I didn't know there were so many types of flux until recently, and there's probably more than what I listed below. What do you like for modding? Do I even want to know the benefit and drawbacks of all these types of flux and flux devices?
There are three primary types. RMA, No Clean and Water Soluble.
Water Soluble flux MUST be completely washed off after being used. At home, it's HIGHLY unlikely you have the equipment/ability to do so.
No Clean and/or RMA should be used in 99% of modding projects. They both work in a similar way, but my preference between the two is RMA. Is doesn't have to be cleaned after use - but it can be, with Alcohol (isoProp or Ether).
Kester #186 is one of the best RMA Fluxes on the market.
Kester 186 ordered. What do you think about the needle syringes for applying it? I would think the squeeze bottle type is better than the plunger type. I have some plastic pipettes like that seller sells, but I think it'd flow too much.
What's the real story with shelf life? I have stuff I use regularly that's way over the typical '2 month' life but haven't noticed any change at all in how it works. I kept my solder paste in the fridge for a while but that got annoying quick, I decided to just leave it out on the bench and see what happened... apparently nothing happened, so far.
What happens when it goes bad, what are the signs it's time to throw it out?
A little late, but to add to this thread, get a nice alcohol pump bottle like one of these, http://www.fasttech.com/search?alcohol%20bottle
And either isopropyl alcohol or a can of denatured alcohol, and a few cheap bristle brushes to clean up with.
I use paste flux too, it’s great for when you need to stick down a component. Had the same tin for ages. It’s gotten quite a bit thicker of the years, but it still works, dab it on with a toothpick.