Metal working – Method of mechanical manufacture – Heat exchanger or boiler making
Reexamination Certificate
2001-09-27
2003-10-28
Cuda-Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Heat exchanger or boiler making
C029S890054, C228S183000
Reexamination Certificate
active
06637109
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the manufacture of heat sinks, and in particular the manufacture of high fin density heat sinks.
BACKGROUND OF THE INVENTION
Electronic components such as those being attached to e.g. printed circuit boards dissipate heat during operation and thus need to be cooled, so as to prevent damages caused by rapidly increasing component temperatures.
To this end, heat sinks are frequently employed for enlarging the heat-emitting surface of such components. However, equipment comprising such electronic components has, due to technological advances, become more and more compact, which also effects the size of the heat sinks in a corresponding way. Still, the heat dissipation of the components has not decreased to the same extent. Thus, great demands are put on heat sink efficiency, and therefore the ratio between heat sink cooling capacity and heat sink dimensions needs to be maximised.
One common type of a heat sink
51
is shown in
FIG. 2
, which to the right is partly cut away. The heat sink comprises a top base plate
53
, a bottom base plate
55
and a plurality of webs
57
or fins connecting the top and bottom base plates. The material is commonly aluminium alloys. The top base plate
53
and the bottom base plate
55
, each have an upper surface
59
and a lower surface
61
serving as mounting surfaces for electronic, heat generating components
63
(components are for the sake of clarity only shown on the upper surface
59
). These components
63
may be adhered or by other suitable means bonded to the surfaces. During operation of the electronic components
63
heat is generated by the components, which heat is transferred to the heat sink
51
and further being distributed to the fins
57
. Gaps
65
between the fins are serving as passageways for a not shown forced convection air flow, which is cooling the fins
57
of the heat sink, by transporting heated air to the surroundings. An effective heat sink requires that the fin spacing should be as low as possible (i.e. high fin density), which imply a large heat-emitting surface.
The research and development for such high fin density heat sinks are continuously under progress, and several methods of manufacture are well known in the art. However, many of these related art methods suffer from various disadvantages resulting in heat sinks not complying with stipulated cooling requirements.
One way of manufacturing the above mentioned type of heat sinks is by extruding a complete heat sink in one single operation. However, extrusion and die cast tooling limitations restrain required fin height to air gap thickness ratios, whereby desired shapes, i.e. extremely high fin density structures, are impossible to accomplish.
To overcome this drawback an other method may imply the assembly of two base plates
73
,
75
with a plurality of parallel fins
77
, as schematically shown in FIG.
3
. In this case each base plate is extruded in a separate operation. The base plates
73
,
75
are provided with recesses
79
intended for corresponding fins
77
during assembly of a complete heat sink profile
71
. It is obvious for the man skilled in the art that desired fin height to air gap thickness ratios more easily can be achieved by this method in comparison with the complete extrusion method described above, but the assembly is very time-consuming. Moreover, the fins
77
need to be bonded in some way to the recesses of the base plates
73
,
75
.
Yet an other method would be to extrude length sections
91
comprising upper and lower base plate portions
93
,
95
connected by a web
97
as schematically shown in FIG.
4
. Each length section
91
is provided with upper and lower slots
99
,
101
as well as upper and lower protrusions
103
,
105
, which protrusions are intended to fit into the slots of an adjacent length section
91
during assembly of the various length sections. These length sections are then bonded to each other creating a complete heat sink. Although this method is less time consuming in a assembling point of view, compared to the latter method, and that high fin height to air gap thickness ratios easily may be achieved, the various length sections still need to be bonded together in some way.
As mentioned above all these methods would require bonding in some way. Below follows a variety of bonding methods and reasons why they are not suitable for these applications.
If an adhesive is used as a bonding material, in the junctions between the parts to be assembled, a deteriorated heat conductivity could be the consequence, since the coefficient of thermal transmission of adhesives generally is very poor. Certainly, the coefficient of thermal transmission may be sufficient if special adhesives containing, e.g. powdered silver are used, but such adhesives are very expensive.
Soldering and conventional welding would as a bonding method imply extensive heating of the various parts. High temperatures are required and the whole structure is normally intensively heated, whereby deformation of the material is likely to occur leading to rejections of material. Furthermore, additives such as solder metal is added to the joints between the parts to be bonded, which may deteriorate the overall heat conducting properties of the heat sink. Moreover, extensive cleaning is required of the parts to be assembled prior to the soldering and welding operations.
The parts to be assembled could also be press fitted as disclosed in U.S. Pat. No. 6,138,352. However, the tolerances when manufacturing these parts need to be rigorous, which make the method more expensive. Furthermore, oxidation in the junctions between the parts to be assembled are also probable, which will deteriorate the overall thermal conductivity of the heat sink. Moreover, the method also give rise to small air cavities in the junctions between fins and base plates, due to tolerance limitations of the various parts. These air cavities reduce the heat conductivity to the fins but also in the lateral directions of the base plates. Furthermore, screw holes disposed in the top or bottom base plates may jeopardise the press joints when the screws are tightened.
OBJECT OF THE INVENTION
An object of the present invention is to provide a simple and reliable, and thus cost effective, method for manufacturing a high performance heat sink having a high fin density.
Yet an object of the present invention is to provide a method for manufacturing a high performance heat sink without the disadvantages associated with related art methods.
SUMMARY OF THE INVENTION
These objects are achieved according to the present invention by means of a method having the features mentioned in the independent claims.
In a first embodiment of the present invention the method comprises the steps of aligning a plurality of length sections side by side in a mutual parallel arrangement, said length sections having a cross-section comprising a first end portion, a second end portion and a web portion connecting said first and second end portions, said first and second end portions having a width wider then the width of the web portion; clamping the parallelly arranged length sections together, such that said first and second end portions of adjacent parallel length sections are abutting against each other; and bonding the length sections together by applying at least one friction stir welding (FSW) seam across the end portions of the parallelly arranged length sections.
In a second embodiment of the present invention the method comprises the steps of: extruding an elongated profile bar having a cross-section comprising a first end portion, a second end portion and a web portion connecting said first and second end portions, said first and second end portions having a width wider then the width of the web portion; cutting up said elongated profile bar into a plurality of length sections; aligning said plurality of length sections side by side in a mutual parallel arrangement; clamping the parallelly arranged length sections together, such that
Cuda-Rosenbaum I
Emerson Energy Systems AB
Harness & Dickey & Pierce P.L.C.
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