JPH11135701A - Lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain corrosion resistance that is more superior that conventional one by a coating of a PdNi alloy that is thinner than the conventional, in a lead frame of an IC package or the like. SOLUTION: When the thickness of one electroplated layer of a palladium- nickel alloy is set to 0.02 μm or more and a plurality of the electroplated layers are laminated on the surface of a lead frame, pin holes a lower layer (base material side) is covered with an upper layer, pin holes of the upper layer is obstructed by the lower layer even when the pin holes are generated on the upper layer, thus preventing the pin holes of the upper layer from reaching the base material. More specifically, since almost no pin holes occar that reach base material from a surface layer by laminating the electroplated layer, corrosion resistance is very much improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a lead frame, and more particularly, to a film treatment of a surface thereof.

[0002]

2. Description of the Related Art A package such as an IC has been mounted on a printed circuit board or the like via a lead frame extending from the inside of the package to the outside. 42% for lead frame
Fe-Ni-based alloys containing about nickel have been used. In addition, metal (or alloy) is used on the surface of the lead frame for the purpose of improving the bonding property during wire bonding and the soldering property during mounting.
Film was provided.

[0003]

Among such films, a palladium-nickel alloy (hereinafter also referred to as a PdNi alloy) is effective in improving the corrosion resistance of the lead frame.
Palladium is cheaper than gold, for example, but higher than silver, and is required to have high corrosion resistance with as little as possible.

However, if the thickness of the PdNi alloy film is less than 0.3 μm, the number of pinholes increases and the corrosion resistance is reduced, so that it is difficult to further reduce the film thickness, that is, to reduce the amount of palladium used. In addition, by forming a base layer of palladium or its alloy by electroless plating and forming a surface layer of palladium or its alloy by electroplating thereon, it is possible to prevent the cracks of the surface layer from reaching the substrate. There is a technique (Japanese Patent Application Laid-Open No. 9-45135), but it is still insufficient in terms of thinning the film.

An object of the present invention is to provide a lead frame with a thinner coating of a PdNi alloy than in the prior art to obtain more corrosion resistance than in the past.

[0006]

According to a first aspect of the present invention, there is provided a lead frame, comprising: a palladium-nickel-based alloy electroplating layer on a surface of the lead frame;
It is characterized in that a plurality of layers are stacked with the thickness of one layer being 0.02 μm or more.

According to a second aspect of the present invention, there is provided the lead frame according to the first aspect, wherein the lower the electroplating layer, the lower the content of palladium.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the lead frame according to the present invention, a plurality of electroplating layers of a palladium-nickel alloy are laminated on the surface of the lead frame with one layer having a thickness of 0.02 μm or more. As schematically shown in FIG. 1, the upper layer covers the pinhole of the lower layer (substrate side),
Even if a pinhole is formed in the upper layer, the lower layer blocks the lower layer, so that the pinhole in the upper layer does not reach the substrate. That is,
By laminating the electroplating layer, there is almost no pinhole reaching from the surface layer to the substrate, so that the corrosion resistance is extremely high.

[0009] The composition of the PdNi alloy is 9% by Pd content.
0% (90Pd20Ni) to 20% (20Pd80N)
The range of i) is preferable. This is because the Pd content is 90%.
%, The difference in raw material cost from the case of using pure Pd becomes small and the merit of using the alloy becomes insufficient. If the Pd content is less than 20%, the corrosion resistance may be slightly inferior. That's why.

[0010] The minimum number of layers of the PdNi alloy electroplating layer is two, but in the case of two layers, the lower pinhole and the upper pinhole overlap (a pinhole reaching from the upper layer to the base is formed). There is a slight possibility. However, if this is made into three layers, it can be said that there is almost no possibility of forming a pinhole extending from the uppermost layer to the base. Also, cost performance is not so good even with four or more layers. Therefore, the number of layers of the PdNi alloy electroplating layer is preferably at least two, and more preferably three.

The reason why the thickness of one electroplating layer of the PdNi alloy is set to 0.02 μm or more is that if the thickness is less than 0.02 μm, the number of pinholes increases, and pinholes may remain even with the effect of the above-described lamination. It is. Therefore, in order to reliably prevent pinholes, it is desirable that the thickness of one layer be 0.05 μm or more. Also, as the thickness of one layer increases, the corrosion resistance improves,
Since this deviates from the purpose of thinning the film, the thickness needs to be within a range that does not impair this purpose. Although the upper limit of the thickness of this one layer varies depending on the number of layers to be laminated, it is 0.2 μm.
m or less. That is, the thickness of one of the PdNi alloy electroplating layers is 0.05 μm to 0.2 μm.
The range of m is preferred.

The higher the Pd content, the higher the corrosion resistance of the PdNi alloy, but the higher the spontaneous potential. Therefore, in the lead frame according to the second aspect, the lower the electroplating layer, the lower the content of palladium. By doing so, the corrosion resistance becomes higher as the upper layer is formed. In addition, since the natural potential of the film is gradually reduced from the upper layer to the lower layer, the natural potential difference between the layers and the natural potential difference between the lowermost layer and the substrate become smaller, so that the formation of the local battery can be eased. Therefore, claim 2
With this configuration, the occurrence of corrosion can be further suppressed, and the corrosion resistance of the lead frame can be further improved.

[0013]

Example: 80% Pd, 65% Pd and 50% Fe-Ni alloy (42% Ni) lead frame (material)
Pd-Ni-based alloy of Pd (PNP-
80, PNP-65, PNP-50) as plating materials,
Under the conditions shown in Table 1 below, multilayer electroplating was performed as shown in Table 2 to obtain evaluation samples. Each evaluation sample was sprayed with a 5% aqueous sodium chloride solution, and left in a thermostat at 35 ° C. for 24 hours. The occurrence of corrosion was evaluated.

[0014]

[Table 1]

[0015]

[Table 2]

As is evident from Table 2, Examples 1, 2, and 3, which are within the scope of the present invention, in which a plurality of Pd--Ni-based alloy plating layers are laminated, have excellent corrosion resistance. On the other hand, Pd-
Comparative Example 1 in which one layer of a Ni-based alloy was plated and Comparative Example 2 in which two layers of Pd were plated were inferior in corrosion resistance. From this, the effect of the present invention can be confirmed.

The present invention is not limited to these embodiments, and it goes without saying that various embodiments can be made without departing from the scope of the present invention.

[0018]

As described above, according to the present invention,
By laminating a plurality of electroplating layers of a palladium-nickel alloy on the surface of the lead frame with one layer having a thickness of 0.02 μm or more, a palladium thinner than the conventional one is obtained.
The nickel-based alloy film can provide higher corrosion resistance than before.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating the structure of a plating layer of a lead frame according to the present invention.

Claims (2)

[Claims] An electroplating layer made of a palladium-nickel alloy is formed on the surface of a lead frame to a thickness of 0.02.
A lead frame comprising a plurality of layers each having a thickness of at least μm. 2. The lead frame according to claim 1, wherein the lower the electroplating layer, the lower the content of palladium.