JP2639742B2 - Lead frame manufacturing method - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a lead frame, and more particularly to adding strength and twisting of a lead frame for a high-density integrated circuit having a large number of leads. Regarding the correction.

(Prior art) For example, a normal IC is mounted on a die pad of a lead frame.
It is manufactured by fixing a semiconductor element, connecting a bonding pad of the semiconductor element to an inner lead of a lead frame by a bonding wire of a gold wire or an aluminum wire, and sealing these with a resin.

The lead frame used here is a die pad 22 for mounting a semiconductor element, as shown in an example in FIG.
An inner lead 24 having a tip extending so as to surround the die pad, a tie bar 27 extending in a direction substantially perpendicular to the inner lead and integrally supporting these inner leads, and a tie bar 27 outside the diver. Outer leads arranged to connect to each inner lead
28 and a support bar 29 for supporting the die pad 22. 25 is a side rail.

By the way, as the number of lead pins increases with the increase in the density and integration of a semiconductor device, the package tends to be the same as before or the size has been reduced.

As the number of inner leads increases within the same area, the width of the inner leads and the distance between adjacent inner leads naturally decrease. For this reason, deformation of the inner leads due to a decrease in strength and short-circuiting between the inner leads due to the deformation may occur.

In particular, when the lead frame is formed by stamping, it is necessary to punch 0.1 to 0.12 mm width for a board thickness of 0.15 mm.Even if stamping is performed without any problem, the effect of internal residual stress is also affected. In some cases, deformation and short-circuiting may occur in a subsequent process even if only a small external force is applied.

This is also a problem when the shape is processed by etching.

However, in recent years, the size of the semiconductor device has been steadily reduced, and it has become impossible to sufficiently suppress the deformation of the thin and fine inner lead.

Therefore, in order to remove such internal residual stress and harden the surface, a method has been proposed in which, after shape processing, the lead frame is heated in a neutral atmosphere furnace and gradually or rapidly cooled.

As this heating means, a high-frequency induction heating type heating device as shown in FIG. 8 is used.

This device includes a heating coil 2 wound around a dust core 1.
Thus, a predetermined space is interposed therebetween, and a lead frame as a body to be heated is caused to run in this space.

However, in such a conventional apparatus, since the shape and dimensions (width and area) of the lead frame are partially different, uniform heating cannot be performed, and rather, a drawback such as distortion due to thermal stress occurs. was there. Also, at most 15
There has been a problem that the temperature can be raised only to 0 to 200 ° C., and sufficient surface hardening cannot be performed.

Further, there is a problem that it takes a long time to raise the temperature, the thermal efficiency is poor, and even if there is a twist, it is cured as it is.

(Problems to be Solved by the Invention) As described above, as the integration of the semiconductor device increases, the lead width and the interval become smaller, and the heat treatment for sufficiently removing the internal residual stress, correcting the twist, and hardening the surface is performed. A way was desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly reliable lead frame by preventing displacement of the tip of an inner lead.

[Configuration of the invention]

(Means for Solving the Problems) Therefore, in the method for manufacturing a lead frame according to the present invention, after the shape processing by press working or etching work, the heating plate of the heating means made of a ferromagnetic material is formed on one surface of the induction heating coil. The lead frame is pressed by a pressing plate so as to make surface contact with the lead frame, heated, and rapidly or slowly cooled.

(Function) According to the present invention, after the shape processing by press working or etching processing, the heating element is pressed to perform heating, so that heating can be performed efficiently. In addition, since both sides can be fixed and the whole surface can be heated while being pressed, deformation is small and permanent distortion due to torsion can be removed.

Preferably, the pressing plate is constituted by a heating plate,
Since the lead frame is sandwiched between two heating plates made of ferromagnetic material arranged so as to face each other and heated while being pressed, both surfaces are heated to the same state and sandwiched, so that the reliability is extremely high. High permanent distortion can be removed.

Furthermore, the internal residual stress can be removed and the hardness can be maintained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing a high-frequency heating device used in the method of the embodiment of the present invention.

This heating device intermittently interposes a lead frame F having a shape processed between an unwinding device (not shown) having a tension adding function and a winding device (not shown) having a tension adding function. While carrying, high frequency heating is performed on a predetermined area of the lead frame,
It is composed of a high-frequency heating unit 10 and a cooling unit 20.

As shown in FIG. 2, a high-frequency heating unit 10 includes an induction heating coil 2 made of a hollow rectangular copper wire wound around a dust core 1 and a heating plate 4 made of a Cr ferromagnetic material. And a pressing plate 6 disposed opposite to the heating unit 5 and configured to be able to press the lead frame in the direction of the heating unit 5 by the actuator 21. The pressing plate 6 is moved in the direction of the heating plate 4 of the heating means, and is heated while pressing an area other than the side rails of the lead frame.

Further, the cooling unit is disposed opposite to the first cooling plate 20a and the first cooling plate 20a.
A second cooling plate 20b configured to be able to be pressed in the direction of 20a, and moving the second cooling plate 20b in the direction of the first cooling plate 20a to remove the heated area of the lead frame. It is configured to cool while pressing.

Here, 7 is a guide pin, 8 is a mask plate for heating only a desired area, and 9 is a support plate.

Next, a method for manufacturing a lead frame using this heating device will be described.

3 (a) to 3 (e) are views showing the steps of manufacturing the lead frame according to the embodiment of the present invention.

First, as shown in FIG. 3 (a), a strip material is processed by a stamping method, and the tip of the inner lead 24 facing the die pad 22 is slightly connected to the adjacent inner lead by the connecting piece T. Mold.

Next, after performing a coining process to secure the flat width of the tip of the inner lead, the lead frame F is mounted on the high-frequency heating device shown in FIG. Here, the thickness of the tip of the inner lead after coining is 0.12 mm.

Then, while the lead frame F is intermittently transported between the unwinding device having the tension adding function and the winding device having the tension adding function, the pressing plate is moved by the actuator 21 in the direction of the heating plate. To the heating plate by high frequency heating
Heating is performed at 0 ° C. for 1 second, and a heat treatment is performed by pressing against a region of the lead frame other than the side rails. Thereafter, the pressing of the pressing plate is released by the actuator 21, the one-pitch lead frame is transported, transferred to the heating section cooling section, and rapidly cooled by the cooling section 20. At this time, in the high-frequency heating unit 10, adjacent units perform high-frequency heating in parallel. FIG. 3B shows a processing region R by this heating.

Thereafter, as shown in FIG. 3 (c), through a predetermined plating step, taping step, and the like, the connecting piece is punched out, and the tip of the inner lead is separated to complete the lead frame.

After the semiconductor chip is mounted on the die pad 22 of the lead frame, the semiconductor chip and the lead frame are electrically connected by wire bonding.

Then, a semiconductor device is completed through a resin sealing step, a tie bar cutting step, and an outer lead forming step.

The lead frame thus formed is hardened by quenching using high-frequency heating, internal stress due to shape processing is removed, twist is corrected, and extremely high precision is achieved. Since the leading ends of the leads can maintain a good positional relationship with each other, not only short-circuiting between the leads but also short-circuiting with the bonding wire is prevented, resulting in extremely high reliability. Further, the thickness of the lead frame may be 0.15 mm or less.

In addition, since the connecting piece is removed after reinforcement with an insulating tape, the inner lead can have a reduced lead width at the tip. As a result, the tip of the inner lead can be brought closer to the die pad, the amount of bonding wire used can be reduced, and the manufacturing cost can be reduced. Furthermore, the bonding wire can be shortened, and a short circuit is prevented.

Furthermore, in the above-described embodiment, the lead frame was molded in a state of being connected by the connecting piece, and after attaching the insulating tape, the connecting piece was removed, but the lead frame was molded without leaving the connecting piece. Needless to say, it can also be used.

In addition, in the above embodiment, the lead frame of the wire bonding type has been described, but the present invention is also applicable to a lead frame of the direct bonding type.

In the above-described embodiment, the high-frequency heating unit 10 is provided with a heating means only on one side, and is constituted by a pressing plate on the other side. However, as shown in a modified example in FIG. Heating means 5a and 5 constituted by bringing a heating plate 4 made of Cr ferromagnetic material into contact with one surface of the turned induction heating coil 2
b are disposed opposite each other, and these two heating means 5a,
The lead frame may be sandwiched by 5 and heated while being pressed.

In addition, as shown in FIG.
The induction heating coil 2 may be wound directly around the heating plate 4 made of a ferromagnetic material, and the first and second heating means 5a and 5b may be provided.

In addition, as shown in FIG. 6A, two high-frequency heating units 10a and 10b may be arranged at a predetermined pitch in the running direction of the lead frame. The heating area at this time is shown in FIG. Here, only the die pad and the inner lead are heated.

In the above embodiment, Cr was used as the heating plate.
In addition, any ferromagnetic material such as nickel may be used.

〔The invention's effect〕

As described above, according to the present invention, in the method for manufacturing a lead frame according to the present invention, after shape processing by press working or etching processing, the heating plate made of a ferromagnetic material is placed at a predetermined position on the body to be heated. Pressing and heating are performed, so that distortion can be suppressed, distortion and other deformation can be corrected, and uniform and efficient heating can be performed. The lead can be obtained, and a highly reliable lead frame can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a high-frequency heating apparatus according to an embodiment of the present invention, and FIG.
FIGS. 3 (a) to 3 (c) are views showing a manufacturing process of a lead frame according to the embodiment of the present invention, and FIGS. FIG. 6 (b) is a diagram showing a processing area in the device of FIG. 6 (a), FIG. 7 is a diagram showing a normal lead frame, FIG. 8 is a view showing a conventional heating device. F: Lead frame, 1: Dustor store, 2: Induction heating coil, 4: Heating plate, 5: Heating means, 7: Guide pin, 8: Mask plate, 9: Support plate, 10 ... ... High frequency heating section, 20 ... Cooling section, 20a ... First
Cooling plate, 20b ... second cooling plate, 21 ...
Actuator, 22 ... die pad, 24 ... inner lead, 28 ... outer lead, 29 ... support bar, T
…… Connection piece.

Claims (2)

(57) [Claims] 1. A shaping step for shaping a lead frame by pressing or etching, and a heating plate of a heating means comprising a heating plate made of a ferromagnetic material in contact with one surface of an induction heating coil. A high-frequency heating step of pressing and heating a predetermined area of the lead frame with a pressing plate so as to make surface contact with the predetermined area, and a cooling step of rapidly or gradually cooling the heated area of the lead frame. Lead frame manufacturing method. 2. The pressing plate is also formed of a heating plate made of a ferromagnetic material, and the high-frequency heating step includes the step of mounting the lead frame between two heating plates made of a ferromagnetic material arranged so as to face each other. 2. The method for manufacturing a lead frame according to claim 1, wherein the scissors are heated while being pressed.