JPH0547977A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To form inner leads while the twist of the tip parts of the inner leads is prevented from being generated in the formation of a lead frame. CONSTITUTION:When inner leads 1 are punched into a prescribed pattern, the side surfaces of each lead 1 are punched to the place on this side 0.25 to 0.3mm apart from the tip 5 of each lead 1 by a first punching, the tip parts of the leads are left unformed and the tip parts of the leads are formed by a second punching in after a heat treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a lead frame used in a semiconductor device, and more particularly to a method of increasing the finish dimensional accuracy of inner leads of a multi-pin lead frame punched by a press.

[0002]

2. Description of the Related Art Conventionally, when a lead frame is manufactured by punch press working, a punching material is intermittently supplied to a progressive die, and punching is started from a guide hole portion, then a pad portion, an inner lead portion, an outer portion. The lead parts are sequentially punched and processed into a predetermined pattern. Since this lead frame is thin, distortion is likely to occur at the time of punching by a press. Especially, in the inner lead, depending on its shape, the inner lead may not be in the same plane,
Deformation such that the inner lead spacing does not fall within a predetermined dimension is likely to occur. In particular, a lead frame for a multi-pin product having an elongated inner lead having an inner lead width of a plate thickness or less than the plate thickness becomes more sensitive to deformation.

As a countermeasure against this, in some cases, in order to prevent the inner lead from being twisted, a procedure of punching out the pad portion after punching out the inner lead is adopted.
A method of punching the inner leads is used in which the tip of the inner leads are connected by a pad portion or a connecting piece. (See JP-A-1-248655). In this method, the tips of the inner leads are formed at the same time when the pads are formed.

In the case of the prior art in which the inner lead punching is performed in the form in which the tip of the inner lead is continuously provided by the pad portion or the connecting piece, the punch forming the tip of the inner lead is used only for forming the tip of the inner lead. The side surface of the inner lead is not formed.
Therefore, in order to form the side surface of the inner lead before forming the tip of the inner lead, the inner lead side surface punching punch is used. However, in order to form the side surface that intersects the inner lead tip properly, the inner lead side surface punching punch projects in front of the inner lead tip, and the width of the connecting portion of the punching tip is 55 to 65% of the material thickness. Will be.

After the inner lead side surface punching, the punched inner lead portion and the pad portion or the connecting piece are connected like a neck at the connecting portion between the punching tips. If the connecting portion has a width of 55% to 65% of the material thickness, it is difficult to prevent the inner lead from being twisted after the lead frame is pressed, and as a result, defective wire bonding may occur during assembly of the semiconductor device. Becomes

In order to solve the above problems, Japanese Patent Publication No. 62-
As indicated by 44422, it is proposed to perform a heat treatment to eliminate the internal residual strain that the band has in the lead frame member. However, in the heat treatment, x. y. Although the displacement in the z direction can be prevented, it is practically impossible to prevent the inner lead from twisting.

Further, there is a method of improving the plate pressing pressure or finely adjusting the clearance between the punch and the die at the time of punching, but the one having the elongated inner lead as described above is for a multi-pin product. In the lead frame, it is not suitable in practice because it is difficult to establish the constraint condition for the plate pressing and it is difficult to finely adjust the clearance between the punch and the die due to the influence.

[0008]

SUMMARY OF THE INVENTION The present invention prevents the occurrence of wire bonding failure in assembling a lead frame into a semiconductor device in which the twisting generated when the inner lead is punched remains, and prevents the inner lead from being broken. It is an object of the present invention to provide a lead frame manufacturing method capable of improving finished dimension accuracy and improving semiconductor productivity.

[0009]

In order to solve the above-mentioned problems, in the manufacturing method of the present invention in which a lead frame is manufactured by press forming from a lead frame material,
When forming a plurality of inner leads extending so as to gradually decrease in width toward the pad, the first punching process is performed to the side surface of each inner lead to a position shorter by 0.25 to 0.3 mm than the tip of the inner lead. After punching and performing the heat treatment for strain relief for a short time at high temperature in a state where the inner lead tips are not formed and the adjacent inner leads are connected to each other, the inner leads are punched by the second punching. It is characterized in that a tip and a side surface connected to the side surface formed by the first punching from the tip are formed.

[0010]

[Function] The first punching for punching out most of the inner lead whose width is gradually reduced toward the tip is performed by punching the side surface to a position shorter by 0.25 to 0.3 mm than the punching tip of the inner lead. Since the width of the continuous portion between the punching tips of the inner leads is relatively large at the end of the step, it has sufficient rigidity to prevent twisting of the tip portions of the inner leads. Then, after performing a heat treatment for removing the strain remaining at the tip portion of the inner lead, a second punching is performed to form the tip end of the inner lead and a side surface connecting the tip and the side surface formed by the first punching. As a result, it is possible to prevent the inner lead from being displaced from the proper position and the inner lead from being twisted after the inner lead is completed. Therefore, the deformation of the inner lead is prevented, and the finished size of the inner lead satisfies the standard.

[0011]

EXAMPLE FIG. 3 shows a lead frame 2 made from a 42 alloy material having a thickness of 0.25 mm. The lead frame 2 has 64 inner leads 1 having a width of 0.20 mm at the tips of the inner leads.

In this embodiment, when the inner lead 1 is punched into the pattern shown in FIG. 3, the first punching is performed by a distance x = 0.25 to 0.3 mm from the inner lead tip 5 as shown in FIG.
For example, the side surface portion 3 of the inner lead was punched up to 5a 0.28 mm before. At this time, since the connecting portion 5b between the punching tips 5a has a relatively large width, it has rigidity enough to withstand twisting during the processing operation. Although the connecting piece 6 is connected to the pad portion 8 in this embodiment, it may be separated from the pad portion 8. The punching tip portion 5c which has been removed by the conventional method is shown by an imaginary line.

In a state in which the inner lead portion 1a thus formed by the first punching is connected by the connecting piece 6, the inner lead portion 1a and the unformed portion, that is, the connecting piece 6 are formed.
Heat treatment was performed for the purpose of removing the residual strain. The heat treatment conditions were set to 700 ° C. for 1 minute as a result of conducting a test for examining the plane dimension displacement as shown in Table 1. In addition, 7
The material was softened by heat treatment at 00 ° C for 1.5 minutes.

After the heat treatment, as shown in FIG. 2, punching of the side surface 4 of the inner lead tip 5 and formation of the tip 5 were simultaneously performed by the press tool 7 in the second punching.

In the lead frame manufactured in this embodiment, the plane dimension displacement of the inner lead is 0.01 to
0.02 mm, the inner lead has a twist of 0.0
08 mm and each standard 0.06 mm or less, 0.
It was possible to fully satisfy the value of 02 mm or less.

[0016]

[Table 1]

[0017]

According to the present invention, when the inner lead is punched and formed, the inner lead 0.25 to 0.
The first punching is performed up to 03 mm short, the shape is processed so that the inner lead tip portion is connected without being formed, and the heat treatment for removing the strain remaining at the inner lead tip portion is performed. The tip portion of the formed inner lead is removed by the second punching to form the tip of the inner lead and the side surface near the tip, so that the lead frame can satisfy the plane dimension displacement standard and the twist standard of the inner lead.

As a result, the finished dimensional accuracy of the inner leads can be improved, and the wire bondability and yield can be improved.

[Brief description of drawings]

FIG. 1 is a plan view of the vicinity of the tip of the inner lead before forming the tip of the inner lead and a side surface near the tip.

FIG. 2 is a plan view of the tip of the inner lead when forming the tip of the inner lead and the side surface in the vicinity thereof, showing a part of the punch press for punching in cross section.

FIG. 3 is a plan view of a lead frame manufactured by the method of the present invention.

[Explanation of symbols]

1 Inner lead 2 Lead frame 3 Side punching part retracted by 0.25 to 0.3 mm from the inner lead tip 4 Side punching part near the inner lead tip 5 Inner lead tip 6 Connection part 7 Punch press for punching 8 Pad

Claims (1)

[Claims] 1. A method of manufacturing a lead frame, which is formed by pressing from a lead frame material, wherein a plurality of inner leads extending so as to gradually decrease in width toward a pad are formed by a first punching. Partial punching of the side surface of each inner lead is performed to a position that is 0.25 to 0.3 mm shorter than the inner lead tip, and the inner lead tips are left unformed and adjacent inner leads are connected to each other. A lead frame characterized by forming a tip of the inner lead and a side surface connected to the side surface formed by the first punch from the tip by second punching after performing heat treatment for removing strain at high temperature for a short time Method.