JPH04314359A - Manufacture of semiconductor device lead frame - Google Patents

Abstract

PURPOSE:To prevent any deformation from being produced by removing residual stress by a heat treatment for twice stress removal, and cutting a thin wall part extending from the tip end of an inner lead or reaching a binder upon removal of the binder. CONSTITUTION:A first heat treatment is performed to remove internal stress produced in a band-shaped material 50 after slitting, and thereafter a lead frame pattern is blanked stepwise separately by a first pressing process including succesive feed molds constructed with a plurality of blanking processes. Then, a second heat treatment is applied to the intermediate product formed as above in order to remove the stress produced in the first pressing process. Further, in a final stage, a binder is cut off by a second pressing process to yield one where the tip end of each inner lead is separated, whereby formation of a lead frame pattern is completed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing lead frames for semiconductor devices, and in particular to a lead frame in which the shape and dimensions of the reference holes used for positioning in each process and the leads themselves are consistent. Relating to a manufacturing method.

0002

2. Description of the Related Art As one of the methods for manufacturing lead frames used for assembling semiconductor devices, a method is generally adopted in which a pattern is punched out from a band-shaped metal material by press working. FIG. 5 shows a plan view of a pattern punched out of the lead frame by press working.

[0003] Strip material 5 supplied to the press processing line
0 includes a stage 1 on which a semiconductor element is mounted, a large number of inner leads 2 arranged around the stage 1, tabs 3 arranged around the periphery to connect these inner leads 2, and outer leads corresponding to each inner lead 2. Outer lead 4 protruding to
, and the suspension lead 5 that supports the stage 1 are each punched out. Simultaneously with punching out these patterns, reference holes 6 to be used for positioning in subsequent processes such as plating and wire bonding are formed on both sides of the strip material 50.

[0004] On the other hand, semiconductor devices have become more sophisticated due to higher integration, faster calculations, higher performance such as hybridization, and an increase in the number of lead pins. It is also necessary to maintain high positional accuracy. To solve this problem, for example, in Japanese Patent Publication No. 62-44422, a wide metal sheet material is slit to form a band-shaped material as shown in FIG. 5, and as shown in the process diagram of FIG. A method is described in which, after forming a lead frame pattern, heat treatment is performed to remove residual stress generated between slitting and press processing, and further press processing is performed to form the final pattern. FIG. 7 shows the distribution of residual stress generated in the strip-shaped material 50 when the strip-shaped material 50 is formed by slitting a metal thin plate. As can be seen, the tension and compression stress distributions are different between the edges of the strip material 50 in the width direction and the center portion excluding the edges. Such stress distribution balances the entire band-shaped material 50 and maintains its flatness.

However, when the strip-shaped material 50 having a stress distribution is pressed and punched into a lead frame pattern, the stress is released by removing the material or the like. Then, stress due to this press working is also applied, which causes the band-shaped material 50 to deform along an arcuate shape as shown by the broken line in FIG.

[0006]

[Problem to be Solved by the Invention] As described above, when a wide metal material is slit to form the band-shaped material 50, and a lead frame pattern is press-formed on this material in order using a mold, residual stress can be reduced. It is unavoidable that the strip material 50 is deformed as shown in FIG. 8 due to the influence. Further, when press working is performed many times using a progressive mold during pattern formation, residual stress is released by removing the punched portion, and the stress distribution changes. For this reason, the width dimension of the tip end of the inner lead 2 is not uniform, and the distance between the tip end and the outer circumferential surface of the stage 1 is likely to vary. Therefore, the stress distribution remaining in the band-shaped material 50 has a negative effect on uniformly thinning the inner lead 2, which is necessary in the case of a tendency to increase the number of pins, and on wire bonding.

Furthermore, since the pattern of the lead frame is created by repeating press working after slitting, as the region of the punched out part in the center expands, camber, crossbow, etc. are formed in the longitudinal and width directions of the strip material 50. This results in deformation. Such deformation also causes variations in the pitch dimension of the reference holes 6 formed in a row on the edge of the strip-shaped material 50. Therefore, the feeding of the strip-shaped material 50 to subsequent processes including during the pressing process becomes inadequate, and the positioning accuracy also deteriorates.

Furthermore, in the device described in the above publication, in order to prevent the tips of the inner leads 2 from being deformed, connecting pieces that connect the tips of the inner leads 2 are arranged around the stage 1. . However, as described above, since the inner lead 2 itself is also deformed, this connecting piece is also deformed, such as torsion. Therefore, if the thus deformed connecting piece is punched out and removed using a press, residual stress will be generated at the tip of the inner lead 2. Therefore, even if an attempt is made to prevent deformation of the inner lead 2 by providing a connecting piece, the problem of deformation of the inner lead 2 and residual stress will ultimately remain.

[0009] The problem to be solved by the present invention is to slit a wide metal material to form a band-shaped material, and when punching and forming a lead frame pattern on this band-shaped material in order, the problem to be solved by the present invention is to reduce the amount of band-shaped material generated during press processing. The purpose is to prevent deformation due to residual stress, suppress the generation of residual stress in the process up to final punching, and make it possible to mold a highly accurate lead frame pattern.

0010

[Means for Solving the Problems] The present invention provides a lead frame manufacturing method in which a wide metal thin plate material is slit into a band-shaped material, and a lead frame pattern is punched into the band-shaped material in stages using a progressive die. a first heat treatment for removing residual stress caused by slitting the slitted strip material; a first press step for punching and forming a lead frame pattern on the strip material after the first heat treatment; After the first press process, a second heat treatment to remove residual stress due to punching and a second press process to complete the pattern of the lead frame are performed in this order, and in the first press process, the lead frame pattern is completed. While molding the stage, inner leads, and outer leads of the frame, the binder connecting the tips of the inner leads is left, and the tips of the inner leads between the binder or the tips including the tips are molded to the binder. forming a thin part in the width direction by pressing down all upper surfaces of the binder, and further, in the second pressing step, the binder and the inner lead are separated by a cutting line running through the thin part at the tip of the inner lead. It is characterized by

[0011]

[Operation] Residual stress generated in the strip material due to slitting is removed by the first heat treatment, and residual stress generated in the first pressing step using the progressive die is removed by the second heat treatment. Furthermore, the spacer holes that form the gaps between the binder and the stage formed in the first pressing process can release the stress that occurs when the tip of the inner lead or the region including the binder is pressed down to form a thin section. can. In addition, since it has been known that the relationship T of the strip material <= lead width W is known as a suitability condition for press working, when cutting a thin part in the second press process, distortion or deformation of the tip of the inner lead can be avoided. Occurrence is also prevented. Moreover, the first heat treatment and the second heat treatment eliminate deviations in the position and shape of the reference hole for feeding and positioning the strip material and the leads themselves, and also suppress the occurrence of deformation due to residual stress after press working.

0012

EXAMPLE FIG. 1 schematically shows a process diagram of the manufacturing method of the present invention.

In this manufacturing process, as explained in the prior art section, a wide metal sheet material is slit to a width that matches the size of the lead frame pattern as shown in FIG. We begin by creating a strip of material 50. After this slitting, the strip material 5
A first heat treatment (stress relief annealing) is performed to remove the internal stress generated in the lead frame, and then the pattern of the lead frame is separated in stages by a first press process equipped with a progressive mold consisting of multiple punching processes. Punch it out. In other words, instead of punching out excess parts to form the entire pattern at once, a certain part is punched out in the first punching process, and in the next process, other parts are punched out to get closer to the desired pattern. I do. In this process, the entire pattern is not punched out, and a binder that connects the inner leads to each other is left at the tips of the inner leads, and the tips of the inner leads are not subjected to final processing.

[0014] Next, for such an intermediate product, a first
A second heat treatment (stress relief annealing) is performed to remove stress generated by the pressing process. In the final stage, the binder is separated by a second press process to separate the tips of each inner lead, thereby completing the molding of the lead frame pattern.

FIG. 2 is a plan view showing the pattern of the lead frame at an intermediate stage after the first press working in the manufacturing method of the present invention.

In the figure, a strip material 50 whose stress has been removed by a first heat treatment after slitting is treated with a first heat treatment.
A pattern is formed by the second press process. This pattern is similar to the conventional example: stage 1, inner lead 2, tab 3, outer lead 4, hanging lead 5.
It also has a reference hole 6 for positioning and feeding.

For such a pattern, the tips of the inner leads 2 are tied together by a binder 7,
The tips of each inner lead 2 are restrained to each other to prevent vibration. This binder 7 has both ends connected to the suspension lead 5, and in the illustrated example, four binders are formed around each side of the stage 1, and spacer holes 8 are formed between the binder 7 and the outer peripheral surface of the stage 1.

FIG. 3 shows details of the binder 7 portion,
(a) of the same figure is an enlarged plan view of the part surrounded by circle A in Fig. 2;
(b) of the same figure is a sectional view taken along the line BB in (a) of the same figure.

The binder 7 integrally formed with the suspension lead 5 is connected to the connection point with the suspension lead 5 by a supporting piece 7a having a reduced width. This support piece 7a
is smaller in width than the binder 7, so when the punching force during pressing is applied to the tip of the binder 7 and the inner lead 2 integrated with it, the rigidity is reduced and the width of the binder 7 and the inner lead 2 are reduced. support. Further, the support piece 7a also serves to release the stress generated when the tip end of the inner lead 2 is rolled down, thereby making it possible to reduce the influence of processing stress.

[0020]Furthermore, the upper surface of the inner lead 2 extending from the tip end to the binder 7 is reduced in the first pressing step to provide a thin wall portion 2a. As shown in FIG. 3(b), this thin part 2a becomes thinner than the other parts of the inner lead 2, and in the second pressing process, the thin part 2a, which is thinner than the other parts, is separated. It will be.

[0021] In this way, in the first pressing process,
While the binder 7 remains integrated with the tip of the inner lead 2, the upper surface of the tip of the inner lead 2 is pressed down and crushed to form the thin portion 2a. Even when this thin part 2a is formed by rolling down, the spacer holes 8 are formed between the binder 7 and the surface facing the outer peripheral edge of the stage 1, so that excess material can escape to the side of the spacer holes 8. be able to. For this reason, even if the tip of the inner lead 2 or the binder 7 portion is pressed down,
The spacer holes 8 can absorb the excess meat caused by this, and the residual stress caused by the reduction can be reduced. Also,
During this rolling down, the binder 7 is also subjected to an acting force at the same time, but since the supporting piece 7a that connects it to the hanging lead 5 is narrow, the supporting piece 7a receives the acting force gently and buffers it. do. In other words, both ends of the binder 7 are loosely connected to the suspension lead 5, and the support pieces 7a are more likely to deform to accommodate the rolling force than if both ends were rigidly supported. Therefore, it is possible to suppress the application of unreasonable force to the binder 7 and the tip portions of the inner leads 2, and to prevent the inner leads 2 from bending or twisting.

The stress of the strip material 50 in which the thin portion 2a is formed on the upper surface of the inner lead 2 is removed by the second heat treatment process. That is, the residual stress generated when the lead frame pattern is press-molded in stages on the strip material 50 using a progressive mold is removed by this second stress-relieving annealing.

Next, the stress-removed strip material 50 undergoes a second pressing process, in which the binder 7 is removed and each inner lead 2 is separated into independent parts. As mentioned earlier, this removal of the binder 7 is performed by removing the thin wall 7a.
This is done by cutting the thinner part of the meat. That is, as shown by the dashed line in FIG. 3A, the binder 7 is cut off from the tip of the inner lead 2 in the second press step so that the cut line passes through the thin portion 7a.

In this way, since the thin wall 2a of the inner lead 2 is cut, the residual stress generated during this cutting cuts other parts of the inner lead 2 having the thickness of the strip material 50. smaller than the case. Therefore, the residual stress generated at the tip of the inner lead 2 is also reduced, and the occurrence of twisting, bending deformation, etc. at the tip of the inner lead 2 in a subsequent process is suppressed.

As described above, the residual stress generated after slitting the thin metal sheet material is removed by the first heat treatment, and the binder 7 remains integrated with the tip of the inner lead 2 in the first pressing process. In addition, a thin portion 2a is formed on the upper surface from the tip of the inner lead 2 to a portion of the binder 7. In this pressing process, residual stress in the strip material 50 is removed by the first heat treatment, so deformation such as camber or crossbow in the strip material 50 is suppressed. Therefore, there is no deviation in the shape and pitch of the reference hole 6, the shape of the inner lead 2, etc., and even in the process of punching out patterns step by step with a progressive die, the belt-like material 50 can be fed correctly. Accurate positioning is maintained. Therefore, the pattern of the lead frame can be accurately punched out with high precision.

Further, in the second heat treatment, the residual stress generated by punching out the pattern of the lead frame is removed, and at the same time, the residual stress in the thin portion 2a at the tip of the inner lead 2 is also suppressed. Therefore, even if this thin portion 2a is cut in the second pressing process, residual stress generated at the tip of the inner lead 2 is reduced, and deviations in its dimensional accuracy and shape can be suppressed.

FIG. 4 shows the main parts of another embodiment, in which (a) is a plan view of the tip of the inner lead and the binder portion, and (b) is a plan view of the tip of the inner lead and the binder portion. FIG. 2 is a sectional view taken along line CC of FIG.

In this example, the entire binder 7 is rolled down from the tip of the inner lead 2 to form a thin portion 2b. The thin portion 2b is formed by the first pressing step as in the previous embodiment, and the other heat treatment steps and the like are completely the same.

By providing the thin portion 2b wide in this manner, it is possible to manufacture a highly accurate lead frame that does not cause distortion or deformation of the tip of the inner lead 2, as in the case described above.

[0030]

[Effects of the Invention] In the present invention, residual stress generated from slitting to final press processing is removed by heat treatment for stress removal twice, and the binder that maintains the shape and dimensions of the tip of the inner lead is removed. In this case, since the tip of the inner lead or the thin part extending over the binder is cut, it is possible to suppress the occurrence of distortion due to stress or distortion when removing the binder. In addition, the position and shape of the reference hole used for positioning and feeding the strip material in each process will not be distorted, even if the lead frame pattern has a thin inner lead tip and a small gap. , high precision processing becomes possible.

[Brief explanation of drawings]

FIG. 1 is a process diagram of a lead frame manufacturing method of the present invention.

FIG. 2 is a plan view when a lead frame pattern is formed on a band-shaped material by a first press process.

3 is a diagram showing the details of the binder part, in which (a) is an enlarged plan view of the part surrounded by circle A in FIG. 2, and (b) is an enlarged plan view of the part surrounded by circle A in FIG. - It is a sectional view taken along the line B.

4 is a diagram showing an example in which a thin wall portion is provided throughout the binder, in which (a) of the figure is a plan view of the main part corresponding to (a) of FIG. 3, and (b) of the same figure is a plan view of the main part corresponding to (a) of FIG. FIG. 2 is a cross-sectional view taken along line CC in FIG.

FIG. 5 is a plan view of a lead frame formed by the first press working in a conventional process.

FIG. 6 is a process diagram for manufacturing a conventional lead frame.

7 is a diagram showing the distribution of residual stress generated in the lead frame of FIG. 5 after press working; FIG.

8 is an explanatory diagram showing deformation occurring in a strip-shaped material having the residual stress distribution shown in FIG. 7. FIG.

[Explanation of symbols]

1 Stage 2 Inner lead 2a Thin wall part 2b Thin wall part 3 Tab 4 Outer lead 5 Hanging lead 6 Reference hole 7 Binder 7a Support piece 8 Spacer hole

Claims (1)

[Claims] 1. A method for manufacturing a lead frame, comprising: slitting a wide metal thin plate material into a band-shaped material; and step-by-step punching and forming a lead frame pattern on the band-shaped material using a progressive die; The first step is to remove the residual stress caused by slitting the strip material.
heat treatment; and a first press step of stamping and forming a lead frame pattern on the strip-shaped material after the first heat treatment;
After the first pressing process, a second heat treatment for removing residual stress due to punching and forming, and a second press process for completing the pattern of the lead frame after the second heat treatment are performed in this order, and in the first press process, , while molding the stage, inner leads, and outer leads of the lead frame, leaving a binder connecting the tips of the inner leads, and including the tips of the inner leads between the binder and the tips, All the upper surfaces up to the binder are pressed down to form a thin part in the width direction, and further, in the second pressing step, the binder and the inner lead are separated by a cutting line running inside the thin part at the tip of the inner lead. A method for manufacturing a lead frame for a semiconductor device, the method comprising separating the lead frame.