The Korean Society of Surface Science and Engineering

Palladium (Pd) coatings were electrodeposited on copper (Cu) substrates using an ammonium-free electrolyte to investigate the effect of coating thickness on the microstructure and electrochemical properties. SEM analysis revealed that the Pd coating exhibited a porous and discontinuous surface at 0.25 μm, whereas a dense and smooth morphology was obtained at 1.0 μm. At 1.5 μm, localized overgrowth and surface roughening were observed due to stress accumulation during prolonged electrodeposition. TEM analysis of the Pd/Cu interface confirmed a coherent lattice structure without amorphous transition, indicating strong interfacial adhesion. XRD results showed typical face-centered cubic (fcc) Pd peaks corresponding to the (111), (200), and (220) planes, with the (111) reflection becoming dominant as the coating thickness increased. A weak PdO peak was detected near 34° for the 1.5 μm coating, implying partial surface oxidation. Electrochemical measurements in 3.5 wt% NaCl solution demonstrated that the corrosion potential Ecorr shifted positively from −0.30 V to −0.15 V, and the charge transfer resistance Rct increased from 1.2 × 10³ to 4.1 × 10³ Ω·cm² as the thickness increased from 0.25 to 1.0 μm. The coatings with thicknesses of 0.5–1.0 μm exhibited the highest corrosion resistance and electrochemical stability, attributed to their compact microstructure and strong (111) orientation. These findings confirm that optimizing the Pd coating thickness significantly enhances corrosion resistance and interfacial stability, establishing Pd electrodeposition as a promising and environmentally sustainable alternative to Au plating for electronic and semiconductor applications. This study aims not only to elucidate the relationship between Pd coating thickness, microstructural evolution, and electrochemical stability, but also to provide design criteria for the development of eco-friendly plating processes applicable to high-reliability electronic components.

키워드 Palladium (Pd) coating; Copper substrate; Ammonium-free electrolyte; Microstructure; Corrosion resistance; Electrochemical impedance spectroscopy (EIS).