JPS63190151A - Copper alloy material for lead frame - Google Patents

Abstract

PURPOSE:To inexpensively obtain a copper alloy material for lead frames excellent in strength and electric conductivity, by applying cold working to an ingot of single crystal or single-crystal state prepared by subjecting a molten metal to unidirectional solidification in a mold equipped with a heating device. CONSTITUTION:A molten metal 4 of a copper alloy of Cu-1% Sn, etc., is melted and held in a casting furnace 1. This molten metal 4 is introduced into a mold 2 and cooled by means of a cooling device 7 so as to be formed into an ingot 5, which is then drawn by means of pinch rolls 6. At this time, the mold 2 is heated by the heating device 3 so as not to form the nucleus of solidification, and the molten metal 4 is cooled via the ingot 5 by means of the cooling device 7 provided to the outlet of the mold 2, by which the ingot 5 is formed into a unidirectionally solidified structure. The resulting ingot 5 of single crystal or single-crystal state is cold-worked at a proper draft, so that inexpensive high strength- and high-conductivity-type copper alloy can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copper alloy material for lead frames that has excellent strength and electrical conductivity.

[Conventional technology and problems]

A lead frame is a frame structure used for mounting electronic components such as transistors and ICs.This lead frame material has high strength and conductivity, excellent repeat bendability, plating adhesion, punching workability, etc., and is inexpensive. is required.

In recent years, technological innovation in the electronics industry has progressed rapidly and in a pinch, especially in the field of semiconductor technology, where studies are being conducted not only to increase the density of elements, but also to miniaturize, improve performance, and lower prices. It is being replaced by the high-strength, low-conductivity type 42AIIoy (Fe-Ni-based) v4 alloy material.

The main reason why copper-based materials are used as lead frame materials is that copper-based materials have high thermal conductivity, that is, high electrical conductivity, and are suitable for diffusing Joule heat generated in devices due to high density. Therefore, in order for copper-based materials to be used extensively as a substitute for 42AIloy, high strength and
The development of highly conductive copper alloys is considered essential.

As shown in Figure 1, conventional copper alloy materials for lead frames are mainly of high strength/low conductivity type, medium strength/medium lead type, and low strength/high conductivity type. Conductive copper alloy, especially tensile strength of 80 kg/m+a” or more, conductivity of 70
There are no alloys greater than %lAC3.

Conventionally, copper alloys for lead frames are mainly work hardening type and precipitation hardening type.The former is made by dissolving the alloying elements in the copper matrix and then applying processing such as rolling to strengthen it. Because the alloying elements are dissolved in solid solution, the conductivity decreases significantly. In the latter method, solid solution elements are finely precipitated in the cavity matrix by aging treatment to strengthen the copper matrix, but since the solid solution elements remain to some extent in the copper matrix, very high conductivity cannot be obtained.

Even if a precipitation-hardened alloy is subjected to cold working to further strengthen it, the alloy lacks toughness and breaks during rolling, making it impossible to obtain sufficient strength.

As described above, it is difficult to obtain a material with high strength and high conductivity using conventional copper alloy materials.

Furthermore, all of these copper alloy materials have the disadvantage of high manufacturing costs because they require a heat treatment process that requires strict temperature control.

[Means for solving problems]

The present invention was made in view of the above situation, and it is an object of the present invention to provide a high-strength, high-conductivity copper alloy material for lead frames at a low cost.

That is, the present invention is a copper alloy material for a lead frame, which is obtained by unidirectional solidification and cold working of a single crystal or single crystal ingot.

[Effect]

The present inventors succeeded in producing long copper and copper alloy ingots by the unidirectional solidification method, and as a result of investigating their properties, they discovered a unique behavior in the unidirectional solidification material. In other words, Figure 2 shows 15LX manufactured using a conventional water-cooled mold.
This figure shows the work hardening properties of an oxygen-free copper ingot of 100' and an oxygen-free copper ingot of Is' The tensile strength of the ingot is 25kg/+nn
+", the tensile strength increases rapidly at the beginning of processing, and at about 45 kg/m1I11", the increase in tensile strength becomes slow, and reaches the processing limit at about 50 kg/am"99.
A processing rate of 9% or higher cannot be achieved.

Further, the electrical conductivity shows a completely opposite tendency to the tensile strength, and decreases rapidly at the initial stage of processing, and thereafter decreases at an approximately constant rate.

On the other hand, unidirectionally solidified oxygen-free copper has lower tensile strength in the form of an ingot than conventional materials, but higher electrical conductivity. Furthermore, the rapid increase in tensile strength and the i in electrical conductivity at the initial stage of processing
, there is no drastic decrease, and they increase and decrease at an almost uniform rate. In addition, this ratio is smaller than that of the conventional 4Kimura, and the rate of decrease in electrical conductivity is particularly small.Furthermore, there is no processing limit for unidirectionally solidified material, and it is possible to process up to 99.999% or more, and the tensile strength increases monotonically. .

As a result of investigating the causes of these differences, we found that the copper and copper alloy materials conventionally used for lead frames are
Because a large ingot is hot-worked and then cold-worked and heat-treated repeatedly to form a thin plate, there are many grain boundaries inside the ingot, and as these are worked, the strain caused by the working causes these grains to form. In contrast, in unidirectionally solidified materials, there are almost no grain boundaries that cross the ingot, and a small number of grains extend in the longitudinal direction. It has an elongated single-crystal or single-crystal-like structure, so there is almost no place for strain to accumulate, and strain lines only exist in the longitudinal direction as lines or planes, and unlike conventional materials, grain boundaries at the processing limit It turned out that this was to prevent breakage.

In this manner, the present inventors have discovered that copper and copper alloy materials having various properties can be produced by only cold working by using a directionally solidified material.

Furthermore, in the present invention, high strength can be achieved by cold working, so the manufacturing cost is low.

〔Example〕

The present invention will be explained in detail below using examples.

Methods for manufacturing long plate-shaped unidirectionally solidified ingots include a heating mold continuous casting method (hereinafter abbreviated as OCC method) in which the mold is heated above the melting point of the cast metal, and a horizontal continuous mold vibrating mold using a water-cooled mold. Although there are casting methods, etc., the OCC method is more advantageous in easily manufacturing single crystal materials. Therefore, an example in which a temporary ingot was cast by the OCC method will be described.

Figure 6 shows an overview of the continuous heating mold casting apparatus.

This apparatus is comprised of a casting furnace 1, a mold 2, a cooling device 7 for cooling the ingot 5, and pinch rolls 6 for drawing out the ingot. The cast metal melted in the melting furnace is introduced into the casting furnace 1 through the gutter. A heating element is built into the furnace wall of the casting furnace 1, and the cast metal is heated above its melting point and held as a molten metal 4.

This molten metal 4 enters the SR mold and is cooled to form an ingot, which is pulled out by pinch rolls 6.

At this time, the mold 2 is heated above its melting point by the heating device 3 installed around the mold, so no solidification nuclei are generated in the molten metal 4 on the inner surface of the mold 2, and the cooling device 7 installed at the outlet of the mold 2 , since it is cooled through the ingot 5, it becomes a unidirectionally solidified structure.

With this device, oxygen-free copper, Cu-0.7%Sn, Cu-
1%Ag and Cu-0,5%Be-2,5%Co alloys were melted and held at a melt temperature of 1150℃, and 15tX
A 200' plate-shaped ingot was cast. The structure of this ingot was a single-crystal or single-crystal-like structure in which a small number of crystal grains extended in the longitudinal direction, with almost no grain boundaries crossing the ingot. As a comparison material, a 15t x 200' rolled material was prepared by hot rolling a 100' x 200' ingot cast using a conventional water-cooled mold at 850°C.

These materials were cold-rolled to various thicknesses, and the tensile strength and electrical conductivity of each material were measured.

The results are shown in Figures 3-5. Regarding oxygen-free copper, please refer to the second
Since the results were exactly the same as those shown in the figure, they have been omitted.

FIG. 3 shows the relationship between the amount of processing strain, tensile strength, and electrical conductivity of the Cu-0.7% Sn alloy.

As is clear from this figure, as the amount of processing strain increases, the tensile strength increases and the electrical conductivity decreases, but when the plate material obtained by the conventional method is rolled from 15mm thick to 0.17mm thick, 0. At 17mm, the plate broke frequently and no further processing was possible. The amount of distortion at this time! ! , n(1510,17)
=4.48"il' ant, tensile strength mackerel 59.5kg/
mm”, conductivity is 66.8%lAC3 (hereinafter abbreviated as %)
Met.

On the other hand, the unidirectionally solidified material could be cold-worked to any extent, and could be sufficiently rolled to a thickness of 20 μm. The amount of distortion at this time is i
n (1510,02) = 6.62, tensile strength is 7
5 kg/m'', and the conductivity was 64.5%.

The results for the Cu-1%Ag alloy are shown in FIG.

This alloy is somewhat difficult to process compared to the Cu-0.7%Sn material, and the conventional material suffered temporary breakage at a strain of 3.5, or 0.45 mm in thickness, but the unidirectionally solidified material produced a Cu-0.7% Sn alloy. 0.7%Sn
As with the material, it was possible to roll it to 20〃2.

The results for the Cu-0.5% Be-2.5% Co alloy are shown in FIG. This -alloy is easy to work harden (conventional material has strain f
Although plate breakage occurred at 1.5 ft, that is, 3.3 am', the unidirectionally solidified material could be processed to 0.10 mmL.

As described above, when a unidirectionally solidified material is used, the workability is much better than that of conventional materials, and in particular, high strength, which cannot be obtained with conventional materials, can be obtained with an alloy of the same composition.

Conventionally, copper and copper alloy lead frame materials have a processing rate (t/loX) of 40% or less of the processing limit for reliability.
100%: t〇 - Annealed material plate thickness, - Processing W, ), so based on the results in Figures 3 to 5, the tensile strength and conductivity at a processing rate of 40% of the processing limit are calculated. The alloy of the present invention was compared with a conventional alloy. The results are shown in Table 1.

As is clear from Table 1, the alloy of the present invention shows a slight decrease in electrical conductivity and a large improvement in tensile strength compared to conventional alloys.

〔Effect of the invention〕

The copper alloy material for lead frames of the present invention is obtained by strongly processing conventionally used copper alloy materials, and has greatly improved tensile strength without substantially reducing electrical conductivity. Since the cost is low, it has a remarkable industrial effect.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the tensile strength and electrical conductivity of copper alloys for lead frames, Figures 2 to 5 are explanatory diagrams showing the relationship between the amount of strain, tensile strength, and electrical conductivity, and Figure 2 is an oxygen-free Copper, Figure 3 is C
u-0.7%Sn alloy, Figure 4 shows Cu-1%Ag alloy,
FIG. 5 is an explanatory diagram of the Cu-0,5% Be-2,5% Co alloy, and FIG. 6 is an explanatory diagram of the hot mold continuous casting apparatus used in this example. l...Casting furnace 2...Mold 3...Heating device 4...Easing device 5...Ingot 6...Pinch roll 7...Cooling device

Claims (1)

[Claims] A copper alloy material for lead frames, characterized in that it is obtained by cold working a unidirectionally solidified single crystal or single crystal ingot.