JPH05308092A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a lead frame that allows easy junction of fingers and a semiconductor chip. CONSTITUTION:When thin section 4c is laid between a finger base section 4b of an array of fingers 4 laid laterally on a lead frame 10 and a bump 4a widely in the lateral direction of finger base section 4b and in the direction in which the bump 4a is bonded to semiconductor chip 1, the lateral dislocation of tips of the array of fingers caused by bonding the fingers by pressing can be protected with the aid of the enhanced yield strength obtained for deformation by widely laying the thin section 4c in the lateral direction and the yield strength for deformation of the bump 4a to be caused by bonding can be reduced by the thickness of thin section 4c, thereby enabling the fingers to be securely connected to one another.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame used for fixing semiconductor chips such as IC and LSI.

[0002]

2. Description of the Related Art Conventionally, a metallic lead frame has been used for assembling a semiconductor device in which a semiconductor chip is integrated with a resin mold and a plurality of pins are projected. The lead frame 10 is formed by punching a thin metal plate with a press, etching or the like, and its shape is shown in FIG.
, A tab lead 3 for supporting a rectangular tab 2 for mounting the semiconductor chip 1 at its four corners, and a tab 2
A plurality of fingers 4 whose inner ends are exposed to the peripheral edge of, and a frame portion 5 which supports the outer ends of these fingers 4 and tab leads 3.
The sprocket holes 6 are provided at regular intervals along both side edges of the frame portion 5.

To assemble a semiconductor device using such a lead frame 10, first, the semiconductor chip 1 is attached so as to face the tab 2, and then the electrodes of the semiconductor chip 1 and the inner ends of the fingers 4 corresponding thereto are attached. Wires or direct connection without using wires, then the inner region of the rectangular frame 5 is molded with synthetic resin to cover the semiconductor chip 1, and then the frame 5 is cut off to obtain a flat lead or in-line type semiconductor device. Of.

As shown in FIG. 7, in which the aluminum electrode 8 formed on the silicon 7 is thinner than the protective film 9 formed on the silicon surface and is directly connected to the inside of the semiconductor chip 1 as shown in FIG. Is formed on the tip of the finger 4 connected to the electrode 8, the bump 4a
Is projected to ensure reliable contact. Such bumps 4a are formed by a method in which the tips of the fingers 4 are left to be etched until they become thin, or by joining bump projections, which are separately manufactured, to the tips of the thin fingers 4.

[0005]

In the above semiconductor device, however, it is extremely difficult to connect the fingers 4 of the lead frame 10 to the electrodes of the semiconductor chip 1. Recently, the number of pins of the semiconductor device, that is, the number of fingers 4 of the lead frame 10 has been increased, and the gap between the adjacent fingers 4 is small due to the miniaturization.
As the width of itself becomes narrower, the efficiency and certainty of connection work cannot be ignored with respect to the product cost.

In particular, when the bumps 4a are bonded to the electrodes 8 of the semiconductor chip 1, if the amount of crushing deformation of the bumps during pressing is not uniform in all the bumps, the fingers are inclined or bent in the lateral arrangement direction ( Lateral slippage occurs, which makes it easy to abnormally approach adjacent fingers, resulting in a low yield. In order to suppress this, it is necessary to make the fingers thick, but this has to increase the finger pushing and bending force during the pressing processing force, which is not preferable for the chip.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a high mechanical strength so that a finger and a semiconductor chip can be easily connected to each other and the connected semiconductor chip can be accurately maintained. It is intended to provide a lead frame.

As a means for achieving the above-mentioned object, the present invention is wide between the finger base portions 4b and the bumps 4a of the fingers 4 arranged in a side-by-side arrangement in the lead frame 10 and is wide in the side-by-side arrangement direction of the finger base portions 4b. A thin portion 4c is arranged in the joining direction of 4a to the semiconductor chip 1.

[0009]

The thin portion 4c of the finger thus constructed
Has a wide width in the side-by-side direction of the finger base portions 4b, and thus is not easily bent and deformed in the side-by-side direction and maintains a predetermined pitch without abnormally approaching the adjacent fingers. Since it has a thin wall in the joining direction to, it deforms by following the pressing processing force of a bonding tool or the like well, and does not require an excessive pressing processing force. It is possible to surely connect to the electrode 8 while maintaining the positioning.

[0010]

1 is a perspective view of a lead frame 10 manufactured in accordance with an embodiment of the present invention, in which a part thereof is shown in section.

The lead frame 10 is composed of a base material made of a synthetic resin such as polyimide or polyester as a base for electroforming, for example, nickel or other conductive metal thin film laminated on the film 11, and is similar to the conventional example. The rectangular tab 2 for mounting the semiconductor chip 1 on the, the four tab leads 3 for supporting the tab 2, the plurality of fingers 4 whose inner ends face the periphery of the tab 2, and the outer ends of these fingers 4 and tab leads 3. The film 1 having a supporting frame portion 5
A device hole 12 is formed at a position facing the tab 2 of FIG. 1, and sprocket holes 6 which are positioning holes for assembling and carrying the lead frame 10 are formed at both ends of the frame portion 5 of the film 11. is there.

FIG. 2 is a view showing a molding process of this lead frame. First, as shown in FIGS. 2A to 2B, a pushback method is applied to a film 11 as a base material made of a synthetic resin such as polyimide or polyester. The device hole 12 is formed by pressing. Pushback method is (a)
As shown in the drawing, a desired part is first punched out by a pressing die, and then the receiving die is raised again to fit and hold the cut-out piece 11a in the device hole 12 which is once punched as shown in FIG. Therefore, after processing, the film 11 is maintained in the state shown in FIG. 7B in which the device holes 12 are not opened and can be handled as a single sheet. When the device hole 12 is formed, other window portions such as the sprocket hole 6 can be formed at the same time.

Next, a conductive metal layer 13 of copper or the like is formed on the film 11 which is not opened by a means such as electroless plating or vapor deposition as shown in FIG. Further, a photoresist layer 14 is applied on the conductive metal layer 13 as shown in FIG. 2D, and a photomask 14 is applied to expose a desired pattern, followed by washing, so that a positive type resist is used. The resist layer 14 is formed on the conductive metal layer 13 as shown in FIG. Of course, when a negative type resist is used, the pattern of the photomask 14 is reversed. The conductive metal layer and the photoresist layer after pushback have a function as a temporary fixing means for preventing unnecessary detachment of the cut-out piece 10. Compared with the case where the base material is relatively thick, it is like a film. It is particularly effective for temporarily fixing thin objects such as push-backed objects that are easy to fall off.

Next, a peeling treatment is applied to the fingers 11 with selenious acid, caustic soda, or the like, and a metal such as nickel is electroformed. Then, as shown in FIG.
The lead frame 10 having a desired pattern is formed on the conductive metal layer 13 on which 4 is not formed.

When electroforming a lead frame with a metal such as nickel, 0.07% or less of a brightening agent (carbon 0.01
.About.0.04%, sulfur 0.01 to 0.04%, and the sum of these is 0.07% or less). The content of the brightener is usually about 0.1%, but if the content is high as described above, the temperature of the lead frame during the joining with the IC chip causes the nickel to become brittle. Therefore, it is preferable to limit the content of the brightening agent to 0.07% or less. Further, if no brightening agent is contained, sufficient mechanical strength cannot be obtained, and there is a risk of short-circuiting with the adjacent lead due to deformation during processing.

Therefore, in this embodiment, the peeled film is first electroformed with a metal such as nickel with or without a brightening agent, and then with a brightening agent content higher than the above proportion. By electroforming, a lead frame in which two layers of a soft layer and a hard layer are superposed is produced.

Of course, three or more layers can be obtained by performing another electroforming with different contents of the brightening agent. If electroforming is performed without adding a brightening agent, the surface will be roughened and the irregularities will be marked, so that temperature concentration when joining with the IC chip, especially when joining in a pressure-welded state, tends to occur. It can be assured. On the other hand, if a layer containing a brightener is provided on the side opposite to the joint surface, the mechanical strength of the lead frame can be secured. The content of the brightening agent is preferably limited to 0.07% or less as described in the above embodiment.

After electroforming, the resist layer 14 is removed, and then the cut-out piece 11a that closes the window portion including the device hole 12 is pulled out, so that the lead frame 10 having a cross section as shown in FIG. It is formed on 11. In this case, the conductive metal layer 10 is thick enough to ensure conductivity for electroforming, for example 5 to 10 μm.
Since it is about the degree, the pulling-out force is small and the lead frame 13 is not deformed.

In the above embodiment, the lead frame 10 is formed on the synthetic resin film 11, but instead of the synthetic resin film 11, a conductive metal stainless steel or the like is used as a base for electroforming and its surface is formed. Various materials such as a thicker material than a film-shaped material can be applied as long as the material has conductivity.

In this case, the conductive metal layer 13 made of copper or the like as shown in FIG.
It is possible to form the photoresist layer 14 on the stainless steel base material 11 and directly form the lead frame 10 made of nickel on the stainless steel base material by electroforming.

The fingers 4 of the lead frame obtained in this state are formed in two layers such as a soft layer and a hard layer so that the hardness on the opposite surface side is higher than the hardness on the bonding surface side with the semiconductor chip. It has a certain thickness. Therefore, only the position indicated by the broken line in FIG. 3 is pressed from the soft layer side. That is, as shown in FIG. 4, the upper die A and the lower die B are provided so as to be movable with respect to the upper die A in a state in which the frame portion 5 of the lead frame 10 and the finger base portion 4b of the finger 4 are preloaded. 2 Lower the upper mold C slightly. As a result, as shown in FIGS. 5A and 5B, the intermediate portion between the finger base portion 4b and the tip is easily deformed from the soft layer side, and the thin portion 4c is formed.
And a bump 4a that bulges at the same time at the tip of the finger that is not pressed by the upper die and the lower die. Generally, the height of the bump 4a (the step between the upper surface of the thin portion 4c and the upper surface of the bump 4a) may be about 12 to 15 μm.

In this way, the thin portion 4c formed between the finger base 4b and the bump 4a is wide in the side-by-side direction of the finger base 4b, and the bending deformation resistance in this direction is large and the bump 4a becomes thin in the bonding direction to the semiconductor chip 1, and the bending deformation force in this direction can be made small.

When connecting the bumps 4a to the electrodes of the semiconductor chip 1, the bumps 4a are pressed relative to the semiconductor chip 1 by a bonding tool or the like. Since it is deformed and dealt with, it is not necessary to increase the pressing force more than necessary,
Further, at this time, since the thin portions 4c are respectively deformed in the joining direction to correspond to each other, it is not necessary to increase the pressing processing force more than necessary, and at this time, since the thin portions 4c are not easily deformed in the side-by-side arrangement direction of the fingers 4, It is possible to prevent lateral displacement without the pitch between adjacent fingers approaching abnormally. In this way, dimensional errors can be absorbed and the electrodes can be connected without disconnection.

Further, by pressing from the bump side connected to the semiconductor chip 1, the thin portion 4c is deformed into a warp shape toward the bump side after pressing, so that the bump portion protrudes from the finger 4 toward the semiconductor chip side more. Making the connection easier. In particular, this effect is more remarkable because the fingers are soft on the connection surface side and hard on the back surface side. Of course, the same effect can be obtained when wire bonding is performed between the tip of the finger 4 and the electrode of the semiconductor chip 1.

Although the entire lead frame is formed by electroforming in the above embodiment, the present invention is not limited to this, and is also applicable to a lead frame integrally formed by press forming, etching, or the like. It is clear that you can do it.

[0026]

As described above, according to the present invention, between the finger bases 4b and the bumps 4a of the fingers 4 of the lead frame 10 which are arranged side by side, a semiconductor having a wide bump 4a in the horizontal direction of the finger base 4b is formed. Since the thin thin portion 4c is arranged in the joining direction to the chip 1, the fluctuation of the pressing force between the finger and the semiconductor chip at the time of connection is relieved at the thin portion, and the chip can be securely connected without being damaged. The finger's lateral displacement force concentrates on the thin-walled part and tries to deform it in the side-by-side direction. It is possible to easily and accurately obtain a semiconductor device even if there are many semiconductor devices.

[Brief description of drawings]

FIG. 1 is a partial perspective view showing a lead frame of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a part of the lead frame manufacturing process according to the embodiment.

FIG. 3 is a plan view showing a press position at the time of bump formation in the lead frame manufacturing process of the example.

FIG. 4 is a cross-sectional view illustrating a pressing operation in the lead frame manufacturing process of the example.

5 (a) and 5 (b) are a sectional view and a perspective view showing the finger shape of the embodiment.

FIG. 6 is a plan view showing a general lead frame shape.

FIG. 7 is a cross-sectional view showing the relationship between bumps and electrodes of a semiconductor chip.

[Explanation of symbols]

 1 Semiconductor Chip 4 Finger 4a Bump 4b Finger Base 4c Thin Wall 8 Electrode 10 Lead Frame

Front Page Continuation (72) Inventor Eiji Sakata 4680 Ikata, Ikata Castle Town, Tagawa-gun, Fukuoka Prefecture Kyushu Hitachi Maxell Co., Ltd.

Claims (1)

[Claims] 1. Between the finger base portions 4b of the fingers 4 arranged side by side in the lead frame 10 and the bumps 4a, the width is wide in the side by side direction of the finger base portions 4b and thin in the bonding direction of the bumps 4a to the semiconductor chip 1. Thin part 4c
A semiconductor device in which