Soldering Problems

sissysphoto · Jun 18, 2018

Attached is a photo of a Nikon finder I'm working on. I didn't take the photo, it came off the internet. But for purposes of this post it could have been a million small electronics I've worked on. You know the story. Move the parts around too much and the wire breaks off at the solder joints. And my eternal irritation begins. Strip off 3/16 or so of insulation, twist the ends and solder. But it won't solder. And the more you try, the more the wire rejects the solder. So instead I tin the end of the wire, but it won't tin. no amount of heat will make the wire take the solder. I've always attributed it to the wire being old and oxidized. Or perhaps it's something I never knew or learned. This business of spending hours trying to get the wire to attach to the circuit board even by a strand has got to stop. Is there something I don't know? Thank you.

CMoore · Jun 18, 2018

Flux.?
Are you soldering to a trace...will the trace take solder by itself.?

sissysphoto · Jun 18, 2018

I'm talking about soldering to the original blob of solder It's the wire itself that I fight to try to get it take solder fresh solder or old. Like I said, its the wire that is the big offender. It won't wick the solder, and won't even tin with it.

shutterfinger · Jun 18, 2018

Clean off all the old solder. I trust you're using rosin core solder, if not get some.
What wattage of iron are you using?
Too small an iron will heat the wire, melt the insulation but not get the wire hot enough to melt the solder.
Do you clean the tip of your iron regularly while soldering? Is there air from an open window, fan, air conditioner or similar blowing in the area where you are soldering?
You may need to use a mild acid to etch the wire, try soaking the wire end in cider vinegar for 5 minutes, rinse in water then try to tin the wire.

AgX · Jun 18, 2018

Such happens with cables in an oily or corrosive atmosphere. These should be cleaned, maybe even abrasively, before soldering. But the standard oxidation of the strands the flux incorporated in the solder wire should take care of.

However in such tricky situations with minuscule isolation which tend to shrink off I often add a tiny amount of commercial colophonium paste to the strands to speed up wetting of the strands.

In your case though I assume the PVC of the wire insulation has been sweating out plasticizer, which evaporated at the outside but stayed at the inside at the cable strands. Clean the strands with organic solvent before soldering.

bernard_L · Jun 18, 2018

CMoore said:
Flux.?

AgX said:
commercial colophonium paste

+1 to the use of flux. Sometimes called rosin flux in the US.

Billy Axeman · Jun 18, 2018

I agree with AgX that probably some PVC from the isolation has coated the wires which prevents soldering and you need to clean up that first.

You can also get a flux for stainless steel that is very aggressive to solder almost everything. However it needs a thorough cleanup afterwards to prevent corrosion, which is difficult when the flux is partly sucked up inside the wire below the isolation.

When everything fails you can make a semi-mechanical connection to a short new piece of (multiple strand) wire to extend the old one as follows.

If both wires are multiple strand push both ends head-on until the thin wires overlap and intertwine, then wrap a single thin copper wire (from another multiple strand wire) around the connection along the total length of the bare parts and then solder it. This will solder the thin wire on the outside to the new part and locks up the old part.

When the original wire has only one solid core simply hold both ends side-by side before wrapping the thin wire around it.

Preferably use rosin core solder (which has the flux inside the tin wire), it is not aggressive and you don't get corrosion.

AgX · Jun 18, 2018

Billy Axeman said:
Preferably use rosin core solder (which has the flux inside the tin wire), it is not aggressive and you don't get corrosion.

There are basically two types of solder wire, the ones for mechanical and the ones for electrical connections. They differ in their Lead/Tin ratio. But from early teenage years when started seriously soldering I did not come across electrical solder wire without a flux core.

However my first electrical soldering at the age of 12 or so by ignorance I did with mechanial solder and soldering-grease, containing likely Zincchloride. What a mess.

Billy Axeman · Jun 18, 2018

The composition of soft solder is traditionally lead-tin in different proportions for various melting points, but composition has changed last few years due to regulations to reduce lead. The lead has been replaced by copper, silver or other metals and it usually has a slightly higher melting point.

I have designed electronic instruments in my previous life and also repaired them, but I can't remember a single instance that a wire wouldn't solder. Just cleaning it up mechanically until you have bare metal always solves those problems.

AgX · Jun 18, 2018

I had problems in otherwise benigne circumstances like the OP describes. Thus my hint at the plasticizer. And I came across deteriorating PVC cables even messy outside.

In other circumstances: rubber mains cables may have talkum or something similar as gliding compound around the strands. Such may hamper soldering too.

ron917 · Jun 18, 2018

Are you sure that the wire is copper? It's unlikely that it is aluminum or stainless steel, as that makes no sense in a camera or other normal electronics. But neither will solder with normal electronic solder and flux.

The only times I've found Al or SS wiring is in very high temperature applications - for example oxygen sensors in vehicles or control circuits for ovens. Crimping is required in those applications. And the insulation is Teflon or other high-temp materials - very expensive to use where it is not necessary.

Billy Axeman · Jun 18, 2018

ron917 said:
Are you sure that the wire is copper? It's unlikely that it is aluminum or stainless steel, as that makes no sense in a camera or other normal electronics. But neither will solder with normal electronic solder and flux.

The only times I've found Al or SS wiring is in very high temperature applications - for example oxygen sensors in vehicles or control circuits for ovens. Crimping is required in those applications. And the insulation is Teflon or other high-temp materials - very expensive to use where it is not necessary.

I have thought of thermocouple wire running directly to a sensor, but it's very unlikely.

Mainecoonmaniac · Jun 18, 2018

CMoore said:
Flux.?
Are you soldering to a trace...will the trace take solder by itself.?

Sounds like a flux problem. I'm far from a soldering expert, but make sure it's rosin core solder. As most people that have done soldering, don't let the iron melt the solder. Heat what you're soldering and let it melt the solder. Solder won't soak into cold metal. A good solder will look shiny while a "cold" solder joint, a bad one will look dull.

sissysphoto · Jun 18, 2018

Thank you for these answers. I don't see much here though I didn't know. Here's what I thing: I thing these 40 1nd 50 year old fine stranded wired oxidize even in their insulations and won't take the solder. We're talking about very fine wire. That's why I attempt to tin the wire after stripping it.It won't tin. And if it won't tin, it certainly isn't going to solder back to where it goes. I guess if anybody was a serious repairman they's be smart to just stock fine wire in all its colors. So if one end breaks off, just replace the entire wire at both ends.

Sirius Glass · Jun 18, 2018

CMoore said:
Flux.?
Are you soldering to a trace...will the trace take solder by itself.?

Either the solder does not have flux or you have to add flux.

CMoore · Jun 18, 2018

At this point...IMHO... the easiest thing to try would be flux.
Not the easiest or cheapest thing to find if you only need it once every 5-10 years.
If you get stuck and do not have any, shoot me a PM and i can mail you some paste.

sissysphoto · Jun 18, 2018

It's just plain old Radio Shack light duty Rosin Core Colder, .032 60/40. And a total cheapo Soldering iron from Northern Hydraulic, which has been a heck of a little iron I must say. Heats up to burn the heck out of paper in no time. Plenty for this job.

AgX · Jun 18, 2018

CMoore said:
At this point...IMHO... the easiest thing to try would be flux.
Not the easiest or cheapest thing to find if you only need it once every 5-10 years.
If you get stuck and do not have any, shoot me a PM and i can mail you some paste.

If one gets a tube like the german one I hinted at, keep the nozzle clean and once the threads have got paste on them clean them, aided with alcohol. Otherwise you would not get that cap off again after some time.

Sirius Glass · Jun 18, 2018

Rosin flux not acid flux.

faberryman · Jun 18, 2018

A small plastic container of rosin flux is available here.

CMoore · Jun 18, 2018

Wow...Free Shipping, hard to beat that.!

Anon Ymous · Jun 19, 2018

sissysphoto said:
It's just plain old Radio Shack light duty Rosin Core Colder, .032 60/40. And a total cheapo Soldering iron from Northern Hydraulic, which has been a heck of a little iron I must say. Heats up to burn the heck out of paper in no time. Plenty for this job.

What does the tip look like? Is it shiny and clean? If it's oxidised and solder doesn't stick to it, this might be the problem. By the looks of it, it should be a trivial soldering job, shouldn't cause you such trouble.

Nodda Duma · Jun 19, 2018

Easiest thing to do would be to replace the entire wire.

AgX · Jun 19, 2018

I guess this thread is actually more about getting insight into the cause of trouble.
Also there may be cases where one would think twice to exchange the wire as the other end may lead down intio dark innards one better not explores.

John Koehrer · Jun 19, 2018

There's an argument for a junk camera or two lying around. Buying wire in small gauges isn't worth buying a spool or five but a junk camera
of any brand makes a decent source of wire.

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