A method for mounting a semiconductor package onto PCB is disclosed. A semiconductor package is provided, which comprises a plurality of outer terminals exposed out of an encapsulant. A PCB is provided and has a surface with a plurality of contact pads. Each contact pad has a first exposed side, an opposing exposed second side and a center between the exposed sides. A plurality of first pre-solders and a plurality of second pre-solders are formed on the surface by one single printing. The first pre-solders and the second pre-solders respectively cover the first and second exposed sides of the contact pads, spaces between the opposing first and second pre-solders expose the centers of the contact pads. Then the first and second pre-solders are reflowed and the semiconductor package is mounted on the PCB. When the outer terminals is connected to the contact pads, each first pre-solder and second pre-solder are flowed toward the corresponding exposed centers of the contact pad to prevent the fine pitch contact pads from bridging.