JPS6347272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead frame, and particularly to a lead frame for a semiconductor integrated circuit device (hereinafter referred to as an IC).

To make an IC, for example, in the case of a resin-sealed IC, a lead frame is used that has a tab (element fixing part) and multiple leads formed on a thin metal plate by etching or press processing, and after fixing the IC element to the tab. It is assembled by connecting the tip of the inner lead and the electrode of the IC element with a thin metal wire, and sealing the IC element and the inner lead portion with resin.

Connections using thin metal wires are usually made using an automatic bonder, but an important requirement for the lead frame here is that the portion of each inner lead tip to be bonded be in a predetermined position. This is because if the inner lead is deformed,
This is because if the tip position deviates from the predetermined position, the automatic bonder will not be able to connect the thin metal wire to the inner lead, resulting in a fatal defect in the IC.

In general, in conventional lead frames, each inner lead 2 has a shape in which each inner lead 2 is elongated from the resin-fixing dam bar 3 toward the tab 1, as shown in the plan view of FIG. easy. This deformation is caused by internal stress in the lead frame material appearing as deformation due to punching, or by handling operations during the subsequent plating or assembly process.

In recent years, with the expansion of IC functionality, there has been a demand for an increase in the number of leads, higher density, and miniaturization, and each inner lead is becoming longer and thinner, making it easier to shape. However, in the lead frame manufacturing method using press punching or etching, the minimum distance between inner leads is limited to the thickness of the lead frame.

Therefore, in order to compensate for this defect even slightly, in conventional lead frames, after forming the leads by press punching or etching, as shown in the perspective view of Figure 2, the tips of the inner leads are formed using the same or another mold. Crushed processing (coining) is applied,
The area that could be bonded with thin metal wire was made as large as possible. That is, the gap between the inner leads is narrowed to the limit by press punching or etching, and coining is further performed to widen the tip width of the inner leads. In this case, the depth of coining is uniform for all the inner leads, and therefore the expansion of the lead width due to coining is proportional to the coined area of the inner leads. However, since thin metal wires are connected using an automatic bonder, it is often not possible to design all the lead shapes and lead widths to be the same, depending on the arrangement of each electrode of the IC element. In this case, if coining is done to ensure a sufficient bonding area for the narrow inner lead, the bonding area for the wide inner lead will become too wide.
As the gap between the leads becomes narrower, a slight deformation of the leads causes various defects such as shorting of the leads, shorting of the leads and adjacent thin metal wires, and deterioration of the electrical characteristics between the leads.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lead frame that allows fine metal wire connections to be made more reliably using an automatic bonder and eliminates the aforementioned defects.

Examples according to the present invention will be described below. FIG. 3 shows a plan view of an embodiment of the present invention, in which the chain line shows the shape of the inner lead before the coining process, and the solid line shows the shape of the inner lead after the coining process.
That is, the lead frame of the present invention consists of a tab 1 for fixing an IC element, and inner leads 2a and 2b arranged around the tab 1 and having different coining depths at their tips. Here, 2a is an inner lead with a deep coining depth, and 2b is an inner lead with a shallow coining depth.Since 2a has a deeper coining depth, the amount crushed by coining is larger. For example, when manufacturing a lead frame using a progressive press die, the coining of the tips of the inner leads is usually carried out after forming the inner leads, but as shown in FIG. 3, first only the tips of the inner leads 2a are coined. The amount of coining is determined so that the lead spacing α is minimized by taking into consideration the deformation of the lead and the electrical characteristics between the leads, and processing is performed using a coining die A. Then, the tip of the inner lead 2b is similarly set so that the lead spacing β is If the coining die B is used to minimize the depth of coining, then the coining dies A and B, which have different heights, can be used to independently create an arbitrary coining depth. In addition, as shown in the perspective view of FIG.
If the portion 4b and the portion 4b to be coined are divided into two sides and made into a stepped shape, it is possible to obtain any coining depth for any tip of the inner lead in one press step.

According to the present invention, it is possible to select the optimum coining depth that matches the width of the inner lead tips, so the maximum area within which the inner lead tips do not touch each other can be obtained, making wire bonding with an automatic bonder extremely easy. This has the advantage of making it more reliable.

Incidentally, although the above-mentioned embodiment has been described in the case where the lead frame is manufactured using a progressive press mold, it goes without saying that the coining process may be carried out as described above also for lead frames manufactured by etching.

[Brief explanation of drawings]

Figure 1 is a plan view showing a conventional lead frame.
Fig. 2 is a perspective view of the tip of the inner lead of a conventional lead frame that has been subjected to coining processing, and Fig. 3 is a plan view of the central part of the lead frame according to the embodiment of the present invention. Inner lead shape, the solid line shows the inner lead shape after coining processing. FIG. 4 is a perspective view showing an example of a coining die used to carry out the present invention. 1...Tab, 2...Inner lead, 2a...Inner lead with deep coining depth, 2b...Inner lead with shallow coining depth, 3...Dam bar, 4
a...Part for coining 2a, 4b...Part for coining 2b.

Claims (1)

[Claims] 1. A lead frame in which bonding portions of a plurality of inner leads are coined, characterized in that the amount of coining is two or more types depending on the area of the coined portion of the bonding portion.