Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1999-05-07
2001-02-13
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C439S939000, C361S753000, C361S799000, C361S818000, C174S034000
Reexamination Certificate
active
06188017
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of electromagnetic interference (EMI) shields, and in particular, to an EMI shield for a circuit board assembly that prevents unacceptable levels of electromagnetic radiation from exiting the circuit board assembly.
BACKGROUND OF THE INVENTION
Electronic chassis typically include a plurality of circuit board assemblies. Each circuit board assembly is comprised of at least one printed circuit board that is attached to C-shaped channel member that serves as the faceplate for the assembly. The printed circuit board typically includes at least one surface mounted connector (such as, for example, an F-series connector). The channel member typically has at least one opening therein to allow a portion of the connector to extend through the opening in the bracket to enable a technician to plug an input cable or cord into the connector.
When the connector is inserted through the opening in the channel, the gap around the opening in the bracket must be properly sealed to prevent electromagnetic radiation generated by the electronic components of the printed circuit board from exiting through the channel. Excessive electromagnetic interference (EMI) is a widespread problem in many electronic devices, especially in high-speed telecommunication and networking applications. These electronic devices must meet very stringent emissions standards in the United States and in other foreign countries.
Shielding components are available which can be used to reduce EMI emissions that exit through an opening formed in the channel member. Typically, a flat metal nut is positioned over the connector on the outer surface of the channel member, and is mechanically attached to the channel. There are several disadvantages to this arrangement, including increased manufacturing costs associated with having to use fastening tools to manually fasten these nuts to the channel. The installation of these nuts with fastening tools may also create unacceptable loads on the solder joints of the connectors, which may cause the joints to fail. Moreover, rigid metal nuts do not provide any flexibility to compensate for components that are out of tolerance, which may result in excessive amounts of electromagnetic radiation exiting the assembly through gaps formed between the components.
In addition, flat metal nuts typically occupy a considerable amount of space on the outer surface of the channel, which limits the number of available input/output connections and the amount of artwork on the outer surface. Also, the outer surface of the channel must be masked before painting to ensure that there is metal to metal contact between the nut and the surface of the channel. Once installed, the nut itself typically has to be painted to match the color of the outer surface. This two step painting process also increases manufacturing costs.
Accordingly, it would be desirable to have an EMI shielding apparatus that overcomes the disadvantages described above, and to provide a simple and cost effective EMI shielding apparatus.
SUMMARY OF THE INVENTION
One aspect of the invention provides an electromagnetic interference (EMI) shielding apparatus. A circuit board assembly includes a bracket and a circuit board attached to the bracket. The circuit board includes a connector for insertion through an opening in the bracket. A compressible member includes an outer conductive portion and is positioned between the connector and an inner surface of the bracket. The compressible member is in contact with the connector and the inner surface of the bracket to prevent electromagnetic emissions from exiting through the opening in the bracket. The compressible member may preferably be comprised of a foam body and may preferably compress between 5% to 60%. The compressible member may preferably include an opening formed therein for receiving the connector. The outer conductive portion may preferably be comprised of metalized fabric. The outer conductive portion of the compressible member may preferably be in contact with the inner surface of the bracket. The bracket may preferably include a flange portion, and the outer conductive portion of the compressible member may preferably be in contact with the flange portion. The outer conductive portion of the compressible member may preferably include a first flat surface in contact with the flange portion. The outer conductive portion of the compressible member may preferably be in contact with the circuit board to provide continuous electrical grounding between the circuit board and the bracket. The outer conductive portion of the compressible member may preferably include a second flat surface in contact with the circuit board.
Another aspect of the invention provides a method of shielding electromagnetic interference (EMI). A circuit board assembly including a bracket and a circuit board attached to the bracket is provided. The circuit board includes a connector for insertion through an opening in the bracket. A compressible member includes an outer conductive portion. The compressible member is positioned between the connector and an inner surface of the bracket. The compressible member is compressed, and electromagnetic emissions are prevented from exiting through the opening in the bracket. The outer conductive portion of the compressible member may preferably be in contact with the circuit board and the circuit board may preferably be grounded to the bracket.
Another aspect of the invention provides a method of assembling an electromagnetic interference (EMI) shielding apparatus. A circuit board assembly including a bracket and a circuit board is provided. The circuit board includes a connector. A compressible member includes an outer conductive portion. The compressible member is positioned between the connector and an inner surface of the bracket. A portion of the connector is positioned through an opening in the bracket and the compressible member is compressed between the connector and the inner surface of the bracket. The circuit board is fastened to the bracket. The circuit board may preferably be in contact with the compressible member. A flange portion of the bracket may preferably be in contact with the compressible member.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.
REFERENCES:
patent: 5317105 (1994-05-01), Weber
patent: 5980275 (1999-11-01), Beaman et al.
3Com Corporation
Baniak Pine & Gannon
Kincaid Kristine
Ngo Hung V
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