Electromagnetic interference and heatsinking

• US 6,583,987 B2
• Filed: 04/16/2002
• Issued: 06/24/2003
• Est. Priority Date: 02/26/1999
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Skinner, Harry G., Kirkbride, Walter M.
• Primary Examiner(s): DATSKOVSKIY, MICHAIL V
• Application Number:
  US10/123,971
• Publication Number:
  US 20020114134A1
• Time in Patent Office: 434 Days
• Field of Search: 361/689, 361/700, 361/702-712, 361/714-719, 361/721-727, 257/659, 257/706-727, 257/796, 257/668, 257/699, 257/698, 165/80.2, 165/80.3, 165/80.4, 165/185, 174/15.1, 174/16.3, 174/252, 174/35.GC, 174/35.R
• US Class Current: 361/704
• CPC Class Codes: H01L 23/36 Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks H01L23/28, H01L23/40, H01L23/42, H01L23/44, H01L23/46 take precedence; heating H01L23/345
• CPC Class Codes: H01L 23/4334 Auxiliary members in encapsulations H01L23/49568 takes precedence
• CPC Class Codes: H01L 23/552 Protection against radiation, e.g. light or electromagnetic waves
• CPC Class Codes: H01L 24/32 of an individual layer connector
• CPC Class Codes: H01L 2924/01006 Carbon [C]
• CPC Class Codes: H01L 2924/01013 Aluminum [Al]
• CPC Class Codes: H01L 2924/01029 Copper [Cu]
• CPC Class Codes: H01L 2924/01033 Arsenic [As]
• CPC Class Codes: H01L 2924/16152 Cap comprising a cavity for hosting the device, e.g. U-shaped cap
• CPC Class Codes: H01L 2924/19041 being a capacitor
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding
• CPC Class Codes: H05K 7/20454 with a conformable or flexible structure compensating for irregularities, e.g. cushion bags, thermal paste
• CPC Class Codes: H05K 9/0028 with retainers or specific soldering features

Abstract

A first apparatus includes a semiconductor device and a heat dissipating device (e.g., a heatsink) thermally coupled to the semiconductor device. The heat dissipating device is located and formed to screen the semiconductor device from external electromagnetic radiation or to contain radiation produced by the semiconductor device. A second apparatus includes a semiconductor device, a heat dissipating device thermally coupled to the semiconductor device, and a grounding structure having a capacitive coupling to the heatsink.

Claims

1. An apparatus comprising:

a semiconductor device;

a heat dissipating device thermally coupled to and DC-isolated from the semiconductor device, the heat dissipating device being formed at least in part as a substantially planar element and configured relative to the semiconductor device to perform at least one of screening the semiconductor device from external electromagnetic radiation and containing radiation produced by the semiconductor device; and

a conducting layer connected to signal ground and disposed substantially parallel to the planar element to form a capacitive structure that AC-couples the heat dissipating device to signal ground; and

wherein the heat dissipating device forms a cavity with a mouth covered by the conductive layer to form a substantially closed cage, the semiconductor device being inside the cage.

2. The apparatus of claim 1, wherein the cage provides substantial shielding to the semiconductor device from external electromagnetic radiation having frequencies of up to about 10 gigahertz.

3. The apparatus of claim 1, wherein the cage substantially contains electromagnetic radiation produced by the semiconductor device from leaking out for frequencies of up to about 3 gigahertz.

4. The apparatus of claim 1, further comprising:

a motherboard, the semiconductor device being electrically connected to the motherboard.

5. The apparatus of claim 4, wherein the conducting layer is fixed to the motherboard.

6. The apparatus of claim 1, further comprising:

a gasket positioned to provide a space between the heat dissipating device and the conductive layer.

7. The apparatus of claim 1, wherein the device further comprises:

a semiconductor die; and

a plastic package encapsulating the semiconductor die and a portion of the conducting layer, the heat dissipating device being located outside of the plastic package.

8. The apparatus of claim 1, wherein the device further comprises:

a semiconductor die; and

a plastic package encapsulating the semiconductor die and the heat dissipating device.

9. The apparatus of claim 8, wherein the conductive layer is encapsulated by the package.

10. The apparatus of claim 9, wherein the die is fixed to the conductive layer and the conductive layer provides structural support to the die.

11. The apparatus of further claim 1, further comprising:

one of a thermally conductive grease and a soft conductor forming a thermal contact between the heat dissipating device and the semiconductor device.

12. An apparatus comprising:

a semiconductor device;

a heat dissipating device thermally coupled to and DC-isolated from the semiconductor device;

a capacitive grounding structure connected to signal ground and configured to AC-couple the heat dissipating device to signal ground, wherein the capacitive grounding structure comprises a conducting plate directly coupled to signal ground and being positioned relative to the heat dissipating device to form a capacitor; and

wherein the heat dissipating device forms a cavity with a mouth covered by the conducting plate to form a substantially closed cage, the semiconductor device being inside the cage.

13. The apparatus of claim 12, wherein the heat dissipating device comprises a heatsink.

14. The apparatus of claim 12, further comprising:

a motherboard, the conducting plate and the semiconductor device being attached to the mother board.

15. The apparatus of claim 12, further comprising:

a lumped capacitor electrically connected between the heat dissipating device and the grounding structure.

16. The apparatus of claim 12, wherein the capacitor has a capacitance at least as large as 20 pico-farads.

17. A computing system comprising:

a microprocessor;

a heat dissipating device thermally coupled to and DC-isolated from the microprocessor, the heat dissipating device formed at least in part as a substantially planar element and configured relative to the microprocessor to shield the microprocessor from external electromagnetic radiation and to substantially contain electromagnetic radiation produced by the microprocessor;

a motherboard, the microprocessor being electrically connected to the motherboard; and

a conducting layer connected to signal ground and disposed substantially parallel to the planar element to form a capacitive structure that AC-couples the heat dissipating device to signal ground, wherein the conducting layer forms a substantially closed cage with the heat dissipating device, the microprocessor being inside the cage.

18. The computing system of claim 17, wherein the cage provides substantial shielding for electromagnetic radiation having frequencies of up to about 40 gigahertz.

19. The computing of claim 17, wherein the microprocessor further comprises:

a semiconductor die; and

a plastic package encapsulating the semiconductor die and at least partially encapsulating the conducting layer.

20. The apparatus of claim 17, further comprising:

a computer housing, the motherboard and cage located inside the housing.

21. A computing system comprising:

a housing;

at least one of a motherboard and a daughterboard located in the housing;

a microprocessor located on the one of a motherboard and a daughterboard;

a heat dissipating device thermally coupled to and DC-isolated from the microprocessor;

a capacitive grounding structure connected to signal ground and configured to AC-couple the heat dissipating device to signal ground; and

wherein the heat dissipating device forms a cavity with a mouth covered by a conductor to form a substantially closed cage, the semiconductor device being inside the cage.

22. The computing system of claim 21, wherein the heat dissipating device comprises a heatsink.

23. The computing system of claim 21, wherein the capacitive AC-coupling substantially reduces emissions of electromagnetic radiation by the heat dissipating device at frequencies above about 30 megahertz.

24. A method of using a heat dissipating device, the method comprising:

generating current in a semiconductor die;

inducing AC current in a heat dissipating device forming a cavity, with a mouth of the heat dissipating device substantially covered by conducting material to form a substantially closed cage, the heat dissipating device thermally coupled to and DC-isolated from the die as a result of the current in the semiconductor die; and

providing electromagnetic emissions shielding by conducting the induced AC current through a capacitive coupling between the heat dissipating device and the conducting material.

25. The method of claim 24, wherein the heat dissipating device comprises a heatsink.

26. The method of claim 24, further comprising:

producing heat from the currents in the semiconductor die; and

conducting the heat away from the die with the heat dissipating device.

27. The method of claim 26, wherein conducting heat away from the die keeps the semiconductor die at a normal operating temperature.

28. The method of claim 24, wherein current is generated in the die at frequencies above 500 megahertz.