Methods for hermetically sealing ceramic to metallic...

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Reexamination Certificate

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C428S632000, C428S660000, C428S680000, C428S472000, C428S702000

Reexamination Certificate

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06221513

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods for hermetically sealing ceramic materials, such as zirconia, to metallic materials, such as titanium alloys, using a titanium-nickel alloy filler material. The methods are especially suitable for use in hermetically sealing ceramic and metallic components for applications such as implantable medical devices, electrical connectors, electronics packages, structural components, and the like.
BACKGROUND OF THE INVENTION
The development of advanced materials has accelerated in recent years. Materials of various types have properties that are desirable for a wide range of applications in diverse environments. Although the materials are highly advanced, it is often difficult to adapt them for use in applications in which they must interface with materials having different properties. Sealing of dissimilar materials at interface surfaces between the materials, for example, has frequently been problematic.
Many applications require materials to be sealed hermetically. Providing reliable hermetic seals at the interface surfaces of materials having different properties, particularly different coefficients of thermal expansion, has been difficult. U.S. Pat. Nos. 5,298,683, 5,433,260, 5,675,122, 5,110,307, 5,041,019, 5,109,594 and 4,690,480 disclose various methods for hermetically sealing different types of materials, particularly materials having different thermal properties, to one another. Many of these patents relate to hermetically sealing various materials for use in electrical connectors and electronics packages using a transition joint or bushing.
U.S. Pat. No. 4,991,582 discloses a sealed ceramic and metal package for electronic devices implantable in living bodies. This patent describes a device in which a ceramic sleeve is sealed to a metallic band having substantially the same coefficient of linear thermal expansion. The sleeve is formed of an inert ceramic material such as alumina or boron nitride, and the metal band is formed of niobium, molybdenum or tantalum. A header plate carrying a substrate on which the electronic components are mounted and having a plurality of electrical connectors is then sealed to the metal band. The ceramic sleeve is sealed to the metal band employing a butt brazing technique using an alloy of 71.5% titanium and 28.5% nickel. Brazing is accomplished by heating the ceramic sleeve, fitted with the metal band and an annular foil of brazing material. The electronic components that are ultimately mounted in the ceramic sleeve cannot tolerate the high temperatures required during the brazing operation, and are inserted into the cavity formed by the ceramic sleeve when the header is joined to the metallic band. The metal to metal seal between the header and the metal band is provided using high temperature welding, such as laser or electron beam welding, having a low heat-affected zone that does not affect the integrity of the electronic components.
U.S. Pat. No. 3,594,895 discloses 50-50 brazing alloys of titanium with iron, cobalt, nickel or mixtures thereof for sealing ceramic to metallic materials, such as tantalum, niobium and group VIII metals. The 50-50 titanium-niobium brazing alloy had a melting point of 1250° C., requiring heating to temperatures just above 1250° C. for brazing. The brazing process, including the heating, melting and cooling process, took about five minutes.
Zirconia ceramic materials and, particularly, stabilized zirconia ceramic materials, are preferred ceramic materials for many applications. Zirconia ceramics are generally stronger and less reactive in harsh environments than alumina ceramics, making them suitable candidates for applications such as implantable devices. The relative expense of zirconia ceramics and the difficulty of providing reliable hermetic seals at the interface of zirconia ceramics with metallic materials have presented challenges in using zirconia ceramics in many applications. Providing a reliable hermetic seal of zirconia ceramic materials to metallic materials, and particularly titanium-containing metallic materials, has been particularly difficult as a result of the active nature of titanium metals. The methods of the present invention are directed to providing reliable, hermetic seals at the interface of ceramic materials, particularly zirconia ceramic materials, with metallic materials, particularly titanium-containing metallic materials.
SUMMARY OF THE INVENTION
The present invention provides methods for hermetically sealing ceramic materials, such as zirconia materials, to metallic materials, particularly titanium-containing and copper-containing metallic materials, using a titanium-nickel sealing alloy. Broadly, the methods of the present invention may be adapted to seal a variety of ceramic and ceramic-like materials, including materials comprising zirconia and stabilized zirconia, alumina, silicon nitride, silicon carbide, titanium carbide, tungsten carbide, titanium nitride, silicon-aluminum oxy-nitride (sialon), graphite, titanium di-boride, boron carbide, zirconia toughened alumina, and molybdenum disilicide. These materials and materials having similar properties are collectively referred to as “ceramic” materials in this specification and the appended claims. Zirconia ceramic materials stabilized with yttria, magnesia, ceria, calcia or combinations thereof, are especially preferred ceramic materials.
Metallic materials to which the ceramic materials may be joined include various titanium-containing, copper-containing and tantalum-containing alloys, such as titanium-niobium alloys and titanium-tantalum alloys, and refractory materials such as molybdenum and zirconium alloys. Titanium-containing and copper-containing metallic alloy materials are preferred, with titanium-niobium and titanium-tantalum alloys being especially preferred. Titanium-niobium alloys preferably comprise at least about 45% titanium and at least about 35% niobium. A titanium-niobium alloy composed of 55% titanium and 45% niobium is especially preferred.
Sealing alloys comprising titanium and nickel are preferred for use in hermetically sealing ceramic interface surfaces to metallic interface surfaces according to methods of the present invention. Titanium-nickel alloys comprising at least 35% nickel and at least 35% titanium are preferred; alloys comprising at least about 45% nickel and at least about 45% titanium are more preferred; and sealing alloys having a 50% titanium and 50% nickel composition are especially preferred.
Interface surfaces of ceramic and metallic components having various conformations and configurations may be hermetically sealed to one another using sealing alloys and methods of the present invention. Surfaces to be sealed are cleaned to remove any foreign or oxidized materials and are arranged adjacent and in proximity to one another, with sealing alloy contacting at least one of the interface surfaces in the vicinity of the intended hermetic seal. The sealing alloy is preferably in physical contact with the metallic interface surface. The sealing alloy may be provided as a thin foil member, as a paste comprising metallic powders, as metallic powders or beads, or as a preformed insert (a “preform”) having the approximate configuration of the surfaces being sealed and fitting generally between the interface surfaces being sealed. Annular washers comprising sealing alloy material may be used, for example, to seal annular or cylindrical interface surfaces.
After the sealing alloy is positioned adjacent the interface surfaces to be sealed, the assembly comprising the interface surfaces and sealing alloy is heated under vacuum conditions to the desired sealing temperature for the desired length of time. Sealing temperatures of less than about 1150° C., generally from about 900° C. to 1150° C. are preferred, with sealing temperatures less than about 1100° C., and preferably from about 1000° C. to 1100° C. being especially preferred. The sealing alloys of the present invention are preferably capable of forming a liquidus at a tempera

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