JPH0542329A - Production of lead frame - Google Patents

Abstract

PURPOSE:To manufacture a lead frame high in dimensional accuracy at a low cost by charging current to an electromagnetic coil to generate electromagnetic inductance and giving a force to the direction of a die to a belt-like member. CONSTITUTION:The side edges of inner leads 11 and outer leads 12 are formed by an electromagnetic forming device through a punching die in sequence to a belt-like material 3. Thereafter, cavity areas are punched by the electromagnetic forming device in the same way and the tip parts of the inner leads are separated individually and the shape of the lead frame is worked completely. The lead frame obtained in this way is high in accuracy and responsibility.

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, and more particularly to improving the accuracy of the lead frame.

[0002].

2. Description of the Related Art In recent years, as semiconductor devices have become smaller, thinner, and more highly integrated, the dimensional accuracy required for lead frames used therein has also become more severe.

In particular, due to the miniaturization of the package size, the outer lead pitch is gradually reduced from 2.54 mm (0.1 inch) to 1.77 mm and 0.8 mm, and recently, 0.25 mm is also required. Is becoming more common.

Conventional methods of manufacturing a lead frame include etching and pressing, but pressing is widely used because of its practicality.

In the production of a lead frame using this pressing method, a metal band-shaped material is punched out by a die attached to the press, and coining or bending is carried out if necessary. Because of this, it cannot be punched at once, and it is divided into several steps up to 30 steps and is sequentially punched using a so-called progressive die.

However, in recent years, the lead frame has become more and more pins, the number of steps has further increased, and the die has become enormous in size. It's becoming a problem.

In order to maintain this precision, it is necessary to make the precision of the individual parts such as the punch and die of each die extremely severe, but the die becomes expensive and impractical.
There are cases where it is technically impossible.

For example, the gap between the punch and the die is generally said to be about 1/10 of the plate thickness, and the gap is made slightly smaller than that in the processing of the lead frame (see FIG. 8). That is, the plate thickness of the lead frame material is 0.25
mm, the gap on one side is 0.010 mm (= 10 μm
), When the thickness of the lead frame material is 0.15 mm, the gap on one side is about 0.005 mm (= 5 μm).
For this reason, the abutting accuracy is ± 0 when the plate thickness is 0.25 mm.
002mm (= 2μm) ± 0.1 when the plate thickness is 0.15mm
012 mm (= 1.2 μm) was required.

Furthermore, when using a progressive die, for example, when 20 parts (dies) are arranged, the accuracy is 1/20 at the worst with respect to a single piece, generally 1/20 square root = 1 / 4.47. , When 30 parts (dies) are lined up, the worst case is 1/30, and generally 1/30 square root = 1 / 5.4.
A precision of 8 is required.

Therefore, when the plate thickness is 0.25 mm and the number of parts is 20, in order to secure the contact accuracy of ± 0.002 mm (= 2 μm), the part accuracy is ± 2 / 4.47 = (± 0.45 μm).
) Will be required. When the plate thickness is 0.15 mm and the number of parts is 30, the mating accuracy is ± 0.0012 mm (= 1.2
μm) to ensure the accuracy of parts = ± 1.2 / 5.4
8 = (± 0.22 μm) is required.

Although a method of dividing a mold has been proposed, it is necessary to use either a large press or a plurality of presses, which results in a decrease in mold manufacturing costs and equipment costs such as presses. There was a problem of increase.

[0012]

As described above, in the conventional lead frame manufacturing method, in order to achieve high accuracy, it is necessary for the die contact accuracy to be extremely high, and there is a limit to miniaturization. there were.

The present invention has been made in view of the above circumstances, and relaxes an extremely high precision of individual component processing for ensuring accuracy of the upper and lower die punch-die abutting, and achieves dimensional accuracy at low cost. The purpose is to provide a high lead frame.

[0014]

Therefore, in the present invention, the strip-shaped member is inserted between the die and the electromagnetic coil, a current is passed through the electromagnetic coil, and a force in the die direction is generated in the strip-shaped member by electromagnetic induction. At least part of the lead frame shape processing is performed.

[0015]

The principle of this structure will be described.

This uses a machining principle called electromagnetic machining.

That is, when a conductor is placed in a magnetic field and an electric current is passed through it, a force is generated in the conductor. This force is called electromagnetic force,
Electromagnetic processing is processing using this.

As shown in FIG. 7, when a cylindrical metalworking material (workpiece) is put in a coil wound several times in a cylindrical shape, and the electric charge stored in the capacitor in advance is flown to the coil, it takes an extremely short time. A large electric current flows through and a strong magnetic field is generated.

This coil is subjected to a direction force according to Fleming's left-hand rule due to an electric current and a magnetic field. On the other hand, the induced secondary current flows on the surface of the workpiece in the direction opposite to the current in the coil (Lenz's law). Therefore, the work receives a force in the opposite direction to the force received by the coil. These two forces work to keep the other from each other.

If the coil is made to be strong enough to withstand this force, the work is momentarily pushed in the direction opposite to the coil.

The present invention pays attention to this point and performs fine processing of the lead frame.

That is, if the cutting die (die) is placed on the side opposite to the coil of the work, the work can be punched. If the bending die is left in place, the bending work can be performed.

According to the above structure, the punch corresponds to the electromagnetic coil, and the force can be applied to the strip-shaped material in a non-contact manner, the punch is not damaged, and the dimensional accuracy is high. It is possible to provide a high lead frame.

Further, in this case, the abutting accuracy is not required, and the molding accuracy is determined only by the accuracy of one die corresponding to the die, so that the accuracy can be greatly improved.

Furthermore, since only one die is required, the die cost can be extremely small.

Further, there is little wear of the die, maintenance and maintenance are easy, no lubricant is required, and there is no contamination of the work and no post-treatment such as cleaning after processing is required.

Further, since the molding is carried out in a non-contact manner, tool flaws and the like do not stick to the work, and the plated work can be directly transferred to the subsequent processing step.

Although the lead frame shape processing may be completed in one step, the progressive feeding may be performed in a plurality of steps.

The area of the fine pattern may be formed by using this electromagnetic forming, and the other area may be formed by a combination with other methods such as using a conventional pressing method.

[0030]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The manufacture of the lead frame of the present invention is performed by forming a band-shaped material using an electromagnetic forming apparatus as shown in the schematic view of FIG. 1 and the perspective view and the sectional view of the main part in FIGS. 2 (a) and (b). It is done by processing.

In this electromagnetic forming apparatus, punching portions 10 composed of four plane coils are arranged in a row at a predetermined interval, and each punching portion is a die (die) 1 and a predetermined die for the die. The strip-shaped member 3 as a work is sandwiched between the flat coil 2 and the flat coil 2 which are arranged with a space of, and the electric charge accumulated in the capacitor (not shown) is instantaneously flown to the flat coil 2 to generate a magnetic field. Then, a secondary current is induced in the strip-shaped member 3 and is pressed against the punching die 1 side by a reaction force to perform punching. 4 is a coil support.

As shown in an enlarged view of FIG. 3, this plane coil is wound concentrically on the same plane.

Next, the manufacturing process of the lead frame of the embodiment of the present invention will be described. Here, FIG. 4 (a) is a view showing a lead frame punching die, and FIG. 4 (b) is a view showing a lead frame punched by the die.

First, an electromagnetic forming apparatus as shown in FIG. 1 was used for the strip-shaped material 3 called alloy 42,
The side edges of the inner leads 11 and the outer leads 12 are sequentially formed with a punching die as shown in FIG.

After the side edges of the inner leads 11 and the outer leads 12 are formed in this way, the cavity region is punched out as shown in FIG. The tip portions are separated and the lead frame shape processing is completed. 13 is a tie bar. Before or after this step, precious metal plating step,
You may make it perform an annealing process etc. suitably.

The lead frame thus obtained is highly accurate and highly reliable. According to this method, high precision component precision is unnecessary.

That is, when forming a lead frame having a lead interval of 120 μm, it is considered that the accuracy needs to be about ± 20 μm.

When progressive molding is carried out using 30 molds, the required accuracy for one mold is ± 20 μm × (3
The square root of 0) = about 3.6 μm.

On the other hand, as described above, it is clear that the conventional pressing method requires ± 0.22 μm, which is more than 10 times as accurate as the present invention.

As is clear from these comparisons, the method of the present invention makes it possible to form a highly accurate lead frame very easily. That is, the accuracy of the abutment is not necessary, and the molding accuracy is determined only by the accuracy of one die corresponding to the die, so that the accuracy can be greatly improved.

Further, since the force can be applied to the strip-shaped material in a non-contact manner, the punch is not damaged.

Further, since only one mold is required, the cost of the mold is extremely low, the wear of the mold is small, the maintenance and the maintenance are easy, and the lubricant is unnecessary and the work is not contaminated. Post-processing such as cleaning after processing is unnecessary.

Further, since the molding is carried out in a non-contact manner, tool flaws and the like do not stick to the work, and the plated work can be directly transferred to the subsequent processing step.

In the above method, the sequential feeding is performed in a plurality of steps, but the lead frame shape processing may be completed in one step.

Further, the electromagnetic forming apparatus may use not only the integrated die shown in FIG. 1 but also a split die as shown in FIG.

Furthermore, as shown in FIGS. 6 (a) and 6 (b) in another embodiment, this electromagnetic forming is used for the fine pattern area, and the conventional pressing method is used for the other area. You may make it shape | mold by combining with a method.

[0048]

As described above, according to the method of the present invention, it is possible to apply a force to the strip-shaped material in a non-contact manner, and it is possible to provide a lead frame with high dimensional accuracy at low cost. Become.

[Brief description of drawings]

FIG. 1 is a diagram showing an electromagnetic forming apparatus according to an embodiment of the present invention.

FIG. 2 is a main part diagram of an electromagnetic forming apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an electromagnetic forming apparatus according to an embodiment of the present invention.

FIG. 4 is a view showing a die used in the lead frame manufacturing method of the embodiment of the present invention and a lead frame obtained by the lead frame manufacturing method of the embodiment of the present invention.

FIG. 5 is a diagram showing an electromagnetic forming apparatus according to another embodiment of the present invention.

FIG. 6 is a diagram showing an electromagnetic forming apparatus according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram of the principle of the present invention.

FIG. 8 is a diagram showing a conventional punching forming method.

[Explanation of symbols]

 1 Die Die 2 Planar Coil 3 Band Member 4 Coil Support 11 Inner Lead 12 Outer Lead 13 Tie Bar

Claims (1)

[Claims] 1. A method for manufacturing a lead frame, comprising: inner leads arranged around a semiconductor element mounting portion so as to extend radially at a predetermined interval; and outer leads extending from the inner leads. In the lead frame shape processing step, a strip-shaped member is inserted between the die and the electromagnetic coil, and electromagnetic induction is caused by passing an electric current through the electromagnetic coil to apply a force in the die direction to the strip-shaped member. Accordingly, the method for manufacturing a lead frame, comprising an electromagnetic forming step of processing the lead frame into a desired shape.