JPH06161093A - Photomask for production of lead frame - Google Patents

Abstract

PURPOSE:To diminish the mis-registration of the front and rear patterns of a lead frame. CONSTITUTION:The photomask for forming regist patterns for etching of the lead frame is provided with alignment marks 5 on the top and bottom of the photomask and is provided with at least one piece of alignment marks 6 for fine adjustment on frame body patterns 3 of the lead frame as well, by which the photomask for production of the lead frame decreasing the mis-registration of the front and rear photomasks is constituted. As a result, the lead frame free from twisting of leads for connection of external circuits is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame used for connecting a semiconductor device or the like to an external circuit.

[0002]

2. Description of the Related Art A lead frame is a member used to connect an integrated circuit body, which has various circuits provided inside a semiconductor device such as an IC or LSI, to an external electric circuit. With the increase in the degree of integration, the intervals between the leads forming the lead frame have become smaller, and the lead frame is required to have extremely high accuracy.

FIG. 3 is a sectional view of a manufacturing process for manufacturing a lead frame by etching both sides of a base material. As shown in FIG. 3 (A), the resist 12 is formed on both sides of the metal thin plate 11. 3B, the front and back resists are aligned with the front and back photomasks 13 and 14 so that the front and back patterns are not misaligned, as shown in FIG. 3B. After contact exposure, the resist pattern 15 was developed to form a resist pattern 15 as shown in FIG. Next, as shown in FIG. 3D, the thin metal plate was etched from both sides using the formed resist pattern, and finally the resist was removed as shown in FIG. 3E.

Photomask 21 for manufacturing a lead frame
As shown in FIG. 4, the photomask for the front surface pattern and the photomask for the back surface pattern form a large number of lead frame assembly patterns 23 in which the lead frame patterns 21 are joined by the frame body patterns 22.
After the front and back are aligned by the alignment marks 24 provided at the positions, contact exposure is performed from both sides, development and etching are performed, and a lead frame is manufactured.

However, FIG. 5 is a plan view (A) of the lead frame 31 manufactured by such a method and an enlarged view of a cross section taken along line BB (B), but more or less the leads. It was unavoidable that the lead cross section of the frame was not an accurate square. The external circuit connecting lead 42 having an accurate non-rectangular cross section is formed by attaching the integrated circuit body, encapsulating the same with a synthetic resin, and then bending the same, as shown in FIG.
As shown in (3), a twist phenomenon called skew was likely to occur. A side view is shown in FIG.
(B) shows a cross-sectional view of a lead in which skew has occurred.
The external circuit connection lead of the semiconductor device in which the skew has occurred has a problem that it cannot be attached to the printed circuit board when it is attached to the printed circuit board because it does not match the circuit portion formed on the printed circuit board. In particular, as semiconductor devices have become highly integrated, the distance between leads for connecting external circuits has become smaller, and the occurrence of skew has been a serious problem.

[0006]

SUMMARY OF THE INVENTION The present invention eliminates the displacement of the front and back sides of the lead frame manufactured by etching the base material as described above, and causes twisting due to an external force applied when the lead for external circuit connection is bent. The present invention is intended to reduce the problem that it cannot be mounted on an electric circuit board and improve the yield rate of semiconductor devices.

[0007]

SUMMARY OF THE INVENTION The present invention has been made as a result of various studies on means for preventing twisting of leads for external circuit connection after encapsulation of a semiconductor device in a lead frame by etching. We found that the closer the cross-sectional shape of the connecting lead was to a square, the more the twisting during bending was significantly reduced.When forming the resist pattern for etching, align the alignment marks on the front and back photomasks with the frame portion of the lead frame. By providing at least one resist pattern on the lead frame, it becomes possible to more accurately align the front and back sides of the resist pattern of the lead frame during plate making exposure, and the cross-sectional shape of the lead for external circuit connection becomes closer to a square shape for stable bending. This can be realized and the twist of the outer lead is significantly reduced.

[0008]

According to the present invention, the alignment marks provided on the photomask pattern for manufacturing the lead frame are provided above and below the photomask, and at least one alignment mark is provided on the frame portion of each lead frame. After aligning the photomask with the alignment marks provided on the top and bottom of the mask, the alignment marks provided on the frame bodies of the individual lead frames make it possible to perform precise alignment. A small number of lead frames can be manufactured, lead twisting is significantly reduced during bending of the external circuit connecting leads, and mounting on a printed circuit board is not impossible.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1A is a plan view of a photomask pattern for manufacturing a lead frame, which is an embodiment of the present invention.
FIG. 6B is an enlarged view of the alignment marks for fine adjustment of registration on the front and back sides. On the photomask 1, a leadframe pattern 2 is drawn together with a frame pattern 3 and a leadframe assembly pattern 4 is drawn. An alignment mark 5 is drawn above and below the photomask, and each leadframe assembly pattern is finely adjusted. Alignment marks 6 are formed.

FIG. 1 shows an example of an alignment mark for fine adjustment.
As shown in (B), precise alignment adjustment can be performed by matching the front surface pattern 7 and the back surface pattern 8. The fine adjustment alignment mark is not limited to the one shown in FIG. 1B, but various types can be used.

An example of a lead frame manufactured by the photomask of the present invention is shown in FIG. In the plan view of the lead frame of FIG. 2A, as shown in FIG. 2B, which is an enlarged cross-sectional view taken along the line AA, the cross-sectional shape of the external circuit connecting lead 9 is close to a square. You can get one.

Example 42 42 having a thickness of 0.15 mm, a length of 300 mm, and a width of 300 mm
The alloy is used as the base material, the base material is degreased with an alkaline degreasing agent, washed with water, and dried to obtain a positive photoresist (OFPR-8).
00, manufactured by Tokyo Ohka Kogyo Co., Ltd. by the dip method
It was applied in a thickness of 6 μm.

A resist pattern was formed on the resist by using a photomask having a quad-type lead frame pattern. The pitch of the leads for external circuit connection of the pattern is 0.65 mm, and the lead width is 300 μm.
It had 160 pins.

With the base material on which the resist pattern is drawn fixed, a ferric chloride solution is sprayed on both sides to perform etching on both sides at the same time. After the etching is completed, the resist film is peeled off with acetone and dried on the lead frame. Was manufactured. A semiconductor integrated circuit was sealed with the obtained lead frame to manufacture a semiconductor device, and the leads for external circuit connection were bent, but a semiconductor device without defects due to twisting could be manufactured.

Further, the following results were obtained by comparing the photomask for manufacturing the lead frame of the present invention with the case where a photomask having no front and back registration alignment marks was used.

[0016]

[Table 1]

[0017]

According to the photomask for manufacturing a lead frame of the present invention, it becomes easy to make the cross-sectional shape of the lead for external circuit connection of the lead frame close to a square, and the defect rate due to misregistration is significantly reduced. The problem that the semiconductor device cannot be attached to the electronic circuit board due to the twisting of the external circuit connecting lead is eliminated.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a photomask for manufacturing a lead frame of the present invention.

FIG. 2 is a diagram illustrating a lead frame obtained by the photomask for manufacturing a lead frame of the present invention.

FIG. 3 is a diagram illustrating a manufacturing process of a lead frame.

FIG. 4 is a view showing a conventional photomask for manufacturing a lead frame.

FIG. 5 is a diagram illustrating a lead frame obtained by a conventional photomask for manufacturing a lead frame.

FIG. 6 is a diagram illustrating a lead frame in which a skew phenomenon has occurred.

[Explanation of symbols]

1 ... Photo mask, 2 ... Lead frame pattern, 3 ...
Frame pattern, 4 ... Lead frame assembly pattern, 5
... Alignment mark, 6 ... Fine adjustment alignment mark, 7 ... Front surface pattern, 8 ... Back surface pattern, 9 ... External circuit connection lead, 11 ... Metal thin plate, 12 ... Resist, 1
3 ... Photomask for front surface, 14 ... Photomask for back surface,
15 ... Resist pattern, 21 ... Photomask, 21 ...
Lead frame pattern, 22 ... Frame pattern, 23 ...
Lead frame assembly, 24 ... Alignment mark, 3
1 ... Lead frame, 32 ... Lead for external circuit connection

Claims (1)

[Claims] 1. A photomask for manufacturing a lead frame for forming a resist pattern for etching from both sides of a substrate, wherein at least one alignment mark for front and back registration is formed in a frame portion of the lead frame pattern. Characteristic photomask for lead frame manufacturing.