Method of connecting metal member, method of connecting inner lead, method of manufacturing semiconductor device, and method of manufacturing electric apparatus

Abstract

To provide a connection method of a metal member capable of suppressing formation of voids even when joining by laser irradiation is performed in a short time.SOLUTION: A metal member connection method for connecting a first metal member and a second metal member by laser joining by irradiating a laser beam in a state in which the first metal member and the second metal member are overlapped, the method comprising: Using a first laser beam and a second laser beam having a longer wavelength than the first laser beam as the laser beam, setting laser irradiation by the second laser beam to a high output in a first irradiation period after an output of the second laser beam reaches a predetermined output, and reducing the output from the high output to a low output in a transition period following the first irradiation period; Performing the laser irradiation with the first laser light at the low output in a second irradiation period subsequent to the transition period, and performing the laser irradiation with the first laser light at a constant output in the first irradiation period, the transition period, and the second irradiation period.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for connecting metal members, a method for connecting inner leads, a method for manufacturing a semiconductor device, and a method for manufacturing an electric device. [Background technology]

[0002] Conventionally, semiconductor modules have been known in which a semiconductor chip is mounted on an insulating circuit board on which a circuit pattern is formed, and the circuit pattern on the insulating circuit board to which the semiconductor chip is bonded is connected by a wiring part such as a lead frame. In connecting such a circuit pattern and a wiring part, a method is known in which a nickel plating film is formed on the surface of a copper material to be irradiated with laser light, and the plating film is irradiated with laser light to bond overlapping copper materials together (see, for example, Patent Document 1). As a result, the copper and nickel melt and alloy, forming a re-solidified part with high fracture strength.

[0003] Patent Document 2 describes that when welding by irradiating a laser beam onto a welding target area, the laser output is oscillated within a predetermined output range in order to reduce the possibility of void formation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2012 / 124255 [Patent Document 2] Patent Publication No. 2021-145481 Summary of the Invention [Problem to be solved by the invention]

[0005] When welding a short range by lap welding, it is necessary to create a deep keyhole in a short time, and therefore it is difficult to provide a time for oscillating the laser output as described in Patent Document 2. When joining by laser irradiation is performed in a short time, it is difficult to apply the invention described in Patent Document 2.

[0006] The present disclosure has been made to solve the above problems, and aims to provide a method for connecting metal members that can suppress the formation of voids even when joining is performed by laser irradiation in a short period of time. [Means for solving the problem]

[0007] The present disclosure has been made to achieve the above-mentioned object, and provides a method for connecting metal members in which a first metal member and a second metal member are overlapped and a traveling laser beam is irradiated thereon to connect the first metal member and the second metal member by laser joining, wherein the laser beams used are a first laser beam and a second laser beam having a longer wavelength than the first laser beam, the laser irradiation with the second laser beam is performed at a high output during a first irradiation period after the output of the second laser beam reaches a predetermined output, and is reduced from the high output to a low output during a transition period following the first irradiation period, and is performed at the low output during a second irradiation period following the transition period, and the laser irradiation with the first laser beam is performed at a constant output during the first irradiation period, the transition period, and the second irradiation period.

[0008] According to this method for connecting metal members, stable laser joining can be achieved while suppressing the formation of voids, even when joining by laser irradiation is performed in a short time.

[0009] In this case, the method for connecting the metal members may be such that the output of the second laser light during the first irradiation period is higher than the output of the first laser light.

[0010] This makes it possible to increase the bonding strength more stably.

[0011] In this case, the method for connecting the metal members may be such that the output of the second laser light during the second irradiation period is lower than the output of the first laser light.

[0012] This makes it possible to more stably suppress the formation of voids.

[0013] In this case, the method for connecting metal members may use an ultraviolet laser or a blue laser as the first laser light, and an infrared laser as the second laser light.

[0014] This allows the metal members to be connected more stably.

[0015] In this case, the method for connecting an inner lead can be such that the first metal member is the metal pattern of a circuit board having a semiconductor chip mounted thereon and a metal pattern on its surface, and the second metal member is the inner lead of a lead frame, and the method for connecting an inner lead joins the inner lead to the circuit board using the method for connecting metal members.

[0016] This makes it possible to bond the inner lead to the circuit board while suppressing the formation of voids.

[0017] In this case, the method for manufacturing a semiconductor device can include a step of joining the inner leads to the circuit board by the above-described method for connecting inner leads.

[0018] This makes it possible to suppress the formation of voids at the joint between the inner lead and the circuit board, thereby enabling the manufacture of a highly reliable semiconductor device.

[0019] In this case, the method for manufacturing an electric device can be realized by using a semiconductor device manufactured by the method for manufacturing a semiconductor device.

[0020] This allows for the manufacture of highly reliable electrical equipment. [Effects of the Invention]

[0021] As described above, according to the method for connecting metal members of the present disclosure, it is possible to suppress the formation of voids even when joining is performed by laser irradiation in a short period of time. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating a method for connecting metal members according to the present disclosure. [Figure 2] 1 is a diagram for explaining a method for joining metal members according to the present disclosure, showing a laser output profile (upper diagram) and a molten state of objects to be joined (lower diagram). [Figure 3] 10A and 10B are diagrams illustrating a method of joining an inner lead and a metal pattern in a manufacturing method of a semiconductor device according to the present disclosure. [Figure 4] 1 is a diagram showing a semiconductor device that can be manufactured by applying a method for connecting metal members according to the present disclosure. [Figure 5] 1A and 1B are diagrams for explaining a method for connecting inner leads according to the present disclosure, and are a cross-sectional view and a top view for explaining an example in which connections are made at multiple locations. [Figure 6] 1 shows an intelligent power module (top view) as a specific example of a semiconductor device. [Figure 7] FIG. 1 is a diagram illustrating an air conditioner as an embodiment of an electrical device. [Figure 8] 1 is a diagram for explaining a method for joining metal members according to a reference example, showing a laser output profile (upper diagram) and a molten state of objects to be joined (lower diagram). DETAILED DESCRIPTION OF THE INVENTION

[0023] The present disclosure will be described in detail below, but the present disclosure is not limited thereto.

[0024] As described above, there has been a demand for a method for connecting metal members that can suppress the formation of voids even when joining is performed by laser irradiation in a short time.

[0025] As a result of extensive research into the above-mentioned problems, the present inventors have discovered a method for connecting metal members in which a first metal member and a second metal member are overlapped and a traveling laser beam is irradiated thereon to connect the first metal member and the second metal member by laser joining, wherein the laser beams used are a first laser beam and a second laser beam having a longer wavelength than the first laser beam, the laser irradiation with the second laser beam is performed at a high output during a first irradiation period after the output of the second laser beam reaches a predetermined output, and is reduced from the high output to a low output during a transition period following the first irradiation period, and is performed at the low output during a second irradiation period following the transition period, and the laser irradiation with the first laser beam is performed at a constant output during the first irradiation period, the transition period, and the second irradiation period, and this method enables stable laser joining while suppressing the formation of voids, thereby completing the present disclosure.

[0026] The following description will be made with reference to the drawings. As described above, the present disclosure aims to solve the problem of bonding by laser irradiation in a short time, but the present disclosure is not limited by the length of time for bonding by laser irradiation. It will be clear from the following description that the effect of the present disclosure, that is, suppressing the generation of voids, can be exerted even when bonding by laser irradiation is performed over a long period of time.

[0027] [Metal component connection method] First, a method for connecting metal members according to the present disclosure will be described. As shown in FIG. 1 , the method for connecting metal members according to the present disclosure involves overlapping a first metal member 1 and a second metal member 2 and irradiating them with a traveling laser beam L to connect the first metal member 1 and the second metal member 2 by laser welding. The laser beams L include a first laser beam L1 and a second laser beam L2 having a longer wavelength than the first laser beam L1. Laser irradiation with the second laser beam L2 is performed at high output during a first irradiation period T1 after the output of the second laser beam L2 reaches a predetermined output. The output is then reduced from high output to low output during a transition period T2 following the first irradiation period T1, and then at low output during a second irradiation period T3 following the transition period T2. Laser irradiation with the first laser beam L1 is performed at a constant output during the first irradiation period T1, the transition period T2, and the second irradiation period T3. When metal members are connected in this manner, stable laser joining can be achieved while suppressing the formation of voids, even when joining by laser irradiation is performed in a short time.

[0028] The wavelengths of the first laser beam L1 and the second laser beam L2 have a relationship of "first laser beam L1<second laser beam L2." The first laser beam L1, which has a short wavelength, is sometimes used for joining thin materials, and the second laser beam L2, which has a long wavelength, is sometimes used for joining thick materials. In the present disclosure, however, the first laser beam L1 and the second laser beam L2 are superimposed and irradiated, so that the first laser beam L1 is used mainly for preheating and the second laser beam L2 is used mainly for melt processing. Note that using the second laser beam L2 at high output tends to increase spatter, so it is advisable to adjust the output to low in order to suppress spatter.

[0029] It is preferable to set the output of the second laser beam L2 during the first irradiation period T1 higher than the output of the first laser beam L1, as this allows for more stable enhancement of the joining strength. It is also preferable to set the output of the second laser beam L2 during the second irradiation period T3 lower than the output of the first laser beam L1, as this allows for more stable joining of the metal members.

[0030] 1 is a diagram illustrating laser irradiation in a method for joining metal members according to the present disclosure, and shows a conceptual diagram of laser joining (welding) performed by simultaneously irradiating (superimposing) a first laser beam L1 and a second laser beam L2 having a longer wavelength than the first laser beam L1, and irradiating the laser in a traveling direction. The area near the surface of the metal material (second metal member 2) is a heated region 27 of the first laser beam L1, and a deeper area of ​​the metal material is a heated region 28 of the second laser beam L2.

[0031] It is preferable to use an ultraviolet (UV) laser or blue laser as the first laser beam L1 and an infrared (IR) laser as the second laser beam L2. With such a combination, the preheating effect of the first laser beam L1 and the processing effect of the second laser beam L2 can be more stably exerted in joining metal materials.

[0032] Metal materials have different light absorption rates for ultraviolet and blue lasers than for infrared lasers. For example, when the metal material is copper (Cu), the absorption rate for blue lasers is approximately 65%, while the absorption rate for infrared lasers is approximately 5% or less. Therefore, by irradiating the metal material (inner lead) with ultraviolet or blue laser light to heat the area near its surface and supplementing the heating with infrared laser light, it is possible to more efficiently and stably melt the joint between the inner lead and the metal pattern. With this type of laser irradiation, the melting required for the joint is essentially performed by the infrared laser. In other words, ultraviolet and blue laser light contribute to stabilizing heating and melting, while also preventing the molten pool from solidifying too quickly.

[0033] When performing laser welding, the traveling speed of the laser beam L is preferably about 200 to 500 mm / sec, for example. The traveling irradiation distance of the laser is preferably about 0.5 to 1.5 mm, for example. This is because the processing throughput is high and stable joining can be achieved.

[0034] A galvano scanner system can be used to control the travel of the laser beam L. In particular, in the case of joining an inner lead and a metal pattern that is performed by short-time laser irradiation, the machine operation is slower than the laser irradiation operation, so the output profile of the second laser beam L2 disclosed herein, which has two stages, high output and low output, can reliably control the melting and solidification states.

[0035] FIG. 2 shows a laser power profile (top) with irradiation time on the horizontal axis and the molten state of the workpieces (bottom) in an example of a method for joining metal members according to the present disclosure. Figure 2A shows the state in which the output of the second laser beam L2 is being adjusted to the target output, and a molten pool 18 is being formed in the second metal member 2. At point B during the first irradiation period T1, when the second laser beam L2 reaches the predetermined output, a molten pool 18 is formed across the second metal member 2 and the first metal member 1. When the output is subsequently reduced from high to low during the transition period T2 (Figure 2C), the depth of the molten pool 18 shrinks. Furthermore, by reducing the output of the second laser beam L2 to low power during the second irradiation period T3, molten metal flows into the cavity at the keyhole 15, gradually reducing the cavity size. The molten pool 18 gradually solidifies from the bottom toward the surface. Therefore, when the output of the laser beam L2 is turned off (Figure 2D), the generation of voids can be suppressed.

[0036] In contrast, in the method for connecting metal members according to the reference example, which does not include a transition period T2 in which the output of the second laser light L2 is reduced from high output to low output and a second irradiation period T3 in which the output of the second laser light L2 is kept at low output, as shown in Figure 8, when the outputs of the first laser light L1 and the second laser light L2 are turned off (C → D in Figure 8), the molten pool 18 solidifies instantaneously, and the hole in the keyhole 15 is likely to become a void 17.

[0037] The output of the second laser beam L2 in the first irradiation period T1 and the second irradiation period T3 may be completely flat over time as shown in Fig. 2, or may fluctuate within a predetermined output range. The direction of traveling irradiation of the laser beam L may be linearly scanned as shown in Fig. 5(B), or the direction may be changed midway depending on the shape of the joining portion, etc.

[0038] [How to connect the inner lead] The above-described method for connecting metal members according to the present disclosure is not particularly limited to the objects or products to be joined as long as it is used to join metal members together, but is preferably applied to a method for connecting inner leads to metal patterns on substrates in the manufacture of semiconductor devices (semiconductor modules). When connecting inner leads, the size of the material at the joining portion (thickness, area of ​​the joining region) is relatively small, so the laser irradiation time for joining is short. The method for connecting metal members according to the present disclosure can stably join inner leads to metal patterns on circuit boards while suppressing voids, especially in the case of such short laser irradiation times.

[0039] The method for connecting an inner lead according to the present disclosure is the method for connecting metal members described above, in which the second metal member 2 is an inner lead of a lead frame and the first metal member 1 is a metal pattern of a circuit board on which a semiconductor chip is mounted and which has a metal pattern on its surface.

[0040] Fig. 3 shows a specific example of a method for connecting inner leads according to the present disclosure. As shown in Fig. 3, a lead frame 20 is used that includes inner leads 21 with bonding areas at their ends. The circuit board used is a circuit board 12 that has a semiconductor chip 30 mounted thereon and a metal pattern 11 with a bonding area on its surface. The lower surface of the inner lead 21 and the upper surface of the metal pattern 11 are opposed to each other, and the inner lead 21 and the metal pattern 11 are bonded together. At this time, as shown in Fig. 3, a laser beam L is irradiated while moving over the inner lead 21 (the traveling direction is perpendicular to the paper).

[0041] This method of connecting the inner leads can suppress the formation of voids at the joint between the inner leads and the circuit board, making it possible to manufacture highly reliable semiconductor devices. Also, the inner leads 21 and the metal pattern 11 can be joined with high productivity.

[0042] In the case of an IPM 200 as shown in Fig. 6, bonding can be performed at multiple bonding locations as shown in Fig. 5 in the same manner as shown in Fig. 3. Fig. 5(A) is a cross-sectional view taken along line ab in the top view shown in Fig. 5(B). For simplification, the semiconductor chip is not shown in Fig. 5.

[0043] [Method of manufacturing a semiconductor device] Furthermore, a method for manufacturing a semiconductor device can be provided that includes a step of bonding an inner lead to a circuit board using the inner lead connection method of the present disclosure. The method for manufacturing a semiconductor device of the present disclosure can suppress the formation of voids at the bonded portion between the inner lead and the circuit board, thereby enabling the manufacture of a highly reliable semiconductor device. FIG. 4 shows a semiconductor device 100 that can be manufactured using the method for manufacturing a semiconductor device of the present disclosure. As shown in FIG. 4, the semiconductor device 100 includes a circuit board 12 having a metal pattern 11 on its surface, a semiconductor chip 30 mounted on the circuit board 12, a lead frame 20 including inner leads 21 whose end bonding regions are connected to the circuit board 12, and a mold resin 40 that resin-encapsulates the semiconductor chip 30 and the lead frame 20. As shown in FIG. 4, the end of the inner lead 21 in the lead frame 20 is bonded to the metal pattern so as to face each other.

[0044] (Semiconductor chip) In the semiconductor device 100, the semiconductor chips are not particularly limited. For example, they may be power chips such as transistors and diodes that handle large amounts of power, or the power chips and control chips such as control ICs that handle less power than the power chips may be arranged in different positions on the circuit board. These may be fixed to the circuit board 12 by soldering, a conductive adhesive, or the like.

[0045] There are no particular limitations on the circuit board 12 as long as it has a metal pattern 11 on its surface. For example, a substrate having metal patterns 11 on both sides of a ceramic substrate 10 as shown in Figures 3 and 4, more specifically a DBC substrate (Direct Bonded Copper substrate) in which a copper material is directly bonded to a ceramic insulating substrate, can be used.

[0046] Fig. 6 shows an example of an intelligent power module (IPM) 200, which is a specific example of a semiconductor device. In the example of Fig. 6, multiple semiconductor chips 30 are provided on a DBC substrate. The method of connecting inner leads and metal patterns according to the present disclosure, which has been described with reference to Figs. 3 and 5, can be suitably applied to the manufacture of an IPM 200 such as that shown in Fig. 6.

[0047] [Manufacturing methods for electrical equipment] Furthermore, it is possible to provide a method for manufacturing an electrical device using a semiconductor device manufactured by the semiconductor device manufacturing method. The above-mentioned semiconductor device can be applied to electrical devices. Using a semiconductor device with improved reliability and reduced cost contributes to improved reliability and reduced cost of electrical devices. Such electrical devices have reduced costs due to reduced costs of the semiconductor device. The electrical devices are not particularly limited, but in particular, the example of the above-mentioned semiconductor device (IPM) 200 can be suitably applied as a small-sized, high-voltage three-phase motor driver to electrical devices for driving compressors in air conditioners, refrigerators, etc.

[0048] 7 is a diagram illustrating an air conditioner 300 as one embodiment of an electrical device. The air conditioner 300 comprises an indoor unit 310 and an outdoor unit 320, each equipped with a fan motor 311, 321, a compressor 322, and an IPM 200, an electrical device. It is recommended that the IPM 200 be designed to have specifications suited to driving the respective motors and compressors. The method for manufacturing an electrical device according to the present disclosure makes it possible to manufacture highly reliable electrical devices.

[0049] As described above in detail, according to the method of connecting metal members disclosed herein, it is possible to stably laser-join metal members while suppressing the formation of voids, even when joining by laser irradiation is performed in a short period of time.

[0050] The present specification includes the following aspects. [1]: A method for connecting metal members, in which a first metal member and a second metal member are overlapped and a traveling laser beam is irradiated to connect the first metal member and the second metal member by laser welding, a first laser beam and a second laser beam having a longer wavelength than the first laser beam are used as the laser beams, laser irradiation with the second laser beam is performed at a high output during a first irradiation period after the output of the second laser beam has reached a predetermined output, and is reduced from the high output to a low output during a transition period following the first irradiation period, and is performed at the low output during a second irradiation period following the transition period; A method for connecting metal members, wherein laser irradiation with the first laser light is performed at a constant output during the first irradiation period, the transition period, and the second irradiation period. [2]: The method for connecting metal members according to [1] above, wherein the output of the second laser light during the first irradiation period is set to be higher than the output of the first laser light. [3]: The method for connecting metal members according to [1] or [2] above, wherein the output of the second laser light during the second irradiation period is set lower than the output of the first laser light. [4]: An ultraviolet laser or a blue laser is used as the first laser light, The method for connecting metal members according to [1], [2] or [3] above, wherein an infrared laser is used as the second laser light. [5]: A method for connecting an inner lead, in which the first metal member is the metal pattern of a circuit board having a semiconductor chip mounted thereon and a metal pattern on its surface, and the second metal member is the inner lead of a lead frame, and the inner lead and the circuit board are joined by the method for connecting metal members described in [1], [2], [3] or [4] above. [6]: A method for manufacturing a semiconductor device, comprising the step of joining the inner lead to the circuit board by the inner lead connecting method according to [5] above. [7]: A method of manufacturing an electrical device, which uses a semiconductor device manufactured by the method of manufacturing a semiconductor device according to [6] above.

[0051] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Explanation of symbols]

[0052] 1...first metal member, 2...second metal member, 10...ceramic substrate, 11...metal pattern, 12...circuit board, 15...keyhole, 17...void, 18...molten pool, 20...lead frame, 21...inner lead, 27...region heated by first laser beam, 28...region heated by second laser beam, 30...semiconductor chip, 40...mold resin, 100... semiconductor device, 200... intelligent power module (IPM), 300...Air conditioner, 310...Indoor unit, 320...Outdoor unit, 311, 321...fan motor, 322...compressor. S...traveling direction, L...laser light, L1...first laser light, L2...second laser light.

Claims

1. A method for connecting metal members, in which a first metal member and a second metal member are overlapped and a traveling laser beam is irradiated thereon to connect the first metal member and the second metal member by laser welding, a first laser beam and a second laser beam having a longer wavelength than the first laser beam are used as the laser beams; laser irradiation with the second laser beam is performed at a high output during a first irradiation period after the output of the second laser beam has reached a predetermined output, and is reduced from the high output to a low output during a transition period following the first irradiation period, and is performed at the low output during a second irradiation period following the transition period; A method for connecting metal members, characterized in that laser irradiation with the first laser light is performed at a constant output during the first irradiation period, the transition period, and the second irradiation period.

2. 2. The method for connecting metal members according to claim 1, wherein the output of the second laser light during the first irradiation period is set higher than the output of the first laser light.

3. 2. The method for connecting metal members according to claim 1, wherein the output of the second laser light during the second irradiation period is set lower than the output of the first laser light.

4. an ultraviolet laser or a blue laser is used as the first laser light, 2. The method for connecting metal members according to claim 1, wherein an infrared laser is used as the second laser beam.

5. A method for connecting an inner lead, characterized in that the first metal member is the metal pattern of a circuit board having a semiconductor chip mounted thereon and a metal pattern on its surface, and the second metal member is an inner lead of a lead frame, and the inner lead and the circuit board are joined by the method for connecting metal members described in any one of claims 1 to 4.

6. 6. A method for manufacturing a semiconductor device, comprising the step of joining the inner leads to the circuit board by the method for connecting inner leads according to claim 5.

7. 7. A method for manufacturing an electric device, comprising manufacturing an electric device using a semiconductor device manufactured by the method for manufacturing a semiconductor device according to claim 6.

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