Abstract:
An electrical interconnect structure for an implantable medical device includes a feedthrough that has a pin extending therefrom. The pin defines a first end and a middle portion. A bonding surface is formed at the first end of the pin, and the bonding surface has a surface area greater than a cross-sectional area of the pin at its middle portion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to implantable medical devices. More particularly, the present invention relates to electrical interconnection structures for implantable medical devices. 
     Electrical feedthroughs provide a conductive path extending between the interior of a hermetically sealed container and a point outside the container. Implantable medical devices may include a connector module for connecting leads to the device. The connector module is electrically connected to circuitry inside a sealed case of the implantable medical device through one or more feedthroughs. Typically, an electronic module assembly (EMA) block is connected also to a feedthrough inside the implantable medical device, opposite the connector module. Wires are then connected to bond pads on the EMA block using conductive solders or brazes to complete the electrical connection across the feedthrough. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a method and structures for making electrical interconnections for implantable medical devices. Arc percussion welding can be used according to the present invention to weld together conductor materials. A connection structure can be formed between a wire and a feedthrough pin having an enlarged head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an implantable medical device having a connector module that is electrically connected to feedthroughs. 
         FIG. 2  is a schematic representation of an interconnection assembly between a feedthrough and bond pads. 
         FIG. 3  is an exploded cross-sectional view of a feedthrough assembly. 
         FIG. 4  is a flow chart of a manufacturing process for creating electrical interconnection structures. 
         FIG. 5  is a schematic representation of an alternative embodiment of an interconnection assembly. 
         FIG. 6  is a schematic representation of another alternative embodiment of an interconnection assembly. 
         FIG. 7  is a cross-sectional view of a feedthrough assembly with a washer. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of an implantable medical device  20  having a connector module  22  (also called a header) that is electrically connected to feedthroughs  24  that pass through a housing or cannister  26  of the device  20 . The feedthroughs  24  can be unipolar or multipolar. The connector module  22  includes electrically conductive ribbons  28  that extend between the feedthroughs  24  and components of the connector module  22 , such as sleeves or sockets  30  for accepting connector pins of leads (not shown). 
       FIG. 2  is a schematic representation of an interconnection assembly between a feedthrough assembly  24  and bond pads  32 A and  32 B that are located inside the canister of a device. A feedthrough pin  34  extends through a ferrule  36  of the feedthrough assembly  24 . The pin  34  has a first end  38 A at an interior side of the ferrule  24 A, and a bonding surface  40  is located at an enlarged portion  42 A of the first end  38 A of the pin  34 . A second end  38 B of the pin  34  also has a bonding surface  40 B on an enlarged portion  42 B. The bonding surfaces  40 A and  40 B provide substantially flat surfaces for making electrical connections. Although  FIG. 2  shows enlarged portions  42 A and  42 B at both ends  38 A and  38 B of the pin  34 , it should be recognized that in further embodiments the pin  34  could have only a single enlarged portion at only one end. 
     The enlarged portion  42 A shown in  FIG. 2  can have numerous alternative configurations according to the present invention. For example, the enlarged portion  42 A can be formed by welding or otherwise connecting a disc to the first portion of the pin  34 . Alternatively, the enlarged portion can be formed by coining the first end  38 A of the pin  34 . In any configuration, the enlarged portion  42 A generally has a greater area than a cross-sectional area of the pin  34  between the enlarged portion  42 A and the ferrule  36 . The enlarged portion  42 A in the illustrated embodiment has a diameter or width of about 30-40 mils. The relatively large surface area provided by the bonding surface  40 A of the enlarged portion  42 A facilitates aligning and connecting wires and other electrical components to the pin  34 . The enlarged portion  42 B can be configured similar to enlarged portion  42 A. 
     The bond pads  32 A and  32 B can be hybrid bond pads of a conventional type known to those skilled in the art of implantable medical device design. The bond pads  32 A and  32 B can be electrically linked to therapy circuits (not shown) or other components of an implantable medical device, as desired. The particular location of the bond pads  32 A and  32 B can also vary as desired. 
     A wire  44  is electrically connected between the pin  34  and the bond pads  32 A and  32 B. In particular, the wire  44  is electrically connected to the bonding surface  40  and to bonding regions  46  of the bond pads  32 A and  32 B. The wire  44  can be any electrical conductor in nearly any shape, for example, a conventional ribbon conductor. 
     The pin  34  and the wire  44  can each be made of a high conductivity material, for example, copper, platinum, tantalum, niobium, palladium, titanium, and alloys thereof. Also, alloys such as MP35N® nickel-cobalt-chromium-molybdenum alloy, nickel- and cobalt-based alloys and stainless steels can be used. Moreover, the wire  44  can be a copper-clad nickel ribbon. It should be recognized that in further embodiments, multiple wires can be connected to the pin  34  as desired. 
       FIG. 3  is an exploded cross-sectional view of one embodiment of a feedthrough assembly  50  that includes a ferrule  36 , a pin  34  extending through the ferrule  36  and a conventional hermetic seal  52  (e.g., a seal made of glass or other non-conductive seal material) between the pin  34  and the ferrule  24 A. A disc  42 A is positioned at the first end  38 A of the pin  34 , and for clarity is shown in an exploded cross-sectional manner in  FIG. 3 . The disc  42 A provides a substantially flat bonding surface  40 A. The disc  42 A can be round, rectangular, or have other shapes, though any shape of the disc  42 A generally provides a substantially flat bonding surface  40 A. 
     In the illustrated embodiment, the disc  42 A has a recess  54  located opposite the bonding surface  40 A. The recess  54  in the disc  42 A is configured to mate with the first end  38 A of the pin  34 , where a welded connection can be made. In further embodiments, the recess  54  can be omitted (see  FIG. 7 ). 
       FIG. 4  is a flow chart of a manufacturing process for creating electrical interconnection structures according to the present invention. Welded connections between components, such as between a wire and a bonding surface or between a disc and an end of a feedthrough pin, can be made using conventional arc percussion welding equipment. 
     With arc percussion welding, the components to be welded are first positioned at a selected distance from each other, such that an air gap is formed (step  60 ). Next, a burst of radio frequency (RF) energy ionizes the air in the air gap (step  62 ). A suitable cover gas is provided. Then an arc is created between the components to be welded to heat them to weldable temperatures, creating two molten masses (step  64 ). The arc can be created by discharging capacitor banks of the arc percussion welding equipment. The weldable temperature, and therefore the amount of electrical energy discharged by the capacitor banks, will vary depending on the particular characteristics of components to be welded. Once the components to be welded have reached a weldable temperature, they are accelerated together (step  66 ). The molten masses combine, metal to metal, are forged together. As the weld cools, a complete alloy bond is formed. One or more electromagnetic actuators can be used to accelerate the components to be welded together. 
     The arc percussion welding process can be performed to make an electrical connection at a feedthrough, and to form structures as shown and described with respect to  FIGS. 1-3 . In such situations, the arc percussion welding process can be performed either before or after the feedthrough has been hermetically sealed (alternative steps  68 A and  68 B). An advantage of the method of forming electrical interconnection structures according to the present invention is that the electrical connections can easily be made after hermetically sealing the feedthrough. 
     It should be recognized that the method described above can be used in conjunction with conventional techniques for making electrical connections in implantable medical devices. For example, gas tungsten arc welding, electron beam welding, resistance welding, ultrasonic welding, laser welding, friction welding, coining and conductive adhesives can also be used. With respect to the structures shown in  FIG. 2 , for instance, the electrical connection between the wire  44  and the bonding surface  40  can be formed by one technique and the electrical connection between the wire  44  and the bond pad  32 A by another technique. 
     The structures and method of the present invention can be applied in numerous ways. The following are some examples of alternative embodiments of the present invention.  FIG. 5  is a schematic representation of an alternative interconnection assembly that includes a feedthrough assembly  124  and a pair of hybrid bond pads  132 A and  132 B. A feedthrough pin  134 , which extends through ferrule  136 , is electrically connected to the hybrid bond pads  132 A and  132 B directly. In other words, the pin  134  is directly connected to the bond pads  132 A and  132 B without the need for a separate wire therebetween. The pin  134  can be specially shaped or deflected to properly align it with respect to the bond pad  132 A to make the electrical connection therebetween. Moreover, the pin  134  can optionally include an enlarged portion in further embodiments. The connection between the pin  134  and the bond pad  132 A can be made using arc percussion welding. 
       FIG. 6  is a schematic representation of another alternative embodiment of an interconnection assembly that includes a feedthrough assembly  224  and a pair of hybrid bond pads  232 A and  232 B. A first wire  224  is connected to the bond pads  232 A and  232 B. A second wire  246  extends from the feedthrough  224  (e.g., from an enlarged end of a pin  234  that extends through a ferrule  236  of the feedthrough  224 ), and is connected to the first wire  244  at a joint location  248 . The first and second wires  244  and  246 , respectively, are connected together in an end-to-end configuration. In this embodiment, the connection between the first and second wires  244  and  246  enables the bond pads  232 A and  232 B and the feedthrough to be assembled and connected to separate wires ( 244  and  146 ) independently and later joined together at the joint location  248 . The joint can be formed using arc percussion welding. 
       FIG. 7  is a schematic representation of a feedthrough assembly  324  that includes a ferrule  36  and a pin  34  with an enlarged portion  42 . The feedthrough assembly  324  is generally similar to those described above. However, the feedthrough assembly shown in  FIG. 7  further includes a non-conductive washer  326  that is positioned around the pin  34 , between the ferrule  36  and the enlarged portion  42  of the pin  34 . The washer  326  reduces the risk of welding splatter when the enlarged portion  42  is formed on the pin  34 , and can be placed around the pin  34  permanently or temporarily (and removed after the enlarged portion  42  is formed on the pin  34 ). The particular size and shape of the washer  326  can vary as desired. 
     The present invention provides for the use of arc percussion welding to weld together conductor materials used in implantable medical devices, and for connection structures to be formed between a wire and a feedthrough pin having an enlarged, nailhead-like head portion. Reliable electrical connections can be easily and simply made between a feedthrough and other components without the need for an electronic module assembly (EMA) block. By omitting the EMA block, manufacturing costs can be reduced and space inside an implantable medical device can be conserved. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the interconnection structures of the present invention can be used with nearly any type of implantable medical device.