JPS6024045A - Semiconductor lead frame - Google Patents

Abstract

PURPOSE:To improve the property of adhesion between an oxide film provided on the surface of a material for the titled lead frame by a method wherein the surface of the material made of copper or copper alloy is provided with a Cu-Sn series alloy plated layer containing 10-15wt% of Sn, and further an Ag plated layer is formed on the lead frame at least at the part for mounting a semiconductor pellet. CONSTITUTION:After the surface of the lead frame 1 made of Cu or Cu alloy is pre-treated by degreasing and pickling, the plated film 2 of approx. 0.2mum thickness is adhered by dipping in a plating bath of Cu-Sn alloy composed of Cu cyanide, soda stannate, and Na cyanide and containing 10-15wt% of Sn. Further, the Ag plated layers 3 of about 5mum thickness are adhered to a tab part 5 to which an Si pellet is brazed and inner leads 6 to which copper wires are bonded. In such a manner, the frame sealing property at the time of resin sealing is improved by the improvement of the adhesion property of film in the formation of the oxide film on the surface by heating in the air.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead frame constituting a semiconductor device.

Iron-based Kovar is used as a lead frame/material for semiconductors.
42 alloy, copper-based Cu-3n, Cu-Fe, and other alloys are used. Copper-based materials are inferior to iron-based materials in terms of strength and coefficient of thermal expansion, but are superior to iron-based materials in terms of heat dissipation and electrical conductivity. In recent years, new copper alloys with improved strength and coefficient of thermal expansion have been developed, and the proportion of copper alloys used in lead frame materials is increasing from the perspective of cost reduction.

Incidentally, in addition to physical and mechanical properties, important characteristics of lead frame bonding include plating performance during semiconductor assembly, solder tropism, and adhesion with plastic resin.

In other words, when assembling a semiconductor device, Si elements are soldered to lead frames, and wire bonding is
Since the process is carried out by heating to a temperature above .degree. C., there is a problem that an oxide film is formed on the copper alloy frame and the adhesion with the plastic resin is reduced. In particular, when partially plating Ag on a copper-based frame, use A to improve the adhesion of Ag.
Before G plating, a thin <Cu plating layer is applied, but when this Cu plating layer is heated in an oxidizing atmosphere (for example, the atmosphere), it forms a thick and brittle oxide film, and the oxide film formed in this way forms a thick and brittle oxide film. has poor adhesion to the material, causing a significant drop in moisture resistance of plastic-sealed semiconductor devices.

Therefore, an object of the present invention is to provide a new lead frame for semiconductors which can overcome the drawbacks of the prior art described above and can significantly improve the resin sealability of a copper-based alloy lead frame.

That is, the gist of the present invention is that Cu containing 10 to 50% by weight of Sn is formed on six sides of a copper lead frame.
- Provide an 8n alloy plating layer, and further provide Ag on at least the portion of the lead frame material where the semiconductor pellet is attached.
This is because a plating layer is provided. Here, the Cu-3n alloy means an alloy mainly composed of Cu and Sn.
In addition to Sn, In and Bi.

Needless to say, it also includes composites made of metals such as Sb and Zn.

In the above Cu-8n alloy, the Sn content is 10 to 5.
The reason for limiting Sn to 0% by weight is that if Sn is less than 10% by weight, the adhesion with the plastic resin will deteriorate;
This is because if the amount exceeds 1, the melting point of the alloy decreases, and therefore the adhesion to Ag deteriorates.

Hereinafter, the present invention will be specifically described by way of examples together with illustrated drawings.

Embodiment l FIG. 1 is a plan view showing an embodiment of a semiconductor lead frame according to the present invention. 1. After pre-treating the surface of the lead frame made of copper alloy by degreasing and pickling, Cu-
A plating film 2j of 0.2μ is provided in an 8μ alloy plating bath (composed of copper anhydride, sodium stannate, and sodium cyanide), and the tab portion 5 to which the Si element is soldered and the Au
A 5 μm Ag plating layer 3 is provided on the inner saw 14 portion 61 to which wire bonding is to be performed to form a semiconductor lead frame (see FIG. 2).

As a comparative example, the surface of the lead frame made of the steel alloy shown in Fig. 1 was pretreated by degreasing and pickling, and then treated with a Cu strike bath (composed of oxidized steel, sodium cyanide, and Rochelle salt) for 0.0%. A 2μ thick Cu plating layer 4 is provided, and a 5μ thick Ag layer is provided on the tab portion 5 and the inner girder 1 portion 6.
A plating layer 3 is provided to form a conventional semiconductor phase lead frame (see FIG. 3).

The lead frame thus formed is subjected to thermal oxidation at 4400°C in the atmosphere, simulating the heating process that occurs in Si pellet soldering and Au wire wire bonding, and then an oxide film is formed on the lead frame surface. The adhesion was evaluated by applying an adhesive tape such as cellophane tape to the bedded surface and examining whether or not the oxide film adhered to the adhesive tape side when it was peeled off. The result is the first
Shown in the table. In the table, the ◯ mark indicates that no oxide film was attached, the Δ mark indicates that the oxide film was locally attached, and the x mark indicates that most of the oxide film was attached.

Table 1 Example 2 Semiconductor lead frame in which a plating film of Cu-8μ alloy with a different composition was provided on the surface of a lead frame made of copper alloy in the same manner as in Example 1, and then Ag plating was partially provided. form.

The adhesion of the oxide film of the -P frame thus prepared was examined in the same manner as in Example 1.

The results are shown in Table 2. In the table, ○, △, and x marks are as described above.

As mentioned above, the semiconductor RI-R frame according to the present invention has the following advantages compared to the conventional Cu strike plating one:
The oxide film formed on the surface by heating in the atmosphere has good adhesion, so when a semiconductor is sealed with plastic resin, the sealing between the resin and the lead frame is perfect. As a result, the temperature resistance of semiconductor devices is improved1-
1 The reliability of the product increases.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing an embodiment of a semiconductor lead frame according to the present invention, Fig. 2 is a sectional view taken along line A-A in Fig. 1, and Fig. 3 is a plan view of a conventional semiconductor lead frame. It is a sectional view showing an example. l...Copper or copper alloy lead frame 2...C
U-3N alloy plating film 3...Ag plating layer 4...Cu plating layer 5...Tab portion 6...Inner lead capital 7...Outer lead portion Rhinoceros 1

Claims (1)

[Claims] A copper-tin alloy plating layer containing 10 to 50% by weight of tin is provided on the surface of a semiconductor lead frame material made of copper or a copper alloy, and further on a portion of the lead frame material where at least the semiconductor R-let can be accessed. A semiconductor lead frame characterized by having a silver plating layer.