JPH0564855B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a method of manufacturing a lead frame used for fixing a semiconductor chip such as an IC or LSI, and particularly relates to a method of manufacturing a finger portion connected to an electrode of a semiconductor chip. .

[Background Art] Metal lead frames have conventionally been used to assemble semiconductor devices in which semiconductor chips are integrated with a resin mold and have a plurality of protruding pins. This lead frame is formed by punching out a thin metal plate with a press or etching it.
Its shape is as shown in FIG.
A tab lead 3 that supports a rectangular tab 2 to which it is attached at its four corners, a plurality of fingers 4 whose inner ends face the periphery of the tab 2, and a frame 5 that supports these fingers 4 and the outer ends of the tab lead 3. It consists of sprocket holes 6 provided at regular intervals along both side edges of the frame portion 5.

To assemble a semiconductor device using such a lead frame 7, after mounting the semiconductor chip 1 on the square tab 2, connect each electrode of the semiconductor chip 1 and the corresponding inner end of the finger 4 with a wire or a wire. After that, the inner region of the rectangular frame portion 5 is molded with synthetic resin to cover the semiconductor chip 1, and then the frame portion 5 is cut out to obtain a flat lead or in-line type semiconductor device.

Incidentally, a lead frame is integrally provided with thin tab leads and fingers, but in recent years there has been a desire for semiconductor devices that are small and have a large number of pins, and the number of fingers has also tended to increase. Therefore, the width of each finger has to become smaller and smaller. For example,
Products with a diameter of about 0.3 mm have already been produced. It is already difficult to form such a lead frame using a punching press, and recently it has become possible to form it using etching, but processing by etching complicates the manufacturing process and increases costs.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a lead frame for a semiconductor device that is easy to manufacture and can sufficiently form fine fingers. The purpose of the present invention is to provide a lead frame manufacturing method that can simultaneously mold bumps.

[Summary of the invention]

As a means for achieving the above object, the present invention involves forming a resist layer in a desired pattern on a base material having conductivity at least on the surface, and electroforming a lead made of a conductive metal layer on a non-resist portion of the base material. A lead frame manufacturing method for forming a frame, wherein a part corresponding to a finger tip of a non-resist part for forming fingers of a lead frame is separated by a resist layer, and the resist layer is formed during electroforming. The tip of the finger is formed to be connected to the finger main body beyond the point, and a thicker bump is formed at the tip of the finger than the finger main body.

〔Example〕

FIG. 1 is a perspective view showing a part of the finger in cross section, and FIG. 2 is a longitudinal sectional view of the tip of the finger. In the figure, the finger 4 is made of conductive metal foil, and there are grooves 4 along the lower surface of the center in the longitudinal direction.
a, and flanges 4b and 4c are provided on both sides. As shown by the two-dot chain line in FIG. 3, the groove 4a is formed in the middle part of the finger 4 except for the base part 4d and the tip part 4e, and the cross-sectional shape in this middle part is approximately U-shaped so that it can be made using a small amount of material. The moment of inertia against bending is increased.

Further, a bump 4f connected to an electrode of the semiconductor chip 1 is formed on the tip end 4e of the finger 4. A recess 4 in a direction substantially perpendicular to the groove 4a is provided on the lower surface of the portion connecting the tip portion 4e and the intermediate portion.
g is formed, and the tip of the concave portion 4g constitutes a bump 4f that protrudes from the upper surface of the finger 4.

FIG. 4 is a perspective view showing another example of the finger 4, in which a metal thin film 4h is further laminated on the upper surface of the finger 4 of the above embodiment. By doing so, the rigidity of the finger 4 can be further increased.

FIG. 5 shows the process of molding the lead frame having the above-mentioned finger structure.

First, as shown in Figures a and b, a device hole 9 is formed in a base material for electroforming, such as a film 8, made of synthetic resin such as polyimide or polyester, by pressing using the pushback method. The pushback method is a processing method in which a desired portion is first punched out using a pressing die as shown in Fig. A, and then the receiving die is raised again to fit and hold the cutout piece 10 in the device hole 9 that has been previously drilled as shown in Fig. B. Therefore, after processing, the film 8 is maintained in the state shown in FIG. b in which the device holes 9 are not opened, and can be handled as a single sheet. Incidentally, when forming this device hole 9, other sprocket holes 6 are formed.
Windows such as the above can also be molded at the same time.

Next, on the unopened film 8, a conductive metal layer 11 made of copper or the like is electrolessly plated as shown in figure c.
It is formed by means such as vapor deposition. Furthermore, a photoresist layer 1 is formed on the conductive metal layer 11 as shown in figure d.
2 is coated, or a dry film resist layer with a thickness of about 150 μm is pasted, exposed to light in a desired pattern using a photomask 13, and then washed to remove only the exposed areas.
A resist layer 12 as shown is formed on the conductive metal layer 11. After being pushed back, the conductive metal layer and photoresist layer function as a temporary fixing means to prevent the cutout piece 10 from falling off unnecessarily, and will not fall off like a thin object like a film that has been pushed back. It is particularly effective for temporarily fixing items that are easy to attach.

Next, a peeling treatment is performed on this film 8 using selenite or caustic soda, and when a metal such as nickel is electroformed, a resist layer 1 is formed as shown in figure f.
A lead frame 7 having a desired pattern is formed on the conductive metal layer 11 on which the lead frame 2 is not formed.

When electroforming lead frames with metals such as nickel, use a brightening agent of 0.07% or less (carbon is 0.01~
0.04%, sulfur 0.01~0.04%, and the total of these is
0.07% or less) is used. The brightener content is usually around 0.1%, but when the content is this high, the temperature of the lead frame increases when it is bonded to an IC chip, causing nickel to become brittle. Therefore, it is necessary to limit the brightener content to 0.07% or less. Furthermore, if no brightener is contained, sufficient mechanical strength cannot be obtained, and deformation during processing may cause short circuits with adjacent leads.

After electroforming, the resist layer 12 is removed, and the cutout piece 10 that closes the window containing the device hole 9 is removed, and a lead frame 7 having a cross section as shown in Fig. g is formed on the synthetic resin film 8. It is. In this case, since the conductive metal layer 10 has a thickness of about 5 to 10 μm, for example, to ensure conductivity for electroforming, the pulling force is small and the lead frame 13 is not deformed. do not have.

In addition, in the above embodiment, the lead frame 7
is formed on the synthetic resin film 8, but if the surface is made of conductive metal such as stainless steel instead of the synthetic resin film 8 as a base for electroforming, it will be better than a film-like material. Various materials such as thick ones can be used.

In this case, there is no need to newly provide a conductive metal layer 11 made of copper or the like as shown in FIG.
Photoresist layer 1 on stainless steel film 8
It is possible to form a lead frame made of nickel, copper, gold, alloys thereof, etc. on a stainless steel film by direct electroforming.

FIG. 6 is a diagram showing the resist pattern of the finger portion in the above manufacturing process.

In the finger portion, in addition to the finger resist layer 12 having a desired pattern, a resist portion 12a is formed at the center of the non-resist portion 14 at a position corresponding to the finger 4 along the longitudinal direction. Correspondingly, the aforementioned grooves 4a are formed.

In addition, a resist layer 1 is provided at the tip of the non-resist portion 14.
A circular non-resist portion 15 is formed separated by a resist layer 11, and when electroforming is performed on a metal having such a resist layer 11, the body of the finger 4 is , is formed separately from the metal layer growing on the circular non-resist portion 15 separated by the resist layer 11, but as electroforming further progresses, the separated non-resist portion 15
The upper metal and the finger body are connected across the resist layer 11. Since the thickness of the metal layered by electroforming depends on the current density, concentrated electroforming is performed on the metal layer on the point-like non-resist part 15 compared to the flat plate-like body part of the finger 4. The thickness becomes thicker, and bumps 4f as shown in FIG. 2 are formed. The effect of increasing the wall thickness by concentrated electroforming is further enhanced by making the shape of the non-resist portion 15 not only circular but also donut-shaped, rectangular with a pointed shape, or star-shaped.

In addition, when forming a metal thin film 4h as shown in FIG. 4, in addition to the electroforming process described above, a second
All you have to do is perform the following electroforming process.

Furthermore, when electroforming a lead frame from a metal such as nickel, it is also possible to create a lead frame in which two layers, a layer that does not contain a brightening agent and a layer that contains a brightening agent, are superimposed. If electroforming is performed without adding a brightener, the surface will be roughened and have significant irregularities, which will likely cause temperature concentration when bonding with an IC chip, especially when bonding under pressure.
Bonding can be ensured. On the other hand, if a layer containing a brightening agent is provided on the side opposite to the bonding surface, mechanical strength as a lead frame can be ensured. Note that it is desirable to limit the content of the brightener to 0.07% or less, as described in the example above.

〔Effect of the invention〕

As described above, in order to form a thick bump at the tip of the finger, the present invention separates the non-resist part corresponding to the bump from the rest to partially increase the current density during electroforming. , the bumps can be formed at the same time as the electroforming of the lead frame, making it easy to form the lead frame with bumps. Moreover, since the bump and the finger main body are connected by the thin portion, the flexibility of this connecting portion facilitates the connection work between the bump and the semiconductor chip electrode.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional perspective view of a finger according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of the finger, FIG. 3 is a plan view showing a portion of the finger, and FIG.
FIG. 5 is a perspective view showing another embodiment of the finger in the present invention, FIG. 5 is a diagram showing the manufacturing process of the lead frame in the embodiment of the present invention, FIG. 6 is an enlarged view showing the resist pattern of the finger portion, FIG. 7 is a plan view showing a general lead frame shape. 4...Finger, 4f...Bump, 7...Lead frame, 8...Film, 12...Resist layer.

Claims (1)

[Claims] 1. A lead frame manufacturing method, comprising forming a resist layer of a desired pattern on a base material having conductivity at least on the surface, and forming a lead frame made of a conductive metal layer on a non-resist portion of the base material by electroforming. Among the non-resist parts for forming the fingers of the frame, the part corresponding to the finger tip is separated by a resist layer, and the finger tip is connected to the finger body by crossing the resist layer during electroforming. , a method for manufacturing a lead frame in a semiconductor device, in which a bump thicker than the finger body is formed at the tip of the finger.