JP4539743B2 - Laser welding method - Google Patents

Description

  The present invention relates to a laser welding method in which metal first and second members are overlapped and laser is irradiated from the surface side of the first member to join both members.

  Conventionally, as this type of laser welding method, a metal first member and a metal second member, both of which are plated on the surface, are overlapped, and laser is emitted from the surface side of the first member. There has been proposed a method of joining these two members by irradiating and forming a melted portion that extends from the surface of the first member to the inside of the second member beyond the interface between the two members (for example, Patent Documents). 1).

In the method disclosed in Patent Document 1, the laser energy efficiency is improved by making the plating applied to the first member having the laser irradiation surface higher in laser absorption than the plating of the second member. And welding. According to this welding method, it is supposed that the explosion of the laser irradiation melted part can be suppressed.
JP 7-214369 A

  However, in the conventional welding method described above, the melting point of the second member is higher than that of the first member. Therefore, if the first member on the laser irradiation side is a thick member such as a lead of an IC package, higher energy is required for melting even if plating with a high laser absorption rate is performed. After all, there is a possibility that the explosion of the plating applied to the first member may occur.

  The present invention has been made in view of the above problems, and a laser welding method in which metal first and second members are overlapped and laser is irradiated from the surface side of the first member to join both members. The present invention aims to provide a laser welding method suitable for suppressing the explosion and sputtering of the plating applied to the first member due to the heat of the laser while enabling welding with low laser energy.

In order to achieve the above object, in the first aspect of the present invention, the first and second members (11, 12) made of metal are overlapped, and laser is irradiated from the surface side of the first member (11). In the laser welding method for joining both members (11, 12), the first member (11) and the second member (12) are each first before the both members (11, 12) are overlapped. The first plating (21) has a higher laser absorptivity than the second plating (22) and the second plating (22). The melting point of the first member (11) is equal to or higher than that of the first member (11). Low absorptivity plating (2 ) And the these two plating (21, 23) is equal to or be placed, arranged and formed so as to mix in a plan view.

According to this, it becomes easy to lower the energy of the laser irradiated to the first member (11) on the laser irradiation side, and the resistance of the first plating (21) to the heat of the laser is improved as compared with the prior art. The Therefore, according to the present invention, it is possible to provide a laser welding method suitable for suppressing the explosion of the first plating (21) due to the heat of the laser while enabling welding with low laser energy. Moreover, in this invention, in the laser irradiation area | region (11a) which is an area | region where a laser strikes among the surfaces of the 1st member (11), from 1st plating (21) and 1st plating (21) Since the low absorptivity plating (23) with low laser absorptivity is arranged and arranged so that these two platings (21, 23) are mixed in a plane, solidification cracks in the melted part (30) occur. This is preferable.

  Here, as in the invention described in claim 2, the first plating (21) is made of Ni whose surface is roughened, and the second plating (22) is the first plating (22). The surface roughness can be made of Ni which is smaller than that of the plating (21).

  Alternatively, as in the third aspect of the invention, the first plating (21) is made of Ni whose surface is roughened, and the second plating (22) is made of Sn. Also good.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
FIG. 1 is a process diagram showing a laser welding method according to the first embodiment of the present invention. In FIG. 1, steps are performed in the order of (a) and (b), and the cross-sectional configuration of each workpiece is shown. In the present embodiment, a welded structure S1 finally shown in FIG. 1B is formed.

  In the laser welding method of the present embodiment, the metal first member 11 and the metal second member 12 are overlapped, the laser L is irradiated from the surface side of the first member 11, and the first These members 11 and 12 are joined by forming a melted portion 30 that extends from the surface of the member 11 to the inside of the second member 12 beyond the interface between the members 11 and 12.

  The first member 11 and the second member 12 are both formed in a plate shape and are applied to general terminals, lead frames, bus bars and the like. The first member 11 is made of copper or a copper alloy, and the second member 12 is made of copper, a copper alloy or an iron alloy.

  Here, first plating 21 and 22 are provided on the surfaces of the first member 11 and the second member 12 before being overlaid, respectively. The laser absorption rate of the first plating 21 is larger than the laser absorption rate of the second plating 22, and the melting point of the first plating 21 is the same as or higher than the melting point of the second plating 22.

  For example, the first plating 21 is made of Au / Pd / roughened Ni plating in which three layers of Ni plating, Pd plating, and Au plating roughened from the first member 11 side, or a single layer. It consists of roughened Ni plating.

  These Au / Pd / roughened Ni plating and one layer of roughened Ni plating are formed by general electroplating or electroless plating. Further, it is known that the degree of roughening of the plating surface can be adjusted by controlling plating conditions such as a chemical solution and temperature.

  Here, the film thickness in Au / Pd / roughened Ni plating is, for example, several μm for roughened Ni plating, several tens of nm for Pd plating, and several tens to 10 nm for Au plating. The film thickness of one layer of roughened Ni plating is, for example, about several μm.

  In addition, examples of the second plating 22 include Ni plating and Sn plating whose surface roughness is smaller than that of the first plating 21. These platings are formed by general electroplating or electroless plating, and the film thickness is, for example, about several μm.

  For example, the first plating 21 can have a laser absorption rate larger than that of the second plating 22. For example, the first plating 21 can have a color tone that can absorb laser more easily. However, in the present embodiment, this is realized by providing a difference in the surface roughness of both the platings 21 and 22.

  This surface roughness can be expressed by a general surface roughness, and is obtained by a known method in which, for example, an image of a surface photographed with an AFM (Atomic Force Microscope) is processed with computer software or the like. Specific surface area per unit area. The large specific surface area means that the number and size of the irregularities on the plating surface are large and the surface roughness is large.

  Then, by controlling the plating conditions as described above, the surface roughness of the first plating 21 is made larger than the surface roughness of the second plating 22, so that the laser absorption rate of the first plating 21 is increased. 2 is larger than the laser absorption rate of the plating 22. This large laser absorption rate leads to welding with less laser power.

  Also, the same melting point of the first plating 21 as the melting point of the second plating 22 may be achieved by forming both the platings 21 and 22 from Ni. When the melting point of the first plating 21 is higher than the melting point of the second plating 22, the material of the first plating 21 may be Ni and the material of the second plating 22 may be Sn. .

  Further, the fact that the electroplating has a higher melting point than the electroless plating may be used even with the same material. In this case, both the platings 21 and 22 are made of Ni, the first plating 21 is roughened Ni plating formed by electroplating, and the second plating 22 is Ni plating formed by electroless plating. In this case, the first plating 21 has a higher melting point.

  As described above, in the present embodiment, the first plating 21 and the second plating 22 are applied to the first member 11 and the second member 12, respectively, and the first plating 21 is more than the second plating 22. Further, it is assumed that the laser absorptance is high and the melting point is equal to or higher than that, and thereafter, both members 11 and 12 are overlapped as shown in FIG.

  Then, the laser L is irradiated from the surface side of the first member 11. This laser L is the same as that used for general laser welding such as YAG laser. As a result, the first plating 21, the first member 11, the second plating 22, and the second member 12 are melted from the surface side of the first member 11, as shown in FIG. In addition, a melted part 30 in which these parts are melted is formed.

  The melting part 30 is continuously formed from the surface of the first member 11 to the inside of the second member 12 beyond the interface between the members 11 and 12. The first member 11 and the second member 12 are joined together with the formation of the melting portion 30. The above is the laser welding method of this embodiment.

  According to this welding method, the first plating 21 on the laser irradiation side has a higher laser absorptance than the second plating 22, so the laser L for irradiating the first member 11 on the laser irradiation side It becomes easy to lower the energy.

  In addition, since the first plating 21 on the laser irradiation side has a melting point equal to or higher than that of the second plating 22, the resistance of the first plating 21 to the heat of the laser L is improved as compared with the conventional case. The Therefore, according to the present welding method, it is possible to suppress the explosion of the first plating 21 due to the heat of the laser L while enabling welding with low laser energy.

  Further, as shown in FIG. 1B, in the present embodiment, the bonding wire 40 made of Al is formed on the first member 11 in a portion other than the welded portion of the both members 11 and 12 in the welded structure S1. It is connected. The wire 40 is formed by a general wire bonding method.

  When the bonding wire 40 is connected to the first member 11 as described above, if the degree of roughening of the first plating 21 of the first member 11 is too large, the bonding property may be deteriorated. is there. Therefore, the present inventor has experimentally obtained a preferable roughening range in consideration of the roughening degree of the first plating 21 and the bonding property.

  First, the first plating 21 made of the Au / Pd / roughened Ni plating was formed on the surface of the first member 11 by electroplating. Here, the above-mentioned specific surface area Sa was used as the roughening degree of the first plating 21, and Au / Pd / roughened Ni plating with the specific surface area Sa varied was formed. Furthermore, the Al wire 40 was connected to each specific surface area by wire bonding.

  For the sample thus prepared, the laser welding energy relative to the specific surface area and the tensile strength of the Al wire 40 relative to the specific surface area were determined. The laser welding energy is the energy of the laser L that can be welded as shown in FIG. 1, and the smaller the energy, the larger the laser absorption rate. Moreover, the larger the wire tensile strength, the better the wire bonding strength and the better the bonding property.

  FIG. 2 shows the specific surface area Sa of the first plating 21 made of the Au / Pd / roughened Ni plating on the horizontal axis, the laser welding energy (unit: J) on the left vertical axis, and the wire tensile strength (unit: N). 2 is a graph showing these relationships. Note that a specific surface area of 1.0 is a mirror surface state having no unevenness.

  As shown in FIG. 2, it can be seen that the larger the specific surface area, that is, the surface roughness, the greater the laser welding energy, that is, the laser absorption rate. This is presumed to be because when the surface roughness of the plating increases, the color tone of the plating surface approaches black, which easily absorbs laser.

  Moreover, it turns out that wire tensile strength, ie, wire bonding property, falls, so that surface roughness becomes large. As described above, the relationship between the surface roughness and the laser absorption rate and the relationship between the surface roughness and the bonding property are in a trade-off relationship. It is considered that the specific surface area is preferably 1.2 to 1.7.

(Second Embodiment)
FIG. 3 is a schematic plan view showing the main part of the laser welding method according to the second embodiment of the present invention, and shows the surface on the laser irradiation side of the first member 11 before welding. In FIG. 3, for the sake of convenience, the surface of the low absorptivity plating 23 is hatched to facilitate the discrimination between the first plating 21 formed on the surface of the first member 11 and the low absorptivity plating 23. It is hatched.

  Here, in FIG. 3, a laser irradiation region 11 a that is a region where the laser L hits the surface of the first member 11 is indicated by a broken-line circle. In general, the laser L is a light beam having a certain diameter, and the region hit by the laser L is a substantially circular region having the same diameter as the light beam.

  And in this welding method, before both the members 11 and 12 are piled up, it is laser rather than the 1st plating 21 and the 1st plating 21 in the laser irradiation area | region 11a among the surfaces of the 1st member 11. A low absorptivity plating 23 which is a plating having a low absorptance is formed so that both the platings 21 and 23 are mixed in a plane. Thereafter, as in the first embodiment, superposition and welding are performed.

  Here, as shown in FIG. 3, the low-absorption rate plating 23 is formed in a circular shape at the center in the laser irradiation region 11a, and the first plating 21 is formed concentrically on the outer side thereof. The low absorptance plating 23 is Ni plating formed by, for example, electroplating or electroless plating and having a surface roughness smaller than that of the first plating 21. Further, both the platings 21 and 23 can be easily formed by dividing the formation region by masking or the like.

  The low absorptivity plating 23 only needs to have a laser absorptance lower than that of the first plating 21, and the relationship between the melting point of the first plating 21, the laser absorptivity of the second plating 22, and the melting point. Is not particularly limited.

  The effect | action by this low absorption rate plating 23 is demonstrated with reference to FIG. 4A shows a case where only the first plating 21 is present in the laser irradiation region 11a as in the above embodiment. In this case, the ratio is obtained by dividing the depth of the melted portion 30 by the width of the melted portion 30. FIG. A certain aspect ratio becomes large. That is, in this case, the melted portion 30 has a steep shape, and the melted portion 30 may be “cracked” due to solidification.

  On the other hand, as in the present embodiment, by mixing the first plating 21 and the low absorptivity plating 23 having different laser absorption rates in the laser irradiation region 11a, solidification cracks are unlikely to occur in the melted portion 30. It was confirmed experimentally. This mechanism is presumed as follows.

  In the present embodiment, at the time of laser irradiation, the first plating 21 having a high laser absorption rate melts relatively quickly, and the low absorption rate plating 23 having a low laser absorption rate melts relatively late. When a difference occurs in the melting speed in this way, as shown in FIG. 4B, the melting part 30 is formed so as to expand in the width direction as compared with the case of only the first plating 21, and the shape of the melting part 30 Is reduced. Therefore, in this embodiment, it is thought that the solidification crack of the fusion | melting part 30 becomes difficult to generate | occur | produce.

  In addition, the arrangement | positioning form of this low absorptivity plating 23 is not limited to the said FIG. Various other examples are shown in FIGS. 5A, 5B, and 5C. Here, in FIG. 5 as well, the surface of the low absorptivity plating 23 is hatched for the sake of convenience in order to facilitate the discrimination between the first plating 21 and the low absorptivity plating 23.

  In the example shown in FIG. 5A, the low absorptivity plating 23 is formed as a plurality of arranged circles in the laser irradiation region 11a, and the first plating 21 is formed in the gap. In the example shown in FIG. 5B, the first plating 21 is formed as a plurality of arranged circles in the laser irradiation region 11a, and the low absorption rate plating 23 is formed in the gaps. Further, in the example shown in FIG. 5C, the first plating 21 and the low absorptivity plating 23 are in a positional relationship opposite to that in FIG.

(Other embodiments)
If the laser absorption rate of the first plating 21 is larger than the laser absorption rate of the second plating 22 and the melting point of the first plating 21 is the same as or higher than the melting point of the second plating 22. The first plating 21 and the second plating 22 are not limited to the materials and thicknesses described above.

It is process drawing which shows the laser welding method which concerns on 1st Embodiment of this invention. It is a graph which shows the relationship between the specific surface area Sa of Au / Pd / roughening Ni plating, laser welding energy, and wire tensile strength. It is a schematic plan view which shows the principal part of the laser welding method which concerns on 2nd Embodiment of this invention. It is a schematic sectional drawing which shows the effect | action by low absorptivity plating. It is a schematic plan view which shows the other various examples of the arrangement | positioning form of absorptance plating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st member 11a Laser irradiation area | region 12 2nd member 21 1st plating 22 2nd plating 23 Low absorption rate plating 30 Melting | fusion part

Claims (3)

The first member (11) made of metal and the second member (12) made of metal are overlapped, and the first member (11) is irradiated with laser from the surface side of the first member (11). These two members (11, 12) are joined by forming a melted part (30) that extends from the surface of 11) to the inside of the second member (12) beyond the interface of these two members (11, 12). In the laser welding method to
Before superimposing the two members (11, 12), the first plating (21) and the second plating (22) are applied to the first member (11) and the second member (12), respectively. In addition, the first plating (21) has a higher laser absorption rate than the second plating (22) and has a melting point equal to or higher than that of the second plating (22). and things,
In the laser irradiation area (11a), which is the area where the laser strikes, of the surface of the first member (11), the first plating (21) and the first plating (21) are more than the first plating (21). A laser welding method, characterized in that a low absorptivity plating (23) having a low laser absorptance is arranged and arranged so that these two platings (21, 23) are mixed in a plane .   The first plating (21) is made of Ni whose surface is roughened, and the second plating (22) has a surface roughness smaller than that of the first plating (21). The laser welding method according to claim 1, wherein the laser welding method is Ni.   The laser welding according to claim 1, wherein the first plating (21) is made of Ni whose surface is roughened, and the second plating (22) is Sn. Method.

Images