Ceramic electronic part

Details Ceramic electronic part Ceramic electronic part

1999-07-27

2001-08-21

Dinkins, Anthony (Department: 2831)

Electricity: electrical systems and devices

Electrostatic capacitors

Fixed capacitor

C361S306300, C361S321200

Reexamination Certificate

active

06278602

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic electronic part, such as a laminated capacitor, and a method for producing the same. More specifically, it relates to a ceramic electronic part with an improved shape for the lateral edges of its internal electrodes and a method for producing the same.
2. Description of the Related Art
FIG. 6
is a cross-sectional view showing an embodiment of a conventional laminated capacitor. The laminated capacitor
51
has a ceramic sintered compact
52
comprising dielectric ceramics. A plurality of internal electrodes
53
a
to
53
d
are formed in the ceramic sintered compact
52
such that they are superimposed in the thickness direction via respective ceramic layers. The internal electrodes
53
a
,
53
c
extend to the end face
52
a
, and the internal electrodes
53
b
,
53
d
extend to the end face
52
b
. External electrodes
54
,
55
cover the end faces
52
a
,
52
b
, respectively.
The ceramic sintered compact
52
to be used in the above-mentioned laminated capacitor
51
is produced by the process described below. A plurality of ceramic green sheets having internal electrodes
53
a
to
53
d
printed thereon are laminated together with an optional number of unprinted ceramic green sheets located on the upper and lower surfaces of the compact so as to obtain a laminated product. A conductive paste is used to form the internal electrodes. After the laminated product has been pressed in the thickness direction, it is baked.
Because the internal electrodes
53
a
to
53
d
are formed by baking the printed conductive paste, they have a substantially homogeneous thickness. The tip (one lateral edge) of the internal electrode
53
a
, that is, the part shown in the circle in
FIG. 6
, is shown in an enlarged view of FIG.
7
A.
As apparent from
FIG. 7A
, the internal electrode
53
a
has a substantially homogeneous thickness to the tip. As shown in
FIG. 7B
, in some cases the tip of the internal electrode
53
a
may have a slight roundness.
However, due to the above-mentioned shape of the internal electrode, when the ceramic sintered compact
52
is formed, peel-off among the ceramic layers or the phenomenon called delamination sometimes occurs. This can be attributed to the fact that when the laminated product is pressed prior to baking, portions where the internal electrodes exist are compressed strongly in the thickness direction so as to have a higher density, whereas portions where the internal electrodes do not exist are insufficiently compressed. As a result, the density of the portions B, C and D shown in
FIG. 7A
before baking vary in the order B>D>C. This variation causes delamination or inter-layer peel-off in the sintered compact. In particular, in the case of an internal electrode with a thickness of 3 &mgr;m or more (used for high reliability), this phenomena has been remarkable.
A method for alleviating the reduction in density in the part shown as C in
FIG. 7A
is disclosed in Japanese Unexamined Patent Publication No. 8-58259. This publication proposes a method of printing a conductive paste, using a special screen printing plate, wherein the thickness of the internal electrode in the vicinity of its outer rim is thinner than at its other parts. The cross-sectional shape of an internal electrode formed according to this method is shown in FIG.
8
. In the vicinity of the outer rim of the internal electrode
56
shown in
FIG. 8
, the internal electrode
56
is thinner at part
56
b
as a result of the presence of step
56
a.
However, even in the sintered compact obtained by the method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 8-58259, delamination and inter-layer peel-off is not satisfactorily prevented, and further improvement is desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a ceramic electronic part such as a laminated capacitor, capable of effectively minimizing delamination and inter-layer peel-off phenomenon by improving the internal electrode shape, and a production method thereof.
A first aspect of the present invention is a ceramic electronic part comprising a ceramic sintered compact and a plurality of internal electrodes in the ceramic sintered compact, at least one lateral edge of at least one of the internal electrodes having a wedge-like cross-sectional shape, the length L of the wedge in the thickness t of the internal electrode at the base of the wedge satisfying the relationship L>2t.
Since the lateral edge of the internal electrode is formed to have a wedge-like cross-sectional shape, with the length L of the wedge and the thickness of the internal electrode at the base of the wedge satisfying the relationship L>2t, delamination or the inter-layer peel-off can be effectively restrained in the ceramic sintered compact. In particular, even in the case the thickness of the internal electrodes is increased to 3 &mgr;m or more, since the lateral edge has the above-mentioned wedge-like shape, generation of delamination can be effectively restrained. Therefore, a ceramic electronic part with an excellent reliability can be provided as the production yield can be improved.
In a second aspect of the present invention, the internal electrodes and the ceramic sintered compact are selected such that the contraction ratio of the ceramic material forming the sintered compact by baking is larger than the contraction ratio of the material forming the internal electrodes. Since the materials are selected such that the contraction ratio of the ceramics by baking is larger than the contraction ratio of the internal electrodes, the lateral edges of the internal electrodes can securely have the above-mentioned wedge-like cross-sectional shape after baking.
In a third aspect of the present invention, the lateral edges of the internal electrodes are formed to have a wedge-like cross-sectional shape, with the length L of the wedge and the thickness of the internal electrode t at the base part of the wedge satisfies L>2t. Since the lateral edges of the internal electrodes are formed to have a wedge-like cross-sectional shape, and to satisfy the relationship L>2t, delamination can securely be prevented also at the side face of the ceramic sintered compact.
In a fourth aspect of the present invention, the ceramic sintered compact is made from dielectric ceramics, and the plurality of the internal electrodes are laminated via a ceramic sintered compact layer in the thickness direction of the ceramic sintered compact so as to provide a laminated capacitor. Since the ceramic sintered compact is made from dielectric ceramics, and the plurality of the internal electrodes are laminated via a ceramic sintered compact layer, a laminated capacitor with an excellent reliability without the risk of generating delamination in the ceramic sintered compact according to the present invention can be provided with a high yield.
In a fifth aspect of the present invention, the thickness of the internal electrodes is in the range of 3 to 20 &mgr;m. With a thickness of 3 &mgr;m or greater, the internal electrodes themselves and the connection between the internal electrodes and the external electrodes can be more reliable, and the current capacity can be larger compared with the case of less than 3 &mgr;m. As to the upper limit of the internal electrode thickness, 20 &mgr;m or less is preferable as mentioned above in view of having a small size.
According to the fifth aspect of a ceramic electronic part of the present invention, since the thickness of the internal electrodes is 3 &mgr;m or greater, a laminated electronic part having a high reliability in the internal electrodes themselves and the connection between the internal electrodes and the external electrodes and a large current capacity can be obtained.
A sixth aspect of the present invention is a production method of a ceramic electronic part with a plurality of internal electrodes arranged in a ceramic sintered compact, comprising laminating a pl

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