JPS61194862A - Lead frame and manufacture thereof - Google Patents

Abstract

PURPOSE:To form a multi-pin lead frame in which almost no interval exists by a method wherein each lead is bent so as to have a step between an adjacent lead and itself. CONSTITUTION:A large number of internal leads 18 surround a stage 12 radially and are connected to an outside frame 16 by external ends of external leads 20 which extend outward. The tip part of the internal lead 18 is separated from an adjacent internal lead 18 by a cut line 24 over a predetermined range and at the same time bent at suitable positions of the lead so as to have a step between the adjacent internal lead 18 and itself. With these steps, ends of the internal leads 18 are prevented from contacting each other at the cut line 24 parts so that required dielectric strength is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lead frame used in a semiconductor device and a method for manufacturing the lead frame.

(Background Art and Problems Therewith) In recent years, semiconductor devices have been becoming more and more densely packed, and the lead frames used therefor have been forced to have a larger number of pins.

There are various problems with increasing the number of pins in such a lead frame.

That is, even if semiconductor elements become denser, the semiconductor elements themselves do not become larger; rather, due to advances in semiconductor manufacturing technology, they tend to become smaller as the density increases.

Furthermore, it is necessary to ensure the lead width to be at least a certain width in order to ensure the reliability of wire bonding with the semiconductor element and to ensure a certain mechanical strength to prevent pull-outs and the like.

Given the above circumstances, in order to increase the number of bins in a lead frame, it is necessary to narrow the lead spacing or to make the window formed by the lead tips larger, as shown in Figure 8 (a) to (b). do not have.

Incidentally, most lead frames are manufactured by press working, but there is a limit to how narrow the lead spacing can be in this press working.

That is, in order to prevent buckling of the punch, the width of the punching process is generally limited to the thickness of the material. Therefore, for example, if the material thickness is 0.25 mm,
It is difficult to reduce the punching width to 0.25 mm or less. In this way, there are processing constraints to narrowing the lead spacing. Note that chemical etching is also used to manufacture lead frames, but it is still difficult to make the lead spacing less than the thickness of the material.

Furthermore, as shown in Figure 8 (1)), it is possible to increase the number of pins by increasing the window size, but this not only goes against the demand for miniaturization of semiconductor devices, but also reduces the bonding distance between the lead tip and the semiconductor element. This may result in a contact accident between the positive wires.

As shown in Figure 9, by processing the leads to make them as narrow as possible and arranging every other lead tip at a different height, we can maintain a large number of pins and maintain sufficient dielectric strength between the leads. A lead frame is known (Japanese Unexamined Patent Publication No. 59-27558), but as mentioned above, there is a limit to narrowing the lead spacing using the above-mentioned methods such as pressing or chemical etching. Therefore, there is a limit to increasing the number of bins.

(Summary of the invention) The present invention has been made to solve the above problems,
Our aim is to provide a lead frame that can meet the demands for increased pin count and an effective method for manufacturing it.
It has the following configuration.

That is, in a lead frame in which a large number of lead parts connected to a semiconductor element by bonding wires are formed so as to be closely located around the semiconductor element to be connected, the lead parts are connected to at least the bonding wires. A predetermined length portion from the tip portion is separated from adjacent lead portions by a cutting line, and
At least the portion separated by the cutting line is bent so as to have a step between adjacent lead portions.

Further, in a method for manufacturing a lead frame in which a large number of lead portions connected to a semiconductor element by bonding wires are formed so as to be closely located around a semiconductor element to be connected, the portions that become the lead portions are connected to at least the bonding wires. a pre-forming step in which a pre-cutting line is formed so that a predetermined length portion from the tip end to which the wire is connected is connected to a portion that will become the adjacent lead portion through a thin portion in which a substantially V-shaped cut is formed; a pressing process in which the lead portion is separated by cutting along the valley line of the preliminary cutting line formed in the molding process;
The method is characterized by comprising a pressing step of bending the separated lead portions so that at least the portion separated by the cutting line forms a step between adjacent lead portions.

Since the leads are separated by the cutting line as described above,
A multi-bin lead frame with narrow lead spacing is provided.

Further, since a preliminary cutting line is formed in advance and then cutting and separation is performed along the valley line of the preliminary cutting line, strain is not placed on the press mold, and a linear lead frame with an extremely narrow lead interval can be manufactured.

(Example) A preferred embodiment of the present invention will be described below based on the drawings.

FIG. 1 shows a lead frame 10 according to the present invention. In the figure, 12 is a stage section on which a semiconductor element is mounted;
It is connected to the outer frame 16 by a stage support par 14.

Reference numeral 18 denotes a large number of internal lead parts, which surround the stage part 12 in a radial manner and extend outward.
0 is connected to the outer frame 16 at the outer end.

2z is a tie bar that connects the external lead parts 20 together, and when used in a resin-sealed semiconductor device, it also serves as a so-called dam bar to prevent resin from flowing out.

The characteristic feature of the present invention is that the tip end of the internal lead part 18 is separated from the adjacent internal lead part 18 by a cutting line 24 over a predetermined range, and as is clear from FIG. This is because the leads are bent at appropriate locations so that there is a step difference between adjacent internal lead portions 18.

The reason for providing such a step is to prevent the edges of the internal lead portions 18 from coming into contact with each other at the cutting line 24 and to maintain a predetermined dielectric strength voltage.

The width of the above cutting line 24 is almost zero, as will be described later. This allows the internal lead portion 18 to have a large number of pins.

FIG. 3 shows another embodiment.

In this embodiment, the above-mentioned tie bar 22 is not provided, and the leads are bent between the outer frame 16 and the external lead portion 2o to form the above-mentioned step. As a result, not only the internal lead portion 18 but also the external lead portion 2o
Also, a lead frame having a step difference between adjacent ones is formed.

Although this embodiment is not suitable for resin-sealed semiconductor devices because it does not have tie bars, it can be used as a modified type for cerdip-type semiconductor devices.

In each of the above embodiments, the step between the leads is formed by bending only one of the two groups of every other lead downward or upward, as shown in FIGS. 4(a), (b), and (0). Alternatively, both groups may be bent.

Next, a method for manufacturing a lead frame will be described based on FIGS. 5(a), (b), and (C).

First, the strip material 30 shown in FIG. 1A is subjected to a predetermined press punching process according to the punching pattern of the lead frame 10 shown in FIG. This press punching process may be divided into a plurality of times and sequentially processed at predetermined portions.

Next, the part corresponding to the above-mentioned cutting line 24 is cut as shown in FIG.
Preforming is performed using a press die having a desired shape so that a pre-cutting line having a cross-sectional shape as shown in FIG. This preforming may be performed only from one side. However, in any case, by this preforming, the inner lead portions 18 that are adjacent to each other are formed in a state in which they are connected at the thin wall portion of the valley of the preliminary cutting line. This preforming can be performed in multiple steps, but in order to prevent stress during forming from concentrating on one part, for example, both symmetrical positions with respect to the center of the preform pattern are processed simultaneously.

Note that the process order of the punching process and the preforming process may be reversed.

Next, as shown in FIG. 3(Q), a press mold is used to cut out the thin walled portion of the valley of the pre-cut line formed by the preforming, and at the same time, the separated inner lead portion 18
Pressing is performed so that every other piece has a step. The separation step and step forming step may be separate steps.

The method of the present invention includes both the above-mentioned simultaneous steps and separate steps.

In the manner described above, the required lead frame can be formed.

Note that, as shown in FIG. 3C, an insulating spacer 32 may be inserted between the separated internal lead portions 18.

FIG. 6 shows a state in which wire bonding is performed between the semiconductor element 34 and the internal lead portion 18. During wire bonding, bonding tools are used to support the lower surface of the internal lead portion 18, which are formed in alternating steps, as shown in FIG. Ingredients 36
This can be done without deforming the internal IJ-doping section 18 using the above.

(Effects of the Invention) As described above, according to the present invention, since the lead spacing is almost zero, it is possible to provide a multi-bin lead frame and cope with the increase in the density of semiconductor devices. . Also, since there are fewer parts to remove, there is no waste of material. Furthermore, with the same number of leads, the tips of the leads can be placed closer to the semiconductor element, which reduces the need for shorter bonding wires, reduces contact accidents, and improves reliability when used as a semiconductor device.

Furthermore, according to the method of the present invention, a preliminary cutting line is formed in advance and the cutting is then performed along the valley line of the preliminary cutting line, so that no strain is placed on the press mold, and a linear lead frame with extremely narrow lead spacing can be manufactured. can do. Furthermore,
In the dense internal pattern area, small chips are not generated, and it is possible to prevent the occurrence of dents caused by chips entering the back side of the material, and also prevent chips from clogging the punch. Because there is no punch, there is no chance of chipping.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is an explanatory diagram showing an example of a lead frame according to the present invention, Fig. 2 is a cross-sectional view showing the state of the level difference in the internal lead part, and Fig. 3 is an explanatory diagram showing an example of the lead frame according to the present invention. An explanatory diagram showing FIG. 4(a),
(b) and (C) are explanatory diagrams showing an example of the bending direction of the lead, Figures 5 (&), (b) and (C) are explanatory diagrams showing the manufacturing process, and Figure 6 is an explanatory diagram showing an example of the bending direction of the lead. An explanatory diagram, FIG. 7 is an explanatory diagram showing a bonding jig, FIG. 8(a). (b) is an explanatory diagram of a conventional example in which the number of pins is increased, and FIG. 9 is an explanatory diagram of a conventional example in which a step is provided in the lead. 10... Lead frame, 12... Stage part,
14... Stage support bar, 16... Outer frame, 1
8... Internal lead part, 20... External lead part, 22
... tie bar, 24 ... cutting line, 30 ... strip material,
32... Insulating spacer, 34... Semiconductor element, 3
6... Bonding jig.

Claims (1)

[Scope of Claims] 1. A lead frame in which a large number of lead portions connected to a semiconductor element by bonding wires are formed so as to be closely located around the semiconductor element to be connected, wherein the lead portion is connected to at least the A predetermined length portion from the tip to which the bonding wire is connected is separated from adjacent lead portions by a cutting line, and at least the portion separated by the cutting line is adjacent to the lead portion. A lead frame that is bent so that there are steps between each other. 2. In a method for manufacturing a lead frame in which a large number of lead parts connected to a semiconductor element by bonding wires are formed so as to be closely located around the semiconductor element to be connected, the part that becomes the lead part is at least connected to the bonding wire. a preforming step of forming a preliminary cutting line so that predetermined length portions from the tip portions to which the wires are connected are connected to mutually adjacent portions that will become lead portions through a thin portion in which a substantially V-shaped cut is formed; a pressing step of separating the lead portions by cutting along the trough line of the preliminary cutting line formed in the molding step; A method for manufacturing a lead frame, comprising: a pressing step of bending so that a step is formed between the parts.