U.S. patent application number 09/972458 was filed with the patent office on 2002-06-13 for liquid-cooled heat sink with thermal jacket.
Invention is credited to Calaman, Douglas P., Connors, Mathew J..
Application Number | 20020070007 09/972458 |
Document ID | / |
Family ID | 24950278 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070007 |
Kind Code |
A1 |
Calaman, Douglas P. ; et
al. |
June 13, 2002 |
LIQUID-COOLED HEAT SINK WITH THERMAL JACKET
Abstract
A liquid-cooled heat sink is provided having a cooling housing
including a peripheral side wall extending from the perimeter of a
bottom wall and a lid sized to engage the peripheral side wall so
as to form a chamber. A fluid inlet port and a fluid outlet port
are defined through the lid, and disposed in fluid communication
with the chamber. In one embodiment, a plurality of pins project
outwardly from the bottom wall so as to be positioned within the
chamber and arranged in a staggered pattern. The pins include an
end that engages the undersurface of the lid. In an alternative
embodiment, a corrugated fin having a plurality of corrugations is
positioned within the chamber so that at least one of the
corrugations engages the bottom wall and at least one of the
corrugations engages the under surface of the lid.
Inventors: |
Calaman, Douglas P.;
(Landisville, PA) ; Connors, Mathew J.;
(Lancaster, PA) |
Correspondence
Address: |
Samuel W. Apicelli
Duane Morris LLP
305 N. Front Street
P.O. Box 1003
Harrisburg
PA
17108-1003
US
|
Family ID: |
24950278 |
Appl. No.: |
09/972458 |
Filed: |
October 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09972458 |
Oct 5, 2001 |
|
|
|
09734092 |
Dec 11, 2000 |
|
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Current U.S.
Class: |
165/80.4 ;
165/170; 257/E23.098 |
Current CPC
Class: |
H01L 2924/00 20130101;
H01L 2924/0002 20130101; H01L 23/473 20130101; H01L 2924/0002
20130101; F28F 3/022 20130101; F28F 3/025 20130101 |
Class at
Publication: |
165/80.4 ;
165/170 |
International
Class: |
F28F 007/00; F28F
003/14 |
Claims
What is claimed is:
1. A liquid-cooled heat sink with thermal jacket comprising: a
housing including a side wall extending from the perimeter of a
bottom wall and a lid sized to engage said peripheral side wall so
as to form a chamber within said housing; a fluid inlet port and a
fluid outlet port defined through said lid so as to be in fluid
communication with said chamber; and a plurality of pins projecting
outwardly from said bottom wall so as to be positioned within said
chamber and arranged in a staggered pattern, said pins including an
end that is secured to a surface of said lid; and a bonding layer
applied to an outer surface of said liquid-cooled heat sink; at
least one porous layer positioned in substantially surrounding and
overlying relation to said bonding layer; a barrier layer
positioned in substantially surrounding and overlying relation to
said at least one porous layer; and a sealant layer positioned in
substantially surrounding and overlying relation to said barrier
layer.
2. A liquid-cooled heat sink with thermal jacket according to claim
1 wherein said bottom wall of said housing includes a recessed
portion formed by a thinned region of said bottom wall and said
porous layer comprises at least one sheet of a porous membrane.
3. A liquid-cooled heat sink with thermal jacket according to claim
1 wherein said plurality of pins project outwardly in substantially
perpendicular relation to said bottom wall and said porous membrane
comprises a mesh screen having a lattice structure including a
plurality of openings.
4. A liquid-cooled heat sink with thermal jacket according to claim
3 wherein said plurality of pins are in substantially perpendicular
relation to a recessed portion of said bottom wall.
5. A liquid-cooled heat sink with thermal jacket according to claim
4 wherein at least a portion of said plurality of pins have a
length that positions said end in engaging relation to said
lid.
6. A liquid-cooled heat sink with thermal jacket according to claim
1 wherein said porous layer comprises at least one sheet of an
porous membrane.
7. A liquid-cooled heat sink with thermal jacket according to claim
1 wherein said plurality of pins are arranged in a series of rows
to form a non-rectangular, staggered pattern of pins such that pins
in adjacent rows are off-set with respect to one another.
8. A liquid-cooled heat sink with thermal jacket according to claim
2 wherein said porous layer comprises a mesh screen having a
lattice structure including a plurality of openings.
9. A liquid-cooled heat sink with thermal jacket according to claim
1 wherein a portion of a coolant fluid flowing through said chamber
and engaging said pins engages each of said pins along their
length, while another portion of said coolant fluid flowing through
said pins passes between a gap formed between adjacent pins in a
first row so as to directly impinge upon a pin positioned in a
second row and spaced from said gap.
10. A liquid-cooled heat sink with thermal jacket according to
claim 2 wherein said porous layer comprises a fabric screen having
a warp and weft.
11. A liquid-cooled heat sink with thermal jacket according to
claim 1 wherein said porous layer comprises a mesh screen that is
sufficiently compliant so as to be conformally shaped to said
cooled heat sink.
12. A liquid-cooled heat sink with thermal jacket according to
claim 1 wherein said porous layer includes multiple sheets of a
mesh screen with one sheet being applied directly over top of a
prior sheet.
13. A liquid-cooled heat sink with thermal jacket according to
claim 1 wherein said porous layer comprises a mesh screen formed
from a polymer having relatively low thermal conductivity.
14. A liquid-cooled heat sink with thermal jacket comprising: a
housing including a side wall extending from the perimeter of a
bottom wall and a lid sized to engage said peripheral side wall so
as to form a chamber within said housing; a fluid inlet port and a
fluid outlet port defined through said lid so as to be in fluid
communication with said chamber; and a fin comprising a plurality
of corrugations positioned with said chamber so that at least one
of said corrugations engages said bottom wall and at least one of
said corrugations is secured to a surface of said lid; and a
bonding layer applied to an outer surface of said liquid-cooled
heat sink; at least one porous layer positioned in substantially
surrounding and overlying relation to said bonding layer; a barrier
layer positioned in substantially surrounding and overlying
relation to said at least one porous layer; and a sealant layer
positioned in substantially surrounding and overlying relation to
said barrier layer.
15. A liquid-cooled heat sink with thermal jacket according to
claim 14 wherein said fin is fixed in position within said housing
by at least one pin.
16. A liquid-cooled heat sink with thermal jacket according to
claim 14 wherein said fin comprises a plurality of fin walls that
are folded relative to one another so as to form a plurality of
substantially flat crests.
17. A liquid-cooled heat sink with thermal jacket according to
claim 16 wherein said fin walls are parallel to one another, with a
constant wall-to-wall separation.
18. A liquid-cooled heat sink with thermal jacket according to
claim 14 wherein said fin includes at least one through hole
arranged so as to receive said at least one when said fin is
positioned within said chamber.
19. A liquid-cooled heat sink with thermal jacket according to
claim 14 wherein said fin is brazed or welded to a recessed portion
of said bottom wall and said lid thereby forming a plurality of
adjacent flow passages.
20. A liquid-cooled heat sink with thermal jacket comprising: a
housing including a side wall extending from the perimeter of a
bottom wall and a lid sized to engage said peripheral side wall so
as to form a chamber within said housing; a fluid inlet port and a
fluid outlet port defined through said lid so as to be in fluid
communication with said chamber; and a plurality of pins projecting
outwardly from said bottom wall so as to be positioned within said
chamber and arranged in a staggered pattern, said pins including an
end that is secured to a surface of said lid; and a bonding layer
applied to an outer surface of said liquid-cooled heat sink; a
porous layer including multiple sheets of a mesh screen with each
successive sheet being applied directly over top of a prior sheet,
said multiple sheets being oriented such that there is a mismatch
between said openings of said sheets from layer to layer, said
porous layer positioned in substantially surrounding and overlying
relation to said bonding layer; a barrier layer positioned in
substantially surrounding and overlying relation to said at least
one porous layer; and a sealant layer positioned in substantially
surrounding and overlying relation to said barrier layer.
21. A liquid-cooled heat sink with thermal jacket comprising: a
housing including a side wall extending from the perimeter of a
bottom wall and a lid sized to engage said peripheral side wall so
as to form a chamber within said housing; a fluid inlet port and a
fluid outlet port defined through said lid so as to be in fluid
communication with said chamber; and a fin comprising a plurality
of corrugations positioned with said chamber so that at least one
of said corrugations engages said bottom wall and at least one of
said corrugations is secured to a surface of said lid; and a
bonding layer applied to an outer surface of said liquid-cooled
heat sink; a porous layer including multiple sheets of a mesh
screen with each successive sheet being applied directly over top
of a prior sheet, said multiple sheets being oriented such that
there is a mismatch between said openings of said sheets from layer
to layer, said porous layer positioned in substantially surrounding
and overlying relation to said bonding layer; a barrier layer
positioned in substantially surrounding and overlying relation to
said at least one porous layer; and a sealant layer positioned in
substantially surrounding and overlying relation to said barrier
layer.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to liquid-cooled
heat sinks, and more particularly to a liquid-cooled heat sink for
electronic devices that includes obstructions for optimizing heat
transfer to the stream of liquid and which includes a thermal
jacket to prevent surface moisture condensation from forming during
subambient operation.
BACKGROUND OF THE INVENTION
[0002] The performance of electronic circuits and their
semiconductor devices is limited by temperature. Semiconductor
device performance degrades when the internal temperature reaches
or exceeds a particular limit. That limit depends upon the nature
of the semiconductor device. In order to maintain or increase the
performance of such devices, they must be cooled in some way. The
manner of cooling depends upon many parameters, including the space
available for the cooling process, the temperatures to be
encountered, power, etc. In some instances simply passing a fluid
over the device or, over a finned heat sink that is attached to the
device, is sufficient to maintain the semiconductor at safe
operating temperatures.
[0003] In one known semiconductor device cooling technique,
convecting fins are attached to a semiconductor package, or the
package is affixed to a larger metal member, referred to as a heat
sink or cold plate. This heat sink draws heat away from the
semiconductor device and can be air cooled or liquid cooled,
depending upon the particular application. If the heat sink is air
cooled it will typically have heat convecting fins.
[0004] Different cooling fluids may be used, when liquid cooled
methods are employed, depending upon the application and the
density of the electronic devices in a given circuit. Boiling
liquids are often used, such as fluorinated hydrocarbon
refrigerants, which are delivered to the cold plate in liquid form
and are boiled to remove heat. These systems often have the highest
heat removal rate for a limited "cold plate" area, but require a
considerable amount of power to operate, i.e. to be pumped to and
from the heat transfer site. In other systems, a cold liquid is
circulated through the cold plate with the cold liquid being
refrigerator cooled, evaporatively cooled, or convectively
cooled.
[0005] A problem exists in the foregoing prior art systems in that
a portion of the liquid used to cool the semiconductor device tends
to stagnate in a region close to the surface of the heat sink. This
stagnation typically refers to a reduction in coolant speed near
the heat sink surface. Here the coolant flows at a slower than
required speed to adequately remove heat from the heat sink
surface. This stagnation reduces the effectiveness of the heat
transfer in the cooling system. Very often, the rate of cooling is
less than the rate at which heat arrives at that interface surface,
which causes an accumulation of heat at the surface. Several
options have been proposed in the art to reduce this effect,
including increasing the speed of the flow of the coolant or
introducing structural features which cause turbulent flow and
increased effective surface area.
[0006] Under certain circumstances, moisture from the ambient
environment may condense on the heat sink or cold plate. In the
case of liquid-cooled heat sinks, there are periods of time during
which the temperature of the heat sink may fall below the
temperature of the surrounding environment, often referred to in
the art as "subambient" operation. This condition may occur any
time the surface temperature of the heat sink falls below the
ambient temperature. When this subambient operation condition
occurs, moisture from the surrounding atmosphere may condense on
the outer surface of the heat sink. The condensed moisture collects
and runs off of the heat sink and into contact with the circuit
board, semiconductors and packages, and other components. This free
liquid can cause significant damage to those components and degrade
the overall performance of the electronic device, or even destroy
it all together.
[0007] There is a need for a liquid-cooled heat sink having a
thermal jacket that can be positioned on or near a semiconductor
package that will provide both optimum turbulent flow and increased
surface area for effective heat transfer to the stream of liquid,
and reduce or prevent condensation from forming in appreciable
quantities on the surface of the device during subambient
operation.
SUMMARY OF THE INVENTION
[0008] A liquid-cooled heat sink having a thermal jacket is
provided including a housing with a peripheral side wall extending
from the perimeter of a bottom wall and a lid sized to engage the
peripheral side wall so as to form a chamber. A fluid inlet port
and a fluid outlet port are defined through the lid, and disposed
in fluid communication with the chamber. A plurality of pins
project outwardly from the bottom wall so as to be positioned
within the chamber and arranged in a staggered pattern. The pins
include an end that engages the lid to provide structural support,
and to prevent deflection of the lid by high liquid pressure. The
liquid cooled heat sink of the present invention also includes a
thermal jacket that reduces the rate of condensation of moisture
during subambient operation of the liquid-cooled heat sink. The
thermal jacket includes a bonding layer positioned in substantially
surrounding and overlying relation to the liquid-cooled heat sink,
at least one porous layer positioned in substantially surrounding
and overlying relation to the bonding layer, a barrier layer
positioned in substantially surrounding and overlying relation to
the at least one porous layer; and a sealant layer positioned in
substantially surrounding and overlying relation to the barrier
layer. In this way, the at least one porous layer traps air close
to the surface of the heat sink so as to provide a thermally
insulating air barrier between the surface of the heat sink and the
ambient environment.
[0009] In one alternative embodiment of the invention, a
liquid-cooled heat sink is provided having a housing including a
peripheral side wall extending from the perimeter of a bottom wall
and a lid sized to engage the peripheral side wall so as to form a
chamber. A fluid inlet port and a fluid outlet port are defined
through the lid, and disposed in fluid communication with the
chamber. A fin having a plurality of corrugations is positioned
within the chamber so that at least one of the corrugations engages
the bottom wall and at least one of the corrugations engages the
under surface of the lid. A thermal jacket is formed on the outer
surface of the heat liquid-cooled sink that includes a bonding
layer positioned in substantially surrounding and overlying
relation to the cooled heat sink, at least one porous layer
positioned in substantially surrounding and overlying relation to
the bonding layer, a barrier layer positioned in substantially
surrounding and overlying relation to the at least one porous
layer; and a sealant layer positioned in substantially surrounding
and overlying relation to the barrier layer. Here again, the at
least one porous layer traps air close to the surface of the heat
sink so as to provide a thermally insulating air barrier between
the surface of the heat sink and the ambient environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other features and advantages of the present
invention will be more fully disclosed in, or rendered obvious by,
the following detailed description of the preferred embodiment of
the invention, which is to be considered together with the
accompanying drawings wherein like numbers refer to like parts and
further wherein:
[0011] FIG. 1 is an exploded perspective view of a liquid cooled
heat sink formed in accordance with one embodiment of the present
inventions;
[0012] FIG. 2 is a top plan view of a housing having an array of
pins, as shown in FIG. 1;
[0013] FIG. 3 is a prospective view of a fully assembled liquid
cooled heat sink;
[0014] FIG. 4 is an exploded perspective view of the heat sink
shown in FIG. 3;
[0015] FIG. 5 is a cross-sectional view of the liquid cooled heat
sink shown in FIG. 3, as taken along line 5-5;
[0016] FIG. 6 is a perspective, exploded view of an alternative
embodiment of the liquid cooled heat sink shown in FIG. 1;
[0017] FIG. 7 is a cross-sectional view of the liquid cooled heat
sink shown in FIG. 6, as taken along line 7-7;
[0018] FIG. 8 is a prospective, exploded view of the liquid cooled
heat sink shown in FIGS. 6 and 7;
[0019] FIG. 9 is a perspective view of a liquid cooled heat sink
having a thermal jacket formed on its outer surface in accordance
with the present invention, with a portion of the thermal jacket
broken away for clarity of illustration;
[0020] FIG. 10 is a perspective, exploded view of the liquid cooled
heat sink shown in FIG. 9, with the various layers of the thermal
jacket exploded away from the top surface of the heat sink for
clarity and illustration;
[0021] FIG. 11 is a perspective, exploded view similar to that
shown in FIG. 10, but illustrating the use of woven material in
some layers;
[0022] FIG. 12 is a cross-sectional view as taken along line 12-12
in FIG. 9; and
[0023] FIG. 13 is a cross-sectional view similar to that of FIG.
12, but taken along line 13-13 in FIG. 9, showing an alternative
form of liquid cooled heat sink used in connection with a thermal
jacket according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] This description of preferred embodiments is intended to be
read in connection with the accompanying drawings, which are to be
considered part of the entire written description of this
invention. In the description, relative terms such as "horizontal,"
"vertical," "up," "down," "top" and "bottom" as well as derivatives
thereof (e.g., "horizontally," "downwardly," "upwardly," etc.)
should be construed to refer to the orientation as then described
or as shown in the drawing figure under discussion. These relative
terms are for convenience of description and normally are not
intended to require a particular orientation. Terms including
"inwardly" versus "outwardly," "longitudinal" versus "lateral" and
the like are to be interpreted relative to one another or relative
to an axis of elongation, or an axis or center of rotation, as
appropriate. Terms concerning attachments, coupling and the like,
such as "connected" and "interconnected," refer to a relationship
wherein structures are secured or attached to one another either
directly or indirectly through intervening structures, as well as
both movable or rigid attachments or relationships, unless
expressly described otherwise. The term "operatively connected" is
such an attachment, coupling or connection that allows the
pertinent structures to operate as intended by virtue of that
relationship.
[0025] Referring to FIGS. 1-4, one embodiment of a liquid-cooled
heat sink 5 formed in accordance with the present invention
comprises a housing 10 including a peripheral side wall 15 that
extends upwardly from the perimeter of a bottom wall 20, and
includes a top edge surface 17 and an outer surface 19. More
particularly, housing 10 is formed from a thermally conductive
material, such as copper, steel, etc., and is typically milled as a
single piece. Bottom wall 20 is often rectilinear in shape, with
side wall 15 arranged in substantially perpendicular relation to a
perimeter edge 21. A recessed portion 23 of bottom wall 20 is
formed by thinning bottom wall 20 so as to reduce its thermal
resistance in that location. The outer surface of recessed portion
23 of bottom wall 20 is adapted to interface with a semiconductor
device directly, or to interface with the semiconductor device's
packaging 24 so as to provide a conduit for thermal energy
generated by the semiconductor device. Such an adaptation may
include the introduction of a material having greater thermal
conductivity properties than the material that forms the housing as
a whole, e.g., silver, diamond, etc.
[0026] A plurality of pins 25 project outwardly in substantially
perpendicular relation to the interior surface of recessed portion
23 of bottom wall 20. Each individual pin 25 is preferably
cylindrically shaped, but may have any number of other
cross-sectional shapes including, but not limited to circular,
rectilinear, elliptical, generally polygonal, etc. At least a
portion of plurality of pins 25 have a length that positions their
free end 27 at or slightly above top edges surface 17 of side wall
15.
[0027] Significantly, plurality of pins 25 are arranged in a series
of rows to form a non-rectangular, staggered pattern or grid of
pins 29, i.e., a series of rows of pins 25 where the pins in
adjacent rows are not placed one behind the other, but rather are
shifted transversely relative to one another such that pins in
adjacent rows are off-set with respect to one another. In this way,
a portion of the coolant fluid flowing through the staggered grid
of pins 29 engages each of pins 25 along their length, while
another portion of the coolant fluid flowing through staggered grid
of pins 29 passes through the gap formed between adjacent pins 25
so as to directly impinge upon a pin positioned in the next row and
spaced from the gap. Unlike prior art pin arrays, however, coolant
that does not initially engage a pin 25 in a first row will
subsequently engage a pin 25 disposed in the next row of pins as a
result of the staggered, off-set pattern. Staggered pattern of pins
29 significantly increases the level of turbulence in the flowing
coolant liquid. No jets of liquid coolant are required to enhance
turbulent flow. Advantageously, coolant entering housing 10 may
impinge directly upon a pin end 27, a portion of a pin end 27, or
directly and entirely onto the surface of recessed portion of 23 of
bottom wall 20 without affecting the heat transfer characteristics
of liquid-cooled heat sink 5. This greatly reduces the cost of
manufacturing of heat sink 5, while at the same time increasing the
heat transfer characteristics of the device.
[0028] A lid 30 is sized and shaped to engage top edge surface 17
of side wall 15 so as to enclose pin grid 29 in a chamber that is
defined between side wall 15, bottom wall 20, and lid 30. Fluid
inlet port 38 and outlet port 39 are arranged on lid 30 so as to be
in fluid communication with pin grid 29 and a conventional conduit,
e.g., hoses 37. A fluid inlet port 38 and a fluid outlet port 39
are defined through lid 30 so as to be in fluid communication with
pin grid 29. Pin ends 27 of at least some of pins 25 engage the
under surface of lid 30, and are preferably brazed or welded to lid
30. In this way, pins 25 also provide structural reinforcement so
as to prevent deflection of lid 30 when high pressure liquid is
introduced into liquid-cooled heat sink 5. Referring to FIG. 4,
liquid-cooled heat sink 5 may be assembled to the structure
supporting the electric circuit by means of a frame 40. Lid 30 is
fastened to frame 40 by conventional fasteners 43, by welding, or
by any other conventional fastening means that will ensure a liquid
tight seal. A thermally insulating gasket 41 is positioned between
the under surface of lid 30 and frame 40 to prevent unwanted
thermal interactions.
[0029] Referring to FIGS. 6-8, an alternative embodiment of the
invention is provided in which a corrugated or folded fin 50 is
fixed in position within housing 10 by a plurality of pins 51. More
particularly, fin 50 is made up of a series of thin, flat fin walls
54, folded relative to one another about crests 56. Crests 56 are
shaped so as to be substantially flat, rather than sharply pointed.
This arrangement provides a surface that is less prone to damage,
and is more suitable for brazing, soldering, or welding to recessed
portion 23 of bottom 20 and to the undersurface of lid 30. Although
crests 56 are not pointed and sharp, fin walls 54 may themselves
have a divergent shape, rather than being parallel to one
another.
[0030] In one embodiment, fin walls 54 are packed so closely as to
be effectively parallel to one another, with a constant
wall-to-wall separation equal to the flat top wall 57 formed by
crest 56. A plurality of through holes 58 are defined through fin
50, and are arranged in a pattern to match the pattern of pins 51
that project outwardly from recessed portion 23 of bottom 20. In
this way, fin 50 may be positioned within housing 10 in such a way
that each pin 51 is received within a respective through-hole 58,
thereby assuring proper alignment of fin 50 within housing 10 and
providing structural support and reinforcement. It will be
understood that only one pin 25 need be received within a
through-hole to properly position fin 50 within housing 10.
[0031] When fin 50 is brazed or welded to recessed portion 23 of
bottom wall 20, and to the undersurface of lid 30, a series of
adjacent flow passages 60 are formed by the inner surfaces of two
adjacent fin walls 54. A liquid-cooled heat sink 5 having a
corrugated fin 50 is operated in the same manner as when plurality
of pins 25 are employed. Here however, the need for turbulent flow
is reduced as a result of the substantially increased heat transfer
properties created by the increased surface area provided by fin
walls 54 within flow passages 60.
[0032] Referring now to FIGS. 9-13, a thermal jacket 100 may be
positioned over those surfaces of liquid-cooled heat sink 5 that do
not directly engage semiconductor package 24, in order to reduce or
eliminate condensation that may form during subambient operation.
Referring to FIGS. 10 and 11, thermal jacket 100 comprises at least
one porous layer 107, a barrier layer 109, a sealant layer 111, and
a bonding layer 113. More particularly, porous layer 107 comprises
one or more sheets of a mesh or screen, such as an porous membrane
having a lattice structure formed by a plurality of openings
(identified by reference numeral 115 in FIG. 10), or a fabric-like
material of the type having a warp and weft associated with the
fibers making up the structure of the fabric (identified by
reference numeral 117 in FIG. 11). Porous layer 107 may be formed
from a polymer, cloth, or other low thermal conductivity material,
and should be sufficiently compliant prior to application to
liquid-cooled heat sink 5 so that it can be shaped to conform to
surface features. Typically, individual sheets of porous layer 107
will have a thickness in the range from about 0.05 to about 6
millimeters (mm), and preferably in the range from about 0.5 mm to
3 mm. Multiple sheets of porous layer 107 may be used in connection
with the present invention, with one sheet being applied directly
over top of a prior sheet, and need not be fastened together. For
example, the polypropylene mesh manufactured by the SEFAR America,
Inc., under the trade name woven thermoplastic mesh has been used
in connection with a multiple layer embodiment of the invention
with good results. Advantageously, porous layer 107 traps air close
to the surface of heat sink 5, via the openings in the lattice
structure or the spaces formed by the warp and weft, so as to
provide a thermally insulating air barrier between the surface of
heat sink 5 and the ambient environment.
[0033] Porous layer 107 is attached to the surface of liquid-cooled
heat sink 5 by bonding layer 113. Bonding layer 113 comprises a
thermally stable adhesive which may be applied in the form of a
conventional "double-sided" tape adhered directly to the outer
surface of liquid-cooled heat sink 5 prior to the application of
porous layer 107. For example, the double-sided tape manufactured
by the 3M company, under the trade name 966 Hitemperature acrylic
has been used with good results. Of course, other thermally stable
adhesives may be used to maintain porous layer 107 in place on the
surface of liquid-cooled heat sink 5.
[0034] A barrier layer 109 is applied to the outer surface of the
last sheet of porous layer 107, followed by a sealant layer 111 to
complete thermal jacket 100. Barrier layer 109 comprises a
relatively thin sheet of low thermal conductivity material such as
a relatively thin polymer or cellulose film or the like. For
example, a conventional polyethylene film or sheet has been used
with good results. Sealant layer 111 is a low thermal constant
(i.e., low "k") epoxy of the type well known in the art. For
example, the low thermal constant epoxy manufactured by the W. R.
Grace & Co., under the trade name Stycast 2850 ST, with 24LV as
a catalyst, has been used with good results. As a result of this
construction, the openings in the lattice structure 115 or the
spaces formed by the warp and weft 117 of porous layer 107 are
prevented from being clogged or blocked by sealant layer 111 as a
result of barrier layer 109.
[0035] Referring to FIGS. 11-13, thermal jacket 100 may be formed
on liquid-cooled heat sink 5 in the following manner. The portions
of the outer surface 19 of liquid-cooled heat sink 5 that do not
act as the direct thermal conduction pathway between the
electronics devices or semiconductor package 24 and liquid-cooled
heat sink 5 are first covered with bonding layer 113. Once covered
with bonding layer 113, at least one sheet of porous layer 107 is
applied to bonding layer 113. If multiple sheets of porous layer
107 are used, they may be "tacked" together (i.e., glued or bonded
in some manner) at discrete positions and at various locations to
hold them in place, since bonding layer 113 may not fully adhere to
all sheets of a multiple sheet porous layer 107. Also, each sheet
of porous layer 107 may be oriented such that there is a mismatch
between the openings of the sheets, from layer to layer, that is
formed by the lattice structure 115 or the spaces formed by the
warp and weft 117. In this way, trapped air in porous layer 107
acts as an effective insulating barrier. This arrangement enhances
the thermal insulating properties of thermal jacket 100. Once
porous layer 107 is complete, barrier layer 109 is applied to the
outer surface of the mesh followed by an application of sealant 111
to close and complete thermal jacket 100. Advantageously, sealant
111 may be molded to conform to the outer profile of liquid-cooled
heat sink 5.
[0036] In this way, when liquid-cooled heat sink 5 is at subambient
temperatures, thermal jacket 100 forms an insulating barrier
between surface 19 and the ambient environment. Thus, the outer
surface of thermal jacket 100, i.e., the exposed surface of sealant
layer 111, remains at or near to the ambient temperature
surrounding the device. As a result, very little, if any, moisture
is able to condense on the surface of thermal jacket 100.
[0037] It is to be understood that the present invention is by no
means limited only to the particular constructions herein disclosed
and shown in the drawings, but also comprises any modifications or
equivalents within the scope of the claims.
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