JP2755793B2 - Lead frame - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to a lead frame structure of a semiconductor device, and particularly to a lead frame structure most suitable for a resin-sealed semiconductor device having a large number of leads. It is.

(Prior Art) A lead frame of a semiconductor device is formed by etching or punching. First, the lead frame etching molding is performed using a sheet material or a coil material as a material, washing it, applying a resist, drying, baking and developing a lead frame pattern.
After removing the resist by etching, cutting and performing offset inspection, spot Au, A on strip automatic plating line
Finish by plating with g etc. On the other hand, in the punching method, the above-described sheet material, coil material and the like are set in a press die and punched according to a lead frame pattern to form a lead frame.

FIG. 3A is a partial plan view of the lead frame 10 formed by such a punching method. Lead frame 10
Is made of a long Fe-42Ni alloy or a material made of Cu. A frame 1 is formed at both ends of the elongated body, and a round guide pin hole 5 and a rectangular guide pin hole 6 are formed periodically at the upper end thereof. A round guide pin hole 5 is formed in the frame 1 at the lower end. The round guide pin hole 5 is a positioning hole for accurately determining the positions of the semiconductor element and the lead frame when the semiconductor element and the lead frame are sealed with a resin. In one process, holes for inserting feed pins for transporting the lead frame from the loader magazine to the unloader magazine are formed, and at least one hole is formed for each lead portion.

Lead portion 12 ₁ is repeatedly formed between the framework 1 at both ends, outer leads 2, the inner lead 4,
The tie bar 8 is formed between the outer lead and the inner lead. The tie bar 8 is provided at the center of the inner lead. Lead portions are separated by slits 9 formed for punching balance the lead portion 12 ₂ adjacent. Square holes 7 are provided near the round and square guide pin holes at both ends of the upper frame 1 and near the guide pin holes of the lower frame.

The square hole 7 is a positioning hole provided for positioning the bonding tool at a correct bonding position when the semiconductor element and the inner lead are bonded by a bonding wire, and the position of the tool is corrected by observing the positioning hole. It becomes possible. The lead section 12
It is arranged one by one between the slits.

By the way, a long body used as a raw material of a lead frame is usually formed by performing hot and cold rolling, and not only crystal grains extend in a rolling direction (for example, a long axis direction), but also a crystal direction is increased. It has a so-called fiber structure aligned in this direction. When a lead frame material having such a structure is punched and formed by a press die, internal stress is generated, and if it is not uniform, a distortion such as warpage or bending occurs in the lead frame. When performing wire bonding, the element moves,
There are problems such as the bonding position cannot be determined accurately.

The reason why the internal stress becomes non-uniform is that the punched shape is asymmetric. The asymmetry will cause variations in heat conduction. Further, when slits, holes, and the like are formed by punching, the fibers in the vicinity are cut off, and as a result, the lead frame is in an uneven state in which the length of the fibers varies depending on the location. When the lead frame is resin-sealed together with the semiconductor element, the lead frame is heated up to about 180 ° C. Since the expansion and contraction ratio of the material due to heat varies depending on the length of the fiber length of the material, distortion is unavoidable in a lead frame that is punched non-uniformly even by thermal stress.

Considering the occurrence of this distortion in a conventional example, the interval between the punching holes 5, 6 such as the guide pin holes of the frame 1 at the upper end of the lead frame 10 in FIG.
0 mm. On the other hand, the punched hole 5 of the frame 1 at the lower end
Is 28 mm. When mounting the element on this lead frame and performing resin sealing via wire bonding, warpage occurs in the lead frame due to the heat of the resin, but the warpage of the top frame is about 0.5 mm. On the other hand (Fig. 3 (b)), the sledge of the frame at the lower end is about 1mm.
Met. It can be seen that warpage is unavoidable as long as the punching process is performed, and the interval between the punched holes is small as it is narrow, and becomes larger as the interval is increased. This is thought to be due to the length of the fiber in the material. FIG. 4 shows the relationship between the warpage and the interval between the punched holes. When the horizontal axis represents the punching hole interval (x) and the vertical axis represents the corresponding warpage size (y), both of them are almost linearly changed. As can be seen from this figure, the size of the frame at the lower end is large,
As described above, this is proportional to the interval (pitch) between the punched holes. When the resin shrinks after the resin is sealed, the longer the pitch is, the stronger the resin is pulled and the more the warp is. Conceivable.

(Problems to be Solved by the Invention) As described above, in a lead frame used in a semiconductor device, guide pin holes and the like are not always formed uniformly, but are often arranged irregularly. There is a problem that the punching balance is not good, and as a result, the length of the fiber of the material becomes uneven, so that there is a problem that the thermal stress increases and the strain increases.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a lead frame for a semiconductor device in which the drawing balance is uniform and the length of the fiber of the material is uniform.

[Configuration of the invention]

(Means for Solving the Problems) The present invention includes a frame formed at both upper and lower ends and having punched holes such as guide pin holes at appropriate intervals, and a lead portion repeatedly formed between the upper and lower frame. The present invention relates to a lead frame of a semiconductor device, in which discarded holes are formed at appropriate intervals between the punched holes to reduce the interval (pitch) between the holes including the punched holes,
The arrangement of the punched holes and the discarded holes is uniform. To make the arrangement of the punched holes and the discard holes uniform is to make the arrangement of the discard holes formed in the upper and lower frame frames symmetrical with respect to the long axis, but it is not necessary to be completely symmetrical. Although some deviation is recognized, the intervals between the punched holes and the like in each frame need to be substantially uniform.

(Operation) By forming the discard holes, the balance of the frame shape can be improved, and the fiber length of the material can be made more uniform than that of the conventional lead frame. There is no particular difference in the function and effect depending on the shape of the disposal hole, and any shape such as a round shape, a square shape, and an oblong shape may be used. However, there is a disadvantage that the blade of the square press die is easily damaged. In order to improve the symmetry of the upper and lower frames, it is advantageous that the shapes of the facing holes are the same.

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1A shows that the lead portion of the first embodiment of the present invention has four leads.
FIG. 1 (b) is an enlarged plan view of a portion A of FIG.
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 stamping a material such as Cu formed by cold rolling using a press die. Although the figure shows a lead portion for four frames, it is actually only a part of a long body. Each of the leads 12 ₁ and 12 ₂ formed on each frame has an island 3. An inner lead 4 is formed around the island 3, and an outer lead 2 is formed outside the inner lead 4 via a tie bar 8. A slit 9 is formed between each lead. This is for the purpose of securing the ease of cutting for each lead portion at the same time as being formed to balance the punching after performing the punching process. Each frame is separated by a slit 9. Except for the discarded hole 11 which is the gist of the present invention, seven punched holes used in this embodiment are formed for each frame. That is, a long hole 6 serving as a guide pin hole for transport, a round hole 5 serving as a positioning hole for performing die bonding, and a square hole 7 for determining a bonding position during wire bonding are formed at the upper and lower ends. ing. The distance between the punched holes 5 and 6 of the frame 1 at the upper end is equal to 10 mm. There is one punched hole 5 in the frame 1 at the lower end.
One formed and punched holes 5 with adjacent ones of the lead portion 12 ₂
There is a distance of 28mm between. This is equal to the hole interval of the conventional frame 1 at the lower end. In this embodiment, a discarded hole is provided almost at the center of the punched hole 5 adjacent to the frame 1 at the lower end.
Form 11. This reduces the hole spacing from 28 mm to 14
mm, the fiber becomes short, and the warpage of the lower short portion of the lead frame 10 after the final treatment is about 0.6 mm (see FIG. 1 (c)). Such a degree of warpage does not cause a failure in the assembly process such as a bonding error. Also, since the difference between the upper and lower warpages is only about 0.1 mm, there is no hindrance to the assembly process. However, a certain degree of symmetry is required in the upper and lower portions. Therefore, in this embodiment, the disposal hole 11 is formed as an elongated hole, which is the same as the guide pin hole for conveyance. This has a major axis of 3 mm and a minor axis of 2 mm (see FIG. 1 (b)).

Second Embodiment Next, a second embodiment will be described with reference to FIGS. 2 (a) and 2 (b). FIG. 2 (a) is a plan view of a main part of the lead frame, and FIG. 2 (b) is a cross-sectional view of the lower part of FIG. Since the same lead frame as that of the first embodiment is used, the discard hole 11 is formed only at the lower end similarly to the second embodiment. As shown in the figure, two round discard holes 11 are formed at equal intervals between adjacent guide pin holes 5 in the lead frame 1 at the lower end. Therefore, the punched holes are arranged at intervals of about 9 mm (FIG. 2 (a)).
reference). Since the fiber is cut at this interval, the warp at this portion is also about 0.4 mm, which is considerably small (FIG. 2 (b)).

Moreover, the warpage at the upper end is about 0.5 mm as in the previous embodiment.
Therefore, there should be almost no difference in the warp between the upper and lower frames, and both should be uniform.

In addition, although the lead frame used Cu in the Example,
The present invention is not limited to this, and all existing materials such as Fe-42Ni alloy may be applied. Also, the size of the punched hole is arbitrary, regardless of the shape, such as a round hole, a square hole, or a long hole. In short, the fibers need only be cut appropriately. However, a square shape is not preferable in terms of mass productivity because the blade of the mold is easily damaged. Since the deformation of the lead frame is small, a long service life of the punch die for cutting and bending, which is a process after resin sealing, can be expected.

〔The invention's effect〕

According to the present invention, the balance of the shape of the frame is improved by the above-described configuration, and the length of the fiber of the material becomes uniform, so that the deformation of the lead frame is reduced.

[Brief description of the drawings]

1 (a) is a partial plan view of a lead frame according to Embodiment 1 of the present invention, FIG. 1 (b) is an enlarged plan view of a portion A shown in FIG. 1 (a), and FIG. FIG. 2 is a sectional view of a lower part of FIG. FIG. 2A is a partial plan view of a lead frame according to a second embodiment, and FIG. 2B is a cross-sectional view of a lower portion of the same. FIG. 3 (a) is a partial plan view of a conventional lead frame, FIG. 3 (b) is a cross-sectional view of the upper part of FIG. 3 (a), and FIG. 3 (c) is that of FIG. 3 (a). It is sectional drawing of a lower part. 4th
The figure is a characteristic diagram showing the relationship between the punching hole interval (x) and the warp size (y) of the lead frame. 1 ... frame frame, 2 ... outer lead, 3 ... island, 4 ... inner lead, 5 ... round hole (guide pin hole), 6 ... long hole (guide pin hole), 7 ... square hole , 8 ... tie bar, 9 ... slit, 10 ... lead frame, 11 ... disposal hole, 12 ₁ , 12 ₂ ... lead part.

Claims (1)

(57) [Claims] 1. A lead frame comprising a frame having punched holes such as guide pin holes formed at appropriate intervals at upper and lower ends and a lead portion repeatedly formed between the upper and lower frame. A lead frame, wherein discarded holes are formed at regular intervals between holes to reduce the distance between the punched holes including the discarded holes, and the punched holes and the discarded holes are arranged at equal intervals.