CU-NI-SI-BASED COPPER ALLOY PLATE, FILM-PLATED CU-NI-SI-BASED COPPER ALLOY PLATE, AND PRODUCTION METHOD FOR CU-NI-SI-BASED COPPER ALLOY PLATE AND FILM-PLATED CU-NI-SI-BASED COPPER ALLOY PLATE

A Cu-Ni-Si based copper alloy containing Ni and Si: in a center portion in a plate thickness direction, containing 0.4% by mass or more and 5.0% by mass or less of Ni, 0.05% by mass or more and 1.5% by mass or less of Si, and the balance Cu and inevitable impurities; where an Ni concentration on a plate surface is 70% or less of a center Ni concentration in the thickness center portion; a surface layer portion having a depth from the plate surface to be 90% of the center Ni concentration; in the surface layer portion, the Ni concentration increases from the plate surface toward the thickness center portion at 5.0% by mass/µm or more and 100% by mass/µm or less of a concentration gradient; to improve the electric connection reliability under high-temperature environment, and even when a plating film such as Sn or the like is provided, the electric connection reliability, the solder wettability, and the adhesiveness of the plating film under the high-temperature environment is improved.