Metal working – Barrier layer or semiconductor device making – Barrier layer device making
Reexamination Certificate
2000-06-30
2002-06-25
Nguyen, Ha Tran (Department: 2812)
Metal working
Barrier layer or semiconductor device making
Barrier layer device making
C361S508000, C361S509000, C361S512000, C361S528000, C361S529000
Reexamination Certificate
active
06409776
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
Reference is hereby made to commonly assigned, co-pending U.S. patent application Ser. No. 09/607,830 filed on even date herewith for IMPLANTABLE MEDICAL DEVICE HAVING FLAT ELECTROLYTIC CAPACITOR FORMED WITH PARTIALLY THROUGH-ETCHED AND THROUGH-HOLE PUNCTURED ANODE SHEETS filed in the names of Yan et al.
FIELD OF THE INVENTION
This invention relates to implantable medical devices (IMDs) and their various components, including flat electrolytic capacitors for same, and methods of making and using same, particularly such capacitors formed of a plurality of stacked capacitor layers each having anode layers formed of one or a plurality of nonthrough-etched and through-hole punctured anode sheets.
BACKGROUND OF THE INVENTION
As described in commonly assigned U.S. Pat. No. 6,006,133, a wide variety of IMDs are known in the art. Of particular interest are implantable cardioverter-defibrillators (ICDs) that deliver relatively high energy cardioversion and/or defibrillation shocks to a patient's heart when a malignant tachyarrhythmia, e.g., atrial or ventricular fibrillation, is detected. Current ICDs typically possess single or dual chamber pacing capabilities for treating specified chronic or episodic atrial and/or ventricular bradycardia and tachycardia and were referred to previously as pacemaker/cardioverter/ defibrillators (PCDs). Earlier developed automatic implantable defibrillators (AIDs) did not have cardioversion or pacing capabilities. For purposes of the present invention ICDs are understood to encompass all such IMDs having at least high voltage cardioversion and/or defibrillation capabilities.
Energy, volume, thickness and mass are critical features in the design of ICD implantable pulse generators (IPGs) that are coupled to the ICD leads. The battery(s) and high voltage capacitor(s) used to provide and accumulate the energy required for the cardioversion/defibrillation shocks have historically been relatively bulky and expensive. Presently, ICD IPGs typically have a volume of about 40 to about 60 cc, a thickness of about 13 mm to about 16 mm and a mass of approximately 100 grams.
It is desirable to reduce the volume, thickness and mass of such capacitors and ICD IPGs without reducing deliverable energy. Doing so is beneficial to patient comfort and minimizes complications due to erosion of tissue around the ICD IPG. Reductions in size of the capacitors may also allow for the balanced addition of volume to the battery, thereby increasing longevity of the ICD IPG, or balanced addition of new components, thereby adding functionality to the ICD IPG. It is also desirable to provide such ICD IPGs at low cost while retaining the highest level of performance. At the same time, reliability of the capacitors cannot be compromised.
Various types of flat and spiral-wound capacitors are known in the art, some examples of which are described as follows and/or may be found in the patents listed in Table 1 of the above-referenced, commonly assigned, '133 patent. Typically, an electrolytic capacitor is formed with a capacitor case enclosing an etched aluminum anode layer (or “electrode”), an aluminum cathode layer (or “electrode”), and a Kraft paper or fabric gauze spacer or separator impregnated with a solvent based liquid electrolyte interposed therebetween. A layer of aluminum oxide that functions as a dielectric layer is formed on the etched aluminum anode, preferably during passage of electrical current through the anode layer. The electrolyte comprises an ion producing salt that is dissolved in a solvent and provides ionic electrical conductivity between the cathode and the aluminum oxide dielectric layer. The energy of the capacitor is stored in the electromagnetic field generated by opposing electrical charges separated by the aluminum oxide layer disposed on the surface of the anode layer and is proportional to the surface area of the etched aluminum anode layer. Thus, to minimize the overall volume of the capacitor one must maximize anode surface area per unit volume without increasing the capacitor's overall (i.e., external) dimensions. The separator material, anode and cathode layer terminals, internal packaging, electrical interconnections, and alignment features and cathode material further increase the thickness and volume of a capacitor. Consequently, these and other components in a capacitor and the desired capacitance limit the extent to which its physical dimensions may be reduced.
Some ICD IPGs employ commercial photoflash capacitors similar to those described by Troup in “Implantable Cardioverters and Defibrillators,”
Current Problems in Cardiology
Volume XIV, Number 12, December 1989, Year Book Medical Publishers, Chicago, and as described in U.S. Pat. No. 4,254,775. The electrodes or anode and cathodes are wound into anode and cathode layers separated by separator layers of the spiral. Most commercial photoflash capacitors contain a core of separator paper intended to prevent brittle, highly etched aluminum anode foils from fracturing during winding of the anode, cathode and separator layers into a coiled configuration. The cylindrical shape and paper core of commercial photoflash capacitors limits the volumetric packaging efficiency and thickness of an ICD IPG housing made using same.
Flat electrolytic capacitors have also been disclosed in the prior art for general applications as well as for use in ICDs. More recently developed ICD IPGs employ one or more flat high voltage capacitor to overcome some of the packaging and volume disadvantages associated with cylindrical photoflash capacitors. For example, U.S. Pat. No. 5,131,388 discloses a flat capacitor having a plurality of stacked capacitor layers each comprising an “electrode stack sub-assembly”. Each capacitor layer contains one or more anode sheet forming an anode layer having an anode tab, a cathode sheet or layer having a cathode tab and a separator for separating the anode layer from the cathode layer. In the '388 patent, the electrode stack assembly of stacked capacitor layers is encased within a non-conductive, polymer envelope that is sealed at its seams and fitted into a chamber of a conductive metal, capacitor case or into a compartment of the ICD IPG housing, and electrical connections with the capacitor anode(s) and cathode(s) are made through feedthroughs extending through the case or compartment wall. The tabs of the anode layers and the cathode layers of all of the capacitor layers of the stack are electrically connected in parallel to form a single capacitor or grouped to form a plurality of capacitors. The aluminum anode layer tabs are gathered together and electrically connected to a feedthrough pin of an anode feedthrough extending through the case or compartment wall. The aluminum cathode layer tabs are gathered together and electrically connected to a feedthrough pin of a cathode feedthrough extending through the case or compartment wall or connected to the electrically conductive capacitor case wall.
Many improvements in the design of flat aluminum electrolytic capacitors for use in ICD IPGs have been disclosed, e.g., those improvements described in “High Energy Density Capacitors for Implantable Defibrillators” presented by P. Lunsmann and D. MacFarlane at
CARTS
96: 16
th Capacitor and Resistor Technology Symposium,
Mar. 11-15, 1996, and at
CARTS
-
EUROPE
96: 10
th European Passive Components Symposium.,
Oct. 7-11, 1996, pp. 35-39. Further features of flat electrolytic capacitors for use in ICD IPGs are disclosed in U.S. Pat. Nos. 4,942,501; 5,086,374; 5,146,391; 5,153,820; 5,562,801; 5,584,890; 5,628,801; and 5,748,439, all issued to MacFarlane et al.
Typically, the anode layer of each capacitor layer is formed using a single highly etched anode sheet or a plurality of such anode sheets cut from a highly etched metallic foil. Highly etched aluminum foil has a microscopically contoured, etched surface with a high concentration of pores extending part way through the anode foil along with tunnels extending all the way t
Crespi Ann M.
Untereker Darrel F.
Yan Jenn-Feng
Medtronic Inc.
Nguyen Ha Tran
Wolde-Michael Girma
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