Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-01-31
2001-04-03
Picard, Leo P. (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S690000, C361S695000, C361S700000, C361S704000, C257S706000, C257S714000, C257S717000, C257S718000, C257S719000, C165S080300, C165S080400, C165S185000, C174S015200, C174S016100, C174S016300
Reexamination Certificate
active
06212074
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to dissipating heat generated by electrical components, and more particularly, to an efficient, cost-effective, and easy-to-manufacture apparatus for transferring heat from a circuit board having a multilevel surface.
BACKGROUND OF THE INVENTION
As the desire for more intensive electronic applications increases, so does the demand for electrical systems that operate at faster speeds, occupy less space, and provide more functionality. To meet these demands, manufacturers design modules containing numerous components with different package types, such as integrated circuits (ICs), multi-chip modules (MCMs), hybrids, and the like, residing in relatively close proximity on a common substrate, for example, a circuit board. Certain components residing on the circuit board, such as a central processing unit (CPU) or processor, generate large amounts of heat which must be dissipated by some means.
Generally, heat is dissipated by transferring the heat to a heat-sinking medium such as air or water. Due to the expense and complexity associated with liquid media and, in many cases, the non-availability of such media, it is desirable to use air as a sinking medium. Heat-transfer from the heat source to the surrounding air is accomplished via direct contact between a component and the surrounding atmosphere, passive thermal transfer schemes (e.g., heat pipes), or active liquid cooling systems (e.g., a closed loop circulating cooling system) or a combination of these schemes. In the case of direct contact, heat transfer is generally enhanced by placing a thermally conductive heat sink with protruding fins in contact with an area of high heat flux, such as the upper surface of a component's package or the component's “face.” The heat sink fins greatly increase the heat transfer area to the surrounding atmosphere and reduce the thermal resistance between the heat source and heat sink. Typically, the surrounding air circulates over the heat sink fins by convection; however, in order to further enhance the heat transfer to the surrounding atmosphere, a fan may be used to mechanically move air over the heat sink fins.
In order to enhance the transfer of heat within the heat sink itself, some heatsinks enclose a heat pipe, while others attach to a separate housing which encloses a heat pipe. Such an enclosed heat pipe provides a thermally efficient conduit for transferring heat from small areas of high heat generation uniformly throughout the heat sink, creating a nearly isothermal surface on the heat sink.
In the prior art, an individual heat sink is typically adhesively bonded to (e.g., with a thermosetting, conducting epoxy) and/or mounted adjacent the face of a single heat-generating component with fastening devices (e.g., clips, retaining rings, press fits, and the like). For circuit boards having a reasonable number of components, with ample component-to-component spacing, the prior art use of individual heatsinks and fastening devices is usually effective for transferring heat away from the critical components of a circuit board.
As the complexity of a circuit board increases, however, the number and type of components are likely to increase, while the allotted space between components is likely to decrease. These two factors result in a densely populated, complex circuit board. These boards also have a multilevel surface due to the various heights of the numerous components, surface anomalies and fabrication tolerances such as inconsistencies resulting from solder ball attachments. Since many, and possibly even all, of the components on a circuit board require cooling, the high component density and multi-level surface coupled with the requirement that each heat sink be in intimate contact with its associated component results in a board with numerous individual closely spaced, multilevel heatsinks.
Furthermore, for dissipating heat generated by high power components, such as the next generation, SUN UltraSPARC® family of processors (in particular, those used in the next generation workgroup server), the size of a heat sink must be relatively large, often ten times the size and weight of the actual component to which it is attached. (UltraSPARC is a registered trademark of SPARC International, Inc. and is licensed by Sun Microsystems, Inc.) This size requirement may be difficult to meet in a densely populated board and the large and heavy heat sinks expose the attached component to shock and vibration problems during handling and shipping, especially with surface mount components (i.e., components electrically connected to a circuit board via solder balls, or the like). Consequently, the clutter of heatsinks, fastening mechanisms, and adhesives often results in a board with inadequate cooling means and unreliable electrical connections. Manufacturing, troubleshooting, and reworking such a board is difficult, and in some cases, practically even impossible.
Therefore, there is a need for an efficient and cost-effective heat sink apparatus that accommodates a circuit board having a multilevel surface with high power components in close proximity. It is also desirable that the apparatus ensure high structural integrity and reliable electrical connections for a heavy complex assembly. Further, the apparatus should simplify manufacturing, rework, and troubleshooting and use conventional cooling devices (e.g., tube axial fans and heatsinks). Finally, it is desirable that the apparatus allow for reuse of the heat sink, circuit board, and components thereon after rework and troubleshooting.
SUMMARY OF THE INVENTION
The present invention teaches an apparatus that is effective in transferring/dissipating heat from a substrate, particularly a heavy complex circuit board having a multilevel surface, which typically results from a plurality of electrical components thereon having different heights. Unlike the prior art, however, the invention offers an efficient solution that substantially reduces the number of individual heatsinks and fastening devices, yet still provides adequate heat spreading/dissipation by using a single heat sink. This results in an apparatus that is both readily attachable to and readily detachable from a circuit board, and thus, facilitates manufacturing, rework, and troubleshooting, and allows for component reuse after rework.
In accordance with the principles of the invention, heat is dissipated from a circuit board having a multilevel surface by transferring the heat to a single heat dissipating member (e.g., a heat sink device) via a phase change material and/or a resilient thermal-conductive filling material. A fastener (e.g., a combination of spring-loaded screws) secures the phase change material and/or the filling material between the bottom portion of the dissipating member and the multilevel surface, and compresses the phase change material and/or the filling material therein, creating a thermal path sufficient to transfer heat from the multilevel surface to the dissipating member so that the board operates within specified design parameters.
In another embodiment of the invention, a plurality of heat dissipating members, substantially less than the number of components on the circuit board, is used to dissipate heat from all of the components. Thus, heat generated by a portion of the board (i.e., a cluster of components) may be provided with a thermal path to a single heat-dissipating member.
In yet another embodiment of the invention, the heat-dissipating member encloses a heat pipe, or alternatively, is attached to a housing that encloses a heat pipe. The heat pipe aids in spreading/transferring heat from the smaller areas of high heat flux, typically a region on a circuit board where high power electrical components reside.
In yet another embodiment of the invention, the circuit board makes up a portion of a heavy/complex module (e.g., the next generation SUN UltraSPARC® workgroup server processor module). In order to provide support and structural integrity, a rigid stiffener plate is configured to receive
Antonuccio Robert S.
Carney James M.
Gonsalves Daniel D.
Montagna Joseph J.
Chervinsky Boris L.
Kudirka & Jobse LLP
Picard Leo P.
Sun Microsystems Inc.
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