Megasound acoustic surface treatment process in the Printed Circuit Board industry

Megasonic (MS) (1MHz) acoustic agitation has been applied to Printed Circuit Board (PCB) surfaces to aid copper electroplating efficiency through enhancement of electrolyte solution transport. Evidence for microbubble acoustic transient cavitation has been observed on the PCB surface, which is attributed as the cause of adverse plating finishes. Additional acoustic artefacts are reported as ridge-like structures of peak-to-trough of 20 μm and are associated with the possible occurrence of Rayleigh-wave surface acoustic waves. Direct Current copper plating deposit thickness within a 175 μm diameter (depth-to-width aspect ratio = 5.7:1), through-hole via interconnect, was measured to increase by 320% on the application of MS assistance. This significant enhancement in electrodeposition is attributed to enhancement of fluid transport within the features.