Semiconductor device, electric appliance, and connection method for inner lead

Abstract

To provide a semiconductor device and a connection method for an inner lead, in which the cost increase about the connection between a circuit pattern and a wiring part is suppressed without decreasing the strength of bonding.SOLUTION: A semiconductor device 100 includes a circuit board 10 having a metal pattern 11 on a surface, a semiconductor chip 30 mounted on the circuit board, a lead frame 20 including an inner lead 21 in which a bonding region at an end part is connected to the circuit board, and a mold resin 40 that seals with resin the semiconductor chip and the lead frame. A bonding region 23 at the end part of the inner lead has a flat upper surface, and includes a lead thin part 24 and a lead thick part 25 in which the distances between the upper surface and a lower surface in contact with the metal pattern are different. A bonding region 13 of the metal pattern includes a pattern thick part 14 and a pattern thin part 15 which are different in thickness of the metal pattern. The inner lead and the circuit board are bonded together in such a way that a lower surface of the lead thin part and an upper surface of the pattern thick part face each other and a lower surface of the lead thick part and an upper surface of the pattern thin part face each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a semiconductor device, an electric device, and a method for connecting an inner lead. [Background technology]

[0002] Conventionally, a semiconductor module is 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 connection between 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 a laser beam, and the plating film is irradiated with a laser beam to bond the overlapping copper materials together (see, for example, Patent Document 1). As a result, the copper and nickel melt and are alloyed, forming a resolidified part with high breaking strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5124056 Summary of the Invention [Problem to be solved by the invention]

[0004] The joining method described in Patent Document 1 is effective for firmly laser joining (welding) copper materials together, but has the problem of increased costs because it is necessary to add a nickel layer to the members.

[0005] The present invention has been made to solve the above problems, and aims to provide a semiconductor device in which the cost increase associated with connecting a circuit pattern and a wiring portion is suppressed without reducing the strength of the bond between the inner lead and the metal pattern, and a method for connecting an inner lead that can suppress the cost increase without reducing the strength of the bond between the inner lead and the metal pattern. [Means for solving the problem]

[0006] The present invention has been made to achieve the above object, and includes a circuit board having a metal pattern on its surface, a semiconductor chip mounted on the circuit board, a lead frame including inner leads whose bonding regions at the ends are connected to the circuit board, and a mold resin for resin-sealing the semiconductor chip and the lead frame. In the semiconductor device, the bonding region at the end of the inner lead includes a lead thin portion and a lead thick portion whose upper surfaces are flat and the distances between the upper surfaces and the lower surfaces in contact with the metal pattern of the circuit board are different. The bonding region of the metal pattern has a pattern thick portion and a pattern thin portion with different thicknesses of the metal pattern. The inner lead and the circuit board are joined such that the lower surface of the lead thin portion faces the upper surface of the pattern thick portion, and the lower surface of the lead thick portion faces the upper surface of the pattern thin portion. A semiconductor device is provided.

[0007] According to such a semiconductor device, an increase in cost related to the connection between the circuit pattern and the wiring portion is suppressed without reducing the bonding strength between the inner lead and the metal pattern.

[0008] At this time, it can be a semiconductor device in which at least the lower surface of the lead thin portion and the surface of the pattern thick portion are welded and joined.

[0009] As a result, it becomes more stable and has sufficient bonding strength.

[0010] At this time, an electric device including the above semiconductor device can be provided.

[0011] As a result, an electric device with cost increase suppressed is obtained.

[0012] The present invention also provides a method for connecting an inner lead, which connects a metal pattern of a circuit board having a semiconductor chip mounted thereon and a metal pattern on its surface, to a lead frame having an inner lead having a lower surface that contacts the circuit board at its end, the method using a lead frame having an inner lead with a flat upper surface and having thin lead portions and thick lead portions in a bonding area at the end portion where the distance between the upper surface and the lower surface of the inner lead to be bonded to the metal pattern is different, and the circuit board having thick pattern portions and thin pattern portions in the bonding area of ​​the metal pattern, the method being such that the lower surface of the thin lead portion faces the upper surface of the thick pattern portion and the lower surface of the thick lead portion faces the upper surface of the thin pattern portion to bond the inner lead to the circuit board.

[0013] According to such a method for connecting the inner lead, it is possible to suppress an increase in cost without decreasing the bonding strength between the inner lead and the metal pattern.

[0014] At this time, the method for connecting the inner leads can include bringing the upper surface of the metal pattern into contact with the lower surface of the end of the inner lead, and irradiating a laser from the upper surface side of the inner lead to perform laser welding.

[0015] This makes it possible to bond the inner leads to the circuit board more easily and with higher productivity.

[0016] At this time, the laser welding may be performed by a method of connecting the inner leads in which a blue laser and an infrared laser are irradiated simultaneously.

[0017] This makes it possible to achieve more efficient and stable laser joining (welding) of the inner leads.

[0018] At this time, the laser welding may be performed in such a manner that the laser is irradiated while moving from the thick lead portion to the thin lead portion of the inner lead.

[0019] This makes it possible to more effectively prevent damage to the laser irradiated portion of the inner lead. Effect of the Invention

[0020] As described above, the semiconductor device of the present invention is inexpensive and highly reliable, suppressing increases in costs associated with connecting a circuit pattern and a wiring portion without reducing the bonding strength between the inner lead and the metal pattern. The method of connecting an inner lead of the present invention makes it possible to suppress increases in costs without reducing the bonding strength between the inner lead and the metal pattern. [Brief description of the drawings]

[0021] [Figure 1] 1 shows an example (cross-sectional view) of a semiconductor device according to the present invention. [Diagram 2] 1 is a cross-sectional view showing the bonding region of an end of an inner lead and the vicinity of the bonding region of a metal pattern in a semiconductor device according to the present invention; [Diagram 3] 1 shows an intelligent power module (top view) as a specific example of a semiconductor device. [Figure 4] 1 is a diagram for explaining a method for connecting an inner lead according to the present invention, showing a cross-sectional view of the bonding area of ​​an end of an inner lead and the vicinity of the bonding area of ​​a metal pattern. [Diagram 5] 1A and 1B are diagrams for explaining a method for connecting an inner lead according to the present invention, and are a cross-sectional view and a top view for explaining an example in which connections are made at a plurality of points. [Figure 6] 4 is a diagram illustrating laser irradiation in the method for connecting an inner lead according to the present invention. [Figure 7] 1 shows an example (cross-sectional view) of a conventional method for connecting a metal pattern and an inner lead and a joint portion thereof. [Figure 8] The cross-sectional observation photograph of the laser welded portion between the metal pattern and the inner lead is shown. [Figure 9]11 is a diagram for explaining laser output when laser light is superimposed and irradiated while traveling; [Figure 10] FIG. 1 is a diagram illustrating an air conditioner as an embodiment of an electrical device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will be described in detail below, but the present invention is not limited thereto.

[0023] As described above, there was a need for a semiconductor device in which the cost increase associated with connecting a circuit pattern to a wiring portion was suppressed without reducing the bonding strength between the inner lead and the metal pattern, and a method for connecting an inner lead that can suppress the cost increase without reducing the bonding strength between the inner lead and the metal pattern.

[0024] As a result of intensive research into the above-mentioned problems, the inventors have found that a semiconductor device comprising a circuit board having a metal pattern on its surface, a semiconductor chip mounted on the circuit board, a lead frame including an inner lead having an end bonding region connected to the circuit board, and a molded resin for resin-sealing the semiconductor chip and the lead frame, wherein the end bonding region of the inner lead has a flat upper surface and comprises a thin lead portion and a thick lead portion having different distances between the upper surface and a lower surface of the circuit board that contacts the metal pattern, the bonding region of the metal pattern has a thick pattern portion and a thin pattern portion having different thicknesses of the metal pattern, and the inner lead and the circuit board are bonded such that the lower surface of the thin lead portion faces the upper surface of the thick pattern portion and the lower surface of the thick lead portion faces the upper surface of the thin pattern portion, thereby suppressing an increase in costs associated with connecting a circuit pattern and a wiring portion without decreasing the bonding strength between the inner lead and the metal pattern, and have completed the present invention.

[0025] The present inventor has also discovered that a method for connecting an inner lead, which connects a metal pattern of a circuit board having a semiconductor chip mounted thereon and a metal pattern on its surface, to a lead frame having an inner lead having a lower surface that contacts the circuit board at its end, uses a lead frame having an inner lead which has a flat upper surface and which has thin lead portions and thick lead portions in a bonding region at the end portion and which have different distances between the upper surface and the lower surface of the inner lead to be bonded to the metal pattern, and a circuit board having thick pattern portions and thin pattern portions of different thicknesses of the metal pattern in a bonding region of the metal pattern, and bonds the inner lead to the circuit board by opposing the lower surface of the thin lead portion to the upper surface of the thick pattern portion and opposing the lower surface of the thick lead portion to the upper surface of the thin pattern portion, making it possible to suppress an increase in costs without decreasing the bonding strength between the inner lead and the metal pattern, and has completed the present invention.

[0026] The following description will be given with reference to the drawings.

[0027] [Semiconductor Devices] A semiconductor device according to the present invention is shown in Fig. 1. As shown in Fig. 1, a semiconductor device 100 according to the present invention includes a circuit board 10 having a metal pattern 11 on its surface, a semiconductor chip 30 mounted on the circuit board 10, a lead frame 20 including inner leads 21 whose end bonding regions 23 are connected to the circuit board 10, and a molded resin 40 that seals the semiconductor chip 30 and the lead frame 20 with resin.

[0028] 1, bonding region 23 at the end of inner lead 21 in lead frame 20 has a flat upper surface, and includes thin lead portion 24 and thick lead portion 25 that have different distances between the upper surface and the lower surface that contacts metal pattern 11 of circuit board 10. Bonding region 13 of the metal pattern includes thick pattern portion 14 and thin pattern portion 15 that have different thicknesses of metal pattern 11. Inner lead 21 and circuit board 10 are bonded such that the lower surface of thin lead portion 24 faces the upper surface of thick pattern portion 14, and the lower surface of thick lead portion 25 faces the upper surface of thin pattern portion 15.

[0029] The thick lead portion 25 only needs to have a thickness, which is the distance between the upper surface and the lower surface, greater than that of the thin lead portion 24. Fig. 2 shows a cross-sectional view of the bonding area 23 at the end of the inner lead 21 and the vicinity of the bonding area 13 of the metal pattern 11. As shown in Fig. 2(A), a sloping portion 26 may be provided between the thin lead portion 24 and the thick lead portion 25, but the sloping portion 26 may not be provided. Furthermore, the thick lead portion 25 and the thin lead portion 24 do not need to be horizontal (the upper surface and the lower surface are parallel) in cross-section, and the entire thin lead portion 24 may be sloping in cross-section as shown in Fig. 2(B), or the entire thick lead portion 25 may be sloping in cross-section as shown in Fig. 2(C).

[0030] It is sufficient that the thick pattern portion 14 and the thin pattern portion 15 have shapes corresponding to the thin lead portion 24 and the thick lead portion 25, respectively. Therefore, as shown in Fig. 2(A), there may be an inclined portion 16 between the thick pattern portion 14 and the thin pattern portion 15, or there may be no inclined portion 16. Furthermore, the cross section of the thick pattern portion 14 or the thin pattern portion 15 does not have to be horizontal (parallel to the upper surface), and the entire thick pattern portion 14 may be inclined in cross section as shown in Fig. 2(B), or the entire thin pattern portion 15 may be inclined in cross section as shown in Fig. 2(C).

[0031] The materials of the inner lead 21 (lead frame 20) and the metal pattern 11 are not limited, and they may be the same material or different materials. The thicknesses of the thin lead portion 24 and the thick lead portion 25 in the bonding area 23 at the end of the inner lead 21, and the thick pattern portion 14 and the thin pattern portion 15 in the bonding area 13 of the metal pattern are not particularly limited, as long as the sum of the thin lead portion 24 and the thick pattern portion 14 and the sum of the thick lead portion 25 and the thin pattern portion 15 are approximately equal. For example, the thicknesses of the thin lead portion 24 and the thin pattern portion 15 can be about 0.1 mm to 0.3 mm, and the thicknesses of the thick lead portion 25 and the thick pattern portion 14 can be about 0.4 mm to 0.6 mm. The thickness ratio of the thin lead portion 24 and the thick lead portion 25 is preferably about 1:1.3 to 6.0, for example. This allows for more stable and high bonding strength. The same applies to the relationship between the thick pattern portion 14 and the thin pattern portion 15.

[0032] The thickness of the bonding region 23 at the end of the inner lead 21 (plate thickness: thin lead portion 24 and thick lead portion 25) can be easily adjusted by, for example, hammering using a stamping method, resulting in low processing costs. Also, the thickness of the bonding region 13 of the metal pattern 11 (thick pattern portion 14 and thin pattern portion 15) can be easily adjusted by plating or lamination methods, resulting in low processing costs. Therefore, the semiconductor device according to the present invention can be easily manufactured at low processing costs compared to the conventional bonding method of adding a nickel layer.

[0033] It is preferable that at least the lower surface of the thin lead portion 24 and the surface of the thick pattern portion 14 are welded together. If the lower surface of the thin lead portion 24 and the surface of the thick pattern portion 14 are welded together, the joint strength will be more stable and sufficient. The lower surface of the thick lead portion 25 and the surface of the thin pattern portion 15 do not necessarily have to be welded together. Such a structure can be formed by laser irradiation as described below, and the formation of damage such as through holes in the inner lead end caused by the laser can be more effectively suppressed.

[0034] (Semiconductor chips) The semiconductor chip in the semiconductor device according to the present invention is not particularly limited. For example, it may be a power chip such as a transistor or a diode that handles high power, or a power chip and a control chip such as a control IC that handles less power than the power chip may be arranged in different positions on the circuit board. These may be fixed on the circuit board 10 by soldering, a conductive adhesive, or the like.

[0035] There are no particular limitations on the circuit board 10 as long as it has a surface having a metal pattern 11. For example, a substrate having metal patterns 11 on both sides of a ceramic substrate 12 as shown in Fig. 1, 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.

[0036] Fig. 3 shows an example of an intelligent power module (IPM) 200, which is a specific example of a semiconductor device. In the example of Fig. 3, a plurality of semiconductor devices 30 are provided on a DBC substrate. The connection structure between the inner lead and the metal pattern of the present invention described in Fig. 1 can be suitably applied to the IPM 200 shown in Fig. 3.

[0037] [Electrical Equipment] The above-mentioned semiconductor device can be applied to electrical equipment. The use of a semiconductor device with improved reliability and reduced cost contributes to improved reliability and reduced cost of electrical equipment. Such electrical equipment has reduced costs due to reduced costs of the semiconductor device. The electrical equipment is not particularly limited, but in particular, the above-mentioned example of the semiconductor device (IPM) 200 can be suitably applied as a small high-voltage three-phase motor driver to electrical equipment for driving compressors in air conditioners, refrigerators, etc.

[0038] 10 is a diagram illustrating an air conditioner 300 as one embodiment of an electrical device. The air conditioner 300 is composed of an indoor unit 310 and an outdoor unit 320, each of which is equipped with fan motors 311, 321, a compressor 322, and an electrical device, an IPM 200. It is preferable to use IPM 200 with specifications suitable for driving the respective motors and compressors.

[0039] [How to connect the inner lead] Next, a method for connecting inner leads according to the present invention will be described. The components constituting the semiconductor device are the same as those described in the above semiconductor device.

[0040] Fig. 4 shows a conceptual diagram of a method for connecting an inner lead according to the present invention. First, as shown in Fig. 4(A), a lead frame is used that has an inner lead 21 with a flat upper surface and a thin lead portion 24 and a thick lead portion 25 in a bonding region 23 at an end, the thin lead portion 24 and the thick lead portion 25 having different distances between the upper surface and the lower surface of the inner lead to be bonded to the metal pattern 11. Note that Fig. 4 shows an example in which an inclined portion 26 is provided between the thin lead portion 24 and the thick lead portion 25. Such an inner lead end shape can be easily formed by, for example, hammering using a stamping method, and therefore the processing cost is low.

[0041] The circuit board used has a semiconductor chip 30 mounted thereon and a metal pattern 11 on its surface, with the metal pattern 11 having a thick pattern portion 14 and a thin pattern portion 15 of different thicknesses in a bonding region 13 of the metal pattern 11. An inclined portion 16 is provided to match the shape of the bonding region 23 at the end of the inner lead 21. The thickness of the bonding region 13 of the metal pattern 11 (thick pattern portion 14, inclined portion 16, thin pattern portion 15) can be easily adjusted by plating or lamination, so that processing costs are low.

[0042] 4(B), the lower surface of the thin lead portion 24 is opposed to the upper surface of the thick pattern portion 14, and the lower surface of the thick lead portion 25 is opposed to the upper surface of the thin pattern portion 15, thereby joining the inner lead 21 to the metal pattern 11. With this method of connecting the inner leads, it is possible to suppress an increase in costs without reducing the strength of the laser joining (welding).

[0043] Although there is no particular limitation on the method for joining the inner lead 21 and the metal pattern 11, it is preferable to bring the upper surface of the metal pattern 11 into contact with the lower surface of the end of the inner lead 21 and irradiate the laser L from the upper surface side of the inner lead to perform laser welding. This makes it possible to join the inner lead 21 and the metal pattern 11 more easily and with higher productivity.

[0044] When joining the inner lead 21 and the metal pattern 11 by laser welding, it is preferable to irradiate the laser L while moving (traveling direction S) from the thick lead portion 25 to the thin lead portion 24 of the inner lead 21, as shown in Figures 4(B) and 6. This forms a molten part 18 as shown in Figure 4(C), and the end of the inner lead 21 and the circuit board 10 (metal pattern 11) are laser welded (joined).

[0045] In the case of an IPM 200 as shown in Fig. 3, multiple bonding points can be bonded in the same manner as shown in Figs. 4 and 6, as shown in Fig. 5. 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.

[0046] For comparison with the present invention, FIG. 7 shows a conceptual diagram of laser bonding when both the lower surface (bonding surface) of the end of the inner lead 21 and the surface of the metal pattern 11 of the circuit board 10 are flat. FIG. 7(A) shows the state of laser irradiation, FIG. 7(B1) shows a cross-sectional view of the bonded (welded) part after laser irradiation, and FIG. 7(B2) shows a top view of the bonded part after laser irradiation. When the laser is irradiated while traveling, due to the relationship between the time from the start of laser irradiation until a certain output is reached and the moving speed of the irradiation, the laser irradiation is performed while the moving speed is not sufficiently increased immediately after the start of irradiation, and as shown in FIG. 7(B), the energy of the laser is concentrated and may become non-uniform in the traveling irradiation direction of the laser. The result of observing the cross section of the bonded part when actually performing bonding as shown in FIG. 7(A) is shown in FIG. 8. It can be seen that the depth of the melted part by the laser irradiation is non-uniform.

[0047] When joining the joining surface of the inner lead 21 and the surface of the metal pattern 11 of the circuit board 10, which are flat as shown in FIG. 7, if the laser energy immediately after the start of laser irradiation exceeds the intended range, the metal material may melt deeply, and damage such as the opening of a through hole 17 in the inner lead may occur as shown in FIGS. 7(B1) and (B2).

[0048] Therefore, as shown in Figures 4(B) and 6, the laser is irradiated while moving (traveling direction S) from the thick lead portion 25 to the thin lead portion 24 of the inner lead 21. If the laser is irradiated to the thick lead portion 25 immediately after the start of irradiation, the laser energy can be effectively absorbed by the thick lead portion 25, and damage to the laser irradiated portion of the inner lead can be more effectively prevented. Furthermore, since the laser irradiation position moves to the thin lead portion 24, laser welding between the thin lead portion 24 and the thick pattern portion 14 can be reliably performed.

[0049] When laser welding is performed by traveling irradiation of the laser L, the traveling speed 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.

[0050] In addition, when the inner lead 21 and the metal pattern 11 are joined by laser welding, it is preferable to perform laser welding by simultaneously irradiating (superimposed irradiation) a blue laser and an infrared laser. The light absorption rate of the metal material is different between the blue laser and the infrared laser. For example, when the metal material is copper (Cu), the absorption rate of the blue laser is about 65%, and the absorption rate of the infrared laser is about 5% or less. Therefore, by irradiating the blue laser to heat the vicinity of the surface of the metal material (inner lead) and supplementing the heating by the infrared laser, it is possible to realize more efficient and stable melting of the joint between the inner lead and the metal pattern. In such laser irradiation, the melting related to the joint is substantially performed by the infrared laser. In other words, the blue laser contributes to the stabilization of heating and melting. When performing traveling irradiation while irradiating the laser in a superimposed manner, the laser output of the blue laser and the infrared laser can be adjusted as shown in FIG. 9.

[0051] 6 is a diagram for explaining laser irradiation in the method for connecting inner leads according to the present invention, showing a conceptual diagram when a blue laser and an infrared laser are irradiated simultaneously (superimposed irradiation) and laser joining (welding) is performed while irradiating the laser in a traveling manner. The area near the surface of the metal material (inner lead 21) is the blue laser heating area 27, and a deeper area of ​​the metal material is the infrared laser heating area 28. When laser joining (welding) is performed while performing superimposed irradiation and traveling irradiation in this way, the thin lead part 24 and the thick pattern part 14 are reliably joined as shown in FIG. 4(C), making it possible to maintain a higher joint strength more stably.

[0052] As described above in detail, the semiconductor device of the present invention suppresses the increase in cost associated with the connection between the circuit pattern and the wiring portion without reducing the bonding strength between the inner lead and the metal pattern. Also, the method of connecting the inner lead of the present invention makes it possible to suppress the increase in cost without reducing the bonding strength between the inner lead and the metal pattern. This contributes to improving the reliability and reducing the cost of the semiconductor device.

[0053] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0054] 10...circuit board, 11...metal pattern, 12...ceramic board, 13 ... bonding area; 14 ... thick pattern portion; 15 ... thin pattern portion; 16 ... inclined portion; 17 ... through hole, 18 ... fusion zone, 20: lead frame; 21: inner lead; 23: bonding area; 24...thin lead portion, 25...thick lead portion, 26...inclined portion, 27...Blue laser heating area, 28...Infrared laser heating area, 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 motors, 322...compressor. S...travel direction, L...laser.

Claims

1. A circuit board having a metal pattern on a surface thereof; A semiconductor chip mounted on the circuit board; a lead frame including inner leads having end bonding regions connected to the circuit board; A semiconductor device comprising the semiconductor chip and a molding resin that resin-seals the lead frame, a bonding region at the end of the inner lead has a flat upper surface, and includes a thin lead portion and a thick lead portion, the distance between the upper surface and a lower surface that contacts the metal pattern of the circuit board being different; the bonding region of the metal pattern has a thick pattern portion and a thin pattern portion, the thicknesses of the metal pattern being different from each other; The semiconductor device is characterized in that the inner lead and the circuit board are joined such that the lower surface of the thin lead portion faces the upper surface of the thick pattern portion, and the lower surface of the thick lead portion faces the upper surface of the thin pattern portion.

2. 2. The semiconductor device according to claim 1, wherein at least the lower surface of said thin lead portion and the surface of said thick pattern portion are joined by welding.

3. 3. An electrical device comprising the semiconductor device according to claim 1.

4. 1. A method for connecting an inner lead to a lead frame having an inner lead with a lower surface that contacts the circuit board at an end portion thereof, the method comprising the steps of: a lead frame including inner leads having a thin lead portion and a thick lead portion in a bonding region at the end portion, the thin lead portion and the thick lead portion having different distances between the flat upper surface and the lower surface of the inner lead to be bonded to the metal pattern; and a circuit board having a thick pattern portion and a thin pattern portion in a bonding region of the metal pattern, the thick pattern portion and the thin pattern portion having different thicknesses of the metal pattern, A method for connecting an inner lead, characterized in that the lower surface of the thin lead portion and the upper surface of the thick pattern portion are opposed to each other, and the lower surface of the thick lead portion and the upper surface of the thin pattern portion are opposed to each other, thereby joining the inner lead to the circuit board.

5. 5. The method for connecting an inner lead according to claim 4, wherein the upper surface of the metal pattern is brought into contact with the lower surface of the end of the inner lead, and a laser is irradiated from the upper surface side of the inner lead to perform laser welding.

6. 6. The method for connecting an inner lead according to claim 5, wherein a blue laser and an infrared laser are irradiated simultaneously in said laser welding.

7. 7. The method for connecting an inner lead according to claim 5, wherein, in the laser welding, the laser is irradiated while moving from the thick lead portion to the thin lead portion of the inner lead.

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