U.S. patent application number 13/751564 was filed with the patent office on 2013-06-06 for cooling system, electronic equipment, and method for cooling heating element.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Nobuyuki HAYASHI, Masaru MORITA, Teru NAKANISHI, Yasuhiro YONEDA.
Application Number | 20130139998 13/751564 |
Document ID | / |
Family ID | 45723011 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130139998 |
Kind Code |
A1 |
HAYASHI; Nobuyuki ; et
al. |
June 6, 2013 |
COOLING SYSTEM, ELECTRONIC EQUIPMENT, AND METHOD FOR COOLING
HEATING ELEMENT
Abstract
A cooling system includes a first cooling part to cool a
connecting part of a heating element with a first coolant having an
electrical insulating property, the connecting part providing
electrical connection between the heating element and a board, and
a second cooling part to cool another part of the heating element
with a second coolant, said other part being different from the
connecting part.
Inventors: |
HAYASHI; Nobuyuki;
(Yokohama, JP) ; YONEDA; Yasuhiro; (Machida,
JP) ; NAKANISHI; Teru; (Isehara, JP) ; MORITA;
Masaru; (Isehara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED; |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
45723011 |
Appl. No.: |
13/751564 |
Filed: |
January 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/064197 |
Aug 23, 2010 |
|
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13751564 |
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Current U.S.
Class: |
165/47 |
Current CPC
Class: |
H05K 7/20236 20130101;
F28F 9/00 20130101; H01L 2924/09701 20130101; H01L 23/473 20130101;
H01L 2224/73204 20130101; H01L 2224/73253 20130101; H01L 2924/15311
20130101; H01L 2224/16225 20130101 |
Class at
Publication: |
165/47 |
International
Class: |
F28F 9/00 20060101
F28F009/00 |
Claims
1. A cooling system comprising: a first cooling part to cool a
connecting part of a heating element with a first coolant having an
electrical insulating property, the connecting part providing
electrical connection between the heating element and a board; and
a second cooling part to cool another part of the heating element
with a second coolant, said other part being different from the
connecting part.
2. The cooling system according to claim 1, wherein the first
cooling part is configured to immerse the connecting part of the
heating element in the first coolant, and the second cooling part
is configured to supply the second coolant to said other part of
the heating element.
3. The cooling system according to claim 2, further comprising: a
casing to accommodate the first coolant and the second coolant,
wherein a specific gravity of the first coolant is greater than a
specific gravity of the second coolant, and wherein the second
cooling part has a first supply unit to supply the second coolant
taken out of the casing to said other part of the heating
element.
4. The cooling system according to claim 3, further comprising: a
circulator to circulate the second coolant that has absorbed heat
from the heating element; and a heat release part provided on a
path of the circulator to remove the heat from the second coolant,
wherein the circulator supplies the heat-removed second coolant to
the first supply unit.
5. The cooling system according to claim 1, wherein the first
cooling part is configured to supply the first coolant to the
connecting part of the heating element; and the second cooling part
is configured to supply the second coolant to said other part of
the heating element.
6. The cooling system according to claim 5, further comprising: a
tank to accommodate the first coolant and the second coolant,
wherein a specific gravity of the first coolant is greater than a
specific gravity of the second coolant, and wherein the first
cooling part has a second supply unit to supply the first coolant
from the tank to the connecting part of the heating element, and
the second cooling part has a third supply unit to supply the
second coolant from the tank to said other part of the heating
element.
7. The cooling system according to claim 6, wherein the second
supply unit forms a curtain flow of the first coolant to surround
the connecting part.
8. The cooling system according to claim 6, further comprising: a
first pipe to supply the first coolant and the second coolant
having been supplied to the heating element to the tank; a second
pipe to supply the first coolant from the tank to the second supply
unit; and a third pipe to supply the second coolant from the tank
to the third supply unit.
9. The cooling system according claim 1, wherein the first coolant
includes one of fluorocarbon, halogenated hydrocarbon, and
dielectric oil.
10. The cooling system according to claim 1, wherein the second
coolant contains water or pure water as a major ingredient.
11. Electronic equipment, comprising: a semiconductor device having
a connecting part for connecting the semiconductor device to a
board; a first cooling part to cool the connecting part of the
semiconductor device with a first coolant having an insulating
property; and a second cooling part to cool another part of the
semiconductor device with a second coolant, said other part being
different from the connecting part.
12. The electronic equipment according to claim 11, wherein the
first cooling part is configured to immerse the connecting part of
the semiconductor device in the first coolant, and the second
cooling part is configured to supply the second coolant to said
other part of the semiconductor device.
13. The electronic equipment according to claim 12, further
comprising: a casing to accommodate the first coolant and the
second coolant, wherein a specific gravity of the first coolant is
greater than that of the second coolant, and wherein the second
cooling part include a first supply unit to supply the second
coolant taken out of the casing to said other part of the
semiconductor device.
14. The electronic equipment according to claim 13, further
comprising: a circulator to circulate the second coolant that has
cooled the semiconductor device; and a heat radiator provided on
the circulator and to remove heat from the second coolant, wherein
the circulator supplies the heat-removed second coolant to the
first supply unit.
15. The electronic equipment according to claim 11, wherein the
first cooling part is configured to supply the first coolant to the
connecting part of the semiconductor device, and the second cooling
part is configured to supply the second coolant to said other part
of the semiconductor device.
16. The electronic equipment according to claim 15, further
comprising: a tank to accommodate the first coolant and the second
coolant having been supplied to the semiconductor device, wherein a
specific gravity of the first coolant is greater than that of the
second coolant, wherein the first cooling part has a second supply
unit to supply the first coolant taken out of the tank to the
connecting part of the semiconductor device, and wherein the second
cooling part has a third supply unit to supply the second coolant
taken out of the tank to said other part of the semiconductor
device.
17. The electronic equipment according to claim 16, wherein the
second supply unit forms a curtain flow of the first coolant to
surround the connecting part of the semiconductor device.
18. The electronic equipment according to claim 16, further
comprising: a first pipe to supply the first coolant and the second
coolant having been supplied to the semiconductor device to the
tank; a second pipe to supply the first coolant from the tank to
the second supply unit; and a third pipe to supply the second
coolant from the tank to the third supply unit.
19. The electronic equipment according to claim 11, wherein the
first coolant one of fluorocarbon, halogenated hydrocarbon, and
dielectric oil.
20. A method for cooling a heating element comprising: cooling a
connecting part of a heating element with a first coolant having an
electrical insulating property; and cooling another part of the
heating element with a second coolant, said other part being
different from the connecting part.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation application of
International Application No. PCT/JP2010/064197 filed on Aug. 23,
2010 and designating the United States, the entire contents of
which are incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein relate to a cooling system,
electronic equipment, and a method for cooling a heating
element.
BACKGROUND
[0003] In recent years and continuing, along with acceleration of
the processing speeds of information processing systems (such as
server systems or computer systems), high-performance semiconductor
equipment has been advancing. As the performance and functions of
semiconductor equipment are enhanced, the sizes of the
semiconductor devices or chips used in the semiconductor equipment
become large and the amount of heat produced is increasing.
Accordingly, techniques for efficiently cooling semiconductor
devices have also been developed.
[0004] FIG. 1A illustrates a technique for cooling semiconductor
equipment, which technique is known as a spray cooling method for
spraying a pressurized coolant 103 from a nozzle 105 onto a
semiconductor device 121 or a package 120. See, for example, Patent
Documents 1 and 2 listed below. FIG. 1B illustrates another
technique for immersing a semiconductor device 121 in a dielectric
liquid (coolant) 104 with a low boiling point. This technique is
known as an immersion cooling (or ebullient cooling) method.
[0005] Both techniques make use of boiling and vaporization of the
coolant 103 or 104 to transfer heat from the semiconductor device
121 which is a heat source generating a large amount of heat during
operation. The coolants 103 and 104 are circulated by a pump 108
and heat is removed by a radiator 106.
[0006] A fan 107 is used to enhance the heat removal
efficiency.
[0007] Still another known technique is forming an air curtain
around the chip during the spray cooling process. See, for example,
Patent Document 3 listed below. In this technique, a chip is held
upside down and coolant is sprayed by the nozzle toward the chip
from underneath the chip, while supplying air flow in the opposite
direction to the spray to produce an air curtain. The air curtain
prevents the coolant from flowing into undesirable areas other than
the heat generating surfaces to be cooled.
[0008] However, the spray cooling method illustrated in FIG. 1A has
a problem because it is undesirable to spray a water-based coolant
103 directly onto the connecting part 125 that ensures electrical
connection between interconnections which are insulated from each
other. Spraying the coolant so as to avoid the connecting part 125
will lead to limited cooling ability. In addition, when the amount
of heat produced by the semiconductor device 121 is large, boiling
bubbles are generated and the efficiency for cooling the
semiconductor device 121 is degraded.
[0009] The immersion cooling method illustrated in FIG. 1B is
advantageous because the connecting part 125 of the semiconductor
device 121 immersed in the dielectric coolant 104 is cooled
directly. However, this technique uses a dielectric coolant 104. If
a fluorinated coolant such as chlorofluorocarbon is used,
environmental burden increases.
[0010] Therefore, it is desired to provide a cooling system and
electronic equipment with the cooling system that can cool heat
generating elements such as semiconductor devices in an efficient
and stable manner while reducing the environmental burden. [0011]
Patent Document 1: Japanese Patent Laid-open Publication No.
H05-160313 [0012] Patent Document 2: Japanese Patent Laid-open
Publication No. H05-136305 [0013] Patent Document 3: Japanese
Patent Laid-open Publication No. H01-025447
SUMMARY
[0014] According to an aspect of the embodiments, a cooling system
is provided. The cooling system includes:
[0015] a first cooling part to cool a connecting part of a heating
element with a first coolant having an electrical insulating
property, the connecting part providing electrical connection
between the heating element and a board, and
[0016] a second cooling part to cool another part of the heating
element with a second coolant, said other part being different from
the connecting part.
[0017] According to another aspect of the invention, electronic
equipment is provided. The electronic equipment includes:
[0018] a semiconductor device having a connecting part for
connecting the semiconductor device to a board;
[0019] a first cooling part to cool the connecting part of the
semiconductor device with a first coolant having an insulating
property; and
[0020] a second cooling part to cool another part of the
semiconductor device with a second coolant, said other part being
different from the connecting part.
[0021] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0022] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive to the invention as
claimed.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1A is a schematic diagram illustrating a cooling system
of a conventional spray cooling type;
[0024] FIG. 1B is a schematic diagram illustrating a cooling system
of a conventional immersion cooling type;
[0025] FIG. 2 is a schematic diagram illustrating electronic
equipment with a cooling system according to the first
embodiment;
[0026] FIG. 3 illustrates a board on which multiple semiconductor
devices are mounted together with other modules in a schematic plan
view and a side view;
[0027] FIG. 4 is a schematic diagram illustrating a cooling system
for cooling the board of FIG. 3;
[0028] FIG. 5 is a schematic diagram illustrating an experimental
model to measure the cooling effect of the cooling system according
to the first embodiment;
[0029] FIG. 6A is a diagram illustrating the cooling effect of the
cooling system of the first embodiment compared with a conventional
spray cooling system;
[0030] FIG. 6B is a table illustrating the cooling effect of the
cooling system of the first embodiment compared with the
conventional spray cooling system;
[0031] FIG. 7 is a schematic diagram illustrating semiconductor
equipment with a cooling system according to the second
embodiment;
[0032] FIG. 8 is a schematic diagram illustrating an experimental
model to measure the cooling effect of the cooling system according
to the second embodiment;
[0033] FIG. 9A is a diagram illustrating the cooling effect of the
cooling system of the second embodiment compared with the
conventional spray cooling system; and
[0034] FIG. 9B is a table illustrating the cooling effect of the
cooling system of the second embodiment compared with the
conventional spray cooling system.
DESCRIPTION OF EMBODIMENTS
[0035] The embodiments of the present disclosure are explained
below with reference to the appended drawings. In the drawings,
those elements with the same structure or functions are denoted by
the same numerical symbols and repetitive explanations are omitted.
In the embodiments, a cooling system is used to cool a
semiconductor package mounted on a board; however, the cooling
system described in the embodiments is suitable for cooling of
arbitrary heat generating devices such as electronic modules or
those devices having a connecting part for providing external
electrical connection.
[0036] In the embodiments, a dielectric coolant and a water-based
coolant, which separate from each other into two layers, are used.
An electrical connecting part that produces a large amount of heat
is directly cooled with a dielectric coolant, and the remaining
heat generating parts other than the electrical connecting part are
cooled with a water-based coolant. This arrangement achieves
efficient and stable cooling, while reducing the environmental
burden. The cooling system making use of two-layer separation is
applied not only to horizontal semiconductor equipment in which a
semiconductor package and a board are placed in a horizontal plane,
but also to vertical semiconductor equipment in which boards are
inserted vertically in a rack.
[0037] In the first embodiment, a cooling system is applied to a
horizontally arranged semiconductor device, and in the second
embodiment a cooling system is applied to a vertically arranged
semiconductor device. In this context, the horizontal arrangement
is one in which a semiconductor device and a board are placed in a
plane perpendicular to the direction of gravity, and the vertical
arrangement is one in which the semiconductor device and the board
are place in a plane parallel to the direction of gravity. In the
description, semiconductor elements (or chips), semiconductor
packages, semiconductor modules and so on may be collectively
called "semiconductor devices". Similarly, circuit boards,
interposer boards, system boards and so on may be collectively
called "boards".
First Embodiment
[0038] FIG. 2 is a schematic diagram illustrating electronic
equipment 10 with a cooling system according to the first
embodiment. In the first embodiment, a horizontally arranged
semiconductor package 20 with a board 30 placed in a plane
perpendicular to the direction of gravity is cooled.
[0039] The semiconductor package 20 includes a circuit board or an
interposer board 22 (which may be simply referred to as "board
22"), and a semiconductor chip 21 electrically connected to the
board 22 via solder bumps 23. The semiconductor chip 21 and the
board 22 are entirely sealed in a package. The semiconductor
package 20 has a connecting part 24 for providing electric
connection between the semiconductor package 20 and a board 30 such
as a printed circuit board. Heat produced by the semiconductor chip
21 is transferred via the solder bumps 23 to the board 22, and
further transferred to the board 30 via the connecting part 24. The
connecting part 24 generates more heat than the other parts and it
needs to be cooled in an efficient manner. Because the connecting
part 24 has a function of providing electrical connection with the
board 30, it is undesirable to cool the connecting part 24 using a
water-based coolant.
[0040] To solve this issue, a dielectric coolant 14 and a
water-based coolant 13, which separate from each other into two
layers in a casing 11, are employed. The dielectric coolant 14 is
used to cool a surface including the connecting part 24 of the
semiconductor package 20 which produces more heat. The water-based
coolant 13 is used to cool the remaining parts of the semiconductor
package 20, other than the connecting part 24 or the surface
including the connecting part 24. The semiconductor package 20 and
the board 30 are placed in the air-tight casing 11, and the
dielectric coolant 14 is supplied in the casing 11 so as to immerse
the connecting part 24 and the side faces of the semiconductor
package 20 in the dielectric coolant 14. The casing 11 is formed of
any suitable material, including a metal, a resin, a ceramic, a
glass, etc. In the embodiment, a metal (such as aluminum) with a
high thermal conductivity is used. The dielectric coolant 14 is
preferably a non-corrosive and chemically stable fluid with an
electrical insulating property. The coolants satisfying the
above-described condition include fluorinated inactive liquids
(such as FC-72), fluorocarbon coolants, hydrochlorofluorocarbons
(such as HFC-365mfc, HFE-7000), halogenated hydrocarbon coolants
(such as pentane), and dielectric oil based coolants containing,
for example, silicone oil.
[0041] On the other hand, water-based coolant 13 is supplied onto
the rear face 26 or other parts different from the connecting part
24 of the semiconductor package 20. The water-based coolant 13 is
for example, water or pure water, which is sprayed onto the rear
face 26 of the semiconductor package 20 from the nozzle 15
positioned above the semiconductor package 20. The specific gravity
or the relative density of the dielectric coolant 14 is greater
than that of the water-based coolant 13. When FC-72, which is a
fluorinated inactive liquid, is used, the specific gravity of the
dielectric coolant 14 is 1.68. Making use of the density
difference, the dielectric coolant 14 and the water-based coolant
13 are separated into two layers.
[0042] The water-based coolant 13 ejected from the nozzle 15 hits
the rear face 26, spreads to the peripheral regions of the
semiconductor package 20 while absorbing the heat from the
semiconductor package 20, and diffuses toward the inner wall of the
casing 11 on the low-temperature side. Since the dielectric coolant
14 with a greater density stays under the water-based coolant 13,
the water-based coolant 13 is prevented from flowing into the
connecting part 24. The temperature of the water-based coolant 13
increases due to the heat absorption from the rear face 26 of the
semiconductor package 20. The heated water-based coolant 13 is
drained out of the casing 11 by the pump 18a, and cooled through
heat exchange at external cooling means such as radiator 16 and a
fan 17. The cooled water-based coolant 13 is supplied to the nozzle
15 by the pump 18b. The pumps 18a and 18b, the external cooling
means 16 and 17 and the nozzle 15 are connected by pipes 19 and
form a circulating system for the water-based coolant 13. The
water-based coolant 13 heated and let out from the casing 11 is
circulated and supplied back to the casing 11 to cool a part other
than the connecting part 24.
[0043] The dielectric coolant 14 staying at the bottom of the
casing 11 is evaporated and becomes vapor due to the heat generated
from the connecting part 24 of the semiconductor package 20. The
vapor of the dielectric coolant 14 dissolves in the water-based
coolant 13. If the temperature of the water-based coolant 13 is
lower than the boiling point of the dielectric coolant 14, the
vapor of the dielectric coolant 14 will condense into liquid upon
contact with the water-based coolant 13, and the liquidized
dielectric coolant 14 naturally circulates back to the lower-layer
dielectric coolant 14. If fluorinated inactive liquid FC-72 is used
as the dielectric coolant 14, the boiling point is 56.degree. C. If
the temperature of the water-based coolant 13 in the casing 11 is
maintained below 56.degree. C. through the circulation, the
dielectric coolant 14 circulates by itself in the casing 1. The
low-boiling point fluorinated liquid 14 is prevented from
vaporizing because the water-based coolant 13 functions as a
shield.
[0044] Although not illustrated in the figure, a second circulating
system for mechanically circulating the dielectric coolant 14 may
be provided to the system in addition to the (first) circulating
system for circulating the water-based coolant 13.
[0045] FIG. 2 illustrates an example of a single semiconductor
package 20 to be cooled for the purposes of simplification.
However, the cooling system of FIG. 2 is applicable to cooling a
multi-CPU system with multiple semiconductor packages 20 and
electronic modules mounted on the system board 30.
[0046] FIG. 3 illustrates a plan view of a multi-CPU system board
30, together with a cross-sectional view taken along the A-A' line
of the plan view. CPUs (semiconductor packages) 20a, 20b, 20c and
20d and other modules 32 are mounted on the board 30. The modules
32 are, for example, memory modules, switches, power modules, and
so on. These modules are collectively denoted as memory modules 32
for the simplification purposes. In operation, the semiconductor
packages 20a-20d and the memory modules 32 produce heat. To cool
the multi-CPU system board 30 using a horizontal-type cooling
system, multiple nozzles 15 may be positioned above the respective
semiconductor packages 20 and the memory modules 32 to supply the
water-based coolant 13.
[0047] FIG. 4 is a schematic diagram illustrating semiconductor
equipment 40 with a cooling system for cooling the multi-CPU system
board 30. The board 30 on which semiconductor packages 20a and 20b
and a memory module 32 are mounted is placed in the air-tight
casing 11. Dielectric coolant 14 is put in the casing 11 so as to
cover the side faces and the connecting parts 24 of the
semiconductor packages 20a and 20b and the memory module 32.
Nozzles 15a, 15b and 15c are positioned above the semiconductor
packages 20a and 20b and the memory module 32, respectively, to
spray the water-based coolant 13 onto the rear faces 26a, 26b and
36 of the semiconductor packages 20a, 20b and the memory module 32.
The connecting parts 24 of the semiconductor packages 20a, 20b and
the connecting part (not illustrated) of the memory module 32 for
connecting the memory module 32 to the board 30 are directly cooled
by the dielectric coolant 14. The water-based coolant 13 is
circulated in the pipes 19 that connect pumps 18a and 18b and the
cooling means 16 and 17. The water-based coolant 13 from which the
heat has been removed is supplied to the nozzles 15a-15c.
[0048] In the examples illustrated in FIG. 3 and FIG. 4, the
semiconductor packages 20a through 20d mounted on the board 30 may
have the same size. Alternatively, semiconductor packages of
different sizes may be mounted on the board 30. In the latter case,
the semiconductor packages are cooled in the same manner as
illustrated in FIG. 4. In still another alterative, a single nozzle
15 may be provided above the semiconductor packages 20 and the
module 32. In this case, the spray direction of the nozzle 15 is
regulated so as to cool the multiple semiconductor packages 20 and
the module 32 evenly.
[0049] As has been described above, the first embodiment makes use
of the difference in specific gravity between the dielectric
coolant 14 and the water-based coolant 13 to separate the two
fluids into two layers. The dielectric coolant 14 is used to cool
the connecting part 24 of the semiconductor package 20 to ensure
electric connection, and the water-based coolant 13 is used as the
major cooling medium to cool the remaining parts such as the rear
face 26 (positioned opposite to the connecting part 24) and to
remove heat from the surroundings. The semiconductor device 21 or
the semiconductor package 20 is cooled efficiently and stably,
while reducing the environmental burden. Because the entirety of
the semiconductor package 20 is immersed in the coolant, the
semiconductor package 20 does not make contact with the external
air. This arrangement is free from dew condensation, and migration
at the connecting part 24 is prevented.
[0050] FIG. 5 is a schematic diagram illustrating an experimental
model used to verify the effect of the first embodiment. A CPU
(CORE 2 QUAD 3 GHz) 20a manufactured by Intel Corporation and a
peripheral component 32 are arranged as heating elements to be
cooled. FC-72 which is a fluorinated inactive liquid is used as the
dielectric coolant 14 in the experiment, and water is used as the
water-based coolant 13. The heating elements are cooled making use
of two-layer separation. The connecting part 24 of the CPU 20a is
immersed in the dielectric coolant 14 with greater relative density
(specific gravity). The water-based coolant 13 with less relative
density (specific gravity) is circulated by the pump 18 at a flow
rate of 3 liter per minute. The water-based coolant 13 is subjected
to heat exchange at a radiation amount of 80 W/h by the radiator
16, and then supplied to the nozzle 15. At CPU utilization of 100%,
the internal temperature of the CPU 20 is monitored and measured.
As a comparison example, the same CPU 20 and the peripheral
component 32 are cooled by a spray cooling method illustrated in
FIG. 1A using only the water-based coolant 13, and the internal CPU
temperature is measured at CPU utilization of 100%.
[0051] FIG. 6A is a graph illustrating the experimental result, and
FIG. 6B is a table in which the averaged CPU temperature and the
equivalent heat generation of the experimental model are presented
compared with those of the conventional model. As is understood
from FIG. 6A and FIG. 6B, the CPU core temperature of the
conventional model illustrated in
[0052] FIG. 1A exceeds 60.degree. C. only a few minutes after the
CPU utilization becomes 100%, and the averaged CPU temperature
under the cooling environment is 61.degree. C. On the contrary, the
averaged CPU temperature at the 100% CPU utilization is 53.degree.
C. The equivalent heat generation of the conventional model is 180
W, while that of the experimental model of the first embodiment is
140 W. The structure of the first embodiment can achieve 40 W
reduction in equivalent heat generation and 8.degree. C. reduction
in averaged CPU temperature. In the actual measurement result
illustrated in FIG. 6A, the CPU core temperature varies at a
certain amplitude. This is due to the influence of the operation of
the CPU, and the stability of the cooling function of the system
itself is guaranteed. By regulating the amount of heat radiation of
the radiator, the flow rate of the pump, the layout of the
nozzle(s) and the direction of the spray, the cooling ability can
be further improved.
Second Embodiment
[0053] FIG. 7 is a schematic diagram illustrating electronic
equipment 70 with a cooling system according to the second
embodiment. In the second embodiment, a semiconductor package 20 is
mounted on a vertical board 30 arranged in a vertical direction
(along the direction of gravity). The structures of the
semiconductor package 20 and the connecting part for providing the
connection with the board 30 are the same as those illustrated in
the first embodiment, and the explanation for them is omitted.
[0054] As in the first embodiment, the connecting part 24 of the
semiconductor package 20 is directly cooled by the dielectric
coolant 14, and other parts such as the rear face 26 (opposite to
the connecting part 24 of the package) except for the connecting
part 24 are cooled by the water-based coolant 13. To realize this
arrangement in the vertical arrangement of the second embodiment, a
first nozzle 75 is positioned above the vertically arranged board
30 with the semiconductor package 20 mounted, to supply the
dielectric coolant 14 via the top edge of the board 30 to the
connecting part 24. A second nozzle 15 is positioned so as to face
the vertically arranged semiconductor package 20 to supply the
water-based coolant 13 toward the rear face 26 of the semiconductor
package 20.
[0055] The first nozzle 75 forms a curtain flow 76 so as to protect
the end faces and the connecting part 24 of the semiconductor
package 20 with the dielectric coolant 14. The dielectric coolant
14 is a chemically stable and non-corrosive fluid with an
electrical insulating property as in the first embodiment. For
example, fluorinated inactive liquids (such as FC-72), fluorocarbon
coolants, hydrochlorofluorocarbons (such as HFC-365mfc, HFE-7000),
halogenated hydrocarbon coolants (such as pentane), and dielectric
oil based coolants containing silicone oil as the manor ingredient
can be used as the dielectric coolant.
[0056] The second nozzle 15 sprays the water-based coolant 13
toward a part other than the connecting part 24, such as the rear
face 26 opposite to the connecting part 24 of the semiconductor
package 20. Since the connecting part 24 is protected by the
curtain flow 76 of the dielectric coolant 14, the water-based
coolant 13 is prevented from flowing into the connecting part 24.
The dielectric coolant 14 and the water-based coolant 13 can be
separated from each other in two layers along the direction of
gravity.
[0057] The temperatures of the dielectric coolant 14 and the
water-based coolant 13 rise through heat exchange with the
semiconductor package 20. The heated dielectric coolant 14 and the
water-based coolant 13 are collected at the bottom of the casing
11. When a fluorinated inactive liquid such as FC-72 is used as the
dielectric coolant 14, the specific gravity is greater than that of
the water-based coolant 13. Because the dielectric coolant 14 and
the water-based coolant 13 flow down to the bottom of the casing
11, portions of the two liquids mix with each other at the bottom
of the casing 11.
[0058] The heated dielectric coolant 14 and the water-based coolant
13 are let out from the bottom or the lower part of the casing 11
via the first pipe 19a, and subjected to heat exchange at the
radiator 16 and the fan 17. The coolants from which the heat has
been removed by the heat exchange are supplied to the separation
tank 79. In the separation tank 79, the dielectric coolant 14 and
the water-based coolant 13 naturally separate into two layers
because of the difference in the specific gravities. The dielectric
coolant 14 separated from the water-based coolant 13 is supplied to
the nozzle 75 via the pump 78a and the second pipe 19b. The
water-based coolant 13 is supplied to the second nozzle 15 via the
pump 78b and the third pipe 19c. Making use of the two-layer
separation of the coolants, the heat-removed water-based coolant 13
and the dielectric coolant 14 can be circulated to the
corresponding nozzles 15 and 75, respectively. With this
arrangement, the vertically arranged semiconductor package 20 can
be cooled efficiently. Another pump may be provided in the first
pipe 19a as necessary.
[0059] The structure of the second embodiment is applicable to a
vertical arrangement of the multi-CPU system board 30 illustrated
in FIG. 3. In this case, the first nozzles 75 may be provided
corresponding to the respective columns of the semiconductor
packages 20 to form a curtain flow for each of the columns.
Alternatively, the number of the first nozzles 75 may be
appropriately determined according to the size, the shape or the
structure of the openings of the nozzles 75, the flow rate of the
dielectric coolant 14 to be sprayed, or the size of the board
30.
[0060] FIG. 8 is a schematic diagram illustrating an experimental
model used to verify the effect of the second embodiment. A CPU
(CORE 2 QUAD 3 GHz) 20a manufactured by Intel Corporation and a
peripheral component 32 are arranged as heating elements to be
cooled. FC-72 which is a fluorinated inactive liquid is used as the
dielectric coolant 14 in the experiment, and water is used as the
water-based coolant 13. The heating elements are cooled making use
of two-layer separation. The dielectric coolant 14 and the
water-based coolant 13 are let out from the bottom of the casing 11
and heat exchange is performed at a radiation amount of 80 W/h by
the radiator 16. The heat-removed dielectric coolant 14 and the
water-based coolant 13 are separated into two layers in the
separation tank 79 such that each layer extends in the horizontal
direction. The dielectric coolant 14 is supplied to the nozzle 75
by the pump 78a, and the water-based coolant 13 is supplied to the
nozzle 15 by the pump 78b. At CPU utilization of 100%, the internal
temperature of the CPU 20 is monitored and measured. As a
comparison example, the same CPU 20 and the peripheral component 32
are cooled by a spray cooling method illustrated in FIG. 1A using
only the water-based coolant 13, and the internal CPU temperature
is measured at CPU utilization of 100%.
[0061] FIG. 9A is a graph illustrating the experimental result, and
FIG. 9B is a table in which the averaged CPU temperature and the
equivalent heat generation of the experimental model are presented
compared with those of the conventional model. As is understood
from FIG. 9A and FIG. 9B, the CPU core temperature of the
conventional model illustrated in
[0062] FIG. 1A exceeds 60.degree. C. only a few minutes after the
CPU utilization becomes 100%, and the averaged CPU temperature
under the cooling environment is 61.degree. C. On the contrary, the
averaged CPU temperature at the 100% CPU utilization is 49.degree.
C. The equivalent heat generation of the conventional model is 180
W, while that of the experimental model of the first embodiment is
120 W. The structure of the second embodiment can achieve 60 W
reduction in equivalent heat generation and 12.degree. C. reduction
in averaged CPU temperature.
[0063] The structure of the second embodiment can realize a more
efficient and more stable cooling system as compared to the first
embodiment. This may be because the dielectric coolant 14 is
supplied as the curtain flow to the connecting part 24 of the
semiconductor package 20 (see FIG. 7). By constantly supplying
heat-removed dielectric coolant 14 to the connecting part 24 with a
large amount of heat generation, high cooling efficiency is
achieved.
[0064] According to the disclosures, the following effects can be
achieved. [0065] (1) High Cooling Efficiency: By combining spray
cooling using a water-based coolant and local cooling using a
dielectric coolant for connecting parts, the entire surfaces of a
semiconductor device can be cooled directly by liquid cooling.
[0066] (2) Large-Area Cooling: The entirety of the system board
including memories, switches, power modules, etc., can be cooled at
once. [0067] (3) Reduced Environmental Burden: By employing
water-cooling as the major cooling means and limiting use of
fluorinated coolant, high cooling efficiency is realized while
reducing the environmental burden. [0068] (4) High Reliability:
Because the board does not contact the external air, condensation
due to temperature difference is avoided and migration is prevented
from occurring. [0069] (5) Reduced Cost: Because the entirety of
the board is cooled, it is unnecessary to provide a thermal module
for each of the CPUs. Heaters for preventing dew condensation can
be omitted, and the number of components and power consumption can
be reduced.
[0070] The present disclosures can be applied to a cooling system
for cooling an arbitrary heating element, and to electronic
equipment with a cooling system. For example, the arrangements of
the disclosures can be applied to a rack server or computer in
which a number of vertical system boards are arranged side by side
or a number of horizontal system boards are stacked.
[0071] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of superiority or inferiority of
the invention. Although the embodiments of the present inventions
have been described in detail, it should be understood that the
various changes, substitutions, and alterations could be made
hereto without departing from the spirit and scope of the
invention.
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