Abstract:
A filtered feedthrough assembly includes a capacitor comprising a top portion, a bottom portion, an outer diameter portion and an inner diameter portion. The inner diameter portion defines at least one aperture extending from the top portion to the bottom portion. An conductive pad of conductive material is applied to the top portion around the at least one aperture. A feedthrough pin extends through each of the apertures and is soldered to the inner diameter portion of the capacitor by application of a solder preform upon the conductive pad of conductive material.

Description:
FIELD 
       [0001]    The present disclosure relates to electrical feedthroughs for implantable medical devices and, more particularly, an improved capacitor assembly for a filtered feedthrough. 
       BACKGROUND 
       [0002]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0003]    Electrical feedthroughs serve the purpose of providing an electrical circuit path extending from the interior of a hermetically sealed container to an external point outside the container. A conductive path is provided through the feedthrough by a conductor pin which is electrically insulated from the container. Many feedthroughs are known in the art that provide the electrical path and seal the electrical container from its ambient environment. Such feedthroughs typically include a ferrule, the conductor pin or lead and a hermetic glass or ceramic seal which supports the pin within the ferrule. Such feedthroughs are typically used in electrical medical devices such as implantable pulse generators (IPGs). It is known that such electrical devices can, under some circumstances, be susceptible to electromagnetic interference (EMI). At certain frequencies for example, EMI can inhibit pacing in an IPG. This problem has been addressed by incorporating a capacitor structure within the feedthrough ferrule, thus shunting any EMI at the entrance to the IPG for high frequencies. This has been accomplished with the aforementioned capacitor device 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. 
         [0004]    Many different insulator structures and related mounting methods are known in the art for use in medical devices wherein the insulator structure also provides a hermetic seal to prevent entry of body fluids into the housing of the medical device. The feedthrough terminal pins, however, are connected to one or more lead wires which effectively act as an antenna and thus tend to collect stray or electromagnetic interference (EMI) signals for transmission to the interior of the medical device. In some prior art devices, ceramic chip capacitors are added to the internal electronics to filter and thus control the effects of such interference signals. This internal, so-called “on-board” filtering technique has potentially serious disadvantages due to intrinsic parasitic resonances of the chip capacitors and EMI radiation entering the interior of the device housing. 
         [0005]    In another and normally preferred 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. 
         [0006]    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 to a cylindrical ferrule of conductive material, wherein the ferrule is electrically connected in turn to the conductive housing or case of the electronic instrument. 
         [0007]    In operation, the discoidal capacitor permits passage of relatively low frequency electrical signals along the terminal pin, while shunting and shielding undesired interference signals of typically high frequency to the conductive housing. 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. 
         [0008]    In the past, feedthrough filter capacitors for heart pacemakers and the like have typically been constructed by preassembly of the discoidal capacitor with a terminal pin subassembly which includes the conductive terminal pin and ferrule. More specifically, the terminal pin subassembly is prefabricated to include one or more conductive terminal pins supported within the conductive ferrule by means of a hermetically sealed insulator ring or bead. See, for example, the terminal pin subassemblies disclosed in U.S. Pat. Nos. 3,920,888, 4,152,540; 4,421,947; and 4,424,551. The terminal pin subassembly thus defines a small annular space or gap disposed radially between the inner terminal pin and the outer ferrule. A small discoidal capacitor of appropriate size and shape is then installed into this annular space or gap, in conductive relation with the terminal pin and ferrule, e.g., by means of soldering or conductive adhesive. The thus-constructed feedthrough capacitor assembly is then mounted within an opening in the pacemaker housing, with the conductive ferrule in electrical and hermetically sealed relation in respect of the housing, shield or container of the medical device. 
         [0009]    Although feedthrough filter capacitor assemblies of the type described above have performed in a generally satisfactory manner, the manufacture and installation of such filter capacitor assemblies has been relatively costly and difficult. For example, installation of the discoidal capacitor into the small annular space between the terminal pin and ferrule can be a difficult and complex multi-step procedure to ensure formation of reliable, high quality electrical connections. Moreover, installation of the capacitor at this location inherently limits the capacitor to a small size and thus also limits the capacitance thereof. Similarly, subsequent attachment of the conductive ferrule to the pacemaker housing, typically by welding or brazing processes or the like, can expose the fragile ceramic discoidal capacitor to temperature variations sufficient to create the risk of capacitor cracking and failure. As described above, a solder, e.g., in the form of a solder preform, may be used to connect the terminal pins with the capacitor. Unfortunately, solder preforms are susceptible to oxidation that may affect the conductivity of the solder and the ability to make a good electrical connection between the pin and the capacitor. Current manufacturing techniques utilize a chemical etching process to remove the formed oxide layers, adding an additional step and expense to the manufacturing process. 
         [0010]    There exists, therefore, a significant need for improvements in feedthrough filter capacitor assemblies of the type used, for example, in implantable medical devices such as heart pacemakers and the like, wherein the filter capacitor is designed for relatively simplified and economical, yet highly reliable, installation. In addition, there exists a need for an improved feedthrough assembly that provides reliable and economical electrical connections between the capacitor and feedthrough pins without performing a chemical etching or other process to remove oxide layers from the solder preforms. The present disclosure fulfills these needs and provides further advantages. 
       SUMMARY 
       [0011]    In various embodiments of the present disclosure, a filtered feedthrough assembly is disclosed. The assembly includes a capacitor that has a top portion, a bottom portion, an outer diameter portion and an inner diameter portion. The inner diameter portion defines at least one aperture extending from the top portion to the bottom portion. The capacitor further includes a conductive pad of conductive material that is applied to the top portion around the at least one aperture. At least one feedthrough pin extends through the at least one aperture and is soldered to the inner diameter portion of the capacitor by application of a solder preform upon the conductive pad of conductive material. 
         [0012]    In various alternative embodiments of the present disclosure, a method of manufacturing a filtered feedthrough assembly is disclosed. The method includes applying a conductive pad of conductive material to a capacitor, in which the capacitor includes a top portion, a bottom portion, an outer diameter portion and an inner diameter portion. The inner diameter portion defines at least one aperture extending from the top portion to the bottom portion. The conductive pad of conductive material is applied to the top portion around the at least one aperture. The method further includes extending a feedthrough pin through the at least one aperture, placing a solder preform upon the conductive pad of conductive material, and soldering the feedthrough pin to the inner diameter portion of the capacitor with the solder preform. 
         [0013]    Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  is an exploded view of a capacitor feedthrough assembly according to various embodiments of the present disclosure; 
           [0016]      FIG. 2  is a perspective view of a capacitor according to various embodiments of the present disclosure; 
           [0017]      FIG. 3  is a top view of the capacitor of  FIG. 2 ; 
           [0018]      FIG. 4  is a cross-sectional view of the capacitor of  FIG. 2  taken along line  4 - 4 ; and 
           [0019]      FIG. 5  is a perspective view of a capacitor and associated conductive pads according to various embodiments of the present disclosure. 
       
    
    
     DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0021]    Referring now to  FIG. 1 , an exploded view of a capacitor feedthrough assembly  10  according to various embodiments of the present disclosure is illustrated. The assembly  10  comprises a ferrule  12 , a plurality of conductor pins  13   a - 13   i,  a capacitor  14 , a spacer portion  15 , a solder bead  16  and a plurality of solder preforms  18   a - 18   h.    
         [0022]    The assembly  10  may be manufactured in the following manner. Feedthrough pins  13   a - 13   i  are inserted through ferrule  12 . In one direction, feedthrough pins  13   a - 13   i  extend outside the implanted medical device (not shown), which is hermetically sealed with the bottom portion  12   a  of the ferrule  12 . In the opposite direction, conductor pins  13   a - 13   i  extend through a spacer portion  15  and capacitor  14  and into the internal portion of the medical device. The spacer portion  15  provides support for the capacitor  14 , and may also inhibit or reduce the flow of solder into the hermetically sealed part of the feedthrough. Once the spacer portion  15  and capacitor  14  are positioned within the top portion  12   b  of the ferrule  12 , electrical connections between the capacitor  14  and conductor pins  13   a - 13   h  may be formed. 
         [0023]    Referring now to  FIGS. 2-4 , a capacitor  14  according to various embodiments of the present disclosure is illustrated. The capacitor  14  includes an outer diameter portion  141  that may substantially surround the capacitor  14 , a top portion  144  and bottom portion  145 . A plurality of feedthrough holes  142   a - 142   h  may extend completely through the body of the capacitor  14  to provide an opening between top portion  144  and bottom portion  145 . As best illustrated in  FIG. 4 , inner diameter portion or portions  143   a - 143   h  are present in the capacitor  14 , and, thus, define the plurality of feedthrough holes  142 . The outer diameter portion  141  and inner diameter portion  143  are each connected to one of the two sets of electrode plates that comprise the capacitor  14  and are electrically isolated from one another. In the capacitor feedthrough assembly of  FIG. 1 , the outer diameter portion  141  is electrically coupled to the ferrule  12  by means of solder bead  16  and the inner diameter portion  143  is coupled to the conductor pins  13   a - 13   h  by solder preforms  18   a - 18   h.    
         [0024]    A reliable electrical connection between the outer diameter portion  141  and ferrule  12  may be made by the solder bead  16 . In one method of assembly according to various embodiments of the present disclosure, the solder bead  16  is placed on top of the capacitor  14  within the top portion  12   b  of ferrule  12 . A chamfer  147  may be formed on the top portion  144  of capacitor  14 . The chamfer  147  will bias the placement of solder bead  16  such that proper placement of solder bead  16  is assured. Solder preforms  18   a - 18   h  may comprise circular or semi-circular rings of solder material, although the use of other shapes (square, rectangular, triangular, etc.) for the solder preforms  18   a - 18   h  are within the scope of this disclosure. Each of the solder preforms  18   a - 18   h  receive one of the conductor pins  13   a - 13   h  such that the solder preform  18  rests on the top portion  144  of capacitor  14 . Once the solder beads  16  and solder preforms  18  are present on the capacitor  14 , a solder reflow process is performed, which is described more fully below, in which heat is applied to melt the solder bead  16  and solder preforms  18  in order to electrically connect the ferrule  12  with the outer diameter portion  141  and conductor pins  13  to the inner diameter portion  143 . 
         [0025]    In various embodiments, solder preforms  18   a - 18   h  may comprise fluxless solder. As described above, oxidation may create an oxide layer on the solder preforms, which will inhibit a reliable electrical connection. An oxide layer on the solder preform, and/or oxide formed on the capacitor  14 , will inhibit the flow of the solder into the holes  142   a - 142   h  and, thus, may lead to inconsistent or imperfect connections between the inner diameter portion  143   h  and conductor pins  13   e - 13   i  of the capacitor feedthrough assembly  10 . In order to ensure adequate flow of the solder, a conductive pad  149  of conductive material, e.g., gold, may be formed on the top portion  144  of the capacitor  14  surrounding each of the holes  142   a - 142   h,  as shown in  FIG. 5 . The conductive pad may be applied to the top portion  144  by any means, including, but not limited to, sputtering, manual application, screen printing, ink jet printing, or even application of the capacitor termination material present on the inner diameter portion  143 . The presence of the conductive pad  149  provides an enhanced flow of solder from the solder preform  18  into the holes  142  of the inner diameter portion  143  surrounding the conductor pins  13 , even if the solder preform has an oxide layer formed on its outside. 
         [0026]    Once the capacitor/feedthrough assembly is assembled and the solder bead  16  and solder preforms  18   a - 18   h  are present on the capacitor  14 , a solder reflow process is performed. The solder reflow process liquefies the solder bead  16  and solder preforms  18  such that solder flows to electrically connect the outer diameter portion  141  and inner diameter portion  143  to the ferrule  12  and conductor pins  13 , respectively. The presence of the conductive pads  149  enhance the solder flow such that the connection between the conductor pins  13  and inner diameter portion  143  of capacitor  14  is ensured. 
         [0027]    Solder bead  16 , in various embodiments of the present disclosure, may be replaced by a different conductive adhesive, e.g., conductive epoxy or brazing. Furthermore, as stated above, the conductive pads may be formed of any conductive material, e.g., gold, silver or silver-palladium. The conductive pads may be formed during the capacitor manufacturing process or may be added to a fully formed capacitor after its manufacture. The solder preforms  18  may be circular of a washer-shaped construction in which the inner diameter is only slightly larger than the diameter of the conductor pins  13  such that proper placement of the solder preforms  18  surrounding the conductor pins  13  is assured. In various embodiments, a counterbore or countersink may be formed around the holes  142  of the capacitor  14  to further assist in the placement of the solder preforms  18 , similar to the chamfer  147  present on the outer diameter portion  141  in  FIG. 1 . 
         [0028]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.