Electroless Plating of Copper on Fluorinated Polyimide Films Modified by Surface Graft Copolymerization with 1-Vinylimidazole and 4-Vinylpyridine

Abstract

Electroless plating of copper via a tin-free activation process was carried out effectively on two types of fluorinated polyimide (FPI) films modified by UV-induced surface graft copolymerization with N-containing monomers, such as 1-vinylimidazole (VIDz) and 4-vinyl pyridine (4VP). The graft copolymerization of VIDz and 4VP was carried out on the argon (Ar) plasma-pretreated FPI films via a solvent-free process under atmospheric conditions. X-ray photoelectron spectroscopy (XPS) results showed that the VIDz graft-copolymerized FPI surface (the VIDz-g-FPI surface) and 4VP graft-copolymerized FPI surface (the 4VP-g-FPI surface) were much more susceptible to the electroless deposition of metals via the Sn-free process than the pristine FPI surfaces, and the FPI surfaces modified by Ar plasma pretreatment alone. T-peel adhesion strengths above 9 N/cm were achieved for the electrolessly deposited copper on both VIDz-g-FPI surfaces (the Cu/VIDz-g-FPI assemblies) and 4VP-g-FPI surfaces (the Cu/4VP-g-FPI assemblies). These adhesion strength values were much higher than those obtained for assemblies involving electrolessly deposited copper on pristine or on Ar plasma pretreated FPI films. The high adhesion strength of the Cu/VIDz-g-FPI and Cu/4VP-g-FPI assemblies was attributed to the synergistic effect of spatial interactions of the grafted VIDz or 4VP polymer chains with the copper atoms, and the fact that the VIDz or 4VP polymer chains were covalently tethered on the FPI surfaces. XPS results also revealed that the Cu/VIDz-g-FPI and Cu/4VP-g-FPI assemblies delaminated by cohesive failure inside the FPI films.