WO2009015438A1

WO2009015438A1 - Method and apparatus for forming a feedthrough electrical connector device

Info

Publication number: WO2009015438A1
Application number: PCT/AU2008/001123
Authority: WO
Inventors: Desmond Mccusker; Mark Spalding; Nicholas Charles Kendall Pawsey; Jeffrey Albert Enke
Original assignee: Cochlear Limited
Priority date: 2007-08-02
Filing date: 2008-08-01
Publication date: 2009-02-05

Abstract

An apparatus (10) is provided for use in the formation of an electrically conducting feedthrough device (52). The apparatus (10) includes first and second portions (12, 14). At least one of the first and second portions (12, 14) is movable with respect to the other portion between an open and closed position. The first portion (14) includes an open-ended mould cavity (20). A moveable cavity member (44) is arranged within the mould cavity (20). The cavity member (44) extends across and is biased towards a position substantially at the open end. The cavity member (44) has a plurality of holes (42) extending therethrough. The second portion (12) includes an electrical conductor feed mechanism for feeding lengths of solid electrically conductive material (24) from the second portion (12) into and through the holes (42) in the cavity member (44). A retaining mechanism (46) receives and retains the ends of the lengths of electrically conductive material (24) fed through the holes (42) in the cavity member (44). An injection nozzle (18) is arranged on the second portion (12) and is directed towards the open end of the cavity (20), when the first and second portions (12, 14) are in the closed position, for injecting electrically insulating material into the cavity (20). The cavity member (44) and the retaining mechanism (46) move against the bias under pressure of injected material to expose the cavity (20) and the lengths of conductive material (24) and allow the electrically insulating material to mould in the exposed cavity (20) and around the exposed lengths of conductive material (24).

Description

METHOD AND APPARATUS FOR FORMING A FEEDTHROUGH

ELECTRICAL CONNECTOR DEVICE FIELD OF THE INVENTION

The present invention generally relates to methods and apparatus for forming electrically conducting feedthrough devices. BACKGROUND TO THE INVENTION

The term 'feedthrough' as used herein refers to the provision of an electrically conducting path extending through an insulative member, from one side of the insulative member to another. The electrically conducting path may extend from the interior of a hermetically sealed container or housing on one side of the insulative member, to an external location outside the container or housing on the other side of the insulative member. Typically, a conductive path is provided by an electrically conductive pin, which is electrically insulated from the container or housing by an electrically insulating body surrounding the pin. A feedthrough device can therefore allow one or more electrical connections to be made with electronic circuitry or components within an hermetically sealed container or housing, whilst protecting the circuitry or components from any damage or malfunction that may result from exposure to the surrounding environment. There are many applications for feedthrough devices that provide an electrically conducting path through the wall of a housing or container whilst also sealing the electrical container or housing from its ambient environment. Historically, the first such devices were widely used in vacuum technology allowing for the transfer of signals between chambers of differing pressures. In such applications, the vacuum tubes had to be sealed because they could only operate under low-pressure conditions.

Over time, and with the advent of electrical devices capable of being implanted in body tissue to provide therapy to a patient, such as cardiac pacemakers, defibrillators and cochlear implants, the need to provide feedthrough devices with improved hermeticity has become increasingly important. As the environment of living tissue and body fluids is relatively corrosive and devices may contain materials which may be detrimental if exposed to the patient, a hermetic feedthrough device is used to provide a barrier between the electronic components of the device and the external corrosive environment of the human body. With implantable medical devices in particular, it is critically important that the hermetic seal of the device be physically rugged and long lasting. For this reason, stringent requirements are imposed on the hermeticity of an implanted device, typically requiring a seal that provides a leakage rate of less than 1O.sup.- 8 cc/sec.

Given this, feedthroughs used in medical implant applications, such as those used in pacemaker devices and cochlear implants, typically consist of a ceramic or glass bead that is bonded chemically at its perimeter through brazing or the use of oxides, and/or mechanically bonded through compression, to the walls of the sealed package. A suitable wire or other conductor passes through the centre of the bead, and this wire or conductor must also be sealed to the bead through chemical bonds and/or mechanical compression. Such feedthroughs are typically cylindrical and the wire(s) or conductors) mounted within the bead are centred or mounted in a uniform pattern, centrally within the bead.

Other materials and processes are known for making feedthroughs which rely, for example, on use of aluminium oxide ceramic and binders. These types of feedthroughs are widely used for cardiac implants and cochlear implants. One of the processes for making such a feedthrough consists of pre-drilling holes in a sintered ceramic plate and then forcing electrical conductive pins through the holes. Examples of such processes are disclosed in US patent no. 5046242. While useful, this method is tedious and slow and does not necessarily guarantee a hermetic seal and generally results in unsatisfactory leakage rates on testing and low yields. It has been found that drill bits wear out quickly when used on ceramics, due to their abrasive nature, hence to meet required tolerances the drill bits tend to be required to be constantly replaced. Furthermore, the build-up of stress around punched or drilled holes can result in cracking after in the sintered ceramic.

A second method involves inserting the conductive pins into an unsintered (or 'green') ceramic plate and then curing the assembly by firing to achieve a hermetic seal. A major disadvantage of this last method is that, historically the manufacturing process has been performed by hand. Such a method of manufacture can lead to inaccuracies and be time consuming, expensive and labour intensive. Moreover, the feedthrough devices resulting from such a process do not necessarily have precisely positioned electrical conductors, with the position of the conductors being greatly dependent upon the process itself. Further, as the conductors are typically wires being of a general cylindrical shape and configuration, the size and shape of the conductor extending from the insulative material of the feedthrough is generally the same as the conductor embedded in the insulative material of the feedthrough.

As implantable devices continue to develop and become thinner, smaller and more electronically sophisticated, the requirements of the feedthrough have also increased. In cochlear implants, for example, where there is presently typically somewhere between 22-24 electrode leads, there is a need for 22-24 conductive pins passing through the feedthrough device. As the desire for more electrodes and smaller feedthroughs increases, the demands placed upon the design of the traditional feedthrough also increases. The problems in fabricating such a feedthrough device on such a large scale are therefore quite significant, especially when one considers the relatively high degree of labour intensity and specialisation of current fabricating methods.

While the above described prior art feedthrough devices and fabrication methods have proven successful, it is a relatively slow and labour intensive process to manufacture such devices. The method of manufacture of the feedthrough also presents limitations as to the construction of the feedthrough.

US patent application no. 2006/0141861, by the present applicant, discloses various embodiments of methods for forming a feedthrough device; the disclosure of which is incorporated herein by way of reference. In the embodiment illustrated in fig. 26 of this US application, an electrically insulating structure having holes for feedthroughs is formed by powder injection moulding (PIM). The mould includes a pair of opposed mould plates. One of the plates carries a number of pins, and the other plate has recesses which operatively receive the pins. The plates are slowly moved apart to expose a partial cavity, into which hot feedstock is injected. The feedstock moulds in the partial cavity around the exposed portions of the pins. The process of moving the plates apart and injecting feedstock into the further exposed cavity continues until the cavity is fully moulded. Once this process is completed, the moulded structure is ejected, the moulded structure having holes formed therethrough where the pins were located. The holes then allow feedthrough conductors to be arranged through the moulded structure. This two step process of forming the moulded structure and then inserting the feedthrough conductors can prove to be time consuming which limits the efficiency of the process.

Other embodiments in US patent application no. 2006/0141861 attempt to improve this efficiency by practically combining the two steps into one. In these embodiments, an electrically conductive structure is provided with feedthrough conductors and sacrificial portions. Electrically insulating material is moulded directly on and around the feedthrough conductors. Following the moulding, the sacrificial portions are removed to leave the moulded feedthrough device. While conceptually efficient in respect of time saving, the process has found to have practical limitations. Firstly, the process has proven difficult to efficiently automate. The process requires an operator to manually load the conductive structure before the moulding cycle. The time taken to load varies between every cycle and varies between operators, consequently causing variations in each cycle time. Another issue relates to flashing around the feedthrough conductors in the conductive structure. Each feedthrough has a minor variation in the amount of flash which also causes variations in the injection pressure. Removing the flash is a labour intensive exercise.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

It is an object of the present invention to provide an improved method and apparatus for use in the forming of an electrically conducting feedthrough device. SUMMARY OF THE INVENTION According to the present invention there is provided an apparatus for use in the formation of an electrically conducting feedthrough device, the apparatus including: first and second portions, wherein at least one of the first and second portions is movable with respect to the other portion between an open and closed position; the first portion including an open-ended mould cavity; a moveable cavity member is arranged within the mould cavity, the cavity member extending across and biased towards a position substantially at the open end; the cavity member having a plurality of holes extending therethrough; the second portion including an electrical conductor feed mechanism for feeding lengths of solid electrically conductive material from the second portion into and through the holes in the cavity member; a retaining mechanism for receiving and retaining the ends of the lengths of electrically conductive material fed through the holes in the cavity member; an injection nozzle arranged on the second portion and directed towards the open end of the cavity, when the first and second portions are in the closed position, for injecting electrically insulating material into the cavity; wherein the cavity member and the retaining mechanism move against the bias under pressure of injected material to expose the cavity and the lengths of conductive material and allow the electrically insulating material to mould in the exposed cavity and around the exposed lengths of conductive material. Preferably, the retaining mechanism includes a retaining member having recesses, aligned with the holes in the cavity member, for receiving the ends of the lengths of electrically conductive material, wherein the member is movable with respect to the cavity member to misalign the recesses with respect to the holes in order to retain the received ends. The retaining member may be rotatable with respect to the cavity member.

In exemplary embodiments, the feed mechanism includes a plurality of rotatable reels for holding the solid electrically conductive material, whereby rotating the reels causes the lengths of conductive material to advance through the second portion. Channels may be provided via which the lengths of electrically conductive material advance through the second portion from the reels.

The feed mechanism may further include a gripping mechanism for receiving and gripping the lengths of conductive material from the reels, wherein the gripping mechanism is movable with respect to the second portion to feed the gripped lengths of conductive material into and through the holes in the cavity member. Ideally, the gripping mechanism includes a first and second gripping member, each gripping member having holes aligned with the holes on the cavity member and arranged to receive the lengths of conductive material from the reels, wherein at least one of the first and second gripping members is movable with respect to the other in order to misalign the respective holes and grip the received lengths of conductive material. The second gripping member may be rotatable with respect to the first gripping member. In exemplary embodiments, the gripping mechanism is adapted to sever the lengths of conductive material.

The present invention further provides a method for forming an electrically conductive feedthrough device employing the above apparatus and feedthrough devices formed by such methods.

The present invention advantageously provides an apparatus and method for forming an electrically conductive feedthrough device which allows for efficient use of automation for large scale fabrication with reduced labour requirements. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view of an apparatus according to a preferred embodiment with the upper and lower portions in a closed position;

Fig. 2 is an enlarged sectional view of the apparatus of Fig. 1 with the gripping mechanism in an upper position;

Fig. 3 is an enlarged sectional view of the apparatus of Fig. 1 with the gripping mechanism in a lower position;

Fig. 4 is an exploded view of the gripping mechanism, cavity member and retaining mechanism of the apparatus of Fig. 1 ;

Fig. 5 is an exploded view of the gripping mechanism and cavity member of the apparatus of Fig. 1 ; Fig. 6 is an exploded view of the gripping mechanism of Fig. 5 with the upper and lower gripping members shown as separated for illustrative purposes; Fig. 7 is a cross-sectional view of the apparatus of Fig. 1 with the gripping mechanism, cavity member and retaining mechanism removed for illustrative purposes;

Fig. 8 is a perspective cross-sectional view of the apparatus of Fig. 1 prior to feedstock injection;

Fig. 9 is a perspective cross-sectional view of the apparatus of Fig. 1 during feedstock injection;

Fig. 10 is a plan cross-sectional view of the apparatus of Fig. 9;

Fig. 11 is a perspective cross-sectional view of the apparatus of Fig. 1 illustrating the severing of the lengths of conductive material;

Fig. 12 is a cross-sectional view of the apparatus of Fig. 1 with the upper and lower portions in an open position;

Fig. 13 is a perspective view of a moulded device; and

Fig. 14 is a cross-sectional view of the moulded device of Fig. 13. DESCRIPTION OF PREFERRED EMBODIMENT

The present invention will be described with reference to a particular implementation and embodiment. It will be appreciated that the present invention may be implemented with variations and that the present implementation described is not intended to be limitative of the scope of the invention. Referring to Figs. 1 and 2, there is shown an apparatus 10 having an upper portion 12 and a lower portion 14 meeting at a parting line 16. The two portions 12, 14 are arranged to be separable. In preferred forms, the upper portion 12 is fixed while the lower portion 14 is movable.

The upper portion 12 carries an injection nozzle 18 via which mouldable electrically insulating material, such as ceramic feedstock, can be injected. The injection nozzle 18 is directed towards an open top end of a mould cavity 20 arranged in the lower portion 14. When the upper and lower portions 12, 14 are brought together into a closed position, an o-ring (not shown) provides a vacuum seal which allows a negative pressure to be provided in the cavity 20. The upper portion 12 is provided with a number of reels 22 carrying lengths of solid electrically conductive material 24, for example platinum wire. A number of channels 26 or tubes extend through the upper portion 12 from the reels 22, providing guides via which the lengths of conductive material 24 can advance through the upper portion 12 from the reels 22 when rotated.

The channels 26 guide the lengths of conductive material 24 to a gripping mechanism 28. The gripping mechanism 28 has an upper and lower gripping member 30, 32, shown in the form of disc-like members arranged around an end of a feed tube 34 for the ceramic feedstock. Referring to Figs. 4-6, the upper and lower members 30, 32 have through-holes 36, 38 aligned with the channels 26, which allow the lengths of conductive material 24 to pass through the gripping mechanism 28. The upper gripping member 30 is rotatably movable with respect to the lower gripping member 32 which causes the corresponding through-holes 36, 38 in the gripping members 30, 32 to offset or misalign. In this way, when the lengths of conductive material 24 are advanced through the through-holes 36, 38 in the upper and lower gripping members 30, 32 and the upper gripping member 30 is slightly moved, the misalignment of the through-holes 36, 38 causes the lengths of conductive material 24 to be gripped by the gripping members 30, 32. The lower gripping member 32 is arranged to be movable in a direction towards and away from the injection nozzle 18.

In operation, the reels 22 are rotated to cause the lengths of electrically conductive material 24 to advance through the channels 26 and through the aligned through-holes 36, 38 of the gripping members 30, 32, when arranged at an upper position as shown in Fig. 2. Ideally, as shown, the ends of the lengths of conductive material 24 are advanced until reaching guiding holes 40 formed around the injection nozzle 18. The upper gripping member 30 is moved to cause the lengths of conductive material 24 to be gripped by the gripping members 30, 32. Once gripped, the lower gripping member 32 is moved towards the injection nozzle 18, as shown in Fig. 3. At this lower position, the end of the feed tube 34 is flush with the injection nozzle 18. Furthermore, the ends of the lengths of conductive material 24 have passed through the guiding holes 40 and past the parting line 16, where they have been received in aligned through-holes 42 arranged in a movable cavity member 44 arranged within the mould cavity 20. Referring to Fig. 8, the cavity member 44 extends across the cavity 20. The cavity member 44 is engaged with a spring-loaded carrier (not shown) which biases the cavity member 44 towards the parting line 16. In this biased position, the cavity 20 is substantially closed to the injection nozzle 18. The through-holes 42 in the cavity member 44 allow the lengths of electrically conductive material 24 to pass from the upper portion 12 and through the cavity member 44 towards a retaining mechanism 46 arranged on the opposite side of the cavity member 44. The retaining mechanism 46 is shown in the form of a disc-shaped retaining member 48 having recesses 50 for receiving the ends of the lengths of conductive material 24 fed through the cavity member 44. The retaining member 48 is arranged to be rotatably movable with respect to the cavity member 44 in order to align and misalign the recesses 50 with the through-holes 42 in the cavity member 44. This arrangement acts like the gripping members 30, 32 in allowing the received ends of the lengths of conductive material 24 to be gripped between the cavity member 44 and the retaining member 48 by rotating the retaining member 48 to slightly offset or misalign the respective holes 42 and recesses 50. Once the ends of the lengths of conductive material 24 are gripped and retained by the retaining mechanism 46, the apparatus 10 is practically ready for an injection step.

Prior to injecting the feedstock via the injection nozzle 18, the upper gripping member 30 is rotated in order to relax the grip on the lengths of conductive material 24. When the feedstock is injected from the injection nozzle 18, the injected feedstock contacts the upper surface of the cavity member 44. The pressure of the injected feedstock causes the cavity member 44 to slide against the spring bias within the cavity 20, thus exposing the cavity 20 to the injected feedstock and allowing the exposed cavity to fill, see Figs 9 and 10. The movement of the cavity member 44 causes the retaining mechanism 46 to similarly move. Given that the ends of the lengths of conductive material 24 is retained and the grip provided by the gripping members 30, 32 is relaxed, the movement of the retaining mechanism 46 and the cavity member 44 pulls on the lengths of conductive material 24 under tension to draw further lengths of the conductive material 24 through the upper portion 12. As shown, as the cavity 20 becomes exposed, similarly, partial lengths of the conductive material 24 extending through the cavity 20 becomes exposed and drawn through the injected feedstock. In this manner, the feedstock gradually fills the cavity 20 and moulds around the exposed lengths of conductive material 24. The gradual exposure of the lengths of conductive material 24 prevents the material deforming or becoming damaged due to the high injection pressures.

In preferred embodiments, an actuator member (not shown) is arranged with respect to the cavity member 44 and is associated with a pressure sensor

(not shown). With this arrangement, the pressure in the cavity 20 can be monitored. Ideally, the pressure sensor is linked in a closed loop arrangement with a controller for the injection process; thereby allowing control of injection pressure and holding pressures within the cavity 20. Ideally, the upper surface of the lower portion 14 is provided with a trench arrangement (not shown) extending from the cavity 20. This trench arrangement allows air to be evacuated from the cavity 20 as the cavity 20 is being filled by the injected feedstock.

Following injection, the lengths of conductive material 24 can be cut to required length. This cutting step is conducted by the gripping mechanism 28.

Rotating the upper gripping member 30 a sufficient distance, provides a shearing force to the lengths of conductive material 24 between the gripper members 30,

32 which severs the lengths, see Fig. 11.

Following moulding and cutting the lengths of conductive material 24, the upper and lower portions 12, 14 are separated to allow the moulded device 52 to be ejected from the mould cavity 20, see Fig. 12. The ejected device 52 has an insulted body 56 with feedthrough connectors 58 extending therethrough, see

Figs. 13 ands 14.

Following ejection, the moulded device 52 undergoes a de-binding process. A suitable de-binding process would include a water de-binding step, in which the device 52 is washed over several hours at 40°C, followed by a thermal de-binding step at approximately 300°C over a period of approximately 24 hours.

Finally, the device 52 is sintered at high temperatures of around 1600⁰C, for example. During the sintering step, the ceramic 56 shrinks and clamps around the connectors 58, thereby creating a hermetic seal.

There are two ideal characteristics which influence the choice of ideal ceramic feedstock. Firstly, the characteristic of the feedstock shrinking in all directions during sintering to clamp around the connectors 58. A second preferred characteristic is the production of a glass phase during sintering which can allow a glaze to form around the connectors 58. Two preferred materials which provide these characteristics are Alumina and Zirconia. These two materials have a high shrinkage rate, in the range of 16-25 percent. A preferred composition of the feedstock would include 94-96 percent Alumina (AI₂O₃) or Zirconia (ZrO₂) with a particle size between 0.5 microns to 3 microns. The composition can preferably include polyethylene which acts as a binder for the composition. Providing trace amounts of Magnesium oxide, Silicon oxide, Zinc oxide or other oxides can stabilize the ceramic and assist in the formation of the glaze.

While the present invention has been described with respect to a specific embodiment, it will be appreciated that various modifications and changes could be made without departing from the scope of the invention. For example, while the connectors 58 in the feedthrough device have been shown and described as appearing in a radial configuration, the apparatus 10 could be readily adapted to provide different configurations, eg a liner configuration. In a linear configuration, the movement of the gripping mechanism 28 and the retaining mechanism 46 may be suitably arranged to provide lateral movement rather than rotational to cause the misalignment of the holes and recesses.

Claims

CLAIMS:

1. An apparatus for use in the formation of an electrically conducting feedthrough device, said apparatus including: first and second portions, wherein at least one of said first and second portions is movable with respect to the other portion between an open and closed position; said first portion including an open-ended mould cavity; a moveable cavity member is arranged within said mould cavity, said cavity member extending across and biased towards a position substantially at said open end; said cavity member having a plurality of holes extending therethrough; said second portion including an electrical conductor feed mechanism for feeding lengths of solid electrically conductive material from said second portion into and through said holes in said cavity member; a retaining mechanism for receiving and retaining the ends of said lengths of electrically conductive material fed through said holes in said cavity member; an injection nozzle arranged on said second portion and directed towards said open end of said cavity, when said first and second portions are in said closed position, for injecting electrically insulating material into said cavity; wherein said cavity member and said retaining mechanism move against said bias under pressure of injected material to expose said cavity and said lengths of conductive material and allow said electrically insulating material to mould in said exposed cavity and around said exposed lengths of conductive material.

2. The apparatus according to claim 1 , wherein said retaining mechanism includes a retaining member having recesses, aligned with said holes in said cavity member, for receiving said ends of said lengths of electrically conductive material, wherein said member is movable with respect to said cavity member to misalign said recesses with respect to said holes in order to retain said received ends.

3. The apparatus according to claim 2, wherein said retaining member rotates with respect to said cavity member.

4. The apparatus according to any one of the preceding claims, wherein said feed mechanism includes a plurality of rotatable reels for holding said solid electrically conductive material, whereby rotating said reels causes said lengths of conductive material to advance through said second portion.

5. The apparatus according to claim 4, wherein said second portion includes channels via which said lengths of electrically conductive material advances through said second portion from said reels.

6. The apparatus according to claim 4 or 5, wherein said feed mechanism further includes a gripping mechanism for receiving and gripping said lengths of conductive material from said reels, wherein said gripping mechanism is movable with respect to said second portion to feed said gripped lengths of conductive material into and through said holes in said cavity member.

7. The apparatus according to claim 6, wherein said gripping mechanism includes a first and second gripping member, each gripping member having holes aligned with said holes on said cavity member and arranged to receive said lengths of conductive material from said reels, wherein at least one of said first and second gripping members is movable with respect to the other in order to misalign the respective holes and grip the received lengths of conductive material.

8. The apparatus according to claim 7, wherein said second gripping member rotates with respect to said first gripping member.

9. The apparatus according to any one of claims 6 to 8, wherein said gripping mechanism is adapted to sever said lengths of conductive material.

10. A method for use in forming an electrically conductive feedthrough device, said method including: providing the apparatus according to any one of claims 1 to 9; moving said first and second portions into said closed position; advancing said lengths of electrically conductive material from said second portion into and through said holes in said cavity member; receiving and retaining the ends of said fed lengths of electrically conductive material in said retaining mechanism; injecting mouldable electrically insulating material from said nozzle; wherein, under pressure of said injected material, said cavity member and said retaining mechanism moves against said bias, exposing said cavity and said lengths of conductive material and allowing said electrically insulating material to mould in said exposed cavity and around said exposed lengths of conductive material; severing the lengths of conductive material; moving said first and second portions to said open position; and ejecting the moulded structure from said cavity.

11. The method according to claim 10, further including the steps of: debinding said ejected structure; and sintering said structure to cause said electrically insulating material to shrink and hermetically seal said lengths of conductive material.

12. An electrically conducting feedthrough device formed according to the method of claim 10 or 11.