JPH06188350A - Semiconductor device and lead frame - Google Patents

Abstract

PURPOSE:To form an outer frame without twisting, and suitably mount it on a circuit board, by forming the section of the bending part of an outer lead to be nearly trapezoidal, in the manner in which a narrow upper bottom side turns to the outside of the bending part. CONSTITUTION:An outer lead 10 protruding from a resin sealing part 12 of a semiconductor device is formed to be trapezoidal in the sections at the bending parts 14, 16, in the manner in which the narrow upper bottom sides 18, 20 turn to the outside of the bending parts 14, 16, and bent in a Z-shape. The position of neutral surface 22 relating to bending stress of the sections A, C, B of the outer lead 10 is in the vicinity of the inside of the bending parts 14, 16 as shown with chain lines. Hence the bend of the outer lead 10 depends only on the shape in the vicinity of a lower bottom 20 of the trapezoid in the sectional form, and the bending along a metal mold is facilitated, so that the outer lead 10 can be formed in a specified shape while restraining the twisting within a small range. Thereby a semiconductor device can be mounted on a circuit board without generating the solder bridge between the outer leads 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a lead frame.

[0002]

2. Description of the Related Art Conventionally, the cross-sectional shape of an external lead of a semiconductor device is formed into a substantially rectangular shape by etching or press punching (stamping). If the width of the external lead is sufficiently wide compared to the thickness of the external lead, the cross-sectional shape will be a flat rectangle, so the cross-sectional shape of the external lead does not have to be an exact rectangle. The external lead was difficult to twist and could be bent into a predetermined shape.

However, in recent years, the pitch between the external leads has become very small, and the width of the external leads has become narrower than the thickness of the external leads.
In order to bend these external leads into a predetermined shape without twisting, it has been ideal that the external leads have an accurate rectangular cross-sectional shape. That is, if the cross-sectional shape is rectangular, the pressing force can be evenly applied to the bent portion of the external lead during the bending process, so that the external lead is not twisted and can be suitably formed into a predetermined shape. Is. When the external lead 1 has a rectangular cross-sectional shape, the neutral surface 3 related to bending stress passes through the center of the thickness of the external lead 1, as shown in FIG. 7.

[0004]

However, in practice, it is difficult to accurately form the cross section of the external lead into a rectangular shape, and as shown in FIG. 6, the external lead 1a of the lead frame formed by etching has a problem. When there is a mask shift, the cross-sectional shape of the external lead 1a becomes a shape close to a parallelogram. Further, the cross-sectional shape of the external lead formed by stamping is transformed into a polygonal shape. This tendency becomes remarkable when the external leads have a fine pitch.

As described above, if the cross-sectional shape of the external lead is not an ideal rectangular shape, the pressing force applied during bending cannot be properly applied to the bent portion of the external lead. . Therefore, when the external lead is bent, the external lead is twisted, and the direction of the external lead is not fixed in a predetermined direction. For example, the external lead flows in a direction inclined with respect to the direction in which it should be bent. There is a problem in that a semiconductor device having such external leads cannot be properly mounted on a circuit board.

Further, the wiring pattern 32 of the circuit board 30
When the external lead 1 of the semiconductor device is soldered up,
As shown in FIG. 5, when the set position of the external leads 1 is deviated, there is a problem that the solder 34 bridges between the external leads 1 in the conventional external lead 1 having a rectangular sectional shape.

Therefore, an object of the present invention is to provide a semiconductor device and a lead frame in which the external frame can be easily molded into a predetermined shape without being twisted and can be suitably mounted on a circuit board. is there.

[0008]

In order to achieve the above object, the present invention has the following constitution. That is, the present invention is
The external lead of the semiconductor device is characterized in that at the bent portion, the cross-sectional shape is formed into a substantially trapezoidal shape with the narrow upper bottom side being the outside of the bent portion. The present invention also resides in a lead frame, wherein the bent portion of the outer lead to be bent has a substantially trapezoidal cross-sectional shape with the narrow upper base side being the outer side of the bent portion. .

[0009]

According to the semiconductor device of the present invention, since the cross-sectional shape of the external lead is formed in a substantially trapezoidal shape with the narrow upper bottom side being the outside of the bent portion, when the external lead is bent, Bending stress can be reduced. In addition, since the external leads have a trapezoidal cross-section, it is possible to apply a bending force with a press die even when there is some misalignment between the upper and lower bottoms when bending. Therefore, the force acting to twist the external lead can be suppressed as small as possible. Therefore, the outer frame can be easily molded into a predetermined shape without being twisted. Furthermore, since the side where the external leads come into contact with the wiring pattern of the circuit board can be set to the upper bottom of the trapezoidal cross section, the semiconductor device is preferably mounted on the substrate so that the solder does not bridge between the external leads. be able to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1A is a side view showing an embodiment of the resin-sealed semiconductor device according to the present invention.
(B), (C), and (D) are cross-sectional views showing the cross-sectional shape of each part of the external lead 10. FIG. 1 shows a resin-sealed semiconductor device in which the external lead 10 is bent in a Z shape. The external lead 10 protruding from the resin-sealed portion 12 has bent portions 14 and 16 whose cross-sectional shape is width. The narrow upper base side 18, 20 is formed in a trapezoidal shape which is the outside of the bent portions 14, 16. That is, since the external lead is bent in the Z shape, in the section A including the first joint 14 that is the bent portion on the resin sealing side, the sectional shape is as shown in FIG. It is formed in a trapezoidal shape so that the upper side in the drawing becomes the narrow upper base side 18. Further, in the section B including the second joint 16 which is the bent portion on the distal end side of the external lead, the cross-sectional shape is as shown in FIG. It has a trapezoidal shape. In this embodiment, in the section C provided between the section A and the section B, the section shape is adjusted and formed so as to be smoothly continuous, and the section shape at the center of the section C is It has a rectangular shape as shown in FIG.

Since the outer lead 10 is formed as described above, the position of the neutral surface 22 relating to the bending stress in each section of the outer lead 10 is foldable as shown by the alternate long and short dash line in FIG. It is in a state of approaching the inner side (inner R surface) of the curved portions 14 and 16. The position of the neutral surface 22 of each section of the external lead 10 is shown in FIG.
In (b), (c), and (d), it is also indicated by a chain line. When the cross-sectional shape is trapezoidal, the neutral surface 22 approaches the lower bottom surface of the trapezoid, and when the cross-sectional shape is rectangular, the neutral surface 22 positioned. In such an external lead 10, the bent portion 14,
As for the bending stress acting on 16, the tensile stress S acts on the outer side and the compressive stress P acts on the inner side with the neutral surface 22 as the boundary, as shown in FIG.

As described above, the neutral surface 22 has the bent portions 14, 1
6, the bending of the outer lead 10 is largely governed only by the shape of the trapezoid in the vicinity of the bottom of the trapezoid in the cross-sectional shape. According to the outer lead 10, the bending of the outer lead 10 along the mold is performed. It will be easier. Further, even if there is a slight mask deviation when the lead frame is manufactured by etching, the influence of the shape of the trapezoidal upper bottom sides 18 and 20 in the cross-sectional shape is small, and twisting due to bending hardly occurs.

By the way, in the conventional external lead whose cross-sectional shape should be rectangular, if there is a mask shift in etching, as shown in FIG.
Since a part of it protrudes, the bending pressing force F
Is hard to apply properly. On the other hand, in the external lead 10 according to the present invention, as shown in FIG.
Even if there is a mask misalignment similar to that in FIG. 6, the cross-sectional shape is within the rectangle of the chain double-dashed line, and the pressing force F for bending can be maintained relatively evenly. Therefore, twisting due to bending is unlikely to occur. Has become.

Also, as shown in FIG.
Also in the section which becomes the board mounting surface (the tip side of section B), the cross-sectional shape is formed into a trapezoid in which the narrow upper bottom side 24 is the board mounting surface side. Therefore, the external lead 10 of the resin-sealed semiconductor device is placed on the wiring pattern 32 of the circuit board 30.
As shown in FIG. 3, even when the set position of the external lead 10 is deviated within a certain limit when the solder is soldered, according to the external lead 10, the external lead 1 on the board mounting surface side is
Since the distance between 0s is wide, the possibility that the solder 34 will bridge between the external leads is very small, and the solder 34 can be mounted favorably.

Although the resin-encapsulated semiconductor device has been described in the above embodiment, the lead frame used for manufacturing the resin-encapsulated semiconductor device is preliminarily provided with the bent portion 14 of the external lead 10 to be bent. It is needless to say that the cross-sectional shape of 16 can be formed into a substantially trapezoidal shape in which the narrow upper bottom sides 18 and 20 are outside the bent portion. This lead frame can be suitably formed into a substantially trapezoidal external lead 10a shape as shown in FIG. 7A by appropriately selecting the mask shapes on the front and back surfaces by etching.

Further, in the above embodiment, the case where the outer lead is bent into the Z shape has been described, but the present invention is not limited to this, and it is also used when the outer lead is bent into the J shape. Of course you can. Also in this case, the outside of the bent portion of the external lead and the board mounting surface side can be the trapezoidal upper bottom side in cross-sectional shape. Therefore, even when the external lead is bent into a J shape, the same effect as when the external lead is bent into the Z shape can be obtained. Although various preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and many modifications can be made without departing from the spirit of the invention. That is.

[0017]

In the semiconductor device and the lead frame of the present invention, in the cross-sectional shape of the external lead, the portion outside the bent portion is formed on the upper side of the narrow trapezoidal width. Therefore, according to the semiconductor device and the lead frame of the present invention, the external lead can be easily molded into a predetermined shape while suppressing the twist as much as possible. And
The semiconductor device can be preferably mounted on the circuit board so that the solder does not bridge between the external leads.

[Brief description of drawings]

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

FIG. 2 is an explanatory view showing stress at a bent portion in the embodiment of FIG.

FIG. 3 is a sectional view showing a mounting state on the substrate by the external lead according to the embodiment of FIG.

FIG. 4 is a sectional view of an external lead according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a mounting state on a substrate by a conventional external lead.

FIG. 6 is a sectional view of an external lead showing a conventional technique.

FIG. 7 is a side view showing a conventional semiconductor device.

[Explanation of symbols]

 10 External Lead 12 Resin Sealing Part 14 First Joint 16 Second Joint 18 Upper Bottom Side 20 Lower Bottom Side 22 Neutral Surface 24 Board Mounting Surface Side

Claims (2)

[Claims] 1. The semiconductor device according to claim 1, wherein the external lead of the semiconductor device has a substantially trapezoidal cross-sectional shape at the bent portion, the upper bottom side of which is narrower than the bent portion. 2. The lead frame, wherein the bent portion of the outer lead to be bent has a substantially trapezoidal cross-sectional shape with a narrow upper bottom side being the outer side of the bent portion.