JP2539548B2 - Method for manufacturing lead frame for semiconductor device - 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 of manufacturing a semiconductor device lead frame, and more particularly to a method of plating the surface of the lead frame.

[0002]

2. Description of the Related Art A lead frame for a semiconductor device is manufactured by a process of forming a pattern of the lead frame by punching or etching a material plate of the lead frame. In this step, the stage on which the semiconductor element is mounted and the inner leads and outer leads around the stage are formed, and the upper surface of the stage and the tips of the inner leads are plated with an appropriate metal composition in preparation for wire bonding.

In recent years, semiconductor devices have been highly integrated,
The distance between the inner lead and the outer lead is extremely small. Along with this, it has become necessary to limit the surface treatment layer such as plating to only the wire bonding region on the upper surface of the tip portion of the inner lead.

In response to such a demand, for example, the actual exploitation 6
As described in JP-A-0-48250, there is a method of forming a metal plating layer in an area smaller than the upper surface of the tip of the inner lead. Further, in JP-A-60-183756, a mask having a plating pattern is manufactured in advance so that a plating layer is applied to a predetermined area, and the mask is brought into close contact with a lead frame for plating treatment. A method is disclosed. All of these methods are intended to optimize the position of the plating region to optimize the wire bonding and to eliminate unnecessary consumption of the plating solution.

However, if the inner lead formed by etching or pressing is thin, the tip end thereof is easily affected by bending or twisting. For this reason,
Even if a highly accurate positioning device is provided to determine the plating area, the plating area often shifts from the proper position in the actual process. For this reason, in the wire bonding in the subsequent step, the connection reliability is lowered, and the productivity of the semiconductor device is greatly affected.

[0006] In order to improve the precision of the position of the plating process for such a problem, for example, Japanese Patent Publication No. 2-20149.
There is also a method of partial plating using a photoresist film, as described in Japanese Patent Laid-Open Publication No. 2003-242242. FIG. 4 is a schematic view showing the steps of this method in order, and the steps are as follows.

First, as shown in FIG. 4B, a first photoresist film 51 is applied to the surface of the metal plate 50 as a material of the lead frame shown in FIG. 4A. Then, the first photoresist film 51 is exposed to light,
As shown in FIG. 6C, the exposed portions 52 and 53 are opened in only the portions corresponding to the stages of the lead frame and the tips of the inner leads, and the photoresist pattern is formed on the metal plate 5.
It forms on the surface of 0. Then, in the step (d) of the drawing, a metal plating layer 54 is applied to these exposed portions 52 and 53,
Further, as shown in FIG. 2E, the plating layer 54 is left and the first photoresist film 51 around it is removed.

Through the above steps, with respect to the metal plate 50,
The plating layer 54 is applied only to the entire surface of the stage of the lead frame to be manufactured and to the tips of the inner leads.
The positions of these plating layers 54 are set to the exposed portions 52, 5
Only because it is determined by 3, these exposed portions 52,
If the precision of forming the pattern of 53 is high, the optimum formation of the plating layer 54 becomes possible.

In order to form the pattern of the lead frame by such a process, a second photoresist film 55 for etching is further applied to the surface of the metal plate 50 as shown in FIG. The exposed portions 56 and 57 are opened so that the pattern of the lead frame can be formed on the second photoresist film 55 as shown in FIG. The exposed portion 56 corresponds to a cavity portion surrounding the stage of the lead frame to be manufactured, and the exposed portion 57 on one side corresponds to a gap between the inner leads. When the etching process is performed using the pattern of the second photoresist film 55, the metal plate 50 in the exposed portions 56 and 57 is exposed as shown in FIG.
Are removed, and the pattern of the lead frame is formed.
Then, if the second photoresist film 55 is removed, the entire surface of the stage 1 and the inner leads 2 are removed as shown in FIG.
A product in which the plating layer 54 is formed only on the upper surface of the tip of is obtained as a product.

[0010]

With such a method, since the plating process is applied to the region corresponding to the pattern of the lead frame to be molded at a stage prior to the etching process, especially at the tip of the inner lead 2. There is no displacement of the plating layer 54. The plating solution does not overflow and adhere to the peripheral surface of the tip of the inner lead 2 and the like, and even if the distance between the inner leads 2 is small, there is no obstacle such as a short circuit.

However, since the etching process for forming the pattern of the lead frame is performed after the plating process,
It is necessary to apply a photoresist film and form a photoresist pattern at each processing stage. For this reason,
Since the number of steps increases and the degree of damage to the lead frame during handling also increases, there is a limit to improving productivity.

Further, since the stage 1 and the inner leads 2 are formed by etching or pressing after the plating process is performed, the plating layer 54 is easily peeled off in the process of this formation. For this reason, it is necessary to perform extra plating, but this extra plating becomes a burr and adheres to the peripheral surface of the tip portion of the inner lead 2 at the final stage. Therefore, when manufacturing a lead frame that tends to have a large number of pins, the occurrence of such burr causes a failure such as a short circuit.

The problem to be solved by the present invention is to enable plating of the tip portions of the stage and the inner leads to be performed with high accuracy, to improve the product accuracy and to cope with the manufacture of semiconductor devices with a tendency toward multiple pins. To do.

[0014]

According to the present invention, a pattern of a stage, an inner lead, an outer lead, etc. is formed,
A method of manufacturing a lead frame, wherein a plating layer for wire bonding or the like is formed on the tip portions of the stage and the inner leads, wherein the inner leads are run along the peripheral surface of the stage during pattern formation of the lead frame. Forming a binder that integrates the tip portions of the two, the subsequent steps, the step of forming a photoresist film on the surface of the lead frame, the step of exposing and removing the photoresist film to the plating region, A step of applying a plating layer from the removed photoresist film to the surfaces of the tips of the stages and the inner leads, a step of peeling and removing the photoresist film after the treatment of the plating layer, and a punching of the binder by press working. It is characterized in that the steps of removing are performed in order.

[0015]

The tip of the inner lead is not a free end because the tip of the inner lead is restrained by the binder until it is plated. For this reason, compared with the inner lead separated from the stage at the stage of forming the pattern of the lead frame, the position of the inner lead including its tip is fixed, and the inner lead is affected by bending and torsional deformation. Do not receive Therefore, when the photoresist film is exposed to the plated surface, the exposed surface can be obtained without displacement from the upper surface of the tip of the inner lead. As a result, the plating layer is formed in conformity with this exposed surface, so that the plating layer having the correct width can be obtained at the correct position at the tip portion of the inner lead.

[0016]

FIG. 1 is a plan view showing an intermediate product after the inner lead of a lead frame and a stage are plated in the manufacturing method of the present invention.

In the figure, the pattern of the lead frame L is formed by etching or pressing using a thin metal plate as a material as in the conventional example.
This pattern is similar to a general lead frame in that a stage 1 on which a semiconductor element is mounted is formed in the center and a large number of inner leads 2 are provided around it. A large number of outer leads 4 are formed around these inner leads 2 via tie bars 3.

Here, since the tip of the inner lead 2 is wire-bonded to the semiconductor element mounted on the stage 1, it is necessary to form a pattern separated from the periphery of the stage 1. For this reason, in the past, etching and press working were performed so as to separate the inner lead 2 from the stage 1. Further, as shown in the conventional example of FIG. 4, the inner lead 2 may be similarly separated from the stage 1 after the plating process.

On the other hand, according to the method of the present invention, when the pattern of the lead frame L is formed, the inner lead 2
Although the tip ends of the inner leads 2 are separated from the stage 1, the tip portions of the inner leads 2 are formed as connected to each other.
FIG. 2 is an enlarged view of a portion inside a circle indicated by A in FIG. 1, and between the tip of the inner lead 2 and the periphery of the stage 1, a binder 5 running along the periphery of the stage 1 is provided. Are formed. The binder 5 is provided so as to be integrated with the inner lead 2 side when the lead frame L is molded, and is integrated with the tip end of each inner lead 2 by a connecting band 5a. This connecting belt 5a
Is smaller than the width of the tip portion of the inner lead 2, and has a planar shape that is united with the inner lead 2 side at the substantially central portion of the tip portion.

After the lead frame L is etched or pressed into a pattern having such a binder 5, the upper surface of the stage 1 and the upper surfaces of the tips of the inner leads 2 are plated for wire bonding. Then, after the plating process, the binder 5 is removed to obtain the final product of the lead frame 4. FIG. 3 shows this step, which will be described in order.

FIG. 3A shows a pattern of the lead frame L in which the binder 5 is provided around the stage 1 as in the case of FIG. And
A photoresist film 6 for forming a plated surface is applied to the entire surface of the pattern having such a binder 5 (FIG. 3B). Then, using a photomask plate (not shown) or the like having a pattern of the plating surface formed in advance, the entire surface of the stage 1 and the inner leads 2 are used.
Of the exposed surfaces 1a, 2a
Are formed ((c) of FIG. 3).

The exposed surface 2a formed on the surface of the inner lead 2 has a size including the entire upper surface of the tip of the inner lead 2 in the width direction. That is, at the tip of the inner lead 2, the entire upper surface from the most distal end portion to both sides in the width direction is exactly the plated surface.

After forming the above exposed surfaces 1a and 2a, the lead frame L is dipped in the plating layer to form these exposed surfaces 1a and 2a.
Plating layers 7 and 8 are formed on a and 2a as shown in FIG. After the plating layers 7 and 8 are formed, the photoresist film 6 is removed and only the plating layers 7 and 8 are integrated with the tips of the stage 1 and the inner lead 2 as shown in FIG. It becomes a thing. In the process so far, the plating layers 7 and 8 are formed in the necessary portions of the lead frame L, and the plating process shifts to the pressing process to obtain the final product.

In this pressing step, the binder 5 connecting the tip portions of the inner leads 2 to each other is punched and removed including the connecting band 5a. By this removal, the inner leads 2 become independent as shown in (f) of the figure, and a final product having a pattern similar to a normal lead frame is obtained.

In the above plating process and formation of the pattern of the lead frame, the tips of the inner leads 2 are connected by the binder 5, so the tips of the inner leads 2 are not free ends. Therefore, when the exposed surfaces 1a and 2a are formed by the photomask plate,
As long as this photomask plate is correctly positioned with respect to the lead frame L, the exposed surfaces 1a and 2a will not be displaced from their original positions. That is, since the tips of the inner leads 2 are restrained from each other and are not displaced, it is possible to form the exposed surfaces 1a and 2a at accurate positions by precisely aligning the openings of the photomask plate. Therefore, in the plating step, for example, the plating layer 8 is not partially formed on the upper surface of the tip of the inner lead 2a, and the plating solution does not drip and adhere to the peripheral wall of the tip of the inner lead 2a. Therefore, the plating layer 8 is formed over the entire width of the upper surface of the tip of the inner lead 2, and the hit rate during wire bonding does not decrease. Further, since the burr of the plating solution does not occur on the peripheral wall of the tip portion of the inner lead 2, it is suitable for manufacturing a multi-pin lead frame.

[0026]

According to the present invention, since the inner lead is fixedly supported by the binder when the plating layer is formed on the inner lead, the plating layer can be formed at the correct position and burrs are formed on the peripheral wall of the inner lead. Also disappears. Therefore, even if the tips of the inner leads are thin and the gaps between the inner leads are small due to the increase in the number of pins, a good plating layer can be obtained, and the accuracy of the wire bonding can be improved. .

[Brief description of drawings]

FIG. 1 is a plan view showing a main part of a lead frame when a plating layer is applied to the tips of a stage and inner leads in the method of the present invention.

FIG. 2 is a detailed view showing a binder portion provided between the tip of the inner lead and the stage.

FIG. 3 is a schematic view showing steps from molding of the lead frame to plating treatment and removal of the binder in the lead frame manufacturing method of the present invention.

FIG. 4 is a schematic view showing a step of a plating treatment by a conventional method.

[Explanation of symbols]

 1 Stage 1a Exposed Surface 2 Inner Lead 2a Exposed Surface 3 Tie Bar 4 Outer Lead 5 Binder 5a Coupling Band 6 Photoresist Film 7 Plating Layer 8 Plating Layer

Claims (1)

(57) [Claims] 1. A method of manufacturing a lead frame, which comprises forming a pattern of a stage, an inner lead, an outer lead, etc., and further forming a plating layer for wire bonding, etc. on the tip of the stage, the inner lead. When forming the pattern of the lead frame, a binder that runs along the peripheral surface of the stage and integrates the tip portions of the inner leads is formed, and the subsequent steps are the steps of forming a photoresist film on the surface of the lead frame. And a step of exposing and removing the photoresist film in accordance with a plating region, a step of applying a plating layer to the surface of the tip portion of the stage and the inner lead from the removed photoresist film, and treatment of the plating layer After that, a step of peeling and removing the photoresist film and punching the binder by press working A method for manufacturing a lead frame for a semiconductor device, characterized in that the steps are sequentially performed.