Filling performance of Acid Blue 1 leveler on blind microvias

Abstract

Void-free blind microvias copper electroplating process is key technology in HDI PCBs manufacturing. This work systematically studied the influence of Acid Blue 1 (AB1) leveler on blind microvias filling. AB1 is of excellent suppressing during electroplating and its suppressing effect is strengthened with rising of AB1 concentration. Chronopotentiometry was used to study the interaction among AB1, SPS and PEG. There is synergistic suppressing interaction between new leveler AB1 and suppressor PEG, while there is competence between AB1 and accelerator SPS. During electrodeposition, AB1 can adsorb on copper substrate to reduce active sites and suppress copper electrodeposition based on theoretical study and in situ infrared spectroscopy. At optimized electroplating process, void-free microvias filling is achieved with 20 mg/L AB1 and successive electroplating confirms the stability of AB1. Based on diffusion differences among additives and the competence between AB1 and SPS, gradient competitive adsorption superfilling mechanism was proposed to illustrate the filing process of AB1-SPS-PEG system. AB1 is beneficial to improve flatness and lower surface roughness of copper layer, which is conducive for lowering the signal losses during high-frequency transmission. Besides, AB1 can modulate the preferential formation of Cu(111) and Cu(200) and is of grain refinement.