is 10% or more and 45% or less.

9. The low-temperature fired ceramic substrate according to any one of claims 1 to 8, wherein the average diameter of the pores is 1 μm or more and 10 μm or less.

10. The low-temperature fired ceramic substrate according to any one of claims 1 to 9, wherein the average diameter of the pores is 1 μm or more and 3 μm or less.

11. A low-temperature fired ceramic substrate according to any one of claims 1 to 10, wherein the relative permittivity at 6 GHz, as measured by the perturbation method, is 3.3 or less.

12. The content of the ZnAl ２ O ４ crystal is 10% by weight or more and 38% by weight or less. The low-temperature fired ceramic substrate according to any one of claims 1 to 11.

13. SiO in the glass component (A1) after firing. ２ The low-temperature fired ceramic substrate according to any one of claims 1 to 12, wherein the content of is 50 mol% or more and 80 mol% or less.

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