Cooling device and method for manufacturing cooling device

Abstract

In this cooling device, a first member formed of a metal and a second member formed of a metal of a type different from that of the first member are joined by irradiating the first member with laser light in a state where the first member and the second member are overlapped. The second member has, on a surface thereof overlapping and contacting the first member, a recessed part recessed so as to be separated from the first member. A portion of the first member opposing the recessed part is melted and enters the recessed part, and is melted and joined to a portion of the second member around the recessed part.

Description

Cooling device and method for manufacturing a cooling device

[0001] The present invention relates to a cooling device and a method for manufacturing a cooling device.

[0002] For example, Patent Document 1 describes a dissimilar metal joint in which a copper material and an aluminum material are in contact, wherein a portion of the aluminum material melts and flows into the interior of the copper material, forming a molten mixed portion that is formed in a continuous and linear shape on the surface of the copper material in contact with the aluminum material, with a depth dimension of 5 to 30 μm from the surface, and a width dimension of the shape of the molten mixed portion that is 10 to 50 μm on the surface of the copper material in contact with the aluminum material, and the component concentration of the copper material inside the molten mixed portion and the component concentration of the aluminum material in the copper material near the molten mixed portion are both less than 10%. For example, Patent Document 2 describes a method for laser welding dissimilar metal members by overlapping a first metal member with a second metal member that has a higher melting point and is harder than the first metal member, wherein the thickness of the first metal member is 0.8 mm or more and 2.0 mm or less, and the thickness of the second metal member is 0.3 mm or more and 0.8 mm or less, and the laser beam is irradiated from above the second metal member with the second metal member overlapping the first metal member, resulting in a penetration depth of the first metal member of 0.15 mm or more and 0.55 mm or less, and the value obtained by dividing the penetration depth by the weld bead width, which is the width of the welded area when viewed from above, is 0.43 or less.

[0003] Japanese Patent Publication No. 5982652, Japanese Unexamined Patent Publication No. 2020-97039

[0004] For example, the material of the metal member used for the heat radiating part of the cooling device may be different from the material of the metal member used other than this heat radiating part. When different metal members are welded and joined together, an intermetallic compound composed of two or more types of metals is generated at the joint. This intermetallic compound generally has a brittle property compared to the case where the same type of metal is welded. Therefore, the cooling device in which metal members of different materials are joined is likely to have a reduced strength. The present invention aims to suppress a decrease in the strength of the cooling device when different types of metal members are overlapped and welded.

[0005] The cooling device to which the present invention is applied is a cooling device joined by irradiating laser light to a first member formed of metal and a second member formed of a different type of metal from the first member in a state where they are overlapped, wherein the second member has a recess recessed away from the first member on a surface that is overlapped and in contact with the first member, a part of the first member facing the recess is melted and enters into the recess, and is fusion-welded to a part around the recess in the second member. Here, the cooling device may be such that the melting point of the first member is lower than the melting point of the second member. Also, the cooling device may be such that the material of the first member is aluminum and the material of the second member is copper. Further, the second member has a flat base part to which heat generated by the heating element is transmitted, and a fin part protruding in a direction intersecting the plate surface of the base part from the base part, the first member is disposed around the second member, and the recess may be provided around the fin part in the base part of the second member. Also, the cooling device may be such that the shape of the recess is such that the depth of the recess is shorter or the same as compared to the width of the recess.

[0006] From another perspective, the method for manufacturing a cooling device to which the present invention applies is a method for manufacturing a cooling device to which a first member made of metal and a second member made of a different type of metal than the first member are joined by irradiating the first member with laser light while the two members are superimposed, comprising the steps of: forming a recess on the surface of the second member that is superimposed on and in contact with the first member, such that it is recessed away from the first member; and irradiating a portion of the first member opposite to the recess with laser light to melt the first member and fusion-join it with the portion surrounding the recess. Here, when irradiating the portion of the first member opposite to the recess with laser light, the second member and the first member may be arranged in a superimposed state such that the opening of the recess faces in the opposite direction to the direction of gravity, and the laser light may be irradiated in the direction of gravity toward the portion of the first member opposite to the recess.

[0007] The present invention aims to suppress a decrease in the strength of a cooling device when welding together different types of metal components.

[0008] This figure shows an example of a cooling device to which this embodiment is applied. This is a cross-sectional view of the cooling device (section II-II in Figure 1). (a) is an enlarged view of area III in Figure 2, illustrating the area where laser welding is performed, and (b) shows the state after laser welding. This is a diagram illustrating the position to which the laser head is moved. This is an experimental result showing an example of the relationship between the groove shape and the state of the molten area in the groove. This is an experimental result showing an example of the relationship between the laser beam irradiation output (W) and shear strength. This is a photograph showing part of the experimental results in Figure 6. This is a photograph showing a comparative example in which a copper plate and an aluminum plate were welded without forming a groove.

[0009] Embodiments of the present invention will be described in detail below with reference to the attached drawings. Figure 1 is a diagram showing an example of a cooling device 1 to which this embodiment is applied. Figure 2 is a cross-sectional view of the cooling device 1 (cross-sectional view taken along line II-II in Figure 1). The cooling device 1 according to this embodiment comprises a heat dissipation section 10 having a plurality of fins 12, and a cover 20 having through holes 21 for arranging the heat dissipation section 10 inside. The cooling device 1 is a device that attaches a heat-generating element to the heat dissipation section 10 and dissipates the heat generated from the heat-generating element through the plurality of fins 12. The cooling device 1 is used, for example, by arranging it in a case having an internal space through which a coolant flows, so that the coolant flows between the plurality of fins 12. The cover 20 is used to cover the opening of this case. Alternatively, the cooling device 1 may be an air-cooled type that promotes heat dissipation by flowing a gas such as air between the plurality of fins 12 of the heat dissipation section 10. The heat-generating element cooled by the cooling device 1 is not particularly limited, but a semiconductor element can be given as an example.

[0010] In the example shown in Figure 1, the multiple fins 12 protrude from the front to the back of the paper. Hereafter, the direction in which the multiple fins 12 protrude may simply be referred to as the "protrusion direction." In the protrusion direction, the tip side of the fins 12 (the lower side in Figure 2) may be referred to as the "first side," and the opposite side of the "first side" (the upper side in Figure 2) may be referred to as the "second side." Also, as shown in Figure 1, the shape of the cooling device 1 when viewed from the protrusion direction is rectangular, and the longitudinal direction of this rectangle may simply be referred to as the "longitudinal direction," and the transverse direction of this rectangle may simply be referred to as the "transverse direction."

[0011] (Heat dissipation section 10) The material of the heat dissipation section 10 is preferably a material with higher thermal conductivity than the material of the cover 20. For example, the material of the heat dissipation section 10 can be copper or a copper alloy. In addition, part or all of the surface of the heat dissipation section 10 may be plated. The material for the plating is not particularly limited, but nickel plating can be used to improve corrosion resistance. The heat dissipation section 10 comprises a flat base section 11 and a plurality of fins 12 protruding from the base section 11.

[0012] The base portion 11 has a shape that is approximately square when viewed from the second side in the protruding direction. The base portion 11 includes a fin side surface 111, which is the surface on which the plurality of fins 12 protrude, and a mounting surface 112 to which the heating element is attached. The base portion 11 also includes a lower portion 13 that overlaps with the upper portion 22 of the cover 20, which will be described later.

[0013] The lower section 13 is located on the outer edge of the heat dissipation section 10 and is stepped, recessed in the first direction from the mounting surface 112 in the protruding direction. When viewed from the second side in the protruding direction, the lower section 13 is a roughly square annular shape and has an upper surface 132 that faces the second side in the protruding direction. The lower section 13 and the upper section 22 are overlapped and welded together to form a molten section 50. A groove 14 for welding is formed in the lower section 13, and the groove 14 will be described in detail with reference to Figure 3.

[0014] Multiple fins 12 protrude from the fin side surface 111 of the base portion 11 in a direction perpendicular to the plate surface of the base portion 11. Multiple fins 12 are an example of fin portions, and when the base portion 11 is viewed from the protruding direction, they protrude from a region that is approximately square. Each fin 12 is a flat plate shape that extends in a direction perpendicular to the plate surface of the base portion 11 and in the short-side direction of the cooling device 1. Multiple fins 12 are arranged in a line in the longitudinal direction of the cooling device 1. The shape of the multiple fins 12 is not particularly limited, and examples of fin shapes include cylindrical or rectangular prism shapes. Furthermore, the shape of the fins 12 is not limited to one, and the multiple fins 12 may be composed of fins 12 of different shapes.

[0015] (Cover 20) The material of the cover 20 can be aluminum or an aluminum alloy, which is lighter than copper. Also, part or all of the surface of the cover 20 may be plated. The material for the plating is not particularly limited, but nickel plating can be used to improve corrosion resistance. The cover 20 is a rectangular plate-shaped member when viewed from the second side in the protruding direction, and a substantially square through hole 21 is formed in the center for arranging the heat dissipation part 10. The cover 20 also has an upper step portion 22 that is recessed from the first side surface of the cover 20 to the second side around the through hole 21. The upper step portion 22 is substantially square and annular in shape when viewed from the first side in the protruding direction, so as to overlap with the lower step portion 13 of the heat dissipation part 10. The upper step portion 22 has a contact surface 221 that contacts the upper surface 132 of the lower step portion 13. The contact surface 221 is the surface facing the first side in the protruding direction.

[0016] [Manufacturing Method] Next, the manufacturing method of the cooling device 1 (see Figure 2) will be described with reference to Figures 3 and 4. Figure 3(a) is an enlarged view of area III in Figure 2, and is a diagram to explain the shape before laser welding is performed. Figure 3(b) is a diagram showing the state after laser welding has been performed. Figure 4 is a diagram to explain the position in which the laser head 151 is moved.

[0017] The manufacturing process for the cooling device 1 involves, in the first step, forming the heat dissipation section 10 and the cover 20 separately. Then, in the second step, stacking the heat dissipation section 10 and the cover 20. Furthermore, in the third step, welding is performed by irradiating with laser light 152.

[0018] In the first step, copper material such as copper or a copper alloy is formed into the shape of the heat dissipation section 10, and aluminum material such as aluminum or an aluminum alloy is formed into the shape of the cover 20. Examples of methods for forming the heat dissipation section 10 and the cover 20 include pressing, forging, casting, and machining. In addition, multiple forming methods may be combined to form the heat dissipation section 10 and the cover 20. For example, as a method for forming the heat dissipation section 10, all parts except the groove 14 of the heat dissipation section 10 may be formed by casting, and the groove 14 may be formed by machining.

[0019] As shown in Figure 3(a), the groove 14 is provided on the upper surface 132 of the lower section 13 and is a rectangular annular groove provided along the lower section 13 when viewed from the second side in the protruding direction. The groove 14 comprises a bottom surface 141 that forms the bottom of the concave groove 14 and a side surface 142 that forms the concave side surface.

[0020] In the second step, as shown in Figure 3(a), the upper surface 132 of the lower part 13 of the heat dissipation unit 10 and the contact surface 221 of the upper part 22 of the cover 20 are brought into contact and overlapped. As described above, the groove 14 is located on the upper surface 132 of the lower part 13. Therefore, at the overlapping portion of the lower part 13 and the upper part 22, the groove 14 is recessed in the direction away from the contact surface 221. In other words, the opening of the groove 14 is in contact with the contact surface 221. Here, the heat dissipation unit 10 and the cover 20 are placed so that the direction in which the groove 14 is recessed is the direction of gravity. In other words, the heat dissipation unit 10 and the cover 20 are placed so that the opening of the groove 14 faces in the opposite direction to the direction of gravity. Here, facing in the opposite direction to the direction of gravity means that the inclination with respect to the vertical direction is 45° or less.

[0021] In the third step, with the lower section 13 and the upper section 22 superimposed, the laser beam 152 is shone onto the cover 20 in the direction in which the groove 14 is recessed (in this case, the direction of gravity). The laser beam 152 is shone at a position that overlaps with the groove 14 when viewed from the second side in the protruding direction.

[0022] As shown in Figure 3(b), the cover 20 melts due to the laser beam 152 irradiated in the protruding direction, forming a molten portion 50. As shown in Figure 3(b), the molten portion 50 penetrates into the groove 14 and melts the area around the groove 14 by contacting the bottom surface 141 (see Figure 3(a)) and side surface 142 (see Figure 3(a)). In the molten portion 50, a single-metal molten portion 51 and a dissimilar-metal molten portion 52 are formed. The single-metal molten portion 51 is the part where the base material of the cover 20 is melted. The dissimilar-metal molten portion 52 is the part where the base material of the cover 20 and the base material of the heat dissipation portion 10 are melted.

[0023] The dissimilar metal molten area 52 is formed when the base material of the cover 20 melts and enters the groove 14, causing the base material of the heat dissipation section 10 to melt. Although the melting point of aluminum, the base material of the cover 20, is lower than that of copper, the area irradiated by the laser beam 152 can reach a temperature higher than its melting point. Therefore, even in a single-metal molten area 51 of aluminum, which has a lower melting point than copper, it is possible to melt copper, which has a higher melting point. Furthermore, since the laser beam 152 is irradiated from a position facing the bottom surface 141, the energy of the laser beam 152 is easily transferred to the bottom surface 141 of the groove 14, suppressing excessive melting of the side surface 142. Therefore, the formation of the dissimilar metal molten area 52 is suppressed on the side surface 142 compared to the bottom surface 141.

[0024] As shown in Figure 3(b), the molten portion 50 penetrates into the groove 14 and melts the area around the groove 14 by contacting the bottom surface 141 and the side surface 142 of the groove 14. The side surface 142 is positioned perpendicular to the top surface 132, and a dissimilar metal molten portion 52 is formed along the protruding direction. The dissimilar metal molten portion 52 is a layer in which copper and aluminum have molten, and is a region where intermetallic compounds are likely to be generated.

[0025] In the third step, the laser head 151 is moved along the groove 14 (along the perimeter of the base portion 11) while continuously irradiating with laser light 152, as shown in Figure 4, thereby welding the upper portion 22 and the lower portion 13 without changing the irradiation direction of the laser head 151.

[0026] [Operation] Figure 8 is a photograph showing a comparative example in which a copper plate and an aluminum plate are welded without forming a groove 14. In Figure 8, the copper plate and the aluminum plate are placed on top of each other, and welding is performed by irradiating the aluminum plate with laser light. In the illustrated example, the aluminum plate is placed on the upper side of the drawing, and the copper plate is placed on the lower side. In the comparative example in Figure 8, a molten area of ​​dissimilar metals is formed at the contact surface between the copper plate and the aluminum plate. In Figure 8, an example of the direction in which shear force acts is shown by an arrow. In the example shown in Figure 8, a shear force acts on the molten area by applying a pulling force to the right on the aluminum plate and to the left on the copper plate. In this case, the pulling force to the left and right is easily applied to the molten area of ​​dissimilar metals, and the generally brittle intermetallic compound portion is easily fractured. On the other hand, in the cooling device 1 of this embodiment, as shown in Figure 3(b), in the molten area 50 of the cooling device 1, a molten area 52 of dissimilar metals, aluminum and copper, is easily formed at the interface between the side surface 142 and the bottom surface 141. In other words, the formation of a dissimilar metal molten portion 52 at the opening of the groove 14, that is, at the position on the surface where the upper surface 132 and the contact surface 221 are in contact, is suppressed. As a result, when forces are applied to the heat dissipation portion 10 and the cover 20 in different directions along the contact surface 221 (upper surface 132), shear force is more likely to be applied to the single metal molten portion 51. In other words, the application of shear force to the dissimilar metal molten portion 52 formed in the groove 14 is suppressed, and fracture from the intermetallic compound portion is suppressed.

[0027] <Summary> As described above, the cooling device 1 is formed by joining a cover 20 made of aluminum and a heat dissipation part 10 made of copper when the cover 20 is superimposed on the cover 20 and irradiated with laser light 152. The heat dissipation part 10 of the cooling device 1 has a groove 14 recessed on the upper surface 132 of the lower part 13 that is superimposed on and in contact with the cover 20, so as to be separated from the contact surface 221 of the cover 20. Furthermore, the part of the cover 20 facing the groove 14 melts and enters into the groove 14, and is fused together at the position of the bottom surface 141 and the side surface 142 of the groove 14 in the heat dissipation part 10.

[0028] In the cooling device 1 formed in this manner, the bottom surface 141 and the side surface 142 of the groove 14 are fused together, thus preventing the formation of a dissimilar metal molten portion 52 in a position continuous with the upper surface 132 of the lower portion 13. As a result, even when a shear force is applied to the heat dissipation portion 10 and the cover 20, the relatively strong single metal molten portion 51 receives the force, increasing the strength against shear force.

[0029] Furthermore, the cooling device 1 according to this embodiment uses copper, which has high heat dissipation performance, for the heat dissipation section 10 and lightweight aluminum for the cover 20, thereby improving heat dissipation performance and reducing weight.

[0030] Comparing the melting points of aluminum and copper, copper has a higher melting point. In this embodiment, the aluminum cover 20 is irradiated with laser light 152. Therefore, compared to the case where the copper of the heat dissipation section 10 is irradiated with laser light 152 to melt it, the energy required for melting can be reduced.

[0031] Furthermore, the cover 20 is positioned around the heat dissipation section 10, and the grooves 14 are provided around the base section 11 of the heat dissipation section 10 and the multiple fins 12. The cooling device 1 of this embodiment achieves high heat dissipation performance and weight reduction by using copper for the heat dissipation section 10 and aluminum for the cover 20.

[0032] In this embodiment, the heat dissipation section 10 has a flat base section 11 to which heat generated by the heat-generating element is transferred, and a plurality of fins 12 that protrude from the base section 11 in a direction intersecting the plate surface of the base section 11. The cover 20 is arranged around the heat dissipation section 10. The groove 14, which is the position for welding the heat dissipation section 10 and the cover 20, is provided around the area of ​​the base section 11 where the plurality of fins 12 protrude. By constructing the heat dissipation section 10, which has a high contribution to heat dissipation, from copper, the contribution to heat dissipation can be increased. On the other hand, by constructing the area around the plurality of fins 12, which has a low contribution to heat dissipation, from aluminum, weight reduction can be achieved.

[0033] In the manufacturing method of the cooling device 1 of this embodiment, a cover 20 made of aluminum and a heat dissipation part 10 made of copper, a metal different from the aluminum material of the cover 20, are superimposed on each other, and a laser beam is irradiated onto the cover 20. In this manufacturing method, in the first step, a groove 14 is formed on the upper surface 132 of the heat dissipation part 10, which is the surface that is superimposed on and in contact with the cover 20, so as to be separated from the contact surface 221 of the cover 20. In the second step, a laser beam is irradiated onto the cover 20. Here, the laser beam is irradiated onto the part opposite the groove 14, melting the cover 20 and melting the bottom surface 141 and side surface 142 of the groove 14, thereby melting and joining them with the surrounding part of the groove 14.

[0034] In the cooling device 1 manufactured in this manner, the bottom surface 141 and the side surface 142 of the groove 14 are fused together, thus suppressing the formation of a molten dissimilar metal portion 52 at a position along the contact surface 221 of the upper portion 22 between the upper surface 132 of the lower portion 13, which is the surface surrounding the groove 14, and the upper portion 22.

[0035] Furthermore, in the manufacturing method of the cooling device 1 of this embodiment, when irradiating the portion of the cover 20 facing the groove 14 with laser light 152, the heat dissipation portion 10 and the cover 20 are arranged in a state where they are superimposed on each other so that the opening of the groove 14 faces in the opposite direction to the direction of gravity. Then, the laser light 152 is irradiated in the direction of gravity toward the portion of the cover 20 facing the groove 14. When the laser light 152 is irradiated in this manner, when the cover 20 melts, the molten portion 50 falls into the groove 14 according to gravity, making it easier for the groove 14 to be filled.

[0036] The inventors conducted experiments to investigate the relationship between the shape of the groove 14 (width H and depth D) and the state of the molten portion 50 in the groove 14. Figure 5 shows an example of the experimental results illustrating the relationship between the shape of the groove 14 and the state of the molten portion 50 in the groove 14. First, the inventors formed a groove in a copper plate, then placed an aluminum plate on top of it, and welded the copper plate and the aluminum plate by irradiating the groove with laser light from the aluminum plate side. Then, they took cross-sectional photographs showing the molten state of the copper plate and the aluminum plate.

[0037] More specifically, an A1100 aluminum plate with a thickness of 2 mm was used as the aluminum plate. A C1020 copper plate with a thickness of 2 mm was used as the copper plate. Grooves were then formed in the copper plate by cutting. Three samples were created with different groove shapes, each groove having a width H of 0.5 mm and a depth D of 1 mm, 0.5 mm, and 0.25 mm. As shown in Figure 5, when the depth D was 1 mm, the molten portion 50 could not fill the groove 14, resulting in poor bonding. When the depth D was 0.5 mm and 0.25 mm, the molten portion 50 filled the groove 14, resulting in good bonding. In other words, when the depth D of the groove 14 is shorter than or equal to the width H, the molten portion 50 fills the groove 14 and good bonding is achieved.

[0038] Next, the inventors joined an aluminum plate and a copper plate by changing the output of the laser beam irradiation while keeping the width H and depth D of the grooves made in the copper plate unchanged, and measured the shear strength. Figure 6 shows an example of the experimental results showing the relationship between the laser beam irradiation output (W) and the shear strength (MPa). Hereafter, the laser beam irradiation output may be simply referred to as "output". Figure 7 is a photograph showing part of the experimental results of Figure 6. First, the inventors formed a groove in the copper plate, placed an aluminum plate on top of it, and welded the copper plate and the aluminum plate by irradiating the groove with laser light from the aluminum plate side. Then, they pulled the copper plate and the aluminum plate in directions parallel to the plate surfaces but in different directions, gradually increasing the pulling force, and recorded the shear force when the copper plate and the aluminum plate separated as the shear strength.

[0039] More specifically, two tests were conducted at three different power levels: 800W, 1000W, and 1200W. Three tests were also conducted at 900W, and one test at 850W. In these tests, the aluminum plate thickness was set to 1 mm. The width H of the groove formed in the copper was set to 0.5 mm, and the depth D was set to 0.25 mm. The wobbling settings for laser irradiation were set to a wobbling diameter of 0.5 mm and a wobbling speed of 1500 mm / s.

[0040] As shown in Figure 6, the shear strength at an output of 800W was 82 MPa and 85 MPa. At an output of 850W, the shear strength was 91 MPa. At an output of 900W, the shear strength was 92 MPa, 79 MPa, and 54 MPa. At an output of 1000W, the shear strength was 15 MPa and 20 MPa. At an output of 1200W, the shear strength was 27 MPa and 29 MPa. As shown in Figure 6, it was found that the shear strength was greater at outputs between 800W and 900W compared to outputs of 1000W and 1200W. Furthermore, if the width H of the groove 14 of the cooling device 1 according to this embodiment is 0.5 mm, the depth D is 0.25 mm, the thickness of the cover 20 is 1.0 mm, the wobbling diameter of the laser beam 152 irradiated onto the cover 20 is 0.5 mm, and the wobbling speed is 1500 mm / s, then if the output power of the laser beam is in the range of 800 W to 900 W, the shear strength of the cover 20, the heat dissipation section 10, and the melting section 50 will increase, and the strength of the cooling device 1 will increase. Also, it is desirable that the wobbling diameter be, for example, 1.5 times or less the size of the groove H.

[0041] Figure 7 is a photograph showing a cross-section of the cover 20 and heat dissipation section 10 after they have been disassembled by a shear test. Even when grooves are provided, as the output of the laser beam 152 increases, the fluidity of the molten section 50 increases, and the copper molten at the bottom surface 141 and side surface 142 of the groove 14 diffuses within the molten section 50. As a result, the relatively brittle dissimilar metal molten section 52 spreads within the molten section 50, reducing its strength. At output levels of 1000W and 1200W, copper melts from the bottom surface 141 and side surface 142, and a large portion of the molten section 50 becomes the dissimilar metal molten section 52, resulting in a smaller shear strength. On the other hand, in the output range of 800W to 900W, the dissimilar metal molten section 52 does not spread as much as at output levels of 1000W and 1200W, resulting in a larger shear strength.

[0042] <Other> In this embodiment, the side surface 142 is perpendicular to the top surface 132. However, the side surface 142 does not necessarily have to be perpendicular to the top surface 132 and may be an inclined surface. For example, the shape of the groove 14 may have a trapezoidal or V-shaped cross-section in which the width gradually increases from the bottom surface 141 toward the opening. Alternatively, the groove 14 may have a semicircular cross-section.

[0043] 1...Cooling device, 10...Heat dissipation section, 14...Groove, 20...Cover, 50...Melting section, 51...Single metal melting section, 52...Dissimilar metal melting section, 132...Top surface, 141...Bottom surface, 142...Side surface, 151...Laser head, 152...Laser beam, 221...Contact surface

Claims

1. A cooling device in which a first member made of metal and a second member made of a different type of metal than the first member are joined by irradiating the first member with laser light while the two members are superimposed, wherein the second member has a recess on the surface that is superimposed on and in contact with the first member, which is recessed away from the first member, and the portion of the first member opposite to the recess melts and enters the recess, and is fused together with the surrounding portion of the second member.

2. The cooling device according to claim 1, wherein the melting point of the first member is lower than the melting point of the second member.

3. The cooling device according to claim 2, wherein the material of the first member is aluminum and the material of the second member is copper.

4. The cooling device according to claim 1, wherein the second member has a flat base portion to which heat generated by the heating element is transferred, and a fin portion that protrudes from the base portion in a direction intersecting the plate surface of the base portion, and the first member is arranged around the second member, and the recess is provided on the base portion of the second member around the fin portion.

5. The cooling device according to any one of claims 1 to 4, wherein the shape of the recess is such that the depth of the recess is shorter than or equal to the width of the recess.

6. A method for manufacturing a cooling device in which a first member made of metal and a second member made of a different type of metal than the first member are joined by irradiating the first member with laser light while the two members are superimposed, comprising the steps of: forming a recess on the surface of the second member that is superimposed on and in contact with the first member, such that it is recessed away from the first member; and irradiating a portion of the first member opposite to the recess with laser light to melt the first member and fusion-join it with the portion surrounding the recess.

7. The method for manufacturing a cooling device according to claim 6, wherein, when irradiating the portion of the first member facing the recess with laser light, the second member and the first member are arranged in a superimposed state such that the opening of the recess faces in the opposite direction to the direction of gravity, and laser light is irradiated in the direction of gravity toward the portion of the first member facing the recess.

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