JP3030401B2 - Lead frame manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame used for a semiconductor device, and more particularly to a method for manufacturing a lead frame for a semiconductor device having a thin flat portion provided at the tip of an inner lead.

[0002]

2. Description of the Related Art As a method of manufacturing a lead frame used for assembling a semiconductor device using an integrated circuit, a method of punching a pattern by pressing a material made of a band-shaped metal material is generally adopted. On the other hand, in semiconductor devices, due to the improvement in integration, the increase in operation speed, the improvement in performance such as hybridization, and the increase in the number of lead pins, it is necessary to maintain high precision in the width of each lead and punching pattern in the manufacture It is. In response to this issue, Japanese Patent Publication No. 62-44
No. 422 discloses that a wide metal sheet material is slit into a narrow metal sheet material, and after a lead frame pattern is formed by press working, the residual material generated from slitting to press working is obtained. A method has been proposed in which heat treatment for removing stress is performed, and further, final processing for forming an end face of the tip of the inner lead is performed.

[0003]

However, the residual stress generated at the time of slitting remains in the slitted thin metal strip in a restrained state, and when the lead frame is patterned in this state, the residual stress is reduced. The lead frame is deformed when it is released, and furthermore, in performing the pattern processing of the lead frame, since the press working is performed sequentially by a progressive die having stations arranged in an appropriate order, a part of the residual stress is released. Then the next press working on the distorted pattern,
The width of the inner lead tip is not uniform or deformed, and the distance between the inner lead tip and the central element mounting part is likely to vary. For lead frames with multiple pins, wire bonding etc. May be difficult to implement. Also, when the number of pins is increased, the tip of the inner lead becomes extremely thin, causing permanent distortion (deformation) such as torsion, which makes wire bonding difficult. Therefore, the tip is crushed together with a part of the connecting piece. The flat part is formed and straightening is performed, but when the front part is crushed, the part expands in a planar manner, which causes stress to propagate around it and the support located on both sides of the connecting piece There is a problem that stress is concentrated on the lead portion and permanent distortion such as warpage or deviation of the lead occurs. The present invention has been made in view of the above circumstances, suppresses the release of internal residual stress retained by slitting or the like at the time of press working, and further corrects residual strain caused by intermediate shape processing of a lead frame. An object of the present invention is to provide a method for manufacturing a lead frame with high precision.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
The method for manufacturing a lead frame according to the present invention is a method for manufacturing a lead frame for a semiconductor device in which a thin flat portion is provided at a tip portion of an inner lead, wherein internal residual stress in a material generated in a material forming stage is restrained. First heat treatment to remove
Process and press working on the heat-treated material,
A second step of forming an intermediate shape of the lead frame by forming an inner lead having an end connected by a central connection pad, an outer lead connected thereto, and a support lead connected to the connection pad; A third step of performing a heat treatment for removing the internal residual stress retained in the intermediate-shaped lead frame generated in the step in a restricted state;
Forming a through hole around the connection pad of the heat-treated intermediate lead frame so as to leave a connection piece connecting the tip of the inner lead, and centering the element mounting portion divided by the through hole. And then
A fourth step of performing a straightening process of providing a thin flat portion at the tip of the inner lead by press working while releasing generated stress into the through hole, and leaving an element mounting portion formed at the center of the connection pad. And a fifth step of removing the connecting piece. Further, in the fourth step, a stress generated when the tip of the inner lead is formed into a thin flat portion at the tip of the support lead. There is an auxiliary through-hole for allowing air to escape. According to a second aspect of the present invention, there is provided a method for manufacturing a lead frame for a semiconductor device, wherein a thin flat portion is provided at a front end of an inner lead, wherein the internal residual material generated in the material forming step is formed. A first step of performing a heat treatment for removing stress in a constrained state, an inner lead whose tip is connected by a central connection pad to the heat-treated material by press working, an outer lead connected to the inner lead, and the connection pad Performing a second step of forming an intermediate shape of the lead frame by forming a support lead connected to the lead frame, and performing a heat treatment for removing the internal residual stress generated in the second step in the intermediate shape lead frame in a restrained state. A third step, connecting a connecting piece connecting the tip of the inner lead around the connection pad of the heat-treated intermediate shape lead frame; A through hole is formed as described above, and an element mounting portion divided by the through hole is formed at the center. Then, while releasing the generated stress to the through hole, the tip of the inner lead is formed by pressing. A fourth step of performing a straightening process of providing a thin flat portion in the first step, and a fifth step of removing the connection piece together with the connection pad and the tip of the support lead, and in the fourth step, An auxiliary through hole is provided at the tip of the support lead to release the stress generated when the tip of the inner lead is formed into a thin flat portion. According to a third aspect of the present invention, in the method for manufacturing a lead frame according to the first or second aspect, in the first step, the internal residual stress retained in the material upstream of the heat treatment is reduced. A straightening process using a spreading roller leveler is provided.

[0005]

In the method for manufacturing a lead frame according to any one of claims 1 to 3, the heat treatment for removing the internal residual stress in the raw material generated in the raw material forming step in the first step in a restrained state is performed. Since the residual stress remaining on the thin strip obtained by slitting to a predetermined width is removed, and the heat treatment is performed in a restrained state, the shape state before the heat treatment is maintained. Therefore, even when the elongated strip-shaped inner leads and outer leads are formed by the subsequent press treatment, distortion caused by releasing the internal residual stress generated in the material forming stage can be prevented. In the second step, the inner lead and the outer lead are formed by pressing, but since the tips of the inner leads are connected and restrained by the connecting pad formed at the center of the lead frame, distortion due to pressing can be prevented, As a result, the tip of the inner lead does not need to be twisted or deformed due to release of the internal residual stress. However, since the tip of the inner lead is restrained by the connection pad, and the press working is performed sequentially by the progressive die, an internal residual stress is generated in the lead frame having an intermediate shape. Therefore, the third
The heat treatment is performed in a state where the tip of the inner lead is restrained by the connection pad at the inner stress by the process, and the internal residual stress generated by the above process is removed.

In a fourth step, a through hole is formed so as to leave a connecting piece connecting the tip of the inner lead, and an element mounting portion formed by the through hole is formed in the connecting pad. Thereafter, the tip of the inner lead is crushed to form a thin flat portion, so that the stress generated in this process escapes to the side of the through hole, and residual stress in the inner lead is prevented as much as possible. it can. An auxiliary through-hole is provided in the support lead to release the stress generated when the tip of the inner lead is formed into a thin flat portion, so that the residual stress remaining in the inner lead is further reduced, and Improve precision. Thereafter, in the method for manufacturing a lead frame according to claim 1, the connecting piece is removed so as to leave the element mounting portion, and in the method for manufacturing a lead frame according to claim 2, together with the element mounting portion, Although the connection piece is removed, the manufactured lead frame, particularly the inner lead, has a small internal residual stress as described above, so that the distortion generated even when the connection piece is removed is small. In the lead frame manufactured by the manufacturing method according to the second aspect, the tip of the support lead is cut off halfway, but is left as it is, and the mold after mounting the semiconductor element is supported by the surrounding frame. be able to. In particular, in the method for manufacturing a lead frame according to the third aspect, since the internal residual stress remaining in the material is diffused using the roller leveler, the internal residual stress can be uniformly removed. Thereby, the heat treatment can be performed in a state where the strip is restrained in a planar shape.

[0007]

According to the method for manufacturing a lead frame according to the first to third aspects, since the internal residual stress generated in the material forming step by slitting or the like is almost completely removed by heat treatment, press working is performed, so that the method is more accurate. It is possible to carry out press working of a suitable lead frame. In addition, heat treatment is performed after pressing an intermediate lead frame in which an inner lead whose tip is connected by a center connection pad, an outer lead connected thereto, and a support lead connected to the connection pad are formed. Because
The internal residual stress generated by the press working which causes the deformation of the lead frame as a product can be removed, and a more precise lead frame can be provided. In forming a thin flat portion at the tip of the inner lead, a through hole is formed around the connection pad, and an auxiliary through hole is provided in the support lead, so that distortion caused by stress generated at the time of processing is reduced. Thus, the internal residual stress which causes deformation can be prevented. In particular,
Since the lead frame manufactured by the method according to the second aspect can support the packaged semiconductor device via the support lead as described above, the handling such as the bending and transport of the outer lead in the subsequent process is improved. Accordingly, the workability of the semiconductor assembly process is improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIGS. 1 to 4 show the first embodiment of the present invention.
FIG. 5 is an explanatory diagram of a method of manufacturing a lead frame according to the embodiment, and FIG. 5 is an explanatory diagram of a method of manufacturing a lead frame according to the second embodiment of the present invention.

First, a heat treatment for removing the internal residual stress generated in the material forming step is performed on the material cut to a predetermined width.
This is because when a 42 alloy (iron / nickel alloy) is used as a material, about 4 mm in vacuum or in an inert gas.
It is performed by heating at 50 to 550 ° C. for about 2 to 20 minutes and cooling in the same atmosphere. In this case, it is preferable that the heat treatment is performed after the material wound in a coil shape is continuously performed while the material is passed, and the material is further flattened through a roller leveler (above, the first step).

Next, as shown in FIG. 1, the heat-treated material is pressed into outer outer leads 1 as shown in FIG.
0, inner inner leads 11, support leads 12 provided on four sides, and connection pads 13 to which the tips of the inner leads 11 are connected are formed. These processes are sequentially punched using a progressive die to produce a lead frame 14 having an intermediate shape. The leading end of each support lead 12 has a width of 1/3 to 1 of the width of the support lead 12.
An auxiliary through hole 15 of about / 2 is formed. The pressing of the auxiliary through-hole 15 may be performed before the support lead 12 is formed, or may be performed later (the second step). Although a plurality of intermediate lead frames 14 are formed along the material, one of them is shown as a representative, and the intermediate lead frame 14 is further provided on a frame 16a outside the intermediate lead frame 14. The pilot holes provided before the frame 14 is formed are not shown.

As described above, when press processing is performed at a plurality of stations in the second step, residual stress in a restrained state is generated in the lead frame 14 having an intermediate shape. In particular, since the tip of the inner lead 11 is restrained by the connection pad 13, when the connection pad 13 is separated, it is twisted, and a residual stress in a restrained state causing deformation such as deviation of the inner lead is generated. . Therefore, a second heat treatment is performed in this state. The conditions may be the same as the first time, but a heating temperature suitable for the shape may be selected. Thereby, the stress staying in the lead frame 14 having the intermediate shape is removed (the above is the third step). In this case, the distal end of the inner lead 11 is subjected to the heat treatment in a constrained state by the connection pad 13.

The through holes 1 are left around the connection pads 13 of the intermediate-shaped lead frame 14 heat-treated in the above steps, ie, at the tip of the inner leads 11 while leaving the connection pieces 16.
7 is formed by press working as shown in FIG.
As a result, an element mounting portion 18 having four corners supported by the support leads 12 is formed at the center of the connection pad 13. Then, as shown in FIG. 3, a thinning flat portion 19 of the inner lead 11 is formed by performing coining processing (crushing processing) on the tip of the inner lead 11 together with the connecting piece 16 connected thereto. This is extremely thin and twisted (residual strain that cannot be removed by heat treatment)
This is because a flat portion is provided by crushing (correcting) the tip of the linear inner lead 11, and this portion is partially plated as necessary to form a wire bonding portion. In this case, the tip of the inner lead 11 and the connecting piece 16 are forcibly crushed by press working, so that the member expands. However, the elongation caused by this is released to the through hole 17 and the auxiliary through hole 15,
Coining can be performed in a state where the residual stress is relatively small (the fourth step).

Next, the connecting piece 16 connecting the tip of the inner lead 11 is removed by pressing. Thereby, the tip of the inner lead 11 having the thin flat portion 19 formed at the tip is separated, and the lead frame 20 as shown in FIG. 4 is completed (the fifth step).

FIG. 5 shows a lead frame 21 according to a second embodiment of the present invention. Instead of the above-described fifth step, after the fourth step, the connecting piece 16 and the element mounting portion 1 are replaced.
8 and the tip of the support lead 12 are removed by press working. Thus, the lead frame 21 having no element mounting portion is completed. By leaving the support leads 12, as described above, the resin-sealed semiconductor device can be supported by the surrounding frame 16a. Note that well-known through holes 22 for stress removal are also formed at the four corners of the lead frame.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for manufacturing a lead frame according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a method for manufacturing a lead frame according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a method for manufacturing a lead frame according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a method for manufacturing a lead frame according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a method for manufacturing a lead frame according to a second embodiment of the present invention.

[Explanation of symbols]

10: Outer lead, 11: Inner lead, 12:
Support lead, 13: connection pad, 14: intermediate lead frame, 15: auxiliary through hole, 16: connection piece, 1
6a: frame, 17: through hole, 18: element mounting portion, 1
9: thin flat portion, 20: lead frame, 21: lead frame, 22: through hole

Claims (3)

(57) [Claims] 1. A method of manufacturing a lead frame for a semiconductor device having a thin flat portion provided at the tip of an inner lead, wherein a heat treatment for removing internal residual stress in a material generated in a material forming step in a constrained state. A first step to be performed, forming an inner lead, an outer lead connected to the inner lead, a support lead connected to the inner pad, and a support lead connected to the connecting pad, by pressing the heat-treated material, by press working. A second step of manufacturing an intermediate shape of the lead frame by heat treatment, a third step of performing a heat treatment for removing the internal residual stress retained in the lead frame of the intermediate shape generated in the second step in a restricted state, Forming a through hole around the connection pad of the lead frame having an intermediate shape so as to leave a connection piece connecting the tip of the inner lead. Together form an element mounting portion which is divided by the through-hole in the middle, then
A fourth step of performing a straightening process of providing a thin flat portion at the tip of the inner lead by press working while releasing the generated stress into the through hole; and leaving an element mounting portion formed at the center of the connection pad. And a fifth step of removing the connecting piece. Further, in the fourth step, a stress generated when the tip of the inner lead is formed into a thin flat portion at the tip of the support lead. A method of manufacturing a lead frame, comprising providing an auxiliary through-hole for allowing the air to escape. 2. A method for manufacturing a lead frame for a semiconductor device, wherein a thin flat portion is provided at a tip of an inner lead, wherein a heat treatment for removing internal residual stress in a material generated in a material forming step in a restrained state is performed. A first step to be performed, forming an inner lead, an outer lead connected to the inner lead, a support lead connected to the inner pad, and a support lead connected to the connecting pad, by pressing the heat-treated material, by press working. A second step of manufacturing an intermediate shape of the lead frame by heat treatment, a third step of performing a heat treatment for removing the internal residual stress retained in the lead frame of the intermediate shape generated in the second step in a restricted state, When a through hole is formed around the connection pad of the intermediate-shaped lead frame so as to leave a connection piece connecting the tip of the inner lead. Forming an element mounting portion divided by the through hole in the center, and then performing a straightening process of forming a thin flat portion at the tip of the inner lead by pressing while releasing generated stress to the through hole. And a fifth step of removing the connection piece together with the connection pad and the tip of the support lead. In the fourth step, the inner part is provided at the tip of the support lead. A method for manufacturing a lead frame, comprising providing an auxiliary through-hole for releasing a stress generated when a tip portion of a lead is formed into a thin flat portion. 3. The method for manufacturing a lead frame according to claim 1, wherein in the first step, a straightening step using a roller leveler for diffusing internal residual stress retained in the material is provided upstream of the heat treatment. .