Welding methods, structures

Abstract

To provide a welding method or the like capable of enhancing beauty of appearance and quality in a weld zone.SOLUTION: There is provided a welding method for radiating a laser beam on overlapping parts of at least either two members among two platy members having a thickness of 2 mm or less and those having materials different from each other to join. The method includes joining two members by radiating a defocused laser beam to one member among two and transmitting the heat of one member to the other one out of the two members to fuse the other member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a welding method and a structure. [Background technology]

[0002] Conventionally, techniques have been proposed for suppressing defects and stabilizing welding quality in direct laser welding of aluminum materials. For example, Patent Document 1 describes a technology for a laser-welded structure formed by overlapping and welding two sheets of aluminum material, in which the aluminum material is aluminum or an aluminum alloy having an electroless Ni-P plating film applied to at least the laser irradiated surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-94382 A Summary of the Invention [Problem to be solved by the invention]

[0004] When performing laser welding, it is desirable to take into consideration the improvement of the appearance of the welded portion and the improvement of quality such as the reduction of defects. An object of the present invention is to provide a welding method and the like that can improve the beauty and quality of the appearance of a welded portion. [Means for solving the problem]

[0005] The present invention, which was completed with this object in mind, is a welding method for joining at least two flat plate-like members each having a thickness of 2 mm or less, or two members made of different materials, by irradiating the overlapping portion of the two members with a laser beam, in which the laser beam is defocused and irradiated onto one of the two members, and the heat of the one member is conducted to the other of the two members, thereby melting the other member and joining the one member to the other member. Here, it is preferable that the two members are made of different materials, and that the melting point of the other member is lower than the melting point of the one member. In addition, the two components may be made of different materials, the melting point of the other component may be higher than the melting point of the one component, and an intermediate component made of a material with a melting point lower than the melting point of the one component may be disposed between the one component and the other component. In addition, the two members may be made of different materials, the melting point of the other member may be higher than the melting point of the one member, and the surface of the other member facing the one member may be plated. From another viewpoint, the present invention is a welding method for joining two members made of different materials by irradiating a laser beam to a butt joint between the two members, in which the laser beam is defocused and irradiated to the butt joint, thereby melting the member having a lower melting point of the two members, and joining the two members. From another viewpoint, the present invention is a welding method for joining two members made of different materials by irradiating the butt joint of the two members with laser light, in which an intermediate member having a lower melting point than the two members is interposed between the two members, and the laser light is defocused and irradiated to the two members and the intermediate member to melt the intermediate member and join the two members. From another viewpoint, the present invention is a welding method for joining two members made of different materials by irradiating a laser beam to a butt joint between the two members, comprising plating one of the two members having a higher melting point, defocusing the laser beam and irradiating the two members with the laser beam to melt the plating and join the two members. From another perspective, the present invention is a structure joined by irradiating laser light to the overlapping portion of at least two of the following two flat plate-like members having a thickness of 2 mm or less and two members made of different materials: the laser light is defocused and irradiated to one of the two members, and the heat of the one member is conducted to the other of the two members, thereby melting the other member and joining the one member to the other member. Effect of the Invention

[0006] According to the present invention, it is possible to provide a welding method and the like that can improve the beauty and quality of the appearance of a welded portion. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram showing an example of a welding method according to a first embodiment. [Diagram 2] FIG. 4 is a diagram showing an example of a welding method according to a first comparative example. [Diagram 3] FIG. 4 is a diagram showing an example of a modified example of the welding method according to the first embodiment. [Figure 4] FIG. 11 is a diagram showing an example of an experimental result regarding the relationship between the laser output and offset distance, and whether or not the first member and the second member can be joined. [Diagram 5] FIG. 11 is a diagram showing an example of energy density when the offset distance and the laser output are changed. [Figure 6] FIG. 11 is a diagram showing an example of the relationship between the laser output and the bead width and welding depth. [Figure 7]1A to 1C are diagrams showing an example of a semiconductor module unit manufactured using the welding method according to the first embodiment. [Figure 8] 6A to 6C are diagrams illustrating an example of a welding method according to a second embodiment. [Figure 9] FIG. 11 is a diagram showing an example of a welding method according to a second comparative example. [Figure 10] FIG. 11 is a diagram showing an example of a modified example of the welding method according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing an example of a welding method according to a first embodiment. The welding method of the first embodiment is a method in which a defocused laser light L is irradiated onto a first member 11, which is an example of one of two overlapping members, and the heat of the first member 11 is conducted to the second member 12, thereby melting the second member 12 and joining the first member 11 and the second member 12.

[0009] More specifically, as shown in FIG. 1(a), the first member 11 is placed on the second member 12, and the first member 11 at the portion where the first member 11 and the second member 12 overlap is irradiated with laser light L from a laser head 151 of a laser device 150. When the first member 11 is irradiated with the laser light L, the first member 11 is irradiated with defocused laser light L. When the defocused laser light L is irradiated to the first member 11, the laser light L is absorbed by the surface 111 of the first member 11 and converted into heat, and the heat is transmitted widely and shallowly. In the welding method according to the first embodiment, as shown in FIG. 1(b), the heat converted by absorbing the laser light L is conducted to the second member 12 to melt the second member 12, and a welded portion 20 is formed by the molten portion of the first member 11 and the molten portion of the second member 12, and the first member 11 and the second member 12 are joined. Hereinafter, welding in which the defocused irradiated laser light L is absorbed and converted into heat, which is then conducted to the second member 12 to melt the second member 12 and join the first member 11 and the second member 12, may be referred to as "thermal conduction welding". Although the irradiation area becomes larger by irradiating the defocused laser light L, it is preferable that the irradiation area of ​​the irradiated portion of the first member 11 is 4 to 16 times the irradiation area at the focal position of the laser light L.

[0010] FIG. 2 is a diagram showing an example of a welding method according to a first comparative example. As shown in FIG. 2(a), a method of irradiating the first member 11 with a focused laser beam L at a portion where the first member 11 and the second member 12 overlap is set as a welding method according to a first comparative example. In the welding method according to the first comparative example, the energy density per unit area is higher than that of the welding method according to the first embodiment, even if the laser output P and the moving speed V of the laser head 151 are the same. Then, a depression is formed on the surface of the first member 11 irradiated with the focused laser beam L. Then, as shown in FIG. 2(b), this depression becomes deeper, and a keyhole 25 is formed in the first member 11 and the second member 12. Hereinafter, welding by irradiating the focused laser beam L may be referred to as "keyhole welding".

[0011] According to the welding method of the first embodiment (thermal conduction welding), the formation of irregularities on the surface 111 of the first member 11 to which the laser light L is irradiated is suppressed compared to the welding method of the first comparative example (keyhole welding), thereby improving the beauty of the appearance of the welded portion 20. In addition, in the welding method according to the first comparative example, for example, when the first member 11 is aluminum, the thermal conductivity of aluminum is higher than that of iron, and the light absorptance is lower. This causes welding defects such as scattering of molten metal during irradiation of the laser light L and generation of cavities in the first member 11 and the second member 12 to be joined. In particular, when the first member 11 is a flat member having a thickness of 2 mm or less, the welding method according to the first comparative example makes it easier for the laser light L to penetrate the first member 11 and reach the second member 12, which causes welding defects. In contrast, the welding method according to the first embodiment has a lower energy density per unit area than the welding method according to the first comparative example, so that welding defects are less likely to occur and welding quality can be improved.

[0012] Furthermore, in the case where the first member 11 and the second member 12 are flat members having a thickness of 2 mm or less, in the welding method according to the first comparative example, the keyhole 25 easily penetrates the first member 11 and the second member 12, and unevenness is easily formed on the surface of the second member 12 opposite to the first member 11 (hereinafter, sometimes referred to as the "rear surface"). In contrast, according to the welding method according to the first embodiment, the second member 12 melts more slowly than in the welding method according to the first comparative example, so that even if the thickness of the second member 12 is 2 mm or less, the keyhole 25 is less likely to be formed. Therefore, according to the welding method according to the first embodiment, welding defects are less likely to occur, and the welding quality can be improved. In addition, unevenness is prevented from being formed on the rear surface.

[0013] Furthermore, the welding method according to the first embodiment may be used when the first member 11 and the second member 12 are made of different materials and the melting point of the second member 12 is lower than the melting point of the first member 11. If the melting point of the second member 12 is lower than the melting point of the first member 11, the second member 12 tends to melt even if the second member 12 is melted by conducting heat from the first member 11 to the second member 12. Therefore, the first member 11 and the second member 12 can be easily joined using the welding method according to the first embodiment.

[0014] FIG. 3 is a diagram showing an example of a modified example of the welding method according to the first embodiment. When using thermal conduction welding, if the first member 11 and the second member 12 are made of different materials and the melting point of the second member 12 is higher than the melting point of the first member 11, it is advisable to place an intermediate member 13 made of a material with a melting point lower than that of the first member 11 between the first member 11 and the second member 12, as shown in Figure 3.

[0015] For example, the first member 11 may be made of an aluminum material (melting point is 480°C to 660°C) and the second member 12 may be made of copper (melting point is 1085°C). In this way, when the melting point of the second member 12 is higher than that of the first member 11, the second member 12 is unlikely to melt even if the second member 12 is melted by conducting the heat of the first member 11 to the second member 12. In such a case, by disposing the intermediate member 13 made of a material having a melting point lower than that of the first member 11 between the first member 11 and the second member 12, the heat of the first member 11 can be conducted to the intermediate member 13 to melt the intermediate member 13, and the second member 12 can be melted by the heat. When the first member 11 is made of an aluminum material and the second member 12 is made of copper, the material of the intermediate member 13 may be solder. In addition, it is preferable that the intermediate member 13 contains flux. For example, between the first member 11 and the second member 12, a solder sheet containing flux may be disposed. In this way, by placing an intermediate member 13 between a first member 11 made of aluminum and a second member 12 made of copper and irradiating the first member 11 with defocused laser light L, the first member 11 made of aluminum and the second member 12 made of copper can be joined.

[0016] However, the intermediate member 13 may be disposed between the first member 11 and the second member 12 only when the difference between the melting point of the first member 11 and the melting point of the second member 12 is equal to or greater than a predetermined temperature. The predetermined temperature can be, for example, 300° C. This is because, if the difference between the melting point of the first member 11 and the melting point of the second member 12 is less than 300° C., the second member 12 will be easily melted sufficiently to join the first member 11 and the second member 12, even if the second member 12 is melted by conducting the heat of the first member 11 to the second member 12.

[0017] In addition, when the first member 11 and the second member 12 are made of different materials and the melting point of the second member 12 is higher than that of the first member 11, a member having a plated surface facing the first member 11 may be used as the second member 12 instead of disposing the intermediate member 13. The plating process can be exemplified as a process in which a metal film made of a material having a melting point lower than that of the first member 11 is deposited.

[0018] For example, when the first member 11 is made of an aluminum material and the second member 12 is made of copper, the plating process can be exemplified as zinc plating process. Thereby, the first member 11 made of aluminum and the second member 12 made of copper can be joined by irradiating the first member 11 at the overlapping portion between the first member 11 made of aluminum and the second member 12 made of copper with defocused laser light L.

[0019] Next, the offset distance D (see FIG. 1) of the focal position with respect to the irradiated portion of the first member 11 and the laser output P will be described. FIG. 4 is a diagram showing an example of an experimental result regarding the relationship between the laser output P and the offset distance D and whether or not the first member 11 and the second member 12 can be joined. FIG. 5 is a diagram showing an example of the energy density when the offset distance D and the laser output P are changed. FIG. 6 is a diagram showing an example of the relationship between the laser output P and the bead width B and the weld depth F.

[0020] In the experiment whose results are shown in FIG. 4, the spot diameter at the focal position of the laser light L (see FIG. 1) was fixed at 50 μm, and the moving speed V of the laser head 151 was fixed at 20 mm / s. The laser output P was changed in increments of 200 W between 800 and 2000 W. The offset distance D was also changed in increments of 0.5 mm between 0.5 and 5.0 mm. The material of the plate was aluminum A3003, and the plate had a thickness of 2 mm, and the laser light L was irradiated onto the plate. If the offset distance D is small, keyhole welding is likely to be performed in which a keyhole 25 is formed in the first member 11 and the second member 12. On the other hand, if the offset distance D is large, the melting depth becomes small, and only the surface of the first member 11 melts, and welding at the marking level of approximately drawing a line is likely to be performed. When the moving speed V is the same, whether the offset distance D results in keyhole welding or not depends on the laser output P. Even if the offset distance D is large, if the laser output P is large, keyhole welding is likely to occur.

[0021] As a result, when the laser output P was 2000 (W), keyhole welding occurred when the offset distance D was between 0.5 and 3.0 (mm), and heat conduction welding occurred when the offset distance D was between 4.0 and 5.0 (mm). When the offset distance D was 3.5 (mm), about half of the multiple attempts were heat conduction welding, but some were keyhole welding.

[0022] When the laser output P was 1800 W, keyhole welding occurred when the offset distance D was between 0.5 and 2.5 mm, and heat conduction welding occurred when the offset distance D was between 3.5 and 5.0 mm. When the offset distance D was 3.0 mm, about half of the multiple attempts were heat conduction welding, but some were keyhole welding.

[0023] When the laser output P was 1600 (W), keyhole welding occurred when the offset distance D was between 0.5 and 2.0 (mm), and heat conduction welding occurred when the offset distance D was between 3.0 and 4.5 (mm). When the offset distance D was 5.0 (mm), the melting depth was small and only the surface of the first member 11 melted. When the offset distance D was 2.5 (mm), about half of the welding performed multiple times resulted in heat conduction welding, but some resulted in keyhole welding.

[0024] When the laser output P was 1400 (W), keyhole welding occurred when the offset distance D was between 0.5 and 1.5 (mm), and heat conduction welding occurred when the offset distance D was between 2.5 and 3.5 (mm). When the offset distance D was 4.0 (mm) or more, the melting depth became small and only the surface of the first member 11 melted. When the offset distance D was 2.0 (mm), about half of the welding was heat conduction welding out of the multiple times it was performed, but some were keyhole welding.

[0025] When the laser output P was 1200 (W), keyhole welding occurred when the offset distance D was between 0.5 and 1.5 (mm), and heat conduction welding occurred when the offset distance D was between 2.5 and 3.5 (mm). When the offset distance D was 4.0 (mm) or more, the melting depth became small and only the surface of the first member 11 melted. When the offset distance D was 2.0 (mm), about half of the welding was heat conduction welding out of the multiple times it was performed, but some were keyhole welding.

[0026] When the laser output P was 1000 W, keyhole welding occurred when the offset distance D was between 0.5 and 1.0 mm, and heat conduction welding occurred when the offset distance D was between 2.0 and 3.0 mm. When the offset distance D was 3.5 mm or more, the melting depth became small and only the surface of the first member 11 melted. When the offset distance D was 1.5 mm, about half of the welding attempts were heat conduction welding, but some were keyhole welding.

[0027] When the laser output P was 800 W, keyhole welding was performed when the offset distance D was 0.5 mm, and heat conduction welding was performed when the offset distance D was between 1.5 and 2.5 mm. When the offset distance D was 3.0 mm or more, the melting depth became small and only the surface of the first member 11 melted. When the offset distance D was 1.0 mm, about half of the welding performed multiple times resulted in heat conduction welding, but some resulted in keyhole welding.

[0028] Here, the energy density per unit area is calculated by the following formula (1). Energy density per unit area (J / mm 2 ) = Laser output P (J / s) ÷ Travel speed V (mm / s) ÷ Irradiation diameter (mm) (1) Based on this formula (1), the spot diameter at the focal position of the laser light L is kept constant at 50 (μm), the moving speed V is kept constant at 20 (mm / s), and the energy density per unit area is calculated when the offset distance D and the laser output P are changed, as shown in Figure 5.

[0029] From the experimental results in FIG. 4 and the calculated values ​​in FIG. 5, the energy density per unit area (J / mm 2 ) is 1911(J / mm 2 )~3345(J / mm 2 It is preferable to set the laser output P, ​​the moving speed V, and the offset distance D so that the energy density per unit area (J / mm 2 ) is 2350(J / mm2 )~3060(J / mm 2 It is advisable to set the laser output P, ​​movement speed V, and offset distance D so that

[0030] Fig. 6 is a diagram showing an example of the relationship between the laser output P and the bead width B (µm) and the welding depth F (µm). Fig. 6 is a diagram showing the bead width B (see Fig. 1), which is the width of the molten part, and the welding depth F (see Fig. 1), which is the depth of the molten part, when the spot diameter at the focal position of the laser light L is constant at 50 (µm), the moving speed V is constant at 20 (mm / s), and the laser output P and the offset distance D are changed. For example, when the laser output P was 800 (W) and the offset distance D was 1.5 (mm), the bead width B was 533 (μm) and the welding depth F was 167 (μm). When the laser output P was 1200 (W) and the offset distance D was 2.5 (mm), the bead width B was 858 (μm) and the welding depth F was 298 (μm). When the laser output P was 1600 (W) and the offset distance D was 3.0 (mm), the bead width B was 1216 (μm) and the welding depth F was 459 (μm). When the laser output P was 2000 (W) and the offset distance D was 4.0 (mm), the bead width B was 1652 (μm) and the welding depth F was 721 (μm).

[0031] For this reason, when the spot diameter is 50 (μm) and the moving speed V is 20 (mm / s), if the thickness of the first member 11 is 0.3 (mm), for example, the laser output P must be greater than 1200 (W) in order for the molten part to not penetrate the first member 11 and not reach the second member 12. The offset distance D at which thermal conduction welding is possible is determined according to the laser output P. Therefore, for example, when the thickness of the first member 11 is 0.3 (mm) and the laser output P is 1600 (W), it is preferable to set the offset distance D between 3.0 and 4.5 (mm) as shown in FIG. 4.

[0032] Furthermore, when the spot diameter is 50 μm, the movement speed V is 20 mm / s, the thickness of the first member 11 is 0.3 mm, and the thickness of the second member 12 is 0.3 mm, there is a risk that the molten portion will penetrate the second member 12 unless the laser output P is less than 1800 W.

[0033] As described above, in the welding method according to the first embodiment, when joining the first member 11 and the second member 12, it is preferable to set the energy density per unit area in accordance with the materials and thicknesses of the first member 11 and the second member 12 so that the molten part penetrates the first member 11 but does not penetrate the second member 12. Then, it is preferable to set the offset distance D in accordance with the laser output P corresponding to the set energy density per unit area.

[0034] FIG. 7 is a diagram showing an example of a semiconductor module unit 100 manufactured by using the welding method according to the first embodiment. The semiconductor module unit 100 includes a semiconductor module 50 and a heat sink 60 . The semiconductor module 50 has an insulating substrate 51, a wiring layer 52 provided on the insulating substrate 51, and a semiconductor element 54 attached to the wiring layer 52 via a solder layer 53. The semiconductor module 50 also has a heat spreader 55 that transfers heat from the insulating substrate 51 to a heat sink 60 and dissipates the heat efficiently and quickly. The heat spreader 55 can be, for example, a flat-plate member made of copper.

[0035] The heat sink 60 has a flat plate-shaped portion 61 and a plurality of columnar fins 62 protruding from the flat plate-shaped portion 61 in a direction perpendicular to the plate surface. The fins 62 can be, for example, columnar in shape, with the protruding direction from the flat plate portion 61 being the columnar direction. The shape of the fins 62 as viewed in the protruding direction (hereinafter, may be referred to as the "cross-sectional shape") can be, for example, circular or elliptical. The cross-sectional shape can be, for example, quadrangular, such as a square, rectangle, or rhombus. The fins 62 may be flat. If the fins 62 are flat, the cross-sectional shape may be a rectangular rod shape, or may be wavy with a partially inclined portion.

[0036] The heat sink 60 may be formed by forging, for example, and may be made of pure aluminum of the A1000 series, such as A1100.

[0037] A flux-cored solder sheet (not shown) is placed on the heat spreader 55 of the semiconductor module 50, and the heat sink 60 is placed on the solder sheet such that the fins 62 are on the opposite side of the flat portion 61 to the semiconductor module 50. Then, the flat portion 61 of the heat sink 60 is irradiated with defocused laser light L to form a welded portion 70 at the molten portion of the heat sink 60 and the molten portion of the heat spreader 55 and bond them together, thereby bonding the semiconductor module 50 and the heat sink 60.

[0038] That is, the semiconductor module unit 100 is an example of a structure bonded by irradiating a laser beam to an overlapping portion of two members made of different materials. In the semiconductor module unit 100, the laser beam L is defocused and irradiated to a heat sink 60 as an example of one of the two members, and the heat of the heat sink 60 is conducted to a heat spreader 55 of the semiconductor module 50 as an example of the other of the two members, thereby melting the heat spreader 55 and bonding the heat sink 60 and the heat spreader 55 together.

[0039] In the semiconductor module unit 100 configured as above, the heat spreader 55 of the semiconductor module 50 and the heat sink 60 are joined by forming the welded portion 70, so that the heat of the semiconductor module 50 is easily transferred to the heat sink 60, as compared with the case where the heat of the semiconductor module 50 is transferred to the heat sink 60 via, for example, thermally conductive grease. As a result, the semiconductor module unit 100 has high performance in cooling the semiconductor module 50 and is inexpensive because it does not require thermally conductive grease. In addition, since welding defects are unlikely to occur in the welded portion 70 formed between the heat spreader 55 and the heat sink 60, the semiconductor module unit 100 has higher welding quality than the case where the heat spreader 55 and the heat sink 60 are joined by, for example, the welding method according to the first comparative example. In addition, as compared with the case where the heat spreader 55 and the heat sink 60 of the semiconductor module 50 are joined by brazing or soldering, it is easier to join them using the welding method according to the first embodiment, and the manufacturing cost can be reduced.

[0040] <Second embodiment> FIG. 8 is a diagram showing an example of a welding method according to the second embodiment. The welding method according to the second embodiment is a joining method for joining two members made of different materials by irradiating a butted portion of the two members with a laser beam L. More specifically, as shown in Fig. 8, a first member 31 and a second member 32 are butted together, and a defocused laser beam L is irradiated from a laser head 151 of a laser device 150 to the butted portion between the first member 31 and the second member 32, thereby melting the member having a lower melting point of the two members and joining the two members.

[0041] When the defocused laser light L is irradiated onto the first member 31 and the second member 32, the first member 31, which has a lower melting point, melts first, and the generated heat is conducted to the second member 32. The second member 32 melts due to being irradiated with the defocused laser light L and the heat being conducted from the first member 31. Then, a welded portion 35 is formed by the molten portion of the first member 31 and the molten portion of the second member 32.

[0042] FIG. 9 is a diagram showing an example of a welding method according to a second comparative example. A method of irradiating the butted portion between the first member 31 and the second member 32 with a focused laser beam L is set as a welding method according to a second comparative example. In the welding method according to the second comparative example, the energy density per unit area is higher than that of the welding method according to the second embodiment, even if the laser output P and the moving speed V of the laser head 151 are the same. Therefore, the melting of the first member 31, which has a lower melting point, is faster than that of the second member 32, which has a higher melting point, and the first member 31 melts before the second member 32 melts, and the first member 31 and the second member 32 may not be joined. In particular, when the irradiation position of the focused laser beam L is shifted toward the first member 31, the first member 31 and the second member 32 may not be joined.

[0043] In contrast, the welding method according to the second embodiment has a lower energy density per unit area than the welding method according to the second comparative example, and therefore is easier to join. Furthermore, when the first member 31 is made of an aluminum material, the welding method according to the second comparative example is prone to welding defects such as scattering of molten metal or generation of cavities in the first member 31 during irradiation with the laser light L, but the welding method according to the second embodiment makes welding defects less likely to occur, and can improve welding quality.

[0044] FIG. 10 is a diagram showing an example of a modified example of the welding method according to the second embodiment. In the case where the laser light L is defocused and irradiated to the butted portion between the first member 31 and the second member 32, and the first member 31 and the second member 32 are made of different materials and the melting point of the second member 32 is higher than the melting point of the first member 31, an intermediate member 33 made of a material having a melting point lower than that of the first member 31 may be interposed between the first member 31 and the second member 32 as shown in Fig. 10. Then, the laser light L may be defocused and irradiated to the first member 31, the intermediate member 33, and the second member 32 to melt the intermediate member 33 and join the first member 31 and the second member 32.

[0045] For example, the first member 31 may be made of an aluminum material (melting point is 480°C to 660°C), and the second member 32 may be made of copper (melting point is 1085°C). In this way, when the melting point of the second member 32 is higher than that of the first member 31, the second member 32 is unlikely to melt even if the melting of the second member 32 is promoted by conducting the heat of the first member 31 to the second member 32. In such a case, by disposing an intermediate member 33 made of a material having a melting point lower than that of the first member 31 between the first member 31 and the second member 32, it is possible to conduct the heat of the first member 31 to the intermediate member 33 to melt the intermediate member 33, and to melt the second member 32 by the heat. When the first member 31 is made of an aluminum material and the second member 32 is made of copper, the material of the intermediate member 33 may be solder. In addition, it is preferable that the intermediate member 33 contains flux. For example, between the first member 31 and the second member 32, a solder sheet containing flux may be disposed. In this way, by placing an intermediate member 33 between a first member 31 made of aluminum and a second member 32 made of copper and irradiating defocused laser light L to the butt joint portion of the first member 31 and the second member 32, the first member 31 made of aluminum and the second member 32 made of copper can be joined.

[0046] However, the intermediate member 33 may be disposed between the first member 31 and the second member 32 only when the difference between the melting point of the first member 31 and the melting point of the second member 32 is equal to or greater than a predetermined temperature. The predetermined temperature can be, for example, 300° C. This is because, if the difference between the melting point of the first member 31 and the melting point of the second member 32 is less than 300° C., the second member 32 will melt easily enough to join the first member 31 and the second member 32, even if the melting of the second member 32 is promoted by conducting the heat of the first member 31 to the second member 32.

[0047] In addition, when the first member 31 and the second member 32 are made of different materials and the melting point of the second member 32 is higher than that of the first member 31, a member having a plated surface facing the first member 31 may be used as the second member 32 instead of disposing the intermediate member 33. The plating process can be exemplified as a process in which a metal film made of a material having a melting point lower than that of the first member 31 is deposited.

[0048] For example, when the first member 31 is made of an aluminum material and the second member 32 is made of copper, the plating process can be galvanization. By irradiating the defocused laser light L onto the butted portion between the first member 31 made of aluminum and the second member 32 made of copper, the first member 31 made of aluminum and the second member 32 made of copper can be joined together. [Explanation of symbols]

[0049] Reference Signs List 11, 31...first member, 12, 32...second member, 13, 33...intermediate member, 20, 35, 70...welded portion, 25...keyhole, 50...semiconductor module, 51...insulating substrate, 52...wiring layer, 53...solder layer, 54...semiconductor element, 55...heat spreader, 60...heat sink, 61...flat portion, 62...fin, 150...laser device, 151...laser head, L...laser light

Claims

1. A welding method for joining at least two flat plate-like members each having a thickness of 2 mm or less and two members made of different materials by irradiating a laser beam to an overlapping portion of the two members, the method comprising: the laser light is defocused and irradiated onto one of the two members, and heat from the one member is conducted to the other of the two members, thereby melting the other member, forming a welded portion between the melted portion of the one member and the melted portion of the other member, and joining the one member and the other member; The one member is made of aluminum, and the other member is made of a material having a melting point lower than that of the one member. Welding method.

2. A welding method for joining two flat members made of different materials and having a thickness of 2 mm or less by irradiating a laser beam to an overlapping portion of the two members, the method comprising: The melting point of one of the two members is higher than the melting point of the other of the two members, an intermediate member made of a material having a melting point lower than that of the one member is disposed between the one member and the other member; The one member is irradiated with the defocused laser light, the heat of the one member is conducted to the intermediate member to melt the intermediate member, and the heat of the intermediate member is conducted to the other member to melt the other member, thereby joining the one member and the other member. Welding method.

3. The intermediate member is a plated surface of the other member that faces the one member. The welding method according to claim 2.

4. A welding method for joining two members made of different materials by irradiating a laser beam to a butt joint of the two members, comprising: The laser light is defocused and irradiated onto the butted portion, melting the member having the lower melting point of the two members, and the heat of the member having the lower melting point is conducted to the member having the higher melting point of the two members, thereby melting the member having the higher melting point, forming a welded portion between the molten portion of the member having the lower melting point and the molten portion of the member having the higher melting point, thereby joining the two members. Welding method.

5. A welding method for joining two members made of different materials by irradiating a laser beam to a butt joint of the two members, comprising: An intermediate member having a melting point lower than those of the two members is interposed between the two members, and the laser light is defocused and irradiated onto the two members and the intermediate member to melt the intermediate member, and the heat of the intermediate member is conducted to the two members, thereby melting the two members and joining the two members. Welding method.

6. A welding method for joining two members made of different materials by irradiating a laser beam to a butt joint of the two members, comprising: The member having the higher melting point of the two members is plated, the laser light is defocused and irradiated onto the two members to melt the plating, and the heat of the plating is conducted to the two members to melt the two members and join them together. Welding method.

7. A structure in which at least two flat plate-like members each having a thickness of 2 mm or less and two members made of different materials are joined by irradiating a laser beam onto an overlapping portion of the two members, the laser light is defocused and irradiated onto one of the two members, heat from the one member is conducted to the other of the two members, thereby melting the other member, and a weld is formed between the melted portion of the one member and the melted portion of the other member, thereby joining the one member and the other member; The one member is made of aluminum, and the other member is made of a material having a melting point lower than that of the one member. structure.

Images