JPH0453158A - Lead frame - Google Patents

Abstract

PURPOSE:To improve balance of a frame shape and unify length of material fibers so as to lessen deformation by forming dead holes at fixed intervals between punched holes. CONSTITUTION:Long holes 6 for guide pins for carrier, of which 7 are formed for every frame, and round holes 5 for positioning at the time of performing die bonding are punched. An interval between punches holes 5, 6 of a frame 1 of the upper end part is 10mm at an equal interval. One punched hole 5 is formed in the frame 1 of the lower end part while being distant from a punched hole 5 lying in the neighboring lead part 122 by 28mm. A dead hole 11 is formed about in the middle between holes 5. Accordingly, the interval becomes 14mm thus to shorten fibers so that a curve of the lower short part of the frame 10 after final treatment becoms about 0.6mm thus causing no impediment in an assembly process such as a bonding error. Further, also a difference in a vertical curve is only about 0.1mm thus causing no hindrance in an assembly process. However, some vertical symmetry is necessary so that the hole 11 is to be made a long hole as in the case of the hole 6.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a lead frame for a semiconductor device, and particularly to a lead frame structure that is optimal for a resin-sealed semiconductor device with a large number of leads. It is.

(Prior Art) A lead frame for a semiconductor device is formed by etching or punching. Etching lead frame molding involves first cleaning sheet material, coil material, etc., applying a resist, drying it, baking and developing the lead frame pattern, and then etching it. After removing the resist, cutting, and offset inspection, spot Au is placed on the strip automatic plating line.

Finish by plating with Ag, etc. On the other hand, in the punching method, the sheet material, coil material, etc. described above is set in a press die and punched out according to a lead frame pattern to form a lead frame.

FIG. 3(a) is a partial plan view of the lead frame 10 formed by such a punching method. Lead frame 1
0 is made of a long material made of Fe-42Ni alloy or Cu. A frame 1 is formed at both ends of the elongated body, and round guide pin holes 5 and oval guide pin holes 6 are repeatedly and periodically formed at the upper end thereof. A round guide pin hole 5 is formed in the frame frame 1 at the lower end. The round guide pin hole 5 is a positioning hole for accurately determining the positions of semiconductor elements and lead frames when resin-sealing them, and the oval guide pin hole 6 is a positioning hole for accurately determining the positions of semiconductor elements and lead frames when they are sealed with resin. This is a hole into which a feed pin is inserted for transporting the lead frame from the loader magazine to the unloader magazine in one step, and at least one hole is formed in each lead city bank.

The lead portion 121 is repeatedly formed between the frame frame 1 at both ends of the outer lead 2. Inner lead 4. Tie bar formed between the outer lead and the inner lead 8. Power is distributed to the center of the inner lead, and it includes an island 3 and the like on which a semiconductor element is placed. The lead part is separated from the adjacent lead part 122 by a slit 9 formed for punching balance. Square holes 7 are provided near the round and square guide pin holes at both ends of the upper frame 1 and the guide pin holes on the lower frame.

The square hole 7 is a positioning hole provided to position the bonding tool at the correct bonding position when bonding the semiconductor element and the inner lead with the bonding wire, and the position of the tool is corrected by observing this hole. becomes possible. The lead part 12 is
One each is arranged between the slits.

By the way, the elongated body that is the raw material for lead frames is usually formed by hot and cold rolling, and not only do the crystal grains stretch in the rolling direction (for example, the long axis direction), but the crystal grains also change in the crystal direction. It has a so-called fibrous structure that is aligned in this direction. When a lead frame material with such a structure is punched and formed using a press die, internal stress is generated.
If this is not uniform, distortion such as warping or bending will occur in the lead frame, so it is difficult to incorporate semiconductor elements into it.

When wire bonding is performed, problems arise such as the element moving or the bonding position not being accurately determined.

One of the causes of this non-uniform internal stress is that the punched shape is asymmetrical.

Asymmetry causes variations in heat conduction.

Further, when slits, holes, etc. are formed by punching, the fibers in the vicinity of the slits or holes are divided, and as a result, the lead frame is in a non-uniform state in which the length of the fibers varies depending on the location. When a lead frame is resin-sealed together with a semiconductor element, the lead frame is heated to approximately 180°C.

Since the expansion/contraction ratio of a material due to heat differs depending on the fiber length of the material, it is inevitable that distortion will occur in a lead frame that is punched out unevenly due to thermal stress.

When considering the occurrence of this distortion in a conventional example, it is found that the distance between the punched holes 5 and 6 such as guide pin holes in the frame frame 1 at the upper end of the lead frame 10 in FIG. 3(a) is 10 ■It is. On the other hand, the interval between the punched holes 5 in the frame frame 1 at the lower end is 28 m.

When an element is mounted on this lead frame and sealed with resin through wire bonding, the lead frame will warp due to the heat of the resin, but the warp of the frame frame at the upper end is approximately 0.5 mm. (Fig. 3(b)), the warp of the frame frame at the lower end was approximately 1 square inch. It can be seen that as long as the punching process is involved, the occurrence of warpage is unavoidable, and the narrower the distance between the punched holes, the smaller the warpage, and the larger the distance, the larger the warp.

This is thought to be due to the length of the fibers in the material. FIG. 4 shows the relationship between warpage and punch hole spacing. When the punched hole interval (X) is taken as the horizontal axis and the corresponding warpage size (y) is taken as the vertical axis, both change almost linearly. As can be seen from this figure, there is a large warpage of the frame frame at the bottom end, but as mentioned above, this is proportional to the interval (pitch) of the punched holes, and when the resin contracts after resin sealing. It is thought that the longer this pitch is, the stronger the tension is on the resin and the larger the warpage.

(Problems to be Solved by the Invention) As described above, guide pin holes and the like are not uniformly formed in lead frames used in semiconductor devices, but are often arranged irregularly. There is a problem in that the punching balance is not good, and as a result, the length of the fibers of the material becomes non-uniform, resulting in increased thermal stress and increased distortion.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a lead frame for a semiconductor device in which the extraction balance is uniform and the fiber length of the material is made uniform.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a frame having punched holes such as guide pin holes formed at both upper and lower ends at appropriate intervals, and a lead portion repeatedly formed between the upper and lower frame frames. This relates to a lead frame of a semiconductor device, and the hole spacing (pitch) including the punched holes can be narrowed by forming sacrificial holes at appropriate intervals between the punched holes, and at the same time, the arrangement of the punched holes and the sacrificial holes can be reduced. It is characterized by making it uniform. To make the arrangement of punched holes and waste holes uniform, it is to make the arrangement of the waste holes formed in the upper and lower ends of the frame symmetrical with respect to the long axis, but it does not have to be completely symmetrical. Although some deviation is allowed, the spacing between the punched holes, etc. in each frame must be approximately uniform.

(Function) By forming the waste holes, the balance of the frame shape can be improved, and the fiber length of the material can also be made more uniform than in conventional lead frames. There is no particular difference in function and effect depending on the shape of the hole, and it may be round, square, oblong, etc., but the square shape has the disadvantage of easily damaging the press die blade. Furthermore, in order to improve the symmetry between the upper and lower frames, it is advantageous for the shapes of the opposing holes to be the same.

(Example 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a partial plan view of a lead frame in which the lead portion of Example 1 of the present invention is shown in four areas (4 frames), and FIG. 1(b) is a partial plan view of a portion A of the same figure. The enlarged plan view, FIG. 1(c), is a sectional view of the lower part of FIG. 1(a). A long body of the lead frame 10 is formed by punching a cold-rolled material, such as Cu, using a press die. The figure shows the lead parts for four frames, but in reality they are just a part of the elongated body, and the lead parts 12□, 12. has an island 3 surrounded by inner leads 4. Further, an outer lead 2 is formed on the outside thereof via a tie bar 8.

A slit 9 is formed between each lead portion. This is to ensure punching balance after punching and at the same time to ensure ease of cutting into each lead metropolitan bank. Each frame is separated by a slit 9. Seven punched holes used in this embodiment are formed for each frame, excluding the waste hole 11, which is the gist of the present invention. That is, a long hole 6 as a guide pin hole for conveyance, a round hole 5 as a positioning hole for die bonding, a square hole 7 for determining the bonding position during wire bonding, etc. are formed at the upper and lower ends. ing. The punched holes 5 and 6 of the frame frame 1 at the upper end are spaced equally apart by 1o. One punched hole 5 is formed in the frame frame 1 at the lower end, and the adjacent lead part 122
The distance of 28 mm between certain punched holes 5 is equal to the hole spacing of the conventional frame 1 at the lower end. In this embodiment, a waste hole 11 is formed approximately in the center of the punched hole 5 adjacent to the frame frame 1 at the lower end. As a result, the hole spacing becomes 14 m from the conventional 281 m, the fibers become shorter, and the warpage of the lower short portion of the lead frame 10 after final processing is approximately 0.6 am (see Figure 1(c)). ).

This degree of warpage will not cause problems in the assembly process such as bonding errors. Additionally, the difference in warpage between the top and bottom is only about 0.1 inch, so it does not interfere with the assembly process. However, a certain degree of symmetry between the top and bottom is necessary, so in this embodiment, the waste hole 1
1 is.

The hole is the same as the guide pin hole for conveyance, and has a long axis of 3 holes and a short axis of 2 holes (see Figure 1 (b)).
.

(Example 2) Next, Example 2 will be explained using FIGS. 2(a) and (b). FIG. 2(a) is a plan view of the main part of the lead frame, and FIG. 2(b) is a sectional view of the lower part of the lead frame. Since the same lead frame as in Example 1 is used, the waste hole 11 is also provided.

As in Example 2, it is formed only at the lower end. As shown in the figure, two round holes 11 are formed at equal intervals between adjacent guide pin holes 5 in the lead frame frame 1 at the lower end. Therefore, the punched holes will be arranged at intervals of about 9 holes (see Figure 2 (a)). Since the fibers are cut at this interval, the warpage in this part is also approximately 0.4+a, which is quite small (Fig. 2(b)).

Moreover, the warpage at the upper end is approximately 0.5 cm, similar to the previous embodiment.
Therefore, there is almost no difference in warpage between the upper and lower frames, and they should be said to be uniform.

In addition, although Cu was used for the lead frame in the example,
The present invention is not limited to this, and all existing materials such as Fe-42Ni alloy can be applied. Further, the punched hole may have any shape, such as a round hole, a square hole, or an elongated hole, and may have any size. In short, the fibers need only be cut as appropriate. However, the square shape is unfavorable in terms of mass production because it easily damages the mold blade, but since the lead frame is less deformed, it can be expected that the punch die for cutting and bending, which is a process after resin sealing, will have a long life.

〔Effect of the invention〕

According to the present invention, the above-described configuration improves the balance of the frame shape, and the length of the fibers of the material is also uniform, so that deformation of the lead frame is reduced.

[Brief explanation of drawings]

FIG. 1(a) is a partial plan view of a lead frame of Example 1 of the present invention, FIG. 1(b) is an enlarged plan view of part A in the same figure,
Figure 1(c) is a sectional view of the lower part of Figure 1(a), and Figure 2(c) is a sectional view of the lower part of Figure 1(a).
a) is a partial plan view of the lead frame of Example 2, FIG. 2(b) is a sectional view of the lower part of the same figure, FIG. 3(a) is a partial plan view of the conventional lead frame, and FIG. ) is a sectional view of the upper part of the same figure, Fig. 3(c) is a sectional view of the lower part, and Fig. 4 is the punched hole interval (X) and the warpage size of the lead frame (
y); FIG. 1...Frame frame, 2...Outer lead,
3...Island, 4...Inner lead,
5... Round hole (guide pin hole), 6... Oblong hole (guide pin hole), 7... Square hole, 8...
・-Tie bar, 9...Slit, 10...
Lead frame, 11... Discarded hole, 12□, 12
2... Lead part. Agent: Patent attorney Yoshiaki Inomata (and one other person) Figure 1 Figure 2 Procedure amendment (method) October 11, 1990

Claims (1)

[Claims] In a lead frame comprising a frame having punched holes such as guide pin holes formed at appropriate intervals on both upper and lower ends, and lead portions repeatedly formed between the upper and lower frame frames, a certain distance between the punched holes is provided. A lead frame characterized in that blank holes are formed at intervals to narrow the interval between the punched holes including the blank holes, and at the same time the punched holes and the blank holes are arranged at equal intervals.