Enhanced chemical bonding of copper-line treated by non-etching alkaline oxidation for high-frequency signal transmission

Strong bonding between fine-line PCB copper and polyimide prepreg is essential for high-frequency and high-density interconnects, yet conventional brown and black oxidation improves adhesion through surface roughening, which can impair signal transmission and fine-line reliability. Here, we show that an on-etching alkaline oxidation can build a copper-side bridging interphase in situ, enabling chemistry-dominated adhesion while preserving ultra-low roughness. The treated interface achieves a peel strength of 1.20 N/mm at an Sa of about 0.25 μm, with lower insertion loss from 10 to 20 GHz and maintained electrical reliability relative to brown oxidation. X-ray photoelectron spectroscopy, Kelvin probe work function mapping, focused ion beam cross-sections, and molecular dynamics simulations identify Cu–O–Si linkages and BTA–Cu+ coordination as key chemical anchors for load transfer and interfacial cohesion. This strategy offers a low-loss interface design route compatible with existing PCB processing for advanced 5G/6G and high-density interconnect applications.