_ The copper metallization will only create reliable electrical connections if the underlying dielectric layer has been properly prepared, and this is where silver catalysts can play an important role in making holes conductive.The PCB industry has long relied on metallic catalysts to activate the dielectric layer surface before depositing electroless copper metallization. Metallic catalysts may either be ionic—relying on the electrostatic attraction of charged metallic ions to a surface—or colloidal.
_ Colloidal catalysts consist of nanoparticles of atomic metals suspended in an aqueous solution.
_ Several metals have been considered as potential catalysts for PCB applications. Palladium (Pd) is the traditional choice, and has been used in both ionic and colloidal forms. Ionic Pd catalysts are especially stable in highly oxidizing environments, such as those in horizontal plating lines. Colloidal Pd-based catalysts, which are popular for many applications, typically also contain tin.