Patent Publication Number: US-2009240314-A1

Title: Implantable electrode lead system with a three dimensional arrangement and method of making the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/039,085, filed 24 Mar. 2008 and entitled “Three-Dimensional System fo Electrode Leads and Method of Making the Same”, which is incorporated in its entirety by this reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to the electrode lead field, and more specifically to an improved three-dimensional system of electrode leads and the method of making this improved system. 
     BACKGROUND 
     Conventional brain interfaces involve electrical stimulation and/or recording from neural ensembles through an electrode lead system implanted in a targeted region of the brain. While conventional electrical stimulation therapy is generally safe and effective for reducing cardinal symptoms of approved diseases, it often has significant behavioral and cognitive side effects and limits on performance. Additionally, the therapeutic effect is highly a function of electrode site position with respect to the targeted volume of tissue and, more specifically, a function of the influence of the delivered charge on the particular neuronal structures proximate to the charge. Neural recording applications, such as cortical neuroprostheses, often involve recording from large-scale neural ensembles in sophisticated brain structures, which have 3-dimensional anatomical shapes. With conventional electrode lead systems, there are limitations on complete and precise sampling and stimulation of the desirable neural structure since electrode sites are generally positioned in a 2-dimensional fashion. Additionally, conventional three-dimensional electrode lead systems are limited by their complexity and low fabrication yield. Thus, there is a need for an improved electrode lead systems to provide fine electrode positioning, selectivity, precise stimulation patterning, and precise electrode lead location. This invention provides such an improved and useful system of electrode leads and a method of making this improved system. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES  
         FIG. 1  is a side view of the electrode lead system of the preferred embodiment including a series of shims and a series of components. 
         FIG. 2  is a perspective view of the shim and a first variation of the alignment features. 
         FIGS. 3A and 3B  are top views and front perspective views, respectively, of the shim and a second variation of the alignment features. 
         FIGS. 4A and 4B  are top views and front views, respectively, of the shim, the first variation of the alignment features, and a first variation of the component receptacle. 
         FIGS. 5A and 5B  are top views and front views, respectively, of the shim, the first variation of the alignment features, and a second variation of the component receptacle. 
         FIG. 6  is a representation of the shim of  FIGS. 4   a  and  4 B, shown with a first variation of a component. 
         FIG. 7  is a representation of the electrode lead system of the preferred embodiment including a series of shims, a series of components, and a first variation of the alignment element. 
         FIG. 8  is a representation of the electrode lead system of the preferred embodiment including a series of shims and a series of components. 
         FIG. 9  is an exploded view of a subassembly of the electrode lead system of the preferred embodiment. 
         FIG. 10  is a schematic of a method of making a shim pictured in a series of side views. 
         FIG. 11  is a representation of the top view of a shim. 
         FIG. 12  is a schematic of a method of making a connector pictured in a series of side views. 
         FIG. 13  is an exploded view of a series of subassemblies of the electrode lead system of the preferred embodiment. 
         FIG. 14  is a representation of a series of connectors, a series of second components, and a series of third components of the electrode lead system of the preferred embodiment. 
         FIGS. 15A and 15B  are top views and bottom views, respectively, of the second component of the electrode lead system of the preferred embodiment. 
         FIG. 16  is a representation of the interconnection feature of a series of second components of the electrode lead system of the preferred embodiment. 
         FIG. 17  is a representation of a series of second components and the third component of the electrode lead system of the preferred embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of preferred embodiments of the invention is not intended to limit the invention to these embodiments, but rather to enable any person skilled in the art to make and use this invention. 
     As shown in  FIG. 1 , the electrode lead system  100  of the preferred embodiments includes a series of shims lo, each having an alignment feature  12 , a series of components  16  in a three dimensional arrangement, a series of second components  20 , and a series of connectors  22  that connect the series of components  16  to the series of second components  20 . The series of shims  10  of the preferred embodiment functions to position the series of components  16  in a three dimensional arrangement and to provide a controlled and configurable spacing between the components. As shown in  FIG. 2 , each shim  10  of the preferred embodiments includes an alignment feature  12  that functions to provide an alignment guide such that multiple shims  10  may be assembled together. The shim  10  may further include a component receptacle  14  that functions to receive a component  16  (shown in  FIG. 6  and described below). The system  100  of the preferred embodiment is preferably designed for an implantable electrode lead system to interface with brain tissue, and more specifically, for an implantable electrode lead system that can interface with brain tissue in a three-dimensional manner. The system  100  of the preferred embodiments, however, may be alternatively used in any suitable environment (such as the spinal cord, peripheral nerve, muscle, or any other suitable anatomical location) and for recording, stimulation, chemical delivery, or any other suitable reason. 
     1. The Shim 
     The series of shims  10  of the preferred embodiment functions to position the series of components  16  in a three dimensional arrangement. The shims  10  provide a controlled and configurable spacing between the components  16 . Each shim  10  in the series of shims may optionally remain empty, may position a single component  16 , or may position more than one component  16 . Therefore, the electrode lead system  100  may include one shim  10  for every component  16 , such that the ratio of shims  10  to components  16  in the electrode lead system  100  is 1:1; the electrode lead system  100  may include one shim  10  for every two or more components  16 , such that the ratio of shims  10  to components  16  in the electrode lead system  100  is less than 1:1; or there may be shims  10  without a component  16 , as shown in  FIG. 1 , such that the ratio of shims  10  to components  16  in the electrode lead system  100  is greater than 1:1. The electrode lead system  100  preferably includes any suitable combination of shims  10  that position zero, one, or more than one components  16 . 
     The shim  10  of the preferred embodiment is preferably generally planar with a specified thickness. The thickness determines the controlled and configurable spacing of the components  16  of the electrode lead system  100 . The specified thickness is preferably determined by the thickness of each individual component  16  and the desired component-to-component spacing. The shims  10  are preferably rectangular, but may alternatively have any suitable geometry. The shims are preferably a silicon substrate, but may alternatively be made from any other suitable material such as metal or polymer. 
     As shown in  FIGS. 2 and 3 , the shim  10  of the preferred embodiment includes an alignment feature  12 . The alignment feature  12  functions to provide an alignment guide such that multiple shims  10  may be assembled together using the alignment features  12  of each shim  10 . The alignment features  12  are preferably fabricated with the shim  10  using microfabrication techniques, but may be made in any other suitable fashion with any suitable material. The alignment feature is preferably one of several variations. In a first variation, as shown in  FIG. 2 , the alignment feature  12  is a hole defined by the shim  10 . The hole is preferably located toward the outer edge of the shim  10 , but may alternatively be located in any suitable location on the shim  10 . In this variation, the shim  10  may define any suitable number of alignment features  12 . In a second variation, as shown in  FIG. 3A and 3B , the alignment feature  12  includes male and female mating elements. As shown in  FIG. 3A , the protruding alignment feature  12  located in the bottom right hand corner of the shim  10  has a corresponding recessed element defined by the shim  10 . The protruding feature, or male element, will mate with a recessed, or female element, on a second shim  10  in a manner similar to LEGO brand building blocks. The alignment features  12  in this variation may be located in any suitable location. In a third variation, the alignment feature  12  is the shape of the shim  10 . As an example, the shim  10  may have two opposing surfaces: a convex surface and concave surface. The two opposing surfaces preferably mate together in a manner similar to PRINGLES brand potato chips. Although the alignment feature  12  is preferably one of these variations, the alignment feature  12  of the preferred embodiment may be any suitable alignment feature in any suitable location on or around the shim  10  such that multiple shims  10  may be assembled together using the alignment features  12  of each shim  10 . 
     As shown in  FIGS. 4 and 5 , the shim  10  of the preferred embodiment may further include a component receptacle  14  that functions to receive a component  16 . The component receptacle  14  is preferably adapted to receive one component  16 , but may alternatively remain empty or receive more than one component  16 . The component receptacle is preferably a cavity (or “negative”) of the component to be received by the component receptacle  14 , but may alternatively be any other suitable shape, such as a generic shape adapted to fit multiple different components. The depth of the component receptacle  14  is preferably a few microns deeper than the depth of the component  16  to be received by the component receptacle  14 , but may alternatively be any other suitable depth. The component receptacle  14  is preferably fabricated with the shim  10  using microfabrication techniques, but may be made in any other suitable fashion with any suitable material. The component receptacle  14  is preferably one of several variations. In a first variation, as shown in  FIGS. 4A and 4B , the component receptacle is preferably a cross like shape adapted to receive a planar electrode array (shown in  FIG. 6 ). This variation preferably provides anchoring in multiple dimensions. In a second variation, as shown in  FIGS. 5A and 5B , the component receptacle is preferably a cylindrical recess adapted to receive a fluidic component. This variation preferably provides anchoring in at least one dimension. Although the component receptacle  14  is preferably one of these variations, the component receptacle may have any suitable geometry and any suitable depth or attachment mechanism to receive a component  16 . 
     As shown in  FIG. 11 , the shim  10  of the preferred embodiment may further include an injection port  24 . The injection port  24  functions to facilitate the backfilling of epoxy into the cavity or negative of the shim  10  during the assembly of the electrode lead system  100 , which is described in more detail in Section 5: Method of Assembly. 
     The shim  10  may also include one or more integrated circuits (e.g., Application Specific Integrated Circuit, or ASICs) to interface with amplifiers, filters, signal processors, multiplexors, power, memory units, fluid flow controllers, or any suitable electrical component. The shim  10  may also include a fluid reservoir for filling fluidic components. 
     The cavity of the shim may also include connection pads to allow for direct integration of the components  16  to the shim and on-shim ASICs. The top surface of the shim may also include shim interconnection pads that electrically connect the shim to another shim and/or the connector  22 . The shim interconnection pads may have equal or fewer pads than the number of active electrode sites depending on the circuitry, such as a multiplexor, in the ASIC. 
     2. Method of Making The Shim 
     The shims  10  of the preferred embodiment, including the alignment feature  12  and the component receptacle  14 , are preferably micro-machined using standard microfabrication techniques, but may alternatively be fabricated in any other suitable fashion. The method of the preferred embodiments, as shown in  FIG. 10 , includes providing a wafer, removing a portion of the wafer S 110 , creating an alignment feature S 112 , and releasing the shims from the wafer. The method is preferably designed for the manufacture of a series of shims. The method, however, may be alternatively used in any suitable environment and for any suitable reason. 
     The step of providing a wafer functions to provide a foundation from which to build the series of shims  10 . The wafer is preferably a standard wafer conventionally used in semiconductor device fabrication and more preferably a SOI wafer (silicon-insulator-silicon substrate), but may alternatively be any suitable wafer, such as a wafer with a machinable silicon substrate and a release mechanism. The wafer is preferably made from silicon, but may alternatively be made from gallium arsenide, indium phosphide, or any other suitable material. The wafer is preferably manufactured with an oxide layer buried a specified distance below the top surface. The depth or thickness of the buried oxide layer preferably determines the thickness of the shim  10 . The wafer preferably has the same thickness as the specified thickness of the shim  10 , such as 50 μm, 100 μm, or any other suitable thickness. 
     Step S 110 , which includes removing a portion of the wafer, functions to define the geometry and the depth of the component receptacle  14 . Additionally, this step may also define the injection port  24 . This step is preferably performed through a deep reactive ion etching (DRIE), but may alternatively be performed through any other suitable removal process, such as other dry etching methods, wet etching, chemical-mechanical planarization, or any combination thereof Removing material is preferably performed after providing a patterned thermal oxidation and masking such that the unmasked material is removed. This step preferably includes a photolithographic mask. Alternatively, the shim  10  may be built up, using any suitable deposition technique, around the geometry of the component receptacle  14  to define the component receptacle in that manner. The component receptacle may alternatively be created by any suitable combination of deposition, removal, and or patterning. The dimensions of the component receptacle  14  are preferably as close to the dimensions of the component  16  as possible to maintain the lateral alignment of the component  16  within the shim  10 , while there is some tolerance between the component  16  and the component receptacle  14  to allow the component  16  to be easily disposed into the component receptacle  14 . The tolerance is preferably less than 100 μm and more preferably less than 10 μm. The depth of the component receptacle is preferably less than 100 μm deep and more preferably about 85 μm deep such that it will completely enclose the component  16  and connector  22  junction, which includes the thickness of the component  16  (about 15 μm), the thickness of the connector  22  (about 15 μm), and the height required for interconnection with an ultrasonic ball bond, flip chip technique or another suitable interconnection method (typically 50 μm or less). The tolerances and thickness of the components and components receptacles may alternatively be any other suitable thickness or depth respectively. 
     Step S 112 , which includes creating an alignment feature  12 , functions to build an alignment feature  12  on the shim  10 . This step may further function to define the shape and size of the shim  10 . The alignment features  12  may be created by removing material or by adding material. The removal of material is preferably performed through a deep reactive ion etching (DRIE), but may alternatively be performed through any other suitable removal process, such as other dry etching methods, wet etching, chemical-mechanical planarization, or any combination thereof. Removing material is preferably performed after providing a patterned thermal oxidation and after masking such that the unmasked material is removed. The addition of material is preferably performed through any suitable deposition process that grows, coats, or transfers a material onto the wafer in any other suitable method. These deposition processes may include physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE), atomic layer deposition (ALD), or any other suitable process. The alignment features may alternatively be created by any suitable combination of deposition, removal, and or patterning. 
     The final step, which includes releasing the shims  10  from the wafer, functions to complete the process and release the manufactured shims  10 . This step is preferably completed by dissolving the built-in sacrificial oxide layer, releasing the shims  10  from the wafer, but may be accomplished in any suitable manner. 
     3. The Component 
     The series of components  16  of the preferred embodiments function to interface with the tissue, or any other suitable substance, within which they have been implanted. The series of components  16  may include any combination of similar or different electrical and/or fluidic components. The component  16  is preferably one of several variations. 
     In a first variation, as shown in  FIG. 6 , the component  16  is a neural interface electrode array, similar to the neural interface electrode array described in US Publication Number 2008/0208283 published on 28 AUG 2008 and entitled “Neural Interface System”, which is incorporated in its entirety by this reference. The electrode array preferably has a plurality of electrode sites and is generally two-dimensional or planar. The electrode sites are preferably tuned for recording, stimulation, chemical sensing, any other suitable function, or any combination thereof. The electrode array may further include fluidic channels providing the capability to deliver therapeutic drugs, drugs to inhibit biologic response to the implant, or any other suitable fluid. The neural interface electrode array is preferably made from a substrate such that there is high density of electrode sites at a first end of the array (the distal end) and bonding regions at a second end of the array (the proximal end). The substrate is preferably silicon, but may alternatively be a thin-film polymer substrate. The polymer substrate is preferably parylene or some combination of parylene and inorganic dielectrics, but may alternatively be made out of any suitable material. The electrode sites are preferably patterned directly onto the substrate. The electrode array is preferably comprised of conductive interconnects disposed between layers of dielectrics that insulate the interconnects on top and bottom sides. At least some interconnects preferably terminate with electrode sites on the distal end and/or with bond pads for electrical connection to external instrumentation and/or hybrid chips on the proximal end. The electrode sites are preferably metal such as iridium, platinum, gold, but may alternatively be any other suitable material. The electrode sites may alternatively undergo further processing such as electroplating and/or site selective coating to tune impedance, increase stimulation level, and/or to release drugs. The conductive leads or traces are preferably metal or polysilicon, but may alternatively be any other suitable material. Polyimide, parylene, inorganic dielectrics, or a composite stack of silicon dioxide and silicon nitride is preferably used for the dielectrics, but any other suitable materials may alternatively be used. 
     In a second variation, the component  16  is a mapping electrode array, which functions to perform clinical deep brain electrophysiological mapping for use in neurosurgical applications. More specifically, the mapping electrode array is preferably adapted to perform simultaneous multichannel neural recording from precisely known locations along the deep microelectrode track. The mapping electrode may further have extended functionality such as multichannel recording and/or stimulation or fluid delivery. The mapping electrode system is preferably a planar electrode array disposed on an insulated metal wire. The metal wire is preferably made from a metal such as tungsten, stainless steel, platinum-iridium, or any other suitable metal. The electrode array preferably includes multiple recording sites. 
     In a third variation, the component is a fluidic component. The fluidic component in this variation is preferably a flexible micro fluidic tube, but may alternatively be any suitable tube, channel, planar electrode array (with or without electrode sites), or any other suitable component to transmit fluid. Although the component  16  is preferably one of these variations, the component  16  may be any suitable element or combination of elements to perform the desired functions. 
     4. The Second Component the Connector, and the Third Component 
     The series of second components  20  of the preferred embodiments function to operate with the first component  16 . The second component  20  may include multiple different electrical subsystems or a series of the same subsystems. The electrode lead system  100  preferably includes a second component for every component  16 , such that the ratio of second components to components  16  is 1:1. By including one second component  20  for every component  16 , the electrode lead system  100  is a modular system with a decreased chance of failure of the entire electrode lead system  100  due to a failure of a single component  16 . Alternatively, the electrode lead system  100  may include one second component for every two or more components  16 , such that the ratio of second components to components  16  is less than 1:1 or may include two or more second components for every component  16 , such that the ratio of second components to components  16  is greater than 1:1. 
     The second component is a suitable electronic and/or fluidic subsystem to operate with the component  16 . Preferably, as shown in  FIG. 14 , the second component  20  is a printed circuit board (PCB). As shown in  FIG. 15   a,  the second component  20  preferably includes on-board integrated circuits and/or on-chip circuitry  25  for multiplexing, signal conditioning, stimulus generation and/or other suitable functions. The PCBs of the second components  20  are preferably made from flexible PCB that is approximately 100 μm thick, but may alternatively have any suitable thickness. The PCBs of the second components  20  may alternatively be made of thin rigid PCBs. Alternatively, the second component  20  may be an Application Specific Integrated Circuit (ASIC), a multiplexer chip, a buffer amplifier, an electronics interface, an implantable pulse generator, an implantable rechargeable battery, integrated electronics for either real-time signal processing of the input (recorded) or output (stimulation) signals, integrated electronics for control of the fluidic components, any other suitable electrical subsystem, or any combination thereof. Although the second component is preferably one of these several subsystems, the second component may be any suitable element or combination of elements to operate any suitable first component(s)  16 . 
     The second component  20  may include one or more mutually coupling interconnection features to enable multiple second components  20  to be coupled to one another and/or to the third component  26 . As shown in  FIG. 15 , the mutually coupling interconnection feature is preferably a mating pair of low profile, zero-insertion-force (ZIF) connectors of opposite genders  21  and  23  (such as Hirose Electric, Japan), but may alternatively be any number of any suitable kind of connector. Each second component  20  preferably has a female connector  21  located on a top face and a male connector  23  located on a bottom face, in such a way that as shown in  FIG. 16 , multiple second components  20  are coupled in a stack by mating female and male connectors  21  and  23  of adjacent second components  20 . Alternatively, the female connector  21  may be located on a bottom face of the second component  20  and the male connector  23  may be located on a top face of the second component  20  to allow adjacent second components  20  to couple in a similar fashion. Alternatively, the mutually coupling feature may be a set of interconnection pads that are coupled together by soldering, flip chip techniques, or any suitable coupling method. 
     The total number of active channels required for the self-coupling interconnection feature is calculated by multiplying of the number of electrode sites from each first component  16  by the number of second components to be coupled together. Alternatively, the total number of active channels required for the mutually coupling interconnection feature can be reduced by utilizing the on-board multiplexing circuitries such that the ratio of active interconnection channels to the total number of the electrode sites from the electrode lead assembly  100  is 1:2 or greater. 
     The connector  22  of the preferred embodiments functions to couple the first components  16  to the second components  20 . The connector may be encased in silicone or any other suitable material. In some situations, the component  16  may have multiple connectors. Preferably, multiple connectors are physically attached along their entire length, using a suitable adhesive such as medical grade adhesive or any other suitable connection mechanism. The connector is preferably connected to the components  16  through ball bonds, flip chip technique, or any other suitable connection mechanism and/or method. Alternatively, the connector may be seamlessly manufactured with the first and/or second component such that it is an integrated connector. The connector may further include fluidic channels adapted to deliver therapeutic drugs, drugs to inhibit biologic response to the implant, or any other suitable fluid. 
     The connector  22  is preferably one of several variations. In a first variation, the connector is a silicon ribbon cable. The ribbon cable in this variation is preferably an integrated ribbon cable with the silicon substrate of the component  16 , but may alternatively be connected in any suitable fashion. In a second variation, the ribbon cable is a polymer ribbon cable. The ribbon cable in this variation is preferably connected to the component  16  via ball bonds or any suitable mechanical connection, but may alternatively be connected in any suitable fashion. Although the connector is preferably one of this variations, the connector may alternatively be any suitable element to couple the first components  16  to the second components, such as wires, conductive interconnects, etc. 
     The connector  22  is preferably fabricated using a microfabrication process. In a first variation, as shown in  FIG. 12 , the connector  22  is preferably fabricated using a polyimide microfabrication process. The process preferably includes two masks. Fabrication preferably starts on a silicon wafer onto which a sacrificial oxide is thermally grown to provide a mechanism for device release. The lower layer of polyimide, (e.g., PI-2611, HD Microsystems) is spun on, partially cured, and plasma etched through a first mask to promote adhesion of the metal leads S 120 . In this variation, gold and an adhesion layer of titanium are next deposited using evaporation S 120 , with preferable layer thicknesses of 250 nm gold and 30 nm titanium, although gold and titanium may be deposited to any suitable thicknesses. The gold and titanium layers are then patterned and etched to define the leads, and the upper polyimide is spun on and fully cured S 122 . An etch, preferably an oxygen and tetrafluoromethane etch, removes the field and open apertures through a second mask that will form the bond pads S 124 . Finally, after the wafers are cleaned, the devices are released from the wafer by dissolving the sacrificial oxide S 126 . In this variation, connector  22  thickness is preferably about 15 mm, but can be modified by changing the thickness of either the top or bottom polyimide layer. The pad layout of the connector  22  at the distal end is preferably designed to interface with the component  16  bond pads to permit ultrasonic ball bonding between the component  16  and the connector  22 . The thickness or height of the bond pad region of the component  16 /connector  22  junction is preferably less than 1,000 μm, and more preferably less than 100 μm. 
     The third component  26  is a suitable system that couples to one or more second components  20  as shown in  FIGS. 14 and 17  and includes input/output connectors to provide a unified interface to access the electrode sites of the electrode lead system  100 . The third component  26  is preferably made of rigid PCB and as shown in  FIG. 17 , preferably includes on-board integrated circuits and/or on-chip circuitry  27  for multiplexing, signal conditioning, stimulus generation, battery powering, wireless communication, and/or any other suitable functions. The third component  26  is preferably coupled to the second component  20  with one or more permanent and/or non-permanent connection methods identical to the connection methods for coupling the connector  22  to the second component  20 , and described in more detail in Section 5: Method of Assembly. However, the third component  26  may alternatively be coupled to the second component  20  with any other suitable method. Alternatively, the third component  26  can be made of flexible PCB. In this variation, multiple second components  20  can be attached to the third component  26 , and as shown in  FIG. 14 , the footprint of the third component  26  can be reduced by folding the flexible circuits. The folding of the flexible circuits is described in more detail in Section 5: Method of Assembly. 
     Additionally, the electrode lead system  100  may further include an enclosure element, such as a cover  28  as shown in  FIGS. 8 and 9 , that protects the shims  10  and components  16  individually and/or the entire assembled electrode lead system  100 . The cover  28  may also include attachment/alignment feature to allow for temperate or permanent interface to handle the assembled electrode lead assembly. 
     5. Method of Assembly 
     The method of assembling the electrode lead systems  100  of the preferred embodiments includes assembling a subassembly  200  (as shown in  FIG. 9 ) and assembling multiple subassemblies  200  (as shown in  FIG. 13 ) to form an electrode lead system  100 . The method is preferably designed for the assembly of the electrode lead system  100  of the preferred embodiments. The method, however, may be alternatively used in any suitable environment and for any suitable reason. 
     As shown in  FIG. 9 , assembling a subassembly  200  includes the steps of providing a shim  10 , coupling a component  16  to a shim  10 , coupling a connector  22  to the component  16 , and coupling a second component  20  to the connector  22 . 
     The steps that include providing a shim  10  and coupling a component  16  to a shim  10 , function to couple a component  16  to a shim  10  with a component receptacle  14  adapted to receive that component  16 , as shown in  FIG. 6 . The component  16  is preferably coupled to the shim  10  by gluing them together using any suitable adhesive, such as epoxy. The component  16  may alternatively be coupled to the shim  10  in any suitable fashion or may be fabricated directly onto the shim  10 . Some shims  10  in this step may not include a component receptacle  14  and/or may not have a component  16  coupled to them, such that some shims  10  remain empty or blank and function as a spacer. 
     The steps that include coupling a connector  22  to the component  16  and coupling a second component  20  to the connector  22 , functions to couple a second component  20  to the component  16 . The connector  22  is preferably connected to the component  16  and the second component  20  via ball bonds or any suitable electrical and/or mechanical connection, or may alternatively be connected in any other suitable fashion. The resulting subassembly  200  is then preferably subjected to an inspection to evaluate its structural and functional characteristics. The alignment of the component  16 /connector  22  with respect to the shim lo, as well as the overall structure of the subassembly  200 , is preferably inspected using either optical or scanning electron microscopy (SEM). The subassembly  200  may also undergo an electrical test to filter out defective devices before being integrated to the electrode lead assembly  100 . The electrical test is preferably impedance spectroscopy. Alternative electrical tests such as cyclic voltammetry may also be performed in conjunction or in place of the impedance spectroscopy. The junction between the component  16  and the connector  22  is preferably countersunk completely within the component receptacle  14  of the shim  10 , while the floor of the component receptacle  14  is preferably thick enough to maintain sufficient mechanical stability of the shim. 
     As shown in  FIG. 13 , assembling multiple subassemblies  200  to form an electrode lead assembly  100  includes the steps of coupling a series of shims  10  (each with and/or without components  16 ) to each other, and coupling the series of second components  20  to a third component  26 . The step that includes coupling a series of shims  10  functions to assemble a series of components  16  in a three dimensional arrangement, as shown in  FIG. 7 . The shims  10  are preferably coupled to one another by gluing them together using any suitable adhesive, such as epoxy. The series of shims  10  may alternatively be coupled in any suitable fashion or may be fabricated directly together. In this step, the alignment features  12  of each shim  10  function to provide an alignment guide such that the multiple shims  10  may be assembled together like building blocks. 
     The alignment features may further require an additional element such as an alignment element  18 . As shown in  FIG. 7 , the alignment element  18  is a pin that functions to fit through the alignment elements  12  of each shim  10  and thereby aligning the series of shims lo. The alignment element  18  in this variation is preferably made from annealed titanium wire (Small Parts, Miramar, Fla.) TIW-0050 with an outer diameter of 125 μm, but may alternatively be any suitable material with any suitable geometry. The alignment elements  18  are preferably cut to length based on the number of subassemblies  200  to be assembled together. The alignment element may alternatively be any suitable element that functions to provide an alignment guide and or additional alignment feature such that the multiple shims  10  may be assembled together. The alignment element  18  may be kept within the resulting structure, or removed before implantation. 
     The alignment features may further require an additional element such as a jig, preferably made from Teflon, that provides additional alignment for the assembly process. The jig preferably anchors the alignment elements  18  at a spacing that matches the alignment features  12  in the shim. With the alignment elements  18  installed, each validated subassembly  200  is preferably positioned and placed over the alignment elements  18  into the jig. A cover  28  is preferably placed over the last subassembly  200  and functions to protect the components  16  and the component  16 /connector  22  junctions. Alternatively, the jig could also include a cavity allowing the subassembly  200  to be precisely stacked by utilizing a variation of alignment feature such as the geometric shape of the shims. The jig may also include a clamp mechanism that can be adjusted to tightly but gently hold the components  16  in place and in perfect alignment during the assembly and during the subsequent oven curing process. The tip of the clamp is preferably composed of a low tension spring or a silicone bead in order to hold the electrode lead assembly  100  together at minimal pressure to prevent breakage. Alternatively, a band or string, such as an elastic rubber band, may be used to hold the stacked subassemblies prior to applying the adhesive. With the clamp in place, each subassembly  200  is preferably backfilled with epoxy through the injection ports  24 . Surface tension and capillary action will preferably draw epoxy into the shim cavities and component receptacles  14 . The entire jig is then preferably placed in an oven to cure the epoxy. 
     The second components  20  can be electrically and mechanically coupled to the third components  26  preferably by non-permanent connectors such as an anisotropic connector or commercially available connectors. Alternatively, the second components  20  can be permanently coupled to the third component  26  preferably via various soldering techniques, anisotropic-adhesive-film, conductive epoxy, or ultrasonic ball bonding. To reduce the footprint of the assembled third component  26 , the connection region can be folded as shown in  FIG. 14  if the PCB of the third component  26  is made of a flexible substrate. To reduce stress applied to the connector  22  after folding the connection region, a portion of the second components  20  are preferably flipped and their respective connectors  22  are preferably twisted prior to folding. The assembly  30  is then fixed and insulated with epoxy (such as EpoTek, 353ND-T). 
     6. The Insertion Tool 
     The electrode lead system  100  of the preferred embodiment is preferably designed for an implantable electrode lead system to interface with brain tissue, and more specifically, for an implantable electrode lead system that can interface with brain tissue in a three-dimensional manner. As shown in  FIG. 8 , the electrode lead system  100  preferably further includes an insertion tool  34  that functions to insert the electrode lead system  100  into brain tissue or any other suitable tissue. The insertion tool  34  preferably includes an insertion driver  36  that functions to move the series of components  16  of the electrode lead system  100  into the tissue at a predetermined speed and an insertion bar  38  that functions to couple the insertion driver  36  to the electrode lead system  100 . 
     The insertion driver  36  can preferably be mounted to a standard stereotactic frame and is preferably one of several variations. In a first variation, the insertion driver is a stepper-motor based actuator, such as a M-230 from Physik Instrumente (Auburn, Mass.). The stepper-motor of this variation is preferably DC powered, offers a travel range of at least 25 mm with step resolution of at least 50 nm, and travel speeds up to about 2 mm/sec. The driver preferably includes a motor controller with computer interface to achieve precise travel distance at programmable speeds. In a second variation, the insertion driver  36  is preferably a high-velocity inserter such as a pneumatic inserter or a spring-loaded inserter. 
     The insertion bar  38  is preferably coupled to the cover  28 , as shown in  FIGS. 8 and 9 . The I/O assembly  30  may also be temporarily mounted to the insertion bar  38  during the insertion of the electrode lead system  100  into the tissue. A temperature-sensitive polymer (such as polyethylene glycol or PEG) is preferably used to temporarily mount the insertion bar  38  to the electrode lead system  100 . After insertion, the insertion bar  38  can preferably be released from the electrode lead system  100  by dissolving away the polymer by applying warm, sterile saline. The insertion bar  38  may alternatively be removed from the electrode lead system  100  in any other suitable fashion, or the insertion bar  38  itself may dissolve or degrade once implanted. Alternatively, the alignment feature  18  can also be used to handle the electrode lead system  100  without the insertion bar  38 . 
     Although omitted for conciseness, the preferred embodiments include every combination and permutation of the various electrode lead systems, the various shims, the various alignment features, the various component receptacles, the various components, the various methods of making and assembly, and the various alignment elements. 
     As a person skilled in the art will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.