HIGH-STRENGTH Cu-Ni-Co-Si BASE COPPER ALLOY SHEET, PROCESS FOR PRODUCING SAME, AND CURRENT-CARRYIN

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[Problem] To provide a copper alloy sheet material that has a very high strength of a 0.2% offset yield strength of 980 MPa or more, and is good in the conductivity, the stress relaxation resistance property and the press workability. [Solution] A copper alloy sheet material : having a chemical composition containing from 2.50 to 4.00% in total of Ni and Co, from 0.50 to 2.00% of Co, from 0.70 to 1.50% of Si, from 0 to 0.50% of Fe, from 0 to 0.10% of Mg, from 0 to 0.50% of Sn, from 0 to 0.15% of Zn, from 0 to 0.07% of B, from 0 to 0.10% of P, from 0 to 0.10% of REM (rare earth elements), from 0 to 0.01% in total of Cr, Zr, Hf, Nb and S, the balance of Cu, and unavoidable impurities, all in terms of percentage by mass; having a number density of coarse secondary phase particles having a particle diameter of 5 µm or more of 10 per mm2 or less, and a number density of fine secondary phase particles having a particle diameter of from 5 to 10 nm of 1.0 × 109 per mm2 or more; and having an Si concentration in the parent phase of 0.10% by mass or more.