levels to less than 500 ppm by increasing the amount of nitrogen provided to the system especially when using lead free solders by using the soldering zone having a glass plate and sensors in accordance with the present invention several advantages are achieved in particular residual oxygen can be measured and monitored to optimize soldering conditions and particularly control the formation of dross this in turn provides much higher quality of the solder bonds for the pcbs by optimizing the amount of nitrogen used during heating soldering and cooling phases of the wave soldering process in order to control the residual oxygen levels in the system fewer short circuits occur and therefore more reliable products are produced at higher yields this is particularly important with the current changes to lead free solders and the use of only organic solderability preservatives osp on the copper layers of the pcbs another advantage of the present invention is that the transparent glass plate allows for visible inspection of the entire soldering process by technicians which allows for greater control and consistency of the wave soldering process in addition the use of a transparent glass plate prevents contact of the sensors with the solder bath which would destroy them further it is possible to monitor other conditions of the soldering process than the oxygen levels in particular measurements of carbon monoxide carbon dioxide and methane can be made to help control the process in addition temperature can be precisely measured which can reveal the exact point where flux vapors burn off during the soldering process and.