JPH04212443A - Lead frame - Google Patents

Abstract

PURPOSE:To improve the adhesion of raw material and a palladium-plated layer, and prevent the generation of rust, by forming a palladium or its alloy layer formed at the inner lead tip of a lead frame or on the outer lead surface, via a Zn-Sn alloy-plated layer or an Sn-Ni alloy-plated layer. CONSTITUTION:A substratum plated layer 1 composed of Zn-Sn alloy is formed on the whole surface of lead frame raw material 10. A palladium-plated layer 2 is formed on the layer 1 of die pads 11, tips of inner leads 12, and outer leads 14. That is, around the die pads 11, the inner leads are radially arranged, and collectively connected by a tie bar 13. The outer lead 14 is continuously arranged to each inner lead, and tips of the outer leads are retained by side bars 15, 16. It is more preferable that an Ni-plated layer 3 is interposed as the intermediate layer of the Zn-Sn-plated layer 1 and the palladium-plated layer 2 of the above lead frame.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lead frames, and more particularly to improving the reliability of palladium-plated lead frames with high-density lead arrangements.

0002

2. Description of the Related Art Lead frames for semiconductor devices such as ICs and LSIs are manufactured to a thickness of 0.25 mm or 0.15 mm by either photo-etching or press processing.
After shaping a metal strip with a thickness of mm by removing unnecessary parts, it is formed through a plating process in which predetermined parts are plated, a taping process in which tape is attached and the inner leads are fixed between each other, etc. .

Incidentally, in recent years, surface mount technology in which the tips of the outer leads are connected to wiring patterns formed on the surface of the mounting board has become popular. Plating has the advantage that solder adhesion is good, and bonding properties can be improved by applying palladium plating to the bonding area at the tip of the inner lead.

[0004] In addition, it has the advantage of being able to be processed at high temperatures due to its higher melting point than conventional solder plating, and since the palladium plating layer is hard, it has sufficient strength even for thin lead frames. can be given, and is not limited to the base material. However, pinholes are easily formed, and exposed lead frame material can cause rust, etc., so if you want to prevent rust, it must be made thicker. This may cause short circuits, etc. Conventionally, a lead frame material 20 made of an iron-nickel alloy called 42 alloy is coated with a base layer made of a nickel (Ni) layer 21, as shown in the cross-sectional view of FIG. It is covered with a palladium plating layer 22.

[0005]

[Problems to be Solved by the Invention] As described above, with the increasing integration of semiconductor devices, the lead spacing and lead width are becoming smaller and smaller, and improving processing accuracy has become a major issue. Lead frames that have undergone this process have been attracting attention, but when pinholes are formed in the base plating layer, the base of the lead frame is exposed, which causes rust.

[0006] Furthermore, when forming the outer lead,
There is a problem in that cracks are likely to occur at the bent portion.

The present invention was made in view of the above circumstances, and provides a lead frame that has good adhesion between the material and the palladium plating layer, does not cause rust, is easy to manufacture, is highly accurate, and is highly reliable. The purpose is to

[0008]

[Means for Solving the Problems] Therefore, in the first lead frame of the present invention, the palladium (Pd) or palladium alloy plating layer formed on at least the tips of the inner leads or the surfaces of the outer leads of the lead frame is replaced with zinc (Zn). )-tin (Sn) alloy plating or tin (Sn)
)-Nickel (Ni) alloy plating is interposed therebetween.

In the second lead frame of the present invention, an intermediate layer containing nickel as a main component is interposed between the base layer and the palladium plating layer in the first structure.

0010

[Function] According to the above structure, the base layer is formed with extremely good adhesion and has good malleability, so when forming the outer lead, no cracks occur at the bent part. The state of material coverage can be maintained well.

[0011] Furthermore, there is no fear of rust occurring due to exposure of the base material, and it is possible to obtain a lead frame with good solder adhesion and high bonding properties during mounting.

[0012] Furthermore, in order to maintain the position between the inner leads or between the outer leads, the temperature must be raised to 180°C or higher when attaching the insulating tape, but in the case of solder plating, the temperature must rise to 180°C or higher. It tends to melt and flow, causing defects such as short circuits with adjacent leads, but when palladium (Pd) or palladium alloy plating is used, it does not melt and is maintained well even when insulating tape is used. .

Furthermore, according to the second aspect of the present invention, since the intermediate layer containing nickel as a main component is interposed between the base layer and the palladium plating layer, the interlayer between the base layer and the palladium plating layer is The adhesion is further improved.

[0014]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The lead frame of the embodiment of the present invention is shown in FIG.
As shown in the plan view in a) and the A-A cross-sectional view in FIG. 1(b), zinc-tin (
It is characterized by using a 30% Zn-70% Sn alloy.

That is, a base plating layer 1 made of a zinc (Zn)-tin (Sn) alloy is formed on the entire surface of the lead frame material 10, and palladium is further applied to the die pad 11, the tips of the inner leads 12, and the outer leads 14 on this upper layer. A plating layer 2 is formed.

That is, inner leads 12 are arranged radially around the die pad 11 and are integrally connected by tie bars 13, and an outer lead 14 is connected to each inner lead. is supported. Here, 17 is a support bar.

Next, a method of manufacturing this lead frame will be explained.

First, a metal strip 10 referred to as an alloy 42 is placed in a progressive die and press-worked to pattern the inner leads 12, outer leads 14, etc. in desired shapes.

Subsequently, a zinc-tin plating layer 1 with a thickness of 1 μm and a palladium plating layer 2 with a thickness of 0.1 μm are formed.

[0021] Then, if necessary, the pinhole is filled with an antioxidant. For example, after soaking in an antioxidant,
The antioxidant outside the pinhole area is peeled off and the antioxidant is filled only into the pinhole area made of the nickel plating layer.

The lead frame formed in this way connects the semiconductor chip on the die pad 11, undergoes a wire bonding process and is sealed with resin, and then the side bar 1 is sealed.
5 and 16, bend the outer leads for surface mounting, position them on the wiring pattern of the mounting board, and fix by heating the mounting board side.

According to this lead frame, the zinc-tin base layer is formed with extremely good adhesion even when bent when forming the outer lead, and has good malleability.
Cracks do not occur, and the state of covering the material can be maintained in good condition. In addition, since the base layer is formed with good adhesion, the palladium plating layer can be formed thinner, and even higher density can be achieved.

Furthermore, there is no fear of rust occurring due to exposure of the base material, and it is possible to obtain a lead frame with good solder adhesion and high bonding properties during mounting.

Furthermore, since the lead frame formed in this manner is reinforced with hard palladium plating, the starting material for the pressing process can be made thinner, thereby obtaining a lead frame with less distortion. be able to. Therefore, it is possible to obtain a lead frame that is less deformed even after the subsequent heating step.

[0026] In this way, even a semiconductor device in which outer leads are formed at high density can be mounted extremely easily and reliably.

[0027] In the above embodiment, a case was explained in which a zinc-tin plating layer with a zinc:tin ratio of 3:7 was used as the base layer, but this component ratio can be changed as appropriate, and other It may also contain tin (Sn).
- Similar effects can be obtained by using a nickel (Ni) alloy layer.

[0028] Furthermore, an intermediate layer may be formed between the base layer and the palladium plating layer. This example will be explained.

The lead frame of the second embodiment of the present invention has a zinc-tin plating layer 1 and a palladium plating layer 2 of the lead frame of the first embodiment, as shown in a sectional view of the main part in FIG.
It is characterized in that a nickel plating layer 3 is interposed as an intermediate layer between the two. The other parts are formed exactly the same as the lead frame of the first embodiment. According to this lead frame, since the nickel plating layer 3 is interposed between the zinc-tin plating layer 1 which is the base layer and the palladium plating layer 2 which is the surface layer, the nickel plating layer 3 is interposed between the base layer and the palladium plating layer. The adhesion is further improved.

In the above embodiment, a nickel layer was used as the intermediate layer, but any layer containing nickel as a main component may be used.

Further, another layer may be interposed between the metal strip 10 and the base layer, and when the material is 42 alloy (iron-nickel alloy) as in the above embodiment, a copper plating layer may be interposed between the metal strip 10 and the base layer. By interposing it, the adhesion is further improved.

In the above embodiment, an antioxidant was applied after the palladium plating process, but after the zinc-tin plating process and before the palladium plating process, the area other than the pinhole area was dipped in the antioxidant to prevent oxidation in areas other than the pinhole area. Alternatively, the antioxidant may be peeled off and removed, the antioxidant may be filled only into the pinhole region formed by the nickel plating layer, and then the palladium plating layer may be formed.

Furthermore, the plating area is not limited to the examples and can be changed as appropriate, and the entire surface of the material may be covered with a plating layer.

In addition, the lead frame material is not limited to the alloy 42, and other materials such as copper may be used.

[0035]

As described above, according to the present invention, when coating at least the inner lead or outer lead surface of a lead frame with a palladium (Pd) or palladium alloy plating layer, zinc-tin is used as a base layer. Since the alloy or tin-nickel alloy layer is interposed, it is possible to provide a highly reliable lead frame without peeling during bending or rusting.

[Brief explanation of the drawing]

[Fig. 1] A diagram showing a lead frame according to an embodiment of the present invention.

[Figure 2
]A diagram showing the main parts of a lead frame according to a second embodiment of the present invention.

[Figure 3] Cross-sectional view of a conventional lead frame

[Explanation of symbols]

1 Zinc-tin alloy layer 2 Palladium plating layer 3 Nickel layer 10 Lead frame material 11 Die pad, 12 Inner lead 13 Tie bar 14 Outer lead 15 Sidebar, 16 Sidebar, 17 Support bar 20 Lead frame material 21 Nickel plating layer 22 Palladium plating layer

Claims (2)

[Claims] 1. A lead frame comprising a plurality of outer leads and a plurality of inner leads connected to the outer leads and extending toward the vicinity of a semiconductor element mounting portion, wherein at least the tip of the inner lead or the surface of the outer lead is , a base layer made of zinc (Zn)-tin (Sn) alloy plating or tin (Sn)-nickel (Ni) alloy plating, and a palladium (Pd) or palladium alloy plating layer formed on the base layer. A lead frame characterized by being coated. 2. A lead frame comprising a plurality of outer leads and a plurality of inner leads connected to the outer leads and extending toward the vicinity of a semiconductor element mounting portion, wherein at least the tip of the inner lead or the surface of the outer lead is , a base layer made of zinc (Zn)-tin (Sn) alloy plating or tin (Sn)-nickel (Ni) alloy plating, and an intermediate layer mainly composed of nickel formed on the base layer; A lead frame characterized by being coated with a palladium (Pd) or palladium alloy plating layer formed on the intermediate layer.