Electroless Plated Copper Thin Film for Metallization on Printed Circuit Board : Neutral Process

We investigated the characteristics of electroless plated Cu films on screen printed Ag/Anodized Al substrate. Cu plating was attempted using neutral electroless plating processes to minimize damage of the anodized Al substrate; this method used sodium hypophosphite instead of formaldehyde as a reducing agent. The basic electroless solution consisted of CuSO4 center dot 5H(2)O as the main metal source, NaH2PO2.H2O as the reducing agent, C6H5Na3O7.2H(2)O and NH4Cl as the complex agents, and NiSO4 center dot 6H(2)O as the catalyser for the oxidation of the reducing agent, dissolved in deionized water. The pH of the Cu plating solutions was adjusted using NH4OH. According to the variation of pH in the range of 6.5-8, the electroless plated Cu films were coated on screen printed Ag pattern/anodized Al/A1 at 70 degrees C. We investigated the surface morphology change of the Cu films using FE-SEM (Field Emission Scanning Electron Microscopy). The chemical composition of the Cu film was determined using XPS (X-ray Photoelectron Spectroscopy). The crystal structures of the Cu films were investigated using XRD (X-ray Diffraction). Using electroless plating at pH 7, the structures of the plated Cu-rich films were typical fcc-Cu; however, a slight Ni component was co-deposited. Finally, we found that the formation of Cu film plated selectively on PCB without any lithography is possible using a neutral electroless plating process.