D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia:

А. А. Kosarev, Postgraduate Student at the Department of Innovative Materials and Corrosion Protection
А. А. Kalinkina, Head of Laboratory, Department of Innovative Materials and Corrosion Protection, Candidate of Chemical Science, e-mail: aakalinkina@mail.ru
D. V. Mazurova, Associate Professor at the Department of Innovative Materials and Corrosion Protection, Candidate of Tehnical Science
Т. А. Vagramyan, Head of the Department of Innovative Materials and Corrosion Protection, Professor, Doctor of Technical Science

This paper looks at the effect of sulphuric acid electrolyte, its composition and reverse current used in the copper electroplating process on the distribution of copper in small through holes of printed circuit boards. Having analysed the polarization curves, the authors suggested that electrodeposition in reverse mode in the presence of a certain combination of additives might help achieve better copper distribution. Application of differential mode high frequency (~50 Hz) reverse current in the Haring-Blum cell resulted in a significant improvement in throwing power compared with its level registered in the base solution under direct current. The increase is ~10%. How evenly copper distributed in through 0.2 mm holes was analysed with the help of microphotographs with 2000 magnification. Unacceptably thin copper coats form in the base electrolyte in direct current mode. Use of special additives helps obtain smooth and evenly distributed copper deposits. However, the deposits produced in direct current mode in the presence of additives and without them had inadequate physico-mechanical properties and failed tensile tests. Application of reverse current helps maintain the thinning of copper in the centre of the hole versus the outside thickness at the minimum allowable level. Thus, the thinning does not exceed 20%. In terms of elongation (~6–7%), the obtained deposits meet the requirements set to electroplated copper coats of printed circuit boards, however they have considerable surface roughness. A combination of additives and reverse current enable to obtain even, smooth and ductile coats in through holes. The highest degree of elongation (~8%) can be reached if using a 50 Hz reverse current mode. Further increase in the frequency (up to 100 Hz) does not improve the ductility of the coats.
This research was funded by D. Mendeleev University of Chemical Technology of Russia, Project No. 015-2018.

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