JP4572984B2 - Laser welding structure and laser welding method - Google Patents

Description

  The present invention relates to a laser welding structure and a laser welding method, and more particularly to a laser welding structure and a laser welding method for welding a lead made of Cu or a Cu alloy and a conductive member with a laser beam.

  Laser welding using laser light has the advantage that the welding process is completed in a short time of about several ms. On the other hand, since laser light has a high reflectance with respect to copper (Cu) or a Cu alloy, Cu or Cu alloy hardly absorbs the energy of the laser light. Further, since Cu and Cu alloys have high thermal conductivity, there is a problem that a portion melted by irradiation with laser light is easily re-solidified, and cracks are easily caused by solidification.

  Therefore, Patent Document 1 discloses welding the tip portions of two superimposed members. Patent Document 2 discloses that Cu or a Cu alloy is welded by an electron beam instead of a laser beam. Furthermore, in patent document 3, the front-end | tip of the member which consists of Cu which formed the plating layer is cut off diagonally, and the implementation | achievement of the welding by a laser beam is aimed at. In Patent Document 4, an elastic force is applied to a member to be welded by thinning or bending the member.

  However, in Patent Document 1, it is assumed that the member to be welded is cylindrical. For this reason, it is difficult to apply, for example, welding between leads of a semiconductor device arranged at a narrow interval and a conductive member. In the case of Patent Document 1, it is not assumed that Cu or a Cu alloy having a high laser beam reflectivity is used. In the case of Patent Document 2, current may flow through a member to be welded during welding with an electron beam. Therefore, for example, when the lead of the semiconductor device and the conductive member are welded by an electron beam, there is a risk of element destruction of the semiconductor device. In addition, welding with an electron beam has a problem in that the apparatus is increased in size and complexity because the welded portion needs to be in a vacuum state. Furthermore, in the case of Patent Document 3, it is necessary to cut the end of the member to be welded obliquely with respect to the plate thickness direction, which causes a problem that mass productivity is reduced. In addition, in the case of Patent Document 4, there is a problem that the member to be welded has a problem in that the productivity is reduced when the end portion needs to be processed thin or a bending process is required.

JP-A-11-104865 JP 2007-54854 A Japanese Patent Laid-Open No. 11-5182 JP 2007-144436 A

  Therefore, the present invention has been made in view of the above-described problems, and the object thereof is to weld an object formed of Cu or a Cu alloy without causing an increase in size and complexity of the apparatus and a decrease in workability. An object of the present invention is to provide a laser welding structure and a laser welding method in which laser welding is performed in a minute range and cracks during welding are reduced.

In the first or seventh aspect of the invention, the Ni plating layer made of a material containing Ni such as electroless Ni—P (nickel-phosphorus) or electric Ni plating is formed on the lead irradiated with the laser beam. By forming such a Ni plating layer on the lead, even when the lead is formed of Cu or Cu alloy, the reflectance of the laser beam is lowered, that is, the energy absorption rate is increased. Further, since the Ni plating layer has a melting point lower than that of Cu or Cu alloy, a portion that becomes a seed at the time of melting is easily formed. Therefore, the lead and the conductive member formed of Cu or Cu alloy can be laser-welded in a minute range without increasing the size and complexity of the apparatus.

In the invention according to claim 1 or 7 , the welded portion is formed in a curved shape having a convex tip. As a result, when the portion melted by the irradiation of the laser beam resolidifies, crystals are generated toward the center, and stress in the compression direction is applied to the welded portion. Further, by forming a curved welded portion with a convex tip, welding with a laser beam is possible regardless of the shape of the tip of the lead. Therefore, leads and conductive members formed of Cu or Cu alloy can be welded with laser light without causing a decrease in mass productivity, and the generation of cracks accompanying re-solidification of the melted part during welding is reduced. Can do.

  According to the second aspect of the present invention, the thickness t2 of the conductive member is set to be not less than twice the thickness t1 of the lead. When the lead and the conductive member are welded, the laser beam is irradiated to the lead superimposed on the conductive member. When the thickness t2 of the conductive member is smaller than twice the thickness t1 of the lead, the irradiated laser beam may melt not only the lead but also the conductive member. When the conductive member melts, it becomes difficult to form the tip of the welded portion into a convex curved shape. Therefore, by setting t2 ≧ 2 × t1, the lead and the conductive member can be stably welded by the laser beam.

  In the present invention, the width w2 of the conductive member is set larger than the width w1 of the lead. When the lead and the conductive member are welded, the laser beam is irradiated to the lead superimposed on the conductive member. When the width of the lead with respect to the conductive member is increased, not only proper alignment is difficult, but it is also difficult to form the tip of the welded portion in a convex curved shape. If the shape of the tip of the welded portion is not a convex curved shape, cracks are likely to occur during resolidification in the welded portion. Therefore, by setting w2> w1, the lead and the conductive member can be stably welded by the laser beam.

  In the invention according to claim 4, the lead has a chamfered portion at the tip. The shape of the tip of the weld formed by irradiating the tip of the lead with laser light varies depending on the shape of the tip of the lead. By providing a chamfered portion at the tip of the lead, the tip of the welded portion can easily form an appropriate convex curved shape. Therefore, the generation of cracks at the time of resolidification in the welded portion can be reduced.

In the invention according to claim 5 or 6, the chamfered portion has a shape obtained by cutting off a corner portion or a convex curved shape. By forming the chamfered portion in this manner, the tip of the welded portion forms an appropriate convex curved shape along the chamfered portion of the lead portion. Therefore, the generation of cracks at the time of resolidification in the welded portion can be reduced. Further, in the invention of claim 5, since the chamfered portion has a shape in which a corner portion is cut off, for example, when a lead formed integrally with the frame is punched from the frame, the chamfered portion is easily formed together with the punching of the lead. . Therefore, the chamfered portion can be formed without increasing the number of steps.
In the invention according to claim 8 , the Ni plating layer is provided on the entire lead including the tip end face of the lead. Therefore, the part melted by the irradiated laser beam is enlarged. Therefore, generation of a welded portion can be promoted.

  In the ninth aspect of the present invention, the diameter of the laser light irradiation range is ½ or more of the width of the lead. The laser light irradiation range includes the tip of the lead. By irradiating the range including the tip of the lead with laser light, a welded portion protruding from the tip of the lead is formed. Then, by setting the diameter of the laser light irradiation range to be ½ or more of the lead width, the laser light is irradiated over a wide range including the tip of the lead. When the width of the lead is larger than the diameter of the laser beam irradiation range, it becomes difficult to form the tip of the welded portion in an appropriate convex curved shape. If the shape of the tip of the welded portion is not a convex curved shape, cracks are likely to occur during resolidification in the welded portion. Therefore, by setting the diameter of the laser light irradiation range to be ½ or more of the lead width, the lead and the conductive member can be stably welded by the laser light.

In the tenth aspect of the present invention, the surface tension of the molten welded portion is changed by supplying an inert gas to the irradiated portion at the time of laser beam irradiation. This surface tension varies depending on the inert gas supplied to the irradiation site. By changing the surface tension, crystal growth is promoted toward the center when the melted portion resolidifies. Therefore, the generation of cracks during re-solidification can be reduced.
In the invention described in claim 11, the output of the laser beam applied to the lead is gradually reduced. Thereby, the temperature change of the molten welded part becomes small. Therefore, the generation of cracks during re-solidification can be reduced.

It is a schematic diagram which shows the laser welding part to which the laser welding structure by 1st Embodiment of this invention is applied, (A) is sectional drawing, (B) is an arrow view from the arrow A direction of (A). Schematic which shows the motor with which the laser welding structure by 1st Embodiment of this invention is applied. The schematic diagram which shows the mold integrated circuit apparatus with which the laser welding structure by 1st Embodiment of this invention is applied. It is a schematic diagram which shows the lead and conductive member of the laser welding structure by 1st Embodiment of this invention, (A) is sectional drawing, (B) is an arrow line view from the arrow A direction of (A). The schematic diagram which shows the crystal | crystallization of the welding part in the laser welding structure by 1st Embodiment of this invention. Schematic showing the crystal of the weld in a conventional laser welded structure The schematic diagram which shows the cross section of the lead | read | reed of the laser welding structure by 2nd Embodiment of this invention, and an electroconductive member. The schematic diagram which shows the planar view of the lead | read | reed and conductive member of a laser welding structure by 3rd Embodiment of this invention The schematic diagram which shows the planar view of the lead | read | reed and conductive member of a laser welding structure by 4th Embodiment of this invention The schematic diagram which shows the laser welding structure by other embodiment of this invention. The schematic diagram which shows the output change of the laser beam in the laser welding by other embodiment of this invention

Hereinafter, a plurality of embodiments of a laser welding structure and a laser welding method of the present invention will be described with reference to the drawings. Note that, in a plurality of embodiments, substantially the same components are denoted by the same reference numerals, and description thereof is omitted.
(First embodiment)
A laser welded portion to which the laser welding structure according to the first embodiment of the present invention is applied is shown in FIG. A laser welded portion 10 shown in FIG. 1 is applied to a mold integrated circuit device 12 that is assembled integrally with a motor 11 as shown in FIG. As shown in FIG. 3, the mold integrated circuit device 12 includes a processing unit 14 and a control unit 15 sealed in a resin package 13. The processing unit 14 is provided with a multi-pin integrated circuit chip 16 such as a CPU and a memory constituting a microcomputer, for example. The control unit 15 is provided with a power element 17 such as a power MOSFET. The substrate 18 on which the integrated circuit chip 16 of the processing unit 14 is mounted and the substrate 19 on which the power element 17 of the control unit 15 is provided are electrically connected by a bonding wire 21 made of, for example, Au (gold). Has been. The mold integrated circuit device 12 has a plurality of leads 22 and leads 30 protruding outward from the resin package 13. The lead 22 is electrically connected to the substrate 18 of the processing unit 14 by a thin bonding wire 23 made of Au or the like. The lead 30 is electrically connected to the power element 17 of the control unit 15 by a thick wire 24 made of Al (aluminum) or the like. The lead 22 is connected to a conductive member 40 provided in the motor 11 as shown in FIG.

  Next, the laser welded portion 10 will be described in detail based on FIG. The laser welding portion 10 is configured at a connection portion between the lead 30 of the mold integrated circuit device 12 and the conductive member 40 of the motor 11. That is, the laser welded portion 10 that is a laser welded structure includes the lead 30 and the conductive member 40 as constituent elements. The lead 30 and the conductive member 40 are connected at the weld 50. The weld 50 is formed from the tip of the lead 30 to the conductive member 40 side. As shown in FIG. 1B, the welded portion 50 has a tip 51 formed in an arc shape. In addition, in this specification, the front-end | tip 51 of the welding part 50 has illustrated circular arc shape as a convex curve shape. However, the tip 51 of the welded portion 50 is not limited to a true arc shape, and may be another similar curved shape as long as it is a convex curved shape. Hereinafter, in this specification, an arc shape will be described as an example of a convex curved shape. As described above, the welded portion 50 is formed in a circular arc shape at the tip 51 portion, that is, the end of the lead 30 opposite to the mold integrated circuit device 12. The welded portion 50 is formed such that a part below the conductive member 40 in FIG. The lead 30 and the conductive member 40 are electrically and mechanically connected by such a weld 50.

  The lead 30 includes a lead body 31 and a plating layer 32 as shown in FIG. The lead body 31 is formed in a thin plate shape from Cu (copper) or a Cu alloy. The plating layer 32 is made of a material containing Ni, such as electroless Ni—P (nickel-phosphorus) plating or electric Ni plating, and is provided on at least both end faces in the thickness direction and both end faces in the width direction of the lead body 31. ing. That is, the plating layer 32 is formed on each surface excluding the front end surface 33 of the lead body 31. On the other hand, the conductive member 40 includes a conductive member main body 41 and a plating layer 42. The conductive member main body 41 is formed in a thin plate shape from Cu or Cu alloy in the same manner as the lead main body 31. The plating layer 42 is made of Sn (tin) plating, and is provided on at least both end faces in the thickness direction and both end faces in the width direction of the conductive member main body 41. The plating layer 42 of the conductive member 40 is not limited to Sn plating but may be other plating.

  As shown in FIG. 2, when the lead 30 and the conductive member 40 are welded by the laser welding portion 10, the lead 30 having the plating layer 32 is superimposed on the conductive member 40 having the plating layer 42 as shown in FIG. 4. Laser light is irradiated from the laser irradiation device 60 to the lead 30 stacked on the conductive member 40. The laser irradiation device 60 irradiates, for example, a YAG laser. The laser light emitted from the laser irradiation device 60 is applied to a circular irradiation range 61 including the distal end surface 33 of the lead 30 as shown in FIG. By irradiating the lead 30 with laser light, the conductive member 40 is melted together with the lead 30, and a weld 50 is formed. As shown in FIG. 1, the welded portion 50 formed by melting the lead 30 and the conductive member 40 has a tip 51 formed in an arc shape.

  Specifically, when the lead 30 is irradiated with laser light from the laser irradiation device 60, the plating layer 32 is melted prior to the lead body 31. This is because the plating layer 32 made of Ni plating has a lower reflectance of the laser beam and a lower melting point than the lead body 31 made of Cu or Cu alloy. In this manner, the plating layer 32 is melted prior to the lead body 31, so that a portion that becomes a seed of melting is generated in the lead 30 by the plating layer 32. The lead body 31 is promoted to melt by the molten plating layer 32. The portion melted by the laser light irradiation further sinks into the conductive member main body 41 while melting the plating layer 42 and the conductive member main body 41 of the conductive member 40. As a result, a weld 50 that connects the lead 30 and the conductive member 40 is formed.

Next, the dimensions of the lead 30 and the conductive member 40 constituting the laser welding part 10 and the irradiation conditions of the irradiated laser beam will be described.
When the plate thickness of the lead 30 including the plating layer 32 is t1, and the plate thickness of the conductive member 40 including the plating layer 42 is t2, it is desirable that t2 ≧ 2 × t1. This is because, when the plate thickness t2 of the conductive member 40 is not sufficient, the conductive member 40 may be melted to the surface opposite to the lead 30 if the output of the laser light applied to the lead 30 is large. Therefore, by setting the plate thickness t2 of the conductive member 40 to be twice or more the plate thickness t1 of the lead 30, melting of the conductive member 40 is avoided regardless of the output of the laser beam. Further, when the width of the lead 30 including the plating layer 32 is w1, and the width of the conductive member 40 including the plating layer 42 is w2, it is desirable that w2> w1. This is because when the width w2 of the conductive member 40 is not sufficient, not only the alignment of the lead 30 and the conductive member 40 becomes difficult, but also the tip 51 of the welded portion 50 does not easily have an appropriate arc shape. Therefore, by setting the width w2 of the conductive member 40 to be larger than the width w1 of the lead 30, it is easy to align the lead 30 and the conductive member 40, and the tip shape of the welded portion 50 is set to an appropriate arc shape. be able to.

  The laser light irradiation range 61 is set to a circular range including the tip surface 33 of the lead 30. At the same time, the diameter d of the laser light irradiation range 61 is set to be ½ or more of the width w 1 of the lead 30. That is, d ≧ w1 / 2. However, it is not desirable that the laser beam irradiation range 61 exceed the width w1 of the lead 30. Therefore, it is desirable that w1> d ≧ w1 / 2. Thus, by setting the irradiation range 61 of the laser beam to the diameter d including the tip surface 33 of the lead 30, the tip 51 of the welded portion 50 has an appropriate arc shape. In other words, the laser beam is irradiated to a position largely deviated to the mold integrated circuit device 12 side from the tip surface 33 of the lead 30, or the diameter d of the laser beam irradiation range 61 is extremely smaller than the width w 1 of the lead 30. If it becomes, the front-end | tip 51 of the welding part 50 will not become a suitable circular arc shape.

  Laser light is irradiated so as to satisfy the above conditions. In addition, the specific example of the dimension of each part in 1st Embodiment is as follows. The plate thickness t1 and width w1 of the lead 30 are t1 = 0.25 mm and w1 = 0.6 mm, respectively. The plate thickness t2 and width w2 of the conductive member 40 are t2 = 0.5 mm and w2 = 0.8 mm, respectively. The laser beam is irradiated at a position of 0.15 mm from the distal end surface 33 of the lead 30 in a range of a diameter d = 0.3 mm. The thickness of the plating layer 32 of the lead 30 is 3 μm to 7 μm, and the thickness of the plating layer 42 of the conductive member 40 is 0.8 μm to 1.5 μm. The thickness of the plating layer 32 and the plating layer 42 can be formed in an arbitrary range regardless of the above example. Also, the plate thickness and width of the lead 30 and the conductive member 40, the irradiation position of the laser beam, and the like can be arbitrarily changed within a range that satisfies the above-described conditions.

  By irradiating the laser beam so as to satisfy the above conditions, the tip 51 of the welded portion 50 forms an appropriate arc shape as shown in FIG. Thus, by projecting the welded portion 50 from the lead 30 and making the tip 51 into an arc shape, the crystal 52 inside the welded portion 50 grows in a contracting direction toward the center as shown in FIG. That is, the welded portion 50 made of a mixture of the plating layer 32, the lead body 31, the plating layer 42, and the conductive member body 41 melted by the laser light irradiation is crystallized and solidified again by stopping the laser light irradiation. The crystal 52 generated at the time of solidification grows toward the center side by making the tip 51 of the welded portion 50 into an arc shape. Thereby, the stress which shrink | contracts to the center side is added to the welding part 50 at the time of re-solidification. As a result, generation of cracks during resolidification of the weld 50 is reduced.

  On the other hand, as shown in FIG. 6, in the case of the conventional example in which the lead 130 and the conductive member 140 are overlapped and then a laser beam is irradiated to a portion away from the tip of the lead 130, the crystal 151 generated when the weld 150 is resolidified. Grows toward the irradiated surface by stopping the irradiation of the laser beam. Therefore, outward shrinkage stress is applied to the weld 150. As a result, the crack 152 is generated when the weld 150 is re-solidified.

As described above, in the first embodiment, the plating layer 32 made of Ni plating is formed on the lead 30 irradiated with the laser beam. By forming the plating layer 32 on the lead 30, even when the lead body 31 is formed of Cu or Cu alloy, the reflectance of the laser beam is reduced and the energy absorption rate to the lead 30 is increased. Further, since the plating layer 32 made of Ni plating has a melting point lower than that of the lead body 31, a portion that becomes a seed at the time of melting is easily formed. Therefore, the lead 30 and the conductive member 40 can be welded using the laser beam without causing an increase in size and complexity of the apparatus, such as welding with an electron beam.
In the first embodiment, the lead 30 and the conductive member 40 can be welded in a minute range by laser welding. Therefore, as in the case where the motor 11 and the mold integrated circuit device 12 are integrated, the welding of the mold integrated circuit device 12 in which the leads 30 are arranged at minute intervals and the conductive member 40 of the motor 11 is reliably performed. Can do.

  In the first embodiment, the welded portion 50 has a tip 51 formed in an arc shape. As a result, when the welded portion 50 melted by laser light re-solidifies, crystals of the welded portion 50 are generated toward the center, and stress in the compression direction is applied to the welded portion 50. Therefore, it is possible to reduce the generation of cracks accompanying re-solidification of the molten part during welding. Further, by forming the welded portion 50 at the tip of the lead 30 and making the tip 51 of the welded portion 50 arc-shaped, it is not necessary to cut the tip of the lead 30 obliquely. Therefore, the lead 30 formed of Cu or Cu alloy and the conductive member 40 can be welded with laser light without causing a decrease in mass productivity.

  In the first embodiment, the lead 30 has a plating layer 32 made of Ni plating. The lead 30 is connected to the power element 17 by a thick wire 24 on the side opposite to the conductive member 40. The plating layer 32 made of Ni plating has a high affinity with the thick wire 24 made of Al. Therefore, by forming the plating layer 32 on the lead, it is possible to connect to the conductive member 40 by the welded portion 50 and to improve the connectivity with the thick wire 24 connected to the power element 17.

(Second Embodiment)
A laser welding structure according to a second embodiment of the present invention is shown in FIG.
In the second embodiment, in the laser welding structure, a plating layer 32 is also provided on the tip surface 33 of the lead 30 as shown in FIG. That is, the plating layer 32 is provided not only on both end surfaces in the thickness direction and both end surfaces in the width direction of the lead 30 but also on the end surface 33. Thus, by providing the plating layer 32 also on the front end surface 33 of the lead 30, the plating layer 32 having a low melting point is enlarged. This facilitates formation of a portion that becomes a seed of melting in the plating layer 32 having a low melting point when irradiated with laser light. Therefore, generation of the weld 50 can be promoted.
When the plating layer 32 is provided on the leading end surface 33 of the lead 30 as in the second embodiment, it is desirable to form the plating layer 32 after the lead 30 is punched from a frame (not shown). In this case, the lead 30 may be formed with a plating layer 32 on each surface except the front end surface 33.

(Third and fourth embodiments)
Laser welding structures according to third and fourth embodiments of the present invention are shown in FIGS. 8 and 9, respectively.
In the third embodiment, the lead 30 has a chamfered portion 34 as shown in FIG. The chamfered portion 34 is formed by cutting off a corner portion on the distal end surface 33 of the lead 30. That is, the tip of the lead 30 is cut out in a planar shape around the laser light irradiation range 61. In FIG. 8, the welded part 50 formed by laser light irradiation is indicated by a broken line.
In the fourth embodiment, the lead 30 has a chamfered portion 35 as shown in FIG. The chamfered portion 35 is provided as the arcuate tip surface 33 of the lead 30. That is, the tip of the lead 30 is formed in an arc shape including the laser light irradiation range 61. In FIG. 9, the welded part 50 formed by laser light irradiation is indicated by a broken line.

  As described above, in the third embodiment, the lead 30 is provided with the chamfered portion 34 with the corners cut off, and in the fourth embodiment, the arc-shaped chamfered portion 35 is provided at the tip of the lead 30. By providing the chamfered portion 34 and the chamfered portion 35 in this manner, the distal end 51 of the welded portion 50 melted at the time of laser light irradiation approximates the shape of the distal end surface 33 of the lead 30. As a result, the tip 51 of the welded portion 50 can easily form a more appropriate arc shape. Therefore, the generation of cracks in the weld 50 can be reduced. Further, by making the chamfered portions 34 and 35 simple, the chamfered portions 34 and 35 can be formed simultaneously with the punching of the lead 30 from a frame (not shown).

(Other embodiments)
As shown in FIG. 10, when the laser irradiation device 60 is accommodated in the gas supply nozzle 63 and the laser beam is irradiated, the inert gas may be supplied from the gas supply nozzle 63 to the laser beam irradiation portion. As the inert gas, N ₂ (nitrogen), Ar (argon), or the like is applicable. By supplying an inert gas to the irradiated portion of the laser beam that becomes the welded portion 50, the surface tension of the molten welded portion 50 changes. This surface tension varies depending on the inert gas supplied to the weld 50. By changing the surface tension, when the weld 50 is solidified again, crystal growth toward the center is promoted. Therefore, the generation of cracks during re-solidification of the weld 50 can be reduced.

Further, as shown in FIG. 11B, the laser beam output may be gradually decreased after the welded portion 50 is melted. Compared to the normal laser light irradiation shown in FIG. 11A, the output of the laser light irradiated to the welded portion 50 is gradually reduced as shown in FIG. The decrease in temperature also becomes moderate. Therefore, when the molten weld 50 is re-solidified, the crystal grows slowly toward the center. Therefore, when the welded part 50 is resolidified, stress toward the center side is generated in the welded part 50, and the generation of cracks can be reduced.
The application destination of the laser welding part 10 described in the above embodiments is an example, and is not limited to the welding between the motor 11 and the mold integrated circuit device 12, but is applied to the welding of other Cu alloy leads and conductive members. can do.

  The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

  In the drawings, 10 is a laser welded portion (laser welded structure), 30 is a lead, 32 is a plated layer (Ni plated layer), 33 is a tip surface, 34 and 35 are chamfered portions, 40 is a conductive member, 42 is a plated layer, Reference numeral 50 denotes a welded portion, and 51 denotes a tip.

Claims (11)

A lead made of Cu or Cu alloy having a Ni plating layer;
A conductive member connected to the lead and made of Cu or Cu alloy;
A connection between the lead and the conductive member is connected by laser welding, and a welding portion in which the tip side is formed in a convex curved shape,
A laser welding structure comprising:   2. The laser welding structure according to claim 1, wherein t2 ≧ 2 × t1, where t1 is a thickness of the lead and t2 is a thickness of the conductive member.   3. The laser welding structure according to claim 1, wherein w2> w1 when the width of the lead is w1 and the width of the conductive member is w2.   The laser welding structure according to claim 1, wherein the lead has a chamfered portion at a tip.   The laser welding structure according to claim 4, wherein the chamfered portion is formed by cutting a corner portion of the lead.   The laser welding structure according to claim 4, wherein the chamfered portion is formed in a convex curved shape at an end portion of the lead.   A step of stacking a lead made of Cu or Cu alloy on which a Ni plating layer is formed on a conductive member made of Cu or Cu alloy;
  Irradiating a tip of the lead with a laser beam on an end surface of the lead opposite to the conductive member of the lead superimposed on the conductive member, and forming a curved welded portion protruding from the lead and having a convex tip. ,
  A laser welding method comprising:   In the step of stacking the leads on the conductive member,
  8. The laser welding method according to claim 7, wherein the Ni plating layer covers both end faces in the thickness direction of the leads, both end faces in the width direction of the leads, and end faces on the front end side. 9. The laser according to claim 7 , wherein an irradiation range of the laser beam irradiated in the step of forming the welded portion includes a tip of the lead and a diameter is ½ or more of a width of the lead. Welding method. 10. The laser welding method according to claim 7, 8 or 9, wherein in the step of forming the welded portion, an inert gas is supplied to a laser beam irradiation site. 11. The laser welding method according to claim 7 , wherein, in the step of forming the welded portion, after the formation of the welded portion, the output of the laser beam applied to the lead is gradually reduced. .

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