JP2008119729A - Laser beam welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam welding by which weld area can be enlarged by suppressing the generation of spatters and, as a result, bonding strength is increased. <P>SOLUTION: The laser beam welding by which weld strength is increased is provided by optimizing the power of the laser beam 7, suppressing the generation of spatters and enlarging the weld area S1 by forming a thin plate working part 2 which is thinner than the thickness L1 of an upper metal plate to be welded in a place (place to be welded) of an upper metal plate 1 to be welded onto which a laser beam 7 is emitted and making the surface 3 to be irradiated of the laser beam in this thin plate working part 2 into a recessed part 4 and its rear 5 into a projecting part 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser welding method capable of suppressing spatter (scattering of members to be welded) generated during welding, expanding a welding area, and increasing welding strength when laser welding two superposed welding plate materials.

5A and 5B are process diagrams showing a conventional laser welding method, in which FIG. 5A is a cross-sectional view of the main part of the welded plate material before welding, and FIG. 5B is a cross-sectional view of the main part of the welded plate material after welding. is there.
In FIG. 5A, the upper welding plate material 51 is superimposed on the upper surface of the lower welding plate material 52, and the laser beam 53 is irradiated from the surface of the upper welding plate material 51. When the laser beam 53 is irradiated on the surface of the upper welding plate material 51, the laser beam 53 is absorbed at the irradiated portion and is converted into thermal energy so that welding proceeds.

  In FIG. 5B, by irradiating the laser beam 53, the irradiated portion of the metal is melted and re-solidified to form a melted and re-solidified portion 54. In this case, if the power (energy) of the laser beam 53 is small, the upper welding plate material 51 has little penetration into the lower welding plate material 52 and the welding strength (joining strength) becomes low. In addition, when a current is passed through this portion, the loss as a wiring increases due to the large resistance.

  When welding is performed by increasing the power of the laser beam 53 in order to increase the welding strength, the state shown in FIG. 6 is obtained. That is, the depth of penetration of the upper welding plate 53 with respect to the lower welding plate 52 is sufficiently ensured, but the heat input is excessive (a state of excessive heat generation), and the molten portion of the upper welding plate 51 is sputtered and the molten member is scattered. As a result, the area of the melting / re-solidifying portion 54 decreases. Further, when the sputter 55 is generated in this way, the power of the laser beam 57 is consumed to generate the sputter 55, and sufficient power for melting is not consumed. Therefore, in the melted / resolidified portion 54 after the melted portion is sputtered, the welding area S3 is not sufficiently widened, the welding strength is lowered, and even when an electric current is passed, the electric resistance is large, which is not preferable.

Such a state appears remarkably when the welded plate material is thick. For example, in the case of a Ni-plated copper plate that is a low melting point material, spatter 55 is increased when the thickness of the upper weld plate 51 exceeds 1.0 mm.
In order to avoid this, a thin plate processed portion 57 (thin thickness portion) is formed in the upper welded plate material 51 where the laser beam 53 is irradiated, and the concave portion 58 of the thin plate processed portion 57 is irradiated with the laser beam 53. Thus, a laser welding method is disclosed in which melting is sufficiently performed without excessively increasing the power (Patent Documents 1 and 2). As shown in FIG. 7A, the cross-sectional view of the main part of the upper welded plate material 51 in which the thin plate processed portion 57 is formed has a concave portion 58 formed as a thin plate processed portion 57 on the surface irradiated with the laser beam 53. The back surface 59 opposite to the surface is flat.
JP-A-2005-71465 JP-A-11-215652

As shown in FIG. 5 described above, when the thickness of the upper welding plate material 51 is thick, a large power is required at the time of laser welding, the generation of spatter 55 occurs, and the welding strength decreases.
7 as disclosed in Patent Documents 1 and 2, as shown in FIG. 7A, the back surface 59 of the upper welded plate material 51 is flat, so that the heat 60 from the laser beam 53 is excessive. Spreading and melting may be incomplete, and the welding area S4 may not be sufficiently large as shown in FIG. If the welding area S4 is small, the welding strength decreases.

On the other hand, if the power of the laser beam 53 is increased to sufficiently melt the laser beam 53, the spatter 55 is generated as shown in FIG. 8 and the welding area S5 cannot be sufficiently increased.
An object of the present invention is to solve the above-mentioned problems and provide a laser welding method capable of increasing the welding area by suppressing the generation of spatter and, as a result, increasing the joining strength.

In order to achieve the above-mentioned object, in a method of laser welding by superposing an upper welded plate material and a lower welded plate material, a thin plate processed portion thinner than the thickness of the upper welded plate material is formed on the upper welded plate material irradiated with laser light. The thin plate processed portion has a concave portion on the laser beam irradiation side, and a convex portion on the back surface opposite to the concave portion, and the convex portion is brought into contact with the lower welding plate material, and the upper welding plate material and the lower welding plate material are overlapped. In addition, the laser beam is irradiated to the concave portion, and the upper welding plate material and the lower welding plate material are laser-welded.

Moreover, the material of the said upper welding plate material and a lower welding plate material is good in a mutually low melting point material.
The low melting point material may be Ni plated copper.
Moreover, the thickness of the said thin plate process part is good to be thinner than the thickness of the location in which the said thin plate process part of the said top weld plate material is not formed.
The thickness of the thin plate processed portion is preferably 1 mm or less.

  The lower welding member may be at least a heat spreader of a semiconductor device, and the upper welding plate may be an external lead-out terminal of the semiconductor device.

  According to the present invention, by forming a thin plate processed portion at the location where the laser beam of the upper welded plate material is irradiated (welded location), by making the laser light irradiation surface of the thin plate processed portion a concave portion and the back surface a convex portion, It is possible to provide a laser welding method capable of increasing the welding strength by optimizing the power of laser light, suppressing the generation of spatter, and increasing the welding area.

  In the embodiment of the present invention, when two welding plate materials are overlapped and laser welding is performed, the thickness of the laser irradiation portion of the welding plate material on the laser irradiation side is reduced (a thin plate processed portion is formed). A concave portion is formed on the irradiation surface side of the portion, a convex portion is formed on the opposite back surface side, and two welding plate materials are overlapped and laser-welded so that the convex portion is in contact. By doing so, the power of the laser beam can be optimized, and the welding area can be expanded and the welding strength can be increased while suppressing the generation of spatter. This will be specifically described in the following examples.

FIG. 1 is a process diagram showing a laser welding method according to a first embodiment of the present invention, in which FIG. 1 (a) is a cross-sectional view of the main parts of the upper and lower welded plates before welding, and FIG. It is principal part sectional drawing of the upper part and lower part welding plate material.
A thin plate processing portion 2 is formed at the laser irradiation portion of the upper welded portion plate material 1, a concave portion 4 is formed on the thin plate processing portion laser irradiation surface side, and the back surface of the thin plate processing portion 2 so as to face the concave portion 4 ( A convex portion 6 is formed on the back surface of the upper welded plate material facing the concave portion.

    The thickness L2 (thickness of the minimum portion) of the thin plate processed portion is made thinner than the original plate thickness (thickness of the portion where the thin plate processed portion is not formed: thickness L1 of the upper welded plate material 1). It is. For example, in the case where the upper and lower welded plate materials 1 and 9 are Ni-plated copper plates which are low melting point materials, the thickness of the upper welded plate material 1 is 1.5 mm and the thickness L2 of the thin plate processed portion is 1.0 mm or less. . In this way, by setting the power of the laser beam 7 to a predetermined value, it is possible to increase the welding area S1 and increase the welding strength while suppressing the occurrence of spatter. Further details will be described.

As shown in FIG. 1 (a), the upper welded plate material 1 in which the thin plate processed portion 2 is formed is overlapped on the upper surface of the lower welded plate material 9, and the laser beam 7 is irradiated from the upper surface of the thin plate processed portion 2 of the upper welded plate material 1. A specific example will be described below.
Using Ni-plated copper plates for the upper and lower welded plate materials 1 and 9, the diameter of the thin plate processed portion 2 is about 1 mm, the thickness L2 of the thin plate processed portion is about 0.5 mm, and the thickness L1 of the upper welded plate material is 0.8 mm. When the thickness L3 of the lower welding plate is about 1 mm, the spot diameter D (focal diameter) of the laser beam 7 is in the range of 0.2 mm to 0.6 mm, and the power of the laser beam 7 is in the range of 1 kW to 10 kW ( By selecting a predetermined value with a power density of about 3 to 5 MW / cm ² ), the welding area S1 can be increased while suppressing spattering, and a large welding strength can be obtained. If the spot diameter D is less than 0.2 mm, the power density of the laser beam 7 is too large and spatter occurs, and if it exceeds 0.6 mm, the power density of the laser beam 7 is too small to be sufficiently melted.

The above example is a case where the thickness L2 of the thin plate processed portion is about 0.5 mm. If the thickness L2 is 1.0 mm or less, the power density of the laser light 7 is set to about 3 to 5 MW / cm ² . By doing so, while suppressing spatter, the welding area can be increased and a large welding strength can be obtained.
In FIG. 1 (b), a melting / resolidifying portion 8 is formed on the upper welded plate material 1 and the lower welded plate material 9 on which the thin plate processed portion 2 is formed. Conventionally, even in the thick upper welded plate material 1 where spatter has been generated, the occurrence of spatter can be suppressed sufficiently by reducing the portion irradiated with the laser beam 7 (welding portion: thin plate processing portion 2). It is possible to ensure a high welding strength.

Next, a method for forming the thin plate processed portion in the embodiment of the present invention will be described.
2A and 2B show a method of forming a thin plate processed portion. FIG. 2A shows a case where the planar shape is a square and the bottom is flat, and FIG. 2B shows a case where the planar shape is a circle and the bottom is flat. (C) is a case where the planar shape is circular and the bottom is hemispherical. This thin plate processing portion 2 is a place where laser welding is performed, and only this portion is thinned.

  In FIG. 2 (a), the upper welded plate material 1a is placed on the support base 12a in which the bottom portion is flat and the planar shape is a quadrangular concave portion 13a, and the surface of the upper welded plate material 1a is pressurized by the prismatic processing jig 11a. By plastically deforming, only the pressurized portion is thinned, and the thin plate processed portion 2a is formed. A convex portion 6a is formed on the bottom surface of the thin plate processed portion 2a, and a concave portion 4a is formed on the surface of the upper welded plate material 1a with a square indentation.

    In FIG. 2 (b), instead of the prismatic processing jig 11a of FIG. 2 (a) described above, a cylindrical pressure jig 11b and a support base 12b in which a recess 13b having a flat bottom and a circular planar shape is formed. This is the case. Also in this case, the bottom surface of the thin plate processed portion 2b is flat, and a circular indentation is formed on the surface of the upper welded plate material 1b in order to pressurize with the cylindrical processing jig 11b. In addition, 4b in a figure is the recessed part formed in the surface side of the upper welding board | plate material 1b, and 6b is the convex part formed in the back surface side.

    In FIG. 2 (c), instead of the processing jigs 11a and 11b shown in FIGS. 2 (a) and 2 (b), a cylindrical processing jig 11c (having a hemispherical tip) and a hemispherical bottom and a planar shape. Is a case where the support base 12c having the circular recess 13c is used. By doing as mentioned above, expansion of a welding area can be aimed at, suppressing spatter by reducing the thickness of a laser welding part (thin plate processed part 2a, 2b, 2c).

In FIG. 2, the case where the thin plate processed portions 2a, 2b, and 2c are formed in a dot shape has been described. However, when the number of welding points is large, a plurality of welds can be welded at a time from the viewpoint of reducing the number of man-hours. Further, the area of the concave portions 4a, 4b and 4c of the thin plate processed portions 2a, 2b and 2c may be increased.
FIG. 3 shows a case where the convex portion, which is a thin plate processed portion of the upper welded plate material, has a band shape. FIG. 3A shows a case where the bottom surface of the concave portion is flat, and FIG. 3B shows a case where the bottom surface of the concave portion is hemispherical. Is the case.

In FIG. 3A, the thin plate processing portion 2d is formed in a strip shape by the strip processing jig 11d, and the bottom surface of the thin plate processing portion 2d is flat.
In FIG.3 (b), the thin plate process part 2e is formed in strip | belt shape with the hemispherical processing jig | tool 11e, and the bottom face is hemispherical. The strip shape is not limited to this, and may be a concave portion having any shape as long as it has an area capable of forming a plurality of weld locations.

By forming the thin plate processed portion into a strip shape, for example, when there are 10 locations to be welded, it is necessary to form 10 spot-shaped thin plate processed portions on the upper welded plate material as shown in FIG. Thus, if it is set as the strip | belt-shaped thin plate process parts 2d and 2e, the thin plate process parts 2d and 2e can be formed by one process, and manufacturing cost can be reduced.
Moreover, when forming many point-like thin-plate processed parts 2a, 2b, 2c, although several thin-plate processed parts 2a, 2b, 2c can be formed simultaneously, in this case, a welding location will be specified. Therefore, different upper welded plate materials 1a, 1b, and 1c are required for each product, which increases the manufacturing cost.

On the other hand, in the case of FIG. 3, since welding can be performed at an arbitrary location of the thin plate processed portions 1d and 1e, the same upper welded plate materials 1d and 1e can be used even if the products are different, so that there is an advantage that manufacturing costs can be reduced. In the figure, 4d and 4e are concave portions formed in the upper welded plate materials 1d and 1e.
FIG. 4 is a cross-sectional view of a main part of a semiconductor device having a heat spreader. A heat spreader 33 made of a Ni-plated copper plate excellent in electrical conduction and heat conduction is soldered 48 on an upper electrode (not shown) of the semiconductor chip 46, and an upper welding plate material (external lead-out terminal 31) of the Ni-plated copper plate is laser welded to the heat spreader 33. Has been. The surface circuit pattern 43 is also laser-welded with an upper welded plate material (external lead-out terminal 31) of a Ni-plated copper plate.

  As shown in FIG. 1, the surface of the external lead-out terminal 31, which is the upper welding plate material, is irradiated with a thin plate processed portion having a concave portion on the front side and a convex portion on the back side. By providing such a thin plate processed portion, the heat generated by the irradiation of the laser beam to the external lead terminal which is the upper welding member is not excessively spread to the heat spreader 33 which is the lower welding member, and the external lead is obtained with a relatively low power. Since the terminal 31 and the heat spreader 33 are melted in an appropriate range to form the melted / resolidified portion 33, the occurrence of spatter is suppressed, a desired welding area is obtained, and a strong welding strength is obtained.

  After the external lead-out terminal 31 is laser welded to the heat spreader 33, the upper part of the ceramics 41 including the semiconductor chip is resin-molded 34. By using this resin mold 34, the heat spreader 33 and the external lead-out terminal 31 are fixed, and even if copper having a large coefficient of linear thermal expansion is used as a material, each member does not move and severe heat stress such as heat cycle is applied. Even in such a case, it has become possible to ensure the reliability of the welded portion that could not be ensured when the gel was used conventionally.

  In the figure, 42 is a copper foil on the back surface, 43, 44 and 45 are front surface circuit patterns, 47 is solder, and 49 is an aluminum wire.

BRIEF DESCRIPTION OF THE DRAWINGS It is process drawing which shows the laser welding method of 1st Example of this invention, (a) is principal part sectional drawing of the upper and lower welded plate material before welding, (b) is the principal of the upper and lower welded plate material after welding. Sectional view This is a method of forming a thin plate processed portion, (a) is a diagram when the planar shape is a square and the bottom is flat, (b) is a diagram when the planar shape is a circle and the bottom is flat, and (c) is a planar shape. When the circle is circular and the bottom is hemispherical This is a case where the convex portion, which is a thin plate processed portion of the upper welded plate material, has a band shape, (a) is a diagram when the bottom surface of the concave portion is flat, and (b) is a diagram when the bottom surface of the concave portion is hemispherical. Cross-sectional view of essential parts of a semiconductor device having a heat spreader It is process drawing which shows the conventional laser welding method, (a) is principal part sectional drawing of the welded plate material before welding, (b) is principal part sectional drawing of the welded plate material after welding. Diagram of welding with increased laser beam power It is process drawing which shows the conventional laser welding method, (a) is a principal part sectional view of the upper and lower welding plate material before welding, (b) is a principal part sectional view of the upper and lower welding plate material after welding. It is another process figure which shows the conventional laser welding method, (a) is principal part sectional drawing of the welded plate material before welding, (b) is principal part sectional drawing of the welded plate material after welding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper welding plate material 2 Thin plate processing part 3 Laser irradiation surface 4 Concave part 5 Back surface 6 Convex part 7 Laser beam 8 Melting | melting / resolidification part 9 Lower welding plate material L1 Thickness of upper welding plate material L2 Thickness of thin plate processing part thickness)
L3 Lower weld plate thickness D Spot diameter (focus diameter)
S1 Welding area

Claims (6)

In the laser welding method in which the upper welding plate and the lower welding plate are overlapped, a thin plate working portion thinner than the thickness of the upper welding plate is formed on the upper welding plate irradiated with laser light, and the thin plate working portion is irradiated with laser light. A concave portion on the side, and a convex portion on the back side opposite to the concave portion, the convex portion is brought into contact with the lower welding plate material, the upper welding plate material and the lower welding plate material are overlapped, and the laser beam is applied to the concave portion. Irradiating and laser welding the upper welded plate material and the lower welded plate material. The laser welding method according to claim 1, wherein the upper welding plate material and the lower welding plate material are low melting point materials. The laser welding method according to claim 2, wherein the low melting point material is Ni plated copper. The laser welding method according to any one of claims 1 to 3, wherein a thickness of the thin plate processed portion is thinner than a thickness of a portion of the upper welded plate material where the thin plate processed portion is not formed. The laser welding method according to claim 4, wherein a thickness of the thin plate processed portion is 1 mm or less. The laser welding method according to claim 1, wherein the lower welding member is at least a heat spreader of a semiconductor device, and the upper welding plate is an external lead-out terminal of the semiconductor device.

Images