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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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  • \$\begingroup\$ put a picture of your wire up, if possible with the label on the thingy it came on. \$\endgroup\$
    – jippie
    May 6, 2012 at 17:21
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    \$\begingroup\$ 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. \$\endgroup\$
    – Armandas
    May 6, 2012 at 17:56
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    \$\begingroup\$ 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. \$\endgroup\$
    – Olin Lathrop
    May 6, 2012 at 19:21
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    \$\begingroup\$ 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. \$\endgroup\$
    – Tom Paris
    May 8, 2012 at 7:58
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    \$\begingroup\$ 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. \$\endgroup\$
    – Cybergibbons
    May 8, 2012 at 8:53

4 Answers 4

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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.

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    \$\begingroup\$ 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. \$\endgroup\$
    – Theran
    May 7, 2012 at 19:50
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    \$\begingroup\$ 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! \$\endgroup\$
    – Polynomial
    May 8, 2012 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.)

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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.

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    \$\begingroup\$ 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. \$\endgroup\$
    – Transistor
    Feb 27, 2019 at 9:57
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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+).

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  • \$\begingroup\$ What is the downvoter's disagreement? \$\endgroup\$
    – rackandboneman
    Dec 7, 2020 at 19:27

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