Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Of electrical article or electrical component
Reexamination Certificate
2000-12-13
2003-07-29
Derrington, James (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Of electrical article or electrical component
C156S089120, C264S615000, C264S616000, C264S617000, C264S618000, C264S669000, C264S670000
Reexamination Certificate
active
06599463
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component and a production process therefor, and to a ceramic paste and a production process therefor. More particularly, the present invention relates to a monolithic ceramic electronic component comprising internal circuit element films formed between ceramic sheets, and ceramic layers which compensate for spaces defined by step-like sections which are formed by the internal circuit element films, each ceramic layer being formed so as to have a pattern negative to that of the corresponding film, and a production process for the component; and to a ceramic paste which is advantageously employed for forming the ceramic layer, and a production process for the paste.
2. Background Art
When a monolithic ceramic electronic component, such as a monolithic ceramic capacitor, is produced, a plurality of ceramic green sheets are provided and the sheets are then laminated. In accordance with the intended function of the monolithic ceramic electronic component, an internal circuit element film, such as a conductive film or a resistive film, is formed on a specific ceramic green sheet, the film being an element of a capacitor, a resistor, an inductor, a varistor, a filter, etc.
In recent years, miniaturization and weight reduction of electronic devices such as mobile communication devices have been progressing. For example, when a monolithic ceramic electronic component is employed as a circuit element in such an electronic device, the size and the weight of the electronic component must be reduced. For instance, there has been increasing demand for a monolithic ceramic capacitor of small size and large capacitance.
A typical process for producing a monolithic ceramic capacitor is as follows. Dielectric ceramic powder, an organic binder, a plasticizer and an organic solvent are mixed together, so as to prepare a ceramic slurry. The resultant ceramic slurry is shaped into a sheet having a thickness of some tens of &mgr;m by means of a doctor-blade method or a similar method on a support, such as a polyester film, which is coated with a silicone resin serving as a peeling agent, to thereby form a ceramic green sheet, and the sheet is then dried.
Subsequently, onto a main surface of the ceramic green sheet, a conductive paste is applied through screen printing, so as to produce a plurality of patterns which are separated from one another. Thereafter, the resultant sheet is dried, to thereby form internal electrodes serving as internal circuit element films on the sheet.
FIG. 1
is a plan view of a portion of a ceramic green sheet
2
on which internal electrodes
1
are formed so as to be distributed at a plurality of positions as described above.
Subsequently, the ceramic green sheet
2
is peeled off the support and cut into pieces of appropriate size. Thereafter, predetermined amounts of the pieces are laminated as partially shown in FIG.
2
. Furthermore, predetermined amounts of ceramic green sheets not containing internal electrodes are laminated on opposite surfaces of the resultant laminate, to thereby form a green laminate
3
.
The green laminate
3
is pressed in a vertical direction with respect to a horizontal plane, and then cut into laminate chips
4
as shown in
FIG. 3
, the chips being of appropriate size so as to be employed as individual monolithic ceramic capacitors. Subsequently, the binder is removed from each of the chips, the resultant chip is fired, and then external electrodes are formed on the chip, to thereby produce a monolithic ceramic capacitor.
In order to reduce the size of such a capacitor and increase the capacitance thereof, the ceramic green sheets
2
and the internal electrodes
1
, which are laminated, must be increased in number, and the ceramic green sheets
2
must be thinned.
However, when the laminated sheets and electrodes are increased in number and the sheets are thinned, the internal electrodes
1
are accumulated. Consequently, difference in thickness becomes more apparent between a portion at which the electrodes
1
are provided and a portion at which the electrodes
1
are not provided; or a portion at which relatively large amounts of the internal electrodes
1
are provided in a vertical direction with respect to a horizontal plane and a portion at which small amounts of the electrodes
1
are provided in the vertical direction. Therefore, for example, as shown in
FIG. 3
, the appearance of the resultant laminate chip
4
is deformed such that a main surface of the chip assumes a convex shape.
When the laminate chip
4
is deformed as shown in
FIG. 3
, a relatively large strain arises during pressing at the portion at which the internal electrode
1
is not provided or the portion at which relatively small amounts of the electrodes
1
are provided in a vertical direction with respect to a horizontal plane. In addition, adhesion between the ceramic green sheets
2
is lowered, and a structural defect such as delamination or micro-cracking tends to occur, the defect being caused by internal stress of the chip during firing.
When the laminate chip
4
is deformed as shown in
FIG. 3
, the internal electrode
1
is undesirably deformed, which may cause a short circuit.
The aforementioned problems may lower the reliability of the resultant monolithic ceramic capacitor.
In order to solve the aforementioned problems, for example, Japanese Patent Application Laid-Open (kokai) Nos. 56-94719, 3-74820, and 9-106925 disclose a method in which a ceramic green layer
5
is formed on a region of a ceramic green sheet
2
on which internal electrodes
1
are not formed, as shown in
FIG. 4
, to thereby substantially compensate for spaces defined by step-like sections which are formed by the internal electrodes
1
on the ceramic green sheet
2
.
In the case in which the ceramic green layer
5
which compensates for spaces defined by the step-like sections is formed, when a green laminate
3
a
is formed as partially shown in
FIG. 5
, there is no substantial difference in thickness between the portion at which the electrodes
1
are provided and the portion at which the electrodes are not provided; or between the portion at which relatively large amounts of the internal electrodes
1
are provided in a vertical direction with respect to a horizontal plane and the portion at which small amounts of the electrodes
1
are provided in the vertical direction. Therefore, as shown in
FIG. 6
, the resultant laminate chip
4
a
tends not to be undesirably deformed as shown in FIG.
3
.
Consequently, the aforementioned structural defect such as delamination or micro cracking, or short circuit due to deformation of the internal electrode
1
tends not to occur, thereby enhancing the reliability of the resultant monolithic ceramic capacitor.
The aforementioned ceramic green layer
5
which compensates for spaces defined by the step-like sections has a composition similar to that of the ceramic green sheet
2
, and the layer
5
is formed by applying a ceramic paste containing dielectric ceramic powder, an organic binder, a plasticizer and an organic solvent onto the green sheet
2
. In order to form the layer
5
through printing at high accuracy so as to attain a thickness (e.g., 2 &mgr;m or less) which is equal to that of the internal electrode
1
, the dispersibility of the ceramic powder in the ceramic paste must be high.
In connection with the foregoing, for example, Japanese Patent Application Laid-Open (kokai) No. 3-74820 discloses a method for preparing a ceramic paste in which ceramic powder is dispersed by use of a three-roll mill. However, it is difficult to increase dispersibility of the ceramic powder through use of a three-roll mill only.
Japanese Patent Application Laid-Open (kokai) No. 9-106925 discloses that a ceramic slurry for forming a ceramic green sheet
2
is prepared by mixing dielectric ceramic powder, an organic binder and a first organic solvent having a low boiling point, and the resultant slurry is employed for f
Kato Koji
Kimura Koji
Miyazaki Makoto
Suzuki Koji
Tanaka Satoru
Derrington James
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
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