U.S. patent application number 10/020845 was filed with the patent office on 2002-05-02 for heat pipe heat spreader with internal solid heat conductor.
Invention is credited to Dussinger, Peter M., Myers, Thomas L..
Application Number | 20020050341 10/020845 |
Document ID | / |
Family ID | 23469829 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050341 |
Kind Code |
A1 |
Dussinger, Peter M. ; et
al. |
May 2, 2002 |
Heat pipe heat spreader with internal solid heat conductor
Abstract
The invention is a flat heat pipe heat spreader with the
addition of a solid heat conductive structure spanning the internal
space in the heat pipe only at the region of contact with the heat
source. Capillary wick is also bonded to the sides of the solid
heat conductive structure. Thus, the solid structure provides both
direct heat conduction from the heat source to a heat sink mounted
atop the heat spreader and also acts as an extended evaporator
surface within the heat pipe. The combination furnishes a decrease
in the thermal resistance compared to a heat pipe without the solid
structure.
Inventors: |
Dussinger, Peter M.;
(Lititz, PA) ; Myers, Thomas L.; (Lititz,
PA) |
Correspondence
Address: |
Samuel W. Apicelli
Duane Morris LLP
502 N. Front Street
P.O. Box 1003
Harrisburg
PA
17108-1003
US
|
Family ID: |
23469829 |
Appl. No.: |
10/020845 |
Filed: |
December 12, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10020845 |
Dec 12, 2001 |
|
|
|
09372839 |
Aug 12, 1999 |
|
|
|
Current U.S.
Class: |
165/104.26 |
Current CPC
Class: |
F28D 15/0233
20130101 |
Class at
Publication: |
165/104.26 |
International
Class: |
F28D 015/00 |
Claims
What is claimed as new and for which Letters Patent of the United
States are desired to be secured is:
1. A heat pipe heat spreader comprising: a first plate and a second
plate shaped and sealed together to form an enclosure, with
non-condensible gases evacuated from within the enclosure and
sufficient liquid loaded into the enclosure to form an operable
heat pipe; a solid heat conductive structure spanning the space
within the enclosure between the first and second plates and
attached to the two plates with a heat conductive bond, the heat
conductive structure being located at that part of the inner
surface of one plate where the outer surface of the plate is in
contact with a heat source being cooled by the heat pipe; and
capillary wick attached to the inside surface of the plate which is
in contact with the heat source cooled.
2. The heat pipe heat spreader of claim 1 wherein the capillary
wick is attached to the interior surfaces of both plates.
3. The heat pipe heat spreader of claim 1 wherein the capillary
wick is attached to the interior surfaces of both plates and to the
surfaces of the solid heat conductive structure which span the
space between the two plates, and the capillary wick on the solid
heat conductive structure is continuous with the capillary wick on
the interior surfaces of the two plates.
4. The heat pipe heat spreader of claim 1 wherein the cross section
of the solid heat conductive structure is the same as the size of
the contact surface of a device being cooled by the heat pipe.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to active solid state
devices, and more specifically to a flat heat pipe for cooling an
integrated circuit chip.
[0002] As integrated circuit chips decrease in size and increase in
power, the required heat sinks and heat spreaders have grown to be
larger than the chips. Heat sinks are most effective when there is
a uniform heat flux applied over the entire heat input surface.
When a heat sink with a large heat input surface is attached to a
heat source of much smaller contact area, there is significant
resistance to the flow of heat along the heat input surface of the
heat sink to the other portions of the heat sink surface which are
not in direct contact with the contact area of the integrated
circuit chip. Higher power and smaller heat sources, or heat
sources which are off center from the heat sink, increase the
resistance to heat flow to the balance of the heat sink. This
phenomenon can cause great differences in the effectiveness of heat
transfer from various parts of a heat sink. The effect of this
unbalanced heat transfer is reduced performance of the integrated
circuit chip and decreased reliability due to high operating
temperatures.
[0003] The brute force approach to overcoming the resistance to
heat flow within heat sinks which are larger than the device being
cooled is to increase the size of the heat sink, increase the
thickness of the heat sink surface which contacts the device to be
cooled, increase the air flow which cools the heat sink, or reduce
the temperature of the cooling air. However, these approaches
increase weight, noise, system complexity, and expense.
[0004] It would be a great advantage to have a simple, light weight
heat spreader for an integrated circuit chip which furnishes an
essentially isothermal surface even though only a part of that
surface is in contact with the chip and also includes a simple
means for assuring a direct heat transfer path between the chip and
a heat sink which dissipates the heat.
SUMMARY OF THE INVENTION
[0005] The present invention is an inexpensive heat pipe heat
spreader for integrated circuit chips which is of simple, light
weight construction. It is easily manufactured, requires little
additional space, and provides additional surface area for cooling
the integrated circuit and for attachment to heat transfer devices
such as cooling fins for disposing of the heat from the integrated
circuit chip. Furthermore, the heat pipe heat spreader of the
invention is constructed to maximize heat transfer from the
integrated circuit chip to the heat sink.
[0006] The internal structure of the heat pipe is an evacuated
vapor chamber with a limited amount of liquid. In the preferred
embodiment of the invention two plates form the casing of the heat
pipe vapor chamber, thus forming an essentially flat heat pipe.
Capillary wick material covers the inside surfaces of at least one
plate, the evaporator surface of the heat pipe casing, which is in
contact with the integrated circuit chip.
[0007] However, because the heat input area at the integrated
circuit chip on the evaporator surface of such a flat heat pipe is
usually much smaller than the fin or other heat removal structure
attached to the opposite surface, a considerable amount of the heat
must first be transferred thrughout the thin plate of the casing
before it can be used to evaporate the liquid from the capillary
wick which is attached to the thin plate.
[0008] Although a heat pipe transfers heat with less temperature
difference than a solid metal conductor, the insertion of the small
cross section path along the casing sides to get to the majority of
the heat pipe evaporator loses some of this benefit. The present
invention therefore adds a parallel heat transfer path which is a
solid metal structure spanning the space within the heat pipe
between the integrated circuit contact area and the center portion
of the fin structure.
[0009] As with any other parallel path, the heat conductive
structure reduces the heat flow resistance, even though its heat
transfer impedance is not quite as effective as would be a heat
pipe of the same dimensions. However, the structure does have a
very low thermal impedance because it has a very short length of
thermal path, only the small internal height of the heat pipe, and
a relatively large cross section. Furthermore, since the sides of
the heat conductive structure are covered with capillary wick
material, there is very little reduction in the effective area of
the evaporator wick.
[0010] The conductive structure also serves other important
purposes. It supports the flat plates and prevents them from
deflecting inward and distorting to deform the flat surface that is
in contact with the integrated circuit chip. This feature is very
important for good heat transfer between the heat spreader and the
integrated circuit chip. The structure also serves as critical
support for the portions of the capillary wick which cover its
sides and span the internal space between the plates. The capillary
wick on the sides of the structure, along with capillary wick
covering the inside surfaces of both of the plates, provides a
gravity independent characteristic to the heat spreader, and the
structure around which the wick is located assures that the
capillary wick on its sides is not subjected to destructive
compression forces.
[0011] The present invention thereby provides a heat pipe with heat
transfer characteristics superior to those of either a single solid
plate or a simple flat heat pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The FIGURE is a perspective view of the preferred embodiment
of the flat heat pipe of the invention with part of one plate of
the envelope removed to view the interior.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The FIGURE is a perspective view of the preferred embodiment
of flat heat pipe 10 of the invention with part of one plate 12 of
the envelope removed to view the interior.
[0014] Heat pipe 10 is constructed with a casing formed by sealing
together two formed plates, contact plate 14 and cover plate 12.
Contact plate 14 and cover plate 12 are formed as shallow pans so
that there is a space between their interior surfaces when they are
joined together at seal 16 on their peripheral lips by conventional
means, such as soldering or brazing, to form heat pipe 10. Heat
pipe 10 is then evacuated to remove all non-condensible gases and a
suitable quantity of heat transfer fluid is placed within it. This
is the conventional method of constructing a heat pipe, and is well
understood in the art of heat pipes.
[0015] The interior of heat pipe 10 is, however, constructed
unconventionally in that solid structure 18 made of a heat
conductive material such as copper spans the interior space between
contact plate 14 and cover plate 12 and is attached to each plate
with a heat conductive bond. Such bonds are typically either
soldered or brazed. The location and size of solid structure 18 is
determined by the location and size of the integrated circuit chip
or other heat source from which heat pipe 10 is spreading heat.
Ideally, solid structure 18 is constructed so that it is aligned
with the heat source being cooled, is of the same cross section as
the size of the contact area of the heat source, and is located on
the opposite surface of contact plate 14 from the heat source.
[0016] Heat pipe 10 also includes internal sintered metal capillary
wick 20 which covers the entire inside surfaces 11 of cover plate
12 and 13 of contact plate 14, including their sides. As is well
understood in the art of heat pipes, a capillary wick provides the
mechanism by which liquid condensed at the cooler condenser of a
heat pipe is transported back to the hotter evaporator where it is
evaporated. The vapor produced at the evaporator then moves to the
condenser where it again condenses. The two changes of state,
evaporation at the hotter locale and condensation at the cooler
site, are what transport heat from the evaporator to the condenser.
In a well designed heat pipe this transfer of heat occurs with
virtually the same temperature at the evaporator as at the
condenser.
[0017] It should be appreciated that in typical use contact plate
14 is held in thermally conductive contact with a heat source such
as an integrated circuit chip (not shown), and cover plate 12 is
attached to a cooling device such an assembly of cooling fins (not
shown). Thus, the function of heat pipe 10 is to spread the heat
generated at the small area of an integrated circuit chip, from
which it is more difficult to dissipate any significant quantity of
heat, to a much larger surface area such as an assembly of cooling
fins. The larger area facilitates heat removal without requiring an
unreasonably high temperature.
[0018] It is also worth recognizing that when capillary wick 20 is
attached to the inside surface of both contact plate 14 and cover
plate 12, heat pipe 10 actually operates independent of
orientation, and it does not matter whether the heat input is at
contact plate 14 or cover plate 12.
[0019] In the preferred embodiment of the present invention, heat
pipe 10 also has capillary wick on sides 22 of solid structure 18,
and that wick is in contact with capillary wick 20 on the inside
surfaces of plates 12 and 14. The wick on sides 22 of structure 18
thereby interconnects wick 11 of cover plate 12 and wick 13 of
contact plate 14 with continuous capillary wick. This geometry
assures that, even if heat pipe 10 is oriented so that the
condenser is lower than the evaporator, liquid condensed upon the
inner surface of either plate will still be in contact with
capillary wick on sides 22 of solid structure 18. The liquid will
therefore be moved by capillary force back to the hotter surface
which functions as the evaporator. Solid structure 18 also prevents
the structurally weaker capillary wick wrapped around it from
suffering any damage.
[0020] However, another important function of the wick on sides 22
of solid structure 18 is its function as additional evaporator
surface. At the same time as solid structure 18 is conducting heat
directly between contact plate 14 and cover plate 12, heat within
solid structure 18 is also evaporating liquid from the wick on
sides 22 of solid structure 18 to add to the heat transfer
capability of heat pipe 10.
[0021] The preferred embodiment of the invention has been
constructed as heat pipe 10 shown in the FIGURE. This heat pipe is
approximately 3.0 inches by 3.5 inches with a total thickness of
0.200 inch. Cover plate 12 and contact plate 14 are constructed of
OFHC copper 0.035 inch thick, and solid structure 18 spans the
0.130 inch height of the internal volume of heat pipe 10. Capillary
wick 22 is constructed of sintered copper powder, averages 0.040
inch thick, and covers essentially all the surfaces inside heat
pipe 10, including sides 24. Solid structure 18 is also constructed
of OFHC copper and is 0.80 inch by 0.80 inch and 0.130 inch
thick.
[0022] The thermal conductivity of solid structure provides
additional heat conduction between plates 12 and 14, and thereby
reduces the temperature difference within heat pipe 10 between the
heat source and the heat sink. This reduction of temperature
difference directly affects the operation of heat pipe 10, and
essentially results in a similar reduction in the operating
temperature of any heat source such as an integrated circuit
chip.
[0023] The invention thereby furnishes an efficient means for
cooling an integrated circuit and does so without the need for
larger heat spreaders which not only add weight but also do not
transfer heat away from the integrated circuit as efficiently as
does the heat pipe of the invention.
[0024] It is to be understood that the form of this invention as
shown is merely a preferred embodiment. Various changes may be made
in the function and arrangement of parts; equivalent means may be
substituted for those illustrated and described; and certain
features may be used independently from others without departing
from the spirit and scope of the invention as defined in the
following claims. For example, the heat conductive solid structure
could be constructed of materials other than copper, and although
it is pictured as a rectangular prism, it could be constructed as
any other shape.
* * * * *