The present invention provides a surface treated steel sheet for electronic
components which does not include lead, which is a hazardous substance
with environmental impact, and, in particular, satisfies the solder
wettability after retort treatment, a rust-proof property and a
whisker-proof property simultaneously. More specifically, the present
invention is a surface treated steel sheet with less environmental impact
for electronic components excellent in solder wettability, a rust-proof
property and a whisker-proof property and having an Sn--Zn alloy layer
which is formed by plating Sn and Zn on a steel sheet or a Ni plated steel
sheet and then applying thermal diffusion treatment, or by plating Sn--Zn
alloy on a steel sheet or a Ni plated steel sheet, characterized in that
the amount of said Sn--Zn alloy layer is not less than 3 g/m.sup.2, the
Zn/Sn ratio (in weight ratio) is 0.01 to 10, more preferably 0.01 to 0.1,
and an inorganic film mainly composed of magnesium phosphate is formed in
the amount of 1 to 100 mg/m.sup.2 in terms of the amount of P+Mg on said
Sn--Zn alloy layer.
