Effects of Brighteners on Throwing Power and Thermal Reliability of Plating through Holes in a Copper Plating Bath

High aspect ratio through holes are commonly designed in printed circuit boards (PCBs) with a high density interconnection. In order to achieve high copper throwing power of through holes by using plating, the copper plating bath has to be added with additives, like chloride ions, suppressors, brighteners and levelers. In this study, several brighteners were screened to understand their performance on copper throwing power of plated through holes (PTHs). The chloride ion concentration was fixed at 60 ppm and the suppressor, Polyethylene glycol, concentration was fixed at 200ppm.The brighteners were 3-mercapo-1-1-propanesulfonate（MPS）, 3-S-Thiuronium-propanesulfonate (UPS) and 3-(benzothiazolyl-2-mercapto)-proyl-sulfonate（ZPS）. Good throwing power of PTHs appeared at 1 ppm MPS, 20 ~ 100 ppm UPS or 20 ~ 60 ppm ZPS. Scanning Electron Microscope（SEM）shows that the electroplated morphology is related with the brightener concentration. Moreover, different brightener results in different plated copper orientation and stress in the copper deposit, which significantly influences the final thermal reliability of the PTHs. The results show that the PTHs with the highest copper TP, which were obtained at 1 ppm MPS, 10 ppm UPS, and 20 ppm ZPS, can pass the thermal shock for 5 cycles. Key words: Throwing power, Reliability, Brightener, Through hole. References: 1. W.-C. Tsai, C.-C. Wan, and Y.-Y. Wang, J . Electrochem. Soc. , 150 , C267 (2003). 2. C. Wang, J. Zhang, P. Yang, B. Zhang, and M. An, J. Electrochem. Soc. , 160 , D85 (2013).