JPS6396231A - Lead frame material combining high strength with high electric conductivity - Google Patents

Abstract

PURPOSE:To obtain the titled lead frame material combining high strength with high electric conductivity and further excellent in adhesive strength of plated tin and solder, by providing a copper alloy containing respectively prescribed amounts of Cr, Zr, and Zn. CONSTITUTION:The lead frame material of this invention, having high strength and high electric conductivity, is composed of a copper alloy consisting of, by weight, 0.1-0.8% Cr, 0.01-0.5% Zr, 0.05-1.0% Zn, and the balance essentially Cu. This lead frame material has an electric conductivity of >=70% JACS and also has excellent adhesive strength of plated tin and/or solder. That is, when an alloy layer is formed on the boundary between the base material of this copper alloy and the plated solder, void formation is prevented and occurrence of peeling can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high strength, highly conductive lead frame material,
More specifically, the present invention relates to a lead frame material used for semiconductors having high strength, high conductivity, and excellent adhesion to tin plated and/or solder.

[Prior Art] Conventionally, 42 alloy, which has a linear expansion coefficient similar to that of elements and ceramics and also has high strength, has been widely used as lead frame materials for semiconductors.

However, recently, with improvements in device bonding technology and sealing materials, copper-based materials with excellent heat dissipation properties have come to be used instead of 42 alloy.

In particular, lead frame materials for integrated circuits have higher thermal conductivity (i.e., electrical conductivity) in order to efficiently dissipate Joule heat generated in devices due to the recent trend toward higher integration. The conductivity is 70
A request greater than %IACS has been issued.

In addition, due to the trend toward miniaturization of integrated circuits due to the high density packaging of integrated circuits, lead frame materials are becoming thinner and higher strength is required at the same time.
Copper-based materials that also have high strength similar to alloys are required as lead frame materials.

A Cu-Cr-Zr alloy is known as a copper alloy that has both high conductivity and high strength as described above. However, this alloy does not impair the high conductivity of the matrix due to the precipitation of Cr and Zr (it has high strength), and although it satisfies the above conditions in terms of strength and conductivity, this alloy The adhesion of plated tin and/or solder is poor.In other words, after tin or solder plating (hot-dip plating or electrolytic plating), it is formed when heated at 150°C for 1000 hours. There is a problem that the plating peels off from the interface between the alloy layer and the base material.

Normally, lead frames are used with tin or solder plating on the external leads, and recently finished products are increasingly being heated for burn-in tests, etc. It is an essential condition that the tin and/or solder plating does not peel off even after 1000 hours of heating. [Problems to be Solved by the Invention] As explained above, in view of the shortcomings of conventional lead frame materials, the present inventor has conducted extensive research, and as a result, a Cu-Cr-Zr based alloy has been developed. We have developed a highly conductive lead frame material with high strength and conductivity of 70% lAC3 or higher, which does not cause the tin and/or solder plating to peel off even when heated, and has excellent adhesion to the tin and/or solder plating. be.

[Means for Solving the Problems] The high-strength, high-conductivity lead frame material according to the present invention has the following characteristics: Cr: 0.1-0.8wt%, Zr: 0.01-0.
5wt%, Zn 0.05-1. It is a copper alloy containing 50% Cu and the remainder substantially Cu, has an electrical conductivity of 70%lAC9 or more, and has excellent adhesion to plated tin and/or solder.

The high-strength, highly conductive lead frame material according to the present invention will be described in detail below.

First, the components and content ratios of the high-strength, high-conductivity lead frame material according to the present invention will be explained.

Cr is an element that imparts strength, and it precipitates through heat treatment to improve strength and conductivity.
．． If it is less than 1wt5, the strength improvement effect (very little, or 0
．． If the content exceeds 8wt%, a large amount of precipitated Cr will remain unetched when the lead frame is etched, and will appear as whisker-like protrusions on the surface of the lead frame, causing problems in use. This may occur, and the conductivity decreases in proportion to the Cr content, so it is not preferable to contain more than the amount necessary to improve the strength. Therefore, the Cr content is 0.1 to 0.
It is set to 8wt%.

Zr is an element that is effective in improving precipitation strength together with Cr, and if the content is less than o, otwt%, this effect is small, and if the content is more than 0.5vt%, it becomes difficult to form ingots. Therefore, the Zr content is 0.01 to 0.5 tons
%.

Zn is an element that contributes to improving the adhesion of plated tin and/or solder. That is, as shown in the micrograph of the metal structure of the bonding interface after hot dipping solder on a copper alloy that does not contain Zn and heating it at a temperature of 150°C for 1000 hours in Figure 2, Cu-Cr that does not contain Zn. - An alloy layer and a large number of voids are formed at the interface 2 between the base material of the Zr-based copper alloy 4 and the plated solder (or tin) 1, and then peeled off. This void is thought to be due to the Kirkendahl effect, but as shown in Figure 1, which is a micrograph of the metal structure of the bonding interface after heating similar to Figure 2, Cu-Or-Zr containing Zn. Although an alloy layer is formed at the interface between the base material of copper alloy 4 and solder plating 1, the formation of voids is prevented and peeling does not occur. And the content is 0.05
Below wt%, the above effect is small, and 1.0wt%
If the content exceeds 70% lAC3, the above effect will be obtained, but the conductivity will decrease and it will not be possible to secure 70%lAC3 or more. Therefore, the Zn content is set to 0.05 to 1 Ovt%.

[Example] Next, an example of the high-strength, high-conductivity lead frame material according to the present invention will be described.

Example A copper alloy having the components and proportions shown in Table 1 was melted in the air under a borax coating using a Kryptor furnace.
50mmtX 70m using cast iron book mold
An ingot with a mwx of 200 mm was cast.

After cutting both the front and back sides of this ingot by 5 mm, hot rolling at a temperature of 900°C to a thickness of 10 mm, cooling with water to remove scale, and cold rolling to a thickness of 1.0 mm.
o.1 was aged at 400°C, and the others were aged at 450°C for 4 hours. Furthermore, after cold rolling to 0.25 mmt, annealing was performed for 20 seconds at a temperature of 350 to 400°C using a saltpetre furnace.

The following tests were conducted on these samples, and the results are shown in Table 2.

(1) The tensile test was performed using JIS1 cut parallel to the rolling direction.
No. 3 B test number test piece.

(2) Electrical conductivity was measured by double bridge using a 10w×3001 test piece.

(3) Repeated bendability is determined by using a 0.5 mm wide lead punched out with a press as a test piece, hanging a 227 g weight at one end, bending it back and forth in one direction by 90°, and measuring the number of times until breakage. It was counted as one test and was calculated as the average value of 5 test pieces. The bending axis was perpendicular to the rolling direction.

(4) For solder adhesion, use weakly activated flux, 23
A test piece plated with molten solder in a 5n60-Pb40 solder bath at a temperature of 0°C was held at a temperature of 150°C for 1000 hours, then bent back by 90° and examined for peeling.

As is clear from Table 2, Nos. 1 to 4 of the high-strength, high-conductivity lead frame materials according to the present invention have high tensile strength;
Comparative Examples 5 and 6, which have excellent repeated bendability and electrical conductivity of 70% IACS or higher, and which do not contain Zn or have a low Zn content, have a 100%
While the solder peeled off after heating for 0 hours, Z
It can be seen that peeling is prevented because an appropriate amount of n is contained.

Table 1 [Effects of the Invention] As explained above, the high-strength, high-conductivity lead frame material according to the present invention has the above structure, so it has high strength and high conductivity of 70% IACS or higher. Furthermore, it has the effect of excellent adhesion between plated tin and solder.

[Brief explanation of the drawing]

Figure 1 shows the metal structure of the bonding interface after melt-plating the copper alloy of NO34 in Table 1, which is a high-strength, high-conductivity lead frame material according to the present invention, with solder and then heating it at a temperature of 150°C for 1000 hours. Micrograph of , Figure 2 is N0 in Table 1.
2 is a microscopic photograph of the metal structure of the bonding interface after the copper alloy of Comparative Example No. 95 was hot-dipped with solder and then subjected to the same treatment as in FIG. 1. 1 - solder layer, 2 - alloy layer, 3 - void, 4 - base material (copper alloy). Procedural amendment (voluntary) I■ Month 06, 1985 1, Indication of case 1988 Patent Application No. 240257 2, Name of invention High strength, high conductive lead frame material 3, Person making the amendment Related Patent Applicant Address 1-3-18 Wakihama-cho, Chuo-ku, Kobe Name (1
19) Kobe Steel, Ltd. Fujiwa Toyocho Co-op 90
No. 1 5. Date of amendment order (voluntary) 6. Subject of amendment Figure 1, Figure 2 7. Details of amendment as attached.

Claims (1)

[Claims] Cr0.1-0.8wt%, Zr0.01-0.5wt
%, Zn0.05 to 1.0 wt%, the remainder being substantially Cu, and has an electrical conductivity of 70% IACS or more, and has good adhesion to plated tin and/or solder. High-strength, high-conductivity lead frame material characterized by superior properties.