Brown corrosion on circuit board

IDencI

I have a circuit board I need to repair 3 buttons on. It's from a Nokia Lumia 520 and there's 4 contacts for each button. 2 contacts on the board have a brown corrosion from when I desoldered the buttons. What's my best coarse of action to remove the corrosion? Can it be fixed?

Bruthal

Might possibly be flux or varnish residue, rather than corrosion.

IDencI

Tbh not really sure, it could be from the soldering iron possibly burning it?

Dufftronic

As Bruthal has suggested, it is most likely the flux in the solder. i wouldn't worry about it.

nmacc

If it has come from desoldering then it's either burnt lacquer or more likely flux residue. Alcohol (IPA) will remove flux, but only when it's fresh. Once it's been there a while you'll have to rub like hell to shift it.

The best stuff to shift it used to be Trichloroethylene dry cleaning fluid or, after it was banned, Trichloroethane (Tippex thinner). Unfortunately that's now banned as well so you could try acetone.

Or of course you could go all-out and buy actual flux remover from Radionics or Maplin

IDencI

nmacc wrote:

If it has come from desoldering then it's either burnt lacquer or more likely flux residue. Alcohol (IPA) will remove flux, but only when it's fresh. Once it's been there a while you'll have to rub like hell to shift it.

Is it possible to solder over it or does it have to be removed?

nmacc

It should be fine to solder through it. Nothing really to worry about unless the buttons are the conductive rubber kind that press down directly into the board to make contact.

IDencI

nmacc wrote:

It should be fine to solder through it. Nothing really to worry about unless the buttons are the conductive rubber kind that press down directly into the board to make contact.

There physical buttons with 4 metal legs?

nmacc

It'll be fine, solder away. Just make sure you get the buttons the right way around. Usually they won't work correctly if they are 90 degrees out and some makes are symmetrical, which can make them tricky to fit. Check carefully.

IDencI

They are so small that it's so difficult not to move them when trying to solder them

IDencI

By the way, Anyone have any idea how much a bottle of flux is?

nmacc

If they are moving around a (very) small dab of glue will help.

You don't normally buy electronic flux by the bottle. For the kind of work you are doing you'd normally use a flux-cored solder such as Ersin Multicore. For fine SMD work you can also get solder paste which contains flux. it comes in a syringe and you apply it and then heat, either with an iron or a heat gun. I wouldn't advise using a heat gun without a lot of practice.

IDencI

nmacc wrote:

You don't normally buy electronic flux by the bottle. For the kind of work you are doing you'd normally use a flux-cored solder such as Ersin Multicore. For fine SMD work you can also get solder paste which contains flux. it comes in a syringe and you apply it and then heat, either with an iron or a heat gun. I wouldn't advise using a heat gun without a lot of practice.

Ah ok, thanks for the info. I need it for the iron itself. I think it might sort the problem of the solder burning/sticking

nmacc

It probably won't.

The bit is probably tinned copper, possibly iron-coated. If it's 'sticking' the iron coating is either worn through or absent. If it's not an iron-coated bit then you need to clean it down with a fine file and tin it properly with fresh solder.

If you bought the iron in Lidl or Aldi then do yourself a favour and throw it, and the solder that came with it, away. You're much better off getting a decent Antex, Weller or similar temperature controlled iron with a small iron-coated bit and some high-quality resin-cored solder.

IDencI

nmacc wrote:

If you bought the iron in Lidl or Aldi then do yourself a favour and throw it, and the solder that came with it, away. You're much better off getting a decent Antex, Weller or similar temperature controlled iron with a small iron-coated bit and some high-quality resin-cored solder.

That was exactly where I got it. I barely ever use it, at most twice a year. Would changing the bit for a better quality one and getting proper solder do any good?

nmacc

To solder effectively you need proper solder - see my previous reply.

To solder effectively you need a proper soldering iron - see my previous reply.

IDencI

nmacc wrote: »

To solder effectively you need proper solder - see my previous reply.

To solder effectively you need a proper soldering iron - see my previous reply.

Fair enough, I can see what your saying. Might have a look around for a cheap but good quality one.