Surface preparation before chemical copper plating of printed circuit board holes. Part II. Activation

• N.S. Grigoryan, S.A. Savitskaya, I.S. Korotkikh, N.A. Asnis, A.A. Abrashov and T.A. Vagramyan

D. Mendeleev University of Chemical Technology of Russia, Moscow, Miusskaya sq., 9, 125047 Moscow, Russian Federation

Abstract: This article is a continuation of a series of publications of the Department of Innovative Materials and Corrosion Protection of the Mendeleev University of Chemical Technology of Russia on the development of compositions for the production of multilayer printed circuit board (MPCB). It deals with the stage of palladium activation of the dielectric before chemical copper plating. The electrical connection of the conductive pattern (CP) of different layers of a MPCB is implemented through metallized holes. In practice, the technology of indirect hole metallization is used most commonly. Its most important stage is chemical copper plating – an autocatalytic process catalyzed by metallic palladium, a layer of which is formed on the surface of the dielectric at the preliminary activation stage. Since chemical reduction is realized only on the catalyst, it is of importance to provide its sufficient amount on the dielectric substrate and good adhesion to it. In most cases, MPCB manufacturers use colloidal palladium activators to activate the dielectric surface. These activators are suspensions of nanosized micelles whose core comprises one or more metallic palladium particles surrounded by a layer of Sn²⁺ and Cl^– ions. It has been found that the functional characteristics of the colloidal palladium activator (the rate of covering dielectric, the continuity of the copper layer, the stability of the activating solution during operation and aging) depend on the size of the colloidal activator micelles, which in turn depend on the sequence and speed of mixing the concentrate components and on their temperature. Ultrasonic treatment of the colloidal palladium activator solution at the aging stage results in a significant decrease in the size of the micelles. The selected anticoagulant from the class of organic monoterpene aldehydes made it possible to enhance the stability of the activator compared to 4-hydroxy-3-methoxybenzaldehyde, which is currently used in practice. The regularities observed enabled the development of the optimal technology for obtaining a colloidal activator by mixing palladium-containing (10 g/L PdCl₂, HCl) and tin-containing (115 g/L SnCl₂, HCl) components heated to 65°C, keeping the resulting mixture for 20 minutes at 65°C, and its ultrasonic treatment, followed by addition of a component containing SnCl₂·2H₂O, HCl (37%) and an anticoagulant additive. The resulting activator is characterized by small micelle sizes (107 nm) and their monodispersity, as well as high stability and activating capacity.

Keywords: printed circuit boards, metallization, colloidal activator, palladium activation, dielectric surface activation, chemical copper plating of printed circuit board holes

Int. J. Corros. Scale Inhib., 2024, 13, no. 3, 1741-1750
doi: 10.17675/2305-6894-2024-13-3-23

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