JPH04184969A - Material for semiconductor device lead frame use and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a highly reliable and low-cost material for semiconductor device lead frame use by a method wherein a Cu-plated layer and an Ag-plated layer, which respectively have a specified thickness, are provided in order on the surface of a copper alloy parent material and a layer obtainable by diffusing the Ag-plated layer of the uppermost surface in the Cu-plated layer by a heat treatment is formed. CONSTITUTION:A rolling prior to a finishing is performed and thereafter, a Cu plating of a thickness of 0.5 to 8mum is applied on the surface of a copper alloy parent material and an Ag plating of a thickness of 0.005 to 0.5mum is applied on the Cu plating. Then, the Ag-plated layer of the uppermost surface is diffused in the Cu-plated layer by a heat treatment and after that, the finishing rolling is conducted. Thereby, a plated layer formed by diffusing the Ag- plated layer in the Cu-plated layer is hardly oxidized, a homogeneous layer is formed on the clean surface of the plated layer and the whole plated layer is soft and is formed into a smooth form. Accordingly, a highly reliable material equivalent to the low-cost and thick Ag plating is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame material used in a semiconductor device and a method for manufacturing the same.

[Prior Art] Various copper alloy materials have been used as lead frame materials for semiconductor devices due to their good conductivity and heat dissipation properties. FIG. 1 is a perspective view showing the lead frame. In the figure, the lead frame (1) has a guide part (2) on which a semiconductor chip is mounted, a semiconductor chip and wires (
Inner lead part (3
), and the outer lead part (
4).

Among these, the surface of the inner lead part (3) and die pad part (2) on the side where the semiconductor chip is usually placed has a thickness of 4 μm.
Ag plating (5) of m or more is applied. This is because when performing so-called wire bonding, which connects the semiconductor chip and the inner lead part (3) with an Au wire or Cu wire, if the inner lead part (3) is not coated with Ag plating (5), the bonding strength will vary greatly. , because it lacks reliability. Ag plating (5) is not necessary for the die pad part (2), but Ag plating (5) is applied only to the inner lead part (3).
Since it is difficult to apply Ag to the Guibat part (2),
Plating (5) is applied.

[Problems to be solved by the invention] However, the above Ag plating process has the following problems: - In order to ensure the reliability of plating, expensive Ag is
It is necessary to plate the material to a thickness greater than the standard.

■Since partial Ag plating is performed after molding, productivity is low and costs are high.

For this reason, thick parts are not plated with Ag after the molding process,
There is a need for a material that allows so-called direct wire bonding, in which an Au wire or a Cu wire is directly bonded to an inner lead portion on the surface of a base material. Currently, Cu wires are bonded directly to lead frames in some cases, but this is currently limited to semiconductor devices that do not require much reliability, and is only used in most semiconductor devices that require high reliability. has not been implemented yet.

In recent years, as a solution to the above-mentioned problems, a method has been implemented in which the surface of the base material is plated with Cu to a thickness of 5 μm or more in the raw state. Plating is possible in the raw state, and the cost is low because it is plated with Cu, which is cheaper than Ag. Moreover, by using Cu plating with a thickness of 5 μm or more, reliability of wire bonding can be ensured without performing Ag plating after molding. However, this Cu plating also has the following problems.

Since the Cu plating layer is very susceptible to discoloration, it is very difficult to manage it from plating to wire bonding. Therefore, it is necessary to perform wire bonding immediately after plating.

In the case of long-term storage, equipment and packaging costs increase because conditions such as temperature and humidity must be adjusted at the storage location.

Furthermore, in order to maintain the reliability of bonding, it is necessary to wash the surface of the Cu plating layer immediately before bonding.

The present invention aims to solve the above-mentioned problems and provide a highly reliable and inexpensive lead frame material.

[Means for Solving the Problems] The semiconductor lead frame material of the present invention provides a Cu plating layer with a thickness of 0.5 to 8 μm on the surface of a copper alloy base material, and
It is characterized by having a layer on the surface of the base material obtained by providing an Ag plating layer with a thickness of 0.005 to 0.5 μm on the plating and diffusing the outermost Ag plating layer into the Cu plating layer by heat treatment. shall be.

Further, in the method for manufacturing the semiconductor lead frame material according to the present invention, the surface of the copper alloy base material has a thickness of 0 after rolling before finishing.
．． Cu plating with a thickness of 5 to 8 μm is applied, and Ag plating with a thickness of 0.005 to 0.5 μm is applied on the obtained Cu plating layer. Next, the outermost Ag plating layer is removed into the Cu plating layer by heat treatment. It is characterized by performing finish rolling after being diffused.

Ag is known to have the highest electrical conductivity and is a noble metal that is difficult to oxidize.As mentioned above, it is widely used as a bonding metal on the lead frame side in wire bonding, but it is not possible to create a single layer like Ag plating. Even if it is not present, if it is contained in steel at a certain concentration or more, it has the effect of suppressing oxidation and improving surface cleanliness.

In addition, in the manufacturing process, copper alloys are repeatedly annealed and rolled to obtain the desired thickness, but in the present invention, plating is performed after pre-finish rolling, and then final annealing and final rolling are performed. Plating can be performed on thick plates,
Furthermore, the heat treatment necessary for Ag diffusion and the final annealing can be used in common, resulting in lower costs.

If conventional Cu plating is still performed, annealing (usually at 400°C or higher) is required to soften the copper alloy base material for rolling.
When this was done, the surface was considerably oxidized unless a completely non-oxidizing atmosphere was created, resulting in a decrease in the reliability of the wire bonding characteristics. However, in the present invention, since Ag is present on the surface, the surface will not be oxidized during the normally performed annealing in a non-oxidizing atmosphere, and the reliability of wire bonding characteristics will not deteriorate.

By plating Cu on the surface of such a copper alloy, then plating Ag on that surface, and then heat-treating it to diffuse it into the AgeCu layer, we can create an inexpensive lead frame material with excellent direct wire bonding properties. Can be provided.

In addition, in the manufacturing method, plating is performed after pre-finish rolling, and then final annealing and final rolling are performed, thereby making it possible to provide the product at a lower cost.

[Function] The reliability of wire bonding generally increases as the gold on the lead frame side is cleaner, softer, and smoother.

A layer formed by Cu plating, Ag plating, and further thermal diffusion has the following characteristics.

■ Contains more Ag than conventional copper plating layers, so it is less likely to be oxidized and forms a clean surface;
If only plating is performed, there are concerns about pinholes, but by diffusing heat into the Cu plating layer, a homogeneous layer is formed; By using the Cu plating layer as a base, the entire plating layer becomes soft and smooth. Make it.

The thickness of the Ag plating was set to 0.005 to 0.5 μm, because if it is too thin, it will not be effective, and if it is thick, it will increase the cost. Similarly, the thickness of Cu plating was 0.5 to 8 μm.

Therefore, even when wire bonding is performed, the bonding reliability is higher than conventional Cu plating and equivalent to thick Ag plating with a thickness of 4 μm or more.

In addition, plating can be performed at the stage of wire bonding material, and since only a thinner Cu plating and an extremely thin Ag plating are applied than before, materials and processing costs are low, resulting in low costs. Furthermore, compared to conventional Cu plating layers, the Ag-diffused layer is less prone to discoloration and is therefore easier to store and manage, allowing long-term storage without special equipment.
There is no need for a surface cleaning process just before wire bonding.

Embodiments Examples of the present invention will be described below. In the examples, percentages of copper alloy compositions are percentages by weight.

CDA151 (a typical copper alloy for lead frames)
0.1% Zr, remainder unavoidable impurities and Cu), CDA1
94 (2.5% Fe, 0.2% Zn, remainder unavoidable impurities and Cu) and MF202 (2.0% Sn, 0.2% N
Examples 1 to 1 were obtained by using a base material (i, remaining unavoidable impurities and Cu) as a base material, and processing this into a lead frame through the following manufacturing process.

As a comparative example of the manufacturing process, among the above steps, the outermost surface is a Cu plating layer that is not subjected to Ag plating or heat treatment (Comparative Examples 1 to 3).
3), without heat treatment after Ag plating (Comparative Examples 4-
6), C with a thickness of 0.3 μm after finishing rolling, degreasing, and forming processing
Conventional products (Comparative Examples 7 to 9) with U undercoat plating and 5 μm thick Ag plating were produced in the same manner.

A wire bonding reliability comparison test was conducted on the manufactured products of the present invention, comparative products, and conventional products under the following test conditions.

Test conditions (1) Bonding conditions Bonding load: 50gf Stage temperature: 250℃ Ultrasonic ratio 0.2W Ultrasonic application time: 50m5ec Atmosphere: N2 Wire: φ25μm (2) Breakage by pull test immediately after evaluation processing and after environmental test It was evaluated based on the strength and wire breakage rate shown by the following formula. N=20
carried out.

(3) Environmental test Temperature: 40℃ Humidity: 90% Period = 14 days The test results are shown in Table 1.

From the results in Table 1, the products of the present invention of Examples 1 to 9 showed values equivalent to the thick Ag-plated materials of Comparative Examples 7 to 9 in terms of breaking strength and wire breakage rate both immediately after processing and after the environmental test.

The Cu-plated materials of Comparative Examples 1 to 3 and those without heat treatment after Ag plating of Comparative Examples 4 to 6 showed values equivalent to the thick Ag-plated materials of Examples and Comparative Examples 7 to 9 immediately after processing. After the environmental test, a significant decrease in breaking strength and wire breakage rate was observed.

In addition, for Examples 7 to 9 of manufacturing process B, manufacturing process A
It showed the same value as Examples 1 to 6.

From the above results, as in the present invention, Cu with a thickness of 0.5 μm or more
It can be seen that after plating, it is necessary to perform Ag plating with a thickness of 0.005 μm or more, and further heat treatment to diffuse Ag into the Cu plating layer. In addition, plating is performed during pre-finish rolling,
By subsequently annealing and finishing rolling, it can be manufactured at a lower cost.

[Effects of the Invention] As described above, according to the present invention, after the surface of the copper alloy base material is plated with Cu to a predetermined thickness, and after the surface of the Cu plating is coated with Ag to a predetermined thickness, By diffusing Ag into the Cu plating layer through heat treatment, a highly reliable and inexpensive lead frame material can be manufactured. Further, by performing plating processing in pre-finish rolling, followed by annealing and final rolling, the lead frame material can be manufactured at a lower cost.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the lead frame.
・Lead frame, 2...Die pad, 3...Isiner lead part, 4...Outer lead part, 5...A
G-plated.

Claims (2)

[Claims] (1) In lead frame materials used in semiconductor devices, a Cu plating layer with a thickness of 0.5 to 8 μm is provided on the surface of a copper alloy base material, and a Cu plating layer with a thickness of 0.005 to 0.0 μm is provided on the Cu plating.
A 5μm Ag plating layer is provided, and the outermost A layer is heated by heat treatment.
A semiconductor device lead frame material having a layer obtained by diffusing a G plating layer into a Cu plating layer on the surface of the base material. (2) In a method for manufacturing lead frame materials used in semiconductor devices, Cu plating with a thickness of 0.5 to 8 μm is applied to the surface of a copper alloy base material after pre-finish rolling, and a thick Ag plating with a thickness of 0.005 to 0.5 μm is applied, and then the outermost Ag plating layer is converted to Cu by heat treatment.
A method for producing a semiconductor lead frame material, which comprises diffusing it into a plating layer and then finishing rolling it.