The invention provides a core material, a solder joint and a bump electrode forming method. The invention provides the core material with high Sb uniformity in a soft solder plating layer and a Sb concentration ration in a preset range. The core material is provided with a Sn-Sb series soft solder alloy which comprises Sn and Sb in a surface plating film on the surface of a core (12). The Sb in the soft solder plating layer (16) is distributed in the soft solder plating layer in a concentration ration in a preset range. The Sb is distributed in the soft solder plating layer in a concentrationof 70.0-125.0%. The Sb in the soft solder plating layer is uniform. Therefore the Sb concentration ratio in a whole area which comprises the inner circumferential side and the outer circumferential side in the soft solder plating layer is in the preset range. Therefore a fact that the inner circumferential side is molten earlier than the outer circumferential side, a volume expansion difference between the inner circumferential side and the outer circumferential side and the core material springs is prevented. The soft solder plating layer is almost uniformly molten, thereby preventing a position offset of the core material caused by melting time deviation, and preventing a worry for shortcircuit between electrodes along with position offset.