JPH01216563A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To uniformly adhere a solder plating by adding a step of coining outer leads, thereby removing the roundness of the corner due to the punching burr of the leads generated in a pressing step so that the shape of a lateral section becomes substantially rectangular. CONSTITUTION:A first metal mold is mounted at the center of a stripelike material, and pressed to pattern a part inside a tie bar 13, i.e., the side of inner leads 2. Then, the material is rotated at 180 deg., second metal molds are mounted at both sides, and pressed to pattern the side of outer leads 14. Thereafter, the leads 14 are so coined in the degree as to collapse burrs in the second mold thereby to flatten the surface so that the section becomes rectangular. Eventually, the leads 14 are dipped in a solder plating solution, and a solder plating layer 16 is formed on its surface. Since a lead frame which is formed in this manner with a uniform plating layer on the whole surface of the outer leads, improper soldering does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a lead frame, and particularly to a method for shaping the outer lead thereof.

[Conventional technology]

Lead frames used for mounting semiconductor devices such as ICs and LSIs are formed by forming a plate-shaped body made of iron-based or copper-based metal material into a desired pattern by press working or etching.

Usually, as shown in FIG. 2, a lead frame integrates a die pad 11 on which a semiconductor integrated circuit chip (hereinafter referred to as a semiconductor chip) is mounted, and a plurality of inner leads 12 arranged to surround the die pad. The tie bars 13 are connected to each other, the outer leads 14 are connected to each inner lead and extend to the outside of the tie bars, the side pars 15 and 16 support the tie bars 13 from both sides, and the support pars 17 support the die pad 11. It is configured.

A semiconductor device mounted using such a lead frame is shown in FIG.
A semiconductor chip 2 is mounted on the die pad 11 of the semiconductor chip, and the bonding pads of this semiconductor chip and the inner leads 12 of the lead frame are connected with bonding wires 3 made of gold or aluminum wire, and these are further bonded with a bonding wire made of resin, ceramic, etc. After sealing with the sealing material 4, the tie bars and side bars are cut and the outer leads are bent into a desired shape to complete the process.

By the way, when such a lead frame is molded by press working, it is manufactured by continuously punching out a band-shaped material in a lead frame punching die, so the punched lead surface is as shown in Figure 4 (a). As shown in d
Due to this, the surface has a convex shape, while a burr b is formed on the back surface.

Incidentally, after or before sealing, the outer lead is soldered over almost the entire surface, bent into a desired shape, and connected to an external circuit such as a printed circuit board.

However, during solder plating, as shown in FIG. 4(b), the solder 18 is difficult to adhere to the sagging portion, and a soldering failure may occur when connecting to an external circuit such as a printed circuit board.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a highly reliable lead frame without causing defects in soldering.

[Means to solve the problem]

Therefore, in the lead frame manufacturing method of the present invention, a step of coining the outer lead is added.

[Effect]

By adding the process of coining the outer lead, the rounded corners caused by the sagging of the outer lead caused by the pressing process are removed, and the shape of the cross section in the width direction is almost square, so the solder plating is uniform. Attach to. Therefore, it is possible to provide a highly reliable semiconductor device without causing soldering defects when connecting it to an external circuit such as a printed circuit board.

〔Example〕

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

The lead frame formed by the method of the embodiment of the present invention has a structure similar to that shown in FIG. 2 in plan view, but after coining the outer lead, the cross-sectional shape of the outer lead is This makes it almost rectangular.

Next, a method for manufacturing this lead frame will be explained.

First, a first mold is attached to the center of the strip material and press working is performed to pattern the material on the inner side of the tie bar 13, that is, on the inner lead 12 side. (Fig. 1 (a)) Next, this strip-shaped material is rotated 180 degrees, second molds are attached to both sides, and press working is performed.
Buttering the outer lead 14 side. (Figure 1 (
b) and FIG. 1(C)) Here, FIG. 1(C) is an A-Alli plane view of FIG. 1(b).

Next, in this second mold, the outer lead 14 is coined to the extent that the edges are crushed so that the cross section becomes approximately square. (Figure 1(d)
)) Finally, the outer lead 14 is immersed in a solder plating liquid to form a solder plating 1116 on the surface. (Fig. 1(e)) The lead frame formed in this way is connected to the circuit pattern on the printed circuit board after going through processes such as mounting the element chip, wire bonding, and resin sealing. Since a uniform plating layer is formed on the entire surface of the lead, soldering is highly reliable without causing defects.

In addition, in the example, the solder plating process was performed on W1 of the element chip.
Although this is done prior to @, it may be done at any time after the coining of the outer leads and after resin sealing.

Further, in the embodiment, pressing was performed using two molds with tie bars as boundaries, but the entire shape may be formed at once with one mold.

Furthermore, coining may be performed from either side.

In addition, the order of molding is not limited to the example, and the molding may be performed in the order of outside and inside.

〔Effect of the invention〕

As explained above, according to the lead frame manufacturing method of the present invention, the outer leads are coined ((
Therefore, the solder plating layer formed on the surface of the outer lead becomes uniform, eliminating the occurrence of soldering defects when connecting to an external circuit, and making it possible to improve the reliability of the semiconductor device.

[Brief explanation of the drawing]

1(a) to 1(e) are manufacturing process diagrams of a lead frame according to an embodiment of the present invention, FIG. 2 is a diagram showing a normal lead frame, and FIG. 3 is a diagram showing a normal lead frame! Diagram showing the P conductor device, No. 4
FIG. 4(a) and FIG. 4(b) are cross-sectional views showing outer leads of a conventional lead frame. 1...Lead frame, 2...Semiconductor chip, 3.
... wire, 4 ... sealing material, °11 ... die pad, 12 ... inner lead, 13 ... tie bar,
14... Outer lead, 15.16... Side bar, 17... Support bar, 18... Plating layer, d
...without sauce, b...without paris. Figure 1(b)

Claims (1)

[Claims] A step of molding a lead frame including a plurality of inner leads, outer leads extending from the inner leads, and tie bars connecting these by a press working method, and coining of the outer leads. A method for manufacturing a lead frame, comprising the steps of: