Cu-Ni-Si-Co copper alloy for electronic materials and manufacturing method thereof

1. A copper alloy strip for an electronic materials containing 1.0-2.5% by mass of Ni, 0.5-2.5% by mass of Co, 0.3-1.2% by mass of Si, and the remainder comprising Cu and unavoidable impurities, wherein the copper alloy strip satisfies both of the following (a) and (b) as determined by means of X-ray diffraction pole figure measurement based on a rolled surface:

(a) among diffraction peak intensities obtained by β scanning at α=20° in a {200} pole figure, a peak height at β angle 145° is not more than 5.2 times that of standard copper powder; and

(b) among diffraction peak intensities obtained by β scanning at α=75° in a {111} pole figure, a peak height at β angle 185° is not less than 3.4 times that of standard copper powder;

wherein a measurement of drooping curl of the copper alloy strip in a direction parallel to a rolling direction is not more than 35 mm.

2. The copper alloy strip according to claim 1 , wherein Ni content [Ni] (% by mass), Co content [Co] (% by mass) and 0.2% yield strength YS (MPa) satisfy a relationship expressed by the following formula (i): −11×([Ni]+[Co]) 2 +146×([Ni]+[Co])+564≧YS≧−21×([Ni]+[Co]) 2 +202×([Ni]+[Co])+436.

3. The copper alloy strip according claim 1 , wherein 0.2% yield strength YS (MPa) satisfies a relationship of 673≦YS≦976, electrical conductivity EC (% IACS) satisfies a relationship of 42.5≦EC≦57.5, and the 0.2% yield strength YS (MPa) and the electrical conductivity EC (% IACS) satisfy a relationship expressed by the following formula (iii): −0.0563×[YS]+94.1972≦EC≦−0.0563×[YS]+98.7040.

4. The copper alloy strip according to claim 1 , wherein among second phase particles precipitated in a matrix phase, the number density of those particles having a particle size of 0.1 μm to 1 μm is 5×10 5 to 1×10 7 /mm 2 .

5. The copper alloy strip according to claim 1 , further containing 0.03-0.5% by mass of Cr.

6. The copper alloy strip according to claim 5 , wherein Ni content [Ni] (% by mass), Co content [Co] (% by mass) and 0.2% yield strength YS (MPa) satisfy a relationship expressed by the following formula (ii): −14×([Ni]+[Co]) 2 +164×([Ni]+[Co])+551≧YS≧−22×([Ni]+[Co]) 2 +204×([Ni]+[Co])+447.

7. The copper alloy strip according to claim 5 , wherein 0.2% yield strength YS (MPa) satisfies a relationship of 679≦YS≦982 and electrical conductivity EC (% IACS) satisfies a relationship of 43.5≦EC≦59.5, and the 0.2% yield strength YS (MPa) and the electrical conductivity EC (% IACS) satisfy a relationship expressed by the following formula (iv): −0.0610×[YS]+99.7465≦EC≦−0.0610×[YS]+104.6291.

8. The copper alloy strip according to claim 1 , further containing a total of up to 2.0% by mass of one or more selected from the group consisting of Mg, P, As, Sb, Be, B, Mn, Sn, Ti, Zr, Al, Fe, Zn and Ag.

9. A method for manufacturing the copper alloy strip according to claim 1 , the method comprising the following steps in order:

step 1 of melting and casting an ingot having a composition selected from any one of the following (1) to (3),

(1) a composition containing 1.0-2.5% by mass of Ni, 0.5-2.5% by mass of Co, 0.3-1.2% by mass of Si, and the remainder comprising Cu and unavoidable impurities,

(2) a composition containing 1.0-2.5% by mass of Ni, 0.5-2.5% by mass of Co, 0.3-1.2% by mass of Si, 0.03-0.5% by mass of Cr and the remainder comprising Cu and unavoidable impurities,

(3) a composition of preceding (1) or (2) further containing a total of up to 2.0% by mass of one or more selected from the group consisting of Mg, P, As, Sb, Be, B, Mn, Sn, Ti, Zr, Al, Fe, Zn and Ag;

step 2 of heating at 950-1050° C. for 1 hour or more, and then performing hot rolling, a temperature at the end of hot rolling being set at 850° C. or more, and then cooling material, an average cooling rate from 850° C. to 400° C. being 15° C./sec or more;

step 3 of performing cold rolling;

step 4 of conducting a solution treatment at 850-1050° C., and then cooling, an average cooling rate to 400° C. being 10° C./sec or more;

step 5 of conducting multiple-stage aging treatment in a batch-type furnace with material being coiled by heating at a material temperature of 400-500° C. for 1 to 12 hours in first stage, and then heating at a material temperature of 350-450° C. for 1 to 12 hours in second stage, and then heating at a material temperature of 260-340° C. for 4 to 30 hours in third stage, wherein cooling rate from the first stage to the second stage and from the second stage to the third stage is 1-8° C./min, temperature difference between the first stage and the second stage is 20-60° C., and temperature difference between the second stage and the third stage is 20-180° C.; and

step 6 of performing cold rolling.

10. The method according to claim 9 , further comprising a step of temper annealing by heating at a material temperature of 200-500° C. for 1 second to 1000 seconds after step 6.

11. The method according to claim 9 , wherein the solution treatment in step 4 is conducted on condition that an average cooling rate to 650° C. is not less than 1° C./sec but less than 15° C./sec and an average cooling rate from 650° C. to 400° C. is not less than 15° C./sec, instead of condition that the average cooling rate to 400° C. is 10° C./sec or more.