JP2000323638A - Lead frame forming method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To apply silver plating to a terminal portion of a lead frame and a semiconductor chip mounting portion with high accuracy, and to eliminate the risk of silver migration. SOLUTION: A guide hole 14 is formed on a lead frame material 10 by primary press working, and a plating solution reservoir hole 18 is formed at each of four corners of a plating area 17. Thereafter, silver plating 17 a is formed on the plating area 17. After that, a second press process is performed to form a lead frame so that a part of the plating region 17 becomes a semiconductor chip mounting portion and a terminal portion and a remaining portion of the plating region is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a lead frame for a semiconductor, and more particularly to a method for treating silver (Ag) plating used in a semiconductor chip mounting and wire bonding process.

[0002]

2. Description of the Related Art When a semiconductor chip is mounted on a lead frame and sealed with a resin, a space between a pad of the semiconductor chip mounted on a chip mounting portion (die island) of the lead frame and a terminal portion of the lead frame. , Gold (Au) wires. In order to make this connection smoothly and without defects, gold or silver is plated on the terminal portion of the lead frame. Recently, silver plating has been generally used for economic reasons.

[0003] It is more effective not only in terms of economy but also in terms of preventing silver migration, to apply this silver plating only to a necessary portion of the lead frame rather than to the entire periphery of the terminal portion. This silver migration is a phenomenon in which moisture or contaminants intruding from the gap between the lead frame and the molding resin that encapsulates the semiconductor chip causes silver to precipitate due to the application of a DC voltage and cause a short circuit between adjacent terminals outside the package. To tell.

[0004] Therefore, for resin sealing of the lead frame,
Many measures are required to block the outside air as much as possible and to prevent the silver-plated portion from being exposed to the outside of the mold resin.

FIG. 5 is a plan view of an SOP (small outline package, having a terminal pitch of 1.27 mm) type lead frame material 10 'before separation. Each lead frame 11 is press-formed. The semiconductor chip mounting portion 12 and the wire bonding terminal portion 13 are formed by punching. Reference numeral 14 denotes a positioning guide hole. FIG. 6 is an enlarged view of the lead frame 11 before separation, and shows the semiconductor chip mounting portion 12 and the wire bonding terminal portion 1.
3 is provided with silver plating 12a, 13a (hatched portion). Reference numeral 15 denotes a punched hole for forming the lead frame 11, and reference numeral 16 denotes a resin mold area of the lead frame 11.

FIG. 7 shows a silver plating jig 20 for performing the plating by electrolysis. 21 is a plating sparger that forms an outer casing, 22 is a plating solution inlet, 23 is a plating solution outlet, 24 is a plating solution nozzle also serving as an anode,
Reference numeral 25 denotes a mask plate for masking a non-plated portion; 26, a similar mask rubber; 27, a pressing rubber for pressing the lead frame material 10 '; and 28, a similar pressing plate.

Here, each lead frame 11 of the lead frame material 10 'shown in FIG.
The plating area 17 (see FIG. 6) on which the metal layer 13a is to be applied is positioned so as to be exposed on the lower surface.
After applying pressure, a DC voltage is applied such that the nozzle 24 side becomes a positive electrode and the lead frame material 10 ′ becomes a negative electrode, and a plating solution is introduced at a predetermined pressure from the inlet 22 and is ejected to the plating area 17 by the nozzle 24. Silver plating.

However, in this method, the lead frame 11 punched by pressing to a shape immediately before cutting and separating into individual lead frames is plated with silver.
As shown in FIG. 8, in addition to the silver plating 13a required for wire bonding of the terminal portion 13, silver plating 13b also adheres to a side surface (cut end surface) irrelevant to the wire bonding, and in particular, the silver plating 13b on the side surface forms a package. If it extends to near the outside and even to the outside, there is a risk of the silver migration described above.

For this reason, the plating 13b on this side surface is peeled off with a silver plating removing liquid or covered with solder, but it cannot be completely removed or covered with solder due to the small terminal pitch. . This was remarkable in a small surface mount package or a microminiature surface mount package having a smaller terminal pitch.

Therefore, as shown in FIG.
A method of applying silver plating to the lead frame material 10 'at the stage where only the lead frame material is formed is adopted. This is a lead frame forming method called “first mask plating + stamping (press working) method”, and the lead frame material 10 ′
Only the guide hole 14 is formed (primary press working), and the guide hole 14 is positioned on the basis of the guide hole 14 and set in a silver plating jig 20. The surface of the plating area 17 is previously subjected to silver plating 17 a, and thereafter, The lead frame 1 shown in FIG.
This is a forming method in which the semiconductor chip mounting portion 12 and the terminal portion 13 are formed by press working (secondary press working) into a shape forming 1 and an offset (step) is formed as necessary. Since the pressing process is performed after the plating process, silver plating does not adhere to the side surface (cut end surface) of the terminal portion 13.

[0011]

However, in this "first mask plating + stamping method", the plating region 17 of the lead frame material 10 'is located at the back of the bag region surrounded by the mask rubber 26 and the mask plate 25. Therefore, as shown in FIG. 10, the plating solution blown up from the nozzle 24 flows so as to form a vortex in the bag region, and bubbles are generated at the corners.

Since there is no escape for the bubbles of the plating solution, a large number of small voids (30 μm
(φ〜50 μmφ), and there was a problem that the plating quality deteriorated due to uneven plating. The portion where the plating unevenness occurs is a portion which is later pressed to be the wire bond terminal portion 13 and greatly affects the quality of the wire bond.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for forming a lead frame in which plating unevenness does not occur in a plating process such as "first mask plating + stamping method". To provide.

[0014]

According to a first aspect of the present invention, a guide hole is formed in a lead frame material by primary processing, and thereafter, a plating area of the lead frame material is plated with silver. And then forming a lead frame shape such that a portion of the plating region becomes a semiconductor chip mounting portion and a terminal portion by secondary processing and a remaining portion of the plating region is removed. At the time of the primary processing, a plating solution pool hole is formed at a corner of the plating area so as to bite at least a part of the plating area.

In a second aspect based on the first aspect, the plating solution reservoir holes are formed at all corners of the plating area.

In a third aspect based on the second aspect, the shape of the plating solution reservoir hole is a key shape bent at 90 degrees so as to surround the plating area.

[0017]

FIG. 1 is a plan view of a lead frame material 10 according to an embodiment of the present invention. FIG. 2 is an enlarged view of the plating area. Reference numeral 14 denotes a guide hole for setting at the time of plating or press working, and reference numeral 17 denotes a plating area, which is the same as that in FIGS. Numerals 18 are pool holes formed at the four corners of the plating area 17.

In this embodiment, the lead frame material 10
During the first press working, the pool hole 1
8 are formed at the same time, and thereafter, a silver plating process is performed on the plating region 17, and thereafter, a secondary press process of punching into a lead frame shape is performed. That is, the lead frame is formed by “first mask plating + stamping method”.

FIG. 3 is an explanatory diagram of this silver plating process.
The same components as those shown in FIG. 10 are denoted by the same reference numerals. Also in this embodiment, the plating region 17 of the lead frame material 10 is located at the back of the bag region surrounded by the mask rubber 26 and the mask plate 25, and the plating solution blown up from the nozzle 24 causes a vortex in this bag region. It flows as if it were made, and bubbles are generated in the corners.

However, this foam is used for the lead frame material 10.
Escapes from the corner of the plating area 17 to the pool hole 18,
Fine voids due to non-plating are not generated, and high-quality silver plating 17a (for example, a plating thickness of 3 μm) can be applied to the entire surface of the plating region 17.

Therefore, the lead frame material 10 is
Next press work, if necessary, offset processing or formation of semiconductor chip mounting part and terminal part, silver plating processing is surely applied to the place where silver plating is required, and plating of the cut end face etc. of the terminal A lead frame having no silver plating on unnecessary portions can be obtained, and there is no fear of silver migration.

The pool hole 18 must be formed so that at least a part of the pool hole 18 bites into the plating region 17, and as shown in FIG. FIG. 4 (b)
As shown in FIG. 5, the reservoir hole 18B may have a round shape, or may have another shape. In the case of the key shape shown in FIG. 4 (a), it is easy to confirm the displacement of the plating area and the presence or absence of a peeling by the inspection after the silver plating after the primary press. Further, in the present invention, the guide hole and the lead frame shape are formed by pressing, but the same effect can be obtained by appropriately selecting and combining the method of pressing and etching, or by combining only etching. Needless to say.

[0023]

As described above, according to the present invention, even in the case of a lead frame having a fine terminal pitch, the terminal portion and the semiconductor chip mounting portion can be plated with silver with high precision, and the silver migration can be prevented. There is no fear.

[Brief description of the drawings]

FIG. 1 is a plan view of a lead frame of a lead frame material according to the present invention before press working.

FIG. 2 is an enlarged view of a plating region of FIG. 1 and pool holes formed at four corners thereof.

FIG. 3 is an explanatory diagram of a plating process on a plating region.

FIGS. 4 (a) and 4 (b) are modified examples of a pool hole formed in a plating area.

FIG. 5 is a plan view of a conventional lead frame made of a lead frame frame material after press working.

FIG. 6 is an enlarged view of a lead frame part of FIG. 5;

FIG. 7 is a sectional view of a jig for silver plating.

FIG. 8 is a partial perspective view of a silver-plated terminal.

FIG. 9 is a plan view of a conventional lead frame made of a lead frame material before press working.

FIG. 10 is an explanatory diagram of a conventional plating process for a plating area.

[Description of References] 10, 10 ': Lead frame material, 11: Lead frame, 12: Semiconductor chip mounting portion, 12a: Silver plating,
13: wire bond terminal portion, 13a: silver plating, 14:
Guide hole, 15: punched hole, 16: resin mold area, 17: plating area, 17a: silver plating, 18, 18
A, 18B: pool hole, 20: silver plating jig, 21:
Plating sparger, 22: plating solution inlet, 23: plating solution outlet, 24: nozzle, 25: mask plate, 26: mask rubber, 27: holding rubber, 28: holding plate

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaaki Ishiyama 2-1-1 Inahira, Musashimurayama-shi, Tokyo Nishihara Riko Co., Ltd. F term (reference) 5F067 AA00 AB02 BA00 BA01 DA13 DC02 DC03 DC05 DC15 DC17 DC20

Claims (3)

[Claims] 1. A guide hole is formed in a lead frame material by primary processing, thereafter, a plating area of the lead frame material is silver-plated, and then a part of the plating area is formed by a secondary processing in a semiconductor. A lead frame forming method for forming a lead frame so as to become a chip mounting portion and a terminal portion and to remove a remaining portion of the plating region, wherein at least the plating region is formed at a corner of the plating region during the primary processing. Forming a reservoir hole for a plating solution that bites into a part of the lead frame. 2. The method for forming a lead frame according to claim 1, wherein the pool holes for the plating solution are formed at all corners of the plating area. 3. The lead frame forming method according to claim 2, wherein the shape of the plating solution reservoir hole is a key shape bent at 90 degrees so as to surround a plating area.