Why is so much general purpose connecting wire so hard to solder?

[sacentre]

I do a lot of custom cabling for computers and often buy the multi-way ribbon cable of the 18 AWG type - like the stuff supplied with computer PSUs (with the 24-pin ATX connectors etc).

The individual strands appear to be copper under an outer coating of some other metal.  This wire is fine for crimped connections but sometimes, I need to solder a connection directly but find solder won't flow easily or quickly.  Whatever is used to "tin" the strands, does not appear to be solder of the type used to pre-tin PCBs etc.  Someone told me that the tinning is really aluminum and is done for cheapness which would explain it. Can this be the case?

The only cable I see these days that has bare, untinned copper strands (and therefore takes solder readily) is the stuff used for the 2 and 3 core AC mains cable, thin speaker cable and a few others.

Does anyone know if it's possible to buy 18 AWG, multi-strand, solder tinned (if that's what I mean) or bare copper cable?
TIA
Trevor

[mariush]

Coating on copper wires should be tin. 
Cheap wires are sometimes copper clad aluminum (CCA ) but you can say copper coated aluminum wires.. not the other way around.
On very cheap cables, you often get a mix of steel wire strands and copper clad aluminum wires or copper wires

My guess is that you simply have to use flux and tin the wires yourself.  I buy liquid flux, it's quite cheap.. under 10 dollars for a 500ml bottle. A solder pot is also cheap, but you can just use a solder iron tip with a "cup" that holds a bit of solder and you can tin the wires quickly.
 
Solder pot is often the way to go if you need to tin or solder a lot of wires .. heat solder, wipe away the dross, wet the wires in liquid flux, insert wire in the solder pot and make a figure 8 and pull out and you're done.

[ChristofferB]

Nobody 'aluminizes' copper cable. That doesn't make sense. For cheapness, copper cable is sometimes actually copper plated aluminium, and it is not impossible to think one could sand or burn through a thin copper layer to the aluminium.

More likely it's tinned copper. I've become a big fan of using a fluxpen for almost everything, it helps a lot.

You can definitely get tinned, or even silvered cable in all thicknesses you'd ever need, check any major supplier. Personally I like RS.

[TMM]

It's probably tinned copper, but the tin is heavily oxidised (due to poor storage/handling during manufacturing) and is therefore causing you more trouble than you expect when soldering. Try using a more aggressive solder/flux (rosin core) and turn up your iron temp (350-400*C).

You'd know if it were aluminium, because it would be virtually impossible to wet with regular electronics solder/flux.

[sacentre]

It's probably tinned copper, but the tin is heavily oxidised (due to poor storage/handling during manufacturing) and is therefore causing you more trouble than you expect when soldering. Try using a more aggressive solder/flux (rosin core) and turn up your iron temp (350-400*C).

You'd know if it were aluminium, because it would be virtually impossible to wet with regular electronics solder/flux.

Well, that describes what I'm seeing.  I thought oxidisation might be the problem so I unrolled a good length off my 10M roll to get a long way from the end but the problem was just as bad even though the strands looked perfectly bright and clean. I have very old but unused PCBs in a drawer that still take solder quickly and cleanly.  Next time I'm at the store, I'll try buying a fresh couple meters and see if it's any better.

[sacentre]

Coating on copper wires should be tin. 
Cheap wires are sometimes copper clad aluminum (CCA ) but you can say copper coated aluminum wires.. not the other way around.
On very cheap cables, you often get a mix of steel wire strands and copper clad aluminum wires or copper wires

My guess is that you simply have to use flux and tin the wires yourself.  I buy liquid flux, it's quite cheap.. under 10 dollars for a 500ml bottle. A solder pot is also cheap, but you can just use a solder iron tip with a "cup" that holds a bit of solder and you can tin the wires quickly.
 
Solder pot is often the way to go if you need to tin or solder a lot of wires .. heat solder, wipe away the dross, wet the wires in liquid flux, insert wire in the solder pot and make a figure 8 and pull out and you're done.

Thanks. I was using the normal flux paste which I've used for years with regular 60/40 leaded solder.  I've never used a solder pot but will keep that in mind.

[sacentre]

Nobody 'aluminizes' copper cable. That doesn't make sense. For cheapness, copper cable is sometimes actually copper plated aluminium, and it is not impossible to think one could sand or burn through a thin copper layer to the aluminium.

More likely it's tinned copper. I've become a big fan of using a fluxpen for almost everything, it helps a lot.

You can definitely get tinned, or even silvered cable in all thicknesses you'd ever need, check any major supplier. Personally I like RS.

Thanks. I think I'll try ordering a roll from RS and see how it behaves. 

[GopherT]

If you are using lead/tin alloy and your wire is likely a lead-free tin alloy with higher melt temp than your solder, you will have problems.  You'll need to heat the solder a bit longer than usual and set your soldering iron about 50°C hotter (or get a hotter tip if using a weller iron with Mag thermostat).

[David Hess]

I have noticed the same thing.  The wire plating is poor quality making it difficult to solder, but presumably this does not matter for crimp connections.

[T3sl4co1l]

I don't know that I've had new wire that didn't tin well, but I've certainly seen that on wire of old age, or unknown provenance.  It seems like the wire is tinned, but the surface has oxidized or corroded or somehow become coated with something that doesn't tin well.  You basically have to sand it down to get a good joint.

Note that nickel plating has a similar effect, but its reluctance to solder is natural (surface oxide); I wouldn't expect nickel plating to show up randomly in hookup wire however -- that's more of a high-temp mil spec / teflon thing (with silver plate being probably more common).  Nickel can be identified easily as it is magnetic.

Tim

[tooki]

If you are using lead/tin alloy and your wire is likely a lead-free tin alloy with higher melt temp than your solder, you will have problems.  You'll need to heat the solder a bit longer than usual and set your soldering iron about 50°C hotter (or get a hotter tip if using a weller iron with Mag thermostat).

Tinned wire isn’t tinned with solder, it’s tinned with tin, so it’s always lead-free.

[TimFox]

I don't know that I've had new wire that didn't tin well, but I've certainly seen that on wire of old age, or unknown provenance.  It seems like the wire is tinned, but the surface has oxidized or corroded or somehow become coated with something that doesn't tin well.  You basically have to sand it down to get a good joint.

Note that nickel plating has a similar effect, but its reluctance to solder is natural (surface oxide); I wouldn't expect nickel plating to show up randomly in hookup wire however -- that's more of a high-temp mil spec / teflon thing (with silver plate being probably more common).  Nickel can be identified easily as it is magnetic.

Tim

I inadvertently bought some nickel-plated mil-spec wire (surplus) and it refused to be soldered.
Most Teflon-insulated stranded wire is silver-plated.  Freshly-stripped, before it sulfides, it solders well with normal rosin flux solder.  Silver is used instead of tin, since the Teflon process is hot enough to melt the tin and tender the stranded wire inflexible.

[WattsThat]

Nickel plating is used for high temperature applications. That’s why you crimp with nickel plated lugs as it is not solderable, not to mention the solder would meld at the temps typically seen. Highly doubtful you’d ever see PVC insulation on nickel plated wire, makes no sense.

Standard PVC hookup wire that has been stored for extended periods of time at high temperatures (50-60C and up) is subject to oxidation from the plasticizers in the PVC breaking down. IIRC, hydrochloric acid is released in the process, leading to mild to severe oxidation of the tin plating.

[T3sl4co1l]

Not sure about oxidation, but exposure to acid fumes causes a catalytic breakdown: the plasticizer is generally an ester like diisononyl phthalate.  Under non-neutral pH and in the presence of moisture, the ester can be cleaved to isononyl alcohol (basically, "long" (oily) IPA; not much of a smell AFAIK, and probably volatile enough that it evaporates over these time scales) and phthalic acid (a modest organic acid on par with say citric or acetic acids).  Which under acidic conditions to start, means this is a catalytic (runaway) reaction.  The phthalic acid in turn can attack the copper, giving a green to black goo that seeps out of holes in the insulation, or at the ends.

AFAIK, the PVC itself is unchanged through this process, though it may be affected by heavy metal radicals, I don't know (seems like more of an iron thing than a copper thing?, but copper is certainly a metal with catalytic potential), and photodegrades to some extent (obviously, N/A if it's in dark storage).  Still, the character of the material can change dramatically, as pure PVC is a brittle material and is wholly dependent on plasticizers (to the tune of >30%wt) for its commonly soft consistency.

I happen to have some test leads that this happened to; ironically, only one went gooey, the other is pretty normal.   And they've been paired the whole time (~15yr).  Both are reasonably flexible, though maybe not virgin.  The reaction would've started in this case from HCl fumes, as they date back to the days when I'd do inorganic chemistry experiments in my parents' basement (much to the detriment of any clean steel in the house... fortunately for me they're tolerant ).

Tim

[David Hess]

I don't know that I've had new wire that didn't tin well, but I've certainly seen that on wire of old age, or unknown provenance.  It seems like the wire is tinned, but the surface has oxidized or corroded or somehow become coated with something that doesn't tin well.  You basically have to sand it down to get a good joint.

Kester makes cleaners for different metals.  For years I have used Copper-Nu #5520 as sort of flux for difficult to solder wire.  Kester used to sell it in 4 ounce bottles but no longer does unfortunately.

Dilute HCl works in a pinch.  The advantage of HCl is that it leaves no residue but keep it away from steel tools because it will quickly promote rust.

[T3sl4co1l]

I wouldn't say that; HCl and salts collect in pores, of which there are myriad due to the etching, and corrosion can pick up years later.

I've seen green crud slowly bubble up under a tinned surface before; this should be impossible with a hermetically sealed (metal) surface, presumably some pinholes went through.  This was something of an extreme case, soldering on wire that had been annealed in air (so, heavy black and red oxides, very rough etched surface).

Same reason other acid fluxes are counterindicated; zinc chloride being a more mild one, which melts to a salt flux which provides cleaning action while also partially decomposing into HCl, which acts to clean the joint (and bleaches the zinc out of a brass surface).

And pores being what they are, you can't really wash it out.  And while heat will drive off water, any salts remaining will present a barrier to metal that would otherwise seep in and coat it.  (Possibly the pores can be cleaned with a nonaqueous solvent, maybe extended ultrasonication in ethanol, with an amine base to dissolve and complex the copper salts/ions?)

Speaking of base, copper and tin are both amphoteric -- it's actually quite effective to clean them in concentrated NaOH/KOH, or if you're feeling really aggressive, melt some (solid) in a spoon and give that a dip -- WEAR EYE PROTECTION as molten lye is wont to splatter, and eyes are particularly vulnerable to attack from bases.  (Copper isn't very soluble this way in aqueous base alone; use ammonia solution instead.  Melt is effective.)

I've used this method when tinning litz made from old enameled wire that I really shouldn't be trying to use as litz -- the enamel just turns to crud on heating, it's utterly unsolderable and has to be stripped.  Treated in this way, the organics burn up, carbon is digested and copper oxides are dissolved.  Washing away the crud with water leaves a clean pink surface ready to tin.

But eh, salt is salt, this should still leave contaminants in pores.  I can come up with some weak reasons why it might be better behaved than acid, but ultimately I can't say I've used base to clean a large enough, cooked enough, surface to really compare effectiveness like this; it's worked in cases like magnet wire because the surface is otherwise fresh and immediately tinned.  YMMV.

Tim

[ANTALIFE]

+1 for a more aggressive flux

Also I find that RoHS flux core solder (vs leaded) tends to have more aggressive flux, which makes it great for soldering to oxidised leads

[Nassau Cable]

Hello. for future occasions. Here you can see a cable reference that could work in https://nassaunationalcable.com/es/products/18-awg-solid-bare-copper-conductor-soft-drawn-wire?_pos=1&_sid=3654c9627&_ss=r

[Gyro]

Definitely a spammer - second occurence today. Reported - I suggest deleting the link (as the other post).

[Ian.M]

IMHO delete both posts by 'Nassau Cable', and ban them.
Feel free to delete this post afterwards 

[Gyro]

^ Likewise

[Wallace Gasiewicz]

For small wire lengths, I like to use jewelry silver plated wire. It solders like a dream. When I make up cables, I also keep the silver plated coax shield in a little jar. This stuff solders easily but is very small diameter. Good for a quick fix on an old board, or for thru hole board problems.

[jonpaul]

Bonjour, oxidation, plating, insulation type all affect the solderability.

We use a lot of very old wire, and cables,

the worst are superflexible like used in headsets, wired phones due to woven in fabric strands.

Agree computer type ribbon flat cables do not solder well as,the insulation tends to burn at low temperature.

General tips....

Use 63/37 Eutectic leaded solder
use a hot iron, larger enough tip
After stripping, use an exacto knife to scrape the wire if it's oxidized.
solder pots are effective especially for multiconductr,  but can be dangerous
we use our Metcal SP-200 smart heat iron with great effectiveness on hard to solder large conductors.

Bon courage

Jon

[EPAIII]

I can give you the why in one, simple word: corrosion.

Copper corrodes. Tin also, but at a slower rate.

The answer is also one, simple word: FLUX.

OK, sometimes just the flux is not enough. In those cases some form of mechanical removal of the corrosion is called for. There are many ways, but three come to my mind.

1. A pencil eraser. Just erase the corrosion from the wire with a few strokes while rotating the wire.

2. Fine sandpaper. Pinch the wire between folded sandpaper and pull it out. Rotate the wire and repeat 3 or 4 times. Extra fine sandpaper is best - 400 grit or finer.

3. In a pinch, just scrape the wire across a sharp knife edge. This must be done carefully so as to not nick or cut the wire. It must be repeated many times while rotating the wire to scrape all sides of the wire strands. This works better with heavy wire gauges and should be avoided with gauges used in things like the ribbon cable you mentioned.

After any of these three or any other mechanical means, add flux and tin the wire with solder. I prefer a paste or jell style of flux. It sticks to the wire/joint better than liquid flux so you get more cleaning action.

[Ian.M]

2. Cut a green pan-scourer in quarters.  Fold a piece round the wire end or lead, pinch and pull.   If you wet it with IPA it even removes most bandoleer tape residue!