JP2007222937A - Laser joining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser joining method where different kinds of metals having different laser reflectivities and thermal conductivities can be efficiently lap-welded in high quality. <P>SOLUTION: In the laser joining method where a lower plate 10 made of an iron based material and an upper plate 11 made of a copper based material having a laser reflectivity and a thermal conductivity higher than those of the iron based material are lapped, and a laser L is emitted from the side of the upper plate 11, so as to lap-weld both the plates, a recessed hole 12 is beforehand formed in the upper plate 11, the laser L is emitted in such a manner that an emission pattern is formed at the bottom of the recessed hole 12, and the thin part 12a at the bottom of the recessed hole 12 is concentrically heated and melted. Since the thin part 12 is heated and melted, the upper plate 11 can be efficiently heated and melted even without so increasing the energy density of the laser, thus the phenomenon of energy over on the side of the lower plate 10 is eliminated, pitting in the lower plate 10 is prevented, and further, the gasification of low boiling point components causing the generation of blow holes is suppressed as well. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser joining method in which two upper and lower plates are welded together by a laser, and more particularly suitable for joining metal plates made of different materials such as thermal conductivity and laser reflectance. The present invention relates to a laser joining method.

  For example, in a semiconductor device in which an electronic circuit (substrate) is housed in a resin housing, the housing and the bus bar are integrally formed, and the end portion of the bus bar extending from the housing is overlapped and bonded to the substrate disposed in the housing. There is something like that (see, for example, Patent Document 1). In such a semiconductor device, various methods are used for bonding the substrate and the bus bar. Recently, in order to further improve the bonding strength, a pad made of an iron-based material ( An electrode) is provided, and a bus bar is laser-bonded to this pad.

  By the way, the bus bar is usually made of a copper-based material such as pure copper or brass, and has a significantly higher laser reflectivity and thermal conductivity than the iron-based material pad described above. For this reason, if a bus bar is placed on the pad and laser is irradiated from the bus bar side, a laser with a very high energy density is required for heating and melting the bus bar, which is the upper plate, avoiding an increase in equipment size and energy consumption. It becomes impossible. Also, if the energy density is forcibly increased to promote heating and melting of the bus bar, the laser reaches the lower pad through the bus bar, and at the same time the energy is over and the pad is overheated. The phenomenon that the holes are bright is likely to occur. Further, when the lower plate is made of an iron-based material as in the case of the bad, the low boiling point component contained in the lower plate is vigorously gasified and tends to remain as a blow hole at the joint.

  Therefore, when laser joining a lower plate and an upper plate made of different materials as described above, for example, as shown in FIG. 8, a small-diameter through-hole (through-hole) is previously formed in the upper plate 2 overlaid on the lower plate 1. ) 3 and an attempt is made to promote melting of the upper plate 2 by irradiating the laser L around the through hole 3 (see FIG. 8 of Patent Document 2). However, since the energy of the laser is usually Gaussian distribution and the central part has a high energy density, the laser central part having a high energy density is transmitted through the through hole 3 in the laser joining method described above. The lower plate 1 is directly irradiated, and as described above, the energy is over on the lower plate 1 side, so that the lower plate 1 is less likely to be perforated.

  On the other hand, in Patent Document 2 described above, as shown in FIG. 9, a relatively large-diameter through hole (through hole) 3 is formed in the upper plate 2, and the same quality as the upper plate 2 is formed in the through hole 3. A plurality of small pieces 4 of material are put, and a laser L is irradiated to the center of the through hole including its periphery, and the lower plate 1 also reaches through the gap between the small pieces 4 so that the upper plate 2, the small piece 4 and the lower plate It has been proposed to heat and melt 1 in a well-balanced manner. However, in such a laser joining method, unless the size and the number of the small pieces 4 put in the through hole 3 are strictly managed, the amount of the laser L reaching the lower plate 1 increases and the lower plate 1 is overheated. There is a risk that perforation occurs in the lower plate 1. In this case, the troublesome work of putting the small pieces 5 uniformly in the through holes 3 is also necessary, and deterioration of workability is inevitable.

  Further, in Patent Document 2 described above, as shown in FIG. 10A, the laser L is shaped into a ring-shaped irradiation pattern by the irregularly shaped convex lens 5, and a ring-shaped portion having a high energy density is formed on the upper plate 2. It has been proposed that the upper plate 2 and the lower plate 1 are heated and melted in a well-balanced manner by irradiating the peripheral portion of the formed through-hole (through-hole) 3. However, in this case, an expensive irregular-shaped convex lens 5 is required, and the cost burden on the apparatus is increased. Further, when the peripheral edge of the hole is heated and melted in this way, as shown in FIG. 5B, there is a possibility that the back side of the fusion part 6 is shaded and the fusion with the lower plate 1 becomes insufficient. In other words, it becomes difficult to obtain a desired bonding strength.

JP 2005-64398 A JP-A-57-91895 (FIGS. 1, 5, and 8)

  The present invention has been made in view of various problems that occur when different types of metals are welded together by the laser described above, and the problem is that different types of metals having different laser reflectivities and thermal conductivities can be used. It is an object of the present invention to provide a laser joining method capable of lap welding with high quality and efficiency.

  In order to solve the above-mentioned problems, the present invention provides an upper plate made of a material having a higher laser reflectivity and / or thermal conductivity than the lower plate, and is irradiated with laser from the upper plate side. In the laser joining method for joining the lower plate, a concave hole is formed in the upper plate in advance, and the upper and lower plates are joined by irradiating a laser around the concave hole.

  In the laser joining method performed in this way, the upper plate is heated at the center of at least the thin portion of the bottom of the recessed hole, so that heating and melting of the upper plate is promoted without specially increasing the energy density of laser irradiation, Since the laser beam is not directly applied to the lower plate, energy is not over on the lower plate side. And as a result of no energy over on the lower plate side, perforation in the lower plate is prevented, and even if the lower plate is made of iron-based material, the low boiling point components will not be vigorously gasified. Also, the occurrence of blowholes at the joint is suppressed.

  In the present invention, the laser may be irradiated so that an irradiation pattern is formed on the bottom surface of the concave hole in the upper plate. In this case, the thin portion at the bottom of the concave hole is intensively heated and melted. Therefore, the heating and melting of the upper plate is further promoted.

  In the present invention, the concave hole formed in the upper plate is a tapered hole that gradually decreases in diameter toward the bottom surface, and the laser is irradiated so that the periphery of the irradiation pattern overlaps the portion along the wall surface of the tapered hole. In this case, the portion along the wall surface of the taper hole is also heated and melted to increase the amount of molten metal formed in the recess, so that the fusion of the upper plate and the lower plate is further promoted.

  In the present invention, the material of the lower plate and the upper plate is arbitrary, but the lower plate can be made of an iron-based material and the upper plate can be made of a copper-based material. The laser reflectivity and thermal conductivity of the copper-based material are significantly higher than those of the iron-based material. However, according to the present invention, laser bonding can be smoothly performed even with such a combination. In this case, the lower plate may be a pad on a substrate disposed in the resin housing of the semiconductor device, and the upper plate may be a bus bar formed integrally with the housing.

  In the present invention, the method of forming the concave hole in the upper plate is arbitrary, but in consideration of mass productivity and cost, it is desirable to form by press molding. In this case, it is desirable that the punch is pushed into the center of the lower hole previously formed in the upper plate. This is because, when molding without a pilot hole, stress concentrates on the opening edge of the concave hole and cracks occur. As described above, when a pinch is pushed around the pilot hole, the stress concentration is relaxed. Cracking is prevented.

  In the present invention, during the laser irradiation described above, the plasma light generated from the irradiated portion may be monitored, and the bonding quality may be determined from the light intensity change of the plasma light. During the laser irradiation, if the bottom plate is perforated, or if the low-boiling components contained in the bottom plate are vigorously gasified, the high intensity of the plasma light generated from the laser irradiation section will change greatly. By monitoring the plasma light, it is possible to reliably grasp the bonding failure.

According to the laser joining method of the present invention, when a material having high laser reflectance or thermal conductivity is lap welded as an upper plate, it is not necessary to increase the energy density of laser irradiation, and the cost required for equipment and energy consumption. The burden is greatly reduced. In addition, since the lower plate side does not become over-energy, a high-quality joint can be obtained stably.
In addition, the above-described unique effect makes it extremely useful, for example, for manufacturing a semiconductor device that requires bonding between a pad on a substrate made of an iron-based material and a bus bar made of a copper-based material.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a first embodiment of the present invention. In the first embodiment, an upper plate 11 made of a copper-based material is overlapped on a lower plate 10 made of an iron-based material, and laser L is irradiated from the upper plate 11 side to weld them both. A concave hole 12 is formed in advance on the upper surface side of 11. In the present embodiment, the size of the concave hole 12 formed in the upper plate 11 is arbitrary as long as an area of a sufficient size necessary and sufficient for laser irradiation can be secured and a sufficient amount of the fusion portion 13 necessary for bonding can be secured. However, as an example, when the plate thickness of the upper plate 11 is 1 mm, the diameter D is set to about 2 to 2.5 mm, and the depth H is set to about 0.2 to 0.5 mm.

  At the time of laser joining, as shown in FIG. 1A, after setting the upper plate 11 on the lower plate 10, the laser L is formed so that an irradiation pattern is formed on the bottom surface of the concave hole 12 of the upper plate 11. Irradiate. By this laser irradiation, the thin portion 12a at the bottom of the concave hole 12 is intensively heated and melted, and the lower plate 10 is also heated and melted by receiving the heat. Then, as shown in FIG. 2B, a fusion portion 13 in which the materials of both the lower plate 10 and the upper plate 11 are fused is formed, and then the fusion portion 13 is solidified. Thus, the lower plate 10 and the upper plate 11 are securely joined.

  By the way, the upper plate 11 made of a copper-based material has remarkably higher laser reflectivity and thermal conductivity than the lower plate 10 made of an iron-based material, and there is no concave hole 12 in the upper plate 11. In order to heat and melt the upper plate 11, a laser having a large energy density is required. However, in the present embodiment, the upper plate 11 is heated around the thin portion 12a at the bottom of the concave hole 12 as described above, so that the upper plate 11 can be heated without increasing the energy density of laser irradiation so much. Melting is promoted. Therefore, even if the laser L reaches the lower plate 10, energy is not exceeded. Further, as shown in FIG. 8, since the laser L is not directly applied to the lower plate 10, the energy is not over on the lower plate 10 side also from this surface. As a result, the lower plate 10 is not overheated, and perforation in the lower plate 10 is prevented. Moreover, the gasification of the low boiling point component contained in the iron-based material of the lower plate 10 is suppressed, and the generation of blow holes due to this gasification is also suppressed.

  FIG. 2 shows a second embodiment of the present invention. The feature of the second embodiment is that, as shown in FIG. 5A, a concave hole formed in the upper plate 11 is a tapered hole 12 'that gradually decreases in diameter toward the bottom surface. The laser L is irradiated so that the periphery of the irradiation pattern overlaps the portion along the wall surface of 12 '. The lower plate 10 is made of an iron-based material, and the upper plate 11 is made of a copper-based material, which is the same as in the first embodiment.

  In the second embodiment, in addition to the thin portion 12a at the bottom of the tapered hole 12 ', the portion along the wall surface of the tapered hole 12' is also heated and melted by the laser L, so the amount of molten metal formed in the concave hole The lower plate 10 is efficiently heated and melted by receiving the heat. As shown in FIG. 2 (b), the joining portion of the lower plate 10 and the upper plate 11 is extensively formed with a fusion portion 13 in which both materials are fused, and then the fusion portion 13 is solidified. By doing so, the lower plate 10 and the upper plate 11 are reliably joined. Further, in this laser bonding, the energy does not become over on the lower plate 10 side, as in the first embodiment. As a result, the lower plate 10 is prevented from being perforated and the lower plate 10 side. The gasification of the low melting point component in is suppressed.

  FIG. 3 shows one embodiment when the laser bonding method is applied to the manufacture of a semiconductor device. In the present embodiment, in the semiconductor device 20, after integrally molding the resin housing 21 and the bus bar 22, the end portion of the bus bar 22 extending from the housing 21 is overlapped with the pad 24 on the substrate 23 disposed in the housing 21. Manufactured by laser bonding. In this semiconductor device, the pad 24 on the substrate 23 is made of an iron-based material, and the bus bar 22 is made of a copper-based material. Therefore, the pad 24 is placed on the lower plate 10 (FIGS. 1 and 2). Reference numeral 22 corresponds to the above-described upper plate 11 (FIGS. 1 and 2).

  As shown in FIG. 4, the bus bar 22 has a crank shape here, and a concave hole 25 corresponding to the above-described concave hole 12 (FIG. 1) or 12 ′ (FIG. 2) is provided at one end thereof. Is formed. The bus bar 22 is integrally formed with the housing 21 at the end opposite to the side where the concave hole 25 is provided. In this state, the end on the side where the concave hole 25 is provided has a lower surface on the pad 24 on the substrate 23. It is positioned so that it touches slightly.

  In order to form the recessed hole 15 in the bus bar 22, it is desirable to use press molding because it can be mass-produced at low cost. In this case, if the punch is simply pushed in, stress may concentrate on the opening edge of the formed concave hole 25 and crack C may occur. Therefore, it is desirable to employ the method shown in FIG.

  In FIG. 5, 30 is a punch, 31 is a lower mold, a protrusion 32 that is pushed into the end of the bus bar 22 is formed at the tip of the punch 30, and a recess 33 that receives the bus bar 22 is formed in the lower mold 31. Yes. When forming the concave hole 25, as shown in FIG. 3A, a pilot hole 34 is formed in advance at the end of the bus bar 22. Then, as shown in FIG. 4B, the end of the bus bar 22 with the lower hole 34 is set in the recess 33 of the lower mold 31 and the punch 30 is lowered. Then, the protrusion 32 at the tip of the punch 30 is gradually pushed into the bus bar 22 around the lower hole 34, and in response to this, the material of the bus bar 22 plastically flows toward the center of the hole 34 and bulges to the side. . Finally, as shown in FIG. 3C, the shoulder 30a of the punch 30 contacts the upper surface of the bus bar 22, and the entire front end of the bus bar 22 is crushed, thereby forming a concave hole 25 having a predetermined shape. Molded. As described above, the material of the bus bar 22 plastically flows toward the center of the lower hole 34 in response to the push-in of the punch 30, so that the stress concentration is alleviated, thereby preventing the occurrence of the crack C (FIG. 4). .

  As an example, a laser bonding apparatus for laser bonding the bus bar 22 and the pad 24 on the substrate 23 is configured as shown in FIG. In the figure, reference numeral 40 denotes a laser torch, and reference numeral 41 denotes a laser oscillator (for example, a YAG laser oscillator). In the laser torch 40, a reflection mirror 42 for emitting the laser L transmitted from the laser oscillator 41 from the tip of the laser torch 40. An optical lens (not shown) is provided. When laser joining the bus bar 22 and the pad 24, the laser torch 40 is inserted into the resin housing 21 (FIG. 3) in an upright posture by an appropriate handling means (robot or the like), and the tip of the laser torch 40 is attached to the upper plate. The bus bar 22 is pressed against the pad 24 serving as the lower plate. In this state, the laser L is irradiated around the recessed hole 25 (FIG. 4) formed in advance on the bus bar 22, and the bus bar 22 and the pad 24 are laser-bonded in the same manner as shown in FIGS.

  By the way, in the laser joining described above, the welding situation fluctuates due to changes in the components of the bus bar 22 and the pad 24, dimensional variations of the bus bar 22 including the recessed holes 25, and in some cases, the lower plate becomes a lower plate. The above-described perforation occurs in the pad 24, or severe gasification of low boiling point components occurs. On the other hand, the light generated in the laser irradiation part includes plasma light having a wavelength of 500 to 600 nm and far infrared light having a wavelength of 1300 to 1700 nm in addition to laser reflected light having a wavelength of 1000 to 1200 nm as shown in FIG. . Among these, plasma light and far-infrared light vary greatly depending on the presence or absence of the perforations and the degree of gasification of low-boiling components. The far-infrared light is generated from the fusion part 13 (FIGS. 1 and 2), and changes according to the surface temperature of the fusion part 13. Therefore, in the present embodiment, as shown in FIG. 6, a monitoring device 50 for monitoring the plasma light and far-infrared light generated in the laser irradiation unit and determining the laser bonding quality is attached to the laser bonding device. is doing.

  More specifically, the monitoring device 50 collects two light condensing light concentrating the laser reflected light, plasma light and far-infrared light generated by the laser irradiation unit (fusion unit 13) coaxially with the optical axis of the irradiation laser L. Lenses 51, 52, a reflection mirror 53 that reflects the light transmitted through the rear collective lens 52, a half mirror 54 that divides the plasma light included in the light, and a far-red light from the light that travels straight from the half mirror 54 A half mirror 55 that branches outside light, a detection unit 56 that detects the light intensity of plasma light and far-infrared light, and a determination unit (personal computer) 57 that determines a welding defect based on the detection result by the detection unit 56. ing. The detection unit 56 is provided in two series corresponding to the two half mirrors 54 and 55. Each series includes bandpass filters 58A and 58B that transmit light of a specific wavelength, and condenser lenses 59A and 59B. The photodiodes 60A and 60B as photoelectric conversion elements and amplifiers 61A and 61B for amplifying the signal level of light.

  In the monitoring device 50, plasma light and far-infrared light are extracted from the light generated by the laser irradiation unit by the dedicated half mirrors 54 and 55, and the intensity of each is detected by the detection unit 56. Accordingly, the correlation between the intensity level of the plasma light and far infrared light and the bonding quality (perforation, blowhole, etc.) is obtained in advance, and an appropriate intensity level corresponding to the plasma light and far infrared light is determined in the determination means 57. By setting this threshold value, it is possible to grasp the presence or absence of perforation and the degree of gasification of low boiling point components. This eliminates the need for internal inspection by X-rays later, thereby reducing the cost burden required for quality assurance.

1 is a cross-sectional view schematically showing a first embodiment of a laser bonding method according to the present invention. It is sectional drawing which shows typically 2nd Embodiment of the laser joining method which concerns on this invention. It is a side view showing one embodiment at the time of applying a laser joining method concerning the present invention to manufacture of a semiconductor device. It is a perspective view which shows the shape of the bus bar used by manufacture of a semiconductor device. It is process drawing which shows the formation process of the recessed hole with respect to the bus-bar shown in FIG. It is a systematic diagram which shows typically the structure of the monitoring apparatus for determining laser joining quality. It is a graph which shows wavelength distribution of the light which generate | occur | produces from laser irradiation. It is sectional drawing which shows typically an example of the conventional laser joining method applied to the lap welding of dissimilar metals. It is sectional drawing which shows typically the other example of the conventional laser joining method applied to the lap welding of dissimilar metals. It is sectional drawing which shows typically the further another example of the conventional laser joining method applied to the lap welding of dissimilar metals.

Explanation of symbols

10 Lower plate 11 Upper plate 12 Recessed hole 12a Thin portion 21 Resin housing 22 Bus bar 23 Substrate 23
24 Pad on substrate 30 Punch 34 Pilot hole 50 Monitoring device L Laser

Claims (7)

  In the laser joining method in which an upper plate made of a material having a higher laser reflectance and / or thermal conductivity than the lower plate is stacked on the lower plate, and the upper and lower plates are joined by irradiating laser from the upper plate side. A laser joining method, wherein a concave hole is formed in the upper plate in advance, and laser irradiation is performed around the concave hole to join the upper and lower plates.   2. The laser bonding method according to claim 1, wherein the laser is irradiated so that an irradiation pattern is formed on the bottom surface of the concave hole of the upper plate.   The concave hole formed in the upper plate is a tapered hole that gradually decreases in diameter toward the bottom surface, and the laser is irradiated so that the periphery of the irradiation pattern overlaps the portion along the wall surface of the tapered hole. The laser joining method described.   The laser joining method according to any one of claims 1 to 3, wherein the lower plate is made of an iron-based material, and the upper plate is made of a copper-based material.   The laser joining method according to claim 4, wherein the lower plate is a pad on a substrate disposed in a resin housing of the semiconductor device, and the upper plate is a bus bar integrally formed with the housing.   The laser joining method according to any one of claims 1 to 5, wherein the concave hole of the upper plate is formed by pressing a punch around a lower hole that is previously opened in the upper plate. The laser bonding according to any one of claims 1 to 6, wherein during laser irradiation, plasma light generated from the irradiated portion is monitored, and bonding quality is determined from a change in light intensity of the plasma light. Method.

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