JP2528765B2 - Lead frames for semiconductor devices - Google Patents

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 semiconductor chips are integrated by resin molding 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 to which the semiconductor chip 1 is attached at its four corners, and a tab 2
A plurality of fingers 4 whose inner ends face the periphery of the, and a frame portion 5 which supports the outer ends of the fingers 4 and the tab leads 3.
The sprocket holes 6 are provided at regular intervals along both side edges of the frame portion 5.

In order 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.

Shall be connected directly without using wires
As shown in FIG. 7 , the aluminum electrode 8 formed on the silicon 7 has the protective film 9 formed on the silicon surface.
It is thinner and is formed inside the semiconductor chip 1 .
For this reason, bumps 4a are provided on the tips of the fingers 4 connected to the electrodes 8 to ensure reliable contact . this
Such a bump 4a is thin with the tip of the finger 4 left.
Etching until it becomes thin or thinly manufactured in advance
Attach a bump projection that was separately manufactured to the tip of finger 4 of
Made by combining.

[0005]

By the way, in the above-mentioned semiconductor device, it is extremely difficult to connect the fingers 4 of the lead frame 10 to the electrodes of the semiconductor chip 1. As has been done recently, the number of pins of a semiconductor device, that is, the number of fingers 4 of a lead frame 10 has increased, and the gap between adjacent fingers 4 has become small due to miniaturization.
As the width of itself becomes narrower, the efficiency and reliability of connection work cannot be ignored for the product cost.

In addition, in order to perform precision press punching, a relatively hard material is required for the fingers, which makes it difficult to correct bending of the fingers and misalignment of the connection position with the semiconductor chip, resulting in low yield. Will be things.

[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 the finger and the semiconductor chip can be easily connected and the connected semiconductor chip can be accurately maintained. It is intended to provide a lead frame.

As a means for achieving the above object, the present invention is to electroform the connection surface side of a finger of a lead frame with a semiconductor chip and the opposite side thereof with the same material, and to use the surface opposite to the connection surface side. Higher content of brightener on the side
Then, the hardness of the opposite surface side is set higher than the hardness of the connection surface side.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view in which a part of a lead frame 10 manufactured according to an embodiment of the present invention 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. A rectangular tab 2 for attaching the semiconductor chip 1 to the semiconductor chip, four tab leads 3 supporting the tab 2, a plurality of fingers 4 having inner ends facing the periphery of the tab 2, and outer ends of the fingers 4 and the tab leads 3. The frame 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 at the time of 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 diagram showing a molding process of this lead frame. First, as shown in FIGS. 1A to 1B, 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, then the receiving die is raised again, and (b) as shown in the figure, the cutting piece 11a is fitted and held in the device hole 12 that has been once drilled. 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 holes 12 are formed, other window portions such as the sprocket holes 6 can also 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. 3D, 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 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 cutout piece 10, and are more like a film than when the base material is relatively thick. It is particularly effective for temporarily fixing thin objects such as push-backed objects that are likely to fall off.

Next, the fingers 11 are stripped with selenious acid or caustic soda, and a metal such as nickel is electroformed to form a resist layer 1 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 brightening agent is usually about 0.1%, but if the content is high in this way, the temperature of the lead frame during 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 example, 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 further electroforming with different brightener contents. If electroforming is performed without adding a brightening agent, the surface will be roughened and the irregularities will be marked. Therefore, temperature concentration at the time of joining with the IC chip, especially temperature concentration at the time of joining in a pressure-welded state is likely 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, there is no need to newly provide 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, and the finger 4 has a thickness of about 70 μm. It has a certain thickness. Therefore
Only the position shown by the broken line in FIG. 3 is pressed from the soft layer side. In other words, while applying a preload by the upper mold A and the lower mold B to the finger <br/> base 4b of the frame portion 5 and the fingers 4 of the lead frame 10 as shown in FIG. 4, to be movable relative to the upper die A The second upper mold C provided is slightly lowered. as a result
As shown in FIGS. 5A and 5B, the finger base 4b and the tip
The intermediate portion with the edge is easily deformed from the soft layer side to form a thin portion 4c with a somewhat wide width, and a bulging bump 4a is simultaneously formed at the tip of the finger not pressed by the upper die and the lower die. 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) is generally 12 to 15 μm.

When the bumps 4a are connected to the electrodes of the semiconductor chip 1, a load is applied to the fingers 4 due to a dimensional error of the mounting position of the semiconductor chip 1 and the lead frame, but the fingers 4 can be moved by the thin portion 4c. Since sufficient flexibility is imparted, these dimensional errors and the like can be absorbed and the electrodes can be connected without breaking. By pressing from the bump side to be connected to the semiconductor chip 1 also after the pressing is thin portion 4c is deformed to warp shape to bump side and therefore the bump portion than the finger 4 is more multi the semiconductor chip side
Has a clause projecting connection easier. In particular, this effect is more remarkable because the finger connection surface side is soft and the back surface side is hard. Of course, the same effect is exhibited when wire bonding is performed between the tip of the finger 4 and the electrode of the semiconductor chip 1.

In the above embodiment, the molding of the entire lead frame was performed by electroforming, but the present invention is not limited to this, and is also applicable to a lead frame integrally molded by press molding, etching or the like. It is clear that you can do it.

[0023]

As described above, according to the present invention, the hardness of the side of the finger of the lead frame opposite to the side of the connection surface with the semiconductor chip is set higher, so that the pressing force between the finger and the semiconductor chip at the time of connection is set. Is softened on the soft side and can be connected securely without damaging the chip.Because it is received on the hard side between the jig and the jig, it is easy to use a small size and a large number of fingers without deforming the fingers abnormally. A highly accurate semiconductor device can be obtained.

[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 a 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 Base 4c Thin Wall 8 Electrode 10 Lead Frame

Continuation of front page (56) References JP-A-59-58833 (JP, A)

Claims (1)

(57) [Claims] 1. A lead frame finger is electroformed with the same material on the side of connection with a semiconductor chip and on the side opposite thereto, and a brightening agent is contained on the side opposite to the side of the connection surface.
A lead frame of a semiconductor device in which the hardness of the opposite surface side is set higher than the hardness of the connection surface side by increasing the rate .