Insulative feed through assembly for electrochemical devices

An insulative feedthrough receives an electrical lead therethrough and includes a ferrule having fist and second open ends and an interior surface. At least one polymeric guide member is positioned substantially within the first end of the ferrule and has an aperture therethrough for receiving the lead. An insulating material is deposited in the ferrule through the second end for sealingly engaging the lead and the interior surface of the ferrule.

FIELD OF THE INVENTION

The present invention generally relates to electrochemical components, and more particularly to an epoxy compression feedthrough assembly for use in electrolytic capacitors, batteries and the like utilized in conjunction with implantable medical devices.

BACKGROUND OF THE INVENTION

The trend toward reductions in the size and thickness of implantable medical devices such as implantable cardioverter-defibrillators (ICDs) has led to the need for miniaturization of the electrochemical components utilized in such devices. Capacitors, for example, are employed in ICDs typically implanted in a patient's chest to treat very fast, and potentially lethal, cardiac arrhythmias. These devices continuously monitor the heart's electrical signals and sense if, for instance, the heart is beating dangerously fast. If this condition is detected, the ICD can deliver one or more electric shocks, within about five to ten seconds, to return the heart to a normal heart rhythm. These electrical stimuli may range from a few micro-joules to very powerful shocks of approximately twenty-five joules to forty joules.

Early generations of ICDs utilized high-voltage, cylindrical capacitors to generate and deliver defibrillation shocks. For example, standard wet slug tantalum capacitors generally have a cylindrically shaped conductive casing serving as the terminal for the cathode and a tantalum anode connected to a terminal lead electrically insulated from the casing. The opposite end of the casing is also typically provided with an insulator structure.

One such capacitor includes a metal container that functions as a cathode. A porous coating, including an oxide of a metal selected from a group consisting of ruthenium, iridium, nickel, rhodium, platinum, palladium, and osmium, is disposed proximate an inside surface of the container and is in electrical communication therewith. A central anode selected from the group consisting of tantalum, aluminum, niobium, zirconium, and titanium is spaced from the porous coating, and an electrolyte within the container contacts the porous coating and the anode.

While the performance of these capacitors was acceptable for defibrillator applications, efforts to optimize the mechanical characteristics of the device have been limited by the constraints imposed by the cylindrical design. In an effort to overcome this, flat electrolytic capacitors were developed. One such capacitor comprises a deep-drawn sealed capacitor having a generally flat, planar geometry. The capacitor includes at least one electrode provided by a metallic substrate in contact with a capacitive material. The coated substrate may be deposited on a casing side-wall or connected to a side-wall. The capacitor has a flat planar shape and utilizes a deep-drawn casing comprised of spaced apart side-walls joined at their periphery by a surrounding intermediate wall. Cathode material is typically deposited on an interior side-wall of the conductive encasement which serves as the negative terminal for the electrolytic capacitor, though such material may also be deposited on a separate substrate and electrically coupled to the capacitor encasement. The other capacitor terminal (i.e. the anode) is isolated from the encasement by an insulator or feedthrough structure including, for example, a glass-to-metal seal. In accordance with one known technique, an anode lead (e.g. tantalum) imbedded into the anode is laser welded to a terminal lead that passes through the ferrule. This anode lead-to-feedthrough terminal weld joint (i.e. cross-wire weld) is formed by shaping one or more of the leads into a “U” or “J” shape, pressing the terminal ends of the leads together, and laser welding the interface.

A valve metal anode made from metal powder is pressed and sintered to form a porous structure, and a wire (e.g. tantalum) is imbedded into the anode during pressing to provide a terminal for joining to the feedthrough. A separator (e.g. polyolefin, a fluoropolymer, a laminated film, non-woven glass, glass fiber, porous ceramic, etc.) is provided between the anode and the cathode to prevent short circuits between the electrodes. Separator sheets are sealed either to a polymer ring that extends around the perimeter of the anode or to themselves.

A separate weld ring and polymer insulator may be utilized for thermal beam protection as well as anode immobilization. Prior to encasement welding, a separator encased anode is joined to the feedthrough wire by, for example, laser welding. This joint is internal to the capacitor. The outer metal encasement structure is comprised essentially of two symmetrical half shells that overlap and are welded at their perimeter seam to form a hermetic seal. This weld is referred to as a rotary weld since the part is welded as it rotates on its side rather than employing a top-down approach. Alternatively, a top-down approach may be utilized to weld a lid onto a deep-drawn container. After welding, the capacitor is filled with electrolyte through a port in the encasement.

The above described techniques present concerns relating to both device size and manufacturing complexity. The use of overlapping half-shields results in a doubling of the encasement thickness around the perimeter of the capacitor thus reducing the available interior space for the capacitor's anode. This results in larger capacitors. Space for the anode material is further reduced by the presence of the weld ring and space insulator. In addition, manufacturing processes become more complex and therefore more costly, especially in the case of a deep-drawn encasement.

The abovementioned method of joining an anode lead to a terminal lead was found to be problematic, however, as the step of cross-wire welding must be performed prior to welding the feedthrough ferrule to the capacitor encasement or sufficient space must be provided in the capacitor anode structure to facilitate clamping and welding following ferrule welding. Producing the cross-wire weld prior to ferrule welding subjects the materials employed in the feedthrough seal to thermal stress and increases the cost and complexity of manufacture. Conversely, performing cross-wire welding after ferrule welding has a negative impact on volumetric efficiency.

As mentioned above, it is common for the anode terminal to be isolated from the encasement by an insulator or feedthrough structure comprised including a glass-to-metal seal. Such seals are well known in the art. To avoid problems which may be encountered due to the rigidity of glass-to-metal seals, polymer-to-metal seals have been employed. For example, it is known to secure an anode lead within a ferrule by means of a series of polymeric sealing layers. These layers may comprise a first layer of a synthetic polymeric material forming a plug on end of the ferrule internal to the electrolytic cell, a second layer of synthetic polymeric material disposed within the ferrule, and a third layer of glass disposed within the ferrule to provide a hermetic seal. Similar assemblies, varying in the arrangement and/or shape of the polymeric layers, are also known. Unfortunately, current methods of manufacturing such assemblies are relatively complex, time-consuming, and expensive.

It should thus be appreciated that it would be desirable to provide an electrochemical device including an improved feedthrough assembly that is volumetrically efficient and simple to manufacture.

BRIEF SUMMARY OF THE INVENTION

According to a broad aspect of the invention there is provided an insulative feedthrough for receiving an electrical lead therethrough. The feedthrough includes a ferrule having fist and second open ends and an interior surface. At least one polymeric guide member is positioned substantially within the ferrule proximate the ferrule's first end and has an aperture therethrough for receiving the lead. An insulating material is deposited in the ferrule through the ferrule's second end for sealingly engaging the lead and the ferrule's interior surface.

According to a further aspect of the invention there is provided a method for feeding a terminal lead through an encasement wall of an electrochemical cell of the type utilized in implantable medical devices to the exterior of the electrochemical cell. A ferrule having first and second ends is positioned through the encasement wall. The ferrule is provided with an aperture having an inner surface. At least one polymeric guide member having an aperture therein is positioned proximate the first end of the ferrule. The lead is received through the guide member and the remainder of the ferrule. An insulating material is then deposited in the ferrule through the ferrule's second end so as to sealingly engaging the lead and the interior surface.

According to a still further aspect of the invention there is provided an electrochemical cell for use in an implantable medical device. The electrochemical cell comprises a shallow drawn encasement having at least one electrode body disposed within the encasement. An electrical lead is coupled to the body, and an insulative feedthrough is coupled through the encasement for receiving the electrical lead therethrough. The insulative feedthrough comprises a ferrule having first and second open ends and an interior surface. At least one polymeric guide member is positioned substantially within the ferrule proximate the ferrule's first end. An aperture is provided within the guide member for receiving the lead. An insulating material for sealingly engaging the lead and the interior surface is deposited within the ferrule through the ferrule's second end.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the invention is merely exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described herein without departing from the scope of the invention.

FIG. 1is a cross-sectional view of an electrolytic capacitor in accordance with the teaching of the prior art. It comprises a cylindrical metal container20made of, for example tantalum. Typically, container20comprises the cathode of the electrolytic capacitor and includes a lead22that is welded to the container. An end seal of cap24includes a second lead26that is electrically insulated from the remainder of cap24by means of a feed-through assembly28. Cap24is bonded to container20by, for example, welding. Feed-through28of lead26may include a glass-to-metal seal through which lead26passes. An anode30(e.g., porous sintered tantalum) is electrically connected to lead26and is disposed within container20. Direct contact between container20and anode30is prevented by means of electrically insulating spacers32and34within container20that receive opposite ends of anode30. A porous coating36is formed directly on the inner surface of container20. Porous coating36may include an oxide of ruthenium, iridium, nickel, rhodium, platinum, palladium, or osmium. As stated previously, anode30may be made of a sintered porous tantalum. However, anode30may be aluminum, niobium, zirconium, or titanium. Finally, an electrolyte38is disposed between and in contact with both anode30and cathode coating36thus providing a current path between anode30and coating36. As stated previously, while capacitors such as the one shown inFIG. 1were generally acceptable for defibrillator applications, optimization of the device is limited by the constraints imposed by the cylindrical design.

FIGS. 2,3, and4are front, side, and top cross-sectional views respectively of a flat electrolytic capacitor, also in accordance with the teachings of the prior art, designed to overcome some of the disadvantages associated with the electrolytic capacitor shown inFIG. 1. The capacitor ofFIGS. 2,3, and4comprises an anode40and a cathode44housed inside a hermetically sealed casing46. The capacitor electrodes are activated and operatively associated with each other by means of an electrolyte contained inside casing46. Casing46includes a deep drawn can48having a generally rectangular shape and comprised of spaced apart side-walls50and52extending to and meeting with opposed end walls54and56extending from a bottom wall58. A lid60is secured to side-walls50and52and to end walls54and56by a weld62to complete an enclosed casing46. Casing46is made of a conductive metal and serves as one terminal or contact for making electrical connections between the capacitor and its load.

The other electrical terminal or contact is provided by a conductor or lead64extending from within the capacitor through casing46and, in particular, through lid60. Lead64is insulated electrically from lid60by an insulator and seal structure66. An electrolyte fill opening68is provided to permit the introduction of an electrolyte into the capacitor, after which opening68is closed. Cathode electrode44is spaced from the anode40and comprises an electrode active material70provided on a conductive substrate. Conductive substrate70may be selected from the group consisting of tantalum, nickel, molybdenum, niobium, cobalt, stainless steel, tungsten, platinum, palladium, gold, silver, cooper, chromium, vanadium, aluminum, zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. Anode40may be selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon, germanium, and mixtures thereof. A separator structure includes spaced apart sheets72and74of insulative material (e.g. a microporous polyolefinic film). Sheets72and74are connected to a polymeric ring76and are disposed intermediate anode40and coated side-walls50and52which serve as a cathode electrode.

As already mentioned, the above described capacitors present certain concerns with respect to device size and manufacturing complexity. In contrast,FIGS. 5,6, and7are front cross-sectional, side cross-sectional, and scaled cross-sectional views of an electrolytic capacitor suitable for use in an implantable medical device and utilizing a feedthrough assembly in accordance with a first embodiment of the present invention. As can be seen, one or more layers of an insulative polymer separator material80(e.g. micro-porous PTFE or polypropylene) are heat sealed around a thin, D-shaped anode82(e.g. tantalum) having an anode lead wire84(e.g. tantalum) embedded therein. Capacitor grade tantalum powder such as the “NH” family of powders may be employed for this purpose. These tantalum powders have a charge per gram rating of between approximately 17,000 to 23,000 microfarad-volts/gram and have been found to be well suited for implantable cardiac device capacitor applications. Tantalum powders of this type are commercially available from HC Starck, Inc. located in Newton, Mass. Of course, materials having higher or lower charge may be utilized depending upon desired results.

Before pressing, the tantalum powder is typically, but not necessarily, mixed with approximately 0 to 5 percent of a binder such as ammonium carbonate. This and other binders are used to facilitate metal particle adhesion and die lubrication during anode pressing. The powder and binder mixture are dispended into a die cavity and are pressed to a density of approximately 4 grams per cubic centimeter to approximately 8 grams per cubic centimeter. After pressing, it is sometimes beneficial to modify anode porosity to improve conductivity within the internal portions of the anode. Porosity modification has been shown to significantly reduce resistance. Macroscopic channels are incorporated into the body of the anodes to accomplish this. Binder is then removed from the anodes either by washing in warm deionized water or by heating at a temperature sufficient to decompose the binder. Complete binder removal is desirable since residuals may result in high leakage current. Washed anodes are then vacuum sintered at between approximately 1,350 degrees centigrade and approximately 1,600 degrees centigrade to permanently bond the metal anode particles.

An oxide is formed on the surface of the sintered anode by immersing the anode in an electrolyte and applying a current. The electrolyte includes constituents such as water and phosphoric acid and perhaps other organic solvents. The application of current drives the formation of an oxide film that is proportional in thickness to the targeted forming voltage. A pulsed formation process may be used wherein current is cyclically applied and removed to allow diffusion of heated electrolyte from the internal pores of the anode plugs. Intermediate washing and annealing steps may be performed to facilitate the formation of a stable, defect free, oxide.

Layers of cathode material86are deposited on the inside walls of a thin, shallow drawn, D-shaped casing88(e.g. titanium) having first and second major sides and a peripheral wall, each of which have an interior surface. In order to optimize the energy density of the electrolytic capacitor, the cathode capacitance must be several orders of magnitude higher than that of anode82. In the past, this was accomplished by incorporating thin, etched aluminum foils between many anode layers, thus providing a large planar surface area and high capacitance. However, in order to promote downsizing as described above, the present invention employs materials of a high specific capacitance rather than large planar area. The capacitive materials may be selected from those described above or selected from the group including graphitic or glassy carbon deposited on titanium carbide, silver vanadium oxide, crystalline manganese dioxide, platinum or ruthenium on surface modified titanium, barium titanate or other perovskites on surface modified titanium, crystalline ruthenium or iridium oxide, or the like.

Anode88and cathode material86are insulated from each other by means of a micro-porous polymer separator material such as a PTFE separator of the type produced by W.L. Gore, Inc. located in Elkton, Md., or polypropylene of the type produced by Celgard, Inc. located in Charlotte, N.C. Separators80prevent physical contact and shorting and also provide for ionic conduction. The material may be loosely placed between the electrodes or can be sealed around the anode and/or cathode. Common sealing methods include heat sealing, ultra sonic bonding, pressure bonding, etc.

The electrodes are housed in a shallow drawn, typically D-shaped case88(e.g. titanium) that may have a material thickness of approximately 0.005 to 0.016 inch. An insulating feed-through90(to be more fully described hereinbelow) is comprised of a ferrule92(e.g. titanium) bonded (as, for example, by welding to case88) to case88. Sealed anode82is inserted into the cathode coated case88, and anode lead wire84passes through feedthrough90as is shown. A lid is then positioned and secured to the case by welding.

After assembly and welding, an electrolyte is introduced into the casing through a fill-port94. The electrolyte is a conductive liquid having a high breakdown voltage that is typically comprised of water, organic solvents, and weak acids or of water, organic solvents, and sulfuric acid. Filling is accomplished by placing the capacitor in a vacuum chamber such that fill-port94extends into a reservoir of electrolyte. When the chamber is evacuated, pressure is reduced inside the capacitor. When the vacuum is released, pressure inside the capacitor re-equilibrates, and electrolyte is pushed through fill-port94into the capacitor.

Filled capacitors are aged to form an oxide on the anode leads and other areas of the anode. Aging, as with formation, is accomplished by applying a current to the capacitor. This current drives the formation of an oxide film that is proportional in thickness to the targeted aging voltage. Capacitors are typically aged approximately at or above their working voltage, and are held at this voltage until leakage current reaches a stable, low value. Upon completion of aging, capacitors are re-filled to replenish lost electrolyte, and the fill-port94is sealed as, for example, by laser welding a closing button or cap over the encasement opening.

The outer metal encasement structure of a known planar capacitor generally comprises two symmetrical half shells that overlap and are then welded along their perimeter seam to form a hermetic seal. Such a device is shown inFIG. 8. That is, the encasement comprises a case96and an overlapping cover98. A separator sealed anode100is placed within case96, and a polymer spacer ring102is positioned around the periphery of anode assembly100. Likewise, a metal weld ring104is positioned around the periphery of spacer ring102proximate the overlapping portion106of case96and cover98. The overlapping portions of case96and cover98are then welded along the perimeter seam to form a hermetic seal.

This technique presents certain concerns relating to both device size and manufacturing complexity. The use of overlapping half-shields results in a doubling of the encasement thickness around the perimeter of the capacitor thus reducing the available interior space for the anode. Thus, for a given size anode, the resulting capacitor is larger. Furthermore, space for anode material is reduced due to the presence of weld ring104and insulative polymer spacer ring102. This device is more complex to manufacture and therefore more costly.

FIG. 9is a cross-sectional view illustrating one of the novel aspects of the present invention. In this embodiment, the encasement is comprised of a shallow drawn case108and a cover or lid110. This shallow drawn encasement design uses a top down welding approach. Material thickness is not doubled in the area of the weld seam as was the situation in connection with the device shown inFIG. 8thus resulting in additional space for anode material.

Cover110is sized to fit into the open side of shallow drawn metal case108. This results in a gap (e.g. from 0 to approximately 0.002 inches) in the encasement between case108and cover110that could lead to the penetration of the weld laser beam thus potentially damaging the capacitor's internal components. To prevent this, a metallized polymeric weld ring is placed or positioned around the periphery of anode100. Weld ring112is somewhat thicker than the case-to-cover gap114to maximize protection. Metallized weld ring112may comprise polymer spacer116having a metallized surface118as shown and provides for both laser beam shielding and anode immobilization. The metallized polymer spacer112need only be thick enough to provide a barrier to penetration of the laser beam and is sacrificial in nature. This non-active component substantially reduces damage to the active structures on the capacitor.

Metallized polymer spacer112is placed around the perimeter of anode100during assembly and may be produced my means of injection molding, thermal forming, tube extrusion, die cutting of extruded or cast films, etc. Spacer112may be provided through the use of a pre-metallized polymer film. Alternatively, the metal may be deposited during a separate process after insulator production. Suitable metallization materials include aluminum, titanium, etc. and mixtures and allows thereof.

FIG. 10is a cross-sectional view illustrating an alternative to the embodiment shown inFIG. 9. Again, the encasement comprises a case108and a cover or lid110resulting in gap114. The anode assembly100is positioned within the encasement as was the situation inFIG. 9. To protect the capacitor's internal components from damage due to the weld laser beam, a metallized tape120is positioned around the perimeter of anode100.

The embodiments shown inFIGS. 9 and 10not only have space saving aspects in the encasement design, but the components are simple and inexpensive to produce. The top down assembly facilitates fabrication and welding processes. The thinness of the weld ring/spacer112or metallized tape120reduces the need for additional space around the perimeter of the capacitor thus improving energy density. The design lends itself to mass production methods and reduces costs, component count, and manufacturing complexity.

It is not uncommon for the encasement of the capacitor itself to serve as the cathode electrode. This may be accomplished by depositing cathode material on an inner wall of the encasement or, if cathode material is deposited on one or more substrates, by electrically connecting the substrates to the encasement. Alternatively, the encasement may be made electrically neutral by not coupling the cathode to the encasement. In this situation, however, it is necessary not only to provide access to an anode electrode at the exterior of encasement88, but provisions must also be made to access a cathode electrode from the exterior of the encasement.

FIG. 11is a cross-sectional view of a feedthrough assembly130in accordance with a first embodiment of the present invention. As can be seen, feedthrough assembly130comprises a ferrule132(e.g. titanium), a polymeric wire-guide member140(e.g. polysulfone), and a body of insulating material142(e.g. epoxy). Ferrule132comprises an aperture having an interior surface133, a first end134, and a second end136. Similarly, polymeric guide140comprises an aperture144, a first end146, and a second end148. As illustrated inFIG. 11, first end146(e.g. in the form of a cap) is positioned proximate (e.g. abuts) first end134, and second end148(e.g. in the form of a plug) is positioned within ferrule132. Polymeric wire-guide140may be made of any suitable material such as polysulfone. As is further illustrated, the apertures provided in ferrule132and guide member140receive and guide an electrical lead138through feedthrough assembly130. More specifically, electrical lead138, which may be embedded in an electrode (e.g. an anode) internal to an electrochemical cell, is received by first end146of guide member140, passes through feedthrough assembly130, and exits through second end136of ferrule132. Electrical lead138is contacted only by insulating material136and polymeric guide member140and thus may insulativley pass from the inside to the outside of an electrochemical cell.

FIG. 12is an isometric view of ferrule132shown inFIG. 11. Referring toFIGS. 11 and 12, second end136comprises a generally cylindrical portion including a receiving shoulder150extending therearound through which electrical lead138passes and within which a body of insulating material142is disposed. Receiving shoulder150facilitates the mounting of feedthrough130onto an electrochemical cell wall by abuttingly engaging the interior of the cell wall to provide a circular seam as will be more fully described hereinbelow. Ferrule132may have an outer diameter of approximately 0.09 inch and an overall height of approximately 0.08 inch. Obviously, these dimensions and the internal or external mounting of the ferrule to the case wall may be varied to suit a particular application. Ferrule32may be made of titanium having a grade in the range of one to five, preferably two; however, other suitable metals such as niobium stainless steel, aluminum, copper, etc., may be utilized. It should be appreciated that although ferrule132is shown inFIGS. 11 and 12as being generally cylindrical in shape, ferrule132may take other forms depending upon a particular application.

FIGS. 13 and 14are respective cross-sectional and isometric views of the guide member140shown inFIG. 11. As can be seen, guide member140comprises a generally cylindrical cap member150and a generally cylindrical plug member149coupled thereto having an outer diameter smaller than that of cap150. Cap150may have, for example, a height of approximately 0.016 inch and an outer diameter of approximately 0.080 inch while plug149may have height of approximately 0.037 inch and an outer diameter of approximately 0.045 inch. Guide member140is also provided with an aperture144therethrough for receiving and guiding electrical lead138. It can be seen that the diameter aperture144gradually increases from first end146to second end148thus giving aperture144a tapered or partially conical shape. In this way, aperture144is configured to partially contact and fix lead138in place proximate first end146while simultaneously providing a space154between the inner surface of aperture144and lead138for receiving insulating material142therein (FIG. 11). For example, aperture144may have an inner diameter proximate first end146of approximately 0.013 inch, an inner diameter proximate second end148of approximately 0.0204 inch, and a length of approximately 0.050 inch. Depending upon the angle formed between inner surface of aperture144and the longitudinal axis of lead138and further depending upon the type of insulating material utilized, insulating material142may substantially fill space154as will be more fully described hereinbelow. It should be appreciated that the dimensions and shape of guide member140as well as the material from which it is made may vary depending upon its intended application. Suitable materials include polyetheretherketone, polyamideimide, poyacetal, polyphenylene sulphide, syndiotactic polystyrene, polyetherimide, polytetrafluoroethylene, etc. to mention only a few.

Referring again toFIGS. 13 and 14, it can be seen that plug149is provided with a raised portion155(e.g. a ridge) protruding outward therefrom. The dimensions of raised portion155are such that, upon pressing fitting plug149into first end134of ferrule132, raised portion155frictionally and interferingly engages inner surface133so as to secure guide140within ferrule132. Raised portion155may, for example, have a height of approximately 0.007 inch and protrude approximately 0.002 inch from the outer surface of plug149. Raised portion155is shown inFIGS. 13 and 14as being ridge-like in shape and extends entirely around the circumference of plug149; however, it should be appreciated that raised portion155may take any suitable shape (e.g. a bump or a group of bumps) and be positioned at any suitable location on the outer surface of plug149.

Prior to press-fitting guide member140into ferrule132, guide member140is positioned or strung onto lead138which in turn passes through ferrule132as depicted inFIG. 15. Once in position, guide member140may be press fit into ferrule132(indicated by arrow153) so that raised portion155frictionally contacts inner surface133fixturing guide member140proximate first end134of ferrule132. The resulting ferrule/guide member configuration is shown inFIG. 15, which is a cross-sectional view of feedthrough130prior to deposition of insulating body142. It also should be noted that raised portion155is not shown inFIG. 15(orFIG. 11) as it is substantially deformed (i.e. compressed) by inner surface133during insertion. Ferrule132may be fixedly coupled to an encasement of an electrochemical cell prior to insertion into ferrule132; however, the cell wall is not shown for clarity.

After the insertion of wire-guide140into ferrule132and positioning lead138through the ferrule, insulating material136is deposited into inner cavity157of the ferrule/guide member configuration including space154through open end136. Insulating material142thus contacts and sealingly engages inner surface133, guide member140, and electrical lead138. If a curable adhesive such as epoxy is deposited within inner cavity157of the ferrule/guide member configuration, the insulating material may substantially self-terminate throughout space154due to capillary forces. This simplifies manufacture since insulating material does not have to be deposited into the ferrule/guide member configuration with a large degree of accuracy. The degree of termination depends largely on the viscosity of the chosen curable adhesive and the angle formed by inner surface144and the longitudinal axis of lead138. In a preferred embodiment of the present invention an especially strong seal is produced by utilizing urethane acrylate as an insulating material and configuring the guide member so that the angle formed by inner surface and the axis of lead is approximately 4 degrees. A further advantage of utilizing an epoxy such as urethane acrylate is that the resulting feedthrough assembly is relatively flexible as compared to, for example, a glass-to-metal seal. Thus, the arrangement provides strain relief by protecting lead138from mechanical stresses. That is, the epoxy fixedly positions the lead with respect to the ferrule and whatever encasement the feedthrough assembly is coupled to and absorbs mechanical stresses placed on the lead. The inventive design also has higher degree of corrosion resistance than do traditional glass-to-metal seals.

FIG. 17is a cross-sectional view of feedthrough assembly130(FIG. 11) deployed in conjunction with an electrochemical cell200including an encasement202and electrode204. As can be seen, receiving shoulder150is fixedly coupled to encasement202. This is accomplished by first placing receiving shoulder150in an abutting relationship with the edges of an aperture in encasement202. This results in the production of a circular seam206at the exterior of encasement202which facilitates coupling (e.g. via laser welding) ferrule132to encasement202. After ferrule132has been fixedly coupled to encasement202, electrical lead138extending from electrode204and partially embedded therein is passed through aperture144of guide member140which partially contacts lead138as described above. By passing the lead directly through the feedthrough assembly, the inventive design simplifies assembly by eliminating the need for internal cross-wire welds such as the “J” shaped electrode-to-feedthrough terminal weld joint discussed hereinabove. After ferrule132has been coupled to encasement202and guide140has been properly positioned on lead138, lead138is passed through ferrule132and consequently through the aperture in encasement202. Plug152of guide140is then press fit into first end134of ferrule132. As described above, this causes raised portion155to deform and frictionally engage inner surface133. Once guide140is secured within ferrule132, insulating material142is deposited through open end136and, if necessary, is cured (e.g. via an ultraviolet light curing system). It should be appreciated that ferrule132was welded to encasement202before the pressing fitting of guide member140or deposition of insulating material142. In this way, the inventive assembly avoids subjecting critical components of the feedthrough assembly to thermal stresses caused by ferrule/encasement welding. Finally, electrochemical cell200is completed by coupling (e.g. laser welding) a lid (not shown inFIG. 17) to encasement202.

Thus, there has been provided a miniature epoxy feedthrough assembly for use in electrochemical cells such as capacitors, batteries, and the like for use in implantable medical devices. The inventive feedthrough assembly provides for a polymer-to-metal seal which offers greater chemical stability over conventional glass-to-metal seals in certain chemical electrolyte environments. The inventive design simplifies assembly by eliminating the need for internal cross-wire welds and improves volumetric efficiency by eliminating significant headspace volume in the capacitor. The inventive feedthrough assembly is assembled after mounting the ferrule to the cell wall thus avoiding thermal stresses on critical feedthrough components such as polymeric guide member. Assembly of the abovedescribed inventive feedthrough assembly is also relatively simple and inexpensive to manufacture.