JPS63168043A - Lead frame - Google Patents

Abstract

PURPOSE:To obtain a sufficient solderability by a method wherein a flash silver-plating is applied to outer lead parts and silver is thinly deposited. CONSTITUTION:A lead frame 10 is made as a copper or copper alloy material and a flash silver-plated film is formed on the outer lead parts 12 thereof. The thickness of this film is limited to 0.1mum or thereabouts and the film is formed by electroplating or displacement plating. A base copper-plating is applied to the surface of the material and by depositing a flash silver-plating on this copper-plating, the surface blemish of the copper family material is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lead frame. It's about frames.

(Prior Art) In order to connect a semiconductor device to an external member such as a circuit board, the outer lead portion of its lead frame is usually soldered.

By the way, the material of the lead frame is 4270I (iron).
Iron-based materials such as nickel alloy), copper-based materials such as copper or copper alloys, etc. are generally used.

When a lead frame undergoes @hysteresis during various assembly processes such as the semiconductor element fixing process, an oxide film may be formed on the outer lead, but in the case of copper-based materials, this can be removed to a large extent even with acid treatment. It is.

Therefore, conventionally, when the material is copper-based,
Normally, the outer lead part is not subjected to any treatment (copper plating may be applied as a base for partial plating of other parts), and the material is exposed as it is, and the oxide film that forms is removed by acid treatment, etc. After removal and necessary solder plating, solder dipping, etc., soldering was performed. Conventionally,
With this level of processing, the soldering properties required for practical use were almost ensured, and there were no particular problems.

(Problems to be Solved by the Invention) However, in recent years, the layers of semiconductor devices have become smaller, lead frames have become more pin-increased, and lead widths have become narrower. Good soldering properties are required, but a problem has arisen in that sufficient soldering properties cannot be obtained.

In other words, the oxide film formed on the copper-based material is CuO1Cu.
These black films such as 2C3 increase in thickness with heating time and heating temperature, resulting in a situation where they cannot be completely removed even with acid treatment. Good soldering properties that can sufficiently meet the high reliability required by the industry have not been achieved.

Therefore, an object of the present invention is to provide a lead frame that provides sufficient solderability to meet the above-mentioned needs.

(Summary of the Invention) The lead frame according to the present invention for the above-mentioned purpose is a lead frame made of copper or a copper alloy, in which flash silver plating is applied to at least the outer lead portion by electroplating or displacement plating to thinly coat silver. It is characterized by being formed by precipitation.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is an explanatory diagram of the lead frame 10.

12 is an outer lead part, 14 is an inner lead part, 1
6 is a stage on which a semiconductor element (not shown) is mounted, and a rail portion 20 .
I am contacting 20.

22 is a dam bar.

The lead frame 10 is made of copper or a copper alloy, and pattern formation is performed by pressing or etching.

A feature of the present invention is that a flash silver plating film is formed on at least the outer lead portion 12 of the lead frame 10.

Of course, the flash silver plating film is lead frame 10.
You can also go to the entire surface.

Here, the flash silver plating film refers to an extremely thin silver film that shows the reddish tint of the underlying copper material, and has a thickness of 0.2 μm or less, preferably about 0.1 μm.

To form a flash silver plating film, either electroplating or displacement plating may be used, as described below. In order to eliminate surface defects of the copper-based material, it is preferable to apply a base copper plating to the surface of the material and deposit flash silver plating on the copper plating.

In the present invention, a flash silver plating film is thus formed on at least the outer lead portion 12, but since this flash silver plating film is extremely thin, a small amount of copper oxide film is still formed. However, the formation of this oxide film is extremely slow because the copper surface is protected by a flash silver plating film, and even if it is formed, it is extremely thin and can be easily removed by acid treatment or the like. Thus, the outer lead portion 12 can be suitably soldered.

When soldering, the flash silver plating film should be
It diffuses into the copper-based material due to thermal history caused by various assembly processes such as the semiconductor element fixing process, but it is necessary to remove the copper oxide film formed due to this thermal history during soldering. Note that if silver remains without being completely diffused and impairs solder adhesion, it is preferable to remove the silver by immersing it in a silver stripping solution.

Note that in order to improve soldering properties, it is preferable that the silver film formed on the outer lead portion 12 be thicker.

However, in this case, since silver is expensive, the cost increases accordingly, and if the solder coating is done by a dip method in which the outer lead portion is immersed in a solder bath, the outer lead portion
Since part of the silver is exposed at the two bases, there is a problem that it causes a so-called migration phenomenon.

In addition, if the silver film has an intermediate thickness of 0.2 μm or more, when removing the copper oxide film that also occurs, the silver film may remain floating in some flakes, and vice versa. Soldering inhibits sex. The silver film can be removed with a stripper, but
Peeling takes a long time, resulting in poor workability.

As mentioned above, the flash silver plating film can be formed by electroplating or displacement plating, but when partially electroplating silver on the inner lead portion 14 and stage 16, the procedure for forming the film poses some problems.

That is, if a flash silver plating film is applied to the lead frame sample before selective silver electroplating,
The flash silver plating film can be formed by either electroplating or displacement plating.

In this case, if displacement plating is performed, partial silver plating will be placed on the displacement film with poor adhesion, so it is not very preferable, but since the displacement film is thin, silver partial electroplating will take its place. Adhesion is not so much of a problem.

On the other hand, if partial electroplating of silver is first formed and then a flash silver plating film is formed thereon, the flash silver plating film may be formed by either displacement plating or electroplating, but displacement plating is preferable. .

In other words, in the case of displacement plating, there is no problem because a flash silver plating film with poor adhesion does not precipitate on the partial electroplating of silver, but in the case of electroplating,
Since a thin flash silver plating film is placed on the partial silver plating, the surface of the partial silver plating changes and affects the fixing of the semiconductor element on the stage 16 and the wire bonding to the inner lead 14, which is not preferable. , hula
7) If the thickness of the silver plating is thin, this will not be a problem.

Recently, in order to reduce costs, the stages and inner lead tips are sometimes used as lead frames without partial plating and are made of copper or copper alloy. Of course, the present invention in which a flash silver plating film is formed on the lead portion can be applied.

Example 1 KAg (CN) 2
Log/I! CN 10g/l
The lead frame was immersed in the above solution for 10 seconds to deposit about 0.1 μm of flash silver over the entire surface of the lead frame.

Flash silver deposition was performed on the samples before and after partial silver plating to obtain each sample.

Example 2 KAg (CN) 2 20g/IKCN
IA/drrf, flash silver plating for 5 seconds was applied to the entire surface of the lead frame using the above plating solution at 50 g/Il, and then necessary partial plating was performed to obtain a sample.

When the three types of lead frame samples obtained in Example 1.2 above and a normal lead frame whose outer lead portion was not subjected to any treatment were heated at 200°C to 400°C, the samples obtained in Example 1.2 were heated. It was confirmed that the generation of oxide film was suppressed in the sample. In addition, the oxide film and flash silver plating film of the same sample could be easily removed, and extremely good soldering properties were obtained.

(Effects of the Invention) As described above, according to the lead frame of the present invention, the formation of an oxide film on the outer lead portion is suppressed, and
The resulting oxide film and flash silver plating film can be easily removed, and extremely good soldering properties are achieved.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a lead frame. DESCRIPTION OF SYMBOLS 10... Lead frame, 12... Outer lead part, 14... Inner lead part, 16...
Stage, 18...Stage support bar, 20
...Rail part, 22...Dam bar.

Claims (1)

[Claims] 1. A lead frame made of copper or a copper alloy, in which at least the outer lead portion is flash silver plated by electroplating or displacement plating to deposit a thin layer of silver. 2. The lead frame according to claim 1, wherein the thickness of the flash silver plating is 0.1 μm or less.