Pulse plating in PCB manufacturing

The continuing trend of miniaturization is driving PCB design more and more towards HDI and multi-layer boards. This means finer tracks, smaller holes and higher aspect ratios. As a consequence, the conventional acid-copper electroplating becomes very demanding and affects the performance and the price of the finished board. The ability to plate sophisticated boards is given by the use of pulse current instead of a DC. Since the pulse plating process takes place at higher current densities, a fine grain structure of the deposit can be obtained and hence the deposit porosity is reduced. Uniform deposit distribution is another advantage offered by the pulse technology. It should be noted, that current "shaping" represents only one way of influencing the complicated system which contains many other process parameters. To understand the interdependence of these parameters with pulse parameters qualitatively, a basic mass transport and its influence to the current distribution are described. Charging and discharging of the double layer, which is a side effect of the pulse plating, represents the main limitation of arbitrary pulse parameters setting. It can be reduced providing sufficient slopes of current pulses. Considering this, we also proposed a new topology of pulse current source and built an experimental model. At the end, the results of copper deposition obtained under bipolar pulse current conditions are collected and compared to the results obtained using conventional technology.