A method of wet etching of polyimide comprising the steps of(a) cleaning a substrate for coating;(b) coating a polyamic acid varnish onto said cleaned substrate;(c) thermal curing the varnish in (b) to form a polyimide layer on the substrate;(d) coating a polyamide-imide varnish onto the layer in (c);(e) curing the varnish in (d),(f) coating a layer of photoresist onto the coated substrate;(g) masked exposing;(h) image developing on said substrate; and(i) wet etching the unprotected portion in the layers of polyimide and polyamide-imide to form a staircase pattern on the substrate.