The impact of current reversal in the presence of inhibitory additives on the thermomechanical stability of galvanic copper coatings

• А.А. Kalinkina, А.S. Vasiliev, А.P. Krasnikova, V.V. Shchеrbakov and Т.А. Vagramyan

Federal State-Funded Educational Institution of Higher Education (FGBOU VO) D. Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, 125047 Moscow, Russian Federation

Abstract: The impact of current reversal on the morphology, physical and mechanical properties and thermomechanical stability of galvanic copper coatings in through holes of printed circuit boards is studied in this work. Copper was electrodeposited from a sulfate electrolyte with a complex additive based on polyalkylene glycols, nitrogen-containing heterocyclic compounds, and organic sulfur-containing compounds. At a constant current in the presence of the inhibitory additive, the surface microrelief is formed by an accumulation of smooth hemispherical micro protrusions. The observed “micro-waviness” of the surface may be associated with the adsorption of the additive components on the surface of the growing deposit and their inhibitory impact on the course of copper electrodeposition. The low plasticity of such coatings may be caused by internal stresses, including those due to inclusion of components of the complex additive into the deposit on the electrode. Current reversal during electrodeposition significantly changes the copper morphology in comparison with that in the DC mode by favoring a decrease in the adsorption of components of the inhibitory additive. However, at the reversal frequency of ~100 Hz, rough, hard and brittle copper coatings that are unstable to thermomechanical loads are obtained. Annealing in order to relieve internal stresses did not improve the plastic properties of copper. Thus, the fragility of coatings in reversal mode at a frequency of ~100 Hz can be associated with a high density of microstructure defects. The use of current reversal with a frequency of ~50 Hz makes it possible to significantly reduce the roughness of the copper layer. The plasticity of electrodeposited copper is improved significantly, which ensures the thermomechanical stability of copper coatings in through holes with various diameters. Both in direct current mode and in current reversal modes, the sizes of coherent scattering regions D are approximately the same. Apparently, the plasticity in the case of current reversal with a frequency of ~50 Hz and the fragility of samples obtained under direct current conditions and with current reversal at ~100 Hz are associated not so much with the size of crystallites as with differences in the stress state of electrodeposited copper due to changes in the adsorption of organic components of the additive.

Keywords: inhibitory additives, current reversal, roughness, plasticity, metallization of through holes, thermomechanical stability

Int. J. Corros. Scale Inhib., 2022, 11, no. 3, 1214-1227
doi: 10.17675/2305-6894-2022-11-3-18

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