Alumina substrate, and method for manufacturing an alumina substrate

Abstract

The present invention provides an alumina substrate that can be warped and have fine wiring installed, and a method for manufacturing an alumina substrate. [Solution] The alumina substrate 1 contains 98.89% by mass or more of aluminum oxide, and additives including silicon dioxide and calcium oxide, wherein the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide, and the number average crystal diameter of aluminum oxide on at least one main surface 11 of the substrate is 0.34 μm or more and 0.57 μm or less.

Description

Technical Field

[0001] The present invention relates to an alumina substrate and a method for manufacturing the alumina substrate.

Background Art

[0002] In recent years, due to the requirements for higher precision and higher reliability of electronic components, the miniaturization of electrodes and resistor films formed on substrates has been progressing. As such a substrate for electronic components, an alumina substrate mainly composed of aluminum oxide may be used. In this case, it is desirable that the alumina substrate be smooth with a small grain boundary step and few surface pores, and for this purpose, it is preferable that the crystal diameter of the substrate be small. For example, Patent Document 1 below discloses an alumina substrate having a particle size on the submicron order.

[0003] Further, after firing of the alumina substrate, the alumina substrate may be warped. In this case, a process of correcting the warp by performing heat treatment while applying a load to the fired substrate may be performed. As disclosed in Non-Patent Document 1 below, since the elastic modulus of aluminum oxide rapidly decreases at 1350°C or higher, it is preferably performed at 1350°C or higher.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, correcting the warp of an alumina substrate at the above temperature may increase the surface roughness of the alumina substrate. If the surface roughness of the alumina substrate increases significantly, there is a concern that wire breakage may occur when creating fine wiring. Therefore, there is a need for an alumina substrate that can be corrected for warping and that allows for the creation of fine wiring.

[0007] Therefore, the present invention aims to provide an alumina substrate that can correct warping and provide fine wiring, and a method for manufacturing an alumina substrate. [Means for solving the problem]

[0008] The alumina substrate of the present invention contains 98.89% by mass or more of aluminum oxide and an additive containing silicon dioxide and calcium oxide, wherein the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide, and the number average crystal diameter of the aluminum oxide on at least one main surface of the substrate is 0.34 μm or more and 0.57 μm or less.

[0009] The inventors, after diligent research, have found that with an alumina substrate under these conditions, even when warping correction is performed at an efficient heat treatment temperature of around 1400°C, a significant increase in the surface roughness of the main surface of the substrate can be suppressed. Therefore, the alumina substrate of the present invention can suppress a significant increase in surface roughness and correct warping. Consequently, the alumina substrate of the present invention can correct warping and provide fine wiring.

[0010] Furthermore, it is preferable that the mass of silicon dioxide in the additive is 1.92 times or more the sum of the mass of calcium oxide and the mass of magnesium oxide.

[0011] Furthermore, it is preferable that the standard deviation of the number-mean crystal diameter is 0.37 or less.

[0012] It is preferable that the area ratio of voids on the main surface of the substrate is 0.60% or less.

[0013] It is preferable that the average diameter of voids on the main surface of the substrate is less than 0.50 μm.

[0014] It is preferable that the maximum diameter of the voids on the main surface of the substrate is less than 1.3 μm.

[0015] It is preferable that the arithmetic mean height Sa of the main surface of the substrate is 0.136 μm or more and 0.146 μm or less.

[0016] Furthermore, the present invention provides a method for manufacturing an alumina substrate, comprising the steps of: preparing a ceramic green sheet in which raw material powder containing aluminum oxide and a sintering aid containing silicon and calcium is dispersed; and firing the ceramic green sheet at 1400°C to 1550°C for 1 hour to 8 hours, wherein the ratio of aluminum oxide in the raw material powder is 98.89% by mass or more when each material contained in the sintering aid is an oxide, the mass of silicon to the mass of calcium in the sintering aid is 5.36 times or more in terms of oxide, and the number-average particle size of the aluminum oxide in the raw material powder is such that the number-average crystal diameter of the aluminum oxide after firing the ceramic green sheet is 0.34 μm or more and 0.57 μm or less.

[0017] According to such a manufacturing method of an alumina substrate, it is possible to manufacture an alumina substrate containing 98.89 mass% or more of aluminum oxide and an additive containing silicon dioxide and calcium oxide, and the mass of silicon dioxide with respect to the mass of calcium oxide is 5.36 times or more. Further, according to this manufacturing method, the number average crystal diameter of aluminum oxide on at least one main surface of the substrate can be 0.34 μm or more and 0.57 μm or less. Therefore, for an alumina substrate manufactured by such a manufacturing method of an alumina substrate, it is possible to suppress a remarkable increase in surface roughness and correct warpage. That is, according to the manufacturing method of the present alumina substrate, it is possible to manufacture an alumina substrate on which warpage is corrected and fine wiring can be provided. Note that the oxide of calcium refers to calcium oxide (CaO), and the oxide of silicon refers to silicon dioxide (SiO2).

Advantages of the Invention

[0018] As described above, according to the present invention, there are provided an alumina substrate on which warpage is corrected and fine wiring can be provided, and a manufacturing method of an alumina substrate.

Brief Description of the Drawings

[0019] [Figure 1] It is a plan view showing an alumina substrate. [Figure 2] It is a cross-sectional view of an alumina substrate. [Figure 3] It is a flowchart showing the procedure of a manufacturing method of an alumina substrate. [Figure 4] It is a view showing a state of producing a ceramic green sheet. [Figure 5] It is a view showing a state of a ceramic green sheet during firing.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments for implementing the alumina substrate and the method for manufacturing the alumina substrate according to the present invention are illustrated together with the accompanying drawings. The embodiments illustrated below are for facilitating the understanding of the present invention and are not for limiting and interpreting the present invention. The present invention can be changed and improved from the following embodiments without departing from the gist thereof within the scope of the claims. In the drawings referred to below, for the sake of easy understanding, the dimensions of each member may be shown changed.

[0021] FIG. 1 is a plan view showing the alumina substrate of the present embodiment, and FIG. 2 is a cross-sectional view of the alumina substrate in the thickness direction. The alumina substrate 1 is an alumina mother substrate on which a plurality of individual pieces 2 serving as alumina substrates for component mounting, shown by broken lines, are provided adjacent to each other. The alumina substrate 1 of the present embodiment is plate-shaped and includes one main surface 11 and the other main surface 12 facing each other. One main surface 11 is, for example, the main surface on the side where circuits such as resistors are arranged, and the other main surface 12 is, for example, the main surface on the side where electrodes and the like are arranged and where it is mounted on a circuit board or the like. In FIG. 1, only one main surface 11 is labeled. In the present embodiment, the main surfaces 11 and 12 are generally rectangular, the length of one pair of opposite sides is approximately 80 mm each, and the length of the other pair of opposite sides is approximately 70 mm each. Also, the thickness of the alumina substrate 1 is 0.1 mm or more and 1.0 mm or less, preferably 0.2 mm or more and 0.5 mm or less, and in this example, it is approximately 0.38 mm.

[0022] The alumina substrate 1 includes aluminum oxide with a content of 98.89% by mass or more and an additive containing silicon dioxide and calcium oxide. Therefore, the content of the additive is 1.11% by mass or less. The mass of silicon dioxide with respect to the mass of calcium oxide is 5.36 times or more. That is, the value obtained by dividing the mass of silicon dioxide by the mass of calcium oxide is 5.36 or more. The mass of silicon dioxide with respect to the mass of calcium oxide is preferably 6.00 times or more, and more preferably 7.00 times or more. Also, the mass of silicon dioxide with respect to the mass of calcium oxide is preferably 7.14 times or less.

[0023] Furthermore, the alumina substrate 1 may also contain magnesium oxide as an additive. In this case, it is preferable that the mass of silicon dioxide is 1.92 times or more the sum of the masses of calcium oxide and magnesium oxide. That is, it is preferable that the value obtained by dividing the mass of silicon dioxide by the sum of the masses of calcium oxide and magnesium oxide is 1.92 or more. By having a mass of silicon dioxide of 1.92 times or more the sum of the masses of calcium oxide and magnesium oxide, it is possible to suppress the increase in surface roughness of the alumina substrate 1 due to straightening and to lower the firing temperature required for densification of the particles. Lowering the firing temperature can extend the lifespan of the furnace material and reduce energy costs. It is more preferable that the mass of silicon dioxide is 2.10 times or more the sum of the masses of calcium oxide and magnesium oxide, and even more preferable that it is 2.40 times or more. It is also preferable that the mass of silicon dioxide is 2.56 times or less the sum of the masses of calcium oxide and magnesium oxide. By keeping the mass of silicon dioxide 2.56 times or less the sum of the masses of calcium oxide and magnesium oxide, the firing temperature required for densification of the particles can be lowered.

[0024] The number-average crystal diameter of aluminum oxide on the main surfaces 11 and 12 of the alumina substrate 1 is between 0.34 μm and 0.57 μm. However, the number-average crystal diameter of aluminum oxide on the main surface 12 may fall outside the range of 0.34 μm to 0.57 μm. In this example, the number-average crystal diameter is measured as follows. Images of the main surfaces 11 and 12 can be obtained, for example, by a scanning electron microscope (SEM). Specifically, for example, an image of a region of approximately 19 μm × approximately 25 μm is obtained using a field emission scanning electron microscope (FE-SEM) "Regulus8100" manufactured by Hitachi High-Tech Corporation, with a semiconductor backscattered electron detector (PD-BSE), an acceleration voltage of 5 keV, and a magnification of 5000x. This image is then analyzed using software "A-zo-kun" manufactured by Asahi Kasei Engineering Corporation to calculate the above number-average crystal diameter.

[0025] The standard deviation of this number-mean crystal diameter is preferably 0.37 or less. In this case, there is a tendency for large crystals to be absent, large steps are less likely to occur around the crystals, and the occurrence of disconnections can be further suppressed when fine wiring is formed on the alumina substrate 1.

[0026] Furthermore, it is preferable that voids are absent from the main surfaces 11 and 12. Even if voids are present on the main surface 12, it is preferable that voids are absent from the main surface 11. Even if voids are present on the main surfaces 11 and 12, it is preferable that the area ratio of such voids on the main surfaces 11 and 12 is 0.60% or less. Furthermore, it is preferable that the average diameter of such voids is less than 0.50 μm. Furthermore, it is preferable that the maximum diameter of such voids is less than 1.3 μm. By having the area ratio, average diameter, and maximum diameter of the voids within the above ranges, the occurrence of disconnections can be suppressed when fine wiring is formed on the alumina substrate 1. The area ratio, average diameter, and maximum diameter of the voids are calculated by acquiring images of the main surfaces 11 and 12 and analyzing the images, in the same manner as when calculating the number-average crystal diameter on the main surfaces 11 and 12, except that an area of ​​approximately 48 μm × approximately 64 μm was observed at a magnification of 2000x.

[0027] Furthermore, it is preferable that the arithmetic mean height Sa of the main surface 11 is between 0.136 μm and 0.146 μm. The arithmetic mean height Sa of the main surfaces 11 and 12 was calculated by measuring the substrate surface using a KEYENCE VK-X200 laser microscope with a 150x objective lens and a height measurement pitch of 0.05 μm. The field of view was the entire measured area, approximately 72 μm vertically and 96 μm horizontally, and was analyzed after tilt correction. No cutoff filter processing was performed.

[0028] If the alumina substrate 1 is warped, the alumina substrate 1 is placed on a base with a flat top surface, and a weight with a flat bottom surface is placed on the placed alumina substrate 1, and the substrate is straightened by heating. The heating temperature is preferably between 1350°C and 1450°C. The heating time is preferably between 1 hour and 6 hours.

[0029] Even after such straightening, the alumina substrate 1 can suppress significant crystal growth of aluminum oxide on the main surfaces 11 and 12, as well as a significant increase in the surface roughness of the main surfaces 11 and 12.

[0030] Next, a method for manufacturing the alumina substrate 1 will be described. Figure 3 is a flowchart showing the method for manufacturing the alumina substrate 1. As shown in Figure 3, the method for manufacturing the alumina substrate 1 comprises a step SP1 for producing a ceramic green sheet and a step SP2 for firing the ceramic green sheet.

[0031] (Step SP1) First, a raw material powder containing aluminum oxide and a sintering aid is prepared. The ratio of aluminum oxide in the raw material powder is 98.89% by mass or more when each material in the sintering aid is considered as an oxide. Therefore, the sintering aid is 1.11% by mass or less when each material in the sintering aid is considered as an oxide.

[0032] Furthermore, the aluminum oxide content is preferably 99.30% by weight or more, and more preferably 99.70% by weight or more. In addition, the sintering aid content is preferably 0.70% by weight or less, and more preferably 0.30% by weight or less, when each material contained in the sintering aid is an oxide.

[0033] The sintering aid contains silicon and calcium, and may also contain magnesium as needed. Silicon, calcium, and magnesium may be included as oxides. Alternatively, silicon, calcium, and magnesium may be included as silicon dioxide, calcium carbonate, and magnesium oxide. The sintering aid mainly remains in the alumina substrate after firing as an oxide additive. However, the sintering aid may remain after firing by forming a composite with aluminum oxide. In this case, examples of composites between aluminum oxide and the sintering aid include spinel (MgAl2O4) and mullite (Al6Si2O4). 13Examples include calcium aluminate (CaAl2O4). However, even if these complexes are formed, the amount of these complexes is sufficiently small compared to the amount remaining as oxides, and may be below the detection limit.

[0034] The prepared raw material powder, binder, dispersant, and organic solvent are stirred in a ball mill or the like to obtain a slurry. A ceramic green sheet is made from this slurry. Figure 4 shows the process of making a ceramic green sheet. As shown in Figure 4, in this embodiment, the slurry is applied onto a carrier film 20, molded into a sheet using a method such as the doctor blade method, and then dried to produce a ceramic green sheet 1S. Since the ceramic green sheet 1S is dried from the main surface 11S on the carrier film 20 side and the main surface 12S on the opposite side, the main surface 12S is sometimes called the drying surface. In the examples and comparative examples described later, the ceramic green sheet 1S was made by this method. However, as long as the ceramic green sheet 1S is made using the above powder and binder, the ceramic green sheet 1S may be made by other methods. The thickness of the ceramic green sheet 1S is such that the alumina substrate 1 after sintering is 0.1 mm or more and 1.0 mm or less.

[0035] For example, acrylic resin or polyvinyl butyral resin can be used as the binder. Preferably, the binder content in the ceramic green sheet 1S is 9 to 12 parts by mass per 100 parts by mass of the total content of aluminum oxide and sintering aid. A binder content of 9 parts by mass or more can suppress cracking of the resulting ceramic green sheet 1S. The surface roughness of the alumina substrate 1 produced by firing the above raw material powder as in step SP2 can be suppressed, but a binder content of 12 parts by mass or less can further suppress the surface roughness of the alumina substrate 1 obtained by firing the ceramic green sheet 1S.

[0036] As a dispersant, for example, sorbitan sesquiolate can be used. The content of the dispersant in the ceramic green sheet 1S is preferably 1.5 parts by mass or more and 3.5 parts by mass or less, based on the total content of aluminum oxide and sintering aids per 100 parts by mass. When the dispersant is in the above content, the dispersibility of aluminum oxide in the ceramic green sheet 1S can be improved.

[0037] Ceramic Green Sheet 1S may contain plasticizers such as dioctyl phthalate or dioctyl adipate, as needed. The inclusion of plasticizers can soften Ceramic Green Sheet 1S, thereby suppressing the occurrence of cracks and other damage.

[0038] (Step SP2) Next, the fabricated ceramic green sheet 1S is fired. Figure 5 shows the state of the ceramic green sheet 1S during firing. As shown in Figure 5, the ceramic green sheet 1S is placed on the shelf plate 30. One main surface 11S of the ceramic green sheet 1S faces away from the shelf plate 30 and is exposed to the air. This main surface 11S is the surface that comes into contact with the carrier film 20 during the fabrication of the ceramic green sheet 1S. The other main surface 12S of the ceramic green sheet 1S faces towards the shelf plate 30 and is in contact with the shelf plate 30. This other main surface 12S is the drying surface that faces away from the carrier film 20 during the fabrication of the ceramic green sheet 1S. In this state, the ceramic green sheet 1S is placed in a firing furnace in an air atmosphere and fired at a temperature of 1485°C to 1550°C. The firing time is 1 hour to 8 hours, and preferably 1 hour to 4 hours. By extending the firing time to one hour or more, the water absorption of the fired alumina substrate 1 can be suppressed, and by extending the firing time to eight hours or less, the surface roughness of the fired alumina substrate 1 can be suppressed. For example, the ceramic green sheet 1S may be fired in an oxidizing atmosphere such as oxygen gas, or in an inert gas atmosphere such as nitrogen gas or argon gas.

[0039] One main surface 11S of the ceramic green sheet 1S becomes one main surface 11 of the alumina substrate 1, and the other main surface 12S of the ceramic green sheet 1S becomes the other main surface 12 of the alumina substrate 1. The number-average crystal diameter of aluminum oxide on one main surface 11 of the alumina substrate 1 fired in this way is 0.34 μm or more and 0.57 μm or less. In this embodiment, the number-average crystal diameter of aluminum oxide on the other main surface 12 is larger than the number-average crystal diameter of aluminum oxide on one main surface 11, but is still 0.34 μm or more and 0.57 μm or less. However, the number-average crystal diameter of aluminum oxide on the other main surface 12 may be outside the range of 0.34 μm or more and 0.57 μm or less. In the examples and comparative examples described later, the alumina substrate 1 was manufactured by this method. In contrast to the above, the ceramic green sheet 1S may be fired with its main surface 12S exposed to the air and its main surface 11S facing the shelf 30.

[0040] Thus, an alumina substrate 1 is obtained that contains 98.9% by mass or more of aluminum oxide and an additive in which the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide.

[0041] If the obtained alumina substrate 1 is large enough, it can be used as an alumina base substrate. However, an alumina substrate 1 of the same size as the individual piece 2, which is an alumina substrate for mounting components, may also be produced by the above procedure.

[0042] As described above, the alumina substrate 1 of this embodiment contains 98.89% by mass or more of aluminum oxide and an additive containing silicon dioxide and calcium oxide, wherein the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide, and the number average crystal diameter of aluminum oxide on at least one main surface 11 of the alumina substrate 1 is 0.34 μm or more and 0.57 μm or less.

[0043] With an alumina substrate 1 under these conditions, as shown in the embodiments described later, even if the warping is corrected at around 1400°C, which is an effective heat treatment temperature for correcting the warping of the alumina substrate 1, a significant increase in the surface roughness of the main surfaces 11 and 12 can be suppressed. Therefore, according to the alumina substrate 1 of this embodiment, it is possible to correct the warping and provide fine wiring.

[0044] Furthermore, the method for manufacturing the alumina substrate 1 of this embodiment comprises the steps of: preparing a ceramic green sheet in which raw material powder containing aluminum oxide and a sintering aid containing silicon and calcium is dispersed; and firing the ceramic green sheet at 1400°C to 1550°C for 1 hour to 8 hours. The ratio of aluminum oxide in the raw material powder is 98.89% by mass or more when each material contained in the sintering aid is an oxide; the mass of silicon to the mass of calcium in the sintering aid is 5.36 times or more in terms of oxide; and the number-average crystal diameter of aluminum oxide is 0.34 μm or more and 0.57 μm or less.

[0045] According to this method for manufacturing an alumina substrate 1, it is possible to produce an alumina substrate containing 98.89% by mass or more of aluminum oxide, and additives including silicon dioxide and calcium oxide, wherein the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide. Furthermore, according to this method, the number-average crystal diameter of aluminum oxide on the main surfaces 11 and 12 can be set to 0.34 μm or more and 0.57 μm or less. Therefore, an alumina substrate 1 manufactured by this method can suppress a significant increase in surface roughness and correct warping. In other words, according to this method for manufacturing an alumina substrate 1, it is possible to produce an alumina substrate 1 that can be warped and has fine wiring.

[0046] The present invention will now be described in more detail by showing examples and comparative examples. However, the present invention is not limited to the following examples.

[0047] (Example 1) A raw material powder was prepared with an aluminum oxide content of 99.85% by mass, and sintering aids magnesium oxide, silicon dioxide, and calcium carbonate content of 0.025% by mass, 0.100% by mass, and 0.025% by mass, respectively. In this raw material powder, the mass of silicon dioxide was 4.00 times the mass of calcium carbonate, and the mass of silicon dioxide was 2.00 times the sum of the masses of calcium carbonate and magnesium oxide.

[0048] The number-average particle size of aluminum oxide was set to 0.24 μm. This number-average particle size was measured by laser diffraction scattering using a Microtrac-Bell MT3300 after crushing aluminum oxide powder with a ball mill and using n-propyl alcohol as the dispersion medium.

[0049] (Examples 2-10, Comparative Examples 1, 2) The raw material powders listed in Table 1 were prepared.

[0050] Next, the raw material powders prepared in Examples 1-10 and Comparative Examples 1 and 2, along with an acrylic binder, a dispersant, and an organic solvent, were placed in a ball mill and mixed and stirred to obtain a slurry. The obtained slurries were formed into sheets using the doctor blade method in the same manner as in the above embodiments, and each of the formed sheets was pressed with a die press to obtain ceramic green sheets. The obtained ceramic green sheets were then fired for 1 hour at the firing temperature shown in Table 1 in the same manner as in the above embodiments to obtain an alumina substrate. The thickness of the alumina substrate was approximately 0.38 mm. TIFF2026058857000002.tif89170

[0051] Next, the content ratios of aluminum oxide, magnesium oxide, silicon dioxide, and calcium oxide in the alumina substrates of Examples 1-10 and Comparative Examples 1 and 2 were calculated from the content ratios of each component in the ceramic green sheet. From these results, the ratio of the mass of silicon dioxide to the mass of calcium oxide, and the ratio of the mass of silicon dioxide to the sum of the masses of calcium oxide and magnesium oxide were determined.

[0052] Furthermore, the number-average crystal diameter of aluminum oxide on the main surface 11 was determined in the same manner as described above, and the number-average crystal diameter of aluminum oxide on the main surface of the alumina substrates of Examples 1-10 and Comparative Examples 1 and 2 was determined. In addition, the standard deviation of the number-average crystal diameter of aluminum oxide on the main surface of the alumina substrates of Examples 1-10 and Comparative Examples 1 and 2 was determined.

[0053] Furthermore, the arithmetic mean height Sa on the main surface of the alumina substrates of Examples 1 to 10 and Comparative Examples 1 and 2 was determined in the same manner as in which the arithmetic mean height Sa on the main surface 11 was determined in the above description.

[0054] The results are shown in Table 2. TIFF2026058857000003.tif89170

[0055] Next, using the same method as described above for measuring voids on the main surface 11, voids on the main surface of the alumina substrates of Examples 1-10 and Comparative Examples 1 and 2 were measured, and their area ratio, average diameter, and maximum diameter were determined. The results are shown in Table 3. TIFF2026058857000004.tif93170

[0056] Next, the warping of the alumina substrates in Examples 1-10 and Comparative Examples 1 and 2 was corrected in the same manner as the warping of alumina substrate 1 described above. In this case, the heating temperature was set to 1400°C and the heating time to 1 hour.

[0057] Next, in the same manner as in which the arithmetic mean height Sa on the main surface 11 was determined in the above description, the arithmetic mean height Sa on the main surface of the alumina substrates of Examples 1 to 10 and Comparative Examples 1 and 2 after straightening was determined, and the change in the arithmetic mean height Sa before and after straightening was calculated. The results are shown in Table 4. TIFF2026058857000005.tif91170

[0058] As shown in Table 4, in Comparative Examples 1 and 2, the surface roughness of the alumina substrate increased significantly, exceeding 0.005 μm.

[0059] Based on the above, the alumina substrates of Examples 1 to 10 were found to suppress a significant increase in surface roughness and correct warping. Specifically, an alumina substrate containing 98.89% by mass or more of aluminum oxide, and additives including silicon dioxide and calcium oxide, wherein the mass of silicon dioxide is 5.36 times or more the mass of calcium oxide, and the number-average crystal diameter of the aluminum oxide on the main surface of the substrate is 0.34 μm or more and 0.57 μm or less, is found to be able to correct warping and provide fine wiring. [Industrial applicability]

[0060] According to the present invention, an alumina substrate capable of correcting warping and providing fine wiring, and a method for manufacturing an alumina substrate are provided, which can be used in the field of electronic components such as chip resistors. [Explanation of symbols]

[0061] 1. Alumina substrate 11. Main surface

Claims

1. 98.89% by mass or more of aluminum oxide, Additives containing silicon dioxide and calcium oxide, It contains, The mass of silicon dioxide relative to the mass of calcium oxide is 5.36 times or more. The number-average crystal diameter of the aluminum oxide on at least one of the main surfaces of the substrate is 0.34 μm or more and 0.57 μm or less. An alumina substrate characterized by the following features.

2. The aforementioned additive further comprises magnesium oxide, The mass of silicon dioxide is 1.92 times or more the sum of the mass of calcium oxide and the mass of magnesium oxide. The alumina substrate according to feature 1.

3. The standard deviation of the number-mean crystal diameter is 0.37 or less. The alumina substrate according to feature 1.

4. The area ratio of voids on the main surface of the substrate is 0.60% or less. The alumina substrate according to feature 1.

5. The average diameter of voids on the main surface of the substrate is less than 0.50 μm. The alumina substrate according to feature 1.

6. The maximum diameter of the voids on the main surface of the substrate is less than 1.3 μm. The alumina substrate according to feature 1.

7. The arithmetic mean height Sa of the main surface of the substrate is 0.136 μm or more and 0.146 μm or less. The alumina substrate according to feature 1.

8. A step of preparing a ceramic green sheet in which raw material powder containing aluminum oxide and a sintering aid containing silicon and calcium is dispersed, The step of firing the ceramic green sheet at 1400°C to 1550°C for 1 hour to 8 hours, Equipped with, The ratio of aluminum oxide in the raw material powder is 98.89% by mass or more when each material contained in the sintering aid is an oxide. The ratio of the mass of silicon to the mass of calcium in the sintering aid is 5.36 times or more in terms of oxides. The number-average particle size of the aluminum oxide in the raw material powder is such that the number-average crystal diameter of the aluminum oxide after firing of the ceramic green sheet is 0.34 μm or more and 0.57 μm or less. A method for manufacturing an alumina substrate, characterized by the following features.

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