Abstract:
An implantable connector electrically connects multi-conductor leads to an implantable medical device such as a neurostimulator. The connector is applicable to a variety of lead contact terminals, including iso-diametric terminals with ring contacts, paddle-shaped terminals with flat pad contacts, and orthogonal lead contact terminals. The connector is assembled directly into a hermetic feedthrough of the device and utilizes the feedthrough housing as a sustaining structure for connector pressurization. The feedthrough pins are integrated with compressible contacts in a manner that confines, protects, and precisely positions the compressible contacts. The compressible contacts can be coil springs, metal-particle-filled elastomer buttons, and fuzz buttons, and can be used with rigid tips where a contact preload and/or an enhanced contact tip robustness is desired. Connector pressurization means include covers fastened with a screw and cam actuated clamping covers which support contact forces and the seal compression by engaging undercuts on the feedthrough housing walls.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 12/882,072 filed Sep. 14, 2010. 
     Application Ser. No. 12/882,072 is a continuation-in-part of application Ser. No. 12/187,392 filed Aug. 8, 2008 (U.S. Pat. No. 7,794,256 issued Sep. 14, 2010), which claims priority of provisional application No. 60/954,954 filed Aug. 9, 2007. 
    
    
     BACKGROUND 
     1. Field 
     This relates to implantable medical devices having external electrical connections and electrical feedthroughs, specifically to miniature implantable connectors for interconnection of implantable devices and associated leads 
     2. Prior Art 
     In a typical implantable electronic device, such as a cochlear implant, a heart pacemaker, or a brain-stimulating device, the device contains electronic circuitry (electronics) that resides in a hermetically sealed housing or case. The device is attached to at least one electrical lead (“lead”) that has sensing and/or stimulating electrodes on its end distal from the device. The electrodes are implanted in the tissue targeted for therapy (cochlea, heart muscle, particular area of brain, etc.). Other leads may connect the device to additional implantable system components, such as drug delivery devices, implantable inductive coils (for energy delivery to the device and/or data communication with the device), or power sources, which may have to reside in a more accessible body location for easier charging and/or replacement. 
     It is preferable that the implantable leads and devices be detachable so that either a device or leads can be implanted or explanted independently. This functionality is provided by a connector on the device&#39;s case, which disengageably connects the lead&#39;s proximal (near-device) contacts to the electronics in the interior of the implantable device. The connections must be made across a hermetic feedthrough so that the hermeticity of the device&#39;s case is not compromised, i.e., the electronics remains sealed from the body fluids and moisture. It is further desirable that the connector has a small size, provides a rapid connection and disconnection without special tools, and allows multiple connect and disconnect cycles without loss of function. 
     In many existing devices the connector is implemented in a molded header (insulating housing), formed from a hard medical grade polymer on the edge of the device&#39;s case, and the connector&#39;s receptacle contacts are connected to the feedthrough pins by discrete wiring, which is subsequently overmolded (covered and sealed by insulating material). The wiring must interconnect two dissimilar and spatially separated contact patterns and can be quite intricate. The assembly and the associated molding and testing can be labor intensive, as discussed in U.S. Pat. No. 7,274,963 (2007) to Spadgenske. 
     The molded header connectors for iso-diametric (having constant diameter) leads typically have blind lead receiving lumens (i.e., the lumens are open at one end only) into which a lead is inserted with significant force which must be adequate to overcome contact engagement forces and to achieve seal compression. For high contact counts, lead insertion force and contact registration in these connectors can be problematic. The header connectors are therefore more suitable for larger-diameter, lower contact-count leads, such as those used with cardiac rhythm management devices which can tolerate significant insertion force and have more liberal contact registration tolerances. 
     U.S. Pat. No. 6,321,126 (2001) to Kuzma shows a header connector design for paddle-shaped lead terminals. This patent addresses the need for a high contact count, small-dimensioned connector, but this design is only applicable to leads with paddle-shaped lead terminals and cannot be adapted for iso-diametric lead terminals. In addition, the contact system appears to rely on an elastomeric backing of the lead terminal body for providing contact pressure. Since elastomeric materials are prone to time-dependent permanent deformation, contact pressure may relax with time, especially because such connections have a low compliance (independent of the elastic backing, the contacts have no elastic deflection reserve). The low compliance is also problematic when repeated mating is required. 
     As the implantable medical devices and systems become more capable and number of the leads and the lead contact count and density increase, there is a need for small but robust connectors to make reliable connections to devices or components of the implantable system. The small size is especially important for devices such as neural and cochlear stimulators which are implanted in the cranium, both for medical reasons (a smaller cranial cavity needs to be created) and for aesthetic advantages. In such cases, it may be desirable to build the connector interface directly into the device&#39;s feedthrough housing cavity so that receptacle contacts are co-located with the feedthrough pins. 
     My U.S. Pat. No. 6,662,035 (2003) shows a feedthrough-based connector design intended for a device implantable beneath the scalp. This patent teaches how to implement reliable direct metal-to-metal connections between lead contacts and the corresponding feedthrough pins. The illustrative dimensions of the two-lead connector are a depth of approximately 6.5 mm, a length of approximately 15.0 mm, and a breadth of approximately 13.0 mm. These dimensions are still excessive for locating the connector on an edge of the device&#39;s case or for use in size-critical applications. Unfortunately, the size of the above feedthrough-based connector cannot be radically reduced because the C-shaped spring contacts have a large footprint and height and are located entirely above the exterior (outwardly facing) surface of the feedthrough&#39;s dielectric substrate, thus adding directly to the connector overall height. Furthermore, the spring contacts are free-standing and thus are susceptible to intra-operative handling damage if made too small and fragile. 
     SUMMARY 
     The present device, in one aspect, addresses the need for improved small implantable connectors built directly into a hermetic feedthrough of an implantable electronic device, such as a cochlear implant, a neurostimulator, a pacemaker, a pain-control device, and the like. The connector in this aspect uses a contact system integrated with the feedthrough pin and employs the feedthrough housing as the sustaining structure for connector assembly and pressurization. The contact system consists of a feedthrough pin, a resilient compressible contact, and a means to position, secure, and protect the compressible contact. 
     A small connector size is realized by utilizing the feedthrough pin to directly interface, confine, protect, and precisely position the resilient contact element. The contact retention feature is provided by the feedthrough pin or by an additional component joined to the feedthrough pin. A variety of compressible contacts can be used, including coil springs, fuzz buttons (a single length of a very fine wire formed into multiple small wavy loops), and metal-particle-filled elastomer buttons. These contact forms have been proven in many applications and can be economically produced in biocompatible versions. The compressible contact may be used with a rigid tip or a cup on the outer end to provide a more robust contact point and/or contact preload. The contact preload helps to assure a consistent contact force. The connector can be adapted to connect implantable leads with a variety of contact terminals, including, but not limited to, circular and rectangular paddle-shaped terminals with planar contact pads and iso-diametric terminals with tubular or ring lead contacts. 
     In order to protect the miniature iso-diametric leads, a lead contact terminal is first inserted into a feedthrough&#39;s connector cavity (paddle-shaped terminals) or a seal (iso-diametric terminals) without encountering significant resistance. Once the lead contact terminal is inserted into the connector cavity and the lead contacts are aligned with the compressible contacts, the connector is pressurized with a clamping means that engages the feedthrough housing. Clamping means include threaded fastener covers and space-efficient cam-driven covers. 
    
    
     
       DRAWINGS 
         FIG. 1  is a perspective view of a device having two planar circular connectors on one side of the implantable device case. 
         FIG. 2  is a perspective view of a device having two planar circular connectors on each side of the implantable device case. 
         FIGS. 3A-B  are exploded perspective views, top and bottom views respectively, of a connector for leads having a circular contact terminal, showing a device feedthrough with integrated compressible contacts, a seal, a lead contact terminal, and a clamping cover. 
         FIG. 4  is a perspective view of a fully assembled connector of  FIGS. 3A-B . 
         FIG. 5  is a cross-sectional view of the connector of  FIG. 4  taken as indicated by the line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a partial cross-sectional view of  FIG. 5 , showing the contact interface in a magnified detail. 
         FIG. 7  is a cross-sectional view of a coil spring contact assembled in a tubular hat, taken as indicated by the line  7 - 7  of  FIG. 8A , showing a cross-sectional detail of the spring-to-hat weld. 
         FIGS. 8A-B  are an exploded and an assembled view respectively of the feedthrough contact assembly comprising a coil spring contact contained in a tubular hat with the top of the hat attachable to the top of the feedthrough pin. 
         FIGS. 9A-B  are an exploded and an assembled view respectively of another feedthrough contact assembly comprising a coil spring contact contained in a tubular hat with the top of the hat attachable to the top of the feedthrough pin. 
         FIG. 10  is an exploded perspective views of a connector for a lead having a circular contact terminal, showing a device feedthrough with integrated compressible contacts, a lead contact terminal with an integral seal, and a clamping cover. 
         FIG. 11  is a fully assembled connector of  FIG. 10 . 
         FIG. 12  is a cross-sectional view of the connector of  FIG. 11  taken as indicated by the line  12 - 12  of  FIG. 11 . 
         FIG. 13  is a partial enlarged view of the cross-sectional view of  FIG. 12 , showing a coil spring contact with a rigid contact tip contained in a tubular feedthrough pin and retained by a welded insert. 
         FIG. 14  shows another embodiment of the contact assembly of  FIG. 13 . 
         FIG. 15  is an exploded perspective view of a connector for a lead having a circular contact terminal, showing a device feedthrough with integrated compressible contacts, a lead contact terminal with an integral seal, and a clamping cover. 
         FIG. 16  is a fully assembled connector of  FIG. 15 . 
         FIG. 17  is a cross-sectional view of the connector of  FIG. 16  taken as indicated by the line  17 - 17  of  FIG. 16 . 
         FIGS. 18A-B  are exploded perspective views of a connector for a lead having a circular contact terminal, showing a device feedthrough with integrated compressible contacts, a lead contact terminal with an integral seal, and a cam-driven clamping cover. 
         FIG. 19  is a fully assembled connector of  FIGS. 18A-B . 
         FIG. 20  is an exploded perspective views of an embodiment of a cam-driven clamping cover showing a top plate, a cam, and a bottom plate. 
         FIGS. 21A-B  show the cam-actuated clamping cover in disengaged and engaged states respectively. 
         FIG. 22  is an exploded perspective view of a connector for a lead having a triangular paddle-shaped contact terminal. 
         FIG. 23  is a fully assembled connector of  FIG. 22 . 
         FIG. 24  is an exploded perspective view of a connector for a lead having iso-diametric contact terminal, showing a device feedthrough with integrated compressible contacts, and a cam-driven clamping cover cooperating with undercuts on the side walls of the feedthrough housing. 
         FIG. 25  is a perspective view of the lead-seal assembly for connector of  FIG. 24 . 
         FIG. 26  is a perspective view of a device having a fully assembled connector of  FIG. 24  on the device&#39;s edge. 
         FIG. 27  is a partial cross-sectional view of the device of  FIG. 26 , as indicated by the line  27 - 27  of  FIG. 26 . 
         FIG. 28  is a partial longitudinal cross-sectional view of the device of  FIG. 26 , taken along the centerline of the lead, as indicated by the line  28 - 28  of  FIG. 26 . 
         FIG. 29  is an exploded perspective view of a connector for iso-diametric leads, adapted for co-planar mounting on a device&#39;s side. 
         FIG. 30  is a perspective view of a device having the connector of  FIG. 29  attached to the device&#39;s side, wherein the leads exit the connector co-planar with the device&#39;s case. 
         FIG. 31  is a partial cross-sectional view of the device of  FIG. 30 , taken across the contacts, as indicated by the line  31 - 31  of  FIG. 30 . 
         FIG. 32  is a partial longitudinal cross-sectional view of the device of  FIG. 30 , taken along the centerline of the lead, as indicated by the line  32 - 32  of  FIG. 30 . 
         FIG. 33  is an exploded perspective view of a connector for a lead with a rectangular paddle-shaped terminal clamped with a cam-driven clamping cover. 
         FIG. 34  is an inverted perspective view of a rectangular paddle-shaped contact terminal showing the lead contact array. 
         FIG. 35  is a perspective view of a device having an edge mounted connector for a lead having a rectangular paddle-shaped contact terminal. 
         FIGS. 36-38  are cross-sectional views of alternative embodiments of the contact assembly which can be used interchangeably with the contact assembly shown in  FIG. 6  and  FIG. 31 . 
         FIGS. 39-40  are a perspective and a cross-sectional view respectively, of a contact assembly having a coil spring contact protectively confined in a counterbore on the exterior side of the dielectric substrate. 
         FIG. 41  is a variation of the contact assembly of  FIG. 40 , wherein the coil spring contact has a tapered outer end. 
         FIG. 42  is a variation of the contact assembly of  FIG. 40 , wherein the outer end of the coil spring contact is protectively confined in an aperture of a discrete seal. 
         FIGS. 43-45  show a coil spring contact assembly wherein the spring contact is retained by a snap-in retention mechanism and the outer end of the coil spring is protected by a profiled head of the feedthrough pin. 
         FIG. 46  is a cross-sectional detail of a contact assembly having a tubular feedthrough pin containing a compressible contact and a rigid contact tip retained by an insert welded to a collar on the outer end of the feedthrough pin. 
         FIG. 47  is a cross-sectional detail of a contact assembly having a tubular feedthrough pin containing a compressible contact and a rigid contact tip retained by crimping the open end of the tubular feedthrough pin. 
         FIG. 48  shows a coil spring contact assembly wherein a coil spring contact is retained on a profiled head of the feedthrough pin by a snap-in of an inwardly formed coil into an undercut in the feedthrough pin. 
         FIG. 49  shows a coil spring contact assembly wherein a coil spring contact is retained in a tubular section of a feedthrough pin by a snap-in of an outwardly formed coil into a slit at the bottom of the tubular section of the feedthrough pin. 
     
    
    
     DETAILED DESCRIPTION 
     FIGS.  1 - 9 —Connector for Annular Lead Terminal—Discrete Seal 
       FIGS. 1 and 2  show exemplary implantable devices  101  and  102  having connectors  103  for detachably connecting electrode leads  104  to the device&#39;s electronic circuitry contained in a hermetically sealed cases  105 . The leads have multiple conductors (not shown) which extend from the device (proximal end) to the sensing and/or stimulating electrodes  106  at the distal end  107 . The connector is based on a hermetic feedthrough attached to the device&#39;s case along the feedthrough housing circumference  108 . 
     The devices are designed to be implanted subcutaneously and/or in a body cavity, typically in the chest, the abdominal cavity, or the cranium. The distal end electrodes are implanted in the tissue targeted for sensing and/or stimulation. Device  101  has connectors on one side of the case, and is therefore suitable for implantation in a cranial cavity. A device may have connectors on both sides of the case as shown in  FIG. 2  to allow connecting additional leads or devices. 
       FIGS. 3  A-B are exploded perspective views, top and bottom view respectively, of connector  103 . The connector comprises a hermetic feedthrough assembly  110 , a discrete seal  111 , a lead contact terminal  112 , and a clamping cover  113 . The feedthrough assembly comprises a housing  115 , a dielectric substrate  116 , and feedthrough pins  117  (seen protruding from the bottom or interior side of the feedthrough assembly in  FIG. 3B ). These components are assembled as shown and are hermetically joined together, typically by brazing. Subsequently, the compressible contacts are integrated with the feedthrough pins to form contact assemblies  118 . 
     On the top or exterior side, the feedthrough has an exterior cavity  119  ( FIG. 3A ) defined by the top or exterior side of dielectric substrate  116 , and a side wall  120  and a central protrusion  121  of the feedthrough housing. The feedthrough exterior cavity accommodates the seal and the lead terminal which are than clamped with cover  113  to pressurize the connector. Central protrusion  121  has a threaded hole  122  which enables cover  113  to be clamped to the feedthrough housing. 
     The feedthrough housing further comprises lead terminal exit slot  123  and keying slots  124  which enable the lead terminal to be received in the feedthrough exterior cavity in a proper orientation and also prevent the lead terminal from being rotated when the connector is being clamped. A flange  125  enables the feedthrough housing to be hermetically attached to the device&#39;s case, preferably by laser welding. 
     Seal  111  has a substantially flat body with a central opening  127  which accommodates the central protrusion of the feedthrough housing. The seal further has an array of contact apertures  128  arranged in a pattern corresponding to that of the feedthrough contact assemblies. 
     The lead contact terminal has a washer shaped body  130  with a central through-hole  126  which accommodates the central protrusion of the feedthrough housing, a substantially flat bottom side  131  cooperating with the seal, and a top side  132  cooperating with the clamping cover. The terminal body contains an array of lead contacts  133  ( FIG. 3B ) which are connected to the respective conductors  134  (seen in  FIG. 5 ) of lead  104 , and are disposed in a pattern mapped directly to the corresponding array of compressible contact assemblies  118 . The lead terminal further comprises a radially extending strain relief  135  which connects the lead terminal to the main body of lead  104 . The lead terminal body has radial keying protrusions  136  which cooperate with the keying slots in the feedthrough housing wall. The terminal body fits closely in the feedthrough exterior cavity  119  and the radial slots in the feedthrough housing&#39;s side wall uniquely align the array of lead contacts to the corresponding array of feedthrough contact assemblies. 
     Cover  113  is essentially a screw with a head having an outline substantially matching the top outline of the feedthrough housing. The threaded stud  141  cooperates with the threaded hole in the central protrusion of the feedthrough housing. A hex hole  142  is provided for clamping the cover with a hex driver.  FIG. 4  shows a fully mated (pressurized) connector  103 . The cover is clamped to the feedthrough housing and maintains contact forces and seal compression. 
       FIG. 5  is a cross-sectional view of the mated connector showing the contact interface. Lead contacts  133  are connected to the respective conductors  134  of the lead, which in turn connect to the respective distal sensing/stimulation electrodes  106  ( FIG. 1 ). Contacts  144  are compressed and electrically connect lead contacts  133  to the corresponding feedthrough pins  117 . In a fully assembled device such as  101 , the feedthrough pins extend into the interior of case  105  and connect to the electronics (not shown) contained in the case. 
     Concurrent with contact pressurization, the seal is compressed between the lead terminal body and the dielectric substrate  116  (interfacial seal) and against side walls  120  of the feedthrough cavity and central protrusion  121  (peripheral seal). This seal system isolates the adjacent and non-common electrical connections from each other and from other conductive components, such as housing  115 , and protects the connector interface from ingression of body fluids, which also tend to be conductive. 
     The lead terminal body can be made from a substantially rigid polymer or high durometer elastomer. The lead contacts may be inserted into a pre-molded lead terminal body and sealed with potting  145  after the conductors are terminated to the respective lead contacts. Alternatively, the lead contacts with terminated conductors can be insert-molded in the lead terminal body. 
       FIG. 6  is a partial enlarged view of  FIG. 5 , showing the feedthrough contact assembly in a greater detail. The contact assembly comprises feedthrough pin  117 , compressible contact  144 , and a tubular hat  146 . The feedthrough pin is sealed in the respective hole of the dielectric substrate by a braze joint  147 , and the dielectric substrate is sealed to the feedthrough housing by a braze joint  148 . Compressible coil spring contact  144  is protectively contained in hat  146  and the top of the hat is conductively attached to the outer end  149  of the feedthrough pin  117  by a weld  150 . The outer end of the coil spring has a centrally extending end portion or filar  151  which provides the contact tip. 
     The spring contact can be pre-assembled with the hat and added to the brazed feedthrough assembly as shown in  FIGS. 7-9 . The open or bottom side  152  of the hat can be crimped to retain the spring contact and/or the inner end of the spring can be joined to the open end of the hat by a weld  153  as seen in  FIG. 7 . The outer end of the feedthrough pin has a substantially arcuate profile with a centrally disposed slot  154  which accommodates and guides contact filar  151 . The hat has a cutout  155  cooperating with the profiled outer end of the feedthrough pin. When the spring-hat assembly is fully seated in the counterbore  156  of the dielectric substrate  116 , the top of the hat is co-planar with the outer end of the feedthrough pin and the complementary edges can be welded as shown in  FIG. 8B . The spring contact is thus fully contained and can be preloaded in order to provide a consistent contact force. Filar  151  is centered and guided all around by the resulting opening. 
       FIGS. 9A-B  show a variation of the design in  FIGS. 8A-B . A hat  161  has a guide hole  162  and a cutout  163 . The hat-contact assembly is placed over the outer end of the feedthrough pin so that cutout  163  is directly over the profiled top of the feedthrough pin, and the hat is welded to the top of the feedthrough pin at the cutout.  FIG. 9B  shows the hat attached to the feedthrough pin by a weld  164  and contact filar being guided by guide hole  163 . 
     FIGS.  10 - 12 —Connector for Annular Lead Terminal Having Integral Seal 
       FIGS. 10-12  show a connector embodiment  170  which is a variation of connector  103  adapted for a lead terminal with an integral seal. The connector has a low profile since the integral seal obviates the need for a discrete seal and the contact assembly resides substantially within the thickness of the dielectric substrate. 
       FIGS. 10-11  show connector  170  in an exploded and a fully assembled state respectively. The connector comprises a feedthrough assembly  171 , a lead contact terminal  172 , and a clamping cover  173 . The compressible contacts are integrated with the feedthrough pins to form contact assemblies  174 . The lead terminal comprises an elastomeric body  175  which provides an integral seal. The top of the terminal body may have a reinforcing lining  176  to add to the structural integrity of the terminal and to facilitate interaction with the clamping cover. 
       FIG. 12  is a cross-sectional view of the mated connector shown in  FIG. 11 , taken through the contacts. The cover is clamped to the feedthrough housing  177  and the lead terminal body is compressed between the cover and the dielectric substrate. Each lead contact  178  is mated to a corresponding compressible contact  179  via contact tip  180 . The compressible contact is contained in a tubular opening of the feedthrough pin  181  and thus can reside substantially within the thickness of the dielectric substrate in which the pin is hermetically sealed. Such contact assembly protects the compressible contact and results in a very thin (low profile) connector. The small radial dimensions of the compressible contacts enable closely spaced contacts. A large number of connections can thus be provided in a small connector volume. The exemplary connector shown in  FIG. 12  can be less than 5 mm thick and the contact spacing can be 1.5 mm. 
     Referring to the enlarged cross-sectional detail of the contact assembly in  FIG. 13 , the tubular feedthrough pin  181  has a collar  182  which seats on the bottom of a counterbore  183  on the exterior side of the dielectric substrate. Rigid contact tip  180  has a shoulder  184  which is preloaded against the compressible contact  179  and shank  185  which is held within the outermost coils of the compressible contact. The compressible contact and the rigid tip are retained by an insert  186  which is attached to the collar of the feedthrough pin by a weld  187 . Both collar  182  and retaining insert  186  reside within counterbore  183  so that only the rigid contact tip extends beyond the exterior side of the dielectric substrate. 
       FIG. 14  shows another embodiment of a compressible contact assembly. A compressible contact  190  is a miniature coil spring, and is protectively confined in the tubular opening of a feedthrough pin  181 . The coil spring contact has a variable pitch and a variable outside diameter. An outer end  191  of the coil spring is tightly wound and the outermost coils may be tapered to form a contact tip  192 . The tightly wound top coils can be further joined together (e.g. by welding) or reinforced by adding a rigid tip insert. An opposite or inner end  193  of the coil spring may have at least one coil with an outside diameter slightly larger than the inside diameter of the tubular section so that the coil spring can be pressed into the tubular opening of the feedthrough pin and retained therein by the radial interference. Alternatively, the inner end (near the bottom) of the tubular opening can have a necking or a slightly reduced diameter to provide an interference fit with the inner end of the contact spring. 
     FIGS.  15 - 17 —Connector for Annular Lead Terminal—Clamping Nut Cover 
     A connector embodiment described in this section is similar to connector  170 , except it has a threaded stud instead of a threaded hole in the central protrusion of the feedthrough housing. Accordingly, a screw cover is replaced by a clamping nut cover. The number of contacts is different for illustrative purposes but the contact system and the construction of the lead terminal can be essentially the same as in connector  170 , so these components have the same reference numerals as in connector  170 . 
       FIG. 15  is an exploded perspective views of connector  200 . The connector comprises a hermetic feedthrough assembly  201 , a lead contact terminal  172 , and a clamping cover  202 . The lead may have a stylet lumen  203 . The compressible contacts are integrated with the feedthrough pins to form contact assemblies  174 . 
     The feedthrough assembly comprises a housing  204 , dielectric substrate  116 , and feedthrough pins  181  (seen in  FIG. 17 ). The compressible contacts are integrated with the feedthrough pins to form contact assemblies  174 . The feedthrough housing further comprises a central protrusion  205 , with a threaded stud  206  which enables cover  203  to be clamped to the feedthrough housing. The feedthrough has an exterior cavity  119  ( FIG. 15 ) defined by the exterior side of the dielectric substrate  116 , and side wall  121  and the central protrusion  205  of housing  204 . The feedthrough exterior cavity accommodates the seal and the lead terminal which are than clamped with cover  203  to pressurize the connector. 
     Cover  203  is essentially a clamping nut with an outline substantially matching the top outline of the feedthrough housing. The threaded hole  207  cooperates with the threaded stud in the central protrusion of the feedthrough housing. Spanner holes  208  are provided for clamping the cover with a spanner wrench. 
       FIG. 17  is a cross-sectional view of the mated connector shown in  FIG. 16 , taken through the contacts. The cover is clamped to feedthrough housing  204  and the lead terminal is compressed between the cover and the dielectric substrate. The lead contacts  178  are mated to the corresponding compressible contacts  179  which are substantially confined in tubular feedthrough pins  181 . 
     FIGS.  18 - 21 —Connector with Cam-Driven Clamping Cover—Circular Terminal 
       FIGS. 18A-B  are exploded perspective views, top and bottom respectively, of connector  210 . The connector comprises a hermetic feedthrough assembly  211 , a lead contact terminal  212 , and a clamping cover  213 . 
     The feedthrough assembly comprises a housing  215 , a dielectric substrate  216 , and feedthrough pins  181  (seen protruding from the bottom or interior side of the feedthrough assembly in  FIG. 18B ). These components are assembled as shown and are hermetically joined together, typically by brazing. Subsequently, the compressible contacts are integrated with the feedthrough pins to form contact assemblies  174 . 
     The feedthrough has an exterior cavity  219  ( FIG. 18A ) defined by the exterior side of dielectric substrate  216 , and a side wall  220  of the feedthrough housing. The lead terminal and the clamping cover are accommodated in the feedthrough exterior cavity and their outlines match closely the outline of the feedthrough exterior cavity. The feedthrough housing side wall has terminal exit slot  123  and cutouts  221 , which enable the lead terminal and the cover assembly to be received in the feedthrough exterior cavity in a proper (unique) orientation. The feedthrough housing side wall further comprises an undercut  222  which is used to engage the clamping cover. A flange  125  enables the feedthrough housing to be hermetically attached to the device&#39;s case. 
     The lead terminal has a body  223  having a substantially flat bottom side  224  cooperating with the exterior side of the dielectric substrate, and a top side  225  cooperating with the clamping cover. The terminal body contains an array of lead contacts  178  which are connected to the respective conductors (not shown) of lead  104 , and are disposed in a pattern mapped directly to the corresponding array of compressible contact assemblies  174 . The terminal body fits closely in the feedthrough exterior cavity  219  wherein the strain relief  226  locates in the exit slot  123  and thus assures proper alignment of the lead contacts to the respective compressible contacts. Similarly, the clamping cover has an outline closely matching the feedthrough exterior cavity into which it is received. A fully assembled connector is shown in  FIG. 19 . 
     The clamping cover construction and operation will be described while referring to  FIGS. 20-21  for additional details. The clamping cover comprises a bottom plate  230 , a top plate  231 , and a cam  232 . The cam has a hub  233  and arms  234  extending radially from the hub. The arms have engagement tips  235 . The hub locates and rotates in a central hole  236  of the top plate. The bottom plate has spacers  237  which maintain the spacing between the top and bottom plates so that the cam can rotate freely. At the same time, the sides of the spacers provide positive stops for the rotating cam. The cam is captivated between the bottom plate and the top plate, which are joined together, e.g., by weld joints  238  at top outside edges of spacers  237 . Thus constrained cam is allowed only to rotate in hole  236 . The hub has a hex hole  239  which enables the cam to be rotated with a hex driver. 
     The top and bottom plates have radial protrusions  241  and  242  which accommodate engagement tips  235  when the cam is in a disengaged state. Protrusion  241  cooperates with the lead exit slot  123  while protrusions  242  cooperate with cutouts  221  in the feedthrough housing wall. Protrusion  241 ′ in the bottom plate also clamps the exit portion of the lead terminal body. 
       FIGS. 18A and 21A  show the clamping cover in a disengaged state. Cam  232  is rotated counterclockwise until the cam arms come to a positive stop against side surfaces  243  of spacers  237  and the engagement tips  235  are aligned with radial protrusions on the top and bottom plates. In the disengaged state, the cover can be received in the feedthrough exterior cavity without interference.  FIG. 21B  shows the clamping cover in a locked or engaged state. The cam is rotated clockwise to a positive stop against spacers  237 . Cam tips  235  protrude beyond the outline of the plates and thus can engage the undercut in the feedthrough housing. 
     After the cover is placed on top of the lead terminal in the feedthrough exterior cavity, the cover can be engaged by rotating the cam approximately 60 degrees in the clockwise direction, until the cam arms stop against side surfaces  244  of spacers  237 . Clockwise rotation of the cam to clamp the cover is consistent with tightening a screw and is therefore intuitive. The engagement tips may have tapers (as shown) on leading engagement edges to facilitate initial engagement of the tips with undercut  222  and to provide the mechanical advantage as the tips are being gradually engaged. 
       FIG. 19  shows a mated (pressurized) connector  210  with clamping cover  213  engaged to feedthrough housing  215 . Marking  245  on the cam and  246  on the top plate can be used to indicate the cover engagement status. When cam mark  245  is aligned with stationary mark  246  on the top plate, the cover is engaged and the connector contact and seal interfaces are pressurized. 
     FIGS.  22 - 23 —Connector with Cam-Driven Clamping Cover—Triangular Terminal 
       FIG. 22  is an exploded perspective view of a connector  250 . The connector comprises a hermetic feedthrough assembly  251 , a discrete seal  252 , a lead contact terminal  253 , and a clamping cover  254 . The feedthrough assembly comprises a housing  255 , a dielectric substrate  256 , and has contact assemblies  118  discussed in conjunction with connector  103 . 
     The functional components of connector  250  are similar to those discussed above. In order to demonstrate adaptability of these components to a variety of connector embodiments, the feedthrough exterior cavity  257  and the cooperating components have triangular outline and the lead terminal is shown having a printed circuit type configuration. The cover assembly is a variation of cover assembly  213 , with top plate  258  and bottom plate  259  adapted to have a triangular shape. Three contacts are shown but other advantageous contact counts can be used, e.g., nine contacts with 3 contacts adjoining each side. 
     The lead terminal has contact pads  260  which are termini of corresponding conductors  261 . If desired, the top side  262  of the lead terminal can be pre-attached to the bottom plate  259  of the clamping cover. 
     FIGS.  24 - 28 —Edge-Mounted Connector for Iso-Diametric Lead 
     This section discloses a connector for iso-diametric lead contact terminals which are typically found in iso-diametric leads. This type of lead is common, especially when the lead is implanted with a cannula and the entire lead must be passable through the cannula. 
       FIG. 24  is an exploded perspective view of connector  270 , which comprises a hermetic feedthrough assembly  271 , iso-diametric lead terminals  272 , a seal  273 , and a clamping cover  274 . The feedthrough assembly comprises a housing  275 , a dielectric substrate  276 , and contact assemblies  277 . The feedthrough has an exterior cavity  278 , bound by the exterior surface of the dielectric substrate  276  and side walls  279  of the feedthrough housing. The side walls have undercuts  280  for engaging the clamping cover. 
     The lead terminal is iso-diametric and has ring contacts  281  which are connected to respective conductors (not shown) of the lead  104 . 
     The seal has an outline closely matching the outline of the feedthrough exterior cavity, a bottom side  282  cooperating with the exterior side of the dielectric substrate, and a top side  283  cooperating with the clamping cover. The seal further has lead-receiving lumens  284  and apertures  285 , the apertures open to the bottom side of the seal and communicating with the lumens. The seal further has a strain relief portion  286 , which cooperates with the lead exit slot  287  in the feedthrough housing side wall. In the embodiment shown, the seal has two lumens side-by-side, so that two leads are accommodated in a single seal. Each lead terminal  272  is received into respective lumen  284 , preferably with a slight interference. A slight interference enhances handling of lead seal assembly and initiates inter-contact seal. When the terminals are fully inserted into the lumens the lead contacts are aligned with seal apertures on the bottom side of the seal, as seen on the inverted (bottom-up) view of  FIG. 25 . This allows a visual verification of contact alignment in the seal prior to connector pressurization. 
     The dual lead-seal assembly is accommodated in a single feedthrough cavity  278 , preferably with a slight interference. When the lead seal is thus inserted into the feedthrough exterior cavity, the lead contacts are aligned with respective compressible contact assemblies  277  and can be accessed by the compressible contacts via the seal apertures. 
     Similar to the previously discussed embodiments, the clamping cover comprises a bottom plate  290 , top plate  291 , and cams  292 . Each cam is rotatably captivated between the bottom and top plates with spacers  293  maintaining the separation between the bottom and top plates so that the cam can rotate freely. The top and bottom plates are joined together, e.g., at the spacers, by welds  238 . The cam has a hex hole  239  which enables the cam to be rotated with a hex driver. Each cam has two arms with engagement tips  294 . The sides of the spacers limit cam rotation to a useful range and provide positive stops when the cam is rotated to a fully engaged or fully disengaged position. The clamping cover further has a tab  295  which cooperates with the lead exit slot of the feedthrough housing and clamps the strain relief portion of the seal. 
     When the lead-seal assembly and the clamping cover are received in the feedthrough exterior cavity, cam engagement tips  294  align with the corresponding undercuts  280  on the feedthrough housing side walls. As the cam is rotated clockwise approximately 45 degrees from the open or disengaged position shown in  FIG. 24 , tips  294  engage undercuts  280  as shown in the cross-sectional view of  FIG. 27 . The leading engagement edges of tips  294  can be tapered (e.g., with a chamfer, a radius, or a combination thereof) to facilitate the initial engagement and to provide the mechanical advantage as the cams are being gradually engaged. Similarly, the initial engagement side of undercut  280  can be slightly wider than the rest of the undercut to facilitate the entry of the tip into the undercut. Marking  246  on the top plate of the clamping cover can be used as a stationary reference for the rotating cam. When cam mark  245  is aligned with stationary mark  246 , the cover is engaged and the connector and seals are pressurized. 
       FIG. 26  shows an exemplary device with connector  270  attached to a case  296  along a weld  297 . The connector is in mated (pressurized) state; the clamping cover is engaged to the feedthrough housing. Cam mark  245  is aligned with the stationary mark  246  on the top plate of the cover, indicating that the cover is engaged. 
       FIG. 27  is a cross-sectional view of a mated connector  270  taken through the contacts. The compressible contact assembly comprises a tubular feedthrough pin  300  and a compressible contact  301 . The compressible contact is a coil spring with a tapered outer end that forms a contact tip  302  and a central extension on the inner end that forms a contact tail  303 . The tubular feedthrough pin has a stepped diameter with the larger diameter outer portion  305  adapted to protectively confine the compressible contact and the smaller diameter inner portion  306  adapted to retentively accommodate end conductively interface contact tail  303 . Contact tail  303  has a wavy shape to facilitate an interference fit but also may alternatively retained in opening  306  by other means such as a conductive adhesive or by crimping the inner end of the tubular pin on the interior side of the dielectric substrate. Top side  283  of the seal and the bottom side of plate  290  are complementarily profiled to optimally direct seal pressure. If desired the seal may be pre-attached to the clamping cover. 
       FIG. 28  is a longitudinal cross-sectional view of a mated connector  270 , taken through the center of the lead and the contacts. The compressed seal  273  electrically isolates the adjacent connections along the lead terminal. 
     FIGS.  29 - 32 —Side-Mounted Connector for Iso-Diametric Leads 
     In some cases, e.g., when the device is implanted in a cranial cavity, it is desirable that the connector is disposed on the side (rather than on the edge) of the device. It may also be desirable that the connector does not add significantly to the device thickness, i.e. the top of the connector is substantially co-planar with the outer surface of the device. A connector embodiment  310  discussed in this section is a variation of connector  270  disclosed in the preceding section adapted for co-planar attachment on the device&#39;s side. The components which are shared without significant change are denoted by the same reference numerals as in connector  270  and their description can be found in the preceding section. 
     The exploded view of  FIG. 29  shows major functional components of connector  310 . The connector comprises a hermetic feedthrough assembly  311 , iso-diametric lead terminals  272  (shown inserted into the seal), a seal  312 , a clamping cover  313 , and a boot  314 . The feedthrough assembly comprises a housing  315 , a dielectric substrate  276 , and contact assemblies  277 . The feedthrough has an exterior cavity  316 , bound by the exterior surface of the dielectric substrate  276  and the adjoining side walls  279  of the feedthrough housing. The side walls have undercuts  280  for engaging the clamping cover. The housing comprises a mounting flange  317  on top of the housing that enables co-planar attachment of the feedthrough assembly to the device&#39;s case. The feedthrough exterior cavity has a ramp  318  which enables the lead to exit the feedthrough exterior cavity so that it is co-planar with the device&#39;s side. 
     The seal has an integral lead support  319  cooperating with the ramp and having grooves or channels for the leads (seen occupied by the leads in  FIG. 29 ). Lead support  319  is molded as shown and can be deflected out of the way when leads are being inserted into the respective lumens of the seal. Once the leads are fully inserted, the lead support is allowed to return to as-molded state and thus applies slight lateral pressure to the lead. The slight lateral tension helps to maintain the lead in a fully inserted position during connector assembly. 
     The clamping cover comprises a bottom plate  320 , a top plate  321 , and cams  292 , assembled as described above. The bottom plate has an extension  322  which facilitates attachment of boot  314 . The boot can be pre-attached to the bottom plate or, alternatively, can be a discrete component installed after the connector is pressurized. When installed over the lead exit from the seal, the boot provides a strain relief and protection for the exiting leads, and forms a smooth outside profile. 
       FIG. 30  is a perspective view of an exemplary device having connector  310  attached to the device&#39;s case  324 . The connector is attached to the case along flange  317  by a weld  325 . The top of the connector is substantially co-planar with the outside surface of the case and the leads exit from the feedthrough exterior cavity tangentially to the device&#39;s side. If the device is implanted in a cranial cavity, lead support  319  may extend beyond the device outline to provide protection as it passes over the cranial cavity outline. 
       FIG. 31  is a transverse cross-sectional view of a mated connector  310  taken through the contacts. The interface between the seal and the clamping cover is shown flat but can instead be complementarily profiled as shown in  FIG. 27 . 
       FIG. 32  is a longitudinal cross-sectional view of a mated connector  310 , taken through the lead and the contacts. 
       FIGS. 33-35  Edge-Mounted Connector for Paddle-Shaped Contact Terminal 
     Connector  270 ′ described in this section is an adaptation of connector  270  for use with leads having a rectangular paddle-shaped contact terminal. A paddle-shaped lead contact terminal replaces the lead-seal assembly of connector  270  while the feedthrough assembly and the clamping cover are essentially unchanged. 
     The exploded view of  FIG. 33  shows the major functional components of connector  270 ′; feedthrough assembly  271 , lead contact terminal  326 , and clamping cover  274 . The feedthrough assembly and the clamping cover have been described in detail in connection with connector  270 . 
     The lead contact terminal  326  has an elastomeric body  327  which contains lead contacts  178  and provides an integral sealing means. The contact terminal body further has a substantially flat bottom  328  (as seen on inverted view of  FIG. 34 ) and a strain relief  329 . The lead contacts are exposed from the bottom of the lead terminal body ( FIG. 34 ) and are disposed in a pattern mapped directly to the plurality of the feedthrough contact assemblies  277 . The contacts are shown recessed from the bottom of the lead terminal to allow unimpeded compression of the integral seal. 
       FIG. 35  shows an exemplary device with connector  270 ′ attached to a device&#39;s case  296  along weld  297 . The connector is in a mated (pressurized) state; the clamping cover is engaged to the feedthrough housing. Cam mark  245  is aligned with the stationary mark  246  on the top plate of the cover, indicating that the cover is engaged. Tab  295  cooperates with the lead exit slot of the feedthrough housing and clamps the strain relief portion of the seal at lead exit slot  287 . 
     While connector  270 ′ is depicted connecting a single lead terminal with an integral seal and having a specific contact assembly, numerous variations are possible. For example, the connector could have a discrete seal and a different contact assembly. The connector could be adapted to connect multiple leads, e.g., two leads exiting the connector in the opposite directions and clamped with a single cover having tab  295  on each end. The number of contacts is easily scalable. For longer connectors, the cover can have more than two cams. 
       FIGS. 36-39  Coil Spring Contacts with Tail Retained in Tubular Feedthrough Pin 
     This section discloses additional contact embodiments which can be used interchangeably with contact assemblies  118  and  277  above. 
       FIG. 36  shows a contact assembly comprising a compressible contact  330 , a tubular hat  331  and a tubular feedthrough pin  332 . The compressible contact is a coil spring having a central filar  151  on the outer end, and contact tail  303  on the inner end. The filar forms a contact tip while the contact tail allows the contact to be retentively accommodated in the tubular opening of the feedthrough pin. The hat protectively confines the compressible contact and has a central opening  333  on the exterior side to allow the contact tip to protrude from the hat. 
     The exploded view of  FIG. 37  shows the components more clearly and illustrates a sequence of assembly. The dielectric substrate has a counterbore  156  on the exterior side  334 . The feedthrough pin is hermetically sealed in a through-hole of the dielectric substrate  276  by braze  147 . The feedthrough pin has a tubular opening  335  open to the exterior side of the dielectric substrate and a flange  337  which rests on the bottom of the counterbore. 
     Before installation in the feedthrough pin, the compressible contact is pre-assembled in the hat as shown in  FIG. 34 . A rim  338  on the interior (bottom) side of the hat can be crimped (formed inwardly) to securely retain and preload the coil spring contact. When the contact is thus preloaded, the outermost coil  339  is preloaded (pressed) against the corresponding internal surface of the hat, and a closely controlled length of the contact tip protrudes from the hat. 
     The pre-assembled compressible contact and the hat can be integrated with the feedthrough pin by pressing contact tail  303  into the tubular opening of the pin until the bottom side rim of the hat rests on the bottom of the counterbore. The outside diameter of the hat is closely matched to the diameter of the counterbore to precisely position the contact. The depth of the counterbore can be selected based on the desired contact height above the dielectric substrate. The contact tail may have a wavy form adapted for a resilient interference fit in the tubular opening of the feedthrough pin so that, upon insertion into the tubular opening, the contact is retentively engaged and electrically connected to the feedthrough pin. Alternatively, or in addition, a conductive adhesive or crimping of the inner end of the feedthrough pin can be used to retain and electrically interface the compressible contact. 
     In the contact assembly variation of  FIG. 38  a compressible contact  340  is used with a rigid contact tip  341 . The contact tip has a shoulder  342 , which is in contact with the outermost coil of the compressible contact and is pressed (preloaded) against the corresponding surface of the hat, so that a closely controlled length of the contact tip protrudes from hole  333  on the exterior side of the hat. 
       FIGS. 39-42  Additional Coil Spring Contacts with Tail Retained in Tubular Feedthrough Pin 
     The coil spring contacts disclosed in  FIGS. 39-42  have a contact tail which is retentively installed in a tubular opening of the feedthrough pin as discussed above, but rather than having a hat, the contacts are protectively confined in a counterbore of the dielectric substrate and/or in the aperture of the seal. The compressible contact is inserted into the tubular opening of the feedthrough pin until the innermost coil rests on flange  337  of the feedthrough pin. This assures a positive support and redundant electrical connection when the contact is compressed. 
       FIGS. 39-40  show coil spring contacts protectively confined within counterbore  156  on the exterior side of dielectric substrate  276 . Coil spring contact  330  ( FIG. 40 ) has central filar  151  on the outer end forming an integral contact tip, while contact  301  ( FIG. 41 ) has integral contact tip  302  formed by the tapered outer end with tightly wound outer coils. In  FIG. 42 , a dielectric substrate  116  has a shallower counterbore  156  and the outer portion of the compressible contact is protectively confined in aperture  128  of seal  111 . 
       FIGS. 43-45  Coil Spring Contacts Protected by Outer End of Feedthrough Pin 
       FIGS. 43-45  show a coil spring contact assembly wherein a coil spring contact  350  is installed directly over the outer end  351  of a feedthrough pin  352 . The inner end  353  of the coil spring (better seen on the inverted view of the spring in  FIG. 44 ) is formed toward the spring central axis so that it can snap into the undercut  354  of the feedthrough pin, thus retaining the spring. Counterbore  156  is sized to closely confine the spring contact. When the spring is compressed, the inner end of the coil spring makes direct pressure connection to a shoulder  355  of the feedthrough pin. A radial excursion of the contact tip is limited by the coil spring being guided on the outer end of the feedthrough pin and contact tip or filar  151  being guided in slot  154 . 
       FIGS. 46-47  Additional Contact Assembly Embodiments with Rigid Contact Tip 
       FIGS. 46-47  show additional embodiments of compressible contact assemblies which can be used interchangeably with those already disclosed. These embodiments provide a robust rigid contact tip and contact preload. The rigid tip can be flat, rounded, or tapered, and may have one or more surface cuts, such as a V-shaped slot, to provide pointed contact features. for a low resistance connection with a lead contact. Such features help in self-cleaning of the contact during mating and thus help to assure a low contact interface resistance at moderate contact loads. 
     In  FIG. 46 , a contact assembly comprises a feedthrough pin  370 , a compressible contact  371 , a rigid contact tip  372 , and a washer-like retaining insert  373 . The compressible contact can be a coil spring or a conductive compressible button such as a fuzz button. The compressible contact and the rigid contact tip are retained in the tubular opening of the feedthrough pin by insert  373 , attached to the top of the feedthrough pin collar  374 , preferably by a weld  375 . The compressible contact can be preloaded (pre-compressed) by the retaining insert to provide a desirable contact characteristics (consistent contact tip extension and lower contact force variation). 
     In  FIG. 47 , a tubular feedthrough pin  380  confines coil spring contact  179  and a rigid contact tip  381 . The shank (necked portion)  382  of the contact tip is accommodated in the outer end coils  383  of the spring. The outer end  384  of the tubular pin is crimped (rolled inwardly) to retain the compressible contact and the rigid tip. The free-state height of spring  179  may be greater than the depth of the tubular opening in pin  380  so that the spring is preloaded when it is assembled as shown. A circumferential form  385  provides a positive stop for seating the pin in a bore of the dielectric substrate. 
       FIGS. 48-49  Additional Contact Assembly Embodiments with Snap-In Contact Retention 
       FIGS. 48-49  show additional embodiments of compressible contact assemblies wherein the compressible contact is attached to the feedthrough pin by a snap-in retention mechanism. 
     In  FIG. 48  a coil spring contact  390  is installed directly over the profiled head  391  of a feedthrough pin  392 . The inner end  353  of the coil spring is formed toward the spring central axis (as seen on the inverted view of the spring in  FIG. 44 ) so that it can snap into the undercut  354  of the feedthrough pin, thus retaining the spring. Counterbore  156  is sized to closely confine the spring contact. 
     In  FIG. 49  a coil spring contact  400  is installed in a tubular section  401  of the feedthrough pin  402 . The inner end  403  of the coil spring is formed outwardly, away from the spring&#39;s central axis, so that it can snap into the slit  404  at the bottom of the tubular section of the feedthrough pin, thus retaining the spring. 
     The connectors disclosed in the specification use common building blocks such as feedthrough assemblies, compressible contacts, sealing means, and clamping means, and demonstrate how these features can be used interchangeably in various connector embodiments. 
     Materials and Fabrication 
     All materials referenced in connection with implantable connectors and leads are biocompatible and accepted for implantation in the human brain or other living tissue. The term “biocompatible” or “implantable grade” is therefore implicit when these materials are listed. 
     Feedthrough housing, dielectric substrate, and feedthrough pins are assembled together and joined by brazing, before the compressible contacts are added. Currently preferred but non-limiting examples of materials include Ti and Ti alloys for the housing, highly purified aluminum oxide (pure alumina ceramic) for the dielectric substrate, platinum and platinum-iridium alloys for the feedthrough pins, and pure gold for brazing. 
     The tubular feedthrough pins can be economically fabricated by deep drawing but can also be adapted for machining. Alternatively, the feedthrough pins can be made out of tubing with one end hermetically sealed by crimping and/or welding. 
     The miniature coil springs and fuzz buttons can be made from a high strength biocompatible alloy, such as 80Pt-20Ir platinum-iridium alloy, which can be drawn into a high strength fine wire with a good formability. The miniature coil springs having outside diameter 0.5 mm and less can be made using known equipment and manufacturing techniques employed in fabrication of miniature coil springs for pogo pins used in electrical test sockets. 
     Clamping components can be stamped or machined from titanium, a titanium alloy, or stainless steel. Cams and fasteners can be made from a high strength alloy, such as titanium alloy 6Al-4V. Larger clamping covers such can also be made from a hard polymer such as polyetheretherketone PEEK, preferably reinforced (e.g. filled with carbon fibers to increase strength and stiffness). Implantable-grade PEEK, also known as PEEK-OPTIMA is available from Invibio, Inc. Ceramic materials such as pure alumina or toughened alumina are also suitable cover materials. 
     The mating surfaces may incorporate a low-friction polymeric lining or a coating, such as a poly-para-xylylene (sold under the trademark Parylene by Specialty Coating Systems, Indianapolis, Ind.), to reduce sliding friction between the two components. 
     The sealing means and lead insulation may be a silicone rubber, a polyurethane, a silicone-urethane copolymer or the like. The material of the integral sealing means can be the same as the material of the lead body. 
     Rigid portions of the lead contact terminal can be made from high durometer elastomers or from rigid polymers. The insulation can be added by overmolding or, if a thermoplastic such as polyurethane is used, can be added in discrete form and heat-formed or heat-sealed in place. 
     Advantages 
     From the description above, a number of advantages of various embodiments of the disclosed connector become evident: 
     (A) A feedthrough-based connector is easier to manufacture than a molded header connector since it does not require fan-out wiring from feedthrough pins to the connector contacts. In contrast to the molded header, which requires sealing of the fan-out connections and forming a lead receiving cavity using molding processes, the feedthrough-based connector requires only addition of compressible contacts, to a pre-fabricated, pre-tested feedthrough. 
     (B) Smaller radial contact dimensions (i.e., dimensions normal to the contact longitudinal axis) are possible as the contact spring length is increased. The compressible contact can be coaxially confined in a tubular section of the feedthrough pin so that even substantial contact length does not significantly impact connector overall height. 
     (C) The small radial dimensions of the compressible contacts and the low profile above the dielectric substrate enable low profile connectors with closely spaced contacts. A large number of connections can thus be provided in a small connector volume. 
     (D) A small connector size is achieved without compromising compressible contact performance. The high-aspect-ratio compressible contacts have a high compliance and high deflection capability at a moderate spring rate, which makes the contact forces less sensitive to the worst case assembly conditions and repeated mating. 
     (E) The compressible contacts are protected from inadvertent handling damage by being confined in a tubular body of the feedthrough pin or in a protective structure attached to the feedthrough pin. A hard contact tip can be added on top of the compressible contact to enhance contact point robustness and the compressible contact can be preloaded to provide a consistent contact force. 
     (G) Numerous small-sized clamping options are enabled when the metal feedthrough housing is used as the sustaining structure for connector pressurization. Cam-driven clamping means have small size and provide indexed cam rotation, quick connect/disconnect, and easy one-piece handling. 
     Ramifications and Scope 
     While the connector has been described by means of specific embodiments, numerous modifications and variations known to those skilled in the art or disclosed may be employed without departing from the scope of the invention set forth in the claims. The materials, dimensions, shapes, and sizes of all parts may be adapted to a particular need. The number of contacts in particular can vary greatly (up to 24 or more) thus significantly affecting envelope dimensions of a connector assembly. The feedthrough housing may be of two-piece construction, the two pieces joined by welding or another method. The feedthrough hermeticity can be achieved with glass-to-metal seals (as opposed to metal-to-ceramic seals or brazing). The exterior side of the feedthrough housing can be made of a polymer, added after feedthrough brazing or glass-to-metal sealing operation. Additional seal components may be added if desirable. The dielectric substrate can be a multi-layer substrate or have a two-piece construction wherein the inner piece provides a hermetic seal and the outer seal provides structural support and accommodates the compressible contacts. Additional components, such as a filter capacitor or a printed circuit board can be added to the interior side of the dielectric substrate. The compressible contacts may be installed directly into metalized holes in a dielectric substrate. 
     As to every element, it may be replaced by one of multiple equivalent alternatives, only some of which are disclosed in the specification. Thus the scope of the invention should be determined, not by the examples or specifics given, but by the appended claims and their legal equivalents.