Factors governing filling of blind via and through hole in electroplating

The purpose of this paper is to present a clear picture of the key factors of blind via and through hole filling in electroplating, e.g. shape of via or hole, electroplating solution, process, as well as the developments of mechanisms and models.

First, the paper details the development trends and challenges of via filling. Then the research status of mechanisms, electroplating solutions, including base solution and additives, numerical model and mass transfer is described. Finally, through hole filling is briefly reviewed.

To achieve excellent via filling performance, the characteristics of the via or hole, the ratio of acid/copper, selection of additives and factors of mass transfer are comprehensively considered in terms of optimization of the electroplating process. It is beneficial to design vias with appropriate aspect ratios, to strengthen the adsorption of the accelerator in the via bottom, to inhibit the increase of surface copper thickness and to form butterfly-shaped copper in the centre of through holes. Optimized process parameters should be taken into consideration in superfilling.

The paper reviews different sets of additives, mechanisms and superfilling models for state-of-the-art via filling and the developments of filling for through holes.