Metal working – Electric condenser making – Solid dielectric type
Reexamination Certificate
2000-06-20
2003-04-22
Walczak, David J. (Department: 3751)
Metal working
Electric condenser making
Solid dielectric type
C029S025410, C029S830000, C029S831000, C156S089120
Reexamination Certificate
active
06550117
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a structure of multilayer electronic elements for use widely in electric products and a manufacturing method therefor, and more particular to a multilayer ceramic chip capacitor and a manufacturing method therefor.
A multilayer ceramic chip capacitor is usually manufactured by the following process.
Initially, a coating material is prepared in which dielectric particles and a binder are dispersed in a solvent. The surface of a support member, made of polyethylene terephthalate or the like, is coated with the coating material so that a green dielectric layer is formed. Then, a conductor pattern (a green internal electrode portion) for the internal electrode is formed on the green dielectric layer. The green internal electrode portion is usually formed by, for example, screen-printing conductor paste. Then, the support member is separated from the green dielectric layer which has the green internal electrode portion. While the positions of the green internal electrode portions are being aligned, a plurality of the green dielectric layers are laminated. Thus, a green laminate is formed.
The obtained green laminate is applied with pressure and compressed, and then cut into a predetermined size. Thus, green chips (divided green laminates) are manufactured. Then, the green chips are burned at predetermined temperatures in a predetermined atmosphere so that sintered bodies are obtained. Then, paste for forming external electrodes is applied to ends of the sintered body so that a multilayer ceramic chip capacitor is manufactured.
FIG. 4A
is a schematic view showing the internal structure of the green laminate realized during the process for manufacturing the multilayer ceramic chip capacitor. As shown in
FIG. 4A
, the multilayer ceramic chip capacitor is constituted by laminating and burning dielectric layers
62
each having a conductor pattern
61
for the internal electrode.
As shown in
FIG. 5
, the multilayer ceramic chip capacitor is constituted by alternately laminating internal electrodes
61
connected to external electrodes
63
disposed opposite to each other. The green internal electrode portions
61
are laminated on the green dielectric layer as follows: In
FIG. 4C
which is a cross sectional view taken along a first cutting direction x-x′ shown in
FIG. 4A
, the green internal electrode portions
61
are aligned through green dielectric layers
62
. In
FIG. 4B
which is a cross sectional view taken along a second cutting direction y-y′, the green internal electrode portions
61
are alternately laminated. The green dielectric layers
62
are cut along cutting lines
64
so that green chips are obtained.
The foregoing structure is formed such that the green internal electrode portions
61
are formed and laminated on the green dielectric layers
62
. As shown in
FIGS. 4B and 4C
, spaces
65
are formed among adjacent green internal electrode portions in the green internal electrode layers. That is, first portions
66
in which the green internal electrode layers and green dielectric layers are alternately laminated and second portions
67
coexist in the green laminate, the second portions
67
being laminated through spaces interposed between upper and lower green dielectric layers. When multilayer ceramic chip capacitors are manufactured by burning the green laminate, the burning process is performed in a state in which the spaces
65
adjacent to the external electrodes are compressed, as shown in FIG.
5
. Therefore, the internal electrodes are not flush with one another. That is, the ends of the internal electrodes are warped, causing the thicknesses to be made different among the ends and the central portion.
The degree of compression of the spaces
65
shown in
FIGS. 4B and 4C
is raised in proportion to the number of laminated layers. Therefore, stepped portions between the first portions
66
and the second portions
67
are enlarged excessively. Thus, the first portions
66
in the form of a laminate which is constituted by dint of hermetic contact between the green internal electrode layers and the green dielectric layers are greatly raised. Since the first portions
66
are pressed and compressed under high pressures as compared with those applied to the second portions
67
, the densities of the first portions
66
and those of the second portions
67
are made to be different from one another. As a result, chip capacitors, which are final products, are deformed, cracks are formed and delamination takes place.
If the thickness of the green dielectric layer is reduced to achieve size reduction and enlargement of the capacity of the capacitor which have been required in recent years, the green dielectric layer can easily be cut in the stepped portion. Therefore, there arises a problem of, for example, short circuit occurring between the internal electrodes.
To overcome the problem caused from the rise of the green internal electrode portion, a variety of suggestions have been made.
In Unexamined Japanese Patent Publications 52-135050 and 52-133553, structures have been suggested in each of which a green dielectric space sheet having a gap corresponding to the green internal electrode portion is interposed in the green laminate so as to prevent a stepped portion.
The dielectric green space sheet must have the same thickness as that of the green internal electrode portion. If the thickness of the green internal electrode portion is 10 &mgr;m or smaller, the green dielectric space sheet cannot accurately be punched to have the same shape as that of the pattern of the internal electrode so as to be inserted as described above. What is worse, processes for laminating some hundreds of layers must be performed such that insertion of the dielectric space sheet is performed for each layer. Therefore, mass production cannot easilybe performed.
A similar method has been disclosed in Unexamined Japanese Patent Publication 53-42353, in which recesses are formed in the portions of the green dielectric layers corresponding to the internal electrodes. Thus, the green internal electrode portions are embedded in the recesses to eliminate the spaces in the green laminate so as to flatten the structure. Another method has been disclosed in Unexamined Japanese Patent Publication 61-102719 in which the green internal electrode portions and the green dielectric sheets are punched to have predetermined shapes to alternately be laminated so as to eliminate the spaces in the laminate. Thus, the structure can be flattened. Each of the above-mentioned suggestions, however, requires a very thin green dielectric sheet to be handled. Therefore, mass production cannot easily be performed.
In Unexamined Japanese Patent Publication 52-135051, a method has been suggested in which a coating process for forming the green internal electrode portions is performed. Then, the space portions are coated with the green dielectric layers to flatten the surfaces of coating so as to laminate the layers. However, seepage of the pattern and erosion by dint of the solvent easily take place vertically or between the adjacent green internal electrode portions and the green dielectric layers. If the thickness of the green dielectric layer interposed between the green internal electrode portions formed vertically is reduced, the boundaries between the green internal electrode portions and the green dielectric layers are obscured by dint of the seepage of the pattern and erosion of the solvent. In this case, there is apprehension that a problem of short circuit between the internal electrodes arises.
Although the techniques of flattening the internal portion of the laminate to eliminate the spaces have been suggested, the foregoing structures have not been put into practical use because the thin green dielectric sheet cannot easily be handled.
In Japanese Patent Publication No. 2636306 and Japanese Patent Publication No. 2636307, techniques have been suggested in which the green internal electrode portions are first formed on the suppo
Nomura Takeshi
Tokuoka Yasumichi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
Walczak David J.
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