Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2000-11-03
2004-02-03
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S509000, C361S516000, C361S520000, C361S519000, C029S025030
Reexamination Certificate
active
06687118
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns implantable medical devices, such as defibrillators and cardioverters, particularly structures and methods for capacitors in such devices.
BACKGROUND
Since the early 1980s, thousands of patients prone to irregular and sometimes life-threatening heart rhythms have had miniature heart monitors, particularly defibrillators and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives.
The defibrillator or cardioverter includes a set of electrical leads, which extend from a sealed housing into the walls of a heart after implantation. Within the housing are a battery for supplying power, monitoring circuitry for detecting abnormal heart rhythms, and a capacitor for delivering bursts of electric current through the leads to the heart.
The capacitor can take the form of a flat aluminum electrolytic capacitor. Flat capacitors include a stack of flat capacitor elements, with each element including one or more separators between two sheets of aluminum foil. One of the aluminum foils serves as a cathode (negative) foil, and the other serves as an anode (positive) foil. Sometimes, two or more foils are stacked one on the other and connected to form a multi-anode stack. The capacitor elements each have an individual capacitance (or energy-storage capacity) proportional to the surface area of the aluminum foil. Sometimes, each anode foil is etched to increase its surface area and thus to increase the capacitance of its capacitor element.
The anode foils and the cathode foils of the capacitor elements are connected together to provide a total capacitance. A connection member such as an aluminum tab is laid across the surface of an anode or cathode foil and then joined to the foil by a method, such as cold welding or swaging, which results in one or more weld joints. After a connection member has been attached to each anode or cathode foil in the capacitor, the respective connection members are crimped or welded together and attached to feedthrough terminals for connection to circuitry outside the capacitor.
The inventors have identified many problems regarding present connection member-to-foil connections, connection member-to-connection member connections, and foil-to foil connections that increase the size of the capacitor and decrease its reliability.
For instance, one drawback to present connection member-to-foil joining techniques is that they limit the amount of etching that can be done to the anode foil. This is because etching the anode foil to increase its capacitive surface area makes the foil brittle and prone to cracking under the strain of present welding techniques. To make up for the lost etching, manufacturers need to use additional capacitor elements or larger foils, both of which increase capacitor size. Thus, present connection member-to-foil joining techniques result in larger than desirable capacitors.
Another drawback is that present connection member-to-foil joining techniques require a relatively large weld, and thus a relatively large aluminum connection member (which is governed by the size of the weld). Large connection members can be a problem since placing an aluminum connection member within each anode stack causes a bulge in the anode stack which increase the capacitor volume. Some manufacturers reduce the bulge by cutting a notch into one of the anodes of the stack so that the aluminum connection member fits within the notch and does not bulge the stack. Unfortunately, having a large connection member requires a large notch, which decreases the surface area of the anode and leads manufacturers to increase capacitor size to make up the loss.
One problem with present connection member-to-connection member connections is that they also undesirably increase capacitor size. Presently, each connection member must be long enough to be crimped to the other connection members, and the extra length or slack required to bring them all together increases capacitor size since the capacitor case must be made larger to accommodate the crimped connection members. Moreover, crimping the connection members together stresses the connection member-to-foil connections and it does not result in connection member-to-connection member connection which is electrically reliable. Also, crimping the connection members together results in an irregular surface on which to attach a feedthrough terminal. Thus the performance and reliability of the capacitor suffers.
One drawback with present foil-to-foil connections is that present connection techniques usually limit the amount of etching that can be done to the anode foils since etching the foil makes the foil brittle and prone to cracking under the strain of staking or cold-welding. Moreover, present connection techniques also limit the types and varieties of foils that can be used in a multi-anode stack. For instance, core-etched foils are easier to stake than tunnel-etched foils because of the extra material provided in the solid core.
Another drawback is that anode foils used in implantable medical devices are only able to charge to about 400 volts without breaking down. To reach needed voltage ranges of 600 volts or higher, as used for an implantable defibrillator, for example, two capacitors must be connected in series to deliver the shock pulse. This also increases the overall size of the implantable device.
SUMMARY
To address these and other needs, the inventors devised foil structures,foil-to-foil assembly methods, connection member-to-foil assembly methods, and connection member-to-connection member assembly methods and other connection structures and capacitor structures. In one embodiment, a method includes joining a connection member to a capacitor foil using a staking tool having a tip of less than or equal to approximately 0.030″ (0.762 mm) in diameter. A capacitor made using the technique includes an anode having a connection member attached to it by a micro-stake weld joint. Among other advantages, the present connection member-to-foil joining method results in a smaller than typical weld joint which permits increased anode brittleness and smaller foil notches. Thus, with all other capacitor factors being equal, it results in a smaller volume capacitor.
Another aspect couples multiple connection members of a capacitor together by edge-connecting each connection member to its neighboring connection member or connection members so that the connection members need not be crimped together. Another aspect includes a capacitor having one or more anodes having connection members attached to their surfaces. Each connection member has a front surface substantially flush with the front surface of adjacent connection members. Among other advantages, these features provide a capacitor which requires less space for its anode connection members and which has a more reliable connection member-to-connection member connection and reduced stress on the connection member-to-foil connection.
One aspect provides a method of foil-to-foil connecting which includes joining one or more foils using a staking tool having a tip of less than approximately 0.060″ (1.524 mm). In other embodiments, the tip ranges from approximately 0.015″ (0.381 mm) to approximately 0.060″ (1.524 mm). In one embodiment, the tip is approximately equal to 0.025″ (0.635 mm) in diameter. Among other advantages, the exemplary foil-to-foil joining method permits increased anode brittleness and allows for different permutations of anode foils.
One aspect provides a capacitor which includes a capacitor case having an electrolyte therein and a high formation voltage anode foil having a porous structure and located within the capacitor case. Among ot
Barr Alexander Gordon
Iyer Rajesh
O'Phelan Michael J.
Poplett James M.
Tong Robert R.
Cardiac Pacemakers Inc.
Dinkins Anthony
Ha Nguyen T.
Schwegman Lundberg Woessner & Kluth P.A.
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