GB2591470A

GB2591470A - Feedthrough comprising interconnect pads

Info

Publication number: GB2591470A
Application number: GB2001185.4A
Authority: GB
Inventors: Patnaik Abhishek; Antalek John
Original assignee: Morgan Advanced Ceramics Inc
Current assignee: Morgan Advanced Ceramics Inc
Priority date: 2020-01-28
Filing date: 2020-01-28
Publication date: 2021-08-04
Also published as: GB202001185D0

Abstract

A feedthrough 1 that may be for an implantable medical device, comprising a ceramic body 2 having first 3 and second 4 sides, a conductor 5 extending between said sides, a conductive pad 6a connected to the conductive element and bonded to the ceramic body through a bonding layer 7 comprising an active braze alloy. The conductor may be in brazed or braze-less contact with the ceramic between the first and second sides. The feedthrough may comprise a plurality of conductors at a density exceeding 1 per 100,000 µm2. The active braze may comprise alloys including Au, Cu, Ag, Ni, Ti, Zr, Nb, Ta, V, Hf, Co, Al, Si, In, Cr, W and Mo. The bonding layer may derive from a structure of two or more layers. The conductive pad may comprise a bonded outer layer. The He hermeticity of the feedthrough may be less than 10-7 L atm/s.

Description

FEEDTHROUGH COMPRISING INTERCONNECT PADS

Field

The present invention relates to feedthroughs comprising interconnect pads and methods of producing thereof. In particular, the present invention relates to implantable medical devices comprising said feedthroughs.

Background

Assemblies comprising metal and ceramic components are used in a wide range of applications. Ceramic-metal assemblies have found particular use in feedthroughs, where io one or more electrical conductors are required to pass through a ceramic insulator to provide one or more electrically conductive connections from one surface of the ceramic insulator to another surface of the ceramic insulator. Such arrangements are widely used, for example, in aerospace, transportation, communication and power tube (e.g. x-ray, radio frequency) and medical applications; the present disclosure is not limited to any one application.

Electronic biomedical implants are being used increasingly to diagnose, prevent and treat diseases and other medical conditions. Implantable electronic devices must necessarily comply with safety standards before being approved for clinical use; for example, such implanted devices are needed to be housed in hermetic packages that incorporate electrical feedthroughs for signal transfer between the housed electronic device and the environment.

By encapsulating electronically active components hermetically, the human or animal body is protected from toxicity of conventional electronic components and the device is also protected from the relatively harsh environment of the body that may otherwise cause the device to fail prematurely. Such implantable devices, especially those that interface with the human nervous system or organs in the human body such as the cochlea or the retina require a multiplex of electrical leads in the small confined space of a miniature feedthrough. Ceramic materials such as alumina or metals such as titanium have a long history of success in bionic feedthroughs in devices including pace-makers and cochlear implants. Biocompatible ceramic-metal feedthrough systems may be considered to be the most reliable choice of materials for such devices owing to their chemical inertness (e.g. biocompatibility) and longevity (e.g. bio-stability).

The application of electronic biomedical implants in interacting with the human nervous system is becoming increasingly complex, particularly in neural prosthesis where high resolution stimulating or recording arrays are positioned near peripheral nerves or in the brain. Densely packed electrical feedthroughs are needed to carry signals input/output (I/O) signals to and from these implanted devices. For certain therapies, it is desirable to increase the number of electrical conductors (which have many names in the art of feedthroughs including: leads, pathways, pins, wires, and vias) in the feedthroughs to increase the overall number of I/O signals to meet the demands of these critical applications.

The challenge to provide densely packed electrical feedthroughs is met with the dimensional constraints placed on reducing the overall size of the feedthrough since it is undesirable to implant large devices (including a large feedthrough) in the human or animal body. In particular, it is also desirable to reduce the invasiveness of the implantation surgeries and/or to the nature of the placement of the device for the target therapies such as in retinal implants where the nature of the application necessitates only those devices that are suitably small. When the device design requires both a large number of conductors (i.e. high pin count) and a small-sized feedthrough, conventional feedthrough manufacturing techniques are inadequate and no longer viable. Existing technologies have limits as to the spacing of conductors within the feedthrough which inhibits the ability to increase the density of conductors in the feedthroughs. Therefore, until now, it has been necessary to opt either to make larger feedthroughs thereby increasing the size of the overall device comprising the feedthrough in order to accommodate a higher density of conductors or to reduce the density of conductors thereby limiting number of I/O signals in favour of a smaller-sized feedthrough, zo both of which fail to meet industrial demands.

The compressive force imparted onto conductors embedded in the ceramic matrix of a feedthrough during co-sintering is often relied upon for hermeticity. The interfaces between the conductors and the ceramic body can lack the hermeticity requirements demanded for suitable feedthroughs in critical and high performance applications.

Co-pending application PCT/EP2019/060196 provides a feedthrough comprising a higher density of conductors. As a consequence of providing a higher density of conductors, the hermeticity of the feedthrough may be compromised, which for some critical applications such as those described herein may be insufficient. A higher density of conductors may result in micro-cracking adjacent to the conductors which results in reduced hermeticity and thereby a feedthrough that is deficient against performance criteria.

Hermeticity and performance of feedthroughs may be monitored using routine quality control testing leading to removal of the feedthrough if a reduction in the hermeticity or performance is detected. In order to avoid any unnecessary complications, such as repeat surgeries, it is desirable to produce a feedthrough device that provides improved hermeticity and overall performance more reliably.

The biocompatibility of implantable ceramic feedthroughs is provided by the chemical inertness of ceramic materials. However, the conductors in a feedthrough are often exposed outside of the chemically inert ceramic body, which is not electrically conductive, in order to enable further electrical connections to be made, for example, as wire bonding sites on the feedthrough. The inventors have found these regions of the feedthrough and interfaces between the conductors and the body to be particularly susceptible to leakages. Hence, feedthroughs are one of the most common failure points of high performance implantable io devices that are required to be hermetic. It is a non-exclusive aim of the present disclosure to provide a hermetic feedthrough which is biocompatible and biostable, particularly for high density feedthroughs. It is also a non-exclusive aim of the present disclosure to meet the demanding package requirement for smaller-sized, high-density and hermetic feedthroughs.

Summary of the Invention

It is the object of the present invention to provide an improved feedthrough device.

In a first aspect of the present invention, there is provided a feedthrough (1) comprising a ceramic body (2) having a first side (3) and a second side (4), a conductive element (5) extending through said ceramic body (2) between said first side (3) and said second side (4), a first conductive pad (6a) electrically connected to said conductive element (5), wherein the first conductive pad (6a) is bonded to said first side (3) of said ceramic body (2) through a bonding layer (7), said bonding layer (7) comprising an active braze alloy.

The feedthrough of the present invention unconventionally uses an active braze alloy to hermetically seal the conductive elements against the ceramic body.

In one embodiment, the first conductive pad (6a) consists of the bonding layer (7). In other embodiments, the first conductive pad (6a) comprises a bonding layer (7) and an outer layer ( 11).

In one embodiment, the feedthrough comprises a plurality of conductive elements (5). The conductive element preferably have a density of conductive elements exceeding 1 conductor per 200,000 pm2 or exceeding 1 conductor per 100,000 pm2 or exceeding 1 conductor per 50,000 pm2 or exceeding 1 conductor per 20,000 pm2 or exceeding 1 conductor per 14,839 pm2 (23 thou2) through a planar cross-section of the ceramic body. The present disclosure has been found to be particularly beneficial in maintaining hermeticity when applied to feedthroughs having a high density of conductive elements.

The ceramic body (2) may comprise advanced ceramic materials including but not limited to oxide or carbide or nitride or silicide ceramic materials. The ceramic body (2) may comprise ceramic-matrix composite materials. The ceramic body (2) may comprise alumina ceramics. The ceramic body (2) may comprise zirconia toughened alumina (ZTA) ceramics. The ceramic body (2) may comprise yttria-stabilized zirconia (YSZ) ceramics io The conductive element (5) may comprise Pt or Ir or combinations thereof. The conductive element (5) may comprise any other suitable conductive elements or materials. The conductive element (5) may comprise including but not limited to a solid rod, wire, lead, pathway, pin, metallic ink or via or another form of a conductor.

The conductive element (5) may comprise a plurality of conductive sub-elements (5a). The first conductive pad (6a) may be electrically connected to at least one of the conductive sub-elements (5a). The maximum linear length of the first conductive pad (6a) may be in the range of about 2 to about 100 times the diameter of each of the conductive sub-elements (5a) or conductive element (5).

The conductive element (5) may comprise at least a first end (14) proximal to said first side (3) of said ceramic body (2) and a second end (15) proximal to said second side (4) of said ceramic body (2). The first end (14) and the second end (15) of said conductive element (5) may be substantially parallel or flush with said first side (3) and said second side (4) of the ceramic body (2) respectively. The first end (14) and the second end (15) of said conductive element (5) may protrude out of said first side (3) and said second side (4) of the ceramic body (2) respectively. The first end (14) and the second end (15) of said conductive element (5) may be sunken into said first side (3) and said second side of the ceramic body (2) respectively.

The first conductive pad (6a) may provide a conductive pathway to said conductive element (5). The sub-elements (5a) may be in the form of a bundle of conductive elements which are housed within a single channel through the ceramic body (2) or plurality of conductive elements (5), with each conductive element housed within its own channel through the ceramic body (2).

The first conductive pad (6a) may act as an "interconnect' for further electrical connections to said conductive element (5). It will be understood that a second conductive pad (6b) may be provided on the second side (4) of the ceramic body (2) which is electrically connected to the first conductive pad (6a) via the conductive element (5).

The conductive element (5) may be brazed to the ceramic body (2) between the first side (3) and second side (4) forming a brazed interface (12a). The brazed interface (12a) may comprise a braze filler alloy comprising one or more elements selected from the list consisting of Au, Cu, Ag, Ti, Ni or combinations or alloys thereof. The brazed interface (12a) to may further comprise of one or more elements originating from the ceramic body (2). The conductive element (5) may be in braze-less contact with the ceramic body (2) between the first side (3) and second side (4) forming a braze-less interface (12b). The braze-less interface (12a) may enable tighter spacing between said conductive element (5) and said ceramic body (2) due to the lack of a braze filler alloy.

The first conductive pad (6a) bonded to said first side (3) of said ceramic body (2) may provide a hermetic barrier over said first side (3) of said ceramic body (2). The first conductive pad (6a) bonded to said first side (3) of said ceramic body (2) may provide a hermetic barrier over the conductive element (5). The first conductive pad (6a) bonded to said first side (3) of the ceramic body (2) may provide a hermetic barrier over said first end (14). The first conductive pad (6a) bonded to said first side (3) of said ceramic body (2) may provide a hermetic barrier over said brazed interface (12a) or said braze-less interface (12b) between said conductive element (5) and said ceramic body (2).

The bonding layer (7) comprising an active braze alloy may have a thickness in the range of about 1 micron to about 150 micron. The bonding layer (7) may have a thickness in the range of about 1 micron to about 100 micron. The bonding layer (7) may have a thickness in the range of about 2 micron to about 50 micron. The bonding layer (7) may have a thickness in the range of about 3 micron to about 30 micron. The bonding layer (7) may have a thickness in the range of about 4 micron to 20 micron.

The bonding layer (7) may have a density of at least 95% or at least 96% or at least 97% or at least 98% of the theoretical density of said bonding layer (7).

The feedthrough (1) may comprise a He hermeticity of less than 1.0 x 10-7 L. atm/s. The feedthrough (1) may have a He hermeficity of less than 1.0 x 10-8 L. atm/s. The feedthrough (1) may have a He hermeticity of less than 1.0 x 10-9 Isatm/s. The first conductive pad (6a) may provide the feedthrough (1) with a hermetic seal or an active braze seal over said first side (3) of the ceramic body (2).

In a further aspect of the present disclosure there is provided a feedthrough (1) comprising: a ceramic body (2) comprising one or more components and having a first side (3) and a second side (4); a conductive element (5) extending through said ceramic body (2) between said first side (3) and said second side (4); a first conductive pad (6) electrically connected to said conductive element (5); wherein the first conductive pad (6) is bonded to said first side (3) of said ceramic body (2) or between adjacent components thereof through a bonding layer (7), said bonding layer (7) comprising an active braze alloy.

In one embodiment a conductive pad (6) may be located between two adjacent components in the ceramic body. The component are preferably layers, although it will be appreciated that the ceramic body may be formed from other geometric configurations. The conductive pad may also extend between the adjacent components and function as a hermetic seal between conductive pathways in opposing components. Conductive pads may be located between several or all adjacent ceramic components in addition to, or as an alternative to, being located on an external surface of the ceramic body. Within this embodiment, holes are made in each of the green ceramic component and the holes filled with a conductive paste (e.g. metallic ink) to form a conductive pathway through the ceramic component.

The conductive paste preferably comprises a metallic conductor, such as a biocompatible metal (e.g. platinum group metal and alloys thereof). The paste may also comprise a binder (preferably a fugitive binder) and/or a ceramic filler to assist in matching the co-efficient of thermal expansion between the conductor and the ceramic body. An active braze may then be coated over at least one end of the conductive pathway. The process may be repeated with one or more further components. The components may then be stacked or otherwise arranged such that the conductive pathway (5) extends from the first side (3) to the second side (4) of the ceramic body (2). In some embodiments, the conductive pathway may extend between the ceramic components as well as through the components. The assembly may be co-fired together such that the one or more conductive pads (6) form an active braze bond between the ceramic components adjacent the conductive pathway.

The conductive pad (6) preferably extends between the components at least 2 pm or at least 5 pm or at least 10 pm from the conductive pathway (5). This overlap enables a hermetic active braze bond to form between components and prevents the formation of gaseous pathways along the interface between the conductive pathway (5) and the ceramic body (2). The conductive pad typically extends no more than a distance equivalent to twice the diameter of the conductive pathway (5) and preferably no more than the diameter (or half the diameter) of the conductive pathway.

This embodiment is particularly advantageous in enabling the use of conductive pastes in the formation of conductive pathways while providing one of more hermetic barriers embedded between the co-fired components of the ceramic body.

Brazing using an active braze alloy also known in the art as "active metal brazing" or "active brazing" is a single step liquid-state joining process usually conducted in vacuum whereby the active braze alloy comprises an "active metal element". The active braze alloy may comprise an active metal element. The active metal element may be a highly reactive element also known in the art as the "active ingredient".

The active braze alloy may comprise two or more elements selected from the list consisting of Ti, Zr, Nb, To, V, Hf, Co, Ni, Au, Al, Si, Cu, Ag, In, Cr, Ta, W and Mo. The active braze alloy may comprise one or more elements from the list consisting of Ti, Hf, Zr, Nb, Ta, and V. The active braze alloy may comprise one or more elements from the list consisting of Ti, Co, and Zr to provide corrosion resistance or biocompatibility. The active braze alloy may comprise a Ti-Co-Zr active braze alloy. The active braze alloy may comprise Cr or Au additions to further enhance corrosion resistance or biocompafibility.

The bonding layer (7) may comprise a Ti-Zr-Co active braze alloy. The Ti-Zr-Co braze alloy may provide good wettability and joint strength with a range of ceramic materials including but not limited to alumina, ZTA, and YSZ ceramics. The Ti-Zr-Co braze alloy may provide a hermetic seal or an active braze seal at the joint interface (16). The Ti-Zr-Co active braze alloy may provide high-strength brazed joints and high hermeticity in the resultant feedthrough.

The Ti-Zr-Co active braze alloy may comprise at least about 35 wt.% Zr and at least about 15 wt.% Ti and at least about 8 wt.% Co. The Ti-Zr-Co active braze alloy may comprise at least about 40 wt.% Zr and at least about 20 wt.% Ti and at least about 10 wt.% Co. The TiZr-Co active braze alloy may comprise Zr in the range of about 45 wt.% to about 50 wt.% and at least about 12 wt.% Co. The Ti-Zr-Co active braze alloy may comprise Zr in the range of about 46 wt.% to about 56 wt.% and Ti in the range of about 25 wt.% to about 35 wt.% and Co in the range of about 15 wt.% to about 25 wt.%.

The sum of Ti, Zr, and Co in the Ti-Zr-Co active braze alloy may exceed 95 wt.% based on the total weight of the active braze alloy. The sum of Ti, Zr, and Co in the Ti-Zr-Co active braze alloy may exceed 97 wt.% based on the total weight of the active braze alloy. The sum of Ti, Zr, and Co in the Ti-Zr-Co active braze alloy may exceed 99 wt.% based on the total weight of the active braze alloy.

The active braze alloy may include up to about 10 %wt of Cr based on the total weight of the active braze alloy. The active braze alloy may include up to about 5 %wt of Cr based on the total weight of the active braze alloy. The active braze alloy may include up to about 2 %wt Nb based on the total weight of the active braze alloy. The active braze alloy may include up to about 1 %wt of Mo based on the total weight of the active braze alloy.

The active braze alloy may comprise an active metal element. The active metal element may comprise one or more elements from the list consisting of Ti, Hf, Zr, Nb, Ta, or V. The active metal element in the range of 0.5 %wt to 10 %wt (or in the range of 1%wt to 51%wt) based on the total weight of the active braze alloy. In another embodiment, the active metal element is present in an amount ranging from about 10 %wt to about 50 %wt based on the total weight of the active braze alloy.

The active braze alloy may comprise one or more alloying elements selected from the list consisting of Co, Ni, Au, Al, Si, Cu, Ag, In, Cr, Ta, W, Mo, Fe or Pt or a combination or alloys thereof. The alloying elements may be present in the range of 50 wt% to 99.5 wt% based upon the total weight of the active braze alloy. In some embodiments the alloying elements are present in an amount ranging greater than 95 %wt or greater than 97.0 %wt based on the total weight of the active braze alloy.

The alloying elements may facilitate or promote the diffusion of the active metal element to the joint interface (16) in the formation of a hermetic seal or an active braze seal.

The active braze alloy may comprise one or more active metal elements and optionally one or more alloying elements to provide an alloy having a eutectic temperature so as to enable a reduced brazing temperature. The alloying elements may form an alloy having a eutectic temperature thereby enabling a reduced brazing temperature.

The active braze alloy may comprise a variety of different forms and geometries including but not limited to discs, wires, wire segments, sheets, shims, rings, washers, powders, foils, or pastes depending on the application and requirements. The active braze alloy may be a io braze foil with a thickness ranging from about 50 micron to about 250 micron. The active braze alloy may be derived from a layered structure having one or more layers.

The active metal element may react with the ceramic forming a chemical bond between the first side (3) of the ceramic body (2) and the active braze alloy, at the joint interface (16). The active metal element may react with the first side (3) of the ceramic body (2) resulting in the formation of a reaction product. The reaction product may form as a continuous reaction layer at the joint interface (16) The bonding layer (7) may comprise a reaction layer (17) proximal to the first side (3) of the ceramic body (2). The active metal element may be present in the reaction layer (17) in an amount ranging from about 70 %wt to about 99.5 %wt based on the total weight of the active braze alloy. The reaction product may comprise including but not limited to an oxide, carbide, nitride, or silicide reaction product depending on the ceramic material selected and the reactions between the active braze alloy and the first side (3) of the ceramic body (2).

The reaction layer (17) may comprise one or more elements originating from the active braze alloy. The reaction layer (17) may comprise one or more elements originating from the ceramic body (2). The reaction layer (17) may comprise one or more elements originating from the base layer (10). The reaction layer may comprise one or more brittle phases.

The reaction layer (17) may comprise one or more layers. The one or more layers may comprise a polycrystalline structure. The one or more layers may comprise one or more compounds The formation of the reaction layer (17) may depend on the chemical activity of the active metal element in the active braze alloy. The chemical activity of the active metal element may depend on the relative amounts of the active metal element and the alloying elements in the active braze alloy and the chemical affinity between them. The chemical activity of the active metal element may depend on the brazing temperature which provides a thermodynamic driving force for diffusion. The chemical activity of the active metal element may depend on the brazing time which provides the time for diffusion to occur at the brazing temperature.

The reaction layer (17) may be continuous layer along the joint interface (16). The reaction layer (17) may add a higher degree of metallic character to the first side (3) of the ceramic body (2) enabling the active braze alloy to wet and spread effectively over said first side (3) of the ceramic body (2). The chemical bond between the first side (3) of the ceramic body (2) and the active braze alloy at the joint interface (16) may provide a hermetic seal or an active braze seal. The reaction layer (17) at the joint interface may provide a hermetic seal or an active braze seal.

The reaction layer (17) may be less than 10 pm thick or less than 5 pm thick or less than 3 pm thick. In one embodiment the thickness of the reaction layer (17) ranges from about 1 pm to about 3 pm.

The bonding layer (7) may comprise one or more constituents comprising different properties, for example, strength, hardness, or coefficient of thermal expansion. The bonding layer (7) may comprise a layered structure having one or more layers (9).

The one or more layers (9) may comprise a first layer (9a) proximal to said first side (3) of said ceramic body (2). The first layer (9a) may provide a higher degree of metallic character to the first side (3) of the ceramic body (2). The first layer (9a) may comprise one or more elements originating from the active braze alloy. The first layer (9a) may comprise one or more elements originating from the ceramic body (2). The first layer (9a) may comprise one or more active metal elements. The first layer (9a) may comprise one or more alloying elements. The first layer (9a) may be a reaction layer (17).

The one or more layers (9) may comprise a second layer (9b) proximal to said first layer (9a). The second layer (9b) may wet and spread over the first layer (9a) during brazing. The second layer (9b) may comprise one or more elements originating from the active braze alloy. The second layer (9b) may comprise one or more alloying elements or combinations or alloys thereof. The second layer (9b) may comprise one or more active metal elements.

The first layer (9a) may enable the second layer (9b) to wet and spread effectively over said first layer (9a). The second layer (9b) may form due to the diffusion of the active metal element to the joint interface (16). The first layer (9a) may comprise one or more brittle constituents. The first layer (9a) may provide a medium for load transfer between the ceramic body (2) and the second layer (9b). The second layer (9b) may comprise one or more ductile constituents capable of plastic deformation. The second layer (9b) may provide a medium for accommodating thermally induced residual stresses or applied stresses.

The first conductive pad (6a) may comprise an outer layer (11) bonded to the bonding layer (7). The outer layer (11) may comprise one or more elements selected from the list consisting of Au, Pt, Ni, Cr, V, Cu, Ta, Ti, Nb, Al, Ag and Sn or combinations or alloys thereof.

The outer layer may function as a passivation barrier (e.g. when comprised of Au or Pt) and/ or as a further bonding layer to connect the conductive pad to further conductive elements, such as wires or other components of an electrical circuit.

The first side (3) of the ceramic body (2) may be provided with a two or more precursor layers (10). The precursor layers are transformed into the bonding layer (7) during the brazing step.

In one embodiment, the conductive pad (6a, 6b) is derived from two or more layers (10, 11) comprising a first layer (10a) bonded to the first side (3) of the ceramic body (2), a second layer (10b) bonded on top of the first layer (10a), and a third layer (11) bonded on top of the second layer (10b).

The first layer (10a) may comprise Ti and Nb. The second layer (10b) may comprise Ni. The third layer (11) may comprise Cr and/or Au.

The first layer (10a) may have a thickness in the range of about 0.1 micron to about 2 micron, or about 0.2 micron to about 1.75 micron, or about 0.3 micron to about 1.5 micron. The second layer (10b) may have a thickness in the range of about 0.1 micron to about 1 micron, or about 0.2 micron to about 0.9 micron, or about 0.3 micron to about 0.8 micron. The third layer (10c) may have a thickness in the range of about 0.1 micron to about 1.6 micron, or about 0.2 micron to about 1.4 micron, or about 0.3 micron to about 1.2 micron.

The first layer (10a) bonded to the first side (3) of the ceramic body (2) may comprise the steps of depositing the first layer (10a) on the first side (3) of the ceramic body (2). The second layer (10b) bonded to the first layer (10a) may comprise the steps of depositing the second layer (10b) on the first layer (10a). The third layer (11) bonded to the second layer (10b) may comprise the steps of depositing the third layer (11) on the second layer (10b).

The bonding layer (7) is preferably formed from the two precursor layers (10a, 10b) during the brazing step.

The outer layer (11) may comprise a coating to provide a passivafion layer over said bonding layer (7). The passivafion layer may protect the first conductive pad (6a) thereby contributing to the hermeticity of the feedthrough (1).

The outer layer (11) may fully encompass the bonding layer (7) so as to form a protective shell over said bonding layer (7) that is hermetic to further enhance the hermetic seal or the active braze seal. The outer layer (11) may comprise Au and/or Pt to provide said passivafion layer.

The outer layer (11) may provide a conductive pathway to the conductive element (5) through the bonding layer (7).

The outer layer (11) may provide further electrical connections to be made, for example, the outer layer (11) may provide a wire bonding site on the first side (3) of the ceramic body (2) for further electrical connections via said conductive pathway to the conductive element (5).

The outer layer (11) may have a thickness of less than about 10 micron or less than about 5 micron or less than about 3 micron or less than about 2 micron.

The feedthrough (1) may comprise a second conductive pad (6b) electrically connected to said conductive element (5) wherein said second conductive pad (6a) is bonded to said second side (4) of said ceramic body (2) through a bonding layer (7), said bonding layer (7) comprising an active braze alloy.

The second conductive pad (6b) may be electrically connected to the first conductive pad (6a) through said conductive element (5) thereby providing an electrical feedthrough with hermetic seals or active braze seals at both ends (14,15) of the conductive element (5).

The second conductive pad (6b) may comprise all embodiments of the first conductive pad (6a) as described herein.

The feedthrough (1) of the present invention may form part of an implantable medical device. 5 In a second aspect of the present disclosure, there is provided a method of producing a feedthrough (1) comprising a first conductive pad (6a) and/or a second conductive pad (6b) according to the first aspect of the present disclosure comprising the step of brazing a bonding layer (7) or a precursor (10) thereto (10) to the first side (3) and/or second side (4) lo of a ceramic body (2) and said conductive element (5), wherein the bonding layer comprises: (I) an active braze alloy; or (ii) said precursor to bonding layer forms a bonding layer comprising an active braze alloy during said brazing step.

The method of producing a feedthrough (1) may include pre-placing the active braze alloy on the first side (3) of the ceramic body (2) to form a brazing assembly. The active braze alloy may be brushed or painted onto the first side (3) of the ceramic body (2).

The bonding layer precursor may comprise two or more layers, each layer comprises different metals.

A method may further comprise the steps of depositing said bonding layer (7) or said two or more precursor layers (10) on the first side (3) of the ceramic body (2) using a thin film deposition technique such as sputter coating. The method of providing the base layer (10) to the first side (3) of the ceramic body (2) may comprise other thin film deposition techniques including but not limited to chemical vapour deposition, physical vapour deposition or screen printing or other thin film deposition techniques known in the art.

Brazing may be performed in a vacuum furnace at pressures ranging from about 4.0 x 10-4 to about 1.0 x 10-7 mbar. Brazing may be performed in a vacuum furnace at a pressure of less than about 1.0 x 10-5 mbar. Brazing may be performed in other chemically inert environments such as those comprising Ar or He or H gases or other chemically inert gases. The evacuation of oxygen in the chemically inert environment may promote diffusion of the active metal element to the joint interface (16).

The brazing assembly may be heated at a heating rate ranging from about 1 °C/min to about 15 °C/min. The brazing assembly may be heated to a brazing temperature for a predetermined time period or brazing time. The brazing assembly may be first heated to a temperature below the brazing temperature for a predetermined time period in the range of between about 2 minutes to about 15 minutes to enable thermal homogenization of all components of the brazing assembly. The brazing temperature may be at least 50°C above the liquidus temperature of the active braze alloy. The brazing temperature may be selected to at least melt a portion of the active braze alloy. The brazing temperature may be selected to enable the diffusion of the active metal element to the joint interface (16). The brazing io time may be in the range of about 1 minute to about 30 minutes, or about 2 minutes to about minutes, or about 3 minutes to about 20 minutes. The brazing time may provide the time available at the brazing temperature for the active metal element to diffuse to the joint interface (16). The brazing time may be selected to control the thickness of the reaction layer (17). The brazing assembly may be cooled at a cooling rate ranging from about 1 °C/min to about 10 °C/min. A slow cooling rate is preferred to minimise thermally induced residual stresses that may be generated as a result of a coefficient of thermal expansion mismatch at the joint interface (16).

The method of producing a feedthrough (1) may comprise a heat treatment comprising the steps of heating said feedthrough (1). The heat treatment may be applied following brazing said active braze alloy to said first side (3) of said ceramic body (2). The heat treatment may further densify the first conductive pad (6a). The heat treatment may further improve hermeticity of the feedthrough (1).

The method of producing a feedthrough (1) may include pre-placing the active braze alloy on the first side (3) of the ceramic body (2) to form a "brazing assembly". In some embodiments, the active braze alloy may be brushed or painted onto the first side (3) of the ceramic body (2), for example, in embodiments where the active braze alloy is in the form of a paste. The brazing assembly may be subsequently mounted in a vacuum furnace for brazing. As will be appreciated by those skilled in the art, brazing fixtures or fittings may be used to support the brazing assembly during brazing and a load may be applied to secure said brazing assembly during brazing. The fixtures or fittings may be cleaned prior to brazing, for example, in an ultrasonic bath comprising acetone or another cleaning agent for about 15 minutes, or using other cleaning methods such as using a vapour degreaser as will be appreciated by those skilled in the art. Optionally, thermocouples may be placed proximal to the brazing assembly to monitor or control the furnace temperature.

The method of producing a feedthrough (1) may further comprise a heat treatment comprising the steps of heating said feedthrough (1). The heat treatment may be applied following brazing said active braze alloy to said first side (3) of said ceramic body (2). The heat treatment may further densify the first conductive pad (6a). The heat treatment has been found to further improve hermeticity of the feedthrough (1).

A method for producing the outer layer (11) bonded to said bonding layer (7) may comprise the steps of brazing (or otherwise bonding) said outer layer (11) over said bonding layer (7).

The outer layer (11) may be bonded to said bonding layer (7) using a variety of possible bonding techniques including but not limited to welding, soldering, brazing, diffusion bonding, laser assisted diffusion bonding, laser welding, thermo-sonic bonding, ultrasonic bonding, soldering or flip chip bonding or other known joining techniques known in the art as will be appreciated by the skilled person.

The outer layer (11) may be bonded to said bonding layer (7) using a variety of thin film deposition techniques such as including but not limited to chemical vapour deposition, physical vapour deposition, sputter coating or screen printing or other thin film deposition techniques known in the art. The outer layer (11) may be applied by screen printing techniques.

Brief Description of Drawings

Embodiments will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which: Figure 1 shows a schematic cross-sectional representation of the feedthrough of the present invention in a first possible embodiment.

Figure 2a shows a schematic cross-sectional representation of the feedthrough of the present invention in a second possible embodiment.

Figure 2b shows a schematic cross-sectional representation of the feedthrough of the present invention in a third possible embodiment.

Figure 3 shows a schematic cross-sectional representation of the feedthrough of the present invention in a fourth possible embodiment.

Figure 4 shows a schematic cross-sectional representation of the feedthrough of the present invention in a fifth possible embodiment.

Figure 5 shows a schematic cross-sectional representation of the feedthrough of the present invention in a sixth possible embodiment.

Figure 6 shows a sectional SEM micrograph of a portion of the feedthrough of the present invention corresponding to the sixth possible embodiment.

Specific Description

The present invention provides an improved feedthrough device. The feedthrough may comprise assemblies comprising metal and ceramic components. The feedthrough may be used to transmit signals, high voltages, high currents, gases or fluids. The feedthrough may provide electrical insulation and high mechanical strength. The feedthrough may be hermetic and maintain ultra-high levels of vacuum and joint integrity that are maintained even at elevated temperatures, in cryogenic conditions, or in harsh environments such as in the human or animal body.

Brazing is one of the industrially preferred methods for joining ceramics whereby a braze alloy is melted at above 450°C on a ceramic surface. The use of metallic braze alloys often results in the poor wetting of chemically inert ceramic surfaces and the generation of thermally induced residual stresses upon cooling due to a coefficient of thermal expansion mismatch at the "joint interface" which can cause the brazed joint to fail prematurely. As will be appreciated by the skilled person, the joint interface comprises the interfacial region along the surfaces of two or more materials that are in contact or bonded together forming a joint.

The present disclosure employs the use of an "active braze alloy" to overcome the abovementioned problems. Brazing using an active braze alloy enhances the capability of providing a hermetic seal or an active braze seal. In one embodiment, the active braze alloy may comprise two or more elements selected from the list consisting of Ti, Hf, Zr, Nb, Ta, V, Co, Ni, Au, Al, Si, Cu, Ag, In, Cr, Ta, W and Mo, for example, an Ag-Ti active braze alloy. In another embodiment, the active braze alloy comprises one or more elements from the list consisting of Ti, Hf, Zr, Nb, Ta, or V. In a specific embodiment, the active braze alloy comprises one or more elements from the list consisting of Ti, Co, and Zr or combinations or alloys thereof to provide corrosion resistance or biocompatibility, for example, a Ti-Co-Zr active braze alloy. The active braze alloy may comprise Cr or Au additions to further enhance corrosion resistance or biocompatibility. In a further embodiment, the bonding layer (7) comprises Cr and/or Au.

In accordance with embodiments of the invention, Figure 1 shows a schematic cross-sectional representation of the feedthrough (1) of the present invention in a first possible embodiment. The feedthrough (1) comprises a ceramic body (2) having a first side (3) and a second side (4) and a conductive element (5) extending through said ceramic body (2) between said first side (3) and said second side (4). A first conductive pad (6a) is electrically io connected to said conductive element (5) wherein the first conductive pad (6a) is bonded to said first side (3) of said ceramic body (2) through a bonding layer (7), said bonding layer (7) comprising an active braze alloy. An optional second conductive pad (6b) is similarly bonded on the second side (4).

In one embodiment, the ceramic body (2) comprises alumina, a cost-effective ceramic material with excellent refractoriness, electrical insulation, wear-and corrosion-resistance making it suitable for use in vacuum feedthroughs and high voltage insulation applications. In another embodiment, the ceramic body (2) comprises ZTA, providing excellent mechanical strength, wear-resistance, and toughness. In another embodiment, the ceramic body (2) comprises YSZ.

The ceramic material selected may depend on the application. For example, alumina may be selected for ultra-high vacuum coaxial feedthroughs used in signal transmission, particle physics, thin film deposition or ion beam applications due to excellent dielectric properties which provides high-voltage insulation with little signal attenuation. Optionally, the ceramic body (2) may comprise a polycrystalline or monocrystalline alumina.

The first conductive pad (6a) electrically connected to the conductive element (5) and bonded to the first side (3) of the ceramic body (2) has been found to improve hermeticity of the feedthrough (1). The first conductive pad (6a) is bonded to the first side (3) of the ceramic body (2) through a bonding layer (7). The bonding layer (7) comprises an active braze alloy. The active braze alloy provides a hermetic seal or an "active braze seal" over said first side (3) of the ceramic body (2) and the conductive element (5). The bonding layer (7) may provide a conductive pathway or "interconnect" to the conductive element (5) without compromising the conductive performance of said conductive element (5). The active braze seal provided by the first conductive pad (6a) provides a feedthrough with improved hermeticity and performance while acting as an "interconnect' for further electrical connections to the conductive element (5).

The conductive element (5) may comprise any suitable conductive material such as Pt or Ir or combinations thereof. The conductive element (5) may comprise other conductive elements or materials. The conductive element (5) extends through the ceramic body (2) between said first side (3) and said second side (4).

Referring to Figures 2a and 2b, in other embodiments, the conductive element (5) io comprises a plurality of conductive sub-elements (5a). The plurality of conductive sub- elements (5a) may provide a densely packed feedthrough. The plurality of conductive sub-elements (5a) may provide a feedthrough (1) with one or more electrical conductors to increase the overall number of I/O signals as required for certain applications. The first conductive pad (6a) may be electrically connected to at least one of the conductive sub-elements (5a). Each of the plurality of conductive sub-elements (5a) may comprise one or more conductors with different properties, for example, a first pin comprising Pt, a second pin comprising Ir, and a wire comprising Pt and Ir.

Referring to Figures 1 to 2b, the conductive element (5) or plurality of conductive sub-elements (5a) extending through said ceramic body (2) between said first side (3) and said second side may comprise at least a first end (14, 14a) proximal to said first side (3) of said ceramic body (2) and a second end (15, 15a) proximal to said second side (4) of said ceramic body (2). In one embodiment, the first end (14, 14a) and the second end (15, 15a) of said conductive element (5) or plurality of conductive sub-elements (5a) is configured to be substantially parallel or flush with said first side (3) and said second side (4) of the ceramic body (2) respectively. The first end (14, 14a) and the second end (15, 15a) of said conductive element (5) or plurality of conductive sub-elements (5a) may be ground flat to be flush with said first side (3) and said second side (4) of the ceramic body (2) respectively. Optionally, the first end (14, 14a) and the second end (15, 15a) of said conductive element (5) or plurality of conductive sub-elements (5a) may protrude out of said first side (3) and said second side (4) of the ceramic body (2) respectively. Optionally, the first end (14, 14a) and the second end (15, 15a) of said conductive element (5) or plurality of conductive sub-elements (5a) may be sunken into said first side (3) and said second side of the ceramic body (2) respectively.

As illustrated in Figure 2b, the feedthrough may comprise the plurality of conductive elements (5), with each conductive element (5) extending from a first side (3) to a second side (4) and being encompassed by said ceramic body (2).

In one embodiment, the first conductive pad (6a) provides a conductive pathway to the conductive element (5). In another embodiment, the first conductive pad (6a) provides a conductive pathway to a plurality of conductive sub-elements (5a). In a further embodiment, as will be discussed hereinafter, the feedthrough (1) may further comprise a second conductive pad (6b) electrically connected to said conductive element (5) wherein said second conductive pad (6b) is bonded to said second side (4) of said ceramic body (2). The first conductive pad (6a) may be electrically connected to the second conductive pad (6b) through said conductive element (5).

The first conductive pad (6a) acts as an "interconnect" for further electrical connections to said conductive element (5). In another embodiment, the first conductive pad provides a first wire bonding site and a second conductive pad (6b) provides a second wire bonding site for further electrical connections to be connected to the feedthrough (1). The first conductive pad (6a) and the second conductive pad (6b) may each provide "interconnects" for further electrical connections to said conductive element (5).

In embodiments in which the further electrical connections are made to the conductive pad through mechanical connections, such as clamping, the bonding site preferably comprises a hard surface. Such hard surfaces may be obtained directly from the bonding layer or through the selection of an outer layer with the required hardness.

As will be appreciated by the skilled person, the conductive element (5) or the plurality of conductive sub-elements (5a) may be embedded in a ceramic matrix and compacted to form a green body that may subsequently be co-sintered to densify and impart mechanical strength to said green body compact forming a feedthrough (1) comprising the conductive element (5) or the plurality of conductive sub-elements (5a).

In one embodiment, the conductive element (5) or the plurality of conductive sub-elements (5a) is brazed to the ceramic body (2) between the first side (3) and second side (4) forming a brazed interface (12a). The brazed interface (12a) may comprise a braze filler alloy comprising one or more elements selected from the list consisting of Au, Cu, Ag, Ti, Ni or combinations or alloys thereof. The brazed interface (12a) may further comprise of one or more elements originating from the ceramic body (2). In another embodiment, the conductive element (5) or the plurality of conductive sub-elements (5a) is in braze-less contact with the ceramic body (2) between the first side (3) and second side (4) forming a braze-less interface (12b). The braze-less interface (12a) may enable fighter spacing between said conductive element (5) and said ceramic body (2) due to the lack of a braze filler alloy.

Optionally, the braze-less interface (12a) may enable tighter pin-to-pin spacing between said plurality of conductive sub-elements (5a) due to the lack of a braze filler alloy.

The conductive pads (6a, 6b) provide a hermetic barrier or hermetic seal, an airtight seal that lo may prevent the passage of air, oxygen, or other gases. The hermeticity, or leak-tightness, of a component may be tested using a variety of methods known in the art including leak testing. Leak testing is a non-destructive method used to locate and measure the size of leaks into or out of a component under vacuum or pressure. A tracer gas is introduced to the component connected to a leak detector. Helium leak testing is an effective test method for hermeticity due to the relatively small atomic size of helium atoms which may easily pass through any leaks in the component. Leak rates with a He hermeticity as low as 1.0 x 10' L. atm/s may be detected. For example, for a component required to be watertight, a leak rate with a He hermeticity of 1.0 x 10-4 Latmis would be sufficient. During a helium leak test, a pressure difference between an inner side and an outer side of a component under examination is produced.

In one embodiment, the bonding layer (7) comprises a Ti-Zr-Co active braze alloy. Brazing using an active braze alloy comprising Ti, Zr, and Co has been found by the inventors to provide good wettability and joint strength with a range of ceramic materials including but not limited to alumina, ZTA, and YSZ ceramics. The Ti-Zr-Co braze alloy is preferred due to its apparent good wettability which contributes to the formation of a hermetic seal or an active braze seal at the joint interface (16). The good wettability provided by the Ti-Zr-Co active braze alloy translates to strong brazed joint and high hermeticity in the resultant feedthrough (1).

In some embodiments, the bonding layer (7) has a Mohs hardness of at least 2.5 or at least 3.0 or at least 3.5 or at least 4.0 or at least 4.5. A high hardness value enables mechanical connections to be made, such as further electrical connections mechanically clamped to the first wire bonding site (5b) provided by the first conductive pad (6a). In applications requiring mechanical connections, the properties of the bonding layer (7) including hardness and strength may be sufficient without the need of a separate outer layer (11), as will be described hereinafter.

In some embodiments, the active braze alloy includes up to about 10 %wt Cr or up to about 5 5 %wt Cr or up to about 2 %wt Nb up to about 1 %wt Mo based on the total weight of the active braze alloy.

The alloying elements may host the active metal element in the active braze alloy. The alloying elements may facilitate or promote the diffusion of the active metal element to the o first side (3) of the ceramic body (2) in the formation of a hermetic seal or an active braze seal. The alloying elements may facilitate or promote the diffusion of the active metal element to the joint interface (16) in the formation of a hermetic seal or an active braze seal.

The alloying elements may comprise one or more elements with a low "chemical affinity" towards the active metal element. As will be appreciated by the skilled person, the low chemical affinity may comprise a low solubility to form phases or a low tendency to form compounds between the active metal element and the alloying elements.

The active metal element may be selected depending on the ceramic material to be brazed, for example, Ti may be selected for an alumina ceramic body (2). The active metal element selected may depend on the alloying elements in the active braze alloy and the chemical affinity between said active metal element and said alloying elements so as not to inhibit the diffusion of said active metal element to the joint interface (16) in the formation of a hermetic seal or an active braze seal.

The active metal element or the alloying elements selected in forming a suitable active braze alloy may further depend on the physical properties of the active braze alloy desired, such as strength, hardness, coefficient of thermal expansion, liquidus temperature, corrosion resistance, biocompatibility and electrical conductivity.

The active braze alloy may comprise one or more active metal elements or one or more alloying elements to provide an alloy having a eutectic temperature so as to enable a reduced brazing temperature. The alloying elements may form an alloy having a eutectic temperature thereby enabling a reduced brazing temperature. A reduced brazing temperature may help to minimise the generation of thermally induced residual stresses due to a coefficient of thermal expansion mismatch at the joint interface (16).

As will be appreciated by the skilled person, the active braze alloy may comprise a variety of different forms and geometries including but not limited to discs, wires, wire segments, sheets, shims, rings, washers, powders, foils, or pastes depending on the application and requirements.

In some embodiments, the active braze alloy may be derived from a layered structure having one or more layers. Each layer may different metals that have a eutectic temperature when formed into an alloy during the brazing process.

In some embodiments, the active braze alloy is in the form of a braze foil having a first central layer comprising the active metal element sandwiched between a first outer layer and a second outer layer. The first central layer may comprise a ribbon of said active metal element. The first outer layer and the second outer layer may comprise alloying elements.

Optionally, the active braze alloy may be manufactured into a braze foil via a cladding process whereby said first central layer is sandwiched between said first outer layer and said second outer layer. The braze foil may be roll-formed and rapidly solidified. Rapid solidification may enable relatively higher amounts of the active metal element to be physically contained in the braze foil without undesirable segregation of phases or compounds. The first central layer comprising the active metal element may be protected by the first outer layer and the second outer layer from reading with gases or vapours such as nitrogen, hydrogen, oxygen, water, etc. usually present in the atmosphere and in pumped down vacuum furnace chambers. In another embodiment, the active braze alloy comprising Ti, Zr, and Co may be derivable from three layers each comprising one of the elemental components, for example, a braze foil comprising a first layer comprising Ti, a second layer comprising Zr, and a third layer comprising Co. The braze foil may comprise one or more layers, each of the one or more layers may comprise one or more active metal elements or one or more alloying elements or combinations or alloys thereof.

Referring to Figure 3, in another embodiment, the bonding layer (7) comprising an active braze alloy comprises a reaction layer (17) proximal to the first side (3) of the ceramic body (2). In one embodiment, the reaction layer (17) substantially comprises of the active metal element. The active metal element is substantially present in the reaction layer (17) proximal to the first side (3) of the ceramic body (2). The active metal element may be present in the reaction layer (17) in an amount ranging from about 70 %wt to about 99.5 %wt based on the total weight of the active braze alloy.

The active metal element may react with the ceramic forming a chemical bond between the first side (3) of the ceramic body (2) and the active braze alloy, at the joint interface (16). During brazing, the active metal element may diffuse to the first side (3) of the ceramic body (2) leading to the formation of a hermetic seal or an active braze seal. The active metal element may react with the first side (3) of the ceramic body (2) resulting in the formation of a reaction product. The active metal element may reduce the ceramic surface of the first side (3) of the ceramic body (2) which may comprise including but not limited to oxygen, carbon, nitrogen or silicon depending on the ceramic material selected. The reaction product may io form as a layer along said joint interface (16), referred to herein as the "reaction layer" (17).

In some embodiments, a reaction layer (17) is present at the joint interface (16) between the bonding layer (7) and the first side (3) of the ceramic body (2). The reaction layer (17) may be continuous layer along the joint interface (16). The reaction product may comprise including but not limited to an oxide, carbide, nitride, or silicide reaction product depending on the ceramic material selected and the reactions between the active braze alloy and the first side (3) of the ceramic body (2). For example, the reaction layer (17) comprises an oxide reaction product when brazing an alumina ceramic or other oxide ceramic using an active braze alloy. The chemical bond between the first side (3) of the ceramic body (2) and the active braze alloy at the joint interface (16) may provide a hermetic seal or an active braze seal. The reaction layer (17) at the joint interface may provide a hermetic seal or an active braze seal.

The reaction layer (17) may add a higher degree of metallic character to the first side (3) of the ceramic body (2) enabling the active braze alloy to wet and spread effectively over said first side (3) of the ceramic body (2). The reaction layer (17) may comprise one or more elements originating from the active braze alloy. The reaction layer (17) may further comprise one or more elements originating from the ceramic body (2). For example, brazing an alumina ceramic using an active braze alloy comprising Ti as the active metal element results in a reaction layer (17) comprising Ti, 0, and Al. Optionally, the reaction layer (17) may comprise one or more elements originating from the ceramic body (2) including one or more impurities or one or more secondary phase elements. For example, ceramic materials that are liquid phase sintered may comprise secondary phase elements including but not limited to Ca, Mg and Si that may react with one or more elements in the active braze alloy.

In some embodiments, the active metal element is present in the active braze alloy in small amounts suitable for enabling said active braze alloy to wet and spread effectively over the ceramic surface through the formation of a continuous reaction layer (17). In some embodiments, the reaction layer (17) may be discontinuous, for example, when using active braze alloys with reduced amounts of the active metal element. The presence and amount of the active metal element in the active braze alloy may influence the properties of the reaction layer (17). The properties of the reaction layer (17) include but are not limited to its continuity at the joint interface (16) and its thickness. The continuity or thickness of the reaction layer (17) may provide a good indication of chemical bonding at the joint interface (16) and the formation of a hermetic seal or an active braze seal.

io The bonding layer (7) may comprise one or more constituents such as phases or compounds comprising different properties, for example, strength, hardness, or coefficient of thermal expansion. In some embodiments, the bonding layer (7) comprises a layered structure having one or more layers (9). In one embodiment, the one or more layers (9) comprises a first layer (9a) proximal to said first side (3) of said ceramic body (2). The first layer (9a) may provide a higher degree of metallic character to the first side (3) of the ceramic body (2). The first layer (9a) may comprise one or more elements originating from the active braze alloy. The first layer (9a) may further comprise one or more elements originating from the ceramic body (2). In specific embodiments, the first layer (9a) may comprise one or more active metal elements. The first layer (9a) may further comprise one or more alloying elements.

In some embodiments, the first layer (9a) is a reaction layer (17). The one or more layers (9) may further comprise a second layer (9b) bonded on top of said first layer (9a). The second layer (9b) may wet and spread over the first layer (9a) during brazing. The second layer (9b) may comprise one or more elements originating from the active braze alloy. In specific embodiments, the second layer (9b) may comprise one or more alloying elements or combinations or alloys thereof. The second layer (9b) may further comprise one or more active metal elements, for example, in embodiments where the active metal element does not completely diffuse to the joint interface (16).

In specific embodiments, the first layer (9a) comprises the active metal element and the second layer (9b) comprises the alloying elements. The first layer (9a) enables the second layer (9a) to wet and spread effectively over said first layer (9a). The second layer (9b) forms due to the diffusion of the active metal element to the joint interface (16). The active metal element may be present in the first layer (9a) in an amount ranging from about 70 %wt to about 99.5 %wt based on the total weight of the active braze alloy. The first layer (9a) may comprise one or more brittle constituents. The first layer (9a) may provide a medium for load transfer between the ceramic body (2) and the second layer (9b). The second layer (9b) may comprise one or more ductile constituents capable of plastic deformation. The second layer (9b) may provide a medium for accommodating thermally induced residual stresses or applied stresses.

Referring to Figure 4, in another embodiment, the bonding layer (7) comprising an active braze alloy comprises a reaction layer (17) proximal to the first side (3) of the ceramic body (2) having one or more layers (18).

In one embodiment, the one or more layers (18) comprises a first layer (18a) and a second layer (18b), the first layer (18a) is proximal to the first side (3) of the ceramic (2) body and the second layer (18b) is bonded on top of the first layer (18a). In another embodiment, the reaction layer (17) comprises the first layer (18a). In another embodiment, the reaction layer (17) comprises the second layer (18b). For example, in some embodiments, the ceramic body (2) comprises an alumina ceramic and the active braze alloy comprises an active metal element and alloying elements. The alloying elements comprises an Ag-Cu eutectic alloy with around 72 %wt Ag and around 28 %wt Cu. In one embodiment, the active metal element comprises Ti in the range of about 1.75 to about 4.5 %wt. The reaction layer (17) comprises the first layer (18a) comprising a thin (e.g. nanometer(s) thick) TiO layer and the second layer (18b) comprising a Ti3Cu30. In another embodiment, the active metal element comprises Ti in the range of less than 1.75 %wt. The reaction layer (17) comprises the first layer (18a) comprising a thin TiO layer. In another embodiment, the active metal element comprises Ti in the range of at least 4.5 %wt. The reaction layer (17) comprises the second layer (18b) comprising Ti3Cu30.

Referring to Figure 5, in another embodiment, the first side (3) of the ceramic body (2) is provided with a bonding layer precursor (10a, 10b) having two or more layers. The first layer (10a) comprises Ti and Nb or Co and Nb, the second layer (10b) comprises Ni, and the third layer (11) comprises Cr and/or Au.

Referring to Figure 6, a sectional scanning electron microscope (SEM) micrograph shows a portion of the feedthrough. The conductive pad (6a) comprises a bonding layer (7), derived from precursor layers (10a, 10b) of Figure 5, and the outer layer (11). The first layer (10a) comprises Ti and Nb, the second layer (10b) comprises Ni, and the third layer (11) comprises Au. The first layer (10a) was sputter coated on the first side (3) of the ceramic body (2) to a thickness in the range of about 0.5 micron to 1.2 micron. The second layer (10b) was sputter coated on the first layer (10a) to a thickness of about 0.3 micron to about 0.6 micron. The third layer (11) was sputter coated on the second layer (10b) to a thickness of about 0.4 micron to 1.0 micron.

Experimental The hermeticity tests were first performed on the nine samples of the feedthrough with and without a conductive pad. The conductive pad was derived from a three layer braze io assembly structure as represented in Figure 5 which was brazed to produce the brazed article of Figure 6.

The feedthroughs were tested for hermeticity using the protocol of MIL-STD-883 test method 1014 and test condition.

Table 1 shows the results of hermeticity testing performed on nine samples of this embodiment, according to the method discussed herein.

The hermeticity tests were subsequently repeated after the first conductive pad was bonded to the first side of said ceramic body. The results showed that the conductive pad provided the feedthrough with an improved hermetic seal or an active braze seal over said first side of the ceramic body.

For each sample, a decrease in the He hermeticity was observed. The average He hermeticity decreased from 2.7 x 10-6 Latm/s to 9.4 x 10-6 Latm/s for the nine samples.

Hermeticity (Latm/s) Sample Without conductive pad With conductive pad 1 6.4x10-16 8.2x10-11 2 5.2x10-9 3.1x10-1° 3 1.3x10-9 6.1x10-11 4 1.9x10-16 2.2x10-1° 4.2x10-6 3.1x10-6 6 3.9x10-7 1.6x10-8 7 8.2x10-6 3.3x10-9 8 7.1x10-6 2.4x10-9 9 4.8x10-6 3.1x10-8 Average 2.7x10-6 9.4x10-9

Table 1

Claims

CLAIMS: 1. A feedthrough (1) comprising: a ceramic body (2) having a first side (3) and a second side (4); a conductive element (5) extending through said ceramic body (2) between said first side (3) and said second side (4); a first conductive pad (6a) electrically connected to said conductive element (5); wherein the first conductive pad (6a) is bonded to said first side (3) of said ceramic body (2) through a bonding layer (7), said bonding layer (7) comprising an active braze alloy.
2. A feedthrough (1) as claimed in claim 1 comprising a plurality of conductive elements (5) 3.
The feedthrough as claimed in claim 2, wherein the density of the conductive elements (5) exceeds 1 conductor per 100,000 pm2through a planar cross-section of the ceramic body (2).
A feedthrough (1) as claimed in any one of claims 1 to 3, wherein said conductive element (5) is in braze-less contact with said ceramic body (2) between said first side (3) and said second side (4) forming a braze-less interface (12a).
5. A feedthrough (1) as claimed in claims 1 to 4 wherein said conductive element (5) is brazed to said ceramic body (2) between said first side (3) and said second side (4) forming a brazed interface (12b).
6. A feedthrough (1) as claimed in claim 5 wherein said brazed interface (12b) comprises one or more elements selected from the list consisting of Au, Cu, Ag, Ni or combinations or alloys thereof.
7. A feedthrough (1) as claimed in claims 1 to 6 wherein said active braze alloy comprises two or more elements selected from the list consisting of Ti, Zr, Nb, Ta, V, Hf, Co, Ni, Au, Al, Si, Cu, Ag, In, Cr, Ta, W and Mo.
8. A feedthrough (1) as claimed in claims 1 to 7 wherein said active braze alloy comprises one or more elements from the list consisting of Ti, Zr, Nb, Ta, V and Hf.
9. A feedthrough (1) as claimed in claims 1 to 8 wherein said active braze alloy comprises Ti and/or Zr.
10. A feedthrough (1) as claimed in claims 1 to 9 wherein said active braze alloy comprises at least one of Co, Ni and Nb.
11. A feedthrough (1) as claim in claims 1 to 10, wherein the active braze alloy comprises: 46 wt.% to about 56 wt.% Zr; wt.% to about 35 wt.% Ti; and 15 wt.% to about 25 wt.% Co.
12.
13.
14.
15.
16.A feedthrough (1) as claimed in claims 1 to 11 wherein said bonding layer (7) is derivable from a layered structure having two or more layers (9).A feedthrough (1) as claimed in claims 1 to 11 wherein said first conductive pad (6a) further comprises an outer layer (11) bonded to said bonding layer (7).A feedthrough (1) as claimed in claim 13 wherein said outer layer (11) comprises one or more elements selected from the list consisting of Au, Pt, Ni, Cr, V, Cu, Ta, Ti, Nb, Al, Ag and Sn or combinations or alloys thereof.A feedthrough (1) according to any one of the preceding claims further comprising a second conductive pad (6b) electrically connected to said conductive element (5) wherein said second conductive pad (6b) is bonded to said second side (3) of said ceramic body (2) through said bonding layer (7).A feedthrough (1) as claimed in any of the preceding claims wherein said feedthrough (1) has a He hermeticity of less than 1.0 x 10 atm/s.
17. A feedthrough (1) as claimed in any of the preceding claims wherein said feedthrough (1) is an implantable medical device.
18. A method of producing a feedthrough (1) comprising a first conductive pad (6a) and/or a second conductive pad (6b) according to any one of the preceding claims comprising the step of brazing a bonding layer (7) or a precursor (10) thereto to the first side (3) and/or second side (4) of a ceramic body (2) and said conductive element (5), wherein the bonding layer comprises: an active braze alloy; or io said precursor to bonding layer forms the bonding layer (7) comprising an active braze alloy during said brazing step.
19. The method according to claim 18, wherein the bonding layer precursor comprises two or more layers, each layer comprises different metals.
20. The method according to claim 19, comprising a first layer comprising one of more elements selected from the list consisting of Ti, Zr, Nb, Ta, V, 1-1fi and a second layer comprising one of more elements selected from the list consisting of Co, Ni, Au, Al, Si, Cu, Ag, In, Cr, Ta, W and Mo.
21. The method according to claims 18 to 20 comprising the steps of depositing said bonding layer (7) or precursor thereto (10) on said first side of said ceramic body (2) using a thin film deposition technique such as chemical vapour deposition, physical vapour deposition, sputter coating or screen printing.
22. The method according to any one of claims 18 to 21, further comprising the step of bonding an outer layer (11) over said bonding layer (7).
23. The method according to claims 18 to 22 wherein said outer layer (11) comprises one or more elements selected from the list consisting of Au, Pt, Ni, Cr, V, Cu, Ta, Ti, Nb, Al, Ag, and Sn.