Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2003-07-08
2004-12-07
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S306100, C361S306300, C361S321200, C361S311000, C361S313000
Reexamination Certificate
active
06829134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laminated ceramic electronic component including a plurality of internal electrodes which are laminated with a ceramic layer therebetween, and the internal electrodes facing each other are alternately led out to the end surfaces on the opposite sides of the ceramic element such that the internal electrodes are connected to external electrodes provided on the end surfaces, and also relates to a method for manufacturing the same.
2. Description of the Related Art
In a monolithic ceramic capacitor, for example, as shown in
FIG. 18
, a plurality of internal electrodes
52
are laminated with a ceramic layer
53
therebetween in a ceramic element
51
. The internal electrodes
52
are alternately led out to the end surfaces on the opposite sides of the ceramic element
51
. The internal electrodes
52
are connected to external electrodes
54
provided on the end surfaces.
In general, the monolithic ceramic capacitor having the above-described structure is manufactured as described below. For example, as shown in
FIG. 19
, ceramic green sheets
53
a
, each provided with an internal electrode pattern
52
a
on the surface through the application of a conductive paste by a screen printing method or other suitable method, are laminated. Ceramic green sheets (dummy sheets)
53
b
provided with no internal electrode are laminated on the top and bottom surfaces, followed by pressure bonding and firing. A conductive paste is applied to both end surfaces of the fired laminate (ceramic element)
51
, followed by baking, such that a pair of external electrodes
54
(
FIG. 18
) are formed.
In the monolithic ceramic capacitor having the above-mentioned structure, water may enter into the interior of the ceramic element
51
from exposed portions of the internal electrodes
52
on the end surfaces, and thereby, characteristics of the capacitor may be degraded and peeling may occur.
In order to overcome the above-described problems, as shown in
FIGS. 20A and 20B
, a monolithic ceramic capacitor is proposed, in which the width W of a lead portion
55
of the internal electrode
52
is less than the width W
0
of another portion (capacitance-forming portion)
56
in order to prevent the entrance of water from outside and the occurrence of peeling (Japanese Unexamined Patent Application Publication No. 8-97071 and Japanese Unexamined Patent Application Publication No. 11-97284).
However, in the monolithic ceramic capacitor in which the width W of the lead portion
55
is reduced, as shown in
FIG. 21
, thicknesses of the internal electrodes
52
are increased at the corner portions (regions A in
FIG. 20B
) of the internal electrode
52
(capacitance-forming portion
56
), boundary portions (regions B in
FIG. 20B
) between the lead portion
55
and the capacitance-forming portion
56
and other portions, and thereby, an internal stress is generated when lamination is performed. As a result, problems occur in that the thermal shock resistance is degraded, and thereby, cracks occur so as to cause degradation of the characteristics. In particular, when an internal electrode pattern is formed through printing of a conductive paste by a screen printing method, the thickness of the internal electrode
52
is likely to be increased at the above-mentioned corner portions A and the boundary portions B, and thereby, problems occur in that the internal stress is increased and the thermal shock resistance is degraded.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide a highly reliable monolithic ceramic capacitor which has no structural defect, e.g. peeling, and which is not susceptible to water from the outside, and to provide a method for manufacturing such a novel monolithic ceramic capacitor.
Preferred embodiments of the present invention provide the following configuration and manufacturing method.
A laminated ceramic electronic component according to a preferred embodiment of the present invention includes a plurality of internal electrodes that face each other with a ceramic layer therebetween and that are provided in a ceramic element, and the internal electrodes facing each other extend to respective end surfaces of a pair of end surfaces of the ceramic element through respective lead portions continued from the respective internal electrode main portions such that the internal electrodes are connected to respective external electrodes of a pair of the external electrodes provided on the pair of end surfaces, wherein each internal electrode of a pair of internal electrodes has a two-dimensional shape including at least one corner portion in the main portion and a portion having a width that gradually decreases in one direction in a portion that extends from the main portion, and wherein the pair of internal electrodes are arranged such that a corner portion of one internal electrode of the pair of the internal electrodes and a portion of the other internal electrode having a width gradually decreasing in one direction are in close proximity to each other with the ceramic layer therebetween while the corner portion of the one internal electrode does not overlap the other internal electrode, or such that a corner portion of the other internal electrode and a portion of the one internal electrode having a width gradually decreasing in one direction are in close proximity to each other with the ceramic layer therebetween while the corner portion of the other internal electrode does not overlap the one internal electrode.
In the above-mentioned laminated ceramic electronic component, the portion having a width that gradually decreases in one direction is preferably in the lead portion of the internal electrode, and the corner portion is preferably located in a portion opposite to the lead portion with the center of the internal electrode main portion therebetween.
In a preferred embodiment of the laminated ceramic electronic component, the width of the portion having a width gradually decreasing in one direction preferably decreases linearly.
In a preferred embodiment of the laminated ceramic electronic component, the width of the portion having a width gradually decreasing in one direction preferably decreases at an angle of about 40 to about 80 degrees.
In a preferred embodiment of the above-mentioned laminated ceramic electronic component, the width of the portion having a width gradually decreasing in one direction more preferably decreases at an angle of about 60 to about 80 degrees.
In a preferred embodiment of the above-mentioned laminated ceramic electronic component, the external electrode-side width in the portion having a width gradually decreasing in one direction is preferably about two-thirds to about three-quarters the width of the internal electrode main portion.
A method for manufacturing a laminated ceramic electronic component having the above-mentioned structure includes the steps of applying a conductive paste on one surface of a ceramic green sheet via a screen printing method to provide an electrode pattern having the above-mentioned shape on the ceramic green sheet surface and laminating a plurality of the ceramic green sheets such that a pair of internal electrodes facing each other with the ceramic layer therebetween have the above-mentioned positional relationship.
In a preferred embodiment of manufacturing a laminated ceramic electronic component, the internal electrode preferably includes a corner portion that located in a portion at which two sides of the internal electrode main portion are in contact with each other, and the portion having a width gradually decreasing in one direction is located in the lead portion.
In the above-mentioned laminated ceramic electronic component, each internal electrode of a pair of the internal electrodes preferably has a two-dimensional shape with at least one of a curve and a chamfering straight line in each of four corner portions, and in a pair of the internal electrodes, the
Kawabata Kazuaki
Matsumoto Hiroyuki
Shimizu Akihiro
Taira Hiroaki
Yamauchi Makoto
Ha Nguyen T.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Reichard Dean A.
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