First, is there any special type of syringe you need to use? I have a 500g jar of lead free solder paste that has a shelf life of 3 months. Will it last longer because I don’t know if I can use all of it in the next 3 months :shock:
It’ll last a long time, it just gradually degrades I guess … I have a tube of paste that’s a couple years past its expiration date and it’s still solder paste. I’m sure the flux isn’t as effective as it was when it was new but it’s still basically usable. I don’t solder any really fine pitch stuff with it or anything though.
Keeping it in the fridge makes it last longer, but be very careful not to contaminate any food surfaces with lead.
oh, I see you said lead-free 
probably less toxic then.