A solder paste for soldering micro components which suppress electro-migration is provided. The solder paste comprising: a powdered Pb-free soldering alloy comprising Cu of 0.1˜3.0 wt. % and In of 0.5˜8.0 wt. % simultaneously in addition to Sn; and a pasty or liquid flux; the powdered Pb-free soldering alloy and the pasty or liquid flux being mixed; whereby effectively suppressing electro-migration occurring at a solder bonding portion. It is possible to add Ag, Sb, Ni, Co, Fe, Mn and Cr as a strength improvement element, Bi and Zn as a melting point drop element and P, Ga and Ge as an anti-oxidant element to the powdered Pb-free soldering alloy.