Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-07-21
2003-06-17
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089160, C264S650000, C264S670000, C241S016000
Reexamination Certificate
active
06579394
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of producing ceramic slurry, a ceramic slurry composition and a ceramic green sheet used for manufacturing a multilayer ceramic electronic part, and a method of producing a multilayer ceramic electronic part. Particularly, the present invention relates to methods of producing ceramic slurry and a ceramic slurry composition used for manufacturing a multilayer ceramic electronic part such as a monolithic ceramic capacitor, a ceramic multilayered substrate, etc., and methods of producing a ceramic green sheet and a multilayer ceramic electronic part using the ceramic slurry or the ceramic slurry composition.
2. Description of the Related Art
A multilayer ceramic electronic part such as a monolithic ceramic capacitor, a ceramic multilayered substrate, or the like is usually manufactured through the steps of laminating ceramic green sheets, compressing the laminated ceramic green sheets, and then heat-treating the laminated product to sinter ceramic and electrodes.
For example, in manufacturing a monolithic ceramic capacitor having a structure in which internal electrodes
2
are provided in a ceramic element
1
, and a pair of external electrodes
3
a
and
3
b
are provided to be connected to the internal electrodes
2
which alternately lead to the different side ends, as shown in
FIG. 1
, the following method is used.
(1) First, a capacity forming internal electrode is provided on a ceramic green sheet to form a sheet
11
provided with an electrode (FIG.
2
).
(2) Next, a predetermined number of the sheets
11
provided with electrodes are laminated, and ceramic green sheets (outer layer sheets)
21
without electrodes are laminated on the upper and lower sides of the laminated sheets, followed by compression to form a laminated product (laminated compressed body) in which the ends of the internal electrodes
2
are alternately end at the different side ends.
(3) The laminated compressed body is burned under predetermined conditions to sinter the ceramic, and then conductive paste is coated at both ends of the laminated product (ceramic element)
1
(
FIG. 1
) after burning, and baked to form the external electrodes
3
a
and
3
b
(
FIG. 1
) connected to the internal electrodes
2
. As a result, the monolithic ceramic capacitor shown in
FIG. 1
is obtained.
Other multilayer ceramic electronic parts such as a laminated ceramic multilayered substrate, etc. are also manufactured through the step of laminating ceramic green sheets.
Each of the ceramic green sheets used for manufacturing the multilayer ceramic electronic parts is generally produced by a method in which a ceramic powder is mixed with a dispersion medium (solvent), a dispersant, a binder, a plasticizer, etc., at a predetermined ratio, and disintegrated by using a medium-type dispersing machine such as a bead mill, a ball mill, an attritor, a paint shaker, a sand mill or the like, to produce ceramic slurry and the thus-produced ceramic slurry is formed in a sheet having a predetermined thickness by the doctor blade method, and then dried.
In recent years, various multilayer ceramic electronic parts such as a monolithic ceramic capacitor, like other electronic devices, have been required to have a smaller size and higher performance. Therefore, the ceramic green sheets used for manufacturing the multilayer ceramic electronic part are required to have a small thickness, thereby causing the need to use very thin ceramic green sheets having a thickness of 10 &mgr;m or less.
In order to product such a thin ceramic green sheet, a ceramic slurry comprising a ceramic raw material sufficiently dispersed therein must be used for producing the ceramic green sheets, and thus a ceramic raw material comprising a fine powder having an average particle diameter of about 0.01 to 1.0 &mgr;m must be used as a ceramic raw material powder.
However, the conventional method of producing ceramic slurry comprising mixing the ceramic powder with a dispersion medium (solvent), a dispersant, a binder, a plasticizer, etc., at a predetermined ratio and then disintegrating the mixture by using a medium-type dispersing machine such as a bead mill, a ball mill, an attritor, a paint shaker, a sand mill or the like, makes it difficult to sufficiently disperse the ceramic fine powder of about 1.0 &mgr;m or less. Under actual conditions, therefore, ceramic slurry having dispersion uniformity cannot be obtained, thereby causing difficulties in producing a high-quality thin ceramic green sheet.
Namely, the ceramic green sheet produced by using the ceramic slurry produced by the above-described conventional method has problems in that (1) the surface smoothness is insufficient, (2) a high density and sufficient tensile strength cannot be obtained, and (3) the rate of shrinkage varies with positions in the burning step after lamination due to nonuniform distribution of resins such as the binder, the plasticizer, etc., to fail to obtain sufficient dimensional precision. Particularly, these problems become significant when using a binder having a high degree of polymerization.
In some cases, the conventional method of producing a ceramic slurry comprises dispersing the ceramic powder by forcedly applying collision or impact using a ball mill filled with balls, or a bead mill filled with beads in order to improve dispersibility. In this case, there is a problem in that the ceramic powder is greatly damaged due to the excessive disintegration force of collision or impact to cause deterioration in crystallinity of the ceramic powder and an increase in the specific surface area, thereby failing to obtain a multilayer ceramic electronic part having desired electric properties.
In some cases, a high-pressure dispersion method is used in which slurry containing a ceramic powder is caused to flow under high pressure so that the ceramic powder is dispersed by collision or impact force. However, in this method, the high-pressure disintegration force alone is lower than the method of disintegrating by forced collision or impact using the medium-type dispersing machine such as a ball mill, a bead mill, or the like, causing difficulties in sufficiently disintegrating strongly agglomerated particles. There is thus a problem in that since sufficiently dispersed ceramic slurry cannot be produced, and a high-quality ceramic green sheet cannot be obtained.
Another dispersion method comprises causing a slurry containing a ceramic powder and discharged from a small orifice or nozzle by applying high pressure thereto to collide with a solid wall of a hard material, for example, such as cemented carbide, ceramic, diamond, or the like, or causing the materials discharged from a plurality of small orifices or nozzles to collide with each other. In this method, when the same energy as the above high-pressure dispersion system is applied to the slurry, the stress loaded on the flowing ceramic powder can be increased. However, even when strongly agglomerated particles can be disintegrated, a sufficiently dispersed ceramic slurry cannot be produced because of poor uniformity, thereby causing the problem of failing to obtain a high-quality ceramic green sheet.
Furthermore, defects such as pinholes readily occur in the thin ceramic green sheet, and the use of such ceramic green sheets for manufacturing the monolithic ceramic capacitor shown in
FIG. 1
causes a short circuit (short circuit failure) between the internal electrodes
2
opposed to each other with the ceramic layer formed therebetween.
The defects of the ceramic green sheet which cause such a short circuit failure, are mainly produced due to the presence of the undissolved binder in the ceramic slurry used for producing the ceramic green sheet. The content of the undissolved binder is found to greatly influence the rate of occurrence of the short circuit failure.
As the binder used for the ceramic slurry used for producing the ceramic green sheet, a polyvinyl butyral resin, a cellulose resin, an acrylic resin, a vinyl acetate res
Naka Kazuyuki
Nakamura Ichiro
Dickstein Shapiro Morin & Oshinsky LLP.
Mayes Curtis
Murata Manufacturing Co. Ltd
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