Stock material or miscellaneous articles – All metal or with adjacent metals – Laterally noncoextensive components
Reexamination Certificate
1999-04-30
2002-03-12
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Laterally noncoextensive components
C428S469000, C428S472000, C428S660000, C428S663000, C428S650000, C361S707000, C361S708000, C361S710000, C257S720000
Reexamination Certificate
active
06355362
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hermetic electronics packages constructed from a primary metallic material and having one or more secondary regions composed of material having disparate physical and/or structural properties. More specifically, electronics packages are provided with one or more regions of a secondary material having a high thermal conductivity and a coefficient of thermal expansion (CTE) that generally matches the CTE of the primary metallic material. In one embodiment, the electronics package comprises a primary metallic titanium component metallurgically bonded to a secondary metal matrix material, such as aluminum silicon carbide.
BACKGROUND OF THE INVENTION
Electronic components are used in countless applications in a wide variety of environments. Such components are subject to faulty operation, degradation and corrosion resulting from contact with dust, water vapor, gases, and the like, as well as from high IC) temperature and/or pressure conditions. Such components are, therefore, generally sealed in a hermetic electronics package to provide protection from the operating environment.
Electronics packages typically comprise a box-like structure, in the interior of which the electronic components are mounted. The package is generally provided with feedthrough holes through which conductive wires are sealed with an insulator such as glass or ceramic and are used to operatively connect electronic components inside the package to electronic and electrical sources and systems outside the package. The conductive wires are electrically insulated from and hermetically sealed into the package. After the electronic components are mounted in the package and operatively connected to the conductive wires, a cover is hermetically sealed to the package base to seal the interior of the electronics package.
Electronics packages are desirably constructed from materials that meet application specific requirements for density, thermal expansion, thermal conductivity, mechanical strength, and the like. For example, electronics packages used in aircraft and spacecraft applications must be lightweight and are therefore constructed from low density materials. Electronics packages that are used in high power applications should be constructed from materials having a high thermal conductivity, so that heat generated within the package is conducted outside the package to maintain lower operating temperature conditions inside the package. In other words, heat must be efficiently dissipated from inside the package. The service life of components is increased considerably when lower temperatures are maintained within the electronics package.
Electronics packages are desirably constructed from materials having a coefficient of thermal expansion (CTE) approximately equal to that of the materials the packages contact. That is, the thermal expansion properties of the electronics package must be compatible with the thermal expansion properties of the circuitry mounted in the package. Otherwise, temperature changes produce stress between the package and its electrical circuitry as they expand and contract at different rates. Additionally, because electronic components are often mounted on ceramic chips having a low CTE, most electronic packaging applications require package materials having a low CTE, generally matching or slightly higher than that of the ceramic chips. The ceramic chips comprise materials such as silicon, gallium-arsenide and alumina. These materials are fragile and susceptible to breakage if they are mounted to a package having an incompatible CTE. Therefore, it is important to mount these chips to a package with similar expansion rate characteristics.
Electronics packages constructed from ferrous alloys, such as Alloy 52 or KOVAR, have a desirably low CTE but are relatively heavy. Electronics packages constructed from aluminum are light in weight, but the CTE of aluminum is higher than desirable and is incompatible with the thermal expansion rates of conventional ceramic chips. Furthermore, many of these electronic chips generate significant heat when operating and it is important for these chips to be mounted to a material having high thermal conductivity characteristics that will dissipate the heat generated by the chips.
Thus, materials having a low density (for light weight applications), a CTE matching or slightly higher than the CTE of the electronic circuitry, high thermal conductivity for heat dissipation, good mechanical strength, and the ability to be hermetically sealed during final package assembly are desirable for electronics packaging applications.
Historically, hermetic electronic packages have been fabricated using a variety of techniques. One conventional approach involves machining or otherwise fabricating the entire package from an iron-based metal such as KOVAR, alloy 42 or a ferrous metal having similar properties. The feedthroughs and/or connectors are installed with standard glass-to-metal-seal technology, or are soldered, brazed or welded directly into the package. These packages have the advantage that the package and the electronic chips have compatible CTE's. They are disadvantageous, however, in that the package is heavy and has poor thermal conductivity. These types of packages are effectively limited to housing circuitry for non-power devices for applications other than aerospace.
Alternatively, the walls of the package may be manufactured from an iron-based alloy such as KOVAR, with the floor of the package composed of a composite metal or metal matrix material having a compatible CTE to that of the metallic package walls. The walls may be joined to the floor to form the electronics package using soldering or brazing techniques. Soldering requires plating of both the wall and floor sections. Welding techniques cannot be is used as a consequence of material incompatibility. Exemplary package floor materials include composite metals such as copper/molybdenum, copper/tungsten, and beryllium/aluminum, and metal matrix materials such as aluminum silicon-carbide, aluminum aluminum-oxide, copper graphite, and beryllium beryllium-oxide.
Another approach involves machining the entire electronics package from an aluminum alloy, such as alloy 6061. The feedthroughs and/or connectors are installed into the package by means of soldering or welding. An aluminum cover may be hermetically sealed to the package base using standard laser welding techniques. This package has the advantage of being lightweight and having a relatively high thermal conductivity, but the CTE of aluminum and aluminum alloys is generally incompatible with the CTE of the electronic chips. An alternative approach involves machining the entire electronics package base and/or connectors from a composite metal such as A40, an aluminum silicon composite, or ALBEMET™, a beryllium/aluminum metallic composite. The feedthroughs and/or connectors may be installed by means of specialized welding or plating soldering techniques.
Metal matrix composite materials, which incorporate a non-metallic reinforcing material dispersed within a metal matrix or host material, generally have desirable properties for electronics packaging applications, including a low density, low CTE, high thermal conductivity and good mechanical strength. These properties may be manipulated somewhat by selecting the metal matrix material and the form, proportion and composition of the reinforcing material. Metal matrix materials comprising aluminum or aluminum alloy matrices incorporating silicon carbide reinforcement material have low density, low CTE, good thermal conductivity, and suitable mechanical strength for use in electronics packaging applications.
Although metal matrix composite materials have desirable properties for use in electronics packaging applications, they have several practical disadvantages. Metal matrix materials cannot be machined using conventional tools and are provided in a three-dimensional configuration, such as an electronics package, using a casting process. The
Jones Herman L.
Taylor Edward A.
Klaniecki Jim
Pacific Aerospace & Electronics, Inc.
Speckman Ann W.
Zimmerman John J.
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