Filling performance of an Acid Blue 1 leveler on blind microvias

Abstract

The void-free blind microvia copper electroplating process is a key technology in HDI PCB manufacturing. This work systematically studied the influence of the Acid Blue 1 (AB1) leveler on blind microvia filling. AB1 exhibits excellent suppression during electroplating, with its effect strengthening as the AB1 concentration increases. Chronopotentiometry was used to study the interaction among AB1, SPS, and PEG. There is a synergistic suppressing interaction between the new leveler AB1 and suppressor PEG, while there is competition between AB1 and accelerator SPS. During electrodeposition, AB1 can adsorb on the copper substrate to reduce active sites and suppress copper electrodeposition, based on theoretical studies and in situ infrared spectroscopy. At the optimized electroplating process, void-free microvia filling is achieved with 20 mg L⁻¹ AB1 and successive electroplating confirms the stability of AB1. Based on diffusion differences among additives and the competition between AB1 and SPS, a gradient competitive adsorption superfilling mechanism was proposed to illustrate the filling process of the AB1–SPS–PEG system. AB1 is beneficial to improving flatness and lowering surface roughness of the copper layer, which is conducive to reducing signal losses during high-frequency transmission. Additionally, AB1 can modulate the preferential formation of Cu(111) and Cu(200) and facilitate grain refinement.