Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
2002-08-23
2004-03-09
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321400, C156S089120
Reexamination Certificate
active
06704191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for manufacturing multilayer ceramic capacitors and other multilayer ceramic electronic components and to multilayer ceramic electronic components manufactured by these methods. More specifically, it relates to improvements for increasing the numbers of layers of ceramic layers and internal electrodes and for thinning these layers.
2. Description of the Related Art
Typical examples of multilayer ceramic electronic components in which the present invention is interested are multilayer ceramic capacitors.
With increasing demands on downsizing, increasing electrostatic capacity and reducing cost in multilayer ceramic capacitors, constitutive ceramic layers composed of a dielectric material have been thinned to a thickness of about 3 &mgr;m. In addition, Cu, Ni and other base metals are used as conductive materials for internal conductor films, i.e., internal electrodes. Recently, multilayer ceramic capacitors each comprising further thinned ceramic layers about 1 &mgr;m thick have been developed.
To increase the electrostatic capacity, the number of layers of internal electrodes for yielding electrostatic capacity has been increased. In an laminated body comprising ceramic layers laminated with the interposition of internal electrodes, portions carrying the internal electrodes have a thickness larger than that of portions carrying no internal electrodes. When the number of layers of the internal electrodes is increased as mentioned above, the portions carrying the internal electrodes have a thickness markedly larger than that of portions carrying no internal electrodes to thereby cause distortion of the resulting laminated body. To avoid this problem, individual internal electrodes must be further thinned.
Such internal electrodes are conventionally formed by subjecting a conductive paste comprising a dispersed metal powder to screen printing to thereby form a pattern of the conductive paste on ceramic green sheets to be the ceramic layers. If thin internal electrodes are formed by screen printing in this manner, electrode breaks frequently occur during co-firing with the ceramic, and the electrostatic capacity of the resulting multilayer ceramic capacitor is less than the designed level. The thickness of the internal electrodes cannot therefore sufficiently be reduced as long as they are formed by screen printing using a conductive paste.
Conductive pastes for use in screen printing are mixtures of a metal powder, a resin (a binder) and a solvent. Accordingly, the physical thickness of the screen-printed internal electrodes is about two to three times as large as that of the constitutive metal component. This also prevents mitigation of the distortion of the laminated body induced by the thickness of the internal electrodes.
As a possible solution to these problems, a metal film formed by a thin film forming method is used as the internal electrodes. When the metal film is used as the internal electrodes, its physical thickness becomes nearly equal to that of the metal powder, and the distortion of the laminated body induced by thickness of the internal electrodes can significantly be mitigated. In the aforementioned internal electrodes formed by screen printing using a conductive paste, the metal powder in the conductive paste may not be dispersed satisfactorily in the resulting internal electrode. In contrast, the internal electrodes comprising the metal film formed by the thin film forming method are free of this problem. Accordingly, this technique is effective to thin the internal electrodes also from this point of view.
The metal film formed by the thin film forming method is nearly free of pinholes and other defects even when its thickness is, for example, less than or equal to 1 &mgr;m.
When a green laminated body comprising a plurality of ceramic green sheets and metal film laminated in alternate order is subjected to removal of a binder contained in the ceramic green sheet, i.e., to debinder (binder burnout), a gas is formed as a result of decomposition of the binder. The metal film is free of pinholes as described above and therefore prevents diffusion of the gas specifically in the lamination direction, thus preventing a sufficient debinder effect. In addition, the resulting multilayer ceramic capacitor tends to invite structural defects such as delamination at the interface between the metal film or the resulting internal electrodes and the ceramic green sheet or the resulting ceramic layers.
A possible solution to these problems is to reduce the amount of the binder (resin) in the ceramic green sheet. However, if the amount of the binder is reduced, the metal film internal electrode does not come into intimate contact with the ceramic green sheet properly when the metal film is brought into contact with the ceramic green sheet. Therefore, the amount of the binder in the ceramic green sheet must be increased in this technique as compared with the process in which the internal electrodes are prepared by screen printing using a conductive paste.
If the ceramic green sheet comprises an increased amount of the binder, the amount of the gas which is formed during the debinder process step as a result of decomposition of the binder increases. The gas formed in an increased amount should be diffused, but the metal film internal electrode prevents diffusion of the gas as described above, and the increased gas further frequently invites structural defects such as delamination at the interfaces between the internal electrodes and the ceramic layers.
In the debinder process step, the gas formed as a result of decomposition of the binder is generally emitted from pores formed as a result of burning of the binder in the ceramic green sheet, and the green laminated body itself shrinks during this process. Adhesion between the internal electrodes and the ceramic layers at the interfaces decreases as the decomposition of the binder proceed. The shrinkage of the green laminated body and the decreased adhesion may also cause structural defects such as delamination at the interfaces between the internal electrodes and the ceramic layers.
These structural defects occur more markedly with a decreasing thickness of the ceramic layer and with a decreasing grain size of the ceramic material powder in the ceramic green sheet. If the ceramic layer has a large thickness of, for example, more than 1.5 &mgr;m, a ceramic material powder having a large grain size adapted to the thickness of the ceramic layer can be used. The amount of the binder essential for the ceramic green sheet can therefore be decreased to thereby decrease the amount of the gas formed as a result of decomposition of the binder. In addition, the green laminated body less shrinks during the debinder process step. Accordingly, structural defects caused by these factors, such as delamination at the interfaces between the internal electrodes and the ceramic layers, can be minimized.
Similar problems also occur in multilayer ceramic electronic components other than the multilayer ceramic capacitors.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for manufacturing a multilayer ceramic electronic component which can solve the above problems, as well as a multilayer ceramic electronic component manufactured by this method.
Specifically, the present invention provides, in a first aspect, a method for manufacturing a multilayer ceramic electronic component including the steps of preparing a ceramic green sheet including a ceramic material powder and a binder; preparing a metal film by a thin film forming method; forming a green laminated body by laminating a plurality of the ceramic green sheets and the metal films; removing the binder by subjecting the green laminated body to a heat treatment; and forming a sintered laminated body by firing the heat-treated green laminated body. To solve the above problems, the green laminated body is subjected to the heat treatment in a pressurized atmos
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Reichard Dean A.
Thomas Eric
LandOfFree
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