JPH08111485A - Method for working lead frame, and lead frame - Google Patents

Abstract

PURPOSE: To remove dross and spatter easily, surely and quickly while a fine and highly accurate form is kept without causing deformation after laser bear machining, relating to a method of working a lead frame. CONSTITUTION: Both surfaces of a metal board 1 are coated with chemical corrosion-resistant films 2, and, cutting grooves 3 passing through the metal board 1 are, by applying a laser beam, formed according to the form of a lead frame. Next, the metal board 1 after laser beam machining is dipped in etchant for chemical polishing process, and further, ultrasonic vibration from an ultrasonic wave generator part is applied to the metal board 1 through the etchant. At that tire, with the use of an acoustic lens, the ultrasonic vibration is locally focussed at least on fine part such as art inner lead, and, convergence position of the ultrasonic vibration is scanned in the area where the fine part exists.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame processing method for forming a lead frame having a fine processing pattern with a large number of pins and a narrow pitch by appropriately cutting a metal plate using laser light, and a method for processing the same. The present invention relates to a lead frame processed by a lead frame processing method.

[0002]

2. Description of the Related Art Conventionally, the mainstream processing method of a lead frame used in a semiconductor device has been press working or etching. However, recently, with the miniaturization and high performance of semiconductor devices, the lead frame has many pins and a narrow pitch,
That is, fine processing has been required, and the above-mentioned press processing and etching processing cannot cope with the miniaturization because there is a technical processing limit. Moreover, in the case of such a lead frame, not only it is difficult to cope with miniaturization, but also strict dimensional accuracy is required, so that a more advanced processing technique than before is required.

For this reason, it has been attempted to carry out fine processing by utilizing the characteristics of laser cutting capable of processing a width narrower than the thickness of a metal plate as a raw material. Processing using laser light (hereinafter referred to as laser processing as appropriate)
Is a cutting method that focuses laser light, which is a high-density energy heat source, on the surface of the work piece and melts and melts the work piece locally and instantaneously. This is a method, and it is possible to perform processing that was impossible with the press processing or etching processing used for conventional lead frame processing.

As a method of processing a lead frame using a laser beam, for example, as disclosed in JP-A-2-247089 and JP-A-3-123063, a narrow pitch portion inside an inner lead is disclosed. There is proposed a method in which the above is processed by laser processing, and a part which is not a narrow pitch such as an outer lead is processed by conventional pressing or etching. Further, in the method disclosed in Japanese Patent Laid-Open No. 2-301160, laser processing is used to form a predetermined cutting pattern on the lead frame or to cut the dam bar connecting the outer leads of the lead frame.

[0005]

As described above, according to the laser processing, since the laser light can be finely focused and processed, a fine and highly accurate lead frame can be manufactured. The laser processing is a thermal processing in which a metal plate (material to be processed) is rapidly and instantaneously heated by a laser beam that is finely focused, the heated portion is melted and eliminated, and a cutting groove that penetrates the metal plate is formed. Therefore, the molten material adheres to the metal plate as dross or spatter as it is processed. In particular,
Dross tends to adhere to the side of the metal plate where the laser light is irradiated (hereinafter referred to as the back surface) along the side wall of the cutting groove, and spatter is scattered around the cutting groove of the metal plate. Cheap. Further, some dross and spatter also adhere to the wall surface of the side wall of the cutting groove.

If these dross and spatter adhere to the lead frame as a product, the processed shape deteriorates and the dimensional accuracy deteriorates. Also, since dross and spatter easily peel off from the metal plate metal, if a lead frame with the metal attached is used, they may peel off irregularly during the manufacturing process of the semiconductor device, short circuit between leads, semiconductor device There is a high risk of causing defects in the equipment and failures of manufacturing equipment. Furthermore, since dross and spatter are formed so as to project from the back surface of the metal plate, it also leads to deterioration of adhesion during bonding with other parts in the subsequent process, which deteriorates quality and also affects the manufacturing process of semiconductor devices. When attempting to fix and constrain the lead frame, a protruding dross or spatter interferes and the lead frame cannot be fixed and restrained accurately and reliably. If a lead frame having dross or spatter adhered thereto is used as described above, there is a problem that a semiconductor device with good dimensional accuracy cannot be manufactured.

On the other hand, it is necessary to remove dross and spatter attached to the metal plate in advance, but in a fine lead frame, the cutting pitch is 0.
About 3 mm to 0.5 mm, 0.1 in the inner lead part
5 mm to 0.25 mm (0.0 in terms of the width of the cutting groove)
3 to 0.1 mm), and high dimensional accuracy is required for electrical connection between the semiconductor chip and a wiring pattern on an external electronic circuit board. The removal method given to the metal plate cannot be adopted. In addition, the lead frame made of a very thin metal plate having a plate thickness of, for example, 0.1 mm to 0.2 mm has low rigidity, and therefore it is extremely difficult to forcibly remove the attached dross or spatter without causing deformation. Difficult to do. further,
It is almost impossible to mechanically remove dross and spatter attached to the wall surface of the side wall of the cutting groove because the width of the cutting groove is extremely narrow.

[0008] Conventionally, in order to remove these dross and spatter, mechanical grinding with a blade, a grindstone, etc., a method of spraying fine particles (hereinafter referred to as shot blast), and a method of mechanical polishing such as wire brushing have been used. Was adopted. However, the method of forcibly removing dross and spatter by such mechanical force is inefficient, and it is difficult to perform quickly, and at the same time, it is fine and highly accurate and rigid as the object of the present invention. There is a risk that deformation and distortion may remain in a lead frame having a low degree of deterioration, resulting in deterioration of performance and reduction of product yield.

Japanese Unexamined Patent Publication Nos. 2-247089 and 3
Although the above-described problem also exists in the laser processing in Japanese Laid-Open Patent Publication No. 123063, these conventional techniques have not taken any measures against the problem.

Further, in the system disclosed in Japanese Patent Laid-Open No. 2-301160, it is attempted to suppress the adhesion of dross and spatter by blowing off the melt with an assist gas ejected coaxially with the laser beam. There is. However, in the case of a lead frame with a large number of pins and a narrow pitch, since the width of the cutting groove to be formed is extremely narrow, the melted material is not sufficiently removed even if the assist gas having a sufficient pressure is blown, and it is inevitable that the melted material will not be removed after processing. It is unavoidable that the melt remains and dross or spatter adheres to the product lead frame.

An object of the present invention is to provide a lead frame processing method capable of easily, surely and quickly removing dross and spatter while maintaining a fine and highly accurate shape without deformation after laser processing. And a lead frame processed by the lead frame processing method.

[0012]

In order to achieve the above object, according to the present invention, a lead frame having a semiconductor chip mounted thereon and having a large number of leads connected to respective terminals of the semiconductor chip is formed from a metal plate. In the method of processing a lead frame, in which at least a part of the lead frame is formed by laser light irradiation, the first step of irradiating the metal plate with laser light to form a cutting groove penetrating the metal plate And a second step of performing a chemical surface treatment by immersing the metal plate in a chemical treatment liquid after the first step and applying ultrasonic vibration to the metal plate through the chemical treatment liquid. There is provided a method for processing a lead frame, comprising:

In the above, preferably, when the ultrasonic vibration is applied in the second step, the ultrasonic vibration is locally focused on at least a fine portion of the lead to be formed.

In the method of processing a lead frame as described above, preferably, the third step of coating both surfaces of the metal plate with a chemically corrosive resist film before the laser beam irradiation in the first step. Have.

Further, the chemical surface treatment in the second step is a chemical polishing treatment in which a metal plate is immersed in a chemical treatment liquid, or a metal plate is immersed in a chemical treatment liquid and the space between the chemical treatment liquid and the metal plate is reduced. It is preferable that the electropolishing treatment is such that an electric current is passed through.

Further, preferably, the minimum width of the cutting groove formed in the metal plate by the laser beam irradiation in the first step is not more than 1/2 of the plate thickness of the metal plate.

Further, according to the present invention, there is provided a lead frame processed by the above method for processing a lead frame.

[0018]

In the present invention constructed as described above, a metal plate is irradiated with a laser beam to form a cutting groove that penetrates the metal plate, and then the metal plate is immersed in a chemical treatment liquid for chemical surface treatment. To do. By thus performing the chemical surface treatment, dross or spatter generated by laser processing and attached to the metal plate is corroded from the surface or the interface with the metal.

However, if the metal plate is simply immersed in the chemical treatment liquid, it takes a certain amount of time to completely remove dross and spatter by corrosion. Moreover, in the multi-pin, narrow-pitch lead frame to which the present invention is applied, the minimum width of the cutting groove formed by laser processing is about 0.03 mm to 0.1 mm (sheet thickness:
(1 mm to 0.2 mm) and the size is extremely small compared to the plate thickness, the chemical treatment liquid does not sufficiently enter the cutting groove, and the corrosion rate at that portion is high. It takes a very long time to completely remove the dross and spatter attached to the wall surface of the side wall of the cutting groove.

Therefore, in the present invention, ultrasonic vibration is applied to the metal plate through the chemical treatment liquid to improve the chemical treatment speed and to easily, surely and rapidly remove dross and spatter. And improve quality.

The first action by applying ultrasonic vibration is a washing action on the surface of the metal plate which is the surface to be treated. This action is generally used as ultrasonic cleaning. By this cleaning action, the reaction products generated by the chemical surface treatment are promptly removed from the surface to be treated, and dust, dust, oil and fat adhering to the surface to be treated are also positively removed. It is possible to expose an always active surface, ie a surface which is susceptible to chemical surface treatment. further,
With ultrasonic vibration applied, cleaning of the surface to be processed proceeds easily simply by immersing the metal plate as the material to be processed in the processing liquid.

The second action by applying ultrasonic vibration is the stirring action of the treatment liquid. The minimum width of the cutting groove formed in the lead frame having a large number of pins and a narrow pitch as the object of the present invention has a plate thickness of 0.1 mm to 0.2.
In the case of mm, it is about 0.03 mm to 0.1 mm, which is much narrower than the plate thickness, so that it is very difficult to sufficiently pass the chemical treatment liquid into the plate. However, if ultrasonic vibration is applied to the metal plate through the chemical treatment liquid, the ultrasonic vibration can be propagated uniformly in the chemical treatment liquid and in the metal plate, and therefore, the chemical vibration in the cutting groove will occur. The treatment liquid is agitated, and replacement with a fresh chemical treatment liquid is performed quickly and reliably. This prevents a decrease in the chemical surface treatment rate and can contribute to the improvement.

The first and second actions described above improve the corrosion ability of the original chemical surface treatment and accelerate the treatment.

The third action by applying ultrasonic vibration is the action caused by the shape of dross or spatter attached by laser cutting. Dross and spatter are attached in the form of protrusions from the metal of the metal plate, but if ultrasonic vibration is applied to the dross and spatter that are attached in the form of protrusions, they will be removed in a chemical treatment liquid. Forced ultrasonic vibration is applied to, and strong shearing force is applied to the interface part attached to the metal by the forced vibration. There are two types of dross and spatter: solidified molten metal that could not be completely removed due to jetting of assist gas, and solidified molten metal that was once completely removed and then adhered to the metal plate again. However, in either case,
Since it is a metal that has once been in a molten state, an oxide film is formed on the surface thereof, and there is no one that adheres to the metal plate base metal through a perfect joint structure. Therefore, the adhesion strength of the dross and spatter to the metal plate base metal is originally not very strong,
In the chemical treatment liquid to which ultrasonic vibration is applied, the dross and spatter are broken off at the interface portion by the shearing force as described above, and are easily separated and removed from the metal plate base metal.

As described above, by applying ultrasonic vibration to the metal plate through the chemical treatment liquid, dross and spatter adhered by laser processing can be removed easily, reliably and quickly. it can. Moreover, the surface of the metal sheet metal after the dross and spatters are removed is finely finished because it is immersed in the chemical treatment liquid.

Further, since the dross and the sputter process are carried out only while being immersed in the chemical treatment liquid, unnecessary deformation is not given to the metal plate. That is,
It is possible to only remove dross and spatter without damaging the fine and highly accurate lead frame shape achieved by laser processing.

Further, in the fine portion of the lead to be formed, the number of cut portions is large, so that the amount of dross or spatter generated is relatively large. In the present invention, when the ultrasonic vibration is applied, by locally focusing the ultrasonic vibration on at least the above-mentioned minute portion, the sound pressure at the focused portion of the ultrasonic vibration is increased, and The local difference in sound pressure between the parts causes a local flow of the chemical treatment liquid. This causes a difference in processing speed between a portion where ultrasonic vibration is focused and a portion where ultrasonic vibration is not focused in one chemical treatment liquid. Therefore, in the fine portion where the amount of dross or spatter is large, the above-described action of removing dross or spatter easily, reliably and quickly is not impaired.

In the above case, the relatively large-shaped portion near the outer periphery of the lead frame is immersed in the liquid for a predetermined time required for processing, and almost no ultrasonic vibration is applied thereto. Surface treatment (overetching) can be avoided. Therefore, a good processed shape and uniform quality can be secured. In addition, since dross and spatter are intensively processed in the necessary parts, unnecessary deterioration of the chemical treatment liquid can be avoided and its life can be extended, and the cost of chemical surface treatment can be reduced. Is possible.

Further, by coating both sides of the metal plate with a chemically corrosion resistant resist film before the laser light irradiation, the metal of the metal plate base metal which should not be processed at the time of performing the chemical surface treatment. Skinnyness is suppressed.

Further, as the chemical surface treatment, a chemical polishing treatment in which a metal plate is immersed in a chemical treatment liquid, or an electrolysis in which a metal plate is immersed in a chemical treatment liquid and an electric current is passed between the chemical treatment liquid and the metal plate Adopt polishing process. They are,
This is a so-called wet chemical surface treatment method, which is an easy surface treatment method.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a lead frame processing method and lead frame according to the present invention will be described with reference to FIGS.

First, the structure of the lead frame of this embodiment will be described with reference to FIG. In FIG. 2, the lead frame 1
A die pad 101 on which a semiconductor chip is mounted is provided in the central portion of 00, and a large number of inner leads 102 and outer leads 103 continuous with the inner leads 102 are provided so as to surround the die pad 101. The adjacent inner lead 102 and outer lead 103 are supported by a dam bar 104 so as to be connected to each other. Further, a cutout 106 is provided around the die pad 104 except for the arm 105,
The inner lead 102 is separated from the die pad 101 by the notch 106 and is adjacent to the inner lead 1.
02 are separated by the notch 106. Further, a positioning hole 107 is provided on the outer peripheral portion of the lead frame 100 for positioning when the terminals of the semiconductor chip and the inner leads 102 are connected. The dam bar 104 has a role of blocking the resin when the semiconductor chip is molded, and the inner lead 102 and the outer lead 1
It has a role of reinforcing 03 and is removed after molding.

Further, the inner lead 102 extends so as to converge toward the die pad 101, and its tip portion is used for electrical connection after mounting a semiconductor chip (not shown) on the die pad 101. It is wide enough. Therefore, the gap 108 between the adjacent leads on the inner side of the inner lead 102 is particularly narrow and has an extremely fine structure. Further, the processing of this portion is a portion where the dimensional accuracy and cleanliness are the most severe in the processing of the lead frame. is there.

Next, a method of processing the lead frame will be described. FIG. 3 is a flowchart explaining the processing method. First, in step S1 of FIG. 3, preparation for processing is performed. That is, a strip-shaped metal plate wound in a coil,
For example, a metal plate made of steel, copper alloy, 42 alloy, Kovar, or the like is placed on the leveler to remove the curl. Then, the surface of the metal plate is washed to remove dirt, oil and the like. By using a strip-shaped metal plate wound in a coil shape as a material as described above, a large number of lead frames can be continuously processed by unwinding the metal plate, which enables mass production.

Next, in step S2, resist processing is performed. That is, as shown in FIG.
A chemical agent resistant to chemical corrosion is applied to both surfaces of the above and dried. As a result, both sides of the metal plate 1 are covered with the resist film 2 having chemical corrosion resistance. However, generally known resist resins are used in this example, but other chemical corrosion resistant protective agents, for example, oils and fats, synthetic resins such as styrene or nylon, and water glass are coated. May be.

Next, in step S3, laser processing is performed. This laser processing is applied to at least fine and highly accurate dimensions in the lead frame shape,
The portion of the inner lead 102 that needs a shape, that is,
It is a part with a narrow pitch and strict dimensional accuracy and cleanliness. Of course, a relatively large part such as the outer lead 103 and the outer frame part may be laser-processed. Further, the laser processing device for generating the laser beam used at this time may be a general one known in the related art. An example of the laser optical system of such a laser processing apparatus is shown in FIG.

In the laser processing apparatus 200 shown in FIG. 4, the laser beam 202 generated by the laser oscillator 201 is
Bending mirror 2 provided in processing head 203
It is incident on 04 and guided toward the metal plate 1. And
The laser light 202 is focused on the condenser lens 20 inside the nozzle 205.
It is incident on the beam No. 6 and is sufficiently condensed so as to have a required energy density to enable processing, and the processing position X of the metal plate 1 is irradiated from the tip of the nozzle 205. In addition, the nozzle 205
Is provided with an assist gas supply port 207. The assist gas 208 is supplied from the nozzle tip to the laser beam 20.
It is ejected coaxially so as to wrap up 2.

In step S3 of FIG. 3, first, in the laser processing apparatus as described above, the oscillation period and energy density of the laser beam 202, the focus position of the condenser lens 206, the pressure of the assist gas 208, the processing position, etc. are set. Various conditions are set and the laser processing apparatus is prepared.

Subsequently, the metal plate 1 is subjected to laser processing by the laser processing apparatus. FIG. 5 is a view conceptually showing a cross section of the metal plate 1 to be laser processed at this time. In FIG. 5, the laser beam 202 is condensed by a condenser lens 206 so that sufficient heat energy can be supplied, the irradiated portion of the surface of the metal plate 1 is melted, and this becomes a heat source, and this melting is the surface. The metal plate 1 penetrates the metal plate 1 in due course.

The resist film 2 is also processed by heat input by the irradiation of the laser beam 202. That is, the resist film 2 on the front surface is processed by the laser beam 202 to form the opening 4a on the front side, and the resist film 2 on the back surface is processed after the cutting groove 3 is penetrated to form the opening 4b on the back side. It The dimensions of the openings 4a and 4b on the front surface side and the back surface side are substantially the same, and are slightly larger than the cutting groove 3 as shown in the drawing.

Further, most of the molten metal generated by the laser irradiation falls from the back surface of the metal plate 1, but a part of the remaining molten metal solidifies in the shape of a drop near the side wall of the back surface of the metal plate 1 to form dross 5. Become. On the other hand, the scattered molten metal adheres to the surface of the metal plate 1 as the sputter 6 via the resist film 2 or breaks the resist film 2 and directly adheres to the metal plate 1. Although not shown, some dross 5 and spatter 6 also adhere to the wall surface of the side wall of the cutting groove 3. On these dross 5 and spatter 6, the molten metal that could not be completely removed due to the ejection of assist gas and the like solidified, and the molten metal that had been completely removed once adhered to the metal plate again. In any case, since the metal once melted, an oxide film was formed on the surface, and it adhered to the metal of the metal plate 1 through a perfect joint structure. There is nothing. Therefore,
The adhesion strength of the dross 5 and the spatter 6 to the metal plate 1 to the metal is originally not very strong.

In addition to the above, a resolidified layer in which a part of the molten metal that has not been removed and remains on the side wall of the cutting groove 3 is resolidified, and a large residual thermal strain or thermal stress is caused by the thermal history received during laser processing. The heat-affected zone including is formed in a layered manner. The re-solidified layer 7 has a structure similar to that of the dross 5 and has a structure different from that of the base metal of the metal plate 1. The effect is not clear at present, but as with the dross 5 and the sputter 6, deterioration of dimensional accuracy and There is concern that it may cause a short circuit between the leads. Further, the heat-affected zone also has a different structure from the metal of the metal plate 1, and its thermal strain and thermal stress are gradually released, causing deformation of the shape, which causes deterioration of dimensional accuracy. Further, since a high temperature is generated in the vicinity of the portion of the metal plate 1 irradiated with the laser beam 202, an oxide film is formed, which causes a contact failure at the time of terminal connection.

By the above laser processing, cutting grooves 3 penetrating the metal plate 1 as shown in FIG. 1B are sequentially formed according to the lead frame shape. Then, the surface of the metal plate 1 is cleaned. In FIGS. 1 and 5 of this embodiment, dross, spatter, oxide film, etc. attached to the wall surface of the side wall of the cutting groove 3,
The resolidified layer and the heat-affected zone are collectively referred to as a work-affected layer 10.

Next, in step S4 of FIG. 3, chemical polishing treatment and application of ultrasonic vibration are performed. The chemical polishing process itself performed here is the same as the normal etching process. FIG. 6 is a view showing an example of the chemical polishing apparatus used at this time, and FIG. 7 is a sectional view taken along the line VII-VII in FIG.

In FIG. 6 and FIG. 7, the chemical polishing processing apparatus 300 includes an etching liquid tank 303 for storing a chemical processing liquid, that is, an etching liquid 302 fixed on a substrate 301.
An upper lid 304 that covers the etching liquid tank 303, an XY drive table 305 fixed to the upper lid 304, a support frame 306 attached to the XY drive table 305, and a plurality of (six in FIG. 7) fixed to the support frame 306. Sound wave generator 30
7. A roller 308 for conveying the metal plate 1 as a material is provided. However, for simplification, the ultrasonic wave generation unit 307 is schematically illustrated in FIGS. 6 and 7.

The metal plate 1 is a band-shaped material, and is carried into the chemical polishing apparatus 300 by the roller 308 in the direction shown by the arrow in the figure, and the etching solution 30 in the etching solution tank 303 is loaded.
Soak in 2. Then, ultrasonic vibration is applied to the metal plate 1 from the ultrasonic wave generation unit 307 through the etching liquid 302. Further, the XY drive table 305 is similar to an XY table for placing a work, which is provided in a normal laser processing apparatus, and it has two axial directions in the plane of the metal plate 1 which are orthogonal to each other. The support frame 306 is moved in the X-axis and Y-axis directions, and the movement of the support frame 306 causes the ultrasonic wave generator 307 to scan in the XY plane. FIG. 8 shows the main combinations of the composition of the etching solution 302, the temperature, and the processing time.

By applying ultrasonic vibration, as already described in detail, the cleaning action on the surface of the metal plate 1 and the stirring action of the etching solution 302 are strengthened, and the corrosive ability of the original chemical surface treatment is improved. It becomes possible to perform the processing reliably and quickly.

Further, the dross 5 and the spatter 6 are attached in a protruding form from the metal of the metal plate 1. The ultrasonic vibration is applied to the dross 5 and the sputter 6 thus attached in a protruding form. Then, the ultrasonic waves are forcibly applied to them in the chemical treatment liquid, and a strong shearing force is applied to the interface portion adhering to the metal by the forced vibration. Therefore, since the adhesion strength of the dross 5 and the sputter 6 to the metal plate 1 is not very strong from the beginning, the dross 5 and the spatter 6 will not be formed in the etching solution 302 to which ultrasonic vibration is applied due to the shearing force as described above. It is broken off at the interface portion and easily peeled off and removed from the metal of the metal plate 1. At the same time, the work-affected layer 10 described with reference to FIG.
Also peels off from the interface and is almost completely removed.

Further, since the peeling and removal of the dross 5 and the sputter 6 etc. are carried out only while being immersed in the etching solution 302, the metal plate 1 is not unnecessarily deformed. That is, without impairing the fine and highly accurate lead frame shape achieved by laser processing,
Only the dross 5 and the spatter 6 can be removed.

In addition to the above, in this embodiment, the ultrasonic vibration applied from the ultrasonic generator 307 is a region where at least a fine portion of the lead to be formed, such as the inner lead 102 of FIG. 2, exists. Focus on inside. Hereinafter, the configuration for converging the ultrasonic vibration and the operation thereof will be described.

The structure of the ultrasonic wave generator 307 is shown in FIG. In FIG. 9, the ultrasonic vibration source 307a is 100 KH.
The excitation AC voltage of z to 3 MHz is applied to the ultrasonic transducer 307b.
By applying to the (piezoelectric element), the ultrasonic transducer 30
Ultrasonic vibration is generated from 7b, the acoustic lens 307c having a concave surface focuses the ultrasonic vibration on a predetermined focusing position, and the intensity of the ultrasonic wave locally increases near the focusing position. The area is, for example, area 3 shown by a broken line in FIG.
It is 07A. Further, in FIG. 9, an ultrasonic sound field 307B formed on the front surface of the acoustic lens 307c is schematically shown. The configuration itself including the acoustic lens that focuses the ultrasonic vibration on the predetermined focus position as described above has been conventionally known.

Next, the focusing position when focusing the ultrasonic vibration as described above and the size of the sound wave at the focusing position will be described.

First, each physical quantity is defined as follows.

F: Frequency of ultrasonic vibration (Hz) v _e : Sound velocity in water (m / sec) v _s : Sound velocity in lens material (m / sec) λ: Ultrasonic vibration wavelength (cm) a: Radius (cm) of sound source, ie, acoustic lens r: Radius of curvature of concave surface of acoustic lens (cm) where f is about several tens of kHz to several tens of MHz, and v _e is about 1400 to 1500 m / sec. Also, v _s is f
It varies greatly depending on, but for example, iron is 5180m /
sec, 5040 m / sec for aluminum, 53 for quartz
70 m / sec, 650 m / sec for polyethylene, 800 m / sec for polypropylene, 174 for polystyrene
It is 0 m / sec, and nylon is 2380 m / sec. In addition, it is λ = v _e / f.

Using these physical quantities, the focal length F _{L of} the focused ultrasonic vibration and the diameters d _L and d _-6 of the sound wave at the focus position, that is, the focus can be expressed as follows. However, d _L
Is the diameter of the sound wave where the sound pressure first becomes zero on the focal plane, d _-6
Is the diameter of the sound wave at which the sound pressure becomes 1/2 of the peak value (intensity is -6 dB).

[0056]

[Equation 1]

[0057]

[Equation 2]

[0058]

(Equation 3)

For example, a = 3 cm, r = 6 cm, v _e =
F = 1 when 1400 m / s and v _s = 5000 m / s
F _L in the case of 00KHz, d _L, when determined respectively using Equation (1) to (3) to d _-6, as follows.

[0060]

[Equation 4]

[0061]

(Equation 5)

[0062]

(Equation 6)

Here, f = 100 KHz = 10 ⁵ c /
s, v _e = 1400 m / s = 1.4 × 10 ⁵ cm / s, λ
It was utilized that = v _{e /} f = 1.4 cm.

[0064] On the other hand, in the case of f = 2MHz is, F _L,
When d _L and d _-6 are calculated in the same manner, the result is as follows.

[0065]

(Equation 7)

[0066]

(Equation 8)

[0067]

[Equation 9]

Here, f = 2 MHz = 2 × 10 ⁶ c /
s, v _e = 1.4 × 10 ⁵ cm / s, λ = v _e / f = 0.
It was utilized that it was 07 cm. Also, _FL is f = 10
The value is the same as that at 0 KHz.

As described above, by appropriately selecting a, r, and f, it is possible to locally focus the ultrasonic vibration at a desired focusing position (focus point) with an appropriate size through the etching liquid 302. . As a result, the sound pressure at the focused portion of the ultrasonic vibration is increased, and a local flow of the etching liquid 302 (about several mm in diameter) is generated due to the difference in the sound pressure from the surrounding portion. As a result, a processing speed difference occurs between a portion where ultrasonic vibration is focused and a portion where ultrasonic vibration is not focused in one etching solution 302.

In the lead frame as shown in FIG. 2,
In a fine portion such as the inner lead 102 of FIG. 2 among the leads to be formed, the number of cut portions is large, so that the amount of dross 5 and spatter 6 generated is relatively large. On the other hand, in the present embodiment, as described above, the position where the ultrasonic vibration should be focused is in the region where at least the fine portion of the lead exists, so that the dross 5 and the spatter 6 at that portion can be easily formed. And, it can be removed surely and quickly.

Further, the relatively large shaped portions such as the outer leads 103, the positioning holes 107, and other outer frame portions are almost ultrasonically vibrated only by being immersed in the etching 302 liquid for a predetermined time required for processing. Since no voltage is applied, it is possible to avoid excessive etching processing (overetching) in that portion. Therefore, a good processed shape and uniform quality can be secured. Furthermore, since the dross 5 and the spatter 6 are intensively processed in the necessary parts,
Unnecessary deterioration of the etching solution 302 can be avoided and the life of the etching solution 302 can be lengthened, and the cost of the etching process can be reduced.

By the way, in the lead frame 100, the fine parts such as the inner leads 102 are distributed in a region having a certain size, and as compared with this, the focusing range of ultrasonic vibration is a very small range of about several mm in diameter. Is. Therefore, in this embodiment, the focus position of the ultrasonic vibration to be focused as described above is scanned in the region where the fine portion such as the inner lead 102 exists. An example of the scanning method is shown in FIG.
0 schematically shows. In FIG. 10, a portion surrounded by a two-dot chain line in the center indicates the die pad 101 (see FIG. 2), and a hatched region outside the die pad 101 is the inner lead 1
This is a region where a fine portion such as 02 exists. Then, the focus position of the ultrasonic vibration is scanned along the trajectory 307C, for example.

When the removal process of the dross 5 and the sputter 6 is completed by the chemical polishing process and the application of the ultrasonic vibration as described above, the metal plate 1, that is, the lead frame 100 is moved by the roller 308 (see FIG. 7) to the state shown in FIG. It is carried out in the direction of the middle arrow. A cross-sectional view at this point is shown in FIG. After that, the resist film 2 on the surface is removed by a suitable solvent or the like, and further washed and dried. A cross-sectional view after washing and drying is shown in FIG.

Next, in step S5 of FIG. 2, solder plating is immediately applied and dried. This allows
A metal film of solder adheres to the surface of the lead frame 100. Since the metal coating of the solder improves the wettability at the time of joining, the bondability at the time of joining to the semiconductor chip or the printed board is improved. In addition, the surface of the lead frame is protected by the metal film, so that it is possible to avoid scratches and deterioration. The chemical polishing process in step S4
Compared to mechanical polishing that has been conventionally performed to remove dross and spatter, it is advantageous in treating a large amount of products, and the surface cleanliness after treatment is also good. Therefore, it is more advantageous to form an appropriate metal coating such as the solder by plating on the surface of the lead frame 100 after the chemical polishing process. Note that gold plating, silver plating, or the like may be performed instead of solder plating.

Next, in step S6, the appearance such as the processed shape and surface condition and other items are inspected, and the processing is completed.

In the processing of the lead frame processing method as described above, the inner lead 102 (FIG. 2) is required to have at least a fine and highly precise size and shape as described above.
(See), that is, a portion with a narrow pitch and dimensional accuracy and cleanliness are severe. Other outer leads 10
3, the positioning hole 107, and other relatively large parts,
It can be formed by conventional press working or etching which has a high working efficiency and a low working cost. As described above, by appropriately selecting and combining an appropriate processing method according to the processed portion of the lead frame 100, the processing efficiency is improved while the required processing size and processing accuracy are satisfied, and the processing cost is reduced. be able to.

According to the present embodiment as described above, the metal plate 1
After the laser processing on the metal plate 1, the metal plate 1 is etched with an etching solution 3
In addition to the chemical polishing treatment by immersion in 02, ultrasonic vibration is applied to the metal plate 1 through the etching liquid 302, so that the cleaning action on the surface of the metal plate 1 and the stirring action of the etching liquid 302 are strengthened, and the original chemical The corrosion ability of the polishing process is improved, and the process can be performed quickly. Further, since the shearing force caused by the ultrasonic vibration acts on the interface between the dross 5 and the spatter 6 and the metal of the metal plate 1, the dross 5 and the spatter 6 which are originally not so strongly attached to the metal of the metal plate 1 are used. Can be easily peeled off and removed from the metal of the metal plate 1. Further, the work-affected layer 10 including dross, spatter, oxide film, re-solidified layer, heat-affected zone, etc. attached to the wall surface of the side wall of the cutting groove 3 is also peeled from the interface and is almost completely removed. In addition, the surface of the metal of the metal plate 1 after the dross 5 and the spatter 6 are removed is finely finished in the etching solution 302.

Further, since the dross 5 and the sputter 6 are peeled off and removed while being immersed in the etching solution 302, the metal plate 1 is not deformed unnecessarily,
It does not impair the fine and highly accurate lead frame shape achieved by laser processing.

Further, when the ultrasonic vibration is applied, the ultrasonic vibration is locally focused on at least a fine portion such as the inner lead 102.
A flow 02 is generated, and a difference in processing speed can be generated between a portion where ultrasonic vibration is focused and a portion where ultrasonic vibration is not focused in one etching solution 302. Therefore, even in a minute portion where the amount of dross 5 and spatter 6 is large,
It becomes possible to remove these dross 5 and spatters 6 easily, reliably and quickly.

In the above case, the outer lead 103
It is possible to avoid excessive etching processing (overetching) of the positioning hole 107 and other relatively large-shaped portions, and it is possible to secure a good processing shape and uniform quality. Further, since the dross 5 and the sputter 6 are intensively processed in a necessary portion, unnecessary deterioration of the etching solution 302 can be avoided and its life can be extended, and the cost of the etching process can be reduced. It is possible.

If the thickness of the metal plate 1 is set to the thickness of the lead frame 100 of the product to which an extra thickness (reduction due to the chemical polishing treatment) is given in advance, the resist film 2 is used.
It is also possible to process without coating. However, in the chemical surface treatment of the present invention, since dross and spatter can be removed easily, reliably and quickly, the treatment in a short time is completed, and the reduction in the thickness of the metal plate due to the chemical polishing treatment is almost ignored. As few as possible.

Further, instead of focusing the ultrasonic vibration locally on a fine portion in the etching liquid 302 in the above step S4, simply applying the ultrasonic vibration to the entire metal plate 1 in the etching liquid 302. The basic effect is not impaired.

Further, in FIG. 2, the inner lead 1
Although the tip of 02 is individually cut off, a connecting portion may be left in advance at this tip and separated by etching. In that case, the deformation of the inner lead 102 is further suppressed.

Next, another embodiment of the lead frame processing method according to the present invention will be described with reference to FIGS.

In this embodiment, step S of the above-mentioned embodiment is used.
In 4, the electrolytic polishing process is performed instead of the chemical polishing process, and ultrasonic vibration is applied to the entire metal plate instead of being focused on a fine portion. The electrolytic polishing treatment is known as a wet chemical surface treatment method together with the chemical polishing treatment in the examples described in FIGS. 1 to 10, and is an easy surface treatment method. The configuration other than this is the same as that of the above-described embodiment.

FIG. 11 is a diagram showing an example of the electrolytic polishing apparatus used at this time. In the electrolytic polishing apparatus 400 shown in FIG. 11, the band-shaped metal plate 1 that has been subjected to laser processing is carried into the electrolytic processing tank 402 by the feed roll 401a and the guide roll 401b. Electrolytic treatment tank 4
A plurality of electrodes (cathodes) 404a to 404f are immersed in the electrolytic etching solution 403 in 02, while a current-carrying contact (anode) 410 is in contact with the metal plate 1, and the electrodes 404
a to 404f have independent DC power sources 405a to 405a to 404f, respectively.
An electric current is supplied from 405f to cause an electrochemical reaction, and electropolishing is continuously performed. An ultrasonic wave generator 420 is attached to the bottom surface of the electrolytic treatment tank 402, and the electrolytic etching liquid 403 is attached to the metal plate 1 from below.
Ultrasonic vibration is applied via. However, the ultrasonic wave generator 420 does not focus the ultrasonic vibrations as shown in FIGS. 6 and 7, but merely generates the ultrasonic vibrations and applies them to the entire metal plate 1.

As a result, the dross 5 and the spatter 6 adhered to the metal plate 1 are separated from the metal of the metal plate 1, and the dross and spatter adhered to the wall surface of the side wall of the cutting groove 3,
The work-affected layer 10 including the oxide film, the re-solidified layer, the heat-affected zone, etc. is also removed. Then, the metal plate 1 electrolytically polished by the electrolytic etching solution 403 is carried out by the guide roll 401c and the feed roll 401d and fed to the next step. Further, the electrolytic etching solution 403 in the electrolytic treatment bath 402 is replaced with a new one as appropriate.

12 and 13 show examples of combinations of the composition of the electrolytic etching solution 403, the current density, the temperature and the processing time in the electrolytic polishing process. 12 shows the case where the material of the lead frame is an iron-based material such as steel, and FIG. 13 shows the case where the material of the lead frame is copper and a copper alloy. However, the processing time is adjusted by the feed speed of the feed rolls 401a and 401d and the guide rolls 401b and 401c of FIG. However, the electrolytic polishing treatment can be performed under other conditions.

Also according to the present embodiment as described above, FIG.
The same effect as the embodiment described with reference to FIG. 10 can be obtained.

The arrangement of the electrodes and the arrangement of the ultrasonic wave generator may be other than those described above. For example, the electrolytic treatment tank itself may be the cathode,
The effect of this embodiment can be obtained even by disposing the ultrasonic wave generator in the electrolytic etching solution.

Further, the ultrasonic wave generator 420 may have the same structure as that shown in FIG. 9, and the ultrasonic vibration may be locally focused on a fine portion in the electrolytic etching solution 403.

[0092]

According to the present invention, after laser processing a metal plate, the metal plate is immersed in an etching solution for chemical polishing, and ultrasonic vibration is applied to the metal plate through the chemical processing solution. Is applied, it is possible to remove dross and spatter easily, reliably and quickly. Further, the work-affected layer including the dross, the spatter, the oxide film, the re-solidified layer, the heat-affected zone and the like attached to the wall surface of the side wall of the cutting groove can also be removed. Further, the surface of the metal plate base metal can be cleanly finished in a chemical treatment liquid.

Further, since unnecessary deformation is not given after the laser processing, it is possible to manufacture a lead frame having a large number of pins and a narrow pitch without damaging the lead frame shape with high quality and high accuracy.

Further, since the ultrasonic vibration is locally focused on at least a fine portion of the lead to be formed, even in a fine portion where the amount of dross or spatter is large,
It becomes possible to remove dross and spatter easily, reliably and quickly.

Further, since it is possible to avoid excessive etching (over-etching) of a relatively large portion near the outer periphery of the lead frame, it is possible to secure a good processed shape and uniform quality. In addition, since dross and spatter are intensively processed in the necessary parts, unnecessary deterioration of the chemical treatment liquid can be avoided and its life can be extended, and the cost of chemical surface treatment can be reduced. Is possible.

As described above, according to the present invention, since the processing speed of dross and spatter is improved, it is possible to increase the production amount of lead frames and reduce the production cost, and it is also possible to realize mass production. Become.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a metal plate processed by a method for processing a lead frame according to an embodiment of the present invention, FIG. 1A shows a state where both surfaces of the metal plate are coated with a chemical corrosion resistant resist film. FIG. 2B is a view showing a state where a cutting groove is formed in a metal plate by laser processing, and FIG. 3C is a state of a cross section of the metal plate after chemical polishing treatment and application of ultrasonic vibration. FIG. 6D is a diagram showing a state where the removal, cleaning and drying of the resist film are completed.

FIG. 2 is a diagram showing a configuration of a lead frame processed by the method of processing the lead frame of FIG.

FIG. 3 is a flowchart illustrating a method of processing the lead frame shown in FIG.

4 is a diagram showing an example of a laser optical system of a laser processing apparatus used in the laser processing of FIG.

5 is a view conceptually showing a cross section of the metal plate to which the laser processing of FIG. 3 is applied.

FIG. 6 is a diagram showing an example of a chemical polishing treatment apparatus used in step S4 of FIG.

7 is a sectional view taken along the line VII-VII in FIG.

FIG. 8 is a diagram showing a main combination of an etching solution composition, temperature, and processing time used in the chemical polishing processing apparatus of FIGS. 6 and 7.

9 is a diagram showing a configuration of an ultrasonic wave generation unit in the chemical polishing processing apparatus of FIGS. 6 and 7. FIG.

FIG. 10 is a diagram showing an example of a scanning method for scanning the focus position of ultrasonic vibrations.

FIG. 11 is a diagram showing an example of an electrolytic polishing apparatus used in a lead frame processing method according to another embodiment of the present invention.

12 is a diagram showing an example of a combination of the composition, current density, temperature, and processing time of the electrolytic etching solution used in the electrolytic polishing apparatus of FIG. 11, in the case where the lead frame material is an iron-based material. It is a figure.

13 is a diagram showing an example of a combination of composition, current density, temperature, and treatment time of the electrolytic etching solution used in the electrolytic polishing treatment apparatus of FIG. 11, in the case where the material of the lead frame is copper and copper alloy. It is a figure.

[Explanation of symbols]

1 Metal Plate 2 Resist Film 3 Cutting Groove 5 Dross 6 Sputtering 10 Processed Layer 100 Lead Frame 102 Inner Lead 103 Outer Lead 200 Laser Processing Device 201 Laser Oscillator 202 Laser Light 203 Processing Head 205 Nozzle 206 Condenser Lens 207 Assist Gas Supply Port 208 Assist gas 300 Etching device 302 Etching liquid 303 Etching liquid tank 304 Upper lid 305 XY drive stand 306 Support frame 307 Ultrasonic wave generation unit 307a Ultrasonic vibration source 307b Ultrasonic vibrator 307c Acoustic lens 307A Sound wave intensity near the focusing position Locally increased area 307B Ultrasonic sound field 307C Trajectory of focusing position of ultrasonic vibration 308 Roller 400 Electrolytic polishing apparatus 401a Feed roll 401b Guide low Reference numeral 401c Guide roll 401d Feeding roll 402 Electrolytic treatment tank 403 Electrolytic etching solution 404a to 404f Electrodes (cathode) 405a to 405f DC power supply 410 Current-carrying contact (anode) 420 Ultrasonic wave generation portion a Acoustic lens radius r Acoustic lens concave surface Radius of curvature F _L Focal length of focused ultrasonic vibration d _L Diameter of sound wave at which sound pressure first becomes zero on the focal plane

Front Page Continuation (72) Inventor Kojiro Ogata 650 Kazunachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura Plant

Claims (6)

[Claims] 1. When forming a lead frame having a large number of leads connected to respective terminals of the semiconductor chip from a metal plate, at least a part of the lead frame is formed by laser light irradiation. In the method of processing a lead frame, a first step of irradiating the metal plate with a laser beam to form a cutting groove penetrating the metal plate, and a chemical treatment liquid for treating the metal plate after the first step. And a second step of applying ultrasonic vibration to the metal plate via the chemical treatment liquid while immersing the lead frame in the lead frame for chemical surface treatment. 2. The method of processing a lead frame according to claim 1, wherein at the time of applying ultrasonic vibration in the second step, ultrasonic vibration is locally applied to at least a fine portion of the lead to be formed. A method of processing a lead frame, which comprises: 3. The method for processing a lead frame according to claim 1, wherein both sides of the metal plate are coated with a chemically corrosion resistant resist film before the laser beam irradiation in the first step. A method of processing a lead frame, comprising the steps of: 4. The method of processing a lead frame according to claim 1, wherein the chemical surface treatment in the second step involves immersing the metal plate in the chemical treatment liquid. A method of processing a lead frame, which is a chemical polishing process. 5. The lead frame processing method according to claim 1, wherein the chemical surface treatment in the second step involves immersing the metal plate in the chemical treatment liquid. A method of processing a lead frame, which is an electrolytic polishing treatment in which an electric current is passed between the chemical treatment liquid and the metal plate. 6. A lead frame processed by the method for processing a lead frame according to claim 1. Description: