U.S. patent application number 12/747777 was filed with the patent office on 2010-11-04 for cooling fin and manufacturing method of the cooling fin.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Hirofumi Inoshita, Masahiro Morino, Yuya Takano, Yasuji Taketsuna.
Application Number | 20100276135 12/747777 |
Document ID | / |
Family ID | 40329239 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100276135 |
Kind Code |
A1 |
Morino; Masahiro ; et
al. |
November 4, 2010 |
COOLING FIN AND MANUFACTURING METHOD OF THE COOLING FIN
Abstract
A cooling fin includes fin parts integrally extending from a
base part. Each fin part is partially formed at a slant so that a
proximal end portion is straight and a distal end portion is wavy
(corrugated). Each fin part is partially slanted to make each fin
part wavier as coming closer to the distal end portion from the
proximal end portion. In a manufacturing process of the cooling
fin, firstly, a straight cooling fin is produced by extrusion
molding (an extruding step). Subsequently, the distal end portion
of each fin is partially bent in a direction intersecting an
extruding direction into a wave shape (a bending step).
Inventors: |
Morino; Masahiro;
(Okazaki-shi, JP) ; Taketsuna; Yasuji;
(Okazaki-shi, JP) ; Takano; Yuya; (Nishio-shi,
JP) ; Inoshita; Hirofumi; (Nagoya-shi, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
1500 K STREET N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
40329239 |
Appl. No.: |
12/747777 |
Filed: |
November 28, 2008 |
PCT Filed: |
November 28, 2008 |
PCT NO: |
PCT/JP2008/072110 |
371 Date: |
June 11, 2010 |
Current U.S.
Class: |
165/185 ;
29/890.03 |
Current CPC
Class: |
B23P 2700/10 20130101;
H01L 21/4878 20130101; H01L 23/467 20130101; H01L 2924/00 20130101;
B23P 15/26 20130101; H01L 23/473 20130101; H01L 2924/0002 20130101;
H01L 23/3672 20130101; H01L 21/4871 20130101; Y10T 29/4935
20150115; H01L 2924/0002 20130101 |
Class at
Publication: |
165/185 ;
29/890.03 |
International
Class: |
F28F 7/00 20060101
F28F007/00; B21D 53/02 20060101 B21D053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2007 |
JP |
2007-322831 |
Claims
1. A cooling fin comprising a plurality of fin parts arranged in a
row and a base part integrally continuous to one ends of the fin
parts to support the fin parts, wherein each fin part has a shape
in which a proximal end portion continuous to the base part is
straight and a distal end portion is wavy in a flow direction of a
coolant which will flow through the fin parts.
2. The cooling fin according to claim 1, wherein the distal end
portion of each fin part has a wave shape designed to meet an
expression (I): a.gtoreq.f-w (I) where "f" is a pitch of the fin
parts, "w" is a thickness of each fin part, and "a" is a height of
the wave shape of each fin part.
3. The cooling fin according to claim 1, wherein the distal end
portion of each fin part has a wavy shape including a region
oblique with respect to the coolant flow direction.
4. A manufacturing method of a cooling fin comprising a plurality
of fin parts arranged in a row and a base part integrally
continuous to one ends of the fin parts to support the fin parts,
the method comprising the steps of: extruding a straight shaped fin
including a plurality of fin parts each extending from the base
part into a comb teeth shape; and partially bending a distal end
portion of each straight fin part in a direction intersecting an
extruding direction to shape the distal end portion into a wave
shape in a flow direction of a coolant which will flow through
between the fin parts.
5. The manufacturing method of the cooling fin according to claim
4, wherein the bending step includes arranging a jig in a clearance
between the fin parts and bending the fin parts with the jig by
cold working.
6. The manufacturing method of the cooling fin according to claim
5, wherein the bending step includes placing the jig on one side
and the other side of each fin part in a staggered pattern, and
applying a load on the fin part by at least the jig placed on one
side.
7. The manufacturing method of the cooling fin according to claim
4, wherein he bending step includes placing the jig in a position
corresponding to clearances between the fin parts having just been
extruded, and bending the fin parts with the jig by hot
working.
8. The manufacturing method of the cooling fin according to claim
7, wherein the jig has comb teeth insertable in the clearances
between the fin parts, and the bending step further comprises
moving the jig in the direction intersecting the extruding
direction.
9. The manufacturing method of the cooling fin according to claim
4, wherein the bending step further comprises forming the distal
end portion of each fin part into the wavy shape including a region
oblique with respect to the coolant flow direction.
10. The cooling fin according to claim 2, wherein the distal end
portion of each fin part has a wavy shape including a region
oblique with respect to the coolant flow direction.
11. The manufacturing method of the cooling fin according to claim
5, wherein the bending step further comprises forming the distal
end portion of each fin part into the wavy shape including a region
oblique with respect to the coolant flow direction.
12. The manufacturing method of the cooling fin according to claim
6, wherein the bending step further comprises forming the distal
end portion of each fin part into the wavy shape including a region
oblique with respect to the coolant flow direction.
13. The manufacturing method of the cooling fin according to claim
7, wherein the bending step further comprises forming the distal
end portion of each fin part into the wavy shape including a region
oblique with respect to the coolant flow direction.
14. The manufacturing method of the cooling fin according to claim
8, wherein the bending step further comprises forming the distal
end portion of each fin part into the wavy shape including a region
oblique with respect to the coolant flow direction.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cooling fin for
dissipating heat from a heat generating element such as a
semiconductor device into a fluid and a manufacturing method of the
cooling fin and, more particularly, to a cooling fin with high
cooling performance and a manufacturing method of the cooling
fin.
BACKGROUND ART
[0002] Heretofore, a high-pressure-resistant and large-current
power module to be mounted in a hybrid electric vehicle, an
electric vehicle, or the like has to include a cooling structure
having high heat dissipation performance because of a large
self-heating value of the semiconductor device during operation.
FIG. 19 shows one example of a power module having a cooler. A
module 90 comprises a semiconductor device 10 which is a heating
element, a heat spreader 20 supporting the semiconductor device 10,
and a cooler 130 joined to the heat spreader 20 and internally
provided with flow paths.
[0003] The cooler 130 internally includes a cooling fin 131 made of
a material having high heat conductivity (e.g. aluminum). The
cooling fin 131 has a plurality of fin parts 131a arranged in a row
at equal intervals. Distal ends of the fin parts 131a are connected
with a cover plate 132. In the cooler 130, accordingly, flow paths
135 are formed between the fin parts 131a to extend along the
longitudinal direction of each fin part 131a.
[0004] In such cooler 130, a boundary layer develops in coolant
flowing through each flow path 135 between the fin parts 131a. This
boundary layer is a factor which may deteriorate cooling
performance. In order to break the boundary layer, therefore, there
have been proposed an offset fin in which split small blocks
constituting a cooling fin 131 are arranged in a staggered
configuration, and a corrugated fin in which each fin part is of a
wavy or corrugated configuration (for example,
JP10(1998)-200278A).
[0005] However, the aforementioned conventional cooling fins have
the following disadvantages. Specifically, in a manufacturing
process of the offset fin, as shown in FIG. 20, (A) a straight fin
91 is extruded by an extruder 50 through a die 51 formed with
comb-teeth-shaped through holes. Then, (B) small blocks 92 are
produced from the fin 91 by cutting and slit machining the fin 91.
Finally, (C) the small blocks 92 are arranged in an offset pattern
and blocked fin parts 93 are combined in a staggered
configuration.
[0006] The above offset fin manufacturing process needs blocks in
number corresponding to the desired number of offset positions. On
the other hand, to enhance the cooling performance of the offset
fin, it is essentially necessary to increase the number of offset
positions. This is likely to cause a cost increase for fin cutting,
slit machining, and assembling, thus leading to a complicated
manufacturing process and high cost thereof.
[0007] On the other hand, the corrugated fin is made in a sine or
similar curve shape, which cannot be manufactured by extrusion
molding. Accordingly, casting is generally utilized for
manufacturing the corrugated fin. However, this casting cannot
easily produce minute fins well as compared with the extrusion
molding, thus making it difficult to increase the surface area of
each fin. A material available for the casting is poor in heat
conductivity as compared with a material available for the
extrusion molding. The cooling performance of the former material
is not sufficient.
[0008] Both the offset fin and the corrugated fin are configured
such that fin parts uniformly extend from a base part. Accordingly,
a coolant will flow at high speed in the vicinity of the center of
each fin in a height direction thereof and at low speed in the
vicinity of a proximal end of each fin joined to the base part. A
heat exchange rate is therefore poor. Furthermore, the distal end
and its vicinity of each fin part far from the heating element has
a small temperature difference from the coolant as compared with
the proximal end and its vicinity of each fin part close to the
heating element. Thus, the heat exchange rate is further low.
[0009] The present invention has been made to solve the above
problems which may be caused by the conventional cooling fins. The
present invention therefore has a purpose to provide an inexpensive
cooling fin with improved cooling efficiency and a manufacturing
method of the cooling fin.
DISCLOSURE OF THE INVENTION
[0010] Specifically, a first aspect of the present invention
provides a cooling fin comprising a plurality of fin parts arranged
in a row and a base part integrally continuous to one ends of the
fin parts to support the fin parts, wherein each fin part has a
shape in which a proximal end portion continuous to the base part
is straight and a distal end portion is wavy in a flow direction of
a coolant which will flow through the fin parts.
[0011] In the cooling fin of the invention, the fin parts are
integrally formed each extending from the base part and arranged in
a row to flow paths therebetween. Each fin part has the proximal
end portion of a straight shape and the distal end portion
partially slanted to provide a wave shape (corrugated shape) in the
coolant flow direction (a direction from an entrance to an exit of
the coolant). Specifically, each fin part continuously changes so
that the cross section of each fin part in a direction
perpendicular to the height direction on the distal end side is
wavier than the cross section of each fin part on the proximal end
side. Resistance between each fin part and a fluid becomes greater
as a portion of each fin is closer to the distal end, so that the
fluid, i.e. coolant, is not allowed to flow smoothly each flow
path.
[0012] In other words, the coolant is allowed to flow more smoothly
through each flow path as it is closer to the proximal end. Thus, a
flow rate of the coolant in the vicinity of the proximal end will
increase. That is, the coolant will flow in larger amount on the
side closer to the proximal end which is a bottom in the height
direction of each fin part. Accordingly, the cooling performance of
each fin part near the proximal end is enhanced. A heat generating
element is placed near the proximal ends of the fin parts to
efficiently dissipate heat. On the other hand, the distal end
portion of each fin part is formed into a wave shape (corrugated
shape). The fluid, i.e. coolant, will therefore collide with the
fin parts and hence becomes turbulent, thereby inducing breakage of
a boundary layer which tends to develop in the coolant flow. Thus,
a high cooling performance can also be achieved even in the
vicinity of the distal end. Because of the above two reasons, the
cooling performance of the entire cooling fin can be enhanced.
[0013] In the cooling fin of the invention, preferably, the distal
end portion of each fin part has a wave shape designed to meet an
expression (I):
a.gtoreq.f-w (I)
where "f" is a pitch of the fin parts, "w" is a thickness of each
fin part, and "a" is a height of the wave shape of each fin
part.
[0014] Specifically, when the above expression (I) is satisfied, an
area allowing the coolant to linearly flow is decreased in each
flow path on the distal end side. Accordingly, the coolant is
caused to meander, thereby reliably reducing the thickness of the
boundary layer. The cooling performance can therefore be
enhanced.
[0015] According to another aspect, the invention provides a
manufacturing method of a cooling fin comprising a plurality of fin
parts arranged in a row and a base part integrally continuous to
one ends of the fin parts to support the fin parts, the method
comprising the steps of: extruding a straight shaped fin including
a plurality of fin parts each extending from the base part into a
comb teeth shape; and partially bending a distal end portion of
each straight fin part in a direction intersecting an extruding
direction to shape the distal end portion into a wave shape in a
flow direction of a coolant which will flow through between the fin
parts.
[0016] In the invention, in the extruding step, the straight shaped
cooling fin is produced by extrusion molding. Thus, the fin parts
can be formed in finer shape as compared with a cooling fin
produced by casting. The extrusion molding allows the use of a high
heat conductive material. The cooling performance is therefore
high. Furthermore, the manufacturing method is suitable for mass
production to manufacture the cooling fin at low cost.
[0017] In the bending step, the distal end portion of each fin part
is bent into a wave shape (corrugated shape). Specifically, unlike
the offset fin, a cooling fin can be formed singly in a wave shape
without needing a plurality of split blocks. Accordingly, the
invention can provide a simpler manufacturing process with less
number of components and process steps as compared with the offset
fin. According to the cooling fin produced by the manufacturing
method, a wave angle (a bending angle) and a wave pitch of the fin
parts can be determined to adjust the cooling performance.
[0018] Furthermore, in the present invention, the cooling fin with
a straight proximal end portion and a wavy distal end portion is
produced by the two steps, that is, the extrusion molding step and
the bending step. Accordingly, the cooling fin with high cooling
performance can be manufactured in simple steps.
[0019] In the bending of the invention, preferably, the bending
step includes arranging a jig in a clearance between the fin parts
and bending the fin parts with the jig by cold working. The bending
technique in a cold condition (at a room temperature) includes for
example placing the jig on one side and the other side of each fin
part in a staggered pattern, and applying a load on the fin part by
at least the jig placed on one side. This makes it possible to
manufacture the fin parts with the proximal end portion having a
straight shape and the distal end portion having a wave shape. In
such cold bending in the cold working, existing facilities are
available.
[0020] The bending step of the invention, preferably, includes
placing the jig in a position corresponding to clearances between
the fin parts having just been extruded, and bending the fin parts
with the jig by hot working. In the bending technique in a hot
condition, for example, the jig has comb teeth insertable in
clearances (slits) between the fin parts, and the bending step
further comprises moving the jig in a direction intersecting the
extruding direction. According to this method, the entire cooling
fin is high in temperature because of just after extrusion and
hence the fin parts can be processed easily. Thus, a load on the
jig is small in the bending work. Because the heat deriving from
the extrusion working is utilized, it is unnecessary to increase
the temperature of each fin part in hot working. This makes it
possible to shorten a manufacturing time and make efficient use of
energy.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a perspective view showing a schematic
configuration of a power module in a preferred embodiment;
[0022] FIG. 2 is a perspective view showing a schematic
configuration of a cooling fin in the embodiment;
[0023] FIG. 3 is a plan view showing the schematic configuration of
the cooling fin of FIG. 2;
[0024] FIG. 4 is a partial enlarged view showing the details of a
portion of the cooling fin enclosed by a circle X of a dashed line
in FIG. 2;
[0025] FIG. 5 is a sectional view of the cooling fin taken along a
line A-A in FIG. 3;
[0026] FIG. 6 is a sectional view of the cooling fin taken along a
line B-B in FIG. 3;
[0027] FIG. 7 is a sectional view of the cooling fin taken along a
line C-C in FIG. 3;
[0028] FIG. 8 is a schematic view showing a flow speed distribution
in a cooling fin in a conventional art;
[0029] FIG. 9 is a schematic view showing a flow speed distribution
in the cooling fin in the embodiment;
[0030] FIG. 10 is a view showing a shape (a straight shape) of a
fin after extrusion molding;
[0031] FIG. 11 is a schematic view showing an outline of a fin
bending operation by cold working;
[0032] FIG. 12 is a schematic view showing an outline of a fin
bending operation by hot working (extrusion of a straight fin);
[0033] FIG. 13 is another schematic view showing the outline of the
fin bending operation in hot working (bending of the straight
fin);
[0034] FIG. 14 is a perspective view showing a schematic
configuration of a jig used in the hot working;
[0035] FIG. 15 is a view showing each size of a wavy portion of the
cooling fin;
[0036] FIG. 16 is a graph showing correlation between a wave pitch,
a wave angle, and pressure loss in each cooling fin;
[0037] FIG. 17 is a graph showing correlation between a wave pitch,
a wave angle, and a heat transfer rate in each cooling fin;
[0038] FIG. 18 is a perspective view showing a modified form of a
cooler;
[0039] FIG. 19 is a perspective view showing a schematic
configuration of a power module in a conventional art; and
[0040] FIG. 20 is a perspective view showing an outline of a
manufacturing process of an offset fin.
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] A detailed description of a preferred embodiment of the
present invention will now be given referring to the accompanying
drawings. In this embodiment, the invention is applied to a cooling
fin to be built in a cooler of a vehicle-mounted intelligent power
module.
Configuration of Power Module
[0042] A power module 100 in this embodiment includes, as shown in
FIG. 1, a semiconductor device 10 which is a heat generating
element, a heat spreader 20 on which the semiconductor device 10 is
placed, and a cooler 30 internally provided with flow paths for
coolant. In the power module 100, heat from the semiconductor
device 10 will be dissipated into the cooler 30 through the heat
spreader 20.
[0043] The semiconductor device 10 is a device such as IGBT
constituting an inverter circuit. It is to be noted that much more
semiconductor devices are installed on a vehicle-mounted power
module but only a part thereof is schematically illustrated for
facilitating explanation.
[0044] The heat spreader 20 is made of a high heat-conductive
material to dissipate heat from the semiconductor device 10. The
heat spreader 20 is integrally brazed to the cooler 30. A fixing
method of the heat spreader 20 to the cooler 30 is not limited to
the brazing. As an alternative, the heat spreader 20 may be fixed
to the cooler 30 with a bolt.
[0045] The cooler 30 includes a cooling fin 31 and a cover plate 32
joined to a distal end of the cooling fin 31. The cooling fin 31 is
made of a material, such as aluminum alloy, having high heat
conductivity and being light in weight. In the cooler 30, flow
paths 35 for coolant are defined by the cooling fin 31 and the
cover plate 32. The coolant may be selected either liquid or gas.
In this embodiment, cooling water is supplied as the coolant to the
flow paths 35.
Configuration of Cooling Fin
[0046] The details of the cooling fin 31 are explained below. FIG.
2 is a perspective view of the cooling fin 31 and FIG. 3 is a plan
view of the cooling fin 31.
[0047] The cooling fin 31 is constituted of fin parts 1 arranged in
a row at equal intervals and a base part 2 integral with the fin
parts 1 to support the fin parts 1. Each fin part 1 has such a
shape that a proximal end continuous to the base part 2 is straight
in a flowing direction of the coolant (a direction from an entrance
to an exit of the coolant (i.e., from IN to OUT in FIG. 1)) and a
distal end is wavier.
[0048] To be specific, each fin part 1 of the cooling fin 31 in
this embodiment is constituted of first regions 11 vertical to the
base part 2, second regions 12 each slanting at a predetermined
angle with respect to the base part 2, and third regions 13 joining
the first region 11 and the second region 12. A set of the first to
third regions 11 to 13 is shown in FIG. 4 (an enlarged view of a
portion enclosed by a circle X of a dashed line in FIG. 2). The
first region 11 is of a nearly trapezoidal shape having a lower
side at the proximal end and an upper side at the distal end so
that the lower side is wider than the upper side. The second region
12 is of a nearly rectangular shape. The third region 13 is of a
nearly triangular shape having a side corresponding to a ridge line
joining between the upper side of the first region 11 and the upper
side of the second region 12.
[0049] In each fin part 1, the first region 11 and the second
region 12 extend to form the fin part 1 from the same straight line
of the base part 2. In other words, the shape of the fin part 1 is
straight in the proximal end because the lower side of the first
region 11 is continuous to the lower side of the second region 12.
The first region 11 extends vertically with respect to the base
part 2 as shown in FIG. 5 (a sectional view along a line A-A in
FIG. 3). The second region 12 is slanted at the predetermined angle
with respect to the base part 2 as shown in FIG. 6 (a sectional
view along a line B-B in. FIG. 3).
[0050] On the other hand, at the distal end of each fin part 1, the
upper side of the first region 11 and the upper side of the second
region 12 are continuous to each other via the third region 13, so
that the shape of the distal end of each fin part 1 is wavy
(corrugated) in the coolant flow direction. The third region 13 has
a nearly triangular shape having an apex located at the proximal
end of the fin part 1 and a width being wider as coming closer to
the distal end. Specifically, a portion between the first region 11
and the second region 12 in FIG. 3 includes a proximal-end-side
portion vertically extending upward as a part of the first region
11 and a distal-end-side portion slightly slanting as the third
region 13 as shown in FIG. 7 (along a line C-C in FIG. 3).
[0051] The cooling fin 31 in this embodiment is expected to greatly
enhance cooling performance as compared with the conventional
cooling fin on the following two grounds. FIG. 8 shows a flow speed
distribution in a straight fin of a conventional shape. In the
conventional configuration, specifically, the flow speed of the
coolant reaches a peak in an area on or around the center (within a
centermost broken line in FIG. 8) of each flow path in the height
direction of each fin part 1 (a vertical direction in FIG. 8) and
is slow in an area on or around the proximal end. Accordingly, the
cooling performance is poor in the vicinity of the proximal end of
each fin part 1. The coolant flow speed is similarly slow even in
the vicinity of the distal end of each fin part 1. The distal end
side is far from the semiconductor device 10 which is the heat
generating element and therefore has a small temperature difference
from the coolant. Thus, the cooling performance is also poor in the
vicinity of the proximal end.
[0052] On the other hand, FIG. 9 shows a flow speed distribution in
the cooling fin in the present embodiment, having a straight
proximal end and a wavy distal end. In this embodiment, the
cross-section of each fin part 1 in the direction perpendicular to
the height direction is shaped to be wavier on the side closer to
the distal end than the proximal end. Accordingly, resistance
between each fin part 1 and the coolant is larger on the distal end
side than the proximal end side, thereby making the coolant hard to
flow. Thus, a peak (within a centermost broken line in FIG. 9) of
the coolant flow speed comes close to the proximal end as compared
with that in the straight fin, so that a flow amount of the coolant
increases in the vicinity of the proximal end (First grounds). This
makes it possible to enhance the cooling performance in the
vicinity of the proximal end of each fin part 1.
[0053] Each fin 1 is of a wave shape (corrugated shape) in the
vicinity of the distal end. When a coolant collides with such fin
part 1, the flow of coolant is caused to become turbulent. It is
therefore expected to break the boundary layer (Second grounds).
Consequently, high cooling performance can be obtained even in the
vicinity of the proximal end.
Manufacturing Method of Cooling Fin
[0054] An explanation will be given below to the manufacturing
method of the cooling fin 31. A manufacturing process of the
cooling fin 31 includes an extruding step of producing a straight
fin by extrusion molding and a bending step of bending a part of
each fin part into a wave shape.
[0055] In the manufacturing process of the cooling fin 31, firstly,
a fin is produced in the extruding step by extrusion molding which
is inexpensive and adequate for mass production. At that time, a
fin 310 is molded as a straight fin having a plurality of fin parts
1 as shown in FIG. 10. This is because a final fin shape including
a wavy distal end and a straight proximal end is so complicated as
not to be produced by only extrusion molding. The straight fin 310
is therefore first produced.
[0056] In the bending step, subsequently, the distal end portion of
each fin part 1 is shaped to be wavy. In this bending step, as
shown in FIG. 11(A), for example, a special jig 6 is placed on both
sides of each fin part 1. This jig 6 is constituted of supporting
jigs 61 and 62 which are disposed on one side of each fin part 1
and a loading jig 63 which is disposed on the other side. The jigs
61 to 63 are arranged in a staggered pattern so that the supporting
jig 61, the loading jig 63, and the supporting jig 62 are
positioned in the order from upstream in the coolant flow direction
along the fin part 1.
[0057] As shown in FIG. 11(B), thereafter, the loading jig 63
applies a load on the fin part 1. The fin part 1 is thus plastic
deformed partially in a direction intersecting the extruding
direction into a wave shape as shown in FIG. 2. To be concrete, a
slant surface contacting with the loading jig 63 forms the second
region 12 of the fin part 1 and surfaces contacting with the
supporting jigs 61 and 62 form the first regions 11 of the fin part
1. Each surface located between the adjacent jigs form the third
region 13 of the fin part 1.
[0058] The bending step may be not only the above cold working (at
room temperature) but also a hot working to be performed just after
the extruding step. In this hot working, as with the cold working,
the extruding step is executed to produce a straight fin by normal
extrusion molding. Specifically, as shown in FIG. 12, a die 51 for
producing the straight fin 310 is attached to a molding machine 50.
A billet 52 is loaded in the molding machine 50 and a pressurizing
member 53 presses the inside of the molding machine 50. Thus, the
straight fin 310 having the straight fin parts 1 as shown in FIG.
10 is extruded out through the die 51.
[0059] Just after the straight fin 310 is extruded, a special jig 7
is placed across the fin parts 1 as shown in FIG. 13. The jig 7 has
a comb shape having a plurality of comb teeth 71 as shown in FIG.
14. Each of the comb teeth 71 of the jig 7 is inserted between the
fin parts 1. In this state, in conformity to the wave shape of the
cooling fin 31, the jig 7 is periodically moved in a direction
intersecting the extruding direction in plan view seen from above
in the height direction of the fin parts 1. Accordingly, the fin
parts 1 are deformed in a hot condition into the wavy or corrugated
shape as shown in FIG. 2.
[0060] In the above hot working, the temperature of the fin parts 1
is high (about)600.degree. because of just after the extruding
step. Accordingly, the fin parts 1 can be bent easily and thus the
jig 7 receives only a small load during working. The jig 7
therefore can have good durability. Because of just after the
extruding step, furthermore, the heat deriving from the extruding
step can be utilized. It is therefore unnecessary to increase the
temperature of the cooling fin 31 for the bending step. This makes
it possible to shorten a manufacturing time and efficiently utilize
energy. On the other hand, the above cold working can be handled by
existing facilities, leading to a low initial cost.
Material of Cooling Fin
[0061] A material to be used in the extrusion molding is one of
aluminum alloys, especially, an aluminum alloy with high heat
conductivity. Table 1 shows comparison in heat conductivity between
materials. In Table 1, the materials are expressed based on the
Japanese Industrial Standards (JIS).
TABLE-US-00001 TABLE 1 Heat conductivity Technique Material [W/mK]
Extrusion A6063 209 (Present embodiment) Casting ADC12 92
[0062] Casting is one of the techniques for molding the cooling fin
31. However, a material (e.g. ADC12) to be used in the casting is
also an aluminum alloy but it has lower heat conductivity than the
material (e.g. A6063) to be used in the extrusion molding. The
cooling fin 31 in this embodiment is made by the extrusion molding
and therefore can have higher cooling performance than that made by
the casting.
Size of Cooling Fin
[0063] As mentioned above, the shape of the cooling fin 31 is
likely to have a large influence on the cooling performance and the
moldability. It is therefore important to meet a predetermined size
requirement. FIG. 15 shows parameters of the wave shape (corrugated
shape) of the cooling fin 31 on the distal end side. Each parameter
represents as follows.
[0064] .theta.: Bending angle of a wave shape (hereinafter, Wave
angle)
[0065] P: Pitch of a wave shape (hereinafter, Wave pitch)
[0066] f: Pitch of fin parts (Fin pitch)
[0067] w: Fin width (thickness)
[0068] a: Fin bending amount
[0069] c: Length of a straight portion
[0070] The fin bending amount "a" is equivalent to a difference
(height of the wave shape of each fin part 1) in position in a
direction perpendicular to the reference surface between one
surface (a reference surface) of the first region 11 and a surface
of the second region 12 continuous to the reference surface in the
distal end of each fin part 1.
[0071] In the cold working for corrugating the fin parts 1 by the
jig 6, normally, the supporting jigs 61 and 62 are equal in width
to the loading jig 63. Accordingly, the following explanation is
given assuming that the length of a straight portion of each first
region 11 of the fin part 1 is equal to the length of a straight
portion of each second region 12.
[0072] The conditions the above parameters should satisfy are
represented by expressions (1) to (4). The wave pitch (P) can be
represented by the following expression (1) using the length (c) of
the straight portion of the fin part 1, the bending amount (a) of
the fin part 1, and the wave angle (.theta.):
P=2(c+a/tan.theta.) (1)
[0073] As the wave angle (.theta.) in the expression (1) is larger,
the turbulence of coolant flow is more induced, thereby enhancing
the cooling performance. However, if the wave angle (.theta.) is
too large, the fin part 1 is likely to be broken in the bending
step. Assuming a design angle regarded as a breaking limit is a,
accordingly, the wave angle (.theta.) has to meet the following
expression (2):
.theta..ltoreq..alpha. (2)
[0074] The jig 6 (or the jig 7, hereinafter omitted) is placed in
contact with the straight portion over its length (c) in the
bending step.
[0075] If the length (c) is desired to be short, therefore, the jig
6 to be inserted between the fin parts 1 must be narrow in width.
Narrower the width of the jig 6, the strength of the jig 6 tends to
be lower, which is likely to cause breakage of the jig 6. Assuming
a design length regarded as a breaking limit of the straight
portion of the jig 6 is .beta., the length (c) of the straight
portion has to meet the following expression (3):
c.gtoreq..beta. (3)
[0076] If the bending amount (a) of each fin part 1 is small, it is
not expected to break the boundary layer. In order to break the
boundary layer and enhance the cooling performance, it is
preferable to cause the coolant to meander through each flow path
35 by reducing an area allowing the coolant to linearly flow in
each flow path 35. Specifically, it is desired to meet the
expression (4):
a.gtoreq.f-w (4)
[0077] The shape of the cooling fin 31 is determined to satisfy the
desired cooling performance by changing the wave pitch (P) and the
wave angle (.theta.) in a range that meets the above expressions
(1) to (4). In other words, the size is selected to achieve the
cooling performance most highly in such a range as not to break the
fin parts 1 and the bending jig 6.
[0078] An explanation will be given to correlation of the wave
pitch (P) and the wave angle (.theta.) of the cooling fin 31 with
the cooling performance. FIG. 16 shows correlation of P and .theta.
with pressure loss. FIG. 17 shows correlation of P and .theta. with
heat transfer rate. In both the figures; concrete numerals are not
indicated and the cooling performance (pressure loss and heat
transfer rate) is expressed as 1 by assuming an arbitrary wave
angle (.theta.) is 1. In FIGS. 16 and 17, a plot using white
circles shows the cooling performance when the length (c) of the
straight portion is equal but the wave angle (.theta.) and the wave
pitch (P) are different between the cooling fins 31. A plot using
black circles shows the cooling performance when the wave pitch (P)
is equal but the wave angle (.theta.) and the length (c) are
different between the cooling fins 31.
[0079] It is found in both figures that, as the wave angle
(.theta.) is larger and the wave pitch (P) is narrower, the
pressure loss or the heat transfer rate increases. In other words,
it is found that the cooling performance can be adjusted by the
wave angle (.theta.) and the wave pitch (P) of the bent fin part
1.
[0080] The cooling fin 31 in the present embodiment, as explained
above in detail, each fin part 1 is partially formed at a slant so
that the proximal end portion is straight and the distal end is
wavy (corrugated). Such configuration allows the coolant to flow
more smoothly in the vicinity of the proximal end than in the
vicinity of the distal end, thereby increasing the flow rate of the
coolant flowing along the vicinity of the proximal end. This makes
it possible to enhance the cooling performance in the vicinity of
the proximal end of each fin part 1 located close to the
semiconductor device 10. On the other hand, the distal end portion
of each fin part 1 located far from the semiconductor device 10 is
wavy. Thus, the coolant becomes turbulent when collides with the
fin parts 1, inducing breakage of the boundary layer. Accordingly,
high cooling performance can also be obtained in the vicinity of
the distal end of each fin part 1.
[0081] In the manufacturing process of the cooling fin 31 in the
present embodiment, firstly, the straight-shaped cooling fin 310 is
produced by extrusion molding (the extruding step). The fin parts 1
can therefore be formed in smaller or finer shape as compared with
the cooling fin produced by casting. Furthermore, a high heat
conductive material can be used and hence high cooling performance
can be achieved. The cooling fin 310 is suitable for mass
production and can be manufactured at low cost.
[0082] Successively, the distal end portion of each fin part 1 is
partially bent in the direction intersecting the extruding
direction into a wave shape (the bending step). In this embodiment,
unlike the offset fin, the cooling fin can be formed singly in a
wave shape without needing split blocks. As compared with the
offset fin, the present embodiment can provide a simpler
manufacturing process with less number of components and process
steps. Consequently, the cooling fin with reduced cost and improved
cooling efficiency and the manufacturing method of the cooling fin
can be achieved.
[0083] The present invention is not limited to the above
embodiment(s) and may be embodied in other specific forms without
departing from the essential characteristics thereof. In the above
embodiment, for instance, the coolant flow paths 35 are formed by
joining the cover plate 32 to the cooling fin 31. An alternative is
to provide a casing 33 that houses the cooling fin 31 in which
clearances (slits) between the fin parts are closed by an inner
surface of the casing 33 to form flow paths.
INDUSTRIAL APPLICABILITY
[0084] According to the present invention, the cooling fin with
reduced cost and improved cooling efficiency and the manufacturing
method of the cooling fin can be achieved.
* * * * *