Desoldering : soft solder.

[Brian JohnParticipant @brianjohn93961]

I tried to take apart this meths burner for my flame eater engine in order to lower the height. It was soft soldered with 243 degree and 180 degree soft solder. Desoldering has turned out to be a messy business. The solder did not stay soft for very long after heating it up and by the time I put down the burner and picked up the pliers it had cooled again. So I then reapplied the burner but no amount of heat would remelt the solder this time. I even went to my big burner which I used for hard soldering. You can see the result : I ended up bending the brass base plate when I pulled on the scissor frame which was held in a vice….but the solder would not let go !

1. What is the correct method for desoldering soft solder ?

2. Can solder be remelted and used numerous times or is there a limit ? This stuff will not melt a third time no matter how much heat is applied.

Edited By Brian John on 25/08/2016 07:05:38

[Brian JohnParticipant @brianjohn93961]

What is the correct method ?

[BazyleParticipant @bazyle]

When hot the solder dissolves some of the copper it is attached to and forms a new compound that has a higher melting point. Longer you heat it the worse it gets. The thing to do is to have the disassembly force applied before heating, remove as much liquid solder as possible with a solder sucker or desolder braid and do it all quickly.

[Speedy Builder5Participant @speedybuilder5]

You can use this sort of stuff, its main use is for electronics. As the solder melts, it is sucked up into the tape. There are also "solder suckers" which are spring loaded sucking syringes.

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BobH

[peak4Participant @peak4]

Posted by Bazyle on 25/08/2016 07:52:26:

When hot the solder dissolves some of the copper it is attached to and forms a new compound that has a higher melting point. Longer you heat it the worse it gets. The thing to do is to have the disassembly force applied before heating, remove as much liquid solder as possible with a solder sucker or desolder braid and do it all quickly.

Or use a short haired, natural bristle paint brush; works fine, but just be careful which way you flick the molten solder.

[Martin KyteParticipant @martinkyte99762]

Sounds counter intuitive but add some resin cored solder to whats already there and as already suggested use braid to wick the residue up. This will re-alloy the solder and lower the melting point a little. It sounds like you are using a gas torch. You would do better with a heated lump of copper or brass on a metal "stick' with a file handle on the end. Same as an old fashioned tinsmiths soldering iron, heated with a torch it will stay hot enough for long enough.That way you can get the braid between the 'iron' and the job with a certain amount of pressure so everything stays in good contact. When you are heating your 'iron' you can also get some heat into the job too.

Have fun

[Martin KyteParticipant @martinkyte99762]

Oh and if you have any old coaxial cable you can strip the braid out of that.

[not done it yetParticipant @notdoneityet]

The solder sucker is prolly best for desoldering electronics from a pcb. I don't use mine often but very useful – if I can find it! Solder wick is likely better for long runs like you have. Main difference is that the sucker will last years (if you don't lose it!).

[SandgrounderParticipant @sandgrounder]

I use a solder sucker for small joints, but for bigger ones like the ends of copper pipe which need cleaning up for re-soldering I just heat up and wipe the solder off with a clean cloth, I don't know if it would work with your solder that won't remelt, but I find very old soldered joints can be difficult to melt until I apply some new solder and then they melt easily.

John

[AjohnwParticipant @ajohnw51620]

As mentioned don't get it too hot. In this case I would be wondering what fumes I had breathed in.

The best option on something like that would be to heat slowly until the solder melts and full it apart. Probably best not to apply the flame directly onto the solder as the tip of the flame will be too hot. The max temperature you need may be under 250C so if you put it in the right place a domestic oven might do it.

When it's apart the solder can be cleaned up with a file or more heat and wiping etc.

As it is now you will probably have to apply more solder and if you get it too hot that probably wont work out very well. It goes sort of crystalline. I should know. I've done it several times by heating yorkshire plumbing fittings up too quickly / the wrong way.

John

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[Ian S CParticipant @iansc]

Heat it to just a bit over melting point, then using Cotton(not synthetic) cloth, wipe the solder off. The surface will still have a silvery colour because the solder alloys with the parent metal, but only to a very small depth, so a rub on some wet and dry would get rid of that. Any trace of tin/lead solder means that silver solder should not be used on that bit of metal if it is to be rejoined.

Ian S C

[JasonBModerator @jasonb]

Holding it in a vice will act like a heatsink so do it on a flat non flammable surface. Have an old pair of pliers and screwdriver ready to pull the bits apart once hot.

When its all apart use files and then abrasive to clean up the parts, rub the file on a bit of chalk first as that will help stop the teeth filling with solder

[Gordon WParticipant @gordonw]

Best cloth to use for removing solder is from a pair of old jeans, also can be used for wiping joints, if that is still done.

[Ian PParticipant @ianp]

This might not sound logical but I would try adding low melting point solder and flux to the joints that dont seem to be melting now.

This seems to work when removing components from PCBs which have either been assembled with lead free or high melting point solder.

I speculate that the same mechanism that allows copper from the workpiece to migrate into the solder (see Bazyle's post above) might also work in reverse and displace the copper.

You still need to get the the thing hot enough and have the means to separate them in place, 'before' you apply heat.

Ian P

[Ian S CParticipant @iansc]

I you need to hang on to little bits of hot metal with a vice, or a pair of pliers, cut up some cardboard strips to insulate it, might be dificult if you use only a torch, I use a large soldering iron, either a 175W electric, or a large one that needs heating with the blowlamp. I have a plumbers devise used for making wiped joints, also used for wiping the solder off joint, it's called a mole skin, actually it is some material like Corderoy A cotton cloth, folded in a 4" x 4" square X about 1/2" thick, it was among my grandfathers plumbing tools.

Ian S C

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