Abstract: To provide Cu ball that has an excellent alignment performance. In order to control wettability failure of the Cu ball at a moment of soldering, lightness is regulated as an index of determining oxide film thickness on a surface of the ball and the lightness is set to be 55 or more. Further, since it is preferable that the Cu ball has a higher sphericity to measure the lightness accurately, the purity of the Cu ball is set to be 99.995% or less to order to make the sphericity higher. When the lightness is 55 or more, it is preferable that the thickness of oxide film formed on the surface of the Cu ball is 8 nm or less.

Abstract: To provide Cu ball that has less ? dose and high sphericity even when containing at least a certain amount of impurity elements other than Cu. Even when the purity thereof is 99.995% or less and U and Th contents are 5 ppb or less in order to suppress any software errors and decrease connection failure, ? dose is 0.0200 cph/cm2 or less. Further, the sphericity of the Cu ball is unexpectedly improved by making the purity not more than 99.995%.

Abstract: A bump electrode is formed on an electrode pad using a Cu core ball in which a core material is covered with solder plating, and a board which has bump electrodes such as semiconductor chip or printed circuit board mounts such a bump electrode. Flux is coated on a substrate and the bump electrodes are then mounted on the electrode pad. In a step of heating the electrode pad and the Cu core ball to melt the solder plating, a heating rate of the substrate is set to have not less than 0.01° C./sec and less than 0.3.