JP7690357B2 - Lead frame, semiconductor device, and method of manufacturing lead frame - Google Patents

Description

The present invention relates to a lead frame, a semiconductor device, and a method for manufacturing a lead frame.

In recent years, semiconductor devices have become known in which a semiconductor element, such as an IC (Integrated Circuit) chip, is mounted on a metal lead frame. That is, the semiconductor element is mounted on a planar die pad provided in the center of the lead frame, and the semiconductor element is connected to multiple leads provided around the die pad by, for example, wire bonding. The semiconductor element mounted on the lead frame may then be sealed with a resin such as epoxy resin to form a semiconductor device.

Some such lead frames do not have a die pad, but are constructed by joining a heat sink to a frame member having multiple leads. That is, a heat sink that is thicker than the frame member is joined, for example by welding, to the center of a frame member made of a thin metal plate, and a semiconductor element is mounted directly on this heat sink. This allows the heat generated by the semiconductor element to be efficiently dissipated with a simple structure.

Japanese Patent Application Publication No. 11-145364 Japanese Patent Application Publication No. 08-162590

However, when a heat sink is joined to a frame member, there is a problem in that the frame member or heat sink may be deformed or damaged by heat. That is, laser welding is sometimes used to join fine parts such as joining a frame member and a heat sink, but when a laser is irradiated for a long period of time on the frame member and heat sink to be joined, heat is transferred to the surroundings of the joint, which can cause thermal deformation. In particular, when laser welding is performed in the area where the frame member and heat sink overlap, the laser is irradiated until it penetrates the frame member, which is made of a thin plate, and the frame member and heat sink are welded together. As a result, a relatively high-power laser is irradiated on the joint, which can cause deformation or damage to the surroundings of the joint.

On the other hand, if the laser output is reduced or the laser irradiation time is shortened to prevent such deformation or damage, the welding between the frame member and the heat sink will be insufficient, resulting in a decrease in the quality of the lead frame and semiconductor device.

The disclosed technology has been developed in light of these points, and aims to provide a lead frame, a semiconductor device, and a method for manufacturing a lead frame that can prevent unnecessary deformation and damage caused by welding.

In one embodiment, the lead frame disclosed in this application has a support part with a through hole formed at one end, a lead, and a heat sink welded to the support part at one opening of the through hole.

According to one aspect of the lead frame, semiconductor device, and method of manufacturing a lead frame disclosed in the present application, it is possible to prevent unnecessary deformation and damage caused by welding.

FIG. 1 is a diagram showing a structure of a lead frame according to an embodiment. FIG. 2 is a flow diagram showing a method for manufacturing a lead frame. FIG. 3 is a diagram showing a specific example of the molding process. FIG. 4 is a diagram showing a specific example of the through hole forming step. FIG. 5 is a diagram showing a specific example of the shape of the through hole. FIG. 6 is a diagram showing a specific example of a plating process. FIG. 7 is a diagram showing a specific example of a laser welding process. FIG. 8 is a diagram illustrating the laser welding process. FIG. 9 is a diagram showing a specific example of a semiconductor chip mounting surface of a heat sink. FIG. 10 is a diagram showing a specific example of the structure of a semiconductor device. FIG. 11 is a diagram showing a structure of a lead frame according to another embodiment. FIG. 12 is a diagram showing another specific example of the structure of a semiconductor device. FIG. 13 is a diagram illustrating another laser welding process.

Below, an embodiment of the lead frame, semiconductor device, and method for manufacturing the lead frame disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment.

Figure 1 shows the structure of a lead frame 100 according to one embodiment. Figure 1(a) is a plan view of the lead frame 100, and Figure 1(b) is a cross-sectional view taken along line I-I in Figure 1(a).

The lead frame 100 has a structure in which a heat sink 150 is joined to a frame member having a frame body 110, support bars 120, leads 130, and tie bars 140. The frame member is formed from a thin metal plate such as copper or a copper alloy with a thickness of, for example, about 0.1 to 0.25 mm. On the other hand, the heat sink 150 is a plate-shaped member made of a metal such as copper or a copper alloy that is thicker than the thin plate that forms the frame member, for example, with a thickness of 1 mm or more.

The frame 110 defines the outer periphery of one lead frame 100 and supports the support bar 120 and the multiple leads 130 via the tie bar 140. When manufacturing the lead frame 100, the multiple lead frames 100 are manufactured as an assembly of lead frames connected via the frame 110. Then, after a semiconductor chip is mounted on the lead frame 100 and resin-encapsulated, the tie bar 140 between the multiple leads 130 and between the leads 130 and the support bar 120 is cut. Next, the portion including the support bar 120, the multiple leads 130, and the heat sink 150 is cut from the frame 110 to obtain an individualized semiconductor device.

The support bars 120 are a pair of support parts that extend from both ends of the length direction toward the center of the lead frame 100 in the short-side center, and support the heat sink 150 at the end (hereinafter referred to as the "center end") located at the center of the lead frame 100. That is, a through hole 125 is formed at each of the center ends of the pair of support bars 120 at a position where it overlaps with the heat sink 150, and the mounting surface 150a of the heat sink 150 on which the semiconductor chip is mounted is welded to this through hole 125.

As shown in FIG. 1(b), the cross section of the through hole 125 has a tapered shape with the diameter decreasing as it approaches the heat sink 150. The diameter of the opening of the through hole 125 farthest from the heat sink 150 is, for example, about 0.4 mm, and the diameter of the opening of the through hole 125 closer to the heat sink 150 is, for example, about 0.2 mm. Because the through hole 125 has a tapered shape, the inner wall surface of the through hole 125 is exposed even in the plan view shown in FIG. 1(a), for example.

The leads 130 extend parallel to the support bar 120, and are terminals that electrically connect a semiconductor chip to an external component when the semiconductor chip is mounted on the lead frame 100. The leads 130 are shorter than the support bar 120, and the central end of the leads 130 does not overlap the heat sink 150. A plating layer is formed on the surface of the central end of the leads 130 that is farther from the heat sink 150, and when a semiconductor chip is mounted on the lead frame 100, the semiconductor chip is connected to the plating layer by wire bonding.

The heat sink 150 is a copper plate-like member joined to the central ends of the pair of support bars 120. The surface of the heat sink 150 joined to the support bar 120 is the mounting surface 150a on which the semiconductor chip is mounted. The mounting surface 150a is roughened and has a greater surface roughness than the other surfaces. The heat sink 150 dissipates heat generated by the semiconductor chip mounted on the mounting surface 150a from the surface opposite the mounting surface 150a. Therefore, the surface opposite the mounting surface 150a is exposed from the mold resin even when the semiconductor chip is sealed with the mold resin.

Next, a method for manufacturing the lead frame 100 configured as described above will be described with reference to the flow diagram shown in FIG. 2.

First, a frame member is formed by pressing or etching a thin metal plate, such as copper or a copper alloy, having a thickness of, for example, about 0.1 to 0.25 mm (step S101). Specifically, as shown in FIG. 3, for example, a support bar 120, a number of leads 130, and tie bars 140 are formed within the area surrounded by a frame body 110.

Then, a through hole 125 is formed in the central end of the support bar 120 (step S102). That is, as shown in FIG. 4, for example, a tapered through hole 125 is formed in the central end of a pair of support bars 120 in each region surrounded by the frame body 110. Note that the formation of the through hole 125 in step S102 may be performed simultaneously with the molding of the frame member in step S101. Also, the number and shape of the through hole 125 are not limited to one and a tapered shape.

5 is a diagram showing a specific example of the shape of the through hole 125. The through hole 125 may be a cylindrical through hole as shown in FIG. 5(a), or may be a truncated cone-shaped through hole with a tapered cross section as shown in FIG. 5(b). These through holes 125 are formed at positions where the laser is irradiated when the heat sink 150 is joined to the support bar 120 by laser welding. At this time, it is preferable that the spot diameter of the laser irradiated to the through hole 125 shown in FIG. 5(a) is larger than the diameter of the through hole 125 so that the laser is irradiated to the boundary between the support bar 120 and the heat sink 150. That is, as shown by the dashed line in FIG. 5(a), it is preferable that the irradiation range of the laser includes the entire opening of the through hole 125. In addition, it is preferable that the spot diameter of the laser irradiated to the through hole 125 shown in FIG. 5(b) is larger than the diameter of the small-diameter opening of the through hole 125 close to the heat sink 150. That is, as shown by the dashed line in Fig. 5(b), it is preferable that the laser irradiation range includes a part of the inner wall surface of the through hole 125. When the through hole 125 having a tapered cross section as shown in Fig. 5(b) is formed, the inner wall surface of the through hole 125 is exposed in a plan view, so that the laser is directly irradiated onto the inner wall surface of the through hole 125, and the laser irradiation area of the support bar 120 is increased, allowing efficient welding.

The through hole 125 may have multiple through holes, for example, as shown in FIG. 5(c). In this case, it is preferable that the laser irradiation range is a range that spans multiple through holes, as shown by the dashed line in FIG. 5(c). By forming multiple through holes, even if there is some error in the laser irradiation position, the laser is irradiated to the boundary between the support bar 120 and the heat sink 150 at any one of the through holes, and the heat sink 150 can be reliably welded to the support bar 120. Furthermore, the through hole 125 may have a shape having a tab 125a protruding into the inside of the through hole 125, for example, as shown in FIG. 5(d). In this case, it is preferable that the laser irradiation range is a range that includes at least a part of the tab 125a, as shown by the dashed line in FIG. 5(d). Because the tab 125a protrudes into the through hole 125, even if the laser spot diameter is smaller than the diameter of the through hole 125, the laser is irradiated to the boundary between the support bar 120 and the heat sink 150, and the heat sink 150 can be reliably welded to the support bar 120. The tab 125a may be bent to have an inclination toward the heat sink 150. This allows the tip of the tab 125a to be in close contact with the heat sink 150, allowing for stable welding.

Once the through holes 125 are formed in the support bar 120, a plating layer is formed on the center end of the leads 130 (step S103). Specifically, as shown in FIG. 6, for example, a plating layer 130a is formed on the surface of the center end of each lead 130 opposite the surface that is joined to the heat sink 150. The plating layer 130a is formed, for example, by silver plating.

Through these steps, a frame member made of a thin copper plate is completed. A heat sink 150 made of a metal such as copper or a copper alloy and having a thickness of, for example, 1 mm or more is laser welded to this frame member (step S104). That is, for example, as shown in FIG. 7, the heat sink 150 is positioned so as to overlap the through hole 125 of the support bar 120, and a laser is irradiated onto the position of the through hole 125, thereby welding the heat sink 150 to the support bar 120.

Specifically, as shown in FIG. 8(a), the frame member and the heat sink 150 are aligned so that the through hole 125 of the support bar 120 overlaps with the welding position of the mounting surface 150a of the heat sink 150. Then, the laser is irradiated to both the vicinity of the through hole 125 of the support bar 120 and the mounting surface 150 of the heat sink 150. That is, as shown in FIG. 8(b), for example, the laser L is irradiated to a range including the inner wall surface of the through hole 125 and the mounting surface 150a of the heat sink 150. Here, since the cross section of the through hole 125 is tapered, the inner wall surface of the through hole 125 is exposed when viewed from the irradiation source of the laser L. As a result, the laser L is directly irradiated to the inner wall surface of the through hole 125, and the laser irradiation area for the support bar 120 is increased, allowing efficient welding.

In this way, as a result of the laser being irradiated to both the vicinity of the through-hole 125 of the support bar 120 and the mounting surface 150 of the heat sink 150, the boundary between the support bar 120 and the heat sink 150, for example, the area W, is welded as shown in FIG. 8(c), and the frame member and the heat sink 150 are integrated.

The laser used for laser welding can be, for example, a green laser or a fiber laser. Because the through holes 125 are formed in advance in the support bar 120, the laser output can be relatively low, for example, 1.5 kW or less. The laser irradiation time at the position of each through hole 125 can be, for example, about 0.2 to 0.5 seconds. In this way, because the through holes 125 are formed in advance in the support bar 120, the laser output can be low and the irradiation time can be short. As a result, the heat of the laser is not transmitted to any area other than the vicinity of the through holes 125 to be welded, and deformation and damage to the frame member and heat sink 150 can be prevented.

The mounting surface 150a of the heat sink 150 that is welded to the support bar 120 is roughened by roughening treatment. Specifically, as shown in FIG. 9, the surface roughness of the mounting surface 150a of the heat sink 150 is increased by copper roughening plating or anodizing treatment. That is, the surface roughness of the mounting surface 150a of the heat sink 150 is greater than the surface roughness of the surface of the heat sink 150 opposite to the mounting surface 150a. Therefore, the surface roughness of the mounting surface 150a exposed at the bottom of the through hole 125 of the support bar 120 is large, and the reflection of the laser that passes through the through hole 125 and is irradiated to the mounting surface 150a can be suppressed, and the laser absorption is improved, allowing efficient welding.

In this manner, the heat sink 150 is laser welded to the through-hole 125 of the support bar 120 to form the lead frame 100. A semiconductor chip is mounted on the lead frame 100, and the semiconductor chip is sealed with a molding resin such as epoxy resin. The support bar 120 and the leads 130 are then cut from the frame 110 to obtain a semiconductor device.

Figure 10 shows a specific example of the structure of a semiconductor device. Figure 10(a) shows a cross section of the semiconductor device at a position along the support bar 120, and Figure 10(b) shows a cross section of the semiconductor device at a position along the lead 130.

As shown in FIG. 10, the semiconductor chip 210 is mounted on the mounting surface 150a of the heat sink 150, and the semiconductor chip 210 and the leads 130 are connected by wire bonding. That is, the electrodes of the semiconductor chip 210 and the plating layer 130a of the leads 130 are connected by wires 230. The semiconductor chip 210 is then sealed with molded resin 220. At this time, the surface of the heat sink 150 opposite the mounting surface 150a is exposed from the molded resin 220, and the heat generated by the semiconductor chip 210 mounted on the mounting surface 150a can be efficiently dissipated.

The central end of the support bar 120 where the through hole 125 is formed is sealed with the semiconductor chip 210 by the molded resin 220, and the other end of the support bar 120 is bent into a shape similar to that of the lead 130, protruding from the side of the molded resin 220. The support bar 120 bent into a shape similar to that of the lead 130 in this way may be used as a lead for ground wiring. On the other hand, the central end of the lead 130 connected to the semiconductor chip 210 in the plating layer 130a is sealed with the molded resin 220 together with the semiconductor chip 210, and the other end of the lead 130 is bent into a shape similar to that of the lead 130, protruding from the side of the molded resin 220. The end of the lead 130 protruding from the molded resin 220 can be connected to other components such as a wiring board. That is, the lead 130 is used, for example, as a lead for signal wiring.

As described above, according to this embodiment, a through hole is formed in advance in a frame member made of a thin plate, and a heat sink plate, which is thicker than the frame member, is joined by laser welding in the through hole. This allows the output of the laser for welding to be low, and the laser irradiation time to be short. As a result, the heat of the laser is not transferred to any area other than the vicinity of the through hole, and unnecessary deformation and damage due to welding can be prevented.

In the above embodiment, the lead frame 100 is described as being used in a small outline package (SOP) type semiconductor device in which the leads 130 protrude in two directions from the mold resin 220. However, the lead frame 100 similar to that in the above embodiment can also be applied to a quad flat package (QFP) type semiconductor device in which the leads 130 protrude in four directions from the mold resin 220.

It is also possible to apply the lead frame 100 similar to the above embodiment to semiconductor devices in which the leads 130 do not protrude from the mold resin 220, such as SON (Small Outline Non-leaded package) type or QFN (Quad Flat Non-leaded package) type.

Figure 11 is a diagram showing the structure of a lead frame 100 used in a SON type semiconductor device. Figure 11(a) is a plan view of the lead frame 100, and Figure 11(b) is a cross-sectional view taken along line II-II in Figure 11(a).

In the lead frame 100 shown in FIG. 11, the support bar 120 and the leads 130 each extend from the short side of the frame 110 in the longitudinal direction of the lead frame 100. A through hole 125 with a tapered cross section is formed at the center end of the support bar 120, as in the above embodiment, and a heat sink 150 is welded to this through hole 125. The heat sink 150 is welded to the support bar 120 at the mounting surface 150a on which the semiconductor chip is mounted. In addition, the support bar 120 and the leads 130 are bent so that the ends opposite the center end are positioned to become external terminals of the semiconductor device.

Even in such a lead frame 100, the through hole 125 is formed in advance at the central end of the support bar 120, so when laser welding the heat sink 150 to the support bar 120, the laser output can be low and the laser irradiation time can be short. As a result, the heat of the laser is not transmitted to any area other than the vicinity of the through hole, and unnecessary deformation and damage due to welding can be prevented.

Figure 12 shows a specific example of the structure of a semiconductor device. Figure 12(a) shows a cross section of the semiconductor device at a position along the support bar 120, and Figure 12(b) shows a cross section of the semiconductor device at a position along the lead 130.

As shown in FIG. 12, the semiconductor chip 210 is mounted on the mounting surface 150a of the heat sink 150, and the semiconductor chip 210 and the leads 130 are connected by wire bonding. That is, the electrodes of the semiconductor chip 210 and the leads 130 are connected by wires 230. Then, the entire lead frame 100 on which the semiconductor chip 210 is mounted is sealed with molded resin 220. At this time, the surface of the heat sink 150 opposite the mounting surface 150a is exposed from the molded resin 220, and the heat generated by the semiconductor chip 210 mounted on the mounting surface 150a can be efficiently dissipated.

In addition, the ends of the support bar 120 and the leads 130 opposite the central end are exposed from the side and bottom surface of the molded resin 220. By exposing the ends of the leads 130 from the molded resin 220, these ends become external terminals that connect the semiconductor device to other components, such as a wiring board.

In this way, it is possible to form a SON or QFN type semiconductor device in which the leads 130 do not protrude from the mold resin 220 using the lead frame 100 described above.

In the above embodiment, it has been described that the entire opening of the through hole 125 of the support bar 120 is included in the laser irradiation range. For example, a green laser (wavelength: 532 nm) with a spot diameter of about 0.2 to 0.3 mm can be used as such a laser. On the other hand, when laser welding is performed using a fiber laser (wavelength: 1064 nm) with a spot diameter of about 0.024 to 0.044 mm, which is smaller than the green laser, the laser may be irradiated to multiple points of the opening of the through hole 125.

Specifically, as shown in FIG. 13(a), for example, the laser L is irradiated to multiple locations near the boundary between the inner wall surface of the through hole 125 and the mounting surface 150a of the heat sink 150. The output of the laser L irradiated to each of the multiple locations can be relatively low, for example, 1.5 kW or less. The irradiation time of the laser at each of the multiple locations can be, for example, about 0.2 to 0.5 seconds. In this way, since the through hole 125 is formed in advance in the support bar 120, even when laser welding is performed using a fiber laser with a relatively small spot diameter, the laser output can be low and the irradiation time can be short. As a result, the heat of the laser is not transmitted to any area other than the vicinity of the through hole 125 to be welded, and deformation and damage to the frame member and the heat sink 150 can be prevented.

Also, for example, when the through hole 125 is cylindrical as shown in FIG. 13(b), multiple points on the opening edge of the through hole 125 become the laser irradiation range IA, and the support bar 120 and the heat sink 150 are joined at multiple points. In the example shown in FIG. 13(b), four points on the opening edge of the through hole 125 become the laser irradiation range IA, but it is sufficient to have at least two points as the laser irradiation range IA. Since the support bar 120 and the heat sink 150 are joined near each of the multiple laser irradiation ranges IA, the more the laser irradiation range IA, the more the joining reliability between the support bar 120 and the heat sink 150 improves.

Furthermore, even when multiple tabs 125a are formed protruding into the through-hole 125 as shown in FIG. 13(c), the laser irradiation range IA can be, for example, near the tip of each of the multiple tabs 125a. In this case, the laser irradiation range IA may be provided not only near the tip of the tab 125a, but also near the base of the tab 125a or at the opening edge of the through-hole 125. Also, for example, by forming the tab 125a thinner than the surrounding support bar 120 body, it is possible to further reduce the laser output and further shorten the irradiation time.

REFERENCE SIGNS LIST 100 Lead frame 110 Frame body 120 Support bar 125 Through hole 125a Tab 130 Lead 130a Plating layer 140 Tie bar 150 Heat sink 150a Mounting surface 210 Semiconductor chip 220 Molding resin 230 Wire

Claims (17)

A pair of support parts extending such that one end of each of the support parts faces each other, and a through hole is formed in each of the one ends of the support parts;
Lead and
a heat sink welded to the pair of support parts at one opening of the through hole of each of the pair of support parts ,
An inner periphery of one opening of the through hole of each of the pair of support portions is welded to the heat sink.
A lead frame comprising: The through hole is
2. The lead frame according to claim 1, wherein the lead frame has a tapered shape in which one opening has a larger diameter than the other opening. The through hole is
The lead frame according to claim 1 , wherein a plurality of the support portions are formed at one end of each of the pair of support portions. The through hole is
2. The lead frame of claim 1, further comprising an inwardly projecting tab. The heat sink is
The lead frame according to claim 1 , wherein the surface roughness of the surfaces bonded to the pair of supports is greater than the surface roughness of the other surfaces. The heat sink is
2. The lead frame according to claim 1, wherein one opening of the through hole is welded to the pair of supporting portions at a plurality of points. frame body
and
The pair of support parts are
At the center of the frame in a second direction perpendicular to the first direction, the frame extends from both ends in the first direction toward the center such that one end of each of the frame faces the other.
2. The lead frame according to claim 1. A lead frame;
A semiconductor element mounted on the lead frame;
and a sealing resin that seals the semiconductor element.
The lead frame is
A pair of support parts extending such that one end of each of the support parts faces each other, and a through hole is formed in each of the one ends of the support parts;
Lead and
a heat sink welded to the pair of support parts at one opening of the through hole of each of the pair of support parts,
an inner periphery of one opening of the through hole of each of the pair of support portions is welded to the heat sink;
The semiconductor device is
a semiconductor device mounted on one surface of the heat sink and connected to the leads. The heat sink is
9. The semiconductor device according to claim 8 , wherein a surface opposite to the surface on which the semiconductor element is mounted is exposed from the sealing resin. The lead is
The semiconductor device according to claim 8 , wherein a part of the semiconductor device is exposed from the sealing resin. a step of forming a frame member having a pair of support parts extending from a metal plate such that one end of each of the pair of support parts faces each other, each of the pair of support parts having a through hole formed at one end thereof, and a lead;
and welding a heat sink to the pair of support parts at one opening of the through hole of each of the pair of support parts ,
An inner periphery of one opening of the through hole of each of the pair of support portions is welded to the heat sink.
A method for manufacturing a lead frame comprising the steps of: The molding step includes:
13. The method for manufacturing a lead frame according to claim 11 , further comprising forming a frame member having a pair of support parts in which tapered through holes are formed, one of the openings having a diameter larger than the other opening. The method further includes a step of performing a roughening treatment to make the surface roughness of one surface of the heat sink greater than the surface roughness of the other surface of the heat sink,
The welding step includes:
The method for manufacturing a lead frame according to claim 11 , further comprising welding one surface of the heat sink to the support portion. The welding step includes:
2. The method for manufacturing a lead frame according to claim 1 , wherein the laser welding is performed using a laser having a spot diameter larger than the diameter of the through hole. The welding step includes:
13. The method for manufacturing a lead frame according to claim 11 , wherein the laser welding is performed using a laser having a spot diameter smaller than the diameter of the through hole. The welding step includes:
The method for manufacturing a lead frame according to claim 15 , characterized in that the heat sink is welded to the pair of support portions at a plurality of locations on one opening of the through hole. The molding step includes:
forming the frame member further having a frame body;
The pair of support parts are
At the center of the frame in a second direction perpendicular to the first direction, the frame extends from both ends in the first direction toward the center such that one end of each of the frame faces the other.
12. The method for manufacturing a lead frame according to claim 11.

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