Method of manufacturing cu core ball

A method of manufacturing a Cu core ball, comprising:

• providing a Cu ball as an inside ball, of least 99.9 mass percent but not more than 99.995 mass percent of said Cu ball being Cu, said Cu ball having a contained amount of U equal to or less than 5 ppb by mass, a contained amount of Th equal to or less than 5 ppb by mass, a total contained amount of at least one of Pb and Bi equal to or larger than 1 ppm by mass, and a sphericity equal to or higher than 0.95;
• surrounding the inside ball with a solder plating film of a lead free solder alloy whose primary component is Sn;
• thereafter, placing the inside ball, surrounded by the solder plating film, into a quantity of a plating solution and irradiating the inside ball, the solder plating film, and the plating solution with an ultrasonic wave for a period time that is sufficient to provide a Cu core ball having an arithmetic roughness equal to or less than 0.3 μm.