Patent Publication Number: US-7916448-B2

Title: Methods of forming a filtering capacitor feedthrough assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 12/360,882, filed Jan. 28, 2009, now U.S. Pat. No. 7,706,124, which is a continuation of application Ser. No. 11/675,880 filed Feb. 16, 2007, now U.S. Pat. No. 7,502,217,the contents of each is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to methods of forming a filtering capacitor feedthrough assembly for an implantable device. 
     BACKGROUND 
     Implantable active medical devices, such as cardiac disease rhythm management devices (pacemakers and defibrillators) and a variety of implantable muscle/nerve stimulators generally include a battery and battery-powered electronic pulse generator and may include a variety of sending, processing, and telemetry circuits all contained within a hermetically sealed housing or case and attached to a lead connector housing or block. The lead connector block is often affixed to the hermetically sealed housing with brackets, metal solder, and/or a medical grade adhesive. 
     Electronics within the hermetically sealed housing are conductively coupled to the lead connector block with an electrical feedthrough assembly. Electrical feedthroughs serve the purpose of providing a conductive path extending between the interior of a hermetically sealed container and a point outside the hermetically sealed housing. The conductive path through the feedthrough usually includes a conductor pin or terminal that is electrically insulated from the hermetically sealed housing. Feedthrough assemblies are known in the art to provide the conductive path and seal the electrical container from its ambient environment. Such feedthroughs include a ferrule, and an insulative material such as a hermetic glass or ceramic seal that positions and insulates the pin within the ferrule. Sometimes it is desired that the electrical device include a capacitor/filter within the ferrule and around the terminal, thus shunting any electromagnetic interference (EMI) and other high frequencies radiation at the entrance to the electrical device to which the feedthrough device is attached thereby preventing or substantially reducing EMI from entering the device. The capacitor electrically contacts the pin lead and the ferrule. 
     The pin lead/capacitor and capacitor/ferrule connection has been made using solder, weld, braze, and conductive adhesives. While this arrangement has proven to be highly reliable, it involves a variety of expensive manufacturing processes and parts that necessarily increase the cost of the resulting product. 
     BRIEF SUMMARY 
     The present disclosure relates to methods of forming a filtering capacitor feedthrough assembly for an active implantable device. A continuous coil mechanically secures and electrically couples a terminal pin to filtering capacitor and/or a continuous coil mechanically secures and electrically couples a filtering capacitor to a ferrule or housing. 
     In a first embodiment, a method of forming a filtering capacitor feedthrough assembly for an implantable active medical device includes inserting a terminal pin into an aperture of a capacitor, the capacitor configured to be electrically grounded to an electrically conductive feedthrough ferrule or housing of the implantable active medical device, then disposing an electrically conductive continuous coil within the aperture between the terminal pin and the capacitor and then fixing the continuous coil to the terminal pin or the capacitor. The continuous coil includes an inner diameter defined by a plurality of coils, the terminal pin extending through the inner diameter of the continuous coil so that the plurality of coils circumferentially surround the terminal pin. The electrically conductive continuous coil mechanically secures and electrically couples the terminal pin to the capacitor. 
     In another embodiment, a method of forming a filtering capacitor feedthrough assembly for an implantable active medical device includes inserting a terminal pin into an aperture of a capacitor, the capacitor configured to be electrically grounded to an electrically conductive feedthrough ferrule or housing of the implantable active medical device, then disposing an electrically conductive continuous coil within the aperture between the terminal pin and the capacitor and then fixing the continuous coil to the terminal pin. The continuous coil includes an inner diameter defined by a plurality of coils, the terminal pin extending through the inner diameter of the continuous coil so that the plurality of coils circumferentially surround the terminal pin. The electrically conductive continuous coil mechanically secures and electrically couples the terminal pin to the capacitor. 
     In a further embodiment, a method of forming an active medical device is described. The method includes forming the filtering capacitor feedthrough assembly as described above and then electrically connecting a lead connector to the electronics and then hermetically sealing the housing around the electronics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of an active medical device implanted within a human body; 
         FIG. 2  is a schematic exploded view of an implantable active medical device; 
         FIG. 3  is a schematic cross-sectional view of a lead body shown in  FIG. 2  taken along line  3 - 3 ; 
         FIG. 4  is a schematic cross-sectional diagram of an illustrative filtering capacitor feedthrough assembly; 
         FIG. 5A  is a top view of an illustrative continuous coil utilized in a filtering capacitor feedthrough assembly; 
         FIG. 5B  is a cross-sectional side view of the continuous coil and shown in  FIG. 5A ; and 
         FIG. 6  is a schematic cross-sectional diagram of an illustrative multi-pin filtering capacitor feedthrough assembly. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
     The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The term “active implantable medical device” includes, for example, a cardiac pacemaker, an implantable defibrillator, a congestive heart failure device, a hearing implant, a cochlear implant, a neurostimulator, a drug pump, a ventricular assist device, an insulin pump, a spinal cord stimulator, an implantable sensing system, a deep brain stimulator, an artificial heart, an incontinence device, a vagus nerve stimulator, a bone growth stimulator, or a gastric pacemaker, and the like. 
     The terms “hermetic seal” and “hermetically sealed” are used interchangeably and refer to an airtight seal. This term is often used to describe electronic parts that are designed and intended to secure against the entry of microorganisms, water, oxygen, and the like, and to maintain the safety and quality of their contents. 
     The present disclosure relates to a filtering capacitor feedthrough assembly for an implantable device and methods of forming the same. In particular, this disclosure is directed to the use of a continuous coil to mechanically connect a feedthrough pin or terminal to a filtering capacitor and enable an electrical pathway between the capacitor and the feedthrough pin or terminal This disclosure is also directed to the use of a continuous coil to mechanically connect a filtering capacitor to a ferrule or device housing and enable an electrical ground pathway between the capacitor and the ferrule or device housing. While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the examples provided below. 
       FIG. 1  is a schematic diagram of an active medical device  20  implanted within a human body or patient  28 . The implanted active medical device  20  is illustrated as a neurostimulator, however, the implanted active medical device  20  can be any “active implantable medical device” as described above and can be placed in any suitable location within a body cavity. 
     The illustrated active medical device  20  includes a lead extension  22  having a proximal end coupled to the active medical device  20 , and a lead  24  having a proximal end coupled to a distal end  32  of the lead extension  22  and a distal end of the lead  24  coupled to one or more electrodes  26 . In other embodiments, the lead  24  proximal end is coupled to the active medical device  20 , without a need for a lead extension  22 . The active medical device  20  can be implanted in any useful region of the body such as in the abdomen of a patient  28 , and the lead  24  is shown placed somewhere along the spinal cord  30 . In many embodiments, the active medical device  20  has one or two leads each having four to eight electrodes, as desired. Such a system may also include a physician programmer and a patient programmer (not shown). The active medical device  20  can be considered to be an implantable signal generator of the type available from Medtronic, Inc. and capable of generating multiple signals occurring either simultaneously or one signal shifting in time with respect to the other, and having independently varying amplitudes and signal widths. The active medical device  20  contains a power source and the electronics for sending precise, electrical signals to the patient to provide the desired treatment therapy. While the active medical device  20 , in many embodiments, provides electrical stimulation by way of signals, other forms of stimulation may be used as continuous or discontinuous electrical stimulation, as desired. 
     In many embodiments, the lead  24  is a wire having insulation thereon and includes one or more insulated electrical conductors each coupled at their proximal end to a connector and to contacts/electrodes  26  at its distal end. Some leads are designed to be inserted into a patient percutaneously (e.g. the Model 3487A PISCES-QUAD® type lead available from Medtronic, Inc.), and some are designed to be surgically implanted (e.g. Model 3998 SPECIFY® type lead, also available form Medtronic, Inc.). In some embodiments, the lead  24  may contain a paddle at its distant end for housing electrodes  26 . In many embodiments, electrodes  26  may include one or more ring contacts at the distal end of lead  24 . 
       FIG. 2  is a schematic exploded view of the implantable active medical device described above and  FIG. 3  is a schematic cross-sectional view of the lead extension  100  shown in  FIG. 2  taken along line  3 - 3 . The illustrated implantable active medical device includes a lead extension  100  configured to be coupled between an implantable active medical device  102  and the lead  104 . The proximal portion of lead extension  100  includes a lead connector  107  configured to be received or plugged into housing lead connector  105  of an implantable active medical device  102  through a hermetically sealed housing  109  of the implantable active medical device  102  via a feedthrough assembly described below. The distal end of the lead extension  100  includes a connector  110  including internal contacts  111  and is configured to receive a proximal end of lead  104  having contacts  112  thereon. The distal end of the lead  104  includes distal electrodes  114  that are in electrical connection with corresponding contacts  112 . 
     One illustrative lead extension  100  has a diameter of approximately 0.1 inch, which can be larger than that of lead  104  so as to make extension  100  more durable than lead  104 . The lead extension  100  can differ from lead  104  in that each filer  106  in the lead body is helically wound or coiled in its own lumen  108  and not co-radially wound with the rest of the filers as can be the case in lead  104 . The diameter of the lead can be approximately 0.05 inch. This diameter can be based upon the diameter of the needle utilized in the surgical procedure to deploy the lead and upon other clinical anatomical requirements. The length of such lead can be based upon other clinical anatomical requirements and can be 28 centimeters; however, other lengths are utilized to meet particular needs of specific patients and to accommodate special implant locations. 
     The active medical device  102  includes a hermetically sealed housing  109  defining a sealed housing interior. A battery and electronics are in electrical communication and are disposed within the sealed housing  109  interior. Battery and electronics  103  are illustrated schematically in  FIG. 2  as a ‘black box’ within housing  109  interior. The electronics within the hermetically sealed housing  109  are conductively coupled to the lead connector block  105  with an electrical feedthrough assembly (described below). Electrical feedthroughs serve the purpose of providing a conductive path extending between the interior of a hermetically sealed housing  109  and the lead connector block  105  attached to the housing  109 . The conductive path through the feedthrough assembly includes a conductor pin or terminal pin that is electrically insulated from the hermetically sealed housing  109 . The feedthrough also include a ferrule, and an electrically insulating material such as a hermetic glass or ceramic seal that positions and insulates the pin within the ferrule. Filtered feedthroughs include a capacitor within the ferrule and around the terminal pin to shunt any electromagnetic interference (EMI) at high frequencies at the entrance to the electrical device to which the feedthrough device is attached. The capacitor electrically contacts the terminal pin (with active plates) and the ferrule (with ground plates). The terminal pin electrically connects the electronics within the sealed housing to the lead connector. 
       FIG. 4  is a schematic cross-sectional diagram of an illustrative filtering capacitor feedthrough assembly  200 . The filtering capacitor feedthrough assembly  200  includes a capacitor  210  having an aperture  215  defined by an inner surface  216  of the capacitor  210 . In many embodiments, the aperture  215  extends all the way through the capacitor  210  forming a cylindrical lumen or cylindrical aperture through the capacitor  210 . In some embodiments, the aperture  215  defines a ledge  217  within the aperture  215  creating a cylindrical lumen having a first lumen diameter and a second lumen diameter, where the first lumen diameter is less than the second lumen diameter. The inner surface  216  of the capacitor  210  is in electrical contact with active plates  211  within the capacitor  210 . An outer surface  218  of the capacitor  210  is in electrical contact with ground plates  212  within the capacitor  210 . A single active plate  211  and a single ground plate  212  is illustrated, however it is understood that the capacitor  210  includes a plurality of active plates  211  and ground plates  212  as is known in the art. 
     A terminal pin  230  extends into the aperture  215  of the capacitor  210 . In many embodiments, the terminal pin  230  extends through the aperture  215  of the capacitor  210 . An electrically conductive continuous coil  240  is disposed within the aperture  215  and between and in contact with both the terminal pin  230  and the capacitor  210 . The electrically conductive continuous coil  240  mechanically secures and electrically couples the terminal pin  230  to the capacitor  210  inner surface  216 . In many embodiments, the electrically conductive continuous coil  240  has an inner diameter R D  (see  FIGS. 5A and 5B ) slightly less than an outer diameter of the terminal pin  230  and the terminal pin  230  is disposed within the inner diameter R D  of the continuous coil  240 . Thus, the continuous coil  240  is axially or radially disposed about the terminal pin  230 . 
     In embodiments where a ledge  217  is within the aperture  215 , the conductive continuous coil  240  is disposed on or adjacent to the ledge  217 . In some embodiments, the conductive continuous coil  240  is fixed to the terminal pin  230  and/or the inner surface  216  of the capacitor  210 . The conductive continuous coil  240  can be fixed with any useful method or material such as, for example, solder, weld, braze, and/or conductive adhesive. 
     The terminal pin  230  extends through the ferrule  220  or housing  221  and the terminal pin  230  is in a non-conductive relation to the ferrule  220  or housing  221 . An insulator  225  is disposed between the terminal pin  230  and the ferrule  220  or housing  221 . The insulator  225  is disposed fixed to the terminal pin  230  and the ferrule  220  or housing  221  with solder, weld, braze, and/or adhesive  226 , as desired to provide a hermetic seal. An optional second insulator  227  is disposed within the ferrule  220  or housing  221  and adjacent to the capacitor  210 . 
     The outer surface  218  of the capacitor  210  is electrically grounded to an electrically conductive feedthrough ferrule  220  or housing  221  of the implantable active medical device. In some embodiments, an electrically conductive continuous coil  250  is disposed between the outer surface  218  of the capacitor  210  and the electrically conductive feedthrough ferrule  220  or housing  221 . The electrically conductive continuous coil  250  mechanically secures and electrically couples the capacitor  210  to the electrically conductive feedthrough ferrule  220  or housing  221 . In many embodiments, the electrically conductive continuous coil  250  has an outer diameter slightly greater than an inner diameter or circumference of the electrically conductive feedthrough ferrule  220  or housing  221 . Thus, the continuous coil  250  is axially or radially disposed about the capacitor  210 . In some embodiments, a ledge  219  is defined by the outer surface  218  of the capacitor  210  and the conductive continuous coil  250  is disposed on or adjacent to the ledge  219 . 
     While only one continuous coil  240  or  250  is shown mechanically securing and electrically coupling adjacent surfaces, two or more continuous coils  240  or  250  can mechanically secure and electrically couple adjacent surfaces, as desired. In addition, solder, weld, braze or conductive adhesive can be placed adjacent to continuous coil  240  or  250  to assist in mechanically securing and electrically coupling adjacent surfaces, as desired. 
       FIG. 5A  is a top view of an illustrative continuous coil utilized in the filtering capacitor feedthrough assembly described herein.  FIG. 5B  is a cross-sectional view of the continuous coil shown in  FIG. 5A . In many embodiments, the continuous coil is formed of a conductive wire  245  helically wound to form an annular ring referred to herein as a continuous coil. The continuous coil has an inner diameter R D  and a coil diameter C D . In many embodiments, the terminal pin (described above) is disposed within the inner diameter of the continuous coil (e.g,. coil  240  of  FIG. 4 ) and compresses the continuous coil diameter C D  against the inner surface of the capacitor aperture (described above) to form the mechanical interference fit and conductive contact between the terminal pin and the capacitor. In many embodiments, the capacitor outer surface (described above) is disposed within the inner diameter of the continuous coil (e.g., coil  250  of  FIG. 4 ) and compresses the continuous coil diameter C D  against the inner surface of the housing or ferrule (described above) to form the mechanical interference fit and conductive (ground) contact between the capacitor and the housing or ferrule. 
     The inner diameter R D  and the 2×(coil diameter C D ) equals an outer diameter of the continuous coil. The continuous coil is shown in an uncompressed state where the coil diameter C D  has a substantially circular form, in a compressed state (axial compression as shown by the arrows C D ) the coil diameter C D  distends or elastically deforms to an oval form (see  FIG. 4 ). Compressing the continuous coil between adjacent surfaces mechanically secures and electrically couples adjacent surfaces via an interference elastic axial compression fit of the continuous coil diameter C D . As the continuous coil is compressed between adjacent surfaces, the coil will also cant or deflect up to 40%. In many embodiments, the working deflection of the continuous coil is from 10 to 35%. 
     The continuous coil can have any useful dimensions. In many terminal pin to capacitor embodiments, the continuous coil has an inner diameter R D  in a range from 150 to 800 micrometers, or 250 to 750 micrometers, or 350 to 550 micrometers and a coil diameter C D  in a range from 250 to 500 micrometers, or 325 to 425 micrometers and an outer diameter in a range from 750 to 1750 micrometers, or from 1000 to 1400 micrometers and a wire diameter in a range from 25 to 100 micrometers. In many capacitor to ferrule embodiments, the continuous coil has an inner diameter R D  suitable to extend around the capacitor in a range from 500 to 5000 micrometers and a wire diameter in a range from 100 to 1000 micrometers. The continuous coil can be formed of any useful conductive material such as metals, for example, gold, silver, titanium, stainless steel, platinum, copper, and alloys or mixtures thereof. 
       FIG. 6  is a schematic cross-sectional diagram of an illustrative multi-pin or multipolar filtering capacitor feedthrough assembly  201 . In this embodiment, six terminal pins  230  are disposed through the feedthrough assembly  201 . The first terminal pin  230  is now described. The five remaining pins  230  have a substantially similar description and is not repeated but understood to be the same as the first terminal pin  230  assembly. 
     The filtering capacitor feedthrough assembly  201  includes a capacitor  210  having a plurality of apertures  215  defined by an inner surface  216  of the capacitor  210 . In many embodiments, the apertures  215  extend all the way through the capacitor  210  forming a plurality of cylindrical lumens through the capacitor  210 . The inner surface  216  of the capacitor  210  is in electrical contact with active plates within the capacitor  210 . An outer surface  218  of the capacitor  210  is in electrical contact with ground plates within the capacitor  210 . 
     A terminal pin  230  extends into each corresponding aperture  215  of the capacitor  210 . In many embodiments, the terminal pin  230  extends through the aperture  215  of the capacitor  210 . One or more electrically conductive continuous coils  240  are disposed within the aperture  215  and between the terminal pin  230  and the capacitor  210 . The electrically conductive continuous coils  240  mechanically secure and electrically couple the terminal pins  230  to the capacitor  210  inner surface  216 . In many embodiments, the electrically conductive continuous coils  240  have an inner diameter (see  FIGS. 5A and 5B ) slightly less than an outer diameter of the terminal pins  230 . Thus, the continuous coil  240  is axially disposed about the terminal pin  230 . In some embodiments, the conductive continuous coils  240  are fixed to the corresponding terminal pin  230  or inner surface  216  of the capacitor  210 . The conductive continuous coils  240  can be fixed with any useful method or material such as, for example, solder, weld, braze or conductive adhesive. 
     The terminal pin  230  extends through the ferrule  220  and housing  221  and is in a non-conductive relation to the ferrule  220  and housing  221 . An insulator  225  is disposed between the terminal pin  230  and the ferrule  220 . The insulator  225  is disposed fixed to the terminal pin  230  and the ferrule  220  with solder, weld, braze or adhesive  226 , as desired to provide a hermetic seal. 
     The outer surface  218  of the capacitor  210  is electrically grounded to an electrically conductive feedthrough ferrule  220  of the implantable active medical device. In some embodiments, an electrically conductive continuous coil  250  is disposed between the outer surface  218  of the capacitor  210  and the electrically conductive feedthrough ferrule  220 . The electrically conductive continuous coil  250  mechanically secures and electrically couples the capacitor  210  to the electrically conductive feedthrough ferrule  220 . In many embodiments, the electrically conductive continuous coil  250  has an outer diameter slightly greater than an inner diameter of the electrically conductive feedthrough ferrule  220 . Thus, the continuous coil  250  is axially disposed about the capacitor  210 . 
     In this embodiment, one, two and three continuous coils  240  are shown mechanically securing and electrically coupling adjacent surfaces, any number of continuous coils can mechanically secure and electrically couple adjacent surfaces, as desired. In addition, solder, weld, braze or conductive adhesive  228  can be placed adjacent to continuous coils  240  or  250  to assist in mechanically securing and electrically coupling adjacent surfaces, as desired. 
     Utilization of the continuous coils described herein, provides a robust mechanical interference compression attachment between surfaces within the filtering capacitor feedthrough assembly. The continuous coils can function as a strain relief structure during feedthrough pin deflection. In addition the continuous coils described herein provide a multitude of electrical connections between the terminal pin and the capacitor and/or the capacitor and the housing or ferrule. 
     Thus, embodiments of the METHODS OF FORMING A FILTERING CAPACITOR FEEDTHROUGH ASSEMBLY are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.