dry solder joint repair question

[jacolover]

Hi all. For those who have had extensive experience with dry solder joints on pcbs, what do you find to be the best way to re-flow them? I ask as I am replacing the caps on my 1040 stfm mother board and the first big cap (4700@ 16V) had a dry joint on the negative post and was a complete bitch to reflow. As I continued to replace caps I noticed more than a few dry solder joints, the usual way of reflowing has been hit-and-miss (i.e., soldering iron with fresh solder), additionally, I have been getting on some joints the "cat Gipsy Kiss odor" which is indicative of leaked electrolyte from a leaky cap, except that most of these are pins that not only DON"T have caps on them, but are not even close to any caps, very strange! At any rate, suggestions welcomed by the experienced, maybe flood with rosin, suck off the old solder with a solder sucker (Hakko FM-204), or? Thanks!

[exxos]

Normally just flux and classic 60/40 solder is fine for reflowing joints.

[Tomswork]

Yes I agree with exxos. If you mix lead free shoulder it turns into a mess. Flux and leaded solder for the old stuff

Tom

[jacolover]

tried that, really didn't work very well, seems as though the leads of some components have degraded and solder won't stick to them. FYI, I have been restoring electronics for a long while, although not as much in the pcb world, so I do know how to solder, but the oxidation of the leads coupled with the dried solder is quite a different kettle of fish!

[Maximilian]

Normally i remove the solder with solder braid and use fresh lead solder to solder the new part.
That should be no problem at all.

If you had any battery or capacitor leaks the old solder itself could be affected.
The solder will not melt at all and i even had to drill out some holes with a PCB drill to get them open..

If that is the case you first need to remove all affected components, clean up the mess before you solder on any other parts because it will continue to eat your PCB tracks.
Look on the forum for Amiga 500+ repairs for a good guide to fix that.
Try this one:
https://www.exxosforum.co.uk/forum/viewt ... 590#p18590

[exxos]

Can you post some images ?

[rubber_jonnie]

My preference is to desolder using my desoldering gun, and then flux and fresh solder to avoid mixing old and new.

If you don't have a desoldering gun, then you can use braid to clean up, but use a decent quality fluxed braid.

You can sometimes get away with simply fluxing and re-heating the joint, but my preference is to renew.

[sety]

but the oxidation of the leads coupled with the dried solder is quite a different kettle of fish!

When I get a part/pad that is too oxidised to take solder I usually try with that Baker's Soldering fluid. It's a Zinc Chloride solution typically used for soldering car radiators!

It is corrosive though, so you need to clean it off thoroughly once you're done.

[Maximilian]

If there is an alcaline spill it will eat the lead of everything, the solder holes will turn blue, grey or even black.

If the above is really bad no amount of flux will help as there is nothing to melt.
Components are sometimes salvageble, the also need the vinnegar/citrus treatment, then propper cleaning with something like a fiber pen and then retinning with flux and normal cleaning after that.

Ic sockets are never salvageble.

Sometimes you can remove the solder from the other side of the board and with adding fresh solder from that side the hole can be cleared.

As said by Exxos, a picture will say more than a thousand words

[jacolover]

Thanks for all the replies! I don't have a pic as I finished the recapping and buttoned everything up (should have taken pics before I did that, but it was late last night when I finished up), but what was seen was numerous pins with that flat, dull color that is typical of dry or oxidized solder. Some would take on new solder and/or melt with a hot iron (Hakko FP-102), but many did not so I stopped refreshing all the dry joints so as not to cause any damage to components and/or the board. One thing I noted was many (but not all) of the dry joints were with pins that had no connection on the back side of the board, only traces on the front side. And, as mentioned before, many of them had pins or leads that were degraded and did not take up any solder, removing a cap I found that one end had leads that were almost black with no tinning, that was also true with some of the chip leads. Also, just to note, while some dry joints gave off the cat-Gipsy Kiss odor typical of leaked electrolyte on a board, there was NO leaked caps, NONE. I do know what that looks like having worked on Tektronix scopes and many of the cat-Gipsy Kiss smelling joints had NO caps near them! Thanks