Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2003-03-04
2004-08-24
Lam, Cathy F (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C361S321100, C361S321200, C361S307000
Reexamination Certificate
active
06780494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic electronic device and a method of production of the same.
2. Description of the Related Art
As one method for producing a capacitor, piezoelectric device, or other ceramic electronic device, there is known the method of forming a ceramic coating in a sheet on a substrate by the doctor blade method to obtain a green sheet and forming electrode paste on top of this by screen printing. In this case, the ceramic coating includes ceramic powder, an organic binder, a plasticizer, a solvent, etc., while the electrode paste includes palladium, silver, nickel, or other conductive particles.
When desiring to obtain a multilayer structure, green sheets formed with the electrode paste layers are stacked to the desired multilayer structure and then cut by a press to obtain ceramic green chips. The thus obtained ceramic green chips are processed to remove the binder, then fired at 1000° C. to 1400° C. Silver, silver-palladium, nickel, copper, or other terminal electrodes are then formed on the obtained fired bodies to obtain the ceramic electronic devices.
In the above method of production, when producing for example a multilayer ceramic capacitor, to reduce the size and increase the capacity, the technique is adopted of reducing the thickness of each ceramic coating layer and increasing the number of layers. For example, multilayer ceramic capacitors are being developed having over 800 ceramic coating layers with thicknesses of about 3 &mgr;m.
In producing a ceramic electronic device such as a multilayer ceramic capacitor, however, when forming an internal electrode, the general practice in the past has been to coat a ceramic coating on the surface of a tape-like substrate having flexibility to form the ceramic coating layer, then print an internal electrode paste. The substrate has been made of polyethylene terephthalate (PET) film etc.
The ceramic coating used is obtained by mixing an acrylic resin or butyral resin or other organic binder, an organic solvent, a plasticizer, and a ceramic powder.
The internal electrode paste is prepared using a resin serving as an organic binder dissolved in an organic solvent as a vehicle, dispersing in the vehicle an Ag, Pd, Ni, Cu, or other conductive metal powder, and, in some cases, adding a diluent for adjusting the viscosity.
As the organic solvent in the vehicle, terpineol, methyl ethyl ketone, etc. is used. As the binder, ethyl cellulose, nitrocellulose, or another cellulose-based resin or butyl methacrylatet methyl methacrylate, or another acrylic-based resin is used. Further, as the diluent, an aromatic hydrocarbon, a fatty acid hydrocarbon, etc. is used.
When printing an internal electrode paste of such a composition on a ceramic coating layer coated on a substrate in accordance with the conventional method of production, however, the terpineol, methyl ethyl ketone, or other organic solvent contained in the internal electrode paste ends up dissolving the acrylic resin, butyral resin, or other organic binder contained in the ceramic coating layer. This phenomenon is called “sheet attack”.
If sheet attack occurs, it becomes difficult to peel off the ceramic coating layer from the substrate. Further, sometimes holes or wrinkles occur in the ceramic coating layer. If using such a ceramic coating layer to produce a multilayer ceramic capacitor, short-circuit defects where internal electrodes become connected will arise, withstand voltage defects will arise, the targeted electrostatic capacity will no longer be able to be obtained, or other critical defects are liable to occur.
As a means to avoid this problem, there is the method of printing an internal electrode directly on the substrate, coating a ceramic paste over this to form a ceramic coating layer, then peeling off the ceramic coating layer together with the internal electrode from the surface of the substrate (for example, see Japanese Patent No. 2136761).
With this method, however, the adhesion of the internal electrode and ceramic coating layer with respect to the substrate becomes stronger, so it becomes extremely difficult to peel off the ceramic coating layer without damage (holes, wrinkles, tears, etc.)
It may also be considered to coat the surface of a substrate with an agent for facilitating peeling (hereinafter called a “peeling agent”) in advance and form the internal electrode and ceramic coating layer on the surface of the peeling agent. In this case, the difficulty of peeling can probably be avoided.
When printing an internal electrode on the surface of a peeling agent, however, since the affinity between the two is low, the internal electrode is subjected to an agglomerating action due to the surface tension, the shape of the pattern of internal electrode ends up being ruined, and the desired characteristics can no longer be obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a multilayer ceramic capacitor or other ceramic electronic device able to prevent sheet attack and resistant to short-circuit defects, withstand voltage defects, and other structural defects.
Another object of the present invention is to provide a method of production of a high precision, high reliability ceramic electronic device able to remarkably reduce the difficulty in peeling and probability of occurrence of defects in characteristics of the product even if reducing the thickness of the ceramic coating layers.
Still another object of the present invention is to provide a method of production of a ceramic electronic device remarkably reducing step differences between layers due to the electrodes and improving the reliability.
Method of Production and Electronic Device According to First Aspect of Invention
To achieve the above objects, a method of production of a ceramic electronic device of a first aspect of the invention comprises the steps of forming a first ceramic coating layer on the surface of a substrate, forming an internal electrode on the surface of the first ceramic coating layer, and forming a second ceramic coating layer on the surface of the first ceramic coating layer so as to cover the internal electrode, wherein, when a mean particle size of ceramic particles of the first ceramic coating layer is &agr;1, a thickness of the first ceramic coating layer is T1, a mean particle size of ceramic particles of the second ceramic layer is &agr;2, and a thickness of the second ceramic layer is T2, the conditions of &agr;1≦&agr;2, 0.05<&agr;1≦0.35 &mgr;m, T1<T2, and 0<T1<1.5 &mgr;m are satisfied.
Preferably, a stack of the first ceramic coating layer, the internal electrode, and the second ceramic coating, layer is peeled from the substrate.
Preferably, a plurality of stacks peeled from the substrate are successively stacked with the first ceramic coating layers and the second ceramic coating layers in contact.
By satisfying &agr;1≦&agr;2, it is possible to form a dense, high packing density first ceramic coating layer. Therefore, it is possible to avoid to a great extent pinholes in the ceramic layer, withstand voltage defects, and other structural defects of the electronic device.
Further, by satisfying 0.05 &mgr;m<&agr;1≦0.35 &mgr;m, it is possible to reduce sheet attack in the production process and reduce the short-circuit defect rate and withstand voltage defect rate. Note that if viewed just from the standpoint of forming a dense, high packing density first ceramic coating layer, a smaller mean particle size &agr;1 is better, but if the mean particle size &agr;1 becomes smaller than 0.05 &mgr;m, there is a tendency for the dispersibility in the ceramic coating at the time of preparing the ceramic coating to deteriorate and for formation of a uniform ceramic coating layer to become impossible.
Further, by satisfying T1<T2, an increase in thickness due to the thickness T1 of the first ceramic coating layer can be avoided and an increase in thickness of the capacity layer, that is, the ceramic layer (T1+T2), in for example a mul
Ishida Hitoshi
Izumibe Yasushi
Kobayashi Ryou
Saitoh Akira
Ueda Kaname
Lam Cathy F
TDK Corporation
LandOfFree
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