I was at Fry's yesterday, and was looking to get some thin solder for work on a kit (through-hole components).

Two of the solders I was looking at (in the soldering gear isle section) were labeled RA Flux and No Clean. I asked a engineer-in-the-isle for help, and after explaining my application (building an adafruit.com kit), he said I should choose No Clean, as I wouldn't need to clean the board afterwards(?).

Can anyone clarify how one should select solder based on flux type? I had always been under the impression that you just use some sort of rosin-core solder with flux (one size fits all?) built in for basic board work, so I was confused at the different flux labels. I didn't think you had to clean your board (although I do know that after soldering yellow gunk can be left behind, and I suspect this is a flux byproduct). I also know that you should avoid solder with an acidic core for electronics work, as that is for pipes + household plumbing.

The wikipedia page for soldering classifies many of the different types of fluxes, most of which require cleaning:

• R (non-activated)
• RMA (mildly-activated)
• RA (activated)
• No Clean

Can someone explain why/how you should choose a flux type for a given application?