A new nickel-adenine composite stripper layer for preparation of extremely thin copper foils

Extremely thin copper foils are critical for high-speed and high-frequency electronic devices, as they significantly reduce signal transmission losses and minimize heating effects. These foils are typically fabricated by depositing onto a carrier foil coated with a stripper layer, where the design of the stripper layer is pivotal. Although benzotriazole coating is a technically mature organic stripping layer, its potential carcinogenicity and environmental persistence may pose long-term risks to human health and the ecological environment, instead of this, a novel composite stripper layer was developed in this work, which comprises a nickel metallic interlayer and an adenine-based organic layer for extremely thin copper foil fabrication. The peel strength of the resulting copper foils (thicknesses: 3.2 μm, 6.5 μm, and 9.7 μm) was evaluated under a constant current density of 20 A/dm2, yielding values of 0.012 N/mm, 0.010 N/mm, and 0.009 N/mm, respectively. Variations in current density (8.1 A/dm2, 15 A/dm2, and 20 A/dm2) further revealed peel strengths of 0.004 N/mm, 0.010 N/mm, and 0.012 N/mm, indicating that the peeling process is relatively easy. Combined theoretical and experimental analyses elucidated the formation mechanism of the composite stripper layer, demonstrating that the adenine-based organic layer adsorbs onto the nickel surface via N–Ni bonding. This mechanism further offers insights into the design of composite peel-off layers, enabling the preparation of extremely thin copper foils. Such a process holds significant potential for the extensible fabrication of conductive patterns in radio frequency identification (RFID) circuits, flexible printed circuits (FPCs), and other advanced electronics applications.