Morphology and acoustic artefacts of copper deposits electroplated using megasonic assisted agitation

Abstract

Purpose ± A study of the influence of megasonic (MS) assisted agitation on Printed Circuit Boards (PCBs) electroplated using copper 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 studied, through a Design of Experiments (DOE), by measuring surface roughness, characterised by values of the parameter Ra as measured by white light phase shifting interferometry and high resolution scanning electron microscopy. Findings ± An increase of Ra from 400 nm to 760 nm measured after plating, for an increase to acoustic power from 45 W to 450 W. Roughening increase due to micro-bubble cavitation energy, supported through direct imaging of the cavitation. Current thieving effect by the MS transducer induced low-currents, leading to large Cu grain frosting reducing the board quality. Current thieving was negated in plating trials through specific placement of transducer. Wavy electroplated surfaces, due to surface acoustic waves, also observed reducing the uniformity of the deposit. Research limitations/implications ± The formation of unstable transient cavitation and variation of the topology of the copper surface are unwanted phenomena. Further plating studies using megasonic agitation are needed, along with fundamental simulations, to determine how the effects can be reduced or prevented. Practical implications ± 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 ± Quantification of the topographical changes to a PCB surface in response to megasonic agitation and evidence for deposited copper artefacts due to acoustic effects.

Direct metallisation of polyetherimide substrates by activation with different metals

“…Spaces between metallic catalysts lead to increases in inter-pore spacing within electroless deposits, which can have a detrimental effect in terms of ductility and roughness [35,55,56]. [22].…”

“…The ability of the different metals to act as catalytic layers to receive high quality Cu deposits, is therefore reviewed in terms of Cu adhesion and conductivity. A strong adhesion of Cu to PEI and a fast processing time are desirable for long circuit lifetime and low manufacturing costs, respectively [34,35].…”

“…A strong adhesion of Cu to PEI and a fast processing time are desirable for long circuit lifetime and low manufacturing costs, respectively [34,35]. The photoreduction rate is enhanced on the application of the KCl photosensitizer, with rates increasing with sensitizer concentration up to a limiting value defined by mass transfer [36].…”

Copper electroplating of PCB interconnects using megasonic acoustic streaming

“…The application of high frequency acoustics induces streaming mechanisms which have the ability to improve the transport of plating solution down microfeatures [5][6][7], improving the Cu plated thickness down vias over existing agitation techniques. A MS wave is used to deliver a uniform acoustic wave to the surface of the PCB, cathode, to investigate the influence of acoustic agitation within the electrolyte solution [8][9][10][11][12]. Increases in Cu deposition depth and improved uniformity of the Cu filling were obtained for high thickness-to-width aspect ratio (ar) vias, of the order of 8:1 and 3:1 for the THV and BV, respectively, as shown in Table 1.…”

The establishment and simulation of bidirectional Cockcroft-Walton circuit model

“…One disadvantage of the method is that the capacitance value increases to slow the power supply steady response. The circuit simulation method (Fuchs et al , 2013; Jones et al , 2016) has been widely used in circuit design to improve the efficiency of circuit design. The correctness and feasibility of the method are verified by simulation.…”