Solution for pre-pressing surface treatment of the conductive pattern of the inner layers of multilayer printed circuit boards

• O.I. Bardina, N.S. Grigoryan, S.A. Savitskaya, N.A. Asnis, A.A. Abrashov and A.V. Balakirev

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

Abstract: For a long time, a standard oxidation process (GOST 23661-79) was used to enhance adhesion between the inner layers of multilayer printed circuit boards (MPCBs). As a result of this process, an oxide layer is formed on the copper surface, which has a more developed surface, leading to enhanced adhesion due to the mechanical “bonding” of the treated surface to the prepreg, a sheet of fiberglass impregnated with a thermosetting epoxy resin. However, oxidation does not provide the required adhesion of the internal layers of state-of-the-art MPCBs (with high circuit density) since the post-treatment stages of MPCBs may involve the so-called “pink ring” effect, areas of copper without an oxide layer appear around the holes because the acid solutions used at these stages (for example, microetching prior to chemical copper plating of printed circuit board holes) dissolve the oxide layer and penetrate into the interlayer space. A production process has been developed for pre-pressing preparation of the copper surface of the conductive pattern (CP) in the internal MPCB layers using a solution containing (g/L): H₂SO₄ 91, H₂O₂ 14, benzotriazole 8, Cl^– 8–10 mg/L, PEG (1500) 3–7. The process makes it possible to form on a copper surface, at t 35°C and in τ=75 s, a rough adhesive organometallic layer that is not inferior to the world’s best analogs in terms of corrosion resistance, friability, and roughness. It has been shown that the strength of adhesion to the prepreg surface modified in the solution that we developed is comparable to that of the analogs from the world’s best manufacturers of materials for printed circuit boards. It has been found that during the treatment, a rough layer with a thickness of 2.5 μm is formed on the copper surface, and an organometallic layer with a thickness of ~250 Å is formed on the surface of the rough layer itself.

Keywords: multilayer printed circuit boards (MPCBs), pressing of MPCB inner layers, conductive pattern, preparation of copper surface, microetching, adhesion layer, organometallic layer

Int. J. Corros. Scale Inhib., 2024, 13, no. 1, 460-474
doi: 10.17675/2305-6894-2024-13-1-23

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