EMI reduction device and assembly

• US 6,219,239 B1
• Filed: 05/26/1999
• Issued: 04/17/2001
• Est. Priority Date: 05/26/1999
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Chan, Bertram Kim Cheong, Gardner, Susannah, Mellberg, Hans T.
• Primary Examiner(s): THOMPSON, GREGORY D
• Application Number:
  US09/320,412
• Time in Patent Office: 692 Days
• Field of Search: 165/80.2, 165/80.3, 165/185, 174/16.3, 174/35.R, 174/35.GC, 361/704, 361/707, 361/709-710, 361/715, 361/816, 361/818
• US Class Current: 361/704
• CPC Class Codes: H05K 7/1431 Retention mechanisms for CPU modules
• CPC Class Codes: H05K 9/002 with localised screening

Abstract

An EMI reduction device is coupled between a printed circuit board (PCB) assembly and a heat sink. The PCB assembly includes a processor core that is the source of unintentional electromagnetic interference (EMI). The EMI reduction device is attached to a heat sink which is positioned over the processor core such that it capacitively couples emissions from the processor core to a grounding plane resident in the PCB assembly, thereby reducing the unintentional EMI. Simultaneously, the EMI reduction device is able to maintain thermal contact with the heat sink.

Claims

1. An electronic assembly, comprising:

a circuit board having a top surface and a bottom surface, the circuit board including an electronic device mounted on the top surface thereof;

a thermal dissipation device positioned over the top surface of the circuit board and thermally contacting the electronic device; and

an Electromagnetic Interference (EMI) reduction device interposed between the circuit board and the thermal dissipation device, the EMI reduction device having top surface and a bottom surface, the EMI reduction device including a plurality of mounting tabs projecting from the top surface thereof and a plurality of spring fingers projecting from the bottom surface thereof,

wherein the EMI reduction device is attached to the thermal dissipation device via the mounting tabs, and wherein the EMI reduction device contacts the circuit board via the spring fingers.

2. The assembly of claim 1, wherein the mounting tabs project from an outer periphery of the EMI reduction device.

3. The assembly of claim 1, wherein the spring fingers contact the circuit board at contact points that surround the electronic device, and wherein the EMI reduction device has no physical contact with the electronic device.

4. The assembly of claim 1, wherein the EMI reduction device has an aperture defined therein, the aperture communicating with the top surface and the bottom surface of the EMI reduction device, wherein the thermal dissipation device maintains thermal contact with the electronic device through the aperture.

5. The assembly of claim 4, wherein the spring fingers are disposed laterally of the aperture.

6. The assembly of claim 1, wherein the thermal dissipation device has a top surface and a bottom surface, and wherein the thermal dissipation device includes a thermal compound disposed on the bottom surface thereof, the thermal compound of the thermal dissipation device contacting the electronic device.

7. The assembly of claim 1, wherein the EMI reduction device includes a dielectric layer disposed on the bottom surface thereof, the dielectric layer of the EMI reduction device contacting the circuit board.

8. The assembly of claim 1, further comprising:

at least one retention clip passing through the EMI reduction device and securing the thermal dissipation device to the circuit board.

9. The assembly of claim 1, wherein the electronic device is a processor.

10. An Electromagnetic Interference (EMI) reduction device capable of reducing electromagnetic emissions emanating from an electronic device of a circuit board, the EMI reduction device comprising:

a frame having a top surface and a bottom surface;

a plurality of mounting tabs projecting from the top surface of the frame, the mounting tabs adapted to couple the EMI reduction device to a thermal dissipation device; and

a plurality of spring fingers projecting from the bottom surface of the frame, the spring fingers adapted to contact the circuit board at points surrounding the electronic device and position the frame relative to the circuit board.

11. The device of claim 10, wherein the frame has an aperture defined therein, the aperture communicating with the top surface and the bottom surface of the frame, wherein the aperture is adapted to surround the electronic device.

12. The device of claim 11, wherein the spring fingers are disposed laterally of the aperture.

13. The device of claim 10, wherein the mounting tabs project from an outer periphery of the frame.

14. The device of claim 10, wherein the bottom surface of the frame is non-electrically conductive.

15. The device of claim 10, wherein the top surface of the frame is electrically conductive.

16. A method of reducing Electromagnetic Interference (EMI) emissions emanating from and dissipating heat generated by an electronic device mounted on a circuit board, the method comprising the steps of:

providing an EMI reduction device having a top surface and a bottom surface and having an aperture defined therein, the aperture communicating with the top surface and the bottom surface;

attaching the EMI reduction device to a thermal dissipation device with a plurality of mounting tabs projecting from the top surface of the EMI reduction device;

contacting the circuit board with a plurality of spring fingers projecting from the bottom surface of the EMI reduction device; and

contacting the electronic device with the thermal dissipation device through the aperture of the EMI reduction device.

17. The method of claim 16, further comprising the step of:

surrounding an outer periphery of the electronic device with the EMI reduction device.

18. The method of claim 16, further comprising the step of:

securing the thermal dissipation device to the circuit board with at least one retention clip passing through the EMI reduction device.

19. The method of claim 16, wherein the step of contacting the circuit board includes contacting the circuit board at contact points surrounding the electronic device.

20. The method of claim 16, wherein the step of contacting the circuit board includes contacting a ground plane of the circuit board.