PURPOSE: To prevent silver from running to the underside of a lead frame material during silver plating and achieve finer-pitched and microminiaturized inner leads, by reinforcing the second plating side of the lead frame material before the processing of its outline by etching.

CONSTITUTION: A first plating layer 2 is formed on one side of a lead frame material 1 (A). A second plating layer 3 is formed in the specified regions thereon (B). Resist 4 is applied to the lead frame material 1 to form a required resist pattern 4a on the opposite surface to the second plating layer (C). The second plating layer formation side is reinforced by placing a reinforcing material 5 on the resist (D). The lead frame material 1 and the first plating layer 2 are etched from one side of the lead frame material 1 using the resist pattern, to form holes passing through them (E). Second etching is performed to remove excessive portions 3a (F). The reinforcing material 5 is removed, and the resist 4 is stripped.