Abstract:
A method of forming electrode structures comprising a plurality of electrode pads and a plurality of electrically conducting wires extending from the electrode pads. The method comprises coating an electrode structure with a relatively electrically insulating material, arranging each of the electrode pads in a first arrangement; arranging the wires relative to each other to provide a sufficient gap of separation between neighboring wires; securing the wires to a remotely positioned anchor member to preserve a gap of separation between neighboring wires, and applying a coating of relatively electrically insulating material to the electrode structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage application of PCT/AU2006/001855 entitled “Cochlear Implant Assembly”, filed on Dec. 6, 2006. The present application also claims priority from Australian Provisional Patent Application No 2005906847 filed on 6 Dec. 2005. The above patent applications are hereby incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to the field of forming electrode structures for electrical products and, more specifically, forming respectively insulated electrode structures that may be used in electrode arrays. 
     2. Related Art 
     In many electrical devices, particularly those that are manufactured on a very small scale, the manufacture of the wiring and related components is often a labor intensive and specialized craft. In particular, ensuring that the wiring and electrical connection of the various components of the systems occurs correctly is often the most expensive and labor intensive aspect of the manufacturing process. This cost is often passed on to the ultimate consumer. This is also the case when such devices need to be specifically hand-made to a specification as often the availability of the device is dependent upon the time taken to manufacture the device, with the time taken being difficult or impossible to expedite. 
     This is often particularly the case in the field of medical implants and electrical devices that are implanted in the body. Such devices may include, for example, stimulating devices such as pacemakers, cochlear implants, FES stimulators, and the like; recording devices such as neural activity sensors and the like; implantable cables which connect implantable devices to other implantable devices; diagnostic devices capable of carrying out in vivo analysis of body parameters, and other types of implantable devices not yet contemplated. 
     In such devices, it is often desirable to minimize the size to ensure that they are minimally invasive upon implantation. As a result, in such instances, the electronic wiring and connections need also to be relatively very small. As such, manufacturing such devices to ensure that they are reliable and sturdy is a specialized art, requiring much time and expense. 
     Current techniques for the manufacture of electrode arrays for cochlear implant systems, in particular, are relatively highly labor intensive. This is primarily due to the intricate nature of the array and the very small dimensions of the array necessary to allow it to be inserted in the scala tympani of the human cochlea. Being an implantable device capable of delivering and applying electrical currents to surrounding tissue, there is a need to ensure that the elements of the array are electrically isolated from each other to avoid short circuits and the like which may greatly diminish the benefits of such a device, as well as have the potential to cause pain and discomfort to the recipient. 
     SUMMARY 
     According to one embodiment of the present invention, a method of coating an electrode structure with an electrically insulating material, the electrode structure is provided. The method comprises a plurality of electrode pads and a plurality of electrically conducting wires, at least one wire extending from at least one of the electrode pads. The method comprises arranging each of the electrode pads in a first arrangement; arranging the wires relative to each other to provide a gap of separation between neighboring wires; securing the wires to a frame member to preserve the gap of separation between neighboring wires; and applying a coating of electrically insulating material to the electrode structure, wherein the gap is sufficient to enable the application of the coating of electrically insulating material to all surfaces of the wires without webbing between adjacent wires. 
     According to another embodiment of the present invention, a method for of forming an electrode structure comprising a plurality of electrode pads and a plurality of electrically conducting wires extending from the electrode pads, for use in an electrode array of an implantable medical device is provided. The method comprises attaching a sheet of conductive material to a sheet of carrier material; working the sheet to remove predetermined portions thereof to form a plurality of electrode pads of conductive material supported on an electrode support of carrier material, a frame member; and a plurality of wires of relatively electrically conductive material, at least one wire connecting an electrode pad to the frame member; coating the worked sheet with an electrically insulating material; and removing the electrode support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       By way of example only, preferred embodiments of the invention are now described with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a cochlear implant system in which embodiments of the present invention may be advantageously implemented; 
         FIG. 2  is a side view of an electrode array suitable for use with the cochlear implant system of  FIG. 1 ; 
         FIG. 3   a  is a perspective view of an electrode structure supported on an electrode support in accordance with one embodiment of the present invention; 
         FIG. 3   b  is an enlarged view of a portion of  FIG. 3   a , showing the electrode pads arranged in an array upon an electrode support and the wires extending therefrom in an angular arrangement; 
         FIG. 4   a  is a perspective view of the wires of the electrode structure of  FIGS. 3   a  and  3   b  connected to a support frame; 
         FIG. 4   b  is an enlarged view of a portion of  FIG. 4   a , showing the connection of the wires with the support frame; 
         FIG. 5  is a perspective view of the electrode structure of  FIGS. 3   a - 4   b  following removal of the electrode support; 
         FIG. 6  is a plan view of the electrode pad and wire arrangement of the electrode structure in accordance with an alternative embodiment of the present invention; 
         FIG. 7  is a perspective view of a clamping arrangement for securing the wires in accordance with the embodiment of  FIG. 6 ; 
         FIG. 8  is a plan view showing an electrode structure with the distal ends of the wires attached to a sacrificial member in accordance with a prior art assembly method; 
         FIG. 9  is a plan view showing an electrode structure with the distal ends of the wires attached to a sacrificial member in accordance with a method of the present invention; and 
         FIG. 10  is a plan view showing an electrode structure with the distal ends of the wires attached to a sacrificial member in accordance with an alternative method of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present invention generally relate to the field of forming electrode structures for electrical products. In particular, embodiments of the present invention are directed to forming respectively insulated electrode structures that may be used in electrode arrays. Such as arrays may be used for sensors, including biosensors, and implantable devices, such as an implantable recording or stimulating electrodes or pads for use in the body. 
     One type of known cochlear implant system with reference to  FIG. 1 . It will be appreciated that whilst the present invention will be discussed in relation to a cochlear implant system, the present invention is equally applicable to a variety of implantable devices, such as biosensors, pacemakers, FES stimulators and neurostimulators. 
     Known cochlear implants typically consist of two main components, an external component including a speech processor  29 , and an internal component including an implanted receiver and stimulator unit  22 . The external component includes a microphone  27 . The speech processor  29  is, in this illustration, constructed and arranged so that it can fit behind the outer ear  11 . Alternative versions may be worn on the body or clothing. Attached to the speech processor  29  is a transmitter coil  24  that transmits electrical signals to the implanted unit  22  via a radio frequency (RF) link. 
     The implanted component includes a receiver coil  23  for receiving power and data from the transmitter coil  24 . A cable  21  extends from the implanted receiver and stimulator unit  22  to the cochlea  12  and terminates in an electrode array  20 . The signals thus received are applied by the array  20  to the basilar membrane  8  and the nerve cells within the cochlea  12  thereby stimulating the auditory nerve  9 . The operation of such a device is described, for example, in U.S. Pat. No. 4,532,930. 
     An example of an electrode array suitable for use with such a cochlear implant system is shown in relation to  FIG. 2 . In this arrangement, the electrode array  20  comprises a flexible carrier member  15  moulded in a spirally-curved configuration. The carrier member  15  may be made from a material such as silicone, which has the appropriate flexibility properties to enable the electrode array to assume a desired shape to facilitate insertion. A plurality of electrode pads  14  are arranged at dedicated intervals along the length of the inner wall of the carrier member  15  with each electrode pad  14  being connected to the stimulator unit  22  via a wire or conductor  16  which extends within the outer wall of the carrier member  15 . The number of electrode pads  14  present in the electrode array  20  can vary. In one form, there may be 2-2 electrodes positioned along the length of the carrier member  15 , which may be 20-30 mm in length. In this regard, each of the electrode pads  14  are connected to the implanted receiver and stimulator unit  22  via a wire  16 , thereby resulting in the electrode array  20  housing  22  individual wires  16 , each of which are electrically isolated from each other to avoid shorting between the wires  16 , and incorrect stimulation of the nerves. 
     Typically, prior to implantation into the cochlea the electrode array  20  is straightened by the presence of a stylet or other straightening means (not shown) which is received within a lumen formed in the carrier member  15 . Upon removal of the stylet, the electrode array  20  is able to adopt the configuration as shown in  FIG. 2  to conform to the shape of the inner wall of the cochlea such that the electrodes  14  are positioned to deliver appropriate electrical stimulation to the desired nerve cells within the cochlea. It will be appreciated that the degree of curvature of the depicted electrode array is to be taken as illustrative only, and as the electrode curves during implantation the wires  16  also undergo a degree of curvature. 
     The electrode array  20  can be constructed in a variety of ways. In this regard, it should be appreciated that the structure of the electrode array  20  is substantially provided by the electrode pads  14  and the associated wires  16  which are encapsulated within the flexible carrier  15 . The electrode pads  14  and corresponding wires  16  may be formed by either a one-piece or two-piece construction method, and the present invention will now be described in relation to both these methods. 
     A one-piece construction method for creating the electrode pads  14  and associated wires  16  is described in International Patent Application PCT/AU02/00575 (WO 02/089907), the content of which is incorporated herein by reference. In the method described, a foil of conductive material is applied to a carrier or substrate, and portions of the foil and carrier are removed to create a pattern of electrode pads and associated wires. Following creation of a plurality of one-piece electrode pads and associated wires, the top surface of the pads and wires are sprayed or otherwise applied with a layer of relatively electrically insulating and resiliently flexible material, and the carrier or substrate is then removed. The individual one-piece electrode pads and wires are retained together via the layer of insulating and resiliently flexible material, and the areas of foil removed are also filled with an insulating material. The undersurface of the electrode pads and wires are then coated with a layer of insulating and resiliently flexible material, and the region of the electrode pads is preferably masked to ensure they remain uncovered to deliver electrical stimulation. The individual electrode pad and wire sets are then arranged in an appropriate jig and shaped and encapsulated in the carrier material to form the electrode array as shown in  FIG. 2 . 
     As will be appreciated, the method of insulating the individual wires from neighboring wires in the above one-piece construction method is relatively complicated and requires a number of separate insulating steps. As the wires are typically arranged in close proximity to each other, the insulating material may not individually coat each wire but rather create a “web effect” between a group of wires which may not provide total electrical isolation between wires. As a result, shorting may still occur between wires in a web, which can reduce the effectiveness of the electrical stimulation and in some instances cause discomfort to the individual. Similarly, such a “webbing” of neighboring wires increases the rigidity of the wires which can increase the overall rigidity of the electrode array, thereby reducing the ability of the array to adopt various shapes. 
     In order to simplify the manner in which the insulation is applied to the electrode structures in a one-piece construction method, the method of the present invention will now be described with reference to  FIGS. 3   a - 7 . 
     Firstly a foil of conductive material, for example platinum (Pt) or gold (Au), is applied to a carrier or substrate, for example copper (Cu), and portions of the foil and carrier are removed to create a pattern of electrode pads  14  and associated wires  16  as shown in  FIG. 3   a . While each pad  14  is depicted as having one wire  16  extending therefrom, it will be appreciated that one, some or all of the pads  14  could have more than one wire  16  extending therefrom. A variety of material removing methods may be employed to create the desired pattern in the material, for example using electrical discharge machining (EDM) or a variety of etching processes. The foil and substrate is then worked such that a frame  30  remains about the pattern of electrode pads  14  and wires  16  and an electrode support  32  is provided by the substrate which forms a backing for the electrode pads  14 . In this regard, the electrode pads  14  remain aligned together on the electrode support  32  and the wires or conductors  16  are freed from the substrate, as is shown more clearly in  FIG. 3   b . Such selective etching of the substrate may be performed by masking the material with a photo resist layer prior to etching. In alternative embodiments, the electrode pads  14  are not aligned together on the electrode support  32 . 
     In the embodiment shown, the electrode pads  14  are substantially rectangular having a pair of diametrically opposed ends which are formed parallel with the walls of the electrode support  32 , which are in turn connected via a pair of opposed sides, which extend across the surface of the electrode support  32 . However, it will be appreciated that other shapes of the electrode pads are possible and still fall within the scope of the present invention. 
     As shown more clearly in  FIGS. 4   a  and  4   b , whilst the wires  16  are substantially free from the backing substrate, the distal ends of the wires  16  remain attached to the frame  30  of substrate and foil, to prevent the wires  16  from becoming tangled during handling. The wires  16  are integral with the electrode pads  14  and extend angularly from an opposing end of the pads. To facilitate sufficient separation between angularly extending wires  16 , the wires are arranged to extend from alternative opposed ends of adjacent pads  14 . Such an arrangement ensures that the distance between adjacent wires  16  in the structure as shown in  FIGS. 3   a - 4   b , is sufficient to enable coating of the wires  16  with a suitable electrically insulating coating without causing webbing between adjacent wires, as discussed in relation to the previous method. 
     In this regard, the electrode pads  14  can be masked and the entire arrangement as shown in  FIGS. 3   a - 4   b  can be coated with a suitable electrically insulating material, such as parylene, including parylene N and parylene C, thereby ensuring the surfaces of the wires are fully coated and electrically isolated from each other. The coating step may be performed by vapour deposition techniques or other type of spraying or immersion techniques. 
     Following coating of the arrangement, the remainder of the substrate is removed, thereby removing the electrode support  32  and part of the frame portion  30 . The coating may need to be selectively stripped to enable etching of the substrate, and such selective stripping may be performed by a laser or hot wire, to create the electrode structure  35  made up of electrode pads and wires as shown in  FIG. 5 . To aid in aligning the pads  14  and associated wires  16  when the substrate is removed, a layer of thin silicone sheeting may be applied to the surface of the stimulation pads, prior to removal of the substrate. 
     The ends of the wires  16  are separated from the foil portion of the frame  30  by laser cutting or by other suitable methods. The electrode structure  35  may be then placed in an assembly jig and manipulated to form an electrode array such as is shown in  FIG. 2 . In this regard however, all sides of each of the wires  16  are each individually coated with insulating material in one step thereby providing greater electrical isolation between neighbouring wires in the electrode array  20 . 
     In an alternative embodiment, the structure of the electrode pads  14  and associated wires  16  may be arranged such that the wires  16  run parallel to the arrangement of the pads  14  as is shown in  FIG. 6 . In this arrangement, in order to ensure that the spacing between neighboring wires is sufficient to prevent “webbing” and ensure that the electrically insulating coating can be applied to all the surfaces of the wires, prior to coating the arrangement the ends of the wires are separated from the frame  30  and raised to a different height and clamped in place, as shown in  FIG. 7 . 
     A two-piece construction method for creating the electrode pads  14  and associated wires  16  is described in International Patent Application PCT/AU04/001726 (WO 2005/055363), the content of which is incorporated herein by reference. In the method described, the electrode pads  14  are separately formed by punching the desired shape of the electrode pads from a foil of conductive material, such as a foil of platinum (Pt). The electrode pads may have a variety of shapes and are removed from the foil such that they remain connected to each other. Following removal, the electrode pads  14  may be further shaped as desired and an end of an electrically conducting wire is welded to the surface of each of electrode pads. The wire is typically pre-coated with an electrically insulating material and, as such, a small portion of the electrical conducting material is removed from the ends of the wires to enable each wire to be welded to the electrode pad. Similarly, the other end  16   a  of each wire is also welded to a sacrificial plate  10  to ensure alignment. A portion of this process is shown in  FIG. 8 . Following connection of each of the wires  16  to the electrode pads and to the sacrificial plate  10 , the wires can then be separated from the sacrificial plate  10  and the wires and electrode pads assembly can be placed in an appropriate jig and formed into an electrode array such as that shown in  FIG. 2 . In this regard, the method requires the wires  16  to be pre-coated with an appropriate insulating material, which adds to the production costs associated with manufacturing such an electrode array  20 , and also requires an additional step of removing the insulating material from each of the ends of the wires, which is an additional step in the process. 
     As shown in  FIGS. 9 and 10 , the present invention is also applicable to electrode structures of such a two-piece construction wherein the wires  16  are not coated with an appropriate insulating material prior to assembly and a coating step is required following assembly. In the prior art arrangement shown in  FIG. 8 , the wires are positioned in close proximity to each other as they extend between the electrode pads  14  and the sacrificial member  10 , and as such should a coating step be employed there is likelihood of “webbing” occurring between adjacent wires thereby providing rigidity to the structure and increasing the likelihood of shorting occurring between adjacent wires. 
     Therefore, by fixing the ends of the wires to the sacrificial plate  10   a  at greatly spaced intervals along the plate  10   a  such that distance between wires  16  is maximised, as shown in  FIG. 9 , it is possible to employ uncoated conducting wires and then apply a coating step to the structure prior to separating the wires  16  from the sacrificial plate  10   a . Similarly, as shown in  FIG. 10 , the wires  16  can extend laterally from the electrode pads  14 , thereby ensuring that sufficient distance is provided between adjacent wires  16  to enable individual coating of the wires  16  with an insulating coating. Further, to facilitate separation of the wires prior to the coating step, the wires may be separated from the sacrificial plate  10   a  and raised to a different height and clamped in place, similar to that described in relation to  FIG. 7 . 
     It will be appreciated that the coating step will typically involve coating the structure with parylene or any other type of suitable insulating material via vapour deposition methods. As such, the stimulating surfaces of the electrode pads  14  may be masked prior to coating to prevent deposits of insulating material forming thereon and reducing the effectiveness of the electrodes. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.