Implantable medical device having flat electrolytic capacitor with differing sized anode and cathode layers

Flat electrolytic capacitors, particularly, for use in implantable medical devices (IMDs), and the methods of fabrication of same are disclosed. The capacitors are formed with an electrode stack assembly comprising a plurality of stacked capacitor layers each comprising an anode sub-assembly of at least one anode layer, a cathode layer and separator layers wherein the anode and cathode layers have differing dimensions that avoid electrical short circuits between peripheral edges of adjacent anode and cathode layers but maximize anode electrode surface area. The electrolytic capacitor is formed of a capacitor case defining an interior case chamber and case chamber periphery, an electrode stack assembly of a plurality of stacked capacitor layers having anode and cathode tabs disposed in the interior case chamber, an electrical connector assembly for providing electrical connection with the anode and cathode tabs through the case, a cover, and electrolyte filling the remaining space within the interior case chamber. The plurality of capacitor layers and further separator layers are stacked into the electrode stack assembly and disposed within the interior case chamber such that the adjacent anode and cathode layers are electrically isolated from one another. The anode layer peripheral edges of the anode sub-assemblies of the stacked capacitor layers extend closer to the case side wall than the cathode peripheral edges of the cathode layers of the stack of capacitor layers throughout a major portion of the case chamber periphery. The separator layer peripheral edges extend to the case periphery and space the anode layer peripheral edges therefrom. Any burrs, debris or distortions along or of any of the anode layer peripheral edges causing the anode layer edges to effectively extend in the electrode stack height direction causes the anode layer peripheral edges having such tendency to contact an adjacent anode layer. In this way, anode layer surface area is maximized, and short circuiting of the anode layers with the cathode layers is avoided. A case liner can also be disposed around the electrode stack assembly periphery.

FIELD OF THE INVENTION

This invention relates to implantable medical devices (IMDs) and their various components, including flat electrolytic capacitors for same, and methods of making and using same, particularly to an electrode stack assembly comprising a plurality of stacked capacitor layers each comprising an anode sub-assembly of at least one anode layer, a cathode layer and separator layers wherein the anode and cathode layers have differing dimensions that avoid electrical short circuits between peripheral edges of adjacent anode and cathode layers.

BACKGROUND OF THE INVENTION

A wide variety of IMDs are known in the art as described in the above-referenced parent application Ser. No. 09/531,352, and the provisional application that it claims priority from, and in commonly assigned U.S. Pat. No. 6,006,133. Of particular interest are implantable cardioverter-defibrillators (ICDs) that deliver relatively high energy cardioversion and/or defibrillation shocks to a patient's heart when a malignant tachyarrhythmia, e.g., atrial or ventricular fibrillation, is detected. Current ICDs typically possess single or dual chamber pacing capabilities for treating specified chronic or episodic atrial and/or ventricular bradycardia and tachycardia and were referred to previously as pacemaker/cardioverter/defibrillators (PCDs). Earlier developed automatic implantable defibrillators (AIDs) did not have cardioversion or pacing capabilities. For purposes of the present invention ICDs are understood to encompass all such IMDs having at least high voltage cardioversion and/or defibrillation capabilities.

Generally speaking, it is necessary to employ a DC—DC converter within an ICD implantable pulse generator (IPG) to convert electrical energy from a low voltage, low current, electrochemical cell or battery enclosed within the IPG housing to a high voltage energy level stored in one or more high energy storage capacitor, as shown for example, in commonly assigned U.S. Pat. No. 4,548,209. The conversion is effected upon confirmation of a tachyarrhythmia by a DC—DC “flyback” converter which includes a transformer having a primary winding in series with the battery and a secondary winding in series with the high energy capacitor(s) and an interrupting circuit or switch in series with the primary coil and battery that is periodically opened and closed during a charging cycle. 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 switch is closed. The field collapses when the current in the primary winding is interrupted by opening the switch, and 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 of several hundred volts over a charging time of the charge cycle. Then, the energy is rapidly discharged from the high voltage capacitor(s) through cardioversion/defibrillation electrodes coupled to the IPG through ICD leads and arranged about or in a heart chamber or vessel if the tachyarrhythmia is confirmed as continuing at the end of the charge time. The cardioversion/defibrillation shocks effected by discharge of such capacitors are typically in the range of about 25 to 40 Joules. The process of delivering cardioversion/defibrillation shocks in this way may be repeated if an earlier delivered cardioversion/defibrillation shock does not convert the tachyarrhythmia to a normal heart rhythm.

Energy, volume, thickness and mass are critical features in the design of ICD pulse generators that are coupled to the ICD leads. The battery(s) and high voltage capacitor(s) used to provide and accumulate the energy required for the cardioversion/defibrillation shocks have historically been relatively bulky and expensive. Presently, ICD IPGs typically have a volume of about 40 to about 60 cc, a thickness of about 13 mm to about 16 mm and a mass of approximately 100 grams.

It is desirable to reduce the volume, thickness and mass of such capacitors and ICD IPGs without reducing deliverable energy. Doing so is beneficial to patient comfort and minimizes complications due to erosion of tissue around the ICD IPG. Reductions in size of the capacitors may also allow for the balanced addition of volume to the battery, thereby increasing longevity of the ICD IPG, or balanced addition of new components, thereby adding functionality to the ICD IPG. It is also desirable to provide such ICD IPGs at low cost while retaining the highest level of performance. At the same time, reliability of the capacitors cannot be compromised.

Various types of flat and spiral-wound capacitors are known in the art, some examples of which are described as follows and/or may be found in the patents listed in Table 1 of the above-referenced parent patent application Ser. No. 09/531,352.

Prior art high voltage electrolytic capacitors used in ICDs have two or more anode and cathode layers (or “electrodes”) and operate at room or body temperature. Typically, the capacitor is formed with a capacitor case enclosing an etched aluminum foil anode, an aluminum foil or film cathode, and a Kraft paper or fabric gauze spacer or separator impregnated with a solvent based liquid electrolyte interposed therebetween. A layer of aluminum oxide that functions as a dielectric layer is formed on the etched aluminum anode, preferably during passage of electrical current through the anode. The electrolyte comprises an ion producing salt that is dissolved in a solvent and provides ionic electrical conductivity between the cathode and the aluminum oxide dielectric. The energy of the capacitor is stored in the electrostatic field generated by opposing electrical charges separated by the aluminum oxide layer disposed on the surface of the anode and 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's overall (i.e., external) dimensions. The separator material, anode and cathode layer terminals, internal packaging, electrical interconnections, and alignment features and cathode material further increase the thickness and volume of a capacitor. Consequently, these and other components in a capacitor and the desired capacitance limit the extent to which its physical dimensions may be reduced.

Some ICD IPGs employ commercial photoflash capacitors similar to those described by Troup in “Implantable Cardioverters and Defibrillators,”Current Problems in Cardiology, Volume XIV, Number 12, December 1989, Year Book Medical Publishers, Chicago, and as described in U.S. Pat. No. 4,254,775. The electrodes or anode and cathodes are wound into anode and cathode layers separated by separator layers of the spiral. Anode layers employed in such photoflash capacitors typically comprise one or two sheets of a high purity (99.99%), porous, highly etched, anodized aluminum foil. Cathode layers in such capacitors are formed of a non porous, highly etched aluminum foil sheet which may be somewhat less pure (99.7%) respecting aluminum content than the anode layers. The separator formed of one or more sheet or layer of Kraft paper saturated and impregnated with a solvent based liquid electrolyte is located between adjacent anode and cathode layers. The anode foil thickness and cathode foil thickness are on the order of 100 micrometers and 20 micrometers, respectively. Most commercial photoflash capacitors contain a core of separator paper intended to prevent brittle, highly etched aluminum anode foils from fracturing during winding of the anode, cathode and separator layers into a coiled configuration. The cylindrical shape and paper core of commercial photoflash capacitors limits the volumetric packaging efficiency and thickness of an ICD IPG housing made using same.

The aluminum anodes and cathodes of aluminum electrolytic capacitors generally each have at least one tab extending beyond their perimeters to facilitate electrical connection of all (or sets of) the anode and cathode layers electrically in parallel to form one or more capacitor and to make electrical connections to the exterior of the capacitor case. Tab terminal connections for a wound electrolytic capacitor are described in U.S. Pat. No. 4,663,824 that are laser welded to feedthrough pin terminals of feedthroughs extending through the case. Wound capacitors usually contain two or more tabs joined together by crimping or riveting.

Flat electrolytic capacitors have also been disclosed in the prior art for general applications as well as for use in ICDs. More recently developed ICD IPGs employ one or more flat high voltage capacitor to overcome some of the packaging and volume disadvantages associated with cylindrical photoflash capacitors. For example, U.S. Pat. No. 5,131,388 discloses a flat capacitor having a plurality of stacked capacitor layers each comprising an “electrode stack sub-assembly”. Each capacitor layer contains one or more anode sheet forming an anode layer having an anode tab, a cathode sheet or layer having a cathode tab and a separator for separating the anode layer from the cathode layer. In the '388 patent, the capacitor stack of stacked capacitor layers is encased within a non-conductive, polymer envelope that is sealed at its seams and fitted into a chamber of a conductive metal, capacitor case or into a compartment of the ICD IPG housing, and electrical connections with the capacitor anode(s) and cathode(s) are made through feedthroughs extending through the case or compartment wall. The tabs of the anode layers and the cathode layers of all of the capacitor layers of the stack are electrically connected in parallel to form a single capacitor or grouped to form a plurality of capacitors. The aluminum anode layer tabs are gathered together and electrically connected to a feedthrough pin of an anode feedthrough extending through the case or compartment wall. The aluminum cathode layer tabs are gathered together and electrically connected to a feedthrough pin of a cathode feedthrough extending through the case or compartment wall or connected to the electrically conductive capacitor case wall.

Many improvements in the design of flat aluminum electrolytic capacitors for use in ICD IPGs have been disclosed, e.g., those improvements described in “High Energy Density Capacitors for Implantable Defibrillators” presented by P. Lunsmann and D. MacFarlane atCARTS96: 16th Capacitor and Resistor Technology Symposium,11-15 Mar. 1996, and atCARTS-EUROPE96: 10th European Passive Components Symposium,7-11 Oct. 1996, pp. 35-39. Further features of flat electrolytic capacitors for use in ICD IPGs are disclosed in U.S. Pat. Nos. 4,942,501; 5,086,374; 5,146,391; 5,153,820; 5,562,801; 5,584,890; 5,628,801; and 5,748,439, all issued to MacFarlane et al.

A number of recent patents including U.S. Pat. No. 5,660,737 and U.S. Pat. Nos. 5,522,851; 5,801,917; 5,808,857; 5,814,082; 5,908,151; 5,922,215; 5,926,357; 5,930,109; 5,968,210 and 5,983,472, all assigned to the same assignee, disclose related flat electrolytic capacitor designs for use in ICDs. In several of these patents, internal alignment elements are employed as a means for controlling the relative edge spacing of the anode and cathode layers from the conductive capacitor case. In these patents, each anode layer and cathode layer is provided with an outwardly extending tab, and the anode and cathode tabs are electrically connected in common to a feedthrough pin and a step feature of the conductive capacitor case, respectively. The cathode tabs are gathered together against the step feature and ultrasonically welded together and to the step feature. In the '357 patent, the anode tabs are laser welded to one end of an aluminum ribbon that is ultrasonically welded at its other end to an aluminum layer that is ultrasonically welded to the terminal pin. The feedthrough terminal pin is electrically isolated from and extends outside and away from the case to provide an anode connection pin. A cathode connection pin is attached to the case and extends outwardly therefrom. The anode and cathode connection pins are electrically connected into the DC—DC converter circuitry, but the attachment mechanism is not described in any detail.

Thus, the anode layers and the cathode layers of each capacitor layer in the stack are electrically coupled together to form one or more capacitor cathode and anode. In assembling a capacitor of these types, it is necessary that the anode and cathodes remain separated electrically from one another by the separators placed between adjoining cathode and anode layers to prevent short circuiting. It is also important that a minimum separation between the anode and cathode layers be maintained to prevent arcing therebetween, or between an anode layer of the anode and the case, when the case is conductive and coupled to the cathode. 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 commercial cylindrical capacitors, the amount of separator overhang is typically on the order of 0.050 to 0.100 inches (0.127 to 0.254 mm). 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 electrolytic capacitors, anode to cathode alignment is typically maintained through the use of adhesive electrolyte as disclosed in the above-referenced patents to MacFarlane, supra. The above-referenced '851 patent describes 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. Moreover, the above-referenced '082 patent describes use of inwardly directed registration notches in the capacitor electrode stack periphery that are used during registration of the stack within the interior case chamber which reduce capacity. The '082 patent also provides for cathode layer peripheral edges that extend outward beyond the anode layer peripheral edges through a major portion of the electrode stack periphery that can electrically contact the case. This approach is wasteful of space that could be used by anode layers to increase capacity.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to providing efficient usage of the space within the interior case chamber of an electrolytic capacitor particularly adapted for use in IMDs. The capacitor is formed with an electrode stack assembly comprising a plurality of stacked capacitor layers each comprising an anode sub-assembly of at least one anode layer, a cathode layer and separator layers wherein the anode and cathode layers have differing dimensions that avoid electrical short circuits between peripheral edges of adjacent anode and cathode layers due to edge defects but maximize anode electrode surface area.

In a preferred embodiment the electrolytic capacitor is formed of a capacitor case defining an interior case chamber and case chamber periphery, an electrode stack assembly of a plurality of stacked capacitor layers having anode and cathode tabs disposed in the interior case chamber, an electrical connector assembly for providing electrical connection with the anode and cathode tabs through the case, a cover, and electrolyte filling the remaining space within the interior case chamber.

The plurality of capacitor layers and further separator layers are stacked into the electrode stack assembly and disposed within the interior case chamber such that the adjacent anode and cathode layers are electrically isolated from one another. The anode layer peripheral edges of the anode sub-assemblies of the stacked capacitor layers extend closer to the case side wall than the cathode peripheral edges of the cathode layers of the stack of capacitor layers throughout a major portion of the case chamber periphery. The separator layer peripheral edges extend to the case periphery and space the anode layer peripheral edges therefrom. Any burrs, debris or distortions or deformations or other edge defects along any of the anode layer peripheral edges causing the anode layer edges to effectively extend in the electrode stack height direction causes the anode layer peripheral edges having such tendency to contact an adjacent anode layer. In this way, anode layer surface area is maximized, and short circuiting of the anode layers with the cathode layers is avoided.

A case liner can also be disposed around the electrode stack assembly periphery.

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 IMDs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates one embodiment of ICD IPG10in which the capacitor of the present invention is advantageously incorporated, the associated ICD electrical leads14,16and18, and their relationship to a human heart12. The leads are coupled to ICD IPG10by means of multi-port connector block20, which contains separate connector ports for each of the three leads illustrated. Lead14is coupled to subcutaneous electrode30, which is intended to be mounted subcutaneously in the region of the left chest. Lead16is 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.

Lead18is provided with elongated electrode coil28which is located in the right ventricle of the heart. Lead18also includes stimulation electrode34which takes the form of a helical coil which is screwed into the myocardial tissue of the right ventricle. Lead18may also include one or more additional electrodes for near and far field electrogram sensing.

In the system illustrated, cardiac pacing pulses are delivered between helical electrode34and elongated electrode28. Electrodes28and34are also employed to sense electrical signals indicative of ventricular contractions. As illustrated, it is anticipated that the right ventricular electrode28will 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 electrode28and electrode30and between electrode28and electrode32. During sequential pulse defibrillation, it is envisioned that pulses would be delivered sequentially between subcutaneous electrode30and electrode28and between coronary sinus electrode32and right ventricular electrode28. Single pulse, two electrode defibrillation shock regimens may be also provided, typically between electrode28and coronary sinus electrode32. Alternatively, single pulses may be delivered between electrodes28and30. The particular interconnection of the electrodes to an ICD will depend somewhat on which specific single electrode pair defibrillation shock regimen is believed more likely to be employed.

FIG. 2is a block diagram illustrating the interconnection of high voltage output circuit40, high voltage charging circuit64and capacitors265according to one example of the microcomputer based operating system of the ICD IPG of FIG.1. As illustrated, the ICD operations are controlled by means of a stored program in microprocessor42, which performs all necessary computational functions within the ICD. Microprocessor42is linked to control circuitry44by means of bi-directional data/control bus46, and thereby controls operation of the output circuitry40and the high voltage charging circuitry64. Pace/sense circuitry78awakens microprocessor42to 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 circuitry78on reprogramming of the ICD operating modes or parameter values or on the occurrence of signals indicative of delivery of cardiac pacing pulses or of the occurrence of cardiac contractions.

The basic operation and particular structure or components of the exemplary ICD ofFIGS. 1 and 2may correspond to any of the systems known in the art, and the present invention is not dependent upon any particular configuration thereof. The flat aluminum electrolytic capacitor of the present invention may be employed generally in conjunction with the various systems illustrated in the aforementioned '209 patent, or in conjunction with the various systems or components disclosed in the various U.S. patents listed in the above-referenced parent patent application Ser. No. 09/531,352.

Control circuitry44provides three signals of primary importance to output circuitry40. Those signals include the first and second control signals discussed above, labeled here as ENAB, line48, and ENBA, line50. Also of importance is DUMP line52which initiates discharge of the output capacitors and VCAP line54which provides a signal indicative of the voltage stored on the output capacitors C1, C2, to control circuitry44. Defibrillation electrodes28,30and32illustrated inFIG. 1, above, are shown coupled to output circuitry40by means of conductors22,24and26. For ease of understanding, those conductors are also labeled as “COMMON”, “HVA” and “HVB”. However, other configurations are also possible. For example, subcutaneous electrode30may be coupled to HVB conductor26, to allow for a single pulse regimen to be delivered between electrodes28and30. During a logic signal on ENAB, line48, a cardioversion/defibrillation shock is delivered between electrode30and electrode28. During a logic signal on ENBA, line50, a cardioversion/defibrillation shock is delivered between electrode32and electrode28.

The output circuitry includes a capacitor bank, including capacitors C1and C2and diodes121and123, used for delivering defibrillation shocks to the electrodes. Alternatively, the capacitor bank may include a further set of capacitors as depicted in the above referenced '758 application. InFIG. 2, capacitors265are illustrated in conjunction with high voltage charging circuitry64, controlled by the control/timing circuitry44by means of CHDR line66. As illustrated, capacitors265are charged by means of a high frequency, high voltage transformer65. Proper charging polarities are maintained by means of the diodes121and123. VCAP line54provides 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 circuitry78includes an R-wave sense amplifier and 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 microprocessor42via control/data bus80.

Control signals triggering generation of cardiac pacing pulses by pace/sense circuitry78and signals indicative of the occurrence of R-waves, from pace/sense circuitry78are communicated to control circuitry44by means of a bi-directional data bus81. Pace/sense circuitry78is coupled to helical electrode34illustrated inFIG. 1by means of a conductor36. Pace/sense circuitry78is also coupled to ventricular electrode28, illustrated inFIG. 1, by means of a conductor82, allowing for bipolar sensing of R-waves between electrodes34and28and for delivery of bipolar pacing pulses between electrodes34and28, as discussed above.

FIGS.3(a) through3(g) show perspective views of various components of ICD IPG10, including one embodiment of the capacitor of the present invention, as those components are placed successively within the housing of ICD IPG10. In FIG.3(a), electronics module360is placed in right-hand shield340of ICD IPG10. FIG.3(b) shows ICD IPG10once electronics module360has been seated in right-hand shield340.

FIG.3(c) shows a pair of capacitors265formed as described herein prior to being placed within right-hand shield340, the capacitors265being connected electrically in series by interconnections in electronics module340. FIG.3(d) shows ICD IPG10once the pair of capacitors265has been placed within right-hand shield340.

FIG.3(e) shows insulator cup370prior to its placing atop capacitors265in right-hand shield340. FIG.3(f) shows electrochemical cell or battery380having insulator382disposed around battery380prior to placing it in shield340. Battery380provides the electrical energy required to charge and re-charge capacitors265, and also powers electronics module360. Battery380may take any of the forms employed in the prior art to provide cardioversion/defibrillation energy, some of which are identified in parent patent application Ser. No. 09/531,352.

FIG.3(g) shows ICD IPG10having left-hand shield350connected to right-hand shield340and feedthrough390projecting upwardly from both shield halves. Activity sensor400and patient alert apparatus410are shown disposed on the side lower portion of left-hand shield350. Left-hand shield350and right-hand shield340are subsequently closed and hermetically sealed (not shown in the figures).

FIG. 4shows an exploded view of one embodiment of a capacitor layer or single anode/cathode sub-assembly227of capacitor265. The capacitor design described herein employs a stacked configuration of a plurality of capacitor layers or single anode/cathode sub-assemblies227as further described below with respect to FIG.6. Each anode/cathode sub-assembly227comprises alternating substantially rectangular-shaped anode layers185and cathode layers175, with a substantially rectangular-shaped separator layer180being interposed therebetween. The shapes of anode layers185, cathode layers175and separator layers180are primarily a matter of design choice, and are dictated largely by the shape or configuration of case90within which those layers are ultimately disposed. Anode layers185, cathode layers175and separator layers180may assume any arbitrary shape to optimize packaging efficiency.

Anode sub-assembly170dmost preferably comprises a plurality of non-notched anode layers185a,185b,185c, notched anode layer190including anode tab notch200, and anode tab195coupled to anode layer185a. It will be understood that anode sub-assembly170dshown inFIG. 4is but one possible embodiment of an anode sub-assembly170. Cathode layer175dmost preferably is formed of a single sheet and has cathode tab176formed integral thereto and projecting from the periphery thereof.

In one preferred embodiment of the sub-assembly227as depicted in the figures, two individual separator layer sheets180aand180bform the separator layer180that is disposed between each anode sub-assembly170and cathode layer175. Further single separator layer sheets180aand180bare disposed against the outer surfaces of the anode layer185cand the cathode layer175d. When the sub-assemblies are stacked, the outermost single separator layer sheets180aand180bbear against adjacent outermost single separator layer sheets180band180a, respectively, of adjacent capacitor layers so that two sheet separator layers180separate all adjacent cathode and anode layers of an electrode stack assembly225.

It will be understood by those skilled in the art that the precise number of sub-assemblies227selected for use in a electrode stack assembly225will depend upon the energy density, volume, voltage, current, energy output and other requirements placed upon capacitor265. Similarly, it will be understood by those skilled in the art that the precise number of notched and un-notched anode layers185, anode tabs195, anode sub-assemblies170, cathode layers175and separator layers180selected for use in a given embodiment of anode/cathode sub-assembly227will depend upon the energy density, volume, voltage, current, energy output and other requirements placed upon capacitor265. It will now become apparent that a virtually unlimited number of combinations and permutations respecting the number of anode/cathode sub-assemblies227, and the number of un-notched and notched anode layers185forming anode sub-assembly170, anode sub-assemblies170, anode tabs195, cathode layers175and separator layers180disposed within each anode/cathode sub-assembly227, may be selected according to the particular requirements of capacitor265. Anode layers185, cathode layers175and separator layers180are most preferably formed of materials typically used in high quality aluminum electrolytic capacitors.

Anode layers185and190are formed of anode foil that 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/cm2), 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 being about 100 micrometers thick, and a cleanliness of about 1.0 mg/m2respecting projected area maximum chloride contamination. The anode foil preferably 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 are commercially available on a widespread basis.

Individual anode layers185are typically somewhat stiff and formed of high-purity aluminum processed by etching to achieve high capacitance per unit area. Thin anode foils are preferred, especially if they substantially maintain or increase specific capacitance while reducing the thickness of the electrode stack assembly225, or maintain the thickness of electrode stack assembly225while increasing overall capacitance. For example, it is contemplated that individual anode layers185have 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.

Cathode layers175are preferably high purity and are comparatively flexible. Cathode layers175are most preferably formed from cathode foil having high surface area (i.e., highly etched cathode foil), high specific capacitance (preferably at least 200 microfarads/cm2, and at least 250 microfarads/cm2when fresh), a thickness of about 30 micrometers, a cleanliness of about 1.0 mg/m2respecting projected area maximum chloride contamination, and a purity which may be less than corresponding to the starting foil material from which anode foil is made. The cathode foil preferably 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, cathode foil has a specific capacitance ranging between about 100 and about 500 microfarads/cm2, about 200 and about 400 microfarads/cm2, or about 250 and about 350 microfarads/cm2, 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 the cathode foil be as high as possible, and that cathode layer175be as thin as possible. For example, it is contemplated that individual cathode layers175have specific capacitances of about 100 microfarads/cm2, about 200 microfarads/cm2, about 300 microfarads/cm2, about 400 microfarads/cm2, about 500 microfarads/cm2, about 600 microfarads/cm2, about 700 microfarads/cm2, about 800 microfarads/cm2, about 900 microfarads/cm2, or about 1,000 microfarads/cm2. Suitable cathode foils are commercially available on a widespread basis. In still other embodiments, cathode foil is formed of materials or metals in addition to aluminum, aluminum alloys and “pure” aluminum.

Separator layer sheets180aand180bouter separator layers165aand165bare most preferably made from a roll or sheet of separator material. Separator layers180are preferably cut slightly larger than anode sub-assemblies170and cathode layers175to accommodate misalignment during the stacking of layers, to prevent subsequent shorting between anode and cathode layers, and to otherwise ensure that a physical barrier is disposed between the anodes and the cathodes of the finished capacitor. In accordance with the present invention, the anode sub-assemblies170are also cut larger than the cathode layers175.

It is preferred that separator layer sheets180aand180band exterior separator layers165aand165b(shown inFIG. 9) 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. In one preferred embodiment, separator material is a pure cellulose, very low halide or chloride content Kraft paper having a thickness of about 0.0005 inches (0.0013 mm), a density of about 1.06 grams/cm3, a dielectric strength of 1,400 Volts AC per 0.001 inch (0.025 mm) thickness, and a low number of conducting paths (about 0.4/ft2or less). Separator layer sheets180aand180band outer separator layers165aand165bmay 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 like those disclosed in U.S. Pat. Nos. 3,555,369 and 3,883,784 in some embodiments of the capacitor layers

In such capacitor stacks formed of a plurality of capacitor layers, a liquid electrolyte saturates or wets separator layers180and is disposed within case90. It is to be understood, however, that various embodiments 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, 5,146,391 and 5,153,820. Note that an appropriate inter-electrode adhesives/electrolyte layer may be employed in place of paper, gauze or porous polymeric materials to form separator layer180.

Continuing to refer toFIG. 4, a first preferred step in assembling a flat aluminum electrolytic capacitor is to cut anode layers185and190, anode tabs195, cathode layers175and separator layers180. 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 but are less preferred.

Such low clearance results in smooth, burr free edges being formed along the peripheries of anode layers185and190, anode tabs195, cathode layers175and separator layers180. 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 layers185and190, anode tabs195, cathode layers175and separator layers180may result in electrical short circuit and failure of the capacitor. The means by which anode foil, cathode foil and separator materials are cut or formed 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. The use of low clearance dies produces an edge superior to the edge produced by other cutting methods, such as steel rule dies. The shape, flexibility and speed of a low clearance die have been discovered to be superior to those achieved by laser or blade cutting. Other methods of cutting or forming anode layers185and190, anode tabs195, cathode layers175and separator layers180include, but are not limited to, steel rule die cutting, laser cutting, water jet cutting and blade cutting.

In spite of these precautions taken in carefully and cleanly cutting the anode and cathode peripheral edges, some amount of burrs, cutting debris, deformations of the peripheral edges (collectively referred to as edge defects) of the anode layers during cutting or subsequent handling and welding of anode layers into anode sub-assemblies can still occur. The present invention provides a configuration and assembly method that prevents such anode layer edge defects from short circuiting with adjacent cathode layers.

The preferred low clearance of the die apparatus is especially important for cutting thin ductile materials such as the cathode foil. In addition to improving reliability, burr and debris reduction permits reductions in the thickness of separator layer180, 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 layers185and190, anode tabs195, cathode layers175and separator layers180.

In a preferred method, 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-assembly170most preferably includes one notched anode layer190, which facilitates appropriate placing and positioning of anode tab195within anode sub-assembly170. More than one notched anode layer190may also be included in anode sub-assembly170. It is preferred that the remaining anode layers of anode sub-assembly170be non-notched anode layers185. Anode tab195is most preferably formed of aluminum strip material. In one preferred embodiment, the aluminum strip material has a purity of about 99.99% aluminum and a lesser degree of anodization than the anode foil. When anode tab195is formed of a non-anodized material, cold welding of anode tab195to non-notched anode layers185may be accomplished with less force and deflection, more about which we say below. It is preferred that the thickness of anode tab195be about equal to that of notched anode layer190. If more than one notched anode layer190is employed in anode sub-assembly170, a thicker anode tab195may be employed.

Referring now to FIGS.5(a) through5(c), two non-notched anode layers185aand185bare placed on cold welding fixture base layer207of cold welding apparatus202. The various structural members of cold welding apparatus202are most preferably formed of precision machined stainless steel or a high strength aluminum alloy. Layers185aand185bare next aligned and positioned appropriately on cold welding fixture base layer207using spring loaded alignment pins209athrough209e. Pins209athrough209eretract upon top layer208being pressed downwardly upon layers185aand185bdisposed within cold welding cavity220. See also FIG.5(c), where a cross-sectional view of cold welding apparatus202is shown.

Anode layer190is similarly disposed within cavity220, followed by placing anode tab195within anode tab notch200in notched anode layer190. Anode tab195is most preferably positioned along the periphery of notched anode layer190with the aid of additional spring loaded alignment pins209fand209gdisposed along the periphery of anode tab195. Non-notched anode layer185cis then placed atop anode layer190. Stacked anode sub-assembly170is then clamped between top plate208and base plate207. Disposed within base plate207are anode layer cold welding pins206aand anode tab cold welding pin211a. Disposed within top plate208are anode layer cold welding pin206band anode tab cold welding pin211b. Base plate207and top plate208are aligned such that the axes of cold welding pins206aand206bcoincide with and are aligned respecting corresponding cold welding pins211aand211b.

Upper actuation apparatus214of cold welding apparatus202displaces cold welding pins206band211bdownwardly. Lower actuation apparatus215displaces cold welding pins206aand211aupwardly. In one embodiment of upper actuation apparatus214and lower actuation apparatus215, pneumatic cylinders are employed to move pins206a,206b,211aand211b. In another embodiment of apparatus214and apparatus215, a pair of rolling wheels is provided that move simultaneously and perpendicularly to the axes of pins206a,206b,211a, and211b. Still other embodiments of apparatus214and apparatus215may employ hydraulic actuators, cantilever beams, dead weights, springs, servomotors electromechanical solenoids, and the like for moving pins206a,206b,211aand211b. Control of actuation apparatus214and apparatus215respecting 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 plate208, cold welding pins206a,206b,211aand211bare actuated. Cold welds205and210in anode sub-assembly170are formed by compression forces generated when cold weld pins206a,206b,211aand211bare compressed against anode sub-assembly170. See FIG.6(a), where the preferred regions in which cold welds205and210are formed are shown. Cold welds205and210may be described as not only cold welds, but forged welds. This is because the interfacial boundaries between anode layers185are deformed in the region of welds205and210, 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, a plurality of pneumatic cylinders function simultaneously in upper actuation apparatus214and lower actuation apparatus215to drive pins206a,206b,211aand211bagainst anode sub-assembly170. Anode layer cold weld205and anode tab cold weld210are most preferably formed under direct constant load conditions, where pneumatic cylinders are pressurized to a predetermined fixed pressure. Anode layer cold weld205and anode tab cold weld210may also be formed under indirect constant displacement conditions, where pneumatic cylinders are pressurized until a displacement sensor placed across cold welding pins206a,206b,211aor211bgenerates a signal having a predetermined value, whereupon those pins are disengaged from anode/cathode sub-assembly227.

In another embodiment of the method, a cantilever beam mechanism is incorporated into upper actuation apparatus214and lower actuation apparatus215. Anode layer cold weld205and anode tab cold weld210are formed under direct constant displacement conditions, where cantilever beams are actuated and cause upper and lower members208and207to engage anode/cathode sub-assembly227until a hard stop point is reached. An indirect load controlled system may also be employed in apparatus214and apparatus215, 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 pins206a,206b,211aand211bmay be square, circular, oval or any other suitable shape. The shape of the ends of cold weld pins206a,206b,211aand211bmay 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. The ends of cold weld pins206a,206b,211aand211bare most preferably rounded or domed and circular in cross-section. Cold weld pins206a,206b,211aand211bpreferably have a diameter of about 0.060 inches (0.174 mm) and further have a beveled or radiused end. Cold weld pins206a,206b,211aand211bare 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 side walls of cold welding pins206a,206b,211aand211bmay be coated, clad or otherwise modified to increase wear resistance, deformation resistance or other desirable tribilogical attributes of the pins.

The primary function of cold welds205and210is to provide electrical interconnections between layers185a,185b,185cand190and anode tab195, while minimizing the overall thickness of anode sub-assembly170in the regions of welds205and210. 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 inch (0.020 mm). 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 stack as a whole.

In one cold welding method and corresponding apparatus, no or an inappreciable net increase in anode sub-assembly170thickness results when cold weld geometries and formation processes are appropriately optimized. Several embodiments of anode-assembly170have 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. Two, three, four, five, six or more anode layers185and190may be cold-welded to form anode sub-assembly170as described herein.

FIG.6(b) shows a cross-sectional view of a portion of one embodiment of a cold-welded anode assembly formed in accordance with the preferred cold welding method. Anode layers185a,190,185band185chaving anode layer thicknesses ta, tN, tband tc, respectively, are cold-welded together at weld205through the compressive action of pins206aand206bmounted in bottom plate207and top plate208, respectively. Pins206aand206bform central depressions293and294, respectively, in anode sub-assembly170d, and further result in the formation of rims295and296, respectively. Rims295and296project downwardly and upwardly, respectively, from the surrounding surfaces of anode sub-assembly170d, thereby increasing the overall thickness T of anode sub-assembly170dby ΔT (T measured in respect of the non-cold-welded surrounding regions or portions of anode sub-assembly170d).

FIG.6(c) shows a cross-sectional view of another portion of one embodiment of a cold-welded anode assembly wherein anode layers185a,185band185cand anode tab195, having anode layer/tab thicknesses ta, tb, tcand ttab, respectively, are cold-welded together at weld210through the compressive action of pins211aand211bmounted in bottom plate207and top plate208, respectively. Pins211aand211bform central depressions297and298, respectively, in anode sub-assembly170d, and further result in the formation of rims299and301, respectively. Rims299and301project downwardly and upwardly, respectively, from the surface of anode sub-assembly170d, thereby increasing overall thickness T of anode sub-assembly170dby ΔT (T measured in respect of the non-cold-welded surrounding regions or portions of anode sub-assembly170d).

The overall thickness T of anode sub-assembly170dis therefore defined by the equation:
T=nt
The maximum overall thickness T+ΔT of anode sub-assembly170din the region of cold welds205or210is then defined by the equation:
T+ΔT=nt+ΔT
where Tasis the overall thickness of anode sub-assembly170din non-cold-welded regions, n is the number of anode layers185and/or190in anode sub-assembly170d, and t is the thickness of individual anode layers185and/or190or anode tab195where the thicknesses tn, ta, tb, tcand ttab, are assumed to be the same.

It is highly desirable to form anode sub-assembly 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 capacitor265. Additionally, the overall thickness of capacitor265may be reduced when the value of the ratio ΔT/T is made smaller.

Referring now to FIG.6(a), the overall thickness of electrode stack assembly225may be reduced further by staggering or offsetting horizontally the respective vertical locations of tabs195athrough195h(and corresponding cold welds210). In this embodiment, tabs195a195b, for example, are not aligned vertically in respect of one another. Such staggering or offsetting of tabs195permits the increases in thickness ΔT corresponding to each of anode subassemblies170athrough170hto be spread out horizontally over the perimeter or other portion of electrode stack assembly225such that increases in thickness ΔT do not accumulate or add constructively, thereby decreasing the overall thickness of electrode stack assembly225. Cold welds205may similarly be staggered or offset horizontally respecting one another and cold weld210to achieve a reduction in overall thickness of electrode stack assembly225.

In another preferred embodiment, the anode sub-assembly170of each capacitor layer or electrode sub-assembly comprises a plurality of three, four, five or more anode sheets or layers185and190, each sub-assembly most preferably having at least one anode layer having a corresponding anode tab195attached thereto or forming a portion thereof, the layers being cold welded together to form anode sub-assembly170. For example, an anode sub-assembly170may comprise six anode layers185constructed by cold-welding two separate triple anode layers185that were previously and separately cold-welded or otherwise joined together. Alternatively, anode sub-assembly170layer may comprise seven anode layers constructed by cold-welding together one triple anode layer185and one quadruple anode layer185that were previously and separately cold-welded or otherwise joined together. In another preferred embodiment, multiple notched anode layers190may employed in anode sub-assembly170, thereby permitting the use of a thicker anode tab material.

The geometry of base plate207and top plate208in the regions surrounding cold welding pins206a,206b,211aand211bhas been discovered to affect the properties of cold welds205and210. In a preferred method, the mating surfaces of plates207and208surfaces have no radiused break formed in the perimeters of the pin holes. The presence of radiused breaks or chamfers in those regions may cause undesired deformation of cold welds205and210therein. Such deformation may result in an increase in the thickness of anode sub-assembly170, which may translate directly into an increase in the thickness of capacitor265. Note further that the increase in thickness so resulting is a multiple of the number of anode sub-assemblies170present in electrode stack assembly225. Alternatively, radiused breaks or chamfers may be employed in the region of the pin holes in base plate207and top plate208, but appropriate capacitor design accommodations are most preferably made, such as staggering the positions of adjoining stacked cold welds.

Once cold welding pins206a,206b,211aand211bhave been actuated against anode sub-assembly170, top plate208is removed and cold-welded anode sub-assembly170is provided for further stacking of anode/cathode sub-assembly227. As illustrated inFIGS. 4, and6(a), this illustrated embodiment of electrode stack assembly225most preferably comprises a plurality of cold-welded anode sub-assemblies175athrough175h, a plurality of cathode layers175athrough175i, a plurality of separator layers180aand180b, outer separator layers165aand165b, outer wrap115and wrapping tape245.

Outer wrap115is most preferably die cut from separator material 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 tape245is 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 wrap115and wrapping tape245together comprise an electrode stack assembly wrap which has been discovered to help prevent undesired movement or shifting of electrode stack assembly225during 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 stack assembly225during subsequent processing which accomplish substantially the same function as the electrode stack assembly wrap comprising outer wrap115and wrapping tape245. Alternative means for immobilizing and securing electrode stack assembly225other 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 stack assembly225, adhesive electrolytes for forming separator layers180, and so on.

The stacking process by which electrode stack assembly225is most preferably made begins by placing outer wrap115into a stacking fixture followed by placing outer paper or separator layer165athereon. Next, cathode layer175ais placed atop separator layer165a, followed by separator layers180aand180bbeing disposed thereon. Cold-welded anode sub-assembly170ais then placed atop separator layer180b, followed by placing separator layers180aand180bthereon, and so on. The placing of alternating cathode layers175and anode sub-assemblies170with separator layers180aand180binterposed therebetween continues in the stacking fixture until final cathode layer175hhas been placed thereon.

In the embodiment of electrode stack assembly225shown in FIG.6(a), eight anode sub-assemblies (anode sub-assemblies170athrough170h) and nine cathode layers (cathode layers175athrough175i) are illustrated. The voltage developed across each combined anode sub-assembly/separator layer/cathode layer assembly disposed within electrode stack assembly225most preferably ranges between about 360 and about 390 Volts DC. As described below, the various anode sub-assemblies of electrode stack assembly225are typically connected in parallel electrically, as are the various cathode layers of electrode stack assembly225.

Consistent with the discussion hereinabove concerningFIG. 4, it will now be understood by one skilled in the art that electrode stack assembly225shown 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-assemblies170, cathode layers175, separator layers180, anode tabs195, cathode tabs176, 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 stack assembly225, the number of anode layers185employed in each anode sub-assembly170is 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 layers185/190included in selected anode sub-assemblies170(as opposed to adding or subtracting full anode/cathode sub-assemblies227from electrode stack assembly225to thereby change the total capacitance). Following placing of cathode layer175iin the stack, outer paper layer165bis placed thereon, and outer wrap115is folded over the top of electrode stack assembly225. Wrapping tape245then holds outer wrap115in place and secures the various components of electrode stack assembly225together.

The physical dimensions of separator layers165and180are most preferably somewhat larger than those of anode sub-assemblies170and cathode layers175to 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 capacitor265may be compromised if a portion of anode sub-assembly170comes into contact with a conducting case wall, if a burr on the periphery of anode sub-assembly170or cathode layer175comes into contact with an adjoining layer of opposing polarity, or if separator layer180aor180bdoes 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 stack assembly225is referred to herein as separator overhang. Decreasing the amount of separator overhang increases the energy density of capacitor265. 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.

A preferred method for assuring consistent registration of separator layers165and180, anode sub-assemblies170and cathode layers175in electrode stack assembly225involves stacking the various elements of electrode stack assembly225using robotic assembly techniques. More particularly, the various electrode and separator layers of electrode stack assembly225are stacked and aligned using an assembly work cell 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 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, 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. The position of the part is robotically translated from the pickup point into the stacking fixture by the robot arm with an accuracy of 0.005 inch (0.013 mm) 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 placing to be verified. This system can accurately determine the position of each part or element in electrode stack assembly225to 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 permit precise alignment and stacking of separator layers165and180, anode sub-assemblies170and cathode layers175in electrode stack assembly225, while minimizing the addition of undesirable unused volume to capacitor265.

Another method for assuring registration of separator layers165and180, anode sub-assembly170and cathode layer175in electrode stack assembly225involves 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 side walls disposed about its periphery for positioning separator layers165and180. Because cathode layers175and anode sub-assemblies170do not extend to the periphery of the separator, an alternative means for accurately positioning those electrodes becomes necessary.

Positioning of alternating cathode layers175and anode subassemblies170is most preferably accomplished using alignment elements such as posts or side walls disposed about the periphery of cathode tab176and anode tab195. It has been discovered that the accuracy of layer placing 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 tab176in respect of the length of anode tab195. Tabs176and195may 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 stack assembly225during the process of electrode tab interconnection (more about which we say below).

Another method for ensuring registration of separator layers165and180, anode sub-assembly170and cathode layer175in electrode stack assembly225does not require the use of internal alignment elements within capacitor265is enveloping or covering anode sub-assembly170and cathode layer175with separator material. In this method, separator layers180aand180bare combined into a single die cut piece part that is folded around either anode sub-assembly170or cathode layer175. 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 sub-assembly in this manner secures and registers anode sub-assembly170and cathode layer175in respect of the periphery of the separator envelope so formed. The resulting anode/cathode sub-assembly227is then presented for stacking in electrode stack assembly225.

FIG. 7shows a top perspective view of one embodiment of an electrode stack assembly225of the electrolytic capacitor265.FIG. 8shows an enlarged view of a portion of the electrode stack assembly225of FIG.7. After wrapping electrode stack assembly225with outer wrap115and wrapping tape245, interconnection of gathered anode tabs232and gathered cathode tabs233with their respective external terminals is most preferably made.

FIG. 9shows an exploded top perspective view of the embodiment of the capacitor265employing the electrode stack assembly ofFIGS. 6,7and8therein and not employing a case liner. This embodiment includes anode feedthrough120and cathode feedthrough125most preferably having coiled basal portions121and126, respectively. Feedthroughs120and125provide electrical feedthrough terminals for capacitor265and gather gathered anode tabs232and gathered cathode tabs233within basal portions121and126for electrical and mechanical interconnection.

In one method of making tab interconnections and feedthrough terminal connections, feedthrough wire is first provided for construction of feedthroughs120and125, as shown inFIGS. 9 and 10. In one embodiment, a preferred feedthrough wire is aluminum having a purity greater than or equal to 99.99% and a diameter of 0.020 inch (0.510 mm). Wire is trimmed to predetermined lengths for use in anode feedthrough120or cathode feedthrough125. 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 tabs232or gathered cathode tabs233.

Gathered anode tabs232are next gathered, or brought together in a bundle by crimping, and inside diameter131of anode feedthrough coil assembly120is placed over gathered anode tabs232such that anode feedthrough pin130extends outwardly away from the base of gathered anode tabs232. Similarly, gathered cathode tabs233are gathered and inside diameter136of cathode feedthrough coil assembly125is placed over gathered cathode tabs233such that cathode feedthrough pin135extends outwardly away from the base of cathode tab233. Coiled basal portions121and126of anode and cathode feedthroughs120and125are then most preferably crimped onto anode and cathode tabs232and233, followed by trimming the distal ends thereof, most preferably such that the crimps so formed are oriented substantially perpendicular to imaginary axes234and235of tabs232and233. Trimming the distal ends may also, but less preferably, be accomplished at other non-perpendicular angles respecting imaginary axes234and235.

A crimping force is applied to feedthrough coils121and126and tabs232and233throughout a subsequent preferred welding step. In one method, 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 tabs232and233. Following welding of feedthroughs120and125to gathered anode tabs232and gathered cathode tabs233, respectively, pins130and135are bent for insertion through feedthrough holes142and143of case90.

Many different embodiments of the feedthroughs, and means for connecting the feedthroughs to anode and cathode tabs exist other than those shown explicitly in the figures. For example, the feedthroughs include 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 pins130and135to anode and cathode tabs232and233. Various methods of making tab interconnections and feedthrough connections which are not critical to the present invention are disclosed in the above-referenced '133 patent which may be followed in completing the fabrication of capacitor265.

FIG. 10shows an exploded top perspective view of capacitor265ofFIG. 9in a partially assembled state. Case90contains a means for accepting anode ferrule95therein, shown inFIGS. 9 and 10as anode feedthrough hole or opening142. Case90further contains a means for accepting cathode ferrule100, shown inFIGS. 9 and 10as cathode feedthrough hole or opening143. Case90also includes a means for accepting fill port ferrule105, shown inFIGS. 9 and 10as fill port hole139. In a preferred embodiment, case90and cover110are formed of aluminum and are electrically connected to the cathode layers, and where case90and cover110are at the same electrical potential as the cathode layers, i.e., at negative potential.

Ferrules95,100and105are most preferably welded to case90(or otherwise attached thereto such as by a suitable epoxy, adhesive, solder, glue or the like), and together comprise case sub-assembly108. Radial flanges in anode ferrule95and cathode ferrule100provide a region for making a lap joint between the side wall of case90and around the perimeters of feedthrough ferrule holes142and143. In preferred methods, a circumferential laser weld is made in the circumferential joint between the ferrules and the case side wall92, and welding is carried out in two primary steps. First, a series of tack welds is made around the circumference of the joint. 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 joint93.

Wire guides140and141center pins within the inside diameter of the ferrules to permit anode and cathode pins130and135to be electrically insulated from the inside surface of case90, anode ferrule95, and cathode ferrule100. Wire guides140and141may themselves be electrically insulating, and electrical insulation of pins130and135from case90and other components is most preferably enhanced by means of potting adhesive160.

Wire guides140and141most preferably contain annular, ramped, or “snap-in” features formed integrally therein. Those features prevent wire guides140and141from being pushed out of their respective ferrules during handling, but are most preferably formed such that insertion of wire guides140and141in their corresponding ferrules may occur using forces sufficiently low so as not to damage case90or ferrules95or100during the inserting step.

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.

In one embodiment, connector block145is placed on anode ferrule95and cathode ferrule100by guiding anode feedthrough pin130through connector block anode feedthrough hole300, and then guiding cathode feedthrough pin135through connector block cathode feedthrough hole305. Connector block145is next seated flush against the exterior surface of case90. Anode feedthrough pin130is then inserted into anode crimp tube150bof wire harness155. Cathode feedthrough pin135is then inserted into cathode crimp tube150aof wire harness155. Crimp tubes150aand150bare then crimped to feedthrough pins130and135.

In other preferred embodiments, electrical connections in connector block145may 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 wire130or135and harness wire151or152.

The distal or basal portions of crimp tubes150aand150bare crimped on insulated anode lead151and insulated cathode lead152, respectively. Insulated leads151and152are likewise connected to terminal connector153. Terminal connector153may most preferably be connected to electronics module360. Standard methods of making aluminum electrolytic capacitors do not lend themselves readily to very small crimp connections, especially in miniaturized ICD designs. A preferred method permits small crimp connections and interconnection means to be formed, and further permits highly efficient packaging in ICD IPG10.

In the preferred method described above, connector block145and epoxy adhesive provide strain relief to feedthrough pins130and135and to the feedthrough wire crimp connections, and further provide an epoxy seal between wire guides140and141, case90and ferrules95and100. The crimp tubes may also serve as a connection point for device level assembly. Alternatively, the crimp tubes may be integrated within wire harness155prior 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 shown inFIGS. 10 and 11, terminal connector153forms the female end of a slide contact. In another embodiment, terminal connector153is connected to other modules by resistance spot welding, ultrasonic wire bonding, soldering, crimping, or other attachment means.

The particular configuration and fabrication of the feedthroughs, the connections thereto, the connector block, the wire harness, etc., are not important to the present invention. Further details related to the fabrication of the depicted, exemplary form of the feedthroughs, internal and external connections thereto, the connector block, the wire harness, etc., are set forth in detail in the above-referenced '133 patent.

FIG. 11shows a top view of one embodiment of assembled capacitor265with cover110not present and without a case liner separating electrode stack assembly225from the case90and cover110. In one embodiment, the head space portion of electrode stack assembly225(referred to herein as head space230) is insulated from case90and cover110. The means by which head space 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 head space insulators may be formed include all those listed hereinabove respecting materials for forming wire guides140and141. Another means of providing head space insulation is to wrap electrically insulating tape, similar to wrapping tape245, around head space230to prevent the anode or cathode terminals from contacting case90or cover110or each other. Various crimp and joint configurations for joining the cover110to case90are described in detail in the above-referenced, commonly assigned '133 patent. In accordance with one aspect of the present invention, the head space insulation may be provided by a case liner300described further below.FIG. 11may also include a lower half section310of the case liner300described below (not visible inFIG. 11) that the electrode stack assembly225is nested into. An upper half section would be fitted over the electrode stack assembly after completion of the above-described electrical connections for connecting feedthrough pins130and135to anode and cathode tabs232and233.

After all welding steps are completed, the interior case chamber of capacitor265is filled with electrolyte through fill port107welded into a hole139in the side wall of the capacitor case90, the capacitor is aged, the fill port lumen is closed and the capacitor is tested. The capacitor aging, the fill port construction, use in filling the capacitor interior case with electrolyte and the closure of the fill port lumen are not critical to the present invention, and examples of the same are disclosed in detail in the above-referenced, commonly assigned '133 patent. Applications in implantable defibrillators may require two capacitors265to be connected in series. In this embodiment, an insulator is provided by a two sided adhesive being disposed between the capacitors265so that they are joined along opposing faces with the insulator/adhesive strip disposed therebetween. The pair of capacitors265is then provided for assembly in ICD IPG10as shown and described above with respect to FIGS.3(a) through3(g).

In accordance with one aspect of the present invention, the capacitor case sub-assembly108and the case cover110ofFIG. 9define an interior case chamber93when hermetically welded together at the case side wall upper edge as described above. The case90has a base96bounded by a base peripheral edge at the junction of the base96and side wall91extending upwardly at a right angle therefrom to a case opening edge94for receiving cover110whereby the interior case chamber has a case chamber periphery97corresponding in shape to the base peripheral edge and bounded by the interior case side wall surface92.

The electrode stack assembly225located within the interior case chamber93is dimensioned to have a stack periphery226configured in mating relation with the case chamber periphery defined by the interior case side wall surface92as shown inFIGS. 10,11,13(a) and13(b). As described above, the electrode stack assembly225comprises a plurality of capacitor layers227a-227hand lower and upper separator layers165aand165b. The capacitor layers227a-227hand separator layers165aand165bare stacked in registration upon one another and between the case base96and the cover110through a stack height223. Edge portions of two capacitor layers227band227care shown without a liner in FIG.13(a) and with a case liner300in FIG.13(b).

As described above with respect toFIG. 4, and as shown in FIGS.13(a) and13(b), each capacitor layer227a-227hcomprises a cathode layer175a-175hhaving a cathode peripheral edge175a′-175h′ extending toward the interior case side wall92throughout a major portion229of the case chamber periphery97(FIG. 11) and having a cathode tab176a-176hextending in the head space230toward the case side wall92in a minor portion231of the case chamber periphery97. Thus, the stack periphery226similarly consists of a major periphery length229corresponding to major portion229and a minor periphery length241corresponding to minor portion231at the head space230as shown inFIGS. 7 and 8. The stack periphery226is closely spaced from and configured in shape through the major periphery length228to the shape of the major portion229of the case chamber periphery97.

Each capacitor layer227a-227halso includes an anode sub-assembly170a-170hcomprising at least one anode layer185and/or190having an anode sub-assembly peripheral edge170a′-170h′ extending toward the case side wall92throughout the major portion229and having an anode tab195a-195hextending in the head space230toward the case side wall interior surface92in the minor portion231of the case chamber periphery97.

Each capacitor layer227a-227halso includes the electrolyte bearing inner separator layer180formed of two separator layer sheets180aand180bas depicted inFIGS. 4,13(a) and13(b). Each separator layer180has a separator peripheral edge180′ extending toward the interior case side wall92. The separator layers180disposed between each adjacent anode sub-assembly and cathode layer electrically separates each anode sub-assembly from each adjacent cathode layer of the stacked capacitor layers

In reference to the embodiment of FIG.13(a), it is preferred to cut or otherwise form separator layer180such that its outer periphery edge180′ is the outermost surface of the stack periphery226and conforms closely to that of the case chamber periphery97so that the outer peripheral edges180′ contact the adjacent interior side wall surface92In preferred embodiments, the periphery of separator layer is disposed within ±0.009 inches of the adjoining side wall surface92. Such close conformity between the periphery edge180′ and the corresponding internal side walls of case90has been discovered to provide the advantage of permitting separator layers180to immobilize or secure firmly in place electrode stack assembly225in case90. This immobilization occurs because the separator paper forming separator layers180swells after electrolyte is added through the lumen of fill port107into the interior case chamber93of the otherwise assembled and sealed capacitor265.

Further in reference to FIG.13(a), in each capacitor layer227b,227c, et seq., the anode sub-assembly peripheral edges170b′,170c′, et seq., are disposed at a first distance D1from the separator layer peripheral edges180′ and the case interior side wall surface92throughout the major portion229of the case chamber periphery97. The cathode peripheral edges175a′,175b′,175c′, et seq., are disposed at a second distance D2from the case interior side wall surface92and the separator layer peripheral edges180′ throughout the major portion229of the case chamber periphery97. In this example, the second distance D2is greater than the first distance D1, and a separation difference distance D3=D2−D1. The distance D1is preferably on the order of about 0.015 to 0.040 inches (0.381 to 1.016 mm). The distance D2is preferably on the order of about 0.030 to 0.040 inches (0.762 to 1.016 mm). The distance D3is preferably on the order of about 0.000 to 0.015 inches (0.000 to 0.381 mm).

In the embodiment of FIG.13(a), the distance D1constitutes “separator overhang”. Decreasing the amount of separator overhang increases the total amount of “active” electrode material available and the resulting energy density of a given capacitor design. 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 known cylindrical capacitors, we discovered that the amount of separator overhang is typically on the order of 0.100 inches (2.5 mm).

In the embodiment depicted in FIG.13(b), a side wall of an electrically insulating case liner300is interposed between the interior side wall surface92and the anode sub-assembly peripheral edges170b′,170c′, et seq., the separator layer peripheral edges180′, and the cathode layer peripheral edges175a′,175b′,175c′, et seq. In this embodiment, the case liner side wall occupies the distance D1, and the separator layer peripheral edges180′ and the anode sub-assembly peripheral edges170b′,170c′, et seq., are all at about the distance D1from the side wall interior surface92. Preferably, distance D3ranges from 0.050 to 0.100 inches (0.125 to 0.250 mm) more preferably from 0.005 to 0.050 inches (0.013 to 0.125 mm), allowing for maximization of the size of the anode and cathode layers of electrode stack assembly225. The separation difference distance D3remains at D3=D2−D1. But, in this embodiment, D1can be made much thinner, in the range of about 0.001 to 0.100 inches (0.025 to 0.254 mm) and more preferably in the range of about 0.003 to 0.005 inches (0.075 to 0.127 mm). Therefore, the anode layers can be made larger, increasing energy storage capacity by about 4%.

In these ways, the anode layer peripheral edges of the anode sub-assemblies170a-170hof the stacked capacitor layers227a-227hextend closer to the case interior side wall surface92than the cathode layer peripheral edges175a′-175h′ throughout the major portion229of the case chamber periphery97. The tendency of any individual peripheral edges of the outermost anode layers of the anode sub-assembly peripheral edges170a′-170h′to extend toward an adjacent cathode layer peripheral edge175a′-175h′ in the stack height direction causes the anode layer edges having such tendency to contact an adjacent anode layer, not an intervening cathode layer. Therefore, any such edge distortion that is present or any edge burrs or debris present at the anode layer edges merely causes the anode layers to contact one another, and electrical shorting of the anode and cathode layers is avoided.

FIG. 14shows a top view of such an embodiment of assembled capacitor265with cover110not present and with a case liner300separating electrode stack assembly225from the case90and cover110. The case liner300provides an insulating barrier positioned about electrode stack assembly225to cover the stack periphery226throughout the major portion229illustrated in FIG.9and to also cover an edge portion of the outer separator layers165aand165b. Wiring harness connector block145is coupled to the electrode stack108through case90as described above.

FIG. 15illustrates case liner300as used inFIG. 14to enclose electrode stack assembly225. In this illustrated embodiment, case liner300is constructed in an upper half section308and a lower half section310. Electrode stack assembly225is positioned within the upper and lower half sections308and310in the assembly depicted inFIG. 15. Acase liner side wall306that extends throughout the major portion229illustrated inFIG. 9is formed when the assembly depicted inFIG. 15is completed. A cut out section312is made in the case liner side wall306in the minor portion231of the case chamber periphery97shown inFIG. 11to facilitate electrical connections from the feedthrough pins130and135to anode and cathode tabs232and233, respectively. The electrical connections are made after the liner lower half section310is placed in the interior case chamber93and the electrode stack assembly is nested into the lower half section as in FIG.11. The electrical connections illustrated inFIGS. 9-11are completed, and the upper case liner half section308is placed over the upper surface of the electrode stack assembly. A further cut-out hole is provided in the upper and lower half sections308and310in alignment with the fill port107to allow leak testing and introduction of the electrolyte as described, for example, in the above-referenced '133 patent.

Case liner300is made of an appropriate thickness of electrically insulating material depending upon the mechanical design of electrode stack assembly225, the amount of separator layer overhang, the desired distance D1separation between electrode stack periphery226and the case side wall surface92, etc. In one embodiment liner wall thickness is in the range of 0.001 to 0.100 inches (0.025 to 0.254 mm) and more preferably in the range of 0.003 to 0.005 inches (0.075 to 0.127 mm). Liner wall thickness is also a function of the type of insulating material from which liner300is made.

In one embodiment, liner300is made of a polymeric material or polymeric blend of materials, and in one preferred embodiment the polymeric material is polysulfone. Other suitable polymeric materials include polypropylene, polyethylene and ETFE. Optionally, liner300can be formed of other insulating materials, such as those materials previously disclosed herein for construction of the wire guides140and141. Liner300acts as a separator between the electrode stack periphery226and case side wall surface92, and therefore could be made of porous materials or made porous, e.g., by having holes therethrough. Other suitable electrical non-conducting materials for liner300will become apparent to those skilled in the art after reading the present application.

The mechanical design of the liner300may take many different configurations depending upon the configuration of the electrode stack assembly225. In applications where the desired shape of capacitor assembly64has a low thickness to width aspect ratio, a stacked plate electrode108design is preferred to achieve optimal energy density. Liner300can be constructed of a single part, a two part assembly, or optionally made with multiple component construction. Various embodiments of liner300mechanical design are described in detail in the above-referenced parent patent application Ser. No. 09/531,352. The use of liner300extends to cylindrical or other capacitor assembly64shapes. Although liner300is preferably thermoformed or molded, in another preferred embodiment liner300can be coated or deposited on the inside of case100or upon electrode stack assembly225. In this embodiment, the liner300is preferably less than 0.050 inches (0.127 mm) and more preferably less than 0.001 inches (0.025 mm), and more preferably less than 0.0005 inches (0.0013 mm) thick.

Although only a few exemplary embodiments of a capacitor265in which the present invention is advantageously implemented 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 a capacitor structure and method of fabrication thereof and its incorporation into an IMD in accordance with preferred embodiments of the present invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, and existing prior to the filing date of this application or coming into existence at a later time 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.

All patents and printed publications disclosed herein are hereby incorporated by reference herein into the specification hereof each in its respective entirety.