Metal working – Electric condenser making – Solid dielectric type
Reexamination Certificate
2000-02-03
2001-11-27
Hall, Carl E. (Department: 3729)
Metal working
Electric condenser making
Solid dielectric type
C360S327300, C360S327300, C360S327300
Reexamination Certificate
active
06321429
ABSTRACT:
The invention relates to a method of manufacturing an enveloped multilayer capacitor, in which method a support of an electrically insulating material is alternately provided with dielectric layers and electrode layers, after which successive electrode layers are alternately connected with a first and a second end contact, and an electrically insulating envelope is provided.
The invention particularly relates to the manufacture of multilayer capacitors of small dimensions which can suitably be mechanically mounted on a substrate provided with a conductor pattern (printed wiring, printed circuit board, PCB), thereby forming an electric or electronic circuit, and the invention also particularly relates to such capacitors (surface-mountable capacitor, SMC). These capacitors do not comprise leads. Instead they are provided with electric end contacts in the form of a solderable metal layer. The end contacts of the capacitors can be used to secure said capacitors in the printed circuit board in a simple manner by means of soldering. By virtue of the small dimensions of such capacitors and the absence of leads, a high packing density of the capacitors and other components of similar dimensions on the printed wiring board can be achieved.
Methods of manufacturing multilayer capacitors, in particular ceramic multilayer capacitors, are generally known. The ongoing miniaturization requires ever smaller dimensions of multilayer capacitors in an electric or electronic circuit. In the case of multilayer capacitors for mounting in a printed circuit board, these dimensions are of the order of 1×0.5×0.5 mm. When such small multilayer capacitors are provided by mechanical means a high dimensional accuracy is very important. The dimensional accuracy of multilayer capacitors manufactured by means of the known method is often insufficient.
It is an object of the invention to provide a method by means of which electrically insulated multilayer capacitors having a high dimensional accuracy can be manufactured.
In accordance with the invention, this object is achieved, in a manner which is satisfactory in view of the current practice, by a method which is characterized in that
a. a flat supporting plate of an electrically insulating material is provided with through-holes (channels),
b. dielectric layers and electrode layers are provided in the holes (channels) and on both surfaces of the flat supporting plate, said electrode layers being provided from sources situated on either side of the supporting plate, in such a manner that they are alternately provided from one side and from the other side, and the intermediate dielectric layers being provided from sources which are arranged on either side of the supporting plate and which are activated simultaneously,
c. after a sufficient number of layers has been provided for the intended purpose, the supporting plate is covered on both sides with a cover plate of an electrically insulating material which is hermetically secured to the supporting plate of an electrically insulating material,
d. the assembly is subdivided into blocks which each comprise a multilayer capacitor enveloped by an electrically insulating material, with partition planes extending through the electrode layers situated on both surfaces of the supporting plate,
e. and, subsequently, end contacts are provided on two opposing ends of the blocks by providing said ends with solderable metal layers which metal layers sufficiently embrace the ends of the blocks to bring about electric contact with the electrode layers projecting between the portions of the envelope.
An enveloped multilayer capacitor in accordance with the invention is characterized in that said capacitor is built up of alternately provided electrode layers and dielectric layers which are situated on the walls of a through-hole (channel) in a support of an electrically insulating material, which capacitor is encapsulated in a hermetic envelope of glass and/or ceramic material which is composed of several portions, and opposing ends of the envelope are provided with end contacts in the form of solderable metal layers which partly embrace the sides of the envelope and which electrically contact the capacitor encapsulated in the envelope via electrode layers projecting between the portions of the envelope.
Multilayer capacitors thus manufactured exhibit a very high dimensional accuracy which can be achieved even at small dimensions of the order of 1 mm by 0.5 mm by 0.5 mm.
In the method in accordance with the invention, a supporting plate is provided with through-holes in the form of channels which generally extend substantially at right angles to both surfaces of the supporting plate. By means of a suitable process, for example sputtering or physical or chemical vapor deposition, metal films serving as electrode layers and dielectric layers are alternately provided. By arranging the sources of the materials necessary for said process on either side of the supporting plate, the supporting plate can be used as a mask during the application of the layers.
The application of the various layers is essentially carried out as follows. An application source which is arranged on one side of the supporting plate is used to apply an electrode layer to the surface of the supporting plate facing the source and to the wall of the channels in the supporting plate. Subsequently, application sources situated on either side of the supporting plate are used to apply a layer of a dielectric material to both surfaces of the supporting plate and to the wall of the channels. Next, an application source situated on the other side of the supporting plate is used to apply an electrode layer to the surface of the supporting plate facing the application source and to the wall of the channels. Subsequently, in the manner described above, a further layer of a dielectric material is provided, etc. These steps are repeated until the number of applied electrode layers and dielectric layers is sufficient to obtain the intended capacitance of the capacitor. The number of layers is governed by the materials used and the thickness of the layers. The number of layers necessary to attain an intended capacitance can be experimentally established.
The supporting plate may be composed, for example, of a thin plate of an electrically insulating material having a thickness which is preferably in the range between 0.4 and 0.8 mm, for example 0.6 mm. A material which can very suitably be used for this purpose is glass, in particular glass which can be structured photolithographically, such as glass which is marketed by SCHOTT, Mainz, Germany under the trade name FOTURAN. It is alternatively possible to use plates of ceramic materials such as aluminium oxide and zirconium oxide. Through-holes or channels can be formed in the supporting plate by means of known techniques, such as drilling, chemical etching, powder blasting, laser etching and the like.
Properly electroconductive metals, which can be applied from the vapor phase, can be used as the material for the electrode layers. Preferably, metals are used of which an oxide is not electroconductive, such as in particular aluminium (Al
2
O
3
) and tantalum (Ta
2
O
5
). The metals can be provided by sputtering in a vacuum or by physical vapor deposition.
The dielectric material may consist of an electrically non-conductive oxide of the metal used for the electrode layers, if such oxide exists. A very suitable combination consists, for example, of aluminium and aluminium oxide and of tantalum and tantalum oxide. When the oxides of these metals are applied, use can suitably be made of the application sources for these metals while admitting oxygen to the vacuum chamber in which the application process is carried out. The thickness of the individual layers may range, for example, between 0.01 and 1 micron. Other suitable oxidic materials are, for example, silicon dioxide and silicon nitride. If the dielectric material is not the oxide of the metal used for the electrode layers, then it must be applied by means of
Hall Carl E.
Spain Norman N.
U.S. Philips Corporation
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