JP2012071356A - Laser welding member and laser welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser welding member and a laser welding method capable of preventing generation of spatters, and increasing the welding area.SOLUTION: An upper metal plate 3 of copper covered with an electroless nickel-phosphorus plating film 9 is superimposed on an upper surface of a lower metal plate 1 of copper covered with an electrolytic nickel film 8. A laser beam (not shown) is applied to the assembly from the upper surface of the upper metal plate 3 covered with the electroless nickel-phosphorus plating film 9 in such a state that the predetermined pressure is applied to the assembly. Prevention of spatter generation and increase of the welding area can be realized by applying the laser beam to the electroless nickel-phosphorus plating film 9 having the melting point lower than that of copper.

Description

    The present invention relates to a laser welding member and a laser welding method for joining two superposed metal plates by laser welding.

FIG. 9 is a configuration diagram of a conventional laser welding member, in which FIG. 9 (a) is a cross-sectional view of an essential part, FIG. 9 (b) is a plan view of a welded portion cut along line AA in FIG. FIG. 4C is an enlarged view of a C portion of FIG.
9A, the upper metal plate 3 is overlapped on the upper surface of the lower metal plate 1, and laser light (not shown) is irradiated from the upper surface of the upper metal plate 3 for a predetermined time with a predetermined load applied. The metal plate 1 and the upper metal plate 3 are joined by the welded portion 5.

    Here, as a material of the lower metal plate 1 and the upper metal plate 3, copper or a copper alloy is used. FIG. 9A shows an example in which the metal layer 2 is provided on the entire surface of the lower metal plate 1. As a material of the metal film 2, an electrolytic nickel plating film is used to prevent oxidation of the lower metal plate 1. Further, an electrolytic nickel plating film is used on the entire surface of the upper metal plate 3 for the purpose of preventing oxidation of the upper metal plate 3 and improving the laser absorption rate.

Laser light (not shown) is absorbed by the metal film 4 (electrolytic nickel plating film) covering the surface of the upper metal plate 3 and converted into thermal energy, whereby the metal film 4 and the upper metal plate 3 (copper or copper) When the alloy is melted and laser irradiation is continued, the melted portion 5 proceeds in the depth direction with time, and a welded portion 5 as shown in FIG. 9A is obtained.
When the laser power is low and the laser irradiation time is short, the depth of the welded part 5 cannot reach the lower metal plate 1 and is in an unjoined state. When the laser power is high and the laser irradiation time is long, the welded portion 5 penetrates the lower metal plate 1 and is in a perforated state, resulting in insufficient bonding strength.

For this reason, it is necessary to manage the laser power and laser irradiation time during laser welding within an appropriate range. The number of spot points for laser welding can be calculated and determined from the required strength and electrical resistance. From the viewpoint of man-hours, it is desirable in the process to reduce the number of spot points by increasing the welding area per point as much as possible. .
However, in order to reduce the number of welding points, when trying to increase the welding area S1 per point (see FIG. 9B), it is necessary to increase the laser power and lengthen the laser irradiation time. As shown in (), the heat input is excessive and a part of the welded portion 5 is sputtered 6 (the molten metal is scattered). When this configuration is used as a method for joining electronic devices, there is a problem that the spatter 6 that is scattered causes circuit burnout or insulation failure.

As shown in FIG. 9 (c), when the metal films 2 and 4 are formed of the electrolytic nickel plating film as described above on the outside of the welded portion 5, the melting point is higher than the copper of the welded portion 5, and therefore the gap 20 (Unwelded part) is made.
Further, as a method for preventing perforation due to excessive heat input in laser welding, Patent Document 1 discloses a method of forming a low-melting point metal film on at least one of the joint surfaces of two superimposed metal plates. Yes. According to this method, it is stated that perforation can be prevented by covering an Sn-based solder having a melting point lower than that of copper or a tin plating film.

    However, if the entire terminal of a power module or the like is covered with solder or tin plating film, bolting is performed during wiring between the terminal and an external device. The tin plating film is peeled off, the base copper or copper alloy is exposed, and oxidation proceeds. The progress of oxidation may cause deterioration in appearance and contact failure.

In order to avoid this, there is a method in which only a bolted portion is coated with a hard nickel plating film, and other portions including a laser welding portion are coated with Sn-based solder or tin plating film shown in the disclosed patent. However, it is difficult to apply because of high manufacturing cost.
JP 2001-87877 A

    As described above, when the surface of the base material of the laser welding member is covered with the electrolytic nickel plating film 8 and the laser power is increased to obtain sufficient welding strength, the heat input becomes excessive and spatter 6 is generated. In addition, a hole is made in the base material. Further, from the viewpoint of increasing the welding strength, it is necessary to expand the welding area. However, in the case of the electrolytic nickel plating film 8, there is no joint between the electrolytic nickel plating films 8, and only the joint 7 between copper is present. The weld area cannot be made larger than the weld area between copper.

Moreover, in order to prevent the base material from being perforated, as shown in Patent Document 1, when a Sn-based solder having a melting point lower than that of the base material copper or a tin plating film is coated, a terminal of a power module, etc. As described above, inconveniences such as an increase in manufacturing cost occur. Even if perforation can be prevented, it is difficult to prevent sputtering.
An object of the present invention is to provide a laser welding member and a laser welding method capable of solving the above-mentioned problems and preventing spatter generation and expanding a welding area.

In order to achieve the above object, in a laser welding member formed by superposing two metal plates, at least the laser irradiation surface of the upper metal plate is coated with a metal film having a melting point lower than the melting point of the upper metal plate And
Further, in a laser welding member formed by superposing two metal plates, a configuration in which a metal film having a melting point lower than the melting point of the two metal plates is coated on at least one surface of the two metal plates facing each other And

The metal film may be coated on the back surface of the upper metal plate facing the laser irradiation surface.
The material of the two metal plates may be copper or a copper alloy.
The metal film may be an electroless nickel-phosphorous plating film, an aluminum film, or a zinc film.
The thickness of the metal film is preferably 1 μm to 20 μm.

The metal film may be a vapor deposition film. In the laser welding method using the laser welding member, the two metal plates as the laser welding member are overlapped, and the upper metal is covered with a pressure jig. The plate and the lower metal plate are pressed and brought into close contact, and the upper metal plate is irradiated with a laser beam having a wavelength of 0.19 μm to 10.6 μm for laser welding.

According to the present invention, spatter is generated by forming a laser welding member in which a laser irradiation surface of a base material (copper or copper alloy) is coated with a low melting point material (such as an electroless nickel-phosphorous plating film) than the base material. No laser welding is possible.
In addition, by using a laser welding member with a low melting point material (electroless nickel-phosphorus plating film) coated on the joint surface of the base material, the welding area per spot laser welding can be increased and the welding strength increased. Laser welding can be achieved.

    Embodiments will be described in the following examples.

FIG. 1 is a block diagram of a laser welding member according to a first embodiment of the present invention, in which FIG. 1 (a) is a sectional view of an essential part, and FIG. 1 (b) is cut along the line AA in FIG. The top view of the welded part and the figure (c) are the B section enlarged views of the figure (a). The AA line is located at the contact interface between the electroless nickel-phosphorous plating film 9 and the electrolytic nickel plating film 8.
In FIG. 1A, the upper metal plate 3 coated with the electroless nickel-phosphorous plating film 9 is superimposed on the upper surface of the lower metal plate 1 coated with the electrolytic nickel film 8, and a predetermined pressure is applied. The laser beam (not shown) is irradiated from the upper surface of the upper metal plate 3 coated with the electroless nickel-phosphorous plating film 9.

At this time, the lower metal plate 1 and the upper metal plate 3 are made of copper or a copper alloy. The lower metal plate 1 has a thickness of 1 mm, and the upper metal plate 3 has a thickness of 0.3 mm to 1.0 mm. The thickness of the electroless nickel-phosphorous plating film 9 and the electrolytic nickel plating film 8 may be in the range of 1 μm to 20 μm, preferably 3 μm to 7 μm.
The laser energy is converted into thermal energy by the electroless nickel-phosphorous plating film 9 on the laser irradiation surface, and the weld 5 is formed. At this time, the melting points of copper and copper alloy are 900 ° C. to 1083 ° C. Copper alloys include brass and phosphor bronze. Since the melting point of the electroless nickel-phosphorous plating film is 890 ° C., the electroless nickel-phosphorus around the weld 5 located near the interface between the two copper or copper alloy plates shown in FIG. The plating film 9 also melts in the region exceeding the melting point and is joined to the lower electrolytic nickel-phosphorous plating film 8.

The electroless nickel-phosphorous plating film 9 is an electroless plating film 9 in which phosphorus is added to nickel, but the electroless nickel plating film includes an electroless nickel-boron plating film. However, the melting point of the electroless nickel-boron plating film is 1400 ° C., which is higher than the melting point (900 ° C. to 1083 ° C.) of the base material copper or copper alloy, which is not suitable.
Thus, the electroless nickel-phosphorous plating film 9 is formed in the vicinity of the welded portion between the copper by covering the interface between the two copper or copper alloys with a metal film having a melting point lower than the melting point of these metal plates. Compared to the case where the nickel-to-nickel joint portion 12 of the electrolytic nickel plating film 8 is formed and the metal films 2 and 4 such as the electrolytic nickel plating film 8 having a melting point higher than that of copper are coated as shown in FIG. The welding area can be increased by the amount of the joint portion 12 between nickel.

    In FIG. 1B, a joint portion 12 (joint of electroless nickel-phosphorus plating film 9 and electrolytic nickel plating film 8) between nickel plating films is formed around a cut surface 11 where copper base materials are joined. Part 12) has a cut surface 12a, and the welding area is the sum of the area S1 of the cut surface 11 of the copper / copper weld 5 and the area S2 of the cut surface 12a of the nickel-phosphorus / nickel joint 12 . On the other hand, since the welding area of the configuration of the conventional laser welding member shown in FIG. 9 (when the metal layers 2 and 4 are the electrolytic nickel plating film 8) is only S1, the welding area of FIG. growing.

In FIG. 2, oxygen-free copper coated with the electrolytic nickel plating film 8 is used for the lower metal plate 1, and oxygen-free copper coated with the electrolytic nickel plating 8 and the electroless nickel-phosphorous plating film 8 is used for the upper metal plate 3. The measurement results of laser peak power and welding area when YAG laser welding (wavelength 1064 nm) is performed are shown.
The focal length of the YAG laser emission unit used is 70 mm, the fiber core diameter is φ0.4 mm, there is no defocusing (the focal point position (emission unit height is adjusted so as to focus on the surface of the upper metal plate 3)), laser peak The power was 3.5 kW to 6.0 kW, and the irradiation energy was fixed at 100 J. The thickness of the electroless nickel-phosphorous plating film 9 and the thickness 8 of the electrolytic nickel plating film were 5 μm ± 1 μm. The base metal thickness of the lower metal plate 1 was 1.0 mm, and the base metal thickness of the upper metal plate 3 was 0.5 mm.

FIG. 3 is a diagram for explaining the procedure of the laser welding method, and FIG. 3A and FIG. 3B are main part manufacturing process diagrams shown in the order of processes.
First, in FIG. 3A, the lower metal plate 1 is placed on the XY table 41, and the upper metal plate 3 is placed on the upper surface of the lower metal plate 1. The surface of the electroless nickel-phosphorous plating film 9 covering the upper metal plate 3 is visually focused by the CCD camera image incorporated in the emission unit. Focusing is performed by a Z-axis table (not shown) in which the emission unit 42 can move up and down. The emission unit 42 is fixed to the Z-axis table (not shown), and focusing is performed by moving the Z-axis table up and down.

Next, in FIG. 3B, with a predetermined pressure applied from the upper surface of the upper metal plate 3 by the pressing jig 43 (a jig having a shape like tweezers whose tip is divided into two branches) Laser welding is performed by irradiating the upper surface of the electroless nickel-phosphorous plating film 9 covering the upper metal plate 3 with a YAG laser beam 30 with a predetermined power.
The upper metal plate 3 used here is oxygen-free copper, and has a low absorptivity of about 10% in the fundamental wave (1064 nm) of the YAG laser beam 30 and poor weldability. Therefore, as shown in FIG. The one coated with an electrolytic nickel-phosphorus plating film 9 was used. That is, the electroless nickel-phosphorous plating film 9 is processed on the entire surface of the upper metal plate 3. Since the lower metal plate 1 is not directly irradiated with the YAG laser beam 30, it can be used without plating treatment, but the entire surface is covered with an electrolytic nickel plating film 8 for the purpose of preventing oxidation.

As shown in FIG. 2, the same laser peak power is obtained when the electroless nickel-phosphorous plating film 9 is coated than when the upper metal plate 3 is coated with the electrolytic nickel plating film 8. The welding area could be increased.
Moreover, when the electrolytic nickel plating film 8 was coated on the upper metal plate 3, spatter (melted metal scattered) occurred during welding in the entire laser peak power of 3.5 kW to 6.0 kW evaluated. However, when the upper metal plate 3 was coated with the electroless nickel-phosphorus plating film 9, no spatter was generated and the object could be achieved.

By changing the nickel plating film quality from the electrolytic nickel plating film 8 to the electroless nickel plating film 9, it is possible to increase the welding area and suppress the generation of spatter. This is an effect of lowering the melting point of the nickel plating film (the melting point of the electrolytic nickel plating film 8 is 1450 ° C., but the melting point of the electroless nickel-phosphorous plating film 9 is 890 ° C.).
In FIG. 1A, the YAG laser beam 30 is absorbed by the electroless nickel-phosphorous plating film 9 formed on the surface of the upper metal plate 3, and converted into thermal energy, whereby the electroless nickel-phosphorous plating film 9 is It melts when the melting point exceeds 890 ° C.

    When the laser beam is further continuously irradiated, the laser is irradiated to the base material oxygen-free copper, and the melted portion 5 is formed. At this time, the electroless nickel-phosphorous plating film 9 on the surface of the upper metal plate 3 existing at the interface between the upper metal plate 3 and the lower metal plate 1 has a melting point lower than 890 ° C. and the melting point of copper, 1083 ° C. Therefore, the joint portion 12 between the nickel plating films is formed by welding together the portions close to the melting portion 5 (the temperature is at least 1083 ° C., which is the melting point of copper).

In FIG. 1 (b), compared with the welding area S1 when the electrolytic nickel plating film 8 is formed on the upper metal plate 3 under the condition that the lower metal plate 1 does not penetrate (laser peak power 4.0 kW to 5.0 kW). The welding area (S1 + S) when the electroless nickel-phosphorous plating film 9 was coated was able to obtain a welding area approximately three times as large.
Since the welding area has increased, for example, it has become possible to reduce the number of spots where 30 spot laser welding has been conventionally performed to 10 points, and the man-hour can be reduced to 1/3.

Further, when the upper metal plate 3 was coated with the electrolytic nickel plating film 8, spatter was generated, but when the electroless nickel-phosphorous plating film 9 was coated on the same metal plate, the generation of spatter disappeared. A mechanism for preventing the occurrence of spatter will be described with reference to FIGS.
Here, an experiment was performed by coating the surface of copper as a base material with an electrolytic nickel plating film 8 and an electroless nickel-phosphorous plating film 9 and irradiating YAG laser light 30.

    FIG. 4 is a diagram showing the relationship between the pulse width of the laser beam and the depth of the weld. The case of the electrolytic nickel plating film 8 and the case of the electroless nickel-phosphorous plating film 9 are shown. The YAG laser beam 30 is a rectangular wave pulse having a laser peak power of 5.5 kW and a pulse width of 1 ms to 6 ms. The electrolytic nickel plating film 8 increases the depth of the welded portion 5 in a short time, whereas the electroless nickel-phosphorous plated film 9 takes time to increase the depth of the welded portion 5.

    FIG. 5 is a diagram illustrating a state in which the welding depth progresses. The case of the electrolytic nickel plating film 8 and the case of the electroless nickel-phosphorous plating film 9 are shown. In the case of the electrolytic nickel plating film 8, in the stage A, the YAG laser light 30 irradiated on the plating surface 8 is absorbed by this surface and converted into heat energy, and in the stage B, the plating film 8 is welded. . Since the melting point of the plating film 8 is 1450 ° C. and the melting point of the copper 3 which is the base material of the plating film 8 is 1084 ° C., the YAG laser beam 30 is irradiated at the stage C, and the plating layer 8 on the surface is formed. As soon as welding is performed, the underlying metal plate 3 (copper) is presumed to be in a welded state. Further, since the laser (YAG laser) absorptance in the vicinity of the melting point of copper is about 28%, the YAG laser beam 30 can be sufficiently absorbed at the stage D, so that the keyhole is formed quickly. It is considered that the spatter 6 occurred due to the deep penetration during the pulse width of 1 ms to 4 ms.

    On the other hand, in the case of the electroless nickel-phosphorous plating film 9, the YAG laser light 30 irradiated on the plating surface is absorbed by the plating film 9 at the stage A, and reaches the melting point 890 ° C. of the plating film 9 at the stage B. Then it welds. However, since the melting point of the underlying metal plate 3 (copper) is 1084 ° C., the underlying copper is solid even when the electroless nickel-phosphorus film 9 on the surface is welded. When the YAG laser beam 30 is irradiated to (absorption rate 9.1%), the welding progress speed decreases. At the stage D, when a pulse width exceeds a certain threshold, a keyhole-type penetration is formed. It can be inferred that the time (threshold value) until reaching the stage D is about 4 ms later.

    As described above, in the case of the electrolytic nickel plating film 8, the spatter 6 occurs because the abrupt dissolution occurs from the initial stage, and in the case of the electroless nickel-phosphorous plating film 9, the melting proceeds over time. It is presumed that the generation of spatter 6 is suppressed.

    FIG. 6 is a cross-sectional view of the main part of the welded portion of the laser welding member according to the second embodiment of the present invention. This is a case where both the upper metal plate and the lower metal plate are coated with the electroless nickel-phosphorous plating film 9. In this case as well, the same effects as in the first embodiment shown in FIG. Incidentally, reference numeral 13 in the figure denotes a nickel-phosphorus / nickel-phosphorus joint, which is an increase in the welding area.

FIG. 7 is a cross-sectional view of the main part of the welded portion of the laser welding member of the third embodiment of the present invention. The electroless nickel-phosphorous plating film 9 is coated on the upper metal plate 3 side, and a copper base is exposed on the surface of the lower metal plate 1 facing the upper metal plate 3.
Also in this case, the welded electroless nickel-phosphorous plating film 9 is joined by spreading over the surface of the lower metal plate 1, and the same effect as the first embodiment shown in FIG. And no spatter generation). In the third embodiment, only the surface of the lower metal plate 1 facing the upper metal plate 3 is exposed to the copper base. However, the other surfaces of the lower metal plate 1 are exposed to the copper base. You may do it.

    Incidentally, reference numeral 14 in the figure denotes a nickel-phosphorus / copper joint, and this is the amount by which the welding area is enlarged.

FIG. 8 is a cross-sectional view of the main part of the welded portion of the laser welding member according to the fourth embodiment of the present invention. This is the case where the electrolytic nickel plating 8 is formed on the surface of the upper metal plate 3 and the electroless nickel-phosphorous plating 9 is formed on the surface of the lower metal plate 1. In this case, spatter 6 is generated, but the weld area can be enlarged.
Incidentally, reference numeral 15 in the figure is a nickel / nickel-phosphorus joint, and this is the amount of enlargement of the welding area.

In the first to eighth embodiments of the present invention shown in FIGS. 1, 6, 7, and 8, the low melting point metal film covering the upper metal plate 3 and / or the lower metal plate 1 surface is not used. Although the example using the electrolytic nickel-phosphorus plating film 9 (melting point 890 ° C.) is shown, other metal films may be used as long as they are below the melting point (900 ° C. to 1083 ° C.) of the base copper or copper alloy. Similar effects can be obtained.
For example, aluminum (melting point: 660 ° C.) or zinc (melting point: 420 ° C.) may be used as the material of the metal film. Further, these low melting point metal films are preferably processed on the surface of the base metal plate by plating and vapor deposition.

The film thickness of the metal film is in the range of 1 μm to 10 μm. If the thickness is less than 1 μm, the coating effect is lost because the film thickness is too thin. Moreover, even if it exceeds 10 micrometers, an effect does not change so much and only the cost for coating increases. The thickness of the metal film is preferably about 5 μm.
In addition, the laser beam of the above embodiment is the YAG laser beam 30, but not limited to this, any laser beam having a wavelength in the range of 0.19 μm to 10.6 μm can be used. If it is less than 0.19 μm, the energy is too high and the penetration depth of the laser beam is too shallow, so that sputtering is likely to occur. If it exceeds 10.6 μm, the energy is too weak to be melted.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the laser welding member of 1st Example of this invention, (a) is principal part sectional drawing, (b) is a top view of the welding part cut | disconnected by the AA line of (a), (c). Is an enlarged view of part B of (a) Diagram showing the relationship between laser peak power and welding area It is a figure explaining the procedure of a laser welding method, (a) And (b) is the principal part manufacturing process figure shown to process order The figure which shows the relationship between the pulse width of the laser beam and the depth of the weld Diagram showing how the welding depth progresses Sectional drawing of the principal part of the welding part of the laser welding member of 2nd Example of this invention Sectional drawing of the principal part of the welding part of the laser welding member of 3rd Example of this invention Sectional drawing of the principal part of the welding part of the laser welding member of 4th Example of this invention It is a block diagram of the conventional laser welding member, (a) is principal part sectional drawing, (b) is a top view of the welding part cut | disconnected by the AA line of (a), (c) is C of (a). Enlarged view

DESCRIPTION OF SYMBOLS 1 Lower metal plate 2, 4 Metal film 3 Upper metal plate 5 Welded part 6 Sputter 7, 11 Cut surface of copper / copper welded part 8 Electrolytic nickel plating film 9 Electroless nickel-phosphorus plating film 12 Nickel-phosphorus / nickel 12a Nickel-phosphorus / nickel joint cut surface 13 Nickel-phosphorus / nickel-phosphorus joint 14 Nickel-phosphorus / copper joint 15 Nickel / nickel-phosphorus joint 20 Clearance 30 YAG laser 41 XY stage 42 Irradiation unit 43 Pressure jig S1 Area of cut surface of copper / copper weld S2 Area of cut surface of nickel-phosphorus / nickel joint

Claims (7)

In a laser welding member formed by superposing two metal plates, at least one surface where the two metal plates face each other is coated with a metal film having a melting point lower than the melting point of the two metal plates. Laser welding member. The laser welding member according to claim 1, wherein the metal film is coated on a back surface of the upper metal plate facing the laser irradiation surface. The laser welding member according to claim 1 or 2, wherein a material of the two metal plates is copper or a copper alloy. The laser welding member according to any one of claims 1 to 3, wherein the metal film is any one of an electroless nickel-phosphorous plating film, an aluminum film, and a zinc film. The thickness of the said metal film is 1 micrometer-20 micrometers, The laser welding member as described in any one of Claims 1-4 characterized by the above-mentioned. The laser welding member according to any one of claims 1 to 5, wherein the metal film is a vapor deposition film. In the method of performing laser welding using the laser welding member according to any one of claims 1 to 6, two metal plates that are the laser welding member are overlapped, and an upper metal plate and A laser welding method, wherein the lower metal plate is pressed and adhered, and laser welding is performed by irradiating the upper metal plate with laser light having a wavelength of 0.19 μm to 10.6 μm.

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