Ag Nanoparticle Catalyst for Electroless Cu Deposition and Promotion of Its Adsorption onto Epoxy Substrate

Abstract

Ag nanoparticle catalysts were prepared to replace the Pd/Sn catalysts for electroless Cu plating. Suspensions of Ag nanoparticles, of which the average diameter was 4.6 nm, were obtained instantaneously by mixing a solution and a Sn(II)–citrate complex solution at a nearly neutral pH. The composition and electron diffraction patterns of the nanoparticle as well as a high stability of the suspensions suggested that the nanoparticles have the core-shell structure composed of the metallic Ag core surrounded by the shell. The adsorption of Ag nanoparticles onto the epoxy substrates was promoted by conditioning the substrate with alkyltrimethylammonium chloride (ATA) having an alkyl tail longer than C16. A small amount of Sn was also adsorbed. The promotion of the Ag nanoparticle adsorption can be accounted for by the large amount of adsorbed surfactant due to the hydrophobic interaction with the substrate. The positively charged ATA adsorbates acted as an electrostatic glue to adsorb the negatively charged Ag nanoparticles. Electroless Cu deposition was started at the epoxy substrates catalyzed with Ag nanoparticles.