Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1998-08-28
2001-02-20
Kincaid, Kristine (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S508000, C607S005000
Reexamination Certificate
active
06191931
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electronic components for implantable medical devices, and more particularly to charge storage components for cardiac stimulation devices.
BACKGROUND OF THE INVENTION
Defibrillators are implanted in patients susceptible to cardiac arrhythmias or fibrillation. Such devices provide cardioversion or defibrillation by delivering a high voltage shock to the patient's heart, typically about 500-750V. High voltage capacitors are used in defibrillators to accumulate the high voltage charge following detection of a tachyarrhythmia. In the effort to make implantable devices as small and thin as possible, flat aluminum electrolytic capacitors are used.
Such a flat capacitor is disclosed in U.S. Pat. No. 5,131,388 to Pless et al., which is incorporated herein by reference. Flat capacitors include a plurality of aluminum layers laminarly arranged in a stack. Each layer includes an anode and a cathode, with the anodes and cathodes being commonly connected to respective connectors. The layers may be cut in nearly any shape, to fit within a similarly shaped aluminum housing designed for a particular application. Normally, the cathode layers are together connected to the housing, while the anodes are together connected to a feed-through post that tightly passes through a hole on the housing, but which is electrically insulated from the housing. The feed-through post serves as an external connector for interfacing with other components.
Existing capacitors, such as illustrated in
FIG. 1
, and disclosed in U.S. patent application Ser. No. 08/876,274, filed Jun. 16, 1997, entitled “Aluminum Electrolytic Capacitor for Implantable Medical Device,” now U.S. Pat. No. 5,926,357, which is hereby incorporated by reference, have addressed a trade off in the selection of feed-through
10
materials by using a readily solderable beryllium-copper post
12
passing through an insulated sleeve
14
in the housing
16
, and covered within the housing by an aluminum cap
20
to which anode tabs
22
may readily be bonded or welded. A nut
24
is secured externally over the threaded copper post, to draw the cap to compress against an elastomeric gasket
26
. This provides an environmental seal that contains electrolyte fluid within the housing, and which prevents the corrosive electrolyte from contacting and attacking the copper post.
While effective, the advantages of such existing capacitor feed-throughs are achieved at a relatively high manufacturing cost, due to their complexity. In addition, part tolerances must be tight, to avoid a condition in which an overly long sleeve engages the post head before the gasket has been adequately compressed. Further, imprecise manufacturing of the cap/post assembly can generate cracks in the cap that may admit corrosive electrolytic fluid to damage the copper post. Also, existing feed-throughs require a foil strip
30
attached to the anode tabs for connection to the feed-through cap, a difficult and time consuming process requiring skillful and precise alignment of the components to be welded. In addition, when more than one capacitor is used in a single device, external jumpers are needed to connect the capacitors together, typically in series. Such jumpers add to the number of parts and to the complexity of manufacturing.
In the prior art device shown in
FIG. 1
, the nut and adjacent case are sealed with an insulating resin (not shown) to cover the nut
24
and nearby portions of the housing. This normally prevents any arcing between the cathode-connected case and anode connected-nut, which are separated by only a very small gap
32
established by the thickness and radius of the sleeve flange, typically about 0.005-0.010 inch. While arcing is prevented by proper insulation, a minor failure of the insulative coating may generate a serious device failure. Although coating flaws may be detected by careful inspection, a more cost effective method of is desirable. Increasing the sleeve flange thickness would increase the gap, but at a cost of device size, as the post would need to be correspondingly lengthened to provide an adequate free portion for soldering.
SUMMARY OF THE INVENTION
The disclosed embodiment overcomes the limitations of the prior art by providing an electrolytic capacitor with an electrically conductive housing defining a chamber and defining a feed-through aperture providing communication between the interior and exterior of the housing. A number of conductive layers are positioned within the chamber. A feed-through conductor has a first end connected to the layers, an intermediate portion passing through the feed-through aperture, and an elongated external portion extending externally from the housing and terminating at a free end. An insulative sleeve has a first portion closely received within the feed-through aperture and closely receiving the intermediate portion of the feed-through member and has a second elongated portion extending externally from the housing and closely receiving at least a portion of the external portion of the conductor element, so that only a remaining portion of the conductor element is exposed, and is spaced apart from the housing by the length of the second elongated portion. A rigid outer sleeve may be used to fit over the insulative sleeve where it exits the housing to provide strain relief for the insulative sleeve and help maintain seal integrity of the feed-through.
REFERENCES:
patent: 5131388 (1992-07-01), Pless et al.
patent: 5370663 (1994-12-01), Lin
patent: 5522851 (1996-06-01), Fayram
patent: 5749911 (1998-05-01), Westlund
patent: 5903109 (1999-07-01), Fishler
Beauvais Joe
Mar Craig
Paspa Paul
Wong Kenneth
Dinkins Anthony
Kincaid Kristine
Mitchell Steven M.
Pacesetter Inc.
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