Kirkendall Void Nucleation Mechanics in Electroplated Microbumps
Electroplated copper microbump voids nucleate when bath additive sulfur impurities catalyze vacancy condensation along the Cu-Cu3Sn boundary during thermal aging.
Janus Green B
Meaning
Electroplating processes utilize organic additives to control the deposition rate of metal ions on structured surfaces. The addition of Janus Green B acts as a leveling agent during the copper plating of high-aspect-ratio micro-vias. This compound ensures that metal deposition is thicker at the bottom of the via than at the surface.
Chemical Concentration effect
Plating quality depends heavily on the precise measurement of this additive within the acidic bath. If the concentration of Janus Green B is too low, the leveling action is insufficient, which results in voids inside the filled vias. In contrast, excessive concentration can cause complete inhibition of copper growth, stopping the plating process.
Electroplating Bath dynamic
Adsorption of the dye molecules occurs preferentially on high-current-density regions such as the entrance of the micro-via. This localized layer blocks the diffusion of copper ions, forcing them to deposit more rapidly in the deeper, lower-current regions.
Deposition Pattern feedback
Constant monitoring of the electrochemical activity in the bath is necessary to maintain the deposition balance. The dye undergoes electrochemical reduction during the plating process, which decreases its effectiveness over time. Operators must periodically replenish the chemistry to prevent degradation of the filling performance.
This routine maintenance program ensures uniform copper thickness across the entire printed circuit board assembly.