This study presents a novel and highly effective method for fabricating localized, strongly adherent, and highly conductive copper patterns on commercial polyether ether ketone (PEEK) surfaces by integrating green femtosecond laser surface modification with electroless copper plating. The core innovation lies in the precise and controllable surface activation achieved via a 515 nm femtosecond laser, which simultaneously introduces beneficial micro-/nanoscale topography and enhances surface chemistry without causing significant thermal damage to the unprocessed substrate.
The experimental methodology involved systematically modifying PEEK surfaces by a femtosecond laser (515 nm wavelength, 800 fs pulse width, 30 kHz repetition rate) with varying single-pulse energy densities (ranging from 0.38 to 2.17 J/cm²) in a cross-hatch scanning pattern (10 μm hatch spacing). This was followed by a two-step metallization process: activation in a 0.1 mol/L silver nitrate solution at 25 ℃ for 30 min, and subsequent electroless copper plating in a bath containing copper sulfate, potassium sodium tartrate, sodium hydroxide, and formaldehyde at 40 ℃ for 15 min.
A key finding was the evolution of surface morphology with the increasing energy density: from a porous, ablated structure at 0.38 J/cm² to flaky and, ultimately, flocculent microstructures dominated by melt-resolidification at 2.17 J/cm². Correspondingly, the modification depth increased from 7.2 to 41.6 μm. Crucially, the surface chemistry was profoundly altered. X-ray photoelectron spectroscopy (XPS) analysis revealed a significant increase in the proportion of highly active oxygen-containing functional groups (C==O, O—C==O) at the expense of inert C—C/C—H bonds, with this effect being more pronounced at higher energy densities. This chemical activation was accompanied by a tunable wettability transition. While low energy densities (≤0.52 J/cm²) initially increased hydrophobicity (contact angle up to ~100°) due to dominant microstructural effects (Wenzel to Cassie-Baxter transition), higher energies (0.52-1.75 J/cm²) induced a switch to stable hydrophilicity, with a minimum contact angle of 46.2°. This shift was attributed to the combined effect of disrupted air-trapping microstructures and the increased surface concentration of polar oxygen-containing groups.
These laser-induced modifications-morphology, chemistry, wettability-synergistically governed the subsequent metallization quality. At the optimal single-pulse energy density of 1.09 J/cm², the electrolessly plated copper layer exhibited exceptional performance: an extremely low sheet resistance of 39.1 mΩ/sq and superior adhesion classified as 5B according to the ASTM D3359 standard tape test. The underlying mechanism was elucidated through detailed analysis. The hydrophilic surface and abundant active sites at optimal parameters facilitated effective adsorption and anchoring of silver catalyst nanoparticles (both crystalline flakes and nanospheres) within the micro-roughness during activation. This stable catalyst layer ensured uniform and continuous copper deposition, resulting in a dense, conformal copper layer that replicated the laser-generated microstructures. The cross-sectional analysis revealed an interlocking, jagged interface between the copper and PEEK, significantly increasing the contact area and providing robust mechanical anchorage alongside enhanced chemical bonding.
In conclusion, this work demonstrates that green femtosecond laser modification is a powerful tool for the localized, precision engineering of PEEK surfaces, enabling the subsequent fabrication of integrated metal patterns with outstanding electrical conductivity and interfacial adhesion. The process avoids the drawbacks of deep etching or excessive thermal damage associated with other laser types. The detailed investigation of the energy-density-dependent interplay between surface morphology, chemistry, wettability, and final metallization performance provides new fundamental insights and a viable technical pathway for high-value applications such as functionalized polymer skins in aerospace electronics.