JP2002356728A - Copper and copper alloy, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide copper or a copper alloy with excellent balance between the strength and the workability. SOLUTION: The copper or the copper alloy has fine grains of the grain size of <=1 μm and shows the elongation of >=2% in the tensile test after the final cold rolling by performing the rolling of η>=3, where η is the rolling degree in the final cold rolling and expressed by η=ln(T0 /T1 ), where T0 is the thickness before rolling and T1 is the thickness after the rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to copper and copper alloys having fine crystal grains and a method for producing the same, and more particularly, to a method of bending when used for electronic devices such as seed terminals, connectors, and lead frames of semiconductor integrated circuits. The present invention relates to a technique for improving characteristics in processing such as processing.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as terminals and connectors and their components have been miniaturized and thinned, it has been desired that copper or a copper alloy as these materials have high strength. In the terminal and connector materials,
In order to maintain the electrical connection, it is necessary to increase the contact pressure, which requires a high strength of the material. Further, in a lead frame, there is a demand for increasing the number of pins and reducing the thickness of the semiconductor circuit in accordance with higher integration of the semiconductor circuit. For this reason, in order to prevent deformation during handling such as transport of the lead frame, the required strength level has become more severe.

Also, with the miniaturization of electronic devices and their components, the demand for flexibility in moldability has been increasing, and workability of connector materials and the like has become more important. Above all, those having better bendability have been required. In addition, the outer leads of the semiconductor lead frame are required to have excellent bendability even when a gull-wing-shaped bending process is performed.

[0004] In order to obtain good bendability without causing cracks in a bent portion when a material is subjected to bending deformation, it is necessary to increase the ductility of the material or to reduce the crystal grain size. Further, a copper alloy used for electronic devices needs to have a function of transmitting an electric signal and simultaneously releasing heat generated during energization to the outside, and is required to have high thermal conductivity as well as electrical conductivity. In particular, in order to cope with the recent increase in the frequency of electric signals, there is an increasing demand for improved conductivity.

[0005] The conductivity of a copper alloy is in a relationship opposite to the strength. When an alloy element is added to increase the strength, the conductivity decreases. Therefore, the balance between the strength and the conductivity and the price are suitable for the intended use. Alloys are used. Until now, alloys having this strength and conductivity in a well-balanced manner have been actively developed, and generally, Cu-Ni-S
Precipitation-strengthened copper alloys containing second phase particles, such as i-alloys and Cu-Cr-Zr alloys, have come to be used as high-performance materials with an excellent balance between the two.

[0006]

As described above, for the mechanical properties of copper or copper alloy for electronic equipment, it is desired to have high strength and good workability. However, first, strength and ductility have a contradictory relationship, and in each alloy system, ductility decreases when rolling is performed to obtain an increase in strength due to work hardening. Did not. On the other hand, reducing the crystal grain size is not only expected to increase the strength represented by the Hall-Petch equation, but also leads to improvement in bendability. Was generally controlled so as to be smaller.

However, in this method, if the annealing temperature is lowered in order to refine the crystal grains, unrecrystallized grains partially remain, and therefore, substantially, 2 to 2
The limit is to obtain recrystallized grains of about 3 μm, and a technique for further refinement of crystal grains has been awaited. Furthermore, since the strength level is usually unsuitable for practical use when recrystallized, it is necessary to add some rolling afterwards,
As a result, the ductility was reduced as described above. For this reason, it has generally been necessary to perform a strain relief annealing process for recovering ductility after rolling. Due to this process, the strength obtained by the rolling process is inevitably reduced, and sufficient ductility is not obtained even after strain relief annealing. Was.

In recent years, instead of the annealing process,
A report by Ito et al. (ARB (Accumulative Roll-Bonding), Journal of the Japan Institute of Metals, 64 (2000), 429), how to obtain fine crystal grains and high ductility by adding strong shearing to the material, and Hotta (ECAP (Equal-Channel Angular Press), Seminar text of the Institute of Metals, Approach to grain refinement, (20
00), The Japan Institute of Metals, 39), etc. However, these processing methods are not suitable for industrial production because they cannot produce an amount that can be used as a material for electronic devices.

[0009]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by controlling the conditions of the rolling process instead of the annealing, the level which has not been attained until now has been obtained. To obtain fine crystal grains. That is, in the structure of a material cold-rolled at a normal working ratio, when recrystallization occurs due to subsequent annealing, dislocation disappears discontinuously when a recrystallized grain boundary passes through a cell, and Are uneven and large crystal grains are generated intermittently. This is called static recrystallization. According to the study of the present inventors, by making the working degree of cold rolling extremely high, dynamic recrystallization usually exhibited in a high temperature region is also exhibited in cold rolling, and moreover, it is formed during working. It has been found that this is a dynamic continuous recrystallization that occurs when the sub-grains are converted to high-angle grain boundaries. By utilizing this mechanism, a rounded uniform crystal grain size of 1 μm or less can be obtained. According to this method, it is found that fine crystal grains can be obtained without sacrificing strength in order to prevent a decrease in ductility, and that elongation of 2% or more can be obtained immediately after final cold rolling. However, acceptable bendability was obtained. In addition, since elongation is further improved by adding strain relief annealing after the final cold rolling, it is possible to cope with extremely severe bending. Furthermore, according to such a manufacturing method, it is possible to mass-produce the material for electronic equipment industrially. In addition,
The continuous recrystallization will be described later in more detail.

[0010] The copper and copper alloy of the present invention have been made based on the above-mentioned findings, and a dynamic continuous recrystallization is performed by final cold rolling, so that after the final cold rolling, a crystal mainly composed of a curved portion is obtained. It is characterized by having a structure of fine crystal grains having a grain size of 1 μm or less composed of grain boundaries and exhibiting an elongation of 2% or more in a tensile test.

Further, in the method for producing copper and copper alloy of the present invention, when the working ratio η in the final cold rolling is represented by the following equation, the rolling process is performed so that η ≧ 3. After rolling, it has a structure of fine crystal grains having a grain size of 1 μm or less, and exhibits an elongation of 2% or more in a tensile test.

Η = ln (T ₀ / T ₁ ) T ₀ : thickness before rolling, T ₁ : thickness after rolling

Next, the reason for the above numerical limitation will be described together with the operation of the present invention. A. Final cold-rolling workability, elongation, crystal grain size In order to obtain good bendability with a material as final cold-rolled, high ductility is required. In order to obtain good bendability that does not cause cracks in the bent portion, the elongation at break in a tensile test needs to be 2% or more when the gauge length is 50 mm. In order to obtain a breaking elongation of 2% or more in the final cold rolling, the crystal grain size after the final cold rolling is 1 μm.
It is necessary to: Elongation can be obtained as it is in cold rolling by reducing the crystal grain size in such a way. When continuous recrystallized grains are formed, dislocations are deposited on the grain boundaries, and the grain boundaries in non-equilibrium state This is because a structure is formed, whereby grain boundary sliding is developed and ductility is improved.

The grain size and elongation after the final cold rolling are affected by the degree of cold rolling. The working ratio η by final cold rolling until reaching the product sheet thickness is represented by the following equation.

Η = ln (T ₀ / T ₁ ) T ₀ : thickness before rolling, T ₁ : thickness after rolling

In this case, if η is small, the rolled structure remains and clear fine crystal grains are not obtained, or even if obtained, the crystal grain size becomes large and grain boundary sliding does not occur, which is favorable. No good ductility can be obtained. According to studies by the present inventors, it has been found that η should be 3 or more in order to obtain a fine crystal grain size of 1 μm or less.

In the structure of a material that has been cold-rolled at a normal working ratio, the dislocations introduced into the crystal grains may be entangled with each other to form a cell structure. Since the angle of inclination between them was as low as 15 ° or less, they did not have properties as crystal grain boundaries. For this reason, as shown in FIG. 1, when recrystallization occurs due to annealing after cold rolling, as described above, static recrystallization in which non-uniform and intermittently large crystal grains are generated occurs. .

On the other hand, fine grains can be obtained by setting the workability of the cold rolling extremely high because the region which locally undergoes shear deformation in the matrix when the workability is increased becomes the entire material. As shown in FIG. 1, the subgrain structure as a substructure is very developed, and many dislocations are introduced to fill a large misorientation with the matrix, and they are deposited at grain boundaries, as shown in FIG. In this case, a crystal grain boundary having a large inclination angle of 15 ° or more (high inclination angle grain boundary) is generated. In other words, the sub-grain structure, which is the underlying structure of the crystal grains, is originally formed as it is as the crystal grains. In this case, the crystal grain boundaries are significantly different from those in the case of static recrystallization, and the grain boundaries do not have linearity, and the curved portions It is characterized by forming a crystal grain boundary mainly composed of This dynamic continuous recrystallization is often formed at the time of cold rolling, but it has been found that a clearer high-angle grain boundary develops by intentionally performing low-temperature annealing and bringing it to a normal recovery zone. I have. In that case, it has been found that ductility is further improved as described later.

In this mechanism, when a second phase particle such as a precipitate or a dispersion is present in the Cu matrix, the dislocation introduced by the introduction of plastic strain by rolling causes a dislocation loop around the second phase particle. The dislocations are multiplied by, for example, forming a dislocation, and the dislocation density is greatly increased. In this situation, the sub-grain is further promoted to have a smaller particle size, and the strength is further increased. In this case, in the final cold rolling, as long as recovery or recrystallization does not occur due to annealing in the middle, cold rolling with a plurality of rolling mills instead of rolling mills according to the range of sheet thickness, Pickling or polishing may be carried out in order to adjust the quality.

B. Strain relief annealing If the final cold-rolled material is strain relief annealed, ductility is further improved, so that better bendability can be obtained. As the annealing conditions, it is necessary to set appropriate annealing conditions such that the strength is not extremely reduced and the product value is not lost. The annealing conditions vary depending on the alloy system, but by selecting appropriate annealing conditions in a temperature range of 80 to 500 ° C and a range of 5 to 60 minutes, elongation of 6% or more can be easily obtained,
It can respond to severe bending.

As the copper alloy according to the present invention, Ni2Si
Having an intermetallic compound of Ni and Si, such as Ni: 1.
0 to 4.8% by mass, Si: 0.2 to 1.4% by mass, C
u: remainder Cu-Ni-Si alloy, Cr grains and C
Cr having an intermetallic compound of u and Zr: 0.02 to Cr.
4% by mass, Zr: 0.01 to 0.25% by mass, Cu: The balance is particularly preferably Cu-Cr-Zr-based alloy.
Sn, Fe, Ti, P,
One or more of Mn, Zn, In, Mg and Ag may be added in a total amount of 0.005 to 2% by mass. Further, a copper alloy having second phase particles such as other types of precipitates and dispersions may be used.

[0020]

Next, the effects of the present invention will be described more specifically with reference to examples. First, a predetermined amount was put into a vacuum melting furnace together with other additive elements as necessary, using electrolytic copper or oxygen-free copper as a raw material.
An ingot having the component composition shown in No. 3 was obtained. Table 1 shows the components of the Cu-Ni-Si alloy, and Table 2 shows the components of Cu-Cr-Z.
Table 3 shows the components of the r-based alloy and the components of other copper alloys.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

Next, these ingots were subjected to hot rolling at a temperature of 950 ° C. to form plates having a thickness of 10 mm. Thereafter, the oxide layer on the surface layer was removed by mechanical polishing, and a 5 mm plate was formed by cold rolling. Then, in the case of an aging-precipitation type copper alloy, a solution treatment was performed. Otherwise, the first recrystallization annealing was performed. Was done. Thereafter, further cold rolling was performed to obtain a sheet having an intermediate thickness of 1.1 to 3.8 mm, and then aging treatment or second recrystallization annealing was performed at this sheet thickness. When performing aging treatment, adjust the aging temperature conditions so that the strength of the product in each alloy composition is the highest, and
In the case of recrystallization, the temperature condition was adjusted so that the crystal grain size was 5 to 15 μm. Thereafter, a plate having a thickness of 0.15 mm was produced by final cold rolling, and used as a sample for evaluation experiment. Tables 1 to 3 show the final cold rolling conditions.

Various test pieces were sampled from the obtained plate material and subjected to a material test to determine “crystal grain size”, “strength”, “elongation”,
"Bendability" and "conductivity" were evaluated. The “crystal grain size” was obtained by observing a bright-field image with a transmission electron microscope and obtaining the obtained photograph by a cutting method according to JIS H0501. FIG. 1 shows the result of observing the crystal grains. "Strength" and "elongation" are JIS Z
The test was performed by using a No. 5 test piece in accordance with the tensile test specified in 2241, and the tensile strength and the elongation at break were measured and measured. "Bendability" is evaluated by examining the presence or absence of cracks by performing bending using a W bending tester and observing the bent portion with an optical microscope at a magnification of 50 times. Is indicated by ○, and the case where cracks are generated is indicated by ×. "Conductivity" was determined by measuring conductivity using a four-terminal method.

The above evaluation results are shown in Tables 1, 2 and 4. It can be seen that the alloy of the present invention has excellent strength, elongation and bendability. On the other hand, Comparative Examples 6 to 8, 14 to 16, 3
Nos. 3 to 34 are examples in which the desired structure was not obtained due to the low workability of the final rolling, and the ductility was lowered and good bendability was not obtained. Note that FIG. 12 is a transmission electron micrograph of Example 12, in which the formed continuous recrystallization has an average crystal grain size of 1 μm or less, and its crystal grain boundary is rounded mainly in a curved portion. For comparison, Comparative Example No. FIG. 3 shows a transmission electron micrograph of Sample No. 6 in which the grain boundaries are almost straight.

[0027]

[Table 4]

Next, the materials prepared in Examples 9, 22, 26, and 30 of the present invention and Comparative Examples 33 and 34 were further subjected to strain relief annealing and subjected to a tensile test. Table 5 shows the results. It can be seen that the elongation of the alloy of the present invention is further improved by the strain relief annealing as compared with the alloy of the comparative example. This is expected to withstand more severe processing.

[0029]

[Table 5]

[0030]

As described above, according to the present invention,
Copper or a copper alloy having an excellent balance between strength and workability can be obtained, and the performance of electronic device materials such as terminals, connectors, lead frames, and printed circuit boards can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a recrystallization process.

FIG. 2 is a transmission electron micrograph showing the structure of the alloy of the present invention in an example.

FIG. 3 is a transmission electron micrograph showing the structure of the alloy of the present invention in an example.

Claims (6)

[Claims] 1. A structure of fine crystal grains having a grain size of 1 μm or less consisting of a grain boundary mainly composed of a curved portion after the final cold rolling by causing dynamic continuous recrystallization by final cold rolling. And copper and a copper alloy having an elongation of 2% or more in a tensile test. 2. When the working degree η in the final cold rolling is represented by the following formula, by performing rolling processing in which η ≧ 3, fine crystal grains having a grain size of 1 μm or less after the final cold rolling are obtained. A method for producing copper and a copper alloy, which has the following structure and exhibits an elongation of 2% or more by a tensile test. Η = ln (T ₀ / T ₁ ) T ₀ : thickness before rolling, T ₁ : thickness after rolling 3. The copper and copper alloy according to claim 1 or 2, which are subjected to strain relief annealing so that elongation in a tensile test is 6% or more.
2. The method for producing copper and copper alloy according to item 1. 4. Copper and a copper alloy produced by the production method according to claim 2. Description: 5. The method according to claim 1, wherein the copper alloy is a Cu—Ni—Si alloy or a Cu—Cr—Zr alloy. 6. The copper and copper alloy according to claim 4, wherein the copper alloy is a Cu—Ni—Si alloy or a Cu—Cr—Zr alloy.