TO SOLDER OR NOT?
I soldered virtually every joint I made until 1978 when I found a Ministry of Defence report that challenged this approach. I was working on new warships that had hundreds of miles of cables and tens of thousands of joints and connections. As the ships went to sea for the first time wiring defects would emerge, most of which were down to poor workmanship or poorly routed cables. However there were persistent failures that could not be explained and continued to emerge in service. A study revealed that a group of failures were that the copper core had separated from the soldered connector, usually with what looked like a miniature floret of copper strands.
At the time, all cable ends were tinned with solder before being crimped or soldered to the connector, with a rubber sleeve covering the joint. Analysis of the broken joints revealed metal fatigue failure of the copper strands where they met the solder. The results were replicated on a testbed where vibration was revealed as the key factor. Under vibration the copper strands were workhardening where they met the solder and eventually failing.
The study looked at ways of reducing failures; heated insulation strippers that left no fatigue-inducing marks and stiffer heat shrink sleeves improved the situation. However the biggest improvement was achieved by not tinning the conductors on crimped joints.
The study struck a chord. My motorcycles certainly vibrated, I had seen joints fail at the solder junction and I had also occasionally seen the miniature floret of copper strands. Since then I have used crimped joints where possible. However if a joint has to be soldered, I use at least two layers of heat shrink sleeves to protect the joint.