Ion-implantation-induced polyimide reconstruction and Cu interfacial adhesion

Reliable metallization of polymer substrates is essential for flexible electronics, advanced packaging, and high-frequency systems, yet achieving strong metal/polymer adhesion while maintaining good electrical performance remains challenging. Here, carbon-ion, nitrogen-ion, and carbon/nitrogen dual-ion implantation were used to modify polyimide, with the implantation conditions independently adjusted to obtain nearly identical surface free energies of 46.43–47.22 mJ m -2 . Despite the similar wettability, the resulting copper/polyimide peel strengths differed substantially, reaching 0.14, 0.20, and 1.63 N mm -1 for the carbon-, nitrogen-, and carbon/nitrogen-treated samples, respectively, while the corresponding copper-film sheet resistances were 20, 14, and 17 mΩ/□. Scanning electron microscopy showed little microscale morphological variation, whereas atomic force microscopy revealed distinct nanoscale roughening among the implantation conditions. X-ray photoelectron spectroscopy, attenuated-total-reflection Fourier-transform infrared spectroscopy, and Raman spectroscopy further identified distinct implantation-induced chemical and aromatic-framework reconstruction states. In particular, carbon/nitrogen implantation produced the highest nanoscale roughness and strongest copper adhesion, whereas nitrogen implantation yielded the lowest sheet resistance. Despite nearly matched surface free energies, the three implantation conditions therefore produced markedly different Cu/PI adhesion. The contrast between the highest adhesion after C/N treatment and the lowest sheet resistance after N treatment indicates that interfacial adhesion and Cu-film electrical continuity are associated with different features of the implantation-induced reconstructed surface state.