Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
1999-05-12
2001-06-26
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S125000, C427S307000, C427S372200, C427S374100, C427S380000, C427S555000
Reexamination Certificate
active
06251471
ABSTRACT:
FIELD OF THE INVENTION
This invention most generally relates to electrical connectors. More particularly the invention relates to passing electrical current across a barrier having different pressures on either side. Most particularly the invention relates to methods of creating electrical feedthrus for conduction across pressure envelopes where a high vacuum or pressure must be maintained.
BACKGROUND OF THE INVENTION
There currently exist a variety of methods and devices for passing electrical current across a barrier having significant pressure differences on either side. There is a need for such methods and devices for use with electrical and optical systems which use vessels that maintain pressure differentials between the inside and outside of the vessel. Such systems include many that are used with lasers, charge coupled device (CCD) arrays, and outer space applications which use vacuum cavities, as well as systems with pressurized containers.
Various methods of creating electrical feedthrus for conduction across pressure envelopes include epoxy encapsulation of insulated wires within a metal interface housing, and metal to insulator glass firing of single conductors within an interface housing.
It is a widely recognized problem in the field that, in systems which require electrical feedthrus across pressure differentials, the location and construction of the feedthrus are often the site of leaks which can cause hazards in the operation of the systems. Other disadvantages to the above methods include epoxy thermal limitations, vacuum outgassing, and leakage repair limitations for the epoxy type feedthru.
An example of the current state of the art of electrical feedthrus for connection across a pressure barrier is that of U.S. Pat. No. 4,804,330 to Makowski et al. which discloses a Hermetic, Vacuum and Pressure Tight Electrical Feedthru. Makowski et al. discloses a leak tight electrical feedthru for vessels which may be evacuated or pressurized relative to the outside ambient conditions. The Makowski et al. feedthru comprises: a ceramic circuit ring which circumscribes the walls of a vessel which is either pressurized or evacuated; the walls of the vessel have an inner circumference which extends into the interior of the vessel and an outer circumference which is exterior to the vessel; a first set of electrical contacts distributed about the inner circumference and demountably connecting with an interior set of electrical cables; a second set of electrical contacts distributed about the outer circumference and demountably connecting with an exterior set of electrical cables; a plurality of filaments fixed on the ceramic circuit ring each of which connects one of the first set of contacts with one of the second set of contacts; and a means for hermetically sealing the ceramic circuit ring to the walls of the vessel. The means for hermetically sealing is via firing a ceramic annular seal ring, which covers the plurality of filaments and fits between the walls of the vessel and the ceramic circuit ring. Metal rings are brazed to the resulting fused module, allowing welding to a housing and common mechanical assembly techniques. The ceramic circuit ring is then bolted to pull the wall sections tight against the annular seal.
None of the above methods has proved suitable for certain applications involving pressure extremes such as outer space applications. Thus there is still a need for a better, more easily reparable, more leak tight method or system for passing electrical current across a pressure envelope.
SUMMARY OF THE INVENTION
An embodiment of the invention is a method for producing an electrical feedthru comprising electrical traces wherein a thin conductive film is deposited into a shallow trough milled in an insulating machinable ceramic MACOR (R) substrate. The conductive film filling is metalized by firing and the resulting composite, which is the metalized, bonded conductive film and substrate after firing, is then ground flush with the adjacent surface of the insulating machinable ceramic substrate. The surface cohesion of the fired composite (the bonding between the conductive film and substrate material), and the resulting high quality surface finish of the grinding operation, combined with an elastomeric seal, create low leakage barriers capable of supporting a pressure differential while allowing isolated electrical conduction across a pressure or vacuum envelope. The bond between the MACOR and the metallized trace is virtually leak tight, and the surface finish after grinding is O-ring seal quality. The resulting surface electrical traces can be soldered directly to a signal carrying wire, pin/socket, or attached via a contact spring or other mechanical attachment. The traces are solderable in their fired state, thereby allowing wires to be soldered inside an O-ring envelope, and an electronics interface connector to be soldered outside the envelope. The method produces a space saving feedthru requiring significantly less volume for a given signal line than conventional feedthrus, which allows a high signal line density in a limited space. It is relatively simple to assemble—no adhesives are required and fewer seal elements are needed than with current technology, and there is single O-ring sealing across all traces. Applications of the flush grinding of a conductive trace into the surface of an insulator include, by way of non-limiting example, outer space applications such as in gas filled proportional counter plates for NASA instruments, commercial vacuum feedthrus, vacuum testing devices, glove boxes, or other pressure differential applications such as sealed pressure transducers, other positive pressure electrical feedthrus requiring space conservative solutions, or undersea applications for example in submarines, submersibles or scientific equipment. Conductive trace plates of the present invention used in various applications can be removed or replaced without wasting or destroying the rest of the particular assembly.
Therefore one aspect of the invention is to form a virtually leak tight electrical feedthru.
Another aspect of the invention is to provide high signal line density capacity in a limited space, and which can form electrical connections across a vacuum or pressure envelope.
A further aspect of the invention is to provide an electrical feedthru that is simple to assemble and does not require adhesives.
Yet another aspect of the invention is to provide an electrical feedthru trace which has a surface of O-ring sealing quality and which is sealable with a single O-ring across all the electrical traces.
A still further aspect of the invention is to provide a removable conductive trace plate to allow repair and replacement of the electrical connections across a pressure barrier without destroying the complete assembly or device using the electrical trace connections.
Yet another aspect of this design is the flexibility to add the feedthrus to unique geometries of varied design applications.
These and other aspects of the invention, together with other aspects, features and advantages of the invention will be apparent from the following non-limiting description, when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4416156 (1983-11-01), Demark et al.
patent: 4508753 (1985-04-01), Stepan
patent: 4521449 (1985-06-01), Arnold et al.
patent: 4532152 (1985-07-01), Elarde
patent: 4747908 (1988-05-01), Potter
patent: 4922323 (1990-05-01), Potter
patent: 5276963 (1994-01-01), Flanders
patent: 5628850 (1997-05-01), Sanchez et al.
patent: 5656542 (1997-08-01), Miyata et al.
Broderick David
Demaine Phillip D.
Granoff Mark S.
Ingemi Stephen
Devine, Millimet & Branch P.A.
Kohler Kristin
Renus Paul C.
Talbot Brian K.
University of New Hampshire
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