In situ formation of chemically integrated and mechanically interlocked interphases enables robust epoxy-copper adhesion

Catechol-rich lignin reconstructs native CuO during epoxy curing. • A Cu 2 O-rich interphase integrates Cu O bonding and mechanical locking. • Cu shear strength reaches 21.1 MPa with cohesive fracture. • Adhesion remains robust after 85 °C/85% RH aging and 260 °C heating. • Broad substrate adhesion and void-free underfill filling are demonstrated. Robust epoxy‑copper adhesion is widely required in Cu-based electronic devices, protective coatings, and packaging assemblies, yet it is often limited by mechanically fragile native copper oxides that act as weak boundary layers. Here, we introduce a robust epoxy adhesive that spontaneously forms chemically integrated and mechanically interlocked interphases on copper surfaces during curing. The epoxy adhesive achieves a high Cu adhesion strength of 21.1 MPa and demonstrates application-relevant performance, including adhesion to Si, Al, and steel, packaging-relevant reliability, and underfill processability. The epoxy adhesive incorporates catechol-rich demethylated lignin, whose redox-active motifs reconstruct the native CuO-rich surface into a nanostructured Cu 2 O-rich interphase. This unique interfacial architecture enables simultaneous chemical coordination, elemental interpenetration, and mechanical interlocking, thereby transforming the weak native oxide into a load-bearing functional interphase. This work provides a facile strategy for robust epoxy‑copper adhesion in Cu-based electronic and packaging applications. Download: Download high-res image (139KB) Download: Download full-size image