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

Plating through holes (PTH) of a printed circuit board (PCB) by copper electroplating were performed using 3-mercapo-1-1-propanesulfonate (MPS), 3-S-thiuronium propanesulfonate (UPS), and 3-(benzothiazolyl-2-mercapto)-proyl-sulfonate (ZPS) as brighteners in a copper plating bath containing CuSO4, H2SO4, polyethylene glycol and chloride ions in order to compare brighteners' effects on copper throwing power (TP) of PTHs. Before PTHs, the hole walls were metallized by electroless copper deposition using copper nanoparticles (CuNPs) as catalyst rather than a traditional Sn/Pd catalyst. The accelerating effects of brighteners on copper deposition were characterized by a galvanostatic measurement with adding various brighteners in a copper plating cell. The surface roughness and morphology was measured and characterized by a profile meter and a scanning electron microscopy, respectively. Thermal reliability of plated copper films on the hole walls of the plated through hole was evaluated by thermal cycle in a soldering pot at 288 °C. The results shows that USP and ZPS more weakly depolarize copper deposition than MPS, correspondingly, they exhibit good TP of the PTHs. Good thermal reliability of plated copper film was obtained in the copper plating bath that contained 1 ppm MPS or 10 ppm UPS or 20 ppm ZPS.