Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2002-10-02
2004-11-02
Thomas, Eric (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C029S025030, C361S535000
Reexamination Certificate
active
06813140
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the field of solid state capacitors. The invention particularly relates to capacitors of the type in which a powder-formed valve action metal forms a highly porous anode body portion of a capacitor, an electrically insulating dielectric layer is formed through the porous structure of the anode body, and a conducting cathode layer is formed on the dielectric layer which layer is then electrically connected to a cathode terminal, the anode body being electrically connected to an anode terminal.
U.S. Pat. No. 5,357,399 (Salisbury) describes a method for simultaneously manufacturing multiple such capacitors from a porous tantalum layer sintered to a tantalum substrate. The layer is machined to form anode body portions of each capacitor. After processing a top plate (substrate lid) is bonded to the processed anode body top ends. The plate forms a lid which, after machining of the substrate/anode body/plate sandwich, becomes the cathode terminal of each capacitor. United Kingdom patent application no. 9824442.9 concerns a modified version of the Salisbury method in which the volumetric efficiency of the capacitors produced is optimized by removing the need for a substrate lid as the cathode terminal of each capacitor, thereby increasing the specific capacitive volume.
The foregoing methods permit the manufacture of very small but highly efficient capacitors. However the continued pressure of electronic circuit board design towards miniaturization of components and ease of assembly of such boards maintains a continued need for capacitors of improved volumetric efficiency and reduced component windows (or footprint) on the circuit board. There is a particular requirement for a method of producing capacitors which have a low profile on a circuit board, in some cases having a thickness of less than 1 mm.
SUMMARY OF THE INVENTION
The present invention seeks to provide improved capacitors and improved methods of manufacturing such capacitors.
According to one aspect of the present invention there is provided a method of manufacturing solid state capacitors comprising: providing an electrically conducting substrate; forming a plurality of porous bodies comprising valve action material on a surface of the substrate, the bodies each having an upper surface distal to the substrate; forming an electrically insulating layer over the bodies; forming a conducting cathode layer over the insulating layer applied to the bodies; and dividing the substrate into capacitor portions, each portion comprising a body and a portion of substrate, characterized in that an end region of each body portion distal from the substrate is provided with a platform which is locally raised with respect to the rest of the end region, the platform providing a cathode terminal site in the final capacitor, and the substrate portion providing an anode site.
The platform may consist of or be comprised of the porous valve action material from which the bodies are made. In this case the platform may be formed by green or post-sintered forming of the bodies integrally with the platform. Preferably the platform is formed by green molding of the bodies.
Alternatively the platform may be formed by machining of the sintered bodies. In yet another method the platform is formed by green forming of the platform onto pre-formed bodies.
In another aspect of the invention the platform comprises a solid conducting material. In this case the platform may be applied as a planar frame or lattice applied to upper end regions of the bodies, which frame or lattice is subsequently formed into individual platforms for each body.
In yet another aspect, the platform is formed from a conductive material applied as a coating or paste which solidifies to form the platform.
The method of the present invention will almost always further comprise encapsulating each capacitor body portion with a protective insulating material, leaving exposed an outer surface portion of the substrate and an outer surface portion of the platform.
It may be desired to form a capacitor with anode and cathode poles on a common face or side of the capacitor. Hence in yet another aspect of the invention a conducting bridge is applied to each capacitor, extending the anode terminal site over at least a portion of the encapsulation layer. Preferably the portion of the encapsulation layer to which is applied the conducting bridge includes a region adjacent the cathode site platform, whereby electrical anodic and cathodic terminal contact with the capacitors may be made on a common side of each capacitor at terminals corresponding to the platform and the encapsulated region adjacent the platform. The conducting bridge maybe formed by a conducting end cap applied to a sidewall of the capacitor portion, which end cap overlaps the substrate end of the capacitor and encapsulated portion of the platform end of the capacitor. In a preferred arrangement the conducting bridge comprises two end caps applied to opposite sidewalls, thereby to form two anode terminal contacts, one at side of the capacitor and overlapping the platform end of the capacitor.
Typically, the platforms take the form of rectilinear, circular or oval taps or steps. Usefully, the platform is generally centrally located on a substrate-distal end of each body. In one embodiment the platform is located at one side region of the substrate-distal end of each body.
In another aspect of the invention, two or more locally raised platforms are formed on the distal end of each anode body, thereby to form two or more cathode terminal sites on each body.
Generally, the bodies are arranged on the substrate in an array of rows and columns, and the dividing comprises cutting along the rows and columns as is conventional in the art.
The final processing step is usually a termination process. This applies solder-compatible coatings onto the cathode terminal sites on each platform and the cathode terminal sites. The termination process may comprise liquid coating of each terminal contact surface with conducting paste, and allowing the coating to solidify. In addition, or in the alternative, the termination treatment comprises metal plating to form a layer of metal or metals on the respective terminal sites.
The present invention also seeks to provide structurally novel and inventive capacitors, which may be manufactured according to the method of the present invention.
Hence according to a further aspect of the invention there is provided a solid state capacitor comprising: an electrically conducting substrate member; a porous body comprising valve action metal provided on a surface of the substrate; an electrically insulating layer formed over the free surface of the cathode and anode; a conducting cathode layer formed over the electrically insulating layer on the anode body and the cathode body; wherein the body has an upper surface distal to the substrate, which surface is formed with a locally raised platform with respect to the adjacent upper surface of the body, the locally raised portion providing a cathode terminal site and the substrate providing an anode terminal site.
Preferably the body is encapsulated by a sleeve of a protective insulating material, leaving exposed an outer surface portion of the substrate as the anode site and an outer surface portion of the platform as the cathode site.
A conducting bridge may extend between the anode site to an encapsulated surface portion of body, thereby to form an anode terminal extension contact on the encapsulated body portion. Preferably, the encapsulated surface portion at which the anode terminal contact is formed is located adjacent the cathode site corresponding to the platform, whereby both anode and cathode terminal contacts to a printed circuit board may be made on a common side of the capacitor.
The conducting bridge may comprise one or more conducting end caps applied to one side of each capacitor. The caps may be applied as a liquid conductive paste coating, by for example dipping.
The raised platform portion ma
AVX Limited
Dority & Manning P.A.
Thomas Eric
LandOfFree
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