CU-CO-SI-BASED ALLOY SHEET, AND PROCESS FOR PRODUCTION THEREOF

Abstract

 The present invention provides a Cu-Co-Si system alloy sheet, being suitable for use in a variety of electronic device components, in particular, having excellent uniform adhesive property for plate.
The copper alloy sheet for electronic materials, contains 0.5 to 3.0 mass% Co, 0.1 to 1.0 mass% Si, the balance being Cu and unavoidable impurities, wherein an average grain size in the center part of the sheet thickness is 20 µm or less, and
the number of the crystal grain, being tangent to a surface of the sheet and having 45 µm or more of the length of major axis, is 5 or less in the area of 1 mm in a rolling direction.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a Cu-Co-Si system alloy sheet which is a precipitation hardening copper alloy and suitable for use in a variety of electronic device components, in particular, to a Cu-Co-Si system alloy sheet which has excellent uniform adhesive property for plate.

BACKGROUND OF THE INVENTION

[0002] A copper alloy for electronic materials that are used in a connector, switch, relay, pin, terminal, lead frame, and various other electronic components is required to satisfy both high strength and high electrical conductivity (or thermal conductivity) as basic characteristics. In recent years, as high integration and reduction in size and thickness of an electronic component have been rapidly advancing, requirements for copper alloys used in these electronic components have been increasingly becoming severe.

[0003] Because of considerations related to high strength and high electrical conductivity, the amount in which precipitation-hardened copper alloys are used has been increasing, replacing conventional solid-solution strengthened copper alloys typified by phosphor bronze and brass as copper alloys for electronic components. With a precipitation-hardened copper alloy, the aging of a solution-treated supersaturated solid solution causes fine precipitates to be uniformly dispersed and the strength of the alloys to increase. At the same time, the amount of solved elements in the copper is reduced and electrical conductivity is improved. For this reason, it is possible to obtain materials having excellent strength, spring property, and other mechanical characteristics, as well as high electrical and thermal conductivity.

[0004] Among precipitation hardening copper alloys, Ni-Si system copper alloys commonly referred to as Corson alloys are typical copper alloys having relatively high electrical conductivity, strength, and bending workability, and are among the alloys that are currently being actively developed in the industry. In these copper alloys, fine grains of Ni-Si system intermetallic compounds are precipitated in the copper matrix, thereby increasing strength and electrical conductivity.

[0005] With the aim of further improvement for property of Corson alloys, a wide variety of technological developments, such as an addition of alloy constituents except Ni and Si, an exclusion of any constituents adversely affect on the property, an optimization of crystalline structure, an optimization of precipitated grains, have been conducted. For example, it is known that the property will improve by adding Co, or by controlling secondary-phase grains precipitated in a matrix. The followings can be given as latest improvement technologies for Ni-Si-Co system copper alloys.

[0006] Japanese Domestic Republication No. 2005-532477 (Patent document 1) discloses that, with the aim of producing Ni-Si-Co system copper alloys having excellent bending workability, electrical conductivity, strength and stress relaxation resistance, amounts of Ni, Si and Co, and mutual relationships thereof are controlled. Further, it discloses average grain sizes being 20 µm or less. Its production process is characterized in that a first age annealing temperature is higher than a second age annealing temperature (paragraphs 0045 to 0047).

[0007] Japanese patent laid-open publication No. 2007-169765 (Patent document 2) discloses that, with the aim of improving bending workability of Ni-Si-Co system copper alloys, grain coarsening is inhibited by controlling distribution state of secondary-phase grains. This Patent document explains a relationship of precipitates having an effect of inhibiting grain coarsening in high-temperature heat treatment, and distribution states, for copper alloys produced by adding cobalt to Corson alloys. Strength, electrical conductivity, stress relaxation resistance and bending workability are improved by controlling grain size (paragraph 0016). The smaller the grain size is, the more desirable it is. The Patent document discloses that bending workability will improve when the grain size is 10 µm or less (paragraph 0021).

[0008] Japanese patent laid-open publication No. 2008-248333 (Patent document 3) discloses copper alloys for electronic materials in which generation of coarse secondary-phase grains in Ni-Si-Co system copper alloys is inhibited. This Patent document explains that aimed excellent property can be given when generation of coarse secondary-phase grains is inhibited by conducting a hot rolling and a solution treatment under specific conditions (paragraph 0012).

[0009] 

[Patent document 1] Japanese Domestic Republication No. 2005-532477

[Patent document 2] Japanese patent laid-open publication No. 2007-169765

[Patent document 3] Japanese patent laid-open publication No. 2008-248333

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In general, a copper alloy sheet for electronic materials that are used in a connector, switch, relay, pin, terminal, lead frame, and various other electronic components, is often plated with Au. In the case, Ni plate is generally formed as a ground plate. The Ni ground plate becomes thinner in proportion to recent needs for being lighter and thinner in the components.
Under these circumstances, a defect in Ni plate, which has not been thought as a problem in the past, such as a defect that Ni plate does not partially adhere uniformly, becomes obvious.

[0011] Copper alloys described in the Patent documents 1 to 3 are explained about grain size. However, the documents are absolutely not aware of ununiformity of grain size in depth direction, in particular, relationship between coarse crystal made on a surface and adhesive property for plate.
The object of the present invention is to provide Cu-Co-Si system alloy sheet having excellent uniform adhesive property for ground plate, in particular, Ni plate.

MEANS FOR SOLVING THE PROBLEM

[0012] The inventors have diligently studied means for solving the problem, and eventually have found out that, in Cu-Ni-Si system alloy sheet, further improved adhesive property for ground plate can be pursued by using Cu-Co-Si system alloy, wherein Ni is replaced by Co in Cu-Ni-Si system. Further, the inventors have found out that, even when average grain size is totally small, uniform adhesive property for plate will deteriorate because grain size of the Cu-Co-Si system alloy sheet is more likely to coarsen in the surface layer locally than in the inward (in the center part of the sheet thickness), and the coarsened crystal exists in the surface. The present inventions comprise the following constitutions.

(1) A copper alloy sheet for electronic materials, containing 0.5 to 3.0 mass% Co, 0.1 to 1.0 mass% Si, the balance being Cu and unavoidable impurities, wherein an average grain size in the center part of the sheet thickness is 20 µm or less, and
the number of the crystal grain, being tangent to a surface of the sheet and having 45 µm or more of the length of major axis, is 5 or less in the area of 1 mm in a rolling direction.

(2) The copper alloy sheet for electronic materials of (1), wherein Cr is furthermore contained in a maximum amount of 0.5 mass%.

(3) The copper alloy for electronic materials of (1) or (2), wherein a single element or two or more elements selected from Mg, P, As, Sb, Be, B, Mn, Sn, Ti, Zr, Al, Fe, Zn and Ag are furthermore contained in total in a maximum amount of 2.0 mass%.

(4) A method for manufacturing the copper alloy sheet according to any one of (1) to (3), comprising sequentially conducting:

a step for casting an ingot;

a step for heating the ingot for 1 hour or more at material temperature being 950 °C to 1050 °C, thereafter hot rolling the ingot, setting the temperature to 700 °C or more when hot rolling is completed;

a step for conducting an intermediate rolling before a solution treatment, by conducting the last pass at a reduction ratio being 8 % or more;

a step for conducting an intermediate solution treatment, by heating at material temperature being 850 °C to 1050 °C, for 0.5 minute to 1 hour;

a step for conducting aging, by heating at 400 °C to 600 °C; and

a step for conducting last rolling at a reduction ratio being 10 to 50 %.

BRIEF DESCRIPTION OF THE FIGURES

[0013] 

Fig.1 is a micrograph (magnification ratio: x200) of a plate surface of Ni-plated copper alloy sheet of the present invention (inventive example 1).

Fig.2 is a micrograph (magnification ratio: x200) of a plate surface of Ni-plated copper alloy sheet of comparative example (comparative example 11).

Fig.3 is a magnified micrograph (magnification ratio: x2,500) of a plate surface in Fig.2.

PREFERRED EMBODIMENT OF THE INVENTION

(1) Additive amount of Co and Si

[0014] Added Co and Si form an intermetallic compound in copper alloy, with an appropriate heat treatment, and make it possible to increase strength, without adversely affecting electrical conductivity, by precipitation strengthening effect, in spite of the presence of added elements except copper.
When the additive amount of Co and Si are such that Co is less than 0.5 mass% and Si is less than 0.1 mass% respectively, the desired strength cannot be achieved, and conversely, when the additive amount of Co and Si are such that Co is more than 3.0 mass% and Si is more than 1.0 mass% respectively, higher strength can be achieved, but electrical conductivity is dramatically reduced and hot workability furthermore deteriorates. Therefore, the additive amounts of Co and Si are such that Co is 0.5 to 3.0 mass% and Si is 0.1 to 1.0 mass% in the present invention. The additive amounts of Co and Si are preferably such that Co is 0.5 to 2.0 mass% and Si is 0.1 to 0.5 mass%.

(2) Additive amount of Cr

[0015] Cr preferentially precipitates along crystal grain boundaries in the cooling process at the time of casting. Therefore, the grain boundaries can be strengthened, cracking during hot rolling is less liable to occur, and a reduction in yield can be inhibited. That is, Cr, being precipitated along the grain boundaries during casting, is solved again by solution treatment and the like, resulting in producing precipitated grains or compounds with Si (silicide), having a bcc structure mainly composed of Cr in the subsequent aging precipitation. With an ordinary Ni-Si system copper alloy, the portion of the added Si, being not contributed to aging precipitation, remains solved in the matrix, and deteriorates electrical conductivity. Then, the Si content solved in the matrix can be reduced and deterioration of electrical conductivity can be inhibited without compromising strength by adding Cr as a silicide-forming element and causing Si, being not contributed to aging precipitation, to further precipitate as silicide. However, when the Cr concentration exceeds 0.5 mass%, coarse second-phase grains are more easily formed and product characteristics are compromised. Therefore, in the Cu-Co-Si system alloys according to the present invention, Cr can be added in a maximum amount of 0.5 mass%. However, since the effect of the addition is low at less than 0.01 mass%, the additive amount is preferably 0.01 to 0.5 mass%, and more preferably 0.09 to 0.3 mass%.

(3) Additive amount of the third elements

a) Additive amount of Mg, Mn, Ag and P

[0016] The addition of traces of Mg, Mn, Ag and P improves strength, stress relaxation characteristics, and other manufacturing characteristics without compromising electrical conductivity. The effect of the addition is mainly produced by the formation of a solid solution in the matrix, but the effect can be further produced when the elements are contained in the second-phase grains. However, when the total concentration of Mg, Mn, Ag and P exceeds 2.0 mass%, the effect of improving the characteristics becomes saturated and manufacturability is compromised. Therefore, in the Cu-Co-Si system alloy sheet according to the present invention, a single element or two or more elements selected from Mg, Mn, Ag and P can be added in total in a maximum amount of 2.0 mass%. However, since the effect of the addition is low at less than 0.01 mass%, the additive amount is preferably a total of 0.01 to 2.0 mass%, more preferably a total of 0.02 to 0.5 mass%, and typically a total of 0.04 to 0.2 mass%.

b) Additive amount of Sn and Zn

[0017] The addition of traces of Sn and Zn also improves the strength, stress relaxation characteristics, plating properties, and other product characteristics without compromising electrical conductivity. The effect of the addition is mainly produced by the formation of a solid solution in the matrix. However, when the total amount of Sn and Zn exceeds 2.0 mass%, the characteristics improvement effect becomes saturated and manufacturability is compromised. Therefore, in the Cu-Co-Si system alloy sheet according to the present invention, one or two elements selected from Sn and Zn can be added in total in a maximum amount of 2.0 mass%. However, since the effect of the addition is low at less than 0.05 mass%, the additive amount is preferably a total of 0.05 to 2.0 mass%, and more preferably a total of 0.5 to 1.0 mass%.

c) Additive amount of As, Sb, Be, B, Ti, Zr, Al and Fe

[0018] The addition of As, Sb, Be, B, Ti, Zr, Al and Fe also improves electrical conductivity, strength, stress relaxation characteristics, plating properties, and other product characteristics, by adjusting the additive amount thereof, in accordance with the required product characteristics. The effect of the addition is mainly produced by the formation of a solid solution in the matrix, but a further effect can be produced when the above-described elements are added to the second-phase grains or when second-phase grains having a new composition are formed. However, when the total concentration of these elements exceeds 2.0 mass%, the characteristics improvement effect becomes saturated and manufacturability is compromised. Therefore, in the Cu-Co-Si system alloy sheet according to the present invention, a single element or one or greater elements selected from As, Sb, Be, B, Ti, Zr, Al and Fe can be added in total in a maximum amount of 2.0 mass%. However, since the effect of the addition is low at less than 0.001 mass%, the additive amount is preferably a total of 0.001 to 2.0 mass%, and more preferably a total of 0.05 to 1.0 mass%.
Manufacturability is readily compromised when the additive amount of the Mg, P, As, Sb, Be, B, Mn, Sn, Ti, Zr, Al, Fe, Zn and Ag described above exceeds 2.0 mass% as a total. Therefore, the total is preferably 2.0 mass% or less, and more preferably 1.5 mass% or less, and further more preferably 1.0 mass% or less.

(4) Grain size

[0019] It is well-known that high strength can be achieved when grain size is small, and the average grain size in the center part of the sheet thickness, in cross-section surface of rolling direction, is 20 µm or less in the present invention. The average grain size in the center part of the sheet thickness is measured on the basis of JIS H 0501 (cutting method). The average grain size in the center part of the copper alloy sheet thickness of the present invention does not change relatively to a remarkable extent before and after the last rolling at a reduction ratio being 10 to 50 %. Accordingly, if the average grain size is 20 µm or less before the last rolling, the alloy can maintain finer crystal structure than sample copper alloys having the copper average grain size being 20 µm, even after the last rolling. Therefore, even if numerical values of the average grain size after the last rolling cannot be measured precisely because the crystal structure is too fine, it can be judged whether the average grain size exceeds 20 µm or not, by comparing the sample copper alloys, having the copper average grain size being 20 µm before the last rolling, and conducted the last rolling under an identical condition, as the standard. In addition, "the average grain size, being 20 µm or less, in the center part of the sheet thickness" of the present invention is the provision for securing the same high strength with prior art, and "the center part of the sheet thickness" of the present invention is the wording for indicating a measurement position.

[0020] Prior art has not taken particular note of ununiformity of grain size, especially coarsened crystal in the surface, and it has been totally unknown that the coarsened crystal grain in the surface causes adverse effects on uniform adhesive property for plate. However, the surface layer is the most likely to accumulate strain energy in the rolling step, and then the crystal is more likely to coarsen in the surface layer locally than in the inward (in the center part of the sheet thickness) in usual process conditions. Further, a thermal history of the surface layer may differ from that of the inward in heat treatment step, and crystals may coarsen locally compared to the inward (the center part of the sheet thickness). In the case, above mentioned "surface layer" means an area from the surface to 25 µm in depth.
The inventors of the present invention have found out that Cu-Co-Si system alloy sheet for electronic materials, wherein plates can adhere uniformly to the surface of the alloy sheet, can be provided by decreasing crystal grains coarsened in the surface of the Cu-Co-Si system alloy sheet.
In particular, the number of the crystal grain, being tangent to the surface of the sheet and having 45 µm or more of the length of major axis, is 5 or less in the area of 1 mm in a rolling direction. The number of the crystal grain is preferably 4 or less, more preferably 2 or less. If the number of the crystal grain exceeds 5, the plates do not adhere to the surface of the alloy sheet uniformly, and the plated products will be defective products, wherein tarnish can be seen on the plates when observed by the unaided eye.
The number of the crystal grain, being tangent to the cross-section surface of rolling direction and having 45 µm or more of the length of major axis, is measured by micrograph (magnification ratio: x400). The number of the crystal grain is divided by the total length of the measured grain sizes, in the surface area having 2,000 µm in length, provided by the multiple (10 times) measured views, and then indicated by the millimeter.

[0021] The copper alloy sheet of the present invention has excellent uniform adhesive property for plate because the number of the crystal grain, being tangent to the surface of the sheet and having 45 µm or more of the length of major axis, is 5 or less. Various plate materials can be applied to the copper alloy sheet of the present invention. The plate materials include, for example, Ni ground plate which is generally used for a ground plate for Au plate, Cu ground plate, Sn plate and the like.
The plate in the alloy sheet of the present inventions has enough uniform adhesive property in the thickness of 2 to 5µm as well as 0.5 to 2.0 µm.

(5) Method for manufacturing

[0022] The method for manufacturing the copper alloy sheet of the present invention uses general manufacturing processes for the copper alloy sheet (melting and casting → hot rolling → intermediate cold rolling → intermediate solution treatment → last cold rolling → aging). However, intended copper alloy sheet is produced by adjusting the following conditions in those steps. If desired, the intermediate rolling and the intermediate solution treatment may be conducted repeatedly more than once.
It is important to control the conditions of the hot rolling, the intermediate cold rolling and the intermediate solution treatment strictly in the present invention. The reason is that Co is added in the copper alloy sheet of the present invention, secondary-phase grains of Co are likely to coarsen, and a generation and a growing rate of the secondary-phase grains are influenced a great deal by a maintaining temperature during heat treatment, and a cooling rate.
In the melting and casting steps, electrolytic cathode copper, Si and Co, and other starting materials are melted to obtain a molten metal having the desired composition. Then the molten metal is cast in a mold to produce an ingot. In subsequent hot rolling step, it is necessary to eliminate crystallized substances such as Co-Si, generated in casting step, to a maximum extent, by conducting heat treatment uniformly. For example, hot rolling is conducted after maintaining at 950 to 1050 °C for 1 hour or more. When the maintaining temperature before the hot rolling is less than 950 °C, solubilization is not enough. On the other hand, when the maintaining temperature is more than 1050 °C, materials may dissolve.
Further, "a temperature at the end of the hot rolling is less than 700 °C" means "processing treatments of the last pass or a few passes including the last pass in the hot rolling, are conducted at less than 700 °C." When the temperature at the end of the hot rolling step is less than 700 °C, the inward is in the state of recrystallization, while the surface layer ends in the state of being subjected to processing strain. When a cold rolling is conducted in the conditions and then the solution treatment is conducted under normal conditions, the inward is in the state of normal recrystallization structure, while coarsened crystal grains are formed in the surface layer. Accordingly, in order to inhibit the formation of the coarsened crystal grains in the surface layer, the temperature at the end of the hot rolling is preferably 700 °C or more, more preferably 850 °C or more, and it is preferable to conduct rapid cooling after the end of the hot rolling. The rapid cooling can be achieved by water cooling.

[0023] After the hot rolling, an intermediate rolling and an intermediate solution treatment are conducted, by selecting frequency and order of them, within a scope of the purpose. When the reduction ratio of the last pass in the intermediate rolling is less than 5 %, processing strain energy is accumulated only in the surface of materials. Accordingly, coarsened crystal grains are generated in the surface layer. In particular, the reduction ratio of the last pass in the intermediate rolling is preferably 8 % or more. Further, controlling viscosity of rolling oil used in the intermediate rolling and rate of the intermediate rolling is also effective for uniform load of the processing strain energy.
The intermediate solution treatment is sufficiently conducted, in order to eliminate precipitates such as coarsened Co-Si as much as possible, by dissolving crystallized grains generated at solution casting and precipitated grains generated after hot rolling. For example, when the temperature of the solution treatment is less than 850 °C, the solution is not enough and then desired strength of alloys cannot be provided. On the other hand, when the temperature of the solution treatment is more than 1050 °C, materials may be dissolved. Therefore, it is preferable to conduct solution treatment where the materials are heated at 850 to 1050 °C. The solution treatment is preferably conducted for 0.5 minutes to 1 hour.
In addition, as a relation of temperature and time, in order to provide the same effect of heat treatment (for example, the same grain size), based on common sense, it is necessary for the heat time to be short at high temperature, and to be long at low temperature. For example, in the present invention, the heat time is preferably 1 to 2 minutes at 950 °C, and 0.5 to 1 minute at 1000 °C.
After the solution treatment, in general, rapid cooling is conducted in order to inhibit precipitation of dissolved secondary-phase grains.
Next, fine secondary-phase grains are precipitated uniformly by conducting aging treatment at temperature conditions of 400 °C or more and 600 °C or less. When the aging temperature is less than 400 °C, fine secondary-phase grains precipitate insufficiently, and then a problem that desired strength and electrical conductivity cannot be provided, is caused. When the aging temperature is more than 600 °C, the precipitated secondary-phase grains coarsen, and then a problem that desired strength cannot be provided, is caused. The aging temperature is preferably 450 °C or more and 550 °C or less. A reduction ratio of the last pass is preferably 10 to 50 %, more preferably 30 to 50 %. When the reduction ratio is less than 10 %, desired strength cannot be provided. On the other hand, when the reduction ratio is more than 50 %, bending workability deteriorates.

[0024] The copper alloy sheet of the present invention has no coarsened crystal grains on the surface, and then can be used appropriately for lead frames, connectors, pins, terminals, relays, switches, foil material for secondary batteries, and other electronic components and the like.

EXAMPLES

[0025] Hereinafter, working examples will be described with comparative examples in order to understand the present invention and advantages thereof better. However, the present invention is not limited to these examples.

(1) Measuring procedure

(a) Grain size in the center part of the sheet thickness

[0026] Standard samples (Co: 1.0 mass%, Si: 0.66 mass%, the balance being Cu), wherein a solution treatment was finished, a last rolling was not finished, and the average grain size in the center part of the sheet thickness in a rolling direction is 20 µm, were produced. The average grain size was measured according to JIS H 0501 (cutting process). With respect to the standard samples, the last cold rolling (reduction ratio 15 %) was conducted, optical micrographs (magnification ratio: x400) in the center part of the sheet thickness, in cross-section surface of rolling direction, were taken, and then used as a standard. Next, with respect to large or small, optical micrographs (the same magnification ratio as that of the standard) in the center part of the sheet thickness after the last cold rolling, of each example (inventive example and comparative example), and the standard were compared with visual check. Then, the grain size was defined to be more than 20 µm ( > 20 µm) when the grain size of the example is larger than that of the standard, and the grain size was defined to be 20 µm or less ( ≦ 20 µm) when the grain size of the example is equal to or less than that of the standard.

(b) Observation of crystal grain adjacent to the surface layer

[0027] With respect to the surface layer, by using micrographs in cross-section surface layer of rolling direction, a line parallel to the surface was drawn at a depth of 10µm from the surface layer. Then the length of the line was measured, and at the same time, the number of the crystal grains, wherein at least a part of which was tangent to the surface and a grain size was 45µm or more, was counted by line segment method in 10 observation fields. Next, the sum of the number of the crystal grains, having the grain size of 45 µm or more, was divided by the sum of the line segments, and then the number of the crystal grains, having the grain size of 45µm or more, per millimeter, was calculated.

(c) Uniform adhesive property for plate

(Procedure of electrolytic degreasing)

[0028] Samples are electrolytically degreased in alkaline aqueous solution, by using the samples as cathode.
Then the samples are washed by sulfuric acid aqueous solution of 10 mass %.

(Conditions of Ni ground plating)

[0029] 

·Plating bath composition: nickel sulfate 250 g/L, nickel chloride 45 g/L, boric acid 30 g/L

·Plating bath temperature: 50 °C

·Current density: 5 A/dm²

·Ni plate having 1.0 µm in thickness was formed by controlling electrodeposition time. The plate thickness was measured by using CT-1-type electrolysis plate thickness tester (DENSOKU INSTRUMENTS) and electrolyte R-54 (KOCOUR).

(Evaluation of uniformity of adhesive property for plate)

[0030] Optical micrographs (magnification ratio: x200, observation field area: 0.1 mm²) were taken, and then the number and the distribution state of island shaped plates were observed. The evaluations are as follows:

S: None

A: 50 or less island shaped plates / mm²

B: 100 or less island shaped plates / mm²

C: more than 100 island shaped plates / mm²

Fig.1 is the optical micrograph of the plate surface of inventive example 1, and it corresponds to rank "S". Fig.2 is the optical micrograph of the plate surface of comparative example 11, and it corresponds to rank "C". In addition, Fig.3 is the magnified micrograph (magnification ratio: x2,500) of "island shaped plate", observed in the plate surface, and such an island shaped plate was deemed to be one plate. In this way, the number of the island shaped plates in the observation field was counted.

(d) Strength

[0031] Tensile test was conducted in parallel to the rolling direction, and 0.2 % yield strength (YS:MPa) was measured.

(e) Electrical conductivity (EC:% IACS)

[0032] Electrical conductivity was determined by measuring volume resistivity with the aid of double bridge.

(f) Bending workability

[0033] W bending test was conducted to Bad Way (BW: a direction where the bending axis is parallel to the rolling direction) according to JIS-H3130. Then MBR/t, which is the ratio of minimum bending radius (MBR) where cracks were not generated, to sheet thickness (t), was calculated. Bending workability was evaluated by the following standards.
MBR/t ≦ 2.0 Excellent
2.0 < MBR/t Defect

(2) Method for manufacturing

[0034] Copper alloys having the compositions shown in Table 1,were melted in a highfrequency melting furnace at 1300 °C and then cast in a mold to produce ingots having a thickness of 30 mm. Next, the ingots were heated for 3 hours, under the conditions shown in Table 1, hot rolled thereafter to a sheet thickness of 10 mm at the temperature when the hot rolling was finished (ending temperature), and soon after the hot rolling, water-cooled to a room temperature. Next, the metals were faced to a thickness of 9 mm in order to remove scales from the surface, and then sheets having a thickness of 0.15 mm were formed, by appropriately conducting cold rolling, wherein a reduction ratio of the last pass was 5 to 15 %, and intermediate solution treatment for 0.5 minutes to 1 hour, wherein the temperature of material was 900 °C. Soon after the solution treatment, the sheets were water-cooled to a room temperature. Next, the sheets were subjected to an aging treatment in an inert atmosphere at 520 °C for 3 hours, and then the last cold rolling at a reduction ratio being 15 % was conducted to produce each test piece. Measurement result of each test piece is shown in Table 1.

[0035] 

[0036] The reduction ratio of the intermediate rolling in the last pass, in inventive example 1, was 15 %. On the other hand, inventive example 2, having the same composition with inventive example 1, had lower reduction ratio of 10 % and then coarsened grains generated in the surface. Accordingly, inventive example 2 was slightly inferior to inventive example 1 in uniformity of adhesive property for plate. The same was true in the relation between inventive examples 4 and 5.
The ending temperature (temperature when hot rolling was completed), in inventive example 1, was 750 °C. On the other hand, inventive example 3, having the same composition with inventive example 1, had lower ending temperature of 700 °C. Accordingly, inventive example 3 was much inferior to inventive example 1 in uniformity of adhesive property for plate. The same was true in the relation between inventive examples 4 and 6.
In inventive example 1, the starting temperature in hot rolling was 950 °C, and the ending temperature was 750 °C. On the other hand, comparative example 11, having the same composition with inventive example 1, had lower starting temperature of 800 °C and lower ending temperature of 500 °C. Accordingly, coarsened grains generate in the surface, and therefore comparative example 11 was much inferior to inventive example 1 in uniformity of adhesive property for plate.
In addition, when Ni plate of 3.0 µm in thickness was formed on the surface of copper alloy of comparative example 11, island shaped plates became less prominent on the surface of the alloy after plating, and its condition became nearly rank "S".
The same was true in the relation between inventive example 4 and comparative example 14.

[0037] The reduction ratio of the intermediate rolling in the last pass, in comparative example 11, was 15 %. On the other hand, comparative example 12, having the same composition with comparative example 11, had lower reduction ratio of 5 %. Accordingly, more coarsened grains generated in the surface, and therefore comparative example 12 was much inferior in uniformity of adhesive property for plate.
In inventive example 7, the starting temperature in hot rolling was 950 °C, the ending temperature was 750 °C, and the reduction ratio of the intermediate rolling in the last pass was 15 %. On the other hand, comparative example 17, having the same composition with inventive example 7, had lower starting temperature of 800 °C, lower ending temperature of 500 °C and lower reduction ratio of 5 %. Accordingly, coarsened grains generated in the surface, and therefore comparative example 17 was inferior to inventive example 7 in uniformity of adhesive property for plate.
The same was true in the relation between inventive example 8 and comparative example 18.

Claims

1. A copper alloy sheet for electronic materials, containing 0.5 to 3.0 mass% Co, 0.1 to 1.0 mass% Si, the balance being Cu and unavoidable impurities, wherein
an average grain size in the center part of the sheet thickness is 20 µm or less, and
the number of the crystal grain, being tangent to a surface of the sheet and having 45 µm or more of the length of major axis, is 5 or less in the area of 1 mm in a rolling direction.

2. The copper alloy sheet for electronic materials of claim 1, wherein Cr is furthermore contained in a maximum amount of 0.5 mass%.

3. The copper alloy for electronic materials of claim 1 or 2, wherein a single element or two or more elements selected from Mg, P, As, Sb, Be, B, Mn, Sn, Ti, Zr, Al, Fe, Zn and Ag are furthermore contained in total in a maximum amount of 2.0 mass%.

4. A method for manufacturing the copper alloy sheet according to any one of claims 1 to 3, comprising sequentially conducting:

a step for casting an ingot;

a step for heating the ingot for 1 hour or more at material temperature being 950 °C to 1050 °C, thereafter hot rolling the ingot, setting the temperature to 700 °C or more when hot rolling is completed;

a step for conducting an intermediate rolling before a solution treatment, by conducting the last pass at a reduction ratio being 8 % or more;

a step for conducting a intermediate solution treatment, by heating at material temperature being 850 °C to 1050 °C, for 0.5 minute to 1 hour;

a step for conducting aging, by heating at 400 °C to 600 °C; and

a step for conducting last rolling at a reduction ratio being 10 to 50 %.

Drawing