Heat exchange – With retainer for removable article – Electrical component
Reexamination Certificate
2001-07-09
2003-09-09
Flanigan, Allen (Department: 3743)
Heat exchange
With retainer for removable article
Electrical component
C165S185000, C361S704000
Reexamination Certificate
active
06615909
ABSTRACT:
TECHNICAL FIELD
The present invention relates to cooling of electrical and electronic components, and more particularly, to a corrugated matrix heat sink to cool electrical and electronic components.
BACKGROUND OF THE INVENTION
Electrical and electronic components (e.g. microprocessors, IGBT's, power semiconductors etc.) generate heat which must be removed for reliable operation and long life of the components. As the dissipation of heat produced from electronic components continues to escalate, it is increasingly necessary to provide more effective and efficient means of cooling these devices.
One method of removing heat from electronic components is to use a heat sink. A heat sink, which comprises a flat plate with a number of extended vertical fins, has been the focus of attention for many years (20-30) as the primary means of dissipating the heat from electronic components to the surrounding ambient air. Much time and effort has been put into improving heat sinks from both a design optimization aspect, as well as from the manufacturing perspective. What has happened is that the theoretical optimization of the basic geometrical parameters (fin thickness, fin height and number of fins or fin spacing) has resulted in either difficult-to-manufacture (and therefore high cost) or even unmanufacturable heat sink configurations. The problem stems from the fact that often, the optimum heat sink requires a fin density and fin thickness that is unattainable when constrained to the standard manufacturing practices.
Currently, there are five main approaches to manufacturing heat sinks, namely: extrusions, castings, micro-forging, metal-to-metal fabricated fin and corrugated fin. Each of these methods are restricted in their fin designs such that the air passages between the fins are long and narrow (i.e., similar to parallel plates).
The extrusion process involves pushing a billet of heated material through a hollowed tool (called a die) to form a profile. The design of the tool is very critical because the high forces required to push the material through the tool places a lot of stress on the tool, and if not designed properly, the tool will break. The design constraints on the tool are such that the heat sink profile is very difficult to produce, especially when very thin, tall and densely packed fins are required. Currently, extrusion ratios (fin height to gap between fins) of 6:1 and 8:1 are considered easy and are available from many extruders. There are a handful of extruders that can extrude 11:1 and even 15:1, but only within a certain overall size envelope. Presently, the thermal demand in the electronic marketplace can be for heat sinks in the 25:1 and even up to the 40:1 ratio range. These ratios are currently impossible for extruders to obtain.
The casting process involves pouring molten metal into a die so that the metal conforms to the shape cut into the die. The disadvantages of this process are three-fold, namely (1) the thermal characteristics of the material required for this process are lower than the material requirements of the other processes, (2) the fin dimensions and fin density are restricted similar to that of extrusions, but because of mold release issues, and (3) the cost of this process is such that it only lends itself to very high volume applications.
Micro forging is the process of forming a shape by repeatedly pressing (with a high force press) a heated billet into the die cavity. This process also has fin dimension and fin density limitations, as well as high volume requirements.
Fabricated fin heat sinks are made by taking individual fins and joining them to a base plate by an attachment method (either a metal-to-metal deformation process, like swaging, or bonded with an epoxy). This process has surpassed the fin height to gap ratio restrictions of the other processes, but still cannot provide the ratios achievable using corrugated fin technology.
Corrugated fin heat sinks are made by joining a fin pack to a base plate by bonding, soldering or brazing. The fin pack is a continuous piece of sheet metal that has been folded into a corrugated shape. This method releases the fin thickness and density limitations of the other four methods and permits the theoretical optimums to be manufactured. One disadvantage, however, is that maximum fin heights of only 4″ are currently achievable. Nevertheless, heat sinks requiring this fin height are not a common demand in the marketplace. Another disadvantage of this type of heat sink is that for long flow lengths, the high fin densities can incur very high pressure drops which are a detriment to the air flow and resulting cooling capacity.
One common constraint to all the heat sink designs manufactured by the above processes is that the designs primarily utilize the fins in the vertical direction only, i.e., perpendicular to the base plate. A few extrusions and/or fabricated-fin heat sink designs have utilized space in the horizontal direction (perpendicular to the fins), but in a very minor fashion (i.e., small, thick secondary fins, serrations on the fins, or corrugated fins themselves). None of the above designs effectively employ the cooling benefits available by utilizing surface area in the direction perpendicular to the fins.
Therefore, it is the object of this invention to provide a new heat.
It is seen then that there exists a continuing need for an improved method of removing heat from electrical or electronic components, particularly a heat sink design that offers significant manufacturing and ensuing cost advantages to the prior art.
SUMMARY OF THE INVENTION
This need is met by the present invention, which proposes the novel approach of embedding small fin packs, i.e., corrugated fin units, in between the channels of a larger fin pack.
In accordance with one aspect of the present invention, an improved heat sink provides cooling away from the surface of electrical and electronic components. The heat sink comprises at least one primary corrugated fin pack having a continuous series of vertically extending fins defining channels between adjacent pairs of the vertically extending fins. At least one secondary corrugated fin pack fits within the channels of the primary corrugated fin pack, creating a fin pack matrix. The fin pack matrix is then attached to a base plate.
Accordingly, it is an object of the present invention to provide an improved heat sink design for cooling electrical and electronic components. The features of the improvement according to the invention, over the heat sink formed by alternately stacking and brazing together corrugated fins and separator sheets, reside in the reduced number of components and ease of assembly which ultimately result in a lower overall unit cost.
Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.
REFERENCES:
patent: 3552488 (1971-01-01), Grill et al.
patent: 4270604 (1981-06-01), Nakamura
patent: 4884631 (1989-12-01), Rippel
patent: 5558155 (1996-09-01), Ito
patent: 5937517 (1999-08-01), Smith et al.
patent: 6321451 (2001-11-01), Lee et al.
Flanigan Allen
Haushalter Barbara Joan
Thermal Form & Function
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