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I'm always having problems soldering wires to connectors. I've read through the Solder won't stick question, but nothing there seems to have helped.

Here's my procedure:

  • If the connector is being difficult, I rub the surface of the connector with fine-grain sandpaper to clear any oxidisation.
  • Get my iron up to about 175 deg C (it's a temp-controlled iron)
  • Brush the tip across a damp sponge.
  • Add a small spot of solder to the tip.
  • Line up the wire to the connector, usually with a clamp.
  • Hold the tip of the iron on the connector for a short time.
  • Push some solder onto the wire at the edge of the tip, so the solder melts onto the wire.
  • Remove the iron.
  • Brush the tip across the sponge again to clean off the excess solder.

The problem I'm having is that the solder just doesn't stick the wire to the connector. It usually holds for a second, then unsticks from the connector as soon as the wire moves. I've tried more solder, less solder, different solder - same issue.

I've started to notice the same issue when soldering onto stripboard, too. The flow seems to be poor, the solder doesn't look shiny, and it's all rather viscous.

Am I doing something wrong? Is my iron / tip bad?

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Polynomial
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  • put a picture of your wire up, if possible with the label on the thingy it came on. – jippie May 06 '12 at 17:21
  • I don't have any to hand, and it didn't come off a reel. I mainly tend to use the type that computer PSUs use - in fact some of it is actually scavenged from old PSUs. I've also tried with some stuff from one of those beginners kits that comes pre-tinned. – Polynomial May 06 '12 at 17:24
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    The fact that you have a temperature-controlled iron doesn't mean you can solder at low temperatures. Even more so if you use lead-free solder. Come back if you have problems at 300°C. – Armandas May 06 '12 at 17:56
  • I think that you may be using the sponge a bit too much, especially since you're using the low temperature. You're constantly mentioning excess solder. If that's a problem, get a smaller diameter solder wire and practice precisely controlling how much solder you use. Also you're using sponge after finishing soldering. Don't do that as it leaves the tip unprotected and open to oxidation. – AndrejaKo May 06 '12 at 18:20
  • Also what's the power rating of your iron? – AndrejaKo May 06 '12 at 18:22
  • Didn't realise that 175C was low, I'll try upping it. Not sure on the power rating of the iron, since it doesn't say on it and I've lost the box, but it'll do 450C. My solder is Maplin own-brand, lead-free, Sn 99.3%, Cu 0.7%, 1mm diameter. – Polynomial May 06 '12 at 19:10
  • Come to think of it, the solder I used as a kid when I was learning had a significantly lower diameter, and that was great. Perhaps I should get some thinner solder! – Polynomial May 06 '12 at 19:14
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    175 C is only 347 F, which is way too low for soldering. I consider 600 F (316 C) the minimum for normal soldering with lead/tin solder. For certain tasks I use 650 or 700 F, although I turn down the temperature as soon as I'm done with that to avoid unnecessary tip degradation. – Olin Lathrop May 06 '12 at 19:21
  • I'll play around with soldering at higher temperatures, e.g. 350-400C. Maybe that's the problem I've been having. I also think I need to find some thinner solder - this 1mm stuff is a bit hefty. – Polynomial May 06 '12 at 19:23
  • The solder you used as a kid was probably tin+lead solder. Leaded solder just works better than the lead-free solder you are using now. More heat helps. And more flux is always helpful. Thinness of solder is not important: It forgets its shape as soon as it melts. – markrages May 06 '12 at 19:24
  • Is the leaded stuff still around, or is it pretty hard to get hold of? Or is there an alternative that's close to the same quality? I know there are environmental issues with lead. – Polynomial May 06 '12 at 19:27
  • @Polynomial: lead/tin solder is still readily available here in the US. – Olin Lathrop May 06 '12 at 20:39
  • I'm in England. – Polynomial May 06 '12 at 21:09
  • One if the very important aspects that has to do with getting things to stick us the flux. What flux is involved? The flux eats through the components surface oxidation which stops the solder from getting to the component itself. Also, have the wire and connector been stored in a dry non-humid environment? Have been stored for longer that 6 months? Oxidation management is key for joints that won't stick. –  May 07 '12 at 11:09
  • @scorpdaddy I don't actually have any flux. I've always just soldered stuff to boards and it's worked. No idea on the other parts - I order them from places like Farnell / RS, I just assume it's good to go. – Polynomial May 07 '12 at 14:53
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    Sure shipping things to some continents require lead-free solder, but I am sure anything you can buy still has lead solder in it. It's easier to work with, less expensive, and is not a health hazard in common situations. – Tom Paris May 08 '12 at 07:58
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    Sn99.3Cu0.7 is one of the worst solders for hand soldering. It's wetting properties are extremely poor and it melts at 227degC. Last time I bought lead free solder from Maplin it was a much nicer composition with some silver in. All wire solder from Maplin is flux cored as far as I know. I'm confused to how your 175degC iron is melting the solder, sounds like it isn't calibrated properly. High temps are actually good for soldering, as long as you don't push it too much. Solder with lead is available in Maplin and from all other suppliers. – Cybergibbons May 08 '12 at 08:53
  • You should heat the wire, apply the solder to the heated wire, and let the solder flux flow onto the connector. – user207421 Apr 28 '16 at 12:49

4 Answers4

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175C is pretty low for soldering. Low temperature lead solder ("63/37") melts around 185C, RHoS solder even melts around 250C. You also do not seem to use flux - do it. The solder flows fast and evely if the pads/pins have the right temperature. If you have problems with soldering in general check solderingguide.com, the soldering is easy comic or the tons of videos on youtube.

suha
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    A further point to consider is that it's not enough to simply place molten solder next to copper. The temperature and time must be high enough to activate the flux and allow the two metals to diffuse and form a metallurgical bond. – Theran May 07 '12 at 19:50
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    Grabbed myself some Sn 95.5% / Cu 0.5% / Ag 4% solder and a flux pen, retried with the higher temperature and it works wonders. I've now got perfectly neat, smooth, strong solder joints. Thank you! – Polynomial May 08 '12 at 21:43
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  1. Apply flux to both the connector and the wire.
  2. Stay away from lead-free solder; use 60/40 Tin/Lead solder.
  3. Use copper wire. (I've rarely seen solder not bond to copper wire; what are you using?)
  4. Simultaneously heat both parts that are being soldered. The solder should flow onto both of them. You will see that the flux assists this greatly.

Flux is very important. When it heats up, its acidity "eats away" the thin layer of corrosion that can prevent the solder from making contact with the metal.

Never use the abrasive to clean the tip of your soldering iron, by the way. (In case you're tempted.)

Kaz
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Speaker wire can be of several types. One type uses two different coloured wires to make it easy to keep speakers in phase.

This type commonly uses copper for one wire, giving a reddish colour, and aluminium for the other, giving a silver colour. Copper will solder easily. Aluminium won't. For aluminium, ALL the soldering advice above is of no value or use.

Aluminium CAN be soldered - with specialist techniques, solders and fluxes. Not easy to do at home, especially if you are not skilled in the technique needed. One problem is the oxide layer which forms immediately on exposed aluminium surfaces. If your attempts at soldering just result in the silver wire not tinning, but disappearing in a black gunge, that is the oxide layer forming and disintegrating.

If this is your problem, crimp the wire, or buy some wire which is not aluminium.

Dodgy Geezer
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    Welcome to EE.SE. Note that the question has an answer accepted seven years ago and a comment from the OP explaining that solder, flux and temperature were the answer to the problem. – Transistor Feb 27 '19 at 09:57
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175°C is MUCH too low. Turn it up to 400°C, practice and experiment on stuff you are not afraid to damage, and find the ideal "everyday" temperature that matches your solder, your iron, your application and your technique from that point - it might be somewhere from 320°C to 420°C, very likely NOT in the 200°C range or below. Unless you are soldering really really heat-sensitive things (either cheap connectors, polystyrene capacitors, or germanium semiconductors), there is no need to try and go as low as possible. Actually, using too low a temperature can cause damage, since it leads to heat soaking things that are far away from the actual solder joint.

If your intent is simple DEsoldering (with a solder sucker or by pulling on components then heating joints) - going ALL THE WAY UP can actually be the best solution (it might stress your iron tips though!) - solder will melt fastest that way, and as soon as it is molten, the component will pull/the sucker can be used, and the part not be heated further.

If you want to use lead free solder, get a good quality, hand soldering friendly alloy (eg Sn100Ni+).

rackandboneman
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