Patent Application
20070184285
This invention relates generally to manufacture of electronics components and, more particularly, to techniques for protecting electronics components from the harmful effects of x-ray radiation. Most electronics packages used in space applications are expected to be exposed to high doses of “hard” x-ray radiation (typically defined as x-rays at energy levels above 10 keV). Attempts to shield components from such radiation have required the use of shields of Kovar (an alloy of iron, nickel and cobalt), tantalum, or aluminum (either pure or alloyed with other metals). Tantalum (Ta), for example, provides adequate x-ray shielding but is a very heavy metal (density=16.7 g/cc). Aluminum (Al) is lighter than tantalum by a factor of about six, but does not provide adequate x-ray shielding. Similarly, Kovar also provides adequate x-ray shielding but is too heavy for most space applications. Therefore, there is still a need to protect electronics components from ionizing processes caused by x-ray radiation exposure, but preferably without incurring the weight and cost detriment of shields made from heavy metals, such as Kovar or tantalum. Ideally, x-ray radiation protection should be provided directly during manufacturing, rather than added as an additional shielding component. The present invention achieves these goals, as will become apparent from the following summary.
The present invention resides in a light-weight x-ray radiation shield for electronics components, comprising an electronics enclosure having at least one layer of a zinc alloy. The zinc alloy provides excellent radiation protection without adding significantly to the weight of the enclosure.
In one embodiment of the invention, the electronics enclosure is a cast zinc alloy enclosure, typically comprising a housing and a lid. In another disclosed embodiment, each of the housing and the lid comprises a light-weight alloy body, a thin film of a zinc alloy formed over the body and a finish metal layer formed over the thin film of zinc alloy.
In the disclosed embodiment, the light-weight alloy body is of an aluminum alloy. the zinc alloy is of zinc and aluminum and the finish metal layer is of nickel and gold. The zinc alloy film may be on the order of 100 microns thick. In accordance with another aspect of the invention the electronics enclosure further comprises an interior layer of Ti/Pd/Ag (titanium/palladium/silver) to function as a hydrogen and moisture gatherer.
In method terms, the invention may be defined as a method for manufacturing an electronics enclosure with an integral light-weight x-ray radiation shield. Briefly, and in general terms, the method comprises forming a housing that comprises at least one layer of a zinc alloy for radiation protection; and forming a housing lid that also comprises at least one layer of a zinc alloy for radiation protection.
More specifically, each of the forming steps comprises forming a body of a lightweight alloy; forming a zinc alloy layer over the body; and forming a finish metal layer over the zinc alloy layer. Forming the body of the housing may include forming a cavity in the body, to enclose at least one electronics component. Moreover, the steps of forming the body of the housing and forming the body of housing lid, may include casting and machining steps.
Forming the zinc alloy layer may be effected by any of the steps of sputtering, electrochemically depositing, dipping or brushing. In accordance with another aspect of the invention, the method further comprises forming an interior enclosure layer of Ti/Pd/Ag (titanium/palladium/silver) on at least one of the housing and its lid, to function as a hydrogen and moisture gatherer.
It will be appreciated from the foregoing that the present invention represents a significant advance in the protection of electronics components from x-ray radiation in space. In particular, the invention makes use of a zinc alloy to provide radiation protection without adding significantly to the overall weight. Other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings.
As shown in the drawings for purposes of illustration, the present invention is concerned with techniques for shielding electronics components from x-ray radiation, as well as from magnetic fields. Prior to the present invention, adding heavy radiation shields of tantalum or other metals has proven to be costly in terms of either added weight or added cost. Use of aluminum as a shield is much lighter than Kovar or tantalum but is no nearly as effective as a radiation shield.
In accordance with the present invention, an alloy of zinc is used as the primary x-ray radiation shield for electronics components. A first preferred embodiment of the invention is shown in
In a presently preferred embodiment of the structure shown in
Although illustrated and described with reference to the
In accordance with another aspect of the invention, an electronics housing including zinc-based material for radiation protection may also include a thin film layer of Ti/PdAg deposited by sputtering of other means on the inside surface of the housing and lid. This final layer acts as hydrogen and moisture absorber to further protect highly sensitive devices within the housing.
It will be understood from this description that the present invention provides a number of important advantages over prior techniques for x-ray radiation protection of electronics components. Some of these advantages are: (a) lightness in weight; (b) faster removal of heat because of higher conductivity, (c) reduction in grounding resistivity because of higher conductivity, (d) improved ability to absorb hydrogen, (e) improved brazing capability for feedthrough of pins or leads, because brazing material is usually a zinc-based alloy, (f) lower manufacturing cost (if the casting embodiment is used), (g) lower assembly cost, since separate x-ray shields are not needed, (h) lower quality engineering costs because the zinc-based shielding absorbs hard x-rays but is still relatively transparent to soft x-rays used in non-destructive testing (inspection) of the electronics components.
It will be appreciated from the foregoing that the present invention represents a significant advance in the field of x-ray radiation protection for electronics components. Use of a thin layer of a zinc-based alloy in electronics component housing structures, or use of zinc-based materials to cast a complete electronics housing, both result in a structure that provides an effective x-ray radiation shield but also provides other desirable properties, such lightness in weight and good electrical and thermal conductivity. It will also be appreciated that, although specific embodiments of the invention have been illustrated and described, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.
