Abstract:
A feedthrough filter capacitor assembly for an implantable medical device is provided. The assembly includes a conductive lead, a conductive tube coaxial with and insulated from at least a portion of the lead, a conductive substrate through which the lead and tube pass in non-conductive relation therewith, and a filter capacitor associated with each of the lead and tube. The coaxial design of the filter capacitor assembly increases the number of lead connections while minimizing the footprint of the existing feedthrough layout.

Description:
FIELD OF THE INVENTION 
   The present invention relates to electrical feedthrough assemblies, and more particularly to feedthrough filter capacitor assemblies and their use in implantable medical devices. 
   BACKGROUND 
   Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers or defibrillators for providing precisely controlled stimulation pulses to the heart. However, the appended claims are not intended to be limited to any specific example or embodiment described herein. 
   Cardiac pacemakers, and other implantable medical devices such as cardiac defibrillators, are hermetically packaged to isolate the device from the body environment. Such devices require that electrical signals be passed between the packaged device and its external connectors, without compromising the hermeticity of the package. 
   Typically, electrical coupling between the electronic circuits of the implantable medical device and the external connections provided by a connector assembly mounted outside of the implantable device are provided by a feedthrough assembly. The feedthrough assembly extends through the hermetically sealed outer wall of the device and into the connector assembly so as to couple the electronic circuits within the implantable device to lead-receiving receptacles within the connector assembly. A conductive path is provided through the feedthrough by a conductor pin which is electrically insulated from the container. Many such feedthroughs are known in the art which provide the electrical path and seal the electrical container from its ambient environment. 
   Such electrical devices can, under some circumstances, be susceptible to electromagnetic interference (EMI). At certain frequencies for example, EMI can inhibit pacing in an implantable medical device. This problem has been addressed by incorporating a capacitor structure within the feedthrough ferrule, thus shunting any EMI at the entrance to the implantable device for high frequencies. This has been accomplished with the aforementioned capacitor structure by combining it with the feedthrough and incorporating it directly into the feedthrough ferrule. Typically, the capacitor electrically contacts the pin lead and the ferrule. 
   In one approach, a filter capacitor is combined directly with a terminal pin assembly to decouple interference signals to the housing of the medical device. In a typical construction, a coaxial feedthrough filter capacitor is connected to a feedthrough assembly to suppress and decouple undesired interference or noise transmission along a terminal pin. 
   So-called discoidal capacitors having two sets of electrode plates embedded in spaced relation within an insulative substrate or base typically form a ceramic monolith in such capacitors. One set of the electrode plates is electrically connected at an inner diameter surface of the discoidal structure to the conductive terminal pin utilized to pass the desired electrical signal or signals. The other or second set of electrode plates is coupled at an outer diameter surface of the discoidal capacitor directly or indirectly (for example, via a ground lead) to a cylindrical ferrule of conductive material, wherein the ferrule is electrically connected in turn to the conductive housing or case of the implantable medical device. 
   Feedthrough capacitors of this general type are commonly employed in implantable pacemakers, defibrillators and the like, wherein a device housing is constructed from a conductive biocompatible metal such as titanium and is electrically coupled to the feedthrough filter capacitor. The filter capacitor and terminal pin assembly prevent interference signals from entering the interior of the device housing, where such interference signals might otherwise adversely affect a desired function such as pacing or defibrillating. 
   Although feedthrough filter capacitor assemblies of the types described above have performed in a generally satisfactory manner, it would be advantageous to be able to increase the number of lead connections while minimizing the footprint of the existing feedthrough layout and reducing cost of manufacture. 
   SUMMARY 
   A feedthrough filter capacitor assembly for an implantable medical device is disclosed. The capacitor assembly comprises a conductive lead; a conductive tube coaxial with and insulated from at least a portion of the lead; a conductive substrate through which the lead and tube pass in non-conductive relation therewith; a first filter capacitor having a passageway through which the tube extends, the tube being electrically coupled to the first filter capacitor; and a second filter capacitor having a passageway through which the lead extends, the lead being electrically coupled to the second filter capacitor. 
   The coaxial design of the filter capacitor assembly increases the number of lead connections while minimizing the footprint of the existing feedthrough layout, and is expected to simplify the manufacturing process of feedthrough assemblies and reduce costs. 
   Further features, advantages, and benefits will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate typical embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying figures, wherein: 
       FIG. 1  is a perspective view of a terminal subassembly having four terminal leads, four terminal tubes coaxial with the terminal leads, and a ground pin mounted to a conductive ferrule; 
       FIG. 2  is a cross-sectional view of one coaxial terminal lead and tube of the terminal subassembly of  FIG. 1 ; 
       FIG. 3  is a perspective view of the terminal subassembly of  FIG. 1  having filter capacitors coupled to the leads and to the tubes; 
       FIG. 4  is a perspective view of the terminal subassembly of  FIG. 3  mounted to a substrate that is adapted to be electrically coupled to internal circuitry disposed within an implantable medical device; 
       FIG. 5  is a perspective view of a terminal assembly having four terminal leads, a first set of four terminal tubes coaxial with the terminal leads, a second set of four terminal tubes coaxial with the first set of terminal tubes, and a ground pin mounted to a conductive ferrule, which is coupled to a substrate that is electrically coupled to internal circuitry disposed within an implantable medical device; and 
       FIG. 6  is a cross-sectional view of one set of coaxial terminal lead and terminal tubes of the terminal assembly of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
   This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto. 
   The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the present invention. Therefore, the following detailed description is not meant to limit the invention. Rather, the scope of the invention is defined solely by the appended claims. 
   A feedthrough filter capacitor assembly for an implantable medical device is disclosed. The feedthrough filter capacitor assembly includes a conductive terminal lead; a conductive terminal tube coaxial with and insulated from at least a portion of the lead, a conductive substrate through which the lead and tube pass in non-conductive relation therewith, a first filter capacitor having a passageway through which the tube extends, and a second filter capacitor having a passageway through which the lead extends. In the feedthrough filter capacitor assembly, the tube is electrically coupled to the first filter capacitor, and the lead is electrically coupled to the second filter capacitor. 
   A ground lead can be coupled to the conductive substrate and extend into a second passageway of the first filter capacitor in conductive relation therewith and extend into a second passageway of the second filter capacitor in conductive relation therewith. 
   Referring now to the drawings,  FIG. 1  illustrates a perspective view of components of an internally grounded, eight pole feedthrough terminal subassembly  100 . Terminal subassembly  100  includes four conductive terminal leads or pins  102 , four conductive terminal tubes  104 , a ground lead  116 , insulators  106  and  114 , and a conductive substrate or ferrule  112 . The terminal subassembly  100  can comprise a prefabricated terminal subassembly. 
   The conductive terminal leads or pins  102  and terminal tubes  104  can be composed of any suitable conductive material, and can be the same or different material. Suitable materials for the terminal leads  102  and/or terminal tubes  104  include niobium, titanium, titanium alloys such as titanium-6AI-4V or titanium-vanadium, platinum, molybdenum, zirconium, tantalum, vanadium, tungsten, iridium, rhodium, rhenium, osmium, ruthenium, palladium, silver, and alloys, mixtures and combinations thereof. The terminal leads  102  and terminal tubes  104  may both be made of a platinum/iridium alloy. 
   In the feedthrough terminal subassembly  100  illustrated in  FIG. 1 , each of the terminal tubes  104  is coaxial with and insulated from a terminal lead  102 . As illustrated in  FIG. 1  and  FIG. 2 , the terminal tubes  104  and the terminal leads  102  are electrically insulated from one another by ring-shaped insulators  106 . The insulators  106  are fixed to the inner surface  108  of each of the terminal tubes  104  and the outer surface  110  of each of the terminal leads  102 . The insulators can be fixed by methods known to those skilled in the art, including gold brazing. 
   Insulators  106  can be composed of any suitable electrically insulative material, including alumina (or aluminum oxide) or ceramic-containing material having sapphire or zirconium oxide. 
   The conductive substrate or ferrule  112  comprises an elongated ring-shaped structure having a radially outwardly opening channel structure which is adapted to be mounted onto a housing of an implantable medical device in a position extending through an opening of the housing (not shown). The ferrule  112  is typically laser welded to the housing of an implantable medical device, but can be welded by other means, or even soldered or glued thereto. The ferrule  112  can be composed of a suitable biocompatible conductive material such as titanium or titanium alloy such as titanium-6AI-4V. 
   The ferrule  112  has two apertures through which ring-shaped insulators  114  are positioned and hermetically sealed thereto and through which terminal tubes  104  and terminal leads  102  pass in non-conductive relation. The ferrule also has a third aperture in its center in which a ground lead  116  is positioned and brazed or welded to the ferrule  112  to provide a ground connection to the housing of the implantable medical device. 
   The insulators  114  provide electrical insulation between the terminal tubes  104  and the ferrule  112 . The insulators  114  each contain two passageways through which the terminal tubes  104  and terminal leads  102  extend and are preferably hermetically sealed therewith. The insulators  114  can be composed of one or more of the insulative materials listed above for insulator  106 , and can be the same or different material as insulator  106 . 
   The ground lead  116  can be composed of one or more of the materials listed above for the terminal leads  102  and terminal tubes  104 , and can be the same or different material as terminal leads  102  and/or terminal tubes  104 . The ground lead may be made of a platinum/iridium alloy. 
     FIG. 3  illustrates a perspective view of the terminal subassembly of  FIG. 1  having two filter capacitors  118  and  122  coupled to the terminal tubes  104 , terminal leads  102 , and ground lead  116  to suppress and decouple undesired interference or noise transmission along the terminal leads  102  and terminal tubes  104  when used in an implantable medical device. 
   The first filter capacitor  118  is coupled at one end  120  to a surface of the ferrule  112  and the insulator  114  (not shown), and has four passageways, through which each of the four terminal tubes  104  are affixed and electrically coupled to and extend through and a passageway through which the ground lead  116  is affixed and electrically coupled to and extends through. 
   The second filter capacitor  122  has four passageways through which each of the four terminal leads  102  are affixed and electrically coupled to and extend through and a center passageway through which the ground lead  116  is affixed to and extends through. 
   In  FIG. 3 , the first filter capacitor  118  does not and need not physically contact the terminal leads  102 . Similarly, the second filter capacitor  122  does not and need not contact the terminal tubes  104 . 
   The first and second filter capacitors  118  and  122  are typically discoidal filter capacitors having two sets of electrode plates embedded in spaced relation within an insulative substrate or base typically forming a ceramic monolith (not shown). Suitable discoidal filter capacitors are manufactured by AVX Corporation (Myrtle Beach, S.C.) and Greatbatch, Inc. (Clarence, N.Y.). 
   In an embodiment wherein the first filter capacitor  118  is a discoidal capacitor, one set of the electrode plates of the first filter capacitor  118  is electrically connected at an inner diameter surface to the terminal tubes  104 . The other or second set of electrode plates of the first filter capacitor  118  is coupled to the ground lead  116 , which is electrically connected to the ferrule  112  which in turn is electrically connected to the conductive housing or case of the implantable medical device. 
   Similarly, in an embodiment wherein the second filter capacitor  122  is a discoidal filter capacitor, one set of the electrode plates of second filter capacitor  122  is electrically connected at an inner diameter surface to the terminal leads  102 . The other or second set of electrode plates of the first filter capacitor  122  is coupled at an outer diameter surface to the ground lead  116 , which is electrically connected to the ferrule  112  which in turn is electrically connected to the conductive housing or case of the implantable medical device. 
   The number and dielectric thickness spacing of the electrode plate sets varies in accordance with the capacitance value and the voltage rating of the discoidal capacitor. When used in an implantable medical device, the first and second discoidal capacitors  118 ,  122  permit passage of relatively low frequency electrical signals along the terminal tube  104  and terminal pin  102 , respectively, while shielding and decoupling/attenuating undesired interference signals of typically high frequency to the conductive housing. 
   The terminal leads  102  and terminal tubes  104  are adapted to be electrically coupled to internal circuitry disposed within an implantable medical device.  FIG. 4  illustrates a perspective view of the terminal assembly of  FIG. 3  coupled to a substrate  128  that provides electrical coupling to internal circuitry disposed within an implantable medical device (not shown). 
   In  FIG. 4 , substrate  128  is made of a nonconductive material and typically comprises a ceramic material. The substrate contains conductive paths in its interior (not shown) to electrically couple the terminal leads  102 , terminal tubes  104 , and ground lead  116  to internal circuitry of an implantable medical device. 
   A first set of four conductive holders  124  and a second set of five conductive holders  126  are disposed on the substrate  128 . The conductive holders  124  and  126  can be of the same or different conductive material such as, but not limited to nickel, an iron-nickel-cobalt alloy such as KOVAR (29% Ni, 17% Co and 53% Fe), a copper alloy, or a stainless steel alloy such as 446, 29-4-2 or 52 alloy. In addition, the conductive holders  124 ,  126  can be partially or completely plated with gold. In one embodiment, the conductive holders  124 ,  126  are composed of a gold-plated iron-nickel-cobalt alloy such as gold-plated KOVAR. 
   The conductive holders  124 ,  126  can be affixed to the substrate  128  by any suitable method. For example, the conductive holders  124 ,  126  can be brazed to a ceramic substrate  128  at about 1000° C. 
   The first set of four conductive holders  124  is of a suitable shape and size to receive the four terminal tubes  104 . The second set of five conductive holders  126  are of a suitable shape and size to receive the four terminal leads  102  and (in the case of the center conductive holder  132 ) the ground lead  116 . 
   Also as shown in  FIG. 4 , substrate  128  has a plurality of wire bonding pads  130  disposed thereon. The number of wire bonding pads typically equals the number of conductors plus the ground lead. The wire bonding pads may be of any suitable shape and dimension. The wire bonding pads can be composed of any suitable conductive material such as, but not limited to copper. In addition, the wire bonding pads can be partially or completely plated with, for example nickel and/or gold (for example, nickel-plated and then gold-plated). The wire bonding pads may be deposited on or in the substrate by methods known by those skilled in the art. 
   The wire bonding pads  130  are adapted to be conductively coupled to the first or second conductive holders  124 ,  126  by conductive paths in the inside of the substrate  128  (not shown). For example, each of the four of the first set of conductive holders  124  is conductively coupled to an individual wire bonding pad  130 , and each of the five of the second set of conductive holders  126  is conductively coupled to an individual wire bonding pad  130 . Methods of making conductive paths in the substrate  128  between the conductive holders  124 ,  126  and the wire bonding pads  130  are known to those skilled in the art. 
   The wire bonding pads  130  are adapted to be electrically coupled to internal circuitry disposed within an implantable medical device by, for example gold wires attached to the wire bonding pads and to the internal circuitry of the implantable medical device. 
   Also as shown in  FIG. 4 , the four terminal tubes  104  of the terminal assembly  100  are electrically coupled to the first set of four conductive holders  124 , and the four terminal leads  102  are electrically coupled to the second set of four conductive holders  126 . Ground lead  116  is electrically coupled to the center conductive holder  132  of the set of second conductive holders  126 . The terminal tubes  104 , terminal leads  102 , and ground lead  116  can be electrically coupled to conductive holders  124  and  126  by any suitable method, for example by being laser welded. 
   In the embodiment illustrated in  FIG. 4 , the first filter capacitor  118  need not physically contact the substrate  128 , although in other embodiments it may do so. Similarly, the second filter capacitor  122  separates the conductive holders  124  and  126  and need not physically contact the conductive holders nor the substrate  128 , although it may do so. 
     FIG. 5  illustrates a perspective view of a feedthrough filter capacitor assembly  200  having an additional conductive terminal tube  234  coaxial with and insulated from a terminal tube  204  and a terminal lead  202 , mounted to a substrate  228  that is electrically coupled to internal circuitry disposed within an implantable medical device, to form an internally grounded, twelve (12) pole feedthrough terminal assembly. 
   Terminal assembly  200  includes four conductive terminal leads or pins  202 , a first set of four conductive terminal tubes  204 , each first terminal tube  204  coaxial with and insulated from each terminal lead  202 . Terminal assembly  200  further includes a second set of four conductive terminal tubes  234 , coaxial with and insulated from each of the first set of conductive terminal tubes  204  and from each terminal lead  202 . 
   As illustrated by  FIG. 6 , each of the terminal leads  202  and first terminal tubes  204  are electrically insulated from one another by an insulator  206  which is fixed to the inner surface  208  of the first terminal tubes  204  and the outer surface  210  of the terminal leads  202 . The first terminal tubes  204  and the second terminal tubes  234  are electrically insulated from one another by an insulator  236  which is fixed to the inner surface  238  of the second terminal tube  234  and the outer surface  240  of the first terminal tube  204 . 
   Referring back to  FIG. 5 , the terminal leads  202  and the first and second sets of terminal tubes  204  and  234  pass through a conductive substrate or ferrule  212  containing two passageways (as illustrated in  FIG. 1 ) through which two insulators  214  extend. The insulators  214  each contain two passageways (as illustrated in  FIG. 1 ) through which the terminal leads  202  and the first and second sets of terminal tubes  204  and  234  extend. The ferrule  212  also contains an aperture (as illustrated in  FIG. 1 ) in a center portion in which a ground lead  216  is affixed. 
   As illustrated in  FIG. 5 , a first filter capacitor  218  is coupled at one end  220  to a surface of the ferrule  212  and the insulators  214  (not shown), and has four passageways through which each of the second set of terminal tubes  234  are affixed and electrically coupled to and extend through and a center passageway through which the ground lead  216  is affixed and electrically coupled to and extends through. A second filter capacitor  222  has four passageways through which each of the first set of terminal tubes  204  are affixed and electrically coupled to and extend through and a center passageway through which the ground lead  216  is affixed and electrically coupled to and extends through. A third filter capacitor  242  has four passageways through which each of the four terminal leads  202  are affixed and electrically coupled to and extend through and a passageway through which the ground lead  216  is affixed and electrically coupled to and extends through. Thus, a filter capacitor is provided for each of the set of terminal leads  202 , the first set of terminal tubes  204 , and the second set of terminal tubes  234 . 
   As also illustrated in  FIG. 5 , the terminal leads  202  and the first and second sets of terminal tubes  204  and  234  are adapted to be electrically coupled to internal circuitry disposed within an implantable medical device through coupling with a substrate  228 . The applicable materials and methods of attachment of the components illustrated for the embodiments of  FIGS. 1-4  are incorporated herein. 
   In  FIG. 5 , substrate  228  contains conductive paths in its interior (not shown) to electrically couple the terminal leads  202 , first set of terminal tubes  204 , second set of terminal tubes  234 , and ground lead  216  to internal circuitry of an implantable medical device. 
   A first set of four conductive holders  224 , a second set of five conductive holders  226 , and a third set of conductive holders  244  are disposed on the substrate  228 . The first set of conductive holders  224  are of a suitable shape and size to receive the second set of terminal tubes  234 . The outer four of the second set of conductive holders  226  are of a suitable shape and size to receive the first set of terminal tubes  204 . The center conductive holder  232  of the second set of conductive holders is of a suitable shape and size to receive the ground lead  216 . The third set of conductive holders  244  are of a suitable shape and size to receive the terminal leads  202 . 
   Also as shown in  FIG. 5 , substrate  228  has a plurality of wire bonding pads  230  disposed thereon. The wire bonding pads are adapted to be conductively coupled to the first, second, or third set of conductive holders  224 ,  226 ,  244  by conductive paths in the inside of the substrate (not shown). For example, each of the four of the first set of conductive holders  224 , each of the five of the second set of conductive holders  226 , and each of the four of the third set of conductive holders  244  is conductively coupled to an individual wire bonding pad  230 . 
   The wire bonding pads  230  are adapted to be electrically coupled to internal circuitry disposed within an implantable medical device by, for example wires attached to the wire bonding pads and to the internal circuitry of the implantable medical device. 
   Example embodiments of the methods and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible within the scope of the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
   For example, the number of poles for which a coaxial lead/tube feedthrough terminal assembly can be made is not limited, and beyond the eight and twelve pole configurations illustrated can include bipolar (two), tripolar (three), quadripolar (four), pentapolar (five), hexapolar (six), and higher number of poles, depending upon the number of leads and sets of coaxial tubes, including multiple coaxial tubes (e.g., one, two, three, or more sets of coaxial tubes). It should also be understood that a feedthrough terminal assembly having an odd number of poles (e.g. three of five poles) can be made from having one or more leads without a corresponding coaxial tube. 
   Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.