JP5558892B2 - Alumina sintered body - Google Patents

Description

The present invention relates to an alumina sintered body.

Alumina sintered bodies are excellent in mechanical strength, heat resistance, corrosion resistance, etc., and have low dielectric loss tangent (tan δ), so they are used in circuit boards and semiconductor manufacturing apparatuses that receive microwaves and high frequencies. .

However, in order to keep the dielectric loss tangent of the alumina sintered body low, it is necessary to use a low-purity, high-purity raw material, and thus high cost is a problem. Therefore, the present applicant has proposed an alumina sintered body having a low dielectric loss tangent even if it contains alkali (see Patent Document 1).

This technology includes SiO ₂ and MgO in a total amount of 0.2 to 1.0 wt% and ₂ to 4 by weight ratio (SiO ₂ / MgO) in an alumina sintered body, and is generated from the SiO ₂ and MgO. The cordierite phase is 0.3 to 1.4 wt%. According to this, an alumina-based sintered body having a low dielectric loss tangent can be obtained without lowering the alkali accompanied by a significant cost increase.

JP-A-10-120461

However, although the dielectric loss tangent is low, the mechanical strength is not sufficient, so that it may not be applicable depending on the member.

The present invention has been made in view of these problems, and provides an alumina sintered body having a low dielectric loss tangent and a high strength.

In order to solve the above-mentioned problems, the present invention casts a slurry in which raw material powder is dispersed in a mold having a bottom portion of a water-absorbing material and a side wall portion of a non-water-absorbing material, An alumina sintered body obtained by sintering a cast molded body formed by inking a powder, and having a crystal orientation degree O: I ₃₀₀ / (I ₃₀₀ + I ₁₀₄ ) calculated by XRD peak intensity Of these, the difference between the crystal orientation degree O1 of the plane perpendicular to the casting direction of casting and the crystal orientation degree O2 of the plane parallel to the casting direction of casting: O2-O1 is 0.12 to 0.18. The dielectric loss tangent at 1 to 10 MHz is 10 × 10 ⁻⁴ or less, the three-point bending strength is 400 MPa or more, contains SiO ₂ in an amount of 0.08 to 0.8% by mass , and is substantially cordierite. It is characterized by not including a phase . A low dielectric loss tangent and high-strength alumina sintered body can be obtained by including a predetermined amount of SiO ₂ and substantially not including a cordierite phase.

Further, the alumina sintered body of the present invention casts a slurry in which raw material powder is dispersed in a molding die having a bottom portion of a water-absorbing material and a side wall portion of a non-water-absorbing material, together with water absorption of the water-absorbing material. It is obtained by sintering a cast-molded body formed by depositing raw material powder. By using such a molding method, it is possible to form a microstructure that can exhibit a low dielectric loss tangent and high strength.

Furthermore, the alumina sintered body of the present invention has a crystal orientation degree O1 of a plane perpendicular to the casting direction of cast molding among the crystal orientation degree calculated from the XRD peak intensity: I ₃₀₀ / (I ₃₀₀ + I ₁₀₄ ). The difference from the degree of crystal orientation O2 of the surface parallel to the casting direction of casting is O2-O1 is 0.12 to 0.18. According to the present invention, a dielectric loss tangent can be reduced without including a cordierite phase, and a decrease in bending strength can be suppressed, and a high-strength alumina sintered body can be provided.

An alumina sintered body having a low dielectric loss tangent and high strength can be provided.

It is an example of the XRD chart of an alumina sintered compact. Is a diagram illustrating an extracted I ₃₀₀ and _{I 104.} It is the schematic sectional drawing which showed the casting method of this invention. It is a schematic diagram of the alumina sintered body of the present invention.

Hereinafter, the alumina sintered body of the present invention will be described in more detail.

The alumina sintered body of the present invention is formed by sintering a cast molded body. In particular, in the present invention, a cast molding method in which the inking direction is constant is preferable. By forming the raw material powder in a fixed direction, anisotropy occurs in the crystal orientation, and the dielectric loss tangent can be reduced.

The anisotropy of crystal orientation, that is, the degree of crystal orientation O represents the XRD peak intensities of the (300) plane and the (104) plane as I ₃₀₀ and I ₁₀₄ , respectively, and an expression of I ₃₀₀ / (I ₃₀₀ + I ₁₀₄ ) Is calculated by In the alumina sintered body of the present invention, the (300) plane shows the highest peak intensity as a plane parallel to the c-axis, and the (104) plane shows the highest peak intensity as a plane parallel to the a-axis or b-axis. . In the present invention, the relationship between the two was evaluated as the crystal orientation degree O.

FIG. 1 shows a chart example obtained by XRD measurement of the alumina sintered body of the present invention. FIG. 2 shows the peaks of the (104) plane and the (300) plane extracted from such a chart. After obtaining the peak intensities I ₃₀₀ and I ₁₀₄ for each surface, the degree of crystal orientation I ₃₀₀ / (I ₃₀₀ + I ₁₀₄ ) can be calculated.

(A) of FIG. 1 is a chart obtained by XRD measurement of a surface perpendicular to the casting direction of casting for an alumina sintered body, and (b) of FIG. 1 is for the same alumina sintered body. It is the chart obtained by the XRD measurement of the surface parallel to the thickness direction of casting. It can be seen that the peak intensity ratios of the (104) plane and the (300) plane are different in each chart.

The alumina sintered body of the present invention has a predetermined difference between the crystal orientation degree O1 of the plane perpendicular to the casting direction of casting and the crystal orientation degree O2 of the plane parallel to the casting direction of casting. ing. That is, it was found that by setting the difference O2-O1 to 0.12 to 0.18, the dielectric loss tangent can be kept low and high strength is exhibited. The reason for this is not clear, but such crystal orientation makes it difficult for other crystal phases such as cordierite phase and glass phase to form, and a fine structure showing high strength can be obtained by making it grow in a certain direction. it is conceivable that.

FIG. 3 shows the casting method used in the present invention. Casting molding in which a slurry 35 in which a raw material powder is dispersed is cast in a molding die 30 having a bottom 31 of a water-absorbing material and a side wall 32 of a non-water-absorbing material, and the raw material powder is formed together with the water-absorbing material. By using the method, it is possible to make the inking direction constant as indicated by an arrow in the figure.

An alumina sintered body is obtained by firing the molded body 36 obtained by such a casting method. FIG. 4 shows a schematic diagram of an alumina sintered body. The XRD measurement is performed on a surface 41 perpendicular to the casting direction of the casting and indicated by an arrow in the alumina sintered body of FIG. 4 and a surface 42 parallel to the casting direction of the casting. The crystal orientation degree O1 based on the XRD peak intensity of the surface 41 and the crystal orientation degree O2 based on the XRD peak intensity of the surface 42 are obtained, and the difference: O2-O1 is calculated.

Table 1 shows an example of peak intensities obtained by XRD measurement of a surface perpendicular to the inking direction and a surface parallel to the inking direction. According to this, the alumina sintered body of the present invention has a (104) plane peak intensity smaller in the plane perpendicular to the inking direction than in the JCPDS card peak intensity, and in a plane parallel to the inking direction. It can be seen that the peak intensity of the (300) plane is increased. In this example, O1 is 0.28, O2 is 0.45, and O2-O1 is 0.17. In view of this point, the present invention has found that the dielectric loss tangent can be suppressed low and the strength can be increased by setting the difference between the crystal orientation degrees O2 and O1 within a predetermined range.

The alumina sintered body of the present invention has a dielectric loss tangent at 1 to 10 MHz of 10 × 10 ⁻⁴ or less. If the crystal orientation is adjusted as described above, an alumina sintered body substantially free of cordierite phase can be obtained, and a low dielectric loss tangent can be achieved.

Alumina sintered body of the present invention comprises SiO ₂ 0.08 to 0.8 wt%. However, the cordierite phase is substantially not included in the sintered body as described above. This indicates that no cordierite crystal peak is detected in XRD. SiO ₂ is contained in the above range, and the crystal orientation degree O is made to be a high strength alumina sintered body having a low dielectric loss tangent by causing a difference in orientation degree depending on the walling direction at the time of casting. Can do.

Moreover, the alumina sintered body of the present invention has a three-point bending strength (JISR1601) of 400 MPa or more. This is presumably because a unique microstructure that appears as a difference in the degree of orientation depending on the direction of wall formation is formed by being cast in a certain direction during casting, and does not contain other crystal phases or glass phases.

The average grain size of the alumina sintered body is preferably 20 μm or less. In order to achieve both low dielectric loss tangent and high strength, remarkable grain growth is not preferable. It is more preferable to set it as 2-15 micrometers.

The sintered body density of the alumina sintered body is preferably 3.93 g / cm ³ or more.
In order to obtain a low dielectric loss tangent and high strength property, the sintered body density is preferable.

The alkali metal content is preferably 0.2 wt% or less in terms of oxide. In the present invention, a low dielectric loss tangent can be obtained even if an alkali metal is contained within such a range. A more preferable range is 0.1 wt% or less.

Next, the manufacturing method of the alumina sintered body of this invention is demonstrated.

It is desirable to use high-purity alumina powder. The purity is preferably 99% or more, more preferably 99.9% or more. It is preferable to use an alumina powder having an average particle size of 0.5 μm or less. A more preferable range is 0.1 to 0.5 μm. The alumina powder may contain 0.01 to 0.1 wt% Mg.

Examples of SiO _{2 to be} added include SiO ₂ powder, silica sol, silica gel, silicon halide, silicon alkoxide, and water glass. When added as a powder, those having an average particle diameter of 0.5 μm or less are preferably used, and more preferably 0.1 μm or less. Of these, silica sol is preferred when applied to the casting of the present invention.

A slurry of raw material powder is prepared and used for casting. As the solvent for the slurry, known materials such as water and alcohol can be used. The binder used for molding is not particularly limited, and known materials such as polyvinyl alcohol and acrylic emulsion can be used, and a polycarboxylic acid-based general material can be applied as the dispersant. The raw material powder can be mixed by a method using slurry such as stirring and ball mixing.

Casting is performed by casting a slurry 35 in which raw material powder is dispersed in a molding die 30 having a bottom portion 31 made of a water-absorbing material and a side wall portion 32 made of a non-water-absorbing material. It is preferable to use a method of setting the thickness (FIG. 3). According to this method, the thickness direction can be made constant, so that a difference in the degree of orientation depending on the direction of thickness can be generated. The “bottom part” does not necessarily mean that it is at a low position, but means that it is a deep bottom part in the direction of fleshing. Further, the positional relationship between the bottom and the side wall may be a configuration that can be set in a certain direction as shown in FIG.

The density of the cast molded body is preferably increased to 65% with respect to the sintered body density. In the aluminum oxide sintered body of the present invention, since a sintered body of 3.93 g / cm ³ or more is obtained, it is preferable to set the density to at least 2.57 g / cm ^{3 in} the degreased body not including the binder.

Sintering can be performed at normal pressure in various atmospheres such as air, vacuum or inert gas. Of these, atmospheric pressure at normal pressure is most suitable.

The firing temperature can be, for example, in the range of 1300 to 1700 ° C. The sintered body may have an average crystal grain size of 20 μm or less and a temperature at which the sintered body is sufficiently densified.

Examples will be described below.

[Raw material adjustment]
An alumina powder having an average particle diameter of 0.5 μm and a purity of 99.8% alumina powder (containing 0.05 wt% of Mg in terms of oxide) and an average particle diameter of 0.02 μm and a purity of 99.9% silica sol And silica sol were adjusted at a predetermined ratio, and a binder, a dispersant and ion-exchanged water were further added to the resin pot and mixed. An arbitrary amount of Φ10 alumina balls was used as a mixing medium and mixed for 18 hours to obtain a slurry. In the present invention, the median diameter (D50) obtained by laser diffraction particle size distribution measurement is used as the average particle diameter of the raw material powder.

[Casting]
Using a box-shaped mold 30 as shown in FIG. 3, the mold was placed in a horizontal place so that the wall surface of the bottom portion 31 was horizontal. The mold is composed of a water absorbing material bottom 31 made of gypsum, a side wall 32 made of hard plastic and a non-water absorbing material made of hard plastic, and a bottom plate 34 supporting the bottom surface of the bottom, and the connecting portion of the side wall 32 and the bottom plate 34 is made of slurry. Bonded to prevent leakage. Grooves 33 for vacuum suction are formed in the bottom 31 and each of the grooves 33 is connected to a vacuum source (not shown).

The slurry was poured into a mold and vacuum sucked. Excess slurry on the inking layer was discharged when the inking thickness sufficient to extract the shaped body was reached, and a shaped body 36 was obtained. The molded body 36 was heated to 1600 ° C. in a normal pressure atmosphere at a temperature rising rate of 50 ° C./hr, held for 3 hours, and then naturally cooled to obtain a sintered body.

For comparison, sintered bodies of CIP-molded using the same raw materials (Production No. 7) and ordinary cast-molded products whose upper and lower side surfaces are formed by walling on gypsum (Production No. 8) Was also made and evaluated.

[Evaluation]
Various measurements were performed on the obtained alumina sintered body. The sintered density was measured by the Archimedes method. The SiO ₂ content and the alkali metal content were measured by ICP-MS. The three-point bending strength was measured according to JIS R1601. XRD was measured with a CuKα ray source, an acceleration voltage of 40 kV, and 40 mA using a mirror-polished sintered body surface and using a Rigaku X-ray diffractometer MultiFlex. The dielectric loss tangent was measured using a Q meter manufactured by Meguro Radio Co., Ltd. The average particle size was obtained from the intercept method by mirror polishing the sintered body surface, thermally corroding the polished surface to precipitate crystal grain boundaries, and then performing SEM observation. The sintered density was all 3.93 g / cm ³ or more, and the average particle size was 10 μm or less. Further, the alkali metal content was 0.2 wt% or less in terms of oxide.

The XRD measurement is performed on a surface 41 perpendicular to the casting direction of the casting and indicated by an arrow in the alumina sintered body of FIG. 4 and a surface 42 parallel to the casting direction of the casting. The crystal orientation degree O1 based on the XRD peak intensity of the face 41 and the crystal orientation degree O2 based on the XRD peak intensity of the face 42 were determined, and the difference: O2-O1 was calculated. For a sintered body using CIP molding and normal casting, two mutually perpendicular surfaces were calculated as O1 and O2. The results are shown in Table 1.

Difference between the crystal orientation degree O1 of the plane perpendicular to the casting direction of casting and the crystal orientation degree O2 of the plane parallel to the casting direction of casting: O2-O1 is 0.12 to 0.18. Production No. 2 to 5 had a low dielectric loss tangent and a bending strength of 400 MPa or more.

On the other hand, O2-O1 was out of the above range. 1 and Production No. No. 6 has a larger dielectric loss tangent. Production No. In 6, the bending strength decreased. In addition, preparation No. No cordierite phase was detected in the 1-5 alumina sintered bodies.

In addition, production No. 1 using CIP molding and normal casting molding was used. 7 and Production No. In No. 8, there was almost no difference between O2 and O1. Production No. using CIP molding 7 had a low dielectric loss tangent, but the bending strength decreased. Production No. using normal casting molding In 8, the dielectric loss tangent increased and the bending strength also decreased. Further, a cordierite phase was detected in these alumina sintered bodies.

30 Mold 31 Bottom 32 Side wall 35 Slurry 36 Molded body 41 Surface perpendicular to the casting direction of casting 42 Surface parallel to the casting direction of casting

Claims (1)

Casting molding in which a slurry in which raw material powder is dispersed is cast in a molding die having a bottom portion of a water-absorbing material and a side wall portion of a non-water-absorbing material, and the raw material powder is formed with water absorption of the water-absorbing material. An alumina sintered body obtained by sintering the body,
Of the crystal orientation degree O: I ₃₀₀ / (I ₃₀₀ + I ₁₀₄ ) calculated by the XRD peak intensity, the crystal orientation degree O 1 of the plane perpendicular to the casting direction of the casting is parallel to the casting direction of the casting. Difference from the plane crystal orientation degree O2: O2−O1 is 0.12 to 0.18,
Dielectric loss tangent at 1 to 10 MHz is 10 × 10 ⁻⁴ or less, three-point bending strength is 400 MPa or more, SiO ₂ is contained in an amount of 0.08 to 0.8% by mass , and a cordierite phase is substantially contained No alumina sintered body.