Filling through Holes and Blind Micro Vias with Copper Using Reverse Pulse Plating and Insoluble Anodes

This paper presents systematic investigations on complete through hole filling for cores using a Cu electroplating process as an alternative to the common paste plugging process [1]. This technology is targeting at both HDI production and also at the packaging level [2]. This electro plating process consists of two steps, a first process to merge both centers of the through hole walls (X-plating) followed by filling up the resulting blind micro vias. Processes and manufacturing technology are described as well as current limitations and requirements. Complete filling of through holes is achieved by reverse pulse plating, RPP. Examples of filling of mechanically drilled through holes and also the extension of the technology to laser drilled through holes is shown. In detail the influence of electrolyte agitation, current density, reverse pulse parameters, redox mediators (Fe) and temperature on the filling performance are described and discussed for each step of the process. The separate discussion for the two steps mechanism allows a deeper insight and thus a significant process improvement