JPH05319853A - Sorting of hollow granular body and method for regulating particle size - Google Patents

Abstract

PURPOSE:To decrease the generation of coagulated particles by freezing a quartz glass based hollow granular body sorted by air separation and gravity separation, and heating and drying the particles while the frozen state is kept in vacuum. CONSTITUTION:A quartz glass based hollow granular body prepared by mixing organosilicic compounds and a foaming agent, atomized and given thermal decomposition is classified by air separation into that of about 10mum central particle diameter and that of larger particle diameter to be removed. Next, after the hollow granular body of about 10mum central particle diameter is sorted by gravity separation and unfoamed particles and deformed particles are removed, the hollow granular body in slurry is instantaneously frozen. The frozen hollow granular body is heated and dried while frozen state is kept in vacuum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sizing particles in which hollow particles are agglomerated. Due to the need to process a large amount of information quickly, the frequency of signals is increasing and optical communication is being performed.

A circuit board on which an electronic circuit for processing such a high-speed signal is formed needs to have a delay time τ of an electric signal as small as possible. For this purpose,
As shown in equation (1), the dielectric constant ε of the substrate must be small.

Τ = ε ^1/2 / c (1) where ε is the dielectric constant of the substrate c is the speed of light

[0004]

2. Description of the Related Art As a means for solving such a problem, glass ceramics are used as a substrate material.

That is, while a green sheet containing alumina (Al ₂ O ₃ , ε≈10) as a main component requires a firing temperature of 1300 ° C. or higher, a mixture of alumina powder and borosilicate glass powder is mainly used. The glass-ceramic green sheet as a component can lower the firing temperature to 1000 ° C or less, so Cu (melting point 1083 ° C) can be used as a material for forming wiring patterns, and transmission loss can be reduced. ..

However, the dielectric constant of such a glass ceramic substrate is 4 to 6, which is insufficient for the purpose of shortening the signal delay time. Therefore, the inventors have proposed to replace a part of ceramics such as alumina with hollow silica (quartz) powder and use it as a method for realizing a low dielectric constant of a ceramic substrate.

That is, silica (SiO ₂ ) has a dielectric constant ε of 3.
8 is the lowest of the inorganic dielectrics, but by making it hollow, a composite dielectric with air can be formed.
The dielectric constant can be further reduced as shown in equation (2).

Ε ₀ = ε ₁ ^V ₁ × ε ₂ ^V ₂ (2) where ε ₀ is the composite permittivity, v ₁ is the ratio of the dielectric (quartz) of ε ₁ to the total volume, and v ₂ is the total volume. Against ε ₂
Of the dielectric material (air), the hollow silica powder is methoxysilicate [Si (OCH ₃ )
₄ ] and ethoxy silicate [Si (OC ₂ H ₅ ) ₄ ] and the foaming material are mixed and atomized and then thermally decomposed, the foaming agent can be formed by forming bubbles.

The inventors have proposed the use of a glass ceramics substrate having a low dielectric constant by replacing a part of the ceramics constituting the glass ceramics with a hollow silica powder having an average particle size of about 10 μm.

That is, a plasticizer, a binder and a solvent are added to a mixture of hollow silica powder, borosilicate glass powder and ceramic powder, and the mixture is kneaded and then molded to form a green sheet, and a hole for forming a via hole is formed in this green sheet. After opening, a copper (Cu) paste is screen-printed to form a conductor pattern, and then the green sheets are aligned and laminated, integrated, and fired to make a multilayer ceramic circuit board. it can.

Heretofore, hollow particles mainly composed of hollow silica having a small particle diameter have been used as a fluidity adjusting agent for paints, and a large particle having a particle diameter of 100 μm or more has been used. It is used as a lightweight material for concrete and a lightweight material for resin moldings.

[0012] As described above, the main purpose of use of the hollow granular material is to reduce the cost, and the particle diameter, specific gravity, shape, etc. are not taken into consideration, and the hollow granular material is used in the as-manufactured state. Therefore,
In order to form a high quality circuit board by using a hollow granular material as a constituent material of a low dielectric constant ceramic board, strict control of particle size and specific gravity is required.

Therefore, the inventors have carried out specific gravity classification using hollow silica and an alcohol solution having excellent chemisorbability to remove unfoamed products and damaged products, and to suppress variations in particle size and specific gravity. And the classified products
It is proposed that foreign matter on the surface can be removed by heating at a temperature of 750 ° C or lower. (Japanese Patent Application No. 03-190055, filed on July 30, 1991) Then, a low dielectric constant glass ceramic substrate containing hollow silica as a dielectric could be produced by such a method.

However, the hollow granular material separated by the conventional specific gravity classification method and the subsequent heat treatment is agglomerated into agglomerated particles. Therefore, when a ceramic green sheet is formed by using a hollow granular material obtained by classification as a constituent material, aggregated particles are mixed on the surface, and only a non-uniform one having poor moldability can be obtained.

[0015]

As a method of realizing a ceramic substrate having a low dielectric constant, there is a method of containing hollow silica as a dielectric.

Here, in order to obtain a glass-ceramic substrate having excellent characteristics, it is necessary to perform classification and sizing of hollow silica sufficiently, but conventional hollow granules are aggregated with each other to form aggregated particles. Therefore, the formability was not uniform even if the green sheet was formed.

Therefore, this improvement is a problem.

[0018]

[Means for Solving the Problems] The above-mentioned problem is that after classifying a silica glass-based hollow granular material by a wind classification method and a specific gravity classification method, the hollow granular material is frozen to keep the frozen state in a vacuum. This can be solved by constructing a method for classifying and sizing the hollow particles, which is characterized by heating to obtain a dry powder.

[0019]

The air classification method and the specific gravity classification method are known as classification methods for granular materials. That is, it is possible to remove particles having a large particle size by using the air classification method.

On the other hand, the specific gravity classification method using solutions having different specific gravities is a method suitable for classification of particles having a small particle size.
As a result, unexpanded particles and deformed particles can be removed at the same time. However, the hollow granules classified in this way are in the form of a slurry (Slurry) containing liquid, but in the past, since this was dried as it was, powder was generated due to the surface tension when the liquid was removed. Are aggregated.

Therefore, the present invention is to obtain hollow granules without aggregation by using the freeze-drying method. That is, when liquid nitrogen (N ₂ ) is used to freeze the slurry momentarily, and then it is depressurized and dried in vacuum while maintaining the frozen state, sublimation occurs, and it becomes a gas directly from the solid state to the liquid state. Does not elapse.

Therefore, since there is no aggregating action due to the surface tension when the liquid evaporates, the generation of agglomerated particles can be eliminated.

[0023]

Example The obtained hollow silica powder has an average specific gravity of 0.5 and includes unfoamed products and broken products. This hollow granular material was classified by an air classifier into those having a central particle diameter of 10 μm, and those having a large particle diameter were removed.

The average specific gravity after classification increased to about 0.7 due to the fact that hollow particles having a small diameter with insufficient foaming were collected and the hollow particles were damaged during air classification. Next, the classified powder was put in a 4-fold container, mixed with water, allowed to stand for 1 hour, and then, what floated on the liquid surface was collected.

Next, the recovered slurry (hollow granular material containing water) is poured into liquid N ₂ to be frozen, placed in a vacuum container, evacuated to 1 × 10 ^-2 torr, and heated to 50 ° C. As a result of drying for 24 hours at room temperature, a sized hollow granular material was obtained.

For comparison, hollow particles were also produced by a conventional drying method under normal pressure. Then, the aggregation rate was measured for both. Here, the agglomeration rate is 10 g of each hollow granule, lightly loosened and dispersed in ethyl alcohol to form a solution. The amount of powder that passed through a Teflon mesh with a pore size of 122 μm and the amount of powder that did not pass (aggregation The amount was calculated from the following formula.

Aggregation rate = (agglomeration amount / total powder amount) × 100% (3) Further, a green sheet is prepared using this hollow granular material,
The appearance was visually observed.

As a result, the agglomeration rate of the hollow granules was 30% according to the conventional method, whereas it was 0.
It was as low as 5%. In addition, observation of the appearance of the green sheet was also good in that the present invention had few aggregated particles.

[0029]

EFFECTS OF THE INVENTION By carrying out the present invention, it is possible to almost eliminate agglomerates, and thus it is possible to obtain a glass ceramics substrate having uniform characteristics and a flat surface.

Claims (1)

[Claims] 1. A dry powder is obtained by classifying quartz glass hollow particles by a wind classification method and a specific gravity classification method, and then freezing the hollow particles and heating them in a vacuum while keeping the frozen state. A method for classifying and sizing hollow particles, characterized by: