Apparatus for providing RFI/EMI isolation between adjacent circuit areas on a single circuit board

• US 5,252,782 A
• Filed: 06/29/1992
• Issued: 10/12/1993
• Est. Priority Date: 06/29/1992
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: E-Systems Incorporated (Rtx Corporation)
• Inventors: Cantrell, Gregory A., Marshall, Paul V., Parks, David L.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): LEDYNH, BOT L
• Application Number:
  US07/905,305
• Time in Patent Office: 470 Days
• Field of Search: 174/35 R, 174/35 MS, 174/35 GC, 174/261, 174/262, 361/390, 361/391, 361/392-395, 361/397, 361/399, 361/400, 361/401, 361/412, 361/415, 361/424
• US Class Current: 174/387
• CPC Class Codes: H05K 9/0033 disposed on both PCB faces
• CPC Class Codes: H05K 9/0037 Housings with compartments containing a PCB, e.g. partitioning walls
• CPC Class Codes: Y10S 174/34 PCB in box or housing

Abstract

A sensitive circuit area on a circuit board is isolated from an adjacent located non-sensitive circuit area by surrounding the sensitive circuit area with electrically interconnected ground planes positioned on the opposite sides of the circuit board. The isolation system further includes a "clam shell" RF/IF tight shield attached to each side of the circuit board enclosing the sensitive circuit area. A partially conductive gasket is placed between the clam shell and the top and bottom circuit board surfaces to enhance isolation performance.

Claims

1. Apparatus for isolating a first circuit area from an adjacent second circuit area on a circuit board having a top surface and a bottom surface, comprising:

a first ground plane substantially covering the top surface surrounding the first circuit area;

a second ground plane substantially covering the bottom surface opposite from and aligned with the first ground plane surrounding the first circuit area;

means for electrically connecting the first ground plane to the second ground plane, the electrically connected first and second ground planes inhibiting the propagation of interference energy through the circuit board between the first and second circuit areas; and

a conductive clam shell shield for inhibiting airborne propagation of interference energy between the first and second circuit areas, the shield mounted above and below the circuit board to enclose the first circuit area.

2. The apparatus for isolating as in claim 1 wherein the means for electrically connecting comprises a plurality of conductors extending through the board between and connected to the first and second ground planes.

3. The apparatus for isolating as in claim 2 wherein the plurality of conductors are selectively positioned with respect to each other.

4. The apparatus for isolating as in claim 1 wherein the conductive clam shell shield comprises:

an upper half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area, the upper half shell further including a cover mounted to the peripheral wall;

a lower half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area, the lower half shell further including a cover mounted thereto; and

means for attaching the upper half shell to the top surface of the circuit board and the lower half shell to the bottom surface of the circuit board to enclose the first circuit area.

5. The apparatus for isolating as in claim 4 wherein the peripheral walls of the upper and lower halves of the conductive clam shell shield as attached to the top and bottom surfaces of the circuit board are sized and shaped to conform with the first and second ground planes, respectively, surrounding the first circuit area.

6. The apparatus for isolating as in claim 4 further including:

a first partially conductive gasket positioned between the peripheral wall of the upper half of the clam shell shield as attached to the top surface of the circuit board and the first ground plane as covering the top surface of the circuit board; and

a second partially conductive gasket positioned between the peripheral wall of the lower half of the clam shell shield as attached to the bottom surface of the circuit board and the second ground plane as covering the bottom surface of the circuit board.

7. The apparatus for isolating as in claim 6 wherein each peripheral wall includes a base having a channel therein for seating the partially conductive gasket.

8. The apparatus for isolating as in claim 1 wherein each of the first and second ground planes comprises a strip ground plane surrounding the first circuit area.

9. The apparatus for isolating as in claim 1 wherein the first circuit area includes a sub-area therein and wherein each of the first and second ground planes comprises a planar sheet ground plane covering an area within the first circuit area surrounding the sub-area.

10. Apparatus for isolating a first circuit area from an adjacent second circuit area on a circuit board having a top surface and a bottom surface, comprising:

a first ground plane substantially covering the top surface surrounding the first circuit area;

a second ground plane substantially covering the bottom surface opposite from and aligned with the first ground plane surrounding the first circuit area;

means for electrically connecting the first ground plane to t he second ground plane, the electrically connected first and second ground planes inhibiting the propagation of interference energy through the circuit board between the first and second circuit areas;

a third ground plane covering the top surface of the board to divide the first circuit area;

a fourth ground plane covering the bottom surface of the circuit board opposite from and aligned with the third ground plane to divide the first circuit area; and

means for electrically connecting the third ground plane to the fourth ground plane, the electrically connected third and fourth ground planes inhibiting the propagation of interference energy through the circuit board within the first circuit area.

11. The apparatus for isolating as in claim 10 further including means for electrically connecting the connected third and fourth ground planes to the connected first and second ground planes.

12. The apparatus for isolating as in claim 10 further including a conductive clam shell shield attached to each side of the circuit board for enclosing the first circuit area, the conductive clam shell shield comprising:

an upper half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area and at least one interior wall dividing the first circuit area, the upper half shell further including a cover mounted to the peripheral wall;

a lower half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area and at least one interior wall dividing the first circuit area, the lower half shell further including a cover mounted to the peripheral wall; and

means for attaching the upper half shell to the top surface of the circuit board and the lower half shell to the bottom surface of the circuit board whereby the peripheral walls of the upper and lower halves are sized and shaped to conform with the first and second ground planes, respectively, and the interior walls of the upper and lower halves are sized and shaped to conform with the third and fourth ground planes, respectively.

13. Apparatus for isolating a first circuit area from an adjacent second circuit area on a circuit board having a top surface and a bottom surface, comprising:

a first ground plane substantially covering the top surface surrounding the first circuit area;

a second ground plane substantially covering the bottom surface opposite from and aligned with the first ground plane surrounding the first circuit area;

means for electrically connecting the first ground plane to the second ground plane, the electrically connected first and second ground planes inhibiting the propagation of interference energy through the circuit board between the first and second circuit areas;

a third ground plane covering the top surface of the board to surround a third circuit area within the first circuit area;

a fourth ground plane covering the bottom surface of the circuit board opposite from and aligned with the third ground plane to surround the third circuit area; and

means for electrically connecting the third ground plane to the fourth ground plane, the electrically connected third and fourth ground planes inhibiting the propagation of interference energy through the circuit board within the first circuit area.

14. The apparatus for isolating as in claim 13 further including means for electrically connecting the connected third and fourth ground planes to the connected first and second ground planes.

15. The apparatus for isolating as in claim 13 further including a conductive clam shell shield attached to each side of the circuit board for enclosing the first circuit area, the conductive clam shell shield comprising:

an upper half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area and an interior wall defining an area having a size and shape to substantially surround the third circuit area, the upper half shell further including a cover mounted to the peripheral wall;

a lower half shell having a peripheral wall defining an area having a size and shape to substantially surround the first circuit area and an interior wall defining an area having a size and shape to substantially surround the third circuit area, the lower half shell further including a cover mounted to the peripheral wall; and

means for attaching the upper half shell to the top surface of the circuit board and the lower half shell to the bottom surface of the circuit board whereby the peripheral walls of the upper and lower halves are sized and shaped to conform with the first and second ground planes, respectively, and the interior walls of the upper and lower halves are sized and shaped to conform with the third and fourth ground planes, respectively.

16. Apparatus for providing interference isolation on a circuit board having a top surface and a bottom surface, the circuit board further having an adjacent first circuit area and second circuit area identified thereon, comprising:

a first set of opposed interconnected ground planes for inhibiting the propagation of interference energy through the circuit board between the first and second circuit areas, comprising;

a first conductor on the top surface of the circuit board surrounding the first circuit area;

a second conductor on the bottom surface of the circuit board aligned with first conductor;

a plurality of selectively spaced conductors extending through the circuit board connected to and between the first and second conductors; and

a conductive clam shell enclosure shield for inhibiting the airborne propagation of interference energy between the first and second circuit areas, comprising;

an upper half shell having a cover and a peripheral wall mounted thereto, the peripheral wall defining an area sized and shaped to substantially conform to the size and shape of the first circuit area, the upper half shell attached to the top surface of the circuit board so that the position of the peripheral wall substantially coincides with the position of the first conductor surrounding the first circuit area; and

a lower half shell having a cover and a peripheral wall mounted thereto, the peripheral wall defining an area sized and shaped to substantially conform to the size and shape of the first circuit area, the lower half shell attached to the bottom surface of the circuit board so that the position of the peripheral wall substantially coincides with the position of the second conductor surrounding the first circuit area.

17. The apparatus for providing interference isolation as in claim 16 further comprising:

a first conductive gasket positioned between the peripheral wall of the upper half of the clam shell attached to the top surface of the circuit board and the first conductor on the top surface of the circuit board; and

a second conductive gasket positioned between the peripheral wall of the lower half of the clam shell attached to the bottom surface of the circuit board and the second conductor on the bottom surface of the circuit board.

18. The apparatus for providing interference isolation as in claim 16 wherein the first circuit area includes a first and a second sub-areas identified therein, the apparatus further comprising a second set of opposed interconnected ground planes for inhibiting the propagation of interference energy through the circuit board between the first and second sub-areas, comprising:

a third conductor on the top surface of the circuit board separating the first sub-area from the second sub-area;

a fourth conductor on the bottom surface of the circuit board aligned with third conductor; and

a plurality of selectively spaced conductors extending through the circuit board connected to and between the third and fourth conductors.

19. The apparatus for providing interference isolation as in claim 18 further comprising means for electrically connecting the connected first and second conductors to the connected third and fourth conductors.

20. The apparatus for providing interference isolation as in claim 18:

wherein the upper half shell further includes an interior wall mounted therein and positioned to coincide with the positioned third conductor when the upper half shell is mounted to the top surface; and

wherein the lower half shell further includes an interior wall mounted therein and positioned to coincide with the position of the fourth conductor when the lower half shell is mounted to the bottom surface.

21. The apparatus for providing interference isolation as in claim 16 wherein the first and second conductors comprise linear conductive strips.

22. The apparatus for providing interference isolation as in claim 16 wherein the first and second conductors comprise planar conductive sheets.