"Tinned" would probably be estañado, no? This looks like it should mean roughly the same as buen cortado, and another requirement for a good solder joint is a clean, neatly shaped end that isn't frayed—that way the solder goes into the joint and doesn't get stuck on the little projections, and the cable end fits neatly into the connector. If the cable's small, often you can twist it in the fingers to restore the lay of the strands.