JPWO2020085148A1 - Ceramic substrate - Google Patents

Abstract

The ceramic substrate contains Al2O3, SiO2 and MnO as essential components, and at least one of Mo and Cr2O3 as an optional component. In the ceramic base, the content of Al2O3 is 82.0% by mass or more and 95.0% by mass or less, the content of SiO2 is 3.0% by mass or more and 8.0% by mass or less, and the content of MnO. However, the total content of Mo and Cr2O3 in terms of MoO3 is 4.0% by mass or less, and the remaining content is 4.0% by mass or less. It is less than 0.1% by mass.

Description

The present invention relates to a ceramic substrate.

In Patent Document 1, as an example of the ceramic base material, 90% by mass or more of Al ₂ O ₃ , 1 to 6% by mass of SiO _2, and 2 to 8% by mass of _{Mn Al 2} O _{4 in terms of Mn 2} O ₃ An insulating substrate containing 2% by mass or less of Mo is disclosed. It is said that the insulating substrate described in Patent Document 1 preferably contains Mg in a proportion of 0.1 to 3% by mass in terms of oxide in order to improve the stability of strength.

In Patent Document 2, as an example of the ceramic base material, Al ₂ O _{3 as a main component, SiO 2 of} 3 to 7.5% by mass, Mn of ₂ to 5% by mass in terms of Mn 2 O _{3, and MgO} An insulating substrate containing 0.3 to 0.7% by mass of Mg in terms of conversion and 0.3 to 0.7% by mass of Mo in terms of MoO is disclosed.

In Patent Document 3, Al is 89.0 to 92.0% by mass in terms of _{Al 2} O _{3 , Si is 2.0 to 5.0% by mass in terms of SiO 2} , and Mn is 2.0 to 5 in terms of MnO. .0 wt%, 0 to 2.0 wt% of Mg in terms of MgO, ceramic green body containing 0.05 to 2.0 wt% of Zr in terms of ZrO ₂ is disclosed.

Japanese Patent No. 4413224 Japanese Patent No. 5784153 International Publication No. 2015/141099

The ceramic substrates described in Patent Documents 1 to 3 have a problem that dimensional variation is likely to occur. As a result of diligent studies, the present inventors have made a balance excluding _{Al 2} O _{3 which is the main component, SiO 2} and Mn O as sintering aids, and Mo or / and Cr _{2 O 3 as colorants.} We obtained a new finding that the content of is affecting the dimensional variation.

An object of the present invention is to provide a ceramic substrate capable of suppressing dimensional variation.

The ceramic substrate according to the present invention contains Al ₂ O ₃ , SiO ₂ and Mn O as essential components, and contains at least one of _{Mo and Cr 2 O 3 as optional components.} In the ceramic substrate, _{the content of Al 2} O ₃ is 82.0% by mass or more and 95.0% by mass or less, and _{the content of SiO 2} is 3.0% by mass or more and 8.0% by mass or less. the content of MnO is not more than 2.0 mass% to 6.0 mass%, the sum of the content of content and _Cr 2 _{O 3} of Mo calculated as MoO ₃ is 4.0 wt% or less Yes, the content of the balance is less than 0.1% by mass.

According to the present invention, it is possible to provide a ceramic substrate capable of suppressing dimensional variation.

It is sectional drawing which shows the structure of the 1st ceramic package which concerns on embodiment. It is sectional drawing which shows the structure of the 2nd ceramic package which concerns on embodiment. It is sectional drawing which shows the structure of the multilayer circuit board in the 2nd ceramic package which concerns on embodiment.

(Ceramic base)
The ceramic base is a composition obtained by sintering a green sheet obtained by molding ceramic material powder into a tape or a compact formed by compacting ceramic material powder. The ceramic substrate according to the present embodiment is a ceramic package for sealing an oscillator such as a crystal oscillator, a ceramic package for encapsulating a semiconductor element such as a CMOS image sensor, or a ceramic package for encapsulating an optical semiconductor element. Suitable for various ceramic packages.

The ceramic substrate according to the present embodiment contains Al ₂ O _{3 (alumina) as a main component and SiO 2} (silica) and MnO (manganese oxide) as sintering aids as essential components.

The ceramic substrate contains at least one of Mo (molybdenum) and Cr ₂ O ₃ (chromium oxide) as an optional component as a colorant. Ceramic green body, as a colorant, may contain only Mo, may contain only the Cr ₂ O _3, may also contain both of Mo and Cr ₂ O _3, Furthermore, it does not have to contain both Mo and Cr ₂ O _3. When the ceramic substrate contains Mo as a colorant, at least a part of Mo may be present as a metal, or at least a part of Mo may be present in the form of an oxide (eg, MoO ₃ ). good.

The content of each component constituting the ceramic substrate is as follows.

・ Al ₂ O ₃ :
82.0% by mass or more and 95.0% by mass or less ・ SiO ₂ :
3.0% by mass or more and 8.0% by mass or less ・ MnO:
2.0% by mass or more and 6.0% by mass or less ・ Total of Mo content and Cr ₂ O _{3 content in terms of MoO 3:}
4.0% by mass or less ・ Remaining:
Less than 0.1% by mass

As described above, in the ceramic substrate according to the present embodiment, _{the content of the balance other than Al 2} O ₃ , SiO ₂ , MnO and the colorant (Mo or / and Cr ₂ O ₃ ) is suppressed to less than 0.1% by mass. Therefore, each component is uniformly sintered in a dispersed state without segregation. Therefore, in the ceramic substrate according to the present embodiment, dimensional variation is suppressed.

Further, since the content of the balance of the ceramic base material is suppressed to less than 0.1% by mass, each component is uniformly sintered in a dispersed state without segregation, so that the content is low in the flux of the glass component. It is possible to suppress the local generation of the melting point region. Therefore, it is possible to prevent the ceramic base material from sticking to the firing setter.

Further, since the content of the balance of the ceramic base material is suppressed to less than 0.1% by mass, each component is uniformly sintered in a dispersed state without segregation, so that the ceramic base material is uniformly sintered in the back side region on the calcined setter side. The timing at which the glass component melts can be matched with the timing at which the glass component melts in the front region opposite to the firing setter. Therefore, it is possible to prevent the ceramic base material from warping in the thickness direction.

The content of the balance in the ceramic substrate is more preferably less than 0.05% by mass. Thereby, the dimensional variation of the ceramic base material can be further suppressed.

The content of the balance in the ceramic substrate is particularly preferably 0% by mass. As a result, not only the dimensional variation of the ceramic base material can be further suppressed, but also the sticking of the ceramic base material to the firing setter can be further suppressed.

In the ceramic substrate, _{the ratio of the content of SiO 2 to} the content of MnO is not particularly limited, but is preferably 0.8 or more and 3.5 or less. Within this range, the _{precipitation of Mn 3} Al ₂ Si ₃ O ₁₂ in the ceramic substrate can be suppressed, so that the occurrence of color unevenness due to the precipitation of _{Mn 3} Al ₂ Si ₃ O _{12 can be reduced.} .. Further, when the ceramic substrate is applied to a ceramic package for encapsulating a vibrator or a semiconductor element, _{the ratio of the content of SiO 2 to} the content of MnO is particularly preferably 0.8 or more and 2.1 or less. Thereby, the bending strength of the ceramic base material can be particularly improved. On the other hand, when the ceramic substrate is applied to a ceramic package for encapsulating an optical semiconductor element, the ratio of the content of SiO2 to the content of MnO is particularly preferably 1.9 or more and 3.5 or less. As a result, although the bending strength of the ceramic base is slightly reduced, the relative permittivity of the ceramic base can be easily adjusted to 8.0 or more and 9.0 or less.

The ceramic substrate contains a crystalline phase and a glass phase. When the ceramic substrate contains Mo as a colorant, the crystal phase includes an Al ₂ O ₃ crystal phase as a main crystal phase and a Mo crystal phase as a sub crystal phase. The crystal phase may include a _{crystal phase other than the Al 2} O ₃ crystal phase and the Mo crystal phase (hereinafter, referred to as “remaining crystal phase”). On the other hand, when the ceramic substrate does not contain Mo as a colorant, the crystal phase contains an Al ₂ O ₃ crystal phase as a main crystal phase. The crystal phase may contain the remaining crystal phase in addition to _{the Al 2} O _{3 crystal phase.} The crystal phase may contain only one kind of crystal phase or a plurality of kinds of crystal phases as the remaining crystal phase.

Here, when the crystal phase is identified from the X-ray diffraction pattern by crushing the ceramic substrate, the main peak intensity of the X-ray diffraction pattern of the remaining crystal phase is the main peak of the X-ray diffraction pattern of the Al ₂ O ₃ crystal phase. It is preferably 0.5% or less with respect to the strength. As a result, it is possible to suppress the occurrence of distortion in the glass phase due to the presence of the remaining crystal phase, so that the bending strength (so-called bending strength) of the ceramic substrate can be improved.

The bending strength of the ceramic substrate is set according to the properties required for the ceramic package to which the ceramic substrate is applied. For example, when the ceramic base is applied to a ceramic package for encapsulating a vibrator or a semiconductor element, the bending strength of the ceramic base is preferably 700 MPa or more. When the ceramic base is applied to a ceramic package for encapsulating an optical semiconductor element, the bending strength of the ceramic base is preferably 390 MPa or more. In the present embodiment, the "bending strength" means a three-point bending strength, and is a value measured at room temperature in accordance with JIS R1601 (bending test method for fine ceramics).

The relative permittivity of the ceramic substrate is set according to the characteristics required for the ceramic package to which the ceramic substrate is applied. For example, when the ceramic substrate is applied to a ceramic package for encapsulating a vibrator or a semiconductor element, the relative permittivity of the ceramic substrate is not particularly limited. When the ceramic base material is applied to a ceramic package for encapsulating an optical semiconductor element, the relative permittivity of the ceramic base material is preferably 8.0 or more and 9.0 or less.

The porosity of the ceramic substrate is set according to the properties required for the ceramic package to which the ceramic substrate is applied. For example, when the ceramic base is applied to a ceramic package for encapsulating a vibrator or a semiconductor element, the porosity of the ceramic base is preferably 3% or less. When the ceramic base is applied to a ceramic package for encapsulating an optical semiconductor element, the porosity of the ceramic base is preferably 3% or more and 8% or less. In the present embodiment, the "porosity" is a value measured by photographing a polished ceramic cross section with an electron microscope and binarizing it with image processing software.

(Ceramic package)
Here, two configuration examples of the ceramic package to which the ceramic substrate according to the present embodiment is applied will be described with reference to the drawings.

(1) First ceramic package 100
FIG. 1 is a cross-sectional view of the first ceramic package 100.

The first ceramic package 100 includes an insulating substrate 1, a plurality of conductor layers 2, a metallized layer 3, a crystal oscillator 4, a CMOS image sensor 6, a plating layer 8, and a lid 10. The first ceramic package 100 seals the crystal oscillator 4 and the CMOS image sensor 6.

The insulating substrate 1 is made of the above-mentioned ceramic substrate. The content of each component constituting the insulating substrate 1 is as follows.

・ Al ₂ O ₃ :
82.0% by mass or more and 95.0% by mass or less ・ SiO ₂ :
3.0% by mass or more and 8.0% by mass or less ・ MnO:
2.0% by mass or more and 6.0% by mass or less ・ Total of Mo content and Cr ₂ O _{3 content in terms of MoO 3:}
4.0% by mass or less ・ Remaining:
Less than 0.1% by mass

As described above, in the insulating substrate 1 according to the present embodiment, since the content of the remaining portion is suppressed to less than 0.1% by mass, each component is uniformly sintered in a dispersed state without segregation. As a result, dimensional variation is suppressed. The bending strength of the insulating substrate 1 is preferably 700 MPa or more. The porosity of the insulating substrate 1 is preferably 3% or less.

The insulating substrate 1 has a bottom portion 1a and a side wall portion 1b. The side wall portion 1b is arranged on the outer edge of the bottom portion 1a. The bottom portion 1a and the side wall portion 1b may be integrally formed.

Each conductor layer 2 is provided so as to penetrate the bottom portion 1a. The metallized layer 3 is arranged on the upper surface of the side wall portion 1b. The metallized layer 3 is formed in a ring shape. The metallized layer 3 can be formed by using W or Mo as a main component as a conductor and adding a small amount of a ceramic component to the main component. Further, the insulating substrate 1 and the metallized layer 3 according to the present embodiment are produced by simultaneous firing in a reducing atmosphere containing hydrogen, nitrogen, and water vapor.

The crystal oscillator 4 is an example of an oscillator. The crystal oscillator 4 is connected to the conductor layer 2 via the conductive adhesive 5. The CMOS image sensor 6 is an example of a semiconductor element. The CMOS image sensor 6 is connected to the conductor layer 2 via wire bonding 7.

The plating layer 8 is arranged on the upper surface of the metallize layer 3. The plating layer 8 is formed in an annular shape. The lid 10 is arranged on the plating layer 8 via the eutectic Ag-Cu brazing material 9. The lid 10 closes the opening of the side wall portion 1b. The lid body 10 can be made of a metal material.

(2) Second ceramic package 200
FIG. 2 is a cross-sectional view of the second ceramic package 200.

The second ceramic package 200 includes a base 11, an electronic cooling element 12, an optical semiconductor element 13, a multilayer circuit board 14, a frame body 15, a seal ring 16, a lid 17, a translucent window member 18, a pipe 19, and an optical fiber connection. A tube 20a and an optical fiber 20b are provided. The second ceramic package 200 seals the optical semiconductor element 13. The second ceramic package 200 is a so-called optical module.

The base 11 is formed in a plate shape. The base 11 is made of a material having high thermal conductivity such as copper tungsten. The electronic cooling element 12 is arranged on the base 11. The optical semiconductor element 13 is arranged on the electronic cooling element 12.

The multilayer circuit board 14 is arranged on the outer edge of the base 11. The multilayer circuit board 14 is provided with input terminals 30a and 30b exposed to the outside of the package and output terminals 31a and 31b exposed to the inside of the package. A positive phase signal is input to the input terminal 30a from the outside. A positive phase signal and a negative phase negative phase signal are input to the input terminal 30b. The positive phase signal input to the input terminal 30a is output from the output terminal 31a to the optical semiconductor element 13 via the bonding wire 13a. The reverse phase signal input to the input terminal 30b is output from the output terminal 31b to the optical semiconductor element 13 via the bonding wire 13b. In the following description, the positive phase signal and the negative phase signal are collectively referred to as a differential signal.

The frame body 15 is arranged on the multilayer circuit board 14. The seal ring 16 is arranged on the upper surface of the frame body 15. The seal ring 16 is a member for welding the lid 17. Each of the seal ring 16 and the lid 17 can be made of Kovar or the like in which nickel and cobalt are mixed with iron.

The pipe 19 is fitted into the hole 19a formed between the multilayer circuit board 14 and the frame body 15. The pipe 19 accommodates the translucent window member 18. The translucent window member 18 is made of sapphire, glass, or the like. An optical fiber connecting pipe 20a is connected to the pipe 19. Each of the pipe 19 and the optical fiber connecting tube 20a can be configured by Kovar or the like. The optical fiber 20b is fixed to the optical fiber connecting tube 20a.

Here, FIG. 3 is an exploded perspective view showing the configuration of the multilayer circuit board 14.

The multilayer circuit board 14 includes 6-layer circuit boards 14a to 14f, first signal lines 21a, 22a, 23a, second signal lines 21b, 22b, 23b, ground layers 24a, 24b, 24c, ground vias 25a, 25b, 25c. , And ground terminals 26a, 26b, 26c.

Each circuit board 14a to 14f is composed of the above-mentioned ceramic substrate. The content of each component constituting each circuit board 14a to 14f is as follows.

・ Al ₂ O ₃ :
82.0% by mass or more and 95.0% by mass or less ・ SiO ₂ :
3.0% by mass or more and 8.0% by mass or less ・ MnO:
2.0% by mass or more and 6.0% by mass or less ・ Total of Mo content and Cr ₂ O _{3 content in terms of MoO 3:}
4.0% by mass or less ・ Remaining:
Less than 0.1% by mass

As described above, in the circuit boards 14a to 14f according to the present embodiment, since the content of the balance is suppressed to less than 0.1% by mass, each component is uniformly baked in a dispersed state without segregation. By being tied, dimensional variation is suppressed. The relative permittivity of each of the circuit boards 14a to 14f is preferably 8.0 or more and 9.0 or less. The bending strength of each of the circuit boards 14a to 14f is preferably 390 MPa or more. The porosity of each of the circuit boards 14a to 14f can be 3% or more and 8% or less.

The six-layer circuit boards 14a to 14f are laminated in this order. The input terminals 30a and 30b and the output terminals 31a and 31b described above are provided on the sixth layer circuit board 14f.

Of the first signal lines 21a, 22a, 23a, the input side via connection portion 21a is configured as a via conductor penetrating from the sixth layer circuit board 14f to the third layer circuit board 14c, and is configured as a via conductor with the first input terminal 30a. The interlayer wiring portion 22a is connected. Of the first signal lines 21b, 22b, 23b, the input side via connection portion 21b is configured as a via conductor penetrating from the sixth layer circuit board 14f to the fifth layer circuit board 14e, and is configured as a via conductor with the second input terminal 30b. Connect between the interlayer wiring portions 22b.

Of the first signal lines 21a, 22a, 23a, the output side via connection portion 23a is configured as a via conductor penetrating from the sixth layer circuit board 14f to the third layer circuit board 14c, and is configured as the first output terminal 31a. And the interlayer wiring portion 22a are connected. Of the second signal lines 21b, 22b, 23b, the output side via connection portion 23b is configured as a via conductor penetrating from the sixth layer circuit board 14f to the fifth layer circuit board 14e, and is configured with the second output terminal 31b. Connect between the interlayer wiring portions 22b.

A ground layer 24b is arranged between the two interlayer wiring portions 22a and 22b. A ground layer 24a is provided on the first layer circuit board 14a provided with the interlayer wiring portion 22a. A ground layer 24c is provided on the fifth layer circuit board 14e provided with the interlayer wiring portion 22b.

The ground layers 24a, 24b, 24c form a conductive metal electrode. The ground layers 24a, 24b, 24c are connected to the ground terminals 26a, 26b, 26c on the circuit board 14f of the sixth layer via the ground vias 25a, 25b, 25c.

The positive phase signal input to the input terminal 30a by the multilayer circuit board 14 having the above configuration is transmitted to the output terminal 31a via the first signal lines 21a, 22a, 23a, and then via the bonding wire 13a. It is output to the optical semiconductor element 13. Further, the reverse phase signal input to the input terminal 30b is transmitted to the second output terminal 31b via the second signal lines 21b, 22b, 23b, and then output to the optical semiconductor element 13 via the bonding wire 13b. NS. The optical semiconductor element 13 is driven by the differential signals input from the output terminals 31a and 31b, and outputs the laser light signal to the translucent window member 18 side. The optical signal output from the optical semiconductor element 13 is transmitted by the optical fiber 20b.

With respect to the ceramic substrates according to Examples 1 to 17 and Comparative Examples 1 to 8, dimensional variation, sticking to a firing setter, warpage, color unevenness, bending strength and relative permittivity were confirmed.
(Preparation of sample)
Each raw material powder was mixed at the ratio shown in Table 1 to obtain a mixed powder.

Polyvinyl butyral, a tertiary amine and a phthalate ester (diisononyl phthalate: DINP) were mixed as an organic component with the obtained mixed powder, and IPA (isopropyl alcohol) and toluene were further mixed as a solvent to prepare a slurry. ..

Using the prepared slurry, a ceramic tape having a thickness of 50 to 400 μm was prepared by a doctor blade method. The obtained ceramic tape was cut into a length of 50 mm and a width of 50 mm, arranged on a firing setter made of Mo, and fired (2 hours) at the firing temperature (maximum temperature) shown in Table 1. As a result, 100 fired substrates for each of Examples 1 to 17 and Comparative Examples 1 to 8 were prepared. The temperature variation in the furnace when firing at the firing temperature shown in Table 1 was within the range of ± 5 ° C.

(Dimension variation)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the dimensional variation when firing at the firing temperature shown in Table 1 was measured. Specifically, the external dimensions of the fired substrate were measured using a dimensional measuring device, the average value and standard deviation were calculated, and the value obtained by dividing the standard deviation by the average value was defined as the dimensional variation. In Table 1, those having a dimensional variation of less than 0.20 are evaluated as ◯, those having a dimensional variation of 0.20 or more and less than 0.50 are evaluated as Δ, and those having a dimensional variation of 0.50 or more are evaluated as ×. evaluated.

(Attachment to the firing setter)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the number of fired substrates that were attached to the fired setter and had defects in the ceramic substrate was counted. In Table 1, those with no defects were evaluated as ◯, those with defects on 1 to 4 sheets were evaluated as Δ, and those with defects on 5 or more sheets were evaluated as ×.

(warp)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the average value of the amount of warpage of the fired substrate was measured using a three-dimensional shape measuring device. In Table 1, those having a warp amount of less than 100 μm were evaluated as ◯, those having a warp amount of 100 μm or more and less than 200 μm were evaluated as Δ, and those having a warp amount of 200 μm or more were evaluated as ×.

(Color unevenness)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the color unevenness of the fired substrate was observed using a stereomicroscope. In Table 1, those having no color unevenness were evaluated as ◯, and those having color unevenness were evaluated as ×.

(Strength)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the bending strength of the fired substrate was measured at room temperature according to the 3-point bending strength test of JIS R1601.

(Relative permittivity)
For each of Examples 1 to 17 and Comparative Examples 1 to 8, the relative permittivity of the fired substrate was measured at room temperature and a frequency of 10 GHz according to the cavity resonance method of JISR1641.

In Examples 1 to 17, dimensional variation, sticking to the setter, and warpage could be suppressed as compared with Comparative Examples 1 to 8. _{This is because the content of the balance other than Al 2} O ₃ , SiO ₂ , MnO and the colorant (Mo or / and Cr ₂ O ₃ ) contained in the ceramic substrate was suppressed to less than 0.1% by mass, so that each component contained This is because it was possible to uniformly sinter in a dispersed state without segregation. It has been experimentally confirmed that the same result can be obtained even when additives other than MgO, ZrO _{2, CaO and BaO are added.}

Further, in Examples 1 to 9 and 12 to 17 in which the content of the balance was 0.07% by mass or less, the warp could be further suppressed.

Further, in Examples 1 to 8 and 12 to 17 in which the content of the balance was less than 0.05% by mass, the dimensional variation could be further suppressed.

Further, in Examples 1 to 5 and 12 to 17 in which the content of the balance was less than 0% by mass, not only the dimensional variation but also the sticking to the setter could be further suppressed.

Further, in _{Examples 1 to 15 in which the ratio of the content of SiO 2 to} the content of MnO was 0.8 or more and 2.1 or less, the bending strength could be 700 MPa or more. Therefore, it was found that 1 to 15 are suitable for ceramic packages requiring strength (for example, those for encapsulating a vibrator or a semiconductor element).

Further, in _{Examples 15 to 17 in which the ratio of the content of SiO 2 to} the content of MnO was 1.9 or more and 3.5 or less, the relative permittivity of 8.0 or more and 9.0 or less and the bending resistance of 390 MPa or more were obtained. It was possible to achieve both strength and strength. Therefore, it was found that Examples 15 to 17 are suitable for ceramic packages (for example, those for encapsulating an optical semiconductor element) that require a relatively low relative permittivity.

100 1st ceramic package 1 Insulated substrate 200 2nd ceramic package 6 Multilayer circuit board 14a to 14f Circuit board

Claims (5)

Al ₂ O ₃ , SiO ₂ and MnO are contained as essential components, and _{at least one of Mo and Cr 2} O ₃ is contained as an optional component.
The content of Al ₂ O ₃ is 82.0% by mass or more and 95.0% by mass or less.
The content of SiO ₂ is 3.0% by mass or more and 8.0% by mass or less.
The MnO content is 2.0% by mass or more and 6.0% by mass or less.
The total of the Mo content and the Cr ₂ O ₃ content in terms of MoO ₃ is 4.0% by mass or less.
The content of the balance is less than 0.1% by mass,
Ceramic substrate. The content of the balance is less than 0.05% by mass,
The ceramic substrate according to claim 1. The ratio of the content of SiO _{2 to} the content of MnO is 0.8 or more and 3.5 or less.
The ceramic substrate according to claim 1 or 2. The bending strength is 700 MPa or more.
The ceramic substrate according to any one of claims 1 to 3. The relative permittivity at 10 GHz is 8.0 or more and 9.0 or less.
The bending strength is 390 MPa or more.
The ceramic substrate according to any one of claims 1 to 3.

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