Solder Joint keeps snapping off

I have the following stranded wire that I need to solder onto a breakout board:

It's a very thin wire with only a few strands. The top wire is very thick, and hasn't failed even once yet. The device this breakout board is attached to does shake around a lot. I found that over the course of a few weeks the failure rate (e.g. it snaps off) of this particular wire is easily around 20-30%. I use 60-40 lead-based solder, Rosin core.

Any ideas on how to make this connection more robust?

(deleted)

Use a much longer piece of stranded wire, wound into a coil of several turns around a fat marker pen or similar. This should make it more flexible and able to absorb a lot of movement/vibration and put less strain on the solder joint.

Fix the cable to the module, to form a strain-relief.

Thanks guys, I will probably attach the wire to the board, and then solder as normal. That way, all movement force should be absorbed by the glue, not by the solder connection :slight_smile:

Would regular hot glue, or neutral cure silicone rubber be best?

Vitesze:
Would regular hot glue, or neutral cure silicone rubber be best?

No, they cannot absorb the movement/vibration and will still fail, or cause failure elsewhere. See reply #2.

PaulRB:
No, they cannot absorb the movement/vibration and will still fail, or cause failure elsewhere. See reply #2.

I could add some cable clips onto my PCB to keep things in place and absorb forces?

I believe the solution is to TWIST the strands together before you solder. You have them all straightened out. When twisted, the movements will be rotational rather than perpendicular to wires. Exactly where is the breakage occurring? Inside the solder or above the solder?

Paul

Paul_KD7HB:
I believe the solution is to TWIST the strands together before you solder. You have them all straightened out. When twisted, the movements will be rotational rather than perpendicular to wires. Exactly where is the breakage occurring? Inside the solder or above the solder?

Paul

It's a bit tricky to twist it manually - there's only a few wire strands. Breakage always occurs above the solder (i.e. caused by metal fatigue)

Vitesze:
It's a bit tricky to twist it manually - there's only a few wire strands. Breakage always occurs above the solder (i.e. caused by metal fatigue)

They must have been twisted in the original cable. Twisting is how any stranded wire cable is made so the wire doesn't break inside the insulation. How did they get untwisted?

Paul

Paul_KD7HB:
They must have been twisted in the original cable. Twisting is how any stranded wire cable is made so the wire doesn’t break inside the insulation. How did they get untwisted?

Paul

I tried verifying this by cutting up another cable - the wires don’t seem to be twisted at all. Not for the small insulated wire, and not for the thick wire. I don’t know why or if I’m just stupid, but these are some cheap boards I brought through AliExpress so it may not be top quality in terms of manufacturing?

Vitesze:
I tried verifying this by cutting up another cable - the wires don't seem to be twisted at all. Not for the small insulated wire, and not for the thick wire. I don't know why or if I'm just stupid, but these are some cheap boards I brought through AliExpress so it may not be top quality in terms of manufacturing?

That is very interesting! Do you have an id for that cable? Is it some type of coaxial cable for scientific instruments? The picture appears to show an outer layer of wires for shielding. I have seen some low capacitance coax cable 95 or 105 Ohms, used in instrumentation that had one or two strands in the center.

Also, may be important, what metal is the wire? Does your soldering actually wet the wire and make a nice looking joint?

One other thing you might do and that is how you dress the wire connecting to the board. Try a small loop, like a single turn spring and solder the end of the spring to the board.

Paul

Vitesze:
It’s a very thin wire with only a few strands.
Any ideas on how to make this connection more robust?

Could possibly remove all the solder from that particular hole at the board, and clean the hole right out. Then solder a more substantial wire to the hole. Perhaps with more strands etc. This just means solder some other kind of wire to the hole first, and that ‘better’ wire can then be spliced or soldered to your existing wire, which then runs out to where-ever it needed to go. And use heat-shrink where necessary to insulate the soldered splice connections.