提供一种α线量少且真球度高的铜球，或者是此铜球以焊料层被覆之铜核球以助焊剂被覆的助焊剂涂布球。助焊剂涂布铜球1A包括以铜或铜合金构成的铜球2，以及被覆铜球2的助焊剂层3，铜球2所放射的α线量为0.0200cph/cm2以下，U的含量为5ppb以下，Th的含量为5ppb以下，Pb或Bi的其中任一的含量、或者是Pb及Bi的合计含量为1ppm以上，铜的纯度为99.9%以上99.995%以下，真球度为0.95以上。

Provided is a flux-coated ball obtained by coating, with a flux, either a Cu ball which is reduced in [alpha]-ray emission and has a high degree of sphericity or a Cu-core ball obtained by coating the Cu ball with a solder layer. This flux-coated Cu ball (1A) comprises a Cu ball (2) constituted of Cu or a Cu alloy and a flux layer (3) with which the Cu ball (2) is coated, wherein the Cu ball (2) emits [alpha] rays in an amount of 0.0200 cph/cm2 or less, has a U content of 5 ppb or less, a Th content of 5 ppb or less, and a content of Pb and/or Bi of 1 ppm or higher, has a Cu purity of 99.9-99.995%, and has a degree of sphericity of 0.95 or higher.