JPH0455539B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a lead frame,
In particular, it relates to a method of plating the tips of inner leads with precious metals.

[Prior art and its problems]

Lead frames used for mounting semiconductor devices such as ICs and LSIs are made by molding iron-based or copper-based metal materials into desired shapes by press working or etching.

Usually, the lead frame is as shown in Figure 2.
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 1 arranged so as to surround the die pad.
2, a tie bar 13 that integrally connects the inner leads 12, and an outer lead 14 that is connected to each inner lead and extends to the outside of the tie bar.
, side bars 15 and 16 that support the tie bar 13 from both sides, and a support bar 17 that supports the die pad 11.

When implementing, as shown in Figure 3,
The semiconductor chip 2 is mounted on the die pad 11 of the lead frame 1, and the bonding pad of this semiconductor chip and the inner lead 12 of the lead frame are connected.
After connecting these with a bonding wire 3 made of gold wire or aluminum wire and sealing them with a sealing material 4 such as resin, the tie bars and side bars are cut and the outer leads are bent into a desired shape. be completed.

Incidentally, bonding areas such as the tips of inner leads or die pads of such lead frames are plated with a noble metal such as silver plating to improve bonding properties.

Normally, this precious metal plating process is performed after the patterning process in which the lead frame is formed into a desired shape using a punching method or the like, but in this case, the side surfaces of the inner leads are plated, which not only results in wastage of the plated metal, but also leads to a loss in the package. If plated metal is attached to the side surface near the line, migration is likely to occur due to the intrusion of moisture, causing a decrease in the reliability of the semiconductor device.

In order to solve this problem, a method has been proposed in which predetermined areas of a strip material are plated with precious metal in advance before each part of the lead frame is molded, and then the lead frame is molded.

However, in this method, not only the plated surface is damaged during the forming process, but also the scrap area that is to be removed later is also plated, resulting in a large amount of waste of plated metal, that is, precious metal.
Although it is possible to recover the precious metals attached to the unnecessary parts from within the scrap, it is still impossible to avoid a rise in costs because recovery equipment is required.

The present invention was made in view of the above circumstances, and
The purpose is to provide low-cost and highly reliable lead frames.

[Means for solving problems]

Therefore, in the method of the present invention, before plating the tip of the inner lead with precious metal, the edge of the tie bar on the pad side (inner side) is positioned closer to the pad side than the noble metal plating line (edge of precious metal plating) of the inner lead. Pattern the lead frame with the tie bar widened so that the
Finally, the tie bar is shaped to a normal width so that the edge of the tie bar on the pad side is outside the precious metal plating line.

[Effect]

According to the above method, the side surface of the inner lead near the package line is plated while it is not exposed as it becomes part of the wide tie bar, and is formed and exposed after plating, so that the plating metal adheres to it. There's nothing to do. Therefore, migration does not occur and reliability of the semiconductor device can be improved.

Furthermore, since the inner lead tips and the like are patterned prior to plating, the amount of plating metal adhering to unnecessary parts that become scrap can be minimized, and costs can be reduced. Furthermore, since the tips of the inner leads are not shaped after plating, it is possible to complete the process without damaging the plating surface, and there is no deterioration in bonding properties.

Incidentally, in order to ensure that the bonding pads of the semiconductor chip and the tips of the inner leads are on the same plane and improve bonding properties, lead frames are often subjected to day-press processing. In other words, the die pad of the lead frame is
By pressurizing the support bar that supports it again (performing day press processing) and bending it to form a predetermined angle (i.e. day press angle), it will come to a position that is a predetermined height lower than the bonding surface of the inner lead. It is formed like this.

By forming the tie bars at the same time as this day-pressing process, it is possible to complete the process by only slightly deforming the day-pressing mold without requiring any additional process.

〔Example〕

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

First, as shown in FIG. 1a, a lead frame pattern is formed by a normal press working method (here, the same members as those in FIG. 2 are given the same reference numerals). At this time, as shown in a partially enlarged explanatory diagram in FIG. 1b, the tie bar 13' is made wide so that the end edge DL of the tie bar 13' on the die pad 11 side is closer to the die pad than the noble metal plating line ML of the inner lead 12. Let the shape be .
Here, PL indicates the package line.
In addition, UL indicates the punching line in the post-process (the rest is exactly the same as that of the conventional example).

Next, as shown in FIG. 1c, a tape (not shown) is attached to cover the non-plated area, and the plate is immersed in a silver electroless plating solution to form a silver plating layer G.

After this, as shown in Figures 1d and 1e,
The support bar is bent and the die pad surface is formed to be lower than the tip end surface of the inner lead.At the same time, the edge of the tie bar on the die pad side is cut off and day press processing is performed using a mold that creates a tie bar 13 with a normal width. Do this. Here, Figure 1e is the first
It is an AA sectional view of figure d.

The lead frame formed in this way is
As shown in the partially enlarged explanatory diagram in Figure 1 f, the inner lead side surface S near the package line PL, where migration is likely to occur, is maintained without silver plating, so migration occurs due to moisture intrusion. There are no other issues, making it highly reliable.

Further, since only a portion of the tie bar is scrapped, only a small amount of precious metal adheres to the scrapped portion, reducing costs.

Furthermore, since the tie bars are formed in the same process as the day press process, they can be formed without any additional process.

In the example, the tie bars were formed at the same time as the day-pressing process, but it is not necessary to do it at the same time, and even if the die pad is formed separately or integrally, the day-press process can be performed If this is not the case, the tie bars may be formed in an independent process.

In addition, the width of the tie bar can be widened within the range where the tip of the inner lead is located on the side of the pad that extends parallel to the tie bar, and the width can be made the same as the conventional width near the side bar, but the overall width can be widened. Needless to say, it is okay to do so.

Further, in the embodiment, the case where the lead frame is patterned by press working is explained, but it goes without saying that patterning is not limited to press working and is also effective when patterning is performed by etching. .

Further, the shapes of the die pad and support bar are not limited to the embodiments, and can be changed as appropriate. For example, it is also possible to adopt a shape in which the die pad is supported by four support bars. .

〔Effect of the invention〕

As explained above, according to the method of the present invention, a lead frame pattern is formed in which the tie bar is widened so that it comes close to the tip of the inner lead, and precious metal plating is performed on the tip of the inner lead. Since the tie bars are then molded to a predetermined width, it is possible to provide a lead frame with low cost and high reliability.

[Brief explanation of drawings]

1a to 1f are diagrams showing the manufacturing process of a lead frame according to an embodiment of the present invention, FIG. 2 is a diagram showing a lead frame of a conventional example, and FIG. 3 is a diagram showing a conventional mounting of a semiconductor device. It is a figure which shows an example. 11... Die pad, 12... Inner lead, 13... Tie bar, 14... Outer lead, 15, 16... Side bar, 17... Support bar, 1... Lead frame, 2... Semiconductor chip, 3... ...Bonding wire, 4...Sealing material, PL...Package line, ML...Precious metal plating line, DL...Edge of die pad, UL...
...A punching line for tie bars in the post-process.

Claims (1)

[Scope of Claims] 1. A plurality of inner leads having bonding areas made of a precious metal plating layer at their tips, a tie bar that integrally connects the inner leads, and a tie bar that is connected to each inner lead and that is connected to the outside of the tie bar. In the method for manufacturing a lead frame, the tie bar is made wider so that the inner edge of the tie bar is located inward than the edge of the portion of the inner lead where the precious metal plating layer is to be formed. a first forming step for shaping the lead frame; a plating step for forming a noble metal plating layer on the tips of the inner leads of the lead frame; A method for manufacturing a lead frame, comprising: a second molding step of cutting the inner edge of the tie bar so that it is located outward from the edge. 2. A die pad on which a semiconductor chip is mounted, inner leads arranged around the die pad, a tie bar that integrally connects the inner leads, an outer lead connected to each inner lead, and a support that supports the die pad. In the method for manufacturing a lead frame comprising a bar, the lead frame has a shape in which the tie bar is made wider so that the inner edge of the tie bar is located inward than the edge of the area where the noble metal plating layer is to be formed of the inner lead. a first forming step for processing; a plating step for forming a precious metal plating layer on the tips of the inner leads of the lead frame; and a plating step for bending the support bar by a predetermined angle, and simultaneously bending the inner edge of the tie bar. A method for manufacturing a lead frame, comprising: a second molding step of cutting the inner edge of the tie bar so that it is located outside the edge of the noble metal plating layer.