KR19980081206A - Semiconductor device having a lead cutting device and a lead frame processed by the lead cutting device - Google Patents

Abstract

The lead cutting device reciprocally moves the punch 12 from the die 11 into and out of hollow space to cut the unused portion 17 from the lead frame 15 covered with the solder 15b. The punch has an inclined blade surface 12b extending inwardly from the side surface of the boss portion of the die to the bottom surface 12c of the punch, the inclined blade surface inclined 45 degrees with respect to the centerline 16 of the punch Apply a tension component on the unused part. When applying a sharp force on the unused portion of the punch, the inclined blade surface bends the boundary portion between the unused portion and another portion used as a lead, thereby applying a tension component on the boundary portion, wherein the boundary The portion is expanded, compressed and broken, and rounded, leaving the lid 15c on the die.

Description

Semiconductor device having a lead cutting device and a lead frame processed by the lead cutting device

TECHNICAL FIELD The present invention relates to a semiconductor device package technology, in particular a semiconductor device having a lead frame processed by a lead cutting device and a depressed cutting device for external leads.

1 shows a general example of a lead cutting device. The conventional lead cutting device has a die 1 and a punch 2. The die 1 has a blade edge 1a and the lead frame 3 is located on the die 1. The lead 3a forms part of the lead frame 3 and is partially coated with the solder layer 3b. The punch 2 is movable in opposition in the direction indicated by arrow AR 1 and has an inclined blade surface 2a.

When the manufacturer cuts the lid 3a, the lead frame 3 is placed on the die, and a portion of the lid 3a protrudes beyond the blade edge 1a of the die 1. The punch 2 is moved downward so that a portion of the lid 3a is cut between the inclined blade surface 2a and the blade edge 1a. The inclined blade surface 2a and the blade edge 1a are off the inclined surface 3d as shown.

While the punch 2 cuts a portion of the lead 3a, the solder is strongly sprayed onto the inclined surface 3d and forms a thin solder layer 3e as shown in FIG. The thin solder layer 3c becomes thinner from the top surface of the lid 3a to the bottom surface.

In general, the following conditions are preferable for soldering between the circuit board and the leads 3 of the semiconductor device. Firstly, a solder layer 3e is sprayed onto the entire cut surface 3c of the lid 3. If the lead 3 does not meet the first condition, the electrical resistance increases, and the lead 3 is likely to peel off from the circuit board, and the lead 3 can be corroded. Semiconductor devices installed on a circuit board can be rejected through visual overhaul using a microscope, resulting in reduced production.

Secondly, the major surface and the cutting surface 3c of the circuit board form an acute angle. If the leads 3 and the circuit board do not meet the second condition, the semiconductor device is shaken on the main surface of the circuit board. Semiconductor devices that shake on the circuit board make the product thicker, and the second condition is important for scaling down.

Third, it is preferable that the lid 3a has a lead end that is somewhat bent downward. The modified lead ends allow the solder to adhere closely to the circuit board.

When the lead frame 3 is soldered to the conductive pattern 4 of the circuit board 5, the solder layer 6 occurs along the inclined cut surface 3d and is almost at the major surface as shown in FIG. 3. The wall 6a is formed vertically. The wall 6a reduces the thickness upwards, and the entire inclined cut surface 3d is barely covered by the solder wall 6a. For this reason, the lead frame 3 processed by the conventional lead cutting device does not satisfy the first condition, and the product is likely to be defective in visual inspection using light reflection.

If the leads 3 are inclined with respect to the major surface of the circuit board 5, the solder wall 6a is thick enough to pass the visual overhaul as shown in FIG. If the angle θ between the lead 3 and the conductive pattern 4 becomes large, the solder wall has a sufficient thickness and may not be judged bad in visual inspection. However, the lead 3 soldered obliquely to the conductive pattern 4 does not meet the second condition and weakens the adhesion strength.

Therefore, there is a replacement of the lead frame 3 processed by the conventional lead cutting device.

The lead cutting device itself suffers from the irregularities of the leads 3, the durability of the punch 2, the increase of coplanarization, the solder layer 3e incompletely sprayed on the cut surface, and the small deformation of the lead ends. . This is due to the fact that the inclined cut surface exerts side components of the reaction force on the punch 2 during the cutting operation. Lateral components cause the punch 2 to move obliquely, the punch 2 being offset from the target trajectory RT1. The amount of offset is not constant, and the lead cutting device suffers from the problem described above.

It is therefore an important object of the present invention to provide a lead cutting device which minimizes the offset of a punch during a cutting operation.

It is also an important object of the present invention to provide a semiconductor device in which the lead provides a small contact resistance and is strongly attached to the conductive layer to prevent corrosion and an increase in coplanality.

To achieve that object, the present invention proposes to cut a solder-coated conductive strip into leads between punches with slanted blade surfaces on both sides and insert it into holes formed in the die.

According to one aspect of the invention, a die structure having a surface on which the lead frame is mounted and an edge blade defining a hollow space in which the lead frame extends, and a portion of the lead frame in contact with and located on the hollow space below the boss and the boss A lead cutting device is provided that includes a punch having a blade moved in and out of a hollow space along a trajectory of a punch for cutting a blade, the blade having a bottom surface narrower than a cross section of the boss and extending between the side and the bottom surface of the boss and It has an oblique blade surface that is provided symmetrically about the track.

According to another aspect of the invention, there is provided a semiconductor device comprising a lead frame having a lead having a rounded lead end applied with a layer of solder to adhere to a conductive member.

The features and advantages of the lead cutting device and the semiconductor device will be more clearly understood from the following detailed description in conjunction with the accompanying drawings.

1 is a cross-sectional view showing a conventional cutting device disclosed in the unexamined Japanese Patent Application Laid-open No. 3-264146.

FIG. 2 is a front view showing a solder layer covered on the bevel blade surface of the lid. FIG.

3 is a cross-sectional view showing a conventional lead frame soldered to a circuit board.

4 is a cross-sectional view showing the solution of the problems inherent in the conventional lead frame.

5 is a cross-sectional view showing the basic structure of a lead cutting device according to the present invention.

6 is a cross-sectional view showing a lead cut using the lead cutting device.

7 is a front view showing the inner surface of the lid.

8A to 8C are cross-sectional views showing cutting operations performed by the lead cutting device.

9 shows the punch used in the study.

10 is a cross-sectional view showing a semiconductor device according to the present invention.

Explanation of symbols on the main parts of the drawings

11: die 12: punch

13: positioning board 14: actuator

15: lead frame

Referring to FIG. 5, a lead cutting device for realizing the present invention mainly includes a die 11, a punch 12, a positioning board 13, and an actuator 14. The die 11 has a through hole 11a under the punch 12 and provides a plane 11b to the lead frame 15. The positioning board 13 also has a through hole 13a, which is aligned with the through hole 11a. The lead frame 15 is inserted between the die 11 and the positioning board 13. Therefore, the positioning board 13 fixes the lead frame 15 during the cutting operation by the punch 12. Hereinafter, the direction perpendicular to the plane 11b is referred to as the vertical direction or the vertical direction.

The actuator 14 is connected to the punch and moves the punch 12 oppositely in the vertical direction along the target trajectory 16. The punch 12 includes a boss 12a and a blade 12b formed below the boss 12a. The blade 12b has an oblique blade surface on both sides of the punch 12. When the actuator 14 moves the punch 12 downward, the blade 12b artificially deforms the unused portion 17 of the lid 15a of the lead frame 15, and the unused portion of the lid 15a. It penetrates into the through hole 13a / 11a so that 17 may be cut. The lead 15 is covered with a solder layer 15b.

Boss 12a has a width W of 1 millimeter and blade 12b has an oblique blade surface. The oblique blade surface causes the bottom surface 12c to be narrower than the cross section of the boss 12a, and the distance d is 0.15 millimeters.

In this example, the angle α is 45 degrees. When this angle approaches 90 degrees, the blade 12b cuts the lead 15a before plastic deformation of the end 15c of the lead 15a.

The present inventors changed the angle α and investigated the influence of the angle α on the outer shape of the end portion 15c. When the angle α was 45, the punch 12 plastically deformed the end 15c at the first stage of the cutting operation, and the end 15c became close to the arc as shown in FIG. The solder layer 15b was also modified to minimize the exposed area 15d of the lead 15a (see FIG. 7).

The lead cutting device cuts the unused part of the lead frame 25 as follows. 8A to 8C show a cutting process performed by the lead cutting device shown in FIG. 5. First, lead frame 925 is prepared. The lead frame 15 has a conductive metal strip 25a, which covers each of the conductive metal strips 25a with a bonding layer 25b. The lead frame 25 is placed on the flat surface of the die 11, and the unused portion 25c of the lead frame 25 is placed on the through-hole 11a. The lead frame 25 is fixed to the die 11 by the placement board 13.

The actuating device 14 also moves the punch 12 downward, which comes into contact with the bond layer 25b over the unused portion 25c. The punch 12 is also moved downwards to allow force to be distributed on the unused portion 25c and the bond layer 25b. The inclined blade surface forms a tension component in the conductive metal strip 25a and the bond layer 25b from the force distributed, and the bond layer 25b and the conductive metal strip 25a expand as indicated by arrow AR2. (See FIG. 8A).

The punch 12 is also moved downwards, and the force of the tension component causes the conductive metal strip 25a to reach the yield point. The conductive metal strip 25a and the junction layer 25b are limited to form an arc-shaped gentle curve as shown in FIG. 8b.

The punch 12 is also moved downwards, and the conductive metal strip 25a reaches a threshold. Then, the conductive metal strip 25a is broken together with the bond layer 25b, and the punch 12 cuts off the unused portion 25c as shown in FIG. 8C. The remaining conductive metal strip 25a acts as a lead 25d, which has a rounded end 25e. Most of the rounded ends 25e are covered with the expanded bond layer 25b before the threshold.

The inventor has investigated the relationship between the gap T and the expansion between the punch 12 and the die 11. The punch 12 has a blade surface inclined at both sides. The inventor changed the gap T and measured the expansion h of the bond layer 25b (see FIG. 6). We calculate h / H, which is the ratio R1 between the total thickness H and expansion h of the lead and bond layers, and G / H, which is the ratio R2 between the gap G and the total thickness H. It was.

Using the punch 32 in the case where the blade 32a has the blade surface 32b inclined on one side and the vertical blade surface 32c on the other side, the inventors cut The process was carried out and the ratios R1 and R2 were calculated. The results are shown in Table 1. The ratios R1 and R2 are expressed in percent.

The inventor also calculated the ratio R3, ie P1 / S1, between the projection area P1 of the expanded bond layer 25b and the cross-sectional area S1 of the lead 25d (see FIG. 6). And the results are shown in Table 2. The ratio (R3) is also expressed in percent.

R2 10 15 20 25 30 Punch 12 R1 = 33 R = 85 R1 = 85 R1 = 85 Not cut Punch 32 R1 = 20 R = 25 R1 = 25 R1 = 25 Not cut

R2 10 15 20 25 30 Punch 12 R3 = 60 R3 = 85 R3 = 85 R3 = 85 Not cut Punch 32 R3 = 60 R3 = 70 R3 = 70 R3 = 70 Not cut

As can be seen in FIG. 1, when the ratio R2 is 10 percent, the ratio R1 is 33 percent and the lead 25a does not satisfy the first condition. On the other hand, when the ratio R2 is 30 percent, the punch 12 cannot divide the unused portion 25c from the lead 15a.

For this reason, it is advisable to adjust the ratio R2 between 15 and 25 percent.

Comparing the sample cut by the use of the punch 32 with the sample cut by the use of the punch 12, it can be seen that one oblique blade surface only develops narrowly into the bond layer. This phenomenon results from the concentration of force applied to the vertical blade surface. Specifically, while the punch 32 applies the same force to the vertical blade surface and the unused portion, the force applied to the vertical blade surface is actually consumed and the unused portion is cut from the lead frame. After the cut is cut, the punch 32 bends the unused portion, so that the unused portion cannot extend. For this reason, the bond layer does not extend widely.

Also from the table 2, it can be seen that the desired ratio R2 is in the range of 15 to 25 percent. When the bond layer covers most of the round surface, the first conduction is satisfied. If the ratio R2 is equal to or less than 10 percent and the ratio R3 is only 60 percent, the bond layer on the round surface becomes smaller and satisfies the first conduction. On the other hand, when the ratio R2 is 30 percent, the punch 12 hardly cuts the unused portion.

Even if the ratio R2 is within a desired range, the punch 32 does not spread the bonding layer widely on the round surface. The ratio R3 is good at 70 percent. The reason why the ratio R3 does not exceed 70 percent is described earlier in this specification.

10 illustrates a main part of a semiconductor device according to the present invention. The conductive pattern 41 is formed on the insulating surface 42, and the conductive pattern 41 and the insulating substrate 42 combine to form a printed circuit board 43. Semiconductor pellets (not shown) are combined with lead frames 44 machined by the lead cutting device of the present invention, and integrated circuits are formed in the semiconductor pellets. The lead frame 44 has conductive leads 45 for electrically connecting the integrated circuit, but only one conductive lead 45 is shown in FIG. The conductive strip 45a covers the bonding layer 45b and functions as each conductive lead 45. The unused portion is cut from the conductive lead 45 by use of the lead cutting device of the present invention, and each conductive lead 45 has a round surface 45c as described above in the present specification. The lead frame 44 is reversed and bent prior to the joining.

When the lead 45 is bonded to the conductive pattern 41, the manufacturer places the lead frame 44 almost parallel to the conductive pattern and solders the lead 45 to the conductive pattern 41. The bond layer 46 is gradually flared from the round surface 45c by the strong surface stress, and the bond layer 46 strongly adheres the lead 45 to the conductive pattern 41.

As can be seen from the above, the lead cutting device of the present invention uses a punch 12 having a beveled blade surface installed inward in the boss portion 12a, and the beveled blade surface is used with the unused portion and the lid. It develops to the boundary part between 15a, and forms the round surface for the lid 15a. While the punch 12 is deployed to the boundary portion, the bond layer extends over the round surface, and most of the round surface is covered with the bond layer. This increases the contact resistance of the conductive layer bonded to the bonding layer and the adhesion between the lead and the conductive layer, prevents corrosion, and improves the reliability of visual inspection.

In addition, the rounded surface is provided with a wide contact area, allowing the manufacturer to make very close contact with the lead and the conductive layer. For this reason, the lead frame may be suitable for scaling-down. Therefore, the second condition is satisfied. The round surface meets the third conduction.

Pinch 12 has oblique blade surfaces on both sides thereof. Even when the lead frame applies a component of the transverse force to the beveled blade surface, the components of the transverse force cancel each other out, and the punch 12 follows the trajectory of the target. Is moved. For this reason, the leads are even.

While specific embodiments have been shown and described with respect to the invention, those skilled in the art will recognize that various changes and modifications can be made without departing from the spirit and scope of the invention.

For example, the bevel blade surface may be embodied as four bevel blade surfaces disposed symmetrically with respect to the centerline of the punch or the ballistics of the punch. Otherwise, the blade may be formed in a conical configuration. What is important is to offset the component of the lateral action force applied to the beveled blade surface, in order to protect the punch from undesired offsets.

Claims (7)

A die structure (11/13) comprising a surface (11b) for installing lead frames (15, 25) and an edge blade (11a) defining a hollow space in which the lead frame extends; And A punch 12 comprising a boss 12a and a blade 12b adjacent to a lower portion of the boss, the punch 12 for cutting a portion 17, 25c of the lead frame located on the hollow space. In a lead cutting device having the punch 12, which is moved in and out of the hollow space along a trajectory 16: And said blade has a base surface (12c) narrower than a cross section of said boss (12a) and an inclined blade surface extending between said boss surface and said base surface and provided symmetrically with said trajectory. 2. The lead cutting device according to claim 1, wherein the blade surface is met by two warp blade auxiliary surfaces provided on both sides of the raceway (16). The lead cutting device of claim 1, wherein the inclined blade surface extends 45 degrees with respect to a centerline of the punch that is substantially parallel to the trajectory. 2. The lead frame according to claim 1, wherein the lead frame is covered with solder layers (15b, 25b) and has conductive portions (15a, 25a) extending into the hollow space, wherein the lead portion (15a) and the solder layer (15b) The ratio (R2) of the gap (T) between the side surface and the edge blade (11a) to the total thickness (H) is in the range between 15 percent and 25 percent. A semiconductor device having a lead frame (44) comprising a lead (45) having a circular lead end covered with a solder layer (45b) to adhere to the conductive member (41). 6. The semiconductor device of claim 5, wherein the lead end is formed of a conductive metal that is plastically expanded under application of a tension component such that an internal pressure exceeds a pressure generated by the conductive metal. 6. The semiconductor device of claim 5, wherein the circular lead end has a curved surface close to an arc.