trace wrinkles

"Wrinkles" is a rather vague description :). When using soldermask and wave soldering the board, the soldermask itself will wrinkle and I would guess all of us who have worked on boards have seen that one. Since a large board can pick up a fair amount of solder during wave soldering (depending on geometry), this adds useless cost to the assembly of PCBs. That problem was eliminated by going to soldermask over bare copper. The second cause of "wrinkles" (and this is probably what you are referring to) is due to the cooling characteristics of the solder after reflow, and this is usually far more prominent on larger circuit areas. I would not classify these as wrinkles per se, but rather the visual boundries where the solder started to solidify on different parts of the circuit.