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).

Description

TECHNICAL FIELD

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

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.

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.

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).

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.

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.

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.

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.

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

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.

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.

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.

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≧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.

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.

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.

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.

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.

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.

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.

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

FIG. 1 is a perspective view showing a schematic configuration of a power module in a preferred embodiment;

FIG. 2 is a perspective view showing a schematic configuration of a cooling fin in the embodiment;

FIG. 3 is a plan view showing the schematic configuration of the cooling fin of FIG. 2;

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;

FIG. 5 is a sectional view of the cooling fin taken along a line A-A in FIG. 3;

FIG. 6 is a sectional view of the cooling fin taken along a line B-B in FIG. 3;

FIG. 7 is a sectional view of the cooling fin taken along a line C-C in FIG. 3;

FIG. 8 is a schematic view showing a flow speed distribution in a cooling fin in a conventional art;

FIG. 9 is a schematic view showing a flow speed distribution in the cooling fin in the embodiment;

FIG. 10 is a view showing a shape (a straight shape) of a fin after extrusion molding;

FIG. 11 is a schematic view showing an outline of a fin bending operation by cold working;

FIG. 12 is a schematic view showing an outline of a fin bending operation by hot working (extrusion of a straight fin);

FIG. 13 is another schematic view showing the outline of the fin bending operation in hot working (bending of the straight fin);

FIG. 14 is a perspective view showing a schematic configuration of a jig used in the hot working;

FIG. 15 is a view showing each size of a wavy portion of the cooling fin;

FIG. 16 is a graph showing correlation between a wave pitch, a wave angle, and pressure loss in each cooling fin;

FIG. 17 is a graph showing correlation between a wave pitch, a wave angle, and a heat transfer rate in each cooling fin;

FIG. 18 is a perspective view showing a modified form of a cooler;

FIG. 19 is a perspective view showing a schematic configuration of a power module in a conventional art; and

FIG. 20 is a perspective view showing an outline of a manufacturing process of an offset fin.

BEST MODE FOR CARRYING OUT THE INVENTION

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

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.

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.

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.

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

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.

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.

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.

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).

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).

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.

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.

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

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.

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.

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.

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.

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.

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.

In the above hot working, the temperature of the fin parts 1 is high (about)600° 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

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 1
			Heat conductivity
	Technique	Material	[W/mK]
	Extrusion	A6063	209
	(Present embodiment)
	Casting	ADC12	92

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

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.

θ: Bending angle of a wave shape (hereinafter, Wave angle)

P: Pitch of a wave shape (hereinafter, Wave pitch)

f: Pitch of fin parts (Fin pitch)

w: Fin width (thickness)

a: Fin bending amount

c: Length of a straight portion

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.

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.

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 (θ):

P=2(c+a/tanθ)  (1)

As the wave angle (θ) in the expression (1) is larger, the turbulence of coolant flow is more induced, thereby enhancing the cooling performance. However, if the wave angle (θ) 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 (θ) has to meet the following expression (2):

θ≦α  (2)

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.

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 β, the length (c) of the straight portion has to meet the following expression (3):

c≧β  (3)

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≧f−w  (4)

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 (θ) 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.

An explanation will be given to correlation of the wave pitch (P) and the wave angle (θ) of the cooling fin 31 with the cooling performance. FIG. 16 shows correlation of P and θ with pressure loss. FIG. 17 shows correlation of P and θ 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 (θ) 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 (θ) 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 (θ) and the length (c) are different between the cooling fins 31.

It is found in both figures that, as the wave angle (θ) 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 (θ) and the wave pitch (P) of the bent fin part 1.

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.

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.

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.

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

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.

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 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.

the distal end portion of each fin part has a wave shape designed to meet an expression (I): a≧f−w  (I)

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.