JPH0821654B2 - Lead frame manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a lead frame, and more particularly to shape processing of a tip portion of the lead frame.

(Prior Art) Connection methods between a lead frame and a semiconductor element (chip) are roughly classified into a wire bonding method using a wire and a wireless bonding method in which a semiconductor element is directly fixed to a conductor pattern surface without using a wire. .

Among them, in the wire bonding method, a chip is fixed to a die pad of a lead frame by thermocompression bonding or a conductive adhesive or the like, and a gold wire or the like is used for the bonding pad of this chip and the tip of the inner lead 1 of the lead frame. Since they are electrically connected to each other, the time required for bonding is long because they are connected one by one, and there is a problem in reliability.

There are various wireless bonding methods, one of which is a typical one. As shown in FIG. 7, a bump 11a formed on the tip of a thin pattern 11 extending to the tip of the inner lead 1 is used. There is a direct bonding method in which the chip 20 and the inner lead 1 are electrically connected by directly connecting the chip 20 to the bonding pad of the chip 20.

In the direct bonding described above, the tips of all the leads can be bonded at once to the chip instead of bonding one by one like wire bonding, so that the bonding time can be significantly shortened and the wire bonding can be achieved. The height of the wire loop, which is required in the method, becomes unnecessary, and the semiconductor device can be downsized.

However, in such direct bonding, the tips of all the leads are bonded to the chip at once, instead of bonding one by one as in wire bonding. While the temperature is 200 ° C, this direct bonding has a high temperature of 400 ° C to 600 ° C.

Since the inner lead is a rigid body, this heat causes the inner lead to expand, stress concentrates on the connection portion with the bonding pad, and there is a problem that mechanical damage or connection failure of the chip occurs.

Further, after bonding, a molding process of encapsulating the chip in a resin case has to be performed for chip protection, but the heat received in this molding process also causes mechanical damage or connection failure of the chip. .

Furthermore, with the miniaturization, thinning, and high integration of semiconductor devices, the lead width, lead spacing, and plate thickness of the lead frames used for these devices are becoming smaller, and this is an extremely advanced technology for designing and manufacturing. Are becoming required.

A direct bonding type lead frame used for mounting such a semiconductor device has a thin tip end after a band-shaped metallic material (strip material) such as iron or copper is formed into a desired pattern by stamping or etching. It is manufactured by forming bumps on the parts.

In particular, with regard to a lead frame formed by stamping, it is difficult to mold all of the inner leads in a single punching process, so the lead frame is designed to be divided into a plurality of stations for punching.

However, in recent lead frames, the lead pitch tends to be narrower than the plate thickness of the inner lead tip portion, and for example, it may be necessary to punch with a width of 0.1 to 0.12 mm for a plate thickness of 0.15 mm. is there.

If such a minute lead frame is divided into a plurality of stations by the stamping method and punched,
As shown in the figure, it has been observed that the inner leads on both sides are twisted and the cross section of the inner leads is distorted, which reduces the bonding area.

At the leading edge of the inner lead, coining is often used to secure an effective flat width.
Since the inner lead spacing is extremely narrow, if the coining amount is too deep, a short circuit with adjacent inner leads may occur.

Further, with respect to the formation of bumps, there were various problems due to misalignment and miniaturization.

(Problems to be Solved by the Invention) As described above, with the miniaturization of the lead frame, it is not possible to obtain an inner lead having a favorable tip cross-sectional shape, and it is not possible to secure a sufficient bonding area. Due to the misalignment and the like, bonding mistakes and the like frequently occur, which may cause deterioration in reliability.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lead frame that eliminates the positional deviation of the bumps at the tips of the inner leads, increases the effective width of the bumps, and is easy to manufacture and highly reliable. And

(Means for Solving the Problem) Therefore, in the lead frame manufacturing method of the present invention, in the molding step of molding the lead frame from the strip material, first, at least the tip thin portion of the inner lead is left from the strip material, and the outer Shape processing to form a lead frame including leads and tie bars, and press down or push up from the lead frame surface by stamping the portion corresponding to the thin part of the inner lead tip in the area including the vicinity of the inner lead tip left in this process. After dividing the portion corresponding to the area between the inner leads between the inner leads, the portion corresponding to the area between the inner leads is punched out, and a portion of the thin portion corresponding to the inner lead tip thinned portion is extended to the tip to simultaneously perform thinning and bump formation. .

That is, according to the present invention, a direct bonding type lead frame including a plurality of inner leads having a thin portion having a bump at the tip so as to surround the center and a plurality of outer leads continuous with each inner lead is manufactured. In the method, in a molding step of molding a lead frame from a strip material, a first molding step of punching other punching target areas, leaving at least punching target areas connecting the inner lead tip portions, and each inner lead tip portion. By pushing down or pushing up from the lead frame surface by using a stamping method.
Second molding step of semi-separating each inner lead tip from the surface of the punching target area left in the molding step to displace the surface level, and punching out the remaining punching target area, and each inner lead tip And a third molding step for simultaneously performing thinning and bump formation at the same time.

(Operation) The present invention has been made paying attention to that the cross-sectional shape of scrap s generated when punching with a width of 0.1 to 0.12 mm is extremely close to the ideal shape as shown in FIG. 2 (a). When molding near the tip of the inner leads, first, press down or push up the thin portion corresponding to the inner lead tip from the lead frame surface by stamping, and then cut off the portion corresponding to the area between the inner leads with the end left. The portion corresponding to the area between the inner leads separated from the portion is punched out, and a part of the portion corresponding to the thinned portion of the inner end of the inner lead is extended to the tip so that thinning and bump formation are performed at the same time.

That is, the inner lead-corresponding portion has a cross-sectional shape similar to that of the scrap s as shown in FIG. 2B by dividing the inner lead-corresponding portion by pushing down or pushing up. In this state, the remaining area between the inner leads is punched out, so that it is possible to obtain an inner lead having a good cross-sectional shape like scrap, and obtain a good inner lead tip thin portion without distortion. be able to. Also,
Since the bump is integrally formed with the thin tip portion, it is possible to obtain the bump with a sufficient width without displacement.

Furthermore, since there is no twist in the thin part of the inner lead tip, there is little internal residual stress, the inner lead tip position can be maintained correctly, bonding mistakes are reduced, and there is no short circuit accident. It becomes possible to obtain.

(Example) Hereinafter, a method for manufacturing a lead frame according to an example of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1 (a), a band-shaped material containing copper as a main component is used to mold a die (not shown) having a punching die such as an inner lead 1 a, an outer lead 2 and a tie bar 3 having a desired shape. ), And press working is performed, and patterning is performed while leaving the thinned end portion of the inner lead.

Then, as shown in FIGS. 1 (b) and 1 (c), the inner lead tip thin portion 1b corresponding to the inner lead tip thin portion 1b in the region including the inner lead tip thin portion left in the molding step is stamped by a stamping method. By using the lead frame to push down from the lead frame surface, the inner lead inter-area corresponding portion 4 is divided. The dotted line indicates that it is pushed down on the paper surface.

Thereafter, as shown in FIGS. 1D and 1E, the inner lead inter-area corresponding portion 4 separated from the inner lead corresponding portion in the molding step is punched out, and at the same time, the inner lead tip thin portion corresponds. Part of the part is extended to the tip, thinning and bump formation are performed at the same time, and the lead frame shape processing is completed. FIG. 1 (d) is a view showing a cross section of a main part in the mold D.

After that, the lead frame is completed through a plating process of the thin portion of the inner lead tip.

The cross-sectional shape of the thin-walled end portion 1b of the inner lead 1 of the lead frame thus formed has an extremely ideal cross-sectional shape, and bumps are formed at good positions.

Further, since the inner lead is not twisted, the residual stress inside is small, the tip position of the inner lead can be correctly maintained, and the displacement of the bonding position can be reduced.

In addition, since the strip material containing copper as the main component is used, the workability is good and the thermal conductivity is good.

The inner lead tip thinned portion 1b shown in FIGS. 1 (b) and 1 (c) is pushed down from the lead frame surface by using the stamping method, and the inner lead end portion 4 corresponds to the inner lead tip portion. Before or after the step of dividing the thin portion 1b, an annealing step of annealing for stress relief or a step of taping may be added.

Furthermore, although the inner lead corresponding portion is pushed down from the lead frame surface by using the stamping method in the above embodiment, it goes without saying that it may be pushed up.

Further, although copper is used as the lead frame material in the above embodiment, it is needless to say that other materials may be used without being limited to copper.

Further, in the above-described embodiment, the plating process is performed after the lead frame is shaped, but it may be performed during the shaping.

Furthermore, the molding area in each step can be changed appropriately.

〔The invention's effect〕

As described above, according to the lead frame manufacturing method of the present invention, when forming the shape of the lead frame from the strip material, when molding the vicinity of the inner lead tips, first, the inner lead equivalent portion is stamped. After pushing down or pushing up from the lead frame surface to separate from the area corresponding to the area between the inner leads, punch out the area corresponding to the area between the inner leads, and at the same time, extend a part of the area corresponding to the thin section of the inner lead to the tip to reduce the thickness. Since the bumps and bumps are formed at the same time, there is no twist in the thin part of the inner lead tip, so there is little internal residual stress, the inner lead tip position can be maintained correctly, bonding mistakes are reduced, and short-circuit accidents occur. It is possible to obtain a highly reliable lead frame without the occurrence of To become.

[Brief description of drawings]

1 (a) to 1 (e) are explanatory views showing a manufacturing process of a lead frame of an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are sectional shapes obtained by conventional punching. It is a figure which shows the cross-sectional shape of scrap. 1 …… Inner lead, 1a …… Part of inner lead,
1b …… Inner lead tip thin part, 1p …… Bump, 2…
… Outer leads, 3 …… tie bar, 4 …… corresponding area between inner leads.

Claims (1)

[Claims] 1. A method of manufacturing a lead frame of a direct bonding method, which comprises a plurality of inner leads each having a thin portion having a bump at its tip so as to surround the center, and a plurality of outer leads continuous to each inner lead. In the molding process of molding the lead frame from the strip, the first molding process of punching other punching target regions leaving at least the punching target region connecting the inner lead tip portions, and each inner lead tip portion, A second molding step in which the tip of each inner lead is semi-separated from the surface of the punching target region left in the first molding step by pushing down or pushing up from the lead frame surface using a stamping method to displace the surface level. And punching out the remaining punching target area, A method of manufacturing a lead frame, comprising: a third molding step in which the tip portion is stretched to reduce the thickness and simultaneously form bumps.