Abstract: Surface metallization of ultrathin polyimide films is an important development direction in the field of microelectronics, and the deposition of high-performance metal coatings on the surface of ultrathin polyimide films by vacuum coating technology is a key technology that has been widely concerned and studied. But the bonding strength between the substrate and the coating is unsatisfactory due to the large difference in physical and chemical properties and poor compatibility between the PI and copper, which will become a source of microcracks at the interface and limitations on the service life of the coating. The most efficient solution to this problem is to energize the deposited ions by applying a negative bias voltage. Cut the PI films into long strips of 20 mm×200 mm, ultrasonically clean them with acetone and anhydrous ethanol. The filamentless bar-Hall ion source was used to generate a low-energy, wide-amplitude, and large-current ion beam for glow sputtering cleaning and plasma activation under the vacuum condition of 3×10⁻³ Pa, and then metallic copper films were deposited by DC magnetron sputtering coating method, in which the target current was 2.5 A, the applied negative bias power was 0, 0.05, 0.1 and 0.2 kW, respectively, and the thickness of the copper film was 1 mm. Then, the scanning electron microscope (FEI-NOVA NANO 230 type) and the energy spectrometer (X-MAX5 type) were used to observe the microstructure and composition of the metallic copper layer. The X-ray diffractometer (EMPYREAN) and X-ray photoelectron spectroscopy (XPS) methods were used to examine the phase composition of the coating. The RTS-5 dual electrodynamic four-probe was used to test the thin layer square resistance of the coating. The results show that as the negative bias power increases, the copper coating becomes more and more flat and dense, the tiny convexities on the coating surface become less and smaller, the grains become finer, the free and adsorbed oxygen content in the coating decreases, and the oxygen exists more in the form of lattice oxygen. The macroscopic properties of the copper layers were optimized at a negative bias power of 0.1 kW, i.e., a square resistance of 3.2 mΩ/sq and a bond strength of 6.08 MPa. However, a high negative bias above a certain range will likely lead to unfavorable factors such as etching, back-sputtering, and residual stresses, causing defects such as microcracks and pores to develop in the coating, and degrading the coating’s microscopic and macroscopic properties instead.