u00b0 to 350 u00b0 c for 10 to 270 minutes the flexible copper applied substrate of the present invention is more excellent in adhesive strength and curl resistance as compared with a conventional substrate comprising a single polyimide resin layer and a copper foil that is in the present invention the two kinds of polyimide resins are not simply mixed and a synergistic effect due to the formation of the composite is exhibited in consequence according to the present invention the substrates can be provided which have high adhesive strength and which present curling now the present invention will be described in detail in reference to examples and comparative examples but the scope of the present case should not be limited to these examples a stirrer was set to a 500 milliliter three necked flask and the atmosphere in the flask was then replaced with nitrogen afterward 250 ml of purified dimethylacetamide was poured into the flask additionally 8 6 g of paraphenylenediamine and 4 0 g of 4 4 39 diaminodiphenyl ether were then added thereto and dissolved therein after the dissolution while a reaction temperature was controlled so as not to exceed 10 u00b0 c 29 4 g of 3 4 3 39 4 39 biphenyltetracarboxylic acid dianhydride was added thereto little by little with stirring to perform reaction after completion of the addition the reaction was carried out at a reaction temperature of 15 u00b0 c for 5 hours so that a polyamide acid solution was obtained the thus obtained polyamide acid had an inherent viscosity of 1 8 at 30 u00b0 c at a concentration of 0 5 g dl in n methyl 2 pyrrolidone into a b.