Use of Nitrogen in Reflow Soldering Available to Purchase

Several effects of the atmosphere in the soldering oven on both the soldering process itself and the soldering results are discussed. Experiments have been undertaken to compare the results of soldering in air and in nitrogen containing 10,100 and 1000 ppm oxygen, in which, e.g., discolouration, wettability, solderability after reflow, solder bridging and solder‐ball formation were investigated. Unmounted FR‐4 testboards with both an RMA solder paste of known high quality and a low‐residue paste were used. Mounted test boards were used to analyse the self‐alignment of components and to compare the levels of soldering defects obtained in air and in nitrogen. The test results show that a nitrogen atmosphere containing 1000 ppm of oxygen or less is sufficiently pure to realise improved soldering conditions for most types of components. For the low‐residue paste tested, 1000 ppm is too high, but 100 ppm is sufficiently low. All effects on the soldering process will depend on the amount of oxygen in the gas. To produce an oven atmosphere of nitrogen with a very low amount of O2 (e.g., <100 ppm) is rather expensive, if this oven is to work under production conditions. Will the extra cost of investment and gas consumption be worthwhile in view of a better production yield and higher product quality? The authors explain why they do not believe this to be the case.