JPH0821658B2 - Lead frame manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of use) The present invention relates to a method for manufacturing a lead frame, and more particularly to shape processing of the inner lead tips of the lead frame.

(Prior Art) With the recent miniaturization, thinning, and high integration of semiconductor devices, lead widths, lead intervals, and plate thicknesses of lead frames used in these devices are becoming smaller. Extremely high technology is required and research is being conducted repeatedly.

Recently, it has become possible to form even those with more than 100 leads by stamping.

Usually, such a lead frame is formed by stamping or etching a strip-shaped metal material (strip material) such as an iron-based material or a copper-based material into a desired pattern and performing a plating process and the like.

In particular, for a lead frame formed by stamping, it is difficult to mold all of the inner leads in a single punching process, so use a so-called progressive die to divide the inner lead into multiple stations for punching. Is set.

For example, as shown in FIGS. 4 (a) and 4 (b), a strip-shaped material containing copper as a main component is used to form an inner lead (excluding the end face) 1, a tie bar 2, and an outer lead 3 having a desired shape. The first punching area 11 is formed by mounting the die on a die equipped with
The inner lead portion 1 is patterned while leaving the end faces of the inner leads. Here, the punch for punching between the inner leads is configured such that the ends of the punched portions in the cavity region form a circle having a radius of 0.05 mm, which is the same size as the lead interval (0.1 mm).

Then, as shown in FIGS. 5 (a) and 5 (b), the second end of the inner lead end remaining in the molding step is removed.
The punching area 14 (cavity area) is punched out to separate the die pad (pad) 15 from the inner lead tip,
The lead frame shape processing is completed. An overall view of the lead frame thus formed is shown in FIG. Four
Is a support bar.

However, in recent lead frames, the lead interval tends to be narrower than the plate thickness of the inner lead tip portion, and for example, it is necessary to punch with a width of 0.1 to 0.12 mm for a plate thickness of 0.15 mm. is there.

When such a minute lead frame is divided into a plurality of stations by the stamping method and punched, the pad size and the cavity size are determined by the chip size, but extremely minute processing is required.

When punching by the method as described above, the first punching region 11 is formed as shown in FIG. 5 (a), the inner lead portion 1a is formed leaving the end faces of the inner leads, and then orthogonal to this. As shown in FIG. 5 (b), the second punched-out region 14 serving as the cavity region is formed, but fine protrusions 13 may occur at this intersection.

When the projections sandwich a gap between the tips of the inner leads, and when plating is performed after the tips are formed, there is a problem that the plating concentrates on the projections and further narrows the gap between the tips.

In particular, with the recent increase in the density of semiconductor devices, the number of pins on the lead frame has increased, and the gap between the inner lead tips has become narrower, and these minute protrusions cause a short circuit in the circuit. However, there is a drawback in that the productivity and the yield are reduced.

(Problems to be Solved by the Invention) As described above, with the miniaturization of the lead frame, in the second punching for punching a region corresponding to the cavity region near the pad at the tip of the inner lead, the first punching region is formed. There is a problem that fine protrusions are generated at the intersections with the side portions of the obtained inner leads, and the gaps between the inner lead tips are sandwiched.

In particular, when plating is performed after forming the tips, the plating concentrates on the protrusions and further narrows the gap between the tips, causing a short circuit in the circuit and causing a decrease in reliability and yield of the semiconductor device.

The present invention has been made in view of the above circumstances, and in punching a lead frame, at the time of punching a cavity region, it is possible to prevent the influence of fine projections generated at the tips of the inner leads and to improve the reliability of the lead frame. With the goal.

(Means for Solving the Problem) Therefore, in the present invention, a lead frame having a plurality of inner leads arranged so as to surround a region in which a semiconductor element is mounted and a plurality of outer leads continuous with the inner leads are provided. In the manufacturing method, the molding step of molding the lead frame from the strip material is the first molding step of punching other punching target areas from the strip material, leaving at least the punching target areas connecting the inner lead tips. A stamping and molding step of a strip material including a second molding step of punching out a region to be punched remaining in the first molding step, wherein in the first molding step, a width is formed at the tip of each inner lead tip. Punching, including wide punching to form a narrow portion, and so that the narrow portion does not remain in the second molding process. It is characterized by punching into.

(Operation) By forming a punched portion to be a cavity region so as to leave a part of the inner lead tip portion formed to have a narrow width by the wide punched portion, the intersection of the two punched portions is Since the inner leads have a narrow width, the distance between the inner leads can be sufficiently maintained even if the protrusions are formed.

(Example) Hereinafter, a method for manufacturing a lead frame according to an example of the present invention will be described in detail with reference to the drawings.

First, as shown in FIGS. 1 (a) and 1 (b), a strip-shaped material containing copper as a main component is used to form an inner lead (excluding the end face) 1, a tie bar 2, and an outer lead 3 having a desired shape. It is attached to a die equipped with a punching die and press-worked to leave the inner lead ends,
The first punched area 21 is formed, and the inner lead area 22 is formed.
Pattern. Here, as for the punch for punching between inner leads, as shown in the main part in Fig. 3, the ends are wider than the lead interval (0.1 mm) so that the ends are wide.
It is configured to form a wide circle of 0.075 mm. Therefore, the tip of the first punching area 31 has a wide area 24.
Make up 0. Here, 3A is the outer edge of the punch.

Then, as shown in FIGS. 2 (a) and 2 (b), the second punching region 24, which is the cavity region of the inner lead end portion left in the molding step, is punched out, and the second punching region 24 is formed by the wide punching portion. The die pad 25 and the tip of the inner lead are separated while leaving the region formed so as to have a narrow width as the tip of the inner lead, and the shaping of the lead frame is completed. 2 (a) is an overall view,
FIG. 2B is a diagram showing a main part diagram. Here, the intersection of two punching areas, which are the first and second punching areas, ie the end face 28 formed by the second punching area and the side edge 24 formed by the first punching area.
A protrusion 23 is formed at the intersection with 1, but since the inner lead tip is narrow in this region,
The protrusion 23 does not enter the area between the inner leads.

After that, the lead frame is completed through a plating process of the inner lead tip portion and the like.

By forming the lead frame in this manner, the second punching portion is formed so as to leave the inner lead tip portion formed so that the width is narrowed by the wide punching portion. The intersecting portion of the two punched portions serves as a narrow tip portion, and even if a protrusion is formed, the distance between the inner leads can be sufficiently maintained and a circuit short circuit can be prevented.

Further, since the punch for punching between the inner leads used for punching has a wide tip, the buckling strength is improved, the straight portion of the punch can be lengthened, and the punch strength is significantly increased. It is possible to improve the productivity significantly, and it is possible to form a good lead frame with high accuracy.

Here, when the surface pressure of the punch end portion in the first punching step shown in FIG. 1 was measured, it was found that the surface pressure was reduced by 30% or more as compared with the case of using the conventional punch.

Further, although copper is used as the lead frame material in the above-mentioned embodiment, it is needless to say that other materials may be used without being limited to copper.

Further, in the above-described embodiment, the plating process is performed after the lead frame is shaped, but it may be performed during the shaping.

Furthermore, the molding area in each step can be changed appropriately.

〔The invention's effect〕

As described above, according to the lead frame manufacturing method of the present invention, when the lead material is formed into the shape of the lead frame, the punch for punching the inner leads is formed to have a wide tip end. Since the cavity area is punched out so that the punched-out area is left slightly, the intersection of the punched-out areas is a narrow tip, so even if a protrusion is formed, the distance between the inner leads can be maintained sufficiently. Therefore, the reliability can be significantly improved.

[Brief description of drawings]

1 to 2 are explanatory views showing a manufacturing process of a lead frame of an embodiment of the present invention, FIG. 3 is a view showing a main part of a punching punch used in the manufacturing process, and FIGS. 4 and 5 are ,
FIG. 6 is an explanatory view showing a part of a manufacturing process of a conventional lead frame, and FIG. 6 is an overall view of a normal lead frame. 1 ... Inner lead, 2 ... Tie bar, 3 ... Outer lead, 4 ... Support bar, 11,21 ... First punching area, 13,23 ... Protrusion, 14,24 ... Second punching Area, 15,25 ... die pad.

Claims (1)

[Claims] 1. A method of manufacturing a lead frame having a plurality of inner leads arranged so as to surround a region where a semiconductor element is mounted, and a plurality of outer leads continuous with the inner leads, respectively. The molding overstep of molding the frame is left from the first molding step, in which the punching target area connecting at least each inner lead tip part is left from the strip and the other punching target areas are punched out, and the first molding step. A blank forming process including a second forming process for punching out a region to be punched, wherein a wide blank forming is performed in the first forming process to form a narrow portion at the tip of each inner lead tip. It is characterized in that the punching is performed and the punching is performed so that the narrow portion does not remain in the second molding process. Lead frame manufacturing method.