JPS6232623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in lead frames used in semiconductor devices, and in particular, in the manufacturing process of semiconductor devices, it is possible to facilitate the lead frame cutting process after the completion of a package and to improve the finish thereof. This relates to lead frames that can be manufactured.

Generally, in a semiconductor device using a lead frame, a tab for firmly supporting a semiconductor pellet is suspended and supported by a tab lead, and is integrally formed with a plurality of leads as a lead frame.
After attaching pellets, attaching wires, and sealing with resin or the like, the tab leads are cut to separate the package from the frame.

For example, as shown in Figure 1, a lead frame used in a flat package type semiconductor device,
A rectangular tab 2 is placed approximately in the center of the lead frame 1, while a plurality of leads 4 connected to each other by a dam 3 are placed around the tab 2, and the tab 2 has tab leads provided at its four corners. The dam 3 is suspended and supported by a frame 6 at 5, and the lead 4 supports both ends of the dam 3 on the frame 6. Then, a semiconductor pellet (not shown) is fixed to the tab 2, and wires are connected to the pellet and each lead 4.
The package cage 7 is formed by applying a resin mold as shown in the figure, and then the tab lead 5 is cut while cutting the dam 3, etc.
The package 7 is separated from the frame 6 by cutting. In the figure, 8 indicates the cutting point of the tab lead 5, where a half notch (FIG. 2) 9 is usually provided to facilitate cutting.

Incidentally, in the manufacture of this type of lead frame, a so-called etching method has conventionally been adopted in which a plate material such as Kovar is etched using a mask and an etching agent. This method has the advantage that fine parts can be formed relatively easily, but has the disadvantage that the etching process is complicated and the cost is high due to the use of an etching solution. For this reason, in recent years, a method of forming lead frames by press punching has been adopted in an effort to reduce costs. This press punching method has the advantage of being able to mold minute parts of the lead frame as well as the etching method, and at a lower cost, as press technology has improved in recent years.

However, with this press punching method, when forming a half notch (groove in the thickness direction) at the cutting location of the tab lead to facilitate cutting of the tab lead as described above, manufacturing control in the thickness direction is relatively difficult. The problem has arisen that it is difficult to form a deep half notch due to the difficulty in forming a deep half notch. In other words, normally a plate material with a thickness of about 0.15mm has approximately
A half notch with a depth of about 0.07 mm is desired, but in the press punching method, it is extremely difficult to control this level of gap between the die and the punch with high precision, so the half notch becomes too large and cannot be used as a tab lead. In order to prevent the half notch from being cut off, the half notch must be formed shallowly.

However, if the half notch is shallow, it is difficult to concentrate stress at the half notch even if the cutting punch collides with the cut point, and for this reason, the cutting force of the tab lead also affects the package, causing stress to act on the four corners of the package. . Therefore, especially in flat packages with a small mold thickness, the four corners of the package are prone to cracking, making it difficult to cut the package by adjusting the cutting force to prevent this, and making the appearance of the semiconductor device difficult. The reality is that there is a problem of significant damage.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to facilitate cutting with tab leads in a lead frame formed by press punching, to facilitate the cutting operation, and to prevent damage to the four corners of the package cage, thereby reducing the appearance. The purpose is to provide a lead frame that can prevent this.

In order to achieve this object, the lead frame of the present invention has a narrow tab lead width at the cutting point of the tab lead that suspends and supports the tab.
It is characterized by being able to cut with less cutting force.

Embodiments of the present invention will be described below based on the drawings.

FIG. 3 shows the lead frame of the present invention, and FIGS. 4 and 5 show an enlarged view and a sectional view of the main parts thereof. In the figure, 12 is a substantially rectangular tab disposed approximately in the center of the lead frame 11, and 14 is this tab 1.
The leads 14 are connected to each other by a dam 13 and a connecting piece 20, and are connected to a frame 16 forming the outer periphery of the lead frame 11 via the dam 13. ing. In addition, the tab 12 has its four corners connected to the tab leads 1.
The tab 12 is connected to the frame 16 at 5, and the tab 12 is suspended and supported by the tab lead 15. Needless to say, the tab 12, tab lead 15, lead 14, dam 13, connecting piece 20, and frame 16 are formed by press punching a metal plate such as Kovar or 42 alloy.

The tab lead 15 has a package 17 formed by resin molding in a later process.
As shown in FIG. 5, half notches 19 consisting of grooves formed in the thickness direction of the lead frame are formed at the cutting points 18 corresponding to the four corners of the tab lead, and cuts are made in the width direction of the tab lead as shown in FIG. Notch 2
1 and the lead width at the cutting point is made narrow. Of course, the half notch 19 and the notch 21 are formed at the same time when the lead frame is punched out. Further, the half notch 19 is inserted into the tab lead 15 during press punching.
It is necessary to take a certain safety factor into the depth of formation to avoid cutting the half notch 19, and for this reason, it is unavoidable that the depth of the half notch 19 is shallower than the desired depth. Furthermore, the cross-sectional shape of the half notch 19 is generally a V-groove shape. On the other hand, the planar shape of the notch 21 is not particularly limited; in addition to the rectangular shape formed on one side of the tab lead as in this embodiment, it may be V-shaped or may be formed on both sides of the tab lead. good. In any case, the half notch 19 and the notch 21 work together to reduce the cross-sectional area of the tab lead cutting location 18, thereby forming a weak location.

In the lead frame 11 having the above configuration, the tab 1
After a semiconductor pellet (not shown) is fixed to the semiconductor pellet 2, the pellet and each lead 14 are connected with a wire, and then a resin mold is applied to the area indicated by the broken line A to form the package 17. Then, first, the dam 13 and the connecting piece 20 (which may include the tip end portion of the lead 14) are cut, and finally, the tab lead 15 is cut at the cutting point 18, and the package cage 17 is separated from the frame 16. .

At this time, when cutting the tab lead, shearing is performed using a punch, but the cutting location 18 has a structure that is relatively weak against shearing force due to the cooperation of the half notch 19 and the notch 21. Even if the shearing force is not so large, the cut portion will be easily cut. In other words,
Cutting can be performed with the same or lower force than when the half notch is formed deeply. Therefore, in cutting work, there is no need to make various adjustments to the cutting force, making the work easier, and also preventing damage to the package by preventing the influence of the cutting force on the package.
This makes it possible to improve the appearance.

Note that the present invention can be similarly applied to, for example, a dual-inline type lead frame.
This is effective for a flat package type with a particularly large number of leads as in the above embodiment.

As described above, in the lead frame of the present invention, the lead width at the cutting point of the tab lead, which suspends the tab of the lead frame formed by press punching, is narrow, so that the lead width required for cutting the tab lead is narrow. The force can be reduced, which makes cutting work easier, prevents damage to the package, and improves the appearance.

[Brief explanation of the drawing]

Figure 1 is a plan view of a conventional lead frame, Figure 2 is a plan view of a conventional lead frame.
The figure is an enlarged sectional view taken along the - line in Fig. 1, Fig. 3 is a plan view of the lead frame of the present invention, Fig. 4 is an enlarged view of the cut point, and Fig. 5 is a sectional view taken along the - line in Fig. 4. be. 11... Lead frame, 12... Tab, 13... Dam, 14... Lead, 15... Tab lead, 16... Frame, 17... Package cage, 18... Cutting location, 1
9... Half notch, 20... Connecting piece, 21... Notch.

Claims (1)

[Claims] 1. A tab is integrally formed with a plurality of leads,
A lead frame in which the tab is suspended and supported by a tab lead on a frame, characterized in that the lead width of the cutting portion of the tab lead is narrowed after the package is completed. 2. The lead frame according to claim 1, wherein the tab lead is cut at a notch on at least one side. 3. The lead frame according to claim 1 or 2, wherein a half notch is formed at the cutting location of the tab lead.