JPH11330340A - Semiconductor device and mounting structure thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracks from occurring in a lead, by a method wherein a led is possessed of a lower plating film of tin or tin-bismuth alloy, an upper plating film of tin-bismuth alloy which is higher in bismuth content than the lower plating film, and both films are formed on the surface of the lead base material of the lead. SOLUTION: A lower plating film 7 is formed of tin whose bismuth content is 0 to 1 wt.% or tin-bismuth alloy, whereby cracks are prevented from occurring in a lead when the lead is bent in a lead forming process, and the lead is prevented from deteriorating in wettability. An upper plating film 8 is formed of tin-bismuth alloy which is 1 to 10 wt.% in bismuth content, whereby an electrical short circuit can be prevented from occurring between leads which are narrow in space between them and easy to produce whiskers, cracks are prevented from occurring in the leads when the leads are bent in a lead forming process, and the leads are prevented from deteriorating in wettability. Moreover, A lead can be plated with lead-free solder which is excellent in corrosion resistance and harmless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a lead formed by forming a lead-free two-layer plating film on the surface of a lead substrate and bending the lead.

[0002]

2. Description of the Related Art In a so-called packaging process, a semiconductor element such as an IC or an LSI is fixed on a lead frame, electrically connected to the lead frame by wire bonding or the like, and further molded with a molding resin. Then, in order to connect to an external circuit such as a substrate using solder or the like, the lead exposed to the outside of the mold resin is subjected to a tin-lead alloy mainly containing 10 to 40 wt% of lead, so-called lead solder plating. Thereafter, the lead is cut from the frame and bent into a predetermined shape. As described above, the plating on the leads is required to have properties such as solder wettability, heat resistance, whisker resistance, adhesion, bending properties, and corrosion resistance. However, lead solder plating satisfies all of these required characteristics and is widely used in current products.

[0003]

Among the recent environmental problems, environmental pollution due to lead has become a major problem. Lead solder is widely used as a bonding material for electrical parts such as home appliances and automobile parts. When these are turned into shredder dust and discarded outdoors, they are exposed to acidic atmospheres such as acid rain. This leads to a problem that lead in the solder is eluted and contaminates the groundwater.
Therefore, the development of a so-called lead-free solder containing no lead has been promoted, and lead-free solders such as Sn-Ag-Bi based and Sn-Zn-Bi based have been developed. Further, development of lead-free solder plating corresponding to lead-free solder has been advanced, and as a plating film material, palladium, tin-zinc alloy (JP-A-4-212443), tin-silver alloy,
A tin-bismuth alloy and the like are mentioned. However, each of these alloy plating films has a major problem. Palladium cannot be applied to 42 alloy which is a mainstream lead material in terms of corrosion resistance. Tin-zinc alloys are easily oxidized, have poor wettability, and are liable to generate whiskers. The surface of a tin-silver alloy is discolored blue by heating, and the wettability is reduced. Since the tin-bismuth alloy is hard and brittle, cracks occur in the plating film when the lead is bent in the above-described semiconductor element forming step. Therefore, if the heating step is performed after bending the lead, the lead surface is oxidized, and the wettability is reduced.
Also, the corrosion resistance is reduced. Since any of these tin alloys has a major problem, it cannot be used as an alternative plating film for the conventional tin-lead alloy.

Further, Toshiba Technical Publication VOL. 15-6
2, Issue No. 97-0647, pp. 61 and 62 (Issue Date: 1997-9-29), Sn plating or Sn alloy plating is applied to the lead base material portion as a base plating portion, and the surface plating portion is provided. It describes that an Sn-based alloy plating of two or more elements (for example, SnAg, SnZn, SnBi, etc.) is performed. However, no consideration is given to eliminating the occurrence of cracks and whiskers.

An object of the present invention is to solve the above-mentioned problems of the prior art by using a lead-free solder plating to prevent the occurrence of cracks so that there is no decrease in wettability, and excellent in whisker resistance and corrosion resistance. Provided is a semiconductor device having a highly reliable semiconductor device having bent leads formed by soldering, and a semiconductor device and a mounting structure thereof that can be soldered and mounted with high reliability without deteriorating wettability on a substrate. It is in.

[0006]

In order to achieve the above object, the present invention relates to a semiconductor device having a bent lead, wherein the lead is formed on a surface of a lead substrate by using tin or a tin-bismuth alloy. And an upper plating film made of a tin-bismuth alloy having a bismuth content larger than the bismuth content in the lower plating film. The present invention also provides a semiconductor device having a bent lead, wherein the lead is provided on a surface of a lead base material with a lower plating film made of tin or a tin-bismuth alloy having a bismuth content of 0 to 1 wt%, Bismuth content is 1-10wt
% Of a tin-bismuth alloy.

Further, according to the present invention, in the above-mentioned semiconductor device, when the thickness of the two plating films is 10 ± 5 μm,
The thickness of the lower plating film is 1 to 14 μm, and the thickness of the upper plating film is 1 to 12 μm.
Further, in the present invention, in the semiconductor device, when the thickness of the two-layer plating film is about 10 μm, the thickness of the lower plating film is 1 to 9 μm, and the thickness of the upper plating film is 1 μm.
９9 μm. Further, according to the present invention, in the semiconductor device, the thickness of the two-layer plating film is set to 5 μm.
When the thickness is about 1 to 4 μm
Wherein the thickness of the upper plating film is 1 to 4 μm. Further, the present invention provides the semiconductor device, wherein the thickness of the two plating films is set to about 15 μm,
The thickness of the lower plating film is 4 to 14 μm, and the thickness of the upper plating film is 1 to 11 μm.
Further, according to the present invention, in the semiconductor device, cracks and whiskers are prevented from being generated in the two-layer plating film.

In particular, by setting the bismuth content in the lower plating film to 1 wt% or less, the occurrence of cracks is prevented, and the bismuth content in the upper plating film is reduced to 1 wt%.
% Or more prevents the generation of whiskers and the content of 10 wt% or less prevents cracks.

Further, the present invention is characterized in that, in the semiconductor device, the surface of the lead substrate is plated with copper having a thickness of 1 to 10 μm. Also, the present invention provides a method for producing a lower plating film comprising tin or a tin-bismuth alloy, and an upper plating film comprising a tin-bismuth alloy having a bismuth content larger than the bismuth content in the lower plating film. A semiconductor device having a plurality of leads formed by bending and having a plurality of leads, the plurality of leads being solder-connected to electrodes on a substrate and mounted.

[0010] The present invention also provides a lead plating film made of tin or a tin-bismuth alloy having a bismuth content of 0 to 1 wt% on a surface of a lead substrate,
A semiconductor device, comprising: a semiconductor device having a plurality of bent leads having an upper plating film made of a 10 wt% tin-bismuth alloy and mounted by soldering the plurality of leads to electrodes on a substrate. It is a mounting structure of the device. Further, the present invention is characterized in that a pulsed current waveform is applied to obtain a smooth tin-bismach plating surface free of bump-like or whisker-like precipitation.

As described above, according to the above configuration,
It has become possible to manufacture a semiconductor device excellent in corrosion resistance and the like and a mounting structure thereof without a decrease in wettability due to generation of cracks due to bending during lead molding and generation of whiskers. Further, according to the above configuration, the tin-bismuth two-layer plating having a different bismuth content can obtain a smooth plating surface without bump-like or whisker-like deposition by applying a pulse-like current waveform, and 5-
Plating can be performed at a high current density of 30 A / dm ² , and the plating time can be significantly reduced.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a semiconductor device and a mounting structure thereof according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the entire embodiment of a semiconductor device according to the present invention. The semiconductor device is composed of a 42 alloy, which is an iron-Ni alloy having a coefficient of thermal expansion matched to that of the semiconductor element, or a lead frame (lead base) 2 having a surface plated with copper having a thickness of 1 to 10 μm. , L
After fixing the semiconductor element 1 such as an SI, the electrodes of the semiconductor element 1 are electrically connected to the lead frame by wire bonding 3 or the like, and are sealed with a molding resin 4 to be manufactured. Then, the lead frame (lead base material) 6 exposed to the outside of the mold resin 4 is degreased and pickled, and then a plating solution comprising an organic acid, an organic tin, an organic bismuth and an additive is used. By applying a pulse-like current waveform, as shown in FIGS. 2 and 3, tin or tin having a bismuth content of 0 to 1 wt% is applied to the surface.
Lower plating film made of bismuth alloy (having a thickness of 1 to 14μ)
m) 7, 9 and an upper plating film made of a tin-bismuth alloy having a bismuth content of 1 to 10 wt% (having a thickness of 1 to 12).
μm) 8, 10 are plated. Then, lead 5a,
5b is formed by being cut from the frame and bent into a predetermined shape. As described above, the semiconductor device according to the present invention is completed. The leads 5 of the semiconductor device completed in this manner are mounted by soldering (solder joining) to electrodes provided on an external circuit such as a substrate using lead-free solder or the like.

FIG. 2 shows that a lower tin plating film (thickness of 1 to 9 μm when the thickness of the two layers is about 10 μm) 7 and an upper tin-bismuth alloy plating film (2 When the thickness of the layer is about 10 μm, the thickness is 1 to 9 μm
m) 8 shows a two-layer structure. FIG. 3 shows a lower tin-bismuth alloy plating film having a low bismuth content (1 wt% or less) on which cracks are less likely to occur on the surface of the lead base material 6 (thickness when the thickness of the two layers is about 10 μm). 2-9
μm) 9 and higher bismuth content (1 wt%
Above) Upper tin-bismuth alloy plating film in which whiskers are not generated (the thickness is 1 when the thickness of the two layers is about 10 μm).
８8 μm) 10.

Since the lower plating films 7 and 9 are made of tin or a tin-bismuth alloy having a bismuth content of 0 to 1 wt%, they are bent at the time of forming the lead (the bending radius is the same as the thickness of the lead base material when the lead is formed). .15 mm, in reality, the bending radius is about 0.25 mm.), Thereby preventing a decrease in wettability.
The upper plating films 8 and 10 have a bismuth content of 1 to 1
Since it is made of a 0-wt% tin-bismuth alloy, whiskers are easily generated, so that an electrical short circuit due to whisker generation is prevented even in a lead having a small interval, and furthermore, cracks due to bending at the time of forming the lead are prevented to reduce wettability. It is possible to perform harmless lead-free solder plating having more excellent corrosion resistance. That is, if the upper tin-bismuth plating films 8 and 10 containing a certain amount (1 wt%) or more of bismuth are formed on the lower tin or tin-bismuth alloy plating films 7 and 9, bismuth is formed of whisker like lead. Because it has the effect of preventing occurrence,
Whisker formation due to the lower plating films 7 and 9 can be prevented. Further, even if cracks occur in the upper tin-bismuth plating films 8 and 10 when the leads are bent,
Only the upper tin-bismuth plating films 8 and 10 remain and do not reach the lower plating films 7 and 9. Therefore, even after the lead is bent, the lead surface is not oxidized through the heating step, and the wettability does not decrease. Further, since the crack does not reach the surface of the lead base material 6, the corrosion resistance does not decrease.

In the tin-bismuth plating film, when the bismuth content is 1% or less, cracks are hardly generated, but whiskers are easily generated. On the other hand, when the bismuth content exceeds 1%, whiskers are hardly generated, but cracks are sharply generated. More likely to occur.
Therefore, tin or tin-bismuth plating films 7 and 9 having a bismuth content of 1% or less are formed in
The above-described tin-bismuth plating films 8 and 10 may be formed as upper layers. The base material of the lead frame is not particularly limited to a 42 alloy, which is an iron-Ni alloy, a 42 alloy plated with copper, or a copper alloy. The current waveform for plating may be DC or pulse. However, for tin-bismuth plating, it is effective to apply a pulse-shaped current waveform, and a smooth plating surface without bump-like or whisker-like precipitation is effective. And plating at a large current density of 5 to 30 A / dm ² is possible, and the plating time can be shortened. . The pulse waveform is preferably a rectangular wave, and the energizing time and the pause time may be arbitrarily selected from 0.001 seconds to 10 seconds.
01 seconds to 1 second, the ratio of energization time and pause time is 0.2 to
It is preferably 0.8.

Next, an experimental example of the lead-free solder two-layer plating film structure according to the present invention will be described.

[0017]

Example 1 42 alloy as base material, width 3 mm, length 1
A test sample in which 10 leads of 5 mm in thickness and 0.15 mm in thickness were connected was degreased and pickled.
1, tin plating was performed using a plating solution consisting of 60 g / l of stannous sulfate and 30 ml / l of an additive. Room temperature, current density 2 A / dm ² . Subsequently, tin-bismuth plating was performed using a plating solution comprising an organic acid, an organic acid tin (tin concentration 55 g / l), an organic acid bismuth (bismuth concentration 4.7 g / l) and an additive 30 ml / l. Liquid temperature 4
0 ° C., current density 10 A / dm ² . The total thickness of the plating is preferably about 10 ± 5 μm.
m (Table 1). The sample after plating was cut into individual leads, and the following evaluation was performed. A 90 ° bending test was performed using a bending jig having a bending radius of 0.15 mm and 0.25 mm, and the occurrence of cracks in the bent portion was observed with a microscope. Then, the sample was heated at 150 ° C. for 168 hours, and the wettability was evaluated by a dip method. In addition, temperature 8
The state of whisker formation after being left in an environment of 5 ° C. and a humidity of 85% for 336 hours was observed with a microscope. The results are as shown in (Table 1).

[0018]

[Table 1]

The bending radius of 0.15 mm is a standard value which is the same as the thickness of the base material. Bending radius 0.25mm
Indicates the bending radius of the actual product. As shown in Table 1, when the bending radius was 0.15 mm, whiskers were generated at a tin-bismuth plating film thickness of 0.5 μm, and when the tin plating film thickness was 1 μm or less, a decrease in wettability due to cracks was observed. Therefore, the preferred plating film thickness in this case is 1 to 8 μm for tin-bismuth and 2 to 9 μm for tin. When the bending radius is 0.25 mm, tin-bismuth is 9 μm
In this case, although a crack is generated but the wettability is good, the preferred plating film thickness is tin-bismuth of 1 to 1.
9 μm, tin is 1 to 9 μm.

[0020]

Example 2 In the same manner as in Example 1, a test sample made of 42 alloy was plated with tin and tin-bismuth and evaluated. The total plating film thickness is about 5 μm. The results are as shown in (Table 2).

[0021]

[Table 2]

As shown in Table 2, the bending radius is 0.15 m
When the thickness was m, whiskers were generated at a tin-bismuth plating film thickness of 0.5 μm, and when the tin plating film thickness was 1 μm or less, a decrease in wettability due to cracks was observed. Therefore, the preferred plating film thickness in this case is tin-bismuth of 1-3 μm.
m and tin are 2 to 4 μm. When the bending radius is 0.25 mm, when the tin-bismuth is 4 μm, although cracks are generated but the wettability is good, the preferred plating film thickness is tin-bismuth of 1-4 μm and tin of 1-4 μm.
μm.

[0023]

Example 3 In the same manner as in Example 1, a test sample made of 42 alloy was plated with tin and tin-bismuth and evaluated. The total plating thickness is about 15 μm. The results are as shown in (Table 3).

[0024]

[Table 3]

As shown in (Table 3), the bending radius is 0.15 m
In the case of m, whiskers are generated at a tin-bismuth plating film thickness of 0.5 μm. Also, because the plating film became thicker,
Cracks occur when the thickness of the tin plating is 3 μm or less, but the wettability is reduced from 2 μm. Therefore, the preferred plating film thickness in this case is that tin-bismuth is 1-1.
2 μm, tin 3-14 μm. Bending radius 0.25
mm, tin-bismuth is 2 μm, cracks occur, and the wettability is reduced. Therefore, the preferred plating film thickness is 1-12 μm for tin-bismuth and 3 for tin.
１４14 μm. The same results as in Examples 1 to 3 above were obtained in a test sample in which a 42 alloy was plated with 1 to 10 μm of copper and a test sample of a copper alloy.

[0026]

Example 4 In the same manner as in Example 1, a 42-alloy test sample was subjected to tin-bismuth plating with a bismuth content of 0.3%, and then tin-bismuth plating with a bismuth content of 5%. Was performed and evaluated. The plating film thickness is about 10 μm in total. The results are as shown in (Table 4).

[0027]

[Table 4]

As shown in Table 4, the bending radius is 0.15 m.
When m, the thickness of the upper tin-bismuth plating is 0.5 μm
In this case, whiskers were generated, and the tin-bismuth plating film was more brittle than the tin plating film. Therefore, when the thickness of the underlying tin-bismuth plating film was 2 μm or less, a decrease in wettability due to cracks was observed. Accordingly, the preferred plating film thickness in this case is 1 to 7 μm for the upper layer tin-bismuth and 3 to 9 μm for the lower layer tin-bismuth. When the bending radius is 0.25 mm, when the tin-bismuth in the lower layer is 8 μm, although cracks are generated but the wettability is good, the preferred plating film thickness is 1 to 8 μm for the tin-bismuth in the upper layer, and Tin-bismuth is 2-9 μm.

In this example, since both the upper layer and the lower layer are tin-bismuth plating, the application of a pulse current enables plating at a current density of 10 A / dm ^2. The plating time required for plating 10 μm may be 4 minutes.

[0030]

Example 5 In the same manner as in Example 1, a 42-alloy test sample was tin-bismuth-plated with a bismuth content of 0.3%, and then tin-bismuth-plated with a bismuth content of 5%. Was performed and evaluated. The total plating film thickness is about 5 μm. The results are as shown in (Table 5).

[0031]

[Table 5]

As shown in Table 5, the bending radius is 0.15 m
When m, the thickness of the upper tin-bismuth plating is 0.5 μm
Then, whiskers were generated, and when the thickness of the underlying tin-bismuth plating film was 2 μm or less, a decrease in wettability due to cracks was observed. Therefore, the preferred plating film thickness in this case is 1 to 2.5 μm for tin-bismuth in the upper layer and 2.5 to 4 μm for tin-bismuth in the lower layer. Bending radius 0.25mm
In the case of (2), when the tin-bismuth in the lower layer is 2 μm, although cracks are generated but the wettability is good, the preferred plating film thickness is 1 to 3 μm.
m, the lower layer of tin-bismuth is 2 to 4 μm.

[0033]

Example 6 In the same manner as in Example 1, a 42-alloy test sample was subjected to tin-bismuth plating with a bismuth content of 0.3%, and then tin-bismuth plating with a bismuth content of 5%. Was performed and evaluated. The total plating thickness is about 15 μm. The results are as shown in (Table 6).

[0034]

[Table 6]

As shown in Table 6, the bending radius is 0.15 m
When m, the thickness of the upper tin-bismuth plating is 0.5 μm
Then, whiskers were generated, and when the thickness of the tin-bismuth plating layer was 4 μm or less, the wettability was reduced by cracks. Accordingly, the preferred plating film thickness in this case is 1 to 10 μm for the upper layer tin-bismuth and 5 to 14 μm for the lower layer tin-bismuth. When the bending radius is 0.25 mm, when the lower layer tin-bismuth is 4 μm, although cracks are generated but the wettability is good, the preferred plating film thickness is 1-11 μm for the upper layer tin-bismuth.
The lower layer tin-bismuth is 4 to 14 μm.

[0036]

Example 7 In the same manner as in Example 1, a test sample made of 42 alloy was tin-plated, and then tin-bismuth plating was performed thereon by changing the bismuth content, and evaluated. The plating film thickness was 6 μm for tin and 4 for tin-bismuth.
It is about μm. The results are as shown in (Table 7).

[0037]

[Table 7]

As shown in Table 7, whiskers were generated when the bismuth content of the upper layer tin-bismuth plating was 0.5%. In addition, when the bending radius was 0.15 mm, when the bismuth content of the tin-bismuth plating film was 11 wt% or more, a decrease in wettability due to generation of a large crack was observed. Therefore, the preferred bismuth content of the tin-bismuth plating film in this case is 1 to 10 wt%. Bending radius 0.25
mm, since the wettability is good up to a bismuth content of 11%, the preferred bismuth content is 1 to 11 w
t%.

In this embodiment, the thickness of the plating layer is about 6 μm for tin in the lower layer and about 4 μm for tin-bismuth in the upper layer. However, similar results were obtained.

[0040]

Example 8 In the same manner as in Example 1, a 42-alloy test sample was tin-bismuth-plated with a bismuth content of 0.3%, and then tin-bismuth-plated with a different bismuth content. Was performed and evaluated. The plating thickness is about 6 μm for the lower layer of tin-bismuth and about 4 μm for the upper layer of tin-bismuth. The results are as shown in (Table 8).

[0041]

[Table 8]

As shown in Table 8, whiskers were generated when the bismuth content of the upper tin-bismuth plating was 0.5%. Also, tin-bismuth is more brittle than tin,
When the bending radius was 0.15 mm, a decrease in wettability due to generation of a large crack was observed at a bismuth content of 10 wt% or more in the tin-bismuth plating of the upper layer. Therefore, the preferred bismuth content of the plating film in this case is 1 to 9 wt%. When the bending radius is 0.25 mm, since the wettability is good up to a bismuth content of 10%, the preferable bismuth content is 1 to 10 wt%. In this example, the thickness of the plating layer was 6 μm for tin-bismuth in the lower layer and 4 μm for tin-bismuth in the upper layer. However, the same applies to the preferred plating film thickness ranges shown in the above Examples 4 to 6. The result was obtained.

[0043]

Example 9 In the same manner as in Example 1, a test sample made of 42 alloy was plated with tin-bismuth in the lower layer while changing the bismuth content, and then a bismuth content of 5
% Tin-bismuth plating was performed and evaluated. The plating thickness is about 6 μm for the lower layer of tin-bismuth and about 4 μm for the upper layer of tin-bismuth. The results are as shown in (Table 9).

[0044]

[Table 9]

As shown in Table 9, the bending radius is 0.15 m
In the case of m, the lowering of the wettability due to the generation of cracks was observed at a bismuth content of 1% by weight or more in the tin-bismuth plating of the lower layer. Therefore, the preferable bismuth content of the plating film in this case is 0.0001 to 0.9 wt. %. When the bending radius is 0.25 mm, since the wettability is good up to a bismuth content of 1%, the preferable bismuth content is 0.0001 to 1 wt%. In this example, the thickness of the plating film was about 6 μm for tin-bismuth in the lower layer and about 4 μm for tin-bismuth in the upper layer. However, even in the preferred plating film thickness range shown in the above Examples 4 to 6, Similar results were obtained.

The corrosion resistance was good in the preferred range of the plating film thickness shown in Examples 1 to 9. Furthermore, although the example of the 42 alloy lead is shown here,
Similar results were obtained for 42 alloy leads and copper alloy leads plated with copper.

[0047]

According to the present invention, a semiconductor element lead is plated with tin-bismuth (upper layer) and tin (lower layer) in a two-layer structure, or tin-bismuth having a higher bismuth content than lower tin-bismuth. By having a two-layer structure of tin-bismuth having a lower bismuth content than that of the upper layer tin-bismuth, there is no decrease in wettability due to generation of cracks due to bending during lead molding and no generation of whiskers Thus, a semiconductor device having excellent reliability such as corrosion resistance and a mounting structure thereof can be realized.

Further, according to the present invention, by applying a pulse-shaped current waveform to form a tin-bismuth two-layer plating film having a different bismuth content on the lead base material, a bump-like deposition, A smooth plating surface without whisker-like precipitation was obtained, and plating was possible at a high current density of 5 to 30 A / dm ² , and the plating time was greatly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor device according to the present invention.

FIG. 2 is a sectional view showing an embodiment of a lead according to the present invention.

FIG. 3 is a sectional view showing another embodiment of the lead according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor element, 2 ... Lead frame, 3 ... Bonding wire, 4 ... Mold resin, 5, 5a, 5b ... Lead exposed outside mold resin, 6 ... Lead base material, 7 ...
Tin plating film, 8 ... Tin-bismuth alloy plating film, 9 ...
Tin-bismuth alloy plating film with low bismuth content, 1
0: Tin-bismuth alloy plating film having a high bismuth content.

Claims (8)

[Claims] 1. A semiconductor device having a bent lead, wherein the lead is provided on a surface of a lead substrate by tin or tin-tin.
A semiconductor device comprising: a lower plating film made of a bismuth alloy; and an upper plating film made of a tin-bismuth alloy having a bismuth content larger than the bismuth content in the lower plating film. 2. A semiconductor device having a bent lead, wherein the lead is formed on a surface of a lead base material by a lower plating film made of tin or a tin-bismuth alloy having a bismuth content of 0 to 1 wt%; A semiconductor device comprising: an upper plating film made of a tin-bismuth alloy having a content of 1 to 10 wt%. 3. The thickness of the lower plating film is 1 to 14 μm.
3. The semiconductor device according to claim 1, wherein the thickness of the upper plating film is 1 to 12 μm. 4. The method according to claim 1, wherein said lower plating film has a thickness of 1 to 9 μm.
3. The semiconductor device according to claim 1, wherein the thickness of the upper plating film is 1 to 9 [mu] m. 5. The semiconductor device according to claim 1, wherein cracks and whiskers are prevented from being generated in said two-layered plating film. 6. The lead base material has a surface of 1 to 10 μm
2. A copper plating having a thickness of 3 mm.
Or the semiconductor device according to 2 or 3 or 4 or 5. 7. A lower plating film made of tin or a tin-bismuth alloy, and an upper plating film made of a tin-bismuth alloy having a bismuth content larger than the bismuth content in the lower plating film on the surface of the lead substrate. A semiconductor device having a plurality of leads formed by bending having
A mounting structure for a semiconductor device, wherein the plurality of leads are mounted by soldering to electrodes on a substrate. 8. A lead base material having a bismuth content of 0
A semiconductor device having a plurality of leads formed by bending and having a lower plating film made of tin or tin-bismuth alloy of １1 wt% and an upper plating film made of tin-bismuth alloy having a bismuth content of 1-10 wt%. A mounting structure for a semiconductor device, wherein the plurality of leads are mounted by soldering to electrodes on a substrate.