Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-11-30
2003-01-28
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089120, C264S615000, C501S001000, C501S094000, C241S016000
Reexamination Certificate
active
06511564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a ceramic slurry used for fabricating ceramic electronic components, such as monolithic ceramic capacitors and multilayered ceramic substrates, to a method for forming a ceramic green sheet using the ceramic slurry, and to a method for fabricating a monolithic ceramic electronic component using the ceramic slurry.
2. Description of the Related Art
A monolithic ceramic electronic component, such as a monolithic ceramic capacitor or a multilayered ceramic substrate, is usually fabricated by laminating ceramic green sheets, followed by press-bonding and the performance of a heat treatment to sinter the ceramic and electrodes.
For example, in order to fabricate a monolithic ceramic capacitor as shown in
FIG. 1
having a structure in which internal electrodes
2
are arranged in a ceramic element
1
and in which a pair of external electrodes
3
a
and
3
b
are arranged on both sides so as to be electrically connected to the internal electrodes
2
which are alternately extended to one side and the other side of the ceramic element
1
, the method described below is typically used.
First, a sheet
11
provided with an electrode (refer to
FIG. 2
) is formed by arranging an internal electrode for forming capacitance on a ceramic green sheet.
Next, as shown in
FIG. 2
, a predetermined number of sheets
11
, each provided with an electrode, are laminated together, and ceramic green sheets (sheets for outer layers)
21
which are not provided with an electrode are laminated on the upper and lower surfaces of the laminated sheets
11
, and thus a laminate (press-bonded laminate) is formed in which the ends of the individual internal electrodes
2
alternately extend to one side and the other side.
The press-bonded laminate is then fired under predetermined conditions to sinter the ceramic, and a conductive paste is applied to both sides of the sintered laminate (ceramic element)
1
(refer to FIG.
1
), followed by baking, to form the external electrodes
3
a
and
3
b
which are electrically connected to the internal electrodes
2
.
Thus, a monolithic ceramic capacitor as shown in
FIG. 1
can be obtained.
Additionally, other monolithic ceramic electronic components, such as monolithic multilayered ceramic substrates, are also fabricating by laminating ceramic green sheets.
A ceramic green sheet used for fabricating a monolithic ceramic electronic component is generally formed by formulating a ceramic powder, a dispersing medium (solvent), a dispersant, a binder, a plasticizer, etc., at predetermined ratios, followed by mixing and pulverizing with a dispersing machine using a pulverizing medium, such as a bead mill, a ball mill, an ATOLITER, a paint shaker or a sand mill, to form a ceramic slurry, and molding the ceramic slurry into a sheet having a predetermined thickness using a doctor blade process or the like, followed by drying.
However, recently, there have been further demands for reduction in size and higher performance with respect to various monolithic ceramic electronic components, such as monolithic ceramic capacitors, as there are with respect to other electronic elements.
Therefore, ceramic green sheets used for fabricating such monolithic ceramic electronic components must be thinner and very thin ceramic green sheets having a thickness of 10 &mgr;m or less have been required.
In the ceramic slurry used for forming such thin ceramic green sheets, the raw material ceramic powder must be sufficiently dispersed. For that purpose, a fine ceramic powder having an average particle size of 0.01 to 1 &mgr;m must be used as the raw material ceramic powder.
In the conventional method for forming a ceramic slurry, in which a ceramic powder, a dispersing medium (solvent), a dispersant, a binder, a plasticizer, etc., are formulated at predetermined ratios, and mixing and pulverizing are performed with a dispersing machine using a pulverizing medium, such as a bead mill, a ball mill, an ATOLITER, a paint shaker or a sand mill, it is difficult to sufficiently disperse a fine ceramic powder having particles of 1 &mgr;m or less, and it is not possible to obtain a slurry which is homogeneously dispersed. Thus, it is difficult to form thin ceramic green sheets of high quality thereby.
That is, the ceramic green sheet formed using the ceramic slurry produced by the conventional method described above has the problems that 1) the surface thereof is not sufficiently smooth; 2) high density cannot be obtained, resulting in insufficient tensile strength; and 3) resins, such as a binder and a plasticizer, are inhomogeneously dispersed, and the shrinkage factor varies locally in the sintering process after lamination, and thus satisfactory dimensional accuracy cannot be obtained. Additionally, such problems are particularly noticeable when a binder having a high degree of polymerization is used.
In the conventional method for forming a ceramic slurry, in order to improve dispersibility, the ceramic powder may be dispersed by forced impact or collision using a ball mill filled with balls or a bead mill filled with beads. In such a case, the pulverizing force due to impact or collision may be excessively large, thus increasing the level of damage to the ceramic powder, resulting in a decrease in the crystallinity of the ceramic powder or an increase in the specific surface. Thus, it may be difficult to obtain a monolithic ceramic electronic component having desired electrical characteristics.
High pressure dispersion may be used in which a slurry containing a ceramic powder is made to flow under high pressure and the ceramic powder is dispersed by impact or collision. However, since the pulverizing force obtained by the high pressure dispersion alone is smaller than the pulverizing force due to forced impact or collision obtained by the dispersion process using a ball mill or a bead mill, it is difficult to sufficiently pulverize strongly clumped particles, and it is not possible to produce a ceramic slurry which is sufficiently dispersed; thus it is not possible to obtain a ceramic green sheet of high quality.
Even if dispersion treatment is performed in any manner, in the case of a thin ceramic green sheet having a thickness of 10 &mgr;m or less, if minute amounts of agglomerated particles, flocculated particles, dust, contamination or bubbles are present, imperfections are generated at the surface of or inside the ceramic green sheet, resulting in problems, such as short circuiting.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above, and objects of the present invention are to provide a method for producing a ceramic slurry which is suitable for use in fabricating ceramic electronic components, in which a ceramic powder can be homogeneously dispersed without excessive damage and inclusion of foreign matter can be decreased, to provide a method for forming a ceramic green sheet using the ceramic slurry produced by the above method, and to provide a method for fabricating a monolithic ceramic electronic component using the ceramic slurry.
In one aspect, a method for producing a ceramic slurry used for fabricating a ceramic electronic component in accordance with the present invention includes a mixing and pulverizing step for mixing and pulverizing a ceramic powder having an average particle size of about 0.01 to 1 &mgr;m, a solvent and a dispersant by a dispersion process using a pulverizing medium, such as balls or beads, to obtain a mixed and pulverized slurry; and a high pressure dispersion step for performing high pressure dispersion at a pressure of about 100 kg/cm
2
or more after a filtered binder solution is added to the mixed and pulverized slurry to obtain a dispersed slurry (final dispersed slurry), the filtered binder solution being prepared by dissolving a binder in a solvent, followed by filtration.
It is possible to reliably obtain a ceramic slurry in which the ceramic powder is sufficiently dispersed by the above method in which the c
Kurihara Hiroyuki
Nakamura Ichiro
Dickstein , Shapiro, Morin & Oshinsky, LLP
Mayes Curtis
Murata Manufacturing Co. Ltd.
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