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I am having a very bad experience with soldering wires on my boards. The problem is I have tried wires from various manufactures and suppliers but when I solder them initially they appear good but overtime (within couple of days) the insulation near the solder point on PCB starts cracking or in some case the conductor itself starts breaking.

My soldering technique is

  1. Strip the wire end.
  2. Tin the wire with solder end and make sure no split ends.
  3. Solder the wire on the PCB and then cut the bits that might be sticking out.

Any ideas or wire makes that can solve this problem and make the solder last?

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  • \$\begingroup\$ Since you say "the conductor" are these solid core or multi-stranded? Also, a photo would help. Beware that flux can be nasty to some plastics. \$\endgroup\$ – Fizz Oct 17 '15 at 9:03
  • \$\begingroup\$ @RespawnedFluff Multistranded. \$\endgroup\$ – Flood Gravemind Oct 17 '15 at 9:03
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    \$\begingroup\$ A photo is definitely needed, preferrably one immediately aftre soldering and one when the bad things have happened. When I use multi-stranded, I twist after stripping, and there are no wires sticking out after soldering. \$\endgroup\$ – Wouter van Ooijen Oct 17 '15 at 9:15
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    \$\begingroup\$ Are they breaking due to movement of the wires? \$\endgroup\$ – HandyHowie Oct 17 '15 at 9:26
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    \$\begingroup\$ You apparently need a strain relief. Where possible, drill two additional holes and poke the insulated wire through before soldering the end. Otherwise, cover the joint in a blob of epoxy. \$\endgroup\$ – venny Oct 17 '15 at 14:43
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If you're trying to do this properly, then you probably want to use 'board-in' crimps. The wire is crimped to a little metal fitting, which is then soldered to the board.

For some examples: http://www.molex.com/molex/products/group?key=direct_solder__boardin_crimp_terminals&channel=products

Soldering stranded cable which is then flexed is always a problem, because the strain at the end of the rigid soldered section is extremely high, which leads to failure.

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I do costuming-related electronics, and I have found that using hot glue to hold wires in place significantly reduces odd problems that otherwise occur due to wires moving around and damaging solder joints or breaking.

I suggest applying a dab of glue from a hot glue gun soon after soldering the wires in place. The blob of hot glue should be large enough that it can adhere to the wire's insulation, and should also attach to stable, nonmoving parts of the board, thus making the wire held in place by not just its metal parts, but also by its insulation, and eliminating extraneous wire movement that would otherwise lever against the metal join point of the wire to the board and hence weaken it by metal fatigue.

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  • \$\begingroup\$ similarly glue is used to reduce vibration and strain in tall components such as capacitors, so its definitely a valid approach \$\endgroup\$ – Wesley Lee Nov 19 '15 at 23:59
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    \$\begingroup\$ Kapton tape works well as well, add a bend to the wire immediately next to the joint (strain relief) and then tape down with kapton, route the wire to the edge of the PCB with more tape (adding bends where convenient), plenty resilient for prototyping and testing, for production hot glue is more reliable \$\endgroup\$ – crasic Nov 20 '15 at 1:08
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    \$\begingroup\$ Datapoint: Hot glue will detach from almost anything in weeks to months to maybe a year. If the cooled glue "part" is physically constrained by being eg through a hole with a larger width portion on the far side or aroiund a wire etc it will stay in place but may be loose. Think of a moulded plastic part of the same shape - how would it behave. \$\endgroup\$ – Russell McMahon Nov 20 '15 at 1:19
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These are effectively extensions to othert answers:

@venny's advice should be noted. This is an extremely effective way of providing strain relief, cost is minimal (two holes*), it does not degrade with time.

Also note my comment on Some_Guy's answer - hot glue is a quick way of constraining wires and components BUT it releases its bond in under a year. Neutral cure (MUST be NC) Silicone Rubber does the same job, takes longer to harden and lasts for decades in most cases.

  • You can use a single hole as strain relief- pass wire through and then solder to PCB - not as good as 2 holes but MUCH better than 0 holes.

Wire should be thicker than the VERY thin stranded hookup wire which is available. (Was 7 x 0.0076"). These may break if you breathe, bend, look at or think about them.

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