Heat exchange – Intermediate fluent heat exchange material receiving and... – Liquid fluent heat exchange material
Reexamination Certificate
1999-08-03
2002-09-17
Flanigan, Allen (Department: 3743)
Heat exchange
Intermediate fluent heat exchange material receiving and...
Liquid fluent heat exchange material
C165S080300, C361S700000
Reexamination Certificate
active
06450250
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cooling of electronic components and assemblies through the provision of a heat sink.
BACKGROUND OF THE INVENTION
Integrated circuits or other electronic components are generally mounted on printed circuit boards which are then installed in an enclosure for the electronic equipment. A personal computer would be a typical electronic device that houses printed circuit boards having such electronic components. There has been since the advent of the integrated circuit a steady progression of larger and larger devices capable of performing more functions within a single component package. At the same time, there has been a trend toward the packing of a larger number of components onto a printed circuit board and within a given volume of an enclosure. The result of these two trends and others, has resulted in an increasing requirement for low-cost, efficient, heat-dissipating devices for use within the electronic equipment.
One type of heat-dissipating device is a simple fan mounted within the enclosure and designed to circulate air through the enclosure, removing the hot air and introducing cooler air so as to dissipate the heat generated by the electronic components. Another method of removing heat is the use of a heat sink. The term “heat sink” is here used in its normal dictionary definition: “a substance or device for the absorption or dissipation of unwanted heat (as from a process or an electronic device).” Webster's Ninth New Collegiate Dictionary, p. 560 (1983). A typical heat sink used in the electronics industry for dissipating heat from components will comprise a base and a plurality of fins. The heat sink base is secured in firm heat-transfer engagement with the electronic component so as to absorb the heat from the component, passing it into the plurality of fins, which in turn radiate the heat into the surrounding air. Heat sinks are normally constructed from high heat-conducting material, such as metal, including aluminum and copper. Heat sinks may be used in combination with a fan.
A typical heat sink may be formed from an aluminum extrusion in which the base and fins are integral. The extrusion is then cut off in sections, each section forming an individual heat sink. Since the extrusion process results in fins that are in parallel planes, the fins form a plurality of passages between the fins extending in one direction. When a heat sink is formed with passages in one direction, it is desirable to have the fan and heat sink located relative to one another so that the air flow of the fan is parallel with the air passages between the fins. That is of course not always possible or desirable for other reasons. It has therefore been common to machine passages in a perpendicular direction to the extruded air passages, resulting in a series of spike-like fins, as shown in U.S. Pat. No. 5,600,540. In that manner, the positioning of the heat sink relative to the fan offers greater design flexibility.
One of the shortcomings in the heat sinks described above is that they have a fixed heat-dissipating area for a given size determined by the height of the extruded fins. In many electronic assemblies, the electronic components are mounted on the printed circuit board in close relation to one another. Therefore, mounting a heat sink on a particular electronic device is more or less circumscribed by the area (width and length) of the electronic component. Generally speaking, the space in which the heat sink may be mounted is unrestricted as to height as opposed to the area of the component. However, since the height of the fins is predetermined by the extrusion, it is not possible to change the heat-dissipating area of a particular extruded heat sink without infringing upon the air space of adjacent components. The thermal designer for the electronic assembly is therefore faced with specifying a custom-made extruded heat sink of a particular height for a particular application, or attempting to accommodate the limited heat sink dissipation capability by selection of a more powerful fan. Thus, a heat sink with a fixed heat-dissipating area presents the thermal designer with a design restriction that is undesirable.
A related problem with the extruded heat sink is that even after the designer selects a heat sink of a given surface area and therefore heat-dissipating capacity, the use of the component in a particular printed circuit board configuration and in a specific electronic enclosure may change the thermal conditions in which the component and its associated extruded heat sink will be used, requiring redesign of the extruded heat sink or again resorting to removal of heat through a more powerful fan. Even after the manufacturing stage is reached, thermal testing may show that the theoretical calculations did not properly accommodate the heat generated and still further modifications to the heat sink dissipation surface area or fan must be designed.
In short, the thermal designer of electronic equipment is continually faced throughout the design and manufacturing process with the limitation of the surface area of an extruded heat sink because the size of the base is restricted by the crowded “real estate” on the printed circuit board and the height of the extruded heat sink is predetermined. Of course, heat sinks may be made with fins of different height, but that requires stocking of heat sinks of different heights to accommodate changes during the design process that results in different thermal conditions. It also complicates the inventory stocking of heat sinks in manufacturing as well as in customer service.
It is therefore a primary object of the present invention to provide a heat sink in which the heat-dissipating capacity may be varied at any point during design, manufacturing or use.
Another object of this invention is to provide a heat sink in which a plurality of fins may be manually added so as to increase the heat-dissipating surface capacity.
One other object of the present invention is to provide a construction whereby the heat is rapidly and efficiently dispersed to the fins where the heat is dissipated.
Still another object of the present invention is to provide a heat sink in which the air passages are in a plane parallel to the plane of the printed circuit board on which the electronic component is mounted and to which the heat sink is attached so as to accommodate air flow in any direction.
All of the objects of the invention may be accomplished through the provision of a stackable heat sink that includes a plurality of fins which are mounted generally parallel to the electronic component and printed circuit board on a core shaft one end of which is in heat conducting relation with the electronic component, and a base with an opening for receiving the core shaft.
In an improved stackable heat sink, the problem of the limited area available for the fins may be partially solved without increasing the perimeter of the fin by forming a corrugated, rather than a flat, fin. One of the limitations in a stackable heat sink is the ability of the core shaft to transfer heat from one end in contact with the heat source to the other end and thus to the individual fins. It is an object of this invention to promote or facilitate the heat transfer from the heat source to the fins by the use of a heat pipe inserted into an axial opening in the core shaft that supports the fins. Still another problem overcome by the improved stackable heat sink is to form the base with an opening in which the core shaft is press fit and/or including a portion on which a small cooling fan may be mounted so as to move air directly between adjacent fins and in a general direction of the fin corrugation, where the fins are so formed.
Yet another object of the present invention is to provide a heat sink that is of low cost, simple construction, made from common materials, and constructed using machine tools in common use.
SUMMARY OF THE INVENTION
The present invention comprises a heat sink for use with electronic components that includes a
Flanigan Allen
Mays Andrea L.
PSC Computer Products, Inc.
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