A member having a separated structure made by an alloy consisting of two regions having different compositions with each other is formed by casting a molten alloy into a prescribed shape, or by spray-quenching the same from a temperature of Tc+10.degree. C. or more, wherein the molten alloy exhibits two phase separation in a liquid state having a temperature difference .DELTA.T between the maximum temperature Tc (.degree. C.) and minimum temperature Td (.degree. C.) in the region of two phase separation in the liquid state being 10.degree. C. or more, and the molten alloy has a mean composition with a difference of the volume fraction between the two liquid phases of 5% by volume or more. The suitable alloy is a Cu--Fe--X alloy, a Cu--Cr--X alloy, a Cu--Co--X alloy, a Cu--Bi--X alloy, an Al--Sn--X alloy or an Al--In--X alloy. The powder obtained by spray-quenching any one of the molten alloys of the Cu--Bi--X alloy, the Al--Sn--X alloy and the Al--In--X alloy has a separated structure comprising a surface portion having a solder composition and a core portion with a composition mainly comprising Cu and Al being excellent in electrical conductivity and heat conductivity and is suitable as a solder ball.