U.S. patent application number 12/607619 was filed with the patent office on 2010-06-24 for thermal management system using micro heat pipe for thermal management of electronic components.
This patent application is currently assigned to KAZAK COMPOSITES, INC.. Invention is credited to Jerome P. Fanucci, Woodrow W. Holley.
Application Number | 20100155033 12/607619 |
Document ID | / |
Family ID | 42264373 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100155033 |
Kind Code |
A1 |
Holley; Woodrow W. ; et
al. |
June 24, 2010 |
THERMAL MANAGEMENT SYSTEM USING MICRO HEAT PIPE FOR THERMAL
MANAGEMENT OF ELECTRONIC COMPONENTS
Abstract
A thermal management system includes a base element and a heat
producing element disposed for heat transfer from the heat
producing element to the base element. An adherent zone includes an
adherent element in physical attachment between the heat producing
element and the base element. A heat transfer zone, separate from
the adherent zone, includes a heat pipe between the heat producing
element and the base element. The heat pipe includes a circulatory
flow path between an evaporator section and a condenser section,
and a working fluid on the circulatory flow path.
Inventors: |
Holley; Woodrow W.; (Malden,
MA) ; Fanucci; Jerome P.; (Lexington, MA) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
KAZAK COMPOSITES, INC.
Woburn
MA
|
Family ID: |
42264373 |
Appl. No.: |
12/607619 |
Filed: |
October 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61109004 |
Oct 28, 2008 |
|
|
|
Current U.S.
Class: |
165/104.26 ;
29/890.03 |
Current CPC
Class: |
F28D 2015/0225 20130101;
H01L 2924/0002 20130101; F28D 15/046 20130101; H01L 23/427
20130101; H01L 2924/09701 20130101; H01L 2924/0002 20130101; Y10T
29/4935 20150115; H01L 2924/00 20130101 |
Class at
Publication: |
165/104.26 ;
29/890.03 |
International
Class: |
F28D 15/02 20060101
F28D015/02; B21D 53/02 20060101 B21D053/02 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made under Air Force Contract
FA8650-09-M-5013. The Government may have certain rights to this
invention.
Claims
1. A thermal management system comprising: a base element and a
heat producing element disposed for heat transfer from the heat
producing element to the base element; an adherent zone comprising
an adherent element in physical attachment between the heat
producing element and the base element; and a heat transfer zone,
separate from the adherent zone, comprising a heat pipe in thermal
communication between the heat producing element and the base
element, the heat pipe comprising a circulatory flow path
comprising an evaporator section in thermal communication with the
heat producing element and a condenser section in thermal
communication with the base element, and a working fluid on the
circulatory flow path.
2. The system of claim 1, wherein the circulatory flow path of the
heat pipe comprises a central space and a capillary medium
surrounding the central space.
3. The system of claim 2, wherein the capillary medium is comprised
of carbon nanotubes, carbon nanofibers, metal mesh, gauze, felt, a
sintered material, or a foam.
4. The system of claim 1, wherein the adherent element comprises an
annular seal element surrounding the heat pipe between confronting
surfaces of the heat producing element and the base element.
5. The system of claim 4, wherein the seal element comprises an
epoxy material.
6. The system of claim 1, wherein the adherent element comprises an
adhesive material between confronting surfaces of the heat
producing element and the base element.
7. The system of claim 1, wherein the adherent element comprises a
mechanical attachment between the heat producing element and the
base element.
8. The system of claim 1, wherein the heat pipe comprises a well
formed in the base element, a capillary medium disposed adjacent at
least a portion of an internal wall of the well.
9. The system of claim 1, wherein the heat producing element
comprises at least a portion of the evaporator section of the heat
pipe.
10. The system of claim 1, wherein the base element comprises at
least a portion of the condenser section of the heat pipe.
11. The system of claim 1, further comprising a vent tube between
the heat pipe and ambient, the vent tube sealed from ambient during
manufacture.
12. The system of claim 1, further comprising a containment barrier
around the heat pipe.
13. The system of claim 1, wherein the heat producing element
comprises an integrated circuit, a chip, a die, a heat slug, or a
heat spreader.
14. The system of claim 1, wherein the base element comprises a
heat slug, a heat spreader, or a heat sink.
15. A method for manufacturing a thermal management system,
comprising: providing a heat producing element and a base element;
forming a well in the base element; forming a vent passage in a
surface of the base element extending outwardly from an edge of the
well; disposing a capillary medium within the well and surrounding
a central space within the well; placing an adherent element
surrounding the well on the surface of the base element and
crossing the vent passage; assembling the heat producing element
and the base element with the adherent element between confronting
surfaces thereof to form an assembly with a working fluid disposed
in the well; boiling off a portion of the working fluid; and
flowing the adherent element into the vent passage and around the
edge of the well to seal off the well and attach the base element
and the heat producing element.
16. The method of claim 15, wherein the step of boiling off a
portion of the working fluid comprises applying a vacuum to the
assembly through the vent passage.
17. The method of claim 15, wherein the step of boiling off a
portion of the working fluid comprising heating the assembly.
18. The method of claim 15, wherein in the step of placing the
adherent element, the adherent element comprises a solid
ring-shaped perform comprised of an epoxy material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Benefit is claimed under 35 U.S.C. .sctn.119(e) of U.S.
Provisional Application No. 61/109,004, filed Oct. 28, 2008, the
disclosure of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0003] As electronic components become more miniaturized and the
number of interconnects per chip increases, heat removal becomes a
limiting barrier to enhanced performance. A principal pathway for
heat removal is via conductance from the chip base to a heat
spreader and from the heat spreader to the printed wire board or
possibly to a heat sink device. Adherent substances, commonly epoxy
resins, filled with thermally conductive particulates such as
carbon or aluminum are used as an attachment layer between the
electronic components.
[0004] An evaporative cooling system has been used for some
high-end applications, in which an appropriate liquid is sprayed
directly onto the chip surface. The liquid vaporizes (heat
transport) and is then condensed and re-circulated. A mini pump
circulates the recovered liquid through a heat exchanger (heat
removal) and creates the spray force.
[0005] Heat pipes have been used for a variety of applications
including electronic systems. Metallic heat pipes of a tapered
design have been employed for direct cooling of processor chips.
The condenser end is typically attached to a finned heat sink for
heat removal and the evaporator end is attached to the chips or
dies by conventional adherents. These types of heat pipes have been
designed with diameters of about 1 mm and lengths of 10 mm.
Application of heat pipes with respect to electronic applications
has been traditionally directed toward removal of the heat buildup
in the cabinet generally rather than specific components.
SUMMARY OF THE INVENTION
[0006] The present invention provides a thermal management system
in which physical bonding and compliancy issues are separated from
the issue of efficient thermal conductivity. The present system
provides a heat transfer zone(s) directed principally to thermal
conductivity and an adherent zone(s) directed to physical
attachment with only secondary concern for heat conductivity.
[0007] In one embodiment, a thermal management system includes a
base element and a heat producing element disposed for heat
transfer from the heat producing element to the base element. An
adherent zone includes an adherent element in physical attachment
between the heat producing element and the base element. A heat
transfer zone, separate from the adherent zone, is formed of a heat
pipe in thermal communication between the heat producing element
and the base element. The heat pipe is formed as a well in the base
element and includes a capillary medium adjacent at least a portion
of an internal wall of the well. The heat pipe includes a
circulatory flow path having an evaporator section in thermal
communication with the heat producing element and a condenser
section in thermal communication with the base element. A working
fluid flows on the circulatory flow path. The heat producing
element forms at least a portion of the evaporator section. The
base element forms at least a portion of the condenser section. The
adherent element includes an annular seal element surrounding the
heat pipe between confronting surfaces of the heat producing
element and the base element.
[0008] A method for manufacturing a thermal management system is
also provided. In one embodiment, the method includes providing a
heat producing element and a base element, and forming a well in
the base element. A vent passage is formed in a surface of the base
element extending outwardly from an edge of the well. A capillary
medium is disposed within the well and surrounding a central space
within the well. An adherent element is placed surrounding the well
on the surface of the base element and crossing the vent passage.
The heat producing element and the base element are assembled with
the adherent element between confronting surfaces thereof to form
an assembly with a working fluid disposed in the well. A portion of
the working fluid is boiled off. The adherent element flows into
the vent passage and around the edge of the well to seal off the
well and attach the base element and the heat producing
element.
DESCRIPTION OF THE DRAWINGS
[0009] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0010] FIGS. 1A and 1B conceptually illustrate a heat pipe;
[0011] FIG. 2 is a schematic cross-sectional side view of an
embodiment of a heat pipe assembly of a thermal management
system;
[0012] FIG. 3 is a schematic isometric view of a further embodiment
of a heat pipe assembly of a thermal management system; and
[0013] FIG. 4 is a schematic cross-sectional side view of a still
further embodiment of a heat pipe assembly of a thermal management
system.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The disclosure of U.S. Provisional Application No.
61/109,004, filed Oct. 28, 2008, is incorporated by reference
herein.
[0015] A bottleneck in transferring heat between components of
electronics systems lies at the thermal interfaces between
components. Depending on the specific components involved, this
thermal interface may be between the die itself and a heat slug or
spreader, or a heat slug and heat spreader, or a heat spreader and
heat sink. In these cases, an imperfect but comparatively flat
surface is presented to be brought into intimate contact with
another corresponding flat surface. Except for the die itself, the
surfaces are typically metallic, with copper, copper/molybdenum and
aluminum being common.
[0016] None of these components has a completely smooth surface,
and air pockets exist between the two materials. Air has a very
high thermal resistance and hence is a poor heat conductor. To
improve the thermal pathway at this interface, thermal compounds
are used to fill in the gaps between the two surfaces. These
compounds are typically organic polymers filled with thermally
conductive particulates such as carbon or aluminum, and are
commonly provided as thermal tape, thermal pads, thermal grease, or
thermal epoxy. None of these compounds, however, completely removes
the air pockets. Also, the inherent thermal conductivity of most
organic polymers is low. As such, these compounds are an
improvement thermally over having no gap filler, but they are still
a bottleneck in the thermal pathway. These forms of attachment do
perform an adequate job of providing adhesion and compliancy
between the surfaces and are generally an acceptably convenient
method of attachment and detachment.
[0017] The present thermal management system, however, provides a
different and more viable approach to forming the thermal pathway
by separating the mechanical issue of physical bonding and
compliancy from the thermal issue of efficient thermal
conductivity. In general, the thermal management system provides an
attachment area that includes one or more zones dedicated
principally to thermal conductivity and one or more other zones
dedicated principally to mechanical bonding in which heat
conductivity is of secondary concern. The thermal management system
is appropriate for a variety of applications, and is particularly
suitable for improving the thermal pathways for electronic
components. The system can be readily applied to several of the
common components found in typical electronic circuit designs.
[0018] The thermal connection of the system uses a micro sized heat
pipe in an evaporative cooling cycle, conceptually illustrated in
FIGS. 1A and 1B. The heat pipe 10 is formed with a closed housing
12, such as a cylindrical or tapered tube wall with closed ends. A
capillary section 14, formed from any suitable capillary or wicking
material, is applied to the inner wall and surrounds a central
vapor or void space 16. The heat pipe is defined along its axial
length into an evaporator section 18, an adiabatic section 20, and
a condenser section 22. An appropriate working fluid in the vapor
space vaporizes in the evaporator section and flows through the
adiabatic section to the condenser section where it is condensed.
The fluid returns through the capillary section under capillary
pressure for recirculation to the evaporator section. The heat pipe
is shown with a cylindrical configuration in FIG. 1; a tapered
configuration can also be used, for example, by providing a tapered
housing wall and/or tapering the capillary medium.
[0019] The present thermal management system uses this heat pipe
concept while separating the attachment into two zones, one
dedicated to thermal attachment and the other to physical
attachment. The system uses an in situ fabricated heat pipe that is
held in place by various physical attachments, such as polymeric
adhesives and/or mechanical devices or mechanisms, such as clips,
clamps and screws. These physical attachments also serve as the
physical attachment between the components. The thermal pathway
between components is improved by utilizing the surfaces of the
existing components as an integral part of the heat pipe design.
This eliminates the requirement to physically "attach" the thermal
pathway, although physical attachment of the heat pipe walls and of
the components still exists. The efficiency of the
vaporization/condensation mechanism with its latent heat of
vaporization inherently overcomes the problems associated with
conventional attachment from a thermal transport perspective.
[0020] In one embodiment, referring more particularly to FIG. 2, a
micro heat pipe 30 is formed from a container or well 32 provided
in a base element 34, such as a heat spreader. The base element
forms the wall and also serves as the condenser end 36 of the heat
pipe at the bottom of the well. The surface 38 of a chip base 40 (a
die or attached slug), the heat source, serves as the evaporator
end 42 of the heat pipe. Enclosed in the well and attached to the
wall is an appropriate capillary media 46. A working fluid 48 is
sealed within the heat pipe well. The surface 38 of the chip base
and the surface 48 the heat spreader are interfaced by an adherent
element 50. In the embodiment of FIG. 2, the adherent element
includes an annular or O-ring seal element surrounding the well
opening, which seals the heat pipe. Additional adhesive material 52
to hold the components (the chip base and the heat spreader)
together may be applied outside the O-ring seal element.
Alternatively or in addition, a mechanical device or mechanism (not
shown) may be used to clamp or hold the parts together and compress
the O-ring in order to form a pressure tight seal.
[0021] The heat pipe well communicates via a vent passage 56
drilled into the spreader from one of its edges to the outside
environment. During manufacture, the vent passage is used to
evacuate ambient non-condensable gases from the interior of the
heat pipe and is subsequently sealed, discussed further below. The
vent pipe can also serve to introduce the working fluid into the
heat pipe. Application of vacuum to the heat pipe well via a vent
passage can also apply a force to hold the surfaces in place during
manufacture.
[0022] In another embodiment, illustrated in FIG. 3, the vent
passage 56' is formed as a channel in the surface 48' of the base
element 34', such as the heat spreader. The adherent element 50' is
an annular or O-ring seal element surrounding the well 32' on the
surface of the heat spreader. During manufacture, the O-ring
reflows into the vent passage and serves both to seal the well and
adhere the heat spreader to the heat source.
[0023] The container wall isolates the working fluid and capillary
medium from the environment. The wall should be leak proof,
non-porous (to prevent gas diffusion), and capable of maintaining
the pressure differential. The wall material should be compatible
(corrosion resistant) with the working fluid and the external
environment. A good wettability with respect to the working fluid
and low coefficient of thermal expansion are also desirable. High
thermal conductivity also improves the operational efficiency.
Suitable materials for the container wall include metals such as
aluminum and copper. Oxygen-free high conductivity (OFHC) copper
provides good heat dissipative properties for heat pipes.
[0024] The working fluid is chosen with consideration for
thermodynamic concerns relating to heat flow occurring within the
heat pipe. The latent heat that is absorbed by the liquid that
results in vaporization and then released upon condensation is the
primary heat transfer medium of a heat pipe. General considerations
include high latent heat of vaporization, high thermal
conductivity, good compatibility with the wick and wall materials,
good thermal stability, high surface tension, and a vapor pressure
over the operating range that is high enough to avoid high vapor
velocities yet not so high as to require a high pressure wall to
contain it.
[0025] The choice of the working fluid and the selection of the
container material should be considered together. The heat pipe can
be constructed largely from the existing materials used in the
construction of the heat slug, spreader, or sink. The choice of a
working fluid is driven in part by compatibility with the metals
typically used in these applications, such as aluminum, copper and
copper/molybdenum. Corrosion resistance, avoidance of in situ
reactions creating contamination or outgases, and wettability
characteristics are criteria among the working fluid selections in
addition to other operational considerations.
[0026] Several working fluids are known to operate effectively over
the temperature range of the high power electronics and are thus
suitable for heat pipe applications. The selection of fluid depends
on the specific metal surfaces that must be interfaced, the
specific operating temperature range, and optimization with respect
to wettability, viscosity, and surface tension. Compatibility with
the other materials is a concern especially with respect to
chemical reactions that may produce corrosion or out-gassing.
Suitable working fluids for the present system include water,
ammonia, and certain hydro-fluorocarbon solvents.
[0027] The capillary medium, a porous structure with
interconnecting pores, generates a capillary pressure capable of
transporting the condensed working fluid from the condenser section
to the evaporator section of the heat pipe. The capillary medium
also usually assists in distributing the fluid around the
evaporator section to improve its contact with the hot areas.
For operation of a heat pipe, the following criteria apply:
.DELTA.P.sub.Capillary,
Max.gtoreq..DELTA.P.sub.Liquid+.DELTA.P.sub.Vapor+.DELTA.P.sub.Gravity
(Equation 1)
where: [0028] .DELTA.P=the capillary pumping pressure [0029]
.DELTA.P.sub.Liquid=the pressure drop necessary to return liquid
from the condenser [0030] .DELTA.P.sub.Vapor=the pressure drop
necessary to move vapor from evaporator to condenser [0031]
.DELTA.P.sub.Gravity=the pressure due to the gravitational
head.
[0032] Most of the physical characteristics described as desirable
for the wall material also apply to the capillary material. Thus,
it also should be non-corrosive with respect to the working fluid,
have high thermal conductivity, and good wettability to the working
fluid. The maximum capillary head that can be generated by a wick
increases with decreasing pore size. This can be seen from the
generalized equations (see Equations 2, 3 & 4) relating the
pressure drop at the capillary head, and evaporator head to the
capillary driving pressure. The effective radius of the wick pores
appears in the denominator of the equations. Thus, the value of
.DELTA.P increases as r decreases.
.DELTA.P.sub.Capillary=.DELTA.P.sub.Evaporator-.DELTA.P.sub.Condenser
(Equation 2)
.DELTA.P.sub.Evaporator=2.sigma..sub.1(cos .theta..sub.E)/r.sub.E
(Equation 3)
.DELTA..sub.Condenser=2.sigma..sub.1(cos .theta..sub.c)/r.sub.C
(Equation 4)
where: [0033] .DELTA.P.sub.Capillary=capillary driving pressure
[0034] .DELTA.P.sub.Evaporator=capillary head at the evaporator
[0035] .DELTA.P.sub.Condenser=capillary head at the condenser
[0036] .sigma..sub.1=surface energy per unit surface area [0037]
.theta..sub.E and .theta..sub.C=surface angles of the liquid
surface with the evaporator and condenser wick surfaces [0038]
r.sub.E and r.sub.C=effective radii of the evaporator and condenser
wick pores
[0039] A variety of capillary media can be used. In one embodiment,
a carbon nanotube material is a suitable capillary medium. Carbon
nanotube materials exhibit high thermal conductivity and good
corrosion resistance. In this material, carbon nanotubes are
dispersed in a binder material, such as a thermosetting or
thermoplastic resin. The binder material supports the carbon
nanotubes and adheres to the container wall. In one embodiment, a
phenolic resin is used as the binder material for carbon nanotubes.
Other capillary media can also be used, such as other carbon
nanofibers, meshes made of metals (such as stainless steel or
aluminum), gauzes, felts, sintered materials (such as glass or
ceramics), and foams. In another embodiment, open grooves or
channels can be formed in the wall. The open channels can be
further covered with a capillary material, such as, for example,
composite wicks or arterial wicks. Self-supporting materials can
also be used.
[0040] Lower density (equivalent to larger pore size) improves
permeability. A good working balance of permeability and capillary
pressure should be achieved. Also as can be seen from Equations 2,
3, and 4, varying the pore size (fiber density) from evaporator to
condenser from smaller to larger sizes can be used to increase
capillary pressure versus a homogeneous pore size.
[0041] The adherent element can be chosen from conventional
adhesive materials commonly employed for attachment, although more
latitude can be used as the choice is no longer constrained by the
need for the best thermal conductivity. The adherent element (for
example, the O-ring) should have many of the features associated
with the container wall material. This material is a fraction of
the wall length of the well when installed, yet should be able to
meet most of the requirements expected of a suitable wall material
in heat pipe applications. The material should exhibit chemical
inertness with respect to the working fluid so that contaminants or
out-gases are not produced that would diminish the operation of the
heat pipe. The material should be capable of withstanding the high
temperature environment without deterioration and maintain an
effective seal against the internal vapor pressure of the working
fluid. The material should be pliable to form the initial seal and
compliant in operation in order to accommodate thermal expansion
differentials between the two interfaces.
[0042] The present system can take advantage of a wider range of
adherent material choices, because the material is no longer used
as the primary thermal route. This allows opportunities to optimize
its performance with respect to maintaining intimate physical
contact while working against the working fluid's pressure so as to
maintain the seal and to provide additional support to the seal in
the lateral direction to resist deformation or movement.
[0043] A variety of high temperature sealing materials is
available. Epoxy resins and other suitable adherents that are
commercially available are generally acceptable. A stiff B-staged
epoxy has been found to be suitable. Epoxy performs of Epoxy
DC-202LT commercially available from Multi-Seals Inc. of
Connecticut has been found to be suitable, although a wider range
of epoxy systems can be used. The epoxy can be placed between the
heat source and base element during manufacture. The entire
assembly can be placed within a vacuum chamber, which is evacuated
of air and non-condensable gases. The epoxy can then reflow and
cure. In this way, the heat pipe and working fluid can be sealed
off from the local environment. A polytetrafluoroethylene (PTFE)
material may also be a suitable material in this application. Use
of a PTFE, such as TEFLON.RTM., has been limited in prior art
thermal applications partially due to its very low thermal
conductivity. The percentage of PTFE or other polymeric material to
be used in this system is a small fraction of the wall material,
thereby having a minor or negligible negative influence on the
performance. A small groove or channel (not shown) can be used to
help seat the adherent material to the surface of the base element.
Adherent materials can also be applied as preformed sheets or as
liquids that are cured in place.
[0044] The adherent element may include a supplemental attachment
such as a mechanical device or mechanism to clamp or otherwise hold
the components together. Mechanical devices or mechanisms can
include, for example, a spring clip device, clamp, or screws.
Supplement adhesive can also serve to maintain the intimate contact
between the parts and an O-ring as well as provide lateral support
to the O-ring.
[0045] One method for manufacturing a thermal management system,
such as that shown in FIG. 3, is as follows. A heat sink or heat
spreader unit is provided as the base element from a suitable
material, such as aluminum or copper. A well is drilled in the heat
sink or spreader unit to a suitable depth, determined by the
application, for example 0.1 to 1.0 inch for many electronic
components. The width of the well is selected to match the
dimensions of the heat producing device to be cooled. For example,
a width of 0.25 inch matches many typical integrated circuit
dimensions. A micro-channel for the vent is then machined on the
surface extending out perpendicularly from the edge of the
well.
[0046] The capillary medium is then introduced into the well. The
capillary medium can be applied in any suitable manner, such as by
spraying, brushing, or in any other manner. The capillary medium
includes a binder material as needed to adhere to the wall surface
of the well. The capillary medium should adhere to as much of the
wall surface as possible.
[0047] A volume of working fluid is then introduced into the well,
allowing for some fluid to be boiled off under vacuum. A liquid
boils when its vapor pressure reaches its surrounding atmospheric
pressure, as is known in the art. The level of vacuum is selected
so that the boiling temperature of the working fluid is greater
than the cure temperature of the epoxy, so that the fluid does not
boil off before the epoxy reflows and cures.
[0048] A circular or ring-shaped epoxy preform is placed on the
heat spreader surrounding the well and crossing the micro-channel.
The preform is sufficiently stiff to be set in place without
hanging down or impinging into the micro-channel. The preform
dimensions (for example, inner and outer diameters and thickness)
are also sufficient to match the diameter of the well while still
allowing the epoxy to reflow without sealing off or encroaching
into the well during subsequent manufacturing steps.
[0049] The heat producing device is then placed on the heat
spreader, covering the well and the epoxy preform and compressed
with a weight if necessary. The assembly is placed in an oven and
heated to allow the epoxy to reflow and cure. The weight helps
compress the epoxy after the heat is applied. This process provides
a consistent bond line between the heat source device and the heat
spreader or heat sink and forces the epoxy down into the
micro-channel sealing the well off from the surrounding
environment. This manufacturing process avoids the heating,
venting, and sealing steps common to prior art heat pipe
manufacturing processes.
[0050] Other methods of introducing the working fluid and purging
the non-condensable gases are possible, for example, for use with
the embodiment of FIG. 2. One approach is to evacuate the well,
with all components held in place, and then introduce the working
fluid by vacuum suction and pressure assistance if necessary. A
detachable valve system on an external tube attached to the vent
passage can be provided to accommodate this method. The external
tube can then be cold pinch welded closed and the valve system
removed. Another approach involves introducing the working fluid
such as by syringe or other dispensing device and then heating the
well area to produce the working fluid vapor. As a consequence the
non-condensable gases will also be purged along with the escaping
working fluid vapor. When sufficient purging has occurred and with
sufficient working fluid still trapped in the well, the section of
external tubing can be cold pinch welded. Alternatively, the vent
hole may be plugged in any suitable manner to close the system.
[0051] In another embodiment of a thermal management system (FIG.
4), two concentric containment barriers interface between two
surfaces, one surface being a chip base, the other surface being a
heat spreader. The inner barrier retains a capillary medium and
appropriate evaporative fluid encased within. An adherent material
is contained between the inner barrier and the outer barrier.
[0052] In operation, the working fluid gathers heat from the hot
surface (the chip base), vaporizes and travels away from the hot
surface toward the cold surface (the heat spreader) in the void
space. The fluid condenses at or near the cold surface and releases
its heat. Thus, the process effectively moves the heat from the hot
to the cold surface. The condensed fluid through the force of
capillary action is wicked via the capillary media back to the hot
surface and thus restarts the heating phase of the cycle. Thus, for
a small sacrifice of adherent area, a highly thermal conductive
heat pipe area is created.
[0053] The present thermal management system provides a continuous
thermal pathway while adhering the two devices together, being
compliant to the differences in thermal expansion between the two
surfaces, and in many applications being capable of easy removal
and reinstallation for replacement of failed chips.
[0054] The system also address challenges to constructing a micro
sized heat pipe in situ with the materials, structures and
environments presented with most processor components. For example,
the heat pipe must produce sufficient capillary pressure to be an
effective operating system. The physical attachment of the
components must be sufficient to accommodate the pressure in the
heat pipe during operation.
[0055] The present system utilizes a technology that can be more
efficient than current practices. As a general rule heat pipe
capacity increases with diameter and thus design solutions to
benefit a variety of situations are possible. The concept can also
be extended to situations where the components to be thermally
attached are not in close physical proximity to one another.
[0056] The system also permits products to be swapped out under
field conditions with only routine expertise and tools for
replacement of defective processors. The materials involved in the
small quantities needed are not comparatively costly. The
fabrication steps are few and involve techniques and processes that
can be understood by those of skill in the art. Therefore, a
competitively low cost and high value product can result.
[0057] The invention is not to be limited by what has been
particularly shown and described, except as indicated by the
appended claims.
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