JPH04366A - Lead frame material for semiconductor and production thereof - Google Patents

Abstract

PURPOSE:To obtain a lead frame material enabling direct wire bonding with high reliability by plating the surface of a Cu alloy base after final rolling with Ag in a specified thickness and diffusing this Ag in the base by heat treatment. CONSTITUTION:When a lead frame material used for a semiconductor is produced, the surface of a Cu alloy base after final rolling is plated with Ag in 0.005-0.5mum thickness and this Ag is diffused in the base by heat treatment to form a homogeneous Ag-contg. layer in the surface of the base. In the case where the surface of the base has crevices due to mechanical polishing, the surface is preferably smoothened by electropolishing before Ag plating. Plating can be carried out in the stock stage without requiring preplating and cost is reduced.

Description

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

[Prior Art] Various copper alloy materials have been used as semiconductor lead frame materials due to their good conductivity and heat dissipation properties.

FIG. 1 is a perspective view showing a lead frame. In FIG.
inner lead part (3) connected with wire or Cu wire),
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 the case where the semiconductor chip and the inner lead part (3) are made of Au.
This is because when so-called wire bonding, which is a connection using a wire or Cu11, is performed, if the inner lead portion (3) does not have the Ag plating (5), the bonding strength will vary greatly and reliability will be lacking. The die pad part (2) does not need to be plated with Ag (5), but since it is difficult to apply Ag plating (5) only to the inner lead part (3), the die pad part (2) is also plated with Ag (5). 5) is applied.

[Problems to be Solved by the Invention] However, the above-mentioned Ag plating process has the following problems: ■ The cost increases because expensive Ag is plated to a thickness of 4 μm or more.

■When performing Ag plating, a Cu or Ni base plating is applied to improve the adhesion between the base material and the Ag plating, but since this base plating is applied to the entire surface after the lead frame (1) is formed, After molding, it is necessary to peel off the base plating on the outer lead part (4). This is because Sn or solder plating is applied to the outer lead part (4), but if Sn or solder plating is applied on top of the base plating, This is because it becomes easy to peel off at the interface with the underlying plating, reducing plating reliability.

Therefore, there is a need for a material that allows so-called tie-left wire bonding, in which Au or Cu wires are bonded directly to the inner lead portions on the surface of the base material without thick Ag plating. Currently, in some cases, Cu wires are connected directly to lead frames, but this is currently limited to semiconductors that do not require high reliability, and is not applicable to most semiconductors that require high reliability. , has not yet been implemented.

In order to solve the above-mentioned problems, the present invention aims to provide a lead frame material capable of highly reliable direct wire bonding at low cost.

[Means for Solving the Problems] The semiconductor lead frame material of the present invention is produced by plating Ag on the surface of a copper alloy base material to a thickness of 0.005 to 0.5 μm, and then heat-treating the surface of the copper alloy base material to plate Ag. It is characterized by having a layer on the surface of the base material obtained by diffusion into the base material.

In addition, the method for manufacturing a semiconductor lead frame material of the present invention provides that the surface of the copper alloy base material after final rolling has a thickness of 0.005 to 0.
．． The method is characterized in that after 5 μm Ag plating is applied, a layer obtained by diffusing Ag into the copper alloy base material by heat treatment is formed on the surface of the copper alloy base material.

Furthermore, the method for manufacturing a semiconductor lead frame material of the present invention includes electrolytically polishing the surface of the copper alloy base material after final rolling, and then
After applying Ag plating to a thickness of 0.005 to 0.5μ on the surface, a layer obtained by diffusing Ag into the copper alloy base material by heat treatment is formed on the surface of the copper alloy base material. Features.

Ag is known to have the highest electrical conductivity and is a precious metal that is resistant to oxidation.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 as in Ag plating. Even if it is not present, if it is contained in the copper alloy at a certain concentration or more, it has the effect of suppressing oxidation and improving surface cleanliness.

In addition, during the manufacturing process, copper alloys are sometimes subjected to mechanical polishing such as puff polishing after final annealing, but this is because the thick oxidation on the surface formed by annealing occurs when the non-oxidizing atmosphere is not completely formed during annealing. This is for mechanically scraping things off. However, when this mechanical polishing is performed, as shown in FIG. 2(a), holes (7) are formed on the surface of the copper alloy (6). This gap (7) is crushed by rolling, and as shown in Figure 2 (b), minute gaps (8) are formed on the material surface.
form.

This surface gap (8) varies greatly depending on the mechanical polishing method and the processing rate of the final rolling. Among them, the gap (8)
If this is large, treatment liquids such as oil and degreasing liquid remain in the gap (8), which adversely affects the strength of the joint when wire bonding is performed and the plating adhesion when plating is performed.

However, since electrolytic polishing has the effect of preferentially melting the Paris (7), in the present invention, when the copper alloy base material has a surface condition as shown in Figure 2(b), the copper alloy (6) after the final rolling is ) By electrolytically polishing the surface of the material, it is also possible to remove minute particles (7) of about 1 μm on the surface and improve the material surface. Copper alloy (6) is produced by electrolytic polishing after final rolling.
As shown in FIG. 2(c), the surface (7) is removed and a smooth surface (9) is formed.

Next, in the present invention, the surface of the copper alloy is coated with a thickness of 0.005 to 0.
．． 5 μm Ag plating is applied and heat treated to diffuse Ag into the base material. At this time, 0.005
If only ~0.5 μm of Ag plating is applied, there will be many pinholes and it will be easily scraped off mechanically to reveal the base material, but by diffusing it into the base material through heat treatment, a homogeneous Ag-containing layer will be created. is formed on the surface of the base material. heat treatment temperature,
Conditions such as time vary depending on the type of copper alloy, etc., but may be within a range where Ag can be diffused into the base material. The lower limit of the thickness of the Ag plating was set at 0.005 μm, and the upper limit was set at 0.5 μm because the thicker the layer, the higher the cost.

Furthermore, if there are gaps on the surface of the base material due to mechanical polishing, electrolytic polishing is performed to smooth the surface before applying Ag plating.

After the copper alloy surface is plated with Ag in this manner, Ag is diffused into the base material by heat treatment, thereby providing an inexpensive lead frame material with excellent direct wire bonding properties.

[Function] The layer subjected to thermal diffusion after Ag plating contains more Ag than conventional copper alloys, so it is less likely to be oxidized and forms a clean surface. Therefore, even when direct wire bonding is performed, the bonding reliability is equivalent to that of thick Ag plating with a thickness of 4 μm or more. Also, unlike normal plating, since Ag is diffused into the base material, there is no need to worry about peeling of the plating layer. Therefore, there is no need to perform base plating, and the process of peeling off the base plating after molding can be omitted. Furthermore, since plating can be performed at the raw material stage and only an extremely thin Ag plating is applied, material and processing costs are low, resulting in low costs.

In addition, electrolytic polishing can remove the cracks and gaps on the base material surface caused by mechanical polishing and form a smooth surface. Therefore, by performing electrolytic polishing before Ag plating, the base material can be polished. Highly reliable direct wire bonding can be performed regardless of the surface condition.

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

CA151 (0) is a typical copper alloy for lead frames.
, 1% Zr, remainder unavoidable impurities and Cu) CA195 (2.5% Fe, 0.2% Zr, remainder unavoidable impurities and Cu) MP202 (2.0% Sn, 0.2% Ni, remainder unavoidable impurities and Cu) This is used as a base material, finish rolled and degreased to a thickness of 0.25 mm, and the thickness is 0.005 μm or 0.1 μm.
Samples (Examples 1 to 4) were prepared by applying Ag plating, heat treating at 300° C. for 2 hours, and molding by pressing.

As comparative examples, materials as they are without Ag plating and heat treatment (Comparative Examples 1 to 3), materials without heat treatment (Comparative Example 4), and thickness after finishing rolling, degreasing, and forming processing. Cu underplating with a thickness of 0.3 μm and a thickness of 5 μm
Conventional products (Comparative Examples 5 to 7) with Ag plating were similarly prepared.

A wire bonding reliability comparison test was conducted on the samples of Examples and Comparative Examples prepared above under the following test conditions.

Test conditions ■Bonding conditions Bonding load: 50gf Stage temperature = 250℃ Ultrasonic ratio 0.2W Ultrasonic application time: 50m5ec Atmosphere 2N2 Wire φ25μm ■Evaluation Breaking strength by pull test immediately after bonding and after heat cycle test and the following formula Evaluation was made using the wire breakage rate shown in . N=20 tests were conducted.

■Beat cycle test Cycle conditions: -30°C x 30 minutes ←→80°C x 30 minutes Number of cycles = 500 times The test results are shown in Table 1.

From the results in Table 1, Examples 1 to 4 showed values equivalent to the thick Ag plating materials of Comparative Examples 5 to 7 in terms of breaking strength both immediately after bonding and after the heat cycle test, and that of Comparative Examples 1 to 3. A significant improvement was observed compared to the original material. In addition, the wire breakage rate of Examples 1 to 4 was 100% both immediately after bonding and after the heat cycle test.
A significant improvement was observed compared to the 5 to 20% of the materials of Comparative Examples 1 to 3. The electrolytically polished sample of Example 5 showed the same reliability as Examples 1 to 4 regardless of the surface condition of the base material, demonstrating the effect of electrolytic polishing.

Comparative Example 4, which was not subjected to heat treatment, showed the same reliability as the Example immediately after bonding, but a decrease in reliability was observed after the heat cycle test.

From the above results, it can be seen that it is necessary to perform Ag plating with a thickness of 0.005μ or more as in the present invention, and to perform heat treatment to diffuse Ag into the base material after plating.

Furthermore, it can be seen that it is effective to perform electrolytic polishing before Ag plating depending on the surface condition of the base material.

[Effects of the Invention] As described above, according to the present invention, after the surface of a copper alloy is plated with Ag to a predetermined thickness, Ag is diffused into the base material by heat treatment, and the base material is Depending on the surface condition, by applying electrolytic polishing to the manufacturing process, a highly reliable and inexpensive lead frame material can be manufactured.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the lead frame, and Fig. 2(a)
~(c) is a cross-sectional view schematically showing the surface of a copper alloy. In the figure, 1...Lead frame, 2...Die pad, 3
... Inner lead part, 4... Outer lead part,
5...Ag plating, 6...Copper alloy, 7...Paris, 8
···gap. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In lead frame materials used in semiconductors,
It is characterized by having a layer on the surface of the copper alloy base material obtained by plating Ag to a thickness of 0.005 to 0.5 μm on the surface of the copper alloy base material and then diffusing Ag into the copper alloy base material through heat treatment. Semiconductor lead frame materials. 2. In the manufacturing method of lead frame materials used in semiconductors,
The surface of the copper alloy base material after final rolling has a thickness of 0.005 to 0.
A method for manufacturing a semiconductor lead frame, which comprises applying 5 μm Ag plating and then forming a layer obtained by diffusing Ag into the copper alloy base material through heat treatment on the surface of the copper alloy base material. 3. In a method for manufacturing lead frame materials used in semiconductors, the surface of a copper alloy base material after final rolling is electrolytically polished, and then Ag plating with a thickness of 0.005 to 0.5 μm is applied to the surface. A method for manufacturing a semiconductor lead frame, which comprises forming a layer obtained by diffusing Ag into a copper alloy base material through heat treatment on the surface of the copper alloy base material.