A Cu core ball suppresses a soft error and its alpha dose is low. Its surface roughness does not affect a mounting process. A pure degree of the Cu ball as an internal ball is equal to or larger than 99.9% and equal to or less than 95%. A total contained amount of Pb and/or Bi in impurity contained in the Cu ball is equal to or larger than 1 ppm. Its sphericity is equal to or higher than 0.95. A solder plating film coated on the Cu ball is a Sn solder plating film or a solder plating film comprising a lead free solder alloy whose primary component is Sn. In the solder plating film, a contained amount of U is equal to or less than 5 ppb and that of Th is equal to or less than 5 ppb. A total alpha dose of the Cu ball and the solder plating film is equal to or less than 0.0200 cph/cm 2 . An arithmetic average roughness of the Cu core ball is equal to or less than 0.3 µm.