JP5325821B2 - Heat sink manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a heat sink for cooling an electric circuit component that generates heat, and a heat sink.

  In recent years, the electrification of automobiles has progressed and power converters have been installed in automobiles, and power converters are required to be compact and have high performance due to space constraints.

  Conventionally, a heat sink in a vehicle power converter is generally formed of aluminum, but copper and copper alloys having higher thermal conductivity than aluminum have been used due to demands for compactness.

  However, copper and copper alloys have high deformation resistance and poor formability in molding such as extrusion and may not be able to apply the shape adopted in conventional aluminum molding as it is, when dare to perform molding with a limited shape, The load on the mold is increased and the mold life is shortened, resulting in an increase in manufacturing cost.

The present invention is a method of manufacturing a heat sink in which a base plate and fins are integrally molded, and a first intermediate blank including a circular tube base and a plurality of radiating fins arranged radially on the outer periphery of the circular tube base is formed. step and a step of obtaining an arc-shaped second intermediate blank by cutting the first intermediate blank, and arcuate base inner periphery of the said the gap bottom surface of the heat radiating fin of the second intermediate blank second intermediate blank to And a step of planarizing the second intermediate blank by locally narrowing the pressure.

JP2009-81993

In the manufacturing method described in Patent Document 1, since the brazing material is interposed between the base plate and the fin, the thermal resistance is large and the heat conduction is reduced.
Therefore, there is a demand for a manufacturing method for manufacturing a heat sink in which a base plate and fins are integrated at low cost.

The present invention is a method of manufacturing a heat sink in which a base plate and fins are integrally molded, and a first intermediate blank including a circular tube base and a plurality of radiating fins arranged radially on the outer periphery of the circular tube base is formed. And a step of flattening the first intermediate blank by locally narrowing the gap bottom surface of the radiating fin of the first intermediate blank and the arcuate base inner periphery of the first intermediate blank. Features.
The present invention is also a copper or copper alloy heat sink in which a base plate and fins are integrally formed, and includes a first intermediate body including a circular tube base and a plurality of radiating fins arranged radially on the outer periphery of the circular tube base. It is manufactured by forming a blank, planarizing the first intermediate blank by locally narrowing the gap bottom surface of the radiation fin of the first intermediate blank and the arcuate base inner periphery of the first intermediate blank. It is manufactured using a heat sink material.

  ADVANTAGE OF THE INVENTION According to this invention, the integrated heat sink using metal materials, such as copper and copper alloy with high heat conductivity, can be manufactured at low cost.

The longitudinal cross-sectional view which shows the heat sink using the raw material manufactured by 1st Embodiment of the manufacturing method by this invention. The perspective view which shows the raw material formation process by 1st Embodiment. The longitudinal cross-sectional view which shows the state immediately before the process of the 1st intermediate | middle blank forward extrusion process of 1st Embodiment. The longitudinal cross-sectional view which shows the intermediate state of the 1st intermediate | middle blank forward extrusion process of 1st Embodiment. The longitudinal cross-sectional view which shows the next circular tube blank injection | throwing-in state in the 1st intermediate | middle blank forward extrusion process of 1st Embodiment. The longitudinal cross-sectional view which shows the extrusion completion state of the previous circular tube blank in the 1st intermediate | middle blank forward extrusion process of 1st Embodiment. II sectional drawing of FIG. JJ sectional drawing of the heat sink in FIG. The longitudinal cross-sectional view which shows the state just before plane shaping | molding in the process of planarization of the 2nd intermediate | middle blank of FIG. The longitudinal cross-sectional view which shows the state immediately after planar shaping | molding in the process of planarization of the 2nd intermediate | middle blank in FIG. FIG. 11 is a longitudinal sectional view showing a further planarization step after planarization in FIG. 10. It is a figure explaining 2nd Embodiment of the manufacturing method by this invention, Comprising: The longitudinal cross-sectional view which shows the state just before plane shaping | molding in the process of planarization of a 2nd intermediate | middle blank. It is a figure explaining 3rd Embodiment of the manufacturing method by this invention, Comprising: The longitudinal cross-sectional view which shows the state just before plane shaping | molding in the process of planarization of a 2nd intermediate | middle blank.

Embodiments of a manufacturing method according to the present invention will be described below with reference to the drawings.
[First Embodiment]
[Power module]
FIG. 1 is a cross-sectional view when a copper or copper alloy heat sink obtained by the production method of the present invention is used in a power module of an automotive power converter. In a power module 10 of a power conversion device mounted on an automobile, a semiconductor chip 101 mounted with a power semiconductor element typified by IGBT is used. In order to use the power semiconductor element within an allowable temperature, the power conversion device includes a cooling device that cools the semiconductor chip 101.

  The configuration of the power module 10 shown in FIG. 1 will be described. The IGBT chip 101 is brazed on the insulating substrate 102 with the high-temperature solder 103, and the insulating substrate 102 is fixed to the surface of the heat sink 100 with the low-temperature solder 104. Yes.

  The heat sink 100 is configured to include a base plate 100a on the front surface side and a plurality of heat radiation fins 100b integrally projecting downward on the back surface of the base plate 100a. Is brazed. The heat sink 100 is fixed to the water channel forming body 105 with screws 107 or the like, and the heat radiating fins 100 b are inserted into the water channel 105 a formed in the water channel forming body 105. Thereby, the base plate 100a is cooled by the cooling water 106 circulating and flowing through the water channel 105a through the cooling fins 100b, and as a result, the insulating substrate 102 is cooled by water.

  An O-ring storage groove 105b is formed in the water channel forming body 105 so as to surround the water channel 105a, and an O-ring 108 is stored in the O-ring storage groove 105b. While being compressed by the base plate 100a, the O-ring 108 is in close contact with the back surface of the base plate 100a and the inner surface of the O-ring housing groove 105b, and seals the water channel 105a. This prevents the leakage of cooling water.

  The heat sink 100 in which the base plate 100a and the fins 100b are integrated can obtain an extremely excellent cooling effect as compared with a conventional heat sink in which fins are brazed. Further, since the material of the heat sink 100 is copper or a copper alloy, the heat conductivity is higher than that of a conventional heat sink made of an aluminum alloy, and high cooling performance can be obtained.

[Outline of manufacturing process]
As shown in FIG. 2, the heat sink 100 is formed through an intermediate stage of a first intermediate blank 210, a second intermediate blank 220, and a heat sink material 230 using a circular tube blank 200 as a rough material.

The manufacturing process generally includes the following processes (1) to (5).
(1) Circular tube blank production process The circular tube blank 200 is produced. The circular tube blank 200 has a cylindrical shape with a thickness substantially corresponding to the height of the heat sink 100.
(2) 1st intermediate | middle blank production process The circular tube blank 200 is extruded forward, and the 1st intermediate | middle blank 210 is shape | molded. The first intermediate blank 210 is formed by forming a fin shape 214 corresponding to the heat radiating fin 100 b on the outer periphery of the circular tube base 212.
(3) 2nd intermediate blank production process The 1st intermediate blank 210 is cut | disconnected along a central axis, and it divides | segments into 2 and the 2nd intermediate blank 220 is obtained. That is, the second intermediate blank 220 is obtained by dividing the first intermediate blank 210 into two in the radial direction.

(4) Heat sink material preparation step The second intermediate blank 220 is planarized to obtain the heat sink material 230. If the flatness of the heat sink material 230 is insufficient, flattening is further performed.

(5) Heat sink production process The heat sink 100 is obtained by heat-treating the heat sink material 230 and then performing cutting and plating.

[Details of manufacturing process]
Next, details of the manufacturing process will be described for each of the steps (1) to (5) with reference to FIGS.
(1) Circular tube blank production process First, circular tube blank 200 is prepared.
The circular tube blank 200 is manufactured by a method of cutting a pipe material to a required length, a method of extruding a cylindrical blank into a cup shape by forging, and then punching and forming the bottom surface of the cup.

(2) First intermediate blank manufacturing step As shown in FIGS. 3 to 7, a circular tube blank 200 is formed by a forward extrusion step using an extrusion die including an upper die 300 and a lower die 400, and a first intermediate blank is formed. 210 is manufactured.

As shown in FIG. 7, which is a cross-sectional view taken along the line II of FIG. 3, the extrusion mold includes an upper mold 300 and a lower mold 400.
The upper mold 300 includes a columnar opine 310 and a cylindrical ogata 320. The lower mold 400 includes a substantially annular megata (extrusion die) 330, and the megata 330 is reinforced with a reinforcement ring 438 on the outer periphery. The megata 330 is mounted on a megata mounting portion of the lower mold 400 (not shown). The circular tube blank 200 set in the lower die 400 is extruded by the upper die 300, and the first intermediate blank 210 is formed.

  The opin 310 has an inner peripheral molding portion 311 formed at the front end portion thereof, and an oscillating pressing portion 314 formed at the rear end portion thereof. The inner peripheral molding portion 311 has substantially the same shape as the inner peripheral surface 211 (see FIG. 2) of the first intermediate blank 210 to be molded, and has a slightly smaller diameter than the inner peripheral surface 201 of the circular tube blank 210. The rattling pusher 314 is connected to the inner periphery molded part 311 and the body 312.

  Ogata 320 has a cylindrical shape, and a stepped portion 322 having a large diameter toward the rear is formed on the rear end side of the hollow portion, and the rugged push portion 314 is engaged with the stepped portion 322. A forward pushing driving force applied to the opine 310 by a pressurizing device (not shown) is transmitted to the oggart 320 by this engagement structure. The outer diameter of the Ogata 320 is substantially the same as the outer diameter of the outer peripheral surface 202 (see FIG. 2) of the tubular blank 200. While the front end surface of the OG 320 is in contact with the rear end surface of the circular tube blank 200, the circular tube blank 200 is pushed forward.

A hollow portion is formed in the ring-shaped megata 330, and a cavity 333 into which the ogatta 320 is fitted is formed at the rear end side of the hollow portion. Can be done accurately. Thereby, the concentricity of the inner and outer circumferences of the first intermediate blank 210 can be ensured.
The circular tube blank 200 is mounted in the cavity 333 and extruded.

  A fin forming portion 431 corresponding to the heat radiation fin 100 b of the first intermediate blank 210 is formed on the front end side of the hollow portion of the megata 330. In the fin forming portion 431, fins having substantially the same shape (referred to as complementary fins) having a complementary relationship with the heat dissipating fins 100b of the heat sink 100 are radially provided.

Here, the dimension and shape of the fin forming portion 431 will be described with reference to FIGS. 7 and 8.
FIG. 8 is a JJ cross-sectional view of the heat sink 100 (see FIG. 2) after fabrication. The radiating fins 100b are formed with a pitch 100c. The angle of the radiating fin 100 b with respect to the base plate 100 a is set to a predetermined angle as the fin rising angle of the heat sink 100. A space between the fins 100b is referred to as a fin gap 100d.

  FIG. 7 shows the complementary fin pitch 432P on the inner diameter of the fin and the complementary fin pitch 433P on the outer diameter of the fin as the complementary fin pitch of the fin forming portion 431. The complementary fin pitch 432P on the fin inner peripheral diameter is set to a value substantially equal to the fin pitch 100c of the heat sink 100.

  When the first intermediate blank 210 is formed, the circular tube blank 200 is inserted into the cavity 333 of the megata 330 as shown in FIG. 3, and the upper die 300 is advanced (lowered) by the pressing force 340 as shown in FIG. . The circular tube blank 200 is extruded into a gap 437 formed by the fin forming portion 431 and the inner periphery forming portion 311 and is deformed into a forming intermediate product 205 having a remaining portion 205a.

  Next, the upper die 300 is once pulled up, and as shown in FIG. 5, the circular tube blank 200 ′ to be processed next is put on the intermediate product 205 and put into the cavity 333.

  As shown in FIG. 6, the upper die 300 is lowered by the re-pressing force 340 ′, the intermediate product 205 is moved forward together with the circular tube blank 200 ′, and the inner peripheral molding portion 311 of the opine 14 is moved to the bottom portion 334 of the megata 330. When the sheet is discharged, the heat dissipating fins 100b are formed on the remaining portion 205a of the intermediate product 205 and the first intermediate blank 210 is formed. Secondly, the circular tube blank 200 ′ charged into the megata 400 is molded to a state of a molded product 205 ″.

  As shown in FIG. 2, the first intermediate blank 210 formed in this way includes a circular tube base 212 corresponding to the base plate 100 a and radiating fins 100 b arranged radially on the outer periphery of the circular tube base 212. It will be.

  On the other hand, the circular tube blank 200 ′ becomes an in-mold product 205 ′ having a remaining portion 205 ′ and remains in the megater 330.

  In the subsequent first intermediate blank forward extrusion step, the steps of FIGS. 5 and 6 are repeated, and one intermediate product 205 a always remains in the megata 330.

(3) Second Intermediate Blank Making Step Next, the first intermediate blank 210 is cut in the axial direction along the central axis to manufacture the second intermediate blank 220 (see FIG. 2). At this time, it is necessary to cut so as to have a required base plate width W after planarization. Therefore, the circumferential length L of the arc-shaped base outer periphery 221 is set to the base plate width W after planarization and correction.

  In the process design for setting the peripheral length L, the peripheral length LL of the circular tube base outer periphery 213 of the first intermediate blank 210 is set to a multiple of (base plate width W + cutting allowance) after planarization. A plurality of heat sink materials 230 are manufactured from the tube blank 200. As a result, the material yield is excellent.

  In addition, you may shape | mold the 2nd intermediate | middle blank 220 by cut | disconnecting what was continuously extruded by conform extrusion etc. to required length perimeter.

(4) Heat Sink Material Production Step Next, the second intermediate blank 220 is planarized and corrected to form the heat sink material 230. In planarization, as shown in FIGS. 9 and 10, the inner and outer circumferences of the second intermediate blank 220 are clamped by the upper mold 600 and the lower mold 620.

  The lower die 620 includes a horizontal planar flat seat surface 623, a molded portion 621 having a substantially triangular projection protruding upward at one end of the flat seat surface 623, and a semicircular arc-shaped curve continuous to the flat seat surface 623. A seating surface 622 is formed. The forming part 621 can form an arcuate base inner periphery 224 that extends in the axial direction of the second intermediate blank 220 and corresponds to the entire length of the heat radiation fin 100b. The semicircular arc of the curved seat surface 622 is set to a radius substantially corresponding to the arcuate base inner periphery 224 of the second intermediate blank 220.

  The upper die 600 includes a main body 602 that is disposed above the flat seat surface 623 and can swing up and down, and a pressure receiving portion 601 that protrudes downward from the lower surface of the main body 602 at a position above the molding portion 621. The pressure receiving portion 601 has a substantially trapezoidal cross section corresponding to the gap 100d (see FIG. 8) of the radiation fin 100b to be molded.

  At the start of planarization, the second intermediate blank 220 is placed along the curved seating surface 622, and then the second intermediate blank 220 is sequentially shifted in the direction of the flat seating surface 623 while pressing downward on the upper mold 600. 650 (FIG. 10) is added, and the second intermediate blank 220 is clamped by the pressure receiving portion 601 and the molding portion 621.

  The pressure receiving portion 601 is inserted into the gap 100d of the radiating fin 100b, and presses the arcuate base outer periphery 223 at the bottom surface 223a of the gap 100d. Thus, the arc-shaped base outer periphery 223 is formed so as to narrow the angle of the heat radiation fin 100b with respect to the arc-shaped base outer periphery 223. With this molding, the arc-shaped base inner periphery 224 is molded into a flat surface. At this time, the deformation at a position corresponding to the gap bottom surface 223a is particularly large, and the molding portion 621 promotes plastic flow of this large deformation.

Planarization is performed sequentially from the upper end of the second intermediate blank 220 set on the curved seat surface 622. In FIGS. 9 and 10, the bottom surface 223a of the gap between the eighth and ninth radiating fins 100b and 100b is used. Is flattened.
By the planarization, the rising angle of the radiating fin 100b with respect to the arc-shaped base outer periphery 223 is corrected to a predetermined rising angle. That is, molding is performed so that the deviation θ from the set rising angle is eliminated and θ = 0 degrees. In the state immediately before molding in FIG. 9, θ> 0 degrees, but when the molding in FIG. 10 is completed, θ = 0 degrees.

The pressure receiving portion 601 presses only the gap bottom surface 223a and does not apply a load to the radiation fin 100b itself, and the shape of the pressure receiving portion 601 is a substantially trapezoidal cross section corresponding to the gap between the radiation fins 100b to be formed. Therefore, the shape of the radiating fin 100b and the shape of the arcuate base outer periphery 223 are not deformed.
As a result, it is possible to minimize the deformation of the heat dissipating fins 100b and the deviation of the fin pitch 100c, and to perform planarization with excellent accuracy.

  That is, substantially no plastic flow is generated in the vicinity of the gap bottom surface 223a, and the plastic flow 630 is generated mainly in the vicinity of the arcuate base inner periphery 224 that contacts the forming portion 621 that is a triangular protrusion.

  In general, when there is no special constraint, a material subjected to a load causes a plastic flow when a surface pressure exceeding a specified level is reached. The surface pressure suddenly increases in the vicinity of the molding portion 621 of the arc-shaped base inner periphery 224, and only the material in the vicinity thereof plastically flows 630 in the circumferential direction so that the arc-shaped base narrow pressure portion 226 is separated in the circumferential direction ( (Direction of arrow 227).

  Although the molding for planarization needs to be performed on each of the gap bottom surfaces 223a of the radiating fins 100b, the processing conditions at each location can be made uniform, so that the planarization accuracy is stable.

  Furthermore, by providing the curved seat surface 622 continuously with the flat seat surface 623, the position of the second intermediate blank 220 can be fixed before molding, and workability is improved.

  In order to further improve the flatness of the heat sink material 230 planarized by the upper mold 600 and the lower mold 620, for example, as shown in FIG. While constraining with the molds 700 and 720, clamping is performed from above and below to level the undulations and irregularities generated by the flat molding. At this time, the material of the convex portion flows into the concave portion to form a flat surface.

(5) Heat sink production process The heat sink material 230 manufactured by planarization is subjected to heat treatment 240 in order to remove residual stress generated during extrusion or planarization.

(Heat treatment)
Residual stress of the base plate 100a may be released due to the melting heat of the solder when the insulating substrate 102 is brazed to the base plate 10a, the heat generated by the IGBT chip during the operation of the power module 10, and the like. . This causes defects such as cracks in the solder and the substrate.
By the heat treatment, such residual stress is released in advance, and generation of defects is prevented.

(Cutting and plating)
After the heat treatment 240, a substrate brazing surface 100e (see FIG. 2) for brazing the insulating substrate 102, a seal surface 100f (see FIG. 2) for sealing with the O-ring 108, and a screw mounting hole 100g (see FIG. 2). After finishing the above by cutting, plating is performed in consideration of corrosion resistance to obtain the heat sink 100. At the time of cutting, external dimension adjustment and removal of unnecessary radiating fins 100b are also performed.

  As described above, the heat sink material 230 of the present invention is a heat sink material with excellent thermal conductivity of copper or copper alloy in which the base plate 100a and the heat radiating fins 100b are integrally formed. High performance and compactness of the module 10 can be achieved.

  The intermediate blank can be formed by extrusion using a press machine, and can be produced without a special forming machine such as a conform forming machine.

  Moreover, by molding from the circular tube blank 200, abnormally high stress does not occur in the mold during extrusion molding, and the stress state is appropriate. For this reason, a radiation fin having a sufficiently high aspect ratio can be formed.

Furthermore, the following effects can be obtained.
By forming the fin forming portions 431 radially in the first intermediate blank 210, the interval between the fin outer peripheral pitches 433p can be set larger than the fin inner peripheral pitch 432p, and the final pitch 100c of the radiating fins 100b (see FIG. 8). ) Can be set larger than the outer circumferential pitch 433p. As a result, the cross-sectional area between the fins of the extruded circular tube blank 200 can be set larger than in the case of directly extruding planar fins. Therefore, stress relaxation of the fin forming portion 431 in which high stress is generated at the time of molding can be achieved, and the radiation fin 100b having a sufficiently large aspect ratio can be molded.
In addition, the life of the mold can be extended as compared with the case where the heat radiation fin 100b is directly extruded.

  Since the first intermediate blank 210 is cylindrical, the cross section of the fin forming portion 431 has a point-symmetric shape with respect to the central axis of the megata 330, and the stress state is made uniform rather than being directly extruded into the shape of the heat sink 100. In this respect as well, the life of the mold can be extended.

  The reinforcing ring 437 is fitted to the megata 330 by shrink fitting 434 or the like, but since the cross section of the fin forming portion 431 is symmetrical with respect to the central axis of the megata 330, the stress due to reinforcement is uniform and effective on the megata 330. It works in the same way.

  The compressive force generated by shrink fitting 434 generates a compressive stress 435 in the fin outer peripheral diameter 433 and cancels out all or a part of the tensile stress 436 generated during molding. As a result, the occurrence of mold cracking in the fin molding portion 431 is suppressed, and the life of the mold is extended.

In addition, when extruding directly to the shape of the heat sink 100, the stress state becomes non-uniform and an effective reinforcing structure cannot be realized.
[Second Embodiment]

Next, a second embodiment of the manufacturing method according to the present invention will be described with reference to FIG.
In the figure, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the first embodiment, when flattening, the gap bottom surface 223a and the arc base inner periphery 224 are narrowed to flatten the arc base 223. However, as shown in FIG. 12, the main body 602 of the upper mold 600 is used. The tip 100h of the heat dissipating fin 100b may be further pressed.

In short, it is important to plastically flow only the material of the arc-shaped base inner periphery 224 in the circumferential direction.
[Third Embodiment]

Next, a third embodiment of the manufacturing method according to the present invention will be described with reference to FIG.
In the figure, the same or corresponding parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the first embodiment, the arc base inner periphery 224 of the second intermediate blank 220 is a smooth arc surface. However, as shown in FIG. Concavities and convexities 100j in which convex portions and concave portions extending over the entire length in the direction are arranged in the circumferential direction may be formed in advance.

The unevenness 100j is formed, for example, in the first intermediate blank forward extrusion step.
During planarization, the surface pressure at the initial stage of narrowing can be further increased by narrowing the convex portion of the unevenness 100j.
As a result, it is possible to improve the flattening accuracy or reduce the height of the projection-shaped forming portion 621 to reduce the machining allowance of the base brazing surface 100e.

In addition, the heat sink demonstrated above and its manufacturing method are examples, and a various form is employable unless it deviates from this invention.
Accordingly, the present invention is a method of manufacturing a heat sink in which a base plate and fins are integrally formed, and includes a first intermediate blank including a circular tube base and a plurality of radiating fins arranged radially on the outer periphery of the circular tube base. And a step of flattening the first intermediate blank by locally narrowing the gap bottom surface of the radiating fin of the first intermediate blank and the arcuate base inner periphery of the first intermediate blank. It can be applied to the manufacturing method.

100: heat sink 100a: base plate 100b: radiating fin 100d: gap 200: circular tube blank 210: first intermediate blank 223: arc-shaped base outer periphery 223a: gap bottom surface 224: arc-shaped base inner periphery 230: heat sink material 300: upper mold 330 : Megata 601: Pressure receiving part 621: Molding part

Claims (7)

A heat sink manufacturing method in which a base plate and fins are integrally molded,
Forming a first intermediate blank having a circular tube base and a plurality of heat dissipating fins radially disposed on the outer periphery of the circular tube base;
Cutting the first intermediate blank to obtain an arc-shaped second intermediate blank;
A step of planarizing a locally narrow pressure in the second intermediate blank and gap bottom surface and an arc-shaped base inner periphery of the second intermediate blank of the heat dissipation fins of the second intermediate blank,
A method of manufacturing a heat sink. In the manufacturing method of Claim 1,
Wherein during the second step of planarizing the intermediate blank in a circumferential said arcuate base, method for producing a heat sink, characterized in that the protruding shaped portion extending in the axial direction of the second intermediate blank abuts. In the manufacturing method of Claim 1 or 2,
The step of forming the first intermediate blank includes a step of extruding the blank,
The method of manufacturing a heat sink, further comprising the step of preparing the blank prior to the step of forming the first intermediate blank. In the manufacturing method of Claim 3,
The method of manufacturing a heat sink, wherein the extrusion molding step is performed by an extrusion die reinforced by a reinforcing ring. In the manufacturing method of Claim 3 or 4,
The method of manufacturing a heat sink, wherein the blank used for the extrusion is a circular tube. The manufacturing method according to claim 1,
The step of forming the first intermediate blank includes a step of forming irregularities on the inner periphery of the arcuate base of the first intermediate blank. In the manufacturing method of Claim 6,
The flattening step includes a step of pressing the concave and convex portions on the inner circumference of the arc-shaped base to form a flat shape, wherein the method of manufacturing a heat sink.

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