JPS6381967A - Lead frame preventive of falling of lead - Google Patents

Abstract

PURPOSE:To prevent the falling of an outer lead, and to form the outer lead resulting in no difficulty for mounting by setting the width of an upper surface and the width of a lower surface so that these width differs without setting them at an equal value as seen in conventional devices in the cross section of the outer lead on photoetching. CONSTITUTION:A lead frame material 2 is masked in a manner that the width of a lower-surface photo-mask 4 is made wider than an upper-surface photo- mask 3 in the lead frame material 2 on patterning through photoetching. Consequently, an outer lead 1 with a trapezoidal cross section is obtained. Bending moment at the time of cutting molding is halved to the case by conventional lead frames with parallelogram outer lead sections, thus preventing the falling of the lead 1. Even when the photo-mask 3 as an upper surface is 'displaced' to the left side on photoetching, the outer lead 1 with a cross section close to a trapezoid is acquired, and bending moment at the time of the cutting molding of the outer lead 1 is made smaller than conventional lead frames with the parallelogram cross sections, thus reducing the falling of the lead.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame that prevents leads from collapsing.

[Conventional technology]

Lead frames are used when packaging semiconductor devices. Lead frames are generally made by photo-etching or pressing a conductive material such as metal foil into a predetermined shape and patterning it into a so-called ribbon-like shape, which consists of wire bonding parts, external leads, connecting parts, etc. It is composed of This lead frame K is equipped with a berent mount (ceramic paste), sealed after belet bonding and wire bonding, and a semiconductor whose outer leads are drawn out through a lead cutting and separation process in which the connected parts of the leads are separated. A device is obtained. Conventionally, when outer leads are patterned by stacking photomasks on the upper and lower surfaces of the lead frame material, exposing them to light, and photoetching, the outer leads are patterned so that the width of the upper surface and the width of the lower surface in the cross section are equal. This is common.

Examples of documents and patents describing lead frames include "Oko Materials" August 1982 issue, pages 69-74, August 1984 issue, pages 6ε-73, and Japanese Patent Application Laid-Open No. 112273/1984, published by Kogyo Research Association. I can give you things like public notices.

[Problem that is intended to be solved by ``f''] However, when performing photoetching with the widths of the upper and lower surfaces in such a cross section set to be equal, if no misalignment occurs between the photomasks on the upper and lower surfaces. However, if the photomasks on the upper and lower surfaces are misaligned, the outer leads pulled out to the outside of the semiconductor device by subsequent lead cutting and separation will fall diagonally (lead collapse), and the semiconductor device This makes it difficult to mount the device on a mounting board such as a printed circuit board.

Such lead collapse becomes more noticeable as the leads become finer.

An object of the present invention is to provide a lead frame that prevents such lead collapse, and to provide a semiconductor device having external leads that do not cause difficulties in mounting.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Failure to solve the problem]

A brief explanation of two representative inventions among the inventions disclosed in this application is as follows.

In the sixth step, the width of the upper surface and the width of the lower surface of the cross section of the outer lead during photoetching are not set equal as in the conventional method, but are set to be different, and photoetching is performed.

[Effect]

As a result, compared to the conventional parallelogram when the upper and lower photomasks are misaligned during photoetching when set as described above, the present invention becomes a trapezoid or a shape close to this, and the lead When cutting and separating, if the shape is a trapezoid or close to it, compared to a parallelogram, the bending moment (moment in the lateral direction) generated during cutting and forming is reduced, and lead collapse can be prevented.

〔Example〕

Next, the present invention will be explained based on embodiments shown in the drawings.

vJd As shown in Figures A to 4C, in order to obtain a cross section of the outer lead (1) in which the width X of the upper surface and the width Y of the lower surface are equal, these widths X,
Y is set, and accordingly, as shown in Figure 4A, an upper photomask (3) and a lower photomask (4) are stacked on the upper and lower surfaces of the lead frame material (2), respectively, and exposed to light to perform photoetching. In this case, there is a deviation of 1 between the upper photomask (3) and the lower photomask (4).
If there is no outer lead (1), the outer lead (1) has a rectangular cross section as shown in Figure @4B.
1) There is almost no lead collapse in the outer leads (1) of a semiconductor device (6) using a lead frame (5) having a cross section (FIG. 4C).

However, as shown in FIG. 5A, in the above, there is a gap between the upper photomask (3) and the lower photomask (4).
If "misalignment" occurs (generally misalignment is likely to occur), an outer lead (1) having a parallelogram cross-sectional shape as shown in FIG. 5B is obtained; When cutting and separating the leads after loading the pellet using a lead frame, the lateral bending moment becomes large, and as shown in Figure 5C, the outer lead (1)
The lead falls down diagonally, causing the semiconductor device (
6) makes surface mounting on a printed circuit board (not shown) difficult.

Therefore, in the present invention, as shown in FIGS. 1A to 3B, the width X of the upper surface and the width Y of the lower surface in the cross section of the outer lead (1) are set to be different, and photoetching is performed. I will give an example.

To explain the embodiment shown in Figure ilA to Figure 1B,
As shown in Figure 1B, the photo-etching is set to obtain an outer lead (11) in which the bottom width Y is larger than the top width X, so the percentage is as shown in Figure 1A. When patterning by photoetching, the top photomask (3) of the lead frame material (2) is
) The lower photomask (4) is wider than the lead frame material (2) (to mask the lead frame material (2). As shown in FIG. 1) can be obtained.

76, the cross section refers to a cross section cut along the line II shown in FIG. 4C.

A linide cutting and separation process is performed when a semiconductor device is constructed using a lead frame having such a trapezoidal outer lead, and when using a conventional lead frame having a parallelogram outer lead cross section as shown in FIG. 5B. Compared to this, the bending moment during cutting and forming becomes, for example, 1/2, thereby preventing the lead from collapsing as shown in FIG. 5C.

℃, during photoetching as shown in Figure 1A (,
For example, as shown in Figure 2A, at 5, the upper photomask (3
) is shifted to the left side, as shown in Figure 2B, an outer lead (1) with a cross section close to a trapezoid is obtained, which is also compared to the conventional parallelogram cross section. As a result, the bending moment during cutting and forming is reduced, and lead collapse is reduced. Based on the same principle, Figures 3A to 3
As shown in Figure B, the shape may be similar to a trapezoid, with the width of the upper surface being larger and the width of the lower surface being larger.

FIG. 6 shows an example of a semiconductor device in which the lead frame of the present invention can be suitably used, and the device (6) is constructed as a flat package with outer leads (1) drawn out in four directions.

FIG. 7 schematically shows a plan view of the lead frame (5) in the flat package (6).

In FIG. 6, (1) is a ceramic substrate, (8) is a heat sink, and (9) is a cap. Although not shown, a semiconductor element is housed in the cap (9).

Although the invention made by the present inventor has been specifically explained based on examples, the present invention is not limited to the above-mentioned examples, and various modifications can be made without departing from the gist thereof. Needless to say, 1. The lead frame of the present invention can be applied to semiconductor devices other than flat packages.

It is also applied to lead frames that are patterned by press working.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this section (a) is as follows.

According to the present invention, it was possible to provide a lead frame in which lead collapse was prevented, and it was possible to obtain a semiconductor device having outer leads that did not cause difficulties in mounting.

[Brief explanation of the drawing]

The FIA diagram and Figure 1B are a cross-sectional view of the main part showing an embodiment of the present invention, @two-person diagram, and ! 2B is a cross-sectional view of a main part showing other embodiments of the present invention, FIGS. 3A and 3B are cross-sectional views of main parts showing still other embodiments of the present invention, and FIGS. 4A to 4B are FIG. 4C is an explanatory diagram of a semiconductor device without lead collapse. FIGS. 5A and 5B are sectional views of essential parts each showing a conventional example. @5C is an explanatory diagram of a semiconductor device with lead collapse. FIG. 6 is an explanatory diagram of a semiconductor device according to an embodiment of the present invention; FIG. 6 is a full red outline diagram of a semiconductor device showing an embodiment of the present invention; FIG. 7 is a perspective view showing an embodiment of the present invention. 1... Outer lead, 2... Lead frame material,
3... Top photomask, 4... Bottom photomask, 5... Lead frame, 6... Semiconductor device, 7...
...Ceramic base, 8...Heat sink, 9...
・Steel stud, 10...ceramic cap. Figure 413 Figure 45 Figure 6

Claims (1)

[Claims] 1. A lead frame that prevents leads from collapsing, characterized in that the width of the upper surface and the width of the lower surface of the outer leads are different in the cross section of the outer leads before the leads are cut and separated. 2. The lead frame according to claim 1, wherein the lead frame is a flat package lead frame patterned by photo-etching.