Process for etching a semiconductor lead frame

A method for producing a lead frame having a plurality of outer leads and a plurality of inner leads respectively having tips, for a resin-sealed semiconductor package, comprising:

• coating a first and a second major surface of a blank for a lead frame with a first and a second photoresist layer, respectively;
• forming a first resist pattern having a first opening on the first major surface of the blank by exposing the first photoresist layer through a first pattern mask and a second resist pattern having second openings on the second major surface of the blank by exposing the second photoresist layer through a second pattern mask;
• applying a first etchant to at least the first major surface of the blank to form an etched recess;
• cleaning the surface of the etched recess formed in the first major surface of the blank after applying the first etchant;
• pickling the cleaned surface of the etched recess to remove oxides and hydroxides tarnishing the surface of the etched surface;
• forming a protective film over the pickled surface of the etched recess to prevent oxidation and hydraulic;
• forming an etch-resistant layer of an etch-resistant material to fill the etched recess in the first major surface of the blank;
• applying a second etchant to the second major surface of the blank to etch through remaining portions of the blank;
• and
• removing the etch resistant layer, the first resist pattern and the second resist pattern from the resulting lead frame and cleaning the lead frame.