Process of lead-free soldering is deeply monitored starting from July 2006, when RoHS directive was activated. The goal of the work was to analyze influence of 4 control parameters of a process of lead-free soldering on bridging and filling of through holes on a test board.Following control parameters (factors) were taken into account: the solder temperature, the time of a contact between the soldered area and solder, the preheating temperature and flux wettability. Every factor was used in 3 levels. Taguchi orthogonal array of the type L9 was used for process analysis. The analysis showed that bridging is influenced with the preheating temperature and with the time of a contact between solder and a pad dominantly, influence of the solder temperature is minimal. The filling of the through hole depends above all on the preheating temperature; influence of other control parameters is low. It has been also confirmed effectiveness of the use of Taguchi orthogonal array in comparison with full factorial experiments.