JP2000059072A - Emi shield - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanism which is capable of sufficiently shielding with respect to plural EMI radiation heat releasing device which are different from each other in thickness and improving them in thermal conductivity. SOLUTION: An EMI shield 21 is formed of conductive film or conductive mesh screen, which is satisfactory in thermal conductivity and EMI characteristics to surround devices 23, 24, and 25 mounted on a board 22. The shield 21 is connected to the board 22 by a connection mechanism 28 as a conductive mounting mechanism. Heat sinks 26 are jointed to the shield 21, are necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electromagnetic interference shielding, and more particularly to heat transfer interfaces.
(thermal conducting interface).

[0002]

2. Description of the Related Art As the frequency of computers increases and power increases, so does the radiated electromagnetic (EM) energy. EM energy originates from various components in computer systems. The per-system enclosure is no longer sufficient to confine EM energy, thus necessitating the placement of an individual EM interference (EMI) enclosure (or container) over the radiating component. But,
These same components generally generate heat that must be dissipated. Therefore, the EMI enclosure must also cool the components.

In order to attenuate the EMI of a single processor board, it is effective to use a rigid EMI container.
The rigid container is computer machined or cast to precisely match a single processor (or other single device) on the substrate. Because the container is in direct contact with the device, a container made of a thermally conductive material transfers heat to a heat sink device attached to or integrated with the container. The heat sink can be a cooling fin, a fan, or both. However, these containers can generally be processed from a single block of material such as aluminum by a computer numerically controlled fabrication machine. Casting requires considerable tooling and production time. These processes are costly, time consuming, and costly.

[0004] Furthermore, as additional heat generating devices are added to the substrate, the thermal effect of the EMI container is greatly reduced. As shown in FIG. 1, the EMI container 11
2 and attached to devices 13, 14 and 1
5 surrounding. Some heat sinks 16
It is attached to the container 11. Between the heat sink 16 and the container 11 and between the container 11 and the devices 13, 14 and 15, a thermal interface material 17 can be arranged. Note that devices 13, 14, and 15 are not coplanar. This is the processor and RA
It may be due to manufacturing tolerances because of different types of devices, such as M, or if the devices are of the same type. Therefore, a gap 18 exists between the devices 13, 15 and the container 11. The gap shown in FIG. 1 is exaggerated for clarity, but even a small difference, such as 10 mils (1 mil is a thousandth of an inch) is sufficient to reduce thermal conductivity. Please note that. Therefore, heat 19 is efficiently transferred only from the device 14 to the container 11. Heat transfer from the devices 13, 15 is not efficient. The use of thermal interface material 17 removes small gaps inherent in surface roughness, but not enough to remove large gaps 18 from non-coplanar surfaces. The prior art has attempted to remove the gap 18 using a pad (not shown) located between the devices 13, 15 and the container 11. However, the pads are not pre-manufactured and are not designed for a particular gap. Therefore, if the pad is too thin, good heat conduction cannot be obtained. On the other hand, if the pad is too thick, when the container 11 is fixed to the substrate 12, a force will be applied to the underlying device. This force can cause damage to the device or break the connection between the device and the substrate 12 or other device. If the processing of the container 11 is inaccurate, or if the device 14 is slightly thicker than expected due to accumulation of tolerances, the rigid container 11 itself may apply force to the device, especially the device 14. is there. Further, the force can be caused by thermal expansion of the container 11, the substrate 12, the device, and / or the pad. Although a better thermal conductor than air, pads do not provide an acceptable level of thermal conductivity. The container of FIG. 1 provides sufficient EMI shielding, but has poor thermal properties due to the different thicknesses of the heating devices.

[0005]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a mechanism for providing sufficient shielding against EMI radiation and providing good thermal conductivity for a plurality of heating devices of different thicknesses. To provide.

[0006]

SUMMARY OF THE INVENTION These and other objects, features and technical advantages are flexible because they conform to the surface of a substrate, and
This is achieved by systems and methods that utilize EMI shields that have both thermal and electrical conductivity. E of the present invention
The MI shield conforms to the various features of the device mounted on the substrate, so that it directly contacts the heat generating devices in the shield, while confining EMI energy generated by EMI sources within the surrounding portion of the substrate.

[0007] The shield of the present invention is a mesh screen or foil made of a conductive material to form an EMI shield. The EMI shield is also thermally conductive to allow heat transfer to the shield, and allows the shield to be manipulated to conform to devices mounted on the substrate. It is also ductile enough to break it in. The edge of the shield is attached to a portion of the substrate by a conductive coupling mechanism. The cavity formed by the shield and the substrate confine EMI radiation. A heat sink is coupled to the heating device with the shield in between. Note that the shield can be perforated to allow for heat sink and device mounting capabilities. The shield of the present invention is provided with a selective coating of a thermal conductivity improving material, inter alia, at the interface between the shield and the device and at the interface between the shield and the heat sink. Because the shield is a mesh or foil, there is no need to make and attach expensive and wasteful containers. Furthermore, because the shield is flexible, the shield does not apply any force to the device due to thermal expansion of the device, substrate, or shield.

The foregoing, rather broad, general description of features and technical advantages of the present invention is intended to facilitate a more detailed description of the invention that follows. Additional features and advantages, which form the subject of the claims of the invention, will be described hereinafter. As is clear to the technician,
The disclosed concepts and particular embodiments can be readily used as a basis for modifying or designing other structures to carry out the same objects of the invention. Also, as will be apparent to those skilled in the art, such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The mechanism of the present invention is an EMI shield adapted for good thermal and EMI characteristics. FIG.
Shows the EMI shield 21 of the present invention attached to a part of the component substrate 22 by a coupling mechanism 28. The EMI shield 21 is a conductive foil or mesh screen. The EMI shield is
Form a Faraday cage or shield surrounding the devices 23, 24, 25 attached to the substrate 22. Note that the printed circuit board forms part of the Faraday cage, as shown in FIG. The EMI shield is, for example, aluminum,
It can be formed from any conductive material, such as gold, silver, copper, ferrous metals, alloys, or ceramic materials. Other materials can be used as long as they have good thermal conductivity and EMI characteristics and have sufficient flexibility to conform to different devices and shapes on the substrate 22. If the shield 21 is a mesh, it is desirable that the mesh size be sufficient to confine EMI radiation of various frequencies of interest. The shield 21 includes devices 23, 24,
It is flexible so that it can be adapted to external shapes of 25 heights. Even if the thickness of the device is different due to manufacturing tolerances or different device types, the shield 21 can directly contact each heating device without gaps. Therefore, heat 29
Are the devices 23, 24, 2 coupled to the shield 21
5 to the shield 21 efficiently.

The shield 21 is connected to the substrate 22 by a coupling mechanism 28 which is a conductive mounting mechanism. The coupling mechanism electrically connects the shield 21 and the ground plane of the substrate 22 so that EMI confinement is maintained. This mechanism can be a clamp (fastener) or a bar (rod) that fixes the shield 21 in place. The coupling mechanism may be a solder or a screw for attaching the shield 21 to the substrate 22. Mechanism 28
Can be holes provided in a regular pattern on the shield 21 that are coupled to pins arranged on the substrate 22. This pattern is regular, EMI
Must have sufficient spacing to maintain containment. Coupling mechanism 28 is a via (via hole or hole or hole) in a regular pattern through the substrate coupled between the conductive layer on the surface of substrate 22 and the ground plane of substrate 22. Is also possible. Shield 2
1 is a finger gasket, a conductive adhesive, or
It is coupled to the conductive layer via another EMI gasket.
The via pattern must be regular and have sufficient spacing to maintain EMI confinement. The coupling mechanism 28 can also be a conductive adhesive.
Note that the shield need not cover the entire substrate 22 because the shield must surround only one or more portions of the substrate that generate EMI energy. Therefore, the coupling mechanism is not always arranged at the peripheral edge of the substrate, but can be arranged inside the substrate.

A heat sink 26 is coupled to shield 21 as needed. Each heat sink 26
It is possible to adapt to the specific heat dissipation requirements of each of the heating devices. As shown in FIG. 2, the heat sink 26 is disposed at the same place as the heat generating device with the shield 21 interposed therebetween, and is coupled to the heat generating device. According to this configuration, since the heat conduction path is shortest, the most efficient heat transfer is obtained. The heat sink 26 can be attached to the shield 21 by a thermally conductive adhesive, pad, grease, or paraffin wax. The heat sink 26 has at least one of the shields
The three holes 34 allow direct attachment to the device. These holes allow the passage of pins, clamps, or screws that allow for direct attachment of the device to the shield 26. The holes also allow for direct attachment of the shield 26 and the device via a thermally conductive adhesive. The holes are properly positioned and / or sufficiently sized to maintain EMI containment. Unless the shield 21 is broken and the EMI shield is not damaged, the heat sink 26
Can be fixed to the device. Note that the heat sink need only be fixed to the heating device. Furthermore, for example, two heat sinks for five heating devices,
Note also that a single heat sink can handle more than one heating device. further,
Not all heat-generating devices require a heat sink because sufficient heat can be dissipated through the air, substrate 22, or other location.

The shield 21 of the present invention also includes a selectively disposed thermal interface material 27 to fill gaps inherent in surface roughness. This material can be placed on the shield, which is attached to the heat sink 26 and any of the heat generating devices 23,24,25. Alternatively, material 27 may be selected from commercially available paraffin wax, mineral-filled paraffin, silicone grease, and / or adhesive. When sufficient heat and / or pressure is applied, the material will fill the gap.

The shield 21 of the present invention includes a shield 21
Non-conductive coating (not shown) selectively disposed on
Can also be included. Thereby, the shield 21
And / or an unexpected electrical connection between the device and the ground plane via the shield 21 is prevented. The shield may be coated with a material that protects it from the environment, for example, from corrosion. It is also possible to seal the shield against the substrate to prevent air or water from entering. This results in an environmentally sealed unit from contamination by dirt, dust and / or biological waste.

FIG. 3 shows another embodiment of the shield of the present invention. In FIG. 2, the EMI generation device is mounted on only one side of the substrate 22. In FIG. 3, the EMI generation device 33 is
Attached to both sides. Therefore, each side of the substrate 32 must be surrounded by shields 31a, 31b. Each shield must be attached to the substrate 32 by a coupling mechanism 28. Each coupling mechanism can be connected to a ground plane to form two independent Faraday cages, each surrounding one side of the substrate 32. Alternatively, the coupling mechanisms can be connected together to form a Faraday cage surrounding both sides of the substrate 32. In another embodiment, the shield 21 is formed around at least two peripheral edges to form a bag (not shown) surrounding both sides of the substrate. Thus, the coupling mechanism 28 is only needed for the remaining peripheral edges. In this embodiment, the substrate 3
It is advantageous if 2 has electrical connections and mechanical attachments on only one side or on both sides.

Having described the invention and its advantages in detail, of course, various modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.
Alternatives and modifications are possible.

The embodiments of the present invention have been described in detail above. Hereinafter, examples of each embodiment of the present invention will be described.

Embodiment 1 An electromagnetic interference (EMI) shield, a flexible sheet 21 of thermally and electrically conductive material, and a first interface portion of the sheet in contact with a heat sink 26 And heating component 2
Electrically connecting the second interface portion of the sheet in contact with 3, 24, 25, the EMI shield and the conductor 28,
Forming an EMI enclosure to confine EMI energy generated within the enclosure;
An EMI shield including a third interface portion of the sheet.

(Embodiment 2) One of the first plurality of boundary surface portions, each of which contacts the respective heat sink 26 of the plurality of heat sinks.
And the second interface portion is one of a second plurality of interface portions that respectively contact the respective heat generating components 23, 24, 25 of the plurality of heat generating components. The EMI shield according to embodiment 1, wherein

(Embodiment 3) Flexible sheet 21
3. The EMI shield of embodiment 1, wherein the EMI shield is capable of conforming to the outer shape of the heat generating component so that it physically contacts the heat generating component 23, 24, 25.

(Embodiment 4) Flexible sheet 21
Is a foil film, wherein E is a foil film.
MI shield.

(Embodiment 5) Flexible sheet 21
Is a sheet of filament netting, and the size and spacing of the filaments are selected to confine EMI energy.
The EMI shield according to 1.

(Embodiment 6) The thermally and electrically conductive material 21 is selected from the group consisting of an alloy, aluminum, gold, silver, copper, iron metal, and a ceramic material. An EMI shield according to embodiment 1.

(Embodiment 7) First and second boundary surface portions 2
The EMI shield according to claim 1, wherein 1 is coated with a thermal conductivity improving material.

(Embodiment 8) Remaining part 21 of shield
8. The EMI shield of embodiment 7, wherein the EMI shield is coated with an electrically insulating material.

(Embodiment 9) Electromagnetic interference (EMI) energy is generated and a plurality of heat generating components 23, 24,
Surrounding part of the printed circuit board 22 comprising
An EMI enclosure for confining the EMI energy, wherein the flexible sheet 21 is formed of a thermally and electrically conductive material that conforms to the outer shape of each of the plurality of heat generating components, and each of the plurality of heat sinks includes: A plurality of first interface portions of the sheet contacting respective heat sinks 26, and a plurality of second interface portions of the sheet respectively contacting respective heat generating components of the plurality of heat generating components. And electrically connecting the sheet and the conductor 28 to each other,
An EMI enclosure having a third interface portion of the sheet forming the MI enclosure.

Embodiment 10 Encloses electromagnetic interference (EMI) energy generated from a portion of a printed circuit board 22 and dissipates heat generated by a plurality of heat generating components 23, 24, 25 located on that portion of the board. Providing a flexible sheet 21 of thermally and electrically conductive material that conforms to the outer shape of each of the plurality of heat generating components; and providing a plurality of first interface portions of the sheet. Connecting each of the plurality of heat sinks to dissipate heat; connecting each of the plurality of second interface portions of the sheet to each of the plurality of heat generating components. Allowing heat to be conducted through the sheet to the heat sink;
Electrically connecting the third interface portion of the sheet to the electrical conductor to form an EMI enclosure around said portion of the printed circuit board to confine EMI energy.

[0027]

Thus, a technical advantage of the present invention is that it provides good heat transfer characteristics to the EMI shield when the heating device has different height profiles.

Another technical advantage of the present invention is that
Radiation is confined, while thermal interface resistance is minimized.

Another technical advantage of the present invention is that the shield of the present invention requires, among other things, no machining,
It is less expensive than prior art EMI containers.

[Brief description of the drawings]

FIG. 1 shows an EMI container according to the prior art.

FIG. 2 illustrates an EMI heat shield of the present invention used on a substrate.

FIG. 3 illustrates another embodiment of the EMI heat shield of the present invention.

[Explanation of symbols]

 21: Flexible shield 22: Printed circuit board 23, 24, 25: Heat generating component 26: Heat sink 27: Thermal interface material 28: Conductor 29: Heat

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Terrell Morris Garland, Texas, USA Pyramid Drive 1102 (72) Inventor Eric Peterson McKinney, Texas, USA Crossing 2728

Claims (1)

[Claims] 1. An electromagnetic interference (EMI) shield comprising: a flexible sheet of thermally and electrically conductive material; a first interface portion of the sheet in contact with a heat sink; A third interface portion of the sheet that electrically connects the EMI shield and the conductor to form a EMI enclosure and confine EMI energy generated within the enclosure; An EMI shield including a surface portion.