Alumina substrate, and method for manufacturing an alumina substrate

Abstract

The present invention provides an alumina substrate on which fine circuits can be formed on one main surface and electrodes can be firmly fixed to the other substrate. [Solution] The alumina substrate 1 contains 99% by mass or more of aluminum oxide, the arithmetic mean roughness of one main surface 11 is 0.070 μm or less, the arithmetic mean roughness of the other main surface 12 is 0.240 μm or more, and the maximum crystal diameter of aluminum oxide on one main surface 11 is 5 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 reliability of electronic components, the miniaturization of circuits such as wirings and resistor films formed on substrates has been progressing. As such a substrate for electronic components, an alumina substrate containing 99% by mass or more of aluminum oxide as a main component may be used. In such an electronic component using an alumina substrate, electrodes may be provided on the main surface opposite to the main surface on which the circuit is provided on the alumina substrate, and the electrodes may be soldered and mounted. In such an alumina substrate, one main surface on which the circuit is provided may be smooth, and the other main surface on which the electrodes are provided may be roughened. Patent Document 1 below describes an alumina substrate in which one main surface is smooth and the other main surface is rougher than the one main surface. The surface roughness of one main surface of this alumina substrate is about 0.05 μm Ra, and the surface roughness of the other main surface is about 0.20 μm Ra.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been found that, as in the alumina substrate of Patent Document 1 above, even when the surface roughness of the main surface on the side where the circuit is provided is about 0.05 μm, it may be difficult to form a fine circuit with a line width of 10 μm. Further, when the surface roughness of the main surface on the side where the electrodes are provided is about 0.20 μm, it has been found that the fixing strength of the electrodes is insufficient.

[0005] Therefore, the present invention aims to provide an alumina substrate on which fine circuits can be formed on one main surface and electrodes can be firmly fixed to the other main surface. [Means for solving the problem]

[0006] The alumina substrate of the present invention is characterized by containing 99% by mass or more of aluminum oxide, having an arithmetic mean roughness of 0.070 μm or less on one main surface, an arithmetic mean roughness of 0.240 μm or more on the other main surface, and having a maximum crystal diameter of 5 μm or less on the one main surface.

[0007] As a result of diligent research, the inventors have found that if the arithmetic mean roughness of the main surface on which the circuit is provided is 0.070 μm or less, even if a fine circuit with a line width of 10 μm is formed, disconnections and variations in pattern thickness are less likely to occur. Furthermore, they concluded that if the maximum crystal diameter of aluminum oxide on the main surface is 5 μm or less, disconnections are less likely to occur even if such a fine circuit is formed. When the maximum crystal diameter of aluminum oxide is large, steps tend to form around the crystal, and it is thought that disconnections due to steps are likely to occur when a fine circuit is formed on these steps. Therefore, in addition to the arithmetic mean roughness being within the above range, the maximum crystal diameter of aluminum oxide being within the above range makes it possible to form a fine circuit with a line width of 10 μm on one main surface. Also, the arithmetic mean roughness of the other main surface being within the above range makes it possible to firmly fix electrodes to that main surface.

[0008] Furthermore, it is preferable that the difference between the arithmetic mean roughness of the other main surface and the arithmetic mean roughness of the one main surface is 0.300 μm or less.

[0009] By firing the ceramic green sheet in such a way that the difference in arithmetic mean roughness is achieved, the warping of the alumina substrate can be suppressed.

[0010] Furthermore, it is preferable that the alumina substrate contains silicon dioxide, calcium oxide, and magnesium oxide.

[0011] Furthermore, the present invention provides a method for manufacturing an alumina substrate, comprising the steps of: applying a slurry containing a raw material powder with aluminum oxide as the main component and a sintering aid onto a carrier film to produce a ceramic green sheet; and placing the ceramic green sheet on a shelf and firing it, wherein during the firing of the ceramic green sheet, the side of the ceramic green sheet opposite to the carrier film side faces the shelf side, and the side of the ceramic green sheet facing the carrier film side is exposed to the air. [Effects of the Invention]

[0012] As described above, the present invention provides an alumina substrate in which a fine circuit can be formed on one main surface and electrodes can be firmly fixed to the other substrate. [Brief explanation of the drawing]

[0013] [Figure 1] This is a plan view showing an alumina substrate. [Figure 2] This is a cross-sectional view of an alumina substrate. [Figure 3] This is a flowchart showing the procedure for manufacturing an alumina substrate. [Figure 4] This diagram shows the process of manufacturing ceramic green sheets. [Figure 5] This figure shows the state of the ceramic green sheet during firing. [Modes for carrying out the invention]

[0014] The following examples illustrate embodiments for implementing the alumina substrate according to the present invention, along with the accompanying drawings. The embodiments illustrated below are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified and improved from the following embodiments within the scope of the claims without departing from its spirit. Note that in the drawings referenced below, the dimensions of each component may be shown differently for the sake of clarity.

[0015] Figure 1 is a plan view showing the alumina substrate of this embodiment, and Figure 2 is a cross-sectional view of the alumina substrate in the thickness direction. The alumina substrate 1 is an alumina base substrate on which multiple individual pieces 2, which will become alumina substrates for mounting components, are provided adjacent to each other, as shown by dashed lines. The alumina substrate 1 of this embodiment is plate-shaped and includes one main surface 11 and the other main surface 12 that face each other. One main surface 11 is the main surface on which circuits such as resistors are arranged, and the other main surface 12 is the main surface on which electrodes and the like are arranged and mounted on a circuit board or the like. In Figure 1, only one main surface 11 is labeled with a reference numeral. In this embodiment, the main surfaces 11 and 12 are generally rectangular, with the length of one opposite side being approximately 80 mm and the length of the other opposite side being approximately 70 mm. 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.

[0016] The alumina substrate 1 contains aluminum oxide, which is the main component, at a concentration of 99% by mass or more, and minor components including silicon dioxide, calcium oxide, and magnesium oxide. Therefore, the content of the minor components is 1% by mass or less, and the total of the main component and minor components does not exceed 100% by mass. The content of calcium oxide, silicon dioxide, and magnesium oxide is, for example, 0.20% by mass, 0.05% by mass, and 0.05% by mass, respectively. However, the ratio of each oxide in the minor components is not limited to this. Furthermore, while it is preferable for the minor components to contain calcium oxide, silicon dioxide, and magnesium oxide, it is not necessary to contain some of these oxides.

[0017] Furthermore, the arithmetic mean roughness Ra1 of the main surface 11 is 0.070 μm or less. Preferably, the arithmetic mean roughness Ra1 is 0.067 μm or less, and more preferably 0.065 μm or less. Furthermore, the arithmetic mean roughness Ra2 of the main surface 12 is 0.240 μm or more. Preferably, the arithmetic mean roughness Ra2 is 0.260 μm or more, and more preferably 0.290 μm or more. Furthermore, preferably, the arithmetic mean roughness Ra2 is 0.5 μm or less, and more preferably 0.370 μm or less. In addition, from the viewpoint of suppressing warping when manufacturing the alumina substrate 1 by firing the ceramic green sheet as described later, the difference between the arithmetic mean roughness Ra2 of the main surface 12 and the arithmetic mean roughness Ra1 of the main surface 11 is preferably 0.300 μm or less, more preferably 0.250 μm or less, and even more preferably 0.235 μm or less. In other words, it is preferable that the alumina substrate 1 be manufactured such that the difference in arithmetic surface roughness is as described above. The arithmetic mean roughness Ra of the main surfaces 11 and 12 is calculated by measuring the substrate surface using a laser microscope VK-X200 manufactured by Keyence Corporation, with a magnification of 150x and a measurement pitch of 0.05 μm in the height direction. The field of view is the entire measured area, approximately 72 μm vertically and 96 μm horizontally, and the analysis is performed after tilt correction. Cutoff filtering is not required at this time.

[0018] The maximum crystal diameter of aluminum oxide on the main surface 11 of the alumina substrate 1 is 5 μm or less. Preferably, this maximum crystal diameter is 4 μm or less, and more preferably 3.3 μm or less. The maximum crystal diameter of aluminum oxide on the main surface 11 is measured as follows. An image of the main surface 11 can be obtained, for example, by a scanning electron microscope (SEM). Specifically, for example, using a field emission scanning electron microscope (FE-SEM) "Regulus8100" manufactured by Hitachi High-Tech Corporation, a semiconductor backscattered electron detector (PD-BSE) is used, and an image of an area of ​​approximately 22 μm × approximately 29 μm is obtained at an acceleration voltage of 5 keV and a magnification of 5000x. This image is then analyzed, for example, using software "A-zo-kun" manufactured by Asahi Kasei Engineering Corporation to calculate the above maximum crystal diameter.

[0019] Also, it is preferable that there are no voids on the main surface 11. Even when there are voids on the main surface 11, the area ratio of the voids on the main surface 11 is preferably 0.60% or less. Further, the maximum diameter of the void is preferably 1.3 μm or less. By the area ratio and the maximum diameter of the void being within the above ranges, the occurrence of disconnection can be further suppressed when fine wiring is formed on the alumina substrate 1. The area ratio and the maximum diameter of the void are calculated by acquiring an image of the main surface 11 and analyzing the image in the same manner as the calculation of the maximum crystal diameter on the main surface 11, except that a region of about 48 μm × about 64 μm is observed at a magnification of 2000 times.

[0020] Next, a method for manufacturing the alumina substrate 1 will be described.

[0021] FIG. 3 is a flowchart showing a method for manufacturing the alumina substrate 1. As shown in FIG. 3, the method for manufacturing the alumina substrate 1 includes a step SP 1 of producing a ceramic green sheet and a step SP 2 of firing the ceramic green sheet.

[0022] (Step SP 1) First, raw material powder containing aluminum oxide and a sintering aid is prepared. The average particle diameter of the aluminum oxide in the raw material powder is, for example, 1 μm or less, and preferably 0.5 μm or less. The median particle diameter of the aluminum oxide is, for example, 0.46 μm. The ratio of the aluminum oxide in the raw material powder is 99% by mass or more when each material contained in the sintering aid is taken as an oxide. Therefore, the sintering aid is 1% by mass or less when each material contained in the sintering aid is taken as an oxide.

[0023] The sintering aid contains magnesium, silicon, and calcium. Magnesium, silicon, and calcium may be included as oxides. The content of magnesium, silicon, and calcium in the raw material powder is, for example, 0.05% by mass, 0.20% by mass, and 0.05% by mass, respectively, in terms of oxides. Note that the oxide of calcium refers to calcium oxide (CaO), the oxide of silicon refers to silicon dioxide (SiO2), and the oxide of magnesium refers to magnesium oxide (MgO). Silicon and calcium may be included as silicon dioxide and calcium carbonate. Note that the sintering aid mainly remains as a by-component in the alumina substrate after firing. 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 (MgAlO4) and mullite (Al6Si2O 13 Examples include calcium aluminate (CaAl2O4). However, even if these complexes are formed, the amount of these complexes is negligible compared to the amount remaining as oxides, and may be below the detection limit.

[0024] 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, the slurry is applied onto a carrier film 20, formed 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 dries 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. The thickness of the ceramic green sheet 1S is, for example, such that the alumina substrate 1 after sintering is 0.1 mm to 1.0 mm thick.

[0025] As a binder, for example, acrylic resin or polyvinyl butyral resin can be used. The binder content in the ceramic green sheet 1S is preferably 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 described in step SP2 below can be suppressed, and 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.

[0026] 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.

[0027] 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.

[0028] (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 1425°C to 1550°C. In this way, an alumina substrate 1 with an aluminum oxide content of 99% by mass or more is obtained. The firing time is preferably between 1 hour and 8 hours, and more preferably between 1 hour and 4 hours. By firing for 1 hour or more, the water absorption of the fired alumina substrate 1 can be suppressed, and by firing for 8 hours or less, the grain growth of aluminum oxide on one main surface 11S can be suppressed, limiting the crystal growth of aluminum oxide to, for example, 5 μm or less, and suppressing the surface roughness of the fired alumina substrate 1. 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.

[0029] 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 arithmetic mean roughness Ra1 of the one main surface 11 of the alumina substrate 1 fired in this way is, for example, 0.070 μm or less, and the arithmetic mean roughness of the other main surface 12 is, for example, 0.240 μm or more.

[0030] In this way, an alumina substrate 1 can be manufactured that contains 99% by mass or more of aluminum oxide, has an arithmetic mean roughness of 0.070 μm or less on one main surface 11, has an arithmetic mean roughness of 0.240 μm or more on the other main surface 12, and has a maximum crystal diameter of aluminum oxide on one main surface 11 of 5 μm or less.

[0031] Furthermore, in the above, by using a raw material powder containing aluminum oxide as the main component and a sintering aid, and manufacturing an alumina substrate by steps SP1 and SP2, an alumina substrate can be manufactured in which one main surface is rougher than the other main surface. When aluminum oxide is the main component, the raw material powder contains, for example, 90% by weight or more of aluminum oxide.

[0032] If the manufactured 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 manufactured using the above procedure.

[0033] As described above, the alumina substrate 1 of this embodiment contains 99% by mass or more of aluminum oxide, the arithmetic mean roughness of one main surface 11 is 0.070 μm or less, the arithmetic mean roughness of the other main surface 12 is 0.240 μm or more, and the maximum crystal diameter of aluminum oxide on one main surface 11 is 5 μm or less.

[0034] In such an alumina substrate 1, when a circuit is provided on one main surface 11, the arithmetic mean roughness of the main surface 11 is 0.070 μm or less, so even if a fine circuit with a line width of about 10 μm is formed, disconnections and variations in pattern thickness are less likely to occur. In addition, the maximum crystal diameter of aluminum oxide on one main surface is 5 μm or less, which makes it possible to reduce the step height around the aluminum oxide crystals. Therefore, in addition to the arithmetic mean roughness being within the above range, the maximum crystal diameter of aluminum oxide being within the above range makes it possible to form a fine circuit with a line width of 10 μm on one main surface. Furthermore, the arithmetic mean roughness of the other main surface 12 being within the above range allows the electrodes to be firmly fixed by the anchoring effect.

[0035] 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.

[0036] A raw material powder was prepared consisting of 99% or more by mass of aluminum oxide and a sintering aid containing magnesium, silicon, and calcium. This raw material powder formulation was designated as A. The content of aluminum oxide, magnesium, silicon, and calcium was 0.05% by mass, 0.20% by mass, and 0.05% by mass, respectively, in terms of oxides, i.e., magnesium oxide, silicon dioxide, and calcium oxide. The aluminum oxide had a purity of 99.99% or higher and a median particle size of 0.46 μm. Magnesium oxide, silicon dioxide, and calcium carbonate were used as sintering aids.

[0037] The central particle size of aluminum oxide was measured by laser diffraction scattering using a Microtrac-Bell MT3300, with n-propyl alcohol as the dispersion medium.

[0038] The same raw material powder as in the above example was prepared, except that 0.1% by mass of magnesium oxide was used as a sintering aid. This raw material powder formulation was designated as B.

[0039] A raw material powder was prepared in the same manner as in the above example, except that 0.05% by mass of magnesium oxide and 0.20% by mass of silicon dioxide were used as sintering aids. This raw material powder formulation was designated as C.

[0040] Next, the prepared raw material powders A to C, along with the acrylic binder, dispersant, and organic solvent, were placed in a ball mill and mixed and stirred to obtain a slurry. The obtained slurry was applied to a carrier film, formed into a sheet using the doctor blade method, and dried to obtain a ceramic green sheet. Next, the obtained ceramic green sheet was placed on a shelf. At this time, the main surface of the ceramic green sheet facing the carrier film was exposed to the air away from the shelf, and the main surface of the ceramic green sheet opposite the carrier film was in contact with the shelf facing the shelf. Next, the ceramic green sheet placed on the shelf was fired for 1 hour at the firing temperature shown in Table 1 to obtain an alumina substrate. The thickness of this alumina substrate was approximately 0.38 mm. Table 1 shows the combinations of raw material powder and firing time for Examples 1 to 9 and for Comparative Examples 1 to 4. TIFF2026058858000002.tif104170

[0041] Next, in the alumina substrates of Examples 1-9 and Comparative Examples 1-4, the arithmetic mean roughness Ra1 and Ra2 were measured in the same manner as when the arithmetic mean roughness Ra1 and Ra2 were determined on the main surfaces 11 and 12 described above. Specifically, the arithmetic mean roughness Ra1 of one main surface fired in the open air and the arithmetic mean roughness Ra2 of the other main surface fired in contact with the firing shelf were measured. Furthermore, the difference between the arithmetic mean roughness Ra2 and the arithmetic mean roughness Ra1 was calculated from these measurement results.

[0042] Furthermore, in the alumina substrates of Examples 1-9 and Comparative Examples 1-4, the maximum crystal diameter of aluminum oxide on one of the main surfaces exposed to space and fired was determined in the same manner as when the maximum crystal diameter of aluminum oxide on the main surface 11 was determined in the above description. The results are shown in Table 2. TIFF2026058858000003.tif104170

[0043] (Evaluation of thin film thickness variation) In the alumina substrates of Examples 1-9 and Comparative Examples 1-4, a platinum-palladium vapor-deposited layer was formed on one of the main surfaces that was fired in space. Specifically, the vapor-deposited layer was formed using an ion sputtering apparatus E-1010 manufactured by Hitachi High-Tech Corporation, with a vacuum of 10 Pa, a discharge current of 15 mA, and a deposition time of 30 seconds.

[0044] Next, the formed vapor-deposited layer was milled using a Hitachi High-Tech IM4000 ion milling system, and the vapor-deposited layer was observed at a magnification of 100,000x using a Hitachi High-Tech Regulus8100 field emission scanning electron microscope (FE-SEM) to evaluate the variation in the thickness of the vapor-deposited layer. The variation in the thickness of the vapor-deposited layer was evaluated as follows. The size of the observation image below is 956nm × 1274nm. A: The continuity of the vapor-deposited layer is maintained within the observed image. B: While there are some blurs or tears in the observed images, there are no problems with practical use. C: Within the observed image, there are areas where the vapor-deposited layer is not formed and the image is significantly interrupted.

[0045] (Evaluation of vapor-deposited layer fracture) In the alumina substrates of Examples 1-9 and Comparative Examples 1-4, after cleaning the surface, a pair of electrodes measuring 1 mm vertically and 2 mm horizontally were formed on one main surface using a DELTA80T3 spin coating apparatus for thick-film photoresist (manufactured by Suuss Microtec). The distance between electrodes was 12.8 mm, and the electrode material was gold. Two pairs of electrodes were formed on each alumina substrate. In addition, four alumina substrates were used as samples. Therefore, eight pairs of electrodes were formed.

[0046] Next, using a vacuum deposition apparatus RD-1400 (manufactured by Sunvac), nickel-chromium deposition layers were deposited between each pair of electrodes formed on each alumina substrate to create eight thin-film resistors. Each resistor had a line width of 10 μm, and the resistor pattern consisted of five meandering sections with a transverse length of 1 mm between electrodes, spanning 12.8 mm in the longitudinal direction. All meandering sections were bent at right angles, and the thickness of the deposition layer was 50 nm.

[0047] Next, a four-probe cable for sheet resistance measurement (SR4-SS, 1 mm between current probes, manufactured by Asteratec) was connected to a digital multimeter, and the probes were pressed against each pair of electrodes on the alumina substrate to measure the surface resistance of the nickel-chromium vapor-deposited layer at eight locations. The measured resistance value was multiplied by the probe correction value and the vapor-deposited layer thickness to determine the resistance value of the vapor-deposited layer, which was then used as the measured value. The measured value was compared with the theoretical resistance value of the nickel-chromium vapor-deposited layer, and if the value was more than 1000 times higher than the theoretical value, it was determined that the vapor-deposited layer was broken. Based on the measurement results, the state of breakage of the vapor-deposited layer on the alumina substrate was evaluated according to the following criteria. A: There are 0 to 1 location where the value is more than 1000 times higher than the theoretical value. B: There are 2-3 places where the value is more than 1000 times higher than the theoretical value. C: There are four or more locations where the value is more than 1000 times higher than the theoretical value.

[0048] (Evaluation of electrode adhesion) In the alumina substrates of Examples 1-9 and Comparative Examples 1-4, 25 2mm square conductive pads were placed on the other main surface, which was fired in contact with the shelf. The conductive pads were formed by printing and drying silver paste. Next, stainless steel wires were soldered to each conductive pad. After a predetermined time had elapsed since soldering, the wires were pulled using an IMADA ZTS-200N digital force gauge to evaluate the adhesion strength between the alumina substrate and the electrodes. The adhesion strength between the alumina substrate and the electrodes was evaluated as follows. A: The wire broke in 16 or more places. B: The wire broke in 6 to 15 locations. C: The wire broke in 5 places or less, or no wire breakage occurred.

[0049] (Warping evaluation) Two flat glass plates free of scratches and dirt were prepared, cleaned, and a 100 μm gap gauge was placed between them to adjust the distance between the two glass plates to 100 μm. Next, the two glass plates were fixed in place at a 30-degree angle. Then, the alumina substrates of Examples 1-9 and Comparative Examples 1-4 were placed in the gap between the two glass plates, and the warping of the substrates was evaluated as follows by checking the degree of sliding of the alumina substrates. A: The alumina substrate slides down quickly without getting caught between the glass plates. B: The alumina substrate slowly slides down, getting caught between the glass plates. C: The alumina substrate gets stuck between the glass plates and doesn't slide all the way down.

[0050] The results of the above evaluation are shown in Table 3. TIFF2026058858000004.tif104170

[0051] Based on the above, the following can be said about the alumina substrates of Examples 1 to 9: The variation in the thickness of the thin film provided on one main surface can be suppressed. In addition, the maximum diameter of aluminum oxide particles on one main surface is suppressed, and even when a fine thin film circuit with a line width of 10 μm is formed on one substrate, disconnection can be suppressed. This is thought to be because the step difference around the aluminum oxide on one main surface is kept small. Furthermore, when electrodes are provided on the other main surface, the electrodes can be firmly fixed. In addition, warping of the alumina substrate can be suppressed.

[0052] Therefore, it has been found that the present invention provides an alumina substrate in which a fine circuit can be formed on one main surface and electrodes can be firmly fixed to the other substrate. [Industrial applicability]

[0053] According to the present invention, an alumina substrate is provided that can form fine circuits on one main surface and firmly fix electrodes to the other substrate, and can be used in the field of electronic components such as chip resistors. [Explanation of Symbols]

[0054] 1. Alumina substrate 11, 12... Main surface

Claims

1. It contains 99% or more by mass of aluminum oxide, The arithmetic mean roughness of one of the main surfaces is 0.070 μm or less. The arithmetic mean roughness of the other main surface is 0.240 μm or more. The maximum crystal diameter of the aluminum oxide on one of the main surfaces is 5 μm or less. An alumina substrate characterized by the following features.

2. The difference between the arithmetic mean roughness of the other main surface and the arithmetic mean roughness of the first main surface is 0.300 μm or less. The alumina substrate according to feature 1.

3. Contains silicon dioxide, calcium oxide, and magnesium oxide. The alumina substrate according to feature 1 or 2.

4. The process involves applying a slurry containing raw material powder, which includes aluminum oxide as the main component and a sintering aid, onto a carrier film to produce a ceramic green sheet. The step of placing the aforementioned ceramic green sheet on a shelf and firing it, Equipped with, During firing of the ceramic green sheet, the side of the ceramic green sheet opposite to the carrier film side faces the shelf side, and the side of the ceramic green sheet facing the carrier film side is exposed to the air. A method for manufacturing an alumina substrate, characterized by the following features.

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