Hermetic feedthrough assembly for ceramic body

Abstract

A wire extends through a ceramic body. The wire comprises a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium. The wire directly contacts the ceramic body to form a substantially hermetic seal between the ceramic body and the wire.

Claims

1. A feedthrough assembly formed from a method comprising: providing a green ceramic body; forming a through-hole in the green ceramic body having a first diameter; inserting a corrosion-resistant solid wire through the hole, the wire comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium, and the wire having a second diameter; firing the green ceramic body to sinter it thereby forming a sintered ceramic body; and the first and second diameters being selected such that cracking of the sintered ceramic body adjacent the wire as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and the wire, wherein the green ceramic body has a thickness of at least 0.050 inches thick.

2. The feedthrough assembly of claim 1, further comprising an electrode connected to a first end of the wire.

3. The feedthrough assembly of claim 2, wherein the electrode is substantially coplanar with a surface of the sintered ceramic body.

4. The feedthrough assembly of claim 1, wherein the hermetic seal is a diffusion bond between the metal wire and the sintered ceramic body.

5. The feedthrough assembly of claim 1, wherein the wire has a diameter of less than about 0.020 inches.

6. The feedthrough assembly of claim 1, wherein the ceramic body comprises primarily compounds selected from the group consisting of oxides, carbides, borides, nitrides, and silicides of aluminum, zirconium, beryllium, silicon, titanium, hafnium, magnesium, zinc and yttrium.

7. The feedthrough assembly of claim 1, wherein the green ceramic body has a thickness of less than about 0.10 inches.

8. The feedthrough assembly of claim 1, wherein the wire has a diameter of less than about 0.020 inches and the green ceramic body has a thickness of less than about 0.10 inches.

9. The feedthrough assembly of claim 1, wherein the metal wire has a substantially round cross-section or a substantially conical shape.

10. The feedthrough assembly of claim 1, wherein the segment of wire contacting the ceramic body has a substantially spherical shape.

11. The feedthrough assembly of claim 1, further comprising a contact pad connected to a second end of the wire.

12. A feedthrough assembly formed from a method comprising: providing a green ceramic body that surrounds a corrosion-resistant solid wire extending through the green ceramic body, the wire comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium; and firing the green ceramic body to sinter it, thereby forming a sintered ceramic body; whereby cracking of the sintered ceramic body adjacent the wire as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and the wire, and wherein the green ceramic body has a thickness of at least 0.050 inches thick.

13. The feedthrough assembly of claim 12, further comprising an electrode connected to a first end of the wire.

14. The feedthrough assembly of claim 13, wherein the electrode is substantially coplanar with a surface of the sintered ceramic body.

15. The feedthrough assembly of claim 12, wherein the hermetic seal is a diffusion bond between the metal wire and the sintered ceramic body.

16. The feedthrough assembly of claim 12, wherein the wire has a diameter of less than about 0.020 inches.

17. The feedthrough assembly of claim 12, wherein the ceramic body comprises primarily compounds selected from the group consisting of oxides, carbides, borides, nitrides and silicides of aluminum, zirconium, beryllium, silicon, titanium, hafnium, magnesium, zinc and yttrium.

18. The feedthrough assembly of claim 12, wherein the green ceramic body has a thickness of less than about 0.10 inches.

19. The feedthrough assembly of claim 12, wherein the wire has a diameter of less than about 0.020 inches and the green ceramic body has a thickness of less than about 0.10 inches.

20. The feedthrough assembly of claim 12, wherein the wire has a substantially round cross-section or a substantially conical shape.

21. The feedthrough assembly of claim 12, wherein the segment of wire contacting the ceramic body has a substantially spherical shape.

22. The feedthrough assembly of claim 12, further comprising a contact pad connected to a second end of the wire.

23. A multi-conductor feedthrough assembly formed from a method comprising: providing a green ceramic body; forming at least two through-holes in the green ceramic body, each through-hole having a first or second diameter; inserting a corrosion-resistant solid wire through each through-hole, each wire comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium, and each wire having a third or fourth diameter; firing the green ceramic body to sinter it, thereby forming a sintered ceramic body; and the first, second, third and fourth diameters being selected such that cracking of the sintered ceramic body adjacent each wire as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and each wire, wherein the green ceramic body has a thickness of at least 0.050 inches thick.

24. A multi-conductor feedthrough assembly formed from a method comprising: providing a green ceramic body that surrounds a plurality of corrosion-resistant solid wires extending through the green ceramic body, the wires each comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium; and firing the green ceramic body to sinter it, thereby forming a sintered ceramic body; whereby cracking of the sintered ceramic body adjacent each of the plurality of wires as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and each of the plurality of wires, and wherein the green ceramic body has a thickness of at least 0.050 inches thick.

25. An implantable glucose-level sensing device, comprising a feedthrough assembly formed from a method comprising: providing a green ceramic body; forming a through-hole in the green ceramic body having a first diameter; inserting a corrosion-resistant solid wire through the hole, the wire comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium, and the wire having a second diameter; firing the green ceramic body to sinter it, thereby forming a sintered ceramic body; and the first and second diameters being selected such that cracking of the sintered ceramic body adjacent the wire as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and the wire, wherein the green ceramic body has a thickness of at least 0.050 inches thick.

26. An implantable glucose-level sensing device, comprising a feedthrough assembly formed from a method comprising: providing a green ceramic body that surrounds at least a portion of a corrosion-resistant solid wire extending through the green ceramic body, the wire comprising a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium and alloys of platinum, palladium, rhodium, iridium, and osmium; and firing the green ceramic body to sinter it, thereby providing a sintered ceramic body; whereby cracking of the sintered ceramic body adjacent the wire as a result of dimensional changes of the green ceramic body during firing is avoided and a substantially hermetic seal is formed between the sintered ceramic body and the wire, wherein the green ceramic body has a thickness of at least 0.050 inches thick.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1, 2 and 3 are a sequence of diagrammatic vertical sectional views illustrating a method of fabricating a feedthrough assembly in accordance with an embodiment of the invention.

(2) FIG. 4 is a flow diagram of an exemplary method of producing a substantially hermetic feedthrough in a ceramic body where an initial configuration includes the first diameter less than, or equal to, the second diameter.

(3) FIG. 5 is a flow diagram of an exemplary method of producing a substantially hermetic feedthrough in a ceramic body where an initial configuration includes the first diameter greater than the second diameter.

(4) FIG. 6 is a diagrammatic vertical sectional view of an implantable glucose-level sensing device incorporating the feedthrough assembly of FIG. 3.

(5) FIG. 7 is a fragmentary plan view of a portion of the exterior of the container of the sensing device of FIG. 6 illustrating the electrodes of its glucose-responsive detector and its optional background oxygen detector.

DETAILED DESCRIPTION OF THE INVENTION

(6) The entire disclosure of co-pending U.S. patent application Ser. No. 10/925,074 of Mark B. Catlin and Dr. Joseph Y. Lucisano filed Aug. 23, 2004 is hereby incorporated by reference.

(7) There is a need for a feedthrough in a ceramic body that: (1) provides a reliable hermetic seal to prevent moisture, gases, or other vapors on one side of the ceramic body from penetrating the feedthrough and interfering with, reacting with, or damaging electronic circuitry or other sensitive structures or materials on the other side of the ceramic body; (2) allows a multitude of separate electrical pathways to be constructed in a relatively small area; (3) can be constructed using chemically, electrolytically, and physically stable materials, for example materials that are acceptable for implantable applications (otherwise referred to as “biocompatible materials”); and (4) is fabricated using a simplified technique.

(8) Referring to FIG. 1, in accordance with an embodiment of the invention, a method of forming a feedthrough assembly in a ceramic body includes the steps of providing a green ceramic body 10 (FIG. 1) and forming a hole 12 in the green ceramic body 10. The green ceramic body may be made of a powdered inorganic component comprising oxides, carbides, borides, nitrides and silicides of aluminum, zirconium, beryllium, silicon, titanium, yttrium, hafnium, magnesium, and zinc, combined with an organic binder and optionally other organic compounds. The body may be produced using conventional green ceramic forming techniques, such as roll compaction, tape casting, pressing, or molding.

(9) Volume ratios of inorganic powder to organic binder may range from 50:50 to 100:0 with a range of 70:30 to 95:5 being preferred, and a range of 80:20 to 90:10 being most preferred. Major constituents of preferred inorganic powders are: (1) alumina, for example A-16, manufactured by Alcoa and C90LSB, manufactured by Alcan Chemicals; (2) yttria-stabilized zirconia, for example HSY-3 manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.; and (3) mixtures and combinations thereof, although numerous other ceramic powders and mixtures can be used. A wide range of particle sizes is acceptable, so long as the particles sinter during firing such that the bulk of the green ceramic body 10 becomes hermetic after firing. Consistent with conventional ceramic processing guidelines, powders with median particle sizes ranging from 0.2 microns to 2 microns are preferred. Numerous organic binders and binder systems are suitable, so long as they can be decomposed or otherwise removed at a temperature below the sintering temperature of the ceramic powder. Examples of acceptable binders include various waxes, polyvinyl acetate, polyvinyl alcohol, polymethylmethacrylate (PMMA), polyvinyl butyral, polyethylene glycol (PEG), polyethylene oxide, ethylene-vinyl acetate copolymers, and numerous other compounds, as single components or mixtures, either plasticized by incorporation of additional organic compounds, or unplasticized. The binder may also include one or more dispersing agents, wetting agents, or fillers.

(10) Because of the innate chemical stability of fired ceramics that contain high concentrations of alumina, inorganic powder formulations containing 95% or greater alumina are preferred, and formulations containing 99% or greater are most preferred, including, for example, formulations that provide ceramics meeting the composition requirements of industry standard ASTM F 603-00. In preferred formulations, the 1% to 5% other oxides in the inorganic powder typically include oxides of lower melting point, which function as high temperature flux to aid in sintering. Other formulations may be employed when chemical stability requirements are less stringent, including other combinations of ceramic powders with varying amounts of glasses. Formulations containing zirconia, and/or yttria-stabilized zirconia, alone or in combination with alumina, may be selected when mechanical strength is of high importance.

(11) The hole 12 may be formed by mechanical drilling or punching, or it may be formed with a high pressure water stream, or it may be formed with a laser, or it may be formed by molding, or it may be formed in any other suitable way that allows control over both its location and diameter. The thickness of the green ceramic body 10 in the region of the hole 12 may be of any dimension appropriate to meet the mechanical strength requirements for the intended application of the assembly, with a minimum thickness of 0.002 inch being preferred and a minimum thickness of 0.025 inch being most preferred.

(12) The next step of the method involves inserting a wire 14 (FIG. 2) through the hole 12. A small drop of liquid, for example water or an organic liquid such as cyclohexanone, may optionally be applied to the hole 12 as a lubricant to aid insertion of the wire. When using such a lubricant, it is important not to select a compound that acts too aggressively as a solvent for the organic binder system in the green ceramic, because the disruption of the green ceramic produced by application of the lubricant could result in the fired assembly being non-hermetic. The term “wire” is used herein to denote a metallic, electrically-conductive structure that: (1) may be of various uniform and non-uniform cross-sectional geometries, the most typical being uniform circular; and (2) has at least one solid cross section contained within the ceramic body. The wire 14 comprises a material selected from the group consisting of platinum, palladium, rhodium, iridium, osmium, and alloys of platinum, palladium, rhodium, iridium, and osmium, and may have one or both ends tapered or rounded to facilitate insertion. Platinum and the other metals listed for the wire 14 are specified not only for their electrical conductivity, but also because they are biocompatible, resist corrosion in the presence of liquids, and have melting points greater than the required firing temperature of the ceramic. Wires made from platinum and iridium are preferred, and wires made from pure platinum, of a minimum 99% purity, are most preferred. Wire diameters may range from 0.001 inch to 0.100 inch, with 0.002 inch to 0.040 inch being preferred, and 0.005 inch to 0.020 inch being most preferred.

(13) In another embodiment, the wire 14 is inserted through the green ceramic body 10 by pushing or pressing the wire 14 through a solid green ceramic body, without first forming a hole, eliminating the need to separately produce the hole 12.

(14) In another embodiment, the green ceramic body 10 is formed around the wire 14 by molding or pressing green ceramic material in a mold that contains the wire 14, eliminating the need to separately produce the hole 12. Such a process is commonly referred to as “insert molding.”

(15) In another embodiment, the green ceramic body 10 is formed around the wire 14 by first forming a hole 12 in the green ceramic body, placing a wire 14 in the hole 12, and then pressing the assembly in a mold to cause the green body material to flow into close contact with the wire 12.

(16) In the embodiments, the green ceramic body 10 containing the wire 14 is fired to vaporize the organic compounds in the green material and to sinter the ceramic particles, resulting in a rigid, solid structure of high density. Firing is preferably accomplished by heating the green ceramic body in air to temperatures between about 1500 and about 1700 degrees Celsius for periods of at least about 10 minutes to 4 hours.

(17) In one embodiment, the feedthrough assembly 16 (FIG. 3) has a disc-shaped electrode 18 connected to one end of the wire 14 on an exterior side of the fired ceramic body 10′ and a disc-shaped contact 20 connected to the other end of the wire 14 on an interior side of the fired ceramic body 10′. The electrode 18 and contact 20 can be separate pieces of metal formed and bonded to the wire 14 and made of the same metal as the wire 14. Preferably the electrode 18 and contact 20 are formed by trimming the wire above the surface of the fired ceramic body 10′ and flattening the opposite ends of the wire 14 into a disc-shaped configuration. Preferred methods for flattening the ends of wire 14 include grinding and polishing using diamond-based abrasive media, which can also serve to flatten the exposed ceramic surfaces, which may be slightly warped or rough immediately after firing.

(18) The diameter of the hole 12 in the green body 10 and the diameter of the wire 14 are selected such that a close fit is achieved upon insertion of the wire 14 into the hole 12 in the green ceramic body 10 and, after shrinkage of the green ceramic body 10 during firing, a substantially hermetic seal is formed between the sintered ceramic and the wire 14. It is very important that the feedthrough assembly 16 provide a substantially hermetic seal, i.e., that moisture will not creep or diffuse from one side of the fired ceramic body 10′ to the other side between the fired ceramic body 10′ and the wire. It is believed that what is termed in the art a “diffusion bond” or “reaction bond” may be formed between the wire 14 and the fired ceramic body 10′ which provides a high degree of hermeticity. Tests have proven that there is a wide range of allowable diameters of the wire 14, diameters of the hole 12, and thicknesses of the green ceramic body 10 that can be used to achieve the desired hermeticity. The diameter of the hole 12 should be close in dimension to the diameter of the wire 14, but it should not be so small that cracking or significant disruption of the green ceramic material occurs upon insertion of the wire or firing thereafter. In practice, a 0.0005 inch to 0.002 inch differential in diameters, with the wire diameter either larger or smaller than the hole diameter, is preferred to produce acceptable results, although larger differentials may be acceptable when using large diameter wires (for example, greater than 0.020 inch diameter).

(19) In the practice of the method, the initial choice of green body 10, first diameter, second diameter, and wire is herein referred to as an initial configuration. The method of the invention provides means for iterative refinement of the initial configuration to achieve successful levels of hermeticity in the completed feedthroughs.

(20) In an initial configuration, the first diameter may be greater than, equal to, or less than the second diameter. The success rate of hermeticity after firing is dependent upon the choice of first and second diameters and upon the material properties of the green body 10. Brittle green ceramic bodies may fracture upon wire insertion or during early or intermediate stages of the firing process if the first diameter is significantly smaller than the second diameter, thus decreasing success rates. More ductile green bodies may be capable of plastic deformations which can lead to higher success rates with first diameters that are equal to or smaller than the second diameters.

(21) In the method, the green ceramic body 10 with inserted wire 14 is fired to sinter the green ceramic body 10 and produce the fired ceramic body 10′. The diameter of the hole in the green body and the diameter of the wire are selected such that the shrinkage of the ceramic body during firing results in the development of a substantially hermetic seal between the sintered ceramic body and the wire. Techniques are disclosed to guide selection and optimization of the hole size and wire size to achieve substantially hermetic seals.

(22) The wire 14 is preferably in intimate association with the fired ceramic body 10′ throughout the length of its contact, although the invention requires only that the wire 14 and the fired ceramic body 10′ be circumferentially hermetically joined in at least one location along the length of the wire 14.

(23) FIGS. 4 and 5 are flow diagrams that illustrate alternate embodiments of the method of the present invention. FIG. 4 illustrates an embodiment of a method for achieving a substantially hermetic feedthrough in a body where an initial configuration includes the first diameter less than, or equal to, the second diameter. FIG. 5 illustrates an embodiment of a method for achieving a substantially hermetic feedthrough in a body where an initial configuration includes the first diameter greater than the second diameter. These embodiments exemplify techniques that lead to substantially hermetic feedthroughs but are not inclusive of all possible methods for producing the invention described herein.

(24) The following is a brief description of the embodiment illustrated in FIG. 4 of the method for creating a hermetic seal in a body having an initial configuration with the first diameter less than, or equal to, the second diameter. This embodiment is preferred if the green body appears ductile such that it may support sufficient plastic deformation to avoid cracking or other mechanical failure during wire insertion, however this case may also be implemented with brittle green bodies. The first step 100 is to create an initial configuration with a hole diameter less than, or equal to, the wire diameter. In step 102 the wire is inserted in the green ceramic body. The wire is inserted into the hole in the green body or directly into the green body without a pre-defined hole. In step 104 the existence of significant body damage is determined. If cracking or significant mechanical damage is visible, the first diameter is enlarged in step 106, iteratively, in new ceramic bodies until such mechanical damage is not observed upon wire insertion in step 102. Once a wire has been inserted into the green body without significant body damage the body is fired in step 108 and its hermetic seal is tested in step 110. If the seal is not substantially hermetic, the first diameter is again increased by creating a new green ceramic body with a larger hole in step 112 and steps 102, 104, 108, and 110 are repeated until substantial hermeticity is established in step 114 and the assembly is complete. Once the parameters for substantial hermeticity have been established, additional assemblies may be produced using the selected materials and determined dimensions.

(25) The following is a brief description of the embodiment illustrated in FIG. 5 of the method for creating a hermetic seal in a body having an initial configuration with the first diameter greater than the second diameter. The embodiment of FIG. 5 is preferred if the green body appears brittle such that it may not support sufficient plastic deformation to avoid cracking or other gross mechanical failure during wire insertion, however this case may also be implemented with ductile green bodies. The first step 200 is to create an initial configuration with a hole diameter greater than the wire diameter. An initial configuration is chosen such that the first diameter is greater than the second diameter. In step 202 the wire is inserted into the hole in the green ceramic body. In step 204 the assembly is fired and inspected and then the hermetic seal is tested to ensure that the body is in intimate contact with the wire due to body shrinkage during sintering. In step 206 if intimate ceramic-wire contact is not observed, the first diameter is decreased in a new ceramic body in step 208, iteratively, in new ceramic bodies, and steps 202, 204, and 206 are repeated until intimate ceramic-wire contact is observed. The seal between the wire and the fired ceramic body is then tested in step 210. If the seal is not substantially hermetic, the first diameter is again decreased in a new ceramic body in step 212 and steps 202, 204, 206, and 210 are repeated until substantial hermeticity is established in step 214 and the assembly is complete. Once the parameters for substantial hermeticity have been established, additional assemblies may be produced using the selected materials and determined dimensions.

(26) In accordance with another embodiment of the invention an implantable glucose-level sensing device 30 (FIG. 6) includes a generally circular or rectangular container 32 having a ceramic body 34 forming at least a portion thereof. The remainder 36 of the container 32 is preferably made of a metal such as titanium and is hermetically joined to the ceramic body 34 via brazing 38. Six electrodes 40, 42, 44, 46, 48 and 50 (FIG. 7) are formed on an exterior surface of the ceramic body 34 for contacting fluid in body tissue 52 (FIG. 6) when implanted. A plurality of feedthrough assemblies such as 54 are formed in the ceramic body 34, each electrically connected to a corresponding one of the electrodes. Each of the feedthrough assemblies 54 is constructed in the manner described in connection with FIGS. 1, 2 and 3. Each of the feedthrough assemblies 54 directly contacts the ceramic body 34 to form a substantially hermetic seal between the ceramic body 34 and the feedthrough assemblies 54.

(27) Referring again to FIG. 7, a reference electrode 40, a counter electrode 42, and a working electrode 44 form part of a glucose responsive detector portion of the sensing device 30. A working electrode 46, a counter electrode 48, and a reference electrode 50 form part of a background oxygen detector of the sensing device 30. A glucose oxidase element 55 is supported adjacent the working electrode 44.

(28) Referring to FIG. 6, an electrolyte gel layer 56, an internal polymer hydrophobic membrane 58, a silicone rubber layer 60 and an optional external membrane 62 are sandwiched together, overlie the exterior of the container 32, and surround the electrodes 40, 42, 44. Except for glucose oxidase element 55, these layers are not illustrated in FIG. 7. The electrolyte layer 56 (FIG. 6) maintains the electrodes 40, 42 and 44 in ionic contact with one another. Suitable techniques for preparation of the electrolyte gel layer 56 and the polymer hydrophobic membrane 58 are disclosed in U.S. Pat. No. 4,703,756 granted Nov. 3, 1987 to David A. Gough and Joseph Y. Lucisano et al., the entire disclosure of which is hereby incorporated by reference. See also U.S. Pat. No. 4,890,620 granted Jan. 2, 1990 to David A. Gough, the entire disclosure of which is hereby incorporated by reference.

(29) The glucose oxidase element 55 may have a composite or laminate construction. Suitable constructions are disclosed in U.S. Patent Application No. US 2002/0156355 A1 of David A. Gough published Oct. 24, 2002, and U.S. Pat. No. 6,721,587 granted to David A. Gough on Apr. 13, 2004, the entire disclosures of which are hereby incorporated by reference.

(30) A circuit (not illustrated) is mounted inside the container 32 and is electrically connected to the electrodes via the feedthrough assemblies 54 and determines a glucose-level in a body fluid contacting the electrodes. Preferably the implanted sensing device 30 is battery powered and transmits information and receives instructions with respect to an electronic module outside the body via a radio frequency (RF) data link. See the circuitry illustrated in FIG. 6 of the aforementioned U.S. Pat. No. 4,703,756, for example. While the glucose responsive detector of sensing device 30 includes three electrodes, the reference electrode 40 and counter electrode 42 could be combined. The same is true of the background oxygen detector.

(31) While we have described several embodiments of our invention, those skilled in the art will appreciate that it may be modified in both arrangement and detail. For example, whereas the wire 14 has a round cross-section, it could also have other cross-sectional shapes, including, but not limited to, uniform oval, square, and rectangular, as well as cross sections that vary in shape and size over the length of the wire. As another example, the wire could be of a branching structure, or it could follow a path through the ceramic body that was not straight. As another example, the green or fired ceramic body containing the wire could have additional layers of material, for example ceramic-based material, applied to one or both surfaces, either before, or after firing. As another example, the sensing device 30 is particularly suited for detecting glucose levels subcutaneously, but its basic structure can be modified to accommodate other electrochemical processes using different types of membranes and coatings, as well as other implantation locations. Also, the feedthrough structure 54 could be utilized to advantage in other instruments or devices requiring hermetic seals, including implantable medical devices such as pacemakers, neural stimulators, cochlear implants, and implantable hearing aids. Therefore, the protection afforded our invention should only be limited in accordance with the appended claims. Likewise, the following examples that illustrate particular embodiments are not intended to define the scope of the invention, which is limited only by the appended claims.

EXAMPLES

(32) Green ceramic bodies of uniform thickness were prepared as follows: 1) Thickness (in inches in the green state): 0.013, 0.0195, 0.032, 0.050, 0.071 and 0.075. 2) Number of wires per body: 1 to 24 3) Hole diameter (inches): None, 0.002, 0.005, 0.0059, 0.006, 0.0063, 0.0079, 0.0087, 0.011, 0.016, 0.0135, 0.0160, 0.0197, 0.0217, 0.0236, 0.031 4) Ratio of (distance between holes) to (thickness of green body): range from 0.7 to 13.5

(33) Each green ceramic body was formed from one of the following mixtures: 1. (1) 83% by volume ceramic powder (minimum 99.5% Al.sub.2O.sub.3, balance silica, talc, or wollastonite); and (2) 17% by volume organic polymer binder containing poly vinyl acetate and butyl benzyl phthalate plasticizer. This green mixture was used to form what is herein referred to as a ductile alumina green body. This mixture, after firing, meets or exceeds the material composition requirements of ASTM F 603-00. 2. (1) 81% by volume ceramic powder (minimum 99.5% Al.sub.2O.sub.3, ≦0.5% MgO, and ≦0.1% other oxides); and (2) 19% by volume wax-type organic polymer binder. This green mixture was used to form what is herein referred to as a brittle alumina green body. This mixture, after firing, meets or exceeds the material composition requirements of ASTM F 603-00. 3. (1) 79% by volume ceramic powder (a mixture of ZrO.sub.2, HfO.sub.2, and Y.sub.2O.sub.3, containing 4.5% to 5.4% Y.sub.2O.sub.3, ≦5% HfO.sub.2≦0.5% Al.sub.2O.sub.3, and balance ZrO.sub.2); and (2) 21% by volume organic polymer binder containing poly vinyl acetate and butyl benzyl phthalate plasticizer. This green mixture was used to form what is herein referred to as a zirconia green body. This mixture, after firing, meets the material composition requirements of ASTM F 1873. 4. (1) 79% by volume ceramic powder (a mixture of 18% to 22% Al.sub.2O.sub.3, 73% to 76% (ZrO.sub.2 and HfO.sub.2), and 4.14% to 4.16% Y.sub.2O.sub.3); and (2) 21% by volume organic binder containing poly vinyl acetate and butyl benzyl phthalate plasticizer. This green mixture was used to form what is herein referred to as an alumina-toughened zirconia or ATZ green body.

(34) The bodies exhibited material properties in the green state which were categorized as either ductile or brittle. The ductile green bodies tend to deform without cracking during the wire insertion process, whereas the brittle green bodies were incapable of substantial plastic deformation. Features or holes in these bodies were produced by drilling with carbide twist drills, by laser-machining, or by sharp wire insertion without pre-defined holes.

(35) Platinum wires, a minimum of 99.9% pure (Alfa Aesar), or alloyed wires containing 90% platinum and 10% iridium (Sigmund Cohn) of diameters 0.005, 0.006, 0.008, 0.014, 0.020, 0.030, 0.040 inches were cut to 0.5-inch lengths and sharpened to aid insertion. The sharpened wire parts were cleaned by sonication in a solution of 70% isopropanol in water and air-dried. For the wire insertion process, the green ceramic body was typically supported mechanically by a layer of silicone rubber at least 3/16 inch thick, with ⅛ inch holes aligned directly below the green ceramic body holes. The wires were introduced into the body in such a way that they completely penetrated the green body and the tapered region of the wire was exterior to the green body thickness.

(36) Alternatively, platinum wires, a minimum of 99.9% pure (Alfa Aesar), or alloyed wires containing 90% platinum and 10% rhodium (Alfa Aesar) of diameters 0.002 and 0.005 inches were cut to lengths equal to the thickness of the green body into which they were inserted. The green body containing the wire was placed in a laminating mold and compressed to between 19,000 lbs/in.sup.2 and 40,000 lbs/in.sup.2 for between 2 and 30 minutes at between room temperature and 190° C.

(37) The assemblies were fired to maximum temperatures between 1515° C. and 1700° C. These maximum temperatures were held for between 60 to 240 minutes before ramping down to room temperature. The firing profiles contained ramp rates between 1 and 10° C./min. Pre-sintering binder burnout was accomplished by executing profiles with dwells of up to 360 minutes at temperatures between 250° C. and 500° C. Success rates for achieving hermetic wire-to-body seals showed no dependence on ramp rate or dwell time for the abovementioned ranges.

(38) Hermeticity was determined by measuring the helium leak rate of each wire-to-body seal using a Varian Multi-Test 947 helium leak detector. For the purpose of this set of examples, a hermetic seal between a wire and its ceramic body was defined as one which exhibited a helium leak rate of less than 1.0×10.sup.−8 atm cc/s. Acceptable hermeticity of a group was defined as 90% or greater of the wire-to-body seals being hermetic by the abovementioned definition.

(39) Results exemplifying combinations of materials, green body thicknesses, green body material properties, hole creation methods, hole sizes, wire materials, wire diameters, and test results are summarized below.

Example 1

(40) In this example, alumina green bodies 0.071-inch thick, exhibiting brittle material properties, were drilled with holes of 0.0079-inch diameter. Platinum wires of 0.008-inch diameter were placed in the 0.0079-inch diameter holes. In some cases, body cracking was observed upon wire insertion. The assemblies were fired and the seals were tested. Although some of the seals were hermetic, an acceptable success rate of hermeticity was not achieved.

(41) A second set of alumina green bodies was created with the only difference being that holes were drilled 0.0087-inch in diameter. Platinum wires of 0.008-inch diameter were placed in the holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(42) The results of this example are provided in tabular form below:

(43) TABLE-US-00001 EXAMPLE 1 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Brittle 0.071 Drilled 0.0079 Platinum 0.008 Not Acceptable Alumina Brittle 0.071 Drilled 0.0087 Platinum 0.008 Acceptable

(44) This example illustrates an iterative hole diameter optimization method of the invention.

Example 2

(45) In this example, alumina green bodies 0.075-inch thick, exhibiting ductile material properties, were drilled with holes of 0.0063-inch and 0.0087-inch in diameter. Platinum wires of 0.006-inch and 0.008-inch diameter were placed in the 0.0063-inch and the 0.0087-inch holes, respectively. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(46) A second set of alumina green bodies was created with the only difference being holes that were drilled 0.0059-inch and 0.0079-inch in diameter. Platinum wires of 0.006-inch and 0.008-inch diameter were placed in the 0.0059-inch and the 0.0079-inch holes, respectively. The assemblies were fired and the seals were tested. Acceptable hermeticity was established. Although acceptable hermeticity was established in both cases, higher success rates were measured in the case in which the holes were drilled smaller than the wire diameter.

(47) TABLE-US-00002 EXAMPLE 2 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Ductile 0.075 Drilled 0.0063 Platinum 0.006 Acceptable Alumina Ductile 0.075 Drilled 0.0059 Platinum 0.006 Acceptable Alumina Ductile 0.075 Drilled 0.0087 Platinum 0.008 Acceptable Alumina Ductile 0.075 Drilled 0.0079 Platinum 0.008 Acceptable

Example 3

(48) Platinum wires of 0.005-inch diameter were pushed through ductile alumina green bodies with 0.032-inch and 0.050-inch thicknesses having no pre-defined holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(49) Platinum wires of 0.006-inch diameter were placed in holes drilled to 0.0063-inch diameter in brittle alumina green bodies 0.071-inch thick. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(50) Platinum wires of 0.008-inch diameter were placed in 0.032-inch thick ductile alumina green bodies drilled with 0.0079-inch holes and 0.050-inch thick ductile alumina green bodies drilled with 0.0079-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(51) Platinum wires of 0.014-inch diameter were placed in 0.020-inch thick ductile alumina green bodies drilled with 0.011-inch holes, 0.032-inch thick ductile alumina green bodies drilled with 0.011-inch holes, 0.032-inch thick ductile alumina green bodies drilled with 0.0135-inch holes, and 0.075-inch thick ductile alumina green bodies drilled with 0.0135-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(52) Platinum wires of 0.020-inch diameter were placed in 0.020-inch thick ductile alumina green bodies drilled with 0.016-inch holes, 0.032-inch thick ductile alumina green bodies with 0.0197-inch holes, and 0.075-inch thick ductile alumina green bodies with 0.0197-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(53) The results of this example are provided in tabular form below:

(54) TABLE-US-00003 EXAMPLE 3 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Ductile 0.032 Wire pushed None Platinum 0.005 Acceptable Alumina Ductile 0.050 Wire pushed None Platinum 0.005 Acceptable Alumina Brittle 0.071 Drilled 0.0063 Platinum 0.006 Acceptable Alumina Ductile 0.032 Drilled 0.0079 Platinum 0.008 Acceptable Alumina Ductile 0.050 Drilled 0.0079 Platinum 0.008 Acceptable Alumina Ductile 0.020 Drilled 0.011 Platinum 0.014 Acceptable Alumina Ductile 0.032 Drilled 0.011 Platinum 0.014 Acceptable Alumina Ductile 0.032 Drilled 0.0135 Platinum 0.014 Acceptable Alumina Ductile 0.075 Drilled 0.0135 Platinum 0.014 Acceptable Alumina Ductile 0.020 Drilled 0.016 Platinum 0.020 Acceptable Alumina Ductile 0.032 Drilled 0.0197 Platinum 0.020 Acceptable Alumina Ductile 0.075 Drilled 0.0197 Platinum 0.020 Acceptable

Example 4

(55) Wires of alloyed platinum and iridium, 0.006-inch in diameter, were placed in holes drilled to 0.0059-inch diameter in ductile alumina green bodies 0.020-inch thick. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(56) The results of this example are provided in tabular form below:

(57) TABLE-US-00004 EXAMPLE 4 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Ductile 0.020 Drilled 0.0059 Platinum- 0.006 Acceptable iridium alloy

Example 5

(58) Platinum wires of 0.005-inch diameter were placed in 0.020-inch thick ductile zirconia green bodies laser-bored with 0.003-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(59) Platinum wires of 0.008-inch diameter were placed in 0.013-inch thick ductile zirconia green bodies laser-bored with 0.005 holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(60) Platinum wires of 0.014-inch diameter were placed in 0.013-inch thick ductile zirconia green bodies drilled with 0.011-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(61) Platinum wires of 0.030-inch diameter were placed in 0.075-inch thick ductile zirconia green bodies drilled with 0.0236-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(62) Platinum wires of 0.040-inch diameter were placed in 0.075-inch thick ductile zirconia green bodies drilled with 0.031-inch holes. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(63) The results of this example are provided in tabular form below:

(64) TABLE-US-00005 EXAMPLE 5 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Zirconia Ductile 0.020 Laser-bored 0.003 Platinum 0.005 Acceptable Zirconia Ductile 0.013 Laser-bored 0.005 Platinum 0.008 Acceptable Zirconia Ductile 0.013 Drilled 0.011 Platinum 0.014 Acceptable Zirconia Ductile 0.075 Drilled 0.0236 Platinum 0.030 Acceptable Zirconia Ductile 0.075 Drilled 0.031 Platinum 0.040 Acceptable

Example 6

(65) Twenty-four wires of alloyed platinum and iridium of 0.005-inch diameter were placed into twenty-four different laser-machined holes 0.002-inch in diameter in a 0.015-inch thick ductile alumina green body. The assembly was fired and the seals were tested. Acceptable hermeticity was established.

(66) The results of this example are provided in tabular form below:

(67) TABLE-US-00006 EXAMPLE 6 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Ductile 0.015 24 locations, 0.002 Platinum- 0.005 Acceptable laser-bored iridium alloy

Example 7

(68) Platinum wires of 0.005-inch diameter were placed in 0.026-inch thick ductile ATZ green bodies laser-machined with 0.004-inch holes. These assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(69) The results of this example are provided in tabular form below:

(70) TABLE-US-00007 EXAMPLE 7 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity ATZ Ductile 0.026 Laser-bored 0.002 Platinum 0.005 Acceptable

Example 8

(71) Platinum wires of 0.005-inch diameter were placed in 0.071-inch thick ductile alumina green bodies laser-machined with 0.006-inch holes. The assemblies were pressed in a laminating mold at 190° C. for 30 minutes at 11,000 lbs/in.sup.2 pressure. These conditions were sufficient to establish intimate contact between the wire and the green body. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(72) The results of this example are provided in tabular form below:

(73) TABLE-US-00008 EXAMPLE 8 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Ductile 0.071 Laser-bored, 0.006 Platinum 0.005 Acceptable then pressed before pressing

Example 9

(74) Platinum wires of 0.002-inch diameter were placed in 0.006-inch diameter holes that were drilled in 0.075-inch thick brittle alumina green bodies. These assemblies were pressed in a closed laminating mold at room temperature for 2 minutes at 40,000 lbs/in.sup.2 pressure. These conditions were sufficient to establish intimate contact between the wire and the green body. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(75) The results of this experiment are provided in tabular form below:

(76) TABLE-US-00009 EXAMPLE 9 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Brittle 0.075 Drilled, 0.006 Platinum 0.002 Acceptable then pressed before pressing

Example 10

(77) Wires of alloyed platinum and rhodium of 0.005-inch diameter were placed in 0.006-inch diameter holes that were drilled in 0.075-inch thick brittle alumina green bodies. These assemblies were pressed in a closed laminating mold at room temperature for 2 minutes at 19,000 lbs/in.sup.2 pressure. These conditions were sufficient to establish intimate contact between the wire and the green body. The assemblies were fired and the seals were tested. Acceptable hermeticity was established.

(78) The results of this experiment are provided in tabular form below:

(79) TABLE-US-00010 EXAMPLE 10 Green Green body body Hole Wire Body material thickness Hole Diameter Wire Diameter material properties (inch) Type (inch) type (inch) Hermeticity Alumina Brittle 0.075 Drilled, 0.006 Platinum- 0.005 Acceptable then pressed before rhodium pressing alloy

Example 11

(80) Multi-conductor feedthrough assemblies, fabricated in accordance with the methods of the invention, consisting of ceramic bodies with a plurality of substantially hermetic feedthroughs were subjected to a thermal-shock test. The thermal-shock test consisted of cycling the temperature of the multi-conductor feedthrough assemblies between 0° C. and 100° C. by transferring the multi-conductor feedthrough assemblies from a boiling-water bath to an ice-water bath and then back to the boiling-water bath a total of fifteen times. In substantial accordance with the methods of MIL-STD-883G Method 1011.9 “Thermal Shock”, the multi-conductor feedthrough assemblies were held in each bath for a dwell time greater than two minutes with less than ten seconds of transfer time between the baths. The multi-conductor feedthrough assemblies were dried, by baking, for greater than one hour at 150° C., cooled to room temperature, and then subjected to a helium-leak test.

(81) Multi-conductor feedthrough assemblies were produced from 0.071-inch thick brittle alumina green bodies and platinum wires of 0.008-inch diameter. These multi-conductor feedthrough assemblies were subjected to the thermal-shock test. Acceptable hermeticity was maintained.

(82) Multi-conductor feedthrough assemblies were produced from 0.075-inch thick ductile green alumina bodies and platinum wires of 0.006-inch diameter. These multi-conductor feedthrough assemblies were subjected to the thermal-shock test. Acceptable hermeticity was maintained.

(83) Multi-conductor feedthrough assemblies were produced from 0.075-inch thick ductile green alumina bodies and platinum wires of 0.014-inch diameter. These multi-conductor feedthrough assemblies were subjected to the thermal-shock test. Acceptable hermeticity was maintained.

(84) The results of this experiment are provided in tabular form below:

(85) TABLE-US-00011 EXAMPLE 11 Green body Green body Wire Post-thermal- Body material thickness Feedthrough Diameter shock material properties (inch) Type Wire type (inch) hermeticity Alumina Brittle 0.071 Multi-conductor Platinum 0.008 Acceptable Alumina Ductile 0.075 Multi-conductor Platinum 0.006 Acceptable Alumina Ductile 0.075 Multi-conductor Platinum 0.014 Acceptable