mixed n2 and co2 are great for welding (TIG or MIG), but not common  
for soldering... CO2 form carbide, N2 for nitride that great for  
grain refinement, but soldering temp might not enough for form such  
inclusion (compare to steel...) and very little benefit comes for  
such inclusion, if you want high conductivity of solder (not like  
steels, mechanical strength is major concern for welding).  N2/H2 is  
better, N2 mostly provent to form oxide (oxide is bad in terms  
electrical conductivity), H2 provide reducing effect if it is high  
enough temp... of course, you an use some  sort of catalytic effect  
to get H2 dissociation temperature down to the soldering  
temperature... fluxless soldering can  happen if H2 content is high  
enough... IMHO.
On Sep 26, 2017, at 11:16 AM, Alasdair Green wrote:

> Nitrogen is a cheap inert gas which is collected as part of  
> liquefaction of oxygen. Argon is expensive, and CO2 is not  
> traditionally captured.