Manufacturing method of semiconductor package

A manufacturing method of a semiconductor package, comprising:

• etching a first surface and a side surface of a base substrate, the base substrate including the first surface, a second surface opposed to the first surface and the side surface positioned between the first surface and the second surface, the base substrate containing at least one kind of metal;
• attaching a metal different from the at least one kind of metal contained in the base substrate to the first surface and the side surface;
• disposing a semiconductor device on the second surface of the base substrate, the semiconductor device having an external terminal;
• forming a resin insulating layer sealing the semiconductor device;
• forming a first conductive layer on the resin insulating layer;
• forming an opening, exposing the external terminal, in the first conductive layer and the resin insulating layer;
• and
• forming a metal layer on the first surface and the side surface of the base substrate, on the first conductive layer and in the opening;
• wherein a surface of the semiconductor device on which the external terminal is not provided faces the base substrate.