Desoldering techniques. - UK Vintage Radio Repair and Restoration Discussion Forum

David G4EBT · 2nd Jul 2006, 9:01 pm

Just a little tip on removing solder from old connections of whatever type - especially solder tags or valveholder bases:

Remember that when the connections were made many years ago, to get the solder to flow properly and make a secure joint, it was necessary to apply flux.

You would expect a good connection without flux, so why expect a good disconnection without it?

To desolder the connection quickly and efficeinetly, you need to apply flux again. The good thing about this is that you can use an aggressive flux such as plumbers' flux which all the DIY stores sell, as you will of course be cleaning up the contacts prior to resoldering (with for example, non-corrosive resin cored flux).

It always amazes me that some people will apply a hot iron - often an underpowered one, really meant for modern printed circuit work, then tug away at wires in the forlorn hope that they can work them loose without causing any damage.

I always have some plumbers' flux handy, which I keep in one of those plastic syringes used for re-filling printer cartridges. A tiny blob of flux is all that's needed, togther with either a desoldering pump or braid to soak up the solder.

This works a treat on re-tinning oxidised connections on old components such as valve bases, potetiomenters sockets etc. Just make sure you clean all the flux off before re-making any joints or putting the components into the spares box.

Hope that helps.

David.
G4EBT

igranic · 3rd Jul 2006, 7:27 pm

Removing plumber's flux from a piece of copper pipe is fairly straightforward since it is possible to wash it away with copious amounts of water and a rag.

However, removing plumber's flux in the confines of an old radio, with many cracks and crevices into which the flux can be driven by vapourisation or capillary action, is very difficult to achieve with any degree of certainty?

Most plumbers flux that I have used is acidic, and is likely to attack aluminium, brass, and plated parts. If it can't be washed away or neutralised it will attack that which we are ultimately trying to preserve. You only have to look at the damage wrought by a minor battery leak to understand the problems it can cause.

Using any form of corrosive flux on electronic equipment of any kind is, imho, not to be recommended.

Nickthedentist · 5th Jul 2006, 1:59 pm

You can buy "rework flux" in aerosols for electronic use.

I tend to just add a little more resin-cored solder, which has the effect of making the old solder flow away more easily when used in conjunction with a sucker or braid.

Nick.

2nd Jul 2006, 9:01 pm	#1
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,760	Desoldering techniques. Just a little tip on removing solder from old connections of whatever type - especially solder tags or valveholder bases: Remember that when the connections were made many years ago, to get the solder to flow properly and make a secure joint, it was necessary to apply flux. You would expect a good connection without flux, so why expect a good disconnection without it? To desolder the connection quickly and efficeinetly, you need to apply flux again. The good thing about this is that you can use an aggressive flux such as plumbers' flux which all the DIY stores sell, as you will of course be cleaning up the contacts prior to resoldering (with for example, non-corrosive resin cored flux). It always amazes me that some people will apply a hot iron - often an underpowered one, really meant for modern printed circuit work, then tug away at wires in the forlorn hope that they can work them loose without causing any damage. I always have some plumbers' flux handy, which I keep in one of those plastic syringes used for re-filling printer cartridges. A tiny blob of flux is all that's needed, togther with either a desoldering pump or braid to soak up the solder. This works a treat on re-tinning oxidised connections on old components such as valve bases, potetiomenters sockets etc. Just make sure you clean all the flux off before re-making any joints or putting the components into the spares box. Hope that helps. David. G4EBT

3rd Jul 2006, 7:27 pm	#2
igranic Rest in Peace Join Date: Jan 2005 Location: North Bedfordshire, UK. Posts: 395	Desoldering techniques. Removing plumber's flux from a piece of copper pipe is fairly straightforward since it is possible to wash it away with copious amounts of water and a rag. However, removing plumber's flux in the confines of an old radio, with many cracks and crevices into which the flux can be driven by vapourisation or capillary action, is very difficult to achieve with any degree of certainty? Most plumbers flux that I have used is acidic, and is likely to attack aluminium, brass, and plated parts. If it can't be washed away or neutralised it will attack that which we are ultimately trying to preserve. You only have to look at the damage wrought by a minor battery leak to understand the problems it can cause. Using any form of corrosive flux on electronic equipment of any kind is, imho, not to be recommended.

5th Jul 2006, 1:59 pm	#3
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,841	Desoldering techniques. You can buy "rework flux" in aerosols for electronic use. I tend to just add a little more resin-cored solder, which has the effect of making the old solder flow away more easily when used in conjunction with a sucker or braid. Nick.