A method for producing a flexible substrate layer, comprising feeding a carrier substrate layer made of a polyimide resin obtained from a reaction of 3,3',4,4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine, forming a polyamic acid resin and curing the polyamic acid resin at a curing temperature of 250 °C to 500 °C, forming a flexible substrate layer comprising a curable polymer on the carrier substrate layer, peeling the flexible substrate layer from the carrier substrate layer by the application of a mechanical stimulus without causing chemical changes in the carrier substrate layer and the flexible substrate layer, and winding the flexible substrate layer separated from the carrier substrate layer to collect the flexible substrate layer in the form of a roll wherein the steps are performed by a roll-to-roll process, the method further comprising forming metal patterns directly on the carrier substrate layer without an intervening debonding layer between the carrier substrate layer and the flexible substrate layer before formation of the flexible substrate layer to produce a flexible substrate layer with the metal patterns, wherein the metal patterns are embedded in the flexible substrate layer, and at least a portion of the flexible substrate layer is in direct contact with the carrier substrate layer, the mechanical stimulus is a tension applied during winding and collection of the carrier substrate layer and the flexible substrate layer, and wherein the carrier substrate layer has a peel strength not greater than 0.3 N/cm from the flexible substrate layer after application of the tension applied during winding, wherein the peel strength refers to the adhesion strength of the carrier substrate layer to the flexible substrate layer after application of the tension applied during winding and is measured by forming the flexible substrate layer on the carrier substrate to prepare a laminate structure, cutting the sample into a rectangular shape having a width of 10 mm by applying a physical stimulus, and measuring the force required to detach the flexible substrate layer at an angle of 90° from the carrier substrate layer while holding one end of the flexible substrate layer using a tester under conditions as disclosed in the specification, and wherein the carrier substrate layer has an adhesion strength of at least 1 N/cm to the flexible substrate layer before application of the tension applied during winding, wherein the adhesion strength refers to the adhesion strength of the carrier substrate layer to the flexible substrate layer before application of the tension applied during winding and is measured by forming the flexible substrate layer on the carrier substrate layer to prepare a 100 mm wide laminate structure, attaching a 10 mm wide tape to one end of the flexible substrate layer, and measuring the force required to detach the tape at an angle of 90° from the carrier substrate layer while holding one end of the tape using a tester under conditions as disclosed in the specification. the method further comprising forming metal patterns directly on the carrier substrate layer without an intervening debonding layer between the carrier substrate layer and the flexible substrate layer before formation of the flexible substrate layer to produce a flexible substrate layer with the metal patterns, wherein the metal patterns are embedded in the flexible substrate layer, and at least a portion of the flexible substrate layer is in direct contact with the carrier substrate layer, the mechanical stimulus is a tension applied during winding and collection of the carrier substrate layer and the flexible substrate layer, and wherein the carrier substrate layer has a peel strength not greater than 0.3 N/cm from the flexible substrate layer after application of the tension applied during winding, wherein the peel strength refers to the adhesion strength of the carrier substrate layer to the flexible substrate layer after application of the tension applied during winding and is measured by forming the flexible substrate layer on the carrier substrate to prepare a laminate structure, cutting the sample into a rectangular shape having a width of 10 mm by applying a physical stimulus, and measuring the force required to detach the flexible substrate layer at an angle of 90° from the carrier substrate layer while holding one end of the flexible substrate layer using a tester under conditions as disclosed in the specification, and wherein the carrier substrate layer has an adhesion strength of at least 1 N/cm to the flexible substrate layer before application of the tension applied during winding, wherein the adhesion strength refers to the adhesion strength of the carrier substrate layer to the flexible substrate layer before application of the tension applied during winding and is measured by forming the flexible substrate layer on the carrier substrate layer to prepare a 100 mm wide laminate structure, attaching a 10 mm wide tape to one end of the flexible substrate layer, and measuring the force required to detach the tape at an angle of 90° from the carrier substrate layer while holding one end of the tape using a tester under conditions as disclosed in the specification.