JPH03126658A - Production of alumina base plate - Google Patents

Abstract

PURPOSE:To obtain an alumina base plate which is excellent in mechanical, thermal and electric properties and has a smooth surface by molding high purity alumina fine powder contg. trace of magnesia and thereafter calcining this molded body and applying colloidal soln. of alumina hydrate to the surface and recalcining the molded body. CONSTITUTION:The raw material of an alumina base plate is prepared by adding trace of magnesia to a high purity alumina fine powder. This raw material is molded and the molded body is calcined to form a calcined alumina plate. Then the objective alumina base plate is obtained by applying calloidal soln. of alumina hydrate to the surface of this calcined plate and recalcining it. In the above-mentioned method, magnesia for a growth inhibitor of grains is added to the alumina fine powder and therefore the alumina base plate which is dense and excellent in electric characteristics is obtained. Furthermore, colloidal soln. of alumina hydrate is filled into defects such as recessed part, flaws and pinholes caused on the surface of the calcined plate and this calcined plate is recalcined. Therefore, the defects of the calcined alumina plate are buried by alumina contained in calcined alumina hydrate and high degree surface smoothness is obtained.

Description

[Detailed description of the invention] [Field of application on the M leaf] The present invention relates to a method for manufacturing an aluminum-based substrate, and more specifically, an aluminum-based substrate with a dense and extremely smooth surface. Relating to a method of manufacturing.

[Background Art and Problems thereof] In recent years, with the increase in speed and density of microelectronic components, aluminium-based materials have been frequently used as substrate materials. As the characteristics of this substrate, importance is placed on electrical, mechanical, and thermal characteristics as well as surface smoothness.

In particular, substrates for thin film hybrid integrated circuits are desired to have a high level of smoothness, for example, in order to stabilize the resistance value of thin film resistors.

Therefore, conventionally, for this type of use, a glazed substrate, which is an alumina substrate whose surface is glazed and coated with a glass glaze to make the surface smooth, has been used. For example, Japanese Patent Application No. 55-188236 and Japanese Patent Application No. 1-29077
As the glaze, Si02
-AIS102-AI20a- type glass is used. However, this glazed alumina substrate has the disadvantage that heat dissipation from circuit elements mounted on the alumina substrate is restricted due to the poor thermal conductivity of the glass glaze. Additionally, because glass glaze has poor heat resistance, it cannot be used as a substrate for forming thin films (for example, substrates for barium titanate, lead titanate, etc.) that require forming thin films at high temperatures of 1000°C or higher. There was a problem. As described above, glazed substrates are significantly inferior in terms of thermal properties, so an alumina substrate is desired that can provide surface smoothness without glazing.

Furthermore, in order to remotely approximate the surface smoothness of an alumina substrate, an alumina substrate whose surface is mechanically polished after firing is used. However, since alumina has extremely high hardness, it is impractical to smooth the surface by polishing after firing, which doubles the substrate cost.

On the other hand, when magnesium oxide (Mg0) is added to high-purity alumina (AI.03) fine powder, the increase in crystal grains during sintering is controlled to a certain extent, and a dense alumina substrate with excellent electrical properties can be obtained. well known. However, 1 raw sheet of alumina added with magnesium oxide
If fired at a temperature of 700°C or higher, a dense substrate with good electrical properties can be obtained, but the surface smoothness will not be maintained, whereas if fired at a lower temperature of 1600°C, the surface smoothness will not be maintained. However, this has been accompanied by the problem that pores are likely to be formed inside and dielectric loss increases.

Therefore, in Japanese Patent Publication No. 5B-120, a trace amount of chromium oxide (Crabs) and a trace amount of magnesium oxide as a sintering aid are added to high-purity alumina fine powder, and the pores generated by low-temperature firing are removed from the chromium oxide. A method is disclosed to increase damming, reduce porosity, and simultaneously improve surface smoothness.

However, with this method, large shrinkage occurred in the alumina substrate due to sufficient grain growth for densification, resulting in large warpage during firing, which required treatment to correct the warpage after firing. . Furthermore, in the process of straightening the warpage, there is a problem in that defects such as scratches and missing particles are likely to occur on the surface of the alumina substrate due to friction with the holding plate for straightening the warp. Furthermore, the surface smoothness of the alumina substrate was inferior to that of the glazed substrate or polished substrate.

The present invention has been made in view of the above-mentioned prior art, and its purpose is to provide a method for manufacturing an alumina substrate with excellent mechanical, thermal and electrical properties and a smooth surface. There is a particular thing.

[Means for Solving the Problems] Therefore, in the method of manufacturing an alumina substrate of the present invention, a trace amount of magnesium oxide is added to high-purity alumina fine powder to prepare a raw material for an alumina substrate. The method is characterized in that a raw material is molded and fired to form a fired alumina plate, and then a colloidal solution of alumina hydrate is applied to the surface of the fired alumina plate and fired again.

[Function] In the method of the present invention, since magnesium oxide as a grain growth inhibitor is added to the fine arsina powder, an alumina substrate that is dense and has excellent electrical properties can be obtained.

In addition, defects such as recesses, scratches, and pinholes that occur on the surface of the fired alumina plate are filled with a colloidal solution of alumina hydrate and refired, so that the defects in the fired alumina plate are removed from the fired alumina hydrate. It is filled with alumina in the material, and a high degree of surface smoothness can be obtained.

[Example] An embodiment of the present invention will be described below in accordance with the manufacturing order.

First, in the preparation process of the alumina substrate raw material, 99.
An alumina substrate raw material is prepared by adding 0.1 wt % of magnesium oxide as a grain growth inhibitor to fine alumina powder having a purity of 9% or more, adding an organic solvent such as toluene to this, and further adding 0.1 wt % of magnesium oxide as a dispersant. Add 5 wt% of dioctyl phthalate ('DOP) and thoroughly knead and disperse to form a slurry. After dispersion, as a binder 10
Wt % of polyvinyl butyral (PVB) is added and further mixed in a bowl to produce a slurry with a high powder content. Next, in the green sheet manufacturing process, the slurry made as described above is supplied in the form of a sheet onto a PET film with a smooth surface using a doctor blade method, etc., and this is dried to form a green sheet. . The green sheet thus formed has a very smooth surface because the surface smoothness of the film is transferred thereto. A raw alumina substrate sheet of desired dimensions is punched out from this green sheet, placed on a furnace material for alumina firing, and fired to obtain an alumina fired plate. After this,
For warped alumina fired plates, if necessary,
Press it flat with a press plate and fire it again to correct any warping. Next, these aluminum sintered plates are immersed in a colloidal solution of a boehmite-based aluminum hydrate, coated on the surface, and dried in air at 150°C.

As a result, a coating layer made of alumina hydrate is formed on the surface of the Al-wind fired plate.

Note that the thickness of this coating layer can be controlled by the viscosity of the colloidal liquid, the number of immersion times, and the number of drying treatments. After drying the alumina hydrate coating layer,
An alumina substrate is manufactured by firing this Al-wind fired plate again at 1100 to 1300°C. Defects such as scratches, pinholes, depressions, and missing particles occur on the surface of Al-wind fired plates during the firing and re-warping processes. By immersion, the defects in the alumina hydrated board are filled with a colloidal solution of alumina hydrate, and by re-baking, the defects are filled with alumina and the surface of the alumina substrate becomes smooth. Furthermore, by forming a thin coating layer of alumina over the entire surface of the aluminum-coated substrate as in this embodiment, the surface smoothness of the aluminum-coated substrate is improved.

In order to manufacture alumina substrates with good surface smoothness,
The firing temperature of the coating layer is 1100~1100 as described above.
The temperature range of 1300°C was optimal, and the thickness of the coating layer was preferably 1 to 7 μm.

Note that if a raw sheet of alumina substrate is fired at a high temperature of around 1700°C, an alumina substrate with excellent electrical properties can be obtained, so by filling in the defects as described above, the electrical properties and surface smoothness can be improved. It is possible to manufacture an alumina substrate with excellent hardness.

In addition, when a raw sheet of alumina substrate is fired at a low temperature of about 1600°C, pores are generated inside. Since the vacancies can also be filled, the electrical properties can also be improved, and an alumina substrate with good electrical properties and surface smoothness can be manufactured.

(Experimental Example) Next, several types of samples of alumina substrates were manufactured, and the results of measuring their surface roughness will be explained together with the reasons for limiting the above numerical values.

After producing an alumina fired plate through the process described in the above example, a coating layer of a colloidal liquid of boehmite-based alumina hydrate is formed on the surface, and the firing temperature of the coating layer is set in a range of 1000°C to 1550°C. at 50°
Burn out by changing each C, 1 μm or less, 1 ~ 3 μm, 3 ~ 5
Coating layers with thicknesses of 15 to 7 μm, 17 to 9 μm, and 9 μm or more were formed, and the surface roughness of each sample was measured. The results are shown in Table 1. The surface roughness of the Al-wind fired plate before coating is 0.05μmRa.
Met.

As can be seen from Table 1, this experimental example had the effect of improving the surface smoothness in the area surrounded by the thick solid line. That is, a coating layer with a thickness of 1 to 7 μm was formed using colloidal liquefied alumina hydrate, and
By firing at a temperature of ~1300°C, the surface smoothness could be improved. This is higher smoothness than the method using CrJs addition, and comparable to the surface smoothness of a polished substrate.

On the other hand, when the thickness of the coating layer is thinner than 1 μm, the effect of improving the roughness of the alumina substrate surface does not appear, and when the firing temperature exceeds 1350°C, the alumina particles in the coating layer The growth was significant and resulted in an increase in the roughness of the alumina substrate surface.

In addition, in Table 1, the thickness of the coating layer is 7 μm.
m, and the firing temperature is 110 m.
The reason why the column is left blank when the temperature is lower than 0°C is as follows. First, if the thickness of the coating layer is thicker than 7 μm, the shrinkage force of the coating layer will be strong and the coating layer will peel off during firing. Further, if the firing temperature is lower than 1100° C., the alumina substrate will not be sufficiently converted into an α phase, and will become thermally unstable.

[Effects of the Invention] According to the present invention, the defects can be filled by filling the colloidal liquid of alumina hydrate into the defects on the surface of the alumina substrate and firing it, thereby improving the surface smoothness of the alumina substrate. I was able to do it.

Therefore, in addition to the mechanical properties (strength, hardness) and thermal properties (heat resistance, thermal conductivity) that alumina substrates originally have, by adding magnesium oxide, we can obtain good electrical properties. Alumina substrates with a high degree of surface smoothness can be manufactured.

Claims (1)

[Claims] (1) Prepare an alumina substrate raw material by adding a small amount of magnesium oxide to high-purity alumina fine powder, shape and sinter this alumina substrate raw material to form an alumina sintered plate, and then apply the alumina sintered plate to the surface of the alumina sintered plate. A method for producing an alumina substrate, comprising applying a colloidal solution of alumina hydrate and firing it again.