Patent Publication Number: US-6212063-B1

Title: Implantable medical device having flat electrolytic capacitor with connector block and sealed feedthroughs

Description:
RELATED APPLICATION 
     This application claims priority and other benefits from U.S. Provisional Patent Application Ser. No. 60/080,564 filed Apr. 3, 1998 entitled “Flat Aluminum Electrolytic Capacitor.” 
    
    
     FIELD OF THE INVENTION 
     This invention relates to implantable medical devices such as defibrillators and AIDs, and their various components, including flat electrolytic capacitors for same, and corresponding methods of making and using same. 
     BACKGROUND OF THE INVENTION 
     Implantable medical devices for therapeutic stimulation of the heart are well known in the art. In U.S. Pat. No. 4,253,466 issued to Hartlaub et al., for example, a programmable demand pacemaker is disclosed. The demand pacemaker delivers electrical energy, typically ranging in magnitude between about 5 and about 25 micro Joules, to the heart to initiate the depolarization of cardiac tissue. This stimulating regime is used to treat heart block by providing electrical stimulation in the absence of naturally occurring spontaneous cardiac depolarizations. 
     Another form of implantable medical device for therapeutic stimulation of the heart is an automatic implantable defibrillator (AID), such as those described in U.S. Pat. No. Re. 27,757 to Mirowski et al. and U.S. Pat. No. 4,030,509 to Heilman et al. Those AID devices deliver energy (about 40 Joules) to the heart to interrupt ventricular fibrillation of the heart. In operation, an AID device detects the ventricular fibrillation and delivers a nonsynchronous high-voltage pulse to the heart through widely spaced electrodes located outside of the heart, thus mimicking transthoracic defibrillation. The technique of Heilman et al. requires both a limited thoracotomy to implant an electrode near the apex of the heart and a pervenous electrode system located in the superior vena cava of the heart. 
     Another example of a prior art implantable cardioverter includes the pacemaker/cardioverter/defibrillator (PCD) disclosed in U.S. Pat. No. 4,375,817 to Engle et al. This device detects the onset of tachyarrhythmia and includes means to monitor or detect the progression of the tachyarrhythmia so that progressively greater energy levels may be applied to the heart to interrupt a ventricular tachycardia or fibrillation. 
     Another device is an external synchronized cardioverter, such as that described in “Clinical Application of Cardioversion” in Cardiovascular Clinics, 1970, Vol. 2, pp. 239-260 by Douglas P. Zipes. This type of external device provides cardioversion shocks synchronized with ventricular depolarization to ensure that the cardioverting energy is not delivered during the vulnerable T-wave portion of the cardiac cycle. 
     Another example of a prior art implantable cardioverter includes the device disclosed in U.S. Pat. No. 4,384,585 to Douglas P. Zipes. This device includes circuitry to detect the intrinsic depolarizations of cardiac tissue and pulse generator circuitry to deliver moderate energy level stimuli (in the range of about 0.1 to about 10 Joules) to the heart synchronously with the detected cardiac activity. 
     The functional objective of such a stimulating regimen is to depolarize areas of the myocardium involved in the genesis and maintenance of re-entrant or automatic tachyarrhythmias at lower energy levels with greater safety than was possible with nonsynchronous cardioversion. Nonsynchronous cardioversion always incurs the risk of precipitating ventricular fibrillation and sudden death. Synchronous cardioversion delivers the shock at a time when the bulk of cardiac tissue is already depolarized and is in a refractory state. Other examples of automatic implantable synchronous cardioverters include those of Charms in U.S. Pat. No. 3,738,370. 
     It is expected that the increased safety deriving from use of lower energy levels and their attendant reduced trauma to the myocardium, as well as the smaller size of implantable medical devices, will expand indications for use beyond the existing patient base of automatic implantable defibrillators. Since many episodes of ventricular fibrillation are preceded by ventricular (and in some cases, supraventricular) tachycardias, prompt termination of the tachycardia may prevent ventricular fibrillation. 
     Consequently, current devices for the treatment of tachyarrhythmias include the possibility of programming staged therapies of antitachycardia pacing regimens, along with cardioversion energy and defibrillation energy shock regimens in order to terminate the arrhythmia with the most energy-efficient and least traumatic therapies, when possible. In addition, some current implantable tachycardia devices are capable of delivering single or dual chamber bradycardia pacing therapies, as of which are described, for example, in U.S. Pat. No. 4,800,833 to Winstrom, U.S. Pat. No. 4,830,006 to Haluska et al., and U.S. patent application Ser. No. 07/612,758 to Keimel for “Apparatus for Delivering Single and Multiple Cardioversion and Defibrillation Pulses” filed Nov. 14, 1990, and incorporated herein by reference in its entirety. Furthermore, and as described in the foregoing &#39;833 and &#39;006 patents and the &#39;758 application, considerable study has been undertaken to devise the most efficient electrode systems and shock therapies. 
     Initially, implantable cardioverters and defibrillators were envisioned as operating with a single pair of electrodes applied on or in the heart. Examples of such systems are disclosed in the aforementioned &#39;757 and &#39;509 patents, wherein shocks are delivered between an electrode is placed in or on the right ventricle and a second electrode placed outside the right ventricle. Studies have indicated that two electrode defibrillation systems often require undesirably high energy levels to effect defibrillation. 
     In an effort to reduce the amount of energy required to effect defibrillation, numerous suggestions have been made with regard to multiple electrode systems. Some of those suggestions are set forth in U.S. Pat. No. 4,291,699 to Geddes et al., U.S. Pat. No. 4,708,145 to Tacker et al., U.S. Pat. No. 4,727,877 to Kallock, and U.S. Pat. No. 4,932,407 issued to Williams where sequential pulse multiple electrode systems are described. Sequential pulse systems operate based on the assumption that sequential defibrillation pulses delivered between differing electrode pairs have an additive effect such that the overall energy requirements to achieve defibrillation are less than the energy levels required to accomplish defibrillation using a single pair of electrodes. 
     An alternative approach to multiple electrode sequential pulse defibrillation is disclosed in U.S. Pat. No. 4,641,656 to Smits and also in the above-cited &#39;407 patent. This defibrillation method may conveniently be referred to as a multiple electrode simultaneous pulse defibrillation method, and involves the simultaneous delivery of defibrillation pulses between two different pairs of electrodes. For example, one electrode pair may include a right ventricular electrode and a coronary sinus electrode, and a second electrode pair may include a right ventricular electrode and a subcutaneous patch electrode, with the right ventricular electrode serving as a common electrode to both electrode pairs. An alternative multiple electrode, single path, biphasic pulse system is disclosed in U.S. Pat. No. 4,953,551 to Mehra et al., which employs right ventricular, superior vena cava and subcutaneous patch electrodes. 
     In the above-cited prior art simultaneous pulse multiple electrode systems, delivery of simultaneous defibrillation pulses is accomplished by simply coupling two electrodes together. For example, in the above-cited &#39;551 patent, the superior vena cava and subcutaneous patch electrodes are electrically coupled together and a pulse is delivered between those two electrodes and the right ventricular electrode. Similarly, in the above-cited &#39;407 patent, the subcutaneous patch and coronary sinus electrodes are electrically coupled together, and a pulse is delivered between these two electrodes and a right ventricular electrode. See also U.S. Pat. Nos. 5,411,539; 5,620,477; 5,6589,321; 5,545,189 and 5,578,062, where active can electrodes are discussed. 
     The aforementioned &#39;758 application discloses a pulse generator for use in conjunction with an implantable cardioverter/defibrillator which is capable of providing all three of the defibrillation pulse methods described above, with a minimum of control and switching circuitry. The output stage is provided with two separate output capacitors which are sequentially discharged during sequential pulse defibrillation and simultaneously discharged during single or simultaneous pulse defibrillation. The complexity of those stimulation therapy regimens require rapid and efficient charging of high voltage output capacitors from low voltage battery power sources incorporated within the implantable medical device. 
     Typically, the electrical energy required to power an implantable cardiac pacemaker is supplied by a low voltage, low current drain, long-lived power source such as a lithium iodine pacemaker battery of the type manufactured by Wilson Greatbatch, Ltd. or Medtronic, Inc. While the energy density of such power sources is typically relatively high, they are generally not capable of being rapidly and repeatedly discharged at high current drains in the manner required to directly cardiovert the heart with cardioversion energies in the range of 0.1 to 10 Joules. Moreover, the nominal voltage at which such batteries operate is generally too low for cardioversion applications. Higher energy density battery systems are known which can be more rapidly or more often discharged, such as lithium thionyl chloride power sources. Neither of the foregoing battery types, however, may have the capacity or the voltage required to provide an impulse of the required magnitude on a repeatable basis to the heart following the onset of tachyarrhythmia. 
     Generally speaking, it is necessary to employ a DC—DC converter to convert electrical energy from a low voltage, low current power supply to a high voltage energy level stored in a high energy storage capacitor. A typical form of DC—DC converter is commonly referred to as a “flyback” converter which employs a transformer having a primary winding in series with the primary power supply and a secondary winding in series with the high energy capacitor. An interrupting circuit or switch is placed in series with the primary coil and battery. Charging of the high energy capacitor is accomplished by inducing a voltage in the primary winding of the transformer creating a magnetic field in the secondary winding. When the current in the primary winding is interrupted, the collapsing field develops a current in the secondary winding which is applied to the high energy capacitor to charge it. The repeated interruption of the supply current charges the high energy capacitor to a desired level over time. 
     In U.S. Pat. No. 4,548,209 to Wielders et al. and in the above-referenced &#39;883 patent, charging circuits are disclosed which employ flyback oscillator voltage converters which step up the power source voltage and apply charging current to output capacitors until the capacitor voltage reaches a programmed shock energy level. 
     In charging circuit 34 of FIG. 4 in the &#39;209 patent, two series-connected lithium thionyl chloride batteries 50 and 52 are connected to primary coil 54 of transformer 56 and to power FET transistor switch 60. Secondary coil 58 is connected through diode 62 to cardioversion energy storage capacitor 64. In this circuit, the flyback converter works generally as follows: When switch  60  is closed, current I p  passing through primary winding 54 increases linearly as a function of the formula V p =L p dl/dt. When FET 60 is opened, the flux in the core of transformer 56 cannot change instantaneously, and so complimentary current I s  (which is proportional to the number of windings in primary and secondary coils 54 and 58, respectively) starts to flow in secondary winding 58 according to the formula I s =(N p N s )I p . Simultaneously, voltage in the secondary winding is developed according to the function V s =L s dI s /dt, thereby causing charging of cardioversion energy storage capacitor 64 to a programmed voltage. 
     The Power FET 60 is switched “on” at a constant frequency of 32 KHz for a duration or duty cycle that varies as a function of the voltage of the output capacitor reflected back into the primary coil 54 circuit. The on-time of power FET 60 is governed by the time interval between the setting and resetting of flip-flop 70, which in turn is governed either by current I p  flowing through primary winding 54 or as a function of a time limit circuit containing further circuitry to vary the time limit with battery impedance (represented schematically by resistor 53). In both cases, the on-time varies from a maximum to a minimum interval as the output circuit voltage increases to its maximum value. 
     The aforementioned &#39;883 and &#39;006 patents disclose a variable duty cycle flyback oscillator voltage converter, where the current in the primary coil circuit (in the case of the &#39;883 patent) or the voltage across a secondary coil (in the case of the &#39;006 patent) is monitored to control the duty cycle of the oscillator. In the &#39;883 circuit the “on” time of the oscillator is constant and the “off” time varies as a function of the monitored current through the transformer. 
     In the &#39;006 patent, a secondary coil is added to power a high voltage regulator circuit that provides V+to a timer circuit and components of the high voltage oscillator. This high voltage power source allows the oscillator circuit to operate independently of the battery source voltage (which may deplete over time). The inclusion of a further secondary winding on an already relatively bulky transformer is disadvantageous from size and efficiency standpoints. 
     Energy, volume, thickness and mass are critical features in the design of implantable cardiac defibrillators (ICDs). One of the components important to optimization of those features is the high voltage capacitors used to store the energy required for defibrillation. Such capacitors typically deliver energy in the range of about 25 to 40 Joules, while ICDs 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 devices without reducing deliverable energy. Doing so is beneficial to patient comfort and minimizes complications due to erosion of tissue around the device. Reductions in size of the capacitors may also allow for the balanced addition of volume to the battery, thereby increasing longevity of the device, or balanced addition of new components, thereby adding functionality to the device. It is also desirable to provide such devices at low cost while retaining the highest level of performance. 
     Most ICDs 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 U.S. Pat. No. 4,254,775 for “Implantable Defibrillator and Package Therefor”. The electrodes in such capacitors are typically spirally wound to form a coiled electrode assembly. Most commercial photoflash capacitors contain a core of separator paper intended to prevent brittle anode foils from fracturing during coiling. The anode, cathode and separator are typically wound around such a paper core. The core limits both the thinness and volume of the ICDs in which they are placed. The cylindrical shape of commercial photoflash capacitors also limits the volumetric packaging efficiency and thickness of an ICD made using same. 
     As noted above, electrodes and separators used in the assembly of photoflash capacitors are typically coiled, with a resulting cylindrical capacitor geometry. Anodes employed in photoflash capacitors typically comprise one or two layers of a high purity (99.99%), porous, highly etched, anodized aluminum foil. Cathode layers in such capacitors are formed of a nonporous, highly etched aluminum foil which may be somewhat less pure (99.7%) respecting aluminum content than the anode layers. The thickness of such foils is on the order of 100 micrometers and 20 micrometers for anode foils and cathode foils, respectively. The capacitance of the cathode is balanced respecting that of the anode to ensure reliable performance over the life of the device. Separating the anode and cathode is a separator material that typically comprises two layers of Kraft paper. 
     Prior art electrolytic capacitors generally include a laminate comprising an etched aluminum foil anode, an aluminum foil of film cathode and a Kraft paper or fabric gauze spacer impregnated with a solvent based liquid electrolyte interposed therebetween. A layer of oxide is formed on the aluminum anode, preferably during passage of electrical current through the anode. The oxide layer functions as a dielectric layer. The entire laminate is rolled up into the form of a substantially cylindrical body and encased, with the aid of suitable insulation, in an aluminum tube or can subsequently sealed with a rubber material. 
     The energy of the capacitor is stored in the electromagnetic field generated by opposing electrical charges separated by an aluminum oxide layer disposed on the surface of the anode. The energy so stored is proportional to the surface area of the aluminum anode. Thus, to minimize the overall volume of the capacitor one must maximize anode surface area per unit volume without increasing the capacitor&#39;s overall (i.e., external) dimensions. Separator material, anode and cathode terminals, internal packaging and alignment features and cathode material further increase the thickness and volume of a capacitor. Consequently, those and other components in a capacitor limit the extent to which its physical dimensions may be reduced. 
     Recently developed flat aluminum electrolytic capacitors have overcome some disadvantages inherent in commercial cylindrical capacitors. For example, U.S. Pat. No. 5,131,388 to Pless et. al. discloses a relatively volumetrically efficient flat capacitor having a plurality of planar layers arranged in a stack. Each layer contains an anode layer, a cathode layer and means for separating the anode layers and cathode layers (such as paper). The anode layers and the cathode layers are electrically connected in parallel. 
     In a recent paper “High Energy Density Capacitors for Implantable Defibrillators” presented at CARTS 96: 16th Capacitor and Resistor Technology Symposium, Mar. 11-15, 1996, several improvements in the design of flat aluminum electrolytic capacitors are described. Described are the use of a solid adhesive electrolyte for strengthening the separator and allowing use of a thinner separator. Also described are a triple anode formed from a non-porous foil disposed between two porous foils. By increasing the number of anode foils per anode layer, the total number of separator and cathode layers in a given stack assembly is reduced, thereby decreasing thickness and volume. Next described are an embedded anode layer tab, where a notch is cut in the anode and a tab of the same thickness as the center anode is placed in the notch. Three anode layers are welded to one another and to the tabs by a cold welding process. See also U.S. Pat. Nos. 5,562,801; 5,153,820; 5,146,391; 5,086,374; 4,942,501; 5,628,801 and 5,584,890 to MacFarlane et al. 
     In U.S. Pat. No. 5,522,851 to Fayram, manufacturing improvements in flat capacitors relating to the use of internal alignment elements are disclosed. Internal alignment elements are employed as a means for controlling the relative edge spacing of electrode layers and the housing. In the absence of such alignment elements, precision assembly by hand may be required, thereby increasing manufacturing costs. The housing size must also be increased to provide tolerance for alignment errors, resulting in a bulkier device. The &#39;851 patent also describes the use of an electrically conductive housing for grounding some capacitor elements, such as the cathode terminal. 
     A segment of today&#39;s ICD market employs flat capacitors to overcome some of the packaging and volume disadvantages associated with cylindrical photoflash capacitors. Examples of such flat capacitors are described in the &#39;388 patent to Pless et al. for “Implantable Cardiac Defibrillator with Improved Capacitors,” and the &#39;851 patent to Fayram for “Capacitor for an Implantable Cardiac Defibrillators” Additionally, flat capacitors are described in a paper entitled “High Energy Density Capacitors for Implantable Defibrillators” by P. Lunsmann and D. MacFarlane presented at the 16th Capacitor and Resistor Technology Symposium. 
     Anodes and cathodes of aluminum electrolytic capacitors generally have tabs extending beyond their perimeters to facilitate electrical connection in parallel. In U.S. Pat. No. 4,663,824 to Kenmochi, tab terminal connections for a wound capacitor are described as being laser welded to feedthrough terminals. Wound capacitors usually contain two or no tabs joined together by crimping or riveting. Termination of larger numbers of anode tabs is described in the &#39;851 patent as being accomplished through laser welding of the free ends of the tabs, followed by welding of the tabs to an inner terminal. In the &#39;851 patent, cathode tabs are connected by ultrasonic welding to a step in the capacitor housing. 
     In assembling a capacitor, it is necessary that the anode and cathode remain separated electrically to prevent short circuiting. It is also important that a minimum separation between the anode and cathode be maintained to prevent arcing between the anode and cathode, or between the anode and the case. In cylindrical capacitors, such spacing is typically maintained at the electrode edges or peripheries by providing separator overhang at the top and bottom of the anode and cathode winding. In addition, the anode and cathode are aligned precisely and coiled tightly to prevent movement of the anode, cathode and separator during subsequent processing and use. In flat capacitors, anode to cathode alignment is typically maintained through the use of internal alignment posts (as described, for example, in the &#39;851 patent to Pless et al.) screws (see the &#39;851 patent to Pless et al.) or by using an adhesive electrolyte (see the patents to MacFarlane, supra). 
     Sealing of capacitor housings is typically accomplished in a variety of ways. Aultman et al. in U.S. Pat. No. 4,521,830 describes a typical aluminum electrolytic capacitor construction employed from about 1960 to about 1985. Those typical constructions employed a plastic header with two molded-in threaded aluminum terminals of the type shown in Collins et al. in U.S. Pat. No. 3,789,502, where plastic is molded around the terminals. Zeppieri in U.S. Pat. No. 3,398,333 and Schroeder in U.S. Pat. No. 4,183,600 teach prior art capacitors in which an aluminum serrated shank terminal extends through a thermal plastic header. In both patents the aluminum terminal is resistance-heated to a temperature such that the length of the terminal is collapsed and the center diameter is increased to press the serrations into the melted plastic. Aultman teaches a header design employing a compression-fit set of terminals disposed in a polymer header. 
     Hutchins et al. in U.S. Pat. No. 4,987,519 describe a glass-to-metal seal terminal connection with a tantalum outer ring being laser welded into an aluminum case. Kenmochi in U.S. Pat. No. 4,663,824 describes the use of a resin casing that has been previously formed from epoxy, silicon resin, polyoxybenzylene, polyether etherkeytone, or polyether sulfone, and that has high heat resistance. The terminals perforate the walls by molding them into the casing. 
     Pless et al. in U.S. Pat. No. 5,131,388 describe the use of a polymer envelope for encasement of the stack and feedthroughs. A silicon adhesive is used to seal the envelope at the seams. The polymer-enveloped flat stack is then disposed within a stainless steel or Titanium case. Aluminum capacitor terminals are described as being crimped or welded to the feedthroughs. Fayram in U.S. Pat. No. 5,522,851 does not specifically address the issue of feedthrough design. An anode post is described as being electrically insulated from the housing. 
     U.S. Pat. No. 4,041,956 to Purdy et al. for “Pacemakers of Low Weight and Method of Making Such Pacemakers”; U.S. Pat. No. 4,692,147 to Duggan for “Drug Administration Device”; and U.S. Pat. No. 5,456,698 to Byland et al. for “Pacemaker” disclose various means of hermetically sealing housings for implantable medical devices, including laser welding means. 
     Various types of flat and spirally-wound capacitors are known in the art, some examples of which may be found in the issued U.S. Patents listed in Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Prior Art Patents 
               
            
           
           
               
               
               
            
               
                   
                 U.S. Pat. No. 
                 Title 
               
               
                   
                   
               
               
                   
                 3,398,333 
                 Electrical Component End Seal 
               
               
                   
                 3,789,502 
                 Fused Cathode Electrolytic Capacitors and Method of Making 
               
               
                   
                   
                 the Same 
               
               
                   
                 4,183,600 
                 Electrolytic Capacitor Cover-Terminal Assembly 
               
               
                   
                 4,385,342 
                 Flat Electrolytic Capacitor 
               
               
                   
                 4,521,830 
                 Low Leakage Capacitor Header and Manufacturing Method 
               
               
                   
                   
                 Therefor 
               
               
                   
                 4,546,415 
                 Heat Dissipation Aluminum Electrolytic Capacitor 
               
               
                   
                 4,663,824 
                 Aluminum Electrolytic Capacitor and a Manufacturing Method 
               
               
                   
                   
                 Therefor 
               
               
                   
                 4,942,501 
                 Solid Electrolyte Capacitors and Methods of Making the 
               
               
                   
                   
                 Same 
               
               
                   
                 4,987,519 
                 Hermetically Sealed Aluminum Electrolytic Capacitor 
               
               
                   
                 5,086,374 
                 Aprotic Electrolyte Capacitors and Methods of Making the 
               
               
                   
                   
                 Same 
               
               
                   
                 5,131,388 
                 Implantable Cardiac Defibrillator with Improved Capacitors 
               
               
                   
                 5,146,391 
                 Crosslinked Electrolyte Capacitors and Methods of Making 
               
               
                   
                   
                 the Same 
               
               
                   
                 5,153,820 
                 Crosslinked Electrolyte Capacitors and Methods of Making 
               
               
                   
                   
                 the Same 
               
               
                   
                 5,324,910 
                 Welding Method of Aluminum Foil 
               
               
                   
                 5,370,663 
                 Implantable Cardio-Stimulator With Flat Capacitor 
               
               
                   
                 5,380,341 
                 Solid State Electrochemical Capacitors and Their Preparation 
               
               
                   
                 5,545,184 
                 Cardiac Defibrillator with High Energy Storage 
               
               
                   
                   
                 Antiferroelectric Capacitor 
               
               
                   
                 5,522,851 
                 Capacitor for an Implantable Cardiac Defibrillator 
               
               
                   
                 5,584,890 
                 Methods of Making Multiple Anode Capacitors 
               
               
                   
                 5,628,801 
                 Electrolyte Capacitor and Method of Making the Same 
               
               
                   
                 5,660,737 
                 Process for Making a Capacitor Foil with Enhanced Surface 
               
               
                   
                   
                 Area 
               
               
                   
                   
               
            
           
         
       
     
     As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, at least some of the devices and methods disclosed in the patents of Table 1 and elsewhere herein may be modified advantageously in accordance with the teachings of the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention has certain objects. That is, the present invention provides solutions to many problems existing in the prior art respecting flat electrolytic capacitors for implantable medical devices. Those problems generally include one or more of the following: (a) out-gassing or fluid leakage from capacitor cases, resulting in damage to electronic circuitry contained within implantable medical devices; (b) poor or insufficient recharging times in discharged capacitors; (c) insufficient or marginal overall capacitor capacities; (d) decreasing voltage or capacity of capacitors with age; (e) volumetrically inefficient electrode packaging in capacitors; (f) heavy capacitor weights; (g) large physical sizes and volumes of capacitors; (h) expensive manufacturing processes; (i) difficulty in registering capacitor electrode assembly elements, and  0 ) expensive and unreliable capacitor sealing methods and structures. 
     Some embodiments of the invention have certain features generally, including at least one of: (a) an implantable cardiac defibrillator comprising an energy source, a flat electrolytic capacitor and means coupled to the energy source for charging the capacitor; (b) a capacitor comprising a planar layered structure of anode layers, cathode layers and separator layers separating the anode layers from the cathode layers; (c) a plurality of anode sub-assemblies electrically connected in parallel, and a plurality of cathode layers electrically connected in parallel.; (d) a plurality of anode sub-assemblies and the plurality of cathode layers that are interleaved, separated by interposed separator layers and impregnated or covered with a solid or liquid electrolyte to form an electrode assembly; (e) an anode sub-assembly comprising at least two anode layers; (f) at least one anode layer in an anode sub-assembly having a registration tab extending from a perimeter thereof; (g) at least one cathode layer having a registration tab extending from a perimeter thereof; (h) registration tabs for connecting anode sub-assemblies or cathode layers in parallel electrically; (i) registration tabs for connecting anode sub-assemblies or cathode layers to feedthroughs;  0 ) anode and cathode layers comprising aluminum foil; (k) separator layers comprising paper; (k) an aluminum case having an open end for receiving an electrode assembly therewithin; and (I) a case crimpingly or weldingly sealed with a cover. 
     Particular aspects of the various methods and apparatus of the present invention have at least some of the objects, features and advantages described below. 
     A first apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including prior art capacitors that: (a) are prone to electrical shorting between adjacent anode and cathode layers due to the presence of burrs along the edges of cut electrode layers; (b) are prone to electrical shorting between adjacent anode and cathode layers due to the generation of metal particulates during electrode layer cutting processes; and (c) are costly to manufacture due to the large number of components they contain and the relatively slow manufacturing techniques employed to construct them. 
     Some embodiments of the first apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) very low clearance dies for cutting capacitor electrode foil materials to form electrode layers; (b) die punches having faces not parallel to the corresponding floor of a cutting die for cutting capacitor electrode foil materials to form electrode layers; (c) upward die punch motions to cut capacitor foil materials to form electrode layers; and (d) use of air, gas or vacuum systems to clear debris from cut electrode layers. 
     In respect of known flat electrolytic capacitors, the first apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) formed electrode layers having a minimum number and size of edge burrs; (b) electrode foil material cutting and electrode layer forming methods well suited for high speed manufacturing methods; (c) electrode foil material cutting and electrode layer forming methods resulting in reduced cutting debris; and (d) electrode foil material and electrode layer forming methods producing reduced amounts of cutting debris on the surfaces of the electrode layers. 
     A second apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) add extra, inert volume in the form of alignment elements disposed within the capacitor case for registering electrode layers and assemblies; (b) provide means for aligning electrode layers that are too imprecise to permit the amount of paper overhang in electrode layers to be reduced; (c) may not be manufactured using high speed manufacturing techniques; (d) include many piece parts and therefore increase manufacturing costs. 
     Some embodiments of the second apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) tooling and corresponding methods for capturing and aligning electrode tabs and aligning electrode layers; (b) robotic assembly methods for constructing electrode assemblies; (c) a capacitor design that does not require the use of inactive or inert alignment elements disposed within the capacitor case. 
     In respect of known flat electrolytic capacitors, the second apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) a more volumetrically efficient mechanical design providing lower volume and higher energy density; (b) a mechanical design and method for constructing electrode assemblies that permits the use of high speed manufacturing techniques; (c) lower cost capacitors owing to increased manufacturing efficiencies; (d) simple electrode layer and assembly plate geometries, resulting in fewer piece parts and lower cost; and (e) a case having fewer points from which electrolyte may leak. 
     A third apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) have electrode assemblies having electrode and separator layers that must be mechanically secured together by relatively large volume, inert mechanical means; (b) have electrode assemblies prone to movement within the case of the capacitor; (c) have feedthrough connections that may be affected by movement of the electrode assembly within the case. 
     Some embodiments of the third apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) an electrode assembly secured together by a low-volume electrode assembly wrap and corresponding adhesive strip; (b) an electrode assembly secured together by low-volume electrode assembly clamps, bands or wraps disposed about the periphery of the assembly; (c) an electrode assembly which expands and is secured against the interior portions of a capacitor can by electrolyte-swelled separator layers; and (d) separator layers which envelop or are disposed between electrode layers, the separator layers having perimeters and surface areas which exceed those of the electrode layers. 
     In respect of known flat electrolytic capacitors, the third apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) a capacitor having higher energy density owing to more electrode material of greater surface area being disposed therewithin; (b) electrode layers having no holes for registration disposed therethrough, and therefore having increased surface area; (c) a capacitor not having elaborate, volume-consuming mechanisms for retaining or securing the electrode assembly disposed therewithin, and (d) highly reliable feedthrough connections owing to the electrode assembly being tightly secured and retained within the case of the capacitor. 
     A fourth apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) contain anode or cathode tab terminal connections that are difficult to laser weld or otherwise connect or connect to; (b) have tab terminals prone to fracturing during manufacturing; (c) require a two step, and therefore more costly, method for connecting electrode tabs and for connecting feedthroughs thereto; and (d) require an excessive number of components for connecting electrode tab bundles to feedthroughs, thereby increasing cost and volume and decreasing volumetric efficiency. 
     Some embodiments of the fourth apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) direct consolidation and connection of multiple electrode layer tabs to a single feedthrough or feedthrough attachment means; (b) direct consolidation and connection of multiple electrode layer tabs to a coiled distal end of a single feedthrough or feedthrough attachment means; (c) welded feedthrough and electrode tab connections using, for example, laser spot welds, seam welds, ultrasonic welds or resistance welds; (d) an intermediate component disposed between electrode tabs and a feedthrough for providing strain relief. 
     In respect of known flat electrolytic capacitors, the fourth apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) a one-step method for connecting electrode tabs and feedthroughs; (b) a minimum number of components for connecting electrode tabs to feedthroughs; (c) highly reliable feedthrough connections; and (d) lower component and manufacturing costs. 
     A fifth apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) are susceptible to damage of internal capacitor components resulting from laser beams entering the interior of the capacitor case when welding the cover to the case of the capacitor; (b) require means incorporated into the capacitor for aligning the cover to the case during sealing operations that add inert, unusable volume to the capacitor; (c) require separate means for clamping the case and cover together during welding of the case and cover, thereby increasing manufacturing cycle time and cost; (d) have aluminum cases and covers that are difficult to laser weld together in a cost-effective manner yet still produce an hermetic seal; and (e) do not incorporate into the capacitor means for performing leaktightness testing. 
     Some embodiments of the fifth apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) self-alignment and self-engagement elements or structures disposed along the joint between the case and the cover and incorporated into the capacitor to facilitate holding the case and cover together during welding and sealing; (b) case and corresponding cover weld joint and crimp configurations that eliminate or reduce laser beam damage to electrode assemblies during welding; (c) an optimized set of welding parameters for joining and sealing the case and cover of a capacitor; (d) an electrolyte fill port that permits standard helium leaktightness testing of the integrity of the capacitor seal. 
     In respect of known flat electrolytic capacitors, the fifth apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) not being damaged internally by laser beams employed to weld the case to the cover; (b) having means for aligning and maintaining the positions of the case and cover during welding and sealing that add no volume to the capacitor and that require no additional steps during the welding process; (c) providing a relatively wide window of cost-effective laser welding parameters for hermetically welding the case to the cover; (d) a flat capacitor that may be checked for leaktightness using cost-effective standard helium leak rate test methods. 
     A sixth apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) have no means for making simple crimped connections to the device; (b) have no hermetic seals for feedthroughs; (c) have external terminal or feedthrough interconnections that are susceptible to breaking or fracturing when the capacitor is dropped or vibrated excessively during handling or shipping; (d) have no or limited means for providing cost-effective electrically isolated feedthroughs; (e) have no cost-effective means for connecting external devices or circuits to the terminals of the capacitor; (e have no flexible strain-relieving means for connecting electrodes to feedthroughs, or feedthroughs to external devices or circuits; (g) are prone to loss of electrolyte; and (h) susceptible to degradation of electrical properties over time. 
     Some embodiments of the sixth apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) a wire harness assembly having a distal end that permits a wide variety of connection configurations; (b) crimp or slide contacts for device level connections; (c) a connector module mounted on, attached to or engaging the external surface of a capacitor can or cover; (d) an epoxy- or adhesive-sealed feedthrough; (e) feedthrough ferrules and corresponding wire guides; (f) a capacitor case, cover, ferrules, feedthroughs and fill port providing a high degree of hermeticity; and (g) means for connecting capacitor feedthroughs to external devices or circuits that are located away from the case of the capacitor. 
     In respect of known flat electrolytic capacitors, the sixth apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) fewer manufacturing steps and related lower assembly costs when placing the capacitor within an implantable medical device; (b) crimp contact or sliding feedthrough contacts that are easy to connect at the device level; (c) no or little loss of electrolyte from the capacitor owing to its high degree of hermeticity; (d) a capacitor having electrical properties which do not degrade over the lifetime of the implantable medical device within which the capacitor is disposed; and (e) highly flexible means for accomplishing device level interconnection without major redesign of the capacitor terminal structure. 
     A seventh apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) contain means for cold welding electrode layers and tabs to electrode layers that add significant thickness to an electrode assembly, thereby increasing overall thickness of the capacitor and its corresponding implantable medical device; and (b) means for cold welding electrode layers that are not adaptable to high speed manufacturing techniques. 
     Some embodiments of the seventh apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) means for restricting out-of-plane material flow in flat electrode layers during cold welding steps; (b) means for cold welding electrode layers to one another, and for cold welding separator layers to electrode layers, that are adaptable to high speed manufacturing methods; and (c) means for monitoring individual cold weld processing parameters. 
     In respect of known flat electrolytic capacitors, the seventh apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) low clearance cold welds in electrode and separator layers, thereby decreasing the thickness of the capacitor and corresponding implantable medical device; and (b) adaptability to high speed manufacturing techniques. 
     An eighth apparatus and corresponding methods of the present invention provide at least some solutions to problems existing in prior art capacitors for AIDs, including capacitors that: (a) have high equivalent series resistances; and (b) have relatively low total capacitances. 
     Some embodiments of the eighth apparatus and corresponding methods of the present invention have certain features, including at least one of: (a) a capacitor having relatively low equivalent series resistance; (b) a capacitor having relatively high total capacitance; and (c) a capacitor containing a liquid electrolyte that has undergone successive cycles of being subjected to a vacuum and no vacuum while the electrolyte is presented to the cell interior to thereby efficiently and relatively completely saturate the electrode layers of the capacitor. 
     In respect of known flat electrolytic capacitors, the eighth apparatus and corresponding methods of the present invention provide advantages, including one or more of: (a) a capacitor that is capable of delivering high amounts of charge and energy; (b) a capacitor that recharges quickly and efficiently; and (c) a capacitor having charge and discharge performance that does not appreciably degrade over the lifetime of its corresponding implantable medical device. 
     Those of ordinary skill in the art will understand immediately upon referring to the drawings, detailed description of the preferred embodiments and claims hereof that many objects, features and advantages of the capacitors and methods of the present invention will find application in the fields other than the field of implantable medical devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the accompanying detailed drawings of the preferred embodiments in which like reference numerals represent like or similar parts throughout, wherein: 
     FIG. 1 illustrates the physical components of one embodiment of a pacemaker/cardioverter/defibrillator (PCD) and lead system of one embodiment of the present invention; 
     FIG. 2 shows a functional block diagram illustrating the interconnection of voltage conversion circuitry of one embodiment of the present invention with primary functional components of one type of an implantable PCD; 
     FIGS.  3 ( a )-( h ) is an exploded perspective view of the various components of one embodiment of the present invention as they are disposed within the housing of implantable PCD; 
     FIG. 4 shows an exploded view of one embodiment of a single electrode sub-assembly of a capacitor of the present invention; 
     FIG.  5 ( a ) shows an exploded perspective view of one embodiment of a cold welding apparatus in which anode layers of the electrode sub-assembly of FIG. 4 are cold-welded; 
     FIG.  5 ( b ) shows an unexploded view of the cold welding apparatus of FIG.  5 ( a ); 
     FIG.  5 ( c ) shows a cross-sectional view of the cold welding apparatus of FIGS.  5 ( a ) and  5 ( b ) in which anode layers of the electrode sub-assembly of FIG. 4 are cold-welded therein; 
     FIG.  6 ( a ) shows an exploded top perspective view of one embodiment of an electrode assembly of a capacitor of the present invention; 
     FIG.  6 ( b ) shows a cross-sectional view of a portion of one embodiment of a cold-welded anode assembly of the present invention; 
     FIG.  6 ( c ) shows a cross-sectional view of another portion of one embodiment of a cold-welded anode assembly of the present invention; 
     FIG. 7 shows a top perspective view of one embodiment of an electrode assembly of a capacitor of the present invention; 
     FIG. 8 shows an enlarged view of a portion of the electrode assembly shown in FIG. 7; 
     FIG. 9 shows an exploded top perspective view of one embodiment of a capacitor of the present invention employing the electrode assembly of FIGS. 6,  7  and  8  therein; 
     FIG. 10 shows an exploded top perspective view of the partially assembled capacitor of FIG. 9; 
     FIG. 11 shows a top view of one embodiment of a fully assembled capacitor of the present invention having no cover  110  disposed thereon; 
     FIG. 12 shows a top perspective view of the capacitor of FIG. 11 having cover  110  disposed thereon. 
     FIG. 13 shows a flow chart of one method of the present invention for making a capacitor of the present invention; 
     FIG. 14 shows a flow chart of one method of the present invention for making an anode layer of the present invention; 
     FIG. 15 shows a flow chart of one method of the present invention for making an electrode assembly of the present invention; 
     FIG. 16 shows a flow chart of one method of the present invention for making tab interconnections and feedthrough terminal connections of the present invention; 
     FIG. 17 shows a flow chart of one method of the present invention for making tab interconnections and feedthrough terminal connections of the present invention; 
     FIG. 18 shows a flow chart of one method of the present invention for making a case sub-assembly of the present invention; 
     FIG. 19 shows a flow chart of one method of the present invention for sealing a case and cover of the present invention; 
     FIG. 20 shows a flow chart of one method of the present invention for sealing a feedthrough of the present invention; 
     FIGS.  21 ( a ) through  21 ( e ) show perspective, top, cross-sectional, top and cross-sectional views, respectively, of one embodiment of a connector block of the present invention; 
     FIG. 22 shows a flow chart of one method of the present invention for vacuum treating an aged capacitor of the present invention; 
     FIG. 23 shows a flow chart of one method of the present invention for refilling an aged capacitor of the present invention; 
     FIG. 24 shows comparative capacitance data for prior art capacitors and capacitors made according to the methods of FIGS. 22 and 23; 
     FIG. 25 shows comparative equivalent series resistance (ESR) data for prior art capacitors and capacitors made according to the methods of FIGS. 22 and 23; 
     FIGS.  26 ( a ) through  26 ( p ) show various embodiments of the crimp and joint of the case and cover of the present invention; 
     FIG.  27 ( a ) shows a top view of a capacitor of the present invention with a portion of its cover removed; 
     FIG.  27 ( b ) shows an end view of the capacitor of FIG.  27 ( a ), and 
     FIGS.  28 ( a ) through  28 ( c ) show various views of a liquid electrolyte fill port ferrule tube and fill port ferrule of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates one embodiment of implantable PCD  10  of the present invention, its associated electrical leads  14 ,  16  and  18 , and their relationship to a human heart  12 . The leads are coupled to PCD  10  by means of multi-port connector block  20 , which contains separate connector ports for each of the three leads illustrated. Lead  14  is coupled to subcutaneous electrode  30 , which is intended to be mounted subcutaneously in the region of the left chest. Lead  16  is a coronary sinus lead employing an elongated coil electrode which is located in the coronary sinus and great vein region of the heart. The location of the electrode is illustrated in broken line format at  32 , and extends around the heart from a point within the opening of the coronary sinus to a point in the vicinity of the left atrial appendage. 
     Lead  18  is provided with elongated electrode coil  28  which is located in the right ventricle of the heart. Lead  18  also includes stimulation electrode  34  which takes the form of an advanceable helical coil which is screwed into the myocardial tissue of the right ventricle. Lead  18  may also include one or more additional electrodes for near and far field electrogram sensing. A more detailed description of the leads illustrated can be found in the aforementioned &#39;407 patent. However, the invention is also believed workable in the context of multiple electrode systems employing different sets of electrodes, including superior vena cava electrodes and epicardial patch electrodes. 
     In the system illustrated, cardiac pacing pulses are delivered between helical electrode  34  and elongated electrode  28 . Electrodes  28  and  34  are also employed to sense electrical signals indicative of ventricular contractions. As illustrated, it is anticipated that the right ventricular electrode  28  will serve as the common electrode during sequential and simultaneous pulse multiple electrode defibrillation regimens. For example, during a simultaneous pulse defibrillation regimen, pulses would simultaneously be delivered between electrode  28  and electrode  30  and between electrode  28  and electrode  32 . During sequential pulse defibrillation, it is envisioned that pulses would be delivered sequentially between subcutaneous electrode  30  and electrode  28  and between coronary sinus electrode  32  and right ventricular electrode  28 . Single pulse, two electrode defibrillation pulse regimens may be also provided, typically between electrode  28  and coronary sinus electrode  32 . Alternatively, single pulses may be delivered between electrodes  28  and  30 . The particular interconnection of the electrodes to an implantable PCD will depend somewhat on which specific single electrode pair defibrillation pulse regimen is believed more likely to be employed. 
     FIG. 2 is a block diagram illustrating the interconnection of high voltage output circuit  40 , high voltage charging circuit  64  and capacitors  265  according to one embodiment of the present invention with a prior art implantable PCD. As illustrated, the device is controlled by means of a stored program in microprocessor  42 , which performs all necessary computational functions within the device. Microprocessor  42  is linked to control circuitry  44  by means of bidirectional data/control bus  46 , and thereby controls operation of the output circuitry  40  and the high voltage charging circuitry  64 . On reprogramming of the device or on the occurrence of signals indicative of delivery of cardiac pacing pulses or of the occurrence of cardiac contractions, pace/sense circuitry  78  will awaken microprocessor  42  to perform any necessary mathematical calculations, to perform tachycardia and fibrillation detection procedures and to update the time intervals controlled by the timers in pace/sense circuitry  78 . 
     The basic operation of such a system in the context of an implantable PCD may correspond to any of the systems known in the art. More particularly, the flat aluminum electrolytic capacitor of the present invention may be employed generally in conjunction with the various systems illustrated in the aforementioned &#39;209, &#39;585, &#39;006, &#39;883 and &#39;817 patents, or in conjunction with the various systems or components disclosed in U.S. Pat. No. 4,693,253 to Adams, U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No. 5,591,212 to Keimel, U.S. Pat. No. 5,383,909 to Keimel, U.S. Pat. No. 5,354,316 to Keimel, U.S. Pat. No. 5,336,253 to Gordon et al., U.S. Pat. No. 4,384,585 to Zipes, U.S. Pat. No. 4,949,719 to Pless et al., U.S. Pat. No. 4,374,817 to Engle et al., U.S. Pat. No. 4,577,633 to Berkowitz, U.S. Pat. No. 4,880,005 to Pless et al., U.S. Pat. No. 4,726,380 to Vollmann et al., U.S. Pat. No. 4,587,970 to Holley et al., U.S. Pat. No. 5,447,519 to Peterson, U.S. Pat. No. 4,476,868 to Thompson, U.S. Pat. No. 4,556,063 to Thompson, U.S. Pat. No. 4,379,459 to Stein, U.S. Pat. No. 5,312,453 to Wyborny, U.S. Pat. No. 5,545,186 to Olson, U.S. Pat. No. 5,345,316 to Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No. 5,131,388 to Pless, U.S. Pat. No. 3,888,260 to Fischell, U.S. Pat. No. 5,411,537 to Munshi et al. and U.S. Pat. No. 4,821,723 to Baker et al. All the foregoing patents are hereby incorporated herein by reference in their respective entireties. 
     Control circuitry  44  provides three signals of primary importance to output circuitry  40  of the present invention. Those signals include the first and second control signals discussed above, labeled here as ENAB, line  48 , and ENBA, line  50 . Also of importance is DUMP line  52  which initiates discharge of the output capacitors and VCAP line  54  which provides a signal indicative of the voltage stored on the output capacitors C 1 , C 2 , to control circuitry  44 . Defibrillation electrodes  28 ,  30  and  32  illustrated in FIG. 1, above, are shown coupled to output circuitry  40  by means of conductors  22 ,  24  and  26 . For ease of understanding, those conductors are also labeled as “COMMON”, “HVA” and “HVB”. However, other configurations are also possible. For example, subcutaneous electrode  30  may be coupled to HVB conductor  26 , to allow for a single pulse regimen to be delivered between electrodes  28  and  30 . During a logic signal on ENAB, line  48 , a cardioversion/defibrillation pulse is delivered between electrode  30  and electrode  28 . During a logic signal on ENBA, line  50 , a cardioversioni defibrillation pulse is delivered between electrode  32  and electrode  28 . 
     The output circuitry of the present invention includes a capacitor bank, including capacitors C 1  and C 2  and diodes  121  and  123 , used for delivering defibrillation pulses to the electrodes. Alternatively, the capacitor bank may include a further set of capacitors as depicted in the above referenced &#39;758 application. In FIG. 2, capacitors  265  are illustrated in conjunction with high voltage charging circuitry  64 , controlled by the control/timing circuitry  44  by means of CHDR line  66 . As illustrated, capacitors  265  are charged by means of a high frequency, high voltage transformer  110 . Proper charging polarities are maintained by means of the diodes  121  and  123 . VCAP line  54  provides a signal indicative of the voltage on the capacitor bank, and allows for control of the high voltage charging circuitry and for termination of the charging function when the measured voltage equals the programmed charging level. 
     Pace/sense circuitry  78  includes an R-wave amplifier according to the prior art, or more advantageously as disclosed in co-pending, commonly assigned U.S. patent application Ser. No. 07/612,670 to Keimel et al. for “Apparatus for Monitoring Electrical Physiological Signals,” filed Nov. 14, 1990, which is hereby incorporated herein by reference in its entirety. The present invention is believed workable, however, in the context of any known R-wave amplification system. Pace/sense circuitry  78  also includes a pulse generator for generating cardiac pacing pulses, which may also correspond to any known cardiac pacemaker output circuitry and includes timing circuitry for defining ventricular pacing intervals, refractory intervals and blanking intervals, under control of microprocessor  42  via control/data bus  80 . 
     Control signals triggering generation of cardiac pacing pulses by pace/sense circuitry  78  and signals indicative of the occurrence of R-waves, from pace/sense circuitry  78  are communicated to control circuitry  44  by means of a bi-directional data bus  81 . Pace/sense circuitry  78  is coupled to helical electrode  34  illustrated in FIG. 1 by means of a conductor  36 . Pace/sense circuitry  78  is also coupled to ventricular electrode  28 , illustrated in FIG. 1, by means of a conductor  82 , allowing for bipolar sensing of R-waves between electrodes  34  and  28  and for delivery of bipolar pacing pulses between electrodes  34  and  28 , as discussed above. 
     FIGS.  3 ( a ) through  3 ( g ) show perspective views of various components of implantable PCD  10  of the present invention, including one embodiment of the capacitor of the present invention, as those components are placed successively within the housing of PCD  10 . In FIG.  3 ( a ), electronics module  360  is placed in right-hand shield  340  of PCD  10 . FIG.  3 ( b ) shows PCD  10  once electronics module  360  has been seated in right-hand shield  340 . 
     FIG.  3 ( c ) shows a pair of capacitors  265  of the present invention prior to being placed within right-hand shield  340 , the capacitors being connected electrically in series by interconnections in electronics module  340 . FIG.  3 ( d ) shows PCD  10  once the pair of capacitors  265  has been placed within right-hand shield  340 . 
     FIG.  3 ( e ) shows insulator cup  370  prior to its placement atop capacitors  265  in right-hand shield  340 . FIG.  3 ( f ) shows electrochemical cell or battery  380  having insulator  382  disposed therearound prior to battery  380 &#39;s placement in shield  340 . Battery  380  provides the electrical energy required to charge and re-charge capacitors  265 , and also powers electronics module  360 . 
     Battery  380  is most preferably a high-capacity, high-rate, spirally-wound battery of the type disclosed in U.S. Pat. No. 5,439,760 to Howard et al. for “High Reliability Electrochemical Cell and Electrode Assembly Therefor” and U.S. Pat. No. 5,434,017 to Berkowitz et al. for “High Reliability Electrochemical Cell and Electrode Assembly Therefor,” the disclosures of which are hereby incorporated by reference herein in their respective entireties. 
     Battery  380  may less preferably be a battery having spirally-wound, stacked plate or serpentine electrodes of the types disclosed, for example, in U.S. Pat. No. 5,312,458 and U.S. Pat. No. 5,250,373 to Muffoletto et al. for “Internal Electrode and Assembly Method for Electrochemical Cells;” U.S. Pat. No. 5,549,717 to Takeuchi et al. for “Method of making Prismatic Cell;” U.S. Pat. No. 4,964,877 to Kiester et al. for “Non-Aqueous Lithium Battery;” U.S. Pat. No. 5,147,737 to Post et al. for “Electrochemical Cell with Improved Efficiency Serpentine Electrode” and U.S. Pat. No. 5,468,569 to Pyszczek et al. for “Use of Standard Uniform Electrode Components in Cells of Either High or Low Surface Area Design,” the disclosures of which are hereby incorporated by reference herein in their respective entireties. 
     High-rate hybrid cathode cells are particularly suitable for use in conjunction with the capacitor of the present invention. Examples of hybrid cathode batteries and cells having cathodes comprising lithium anodes and cathodes containing mixtures of various types of silver vanadium oxide and (CF x ) n , are disclosed in U.S. Pat. No. 5,114,810 to Frysz et al.; U.S. Pat. No. 5,180,642 to Weiss et al.; U.S. Pat. No. 5,624,767 to Muffoletto et al.; U.S. Pat. No. 5,639,577 to Takeuchi et al., and U.S. Pat. No. 5,667,916 to Ebel et al., all of which patents are hereby incorporated by reference herein in their respective entireties. 
     In preferred embodiments of batteries suitable for use in conjunction with the capacitor of the present invention, it has been discovered that the electrolyte most preferably comprises about 1.0 M LiBF 4 , the anode most preferably comprises lithium metal, the cathode most preferably comprises about 90% by weight active materials (i.e., 90% by weight of a mixture of (CF x ) n  and SVO), about 7% by weight polymer binder and about 3% conductive carbon. 
     The SVO employed in cells and batteries employed to charge and recharge the capacitor of the present invention is most preferably of the type known as “combination silver vanadium oxide” or “CSVO” as disclosed in U.S. Pat. Nos. 5,221,453; 5,439,760 and 5,306,581 and U.S. patent application Ser. No. 08/792,413 filed Feb. 3, 1997 to Crespi et al., hereby incorporated by reference herein, each in its respective entirety. 
     It is to be understood, however, that any type of suitable silver vanadium oxide (or SVO) may be employed in cathodes and cells used to charge and recharge capacitors of the present invention, including, but not limited to, substitute SVO as disclosed by Takeuchi et al. in U.S. Pat. No. 5,472,810 and as disclosed by Leising et al. in U.S. Pat. No. 5,695,892, SVO made by the decomposition method as disclosed by Liang et al. in U.S. Pat. Nos. 4,310,609 and 4,391,729, amorphous SVO as disclosed by Takeuchi et al. in U.S. Pat. No. 5,498,494, SVO prepared by the sol-gel method as disclosed by Takeuchi et al. in U.S. Pat. No. 5,558,680, and SVO prepared by the hydrothermal process. 
     Additionally, it is preferred that batteries used in conjunction with the capacitor of the present invention be cathode limited to permit accurate, reliable prediction of battery end-of-life on the basis of observing voltage discharge curves since the discharge characteristics of cathode-limited cells are relatively uniform. 
     In its more general aspects, the capacitor of the present invention may be employed in conjunction with electrochemical cells in which the anode comprises any active metal above hydrogen in the EMF series, such as an alkali or alkaline earth metal or aluminum. Lithium is a preferred anode material. 
     Cathode materials in electrochemical cells suitable for use in conjunction with the capacitor of the present invention are most preferably solid and comprise as active components thereof metal oxides such as vanadium oxide (V 6 O 13 ), silver vanadium oxide (Ag 2 V 4 O 11 ), or manganese dioxide. Of those cathode materials, thermally treated electrolytic manganese dioxide is most preferred. As mentioned above, the cathode of the electrochemical cell may also comprise carbon monofluoride (CF x ) and hybrids thereof, e.g., CF x +MnO 2 , or any other known active electrolytic components in combination. By “solid” cathodes, we mean pressed porous solid cathodes, as known in the art. Such cathodes are typically made by mixing one or more active components with carbon and poly (tetrafluorethylene) and pressing those components to form a porous solid structure. 
     It is to be understood, however, that battery chemical systems other than those set forth explicitly above may be employed in conjunction with the capacitor of the present invention, including, but not limited to, cathode/anode systems such as: silver oxide/lithium; MnO 2 /lithium; V 2 O 5 /lithium; copper silver vanadium oxide/lithium; copper oxide/lithium; lead oxide/lithium; CF x /lithium; chromium oxide/lithium; bismuth-containing oxides/lithium and lithium ion rechargeable batteries. 
     FIG.  3 ( h ) shows PCD  10  having left-hand shield  350  connected to right-hand shield  340  and feedthrough  390  projecting upwardly from both shield halves. Activity sensor  400  and patient alert apparatus  410  are shown disposed on the side lower portion of left-hand shield  350 . Left-hand shield  350  and right-hand shield  340  are subsequently closed and hermetically sealed (not shown in the Figures). 
     FIG. 4 shows an exploded view of one embodiment of a single anode/cathode sub-assembly  227  capacitor  265  of the present invention. The capacitor design described herein employs a stacked configuration, where anode/cathode sub-assembly  227  comprises alternating substantially rectangularly-shaped anode layers  185  and cathode layers  175 , with substantially rectangularly-shaped separator layers  180  being interposed therebetween. In one preferred embodiment of the present invention, two individual separator layers  180  are disposed between anode sub-assembly  170  and cathode layer  175 . One anode layer  185   a  has anode tab  195   d  attached thereto, more about which we say below. Cathode layer  175   d  most preferably has cathode tab  176  formed integral thereto and projecting from the periphery thereof. 
     The shapes of anode layers  185 , cathode layers  175  and separator layers  180  are primarily a matter of design choice, and are dictated largely by the shape or configuration of case  90  within which those layers are ultimately disposed. In a die apparatus according to one preferred method of the present invention, the punch and cavity of the present invention employed in forming those layers should be configured to produce layers having a desired predetermined shape, such as those shown in FIG. 4. A principal advantage of the capacitor construction of the present invention is that anode layers  185 , cathode layers  175  and separator layers  180  may assume any arbitrary shape to optimize packaging efficiency. 
     Anode layers  185 , cathode layers  175  and separator layers  180  are most preferably formed of materials typically used in high quality aluminum electrolytic capacitors. Individual anode layers  185  are typically somewhat stiff and formed of high-purity aluminum processed by etching to achieve high capacitance per unit area. Cathode layers  175  are preferably high purity and are comparatively flexible. Paper separators  180  are most preferably made slightly larger than cathode layers  175  and anode layers  185  to ensure that a physical barrier is disposed between the anodes and the cathodes of the finished capacitor. 
     In one embodiment of capacitor  265  of the present invention, and as shown in FIGS. 6 and 9, sub-assembly  227   d  shown in FIG. 4 is but one of a plurality of anode/cathode sub-assemblies  227   a  through  227   h  disposed within capacitor  265 . Likewise, a plurality of anode layers  185  and separator layers  180  is most preferably disposed within each sub-assembly, while a single cathode layer  175  is disposed within each sub-assembly  227 . FIG. 4 shows anode sub-assembly  170   d , one of a plurality of anode sub-assemblies disposed in capacitor  265 . Anode sub-assembly  170   d  in FIG. 4 is but one embodiment of anode sub-assembly  170  of the present invention, and is shown therein as most preferably comprising three unnotched anode layers  185 , one notched anode layer  190  and one anode tab  195 . 
     It will be understood by those skilled in the art, however, that the precise number of sub-assemblies  227  selected for use in a given embodiment of the present invention will depend upon the energy density, volume, voltage, current, energy output and other requirements placed upon capacitor  265 . As few as two anode/cathode sub-assemblies  227  and as many as  50  anode/cathode sub-assemblies  227  are included within the scope of the present invention. 
     Similarly, it will be understood by those skilled in the art that the precise number of notched and unnotched anode layers  185 , anode tabs  195 , anode sub-assemblies  170 , cathode layers  175  and separator layers  180  selected for use in a given embodiment of anode/cathode sub-assembly  227  of the present invention will depend upon the energy density, volume, voltage, current, energy output and other requirements placed upon capacitor  265 . 
     It will now become apparent that a virtually unlimited number of combinations and permutations respecting the number of anode/cathode sub-assemblies  227 , and the number of unnotched and notched anode layers  185  forming anode sub-assembly  170 , anode sub-assemblies  170 , anode tabs  195 , cathode layers  175  and separator layers  180  disposed within each anode/cathode sub-assembly  227 , may be selected according to the particular requirements of capacitor  265 , and further that such combinations and permutations fall within the scope of the present invention. 
     Referring to FIG. 4 again, anode sub-assembly  170  most preferably comprises a plurality of non-notched anode layers  185 , notched anode layer  190 , anode tab  195  and anode tab notch  200 . Anode layers  185  and  190  are formed of anode foil  65  (not shown in the Figures). It has been discovered that the anode foil of the present invention is most preferably through-etched, has a high specific capacitance (at least about 0.3, at least about 0.5 or most preferably at least about 0.8 microfarads/cm 2 ), has a dielectric withstand parameter of at least 425 Volts DC, a thickness ranging between about 50 and about 200 micrometers, more preferably between about 75 and 150 micrometers, more preferably yet between about 90 and about 125 micrometers, and most preferably 2 being about 100 micrometers thick, and a cleanliness of about 1.0 mg/m 2  respecting projected area maximum chloride contamination. 
     Thin anode foils are preferred in the present invention, especially if they substantially maintain or increase specific capacitance while reducing the thickness of electrode assembly  225 , or maintain the thickness of electrode assembly  225  while increasing overall capacitance. For example, it is contemplated in the present invention that individual anode layers  185  have a thickness of about 10 micrometers, about 20 micrometers, about 30 micrometers, about 40 micrometers, about 50 micrometers, about 60 micrometers, about 70 micrometers, about 80 micrometers, about 90 micrometers, about 100 micrometers, about 110 micrometers, about 120 micrometers, about 130 micrometers, about 140 micrometers and about 150 micrometers. 
     In one preferred embodiment of the present invention, anode foil  65  has a rated surge voltage of 390 Volts, an initial purity of about 99.99% aluminum, a final thickness of about 104 micrometers, plus or minus about five micrometers, and a specific capacitance of about 0.8 microfarads per square centimeter. Suitable anode foils for practicing the present invention are commercially available on a widespread basis. 
     Cathode layers  175  are most preferably formed from cathode foil  70  (not shown in the Figures). Some preferred parameters of cathode foil have been discovered to include high surface area (i.e., highly etched cathode foil), high specific capacitance (preferably at least 200 microfarads/cm 2 , and at least 250 microfarads/cm 2  when fresh), a thickness of about 30 micrometers, a cleanliness of about 1.0 mg/m 2  respecting projected area maximum chloride contamination, and a purity which may be less than corresponding to the starting foil material from which anode foil  65  is made. 
     In one preferred embodiment of the present invention, cathode foil  70  has an initial purity of at least 99% aluminum, and more preferably yet of about 99.4% aluminum, a final thickness of about 30 micrometers, and an initial specific capacitance of about 250 microfarads per square centimeter. 
     In other embodiments of the present invention, cathode foil  70  has a specific capacitance ranging between about 100 and about 500 microfarads/cm 2 , about 200 and about 400 microfarads/cm 2 , or about 250 and about 350 microfarads/cm 2 , a thickness ranging between about 10 and about 150 micrometers, about 15 and about 100 micrometers, about 20 and about 50 micrometers, or about 25 and about 40 micrometers. 
     It is generally preferred that the specific capacitance of cathode foil  70  be as high as possible, and that cathode layer  175  be as thin as possible. For example, it is contemplated in the present invention that individual cathode layers  175  have specific capacitances of about 100 microfarads/cm 2 , about 200 microfarads/cm 2 , about 300 microfarads/cm 2 , about 400 microfarads/cm 2 , about 500 microfarads/cm 2 , about 600 microfarads/cm 2 , about 700 microfarads/cm 2 , about 800 microfarads/cm 2 , about 900 microfarads/cm 2 , or about 1,000 microfarads/cm 2 . Suitable cathode foils for practicing the present invention are commercially available on a widespread basis. 
     In still other embodiments of the present invention, cathode foil  70  is formed of materials or metals in addition to aluminum, aluminum alloys and “pure” aluminum. 
     Separator layers  180  are most preferably made from a roll or sheet of separator material  75 . In one preferred embodiment, separator material  75  is a pure cellulose, very low halide or chloride content Kraft paper having a thickness of about 0.0005 inches, a density of about 1.06 grams/cm 3 , a dielectric strength of 1,400 ac Volts per 0.001 inches thickness, and a low number of conducting paths (about 0.4/ft 2  or less). Separator layers  180  are preferably cut slightly larger than anode layers  170  and cathode layers  175  to accommodate misalignment during the stacking of layers and to prevent subsequent shorting between electrodes of opposite polarity. 
     It is preferred that separator layers  180  be formed of a material that: (a) is chemically inert; (b) is chemically compatible with the selected electrolyte; (c) may be impregnated with the electrolyte to produce a low resistance path between adjoining anode and cathode layers, and (d) physically separates adjoining anode and cathode layers. Separator layers  180  may also be formed of materials other than Kraft paper, such as Manila paper, porous polymeric materials or fabric gauze materials. For example, porous polymeric materials may be disposed between anode and cathode layers of like those disclosed in U.S. Pat. Nos. 3,555,369 and 3,883,784 in some embodiments of the present invention. 
     In a preferred embodiment of the present invention, a liquid electrolyte saturates or wets separator layers  180  and is disposed within case  90 . It is to be understood, however, that various embodiments of the present invention include within their scope a solid or adhesive electrolyte such as those disclosed in U.S. Pat. Nos. 5,628,801; 5,584,890; 4,942,501 and its continuations, U.S. Pat. Nos. 5,146,391 and 5,153,820. Note that in some embodiments of the present invention, an appropriate inter-electrode adhesives/electrolyte layer may be employed in place of paper, gauze or porous polymeric materials to form separator layer  180 . 
     It will also be understood by those skilled in the art that there exist many different types and methods for making anode  65 , cathode foil  70  and separator material  75 . What we disclose herein, therefore, are only preferred materials, methods and apparatus for making a preferred embodiment of capacitor  265  of the present invention, and its various components, and not all the materials, methods and apparatus suitable for practicing the present invention and falling within the scope thereof. 
     Continuing to refer to FIG. 4, a first preferred step in assembling a flat aluminum electrolytic capacitor is to cut anode layers  185  and  190 , anode tabs  195 , cathode layers  175  and separator layers  180 . Those components are most preferably cut to shape using dies having low wall-to-wall clearance, where inter-wall spacing between the substantially vertically-oriented corresponding walls of the punch and die is most preferably on the order of about 6 millionths of an inch per side. Larger or smaller inter-wall spacings between the substantially vertically-oriented corresponding walls of the punch and cavity, such as about 2, about 4, about 5, about 7, about 8, about 10 and about 12 millionths of an inch may also be employed in the present invention but are less preferred. 
     Such low clearance results in smooth, burr free edges being formed along the peripheries of anode layers  185  and  190 , anode tabs  195 , cathode layers  175  and separator layers  180 . Smooth, burr free edges on the walls of the dies have been discovered to be critical respecting reliable performance of a capacitor. 
     The presence of burrs along the peripheries of anode layers  185  and  190 , anode tabs  195 , cathode layers  175  and separator layers  180  may result in short circuit and failure of the capacitor. The means by which anode foil, cathode foil and separator materials are cut or formed in the present invention may have a significant impact on the lack or presence of burrs and other cutting debris disposed about the peripheries of the formed or cut members. We have found that the use of low clearance dies produces an edge superior to that of other cutting methods, such as steel rule dies. The shape, flexibility and speed of a low clearance die has been discovered to be superior to that of laser or blade cutting. 
     Other methods of cutting or forming anode layers  185  and  190 , anode tabs  195 , cathode layers  175  and separator layers  180  falling within the scope of the present invention include, but are not limited to, steel rule die cutting, laser cutting, water jet cutting and blade cutting. 
     The preferred low clearance of the die apparatus of the present invention is especially important for cutting thin ductile materials such as cathode foil  70 . In addition to improving reliability, burr and debris reduction permits reductions in the thickness of separator layer  180 , thereby improving energy density of the capacitor. Angle cutting, where the face of the punch is not held parallel to the opposing floor of the die during the cutting step, is another less preferred method of cutting or forming anode layers  185  and  190 , anode tabs  195 , cathode layers  175  and separator layers  180  of the present invention. 
     It is preferred in the present invention to cut or otherwise form separator layer  180  such that its outer periphery conforms closely to that of the corresponding sidewalls of the interior of case  90 . In preferred embodiments of the present invention, the periphery of separator layer is disposed within plus or minus 0.009 inches of the corresponding sidewalls of case  90 . Such close conformity between the periphery of separator layer  180  and the corresponding internal sidewalls of case  90  has been discovered to provide the advantage of permitting separator layers  180  to immobilize or secure firmly in place electrode assembly  225  in case  90 . This immobilization occurs because the separator paper forming separator layers  180  swells after electrolyte is added through fill port ferrule  105  into otherwise assembled and sealed capacitor  265 . 
     In a preferred method of the present invention, foil or separator materials are drawn between the punch and cavity portions of a die having appropriate clearances on a roll. An air or hydraulically actuated press is then most preferably employed to actuate the punch or cavity portion of the die. The punch portion of the die is most preferably formed of hardened tool steel, or has other suitable wear resistant materials or coatings disposed on the cutting surfaces thereof. When the cavity of the die is aligned vertically, the punch portion of the die may travel either upwards or downwards towards the die cavity during a cutting cycle. In the former case, components are cut and drop downwardly into a container for use in subsequent assembly operations. In the latter case, components are cut and may be presented directly to automated assembly equipment, such as robots equipped with vacuum or other pick-up tooling, for subsequent processing. Low clearance dies of the type described herein may be supplied by Top Tool, Inc. of Minneapolis, Minn. 
     Anode sub-assembly  170  most preferably includes one notched anode layer  190 , which facilitates appropriate placement and positioning of anode tab  195  within anode sub-assembly  170 . More than one notched anode layer  190  may also be included in anode sub-assembly  170 . It is preferred that the remaining anode layers of anode sub-assembly  170  be non-notched anode layers  185 . Anode tab  195  is most preferably formed of aluminum strip material. In one preferred embodiment of the present invention, aluminum strip  80  has a purity of about 99.99% aluminum and a lesser degree of anodization than anode foil  65 . When anode tab  195  is formed of a non-anodized material, cold welding of anode tab  195  to non-notched anode layers  185  may be accomplished with less force and deflection, more about which we say below. It is preferred that the thickness of anode tab  195  be about equal to that of notched anode layer  190 . If more than one notched anode layer  190  is employed in anode sub-assembly  170 , a thicker anode tab  195  may be employed. 
     FIG. 13 shows a flow chart that describes generally one method, from beginning to end, of making flat aluminum electrolytic capacitor  265  of the present invention. FIGS. 14 through 20, on the other hand, show specific portions of the method or process described generally in FIG.  13 . 
     FIG. 14 shows a flow chart of one method of the present invention for making anode layer  170  of the present invention. In FIG. 14, non-notched anode layers  185 , notched anode layer  190  and anode tab  195  are provided and assembled within cold welder  202  to form anode sub-assembly  170 . 
     Referring now to FIGS.  5 ( a ) through  5 ( c ), two non-notched anode layers  185   a  and  185   b  are placed on cold welding fixture base layer  207  of cold welding apparatus  202 . The various structural members of cold welding apparatus  202  are most preferably formed of precision machined stainless steel or a high strength aluminum alloy. Layers  185   a  and  185   b  are next aligned and positioned appropriately on cold welding fixture base layer  207  using spring loaded alignment pins  209   a  through  209   e . Pins  209   a  through  209   e  retract upon top layer  208  being pressed downwardly upon layers  185   a  and  185   b  disposed within cold welding cavity  220 . See also FIG.  5 ( c ), where a cross-sectional view of cold welding apparatus  202  is shown. 
     Anode layer  190  is similarly disposed within cavity  220 , followed by placing anode tab  195  within anode tab notch  200  in notched anode layer  190 . Anode tab  195  is most preferably positioned along the periphery of notched anode layer  190  with the aid of additional spring loaded alignment pins  209   f  and  209   g  disposed along the periphery of anode tab  195 . Non-notched anode layer  185   c  is then placed atop anode layer  190 . Stacked anode sub-assembly  170  is then clamped between top plate  208  and base plate  207 . Disposed within base plate  207  are anode layer cold welding pins  206   a  and anode tab cold welding pin  211   a . Disposed within top plate  208  are anode layer cold welding pin  206   b  and anode tab cold welding pin  211   b . Base plate  207  and top plate  208  are aligned such that the axes of cold welding pins  206   a  and  206   b  coincide with and are aligned respecting corresponding cold welding pins  211   a  and  211   b.    
     Upper actuation apparatus  214  of cold welding apparatus  202  displaces cold welding pins  206   b  and  211   b  downwardly. Lower actuation apparatus  215  displaces cold welding pins  206   a  and  211   a  upwardly. In one embodiment of upper actuation apparatus  214  and lower actuation apparatus  215  of the present invention, pneumatic cylinders are employed to move pins  206   a ,  206   b ,  211   a  and  211   b . In another embodiment of apparatus  214  and apparatus  215  of the present invention, a pair of rolling wheels is provided that move simultaneously and perpendicularly to the axes of pins  206   a ,  206   b ,  211   a , and  211   b . Still other embodiments of apparatus  214  and apparatus  215  of the present invention may employ hydraulic actuators, cantilever beams, dead weights, springs, servomotors electromechanical solenoids, and the like for moving pins  206   a ,  206   b ,  211   a  and  21   b . Control of actuation apparatus  214  and apparatus  215  respecting pin displacement force magnitude and timing may be accomplished using any one or combination of constant load, constant displacement, solenoid controller, direct or indirect means. 
     Following clamping with top plate  208 , cold welding pins  206   a ,  206   b ,  211   a  and  211   b  are actuated. Cold welds  205  and  210  in anode sub-assembly  170  are formed by compression forces generated when cold weld pins  206   a ,  206   b ,  211   a  and  211   b  are compressed thereagainst. See FIG.  6 ( a ), where the preferred regions in which cold welds  205  and  210  are formed are shown. Cold welds  205  and  210  may be described as not only cold welds, but forged welds. This is because the interfacial boundaries between anode layers  185  are deformed in the region of welds  205  and  210 , thereby disrupting oxide layers and bringing base metals into direct contact with one another where metallic bonding occurs. Metallic bonding increases the strength of the welds. 
     In one embodiment of the method of the present invention, a plurality of pneumatic cylinders function simultaneously in upper actuation apparatus  214  and lower actuation apparatus  215  to drive pins  206   a ,  206   b ,  211   a  and  211   b  against anode sub-assembly  170 . Anode layer cold weld  205  and anode tab cold weld  210  are most preferably formed under direct constant load conditions, where pneumatic cylinders are pressurized to a predetermined fixed pressure. Anode layer cold weld  205  and anode tab cold weld  210  may also be formed under indirect constant displacement conditions, where pneumatic cylinders are pressurized until a displacement sensor placed across cold welding pins  206   a ,  206   b ,  211   a  or  211   b  generates a signal having a predetermined value, whereupon those pins are disengaged from sub-assembly  227 . 
     In another embodiment of the method of the present invention, a cantilever beam mechanism is incorporated into upper actuation apparatus  214  and lower actuation apparatus  215 . Anode layer cold weld  205  and anode tab cold weld  210  are formed under direct constant displacement conditions, where cantilever beams are actuated and cause upper and lower members  208  and  207  to engage sub-assembly  227  until a hard stop point is reached. An indirect load controlled system may also be employed in apparatus  214  and apparatus  215 , where cantilever or other means include a load measuring sensor for controlling the stop point of the cantilever beam, for example, when a predetermined load is measured by the sensor. 
     The cross-sectional shape of cold weld pins  206   a ,  206   b ,  211   a  and  211   b  may be square, circular, oval or any other suitable shape. The shape of the ends of cold weld pins  206   a ,  206   b ,  211   a  and  211   b  may be flat, rounded, domed or any other suitable shape appropriate for selectively controlling the properties of the cold welds produced therein. Likewise, more or fewer than four cold weld pins may be employed in the present invention. The ends of cold weld pins  206   a ,  206   b ,  211   a  and  211   b  are most preferably rounded or domed and circular in cross-section. In a preferred embodiment of the present invention, cold weld pins  206   a ,  206   b ,  211   a  and  211   b  have a diameter of about 0.060″ and further have a beveled or radiused end. Cold weld pins  206   a ,  206   b ,  211   a  and  211   b  are preferably made from a high strength material that does not readily deform under the pressures obtained during welding, such as stainless steel, titanium, tool steel or HSLA steel. The ends or sidewalls of cold welding pins  206   a ,  206   b ,  211   a  and  211   b  may be coated, cladded or otherwise modified to increase wear resistance, deformation resistance or other desirable tribilogical attributes of the pins. 
     The primary function of cold welds  205  and  210  is to provide electrical interconnections between layers  185   a ,  185   b ,  185   c  and  190  and anode tab  195 , while minimizing the overall thickness of anode sub-assembly  170  in the regions of welds  205  and  210 . We have discovered that typical prior art commercial cylindrical capacitors exhibit a significant increase in the thickness of the anode layer in the regions of the cold welds. This increase in thickness is typically on the order of about two times the thickness of the tab, or about 0.008 inches. In the case of cylindrical capacitors where only one or two non-coincident tab connections are present, the overall effect on anode layer thickness may be minimal. In a stacked layer design having many more interconnections and welds, however, increases in weld zone thickness have been found to significantly increase the overall thickness of the anode layer and the capacitor. 
     In one method and corresponding apparatus of the present invention, no or an inappreciable net increase in anode sub-assembly  170  thickness results when cold weld geometries and formation processes are appropriately optimized. Several embodiments of anode-assembly  170  have been found to have no more than about a 20% increase in layer thickness due to the presence of cold welds, as compared to about a 200% increase in thickness resulting from cold welds found in some commercial cylindrical capacitors. In the present invention, two, three, four, five, six or more anode layers  185  and  190  may be cold-welded to form anode sub-assembly  170 . 
     FIG.  6 ( b ) shows a cross-sectional view of a portion of one embodiment of a cold-welded anode assembly of the present invention. Anode layers  185   a ,  190 ,  185   b  and  185   c  are cold-welded together at weld  205  through the compressive action of pins  206   a  and  206   b  mounted in bottom plate  207  and top plate  208 , respectively. Pins  206   a  and  206   b  form central depressions  293  and  294 , respectively, in anode sub-assembly  170   d , and further result in the formation of rims  295  and  296 , respectively. Rims  295  and  296  project downwardly and upwardly, respectively, from the surrounding surfaces of anode subassembly  170   d , thereby increasing the overall thickness T of anode subassembly  170   d  by ΔT in respect of the non-cold-welded surrounding regions or portions thereof. 
     FIG.  6 ( c ) shows a cross-sectional view of another portion of one embodiment of a cold-welded anode assembly of the present invention. Anode layers  185   a ,  185   b ,  185   c  and tab  195   d  are cold-welded together at weld  210  through the compressive action of pins  211   a  and  211   b  mounted in bottom plate  207  and top plate  208 , respectively. Pins  211   a  and  211   b  form central depressions  297  and  298 , respectively, in anode sub-assembly  170   d , and further result in the formation of rims  299  and  301 , respectively. Rims  299  and  301  project downwardly and upwardly, respectively, from the surface of anode subassembly  170   d , thereby increasing overall thickness T of anode subassembly  170   d  by ΔT in respect of the non-cold-welded regions thereof. 
     Anode subassembly  170   d  has a thickness defined by the equation: 
     
       
         T=nt  
       
     
     where T is the overall thickness of anode subassembly  170   d  in non-cold- welded regions, n is the number of anode layers  185  and/or  190  in anode subassembly  170   d , and t is the thickness of individual anode layers  185  and/or  190  or anode tab  195 . The maximum overall thickness of anode subassembly  170   d  in the region of cold welds  205  or  210  is then defined by the equation: 
     
       
         
           T+ΔT=nt+ΔT  
         
       
     
     We have discovered that it is highly desirable to form anode subassembly such that the ratio ΔT/T is less than or equal to 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 or 0.50. The lower the value of the ratio ΔT/T, the greater the volumetric efficiency of capacitor 265. Additionally, the overall thickness of capacitor  265  may be reduced when the value of the ratio ΔT/T is made smaller. 
     Referring now to FIG.  6 ( a ), we have further discovered that the overall thickness of electrode assembly  225  may be reduced further by staggering or offsetting horizontally the respective vertical locations of tabs  195   a  through  195   h  (and corresponding cold welds  210 ). In this embodiment of the present invention, tabs  195   a    195   b , for example, are not aligned vertically in respect of one another. Such staggering or offsetting of tabs  195  permits the increases in thickness ΔT corresponding to each of anode subassemblies  170   a  through  170   h  to be spread out horizontally over the perimeter or other portion of electrode assembly  225  such that increases in thickness ΔT do not accumulate or add constructively, thereby decreasing the overall thickness of electrode assembly  225 . Cold welds  205  may similarly be staggered or offset horizontally respecting one another and cold weld  210  to achieve a reduction in overall thickness of electrode assembly  225 . 
     In another embodiment of the present invention, anode sub-assembly  170  comprises a plurality of three, four, five or more anode layers  185  and  190 , each sub-assembly most preferably having at least one anode layer having a corresponding anode tab  195  attached thereto or forming a portion thereof, the layers being cold welded together to form anode sub-assembly  170 . For example, an anode sub-assembly  170  may comprise six anode layers  185  constructed by cold-welding two separate triple anode layers  185  that were previously and separately cold-welded or otherwise joined together. Alternatively, anode sub-assembly  170  layer may comprise seven anode layers constructed by cold-welding together one triple anode layer  185  and one quadruple anode layer  185  that were previously and separately cold-welded or otherwise joined together. In another embodiment of the present invention, multiple notched anode layers  190  may employed in anode sub-assembly  170 , thereby permitting the use of a thicker anode tab material  70 . 
     The geometry of base plate  207  and top plate  208  in the regions surrounding cold welding pins  206   a ,  206   b ,  211   a  and  211   b  has been discovered to affect the properties of cold welds  205  and  210 . In a preferred method of the present invention, the mating surfaces of plates  207  and  208  surfaces have no radiused break formed in the perimeters of the pin holes. We have found that the presence of radiused breaks or chamfers in those regions may cause undesired deformation of cold welds  205  and  210  therein. Such deformation may result in an increase in the thickness of anode sub-assembly  170 , which may translate directly into an increase in the thickness of capacitor  265 . Note further that the increase in thickness so resulting is a multiple of the number of anode sub-assemblies  170  present in electrode assembly  225 . In less preferred methods of the present invention radiused breaks or chamfers may be employed in the region of the pin holes in base plate  207  and top plate  208 , but appropriate capacitor design accommodations are most preferably made, such as staggering the positions of adjoining stacked cold welds. 
     As shown in FIG. 14, once cold welding pins  206   a ,  206   b ,  211   a  and  211   b  have been actuated against anode sub-assembly  170 , top plate  208  is removed and cold-welded anode sub-assembly  170  is provided for further stacking of electrode subassembly  227 . FIG. 15 shows a flow chart corresponding to one preferred method for making electrode assembly  225  of the present invention. See also FIG.  6 ( a ), where an exploded top perspective view of one embodiment of an electrode assembly  225  of capacitor  265  of the present invention is shown. As illustrated in FIGS. 4,  6 ( a ) and  15 , electrode assembly  225  most preferably comprises a plurality of cold-welded anode sub-assemblies  175   a  through  175   h , a plurality of cathode layers  175   a  through  175   l , a plurality of separator layers  180 , outer separator layers  165   a  and  165   b , outer wrap  115  and wrapping tape  245 . 
     Outer wrap  115  is most preferably die cut from separator material  75  described supra, but may be formed from a wide range of other suitable materials such as polymeric materials, aluminum, suitable heat shrink materials, suitable rubberized materials and synthetic equivalents or derivatives thereof, and the like. 
     Wrapping tape  245  is most preferably cut from a polypropylene-backed acrylic adhesive tape, but may also be replaced by a staple, an ultrasonic paper joint or weld, suitable adhesives other than acrylic adhesive, suitable tape other than polypropylene-backed tape, a hook and corresponding clasp and so on. 
     Outer wrap  115  and wrapping tape  245  together comprise an electrode assembly wrap which has been discovered to help prevent undesired movement or shifting of electrode assembly  225  during subsequent processing. It will now become apparent to one skilled in the art that many means other than those disclosed explicitly herein exist for immobilizing and securing electrode assembly  225  during subsequent processing which accomplish substantially the same function as the electrode assembly wrap comprising outer wrap  115  and wrapping tape  245 . Alternative means for immobilizing and securing electrode assembly  225  other than those described hereinabove exist. Such alternative means include, but are not limited to, robotic or other mechanical clamping and securing means not necessarily forming a portion of electrode assembly  225 , adhesive electrolytes for forming separator layers  180 , and so on. 
     The stacking process by which electrode assembly  225  is most preferably made begins by placing outer wrap  115  into a stacking fixture followed by placing outer paper or separator layer  165   a  thereon. Next, cathode layer  175   a  is placed atop separator layer  165   a , followed by separator layers  180   a  and  180   b  being disposed thereon. Cold-welded anode sub-assembly  170   a  is then placed atop separator layer  180   b , followed by placing separator layers  180   a  and  180   b  thereon, and so on. The placement of alternating cathode layers  175  and anode layers  170  with separator layers  180   a  and  180   b  interposed therebetween continues in the stacking fixture until final cathode layer  175   h  has been placed thereon. 
     In the embodiment of electrode assembly  225  shown in FIG.  6 ( a ), eight anode sub-assemblies (anode sub-assemblies  170   a  through  170   h ) and nine cathode layers (cathode layers  175   a  through  175   i ) are illustrated. The voltage developed across each combined anode sub-assembly/separator layer/cathode layer assembly disposed within electrode assembly  225  most preferably ranges between about 360 and about 390 Volts DC. As described below, the various anode sub-assemblies of electrode assembly  225  are typically connected in parallel electrically, as are the various cathode layers of electrode assembly  225 . 
     Consistent with the discussion hereinabove concerning FIG. 4, it will now be understood by one skilled in the art that electrode assembly  225  shown in FIG.  6 ( a ) is merely illustrative, and does not limit the scope of the present invention in any way respecting the number or combination of anode sub-assemblies  170 , cathode layers  175 , separator layers  180 , anode tabs  195 , cathode tabs  176 , and so on. The number of electrode components is instead determined according to the total capacitance required, the total area of each layer, the specific capacitance of the foil employed and other factors. 
     In another embodiment of electrode assembly  225  of the present invention, the number of anode layers  185  employed in each anode sub-assembly  170  is varied in the stack. Such a design permits the fabrication of capacitors having the same layer area but nearly continuously varying different and selectable total capacitances that a user may determine by increasing or decreasing the number of anode layers  180  included in selected anode sub-assemblies  170  (as opposed to adding or subtracting full anode/cathode sub-assemblies  227  from electrode assembly  225  to thereby change the total capacitance). Following placement of cathode layer  175   l  in the stack, outer paper layer  165   b  is placed thereon, and outer wrap  115  is folded over the top of electrode assembly  225 . Wrapping tape  245  is then holds outer wrap  115  in place and secures the various components of electrode assembly  225  together. 
     The physical dimensions of separator layers  165  and  180  are most preferably somewhat larger than those of anode sub-assemblies  170  and cathode layers  175  to prevent contact of the electrodes with the case wall or electrical shorting between opposing polarity electrode layers due to the presence of burrs, stray or particulate material, debris or imperfections occurring therein. The reliability and functionality of capacitor  265  are compromised if a portion of anode sub-assembly  170  comes into contact with a conducting case wall, if a burr on the periphery of anode sub-assembly  170  or cathode layer  175  comes into contact with an adjoining layer of opposing polarity, or if separator layer  180   a  or  180   b  does not provide sufficient electrical insulation between adjoining opposite-polarity electrode layers and conducting particulate matter bridges the gap therebetween. 
     The additional separator material most preferably disposed about the periphery of electrode assembly  225  is referred to herein as separator overhang. Decreasing the amount of separator overhang increases the energy density of capacitor  265 . It is beneficial from an energy density optimization perspective, therefore, to decrease the amount or degree of separator overhang. The amount of separator overhang required has been discovered to be primarily a function of the stack-up tolerance characteristic of the stacking method employed. 
     In commercial cylindrical capacitors, we discovered that the amount of separator overhang is typically on the order of 0.050″ to 0.100″. Fayram et al. in the foregoing &#39;851 patent describe a flat aluminum electrolytic capacitor wherein the housing of the capacitor has at least two internal alignment members. Those alignment members necessarily add volume to the capacitor while taking away from the total amount of “active” electrode material available, thereby decreasing the energy density of the capacitor. 
     We discovered a method of the present invention for assuring consistent registration of separator layers  165  and  180 , anode sub-assemblies  170  and cathode layers  175  in electrode assembly  225 : stacking the various elements of electrode assembly  225  using robotic assembly techniques. More particularly, the various electrode and separator layers of electrode assembly  225  are stacked and aligned using an assembly workcell comprising four Seiko 4-axis SCARA Model No. TT8800 and TT8500, or equivalent, to pick up and place the various electrode and separator elements in an appropriate stacking fixture. Other suitable methods of the present invention for stacking and registering electrode and separator layers include cam driven walking beam assembly machine techniques, rotary table machine techniques, multiple station single stacking machine techniques, and the like. 
     In a preferred method of the present invention, a pre-formed or cut separator, electrode layer or sub-assembly is presented to a robot arm, which then picks the part up with end-of-arm tooling. A Venturi system produces a vacuum in the end-of-arm tooling. The system creates a vacuum at an appropriate time such that the part is sucked up onto the end-of-arm tooling. The vacuum is next released when the part is placed in the stacking fixture. A direct vacuum system, such as rubber suction cups, or other contact or non-contact pick up robotic or manual assembly methods may also be employed in accordance with other methods of the present invention. The position of the part is robotically translated from the pickup point into the stacking fixture by the robot arm with an accuracy of 5 thousands of an inch or less. After placing the part in the stacking fixture, part alignment is most preferably verified electronically with a SEIKO COGNEX 5400 VISION System, or equivalent, in combination with a SONY XC-75 camera, or equivalent. The camera is mounted on the robot arm to permit the accuracy of part placement to be verified. This system can accurately determine the position of each part or element in electrode assembly  225  to within 0.01 millimeters. Once all layers have been placed in the stacking fixture by the robot arm, the stack is presented for wrapping. 
     The foregoing methods of the present invention permit precise alignment and stacking of separator layers  165  and  180 , anode sub-assemblies  170  and cathode layers  175  in electrode assembly  225 , while minimizing the addition of undesirable unused volume to capacitor  265 . 
     We discovered another method for assuring registration of separator layers  165  and  180 , anode sub-assembly  170  and cathode layer  175  in electrode assembly  225 , wherein alignment elements disposed within the stacking fixture are employed in a manual process which utilizes fixture registration points. In such a method, the stacking fixture has several alignment elements such as posts or sidewalls disposed about its periphery for positioning separator layers  165  and  180 . Because cathode layers  175  and anode sub-assemblies  170  do not extend to the periphery of the separator, an alternative means for accurately positioning those electrodes becomes necessary. 
     Positioning of alternating cathode layers  175  and anode sub-assemblies  170  is most preferably accomplished using alignment elements such as posts or sidewalls disposed about the periphery of cathode tab  176  and anode tab  195 . It has been discovered that the accuracy of layer placement and positioning is primarily a function of the length of the electrode tabs. The longer the tab, the less significant the alignment error becomes. Electrode tab length must typically be balanced against the loss of electrode material which occurs during die cutting, which in turn results primarily due to the longer length of cathode tab  176  in respect of the length of anode tab  195 . Tabs  176  and  195  may include or contain alignment features therein having any suitable geometry for facilitating registration and positioning in respect of alignment elements. Any additional tab length utilized for registration of the electrode layers is most preferably trimmed from electrode assembly  225  during the process of electrode tab interconnection (more about which we say below). 
     Another method of the present invention for ensuring registration of separator layers  165  and  180 , anode sub-assembly  170  and cathode layer  175  in electrode assembly  225  which does not require the use of internal alignment elements within capacitor  265  is enveloping or covering anode sub-assembly  170  and cathode layer  175  with separator material. In this method of the present invention, separator layers  180   a  and  180   b  are combined into a single die cut piece part that is folded around either anode sub-assembly  170  or cathode layer  175 . The free edges of the separator are then secured by doubled-sided transfer tape, another adhesive, stitching or ultrasonic paper welding. Construction of an electrode subassembly in this manner secures and registers anode sub-assembly  170  and cathode layer  175  in respect of the periphery of the separator envelope so formed. The resulting electrode subassembly  227  is then presented for stacking in electrode assembly  225 . 
     Yet another method of the present invention we have found for securing the separator to anode sub-assembly  170  is through the use of pressure bonding techniques. In such a method, separator layer  165  or  180  is pressed into a surface of anode sub-assembly  170  or anode layer  185  over a localized region thereof with sufficient force to rigidly affix the separator paper to anode sub-assembly  170 , but not with such great force that a portion of underlying anode sub-assembly  170  is fractured. Other methods of securing all or portions of separator layer  165  or  180  to anode sub-assembly  170  or anode layer  185  include, but are not limited to, stitching, adhesive bonding and ultrasonic paper welding techniques. 
     FIG. 7 shows a top perspective view of one embodiment of an electrode assembly of a capacitor of the present invention. FIG. 8 shows an enlarged view of a portion of the electrode assembly of FIG.  7 . After wrapping electrode assembly  225  with outer wrap  115  and wrapping tape  245 , interconnection of anode tabs  232  and cathode tabs  233  with their respective external terminals is most preferably made. 
     FIG. 9 shows an exploded top perspective view of one embodiment of a capacitor of the present invention employing the electrode assembly of FIGS. 6,  7  and  8  therein. This embodiment of the present invention includes anode feedthrough  120  and cathode feedthrough  125  most preferably having coiled basal portions  121  and  126 , respectively. Feedthroughs  120  and  125  provide electrical feedthrough terminals for capacitor  265  and gather anode tabs  232  and cathode tabs  233  within basal portions  121  and  126  for electrical and mechanical interconnection. 
     FIG. 16 shows a flow chart corresponding to one method of making tab interconnections and feedthrough terminal connections of the present invention. In such a method, feedthrough wire is first provided for construction of feedthroughs  120  and  125 , as shown in FIGS. 9 and 10. In one embodiment of the present invention, a preferred feedthrough wire is aluminum having a purity greater than or equal to 99.99% and a diameter of 0.020 inches. Wire is trimmed to predetermined lengths for use in anode feedthrough  120  or cathode feedthrough  125 . One end of the trimmed wire is coiled such that its inside diameter or dimension is slightly larger than the diameter or dimension required to encircle gathered anode tabs  232  or gathered cathode tabs  233 . 
     Anode tabs  232  are next gathered, or brought together in a bundle by crimping, and inside diameter  131  of anode feedthrough coil assembly  120  is placed over anode tabs  232  such that anode feedthrough pin  130  extends outwardly away from the base of anode tabs  232 . Similarly, cathode tabs  233  are gathered and inside diameter  136  of cathode feedthrough coil assembly  125  is placed over cathode tabs  233  such that cathode feedthrough pin  135  extends outwardly away from the base of cathode tab  233 . Coiled basal portions  121  and  126  of anode and cathode feedthroughs  120  and  125  are then most preferably crimped onto anode and cathode tabs  232  and  233 , followed by trimming the distal ends thereof, most preferably such that the crimps so formed are oriented substantially perpendicular to imaginary axes  234  and  235  of tabs  232  and  233 . Trimming the distal ends may also, but less preferably, be accomplished at other non-perpendicular angles respecting imaginary axes  234  and  235 . 
     In some methods of the present invention, a crimping force is applied to feedthrough coils  130  and  135  and tabs  232  and  233  throughout a subsequent preferred welding step. In one method of the present invention, it is preferred that the crimped anode and cathode feedthroughs be laser or ultrasonically welded along the top portion of the trimmed edge of the distal ends to anode and cathode tabs  232  and  233 . 
     Following welding of feedthroughs  120  and  125  to anode tabs  232  and cathode tabs  233 , respectively, pins  130  and  135  are bent to insertion through feedthrough holes  142  and  143  of case  90 . 
     Many different embodiments of the feedthroughs, and means for connecting the feedthroughs, of the present invention to anode and cathode tabs exist other than those shown explicitly in the Figures. For example, feedthroughs of the present invention include within their scope embodiments comprising basal portions having open sides, forming “U” or “T” shapes in cross-section, forming a coil having a single turn of wire, forming a coil having three or more turns of wire, formed from flattened wire, or basal portions formed from crimping sleeves or layers of metal for connecting feedthrough pins  130  and  135  to anode and cathode tabs  232  and  233 . 
     FIG. 17 shows a flow chart corresponding to one method of the present invention for making tab interconnections and feedthrough connections. In this method, anode feedthrough  120  and cathode feedthrough  125  have no coiled portions. Anode tabs  232  and cathode tabs  233  are gathered and trimmed, followed by the basal portions of anode and cathode feedthroughs  120  and  125  being placed propinquant to anode tabs  232  and cathode tabs  233 , respectively. The basal portions of feedthroughs  120  and  125  are then joined to anode tabs  232  and cathode tabs  233 , respectively, most preferably by ultrasonic welding means. 
     In yet another method of the present invention, the basal portions of feedthroughs  120  and  125  are flattened to facilitate welding to anode and cathode tabs  232  and  233 . In still another method of the present invention, the basal portions of feedthrough pins  130  and  135  are formed such that they engage anode tabs  232  or cathode tabs  233  around the periphery of the tabs by means other than coiling. For example, basal portions  121  and  126  of feedthroughs  120  and  125  may be “flag shaped,” and the flag portions thereof may be wrapped around tabs  232  and  233 . In yet other methods of the present invention, feedthrough pins  130  and  135  may be attached to anode and cathode tabs  232  and  233  with resistance welds, cold welds, brazing, friction welds, or an additional feedthrough component such as a crimping sleeve may capture and join tabs  232  and  233  for providing electrical and mechanical connections thereto. 
     It has been discovered that the processes of forming electrical connections between tabs  232  and  233  and feedthrough coil assemblies  120  and  125  can introduce undesirable stress on tabs  176  and  195 . The resultant strain induced in those tabs has further been found to manifest itself as tears in cathode layer  175  at the base of cathode tab  176 , or as fractures in relatively low strength cold welds  205  or  210  within anode sub-assembly  170 . One advantage of the coiled portions of feedthroughs  120  and  125  is that they can provide strain relief between feedthrough pins  130  and  135  and tabs  232  and  233 . Thus, the strain relief features of feedthroughs  120  and  125  help minimize or eliminate undesirable stress in feedthrough connections. 
     The foregoing means for connecting multiple electrode tab elements to feedthroughs may also be employed in other energy storage devices such as batteries, electrochemical cells and cylindrically wound capacitors. 
     As employed in the specification and claims hereof, the term “laser welding” means, but is not necessarily limited to, a method of welding wherein coherent light beam processing is employed. Other means of coherent light beam processing falling within the scope of the method of the present invention include electron beam or laser welding methods (e.g., Nd:YAG, CO 2  processes) having hard or fiber optic beam delivery in pulsed, continuous, or q-switched modes. Still other welding means fall within the scope of the method of the present invention, such as micro metal inert gas welding and micro plasma welding processes. 
     Table 2 sets forth optimized, preferred processing parameters we have discovered under which various components of capacitor  265  are laser welded to one another. The parameters set forth in Table 2 correspond to those for a Model No. JK702H pulsed Nd:YAG laser welding system having hard optic beam delivery manufactured by Lumonics Laserdyne of Eden Prairie, Minn. 
     Table 3 sets forth a range of parameters under which the same type of laser welding system provides acceptable weld characteristics in accordance with other methods of the present invention. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Optimized Nd:YAG Laser Welding Parameters 
               
            
           
           
               
               
            
               
                   
                 Optimized Laser Welding Parameters* 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Energy 
                   
                   
                   
                   
               
               
                   
                 per 
                   
                   
                 Pulse 
               
               
                   
                 Pulse 
                 Pulse 
                 Feed Rate 
                 Width 
                 Argon 
               
               
                   
                 (Joules/ 
                 Frequency 
                 (inches/ 
                 Gas 
                 Cover 
               
               
                 Weld Type 
                 pulse) 
                 (Hertz) 
                 min) 
                 (msec) 
                 (SCFH) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Feed through Ferrule to Case 
                 13.5 
                 4.5 
                 3 
                 5 
                 35 
               
               
                 Tack 1 
               
               
                 Feed through Ferrule to Case 
                 9.75 
                 20 
                 2 
                 4.5 
                 35 
               
               
                 Weld 
               
               
                 Fillport Ferrule to Case 
                 13.5 
                 4.5 
                 3 
                 5 
                 35 
               
               
                 Tack 1 
               
               
                 Fillport Ferrule to Case 
                 15 
                 15 
                 2 
                 6 
                 35 
               
               
                 Weld 
               
               
                 Anode Feedthrough Tabs 
                 8 
                 10 
                 2 
                 5 
                 35 
               
               
                 Cathode Feedthrough Tabs 
                 4 
                 10 
                 2 
                 5 
                 35 
               
               
                 Cover to Case 
                 7.5 
                 40 
                 6 
                 5.4 
                 60 
               
               
                 Filltube Seal 
                 13.5 
                 15 
                 4 
                 7 
                 30 
               
               
                   
               
               
                 *Lumonics JK702H Nd:YAG laser having an initial beam diameter of approximately one inch passing through a final focusing lens with a 146 mm focal length (purchased having “160 mm lens”, actual fine focal point measured was 146 mm) and a spot size at the joint surface of 0.022 inches. The cover gas was coaxial. It will be understood that variations respecting the manufacturer of the laser, beam delivery optics, the initial beam size,  
               
               
                 # final focusing Lens, spot size of the beam and the like fall within the scope of a method of the present invention.  
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Generalized Nd:YAG Laser Welding Parameters 
               
            
           
           
               
               
            
               
                   
                 Generalized Laser Welding Parameters* 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Energy 
                   
                   
                   
                   
               
               
                   
                 per 
                   
                   
                   
                 Argon 
               
               
                   
                 Pulse 
                 Pulse 
                 Feed Rate 
                 Pulse 
                 Cover 
               
               
                   
                 (Joules/ 
                 Frequency 
                 (inches/ 
                 Width 
                 Gas 
               
               
                 Weld Type 
                 pulse) 
                 (Hertz) 
                 min) 
                 (msec) 
                 (SCFH) 
               
               
                   
               
               
                 Feedthrough Ferrule to Case 
                 2-15 
                 3-30 
                 1-5 
                 3.5-8 
                 30-60 
               
               
                 Fillport Ferrule to Case 
                 2-15 
                 3-30 
                 1-5 
                 3.5-8 
                 30-60 
               
               
                 Feedthrough Tabs 
                 1-10 
                 1-20 
                 1-7 
                 3.5-8 
                 30-60 
               
               
                 Cover to Case 
                 5-25 
                 10-40  
                 1-7 
                 3.5-8 
                 30-60 
               
               
                 Filltube Seal 
                 8-20 
                 5-20 
                  1-10 
                 3.5-8 
                 30-60 
               
               
                   
               
               
                 *Lumonics JK702H Nd:YAG laser having an initial beam diameter of approximately one inch passing through a final focusing lens with a 146 mm focal length (purchased having “160 mm lens”, actual fine focal point measured was 146 mm) and a spot size at the joint surface of 0.022 inches. The cover gas was coaxial. It will be understood that variations respecting the manufacturer of the laser, beam delivery optics, the initial beam size,  
               
               
                 # final focusing lens, spot size of the beam and the like fall within the scope of a method of the present invention.  
               
            
           
         
       
     
     FIG. 10 shows an exploded top perspective view of capacitor  265  of FIG. 9 in a partially assembled state. FIG. 18 shows a flow chart of one method of making case subassembly  108 . Case  90 , anode ferrule  95 , cathode ferrule  100 , and fill port ferrule  105  are first provided. Case  90  contains a means for accepting anode ferrule  95  therein, shown in FIGS. 9 and 10 as anode feedthrough ferrule hole  142 . Case  90  further contains a means for accepting cathode ferrule  100 , shown in FIGS. 9 and 10 as cathode feedthrough ferrule hole  143 . Case  90  also includes a means for accepting fill port ferrule  105 , shown in FIGS. 9 and 10 as fill port hole  106 . In a preferred embodiment of the present invention, case  90  and cover  110  are formed of aluminum. In other embodiments of the present invention, case  90  or cover  110  may be formed of any other suitable corrosion-resistant metal such as titanium or stainless steel, or may alternatively be formed of a suitable plastic, polymeric material or ceramic. 
     Case  90 , cover  110  and capacitor  265  of the present invention may additionally form a case negative capacitor (where can  90  and cover  110  are electrically connected to the cathode layers, and where can  90  and cover  110  are at the same electrical potential as the cathode layers, i.e., at negative potential), or a floating case capacitor (where can  90  and cover  110  are electrically connected neither to the cathode layers nor to the anode sub-assemblies, and where can  90  and cover  110  are at substantially no electrical potential or at an electrical potential that floats with respect to the respective potentials of the cathode layers and the anode sub-assemblies). In some embodiments of the present invention, case  90  or cover  110  may be formed of an electrically non-conductive material or substantially electrically non-conductive material such as a suitable plastic, polymeric or ceramic material. 
     Ferrules  95 ,  100  and  105  are most preferably welded to case  90  (or otherwise attached thereto such as by a suitable epoxy, adhesive, solder, glue or the like), and together comprise case subassembly  108 . Radial flanges in anode ferrule  95  and cathode ferrule  100  provide a region for making a lap joint between the side wall of case  90  and around the perimeters of feedthrough ferrule holes  142  and  143 . In preferred methods of the present invention, a circumferential laser weld is disposed in joint  93 , and welding is carried out in two primary steps. First, a series of tack welds is made around the circumference of joint  93 . The tack welds are most preferably made either by making adjoining, successive tack welds around the perimeter or by making a first tack weld at a first location along the perimeter, making a second weld diametrically opposed from the first weld along the perimeter, making a third weld adjacent to the first weld, making a fourth weld adjacent to the second weld, and so on. Finally, a final closing weld is made around the hole perimeter to hermetically seal tack welded joint  93 . 
     Table 2 sets forth an optimized set of parameters under which anode ferrule  95  and cathode ferrule  100  are joined to case  90 . Table 3 sets forth a range of general parameters under which the same laser welding system provides acceptable weld characteristics for joining anode ferrule  95  and cathode ferrule  100  to case  90 . 
     FIG. 18 shows steps for inserting anode wire guide  140  into the inside diameter of anode ferrule  95 , and inserting cathode wire guide  141  into the inside diameter of cathode ferrule  100 . Wire guides  140  and  141  center pins within the inside diameter of the ferrules to permit anode and cathode pins  130  and  135  to be electrically insulated from the inside surface of case  90 , anode ferrule  95 , and cathode ferrule  100 . Wire guides  140  and  141  may themselves be electrically insulative, and electrical insulation of pins  130  and  135  from case  90  and other components is most preferably enhanced by means of potting adhesive  160 . FIG. 20 shows further details concerning one method of the present invention for forming electrical insulation between pins  130  and  135  and anode ferrule  95  and cathode ferrule  100 . 
     Wire guides  140  and  141  most preferably contain annular, ramped, or “snap-in” features formed integrally therein. Those features prevent wire guides  140  and  141  from being pushed out of their respective ferrules during handling, but are most preferably formed such that insertion of wire guides  140  and  141  in their corresponding ferrules may occur using forces sufficiently low so as not to damage case  90  or ferrules  95  or  100  during the inserting step. 
     Wire guides  140  and  141  may be formed from any of a wide variety of electrically insulative materials that are stable in the environment of an electrolytic capacitor. In one preferred embodiment of the present invention, the material from which wire guides  140  and  141  is made is an injection molded polysulfone known as AMOCO UDEL supplied by Amoco Performance Products of Atlanta, Ga. In other embodiments of the present invention, wire guides  140  and  141  may be formed from other chemically resistant polymers such as fluoroplastics (e.g., ETFE, PTFE, ECTFE, PCTFE, FEP, PFA or PVDF), fluoroelastomers, polyesters, polyamides, polyethylenes, polypropylenes, polyacetals, polyetherketones, polyarylketones, polyether sulfones, polyphenyl sulfones, polysulfones, polyarylsulfones, polyetherimides, polyimides, poly(amide-imides), PVC, PVDC-PVC copolymers, CPVC, polyfurans, poly(phenylene sulfides), epoxy resins, silicone elastomers, nitrile rubbers, chloroprene polymers, chlorosulfonated rubbers, polysulfide rubbers, ethylene-polypropylene elastomers, butyl rubbers, polyacrylic rubbers, fiber-reinforced plastics, glass, ceramic and other suitable electrically insulative, chemically compatible materials. 
     As used in the specification and claims hereof, the foregoing acronyms have the following meanings: the acronym “ETFE” means poly(ethylene-co-tetrafluoroethylene); the acronym “PTFE” means polytetrafluoroethylene; the acronym “CTFE” means poly(ethylene-co-chlorotrifluoroethylene); the acronym “PCTFE” means polychlorotrifluoroethylene; the acronym “FEP” means fluorinated ethylene-propylene copolymer; the acronym “PFA” perfluoroalkoxy fluoropolymer; the acronym “PVDF” means polyvinylidene fluoride; the acronym “PVC” means polyvinyl chloride; the acronym “PVDC-PVC” means polyvinylidene chloride -polyvinyl chloride copolymer; and the acronym “CPVC” means chlorinated polyvinyl chloride. 
     FIG. 11 shows a top view of one embodiment of assembled capacitor  265  of the present invention with cover  110  not present. Electrode assembly  225  has been inserted into case subassembly  108  through wire guides  140  and  141 . In one embodiment of the present invention, the headspace portion of electrode assembly  225  (referred to herein as headspace  230 ) is insulated from case  90  and cover  110 . The means of the present invention by which headspace insulation may be provided include molded, thermally-formed, die cut, or mechanically formed insulating materials and means, where the materials and means are stable in the environment of an electrolytic capacitor. Suitable materials from which headspace insulators may be formed include all those listed hereinabove respecting materials for forming wire guides  140  and  141 . Another means of providing headspace insulation is to wrap electrically insulative tape, similar to wrapping tape  245 , around headspace  230  to prevent the anode or cathode terminals from contacting case  90  or cover  110 . 
     FIGS.  26 ( a ) through  26 ( p ) show different embodiments of joint  93  and the crimp of the present invention. Various types of crimp and joint configurations for joining the cover  110  to case  90  are illustrated in cross-section in those figures. 
     The inventors of the present invention have discovered that the particular structural configuration of joint  93  is of the utmost importance in respect of the suitable laser weldability thereof. More particularly, it has been discovered that joints for covers of prior art flat capacitors having metal cases and covers and conventional joint structures generally permit laser energy to enter the interior of capacitor  265  through the joints formed between the covers and cases thereof, thereby damaging or heating up components disposed inside case  90 . Joints of the prior art which permit such undesired penetration of laser energy inside capacitor  265  were discovered to generally have a common feature: a joint geometry wherein a straight or substantially straight line of sight or portion existed or was disposed through the joint between the interior of the capacitor and the exterior of the capacitor. Joints having no such straight line of sight or portion through the joint between the exterior and interior of the capacitor were found to eliminate or at least diminish substantially the ill effects attending laser energy penetration to the interior of the capacitor. 
     In one embodiment of the present invention, case  90 , cover  110 , joint  93 , upper edge  94 , raised portion  95 , stepped portion  96 , groove  97 , stepped portion  98  and outer edge  111  cooperate with one another to cause laser energy entering joint  93  from the exterior of capacitor  265  to be reflected or scattered to the outside of capacitor  265 , and further to be contained or absorbed within joint  93  in such a manner that no or substantially no laser energy penetrates joint  93  and enters the interior of capacitor  265  while simultaneously forming a suitable weld in joint  93  between case  90  and cover  110 . This absorption, containment, backscattering or reflecting of laser energy by joint  93  results at least partially from the multiple orientations of joint  93  as it wends its way from the exterior of capacitor  265  to the interior thereof. In other words, and as illustrated in FIGS.  26 ( a ) through  26 ( p ), joint  93  of the present invention has multiple portions that are bent, non-parallel or serpentine respecting one another. 
     In one method of the present invention for laser welding joint  93 , an axis of a laser beam is directed inwardly along or parallel to the surfaces defining a first portion of joint  93  (e.g., parallel to imaginary axis  102  or imaginary axis  101 , depending on the particular embodiment of the present invention at hand). Upon entering the first portion of joint  93  or a region propinquant thereto, the laser beam encounters at least a second portion of joint  93  defined by surfaces that are bent or not parallel respecting the surfaces defining the first portion of joint  93 . As shown in FIGS.  26 ( e ) through  26 ( h ) and  26 ( m ) through  26 ( p ), joint  93  of the present invention may also have a third portion defined by surfaces that are bent or non-parallel respecting the surfaces defining the second portion of joint  93 . Consequently, and providing appropriate parameters are selected by a user for operating the laser welding system of the present invention, no portion of the laser beam impinging upon the first portion of joint  93  may penetrate joint  93  sufficiently far such that the laser beam reaches the interior of capacitor  265  without first being absorbed, reflected or scattered. 
     In another method of the present invention for laser welding joint  93 , an axis of a laser beam is directed inwardly along or parallel to the surfaces defining a second portion of joint  93  (e.g., parallel to imaginary axis  102  or imaginary axis  101 , depending on the particular embodiment of the present invention at hand). Upon entering the second portion of joint  93  or a region propinquant thereto, the laser beam encounters at least a first or third portion of joint  93  defined by surfaces that are bent or not parallel respecting the surfaces defining the second portion of joint  93 . 
     FIGS.  26 ( a ) through  26 ( d ) show a first embodiment of joint  93  and the crimp of the present invention, wherein case  90  has inner and outer sidewalls  91  and  92  extending upwardly from a flat planar base of case  90  to form an open end that terminates in upper edge  94  disposed between inner and outer sidewalls  91  and  92 . Upper edge  94  most preferably comprises at least one stepped portion  96  and at least one raised portion  95 . Substantially planar cover  110  seals the open end of the case, cover  110  having upper and lower surfaces  112  and  113 , respectively, separated by outer edge  111 . At least portions of outer edge  111  are shaped to engage at least one stepped portion  96  of upper edge  94  such that cover  110  self-registers on case  90  when cover  10  is disposed over the open end of case  90 , outer edge  111  is aligned approximately upper edge  94 , and cover  90  is placed thereon. 
     As shown in FIGS.  26 ( a ) and  26 ( c ), at least one raised portion  95  of upper edge  94  initially extends above upper surface  112  of cover  110  when at least portions of outer edge  111  are placed on and engage at least one stepped portion  96 . As shown in FIGS.  26 ( b ) and  26 ( d ), at least one raised portion  95  is crimped or folded inwardly over or along upper surface  112  of cover  110  to form joint  93  after at least portions of outer edge  111  are placed on and engage the least one stepped portion  96 . Next joint  93  is laser welded to hermetically seal cover  110  to case  90 . 
     In the laser welding step, the laser beam may be directed substantially parallel to axes  101  and  102  of FIG.  26 ( b ) to form a weld in the first or second portions of joint  93 . Alternatively, the laser beam may be directed substantially parallel to axis  101  of FIG.  26 ( a ) (i.e., substantially parallel to upstanding sidewalls  91  and  92 ) after raised portion  95  is crimped over cover  110  such that at least portions of raised portion  95  melt and thereby weld first, second, third or other portions of joint  93  closed. Our laser welding method invention includes within its scope laser welding steps where the laser beam is oriented in directions other than those set forth explicitly above. 
     In FIGS.  26 ( a ) and  26 ( c ), imaginary axes  101  and  102  are oriented at an angle theta of about 90 degrees respecting one another, where imaginary axis  101  defines the initial orientation of upper edge  94  and imaginary axis  102  defines the orientation of the plane within which cover  110  is disposed. In FIGS.  26 ( b ) and  26 ( d ), after upper edge  94  has been crimped or folded inwardly over or along upper surface, imaginary axis  101  is oriented at an angle theta of about 0 degrees respecting imaginary axis  102 . 
     FIGS.  26 ( e ) through  26 ( f ) show a second embodiment of the crimp and joint  93  of the present invention, where case  90  has inner and outer sidewalls  91  and  92 , respectively, extending upwardly from a flat planar base of case  90  to form an open end terminating in upper edge  94  disposed between inner and outer sidewalls  91  and  92 . Substantially planar cover  110  seals the open end of case  90 . Cover  110  comprises upper and lower surfaces  112  and  113 , respectively, separated by outer edge  111 . Lower surface  113  of cover  110  has disposed thereon at least one of groove  97  (see FIGS.  26 ( e ) and  26 ( f )) and stepped portion  98  (see FIGS.  26 ( g ) and  26 ( h )). Groove  97  or stepped portion  98  is disposed radially inward from outer edge  111 . 
     At least portions of groove  97  or stepped portion  98  are shaped to engage corresponding portions of upper edge  94  such that groove  97  or stepped portion  98 , in combination with upper edge  94 , cause cover  110  to self-register on upper edge  94  when cover  110  is disposed over the open end of case  90 , groove  97  or stepped portion  98  is aligned approximately with upper edge  94 , and cover  110  is placed on upper edge  94 . Outer portions  117  of cover  110  extending between outer edge  111  and groove  97  or stepped portion  98  are crimped or folded downwardly over at least portions of outer sidewall  92  of case  90  to form joint  93  after cover  110  is placed on the open end of can  90 . Joint  93  is laser welded to hermetically seal cover  110  to case  90 . 
     In the laser welding step, the laser beam may be directed substantially parallel to axes  101  and  102  of FIG.  26 ( f ) to form a weld in the first, second or other portions of joint  93 . Alternatively, the laser beam may be directed substantially parallel to axis  102  of FIGS.  26 ( e ) or  26 ( g ) (i.e., substantially parallel to the plane forming cover  110 ) after outer portion of cover  110  is crimped over outer sidewall  92  such that at least portions of outer portions of cover  110  melt and thereby weld first, second, third or other portions of joint  93  closed. Our laser welding method invention includes within its scope laser welding steps where the laser beam is oriented in directions other than those set forth explicitly above. 
     In FIGS.  26 ( e ) and  26 ( g ), imaginary axes  101  and  102  are initially oriented at an angle theta of about 90 degrees respecting one another, where imaginary axis  101  defines the orientation of upper edge  94  and imaginary axis  102  defines the initial orientation of outer edge  111 . In FIGS.  26 ( f ) and  26 ( h ), after outer edge  111  has been crimped or folded downwardly over at least portions of outer sidewall  92 , imaginary axis  102  is oriented at an angle theta of about 0 degrees respecting imaginary axis  102 . 
     FIGS.  26 ( i ) through  26 ( p ) show yet other embodiments of the crimp and joint of the present invention, where the angle theta defining the orientations of imaginary axes  101  and  102  respecting one another after upper edge  94  has been crimped or folded inwardly, or outer edge  111  has been crimped or folded downwardly, is greater than or equal to 0 degrees but less than 90 degrees. The embodiments of the present invention shown in FIGS.  26 ( i ) through  26 ( p ) have been discovered to be particularly efficacious for providing good access to joint  93  for a laser welding beam. 
     Note, however, that many variations of the particular cover, case and joint geometries disclosed explicitly herein are possible and fall within the scope of the apparatus and corresponding methods of the present invention. For example, the case and cover of the present invention may form two aluminum-containing half-cases having upwardly and downwardly extending sidewalls, the two half-cases forming two open ends that are subsequently laser welded together. Alternatively, the case and cover may form two substantially planar aluminum-containing members separated by a single or multiple sidewall members, the two planar members being laser welded to the intervening sidewall members. 
     FIGS.  26 ( a ) through  26 ( p ) also show registration marks or alignment features  99  disposed on case  90  or cover  110 . Registration mark or alignment feature  99  is employed to establish a reference position in joint  93  for the welding apparatus after the case or cover has been crimped or folded, thereby ensuring precise position of the welding apparatus in respect of case  90 , cover  110  and joint  93  when a weld is being formed in joint  93 . It has been discovered that optimum results are obtained when registration mark  99  is disposed on upper surface  112  of cover  110 . 
     FIG. 19 shows a flow chart according to one method of the present invention for sealing case  90  and cover  110 . Case subassembly  108  is provided with electrode assembly  225  inserted in case  90 . Cover  110  is disposed atop upper edge  94  formed in case  90 . In one method of the present invention, raised portion  95  of upper edge  94  extends about 0.014″ above upper surface  112  of cover  110  when cover  110  is placed on upper edge  94 . The assembly is placed within a crimping mechanism or nest, and a clamp is actuated to hold cover  110  against upper edge  94  and stepped portion  96 . The crimping mechanism is actuated to crimp or fold over inwardly raised portion  95  onto, along or over upper surface  112  of cover  110 . 
     In another method of the present invention, crimping of raised portion  95  is accomplished using a die cut to the shape of case  90  and further having angled or ramped sidewalls for engaging and pressing inwardly raised portion  95  over upper surface  112  of cover  110 . A crimp may also be formed with a moving crimp apparatus that travels around the perimeter of case  90  while continuously crimping raised portion  95  over upper surface  112  of cover  110 . The foregoing methods may be readily adapted to permit the crimping or folding of edge  111  of cover  110  downwardly over outer sidewall  92 . 
     Crimping of raised portion  95  onto cover  110  or outer edge  111  onto sidewall  92  provides several advantages. First, laser welding of cover  110  to case  90  may be accomplished using relatively simple tooling, thereby resulting in short process times. Laser welding often provides a bottleneck in manufacturing process flow when components such as case  90  and cover  110  typically must be aligned precisely respecting one another. The elimination of such alignment steps during the laser welding process has been discovered to help eliminate manufacturing process bottlenecks. Folding or crimping raised portion  95  or outer edge  111  prevents a laser beam from entering the interior of capacitor  265 . Instead, a laser beam is forced to couple with the material of case  90  and cover  110  to thereby induce melting. It was discovered that joints  93  not having crimps forming at least a portion thereof may permit a laser beam to damage components inside capacitor  265 . 
     Another advantage of the crimped joint of the present invention is that the crimp provides additional metal in the weld zone. Aluminum, having a high thermal expansion coefficient, is sensitive to cracking upon rapid cooling from the high temperatures characteristic of welding processes. We discovered that the additional metal provided by the crimp decreases cracking sensitivity in joint  93 . Joint  93  of the present invention is formed such that imaginary axes  101  and  102  are oriented at an angle theta respecting one another where theta is less than 90 degrees but greater than or equal to 0 degrees. It is notable that crimping of case  90  and cover  110  to one another helps registration of case  90  and cover  110  in respect of one another prior to the welding of at least portions of joint  93  being undertaken. 
     Crimped case  90  and cover  110  are next removed from the crimp fixture and placed in a welding fixture. A laser weld is made in joint  93  to hermetically seal case  90  to cover  110 . Table 2 sets forth an optimized set of parameters under which the crimped case/cover joint may be sealed using a pulsed Nd:YAG laser welding system. Table 3 sets forth a generalized range of conditions under which the same laser welding system provides acceptable results. 
     In a preferred method of the present invention, machined, stamped, etched or otherwise-formed registration marks or alignment features  99  are disposed on cover  110  or case  90  to permit the relative positions of cover  110  and case  90  to be determined precisely for the laser welding step. Connectors are then attached to the welded case/electrode assembly. 
     FIG. 20 shows a flow chart according to one method of the present invention for sealing anode feedthrough portion  235  and cathode feedthrough portion  240  of capacitor  265 . See also FIG.  10 . FIGS. 9 through 12 show various embodiments of the sealing and connector attachments of the present invention in capacitor  265 . 
     FIG. 21 shows several top, perspective and cross-sectional views according to one embodiment of capacitor connector block  145  of the present invention. In preferred embodiments of connector block  145  of the present invention, connector block  145  is disposed atop or otherwise connected to case  90  and/or cover  110 , and has wire harness  155  and potting adhesive disposed therein. 
     A preferred material for forming connector block  145  is an injection molded polysulfone known as AMOCO UDEL supplied by Amoco Performance Products of Atlanta, Georgia. Connector block  140  may also be formed from any suitable chemically resistant thermoplastic polymers such as a flouroplastic (e.g., ETFE, PTFE, ECTFE, or PCTFE, FEP, PFA, PVDF), polyester, polyamide, polyethylene, polypropylene, polyacetal, polyarylketone, polyether sulfone, polyphenyl sulfone, polysulfone, polyarylsulfone, polyetherimides, polyimide, poly(amide-imide), PVC, PVDC-PVC copolymer, CPVC, polyfuran, poly(phenylene sulfide), epoxy resin and fiber reinforced plastic. 
     In one embodiment of the present invention, connector block  145  is placed on anode ferrule  95  and cathode ferrule  100  by guiding anode feedthrough pin  130  through connector block anode feedthrough hole  300 , and then guiding cathode feedthrough pin  135  through connector block cathode feedthrough hole  305 . Connector block  145  is next seated flush against the exterior surface of case  90 . Anode feedthrough pin  130  is then inserted into anode crimp tube  150   b  of wire harness  155 . Cathode feedthrough pin  135  is then inserted into cathode crimp tube  150   a  of wire harness  155 . Crimp tubes  150   a  and  150   b  are then crimped to feedthrough pins  130  and  135 . 
     In other embodiments of the present invention, electrical connections in connector block  145  may be established using techniques such as ultrasonic welding, resistance welding and laser welding. In such joining techniques, the joint geometry may also be a cross-wire weld between feedthrough wire  130  or  135  and harness wire  151  or  152 . The present invention includes within its scope an embodiment having case  90  at cathode potential. In such an embodiment of the present invention, a separate cathode terminal connection is most preferably provided to permit additional design flexibility. 
     The distal or basal portions of crimp tubes  150   a  and  150   b  are crimped on insulated anode lead  151  and insulated cathode lead  152 , respectively. Insulated leads  151  and  152  are likewise connected to terminal connector  153 . Terminal connector  153  may most preferably be connected to electronics module  360 . Standard methods of making aluminum electrolytic capacitors do not lend themselves readily to very small crimp connections, especially in miniaturized ICD designs. A method of the present invention permits small crimp connections an interconnection means to be formed, and further permits highly efficient packaging in PCD  10 . 
     In the preferred method described above, connector block  145  and epoxy adhesive provide strain relief to feedthrough pins  130  and  135  and to the feedthrough wire crimp connections, and further provide an epoxy seal between pins  140  and  141 , case  90  and ferrules  95  and  100 . The crimp tubes may also serve as a connection point for device level assembly. Alternatively, the crimp tubes may be integrated within wire harness  155  prior to capacitor assembly. The wire harness may then serve as a means of routing capacitor electrical connections as desired in, for example, device level assembly steps. 
     In the embodiment of the present invention shown in FIG. 11, terminal connector  153  forms the female end of a slide contact. In another embodiment of the present invention, terminal connector  153  is connected to other modules by resistance spot welding, ultrasonic wire bonding, soldering, crimping, or other attachment means. 
     Referring again to FIG. 21, insulated anode lead  151  is inserted into anode block channel  310 . Anode feedthrough pin  130  is centered in connector block anode feedthrough hole  300  by anode pin block guide  320 . Insulated cathode lead  152  is inserted into cathode block channel  315 . Cathode feedthrough pin  135  is centered in connector block cathode feedthrough hole  305  by cathode pin block guide  325 . Centering of the pin through the ferrule assures that the pin does not contact the conducting wall of the ferrule, and also permits a more concentric epoxy seal to be formed around the pin. Centering of the pin may also be accomplished through means disposed in or on the epoxy dispensing or curing tools. Once the epoxy has hardened sufficiently, the centering tool is removed. 
     When employed, a potting adhesive is mixed and dispensed through connector block feedthrough holes  300  and  305  and block channels  310  and  315 . Such an adhesive may also be dispensed through connector block hole  330  between connector block  145  and case  90 . Adhesive bonding between block  145  and case  90  enhances structural stability of capacitor  265 . The epoxy is then cured and capacitor  265  is filled with electrolyte. 
     The life of capacitor  265  may be appreciably shortened if solvent vapor or electrolyte fluid escapes from the interior of capacitor  265 . Moreover, if capacitor  265  leaks electrolyte, the electrolyte may attack the circuits to which capacitor  265  is connected, or may even provide a conductive pathway between portions of that circuit. The present invention provides a beneficial means for preventing the escape of solvent and solvent vapor from capacitor  265 . More particularly, capacitor  265  most preferably includes hermetic laser welded seams between joint case  90  and cover  110 , and between ferrules  95 ,  100 , and  105  and case  90 . Additionally, anode feedthrough portion  235  and cathode feedthrough portion  240  most preferably have an adhesive seal disposed therein for sealing the ferrule walls and the feedthrough wires. 
     The epoxy adhesive or potting material of the present invention is most preferably chemically resistant to the electrolyte employed in capacitor  265  and adheres well to surrounding surfaces. Adhesion promotion (such as by chemical deposition, etching, corona or plasma treatment of the polymeric wire guide of a polymeric case) may be employed to maximize the reliability of capacitor  265 . In one preferred embodiment of the present invention, an aliphatic epoxy such as CIBA-Geigy Araldite 2014 is employed. Other suitable potting adhesives include chemically resistant thermoplastic hot melt materials such as polyamides, polyesters, polyurethanes, epoxies, and polyethylene-vinyl acetates, UV curable resins such as acrylates and methacrylates, and other thermosetting resins such as aliphatic and aromatic epoxies, silicones, polyamides, polyesters and polyurethanes. Many suitable potting adhesives may be thermally cured or cured with ultraviolet light. A focused IR procedure may be employed in some instances to minimize cure time and localize heat. 
     Since hermeticity is desirable in feedthrough assemblies of the present invention, the method by which the feedthrough seals are made should be predictable, uniform, reliable and produce high-quality hermetic seals. In a preferred method of the present invention, an epoxy adhesive is employed which has few or no voids and cracks and completely or substantially completely adheres to the surrounding pin, ferrule wall and wire guide components. Filling of the ferrule hole with sealing adhesive may be accomplished in several ways, depending largely on the viscosity of the potting agent selected. A balance in viscosity characteristics of the sealing adhesive has been found to be desirable. More particularly, it is desired that the sealing adhesive be thin enough to fill without voids forming and to wet the surface, yet thick enough not to escape around or through the wire guide. The potting adhesive may be B-staged and inserted as a plug; likewise a hot melt adhesive may be applied in similar fashion. Subsequent heating completes curing of the sealing adhesive. In a preferred method of the present invention, CIBA Geigy Araldite 2014 epoxy is mixed with a static mix tube and dispensed within 45 minutes. The assembly is cured in an oven for 30 minutes at 90 degrees Celsius. 
     In another embodiment of the present invention, connector block  145 , ferrules  95  and  100 , and wire guides  140  and  141  are formed from a single molded component formed of a suitable chemically resistant thermoplastic or thermoset material that is sealed to case  90  using a potting adhesive. Channels or voids may be included in the basal portions of connector block  145  to permit potting adhesive to flow between those basal portions and case  90 . Such a seal between the case and connector block  145  may replace the aforementioned laser welded seal between the ferrule and the case. Such a sealing method eliminates the requirement for several components and removes several processing steps, leading perhaps to significant manufacturing cost reductions. 
     Referring again to FIG. 13, capacitor  265  is filled with electrolyte. The electrolyte may be any suitable liquid electrolyte for high voltage electrolytic capacitors. In a preferred embodiment of the present invention, the electrolyte is an ethylene glycol based electrolyte having an adipic acid solute. It is contemplated in the present invention that other electrolytes suitable for use in high voltage capacitors may also be employed. 
     In accordance with a preferred method of the present invention, capacitor  265  is filled with a suitable liquid electrolyte via fill port tube  107  in multiple vacuum impregnation cycles. The capacitor and the electrolyte are placed in a vacuum chamber with fill port tube  107  connected to the electrolyte by a temporary tube. Multiple vacuum impregnation cycles are then performed at pressures exceeding the vapor pressure of the electrolyte. In a less preferred method of the present invention, capacitor  265  is filled with electrolyte by immersing capacitor  265  in the electrolyte or by vacuum-filling capacitor  265  with a metered filling machine. Note, however, that a single vacuum impregnation cycle falls within the scope of at least one method of the present invention. 
     Fill port tube  107  of the present invention provides a means for filling capacitor  265 . In preferred embodiments of the present invention, fill port tube  107  includes helium leak verification capabilities and easy sealing characteristics. The hermeticity of capacitor  265  is preferably measured using a helium leak test. A helium leak testing apparatus forms a seal around the tube of fill port tube  107 . The testing apparatus then pulls a vacuum on the interior of sealed capacitor  265 , and the gas pulled from the interior of capacitor  265  is directed past a tuned mass spectrometer. Next, the exterior of capacitor  265  is exposed to helium gas, and the leak rate for helium through the materials and joints within capacitor  265  is determined by the mass spectrometer. This measure of leaktightness or hermeticity provides a means of assuring the quality of the joints being made. 
     In another embodiment of the present invention, “bombing” or filling of the interior of capacitor  265  with helium gas is accomplished immediately prior to sealing of fill port ferrule  105 . The exterior of sealed capacitor  265  is then monitored under vacuum conditions with a tuned mass spectrometer to determine the rate of helium leakage past the materials and joints of capacitor  265 . 
     Once capacitor  265  is filled with electrolyte, it is preferred that an aging process be undertaken. Aging is generally accomplished by applying a current through the capacitor terminals and gradually raising the voltage across those terminals from zero to the peak aging voltage of the capacitor (usually between about 360 and about 390 Volts DC). Once the aging voltage is attained, capacitor  265  is held at that voltage until the leakage current stabilizes at an acceptably low value. It is preferred that capacitor  265  be aged until a voltage of about 370 Volts is attained during a current limiting process. 
     In one preferred method of the present invention, the aging process is carried out with the voltage set at 370 Volts and the current limited to about 1.5 mA (for capacitor  265  having a capacitance of 214 microfarads). We have also found that it is beneficial to increase the temperature of the aging system at higher voltages. In one preferred method of the present invention, the temperature is increased to about 70 degrees Celsius when the voltage reaches 230 Volts. After aging to 370 Volts, the capacitors are most preferably permitted to continue aging with the voltage held at 370 Volts until the leakage current decreases to a predetermined value, a predetermined time at 370 Volts has elapsed, or until a predetermined rate of decrease in leakage current has been obtained. 
     Following aging, post aging vacuum treatment or filling of the capacitor contributes to significant improvements in capacitance and equivalent series resistance (ESR). FIG. 22 shows a flow chart describing one method of vacuum treating the aged capacitor. The aged capacitor is placed inside a vacuum chamber and held at 27 inches of mercury for three minutes. The chamber is vented and then held at 27 inches of mercury for three minutes for two additional cycles. The capacitor is then provided for fill port sealing. 
     FIG. 23 shows a flow chart describing a preferred method for a vacuum refilling operation after aging. Aged capacitor  265  is placed inside a vacuum chamber, a temporary fill tube connected to fill port tube  107  being immersed in electrolyte. The chamber is then held at 27 inches of mercury for three minutes and vented. This step is repeated once with the temporary tube in the electrolyte and a second time with the temporary tube out of the electrolyte. The third cycle is intended to draw excess electrolyte from capacitor  265 . Fillport ferrule tube  107  is now ready for sealing. 
     FIG. 24 is a graph showing the increase in capacitance of five capacitors following the vacuum refilling operation of FIG.  23 . The noted increase in capacitance is on the order of about 1 to about 2 microfarads (˜0.3%). FIG. 25 is a graph showing the decrease in ESR of the same five capacitors after the vacuum refilling operation of FIG.  23 . The noted decrease in ESR is on the order of about 0.2 ohms (˜20%). The vacuum treatments are believed to remove entrapped gas that evolves during aging and refilling, and are also believed to replace electrolyte lost during aging, thereby permitting the microstructural pores of the anode and separator layers to be substantially fully filled and saturated with electrolyte. Excess electrolyte may also be removed through vacuum cycling with the fill tube pointing downwardly. 
     After vacuum refilling, distal end  106  of fill port tube  107  is most preferably crimped shut mechanically by pliers or other suitable means such as compression rollers or welding. The crimped or closed joint so formed is next most preferably trimmed with side cutter metal shears or in a metal die, and sealed. It is an advantage of the present invention that the fill port thereof may be closed and sealed quickly at minimum cost without any requirement for additional high tolerance, expensive piece parts or components for sealing fill tube  197 . 
     Sealing of fill port tube  107  is most preferably accomplished using joining techniques such as ultrasonic welding, cold welding or laser welding. See, for example, Tables 2 and 3. Sealing of fill port tube  107  may also be accomplished by glueing, epoxying, or any other suitable means. For example, fill port tube  107  may be sealed by inserting a compression-fit spherical ball into a corresponding spherical recess disposed inside fill port tube  107  or ferrule  105 . The ball is most preferably formed from a metal, plastic or ceramic material that is stable in the capacitor electrolyte. Dimensional control of the fill port tube or ferrule inside diameter in respect of the diameter of the ball is critical to controlling the quality of the seal being made. Ideally, the ball fits in the inside diameter in as tight an interference fit as possible without damaging the fill port ferrule weld or deforming case  90  to any significant extent. The “ball” need not conform to a spherical geometry, and may be a fitting that is cylindrically, conically or otherwise-shaped. 
     Still another method for sealing fill port ferrule  105  is to integrate a hydrogen permeable membrane seal into or propinquant to fill port ferrule  105  that does not permit electrolyte components to escape through fill port tube  107  but that does permit hydrogen gas evolved through charge and discharge of capacitor  265  to escape from the interior thereof. By sealing fill port tube  107  with a barrier having sufficient chemical resistance, but that is selective to hydrogen gas (such as some silicones, polyphenylene oxides, cellulose acetates and triacetates and polysulfones), no electrolyte is lost. Several potting adhesives (such as epoxy or silicone) have the foregoing chemical resistance and hydrogen permeability properties and thus are suitable for use in the present invention. Those adhesives most preferably seal feedthroughs while permitting hydrogen gas to escape from otherwise hermetically sealed capacitor  265 . 
     In yet another embodiment of the present invention, the seal of fill port tube  107  is be a simple adhesive strip disposed over distal end  106  of fill port tube  107 , similar to the types of seals employed in commercial ethylene glycol coolant canisters. 
     It is preferred that fill port ferrule  105  and fill port tube  107  form a single integrated piece of metal, although components  105  and  107  may form separate non-integral components and may further be formed of materials other than metal, such as ceramic or plastic. Fill port ferrule  105  fits within and is sealingly engaged to an opening disposed in the sidewall of case  90  or in cover  110 . Additionally, height  109  of fill port tube  107  shown in FIG.  28 ( c ) is most preferably about 0.200 inches with respect to the embodiment of capacitor  265  shown in the drawings hereof, although other heights  109  are contemplated in the present invention such as 0.065 inches, 0.300 inches, and so on. 
     It is preferred that height  109  be sufficiently great to accommodate a fitting of a helium leaktightness testing apparatus, the fitting being fitted in sealing engagement over the fill tube. It is preferred that an O-ring be disposed between the fitting and the fill tube as a vacuum of about 50 Tor is pulled on the interior of capacitor  265 . Helium gas is then emitted about and around capacitor  265 , cover  110 , case  90 , joint  93  between cover  110  and case  90 , connector block  145 , ferrule  105 , tube  107  and other components while the helium leaktightness testing apparatus tests gas and molecules evacuated from the interior of capacitor  265  for the presence of helium gas which has leaked from the exterior of capacitor  265  into the interior thereof. 
     A tuned mass spectrometer is most preferably included in the helium leaktightness testing apparatus. The spectrometer is sensitive to the presence of helium atoms or molecules. An example of such an apparatus is a LEYBOLD INFICON Model No. UL-200 Helium Leaktester manufactured in East Syracuse, N.Y. An O-ring having a leaktightness rating of about 1×10 −9  cm 3 /sec. is most preferably employed in conjunction with the fill tube and the fitting of the leaktightness testing apparatus. A typical fail point specification for the leaktightness testing apparatus when employed with the capacitor of the present invention is about 1×10 −9  cm 3 /sec. 
     FIG.  27 ( a ) shows a top view of capacitor  265  with a portion of cover  90  removed and a portion of electrode assembly  225  exposed therewithin. Fill port ferrule tube  107  projects outwardly from an end of case  90  from fill port ferrule  105 . FIG.  27 ( b ) shows an end view of capacitor  265  of FIG.  27 ( a ), and a corresponding end view of fill port tube  107  and fill port ferrule  105 . FIGS.  28 ( a ) through  28 ( c ) show various views of one embodiment of liquid electrolyte fill port tube  107  and fill port ferrule  105  of the present invention. 
     In another embodiment of fill port tube  107  of the present invention, case  90  is formed of a suitable metal, and a fill port tube  107  is extruded from, punched in or otherwise integrally formed in a sidewall or other portion of case  90 . Such a design eliminates the need for fill port ferrule  105  disposed in a wall or surface of case  90 . For example, a tapered punch may be employed to initially punch a small diameter hole in a sidewall of case  90 , followed by causing the punch to travel through the hole, causing metal from sidewall  90  to be extruded outwardly from the sidewall, and forming an outwardly projecting cylindrically or otherwise shaped fill port tube  107 . 
     Once sealed, the capacitor is electrically tested. Applications in implantable defibrillators may require two capacitors to be connected in series. In this case an insulator is provided by a two sided adhesive being disposed between the capacitors. Two capacitors are joined along opposing faces with the insulator/adhesive strip disposed therebetween. The pair of capacitors is then provided for assembly in PCD  10 . See FIGS.  3 ( a ) through  3 ( h ). 
     The scope of the present invention is not limited to defibrillation or cardioversion applications, or to applications where a human heart is defibrillated, but includes similar applications in other mammalians and mammalian organs. Those of ordinary skill will now appreciate that the method and device of the present invention are not limited to aluminum electrolytic capacitors for implantable medical devices, but extend to non-aluminum or partially-aluminum electrolytic capacitors for implantable medical devices, as well as to methods and corresponding capacitors and power sources for non-implantable medical devices and for electronic devices generally. 
     Additionally, although only a few exemplary embodiments of the present invention have been described in detail above, those skilled in the art will appreciate readily that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the following claims. 
     The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the invention or the scope of the appended claims. 
     In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts a nail and a screw are equivalent structures. 
     All patents and printed publications disclosed hereinabove are hereby incorporated by reference herein into the specification hereof, each in its respective entirety.