JPH01192155A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To offer a lead frame of a high dimensional accuracy by a method wherein a plurality of inner leads are once molded in a state that their point parts are coupled integrally with one another through a coupling member, the point parts of the inner leads are flat-braided prior to the cut-off of the coupling member and a coining is performed after the cut-off of the coupling member. CONSTITUTION:A lead frame provided with a die pad 1 for placing a semiconductor chip, a plurality of inner leads 2 elongated radially toward the pad 1, tie bars coupled integrally with the leads 2 and an outer lead 4 connected continuously to each inner lead 2 is subjected to a shape processing by a press working. At this time, the points of the leads 2 are in a state that the points are connected integrally with one another through a coupling frame 5 connected continuously to the points and grooves N for cut-off are formed from the rear side of the lead frame between the leads 2 and this frame 5. Then, the point parts of the inner leads are flat-braided to flatten torsions and warpages. Moreover, regions, where are each used as a bonding area, of the point parts of the inner leads are subjected to a coining.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a lead frame.

(Prior Art) A lead frame used for assembling a semiconductor device such as an IC, for example, as shown in FIG. A die pad 1 for placing the die pad 1, a plurality of inner leads 2 arranged so as to surround the die pad 1, etc.
Tie bar 3 that integrally connects and supports the inner lead
and an outer lead 4 which is connected to each inner lead and extends outward. Here, 6 is a support bar that supports the die pad, and 7 is a site rail.

Such a lead frame is usually formed by shaping a band-shaped body by pressing or etching.

In particular, lead frames manufactured by press working tend to suffer from processing distortion due to residual stress, and in particular, there is a problem in that inner leads whose tips are free ends are easily deformed.

In addition, in order to improve bonding properties, the tips of the inner leads or bonding areas such as die pads are plated after shaping (plating process), and the tips of the inner leads are fixed with insulating tape made of polyimide or the like to prevent deformation. (taping process). The tips of the inner leads are likely to be deformed during the plating process, the taping process, or during transportation between processes.

Recently, in particular, semiconductor devices have become highly integrated, and the lead width and lead spacing of lead frames are becoming smaller and smaller. Therefore, the leads are easily deformed, and even if the tips of the leads are slightly deformed, short circuits are likely to occur due to contact between adjacent leads or contact between bonding wires.

Therefore, in order to suppress the deformation of the tip of the inner lead, the present applicant has developed an inner lead 2 as shown in FIG. 3(a).
The leading end of the lead frame is shaped so that it is integrally supported and connected by the connecting frame 5, and after passing through each process of coining process, plating process, and taping process, the connection state is released as shown in FIG. 3(b). Here, C' is a coining area and N is a cutting groove.

With this method, deformation of the inner lead that occurs during the coining process, plating process, taping process, and during transportation between these processes can be suppressed.

[Problem to be solved by the invention]

However, even with the above method, particularly long inner leads tend to be deformed, such as twisting between the tie bar and the connecting frame, or warping in the vertical direction. Mama Coining/I! There were variations in the effective flat width of the leading edge of the lead, which becomes the bonding area.

Finally, the connecting frame is removed using the punching method, and the third
As shown in Figure (C), when the connected state is released, there is a problem that a pull-out sag D occurs and the effective flat width W' decreases, which causes bonding defects.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a lead frame with excellent dimensional accuracy and high reliability.

[Means to solve the problem]

Therefore, in the present invention, first, the tips of a plurality of inner leads are formed via a connecting part so that they are integrally connected, and after flattening the vicinity of the tips of the inner leads,
The connecting portion is removed, and then the tip of the inner lead is coined.

[Effect]

With the above configuration, even if the inner lead is twisted between the tie bar and the connecting part or warped in the vertical direction, especially when the inner lead is long, the above flattening process will flatten it correctly. Therefore, a lead frame with high dimensional accuracy can be obtained without causing variations in the effective flat width due to coining.

Also, by performing coining after cutting off the connecting part,
Since the extraction sag that occurs when cutting off the connecting portion is also flattened, it becomes possible to form the effective flat width of the tip/end of the inner lead as designed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

First, as shown in FIG. 1(a), a die pad 1 for mounting a semiconductor chip, a plurality of inner leads 2 extending radially toward the die pad 1, and the inner leads are integrally formed by press working. A lead frame including a connecting tie bar (not shown) and an outer lead 4 connected to each inner lead 1 is shaped. At this time, the tip of the inner lead 2 is integrally connected via the connecting frame 5 connected thereto, and there is a gap between the inner lead 2 and the connecting frame 5 from the inside side. An ablation WiN is formed. The other parts are the same as the lead frame shown in FIG. In this state, heat treatment is performed to remove residual strain.

Next, as shown in an enlarged view of the main part in FIG. 1(b), the tips of the inner leads are flattened to flatten any twists or warps. In the figure, F indicates a flattened area. Here, K indicates the cutting line.

Furthermore, as shown in FIG. 1(d), the area at the tip of the inner lead that will become the bonding area is coined.

C is a coining area flattened by coining. (FIG. 1(e) is a diagram showing the vicinity of the die pad at this time.) Thereafter, a plating process and a taping process are performed to complete the lead frame.

The lead frame formed in this way has a connecting frame 5
By flattening the tip of the inner lead with the tip supported in the correct position, it is possible to remove twists and warpage that tend to occur at the tip of the inner lead, especially in the area between the tie bar and the connecting part. , it becomes possible to maintain high dimensional accuracy.

Unfortunately, since coining was performed after cutting out the connecting frame, the effective flat width was reduced by the sagging that occurred during cutting. In this case, the effective flat width W is restored to a value close to the design value.

(Effects of the Invention) As described above, according to the lead frame manufacturing method of the present invention, - first, the tips of a plurality of inner leads are integrally connected via a connecting body; The tips of the inner leads are flattened prior to cutting off the connecting bodies to eliminate twisting and warping, and coining is performed after cutting off the connecting bodies, providing a lead frame with high dimensional accuracy. It becomes possible to do so.

[Brief explanation of the drawing]

1(a) to 1(e) are diagrams showing the manufacturing process of a lead frame according to an embodiment of the present invention, FIG. 2 is a diagram showing one unit of a normal lead frame, and FIG. ) to FIG. 3(C) are diagrams showing the manufacturing process of a conventional lead frame. 1... Die pad, 2... Inner lead, 3...
・Tie bar, 4...Outer lead, 5...Connection part, 6...Support bar, 7...Sight rail, F.
... Flat hitting area, C... Coining area, N... Groove for cutting. Figure 1 (Q) Figure 1 (b) Figure 1 (C) Figure 1 (d)

Claims (1)

[Scope of Claims] A molding step in which the tips of the plurality of inner leads are shaped while leaving connecting portions so that the tips are integrally connected; and a flattening step in which the tips of the inner leads are hammered by hand. A method for manufacturing a lead frame, comprising: a separating step of removing a connecting portion and separating the inner leads individually; and a coining step of coining the tips of the inner leads.