Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-06-30
2001-08-21
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S709000, C361S753000, C174S051000, C024S563000
Reexamination Certificate
active
06278615
ABSTRACT:
BACKGROUND
1. Field of the Present Invention
The present invention generally relates to the field of heatsinks for computer systems and more particularly to an effective method for effectively grounding a heatsink to minimize electro-magnetic interference.
2. History of Related Art
The use of heatsinks in connection with electronic components such as the integrated circuits modules of a computer system is well known. Comprised of a relatively massive piece of conductive metal, heatsinks placed in contact with the package of an integrated circuit module are effective in increasing the rate at which heat produced by the module is dissipated thereby beneficially enabling the module to maintain lower case and junction temperatures. Unfortunately, the conductive material that makes heatsinks effective as a heat dissipation mechanism can also render them effective as secondary antennas that can radiate electronic energy and cause elevated levels of electromagnetic interference. Because even slight amounts of interference can jeopardize the reliable operation of high speed, low power integrated circuits it is desirable to minimize the radiation effect of a heatsink. The level of interference can be effectively reduced by providing multiple ground paths between the heatsink and the ground plane of the circuit board to which the module is mounted. Therefore, it is advantageous to provide a duplicity of conductive paths between the heatsink and ground. Moreover, it is important to provide the ground paths without significantly increasing the cost of the product and without unnecessarily encumbering the heatsink. Heatsinks are frequently employed in the cooling of modules that are socketed to enable easy replacement of the module. Heatsink grounding solutions that involve permanent connections such as solder joints or the like are typically ill suited for use in such environments. Therefore it is desirable to provide an effective means of grounding integrated circuit module heatsinks in such a manner that the grounding mechanism is easily removed or replaced.
SUMMARY OF THE INVENTION
The problems identified above are in large part addressed by a heatsink grounding mechanism in which multiple conductive spring arms of a grounding piece are arranged to contact multiple grounding pads of a printed circuit board to which an integrated circuit module is attached. The spring arms force a ring portion of the grounding piece into contact with the bottom surface of a heatsink positioned in close proximity to an upper surface of the module package. A shielding piece may be used advantageously in conjunction with the grounding piece to prevent inadvertent movement or displacement of the springs arms.
Broadly speaking the invention contemplates a heatsink grounding mechanism and an associated circuit card and computer system. The circuit card includes a printed circuit board to which an integrated circuit module is attached. A heatsink is positioned in contact with or in close proximity to the integrated circuit module package. A heatsink grounding piece of the grounding mechanism is utilized to provide a conductive path between the heatsink and system ground. The grounding piece includes a substantially rectangular and conductive grounding piece ring that defines an aperture. The dimensions of the are suitable for receiving and circumventing the integrated circuit module. The grounding piece includes a set of semi-rigid conductive spring arms that extend away from the grounding piece ring. The spring arms are positioned and oriented such that termination points of the spring arms contact grounding pads on the printed circuit board when the grounding piece is compressed between the heatsink and the circuit board. The force of the spring arms against the circuit board maintains the grounding piece ring in electrical contact with the heat sink and the termination points of the spring arms in electrical contact with the grounding plates.
Preferably, the grounding piece is comprised of spring steel or stainless steel. In one embodiment, the grounding piece ring further defines a set of fastener holes suitable for receiving a corresponding set of fasteners used to attach the heatsink to the circuit board. The heatsink itself is preferably comprised of a conductive slab from which a plurality of conductive fins extend substantially perpendicularly such that the fins are substantially parallel to one another. In the preferred embodiment, the grounding piece fastener holes align with corresponding holes in the heatsink. The springs arms of the grounding piece may be integrally formed with the grounding piece ring by stamping portions of the grounding piece ring to form the spring arms. In addition to the grounding piece, the heatsink grounding mechanism may further include a shielding piece. In this embodiment, the shielding piece preferably includes a substantially rectangular shielding piece ring that defines a shielding piece aperture. Like the grounding piece aperture, the shielding piece aperture is preferably dimensioned for receiving the integrated circuit module. The shielding piece further includes a set of shielding piece walls that extend substantially perpendicularly from the shielding piece ring. The shielding piece walls are positioned to substantially enclose the spring arms of the grounding piece when the shielding piece ring is positioned between the grounding piece ring and the heatsink. The shielding piece is comprised of steel in the preferred embodiment. In one embodiment, the shielding piece ring further defines a set of aperture holes suitable for receiving the corresponding set of fasteners.
REFERENCES:
patent: 5053924 (1991-10-01), Kurang
patent: 5357404 (1994-10-01), Bright et al.
patent: 5373101 (1994-12-01), Barabolak
patent: 5566052 (1996-10-01), Hughes
patent: 5653600 (1997-08-01), Ollivier
Brezina Johnny Roy
Corbin, Jr. John Saunders
Massey Daniel Edward
Gandhi Jayprakash N.
International Business Machines - Corporation
Lally Joseph P.
McBurney Mark E.
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