The photo onthe left shows the impact of nitrogen onthe same component seen above using nitrogen blanketing at the wave solder. While the above photo shows exposed copper around the soldered leads during bottom-side assembly, exposed copper is not observedwhen nitrogen is used.
Nitrogen would be beneficial especially to barecopper assemblies, which will have seen multiple heatingcycles prior to wave soldering. Nitrogen will also reduce bridging and icicling. Thicker boardswill also benefit with better hole-fill.
Below are photos showinggoodsoldering of bottom-side SMD’s and another photo showing the effects of icicling usinglead-freesolders. Icicling has a highertendency to occursince thesurface energyof lead- free solderssuch as SAC and SnCu based alloys ishigher. To avoid this insure the flux has good sustained activity and therefore flux is still present at the exiting point of the boardas to offer a good peel back of the solder. This defect is more commonwith low residue no-clean fluxes.