PURPOSE: To suppress the erosion of nickel and copper by incorporating specific sppressors of nitric acid into an etching soln.

CONSTITUTION: This etching soln. contains ≥1 of the suppressors selected from nitric acid, a block copolymer of propylene oxide and ethylene oxide, polyethylene glycol of a mol.wt. of ≥2000 and polyol. These suppressors are added to the etching medium in such a manner, by which the erosion to Ni and Cu are substantially completely suppressed. Then, the layers of lead/tin, lead or tin coated with the Ni or Cu may be surely removed without damaging the Ni or Cu material and without requiring the special process control by the etching soln. The etching soln. is stable.