Recent flexible printed circuit applications of high-frequency wireless communication systems require thicker metal layers on substrates for lower ohmic losses. In this paper, a Cu layer over 50-micron thick was directly generated on the polyimide substrate by heterogeneous bonding method without interlayer. The polyimide was first sputtered a 200 nm-thick Cu layer, and then was activated by oxygen plasma to improve its hydrophilicity and achieve direct adhesion between polyimide and nanoscale Cu deposition, and eventually was bonded with a 50micron-thick Cu foil in a Pt-catalyzed formic acid atmosphere by thermo-compression. The effectiveness of this method was verified by comparing bonding interfaces, shear strength, and fracture modes of bonded samples with and without a Cr interlayer. This method provides a new idea for the integration of heterogeneous materials needed in wearable products and flexible printed circuits.