Heat exchange – With retainer for removable article – Electrical component
Reexamination Certificate
1999-11-24
2001-09-11
Atkinson, Christopher (Department: 3743)
Heat exchange
With retainer for removable article
Electrical component
C165S185000, C257S719000, C257S718000, C361S704000
Reexamination Certificate
active
06286586
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of mounting heat sinks to circuit components and other devices that generate thermal energy so as to provide assisted cooling to such devices. The invention comprises a torsion bar clamp apparatus and a method for applying a compressive force to stacked electronic components for improving thermal and mechanical contact between a heat dissipating device and a heat generating circuit component.
BACKGROUND OF THE INVENTION
Electronic components on circuit boards, such as, for example, power transistors, processors and the like can generate significant amounts of heat which must be removed in order to ensure reliable component operation. Some of the heat can be, and is dissipated through the components' leads. Much of the excess heat, however, is removed to ambient air. Cooling can be assisted and improved by thermally coupling a finned, pinned or other type of heat sink to the circuit component, thereby increasing the surface area over which heat from the component may be dissipated to ambient air.
In a number of known configurations, a heat sink having fins, pins, or other heat radiating structures is mounted via a releasable leaf spring type spring clip to an upper surface of a circuit component. The circuit component usually is releasably mounted in a socket which is in turn attached to a circuit board. The known spring clip may attach to bosses projecting from opposite peripheral sides of the component or of the socket in which the component is mounted. A portion of the clip crossing over the heat sink bears down on the top of the heat sink, applying a compressive force to retain the heat sink in intimate stacked relation to the heat generating components.
A common problem with such prior art clamping methods is that the high forces required to install or remove the clips often result in the circuit board being damaged during installation and/or removal of the clips. Two “failure” mechanisms resulting from installation or removal-related damage are understood. First, the ends of the clips can contact and damage conductor traces on the surface of the circuit board during installation or removal. Second, some clips require tools for installation and/or removal, and the tools may either flex or strike the circuit board or other components, causing damage. This second form of damage is especially likely to occur if the tool is misused, or if an improper substitute tool is used. Additionally, the need for any type of tool for installation or removal of a clip is seen as an unfavorable alternative in the industry, regardless of the risk of board damage.
In addition, prior art clamping systems have typically been made of metal, which creates the danger of shorting circuit boards or components mounted thereon should the clip become disengaged from the devices to which they are clamped. This potential for circuit board damage and failure has led many in the industry to avoid using labor saving clamps in favor of more labor intensive but safer methods of mechanical fastening, such as screws, bolts and the like.
As a result of the disadvantages present in the prior art, there is a need for a device and method for thermally and mechanically coupling a heat sink to an electronic component or other device needing cooling which poses less risk of damage to a circuit board during installation, does not require tools to install or remove, and will not short out a circuit board or adjacent components should the clip become dislodged during installation or use.
SUMMARY OF THE INVENTION
The clamping device of the present invention provides a compressive force to stacked components without the potential for damaging a printed circuit board and without the need for tools to accomplish installation and removal. In addition, the invention may be manufactured using non-conductive plastic, eliminating the possibility of shorting expensive circuit boards and/or other components in the unlikely event that the clamp becomes dislodged during use.
The clamping device includes a torsion bar having at least one lever and mounting means for securing the torsion bar in operative position above a heat sink stacked atop a heat generating circuit component. When installed, the torsion bar is stressed causing the lever to impart a force to the heat sink and the mounting means to impart an opposing force to the component or other surface to which the clamping device may be mounted, thus causing the stacked heat sink and component to be clamped together. These torsion bar/lever and mounting means can be manufactured separately and later joined, or they can be manufactured as a single, unitary, device, as a matter of design choice.
In the preferred embodiment of the invention, the torsion bar and mounting means are injection molded as a single piece made preferably of an essentially non-conductive plastic. The torsion bar comprises two integral, outwardly projecting levers, each extending in a different direction and biased toward the device to be clamped such that pressing the levers against the device causes rotational stress on the torsion bar. The torsion bar is frangibly attached to two mounting legs located at the ends of the bar.
The mounting legs include structures that attach to corresponding structures forming a part of either the component to be cooled or of a mounting socket in which the component is mounted or of the circuit board. In use, the clamp is aligned atop a heat sink such that the ends of the levers contact the surface of the heat sink and the structures on the mounting legs will engage the corresponding structures of the component or socket when a downward force is applied to the clamp. As downward force is then applied to the clamp, the levers engage the heat sink and stress the torsion bar by causing it to rotate in opposite directions. As continued pressure is applied the torsion bar is stressed to such a point that the bar rotates and breaks the frangible attachment between bar and mounting legs. Finally, the mounting legs engage bosses or other structures on the device or socket and are retained in place, installation thus being completed. When installed the torsion bar is held in a state of rotational stress by the oppositely applied pressure of the levers against the heat sink. This stress imparts a corresponding downward force to the top of the heat sink base and an opposing upward force to the mounting legs where the mounting legs engage the component or socket, effectively clamping the heat sink and component together.
In another embodiment of the invention, the torsion bar and mounting legs are injection molded separately and assembled together such that the separate parts operate in the same manner as the preferred embodiment.
In another embodiment of the invention, the torsion bar and mounting legs are injection molded separately, and the mounting legs include mounting slots along a top edge for snap fit mounting of the torsion bar therein. The legs are joined by a separate cross member, thus forming a mounting bracket assembly that may be attached to the component or socket prior to installing the torsion bar or the heat sink. In this embodiment, the mounting bracket is first installed on the component or socket, and then the heat sink is positioned atop the component. The torsion bar is positioned above the heat sink and aligned with the top mounting slots. A downward force is then applied to the torsion bar causing it to engage the base of the heat sink and snap into the top mounting slots which hold the bar in place.
In still another embodiment, the torsion bar is molded with a single lever and the ends of the bar are permanently attached to the mounting legs. In this embodiment, the bar is located at one edge of the heat sink and the end of the lever contacts a central region of the heat sink when installed.
In all embodiments of the present invention, the geometric and structural design constraints of the torsion bar are largely divorced from those of the mounting legs. The invention is therefore highly
Aavid Thermalloy LLC
Atkinson Christopher
Cohen & Pontani, Lieberman & Pavane
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