5-Amino-1,3,4-thiadiazole-2-thiol as a new leveler for blind holes copper electroplating: Theoretical calculation and electrochemical studies

High density interconnection printed circuit board PCB puts forward high requirements for defect free blind holes copper filling. Here, 5-amino-1,3,4-thiadiazole-2-mercaptan, a small molecular compound containing sulfur and nitrogen heterocycles, is proposed as a new leveling agent to try to meet the top-down blind holes filling of high-density interconnected printed circuit board (PCB). The cross-sectional images of blind holes captured by optical microscopy show that the selected heterocyclic compounds with small molecules containing nitrogen and sulfur have good leveling ability and can realize the top-down super filling of blind holes. The electrochemical measurements were used to analyze the inhibition behavior of the leveling agent on copper ion deposition and its interaction with other additives. An atomic force microscope (AFM) and X-ray diffractometer (XRD) were used to study the effect of inhibitors on the surface morphology and crystal structure of copper crystals. In addition, quantum chemistry calculations and molecular dynamics simulations also were used to analysis the structure-performance correlation (active sites) and adsorption energy of the leveler at the molecular level to further understand the function of the levelers in the electrolyte system. This work will be inspiring for discovering new and effective levelers in the future.