Glass-metal feedthrough

Abstract

A glass-metal feedthrough consists of an external conductor, a glass material and an internal conductor. The internal conductor has a coefficient of expansion α.sub.internal, the glass material has a coefficient of expansion α.sub.glass, and the external conductor has a coefficient of expansion α.sub.external. The coefficient of expansion of the internal conductor α.sub.internal is greater than the coefficient of expansion of the glass material α.sub.glass and the coefficient of expansion of the external conductor α.sub.external is at least 2 ppm/K, such as at least 4 ppm/K, greater than the coefficient of expansion of the glass material α.sub.glass in the temperature range of 20° C. to the glass transformation temperature.

Claims

1. A glass-metal feedthrough, consisting of: a glass material having a coefficient of expansion α.sub.glass; an external conductor having a coefficient of expansion α.sub.external that is greater than the coefficient of expansion of the glass material α.sub.glass, a difference between the coefficient of expansion of the external conductor α.sub.external and the coefficient of expansion of the glass material α.sub.glass is at least 2 ppm/K in a temperature range of 20° C. to a glass transformation temperature of the glass material, the external conductor consisting of a nickel-free, non-corrosive, chemically stable austenitic steel; and an internal conductor having a coefficient of expansion α.sub.internal that is greater than the coefficient of expansion of the glass material α.sub.glass, the internal conductor directly contacting the glass material and consisting of one of the following materials: steel; stainless steel; nickel-free ferritic stainless steel; molybdenum; tungsten; platinum; niobium; titanium; or platinum and iridium; wherein the coefficient of expansion of the internal conductor α.sub.internal and the coefficient of expansion of the external conductor αexternal are such that a joint pressure on the internal conductor of at least 30 MPa is generated in the temperature range of 20° C. to the glass transformation temperature of the glass material.

2. The glass-metal feedthrough of claim 1, wherein the coefficient of expansion of the internal conductor αinternal is 1.1 times to 4 times greater than the coefficient of expansion of the glass material α.sub.glass.

3. An element for insertion into or attachment to a human or animal body or biological living cells containing cell cultures, said element comprising: a glass-metal feedthrough comprising: a glass material having a coefficient of expansion α.sub.glass; an external conductor having a coefficient of expansion α.sub.external that is greater than the coefficient of expansion of the glass material α.sub.glass, a difference between the coefficient of expansion of the external conductor α.sub.external and the coefficient of expansion of the glass material α.sub.glass is at least 2 ppm/K in a temperature range of 20° C. to a glass transformation temperature of the glass material, the external conductor consisting of an austenitic steel; and an internal conductor having a coefficient of expansion α.sub.internal that is greater than the coefficient of expansion of the glass material α.sub.glass, wherein the external conductor and the internal conductor consist of metals which are configured to come into contact with the human or animal body or the cell cultures and do not release at least one of any nickel or any chrome, the internal conductor directly contacting the glass material and consisting of one of the following materials: steel; stainless steel; ferritic stainless steels; platinum; platinum and iridium; niobium; titanium; molybdenum; tungsten; and combinations thereof; wherein the coefficient of expansion of the internal conductor α.sub.internal and the coefficient of expansion of the external conductor α.sub.external are such that a joint pressure on the internal conductor of at least 30 MPa is generated in the temperature range of 20° C. to the glass transformation temperature of the glass material.

4. The element of claim 3, wherein the metal of the internal conductor consist of at least one of nickel-free steel or chrome-free steel at least in surface areas which are configured to come into contact with the human or animal body or with biological cells of the cell culture in their operational use.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a schematic illustration of an exemplary embodiment provided in accordance with the present invention;

(3) FIG. 2A is a flow chart of joint pressure of conductor and glass; and

(4) FIG. 2B is a flow chart of joint pressure of conductor and glass.

(5) Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 is a schematic depiction of a cross section through an exemplary embodiment provided in accordance with the invention. In the glass-metal feedthrough through a housing 1 illustrated in FIG. 1 which may be made of aluminum, a feedthrough 3 is inserted into an opening 5 in housing 1. Feedthrough 3 includes a feedthrough conductor or respectively an internal conductor 7 which is inserted into an external conductor 9. External conductor 9 may also be referred to as base body and may consist of an austenitic high grade stainless steel with a high thermal coefficient of expansion. The external conductor may also be referred to as base body and is joined with the housing, by, for example, welding. The internal conductor is glazed centrally into the external conductor or feedthrough conductor 7. This is achieved in that internal conductor 7 in an insulating glass body 11, completely fills the space inside external conductor 9. The glass into which the internal conductor 7 is fused may be a bio-compatible glass.

(7) Also illustrated in FIG. 1 is diameter d of feedthrough conductor 7, as well as the so-called hole diameter D of opening 5.

(8) According to the invention it is provided that the glass has a coefficient of expansion α.sub.glass, that the internal conductor has coefficient of expansion α.sub.internal and that the external conductor has a coefficient of expansion α.sub.external. The materials are selected in such a manner, that the coefficient of expansion of the internal conductor α.sub.internal is greater than that of the glass α.sub.glass. The difference between the coefficient of expansion of the external conductor and the coefficient of expansion of the glass is at least 2 ppm/K, such as at least 4 ppm/K. The coefficient of expansion of the external conductor α.sub.external in the temperature range of 20° C. to the transformation temperature is greater than the coefficient of expansion α.sub.glass. Thus, a joint pressure is provided at the internal conductor of at least 30 MPa, such as of at least 50 MPa or of at least 100 MPa.

(9) If, as demanded by the invention, the coefficient of expansion of the internal conductor α.sub.internal is greater than that of the glass α.sub.glass, it will become problematic to provide a sufficiently tightly sealed feedthrough. In such a case, a sufficiently tight seal is ensured only if the external conductor can generate a sufficiently high joint pressure upon the glass. The joint pressure is relevant to d/D according to the state of the art is illustrated in FIG. 2A. Kovar which, with an a of 7.3 to 6.6 10.sup.−61/K is slightly above the value of the coefficient of expansion α.sub.glass and which is not covered by the invention was used as the material for the feedthrough conductor. d indicates the diameter of the conductor and D the diameter of opening 5. d/D specifies the relationship between the diameter of conductor d and hole diameter D. Generally, small d/D values characterize the large gap between conductor and opening and large d/D values characterize a small gap between conductor and opening.

(10) The feedthroughs according to FIG. 2A are hermetically sealed. They however have the disadvantage that Kovar alloys have a high nickel content, so that nickel could be released from the feedthrough conductors.

(11) Thus, it is provided according to the present invention to replace the Kovar feedthrough conductor with a material which does not release nickel. Surprisingly it was found that a material suitable for this purpose is a ferritic, Ni-free high grade stainless steel, in particular AISI 430. The disadvantage with a Ni-free high grade stainless steel, for example AISI 430 is however, that α.sub.internal is at 11.5.Math.10.sup.−6K.sup.−1 and is thus clearly above the coefficient of expansion α.sub.glass of the glass material. The coefficient of expansion of the used glasses α.sub.glass is namely in a range of 6.1.Math.10.sup.−6 K.sup.−1 to 10.6.Math.10.sup.−6K.sup.−1.

(12) In order to achieve a pressure tight glazed seal with such a constellation, a sufficiently high joint pressure which is applied by the external conductor must be generated.

(13) The joint pressure for feedthroughs of this type is illustrated in FIG. 2B and is relevant to d/D.

(14) As can be seen from FIG. 2B, a sufficiently high joint pressure for the use of AISI 430 as material for the feedthrough component results, especially if the external conductor consists of an austenitic high grade stainless steel with a α.sub.external of 18.3 10.sup.−6/K. Such composition provides a sufficiently high joint pressure to ensure a tight seal. The joint pressure of such a material combination is identified with reference numbers 100 and 200. The joint pressure increases with a larger d/D and thus small gap, to values of above 150 MPa.

(15) Curves 300 and 400 describe the joint pressure for an AISI 430 feedthrough conductor, wherein the external conductor is AISI 430 or AISI 630 and wherein the glass has a coefficient of expansion of 10.6.Math.10.sup.−6 and is thus within the range of the coefficient of expansion of the external conductor as well as that of the feedthrough conductor. Because of this, the necessary joint pressure cannot be generated. Such material combinations generally demonstrate a low joint pressure. Curves 300 and 400 progress flat with little influence of the diameter due to the diameter ratio.

(16) The materials of the different curves in the diagram according to FIG. 2B “joint pressure over d/D” are specified in the table below:

(17) TABLE-US-00001 Ex- Glass Con- ternal Tg Glass ductor External CTE in CTE Conductor CTE Curve material to TG ° C. to Tg Material to TG Symbol 200 AISI316L 18.3 525 10.6 AISI430 11.5 .circle-solid. 100 AISI316L 18.4 565 6.1 AISI430 11.6 .box-tangle-solidup. 600 AISI430 11.5 525 10.6 AISI430 11.5 .square-solid. 400 AISI430 11.6 565 6.1 AISI430 11.6 300 AISI630 11.4 525 10.6 AISI430 11.5 .diamond-solid. 500 AISI630 11.4 565 6.1 AISI430 11.6

(18) The material components of curves 100, 300 show an especially high joint pressure, so that a hermetic seal of the feedthrough is provided.

(19) The specified glass-metal feedthroughs can be used in implantable medical devices or equipment. They can be produced cost effectively and are characterized by very low Ni release. Because of the high joint pressure they moreover are hermetically sealed—in other words feature a helium leakage of less than 1.Math.10.sup.−8 mbar/sec.

(20) While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.