Reflowing solder

[xtian]

There have been a few threads recently where the suggestion was to resolder, or reflow the solder of, suspicious connections, in order to solve strange sounds or inexplicable behavior.

Would it suffice to simply reheat the existing solder at each connection, or do you need to remove the old solder and apply new?

My suspicion is that, if the solder connection is bad, and the solder is old and contaminated with dirt or resin, that it won't reflow and make good contact.

What do you think?

[DonMoose]

My practice - and this applies to surface mount stuff, too - is to add a bit of new solder or a bit of flux to help clean things up. You only need to remove the old solder if you wind up with a blob that risks shorting adjacent pins or components.

Less successful with the lead-free stuff -- that takes a TON of new flux and a bunch of cleanup.

[Bob-I]

My take is if you're taking the time to re-flow a joint, make sure it's 100%. I usually suck the old solder out, make sure the connections are sound and resolder. I'm not big on removing flux from the surrounding areas, it typically doesn't harm anything and in removing you can damage things, just leave it.

[KindaFuzzy]

Most of the time the joint was moved just before the solder cooled and made a bad connection, so just re-heating is all that's needed. But couldn't hurt to suck out the old solder and add fresh stuff, I usually add a bit of new solder anyways even if it's just a re-heat.

[Cliff Schecht]

When you move a joint as it cools, depending on how much you have already heated the solder, you could or could not need to apply more solder and/or flux. If you've heated the joint enough to burn off all of the flux then you need to reapply rosin-core solder or some flux. If there is no flux left, the solder won't properly wet and your joint won't flow properly. If there is still some flux left on the joint, it should be able to wet and flow as it should.

If I put too much solder down, I almost always go to solder braid to remove it. The braid has flux in it but putting down some extra flux will help on those stubborn joints.