RF shield for circuit card having a solid first flange

• US 5,774,344 A
• Filed: 12/06/1995
• Issued: 06/30/1998
• Est. Priority Date: 12/06/1995
• Status: Expired due to Term

• Current Assignee: Google Inc. (Alphabet Inc.)
• Original Assignee: Metricom, Inc.
• Inventors: Casebolt, Matthew P.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): Dinkins, Anthony
• Application Number:
  US08/569,403
• Time in Patent Office: 937 Days
• Field of Search: 361/816, 361/818, 361/752, 361/753, 361/800, 361/799, 361/737, 361/791, 361/802, 361/212, 361/220, 361/814, 174/35 R, 174/35 GC, 174/35 TC, 174/51, 307/89.9, 330/68, 334/85
• US Class Current: 361/800
• CPC Class Codes: H05K 9/0037 Housings with compartments containing a PCB, e.g. partitioning walls

Abstract

A metallized plastic RFI/EMI shield is provided against electromagnetic energy for a circuit card wherein the shield is formed of a box enclosure with two casing halves to enclose the card, the first casing half having a solid flange side walls surrounding the card and the second casing half having a flange formed by flat, plate-like closely-spaced fingers, the fingers confronting, being in electrical contact with and mating in full length with substantially the entire periphery of the side walls of the first casing half. The fingers are preferably spaced with a separation of less than 1/4 wavelength of any measurable harmonic of the intended operating frequency, typically up to the tenth harmonic. A slot may be provided to receive the fingers on the outside of the side walls, and closely-spaced grounding pins arranged around the periphery of the card may extend between the first and second casing halves through ground plated perforations along the edge of the side walls.

Claims

1. A shield against electromagnetic energy for an electromagnetic circuit card, said shield comprising:

a box enclosure for said electromagnetic circuit card, said box enclosure having a first casing and a second casing, said first casing having a solid first flange of a first contour defining side walls surrounding said electromagnetic circuit card and said second casing having a second flange of a second contour defining side walls, wherein said second flange comprises closely-spaced fingers, said fingers confronting, being in electrical contact with and mating in substantially full length with said first contour along substantially the entire periphery of said side walls.

2. The shield according to claim 1 wherein said fingers are spaced from one another at a distance substantially less than 1/4 wavelength of a measurable harmonic of a fundamental operating frequency of said electromagnetic circuit.

3. The shield according to claim 1 wherein said fingers are flat plates having a face for flexibly confronting said first contour.

4. The shield according to claim 3 wherein said second casing is formed of metallized plastic, and wherein said fingers flexibly conform to said first contour.

5. The shield according to claim 1 wherein said side walls are disposed within boundaries defined by said fingers.

6. The shield according to claim 5 wherein said first casing further includes a lip disposed in parallel to said side walls to define a receiving slot for said fingers.

7. The shield according to claim 6 wherein said electromagnetic circuit card has a plated periphery and further including a plurality of closely-spaced pins mating to said periphery and coupling said first casing to said second casing through said periphery.

8. The shield according to claim 6 wherein said electromagnetic circuit card has a periphery of grounded perforations and said first casing further includes a plurality of closely-spaced pins mating to said perforations and coupling said first casing to said second casing through said periphery.

9. A shield against electromagnetic energy for an electromagnetic circuit card, said shield comprising:

a box enclosure for said electromagnetic circuit card, said box enclosure having a first casing and a second casing, said second casing being formed of metallized plastic, said first casing having a solid first flange of a first contour defining side walls surrounding said electromagnetic circuit card and said second casing having a second flange of a second contour defining side walls, wherein said second flange comprises closely-spaced fingers, said fingers confronting, being in electrical contact with and mating in substantially full length with said first contour along substantially the entire periphery of said side walls, wherein said fingers are flat plates having a face for flexibly confronting said first contour and are spaced from one another at a distance substantially less than 1/4 wavelength of a measurable harmonic of a fundamental operating frequency of said electromagnetic circuit.

10. The shield according to claim 9 wherein said first casing further includes a lip disposed in parallel to said side walls to define a receiving slot for said fingers.

11. The shield according to claim 10 wherein said electromagnetic circuit card has a plated periphery and further including a plurality of closely-spaced pins mating to said periphery and coupling said first casing to said second casing through said periphery.

12. A shield against electromagnetic energy for an electromagnetic circuit card, said shield comprising:

a box enclosure for said electromagnetic circuit card, said box enclosure having a first casing and a second casing, said first casing having a solid first flange of a first contour defining side walls surrounding said electromagnetic circuit card and said second casing having a second flange of a second contour defining side walls, wherein said second flange comprises fingers spaced from one another at a distance substantially less than 1/4 wavelength of a measurable harmonic of a fundamental operating frequency of said electromagnetic circuit, said fingers confronting, being in electrical contact with and mating in substantially full length with said first contour along substantially the entire periphery of said side walls.

13. A shield against electromagnetic energy for an electromagnetic circuit card having a plated periphery, said shield comprising:

a box enclosure for said electromagnetic circuit card, said box enclosure comprising

a first casing having a solid first flange of a first contour defining side walls surrounding said electromagnetic circuit card and a lip disposed in parallel to said side walls;

a second casing having a second flange of a second contour defining side walls, wherein said second flange comprises closely-spaced fingers, said side walls disposed within boundaries defined by said fingers, said fingers confronting, being in electrical contact with and mating in substantially full length with said first contour along substantially the entire periphery of said side walls, said lip and said side walls defining a receiving slot for said fingers; and

a plurality of closely-spaced pins mating to said periphery and coupling said first casing to said second casing through said periphery.

14. A shield against electromagnetic energy for an electromagnetic circuit card having a periphery of grounded perforations, said shield comprising:

a box enclosure for said electromagnetic circuit card, said box enclosure comprising

a first casing having a solid first flange of a first contour defining side walls surrounding said electromagnetic circuit card and a lip disposed in parallel to said side walls;

a second casing having a second flange of a second contour defining side walls, wherein said second flange comprises closely-spaced fingers, said side walls disposed within boundaries defined by said fingers, said fingers confronting, being in electrical contact with and mating in substantially full length with said first contour along substantially the entire periphery of said side walls, said lip and said side walls defining a receiving slot for said fingers; and

a plurality of closely-spaced pins mating to said perforations and coupling said first casing to said second casing through said periphery.

15. A shield against electromagnetic energy for an electromagnetic circuit card, said shield comprising:

a first casing having a first flange defining side walls having an inner perimeter and an outer perimeter and bordering said electromagnetic circuit card; and

a second casing comprising;

a solid wall having a periphery substantially similar to said inner perimeter of said first flange; and

a second flange comprising fingers having an inner periphery substantially similar to said outer perimeter of said first flange, said solid wall and said second flange defining a channel adapted to receive said first flange.

16. An electromagnetic shield for use with a circuit card having a plurality of conductive through holes in a conductive pattern on said card, said shield comprising:

a first casing;

a second casing; and

a plurality of closely-spaced pins, arranged in accordance with said pattern, coupling said first casing to said second casing through said through holes.

17. The electromagnetic shield of claim 16 wherein said conductive pattern is disposed about a periphery of said circuit card, at least said first casing being physically coupled to at least a portion of said pattern.

18. The electromagnetic shield of claim 16 wherein said conductive pattern is disposed within a periphery of said circuit card, at least said first casing being physically coupled to at least a portion of said pattern to provide electromagnetic shielding between a first portion of said circuit card and a second portion of said circuit card.