JPH0536878A - Lead frame for semiconductor package - Google Patents

Abstract

(57) [Summary] [Object] To provide a lead frame for a semiconductor package capable of preventing stress corrosion cracking of a lead frame made of a zinc-copper alloy. In a lead frame for a semiconductor package obtained by press working, a main metal layer forming the lead frame is made of a zinc (Zn) -copper (Cu) alloy, and a surface layer forming a surface of the lead frame is It is characterized by being composed of palladium (Pd) metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor package lead frame, and more particularly to a semiconductor package lead frame obtained by press working.

[0002]

2. Description of the Related Art Lead frames for semiconductor packages are
Conventionally, it is formed by pressing. At this time,
As the metal plate to be pressed, a metal plate made of a metal having high ductility such as a copper alloy of 99.9% copper (Cu) and 0.1% zirconium (Zr) is used.

[0003]

The lead frame made of such a copper alloy having a high ductility is capable of exhibiting good thermal conductivity in which stress corrosion cracking is unlikely to occur. However, when a lead frame is formed by pressing a metal plate made of a metal having a high ductility, burrs and / or twists are easily generated in the lead frame obtained due to the high ductility and punching resistance of the metal plate, Since the frequency of polishing the die used for press working increases, the life of the die also shortens.

Further, recently, as the number of pins has been increased and the size of semiconductor devices has been reduced due to higher integration of semiconductor chips, finer leads and higher lead formation density have been achieved in lead frames. It's being done. On the other hand, in a lead frame in which burrs and / or twists of the leads are likely to exist, such as a lead frame obtained by pressing a metal plate having high ductility in the related art, a short circuit occurs due to the twists of the burrs and / or the leads. Or, it may be difficult to bond the semiconductor chip to be mounted. Therefore, such a lead frame cannot sufficiently deal with finer leads and higher lead formation density.

The inventors of the present invention compare the metal sheet with high ductility that has been conventionally used in order to reduce the burrs and the twisting of the lead that occur in the obtained lead frame by improving the press workability. Then, press working was performed using a metal plate made of a zinc-copper alloy known as a copper alloy having a good punching breakability. The lead frame obtained had less burrs and twisting of the lead than conventional lead frames, but it has the drawback of being susceptible to stress corrosion cracking, so it can be used as is as a lead frame for semiconductor packages. It turned out to be impossible. However, a lead frame made of a zinc-copper alloy can sufficiently cope with finer leads and higher lead forming density if the stress corrosion cracking can be prevented.

Therefore, an object of the present invention is to provide a lead frame for a semiconductor package which can prevent stress corrosion cracking of a lead frame made of a zinc-copper alloy.

[0007]

Means for Solving the Problems As a result of repeated studies to achieve the above object, the inventors of the present invention prevent stress corrosion cracking by applying palladium (Pd) plating to a lead frame made of a zinc-copper alloy. They have found what they can do and have reached the present invention. That is, in the present invention, in a lead frame for a semiconductor package obtained by press working, the main metal layer forming the lead frame is zinc (Zn) -copper (C
u) A lead frame for a semiconductor package, characterized in that it is made of an alloy and a surface layer forming a surface of the lead frame is made of palladium (Pd) metal. In the present invention having such a constitution, the lead obtained by press working is that the zinc (Zn) / copper (Cu) ratio of the zinc (Zn) -copper (Cu) alloy is 10/90 to 40/60. Burrs in the frame and twisting of the leads can be further reduced. In addition, the thickness of the surface layer made of palladium (Pd) metal being 0.05 μm or more enables bonding with the semiconductor chip directly to the palladium layer without forming a new bonding metal layer. Further, between the main metal layer and the surface layer, nickel (Ni), cobalt (C
The formation of o) or the intermediate layer made of these alloys can suppress the diffusion of the copper metal forming the main metal layer.

[0008]

According to the present invention, zinc (Z
Since the lead frame body can be formed by pressing a metal plate made of n) -copper (Cu) alloy (hereinafter sometimes referred to as zinc / copper alloy), burrs and twisting of the lead occur in the resulting lead frame. Can be extremely reduced. Moreover,
The stress corrosion cracking of the lead frame obtained by pressing a zinc / copper alloy metal plate can be prevented by covering the surface of the lead frame with a palladium metal layer.
Therefore, a lead frame made of a zinc / copper alloy, which has hitherto been unsuitable for a semiconductor package because stress corrosion cracking easily occurs, can now be adopted as a lead frame for a semiconductor package. As a result, it is possible to provide a lead frame with less burrs and twisting of the leads, and elimination of stress corrosion cracking, etc., and it is sufficiently compatible with finer leads and higher lead formation density accompanying the increase in the number of pins in semiconductor devices. can do.

[0009]

According to the present invention, in a lead frame for a semiconductor package obtained by press working, the main metal layer forming the lead frame is zinc (Zn) -copper (C
u) It is important to consist of an alloy. Since the lead frame is mainly formed of the zinc / copper alloy in this way, a zinc / copper alloy metal plate having good press workability is pressed to obtain a lead frame with less burrs and / or twisting of the leads. You can do it. The zinc / copper alloy metal plate has a zinc / copper ratio of 10/90 to
It is preferably 40/60 because the press workability and the mechanical properties of the lead frame obtained can be improved. Here, when a metal plate having a zinc / copper ratio of less than 10/90 is used (when the copper ratio exceeds 90), the effect of improving press workability tends to be reduced.
Further, when a metal plate having a zinc / copper ratio of more than 40/60 is used (when the copper ratio is less than 60), the lead frame obtained tends to be brittle.

In the present invention, mainly zinc (Zn) -copper
(Cu) alloy lead frame surface layer is palladium
It is important that it is formed of (Pd) metal. Thus, by covering the surface of the lead frame with the palladium metal layer, it is possible to prevent the stress corrosion cracking peculiar to the lead frame obtained by pressing the zinc / copper alloy metal plate. When the thickness of the palladium metal layer is set to 0.05 μm or more, stress corrosion cracking of the lead frame can be prevented, and the palladium metal layer can be directly wire-bonded to the palladium metal layer without partially forming a metal layer such as silver. Can be applied. The upper limit of the thickness of the palladium metal layer is not particularly limited, but the effect reaches saturation even when the palladium metal layer having a thickness of more than 1 μm is formed. Therefore, it is preferable from the viewpoint of processing cost and material cost that the palladium metal layer has a thickness of 1 μm or less, particularly 0.5 μm or less.

Since the lead frame of the present invention is mainly formed of a zinc / copper alloy, when diffusion of copper is concerned, a nickel (nickel) layer is formed between the zinc / copper alloy metal layer and the palladium metal layer. The diffusion of copper can be prevented by forming an intermediate layer made of Ni), cobalt (Co), or an alloy thereof. The thickness of the intermediate layer is also preferably a thin layer of 1 μm or less. The palladium metal layer and the intermediate layer described so far can be formed by plating, and these platings can be performed by subjecting a lead frame obtained by press working with a commercially available plating solution to electroplating. it can.

[0012]

EXAMPLES The present invention will be described in more detail with reference to Examples. Example 1 A CDA220 alloy plate (N / C ratio of 10/90 (N
0.1), a CDA260 alloy plate (N0.2) having a zinc / copper ratio of 30/70, and a zirconium / copper ratio of 0.1 / 99.9 which has been used for a conventional lead frame.
Using each of the CDA151 alloy plates (N0.3) of No. 3, a lead frame having the same shape was formed by press working.
The physical properties of each metal plate are shown below. Tensile strength (Kg / mm ² ) Elongation (%) CDA220 alloy plate (NO.1) 39 3.5 CDA260 alloy plate (NO.2) 43 4.5 CDA151 alloy plate (NO.3) 48 12.0 Obtained The maximum height of the burr generated on the lead frame and the twist angle of the lead were measured with the passage of processing, and the results are shown in Table 1.

[0013]

[Table 1]

As is clear from Table 1, NO. 2 using a zinc / copper alloy metal plate. 1 and NO. No. 2 using a metal plate of zirconium / copper alloy that has been used for conventional lead frames. As compared with No. 3 (Comparative Example), it is possible to obtain a lead frame with less burrs and twisting of the leads due to press working. Further, the life of the mold can be extended as compared with the conventional one.

Example 2 No. 1 obtained when processing 5 × 10 ⁵ pieces of Example 1. 1 and NO. No. 2 lead frame has a thickness of 0.
A lead frame subjected to a surface treatment for forming a palladium metal layer having a thickness of 076 μm or 0.25 μm, and a nickel layer having a thickness of 0.50 μm formed by plating, and then a surface treatment for forming a palladium metal layer having a thickness of 0.076 μm The following corrosion resistance test and stress corrosion cracking test were performed on the lead frame subjected to the test, and the results are shown in Table 2. (1) Corrosion resistance test 5% NaCl salt water was sprayed onto the lead frame in an atmosphere where the atmospheric temperature was kept at 35 ° C, and the presence or absence of corrosion was examined 48 hours later. (2) Stress corrosion cracking test (according to JIS C-8306) 2 leadframes in an atmosphere containing ₃ vol% NH _3.
It was left for 0 days and examined for the presence of stress corrosion cracking. As a comparative example, N of Example 1 obtained by press working
O. The above-mentioned test was conducted without applying any surface treatment to the lead frames 1 to 3. The results are also shown in Table 2.

[0016]

[Table 2]

As is clear from Table 2, even in a lead frame made of a zinc / copper alloy, a stress corrosion cracking peculiar to the lead frame made of the zinc / copper alloy is obtained by performing a surface treatment for forming a palladium metal layer on the surface. The corrosion resistance can be eliminated and the corrosion resistance can be improved.

Example 3 Example 2 in which a surface treatment for forming a palladium metal layer was performed
The wire bonding property of the lead frame of No. 1 was investigated, and the results are shown in Table 3. The wire bondability was represented by the load at the time of peeling the wire after conducting a wire pull test after heating the wire bonded lead frame at 150 ° C. for 168 hours. The larger the load, the better the wire bondability, and the one having a tensile strength of 5 g or more is acceptable. Conventionally, a silver (Ag) layer is formed on the lead frame to improve the wire bondability, but the wire bondability of a lead frame formed by plating a silver layer with a thickness of 3.81 μm is also shown in Table 3 for reference. It is also shown.

[0019]

[Table 3]

As is clear from Table 3, the palladium metal layer can exhibit wire bondability comparable to that of the silver layer.

Example 4 In Example 2, NO. 3 having a 0.076 μm-thick palladium metal layer as a surface layer was used. 1 and NO. The solderability to the lead frame of No. 2 was investigated. Regarding the solderability, the lead frame was immersed for 5 seconds in a solder bath (without flux) which was melted and kept at 235 ° C., and the wettability with respect to solder was visually determined. At that time, soldering was performed on the level of the lead frame being heated at 315 ° C. for 30 seconds and then immersed in the solder bath, the level of being heated at 315 ° C. for 60 seconds and then immersed in the solder bath, and the level of being immersed in the solder bath without heating. The sex was investigated. Thickness 0.076 μm
With the palladium metal layer of NO. 1 and NO.
It was found that the lead frames of No. 2 had good solder wettability and solderability at any level.

[0022]

According to the present invention, a lead frame having less burrs and / or twisting of leads and stress corrosion cracking can be obtained by press working, which leads to finer leads and higher lead formation density. Since it is possible, high integration of the semiconductor chip and miniaturization of the semiconductor device can be achieved.

Claims (4)

[Claims] 1. A lead frame for a semiconductor package obtained by press working, wherein a main metal layer forming the lead frame is made of a zinc (Zn) -copper (Cu) alloy, and a surface forming a surface of the lead frame. A lead frame for a semiconductor package, wherein the layer is made of palladium (Pd) metal. 2. A zinc (Zn) -copper (Cu) alloy zinc (Zn) / copper (C
u) The lead frame for a semiconductor package according to claim 1, wherein the ratio is 10/90 to 40/60. 3. The lead frame for a semiconductor package according to claim 1, wherein the surface layer made of palladium (Pd) metal has a thickness of 0.05 μm or more. 4. The lead frame for a semiconductor package according to claim 1, wherein an intermediate layer made of nickel (Ni), cobalt (Co), or an alloy thereof is formed between the main metal layer and the surface layer.