GB2166606A - Cochlear prosthetic package with connector - Google Patents

Abstract

A cochlear prosthetic package has a cup-shaped titanium case 10 with a ceramic plate 32; a plurality of hermetically-sealed feedthroughs 34 are formed in the plate 32 by sintering the plate with hollow metallic tubes located in plate holes and then sealing at least one end of each tube. An electrode cable connector 36 is provided which allows removal and replacement of a case even in the presence of body fluids. The connector comprises a rigid cap 18; a plurality of contacts disposed in holes in a resilient pad 36 and arranged to cooperate with the respective feedthroughs 34, each contact being connected to a wire 26 of cable 16; and a retaining device 20, 42 which clamp the cap 18 to the ceramic plate 32, the resilient pad distributing the force evenly to keep all the contacts in engagement with the feedthroughs. <IMAGE>

Description

POOR QUALITY 1

SPECIFICATION

Cochlear prosthetic package and method of making 65 same This invention relates to implantable medical elec tronic devices such as pacemakers and coch I ear prostheses, and more particu I a rly to a coch I ear prosthesis which must be hermetically sealed and have a telemetry capability.

Imp;antable medical prostheses of many different types are now in common use throu g hout the,,,,jorld.

These devices, such as pacemakers and bone g rol,,,-,h stimulators, not only provide electrical stimu I ation but also often interact in two-way telemetry systems.

Operation of a prosthesis can be controlled by an externally transmitted signal, and the prosthesis itself can generate and transmitto the outside world a signal indicative of its operation or patient condition.

There is a great degree of cross-fertilization in the sense thattechniques developed for one particular type of prosthesis are often eventually used in connection with others. A good example of this are the 85 techniques of hermetic sealing, originally developed for pacemakers but now used for medical prosthesis in general.

Depending on the particular prosthesis device which is involved, the solution of one problem may be morevexing than the solutions of others. But there is one type of device, a cochlear prosthesis, for which a confluence of design criteria (some of which are competing) has severely limited progress.

In its usualform, a cochlear prosthesis "system" consists of two parts.Thefirst is an "electronics" packagewhich is implanted in the mastoid bone behindthe ear; a connector assembly, having perhaps 22 individual electrodes extended to a cochlea, is removably attached to the package.The second part of the system consists of an external transmitter/ receiver. The external unit not only functions in a telemetry capacity, but also serves to transfer power to the implanted unit.

The cochlear prosthetic package must be con structed in such a waythat only bio-compatible materials are in contact with body tissues, a design criterion common to implantable prosthetic devices in general. Similarly, the entire package should be hermetically sealed to prevent the ingress of body fluids which could have a damaging effect on the electronic circuits in the package, and to prevent potentially harmful substances which may be inside the package from contacting bodyfluids. long life is assured by hermetic sealing, and it is known that a pacemakerJor example, can operate for many years before a replacement is necessary, e.g., because of battery depletion.

The problem with a cochlear prosthesis is that entire replacement of the device is probably notfeasible.

The electrode assembly, once it has been in place in a cochlea for several years, probably cannot be ex planted without damaging the cochlea itself. Thus the electrode assembly itself must have a long life, e.g., GB 2 166 606 A 1 fif',yyears.The package containing the electronic circuits can be designed for long life, e.g., as in pacemaker technology. However, in the unlikely event ol a failure, it is more likely to be in the electronics package than the electrode assembly. In addition, projected advances in technologywill make it desirable to be able to replace the electronics packagewith a more sophisticated unit.Thus it is necessary to be able to disconnect the electronics package from the electrode assembly to enable replacementwith another package, and a connector arrangement is required. Permanent, hermetic connections (such as conventionally used in pacemaker) are unsuitable because disconnection and re-connection are not possible.

The connector problem is much more severe in the case of a cochlear prosthesis than it is in the case of a pacemaker. A typical pacemaker requires at mostfour electrodes to be connected to the internal electronics via hermetically sealed electrical feedthroughs.The pacemaker feedth roughs are much more widely separated than are those of a cochlear prosthesis primarily because of the large number of feedthroughs in the latter, typically 10-22 in number. Each of the many connections between the hermeticallysealed electronics package and an individual electrode in the electrode assembly must have low electrical resistance. Conversely, it has been found important ' thatthe resistances between contacts be maintained as high as possiblefor long-term proper operation of the device. What further complicates matters isthatnot only must the connector becapable of attaching the electrode assemblyto the electronics package several times without degrading theperformance, buteach re-assembly musttake placein an environment where fluid ingress cannot be prevented; since the elecrode assemblyis permanently implanted, every attachmentof a new packagetothe electrode musttake placein the patient's head.

Rwill be apparent to those skilled inthe artthatthis type of -connectorproblem is notlimitedto implantable medical prostheses. There ire manyfieldsof electronics where itis necessaryto make a similar high quality but difficult connection,such as in high pressure, high temperature, marine orchemically reactive environments. As will become apparent below,the connector aspects of the presentinvention are equally applicableto such other electronic systems, as is the technique for making feedthroughs which will now be described.

The second major problem in the design and construction of a cochlear prosthetic package relates to the feedthroughs.The most pertinent prior art in this regard consists of techniques for making feedthroughs in pacemakers. A pacemaker is typically contained in a biocompatible titanium case. In order to connect the electronics inside the package to the electrodes, it is necessary to extend through the case up to four conducting pins.This is usually accomplished by providing ceramic feedthroughs. Foreach pin, a holeis provided in thetitanium case and a ceramic bushing is placed inthe hole. A conducting The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

2 POOR QUALITY pin is extended through a hole in the ceramic bushing to connect an external electrode to the electronic circuit.' nside the case. An hermetic seal is established by utilizing brazing techniques -both at the case/ ceramic interface and the ceramiclpin interface. The ceramic bushings are not only bio-compatible, but they also serve as insulators.

For a pacemaker, it is anticipateed that more and more feedthroughs will be required as the years go by.

Whilst most priorart pacemakers utilize only one or two feedthroijghs, with the advent of dual chamber pacemakers itis apparent that four feedth roughs are desirable. Furthermore, as miniaturization technique improve, it is expected that pacemakerswM include many more sensing functions than they now have, and this will in turn require additional feedthroughs for connecting the electronic circultsto sensorleads.

Butit is presently in the case of a cochlear prosthesis thatthe problems in fabricating the feedthroughs are mostsevere. In the illustrative embodiment of the invention, 22feedthroughs are required. ltis extreme ly time-consuming and costlyto provide such feed throughs using prior arttechniques. If prior art techniques are used, not only must22 individual feedthroughs be assembled, but a brazing operation at22 sites is required-all in a very confined space.

Because of the large numberof hermetic brazes required to be performeed atonce, 1 have discovered thatthe brazing technique results in lowyields, leading to prohibitive manufacturing costs. Itis clear that if the costs of making cochlear prostheses (and future pacemakers) are notto get out of hand, a different approach must be taken for implementing feedthroughs.

Still anothergeneral problem relates to packaging 100 of telemetry systems. The present invention does not concern itself with the electronic aspects of an implantable medical prosthesis, but ratherwith pack aging of the telemetrycoil. (Telemetry systems which are particularly advantageous for use in an implant- 105 able cochlear prosthesis are disclo - sed in British Patent Applications Nos. 8218658 and 8226438 entitled respectively "Implantable Tissue-Stimulating Prosth esis- and---On-Chip CMOS Bridge CircuiV). The package must be designed in such away that efficient 110 transfer of power and information between the external and internal coils is possible. The sing] e coil in the implanted package maybe used for either transmitting or receiving of information, or both, as well as for receiving powerfrom the external part of the system.

There are two standard prior art coil packaging designs. The first is to include one or more coils inside the same packagewhich contains the electronic circuits.This approach requires the package to be made of a non- conducting material (i.e., not metal) to allow the efficierittransfer of power and data at useful frequencies. Achieving an hermetic seal in such a case is difficult. Even if the package is non-metallic, but W uses a metallic band to provide the hermetic sealing (e.g., involving conventional brazing materials such as are used in the Gemiconductor industry to provide hermetic sealing of integrated circuit packages), the seal itself will act as a short-circuited turn of wire and will degrade the efficiency of power and information 130 GB 2 166 606 A 2 transfer. (Conventional brazing materials for joining metallic to ceramic components, e.g., in the semiconductor industry, are often gold based, or use some other metal, and have unproven bio-compatibility.

Brazing materials such as commonly used in pacemakers forjoining ceramic to titanium are acceptable.) The use of a metallic lid, even if it is on the side of the package facing away from the incoming radiation, also has a degrading effect on the transmission.

efficiency. An even greater shortcoming of the coil inside-the-package approach is thatan obvious con straint is placed on the size of the coil; in ge ' neral, larger coilswill allow more efficient power and information transfer, but the package size is limited by implant requirements.

The second prior art approach involves using an external coil which is connected to the electronic circuits inside the hermetical ly-sealed package via a pair of feedthroughs. There are two problemswith this approach.The first is that it is not possible to hermetically isolate thewirefrom the surrounding body fluids. While epoxy or Silastic material may be placed around the coil, such coatings do not provide an hermetic seal and the ingress of bodyfluids can give rise to short useful life. The second problem relatesto the large voltages which may be generated. Typically, potential differences in the order of a volt may be induced across the two ends of each individual turn in the coil. If there are 15 turns, as there are in the illustrative embodimentof the invention, a large voltage signal may be induced across the two ends of the coil as a result of the incoming signal from the outside world. Such a large potential across the feedthrough pins may lead to corrosion, and may be biologically harmful.

It is a general object of this invention to provide a package for a cochlear prosthesis or other implantable medical electronic device which overcomesthe aforesaid problems.

Briefly, in accordancewith the principles of the invention,the feedthroughs are made using an approach which is totally different from those of the prior art. A plate or carrier of unfired or "green" ceramic is formed with 22 small holes arranged around a larger central hole. Twenty two platinum tubes are placed in the smaller holes. Each tube has an outside diameter approximately the same as the respective hole so that a snug fit is obtained. The length of the tube is about twice the thickness of the ceramic plate. 1 have discovered that a wall thickness of about one tenth the outside diameter of the patinum tube gives good results. The platinum is 99.9% pure, or better. The tubes are placed on a flat, high alumina ceramic sheet so that one end of the tubes is flush with one surface of the green ceramic plate.

The assembly is then placed in a furnace and the green ceramic is sintered orfired in the usual way. As the cermaic sinters, it shrinks, typically in the order of 10-15% in all dimensions. The process of shrinking causes pressure to be exerted around the platinum tubes, such that a platinum-to-ceramic reaction bond is formed between thetube and the ceramic along the length of the tube in the ceramic, and around the entire circumference. The bond so formed results in 3 an hermetic seal between the platimu m and the ceramic.

The physical properties of the materials are impor tant. First, a ceramic should be used such that the firing temperature is about 0.9 times the melting point of platinum (i.e., about 1500 degrees C). Other metals and ceramics may be used, but thistemperature ratio is important. Second, the platinum is a ductile material, and furthermore the process of heating and slow cooling anneals the platinum. Thus, in the 75 cooling of the assembly, as the whole assembly shrinksfurther, the bond between the platinum and ceramic is not broken by-,.is platinum shrinking away from the ceramic as a result of different coefficients of thermal expansion, because the platinum is able to deform.Third, at the sintering temperature of the ceramic, the material becomes partly plastic, and does not crack around the platinum tubes.

This technique is quite differentfrom conventional platinum-to-ceramic reaction bonding techniques in several important ways. Conventional bonding is usually between flat pieces of ceramic and platinum foil or sheet. 1 have developed this technique for a circular bond. In addition, it is extremely difficult to make a large number of platinum-to-ceramic bonds simultaneously using the conventional technique of externally applied pressure. Particularly important in this invention is the fact that independent pressure is produced in each hole around each platinum part, and there is thus no theoretical limitto the numberof simultaneous bonds possible: also,the dimension may be extremely small orquite large with good results. The prior art technique is often used to join two pieces of ceramic together, and in orderto make a single sided bond, another refractory material is 100 required to applythe pressureto the platinum. This is often graphite, butthe use of graphite requires either a vacuum furnace oran inert atmosphere (e.g., argon) to preventthe graphitefrom burning atthe higher temperatures involved.

Following sintering, at least one end of the tube is closed off, e.g., by welding, to complete the hermetic seal. Alternatively, pre-formed platinum partswith an end or ends already closed off may be used. It is importantonly thatthe portion of the platinum part in the ceramic is not solid in cross section.

Despite the simplicity of the technique, it has been found that consistent perfect hermetic seals are achieved. (Thus far, the technique has been found to work only if feedthrough tubes, ortubular pre-formed parts, are used, rather than solid rods.) The net result is that a plurality of feedthroughs maybe formed with a minimum of effort since very little individual feedthrough processing is required. A completely hermetically sealed package may be obtained simply 120 by brazing the circumferential edge of the ceramic plateto an opening in an otherwise completely closed titanium case. Instead of requiring an individual braze on each feedthrough, all thatis required is a single brazing of the ceramic plate to the case. Closed feedthrough spacings can be achieved because the only "work" required on each feedthrough is the closing of at lest one end of the respective tube. Even this can be eliminated by the use of pre-formed parts.

There remains the problem of connecting the 130 GB 2 166 606 A 3 electrode assemblyto the casein a mannerwhich assuresthe electrical characteristics described above, aswell as allowing occasional replacement& the case. In the illustrative embodiment of the invention, it is only the end of each tube inside the case which is sealed. The open end of each of feedthrough, which extends away from the hermetically sealed case, is formed to have a concavity. The connector itself consists of a series of platinum wires (connected to the individual electrodes in the electrode assembly), each of which terminates at an end shaped to matewith a. respective formed feedthrough concavity. The wire conacts themselves are embedded in a Silastic sheet (type 4120). This sheet is backed by a titanium cover, with another Silastic sheet (also type 4210) being interposed between the cover and the Silastic sheet which contains the wire contacts. Asingle screw extends up from the ceramic plate. (The screw has a special configuration, as will be described below).

This screw passes through the two Silastic sheets and the titanium cover, and is secured by a nut. The force holding the connector together is provided by a single centrally-located screw, butthe force is distributed overthe connector surface bythe elastic properties of the Silasticsheets, especially the sheet dispposed against the cover. As will become apparent below, if the exposed surface of the cermaic plate is highly polished to a mirrorfinish, and the cover is held on with sufficient pressure, fluid is excluded in the connectorwhich could form a conducting path between contacts.

As forthe coil, the advantages of both the internal and external approaches are achieved, without the disadvantages of either.The coil is contained inside a metallic tube made of bio-compatible material. The preferred material is platinum, although titanium or stainless steel may be suitable.The tube is attached via a pair of insulating ceramic bushingswhich are brazed to the titanium package. (The tube ends are secured in the bushings, with an hermetic seal, in a manner comparable to the way the feedthroughs are made.) The metallictube is thus topological ly continuouswith the inside of the package. Because the ends of the tube are not electrically connected together (other than through the tube), the tube does not form a shorted turn which otherwise would make impossible the performance of the data and power link. There is no metal inside the coil, otherthan the tube which contains the coil, which would otherwise similarly degrade the data and power link efficiency. The coil size is not limited by the package, the tube can be bent to any desired shape, and a complete hermetic seal is achieved.

Further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description in conjunction with the drawing, in which:

FIG. 1 is a top view of the package of the illustrative embodiment of the invention (with the details of the electrode assembly being omitted since such assemblies a re well known in the art); FIG. 2 is a side view of the package of FIG. 1; FIG. 3 is an exploded perspective view showing the several component parts of the package of FIG. 1; FIG. 3A is a sectional view showing how ceramic 4 GB 2 168 606 A 4 plate 32 is secured to lid 44:

FIG. 4 is a detailed view showing the manner in which a connector contact is made with each of the feedthroughs; FIG. 5A is a detailed view illustrating the shape of the 70 screw which extends through the connector, and FIG.

513 is an alternative embodiment of the screw; and FIGS. 6A, 613 and 6C illustrate the mannerin which the feedthroughs are fabricated, with FIG. 6A depict ing the start of the feedthrough fabrication, and FIGS. 75 6B and 6C showing successive steps performed on an individual feedthrough in the overall method.

The package illustrated in FIGS. 1 and 2 includes a titanium case 10, and a titanium connector cover 18.

The cover is coupled to the case by a titanium screw 42 80 and a titanium nut20. Cable 16, extended to the electrode assembly (notshown), exits the cover 18 as shown. A pairof ceramic insulating bushings 14 are brazed to the titanium case, as shown at 14a, in a conventional manner.

Platinum tube 12 hastwo ends inserted into the holeswhich extend through the ceramic bushings, and the ends of thetube are hermetically sealed to the bushings aswill be described below. An important feature ofthe design isthatthetwo ends of thetube 90 are notelectricaliy connected so thatthe tube does not comprise a shorted turn which would otherwise absorb radiated power. In the illustrative embodiment of the invention, the coil (not shown) comprises 15 turns, each turn passing through the tube and the 95 inside of the case from one bushing to the other. The two ends of the 15-turn coil are connected to the' electronic circuits (not shown) inside the case.

An alternative embodimentwhich has been found to be useful is to use a single-turn coil which is coupled 100 into a small transformer wound on a ferrite toroid, where the numberof turns on the secondary maybe adjusted to give the required voltage, and maybe optimized for best transfer efficienty. In one embodi- ment, the single-turn coil can be a single turn of insulated copperwire contained within the platinum tube. Alternatively, multi-stranded platinum wire may be welded to the platinum tube coming through the ceramicfeedthroughs brazed into the titanium case.

Thatis, instead of the tube being continuous from one ceramic bushing to the other, only short pieces of tube are used, and solid or stranded wire is hermetically welded to the tubes to complete the coil.This technique has the advantages that the whole assem- bly is more robust, since the receiving coil is solid wire, and can be easily bent (as opposed to a tube which issubjeetto kinking and fracture on bending). In addition,there are some advantagesto be gained in the electrical performanc(i by using a single-turn receivercoil.

-As mentioned above,the details of the electronic circuits are not importantforan understanding of the present invention. The entire assembly may be encased in Silastic (not shown), to insure that no sharp edges are exposed, and to cushion and proteetthe package once it is implanted in the body.To remove the casefrom the connectorthe Silastic can be cut. When a newcase is then attached to the connector, the newcase can be encased in Silastic before reimplanta- around the overall initial implant and around a subsequent implant is that the coating is not continuous in the latterwhere the connector is secured to the case. This is of little moment because the Silastic coating does not function as an hermetic seal in the first place.

The overall assembly can be best appreciated by considering the exploded view of FIG. 3. A general description of the arrangement of parts will be described, followed by a more detailed consideration of the salientfeatures of the invention.

Titanium case 10 is cup-shaped and can be mad.e by machining a solid rod or by sheet metal forming. Two holes are drilled in the side of the cup forthe coil insulating ceramic bushings 14. A platinum (in the preferred embodiment) tube 12 is attached to the bushings such that an hermetic seal isformed. The bushings are attached to the cup by using conventional ceramic-to-titanium brazing techniques (see 14a in FIG. 2), techniques which are well known to manufacturers of pacemakers.

Ceramic plate 32 (illustratively circular) contains multiple conducting feedthroughs 34. The mannerof securing thefeedthroughs in the ceramieplate and achieving an hermetic seal, as well as the detailed shape of the feedthroughs, will be described below. Titanium screw42 is inserted through hole 32a of the ceramic plate, and the head of the screw is brazed to the underside of plate 32, around hole 32a, so that an hermetic seal is formed. Atthe time that the screw is attached to the ceramic plate containing the feedthroughs, the plate is brazed to titanium lid 44 around its circumference. as shown by the numeral 68 in FIG 8A. Itshould be observed thatscrew42 has a position which is generally central to the positions of the feedthroughs.

The electronic components arethen assembled on lid 44with electrical connections being made to all of the feedth roughs. The coil is wound within tube 12 as described above and the two ends are connected to the electronic circuits. Lid 44 isthen attached to the wall of cup 10 with a circumferential weld using conventional TIG titanium welding techniques.

The electronic circuits insidethe case may be mounted on aflexible printed circuit board which is soldered to the feedthroughs and the two ends of the coil. Alternatively, if the numberof electronic components is small,they may be assembled inside the case using point-to-point wiring. For example, an inte- grated circuit chip carrier may be attached by glue to the end of the titanium screw,with wires being run between thefeedthroughs and the connections on the chip carrier. Small components may be soldered in place onto the chip carrier, as may the end connections of the coil threaded through the tube.

The case thus completed is one part of the cochlear prosthesis package, the internal replaceable part. it should be noted that the unit is hermetically sealed. Although it might appear from the description thusfar that the feedthroughs open the inside of the case to the outside, reference to FIG. 4, to be described in detail below, shows that the bottom of each feedthrough tube is closed (prior to lid 44 being welded to cup 10).

tion. The only difference between the Silastlic coatings 130 The remaining elements in FIG. 3 constitute the 1 11 1 I.:.

connector for connecting the electrodes to the feedthroughs, the connector being permanently attached to the electrodes and ideally never requiring replacement. Silastic sheet36 contains 22 preformed plaii5 num parts which male with the feedthroughs on the 70 ceramic plate 32. The preformed parts in FIG. 3 are shown as terminating in spheres, although in FIG. 4 their ends are shown as having a conical shape; these are only two of the possible shapes which may be used. FIG. 4, which depicts the construction of the elements associated with Silastic sheet 36M11 be described in detail below. Awire 26 is connected to -2,:h connector elen-..:-nt30, and all of the wires a,e extended to electrode cable 16 (which does not form part of this invention). See, generally, "Development of Multichannel Electrodes For An Auditory Prosth esis", Repor-t on Progress, September 1, 1980 through November 30, 1980, N1H Contract No. NO1 -NS-0-2337, by Merzenich et a].

Silastic sheet 24 is placed against the inside flat 85 surface of a rigid titanium cover 18. Silastic sheet 36 is positioned against Silastic sheet 24. Actually, Silastic sheet 36 is molded inside cover 18. The cover is invericd and Silastic sheet 24 is placed in it. The 22 connector p@ rts are then held in place while Silastic 90 material is poured on top of sheet 24 in order that sheet 36 be formed to hold the connector parts. It should be noted that sheet 24 and cover 18 have a respective cut-out and hole 24a, 18a foraflowing cable 16to pass through the cover. Holes 36a, 24b and 18b 95 allow screw 42 to pass through them during final assembly.

During the final assembly step, the connectoris placed on top of ceramic plate 32, with each individual connector part in the connector being seated in a respective one of the feedthroughs as will be described in connection with FIG. 4. Screw 42 extends up through the connector and the two parts are held in compression against each other by tightening titanium nut20 on the screw.The head on nut 20 sits in the depression which surrounds hole 1 8b in the cover.

FIG. 5A depicts the manner in which screw 42 is attached to the underside of ceramic plate 32. The screw is shaped so that it has an undercut 42a in its head. The brazing of the screw to the ceramic plate is shown at 50, and because ofthe undercut the brazing lakes place on athin ring around the edge of the screw head. The reason for insuring that the brazing takes place only along a thin ring is that were the brazing to be over theentire flat undersurface of the screw head, the brazed joint would be subject to strong shear forces during cooling after the brazing, and these shear forces would tend to break the bond. By insuring that the braze is only over a relatively small area, this 55'. effect is reduced. Undercut 42a, and the fact that the diameter of hole 32a is larger than the diameter of the screw, provide minimal contact between the screw and the ceramic feedthrough carrier.

An alternative embodiment for attaching the screw to the ceramic plate is shown in FIG. 5B. In this technique, another plalinurn tube 61 (of larger diameter and longer than the tubes used for the feedthroughs) is joined to the ceramic plate 60, in the same way as the platinum tubes for the connector contacts. that is, by reaction bonding. After attach- GB 2 166 606 A 5 ment to the ceramic, the exposed end of the tube is flared (or this may be preformed prior to assembly) and a screw with a head of matching shape 62 is inserted into the platinum tube. The tube is then folded over the head of the screw and joined, e.g., by welding or brazing as shown by the numeral 63. This technique has the advantage that a metal-to-metal (i.e., platinum tube-io-screw) bond is required, and maythus be done in a variety of ways utilizing a variety of materialsforthe screw, e.g., titanium, platinum or biocompatible stainless steel. In addition, by appropriate choice of the shape of the screw head, all the rotational forces on the screw during tightening of the connector are not borne by the bond between the tube and the screw, but by the geometric arrangement of the screw head and tube. For example, if the screw head were hexagonal instead of circular, then the deformation of the platinum tube over the screw head would tend to strongly hold the screw in place. Thus the major function of the bond between the platinum tube and the screw is to provide an hermetic seal.

The fleedthrough construction is illustrated in FIGS. 6A- 6C. Green ceramic 32, formed to shape but not yet sintered, is sized so that so that following sintering and the resultant shrinking, the plate will fit in lid 44 (FIG. 3) as desired. Holes in the required positions for the feedthroughs are drilled in the green ceramic plate, and a furiherhole 32a is drilled to allowscrew 42 (FIG. 3) io pass through it. Platinum tubes 34 are then placed in respective holes in the plate.The length of each tube, relative to the thickness of the plate, is shown in FIG. GB. The tubes fit snugly in the holes in the plate, and they are pjaced so that a relatively large length protrudes from the upper surface of the plate (the surface which is shown as the undersurface in FIG. 3), and only a small length protrudes from the bottom. As seen most clearly in FIG. 6B, the thickness of the wall of each of tubes 34 is about one-tenth the outside diameter of the tube.

The green ceramic plate containing the platinum tubes in position is then placed on a flat surface within an oven and the oven is operated at the appropriate temperature and for the appropriate time necessary to sinterthe ceramic plate. The sintering is no different from that of the prior art, As the ceramic sinters it shrinks, and thus shrinks around each of the platinum tubes. With the pressures involved due to the shrinkage, and thetemperatures of sintering, a platinum reaction bond is formed between the ceramic and each platinum tube along iti entire length in the ceramic around its circumference, to form an hermetic seal between the ceramic and the platinum tube. The process forforming so many hermetic seals in so tight a space is amazingly simple and cost-effective. The physics involved in the reaction bonding process is not completely understood. However, there is no question that the results are reproducible with every seal being hermetic. After sintering, the outer cir- cumference of the plate may be ground to the correct dimensions, if necessary.

The general technique of reaction bonding metals to ceramics or-glasses is known, and is used, for example. in the manufacture of high-lemperature platinum thermocouples. However, prior art techni-

GB 2 166 606 A 6 ques require the application of external pressures under high temperature to achieve the bond. In the practice of the present invention, it is the forces associated with the shrinkage of the ceramic during sintering that achieves the bond. It is also known in the 70 prior art to use ceramic which is initially sintered. The prior art techniques are described generally in Klomp, "Bonding of Metals to Ceramics and Glasses", Cera mic Bulletin, Volume 51, No. 9 (1972).

0 The ceramic plate is initially formed so that the 75 bottom end of each feedthrough hole through the plate has a conical shape as shown by the numeral 32b in FIG. 6B. FIG. 6C depicts, in enlarged form, an individual platinum tube within the cerarnic plate after the plate is fired and after subsequent processing. The 80 bottom end of each tube is preferably formed to a concave shape, as shown by the numeral 34c in FIG.

6C, to provide a better contact area for the respective connector part. The bottom surface of the ceramic W pia' te is then lapped to provide a high-quality "mirror" 85 surface finish, for a reason to be described below.

Finally, the upper end of each platinum tube (which is the lower end in FIG. 3) is closed off by using a standard welding technique, in orderto complete the hermetic seal. The upper end is pinched, as shown by 90 the numeral 34a in FIG. 6C, follo,,,!ing which the tip is welded as shown bythe numeral 34b.

Instead of forming the connector parts afterfiring, it is possibleto use preformed platinum parts with closed ends.The region of the connector part which 95 passesthrough the ceramic should betubular. Reac tion bonding has beenfoundtotake placewhenthe connectorpartis a hollowtube inthe regionwherethe bonding is desired.

A similar technique is utilized for securing the ends of tube 12within ceramic carrier bushings 14 (FIG. 3), since hermeticseals are also required for the tube ends. Ceramic bushings are made of green ceramic.

each having a central hole such that one end of hollow tube 12 fits snugly in the hole. (As in the case of ceramic plate 32, if there is a large degree of shrinking, the part being secured within a hole in a ceramic piece need not even fit snugly around the inserted tubular par.t).The entire tube and the two bushings at its ends are then placed in an oven so that the ceramic 110 bushingssinter.

The bushings shrink and once again hermetic bonds are formed between each bushing and the platinum tube which itsurrounds. Afurther advantage of this approach is that in the process the tube is annealed so 115 that it maybe easily and safely bent to any desired shape during implantation. After the bushings are thus attached to the ends of the tube, the bushings are attached tothe titanium case 10 using any convention- al brazing technique employed in fabricating pacemaker f aedth roughs. During this process, care must be taken that none of the braze alloy be allowed to form an, electrical connectioin between the metal case and the coil-enclosing tube. An important feature of the construction is that while the inside of the tube and 125 the inside of the case are topologically continuous. they are not electrically connected so that the tube does not form a shorted turn which would otherwise absorb electromagnetic radiation to a significant degree.

An enlarged viewof the mannerinwhich a connector part makes contact with a feedthrough is shown in FIG.4. Ceramicplate 32isshownwith a single feedthrough 34, the upper end of the feedthrough having a concavity 34c. At the bottom of the connector a platinum wire 30 terminates in a conical head 30a (although a spherical termination, as shown in FIG. 3, as well as other shapes, also suffice). An enlarged head is advantageous in that it contributes to better seating of the pin in the feedthrough, aswell as proving a larger contact area. Pin 30 is held in molded Silastic sheet 36, this sheat bearing against Silastic sheet 24 which is adjacent to titanium cover 18. Pin 30 is connected to a wire 26, the wire in turn being extended through the electrode cable to a particular electrode. One end of wire 26 is resistance welded to pin 30, as shown by the numeral 28. Each of pins 30 is in reality nothing morethan a short segment of wire, one of whose ends is formed into a desired shape.The wire has a diameter of.005 inches. The wire is too thick to be extended directly through the electrode cable, and wire 26 has a diameter of only.001 inches. Itisfor this reason thatthe two of them must bewelded togetherwithin the connector; the wirewhich contacts the feedthrough is too thickfor the electrode cable, and the wire in the electrode cable is too thin to establish sufficient contact with thefeedthrough.

The uppersurface of ceramic plate 32 is highly polished, as described above. Even though only a single screw is utilized for establishing the connection, due to the provision of Silastic sheet 24, Silastic sheet 36 is held against the gerernic plate with an even and consistent pressure. (It is metallic eever 18, of course, which distributes the screwforce to the backing Silastic sheet 24.) Because of the uniform pressure throughout the interface between Silastic sheet36 and ceramic plate 32 (resulting from the resiliency of the Silastic sheets), and because of the high polish on the surface of the latter, any fluid between the two surfaces is squeezed out into the empty space around head 30a of the connector part, the empty space around head 30a of the connector part, the empty being shown by the numeral 38 in FIG. 4.Thefact that fluid may surround a connector part is of no moment; what would be a problem would be the existence of fluid between adjacent feedthroughs or connector parts and it is forthis reason that fluid is excluded at the interface of the ceramic plate and Silastic sheet 36. The high polish of the ceramic plate prevents f luid from being trapped in microscopic depressions in the surface so that a very high inter-electrode resistance may be maintained.

It should be noted that the arrangement of connection points is such that the connector is self-locating, i.e., it can only be assembled in one way. Proper placement of the connector, with each of the 22 connector partsfitting in a respective feedthrough, can be sensed during assembly, and onlywhen proper seating is achieved should nut20 (FIG. 3) be tightened on screw 42.

Referring to FIGS. 1-3, itwill be seen thattube 12 extends to one side of the circumference of the case. Because the case is outside the circumference of the coil, exceptfor the short segmentof each turn which goes through the case between the ceramic bushings, i 1 1; 7 POOR QUALITY the metal of the case does not significantly degrade the performance of the data and power link. It is because the two ends of the tube are not electrically connected together that the tube does not act as a shorted turn which would otherwise absorb most of the radiated power. The tube simply acts as an open circuit turn, with potentials in the order of a volt being developed across its two ends.

Other orientations of the tube are possible. For example, the tube might be bent so that its plane is parallel with the plane of the case with the case contained within the tube. With such an orientation, is s,:!1 possiblep. ovided that.the tube,,.,,ith the coil inside, is between the case and the external transmitter/receiver. Of course, werethe case 80 to be interposed between the tube and the external device, the casewould absorb practically all of the radiated power.

The use of a soft orductile metal allows thetube to be bent to conform to the shape of the cavity into which the package is to be placed. The fact thatthere is little conductive metal within the coil (e.g., the wall of the tube) is advantageous in that any metal placed inside the coil absorbs power. Additional metal inside the coil comprises a short segment of the case wall between two ceramic bushings. Even this can be avoided if the case itself is made entirely of ceramic. The disadvantage of using ceramic material, however, is that a thicker wall thickness would be required, thus increasing the volume of the case.

It should also be appreciated that the shape of the tube need not be circular; anyshape required bythe implantandthe anatomical site of implantation may be used.The diameterof the coil and its enclosing tube is not determined by the diameter of the case containing the electronic circuits, thus allowing flexibility in design and a reduction of the total volume of the implant. Another advantage of the use of the tube is that it may serve as a convenient anchoring point for the implant, either by using sutures or by including a fibrous mesh across the tube, should there be no other convenient way to anchor the implant.

Referring to FIG. 1, it will be seen thatthe unit is symmetrical around a vertical planethrough the center. The advantage of this is thatthe package is not 110 "handed", eliminating the need to make two different versions of the packagefor eitherside of the head.

The connector configuration satisfies all of the requirementsfor a cochlear prosthesis.The firm seating of the connecting parts in the feedthroughs and the large contact areas insure that tere is low electrical resistance in series with each electrode lead. Current leakage paths between connector points have high electrical resistance due to the usage of the Silastic/polished-ceramic interface. The connector may be disconnected and connected to another case a small number of times without any degradation in performance, even though reconnection in a fluidsurrounded body environment does not allowfluid ingress to be prevented.

Needless to say, one of the most important characteristics of the overall unit is that onlywell-proven bio-compatible materials are used, including titanium, platinum, ceramic, and medical-grade Silastic.

Although the invention has been described with GB 2 166 606 A 7 reference to a particular embodiment, itisto be understood thatthis embodiment is merely illustrative of the application of the principles of the invention. For example, the feedthrough pieces (,.,.,hich can be pre-formed) need not be circular in cross-section; an elliptical or even a non-uniform shape may be acceptable. Similarly, instead of platinum, other noble metals may be acceptable. Nor need the feedthroughs function in an electrical capacity. By utilising tubes both of whose ends are not sealed, fail-safe communication can be had to a hostile environment, e.g. to sample chemical reactions such as in a blast furnace or in pi...astics.-,:in,.. jfactur.ng, to introduce reagents, or to p,,,-fortii a sensing function. The connector may be used for a cable-to-cable coupling rather than a cable-to-case coupling. In those cases where a telemetry capability is required, the package might be provided with only one tube bushing, solid or stranded wire being welded to the

Claims (1)

1. tube and functioning as an "aerial" with a free end. CLAIMS

   1. A connector for attachment to the case of an implantable medical prosthetic package comprising a rigid cover, an electrode cable extending through said rigid cover, resilient material within said rigid cover containing a plurality of connector partsfor mating with respective contacts on the case, each of said connector parts being coupled to a respective wire in said electrode cable, holes in said resilient material and said rigid cover for allowing a shaft extending from the case to pass therethrough when said cover is placed on the case, and meansfor attachmeritto the shaftforforcing said connector againstthe case.

   2. A con nectorfor attachment to the case of an implantable medical prosthetic package in accordance with claim 1 wherein said resilient material is adapted to distributethe force applied by said attachment means uniformly across the region of the case on which said cover is placed.

   3. A connector for attachment to the case of an implantable medical prosthetic package in accordancewith claim 2wherein said resilient material includes a first sheet adjacent to said rigid cover, and a second facing sheetcontaining said connectorparts.

   4. A connector for attachment to the case of an implantable medical prosthetic package in accordance with claim 1 wherein each of said connector parts has a configuration which allows a cavity to form between said resilient material and the case on which said cover is placed around each of said connector p a rts.

   5. A connectorfor attachment to the case of an implantable medical prosthetic package in accordance with claim 1 wherein each of said connector parts includes a pin extending partially into said resilient material, and the electrode cablewire connected to said pin has a diameterwhich is substantially smaller than that of said pin.

   6. A connector for attachment to the case of an implantably medical prosthetic package comprising a rigid cover, an electrode cable extending through said rigid cover, resilient material within said rigid cover containing a plurality of connector parts for mating with respective contacts on the case, each of said connector parts being coupled to a respective wire in POOR QUALITY 1 said electrode cable, and means for attaching the connector to the case, said resilient material being adapted to distribute the force applied by said attaching means uniformly across the region of the case to which the connector is attached.

   7. A connector for attachment to the case of an implantable medical prosthetic package in accordance with claim 6 wherein said resilient material includes a first sheet adjacent to said rigid cover, and a second facing sheet containing said connector parts.

   8. Aconnectorforattachmentto the case of an implantably medical prosthetic package in accordancex.,,,th claim 6wherein each of said connector parts has a con figurat Lion which allows a cavity to forrii between said resilient material and the case to which the connectoris attached around each of said connector parts.

   9. A connector for attachment to the case of an implantable medical prosthetic package in accord- ancewith claim 6 wherein each of said connectorparts 85 includes a pin extending partially into said resilient material, and the electrode cable wire connected to said pin has a diameterwhich is substantially smaller than thatof said pin.

   10. A connectorfor attachment to the case of an electronic package comprising a rigid cover, a cable extending through said rigid cover, resilient material within said rigid cover containing a plurality of connector parts for mating with respective contacts on the case, each of said connector parts being coupled to a respective wire in said cable, holes in said resilient material and said rigid coverfor allowing a shaft extending f rom the case to pass therethrough when said cover is placed on the case, and means for attachment to the shaftforforcing said connector againstthe case.

   11. A connector in accordance with claim 10 wherein said resilient material is adapted to distribute the force applied by said attachment means uniformly across the region of the case on which said cover is placed.

   12. A connector in accordance with claim 11 wherein said resilient material includes a firstsheet adjacent to said rigid cover, and a second facing sheet containing said connector parts.

   13. A connector in accordance with claim 10 wherein said holes are generally central to the positions of said connector parts.

   14. A connector in accordance with claim 10 wherein each of said connector parts has a configuration which allows a cavity to form between said resilient material and the case on which said cover is placed around each of said connector parts.

   15. A connector in accordance with claim 10 wherein each of said connector parts includes a pin extending partially into said resilient material, and the electrode cable wire connected to said pin has a diameterwhich is substantially smaller than that of said pin.

   15. A connector for attachment to a plate containing a plurality of contacts comprising a rigid cover, a cable extending through said rigid cover, resilient material within said rigid covercontaining a plurality of connectorparts for mating with respective contacts on said plate, each of said connector parts being GB 2 166 606 A 8 coupled to a respective wire in said cable, and means for attaching the connector to said plate, said resilient material being adapted to distribute the force applied bysaid attaching means uni,ormly across the region of said plate to which the connector is attached.

   17. A connector in accordance with claim 16 wherein said resilient material includes a first sheet adjacent to said rigid cover, and a second facing sheet containing said connector parts.

   18. A connector in accordance with claim 16 wherein each of said connector parts has a configuration which allows cavity to form between said resilient material and said plate to which the connector is attachedaround each of said con.nector parts.

   19. A connector for attachment to a plate containing a plurality of contacts comprising a rigid cover, a cable extending through said rigid cover, resilient material within said rigid covercontaining a plurality of connector partsfor mating with respective contacts on said plate, each of said connector parts being coupled to a respective wire in said cable, holes in said resilient material and said rigid coverfor allowing a shaft extending from said plateto pass therethrough when said cover is placed on said plate, and meansfor attachment to the shaftforforcing said connector againstsaid plate.

   20. A connector in accordance with claim 19 wherein said resilient material is adapted to distribute the force applied by said attachment means uniformly across the region of said plate on which said cover is placed.

   21. A connector in accordance with claim 20 wherein said resilient material includes a first sheet adjacent to said rigid cover, and a second facing,sheet containing said connector parts.

   22. A connector in accordance with claim 19 wherein said holes are generally central to the positions of said connector parts.

   23. A connector in accordance with claim 19 wherein each of said connector parts has a configuration which allows a cavity to form betwen said resilient material and said plate on which said cover is placed around each of said connector parts.

   Amendments to the claims have been filed, and have the following effect:Claims 7 to 23 above have been deleted.

   Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 5186 113996. Published at the Patent Office, 25 Southampton Buildings, London WC2A lAY, from which copies may be obtained.