Method and composition for etching of Al-Cu layers to form electronic circuits

An etchant useful for chemically milling aluminium from tri-metal layers of copper-aluminium-copper being copper circuit patterns present on opposing surfaces of an aluminium foil, one of the copper patterns being laminated onto a substrate, the etchant comprising an aqueous solution of: (1) 60 to 500 g/l base selected from (a) sodium hydroxide, (b) potassium hydroxide, and (c) their mixture; and (2) 30 to 500 g/l of a nitrite salt, borate salt, a bromate salt, or a mixture of any of them.