Morphology and acoustic artefacts of copper deposits electroplated using megasonic assisted agitation
Abstract
Purpose
This study aims to understand the influence of megasonic (MS)-assisted agitation on printed circuit boards (PCBs) electroplated using copper (Cu) electrolyte solutions to improve plating efficiencies through enhanced ion transportation.
Design/methodology/approach
The impact of MS-assisted agitation on topographical properties of the electroplated surfaces was studied through a design of experiments by measuring surface roughness, which is characterised by values of the parameter Ra as measured by white light phase shifting interferometry and high-resolution scanning electron microscopy.
Findings
An increase in Ra from 400 to 760 nm after plating was recorded for an increase in acoustic power from 45 to 450 W. Roughening increased because of micro-bubble cavitation energy and was supported through direct imaging of the cavitation. Current thieving effect by the MS transducer induced low currents, leading to large Cu grain frosting and reduction in the board quality. Current thieving was negated in plating trials through specific placement of transducer. Wavy electroplated surfaces, due to surface acoustic waves, were also observed to reduce the uniformity of the deposit.
Research limitations/implications
The formation of unstable transient cavitation and variation of the topology of the Cu surface are unwanted phenomena. Further plating studies using MS agitation are needed, along with fundamental simulations, to determine how the effects can be reduced or prevented.
Practical implications
This study can help identify manufacturing settings required for high-quality MS-assisted plating and promote areas for further investigation, leading to the development of an MS plating manufacturing technique.
Originality/value
This study quantifies the topographical changes to a PCB surface in response to MS agitation and evidence for deposited Cu artefacts due to acoustic effects.
Keywords
Acknowledgements
This work was performed as a part of the Engineering Doctorate Degree in Photonics funded by the Engineering and Physical Research Council (EPSRC) under the grant number EP/G037523/1. The authors would also like to acknowledge the financial support of Merlin Circuit Technology Ltd. Discussions on the fundamentals of MS electroplating with Dr Nadia Strusevich and researchers at Greenwich University and Dr Suzanne Costello, at MCS Ltd., Roslin, are also gratefully acknowledged.
Citation
Jones, T.D.A., Flynn, D., Desmulliez, M.P.Y., Price, D., Beadel, M., Strusevich, N., Patel, M., Bailey, C. and Costello, S. (2016), "Morphology and acoustic artefacts of copper deposits electroplated using megasonic assisted agitation", Circuit World, Vol. 42 No. 3, pp. 127-140. https://doi.org/10.1108/CW-03-2016-0006
Publisher
:Emerald Group Publishing Limited
Copyright © 2016, Emerald Group Publishing Limited