Flow measurements in micro holes with electrochemical and optical methods

The decreasing feature size of electronic compounds down to the micrometer range is paralleled by an increase in the aspect ratio, worsening all mass transport related processes. In this paper the conditions of liquid flow into micro holes and blind micro vias (BMV) with diameter of 100-300 μm and depth between 100 μm and 1.5 mm are investigated. The flow was induced by surface directed jet flows, visualised by microscopy aided particle image velocimetry (μ-PIV) and correlated with electrochemical mass transfer measurements using the ferro/ferri-hexacyanide redox couple. It was found that the mean flow velocity in the holes and the penetration depth in the blind holes are influenced especially by the roughness of the inner walls and, at a lower scale, by the velocity and the impinging angle of the jet. The results enable the estimation of the mean flow rate in through holes and the penetration depth in BMV at defined hydrodynamic conditions in the bath. This is one of the preconditions for the appropriate engineering of plating lines designed for micro structures