JPH04265268A - Manufacture of alumina substrate - Google Patents

Abstract

PURPOSE:To manufacture an alumina substrate having small surface roughness causing circuit burnout by obtaining molded article with less aggregated powder before calcining. CONSTITUTION:In addition to the processes such that slurry containing alumina powder, a filtrate of water solution of methylcellulose and an additive is dried, and then water is added to the dried product thus obtained and mixed with it, calcining of molded article obtained by extrusion molding is included in the process. Thereby the dried product in the form of granulated powder consisting of alumina powder whose surface is coated with methylcellulose is uniformly dispersed to become a state of water solution by the water addition. Since the filtrate of water solution of methylcellulose is free from a water- insoluble component contained in methylcellulose, an alumina substrate obtained by calcining the molded article without aggregated powder before the calcining is the one with smoothness and with no development of pores.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an alumina substrate, and the alumina substrate manufactured by this method is useful as an insulating substrate for forming circuit patterns, for example.

0002

[Prior Art] Ceramic substrates, typified by alumina substrates, are used as insulating substrates for circuit boards with circuit patterns formed by thick film printing using conductive paste on the substrate surface, thin film printing by vapor deposition, or plating. However, in recent years, as circuit boards have become smaller and more multifunctional, so-called fine patterns, in which circuit patterns have higher densities and narrower circuit widths, have been required. Naturally, alumina substrates that meet such demands are required to have high dimensional accuracy, low warpage, and other qualities.

[0003] Such dimensional accuracy and warpage are closely related to the manufacturing method of the alumina substrate, and it is generally advantageous to have a small shrinkage rate during firing. Molded products that undergo firing to obtain alumina substrates are generally obtained by extrusion molding and the doctor blade method, but extruded molded products have high density and have a small shrinkage rate during firing. accuracy,
Advantageous against sledding.

In addition to these, the demand for alumina substrates for high frequency applications has increased rapidly in recent years, and the conventional purity of 96% has increased.
Since alumina substrates with a purity of 99% or higher cannot fully meet these requirements, high-purity alumina substrates with a purity of 99% or higher have been used to meet these requirements. The alumina powder used for such high-purity alumina substrates is a fine powder with a small particle size, so if extrusion molding is used, which is suitable for manufacturing molded products with a small shrinkage rate, the surface energy of the powder will be reduced. Because it is large, it tends to aggregate,
In addition, the clay used during extrusion molding has a low moisture content, so powder aggregates are likely to form in the molded product, and although these aggregates become somewhat smaller after firing, the resulting alumina substrate has a large surface roughness. .

Furthermore, when methylcellulose is used as a binder in a molded article, if the methylcellulose contains components that are insoluble in water, these insoluble components will cause pores to occur after firing. These pores can cause circuit disconnections, and the finer the pattern, the greater the risk of circuit disconnection.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to produce an alumina substrate with a small surface roughness by obtaining a pre-fired molded product with less powder agglomerates.

[0007]

[Means for Solving the Problems] The method for producing an alumina substrate according to the present invention includes a step of drying a slurry containing alumina powder, a filtrate of an aqueous methylcellulose solution, and an additive, and a drying process of drying the dried product obtained in this drying step. The method is characterized by including a step of adding water and kneading, and then firing the molded product obtained by extrusion molding.

The present invention will be explained in detail below. The average particle size of the alumina powder used in the present invention is approximately 1. Fine powder of 0 μm or less is preferred. In the step of drying a slurry in which methylcellulose as a binder of alumina powder and other additives are dispersed in water, the feature of the present invention is that methylcellulose that has undergone a specific treatment is used. That is, methylcellulose is used as a filtrate obtained by filtering an aqueous solution in which the raw material methylcellulose is dissolved in water. Additives include, for example, plasticizers, mold release agents, lubricants, etc., which are appropriately dissolved and contained in the slurry, and of course other additives are not excluded from the slurry.

[0009] When the above slurry is dried, a dried product is obtained in which the surface of the alumina powder is coated with methylcellulose and is granulated into granules. This granular dry material becomes soft due to the cellulose being dissolved by hydrogenation.
The granules are destroyed by kneading, and the alumina powder takes on the properties of primary particles in which the powder is independently dissociated, and is uniformly dispersed into an aqueous solution. Here, the ease of breaking the granular dry product is related to the ease of dissolving the methyl cellulose coated on the surface of the alumina powder, and it is effective to prepare the dry product with a moisture content of 3 wt % or more. That is, when there is a large amount of water contained in the dried material, the penetration of water into the granular dried material is promoted, methyl cellulose is also easily dissolved, and the uniform dispersion of the alumina powder is enhanced. In addition, the moisture content of the dry product is 3wt.
%, it will take time to dissolve the methylcellulose, so it will be necessary to let it sit before kneading. If the upper limit of the moisture content of the dry product exceeds 15 wt%, it will be difficult to produce a molded product that maintains a constant shape by extrusion molding.

[0010] The molded product obtained by extrusion molding is fired to become the desired alumina substrate. The firing conditions are:
There are no particular restrictions and the firing temperature is usually about 1600°C.

[0011]

[Example 1] Average particle size: 0. 100 parts by weight of 4 μm alumina powder (trademark: AES-11C, manufactured by Sumitomo Chemical Co., Ltd.)
(hereinafter simply referred to as "parts") is a dispersant consisting of polycarboxylic acid ammonium salt (manufactured by Kao Corporation; trademark: Poise 532A).
) as 1. 25 parts and 30 parts of ion-exchanged water were added and mixed in a ball mill for 20 hours to prepare a primary slurry containing alumina powder as primary particles. As a binder, powdered methyl cellulose (manufactured by Matsumoto Yushi Co., Ltd., trademark: Marporose 60SH-4000) was once dissolved in ion-exchanged water to prepare a 2% aqueous solution, which was then filtered through a filter paper with a pore size of 10 μm. 300 parts of this filtrate was added to the above primary slurry, 4 parts of glycerin as a plasticizer, 2 parts of a mold release agent consisting of sorbitan monocaprylate complex ester (trademark: Ceramisol C-08, manufactured by NOF Corporation), and further added polyester. A lubricant consisting of oxyalkylene butyl ether (
Two parts of Uniloop 50MB-26 (manufactured by NOF Corporation) were added and thoroughly mixed to obtain a secondary slurry. This secondary slurry was dried in a rotary kiln to obtain a dried product. The moisture content of this dried product is 10. It was 5wt%. The moisture content was determined from the change in weight when drying at 110° C. for 2 hours.

[0012] Using this dried material, alumina powder 100
5 parts of water was added so that the amount of water was 17 parts per part, and after thorough mixing, the mixture was kneaded using three ceramic rolls to obtain a clay for extrusion molding. This clay is molded into a molded product using an extrusion molding machine to a thickness of approximately 0. An 8 mm green sheet was obtained. Further, the green sheet of this molded product was punched into approximately 10 cm square pieces and fired at 1600°C to form an alumina substrate.

[0013]

[Example 2] The secondary slurry in Example 1 was dried with a drum dryer to obtain a dried product. The moisture content of this dried material is 2
．． It was 2wt%. Using this dried product, 14.5 parts of water was added so that the amount of water was 17 parts per 100 parts of alumina powder, and the mixture was thoroughly mixed. Next, this material was sealed in a plastic bag to prevent water from evaporating, and after being left for 24 hours, it was kneaded using three ceramic rolls to obtain a clay for extrusion molding. Using this clay, a target alumina substrate was obtained under the same conditions as in Example 1.

[0014]

[Comparative Example 1] Average particle size: 0. Add 6 parts of the methyl cellulose powder of Example 1 as a binder to 100 parts of the 4 μm alumina powder of Example 1, mix thoroughly with a ball mill, then add 4 parts of glycerin as a plasticizer and 2 parts of the mold release agent of Example 1. , 2 parts of the lubricant of Example 1 and 17 parts of water were added and mixed thoroughly. After mixing, a green sheet as a molded product and a ceramic substrate as a final product were obtained under the same conditions as in Example 1.

A 1 cm square surface of the green sheets and alumina substrates obtained in the above Examples and Comparative Examples was observed with a microscope at a magnification of about 100 times, and the number of powder aggregates appearing as protrusions of 50 μm or more was counted. This observation was performed at five points for each sample, and the average value is shown in Table 1 as the number of powder aggregates for that sample.

[0016] Regarding the surface roughness of the alumina substrate, the surface roughness Ra and Rmax according to JIS-B0601 are
was measured. Furthermore, after dyeing the entire surface of the alumina substrate with a dye, it was washed away and only the pores were dyed, and the number of pores of 30 μm or more was counted in a 5 cm square at a magnification of about 100 times using a microscope. The results are also shown in Table 1.

[0017]

[Table 1]

[0018]

According to the method of manufacturing an alumina substrate according to the present invention, an alumina substrate with a small surface roughness can be manufactured, and it is effective for forming a fine circuit pattern.

Claims (2)

[Claims] Claim 1: A step of drying a slurry containing alumina powder, a filtrate of an aqueous methylcellulose solution, and an additive, and adding water to the dried product obtained in this drying step, kneading it, and then extruding it. 1. A method for producing an alumina substrate, comprising the step of firing a molded product. 2. The method for producing an alumina substrate according to claim 1, wherein the moisture content of the dried product is 3 wt% or more.