Through-Hole Filling by Copper Electroplating

Through holes (THs) with different shapes were formed by laser drilling on a printed circuit board to evaluate the filling capability of two copper plating formulas. The shapes of these THs were cylindrical, V- and X-shaped. Two copper plating formulas, accelerator-free formula (AFF) and accelerator-containing formula (ACF), were employed in this work. The AFF contained only one organic additive and the ACF was composed of multiorganic additives. The electrochemical characteristics of the AFF were investigated by cyclic voltammetry, which could be utilized to explain the results of filling plating. The plating results showed that the cylindrical TH could be fully filled using AFF. However, the V- and X-shaped THs could be fully filled using ACF. TH and microvias could be simultaneously filled in one plating bath using the AFF. A filling mechanism based on an adsorption/consumption/diffusion mode was proposed to explain these plating results.