Solder Wicking
Wicking is molten solder travelling up through the narrow gaps between the strands of a stranded conductor. The region the solder reaches loses its flexibility and behaves like a solid rod. The point where the wicking ends is the point where breakage starts under vibration.
Liquid solder advances by itself in narrow channels because of surface tension; this is part of how soldering works, but it is an unwanted side effect on stranded cable. The wicking mostly runs up under the insulation and is invisible to the eye.
- Symptom: the few millimetres behind the soldered end feel stiff when bent by hand.
- Consequence: vibration or repeated movement collects the stress at this stiff boundary; the conductor breaks inside the insulation within months.
- Fault type: intermittent contact — the device sometimes works, and no problem can be found while measuring.
To reduce wicking, keep the soldering time short, hold the end horizontally rather than upright and do not use more solder than needed. The real solution is to change the method: if you are terminating at a moving or vibrating point, use a crimped terminal. When diagnosing in the field, gently bending the region behind the end you suspect and watching whether the device behaviour changes is the fastest way to catch this fault.
Context in which this term is used: Installation, redundancy and field continuity