Electrodeposition of low-ordered Ni–W as a release layer for ultrathin Cu foils: experimental and theoretical insights

Ultra-thin copper foil is critical for high-density interconnects and flexible electronics, yet developing a reliable release layer remains challenging. Here, we report an amorphous Ni–W alloy release layer and systematically evaluate its performance through experimental characterization and theoretical analysis. The Ni–W alloy (59.9 % Ni, 40.1 % W) forms a smooth, defect-free surface with an average roughness of 0.9 μm. In 50-cycle peel tests, the average peel strength stabilizes at 0.038 N/mm with a standard deviation of only 0.003, demonstrating highly controllable and stable cyclic peel behavior. The release layer maintains thermal stability below 600 °C, and atomic diffusion of Ni and W at 200 °C over 50 h has negligible impact on the copper foil conductivity. Theoretical calculations indicate that the Cu/Ni–W interface exhibits lattice mismatch, leading to weak adhesion (W a d = 1.45 J/m 2 ); in contrast, a co-deposited Ni-enriched transition layer achieves coherent lattice matching, significantly enhancing Ni–W/Cu interfacial strength and enabling differential control of interface bonding. This study represents the first scalable electro-deposition of an amorphous alloy release layer, providing precise control over peel strength and robust industrial applicability for ultra-thin copper foil production.