JP3180296B2 - Die device for punching tape for bonding semiconductor elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold used for improving the accuracy of a bonding position when a hard adhesive tape is punched and bonded to a lead frame having a LOC structure.

[0002]

2. Description of the Related Art A lead frame for resin-molding a semiconductor element (hereinafter, also referred to as a chip as required) is provided with a portion for fixing a chip called an island or a die pad. In order to bond the chip to the island portion, a eutectic alloy of gold and silicon has been used before, and a paste adhesive such as silver epoxy has been used recently.

On the other hand, in recent years, a lead frame has been developed in which the island portion is eliminated in order to enable higher-density mounting, and the occupation ratio of the chip to the mold resin per area is increased. This lead frame is called a lead frame having a lead-on-chip (LOC) structure because leads are immediately placed on the chip. FIG. 3 is a plan view schematically showing the outline of the lead frame 5 having the LOC structure. In this case, as shown in FIG. 3, the lead 7 plays the role of a conventional island. A lead frame having this structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 61-2181.
No. 39, U.S. Pat. No. 4,916,519 and the like.

The material for fixing the chip to the lead frame having the LOC structure has a high insulating property so that the leads are not electrically short-circuited to each other, and has a rigid adhesive tape after the chip is bonded to the lead. Characteristics, such as being able to maintain a constant distance between the lead and the chip, and having a small amount of volatile components. As a material capable of satisfying all of these characteristics, a tape in which an adhesive is applied to both sides of a support made of a plastic material such as a polyimide resin in a sheet shape (hereinafter, this tape is referred to as an adhesive tape) has been developed. ing.

When a chip is fixed to a lead frame having such a LOC structure, it is necessary to attach an adhesive tape to the lead in advance.
First, the adhesive tape is cut into a predetermined shape (usually rectangular) with high dimensional accuracy, and then the obtained adhesive tape piece is accurately attached to a predetermined position on the lead frame.

[0006] In these operations, the dimensional accuracy of the cutting and attaching positions of the adhesive tape is required to be extremely high, not more than 0.1 mm. This is because the electrodes of the chip must be located in extremely narrow gaps between the leads provided on the lead frame, and the area occupancy of the chip in the molding resin is as high as possible. This is because the reliability of the resin-molded semiconductor element is reduced even if the margin of the dimension becomes small and a slight shift occurs.

FIG. 4 is an explanatory view showing an example of a process of cutting and attaching an adhesive tape piece to a lead frame having a LOC structure. (Not shown). A punch press comprising a vertically punchable punch 1 provided with a suction hole 6 communicating with a punch 2 and a die 2 (receiving die) having a through hole 2 ′ having substantially the same shape as the punch 1 in the center. The adhesive tape 3 is set at a predetermined position on the die 2 while using the LOC structure lead frame 5 at a predetermined position on the opposite side of the punch 1 of the die 2.
The adhesive tape 3 is punched while performing a vacuum suction operation in the suction hole 6 of the punch 1 to punch out an adhesive tape piece 4 having a predetermined size and shape. When punching is performed in this manner, the adhesive tape piece 4 punched out by punching is pushed out from the through hole 2 ′ of the die 2 while being suction-fixed to the punch 1, and is immediately moved to a predetermined position of the lead frame 5. The bonding can be performed by pressure bonding the adhesive tape pieces 4. Usually, the adhesive tape 3 and the lead frame 5 are relatively moved in a direction indicated by an arrow and a punch press for a predetermined distance so that a continuous punching operation can be performed.

Thus, in such a punch press mold apparatus, the setting of the adhesive tape 3 on the die 2 is conventionally performed on the die 2 as shown in FIG.
A guide die 11 having a guide hole 11 'through which the punch 1 can pass is fixed by screws or the like, and the adhesive tape 3 punched at the bottom thereof has a guide hole 11' surface,
That is, a tape passage 12 is provided so that the surface of the descending punch 1 can be accurately grasped, and the adhesive tape 3 is inserted into the passage 12.

Then, in this manner, the adhesive tape piece 4
The chip is attached to the lead frame to which the chip is attached by bonding the chip to the tape bonding surface of the adhesive tape piece 4 on the side opposite to the lead bonding surface, and connecting the lead and the electrode of the chip with a fine gold wire or the like. It is.

FIG. 5 is a sectional view showing a state in which a chip is connected to a lead frame having a LOC structure. As shown in FIG. 5, the electrodes 10 of the chip 9 and the leads 7 of the lead frame are connected by a so-called wire bonding method using gold wires 8, and when performing the wire bonding, the leads 7 and the chip 9 are connected. If the adhesive tape piece 4 located in the middle between the two is too soft, the force for pressing the gold wire 8 against the lead 7 is dispersed at the adhesive tape piece 4, and the force required for pressing the gold wire 8 is applied. Therefore, it is desirable that the rigidity of the adhesive tape piece be as high as possible.

Conventionally, as an adhesive applied to the adhesive tape, an adhesive which is cured by heating, such as a rubber-based or epoxy-based adhesive, has been used. When this adhesive is used, when the adhesive tape piece is attached to the lead frame, the adhesive tape piece is soft and easy to handle, so that the adhesive tape piece can be easily cut and the adhesive tape piece having a predetermined dimensional accuracy can be obtained. In addition to being easy to attach, the lead frame can be easily attached to the predetermined position, and the rigidity of the adhesive tape piece can be increased by heating and curing the adhesive after attaching the chip to the lead. It has excellent advantages such as good wire bonding of gold wire to the chip.However, when using an adhesive tape coated with such a thermosetting adhesive, it takes more time to heat cure the adhesive. There was a problem of cost.

[0012]

Recently, an adhesive tape coated with a thermoplastic adhesive which does not involve a curing reaction has been proposed in order to solve the above-mentioned problems. When this adhesive tape is used, it is not necessary to cause a curing reaction, so that the process time can be greatly reduced. This also facilitates continuous processing, so that there is an advantage that variations in manufacturing conditions can be reduced. However, when this adhesive tape is used, a gap occurs when attaching the adhesive tape to the lead frame, and the adhesive tape can be adhered to a desired position with a desired accuracy, as compared with an adhesive tape using a thermosetting adhesive. It turned out to be difficult.

One of the causes is a problem of curling of the adhesive tape 3 using a thermoplastic adhesive. As shown in FIG. 6, curling refers to a phenomenon in which the width of the tape is curved so as to become a part of an arc. This is because a thermoplastic adhesive has a volatile component and a thermosetting adhesive as compared with a thermosetting adhesive. Since the solvent component is small, it has high rigidity itself, and is caused by a difference in a dry state, a change in a coating thickness, and the like after a coating sequence when the adhesive tape is coated on both surfaces. Therefore, when the rigid adhesive tape having such curl is punched and attached to a lead frame, a sufficient gap is formed between the adhesive tape and the suction hole provided at the tip of the punch for punching. It is considered that the suction force is not exerted and the position of the adhesive tape shifts, which results in insufficient accuracy of the attaching position. Attempts to solve the problem of the displacement due to the curl by using a vacuum device having a larger capacity not only increase equipment costs and operation costs, but also cause a new problem of increased noise, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in attaching a hard adhesive tape coated with a thermoplastic adhesive to a lead frame having a LOC structure. Without using a vacuum device of capacity, by increasing the effect of vacuum suction in the suction hole of the punch for punching, it is possible to prevent the piece of adhesive tape from shifting on the punch surface, thereby at least using a conventional thermosetting adhesive. It is an object of the present invention to provide a punch press die apparatus capable of attaching an adhesive tape to a lead frame having a LOC structure with the same attachment position accuracy as an adhesive tape used.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a punch press die apparatus for attaching an adhesive tape for bonding a semiconductor element to a lead frame having a LOC structure. The height of the passage of the adhesive tape gradually decreases from the entrance to the center.

[0016]

Next, details of the present invention and its operation will be described.

First, the movement of the punch for punching and the adhesive tape when the adhesive tape curled by using the conventional mold apparatus is panned will be described. In FIG. 2, the punch 1 for punching is lowered to guide the die. When the punch 1 is passed through the guide hole 11 ′, the punch 1 comes into contact with the adhesive tape 3 installed on the passage 12. When the punch is further lowered, the punch 1 presses the adhesive tape 3 against the die 2,
The curl of the adhesive tape 3 is reduced. This operation continues until the distance between the tip of the punch 1 and the surface of the die 2 becomes equal to the thickness of the adhesive tape. However, since the adhesive tape 3 in contact with the punch surface is on the through hole 2 ′ formed in the die 2, the lower surface is open, so that the adhesive tape 3 in this portion is not completely corrected for curl. Thus, a part of the curl is maintained as it is. Therefore, the punch 1 and the die 2 engage with each other in a state where the adhesive tape 3 does not completely close the vacuum suction hole 6 at the tip of the punch, and the adhesive tape piece 4 is punched. The vacuum suction of the punch 1 is activated before the punching is performed. However, since the adhesive tape 3 does not completely cover the suction hole 6 at the tip of the punch 1 as described above, the punched adhesive tape piece 4 is removed. It is not possible to reliably hold the tip of the punch 1 by suction.

Accordingly, when the punching punch 1 is further lowered after the punching, the adhesive tape piece 4 is moved together with the punch 1 through the through-hole 2 'using the through-hole 2' of the die 2 as a guide.
However, since the adhesive tape piece 4 is not completely sucked and held by the tip of the punch 1, the adhesive tape piece 4 moves freely at this moment.

The moving direction and the distance of the adhesive tape piece 4 are considered to be mainly related to the rigidity of the tape. However, it is difficult to predict the direction and the distance. Therefore, measures such as correction in advance are taken. It is impossible. In the present invention, the shape of the passage of the adhesive tape in the die apparatus for performing punching is modified to correct the curl of the adhesive tape 3 and flatten the tape so that punching can be performed. Since the punching is performed while the suction hole 6 provided at the tip of the punch 1 is completely closed by the adhesive tape piece, the die 2 is fixed and held at the tip of the punch 1 thereafter.
Of the LOC structure lead frame 5 installed under the through hole 2 ', and accurately reaches a predetermined position of the LOC structure lead frame 5, so that the adhesive tape piece 4 can be accurately attached to the lead frame 5. .

That is, in the present invention, as shown in FIG. 1, the height of the adhesive tape passage 12 formed in the guide mold 11 is gradually reduced from the entrance side to the center as a device for correcting the curl of the adhesive tape 3. Then, the height at the portion where the punching was performed was made substantially the same as the thickness of the adhesive tape 3. As a result, at least at the position where the punching is performed, the curl of the adhesive tape piece 4 is corrected, so that the punching can be performed while almost completely closing the suction hole of the punch 1.

In the present invention, the reason why the height of the entrance of the adhesive tape passage 12 is increased so that the height gradually decreases toward the center is that the thickness of the adhesive tape is usually 0.1 m.
If the height of the passage 12 is consistently equal to the thickness of the tape, it is difficult to accurately feed the tape to a predetermined position due to the frictional resistance between the passage ceiling wall formed in the die and the adhesive tape. Because.

[0022]

【Example】

Example The height of the passage of the adhesive tape in the guide mold was 2 mm at the tape entrance, and the height was gradually reduced toward the inside of the mold.
mm, and a height of 25 mm from the center to the tape outlet was formed in the same manner as the inlet from the center. The structure of the other parts of the mold apparatus was the same as the conventional one. Using this mold apparatus, an adhesive tape having a thickness of 0.1 mm, a width of 15 mm, and a curl height of about 1 mm coated with a thermoplastic adhesive containing a polyimide adhesive as a main component is inserted from the entrance of the adhesive tape passage. Then, after setting in a predetermined position, a punch for punching is operated while performing a suction operation by vacuum to perform punching, thereby punching a 5 mm × 6 mm square adhesive tape piece from the adhesive tape, and then punching the adhesive tape. The piece was passed through the through-hole of the die while being suction-held by the punch, and was pressure-bonded to a predetermined position of a LOC structure lead frame installed thereunder. This operation was repeated while moving the adhesive tape and the lead frame by a predetermined distance, and 20 pieces of the adhesive tape were attached to predetermined positions of the predetermined lead frame.

The measurement of the position of the adhesive tape on each lead frame was performed at the center of the lead frame. As a result, the center of the adhesive tape on each lead frame was within 0.1 mm from the predetermined position. The attachment position accuracy was within the accuracy. In addition, the rotational deviation of the adhesive tape was almost negligible within two degrees, and all of these lead frames were able to adhere the semiconductor element with the adhesive tape without any problem.

From the above results, according to the present invention, even when an adhesive tape with a curl coated with a thermoplastic adhesive is used, vacuum suction of a punch for punching when attaching to a LOC structure lead frame by punching. It can be seen that the operation is performed smoothly.

In this embodiment, the minimum height of the adhesive tape passage is set to 0.2 mm because the thickness of the adhesive tape normally used is 0.1 mm, but variations in the thickness at the time of manufacturing are taken into consideration. Then, this value was determined. The reason why the height of the inlet portion is set to 2 mm is that a product having a curl height exceeding 2 mm is not subject to punching as a defective product from the beginning, and if the height is less than this, the adhesive tape is not used. This is because it becomes difficult to smoothly move the passage and set it at a predetermined position. Comparative Example Twenty pieces of adhesive tape were adhered to a lead frame in the same manner as in Example except that a guide mold in which the adhesive tape passage was formed at a uniform height of 2.0 mm as before was used. . As a result, there were only four lead frames in which the center position of the attached adhesive tape piece was within the positional accuracy of 0.1 mm from the predetermined attachment position. For the rest, the deviation of the center position exceeds 0.1 mm and 1 mm
Less than 5 leadframes, 1mm deviation of center position
The above lead frame is 10 sheets, and the center position is 0.
Except for two lead frames within 1 mm, the position of the adhesive tape pieces was so large that it was impossible to use them for bonding semiconductor elements.

As can be seen from the results, when the conventional guide mold is used, the curling of the adhesive tape is not performed, so that the vacuum suction function does not completely function, and therefore the punched adhesive is not used. It can be seen that the tape piece is shifted from a predetermined position at the tip of the punch.

[0027]

As described above, according to the present invention,
When attaching a hard adhesive tape piece coated with a thermoplastic adhesive to the LOC structure lead frame, the height of the adhesive tape passage in the guide die of the punch press to be used is gradually reduced from the entrance of the die toward the center. By doing so, it is possible to correct the curl of the tape in this passage and punch the adhesive tape,
The effect is great because it can be attached with the same positional accuracy as a conventional adhesive tape piece coated with a thermosetting adhesive without expanding the procedure of the vacuum apparatus.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an adhesive tape passage of a guide mold according to the present invention.

FIG. 2 is a perspective view showing an adhesive tape passage of a guide mold according to a conventional method.

FIG. 3 is a schematic plan view of a LOC structure lead frame.

FIG. 4 is an explanatory diagram of a step of attaching an adhesive tape to a lead frame.

FIG. 5 is a schematic cross-sectional view showing a state where a chip is connected to a LOC structure lead frame.

FIG. 6 is a perspective view showing a curved state of an adhesive tape coated with a thermoplastic adhesive.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Punch for punching 2 Die 2 'Through hole 3 Adhesive tape 4 Adhesive tape piece 5 LOC structure lead frame 6 Suction hole 7 Lead 8 Gold wire 9 Semiconductor element (chip) 10 Electrode 11 Guide mold 11' Punch guide hole 12 Adhesive tape aisle

Claims (1)

(57) [Claims] In a punch press die apparatus for punching an adhesive tape for bonding a semiconductor element into a desired shape by punching the adhesive tape onto a lead frame having a LOC structure, a path of an adhesive tape provided in a guide die is provided. Characterized in that the height of the taper is gradually reduced from the entrance toward the center.