Method for etching laminated assembly including polyimide layer

This application is based on applications Nos. 2001-197029 and 2001-331280 filed in Japan, the contents of which are incorporated hereinto by reference. Disclosed is an etching method of a laminated assembly having a metal layer and a non-thermoplastic polyimide layer bonded together via thermoplastic polyimide, which comprises using an etchant at least containing an alkali metal hydroxide, water and oxyalkylamine, wherein the concentrations of the alkali metal hydroxide (X weight %) and of the water (Y weight %) have relationships represented by coordinate points present within a region (inclusive of boundary lines) defined by the following expressions [1] and [2]:provided that X and Y are defined based on the total weight of the alkali metal hydroxide, water and oxyalkylamine expressed as 100.