Unraveling the Synergistic Mechanism and Performance Impact of Tetrazolium Violet: Towards Void-Free Copper Electroplating Filling for Ultra-High Aspect Ratio Through-Holes

PCBs serve as the nerve center of modern electronic devices, and the quality of the copper electroplating directly determines the reliability and performance of electronic products. Achieving void-free filling of ultra-high aspect ratio through-holes remains a critical challenge in high-density interconnection technology. In this work, a novel tetrazolium violet (VTZ) molecule was introduced in an acidic sulfate copper electroplating system. The structural, electronic and adsorption properties of VTZ were systematically investigated through DFT calculations, MD simulations and electrochemical analyses. Results reveal that VTZ exhibits strong planar adsorption on copper surfaces via combined chemical and physical interactions, facilitated by electron transfer from copper to its lowest unoccupied molecular orbital. Electrochemical measurements demonstrate that VTZ synergistically enhances the inhibiting effect of PEG while antagonizing the acceleration effect of SPS, thereby promoting filling of through-holes. Contact angle tests confirm that VTZ significantly improves the wettability of the electroplating bath, facilitating deeper penetration of additives. Practical electroplating experiments validate that the VTZ-containing bath achieves complete, void-free filling of through-holes, in contrast to the defective filling observed in the VTZ-free bath. Furthermore, VTZ induces a preferred (220) crystallographic orientation, and introduces beneficial compressive stress in the copper coating. This work provides a comprehensive understanding of the mechanism of VTZ as a high-performance additive and offers a practical strategy for void-free filling of ultra-high aspect ratio through-holes in advanced PCB manufacturing.