When one is doing re-work on a populated PCB, one often finds that when a component (eg 0805 resistor) is repeatedly soldered on and off a pad, a type of “gunge” then ends up on the pad, and this “gunge” then makes further hand soldering to this pad very difficult.
Does any reader know what this “gunge” is and what can be done to stop it occurring?
It’s probably flux residue. Clean it with some IPA on a cotton bud.
Leon
Yes, its flux. Use the IPA spray and then brush it. I would suggest do not use cotton bud, cos sometimes it can leave very small cotton there.
Thankyou so much,
but i think flux tends to help the soldering. -but this “gunge” hinders soldering badly…i think it might be the PCB’s conformal coating, but i’m not sure?
It’s flux residue and old solder. Once flux is heated to soldering temperatures, it’s not flux anymore; you have to clean off the old residue and add new flux. And if you heat solder too much, the composition will also change and you’ll get a rough gray solder that doesn’t want to flow or wet the joint. In that case, try to add more solder and flux, then wick away everything and redo the joint with fresh solder.