Joined body and cooling device

Abstract

In this joined body, a mixed molten part in which a molten part of a plate-like aluminum material and a molten part of a plate-like copper material are mixed is formed by irradiating the aluminum material with a laser beam in a state where the aluminum material and the copper material are overlapped with each other, and Vickers hardness of the mixed molten part at the interface between the aluminum material and the copper material is 55-150 HV.

Description

Bonded body and cooling device

[0001] The present invention relates to a bonded body and a cooling device.

[0002] Patent Document 1 discloses a dissimilar metal bonded body in which a copper material and an aluminum material are in contact with each other. This metal bonded body has a molten mixed portion formed by melting a part of the aluminum material and flowing it into the copper material.

[0003] Japanese Patent Publication No. 5982652

[0004] In a bonded body of an aluminum material and a copper material, if copper is mixed too much with respect to aluminum in a mixed molten portion where the molten portion of the aluminum material and the molten portion of the copper material are mixed, a large amount of intermetallic compounds may be generated. And in a bonded body of an aluminum material and a copper material, cracks occur due to this intermetallic compound, leading to a decrease in airtightness. The object of the present invention is to improve the airtightness of a bonded body of an aluminum material and a copper material.

[0005] The present invention provides inventions relating to (1) to (6) below. (1) A jointed body (heat dissipation part 2) in which a plate-shaped aluminum material (holding member 15, inner circumference 18) and a plate-shaped copper material (heat sink 10, thin plate part 13) are superimposed and a laser beam is irradiated onto the aluminum material, thereby forming a mixed molten part (joint part 40) in which the molten part of the aluminum material and the molten part of the copper material are mixed, wherein the Vickers hardness of the mixed molten part at the interface (interface 49) between the aluminum material and the copper material is 55 HV or more and 150 HV or less. (2) The jointed body according to (1), wherein the depth from the interface to the bottom (bottom part 45) of the mixed molten part (joint depth D) is 150 μm or more and 500 μm or less, and the Vickers hardness of the mixed molten part at the bottom is 89 HV or more and 330 HV or less. (3) The joint according to (2), wherein the copper material has a recess (recess 135) recessed from the interface, the mixed molten portion is formed by mixing the molten portion of the aluminum material that has melted and entered the recess from the portion of the aluminum material facing the recess, and the molten portion of the copper material that has melted from the portion of the copper material surrounding the recess, and the depth (depth h) of the recess is 150 μm or more and 350 μm or less. (4) The joint according to (1), wherein the depth (joint depth D) from the interface to the bottom (bottom 45) of the mixed molten portion is 0 μm or more and 150 μm or less, and the Vickers hardness of the mixed molten portion at the bottom is 55 HV or more and 150 HV or less. (5) The joint according to (4), wherein when the width of the mixed molten portion at the interface is L and the depth from the interface to the bottom of the mixed molten portion is D, D / L is 0.05 or more and 0.3 or less.(6) A cooling device comprising: a heat sink (heat sink 10) made of copper material having a plurality of fins (fins 12) and a holding member (holding member 15) made of aluminum material that holds the heat sink, and a heat dissipation section (heat dissipation section 2) in which a mixed molten section (joint section 40) is formed by irradiating the holding member with laser light while the molten section of the aluminum material and the molten section of the copper material are superimposed on each other; and a main body section (main body section 3) which houses the fins of the heat sink and has a space (circulation space 35) through which a coolant flows, wherein the Vickers hardness of the mixed molten section at the interface between the aluminum material and the copper material is 55 HV or more and 150 HV or less.

[0006] According to the present invention, the airtightness of the joint between the aluminum material and the copper material can be improved.

[0007] This is an example of a diagram showing the components of a cooling device to which this embodiment is applied in an exploded view. This is a diagram showing an example of a cross-section of the cooling device, specifically a diagram showing an example of a cross-section obtained by cutting the cooling device along the z-direction and the x-direction. This is a diagram showing an example of a cross-section of the cooling device, specifically a diagram showing an example of a cross-section obtained by cutting the cooling device along the z-direction and the y-direction. This is a perspective view showing an example of the configuration of a heat dissipation section to which this embodiment is applied. This is a view of the heat dissipation section from the -z-direction side, which will be described later. This is a cross-sectional view of the VI-VI section in Figure 5. (a) to (b) are diagrams for explaining the method of joining the thin plate portion of the heat sink and the inner circumference portion of the holding member, and are cross-sectional views of the thin plate portion and the inner circumference portion in an overlapping state. This is a diagram for explaining the joint formed between the thin plate portion of the heat sink and the inner circumference portion of the holding member. This is a diagram for explaining the joint formed between the thin plate portion of the heat sink and the inner circumference portion of the holding member. This is a diagram showing the correlation between the ratio of copper in a joint formed by mixing molten aluminum material and molten copper material, and the Vickers hardness of the joint. This is an enlarged view of the joint of the first embodiment shown in Figure 8. This figure shows an example of a joint used in the embodiment.

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. Figure 1 is an example of an exploded view of the components constituting the cooling device 1 to which this embodiment is applied. Figure 2 is a diagram showing an example of a cross-section of the cooling device 1, and is a diagram showing an example of a cross-section obtained by cutting the cooling device 1 along the z-direction and x-direction, which will be described later. Figure 3 is a diagram showing an example of a cross-section of the cooling device 1, and is a diagram showing an example of a cross-section obtained by cutting the cooling device 1 along the z-direction and y-direction, which will be described later. The cooling device 1 according to this embodiment comprises a heat dissipation section 2 having a heat sink 10, and a main body section 3 that houses the heat sink 10 and forms a space through which a coolant flows. The cooling device 1 also comprises bolts 4 that join the heat dissipation section 2 and the main body section 3. The cooling device 1 of this embodiment is a liquid-cooled cooling device that cools a semiconductor module 5, which is an example of a heat-generating element, using a coolant flowing through the main body section 3 and the heat sink 10 of the heat dissipation section 2.

[0009] The main body 3 comprises a case body 21 with a bottomed recess. The main body 3 also includes an O-ring 23 that seals the space between the case body 21 and the retaining member 15 of the heat dissipation section 2, which will be described later. The main body 3 also includes an inlet pipe 25 for introducing coolant into the space inside the case body 21 and an outlet pipe 26 for releasing coolant from the space inside the case body 21. Examples of materials for the case body 21 in this embodiment include A6000 series aluminum alloy such as A6063, die-cast aluminum alloy such as ADC12, and copper.

[0010] The case body 21 has a flat rectangular bottom 31 and four side walls 32 that protrude from the periphery of the bottom 31 in a direction perpendicular to the surface of the bottom 31. A first through hole 323 is formed in the first side wall 321 of the four side walls 32, penetrating the first side wall 321. A second through hole 324 is formed in the second side wall 322, which is opposite to the first side wall 321, penetrating the second side wall 322. An inlet pipe 25 is fitted into the first through hole 323, and an outlet pipe 26 is fitted into the second through hole 324. In addition, grooves 325 are provided on the end faces of the four side walls 32 on the heat dissipation section 2 side, around the opening of the case body 21, into which O-rings 23 are fitted. Furthermore, on the end faces of the four side walls 32 on the heat dissipation section 2 side, female threads 326 are formed at each of the four outer corners of the groove 325, into which bolts 4 are tightened.

[0011] Figure 4 is a perspective view showing an example of the configuration of the heat dissipation section 2 to which this embodiment is applied. Figure 5 is a view of the heat dissipation section 2 from the -z direction, which will be described later. Figure 6 is a cross-sectional view of the VI-VI section in Figure 5. The heat dissipation section 2 comprises a heat sink 10 and a holding member 15 that holds the heat sink 10. The heat dissipation section 2 also has a joint 40 that joins the heat sink 10 and the holding member 15. The heat dissipation section 2 is an example of a joined body.

[0012] The heat sink 10 is made of copper. Examples of copper materials include copper or copper alloys, and it is preferable to use high-purity copper. More specifically, examples of copper materials include C1020, C1100, etc. The copper material may or may not have a plating on its surface. By making the heat sink 10 out of copper, for example, compared to when the heat sink 10 is made of a metal material other than copper, it becomes easier to dissipate heat from the semiconductor module 5 into the coolant, and the cooling efficiency of the cooling device 1 is improved.

[0013] The heat sink 10 has a flat base portion 11, a plurality of fins 12 protruding from the base portion 11 in a direction perpendicular to the plate surface, and a thin plate portion 13 provided on the outer circumference of the base portion 11 that is thinner than the base portion 11. The base portion 11 has a rectangular shape. The base portion 11 has a surface 111 from which the plurality of fins 12 protrude, and a back surface 112 on which the semiconductor module 5 is mounted. The base portion 11 also has a side surface 113 that connects the outer circumference of the surface 111 and the back surface 112. Hereinafter, the direction in which the fins 12 protrude from the surface 111 of the base portion 11 will be referred to as the z direction. The short side of the rectangular base portion 11 will be referred to as the x direction, and the long side of the base portion 11 will be referred to as the y direction.

[0014] Each fin 12 is a flat plate-shaped member. Multiple fins 12 extend in the x-direction on the surface 111 of the base 11 and are arranged side by side in the y-direction with gaps in between. In this example, each fin 12 is provided in the x-direction from the inlet pipe 25 to the outlet pipe 26, in other words, parallel to the flow direction of the coolant in the flow space 35, which will be described later.

[0015] The thin plate portion 13 has a thin plate shape. The thin plate portion 13 is provided so as to protrude outward from the side surface 113 of the base portion 11. The thin plate portion 13 is recessed in the z direction compared to the back surface 112 of the base portion 11, and as a result, it is thinner than the base portion 11. In this embodiment, the thin plate portion 13 of the heat sink 10 is an example of a plate-shaped copper material.

[0016] The thickness of the thin plate portion 13 can be exemplified by a range of 1,000 μm to 3,000 μm. If the thickness of the thin plate portion 13 exceeds 3,000 μm, the entire heat sink 10 becomes thicker, and the weight of the heat sink 10 tends to increase. If the thickness of the thin plate portion 13 is less than 1,000 μm, the joint portion 40 may penetrate the thin plate portion 13, resulting in insufficient joint strength between the heat sink 10 and the holding member 15. Furthermore, the width of the thin plate portion 13, in other words, the length from the side surface 113 of the base portion 11 to the outer edge 131 of the thin plate portion 13, can be exemplified by a range of 2,000 μm to 5,000 μm.

[0017] The retaining member 15 is made of aluminum. Examples of aluminum materials include aluminum or aluminum alloys, and it is preferable to use high-purity aluminum. More specifically, examples of aluminum materials include A1100, A1050, etc. The retaining member 15 is a member that holds the heat sink 10, and a rectangular opening 16 into which the heat sink 10 is inserted is formed in the center. The retaining member 15 has a flat outer peripheral portion 17 located on the outer periphery of the retaining member 15 and attached to the side wall 32 of the case body 21. The retaining member 15 also has a thin, plate-like inner peripheral portion 18 that surrounds the opening 16 and is thinner in thickness than the outer peripheral portion 17.

[0018] The outer periphery 17 has a rectangular outer surface 171 and an inner surface 172, and as a whole has a frame-like shape. The outer periphery 17 has a surface 173 facing the side wall 32 of the case body 21, and a back surface 174 located on the opposite side of the surface 173. In addition, holes 175 for passing bolts 4 are formed at each of the four corners of the outer periphery 17.

[0019] The inner circumference 18 is provided so as to protrude from the inner edge of the outer circumference 17 into the opening 16. The inner circumference 18 is recessed in the -z direction compared to the surface 173 of the outer circumference 17, and is thinner than the outer circumference 17. In this embodiment, the inner circumference 18 of the holding member 15 is an example of a plate-shaped aluminum material. The inner circumference 18 is superimposed on the thin plate portion 13 of the heat sink 10 in the -z direction. In addition, the inner circumference 18 is in contact with the thin plate portion 13 of the heat sink 10, and the inner circumference 18 and the thin plate portion 13 are facing each other. Hereinafter, the xy plane corresponding to the boundary between the inner circumference 18 and the thin plate portion 13 in the heat dissipation portion 2, i.e., the position where the inner circumference 18 and the thin plate portion 13 face each other, will be referred to as the boundary surface 49.

[0020] The thickness of the inner circumference 18 can be exemplified by a range of, for example, 1000 μm to 2000 μm. If the thickness of the inner circumference 18 exceeds 2000 μm, a large amount of energy is required when irradiating with laser light to form the joint 40. In addition, it may become difficult to make the joint depth D of the joint 40 (see Figure 8, described later) the desired size. Furthermore, if the thickness of the inner circumference 18 is less than 1000 μm, the molten aluminum material constituting the inner circumference 18 is more likely to mix with the molten copper material constituting the thin plate portion 13 in the joint 40, and a large amount of intermetallic compounds between aluminum and copper are likely to be generated. As a result, the joint strength between the heat sink 10 and the holding member 15 may be insufficient. In this example, the width of the inner circumference 18 is equal to the width of the thin plate portion 13 of the heat sink 10. As a result, when the inner circumference portion 18 and the thin plate portion 13 of the heat sink 10 are superimposed, the inner edge 181 of the inner circumference portion 18 faces the side surface 113 of the base portion 11 of the heat sink 10. Also, the outer edge 131 of the thin plate portion 13 faces the inner surface 172 of the outer circumference portion 17.

[0021] The heat sink 10 and the retaining member 15 are joined by a joint 40 formed by irradiating the inner circumference 18 side with laser light while the thin plate portion 13 of the heat sink 10 and the inner circumference 18 of the retaining member 15 are superimposed. The joint 40 is formed by mixing the molten aluminum material constituting the inner circumference 18 with the molten copper material constituting the thin plate portion 13, which is melted by the irradiation of laser light. The structure of the joint 40 and the method of joining the heat sink 10 and the retaining member 15 by the joint 40 will be described in detail later.

[0022] The cooling device 1 and semiconductor module 5, configured as described above, are assembled as follows. First, the heat sink 10 of the heat dissipation unit 2 and the semiconductor module 5 are brazed together. More specifically, the semiconductor module 5 is brazed to the back surface 112 of the base 11 of the heat sink 10. Then, the heat dissipation unit 2 is placed over the case body 21 so that the semiconductor module 5 is located externally and the fins 12 of the heat sink 10 are housed inside the main body 3, and the opening of the case body 21 is covered with the heat dissipation unit 2. When placing the heat dissipation unit 2 over the case body 21, an O-ring 23 is fitted into a groove 325 formed in the case body 21. After placing the heat dissipation unit 2 over the case body 21, a bolt 4 passed through a hole 175 formed in the holding member 15 of the heat dissipation unit 2 is tightened into a female thread 326 formed in the case body 21. This creates a circulation space 35 through which the coolant flows in the space enclosed between the heat sink 10 of the heat dissipation unit 2 and the case body 21 of the main body 3. In this example, the direction of coolant flow through the circulation space 35 is parallel to the x-direction, which is the direction in which the fins 12 of the heat sink 10 extend. The circulation space 35 is sealed by the O-ring 23.

[0023] Next, a method for joining the heat sink 10 and the holding member 15 will be described. Figures 7(a) to 7(b) are diagrams illustrating the method of joining the thin plate portion 13 of the heat sink 10 and the inner circumference portion 18 of the holding member 15, and are cross-sectional views of the thin plate portion 13 and the inner circumference portion 18 in an overlapping state. Figures 8 and 9 are diagrams illustrating the joint portion 40 formed between the thin plate portion 13 of the heat sink 10 and the inner circumference portion 18 of the holding member 15. The cutting direction of the thin plate portion 13 and the inner circumference portion 18 in Figures 7(a) to 7(b), 8 and 9 is the same as in Figure 6. In addition, Figures 7(a) to 7(b), 8 and 9 are cross-sectional views in a plane perpendicular to the direction of movement of the laser head when irradiating with laser light. Hereinafter, the cross-section of the thin plate portion 13, the inner circumference portion 18 and the joint portion 40 in a plane perpendicular to the direction of movement of the laser head when irradiating with laser light may simply be referred to as a cross-section.

[0024] In this embodiment, when forming the joint 40 by irradiating it with laser light, a first embodiment can be adopted in which a heat sink 10 having a recess 135 formed in the thin plate portion 13 is used, and a second embodiment can be adopted in which a heat sink 10 having a recess 135 not formed in the thin plate portion 13 is used. Figure 7(a) shows the method of joining the heat sink 10 and the holding member 15 in the first embodiment, and Figure 8 shows the joint 40 formed in the first embodiment. Figure 7(b) shows the method of joining the heat sink 10 and the holding member 15 in the second embodiment, and Figure 9 shows the joint 40 formed in the second embodiment.

[0025] As shown in Figure 7(a), the heat sink 10 used in the first embodiment has a recess 135 recessed in the z direction on the surface of the thin plate portion 13 facing the inner circumference 18 of the holding member 15. The recess 135 is formed continuously in the circumferential direction in the thin plate portion 13 provided along the outer circumference of the heat sink 10. In this embodiment, the cross-sectional shape of the recess 135 is rectangular. The width w and depth h of the recess 135 are determined so that the joint width L and joint depth D of the joint portion 40, which will be described later, are within a desired range. The width w of the recess 135 can be exemplified as being in the range of 350 μm to 650 μm. The depth h of the recess 135 can be exemplified as being in the range of 150 μm to 350 μm, and is preferably 250 μm. Note that the cross-sectional shape of the recess 135 is not limited to a rectangular shape.

[0026] On the other hand, the heat sink 10 used in the second embodiment does not have a recess 135 (see Figure 7(a)) formed in the thin plate portion 13, as shown in Figure 7(b). In addition, in the heat sink 10 used in the second embodiment, the surface of the thin plate portion 13 facing the inner circumference 18 of the holding member 15 is flat.

[0027] When joining the heat sink 10 and the retaining member 15, first, the thin plate portion 13 of the heat sink 10 and the inner circumference portion 18 of the retaining member 15 are overlapped. More specifically, the thin plate portion 13 and the inner circumference portion 18 are overlapped so that the -z-direction side surface of the thin plate portion 13 and the z-direction side surface of the inner circumference portion 18 are in contact. The area where the thin plate portion 13 and the inner circumference portion 18 are in contact becomes the interface surface 49, which is the boundary between the copper material constituting the thin plate portion 13 and the aluminum material constituting the inner circumference portion 18. In the first embodiment, by overlapping the thin plate portion 13 and the inner circumference portion 18, the recess 135 formed in the thin plate portion 13 is recessed from the interface surface 49.

[0028] Then, laser light P is irradiated in the z direction from the inner circumference 18 side to the region where the thin plate portion 13 of the heat sink 10 and the inner circumference 18 of the holding member 15 overlap. More specifically, the laser light P is irradiated while moving the laser head (not shown) of the laser device (not shown) in the circumferential direction along the inner circumference 18 which is formed to surround the opening 16 of the holding member 15. In addition, in the first embodiment using a heat sink 10 in which a recess 135 is formed in the thin plate portion 13, the laser light P is irradiated in the circumferential direction along the portion in which the recess 135 is formed. The laser source used when irradiating with laser light P is not particularly limited. The laser source may be a solid-state laser such as a YAG laser, CO2, etc. ２ Examples include gas lasers such as lasers, fiber lasers using optical fibers as the medium, semiconductor lasers using semiconductors as the medium, and disk lasers.

[0029] When the laser beam P is irradiated, the energy of the laser beam P is converted into heat, causing the copper material constituting the thin plate portion 13 of the heat sink 10 and the aluminum material constituting the inner circumference portion 18 of the holding member 15 to melt. The molten copper material constituting the thin plate portion 13 and the molten aluminum material constituting the inner circumference portion 18 then mix and are rapidly cooled to form the joint portion 40. The joint portion 40 is an example of a mixed molten portion formed by mixing the molten aluminum material and the molten copper material.

[0030] In the first embodiment, which uses a heat sink 10 with a recess 135 formed in the thin plate portion 13, the portion of the aluminum material constituting the inner circumference 18 that faces the recess 135 in the thin plate portion 13 melts and enters the recess 135. The molten portion of the aluminum material that has entered the recess 135 and the molten portion of the copper material that has melted in the area surrounding the recess 135 in the thin plate portion 13 mix together to form a joint 40. On the other hand, in the second embodiment, which uses a heat sink 10 without a recess 135 formed in the thin plate portion 13, the molten portion of the aluminum material that has melted in the area near the interface 49 in the inner circumference 18 mixes with the molten portion of the copper material that has melted in the area near the interface 49 in the thin plate portion 13. This forms a joint 40.

[0031] Next, the structure of the joint 40 will be described in detail. As mentioned above, the joint 40 is formed by mixing the molten aluminum material and the molten copper material. In such a joint 40, if the ratio of copper to aluminum is too high, brittle intermetallic compounds may be formed. When a large amount of intermetallic compounds are formed in the joint 40, cracks may occur in the joint 40 due to the intermetallic compounds, which can lead to a decrease in the airtightness of the joint 40. For example, if the ratio of copper at the interface 49 of the joint 40 exceeds 10 wt%, intermetallic compounds are more likely to form in the joint 40, and a decrease in the airtightness of the joint 40 is more likely to occur. On the other hand, if the ratio of copper at the interface 49 of the joint 40 is less than 1.4 wt%, the mixing of the molten aluminum material and the molten copper material will be insufficient, the joint strength of the joint 40 will be low, and some parts of the thin plate portion 13 and the inner circumference portion 18 may not be joined. In this case as well, a decrease in airtightness at the joint 40 is likely to occur.

[0032] Figure 10 shows the correlation between the ratio of copper in a joint 40 formed by mixing molten aluminum and molten copper, and the Vickers hardness of the joint 40. In Figure 10, the horizontal axis represents the ratio of copper (wt%) in the joint 40, and the vertical axis represents the Vickers hardness (HV) of the joint 40. As shown in Figure 10, the Vickers hardness of the joint 40 formed by mixing molten aluminum and molten copper tends to increase as the ratio of copper increases. In this embodiment, by utilizing the correlation between the ratio of copper in the joint 40 and the Vickers hardness, the Vickers hardness of the joint 40 is set within a predetermined range, thereby suppressing a decrease in airtightness in the joint 40.

[0033] The joint 40 of the first embodiment will now be described. Figure 11 is an enlarged view of the joint 40 of the first embodiment shown in Figure 8. The joint 40 of the first embodiment has a Vickers hardness of 55 HV or more and 150 HV or less at the interface 49. Here, the Vickers hardness at the interface 49 of the joint 40 can be obtained using the cross-section of the joint 40 as follows. First, the center of the joint 40 at the interface 49 is taken as point M1. Also, at the interface 49, points M2 and M3 are taken at positions 100 μm inward from both ends of the joint 40, respectively. Then, the Vickers hardness is measured for each of points M1, M2, and M3, and the average value is taken as the Vickers hardness of the joint 40 at the interface 49. The measurement conditions for Vickers hardness will be described in detail in the later examples.

[0034] In the first embodiment, by having a Vickers hardness of 55 HV or more and 150 HV or less at the interface surface 49 of the joint 40, the ratio of copper at the interface surface 49 can be set to a range in which intermetallic compounds are less likely to form at the joint 40. This suppresses a decrease in airtightness at the joint 40. In addition, it is suppressed that liquid moves from one side to the other of the joint 40 along the interface surface 49 between the thin plate portion 13 and the inner circumference portion 18. More specifically, when the heat dissipation portion 2 (see Figure 2) is applied to the cooling device 1 (see Figure 2), leakage of the coolant from the flow space 35 (see Figure 2) to the outside of the cooling device 1 is suppressed.

[0035] Furthermore, in the first embodiment, the joint portion 40 preferably has a joint depth D, which is the depth from the interface surface 49 to the bottom portion 45 of the joint portion 40, of 150 μm or more and 500 μm or less, and a Vickers hardness of 89 HV or more and 330 HV or less at the bottom portion 45. Here, the bottom portion 45 is the intersection point of a straight line A parallel to the z direction that passes through point M1, which is the center of the joint portion 40 at the interface surface 49, and the outer edge of the joint portion 40.

[0036] Furthermore, the Vickers hardness at the bottom 45 can be obtained using the cross-section of the joint 40 as follows. First, if the length of the diagonal of the indentation formed by pressing a diamond indenter into the joint 40 is taken as d, then point N1 is defined as a position 3d away from the bottom 45 in the -z direction. Also, on the plane where the position of point N1 is equal to the z direction, points N2 and N3 are defined as positions 100 μm inward from both ends of the joint 40. Then, the Vickers hardness is measured for each of points N1, N2, and N3, and the average value is taken as the Vickers hardness of the joint 40 at the bottom 45.

[0037] In the joint 40 of the first embodiment, when the joint depth D is 150 μm or more and 500 μm or less, the copper ratio tends to be higher at the bottom 45 compared to the interface 49. When the joint depth D is 150 μm or more and 500 μm or less, in order to suppress the decrease in airtightness at the joint 40, it is preferable that the copper ratio at the bottom 45 be 4.3 wt% or more and 27 wt% or less. In the first embodiment, by having a Vickers hardness of 89 HV or more and 330 HV or less at the bottom 45, the copper ratio at the bottom 45 can be set to a range that suppresses the area where intermetallic compounds are generated to the vicinity of the bottom 45 and reduces the amount of intermetallic compounds. This suppresses the decrease in airtightness at the joint 40.

[0038] Next, the joint 40 of the second embodiment will be described. In the joint 40 of the second embodiment, the Vickers hardness at the interface 49 is 55 HV or more and 150 HV or less, similar to the first embodiment. The method for measuring the Vickers hardness at the interface 49 is the same as for the joint 40 of the first embodiment. In the second embodiment, by having a Vickers hardness of 55 HV or more and 150 HV or less at the interface 49 of the joint 40, the ratio of copper at the interface 49 can be set to a range in which intermetallic compounds are less likely to be generated in the joint 40. This suppresses a decrease in airtightness at the joint 40.

[0039] Furthermore, in the second embodiment, the joint portion 40 preferably has a joint depth D, which is the depth from the interface 49 to the bottom 45 of the joint portion 40, of 0 μm or more and 150 μm or less, and a Vickers hardness of 55 HV or more and 150 HV or less. The method for measuring the Vickers hardness of the bottom 45 is the same as for the joint portion 40 in the first embodiment. Note that when the joint depth D is 0 μm, the bottom 45 coincides with the interface 49, so the Vickers hardness of the bottom 45 is equal to the Vickers hardness of the interface 49. The Vickers hardness of the interface 49 of the joint portion 40, the Vickers hardness of the bottom 45 of the joint portion 40, and the definition of the bottom 45 are the same as in the first embodiment.

[0040] In the second embodiment, since no recess 135 (see Figure 7(a)) is formed in the thin plate portion 13, the bonding depth D of the joint portion 40 formed by irradiation with laser light P tends to be smaller than in the first embodiment. When the bonding depth D is small, the distance between the interface 49 and the bottom portion 45 is close, so it is preferable that the Vickers hardness at the bottom portion 45 of the joint portion 40 is about the same as the Vickers hardness at the interface 49. In the second embodiment, by having the Vickers hardness at the bottom portion 45 of the joint portion 40 be between 55 HV and 150 HV, the ratio of copper at the bottom portion 45 can be set to a range in which intermetallic compounds are less likely to be generated in the joint portion 40. This suppresses a decrease in airtightness at the joint portion 40.

[0041] Furthermore, in the second embodiment, when the width of the joint portion 40 at the interface surface 49 is defined as the joint width L, it is preferable that the ratio of the joint depth D to the joint width L (D / L) is 0.05 or more and 0.3 or less. In the second embodiment, by having a ratio of the joint depth D to the joint width L (D / L) of the joint portion 40 of 0.05 or more and 0.3 or less, a decrease in airtightness at the joint portion 40 is suppressed.

[0042] In this embodiment, the Vickers hardness at the interface 49 of the joint 40 and the Vickers hardness at the bottom 45 can be set to the above-described range by changing the conditions under which the laser beam P is irradiated when joining the heat sink 10 and the retaining member 15. Examples of conditions under which the laser beam P is irradiated include the intensity of the laser beam P, the speed at which the laser head is moved, and the temperature of the heat sink 10 and the retaining member 15. Alternatively, the Vickers hardness at the interface 49 of the joint 40 and the Vickers hardness at the bottom 45 can be adjusted by changing the thickness of the inner circumference 18 of the retaining member 15, which is an example of an aluminum material. Furthermore, in the first embodiment, the Vickers hardness at the interface 49 of the joint 40 and the Vickers hardness at the bottom 45 can be adjusted by changing the width w, depth h, cross-sectional shape, etc., of the recess 135 formed in the thin plate portion 13 of the heat sink 10.

[0043] Next, the present invention will be described in more detail using examples. However, the present invention is not limited to the following examples. Figure 12 shows an example of a joint used in the examples. (Preparation of test pieces) As a plate-shaped aluminum material, an aluminum plate 210 made of A1100 with dimensions of 30 mm × 70 mm and a thickness of 1.0 mm or 2.0 mm was used. As a plate-shaped copper material, a copper plate 220 made of C1020 with dimensions of 30 mm × 70 mm and a thickness of 1.5 mm was used, with a hole 225 with a diameter of 6 mm formed in the center. As for the copper plate 220, a first embodiment was prepared in which a recess 135 (see Figure 7(a)) with a width w of 500 μm and a depth h of 250 μm was formed in the circumferential direction, and a second embodiment was prepared in which the recess 135 was not formed.

[0044] Then, the aluminum plate 210 and the copper plate 220 were overlapped, and laser light was irradiated while moving the laser head in the circumferential direction from the aluminum plate 210 side to form the joint portion 40. As a result, a joined body in which the aluminum plate 210 and the copper plate 220 were joined by the joint portion 40 was obtained. More specifically, for each of the cases where the copper plate 220 of the first aspect and the copper plate 220 of the second aspect were used, the conditions for irradiating the laser light were made different to form the joint portion 40, and a plurality of joined bodies were obtained. In each of the obtained joined bodies, the circumferential length of the joint portion 40 was 200 mm in total.

[0045] (Method for evaluating airtightness) For the hole 225 of the copper plate 220 of the obtained joined body, helium gas was flowed so that the pressure became 0.2 MPa, and it was confirmed whether helium gas leaked from the joint portion 40, between the aluminum plate 210 and the copper plate 220, etc. The evaluation of the joined body in which no helium gas leakage occurred was regarded as good, and the evaluation of the joined body in which helium gas leakage occurred was regarded as bad.

[0046] (Measurement of Vickers hardness) For the joined body for which the airtightness was evaluated, the Vickers hardness of the joint portion 40 was measured by the following method. First, the joined body was cut along a plane perpendicular to the moving direction of the laser head when the laser light was irradiated, and the cross section of the joint portion 40 was exposed to obtain a test piece. Then, for the joint portion 40 of each test piece, the Vickers hardness at the points M1, M2, M3 (see FIG. 11) described above was measured, and the average value was taken as the Vickers hardness at the interface 49 (see FIG. 11) of the joint portion 40. Also, for the joint portion 40 of each test piece, the Vickers hardness at the points N1, N2, N3 (see FIG. 11) described above was measured, and the average value was taken as the Vickers hardness at the bottom 45 of the joint portion 40. The measurement of the Vickers hardness was carried out in accordance with the method described in JIS Z2244. The test force was 0.01 N, and the holding time of the test force was 10 seconds.

[0047] (Evaluation Results) For the bonded bodies with good airtightness evaluation, in both the first and second aspects, the Vickers hardness at the boundary surface 49 of the joint portion 40 was 55 HV or more and 150 HV or less. As a result, it was confirmed that by having the Vickers hardness at the boundary surface 49 of the joint portion 40 be 55 HV or more and 150 HV or less, the decrease in airtightness at the joint portion 40 can be suppressed.

[0048] Also, among the bonded bodies with good airtightness evaluation, for the bonded body of the first aspect, the bonding depth D of the joint portion 40 was 150 μm or more and 500 μm or less, and the Vickers hardness at the bottom 45 of the joint portion 40 was 89 HV or more and 330 HV or less. As a result, in the first aspect, it was confirmed that when the bonding depth D of the joint portion 40 is 150 μm or more and 500 μm or less, and the Vickers hardness at the bottom 45 is 89 HV or more and 330 HV or less, the decrease in airtightness at the joint portion 40 can be suppressed.

[0049] Further, among the bonded bodies with good airtightness evaluation, for the bonded body of the second aspect, the bonding depth D of the joint portion 40 was 0 μm or more and 150 μm or less, and the Vickers hardness at the bottom 45 of the joint portion 40 was 55 HV or more and 150 HV or less. As a result, in the second aspect, it was confirmed that when the bonding depth D of the joint portion 40 is 0 μm or more and 150 μm or less, and the Vickers hardness at the bottom 45 is 55 HV or more and 150 HV or less, the decrease in airtightness at the joint portion 40 can be suppressed. Furthermore, for the bonded body of this second aspect, the ratio (D / L) of the bonding depth D to the bonding width L of the joint portion 40 was 0.05 or more and 0.3 or less.

[0050] As described above, the embodiments and examples of the present invention have been explained, but the present invention is not limited to the above-described embodiments and examples. Various modifications and combinations may be made as long as they do not go against the spirit of the present invention.

[0051] 1... Cooling device, 2... Heat dissipation part, 3... Main body part, 10... Heat sink, 11... Base part, 12... Fins, 13... Thin plate part, 15... Holding member, 16... Opening, 17... Outer peripheral part, 18... Inner peripheral part, 40... Joint portion, 45... Bottom, 49... Boundary surface

Claims

1. A joint in which a plate-shaped aluminum material and a plate-shaped copper material are stacked on top of each other, and a laser beam is irradiated onto the aluminum material, thereby forming a mixed molten portion where the molten portion of the aluminum material and the molten portion of the copper material are mixed, wherein the Vickers hardness of the mixed molten portion at the interface between the aluminum material and the copper material is 55 HV or more and 150 HV or less.

2. The joint according to claim 1, wherein the depth from the interface to the bottom of the mixed molten portion is 150 μm or more and 500 μm or less, and the Vickers hardness of the mixed molten portion at the bottom is 89 HV or more and 330 HV or less.

3. The copper material has a recess that is recessed from the interface, the mixed molten portion is formed by mixing the molten portion of the aluminum material that has melted and entered the recess, and the molten portion of the copper material that has melted around the recess, and the depth of the recess is 150 μm or more and 350 μm or less, the joined body according to claim 2.

4. The joint according to claim 1, wherein the depth from the interface to the bottom of the mixed molten portion is 0 μm or more and 150 μm or less, and the Vickers hardness of the mixed molten portion at the bottom is 55 HV or more and 150 HV or less.

5. The joint according to claim 4, wherein when L is the width of the mixed molten portion at the interface and D is the depth from the interface to the bottom of the mixed molten portion, D / L is 0.05 or more and 0.3 or less.

6. A cooling device comprising: a heat dissipation section in which a heat sink made of copper material having a plurality of fins and a holding member made of aluminum material that holds the heat sink are superimposed, and a laser beam is irradiated onto the holding member to form a mixed molten portion in which the molten portion of the aluminum material and the molten portion of the copper material are mixed; and a main body section that houses the fins of the heat sink and has a space formed inside through which a coolant flows, wherein the Vickers hardness of the mixed molten portion at the interface between the aluminum material and the copper material is 55 HV or more and 150 HV or less.

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