I was at Fry's yesterday, looking for some thin solder to use on an Adafruit kit with through-hole components.
Two of the solders I found were labeled RA Flux and No Clean, respectively. An engineer who was present said that with my use-case 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 (one size fits all?) rosin-core solder with 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 by-product). 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? Most of the answers below answer "what." I'd like to learn a bit of the theory.
Best Answer
For thru-hole work (which it sounds like you are doing) I would go with an active flux that is water soluble. You need to wash the residue off since it is corrosive and can cause shorts. I have had a number of boards mysteriously come back to life after a good cleaning.
For thru-hole parts that may get damaged by cleaning (LED lenses) or SMD parts with heatsink pads I would use the no clean flux.
I have been using the flux pens from Kester. 2331-ZX for water soluble flux and the 951 for no-clean. To clean the water soluble flux I use an "acid" brush with the bristles clipped to around 0.5". I run the board under the hottest tap water I get (probably around 140-160degF) and scrub with the brush. If I do a small repair job I will clean with the isopropyl alcohol I have on my bench.
Here some of the whys --
Why you need flux -- to get a quality joint at a lower soldering temperature. Using a liquid flux lets you spread the flux better over the two surfaces to be soldered.
Why choose an aggressive flux -- an aggresive flux is more tolerant of soldering temperatures. As Leon mentioned this would be a good candidate for a hobbyist. I like the 2331-ZX for this. Since these leave ionic compounds you need to clean.
Why choose no-clean -- eliminates a process step and the issues associated with the extra process step. For example for soldering XLamp LEDs I use a no-clean flux rather than risk scratching the lens.
For more details take a look at http://www.finishing.com/Library/flux.html and the Kester website.