U.S. patent application number 12/174210 was filed with the patent office on 2009-01-22 for electronic apparatus.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Masayuki SHIMIZU.
Application Number | 20090020272 12/174210 |
Document ID | / |
Family ID | 40263888 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020272 |
Kind Code |
A1 |
SHIMIZU; Masayuki |
January 22, 2009 |
ELECTRONIC APPARATUS
Abstract
In one embodiment, an electronic apparatus is provided. The
electronic apparatus is equipped with an electronic device and a
cooling device for cooling the electronic device. A heat pipe is
provided with a wick and an operating liquid. The electronic device
is disposed inside the heat pipe, and a heat spreader for thermally
connecting the electronic device and the wick is provided inside
the heat pipe. The electronic device further has a connector for
connecting the electronic device to an outside of the heat
pipe.
Inventors: |
SHIMIZU; Masayuki;
(Kawasaki, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
40263888 |
Appl. No.: |
12/174210 |
Filed: |
July 16, 2008 |
Current U.S.
Class: |
165/104.33 |
Current CPC
Class: |
H01L 2924/00 20130101;
H01L 2924/0002 20130101; H01L 2924/0002 20130101; H01L 23/427
20130101 |
Class at
Publication: |
165/104.33 |
International
Class: |
F28D 15/00 20060101
F28D015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2007 |
JP |
2007-185985 |
Claims
1. An electronic apparatus equipped with an electronic device and a
cooling device for cooling the electronic device, comprising: a
heat pipe provided with a wick and an operating liquid, the
electronic device being disposed inside the heat pipe; a heat
spreader thermally connected with the electronic device and the
wick provided within the heat pipe; and a connector connecting the
electronic device to an outside of the heat pipe.
2. The electronic apparatus according to claim 1, wherein the heat
spreader is provided on both sides of the electronic device.
3. The electronic apparatus according to claim 1, wherein the heat
spreader has a buffer plate, and uneven parts or fins.
4. The electronic apparatus according to claim 1, wherein the
connector has optical connection means.
5. The electronic apparatus according to claim 1, wherein the
connector has electric connection means.
6. The electronic apparatus according to claim 1, wherein the heat
pipe has an opening for mounting the electronic device, the
electronic device is disposed on a blocking member airtightly
blocking the opening, and the electronic device is disposed inside
the heat pipe by the blocking member being disposed in the
opening.
7. The electronic apparatus according to claim 6, wherein the
connection means is provided on the blocking member.
8. A heat pipe provided with a wick and an operating liquid inside
a closed vessel and a pipe part, wherein an electronic device and a
heat spreader are provided inside the closed vessel.
9. The heat pipe according to claim 8, wherein the heat spreader is
constructed of a buffer plate and uneven parts or fins.
10. The heat pipe according to claim 8, wherein the heat spreader
is provided on both sides of the electronic device.
11. The heat pipe according to claim 8, further comprising
connection means for connecting the electronic device to an outside
of the closed vessel.
12. An electronic apparatus comprising: a circuit board; an
electronic device mounted on the circuit board; a heat pipe
provided with a wick and an operating liquid therein; and a heat
spreader placed between the electronic apparatus and the wick,
mounted on one side of the electronic apparatus, and arranged so as
to be in contact with the wick.
13. The electronic apparatus according to claim 12, wherein the
heat pipe has an opening formed therein, the opening is configured
to be blocked by the circuit board, and the electronic device and
the heat spreader are provided inside the opening.
14. The electronic apparatus according to claim 12, wherein the
circuit board is joined to a mounting board in the electronic
apparatus.
15. The electronic apparatus according to claim 12, wherein a
surface of the heat spreader in contact with the wick is formed on
an uneven surface.
Description
BACKGROUND
[0001] The present invention relates to an electronic apparatus,
and in particular, relates to an electronic apparatus using a heat
pipe as a cooling device.
[0002] In recent years, increasingly higher functionality and
faster speed of electronic devices such as semiconductor devices
have been pursued. However, if the clock frequency is increased to
speed up semiconductor devices, power consumption of the
semiconductor devices increases, leading to an increase in
calorific value.
[0003] Electronic equipment in which semiconductor devices are
mounted, on the other hand, is becoming increasingly more compact
and thinner. This makes it more difficult to provide a radiation
area of heat produced by semiconductor devices inside the
electronic equipment, and thus, the heat more likely remains inside
the electronic equipment. If such heat is left alone, the
temperature of the semiconductor devices rises, disabling normal
operation. Thus for example, as disclosed in a publicly known
technique, a cooling device for cooling a semiconductor device
using a heat pipe is proposed, for example see Japanese Laid-Open
Patent Application No. 2002-261216.
SUMMARY
[0004] The object described above is achieved by an electronic
apparatus equipped with an electronic device and a cooling device
for cooling the electronic device, wherein a heat pipe provided
with a wick and an operating liquid is used as the cooling device,
the electronic device is disposed inside the heat pipe, a heat
spreader for thermally connecting the electronic device and the
wick is provided inside the heat pipe, and connection means for
connecting the electronic device to an outside of the heat pipe is
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a view for illustrating a cooling structure of a
semiconductor device using a heat pipe;
[0006] FIG. 2 is an enlarged view of a pyramid buffer thermally
connecting a semiconductor chip and the heat pipe;
[0007] FIG. 3 is a longitudinal sectional view showing the
configuration of an electronic apparatus in a first embodiment;
[0008] FIG. 4 is a bottom view showing the configuration of the
electronic apparatus in the first embodiment;
[0009] FIG. 5 is an enlarged view of a buffer plate and fins
applied to the electronic apparatus in the first embodiment;
[0010] FIG. 6 is a view showing a modification of the fins shown in
FIG. 5;
[0011] FIG. 7 is a bottom view of a configuration of an electronic
apparatus in a second embodiment; and
[0012] FIG. 8 is an enlarged view of a buffer plate and fins
applied to the electronic apparatus in the second embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0013] Next, preferred embodiments of an electronic apparatus will
be described together with the drawings.
[0014] FIGS. 3 and 4 show an electronic apparatus 20A in a first
embodiment. FIG. 3 is a longitudinal sectional view of the
electronic apparatus 20A and FIG. 4 is a bottom view of the
electronic apparatus 20A. FIG. 3 is a sectional view taken along an
A-A line in FIG. 4.
[0015] In the present embodiment, a semiconductor chip 21 is used
as an electronic device and a heat pipe 22 is used as a cooling
device. The semiconductor chip 21 is a high-density, fast device
and therefore produces heat while operating. The semiconductor chip
21 is mounted on a closure plate 23A in a bear chip state without
being packaged by, for example, a sealing resin.
[0016] The closure plate 23A is a ceramic substrate in a multilayer
structure. The semiconductor chip 21 is mounted on a top surface
(an upper surface in FIG. 3) of the closure plate 23A, and solder
balls 24 serving as external connection terminals are disposed on
an undersurface of the closure plate 23A. An internal wire 34 is
laminated inside the closure plate 23A, and the semiconductor chip
21 and the solder balls 24 are electrically connected by the
internal wire 34. FIG. 3 shows a state in which the solder balls 24
are joined to a mounting substrate 25.
[0017] In addition, a heat spreader 50A is provided on a rear side
(an upper surface in FIG. 3) of the semiconductor chip 21. The heat
spreader 50A is formed of copper with thermal conductivity and, as
shown in FIG. 5 as an enlarged view, the heat spreader 50A has a
buffer plate 26 and fins 27A. The buffer plate 26 is thermally
connected to the semiconductor chip 21 and the fins 27A comes into
contact with a wick 31 of the heat pipe 22.
[0018] The heat spreader 50A may be in various shapes and, in the
present embodiment, the buffer plate 26 has a rectangular
parallelepiped shape with a plurality of uneven parts (fins) 27A
made of triangle poles formed on the buffer plate 26.
[0019] The buffer plate 26 has a base area about twice the area of
the semiconductor chip 21 in the present embodiment, but a buffer
plate is not limited to the size of twice the area of the
semiconductor chip 21. Further, instead of the uneven parts 27A in
the shape of triangle poles, fins may also be used and, if fins are
used, costs can be reduced in return for a slight increase in
thermal resistance. For convenience of description, a detailed
structure of the heat spreader 50A will be described later.
[0020] The heat pipe 22 has a closed vessel 28 and a plurality of
pipe parts 30. Both the closed vessel 28 and the pipe parts 30 are
formed of copper with high thermal conductivity. The closed vessel
28 has a cabinet-like shape. Each pipe part 30 is disposed, as
shown in FIG. 4. An opening 35 is formed at the bottom of the
closed vessel 28 and the semiconductor chip 21 mounted on the
closure plate 23A is inserted into the closed vessel 28 through the
opening 35.
[0021] The pipe part 30 is communicatively connected with the
closed vessel 28, and the plurality of pipe parts 30 project
outward from the closed vessel 28. By using the plurality of pipe
parts 30 in this manner, the amount of heat transport can be
increased. The wick 31 is disposed inside each pipe part 30. In the
present embodiment, a felt material made of, for example, polyester
fitted to the shape of the heat spreader 50A is used as the wick
31.
[0022] However, the wick 31 is not limited to the felt material
and, a mesh material or a metallic thin line such as a copper thin
line may also be used. Further, instead of the felt material, a
fine groove may be formed in the pipe part 30, which can be used as
a wick. It is desirable than the interval between the uneven parts
27A or fins forming the heat spreader 50A be sufficiently larger
than the groove utilizing surface tension of an operating liquid.
It is also possible to form a groove on the surface of the uneven
parts 27A or fins, thereby flowing back the operating liquid
fitly.
[0023] Chlorofluorocarbon HFC152a (CH3-CHF2) is used in the present
embodiment as the operating liquid of the heat pipe 22. However,
the operating liquid is not limited to chlorofluorocarbon and,
water, methanol, naphthalene and the like may also be used.
[0024] The semiconductor chip 21 is mounted on the heat pipe 22
according to the procedure shown below. First, the heat spreader
50A is fixed to the top surface of the semiconductor chip 21
mounted on the closure plate 23A. The heat spreader 50A is fixed to
the semiconductor chip 21 by using, for example, an adhesive with
high thermal conductivity.
[0025] Subsequently, the semiconductor chip 21 with the heat
spreader 50A fixed thereto is inserted into the closed vessel of
the heat pipe 22 through the opening 35. At this point, the closed
vessel 28 and the pipe parts 30 are filled with the operating
liquid in advance.
[0026] The area of the closure plate 23A is set to be larger than
that of the opening 35. Thus, the closure plate 23A comes into
contact with an outer circumferential edge of the opening 35 of the
closed vessel 28 by the semiconductor chip 21 being inserted into
the closed vessel 28. The opening 35 is airtightly blocked with the
closure plate 23A by the position of contact between the closure
plate 23A and the closed vessel 28 being hermetically sealed by an
adhesive or the like and thus, the closed vessel 28 is hermetically
sealed from the outside.
[0027] In a hermetically sealed state, the semiconductor chip 21 is
in a state of being disposed inside the closed vessel 28 (the heat
pipe 22) (a sealed state). Thus, the heat pipe 22 functions also as
a package to protect the semiconductor chip 21.
[0028] While the semiconductor chip 21 is disposed inside the heat
pipe 22, the semiconductor chip 21 is connected to the solder balls
24 via the internal wire 34 formed in the closure plate 23A. That
is, the closure plate 23A functions as a connection unit for
connecting the semiconductor chip 21 (electronic device) to the
outside of the closed vessel 28 (the heat pipe 22). Thus, even if
the semiconductor chip 21 is disposed inside the closed vessel 28,
the semiconductor chip 21 can reliably be connected electrically to
an external device (the mounting substrate 25 in the present
embodiment).
[0029] The position of contact between the closure plate 23A and
the closed vessel 28 is configured so that the surface of ceramic
having insulating properties comes into contact with the closed
vessel 28. Thus, even if the closure plate 23A has a multilayer
wiring substrate structure having the internal wire 34, the
semiconductor chip 21 and the heat pipe 22 will not
short-circuit.
[0030] Further, since the heat spreader 50A is fixed to the
semiconductor chip 21 in the present embodiment, the buffer plate
26 and the fins 27A of the heat spreader 50A are engaged in the
wick 31 when the semiconductor chip 21 is mounted inside the closed
vessel 28. The contact area between the heat spreader 50A and the
wick 31 can thereby be made wider, reducing thermal resistance
between the semiconductor chip 21 and the wick 31.
[0031] Next, operations of the electronic apparatus 20A in the
above configuration will be described.
[0032] When the semiconductor chip 21 operates and heat is
produced, heat from the semiconductor chip 21 reaches the wick 31
via the heat spreader 50A (the buffer plate 26 and the uneven parts
27A). The wick 31 is in a state of being penetrated by the
operating liquid through capillarity and, as described above, the
heat spreader 50A is engaged in the wick 31. Thus, the operating
liquid is evaporated by the heat of the semiconductor chip 21 to
receive the heat of the semiconductor chip 21 as latent heat.
[0033] The evaporated operating liquid moves to a cooling unit 32
due to a difference of vapor pressure. The evaporated operating
liquid is liquefied by the cooling unit 32, giving off heat to the
cooling unit 32 as latent heat. The liquefied operating liquid is
transported to near the semiconductor chip 21 and the heat spreader
50A by surface tension with the wick 31 and the closed vessel 28.
Since the operating liquid is transported regardless of gravity as
described above, the semiconductor chip 21 can be arranged at any
position of the heat pipe 22. In the present embodiment, the
semiconductor chip 21 is arranged in the middle position of the
heat pipe 22 in consideration of cooling efficiency. Arrows in
broken lines in FIG. 3 indicate the flow of the gaseous operating
liquid and those in solid lines indicate the flow of the liquefied
operating liquid moving inside the wick 31.
[0034] Here, the electronic apparatus 20A according to the present
embodiment and a cooling device shown in FIGS. 1 and 2 will be
compared. The cooling device described with reference to FIGS. 1
and 2 has a pyramid buffer 6, which is a pyramid-shaped buffer
plate. In the comparison described below, a configuration in which
the pyramid buffer 6 is assembled in the electronic apparatus 20A
is assumed in place of the heat spreader 50A used in the present
embodiment to make the comparison simpler. This configuration and a
cooling device of FIGS. 1 and 2 will be compared.
[0035] In the example shown in FIG. 1, a semiconductor chip 1 is
cooled by a heat pipe 2. The semiconductor chip 1 is disposed
inside a package 3 and connected to solder balls 4 via a wire
provided inside the package 3. The package 3 is mounted on a
mounting substrate 5, thereby connecting the semiconductor chip 1
electrically to the mounting substrate 5.
[0036] The heat pipe 2 has a wick 9, and an operating liquid
provided inside a closed vessel 8. The semiconductor chip 1 is
thermally connected to the middle position of the heat pipe 2 and
thus, both side parts of the heat pipe 2 become cooling units 10
for re-liquefying the operating liquid evaporated by heat generated
by the semiconductor chip 1. In the example in FIG. 1, the
semiconductor chip 1 and the heat pipe 2 are thermally connected by
the pyramid buffer 6 made of copper. As shown in FIG. 2 as an
enlarged view, the pyramid buffer 6 has a first surface 6a, and a
second surface 6b whose area is larger than that of the first
surface 6a. The first surface 6a is thermally connected to the
semiconductor chip 1 and the second surface 6b is thermally
connected to the heat pipe 2. With this configuration, heat
generated by the semiconductor chip 1 is conducted to a wider area
of the heat pipe 2 via the pyramid buffer 6.
[0037] In the cooling device shown in FIGS. 1 and 2, only the
second surface 6b of the pyramid buffer 6 comes into contact with
the heat pipe 22, so that the area of the second surface 6b becomes
an area to be thermally connected to the heat pipe 2 (the wick 9).
In contrast, according to the present embodiment, the whole surface
of the pyramid buffer 6 is engaged in the wick 31 and thus, sides
6c of the pyramid buffer 6 are also in contact with the wick 31.
Therefore, the area of contact of the pyramid buffer 6 with the
wick 31 becomes larger compared with that of the example in FIG. 1,
which allows more efficient cooling. Particularly the heat spreader
50A of the present embodiment, which is equivalent to the pyramid
buffer 6 in the above example, has a configuration in which the
plurality of uneven parts 27A in the shape of triangle poles is
provided. Accordingly, the surface area can further be increased,
allowing still more efficient cooling.
[0038] The semiconductor chip 21 is directly disposed inside the
closed vessel 28 in the present embodiment and therefore, thermal
connection between the semiconductor chip 21 and the wick 31 can be
realized fitly via the heat spreader 50A even if the size or weight
of the heat spreader 50A is reduced. In addition, as described
above, the area of contact between the heat spreader 50A (the
buffer plate 26 and the uneven parts 27A) and the wick 31 can be
made larger. If a groove is used as the wick 31, the area in which
the groove is cut can be increased, thereby allowing efficient
cooling.
[0039] Further, in the example in FIG. 1, the semiconductor chip 1
is sealed inside the package 3 in order to protect the
semiconductor chip 1. Since the package 3 is formed of resin,
thermal resistance from the semiconductor chip 1 to the heat pipe 2
increases. In contrast, in the present embodiment, as described
above, the semiconductor chip 21 is disposed inside the closed
vessel 28. Thus, thermal resistance by the package present in the
example in FIG. 1 can be eliminated and the semiconductor chip 21
can also thereby be cooled efficiently.
[0040] Next, a detailed structure of the heat spreader 50A will be
described.
[0041] The heat spreader 50A attempts to improve cooling capacities
by increasing the effective area of contact with the wick 31. The
heat spreader 50A disperses heat by causing the semiconductor chip
21 to thermally bind to the buffer plate 26 having a thickness of
several millimeters.
[0042] By dispersing heat as described above, the area where the
uneven parts 27A in the shape of triangle poles are set up can be
increased compared with that of the top surface of the
semiconductor chip 21. The effective area of contact with the wick
31 increases as the interval at which the uneven parts 27A in the
shape of triangle poles are set up becomes narrower. However, due
to necessity to bring the wick 31 into contact with the surface of
the uneven parts 27A of triangle poles and to cut a groove, it is
desirable to set up the uneven parts 27A of triangle poles at
intervals of about several millimeters.
[0043] The total of surface areas of the heat spreader 50A
increases as the height of the uneven parts 27A in a triangular
shape in cross section becomes higher. However, due to saturation
caused by saturation of thermal resistance of copper, the effective
surface area will gradually not increase even if the height of the
uneven parts 27A is increased. In terms of the cost/performance
ratio, it is suitable to determine the height of the triangle in
cross section of the uneven parts 27A so that effective efficiency
of the uneven parts 27A becomes about 0.7, that is, near a value
satisfying the formula (1).
2IIh/b.lamda.=1 (1)
wherein I denotes the height of the sectional triangle: h denotes
the thermal conductivity to the operating liquid; b denotes the
interval of setting up triangle poles; and .lamda. denotes the
thermal conductivity of copper.
[0044] FIG. 6 shows a heat spreader 50B, which is a modification of
the heat spreader 50A shown in FIG. 5. The heat spreader 50B is a
modification obtained by reducing the weight of the cooling device
shown in FIGS. 1 and 3.
[0045] The heat spreader 50B according to the present modification
and the pyramid buffer 6 shown in FIG. 2 will be compared. Assume,
for example, that the area where uneven parts 27B in the shape of
triangle poles of the heat spreader 50B are set up is 16
mm.times.16 mm, which is equal to the area of the semiconductor
chip 21.
[0046] Since the area where the uneven parts 27B are set up is not
larger than the area of the semiconductor chip 21 under this
assumption, the buffer plate 26 may be thin. More specifically, the
buffer plate 26 has a thickness of about 1 mm. If the uneven part
27B has a shape of a triangle pole with the height of about 13 mm,
it is suitable to set up the uneven parts 27B at intervals of 4 mm
in four rows.
[0047] If the above configuration is adopted, the total of
effective surface areas of the uneven parts 27B in the shape of
triangle poles will be about 1200 mm.sup.2. If thermal conductivity
to the operating liquid is 5000 W/m.sup.2K, thermal resistance to
the operating liquid will be about 0.17 K/W. The weight of the
buffer plate in the present modification is approximately 22 g
including pyramid portions 33 of 4 mm.
[0048] If, on the other hand, thermal resistance to the operating
liquid should be made equal to that using the pyramid buffer 6 in
FIG. 2, an area of 16 mm.times.16 mm to 38 mm.times.38 mm will be
needed for the pyramid buffer 6 with the height of about 10 mm. The
weight of the pyramid buffer 6 in this case will be about 67 g,
which is significantly heavier than the weight (approximately 22 g)
of the heat spreader 50A according to the present modification.
Therefore, the weight of the electronic apparatus 20A can be
reduced by using the heat spreader 50B in the present
modification.
[0049] FIGS. 7 and 8 are views for illustrating an electronic
apparatus 20B of a second embodiment. The same reference numerals
are attached to components in FIGS. 7 and 8 as those of
corresponding components in FIGS. 3 to 6, and a description thereof
is omitted.
[0050] As shown in FIG. 3, the above-described electronic apparatus
20A according to the first embodiment shows a configuration in
which the heat spreader 50A comes into contact with only one side
(the top surface in FIG. 3) of the semiconductor chip 21. In
contrast, the electronic apparatus 20B according to the present
embodiment is characterized in that a heat spreader 50C is provided
on both sides of the semiconductor chip 21. By adopting this
configuration, heat can be transported not only from the front side
of the semiconductor chip 21, but also from the rear side thereof
and further, the effective area of contact with the wick 31 can be
increased.
[0051] The heat spreader 50C is provided on both sides of the
semiconductor chip 21 in the present embodiment, as shown in FIG.
8. With this configuration, the arrangement position of the
semiconductor chip 21 inside the closed vessel 28 becomes higher
than that in the first embodiment. More specifically, the
semiconductor chip 21 is arranged in substantially the middle
position of the closed vessel 28.
[0052] Thus, the present embodiment provides, in addition to a
closure plate 23B, an intermediate substrate 37 as connection means
for connecting the semiconductor chip 21 to the outside of the
closed vessel 28. The closure plate 23B is provided with an
electric connection terminal 38 and an optical connection terminal
41, as well as the solder balls 24 for external connection disposed
thereon.
[0053] The intermediate substrate 37 is provided with electric
connection terminals 39 and optical connection terminals 42, as
well as the semiconductor chip 21 mounted thereon. Further,
electric connection pins 40 are disposed between the electric
connection terminals 38 and the electric connection terminals 39,
and optical fibers 43 are disposed between the optical connection
terminals 41 and the optical connection terminals 42.
[0054] Thus, the closure plate 23B and the intermediate substrate
37 are electrically connected by the electric connection terminals
38 and 39 and the electric connection pin 40, and the closure plate
23B and the intermediate substrate 37 are also optically connected
by the optical connection terminals 41 and 42 and the optical fiber
43. Further, a material of high rigidity is selected for the
electric connection pin 40 and the intermediate substrate 37 is
thereby supported above the closure plate 23B.
[0055] Therefore, if the closure plate 23B is disposed in the
closed vessel 28 so that the opening 35 is blocked, the
semiconductor chip 21 is located in the middle position of the
closed vessel 28 by being supported by the electric connection pin
40 and the like. The heat spreader 50C has fins 27C (in a
rectangular shape in cross section) formed thereon, instead of the
uneven parts 27A and 27B in the triangular shape in cross section,
and is constructed so that the electric connection pin 40 and the
optical fiber 43 can pass between a predetermined pair of the fins
27C.
[0056] According to the above-described electronic apparatus 20B in
the present embodiment, the effective area of contact with the wick
31 can be increased by the heat spreader 50C being provided on both
sides of the semiconductor chip 21, so that cooling efficiency of
the semiconductor chip 21 can still be enhanced. Further, the
distance between other coupling parts and a radiator can be made
longer by the optical connection means (the optical connection
terminals 41 and 42 and the optical fiber 43) being provided and
therefore, the radiator can be designed more flexibly.
[0057] Electronic apparatuses according to an example of
embodiments have been described above, but the present invention is
not limited to the above specific embodiments and may be variously
modified or altered.
* * * * *