Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2002-11-13
2004-03-30
Thompson, Gregory D. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C024S296000, C024S458000, C248S510000, C257S719000, C257S722000, C361S704000, C361S710000, C361S703000, C361S720000
Reexamination Certificate
active
06714416
ABSTRACT:
BACKGROUND OF THE INVENTION
A typical circuit board includes a section of circuit board material (e.g., fiberglass, copper, vias, etc.) and circuit board components that are mounted to the section of circuit board material. Examples of circuit board components include integrated circuits (ICs), resistors, and inductors. Typically, these circuit board components generate heat during operation. A fan assembly typically generates an air stream that passes over the components and carries the heat away. The air stream removes the heat so that the components do not operate in an unsafe temperature range, i.e., an excessively high temperature range that would cause the components to operate improperly (e.g., generate a signal incorrectly) or sustain damage (e.g., overheat, burnout, etc.).
Some ICs include heat sinks to facilitate cooling. In general, a heat sink is a flanged metallic device that attaches directly to the package of the IC. As the IC generates heat, heat flows from the IC package to the heat sink, and dissipates into the surrounding air. The air stream generated by the fan assembly then carries the heat away thus cooling the IC.
One conventional type of heat sink is the folded fin heat sink, typically formed of a folded fin portion and a base portion. The folded fin portion is fabricated from a continuous sheet of thermally conductive material, such as metal, folded into a plurality of base contact portions and a plurality of protrusions or fins to maximize the surface area of the heat sink, thereby maximizing thermal conduction from the IC. Each fin includes a first fin wall, a second fin wall, and a connection portion between the first fin wall and the second fin wall, the connection portion opposing the base contact portion. A plurality of fins connected by a plurality of base portions forms the folded fin portion of the heat sink. The base plate portion is relatively thick and attaches to the base contact portions of the folded fin portion. The base portion is formed from a thermally conductive material, such as aluminum, to provide a thermal coupling between the folded fin portion of the heat sink and the associated circuit board component.
Conventionally, a securing mechanism couples the heat sink to the circuit board component. One mechanism for securing a heat sink to a circuit board component includes a direct attachment mechanism. In the direct attachment mechanism, an assembler (e.g., a technician working in an assembly line) couples the heat sink to the circuit board component using an adhesive. For example, certain circuit board components require assemblers to mount heat sinks to the circuit board components using a flexible adhesive. The flexible adhesive permits thermal expansion of the circuit board components without inducing large displacement stresses between the heat sink and the circuit board component.
Another securing mechanism involves mechanically attaching the heat sink to the circuit board in the vicinity of the circuit board component using springs to secure the heat sink to the circuit board. The springs contact the heat sink and secure the heat sink to the circuit board component by attaching to the circuit board using screws and bolster plates. An assembler places the screws within openings in the circuit board and secures the screws to the bolster plates located on the surface of the circuit board opposite to the heat sink.
Yet another conventional attachment mechanism involves spring clips. Spring clips contact the heat sink and couple the heat sink to the circuit board component. The spring clips secure the heat sink to the circuit board by attaching directly into openings defined by the circuit board in the area of the circuit board component.
SUMMARY OF THE INVENTION
Conventional techniques for securing a heat sink to a circuit board component suffer from a variety of deficiencies.
As described above, one conventional mechanism for securing a heat sink to a circuit board component includes a direct attachment mechanism, such as through the use of an adhesive. When using an adhesive for heat sink attachment to a circuit board component, a user cannot remove the heat sink from the circuit board component without damaging the circuit board component. In cases where the circuit board component having the adhered attached heat sink becomes damaged or malfunctions, a user must replace the circuit board component, rather than attempt to repair to component, because of the potential for damaging the component when removing the heat sink. For relatively expensive heat sinks, such a solution can become costly over time.
Another conventional mechanism of securing the heat sink to the circuit board component, as described above, involves mechanically attaching the heat sink around the circuit board component using springs to secure the heat sink to the circuit board component and using screws and bolster plates to secure the springs to the circuit board. Relatively large circuit board components, however, require a relatively large number of screws and bolster plates to secure the heat sinks to the circuit board components. Using a relatively large number of screws and plates increases the weight of the circuit boards, thereby making the circuit boards cumbersome to handle. Furthermore, relatively large circuit board components (e.g., up to 2500 pins) require relatively large forces to maintain thermal contact between the heat sinks and the components. The large forces require relatively large screws (e.g., 0.375 inch diameter) to secure the springs to the circuit boards and, therefore, require relatively large openings in the circuit board to provide access for the screws. Multiple large openings within the circuit board reduce the area available for electronic components and traces.
Another conventional mechanism for securing the heat sink to the circuit board component, as described above, involves the use of spring clips. T he spring clips couple the heat sink to the circuit board component and secure the heat sink to the circuit board by attaching directly into openings defined by the circuit board in the area of the circuit board component. Similar to the above-described attachment method, the holes for the spring clips are relatively large thereby reducing the area available for electronic components and traces on the circuit board. Furthermore, in this method, after insertion of the spring clips into the openings, each spring clip directly contacts the edge of each opening. Over time, vibrations in the circuit board can cause the spring clip to wear against the hole, thereby abrading the hole and leading to possible failure of the spring clip.
Also as described above, one conventional type of heat sink used in conjunction with circuit board component cooling is the folded fin heat sink. As described, the folded fin heat sink typically includes a folded fin portion and a base portion. While the folded fin heat portion provides thermal dissipation for heat generated by the circuit board component, the base of the folded fin heat sink is, typically, relatively thick, thereby increasing the weight of the circuit board when used. Furthermore, conventional circuit board components typically include non-planar heat sink mounting surfaces. For example, conventional circuit board components, such as application specific integrated circuits (ASIC), include a bow on the heat sink mounting surface of approximately 0.0012 inches. Therefore, an attachment mechanism must generate relatively large forces on a planar base plate of the folded fin heat sink to provide adequate thermal contact between the heat sink base plate and the circuit board component, such as provided by the a heat sink attachment mechanisms described above.
By contrast to the prior heat sink attachment mechanism, embodiments of the present invention significantly overcome such deficiencies and provide mechanisms and techniques for securing a heat sink to a circuit board component. In one embodiment, a heat sink apparatus includes a heat sink having a plurality of circuit board com
Li I-Chyau
McLeod Gary
Chapin & Huang , L.L.C.
Cisco Technology Inc.
Huang, Esq. David E.
Thompson Gregory D.
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