Abstract:
This invention relates to a unipolar or multipolar electrical filter feedthrough device ( 1 ) to be introduced into an aperture of housing ( 26 ) of an implantable electronic therapeutic device with a feedthrough body ( 2 ) to be inserted in the aperture and comprising a fixing means ( 3 ) to connect with the housing wall, and with filter means ( 7 ) designed as capacitors, that are, on one side, connected—in an electrically conductive manner—with one of the electrical pins ( 8 ) that are mutually electrically separated, and, on the other side, with the housing of the therapeutic device carrying a reference potential. Filter means ( 7 ) are arranged outside the feedthrough body ( 2 ) and are connected with this body in such a manner that they basically stick out into the inside ( 4 ) of housing ( 26 ) in a freely suspended manner.

Description:
This invention relates to a unipolar or multipolar electrical filter feedthrough device for an implantable electronic therapeutic device, e.g., a pacemaker. The filter feedthrough is designed to be introduced into an aperture of a housing of the therapeutic device, and comprises contact elements electrically separated from each other, a fixing means for harnessing the filter body around one wall of the housing as well as filter means that are, on one side, connected—in an electrically conductive manner—with one of the contact elements, and, on the other side, with the housing having a reference potential. The filter elements usually comprise capacitive elements. The contact elements are usually designed in the form of rod-shaped pins. 
     BACKGROUND OF THE ART 
     U.S. Pat. No. 4,152,540 describes a filter design for use with an electronic pacemaker, where a filter capacitor is introduced in a borehole in the insulation ceramic material. 
     Furthermore, European Patent publication EP 0 776 016 A2 reveals a filter design with a ceramic filter arrangement with capacities for implantable defibrillators and pacemakers. The filter arrangement is designed as a system of layers and is integrated in the particular device. 
     Another version known from the U.S. Pat. No. 5,650,016 and designed for use with implantable medical therapeutic devices comprises a filter constructed as a chip capacitor or an LC module and its integration with the device occurs through encapsulation. 
     However, the known electrical design versions have the disadvantage that the capacitive filter means as well as the contact areas between the electrical pins and the reference potential are made impermeable by a glass-seal. This results—especially taking into account the preassembly of the filter means—in a substantial costs of manufacturing such a design version and of the introduction of the feedthrough device into the housing of the therapeutic device to be implanted, and its subsequent check for vacuum-tightness. 
     In addition, it is highly disadvantageous that the filter means are firmly connected with the feedthrough device and, therefore, exposed to a high thermal load when the feedthrough device is being welded into the aperture of the housing of the electronic therapeutic device. This requires a very firm mechanic binding of the filter means with the feedthrough device and, on the other hand, it often leads to an irreversible change in the electrical parameters of the filter means, which affects—mostly in an unanticipated manner—the operation of the therapeutic device to be implanted. 
     Based on the shortcomings of prior art, the task of this invention is, therefore, to describe a unipolar or multipolar design of the aforementioned feedthrough device that can be manufactured in an especially cost-effective manner, and can be installed—with a relatively low thermal load of the filter means—in such a manner that a change of the electrical properties of the filter means during the assembly is excluded to a large degree. 
     This task is resolved by a filter design mentioned at the beginning, where the filter means are arranged outside the feedthrough device and connected with it in such a manner that, in installed condition, they basically stick out into the housing in a freely suspended manner. 
     SUMMARY OF THE INVENTION 
     The invention comprises the technical knowledge that the manufacture, assembly and vacuum leakage test of a unipolar or multipolar electrical feedthrough device with filter means after its installation in the housing of an implantable electronic therapeutic device can achieve special advantages if the feedthrough device and the electrical filter means are spatially arranged in a special manner, where a contact between the filter means and the housing wall is ensured and, at the same time, the basically non-vacuum-tight design of the used filter means need not be taken into account. This results in the advantage that the actual tightly closed element, i.e., the insulation ceramic material and its connections with the flange and the pins, can be tested for leakage tightness independently from the filter means. 
     According to this invention, the unipolar or multipolar electrical feedthrough device to be installed in an aperture in the housing of an implantable electronic therapeutic device comprises preferably flange-shaped fixing means that can be introduced in such an aperture and that are designed to connect the feedthrough device with the housing, and, furthermore, filter means designed as a capacitor, which are connected—in an electrically conductive manner—on the one hand, with electrical pins of the feedthrough device arranged in a from each other electrically separated manner, and, on the other hand, with the housing of the electronic therapeutic device having a reference potential, while the filter means themselves are arranged outside the feedthrough device. The filter means are connected with the feedthrough device in such a manner that they basically stick out into the housing in a freely suspended manner. 
     This results in a substantial advantage in that no requirements as for vacuum-tightness need to be made in relation to the filter means. Only the area of the housing, where the feedthrough device is introduced into the wall of the housing, and the feedthrough body itself must be designed in a vacuum-tight manner so that, after the therapeutic device has been implanted, no bodily fluid can enter the inside of the housing. 
     Another advantage is the decrease of thermal or mechanical load so that mechanical damage especially of the filter (which can not be detected or only to a limited degree) can be eliminated. 
     In a preferred design version according to this invention, the filter means form a filter block that is arranged on the same axis as the body of the feedthrough device. Such an arrangement results in simplification during the preassembly of the feedthrough device according to this invention. 
     The fixing means, designed to connect the feedthrough device with the housing of the therapeutic device to be implanted, and located on the feedthrough body, is preferably designed as a ring-shaped flange and is equipped with a metal collar extending towards the inside of the housing. The filter block is fastened at the free end of the collar without any physical integrity with the feedthrough body. The ring-shaped flange forms a sufficient buffer during the introduction of the feedthrough device into the housing aperture to allow a vacuum-tight welded connection between the feedthrough body and the housing wall. In order to achieve a stress-free connection between the feedthrough body and the filter block, i.e., a connection that is not mechanically stressed to an impermissible degree by the warmth released during the welding process, the metal collar is designed in a flexible manner. According to a preferred design version of this invention, such flexibility is achieved in a simple manner by making the metal collar of a band of lamellar structure. The lamellas are essentially uniformly arranged at the collar so that the collar has basically the shape of a crown. 
     During the preassembly of the feedthrough device, the filter block designed in a cylindrical shape is introduced into the space restricted by the crown-shaped collar. The shell of the filter block is then based on the inner side of the lamellas of the collar. 
     The contact between the lamellas and the shell of the filter block form an electrical connection between the individual filter elements assigned to each pin of the feedthrough device and the housing (with the reference potential) of the implantable electronic therapeutic device. 
     The filter block consists of a number of ceramic discs arranged over each other in a stack. This stack comprises a number of discs (corresponding with the same number of electrical pins) designed as metallized substrate discs and each located between two non-metallized ceramic layers in order to form capacitive filter elements of the filter block. 
     In order to form an electrical connection of the filter elements with the housing wall carrying the reference potential it is sufficient that each of the ceramic discs designed as a metallized substrate be connected with only one lamellas of the crown-shaped collar. 
     In another variant of this invention, the multipolar electrical feedthrough device comprises four electric pins so that the filter block consists of four disks designed as coated substrate and four ceramic disks without any coating, which form—arranged in an alternating manner—the entire filter block. 
     An advantageous further variant of this invention comprises an additional connector pin to establish an electrical connection with the signal-generating and signal-processing unit of the electronic therapeutic device. This allows a simple connection of this unit with the reference potential. 
     In an advantageous design version of this invention, such a connection is designed in a band-wise manner, which results in special simplification of the preassembly of the signal-generating and signal processing unit. 
     Other advantageous design variants of this invention are characterized in sub-claims, and are described in detail in the following text by means of figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The figures show: 
     FIG.  1 : A preferred design version of the invention in a perspective view, 
     FIG.  2 : The design version of this invention shown in FIG. 1 in partial sectional view from the side, 
     FIG.  3 : The design version shown in FIG. 1 in view from below as well as [one missing line], 
     FIG.  4 : Illustration of the view of a section along line A . . . A according to FIG. 1, 
     FIG.  5 : Illustration of an alternative design version as a sectional view along line A . . . A according to FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The electrical feedthrough device  1  shown in FIG. 1 comprises an essentially cylindrical feedthrough body  2  carrying a ring-shaped flange  3 . A collar  5  expanding in direction of the inner space  4  (not shown here) of a housing (cf. item  4  in FIG. 4) of an implantable therapeutic device is installed on this flange. At its free end, collar  5  ends in individual lamellas  6 . Lamellas  6  are identically designed in form and size, and are uniformly distributed and arranged on the circumference of the collar. As a result, the collar has the shape of a crown, which is especially flexible in the area of its lamellas. 
     The inner space of this crown is filled out by the filter block  7  consisting of several capacitive filter elements (cf. items  19  to  23  in FIG.  4 ), which is, on its outer side, connected—in an electrically conductive manner—with individual lamellas  6 . 
     Pins  8 , which form electric contact elements, extend from the front connection area  9  of the feedthrough device  1  to the inner space of the housing  4  and thus penetrate both the gadget body  2  and the filter block  7 . FIG. 4 shows the design of the contacts of the pins inside the filter block  7  of the feedthrough device  1 . Ends  11  and  12  of pins  8  are connected with a header  10  or with a signal-generating and signal-processing unit  14  of the implantable electronic therapeutic device. 
     A mounting plate connects an additional contact lug  16  with collar  5 . The lug allows a simple connection of the signal-generating and signal-processing unit  14  with the wall of housing  26  (carrying the reference potential) of the implantable electronic therapeutic device. This arrangement simplifies the assembly of the multipolar feedthrough device. 
     FIGS. 2 and 3 illustrate in detail the form of body  2  of a multipolar electrical feedthrough device  1 . 
     Feedthrough device body  2  consists of a basically cylindrically designed shell  2 . 1 , on which is installed a ring-shaped flange  3 , and a ceramic core  2 . 2 , which completely fills out the inner space of the shell. The mutually adjacent surface areas of shell  2 . 1  and ceramic core  2 . 2  are connected, in a vacuum-tight manner, by a sealing binding material  17  such as solder, bonding material or, as is preferred in this particular case, by gold. Pins  8  are led, in a vacuum-tight manner, in bore holes through this ceramic core. The bonding material connecting the relevant surface areas is marked with  18 . 
     Funnel-shaped expansion  2 . 3  of the bore holes in ceramic core  2 . 2  designed for pins  8  on the header side  9  of the feedthrough device  1  allows, to a small extent, a radial mobility of the ends of the fixed pins  8  sticking out of the ceramic core which results in a simplification during the assembly of the header (cf. item  13  in FIG. 1) after feedthrough device  1  is placed in the housing of the implantable electrical therapeutic device. The main purpose of the funnel-shaped expansions also called countersinks  2 . 3  is the mutual electrical insulation of the pins and especially of the pin flange, since this arrangement prevents any leakage currents on the ceramic surface. 
     FIG. 4 shows filter block  7  of a multipolar electrical feedthrough device  1  in a schematized partial sectional view. 
     Filter block  7  comprises a number of ceramic disks  19 ,  20 ,  21 ,  22 ,  23  arranged above each other, of which disks  20 ,  21 ,  22 , and  23  are designed as metallized substrate. Disks  19  are identically designed and arranged between two layers with metallized coating. This layer design consisting of alternating ceramic discs and metallized layers is preferably achieved with ceramic disks that are suitably metallized. Ceramic discs  19  comprise four identically wide boreholes to conduct pins  8 . Discs  20 ,  21 ,  22 , and  23  paired form a capacitor, where a non-metallized ceramic disc  19  placed in between them serves as a dielectric medium. Each of discs  20 ,  21 ,  23 ,  23 , designed as metallized substrate also in identical manner, has an electric contact with just one of pins  8 . For this purpose, three bore holes  24  are made in these discs, through which three pins penetrate the filter block  7 , while there is a small gap between the discs and the pins. The diameter of the fourth bore hole is smaller than the diameter of bore holes  24 , and essentially equals the outer diameter of pins  8 . This bore hole comprises the contact spot  25  of pins  8  with the relevant metallized disc  20 ,  21 ,  22 , or  23 . Discs  20 ,  21 ,  22 , or  23  are connected, in an electrically conductive manner, at its peripheral area, with lamellas  6  of collar  5 . and thus they are in contact with wall  26  of the housing (carrying the reference potential) of the implantable electronic therapeutic device. The relevant contact spot is marked with  27 . 
     The arrangement of lamellas  6  at the free end of the collar causes a sufficient flexibility of the collar to absorb mechanical stress arising due to warmth development during the manufacture of the connection between housing wall  26  and shell  2 . 1  of the feedthrough body  2 , without mechanically stressing the filter block. The relatively large distance between filter block  7  hovering above the feedthrough body  2  and the welding spot  28  causes that the development of warmth during the welding of feedthrough device  1  into housing  26  of the implantable therapeutic device does not result in such a thermal load of individual filter elements of filter block  7  as to change their electrical parameters in an irreversible way. 
     The design version of a multipolar electrical feedthrough device  1  in FIG. 5 differs from the design variant shown in FIG. 4 essentially in the structure of filter block  7 . 
     In addition to disks  20 ,  21 ,  22 , and  23 , each of which is connected with one of pins  8 , filter block  7  from FIG. 5 comprises four electrically conductive discs  20 . 1 ,  21 . 1 ,  22 . 1 , and  23 . 1  formed by metallized substrate, that are connected, at their peripheral edge, in an electrically conductive manner, with lamellas  6  of collar  5 . Unlike the variant in FIG. 4, each of discs  20 ,  21 ,  22 , and  23  is connected with only one of pins  8 , but not with lamellas  6  of collar  5 . Discs  20 ,  21 ,  22 , and  23  as well as discs  20 . 1 ,  21 . 1 ,  22 . 1 , and  23 . 1  are arranged in pairs facing each other in such a manner that disc  20  faces disc  20 . 1 , disc  21  faces disc  21 . 1 , disc  22  faces disc  22 . 1 , and disc  23  faces disc  23 . 1 . 
     One of each disc pair is connected with one of pins  8 , while the other disc is connected, in an electrically conductive manner, with collar  5 . Each of disc pairs  20 ,  20 . 1 , and  21 ,  21 . 1 , and  22 ,  22 . 1 , and  23 ,  23 . 1  forms a capacitor connected between one of pins  8  a collar  5 . 
     The bore holes  24  in discs  20 ,  20 . 1 ,  21 ,  21 . 1 ,  22 ,  22 . 1 ,  23 , and  23 . 1  are designed in such a manner that always exactly one bore hole  24  in discs  20 ,  21 ,  22 , and  23  is so narrow that the relevant disc (of discs  20 ,  21 ,  22 , and  23 ) contacts the corresponding pin  8 , while all remaining bore holes, especially all bore holes  24  in discs  20 . 1 ,  21 . 1 ,  22 . 1 , and  23 . 1  have a larger diameter so that these discs have a certain distance from the aforementioned pin  8  and have no electrical contact with it. 
     FIGS. 1 to  5  describe multipolar electrical feedthrough devices. Unipolar filter feedthrough devices can be fabricated in a similar manner as the described multipolar designs. So the unipolar design can comprise, e.g., only one pin of the type of pins  8 , that is, e.g., connected with a number of electrically conductive discs such as discs  20 ,  21 ,  22 , and  23 , while a second type of discs such as electrically conductive discs  20 . 1 ,  21 . 1 ,  22 . 1 , are connected, in an electrically conductive manner, with collar  5 . This invention is not restricted to the preferred design examples described in previous text. There exist a number of variants that make use of the presented solution even if they contain some other substantially differing design.