U.S. patent application number 10/085283 was filed with the patent office on 2003-08-28 for flat-plate heat-pipe with lanced-offset fin wick.
Invention is credited to Bowers, Morris, Dantinne, Markus, Sehmbey, Maninder Singh.
Application Number | 20030159806 10/085283 |
Document ID | / |
Family ID | 27753594 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030159806 |
Kind Code |
A1 |
Sehmbey, Maninder Singh ; et
al. |
August 28, 2003 |
Flat-plate heat-pipe with lanced-offset fin wick
Abstract
A passive cooling unit for integrated electronics in form of
flat-plate heat-pipe device having a shallow cavity base member, a
cover plate, and a lanced-offset fin member and associated porous
metal wick material sandwiched therebetween, the fin member being
braced to the base member and cover plate to provide structural
support and also being coated with the wick material. The resultant
flat-plate heat-pipe device, when formed of a lightweight metal
such as aluminum or titanium, results in a passive cooling device
that is lightweight, structurally strong, and of low cost
manufacture.
Inventors: |
Sehmbey, Maninder Singh;
(Hoffman Estates, IL) ; Bowers, Morris;
(Grayslake, IL) ; Dantinne, Markus; (DePere,
WI) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN (MOTOROLA)
233 SOUTH WACKER DRIVE
SUITE 6300
CHICAGO
IL
60606-6402
US
|
Family ID: |
27753594 |
Appl. No.: |
10/085283 |
Filed: |
February 28, 2002 |
Current U.S.
Class: |
165/80.3 ;
165/104.26; 257/E23.088 |
Current CPC
Class: |
H01L 2924/00 20130101;
F28F 3/027 20130101; H01L 2924/0002 20130101; H01L 23/427 20130101;
F28D 15/0233 20130101; F28D 15/046 20130101; H01L 2924/0002
20130101 |
Class at
Publication: |
165/80.3 ;
165/104.26 |
International
Class: |
F28F 007/00; F28D
015/00 |
Claims
We claim:
1. A flat-plate evaporative-fluid type passive cooling device for
use in dissipating heat in electronic applications, comprising in
combination: a base member having a shallow cavity formed
internally therein, said cavity including a plurality of upstanding
support boss members; a cover plate adapted to sealably close off
said base member to enclose said shallow cavity to enable
containing an evaporative fluid medium therewithin; lanced-offset
fin means fitted into said shallow cavity and adapted to support
said cover plate and said base member against external and internal
pressure; and porous metal wick means associated with said
lanced-offset fin means and adapted to permit the evaporative fluid
medium to travel therealong by capillary action once condensed from
an evaporative state.
2. The device of claim 1, wherein said base member comprises a base
plate portion, said plurality of upstanding bosses are formed on
said base plate portion, and a peripheral wall portion extends from
said base plate portion to form said shallow cavity within said
base member.
3. The device of claim 1, and wherein said lanced-offset fin means,
said base member, and said cover plate are formed of metallic
material and said lanced-offset fin means are affixed to said base
member and said cover plate by brazing.
4. The device of claim 3, wherein said porous metal wick means
comprise a powdered metal coating applied directly onto said
lanced-offset fin means.
5. The device of claim 4, wherein said applied coating of said
powdered material is a flame-sprayed coating.
6. The device of claim 4, wherein said applied coating covers all
non-brazed surfaces of said lanced-offset fin means.
7. The device of claim 2, wherein said porous metal wick means is
applied onto the interior surfaces of said base plate and said
cover plate.
8. The device of claim 3, wherein said porous metal wick means is
formed as a sintered metal enclosure covering all non-brazed
surfaces of said lanced-offset fin means, whereby said sintered
metal enclosure permits the evaporative fluid medium to travel by
capillary action in all directions once condensed from an
evaporative state.
9. The device of claim 1, and filler opening means adapted to
permit evacuation, filling, and sealing of said enclosed shallow
cavity.
10. The device of claim 3, wherein said metallic material is formed
from one of aluminum and an aluminum alloy.
11. The device of claim 1, and wherein said porous metal wick means
is formed of aluminum powder.
12. The device of claim 1, wherein said porous metal wick means
comprises flame-sprayed aluminum powder.
13. The device of claim 1, wherein said porous metal wick means is
from approximately 1.0 mm to 2.0 mm thick.
14. The device of claim 2, wherein said base plate portion and said
cover plate are each from approximately 0.5 mm to 1.0 mm thick.
15. The device of claim 1, and extended cooling fin means affixed
to the outer surfaces of at least one end of said respective base
member and said cover plate to permit external heat sink
dissipation of heat collected and released during condensation of
said evaporative fluid medium.
16. The invention of claim 3, wherein said metallic material is
formed from one of titanium and a titanium alloy.
17. A method for providing passive cooling for integrated
electronic devices, comprising the steps of: a) forming a
shallow-cavity metal base member having a base plate member, a
peripheral wall member, and a plurality of upstanding support boss
members; b) fitting a lanced-offset metallic fin member into the
shallow cavity base member; c) installing porous metal wicking
material into said shallow cavity base member; d) enclosing the
shallow cavity by affixing a cover plate to the base member; e)
brazing the lanced-offset metallic fin member to both the base
member and the cover plate; f) forming a fitting opening for the
enclosed shallow cavity; g) evacuating the interior of the enclosed
shallow cavity through the fitting opening; h) introducing a
quantity of evaporative liquid medium into the enclosed shallow
cavity through the fitting opening; and i) sealing off the fitting
opening.
18. The method of claim 17, and the step of forming the shallow
cavity base member, cover plate, and lanced-offset metallic fin
member of aluminum.
19. The method of claim 1, and the step of forming the porous metal
wicking material of aluminum powder.
20. The method of claim 19, and the step of flame-spraying the
aluminum powder.
21. The method of claim 17, and the step of applying said porous
metal wicking material onto the surfaces of the lanced-offset
metallic fin member.
22. The method of claim 17, and the step of applying said porous
metal wicking material onto the interior surfaces of the base plate
member and cover plate.
23. The method of claim 17, and the step of encasing the portions
of the lanced-offset fin member which as extend between the base
plate member and cover plate with the porous metal wicking
material.
24. The method of claim 23, and the step of forming the encasement
of porous metal wicking material about the lanced-offset fin member
by fixturing the fin member between metal plates formed with
depending linear fins, filling the voids between the metal plates
and within and surrounding the exposed surfaces of the
lanced-offset fin member with a metal powder, sintering the metal
powder to the lanced-offset fin member by heating, and removing the
metal plate members.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to passive cooling for
electronic devices, and more particularly to a flat-plate heat-pipe
having an internal lanced-offset fin wick structure with associated
porous wick material, and a method for forming the same.
BACKGROUND OF THE INVENTION
[0002] Electronic devices such as power amplifiers, power supplies,
integrated circuit chips, multi-chip modules, heat spreaders,
electronic hybrid assemblies such as power amplifiers,
microprocessors and passive components such as filters, contain
heat sources which require cooling during normal operation. Various
techniques may be used for cooling electronic devices.
Traditionally, electronic devices have been cooled by natural or
forced convection which involves moving air past conduction heat
sinks attached directly or indirectly to the devices.
[0003] Efforts to reduce the size of electronic devices have
focused upon increased integration of electronic components.
Sophisticated thermal management techniques using liquids, which
allow further reduction of device sizes, have often been employed
to dissipate the heat generated by integrated electronics.
[0004] Two-phase thermosyphons have often been used to provide
cooling for electronic devices. Two-phased thermosyphons typically
include a two-phase material within a housing. The two-phase
material, typically a liquid, vaporizes when sufficient heat
density is applied to the liquid in the evaporator section. The
vapor generated in the evaporator section moves away from the
liquid towards the condenser. In the condenser section, the vapor
transforms back to liquid by rejecting heat to the ambient. The
heat can also be dissipated to the ambient atmosphere by a variety
of means, such as natural convection, forced convection, liquid and
other suitable means. Typifying such two-phase thermosyphons is
U.S. Pat. No. 6,234,242, assigned to the assignee of the present
invention.
[0005] However, there are significant orientation limitations
inherent in the use of such two-phase thermosyphons since they only
work in a vertical orientation. This is because thermosyphons need
the assistance from gravity to get the condensed working liquid
from the condenser section to the evaporator section, i.e., the
condenser must always be higher than the evaporator section.
Additionally, such two-phased thermosyphon devices are not well
suited for very low heat-flux applications.
[0006] Another cooling device often used is the so-called
flat-plate heat-pipe device ("FPHP"). Such FPHP devices are
suitable for low heat-flux and medium heat-flux applications, and
thus, are suitable for many electronics applications such as
cellular telephonic infrastructure products. FPHP devices operate
on the principal of a closed loop of evaporation/boiling and
condensation of a fluid. The working liquid evaporates and boils
off in the areas where heat is dissipated by electronic components,
which components are mounted externally to the FPHP device's walls,
and then travels to the condensation section as a vapor. Contrary
to the boiling occurring in two-phase thermosyphons, the
evaporation in a FPHP device can advantageously occur with a very
small temperature rise between the working liquid and the FPHP
surface. The vapor spreads evenly in the condensation space and
condenses back into liquid form by rejecting heat to the ambient,
as often assisted by externally-mounted fin structure to create a
heat sink. The condensed liquid travels back to the heated section
by a wicking action through porous wick structure formed on the
interior surfaces of the FPHP device's cover plates.
[0007] Importantly, such FPHP devices have the ability to operate
in any orientation. However, commercially available FPHP devices
are typically made of thick-walled copper making such FPHP units
extremely heavy, and therefore impractical for most electronic
cooling situations related to cellular infrastructure products.
They typically use a sintered copper wick on the interior faces of
the cover plate, such that no other wick substructure is present.
Also, due to their method of manufacture, commercially available
FPHP devices are very costly and relatively weak. In fact, because
they are so structurally weak, they are unable to withstand high
internal positive pressures or perform effectively throughout the
broad temperature range found in many cellular and other electronic
infrastructure products. They are generally limited to operating
when internal pressure is lower than 1 atm. Another type of FPHP
that has been typically used employs multiple cylindrical heat
pipes embedded in a solid plate of aluminum. Typifying such prior
FPHP devices are U.S. Pat. No. 4,880,052, which discloses flat
plates with individual heat-pipes embedded within.
[0008] Yet a further cooling device used with integrated
electronics takes the form of an integral heat pipe, heat exchanger
and clamping plate, forming a grid-like pattern of wick-lined
channels, such as typified by U.S. Pat. No. 5,253,702. There, a
base plate functions as an evaporator having a multiplicity of
intersecting parallel and perpendicular internal channels extending
across the baseplate. A sintered copper thermo wick material is
applied to the surfaces of all channels, and there is a series of
vertically aligned condenser tubes forming a condenser region
terminating at their upper ends in cooling fins. This is a
complicated structure formed at great cost, and also has
orientation limitations to its use.
[0009] There is a need for a lightweight and compact flat-plat
heat-pipe cooling device that is structurally robust, thermally
efficient, and has a low cost of manufacture.
SUMMARY OF THE INVENTION
[0010] A lightweight flat-plate heat-pipe device is constructed as
a sealed cavity fabricated by brazing a thin, flat shallow cavity
base member with a cover plate to create a thin-shelled
hollow-enclosure to contain an evaporative working fluid. The base
member includes a number of upstanding bosses which incorporate
holes for locating the fasteners used for installing external
electronic circuit boards, and other modules, on the outer surfaces
of the FPHP device. A lanced-offset fin structure is affixed
internally within the cavity to provide structural support to the
thin base member and cover plate. The lanced-offset fins have an
associated porous wick structure. This overall sandwiched assembly
is brazed together to provide a structurally robust sealed unit
having very thin external walls, and a small opening for the
introduction of a charge of the working fluid. The porous wick
structure associated with the lanced offset fins acts as a
capillary-type wick for transporting the condensed liquid from the
condenser section back to the heated evaporator section. One end of
the respective external faces of the FPHP unit, i.e., at the
condenser section end, can be configured with appropriate cooling
fins to convert the FPHP device into a light-weight heat-sink.
[0011] In one embodiment of the present flat-plate heat-pipe
invention, the porous wick structure is flame-sprayed directly onto
the lanced offset fins. In another embodiment, the porous material
is flame-spayed or otherwise applied to the internal facing
surfaces of the respective base member and cover plate. In a final
embodiment, used for heavy-duty applications, all of the generally
transverse surfaces of the lanced-offset fins, i.e. those surfaces
extending between the respective base member and cover plate, are
encased and all open spaces packed with a sintered metal wick
material to create a structurally supportive porous wick which
permits capillary movement of the working fluid in all directions
and vapor movement in the direction of the fins.
[0012] Preferably, the base member, cover plate and lanced-offset
wick structure are formed of a lightweight aluminum material or
aluminum alloy. Further, the porous wicking material is preferably
formed of aluminum powder that has been flame-sprayed or sintered
in place.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The means by which the foregoing and other aspects of the
present invention are accomplished and the manner of their
accomplishments will be readily understood from the following
specification upon reference to the accompanying drawings, in
which:
[0014] FIG. 1 depicts a front elevation view of the flat-plate
heat-pipe device with lance-offset fin wick structure of the
present invention;
[0015] FIG. 2 is an end elevation view of the flat-plate heat-pipe
device of FIG. 1;
[0016] FIG. 3 is a perspective view of the base member of the
device of FIG. 1;
[0017] FIG. 4 is a perspective view of the lanced-offset fin
structure of the present invention;
[0018] FIG. 5 is an enlarged cross-sectional view, taken at circled
location 5-5 in FIG. 8, of the present flat-plate heat-pipe device
showing the lanced-offset fin structure with associated porous wick
material, and showing circuit board structure, and with certain
components deleted for better viewing;
[0019] FIG. 6 is another cross-sectional view, similar to FIG. 5,
but of an alternative form of the flat-plate heat-pipe device of
the present invention;
[0020] FIG. 7 is yet a further enlarged cross-sectional view,
similar to FIGS. 5 and 6, but of yet a further alternative
embodiment for the flat-plate heat-pipe device of the present
invention;
[0021] FIG. 8 is a side elevation view, similar to FIG. 1, of the
present flat-plate heat-pipe device showing a circuit board
including heat-dissipating electronic devices, and a clam shell
housing; and
[0022] FIG. 9 is a side elevation view of the flat-plate heat-pipe
device of FIG. 8.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Having reference to the drawings, wherein like reference
numerals indicate corresponding elements, there is shown in FIG. 1
an illustration of a flat-plate heat-pipe passive cooling device,
generally denoted by reference numeral 20. The cooling device 20
includes a flat-plate heat-pipe member 22 and external cooling fins
24, to create a passive cooling heat sink assembly. The FPHP member
22 comprises a base member 26 and a cover plate 28. The base member
comprises a base plate 27, a series of upstanding support bosses or
shoulders 48 (described later herein), and a peripheral end wall or
frame 30. Collectively, the components base member 26 create a
shallow cavity generally denoted by reference numeral 34, which
when covered off by the cover plate 28 becomes a sealed enclosed
cavity. The base member 26 and cover plate 28 are preferably formed
of a suitable aluminum material, such as an aluminum-6061 alloy.
The base member 26 can be machined from aluminum plate stock to
yield cavity 34 and raised bosses 48. So as to create a
thin-shelled cooling unit 20, the wall thickness for the aluminum
plates 26, 28 is preferably less than 1 mm in thickness, but not
less than 0.5 mm thick, and preferably approximately 0.7 mm.
Alternatively, instead of using an aluminum alloy for the base
member 26, cover plate 28, and the lanced-offset fin member 36, a
suitable titanium material could be used. This likewise would
provide suitable structural support and rigidity to FPHP member 22,
yet allow it to remain sufficiently lightweight.
[0024] An opening tube 32 (see FIGS. 1 and 7), preferably some 4.8
mm in diameter and welded along the end wall 30 (but which may also
be welded along the baseplate 27 or cover plate 28, but not shown
in either location) can be used to seal off the inner cavity 34.
After the charging process, the filler tube 32 is preferably sealed
off by means of an ultrasonic welder, which pinches and applies
ultrasonic energy to the pinched section of tube 32 to form the
needed closure seal.
[0025] A lanced-offset fin member, generally denoted by reference
numeral 36, is shown in FIGS. 4-7. The lanced-offset fin member 36
is preferably made of an aluminum material, such as an
aluminum-3033 alloy, and is commercially available from vendors
such as Robinson Fin Machines of Kenton, Ohio. This lanced-offset
fin member 36 has a series of generally upstanding channel sections
38 and an intervening valley sections 40, with a width therebetween
in the range from approximately 0.5 mm to 2.5 mm, with the
preferred width range of approximately 1.0 to 2.0 mm. The
transverse wall sections 42 integrally connecting the channel
sections 38 and valley sections 40 comprise a staggered or offset
series of walls 44 as separated by punched openings 46. Selectively
cut clearance holes 47 in fin member 36 permit fin member 36 to fit
over and nestle around respective raised bosses 48 within cavity
34.
[0026] As will be seen in FIGS. 3 and 5, the lanced-offset fin
member 36, while formed as a lightweight component, still creates a
rigid structural member to support the thin-walled base plate 27
and cover plate 28 particularly against the both significant
internal and external pressures that are created within enclosed
cavity 34. The material wall thickness for the overall
lanced-offset fin member 36 is preferably less than approximately
0.5 mm thick. Importantly, besides providing structural support,
the particular punched-wall configuration of the lanced-offset fin
36 presents numerous surfaces (channel sections 38, valley sections
40, and intervening wall sections 42) to support the associated
porous wick material as described below. Other configurations for
the lanced-offset fin member 36 can include a wave-type folded fin
(shaped like the corrugated layer in cardboard), lanced-offset fins
like member 36 but with inclined walls (where the vertical walls
are at approximately 120.degree. to the horizontal walls),
lanced-offset fins with a fine curved pitch (where the upper and
lower horizontal faces are generally curved surfaces instead of
flat), and louvered fins (where the vertical faces of a wave-type
folded fin have vertically aligned louver openings). However,
lanced-offset fin member 36 of FIG. 4 is considered the preferred
design because that design permits the best liquid-vapor movement
perpendicular to general flow direction, to provide the best
thermal performance, such vertical faces provide the best
structural strength, and such horizontal faces provide the best
high strength brazing bond between the fin 36 and base plate 27,
cover plate 28.
[0027] FIG. 5 depicts how the lanced-offset fin member 36 is fitted
into the base member 26 and is sandwiched between the base plate 27
and cover plate 28. During manufacture, the lanced-offset fin 36
can be further shaped by laser cut or EDM to fit into the cavity 34
of base member 26 with needed clearance holes 47 to fit around the
raised bosses 48. As is known in brazing operations, a shim of
suitable brazing material (not shown), such as aluminum alloy 4004
or 4104, is placed over the interior surface of base plate 27, and
the configured lanced-offset fin 36 (with associated porous wick
material as described below), is dropped into place on top of the
brazing material. The cover plate 28 clad with a suitable brazing
material (not shown) is then placed on top of the base member 26
and fin 36, to create a sandwiched assembly. That assembly is then
fixtured to provide uniform pressure over its entire span and then
placed in a vacuum brazing furnace to seal the cover plate to the
base member 26, and to secure affix the fin structure 36 to the
interior surfaces of both base plate 27 and cover plate 28. In this
manner, the lanced-offset fin member 36 operates to structurally
separate and structurally support the respective base member 26 and
cover plate 28 to create a thin-shelled flat, rigidly supported
FPHP device 22.
[0028] Importantly, the use of the lanced-offset fin 36 acts to
eliminate the need for having one of the base plate 27 or cover
plate 28 punched or dimpled for separating the base and cover
plates, such as was required with many prior passive cooling
devices. For example, see the Thermacore (Trademark) product sold
under the product name Thermabase (Trademark).
[0029] The raised bosses 48 (see FIG. 3) each have an opening 50 to
receive a threaded fastener 52, which can be used to secure heat
dissipating members 54 on associated circuit boards 56 to the FPHP
member 22. As seen in FIG. 7, a pair of such circuit boards 56 have
been mounted to the respective front and rear external sides of
FPHP member 22 via fasteners 52 engaging openings 50 in bosses 48.
As seen in FIGS. 7 and 8, a large number of heat-dissipating
members 54 are mounted to the respective circuit boards 56. Devices
54 can comprise power amplifiers, power supplies, integrated
circuit chips, multi-chip modules, heat spreaders, and electronic
hybrid assemblies such as power supplies, microprocessors and
passive components such as filters. All of these electronic devices
contain heat sources which require cooling during normal
operation.
[0030] As seen in FIG. 2, the FPHP member 22 can have cooling fins
28 mounted to both external surfaces at the upper end thereof to
form a complete heat sink assembly. This acts to divide the FPHP
unit 22 into generally an evaporator section 58 and a cooling or
condensing section 60. Alternatively, simply the FPHP member 22 can
be used alone, i.e., without external cooling fins 24, by having
the member's condensing section 60 of member 22 in contact with a
chassis (not shown) which conducts rejected heat away, such as with
a thermal backplane device.
[0031] Turning to FIG. 4, the various external surfaces of the
lanced-offset fin member 36 (comprising channel sections 38, valley
sections 40, and transverse punched wall sections 42) have an
appropriate porous metal wicking material, generally denoted by
reference numeral 62, applied thereon. The porous metal wicking
material 62 forms a porous wick structure to transport fluid medium
therealong, and is supported by fin member 36. Material 62
preferably comprises a porous aluminum foam coating, such as
powdered aluminum which has been preferably flame-sprayed onto the
fin member 36. Advantageously, use of a flame-spraying application
method results in a uniform layered coating of wick material 62.
The porous wicking material layer 62 is preferably between
approximately 1.0 and 2.0 mm thick. Such a porous aluminum wicking
material 62 acts as an excellent capillary-type wick to convey the
condensed working liquid (such as an evaporative liquid medium; not
shown) from the condenser section 60 along the lanced-offset fin
member 36 to the evaporator section 58. As an alternate material to
use for the porous wicking material 62, it could instead be formed
as a sintered copper or sintered bronze material. Either such
alternate material can be suitably flame-sprayed or otherwise
applied to the lanced-offset fin member 36 to again create a
suitable wicking structure for FPHP member 22.
[0032] Due to the presence of the porous wicking material 62 as
flame-sprayed onto the lanced-offset fin member 36, the present
FPHP cooling unit 20 can be utilized in any orientation. That is,
the present invention's FPHP device 20 is not gravity-dependent,
such as were the prior art FPHP and two-phase thermosyphon devices
which were always required to be oriented vertically. Thus, such an
"operable-in-all-orient- ations" feature is a significant
improvement over the previously available passive cooling products.
In sum, besides acting as a structural support for the base plate
27 and cover plate 28, the lanced-offset fin member 36 further acts
as a structural support for the wick surface formed of porous
wicking material 62 inside the inner cavity 34 of the FPHP member
22.
[0033] Referring to FIGS. 1 and 3, using suitable evacuation
equipment, the inner shallow cavity 34 can be evacuated via the
opening tube 32. Then the desired amount of a suitable working
fluid medium, such as acetone, can be introduced through opening
tube 32. Once the evaporative liquid medium has been introduced
into inner cavity 34, the opening tube 32 can be closed, such as by
pinching off opening tube 32, ultrasonic welding, or some other
suitable method to seal off filler tube 32 and the inner cavity 34
thereby retaining the working medium within the FPHP member 22.
Alternatively, instead of using an aluminum alloy for the base
member 26, cover plate 28, and the lanced-offset fin member 36, a
suitable titanium material could be used. This likewise would
provide suitable structural support and rigidity to FPHP member 22,
yet remain sufficiently lightweight.
[0034] An alternate embodiment of the present invention is depicted
in FIG. 6, where like reference numerals are used for like
structural elements relative to the preferred embodiment of FIG. 5.
That is, in FIG. 6, the porous wicking material 62 is shown,
instead of being applied directly on the lanced-offset fin member
36, as being flame-sprayed onto the interior facing surfaces of the
respective base plate 27 and cover plate 28. Thus, in this
embodiment there is no porous wicking material 62 present on the
lanced-offset fin member 36 at all. Otherwise, this alternate
embodiment FPHP member 22' of FIG. 6 is identical to the FPHP
member 22 of the preferred embodiment depicted in FIG. 5.
[0035] Depicted in FIG. 7 is yet a further alternative embodiment
of the present invention, generally denoted by a reference numeral
22". Here, the associated porous wicking material 62 is so formed
and configured that the material 62 encases, and packs all open
spaces, around the walls 44 of punched wall sections 42, upstanding
channel sections 38, and intervening valley sections 40 of
lanced-offset fin member 36. Thus, while no porous wicking material
62 is present or formed directly on the inner surfaces of base
plate 27 and cover plate 28 so that appropriate brazing occurs,
nevertheless there is a substantially larger amount of the porous
wicking material 62 present and structurally supported by the
lanced-offset fin member 36 in this FIG. 7 embodiment than with the
prior two embodiments (of FIGS. 5 and 6).
[0036] The specific configuration for the porous wicking material
62 found in the embodiment of FIG. 6 is formed by utilizing a pair
of stainless steel plates with inwardly-protruding, mating linear
fins (none shown) to sandwich the lanced-offset fin member 36
therebetween. The remaining open spaces are packed with a suitable
powdered metal material, and then sintered in a furnace. A porous
aluminum powdered metal can be used. Then, once suitably adhered to
the lanced-offset fin structure 36, the porous wick structure is
created with the sintered powdered metal being heat fused together
but still essentially retaining to same pore geometry as previously
present between the powdered metal particles. The stainless steel
plates (not shown) are then removed to result in an integral
assembly of lanced-offset fin 36 with sintered wick structure
(formed of porous wick material 62) as shown in FIG. 6.
Importantly, the surfaces of the lanced-offset fin 36 that face and
mate with the base plate 27 and cover plate 28 are free of porous
wick material 62, thus allowing a very high strength braze joint
between the same. The resulting sintered metal wick structure
allows X-Y-Z movement of condensed fluid throughout the structure,
while vapor moves in the open areas where the stainless steel fins
were during sintering. Due to this particular metal wick structure,
a very strong FPHP device 22 is created that is capable of
withstanding significant internal and external pressure, e.g.,
greater than 500 psig.
[0037] It will be understood that the specially-configured sintered
metal wick and lanced-offset fin assembly described above for this
alternate embodiment of FIG. 7 can also be beneficially used in the
heavy-walled copper type FPHP's of the prior art, so as to reduce
their overall resultant weight and cost.
[0038] In FIG. 8 is shown a suitable clam shell-type cover housing
64, which is used to cover off and protect the respective circuit
boards 56 and heat dissipating members 54 carried thereon from
external environment and potential damage. As needed, the cover
housing 64 can be readily removed for suitable installation or
repair purposes. Housing 64 can be formed as a cast aluminum or
cast magnesium component.
[0039] The present FPHP cooling devices are thin-shelled units with
lanced-offset fin structure brazed to both cover plates, resulting
in a structurally strong sealed unit. They can, for example, be
some 406 mm (16 inches) by 254 mm (10 inches) in size. It provides
significant weight, size and cost savings over the prior two phase
thermosyphons, and prior heavy, thick-walled copper-clad FPHP
devices. The present passive cooling FPHP devices are particularly
useful in cellular base station equipment, personal computers,
supercomputers, power supplies, automotive electronic, and
communication infrastructure equipment, e.g., microsite and
picosite cellular equipment. The present invention allows use of a
low cost passive cooling system in such electronics applications,
reduces overall permissible product size and weight, and thus
allows a higher overall electronics package density for the end
user.
[0040] From the foregoing, it is believed that those skilled in the
art will readily appreciate the unique features and advantages of
the present invention over previous types of passive cooling units
for integrated electronic devices. Further, it is to be understood
that while the present invention has been described in relation to
a particular preferred and alternate embodiments as set forth in
the accompanying drawings and as above described, the same
nevertheless is susceptible to change, variation and substitution
of equivalents without departure from the spirit and scope of this
invention. It is therefore intended that the present invention be
unrestricted by the foregoing description and drawings, except as
may appear in the following appended claims.
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